Thomas Gheno

Brian Gleeson

On the hot corrosion of nickel at 700 • C

Keywords: Nickel, Sodium sulfate, Hot corrosion, Sulfidation

The reaction of nickel with Na 2 SO 4 was studied in an O 2 -0.1SO 2 atmosphere at 700 • C, conditions typical of type II hot corrosion. The interaction of NiO with the sulfate was thermodynamically analyzed and compared with the dissolution-precipitation process known to occur at higher temperatures. Here the dissolution stage was short-lived due to a positive solubility gradient for Ni 2+ . The relatively fast growth of a NiO layer above a nickel sulfide layer was attributed to the inward molecular transport of SO 2 -SO 3 through the porous NiO. The influence of environmental variables was further assessed by reacting nickel with and without Na 2 SO 4 in air and then with no deposit in O 2 -0.1SO 2 . The roles of the deposit and atmosphere on the boundary conditions affecting the oxidation-sulfidation process were discussed on the basis of the observed reaction paths.

Introduction

Hot corrosion of high-temperature materials involves the growth of an oxide scale on the metal surface, its dissolution into a molten sulfate (the reactivity of which depends on its interaction with the gas phase), and the formation of sulfides which can also be liquid. Given this mechanistic complexity, pure metals prove particularly useful in the study of hot corrosion, and provide a framework to analyze the yet more complex behavior of alloys and commercial materials. Nickel is of particular interest since it forms the base of many high-temperature materials.

The reaction of nickel with Na 2 SO 4 as the prototypical sulfate deposit has mostly been documented in type I conditions, i.e., at temperatures above the Na 2 SO 4 melting point (T m = 884 • C). The accelerated corrosion may be associated with basic fluxing of NiO [START_REF] Goebel | Na 2 SO 4 -induced accelerated oxidation (hot corrosion) of nickel[END_REF][START_REF] Rapp | Second International Symposium on Molten Salts[END_REF][START_REF] Rapp | Chemistry and electrochemistry of the hot corrosion of metals[END_REF][START_REF] Otsuka | Hot corrosion of preoxidized Ni by a thin fused Na 2 SO 4 film at 900 • C[END_REF]. Briefly, as NiO growth consumes oxygen and oxygen transport in the melt is slow, a p O 2 gradient is established which results in elevated sulfur activities at the oxide/sulfate interface by virtue of the following equilibrium:

SO 3 = 1 2 S 2 + 3 2 O 2 (1)
This can then lead to sulfidation if the oxide is permeable to sulfur-bearing molecules. The simultaneous removal of sulfur and oxygen from the melt at the oxide surface results in a local decrease in p SO 3 , which prompts the basic dissolution of NiO via nickelate ion formation, NiO 2- 2 . Away from the scale, the p SO 3 is higher, and so is the solubility of nickelate ions: this "negative solubility gradient" causes NiO to precipitate within the sulfate as a non-protective scale. [START_REF] Barin | Thermochemical Data of Pure Substances[END_REF][START_REF] Waldner | Thermodynamic modeling of the Ni-S system[END_REF], making the assumption of unit activity for all compounds. The mixed compounds Na 2 NiO 2 and NaNiO 2 are missing by lack of reliable data. Iso-p S2 , iso-p SO2 and iso-a NiSO4 directions are indicated with dashed lines (values of log p S2 and log p SO2 are indicated). The p SO3 at equilibrium between solid and liquid Na 2 SO 4 -NiSO 4 solutions is from Misra et al. [START_REF] Misra | Thermodynamics of molten sulfate mixtures[END_REF]. The cross marks the equilibrium composition of a gas mixture of initial composition O 2 -0.1SO 2 at 700 • C.

Low temperature, or type II hot corrosion, which occurs below the melting point of the applied salt, involves the acidification of the salt by an SO 3 -containing gas, and reaction of the metal oxide to produce a liquid sulfate solution [START_REF] Luthra | Mechanism of Na 2 SO 4 induced corrosion at 600 • C-900 • C[END_REF]. This process of gas-phase-induced acidic fluxing [START_REF] Birks | Introduction to the High Temperature Oxidation of Metals[END_REF] is very sensitive to the gas composition, and potentially leads to very high corrosion rates above the eutectic temperature (e.g., T e (Na 2 SO 4 -NiSO 4 ) = 671 • C). The thermodynamic aspects of the oxide-sulfategas interactions are conveniently represented using stability diagrams. Four species may be present in gases containing oxygen and sulfur at high temperatures (O 2 , S 2 , SO 2 , SO 3 ), but any composition can be described using two independent partial pressures. Following Goebel and Pettit [START_REF] Goebel | Na 2 SO 4 -induced accelerated oxidation (hot corrosion) of nickel[END_REF], p SO 3 and p O 2 were chosen to plot the Ni-O-S diagram at 700 • C in Fig. 1, where the activity of all compounds is taken as unity. The Na-O-S diagram is superimposed. The acidic reaction of NiO is given by NiO + SO 3 = NiSO 4 [START_REF] Rapp | Second International Symposium on Molten Salts[END_REF] and is represented by a vertical line (p SO 3 = constant). This p SO 3 value defines whether a sulfate is considered acidic or basic, relative to NiO. The activities of SO 3 and Na 2 O are related through the sulfate dissociation equilibrium

Na 2 SO 4 = Na 2 O + SO 3 ( 3
)
Nickel sulfate is soluble in solid and liquid Na 2 SO 4 [START_REF] Levin | Phase Diagrams for Ceramists 1975 supplement[END_REF]; thus, as the nickel concentration in solid Na 2 SO 4 reaches the solidus, and inasmuch as the NiSO 4 activity is less than one, a liquid is formed at a lower p SO 3 than that required to stabilize pure NiSO 4 (s). The thermodynamic interaction was studied in detail in Refs. [START_REF] Luthra | Mechanism of Na 2 SO 4 induced corrosion at 600 • C-900 • C[END_REF][START_REF] Misra | Thermodynamics of molten sulfate mixtures[END_REF], and is illustrated in Fig. 1: the dotted vertical line represents the p SO 3 at equilibrium between NiO (s) and solid and liquid Na 2 SO 4 -NiSO 4 solutions estimated by Misra et al. [START_REF] Misra | Thermodynamics of molten sulfate mixtures[END_REF]. Alternatively, the acidic dissolution reaction may be written

NiO = Ni 2+ + O 2- (4)
(solutes are underlined). A relation between the activity of oxide ions and the p SO 3 is obtained by considering the equilibrium

SO 2- 4 = O 2-+ SO 3 (5)
which is equivalent to Eq. ( 3). Reaction mechanisms governing type II hot corrosion are less well understood than those of type I. Luthra [START_REF] Luthra | Low-temperature hot corrosion of cobalt-base alloys. 1. Morphology of the reaction product[END_REF][START_REF] Luthra | Low-temperature hot corrosion of cobalt-base alloys. 2. Reaction mechanism[END_REF] proposed a model for cobalt and Co-base alloys based on a Co 2+ -Co 3+ exchange mechanism, which does not apply to nickel. Most of the work on nickel has focused on gas atmospheres with high SO 2 -SO 3 contents, i.e., much higher than what would be found in a gas turbine, for example. In particular, Lillerud and Kofstad [START_REF] Lillerud | Sulfate-induced hot corrosion of nickel[END_REF] reported a thorough study conducted in O 2 -4 % (SO 2 -SO 3 ) at different pressures at 700 • C, where Ni 3 S 2 formed within the NiO scale, and fast nickel diffusion in the sulfide caused high reaction rates. The outward diffusing nickel was then described to react with NiSO 4 in the liquid sulfate solution to form NiO and Ni 3 S 2 .

Since hot corrosion involves sulfidation, its study can benefit to some extent from the abundant literature which exists in the field of gaseous oxidation-sulfidation (see Refs. [START_REF] Stroosnijder | Review of high temperature corrosion of metals and alloys in sulphidizing/oxidizing environments. I. Corrosion of metals[END_REF][START_REF] Kofstad | High temperature corrosion[END_REF][START_REF] Gesmundo | The high temperature corrosion of metals in sulfidizing-oxidizing environments: a critical review[END_REF] for reviews of the reaction of pure metals). Those previous studies mostly concern SO 2 or O 2 -SO 2 mixtures with high SO 2 /O 2 ratios. The reaction of nickel in such environments produces intermixed NiO-Ni 3 S 2 scales, where the sulfide phase has been shown by resistivity measurements [START_REF] Luthra | Simultaneous sulfidation-oxidation of nickel at 603 • C in argon-SO 2 atmospheres[END_REF] to form a continuous network. Scaling rates vary depending on the phase volume fractions, but can be as much as 10 7 times higher than the oxidation rate at a given temperature [START_REF] Luthra | Simultaneous sulfidation-oxidation of nickel at 603 • C in argon-SO 2 atmospheres[END_REF]. Reaction kinetics are controlled by outward Ni diffusion in the Ni 3 S 2 channels, and indeed Ni 3 S 2 growth rates are about 10 7 times higher than those of NiO (compare data in Refs. [START_REF] Mrowec | Transport properties of sulfide scales and sulfidation of metals and alloys[END_REF][START_REF] Peraldi | Correlations between growth kinetics and microstructure for scales formed by high-temperature oxidation of pure nickel. II. Growth kinetics[END_REF]). Luthra and Worrell [START_REF] Luthra | Simultaneous sulfidation-oxidation of nickel at 603 • C in SO 2 -O 2 -SO 3 atmospheres[END_REF] and Giggins and Pettit [START_REF] Giggins | Corrosion of metals and alloys in mixed gas environments at elevated temperatures[END_REF] published detailed studies of the effect of gas composition on the constitution and growth rates of the reaction products. Some variability exists between those results, which is hardly avoidable given the sensitivity of the reaction processes to local conditions. This paper presents a study of the corrosion of pure nickel coated with Na 2 SO 4 in an oxygen-rich, O 2 -0.1 % (SO 2 -SO 3 ) gas mixture at 700 • C. Results are also reported of nickel reaction with Na 2 SO 4 in air, and with no deposit in O 2 -0.1 % (SO 2 -SO 3 ), all other experimental parameters being unchanged. This allowed for a systematic investigation of the role of gas and sulfate chemistry on the reaction mechanism. This work is part of a broader study of type II hot corrosion aiming to better understand the effects of alloying additions in nickel-base alloys, aspects of which have been published elsewhere [START_REF] Gheno | Reaction morphologies developed by nickel aluminides in type II hot corrosion conditions: the effect of chromium[END_REF].

Experimental procedures

High purity (99.999 %) nickel specimens were cut from a 1 mm thick rolled plate received from Goodfellow. Specimens of dimensions 8 × 8 mm 2 were ground to a P1200 grit finish using SiC paper, then degreased with detergent and ultrasonically cleaned in ethanol before exposure. Isothermal corrosion experiments were conducted at 700 • C using a horizontal tube furnace with flowing O 2 -0.1 % SO 2 . Linear gas flow rates were about 1 mm s -1 at reaction temperature, with a total pressure slightly over 1 atm. The gas was passed through a platinized honeycomb catalyst located directly upstream of the specimens in the hot zone, allowing the otherwise sluggish reaction

SO 2 + 1 2 O 2 = SO 3 (6)
to proceed, with an equilibrium p SO 3 calculated to be 7.1 ×10 -4 atm at 700 • C from data in Ref. [START_REF] Barin | Thermochemical Data of Pure Substances[END_REF]. The resulting O 2 -SO 2 -SO 3 gas mixture will simply be referred to as O 2 -0.1SO 2 . Sodium sulfate was applied by spraying a saturated aqueous solution on the top surface of a preheated specimen. This produced an approximately uniform 2.8 ± 0.5 mg cm -2 Na 2 SO 4 deposit. After exposure, the corrosion products were studied by XRD using a Panalytical Empyrean instrument, with a Co radiation (K α1 = 1.789 Å). Polished sections were then prepared by standard metallographic procedures, using water-free cutting fluid and polishing suspensions to retain water-soluble products (i.e., sodium and nickel sulfates). The cross-sections were characterized by SEM with a JEOL JSM 6510 instrument, and by electron probe micro-analysis (EPMA) using a JEOL JXA 8530F instrument.

The solubility of nickel in Na 2 SO 4 is a function of the p SO 3 , which can be set through equilibrium with the gas environment. On the basis of a regular solution model for the molten sulfate, Misra et al. [START_REF] Misra | Thermodynamics of molten sulfate mixtures[END_REF] determined the Gibbs free energy of the sulfation reaction NiO(s) + SO 3 (g) = NiSO 4 (l) [START_REF] Barin | Thermochemical Data of Pure Substances[END_REF] where the underscore denotes solution in Na 2 SO 4 . They then calculated the minimum p SO 3 required for the reaction to proceed, i.e., for the solubility of NiSO 4 in solid Na 2 SO 4 to be exceeded, and the liquid sulfate to be formed. That minimum p SO 3 , 3 ×10 -4 atm at 700 • C, is shown in Fig. 1 Figure 2 shows the cross-section of a nickel specimen coated with Na 2 SO 4 and exposed to O 2 -0.1SO 2 for 6.5 h at 700 • C. The reaction products will be described in detail in Section 3; we simply note here that the hot corrosion process was visibly not limited to the surface where Na 2 SO 4 was applied, but also extended to the side and bottom faces. The oxide formed on the bottom face near the specimen edge is infiltrated with a Na 2 SO 4 -NiSO 4 mixture (see insert in Fig. 2), which indicates that a liquid sulfate had indeed formed and flowed along the specimen surface. Qualitatively, the formation of a liquid confirms the validity of the system's description based on thermodynamic equilibrium in the gas and the sulfate.

Results

The corrosion of nickel beneath a Na 2 SO 4 deposit in O 2 -0.1SO 2 at 700 • C was studied based on 0.5, 6.5 and 20 h exposures. Analysis by XRD (Fig. 3) showed that the reaction products were NiO and Ni 3 S 2 in all cases. Scale thicknesses varied significantly between the center and the edges of the specimens. For example, after 6.5 h, the scale was found to be on average 40 µm thick in the center, and to exceed 200 µm on the edges (see Fig. 2). This discrepancy prevented global measurement methods such as thermogravimetry to provide reliable results. The abnormally fast reaction near the specimen edges was likely due to repeated breakdown of the scale during exposure. This paper will focus on the specimen centers; even then, scale thicknesses varied significantly, for example from 20 to 65 µm after 6.5 h exposure.

As shown in the following, the reaction morphology evolved with exposure time. Due to the non-uniformity of the process, different reaction stages could be observed at different locations of a given specimen, with usually the more mature reaction morphologies located toward the specimen edges.

After 0.5 h reaction, the corrosion product consisted of a porous NiO scale. The sulfate above the scale was found to contain nickel to variable extents, corresponding to either solid or liquid Na 2 SO 4 -NiSO 4 solutions. In locations where the reaction was in its earliest stage, such as that shown in Fig. 4, nickel sulfide was found locally at the metal/oxide interface, wetting grain boundaries of both the nickel and the NiO. Analysis by SEM-EDS showed the sulfide to be Ni 3 S 2 and to contain a small volume fraction of metallic Ni. This corresponds to the eutectic decomposition of the liquid Ni-S solution upon cooling to room temperature [START_REF] Waldner | Thermodynamic modeling of the Ni-S system[END_REF]. In these regions, the NiO was ∼2 µm thick and fully infiltrated with Na 2 SO 4 -NiSO 4 . In other regions, nickel sulfide formed a continuous layer, the NiO was 5-10 µm thick and only its outer half was permeated with the mixed sulfate.

Micrographs and WDS maps of the reaction product observed after 6.5 h reaction are shown in Fig. 5. The scale contains three distinct zones: an outer part of porous NiO infiltrated with Na 2 SO 4 -NiSO 4 , an intermediate NiO layer with no sulfate, and a sulfide layer in contact with the metal. Examination of this specimen showed variations in the reaction morphology, which visibly represented successive stages of the same process. In Fig. 5a, the outer part of the scale has a complex, multi-layered microstructure, where a foam-like NiO network is embedded in a mixed sulfate (see insert). The intermediate, sulfate-free NiO layer displays an extensive, coarse porosity. Figure 5b shows a later stage: as the scale thickened, the intermediate layer constitutes an increasing proportion, it exhibits a finer porosity, and includes a significant fraction of Ni 3 S 2 . In places where the morphological evolution was visibly the most advanced, the scale consists of NiO with a fine, uniform porosity but no sulfate or sulfide, overlaying a sulfide layer. This morphology was observed along the entire specimen after 20 h. As shown in Fig. 6, in this later stage, the sulfur and sodium contents in the NiO layer showed local variations but remained small.

The presence of a significant fraction of nickel sulfide within the oxide layer, and its absence in a later stage, reflect important changes in the boundary conditions, which will be discussed in Section 4. Furthermore, the reaction products reflect both the reaction of NiO with the deposited sulfate, as is usually observed in hot corrosion, and a process of oxidation-sulfidation typical of exposures to SO 2 -containing atmospheres. In order to evaluate the role of the Na 2 SO 4 deposit and the gaseous The NiO scale grown in air with no deposit was 5 ± 1 µm thick, and displayed a cellular morphology typical of nickel oxidation at this temperature [START_REF] Peraldi | Correlations between growth kinetics and microstructure for scales formed by high-temperature oxidation of pure nickel. I. Morphologies and microstructures[END_REF]. Reaction with Na 2 SO 4 in air produced a porous, 15 ± 5 µm thick NiO scale, which contained a small amount of sulfur (1-2 at. %). Nickel sulfide was found locally below the NiO. It did not quite form a continuous layer, but wetted the nickel grain boundaries. The sulfate deposit was found to contain small amounts of nickel (< 2 at. %), which corresponds to sub-solidus compositions [START_REF] Levin | Phase Diagrams for Ceramists 1975 supplement[END_REF]. Its microstructure also indicated that it had remained solid. Exposure to O 2 -0.1SO 2 with no deposit produced a similar reaction morphology. Qualitatively, the extent of sulfidation was smaller, but the NiO scale was thicker (30 ± 10 µm). Finally, the Na 2 SO 4 -coated specimen reacted in O 2 -0.1SO 2 formed a 65 ± 10 µm NiO layer, with little sulfur and sodium, and a continuous layer of nickel sulfide. The latter penetrated the nickel grain boundaries down to several hundreds of microns. Figure 8 shows the Ni-Ni 3 S 2 mixture formed after decomposition of the Ni-S liquid solution. The NiO layer is seen in Fig. 8 to be significantly porous -this was consistently observed throughout its entire thickness.

Discussion

The discussion will first consider the morphological evolutions observed during reaction of nickel with Na 2 SO 4 in O 2 -0.1SO 2 , with a particular emphasis on the NiO dissolution process and in comparison with fluxing mechanisms known to occur at higher temperatures. We will then address the effect of the sulfate deposit on the oxidation-sulfidation process, in light of mechanisms prevailing in the absence of a deposit.

Mechanism of nickel reaction with Na 2 SO 4

The stages of nickel reaction with Na 2 SO 4 in O 2 -0.1SO 2 at 700 • C are represented in Fig. 9 and can be summarized as follows. Oxidation first produces an NiO scale, which reacts with the sulfate to form a liquid Na 2 SO 4 -NiSO 4 solution. The melt then penetrates the porous NiO, eventually forming a layer of sulfate-infiltrated oxide in the outer part of the growing scale. Simultaneously, sulfidation occurs, first at the metal/oxide interface and in the inner part of the scale (Fig. 9a), then progressing until a significant fraction of the scale consists of nickel sulfide (Fig. 9b).

In a later stage, the sulfate solution is no longer embedded in a distinct layer, but instead spread throughout the scale; sulfides are no longer present within the oxide, and sulfidation proceeds by thickening of a sulfide layer at the base of the scale (Fig. 9c). This complex corrosion behavior can be analyzed in terms of two distinct yet interdependent processes: oxidation-sulfidation, which will be discussed subsequently, and the interaction between NiO and the sulfate in the outer part of the scale. The latter is addressed now, with an emphasis on the differences with type I hot corrosion.

In the early stage of the reaction, NiO dissolves into an initially nickel-free sulfate, i.e., along a negative concentration gradient. However, SO 3 consumption to form NiSO 4 results in a local p SO 3 decrease at the oxide/sulfate interface, and, since the Ni 2+ solubility is an increasing function of p SO 3 , this produces a positive solubility gradient, as represented in Fig. 10. The opposed concentration and solubility gradients lead to rapid saturation of the melt with Ni 2+ . Furthermore, the continued consumption of oxygen and sulfur (associated with the oxidation-sulfidation of the nickel) maintains a reduced p SO 3 , which favors the precipitation of NiO at the oxide/sulfate interface. This results in the foam-like oxide microstructure observed in the outer part of the scale (see insert in Fig. 5a). Indeed, as noted by Misra and Whittle [START_REF] Misra | Effects of SO 2 and SO 3 on the Na 2 SO 4 induced corrosion of nickel[END_REF], if the p SO 3 at the oxide/sulfate interface decreases below a certain value, the liquid solution is no longer stable, and dissociates into NiO and a solid Na 2 SO 4 -NiSO 4 solution. In the present situation where the gas p SO 3 is only slightly higher than the threshold value (Fig. 1), this is expected to occur. The precipitation explains why the sulfate solution is confined to an outer region of the scale, and does not infiltrate the oxide to a deeper level. Thus, during the course of the corrosion process, the system chemistry evolves to allow the acidic dissolution of NiO, and its precipitation. Yet these occur as successive events at the same interface (oxide/sulfate): after the sulfate is saturated with Ni 2+ due to the decrease in p SO 3 , the conditions for NiO dissolution are no longer met, and the reverse process, precipitation, occurs instead. This is an essential difference with type I conditions, where basic dissolution and precipitation occur simultaneously at two different interfaces (oxide/sulfate and sulfate/gas, respectively), and both can be sustained for some time (before eventually stopping, see details in Ref. [START_REF] Goebel | Na 2 SO 4 -induced accelerated oxidation (hot corrosion) of nickel[END_REF]). Specifically, no negative solubility gradient can be established during type II hot corrosion of a pure metal with a pure Na 2 SO 4 deposit. Indeed, at temperatures below the melting point of Na SO 4 , the formation of a liquid requires the acidic dissolution of the metal oxide, which involves a relatively acidic atmosphere. Thus the direction of the p SO 3 gradient imposes a positive solubility gradient for acidic solutes. Several authors [START_REF] Otsuka | Hot corrosion of preoxidized Ni by a thin fused Na 2 SO 4 film at 900 • C[END_REF][START_REF] Luthra | Low-temperature hot corrosion of cobalt-base alloys. 2. Reaction mechanism[END_REF] anticipated that in these conditions, and in the absence of an M 2+ -M 3+ exchange mechanism for nickel, no accelerated corrosion would take place.

This prediction is verified here to some extent, since no continued dissolutionprecipitation occurs, and the corrosion product does not present the layered morphology typical of type I conditions. In the longer term, oxidation causes the nickelsaturated Na 2 SO 4 -NiSO 4 solution to be embedded in an increasing volume of oxide, until it no longer forms an interconnected phase but is dispersed throughout the scale. So long as no fresh Na 2 SO 4 is provided, the reaction is limited to an oxidation-sulfidation process. However, while it is interconnected, the sulfate solution does have an influence on the extent of oxidation and sulfidation; this will be discussed now.

Mechanism of the oxidation-sulfidation process

From a simple gas-phase thermodynamics perspective, sulfidation is not expected to occur in O 2 -0.1SO 2 at 700 • C, since the equilibrium gas composition is oxidizing but non-sulfidizing to nickel (Fig. 1). However, as proposed by Goebel and Pettit [START_REF] Goebel | Na 2 SO 4 -induced accelerated oxidation (hot corrosion) of nickel[END_REF], in the presence of a sulfate deposit, oxygen consumption to form NiO may lead to an elevated sulfur activity at the oxide/sulfate interface, by virtue of Eq. [START_REF] Goebel | Na 2 SO 4 -induced accelerated oxidation (hot corrosion) of nickel[END_REF]. Even in the absence of a deposit, sulfidation may occur if the oxide is permeable to sulfurbearing molecules, and the SO 2 pressure is high enough for the p S 2 to exceed the sulfide dissociation pressure at the low p O 2 prevailing within the scale, as discussed by Birks et al. [START_REF] Birks | Corrosion mechanisms of metals and alloys in multicomponent oxidative environments[END_REF][START_REF] Pope | The penetration by sulfur of NiO scales growing on nickel[END_REF]. This requires the oxide defects to be sufficiently small for the molecular species they contain to be in (or tend to) local equilibrium with the surrounding oxide, such that activity gradients develop. Sulfides may then form within the oxide or at the metal/oxide interface, where the p O 2 is minimum and the p S 2 maximum.

Here both the presence of a sulfate deposit and local equilibrium within the oxide scale contribute to the establishment of sulfidizing conditions. The constitution of the reaction products indicates that a moderately high sulfur activity was reached initially. At 700 • C, the sequence of phases in the Ni-S system is [START_REF] Waldner | Thermodynamic modeling of the Ni-S system[END_REF]: Ni, Ni-S (l), Ni 3 S 2 , Ni 1-x S, NiS 2 , S 2 (g); yet Ni 1-x S and NiS 2 were not observed. Sulfidation is seen to occur first atop nickel grain boundaries (Fig. 4); preferential nucleation at the triple junction reflects a limited sulfur supersaturation, which favors the lower sulfides. (In addition, once the liquid sulfide is formed, fast diffusion maintains a nickel activity close to unity at its surface, thus destabilizing the higher sulfides). As the reaction proceeds, however, a continuous Ni-S (l) layer is established at the metal/oxide interface, and Ni 3 S 2 is eventually formed throughout the scale (Fig. 5b). The requisite increase in p S 2 for this to occur is related to the deposit. Specifically, in the outer part of the scale, the sulfate forms an interconnected solution, effectively sealing the scale and allowing the p O 2 to further decrease and the p S 2 to further increase. Eventually, as the sulfate is dispersed throughout the growing scale, the p S 2 is reduced and Ni 3 S 2 is no longer stable within the scale. Local equilibrium between SO 2 -SO 3 and NiO still maintains sulfide stability at the metal/oxide interface.

The discussion now turns to the question of sulfur transport through the NiO. As noted in the Introduction, mixed NiO-Ni 3 S 2 scales formed during gaseous oxidationsulfidation of nickel in high SO 2 /O 2 environments can grow as much as seven orders of magnitude faster than NiO would, due to the fast diffusion of nickel in the sulfide. In the present case, the Ni 3 S 2 present within the NiO was, at some stage of the process, interconnected (see Fig. 5b), and presumably sustained such a rapid reaction for a period. Yet the sulfides eventually dissociated, and scale growth must then have relied on another transport mechanism. Measuring reaction kinetics proved difficult because of the non-uniformity of the scale and the succession of different reaction regimes. On the basis of scale thickness measurements, the reaction rate is qualitatively seen to decrease with time. Assuming parabolic kinetics for comparison purposes, a k p is estimated to be 10 -9 cm 2 s -1 , while that of sulfidation is reported to be about 10 -6 cm 2 s -1 at 700 • C [START_REF] Mrowec | Transport properties of sulfide scales and sulfidation of metals and alloys[END_REF], three orders of magnitude higher. On the other hand, the estimated k p far exceeds that of NiO growth, about 10 -13 cm 2 s -1 , which at this temperature is supported by short-circuit nickel diffusion [START_REF] Peraldi | Correlations between growth kinetics and microstructure for scales formed by high-temperature oxidation of pure nickel. II. Growth kinetics[END_REF]. Thus, the observed scaling is too fast to be sustained by solid-state diffusion. Since the scale is extensively porous (see Fig. 8), inward molecular oxygen transport is a more likely candidate.

The diffusivity of sulfur in NiO at 700 • C is not known, and extrapolation to 700 • C of measurements made at higher temperatures using single crystals would be unreliable, since grain boundary diffusion predominates at lower temperatures. Reviewing the limited solubility and diffusivity data available, several authors [START_REF] Birks | Introduction to the High Temperature Oxidation of Metals[END_REF][START_REF] Young | High Temperature Oxidation and Corrosion of Metals[END_REF] have argued that the continued growth of a sulfide layer below the oxide scale in situations of oxidation-sulfidation must involve transport of sulfur-bearing molecules across the scale. It is concluded that in the present case, molecular transport via SO 2 -SO 3 allowed the rapid supply of both oxygen and sulfur across the porous NiO layer. The relative amounts of SO 2 and SO 3 depend on the local thermodynamic conditions. Even though the NiO layer is porous, local equilibrium imposes a p O 2 gradient, such that the equilibrium SO 2 /SO 3 ratio increases toward the sulfide/oxide interface. Using the equilibrium constant for reaction (6) at 700 • C calculated from data in Ref. [START_REF] Barin | Thermochemical Data of Pure Substances[END_REF], limiting values of this ratio are found to be 4 ×10 -1 for p O 2 = 1 atm and 5 ×10 7 at the NiO dissociation pressure on Ni, p O 2 = 5 × 10 -17 atm. Whether SO 2 actually predominates within the scale depends on the ability of NiO to catalyze reaction [START_REF] Birks | Introduction to the High Temperature Oxidation of Metals[END_REF]; if the reaction is sluggish, the gas mixture might become supersaturated with SO 3 at low p O 2 values.

The liquid Ni-S is likely a fast diffuser of both nickel and sulfur. As a consequence, sulfide growth may occur together with NiO at the sulfide/oxide interface 7Ni + 2SO 2 = 4NiO + Ni 3 S 2 [START_REF] Waldner | Thermodynamic modeling of the Ni-S system[END_REF] and at the metal/sulfide interface by sulfur diffusion inward. In the latter case NiO - is formed at the expense of the sulfide by the displacement reaction:

Ni 3 S 2 + 3 2 SO 2 = 3NiO + 7 4 S 2 (9)
(the sulfide is assumed to have the stoichiometry of Ni 3 S 2 for simplification). Of course, as noted earlier, the formation of a sulfide layer implies that it is more stable than the oxide at the metal surface; however, the activity gradients across the scale cause reaction [START_REF] Waldner | Thermodynamic modeling of the Ni-S system[END_REF] to proceed to the right at the sulfide/oxide interface. Whether the net result at the sulfide/oxide interface is growth or consumption of the sulfide depends on the relative rates of mass transport and of reactions ( 8) and ( 9)this question has been discussed in detail by previous investigators [START_REF] Birks | Introduction to the High Temperature Oxidation of Metals[END_REF][START_REF] Kofstad | High temperature corrosion[END_REF][START_REF] Gesmundo | The high temperature corrosion of metals in sulfidizing-oxidizing environments: a critical review[END_REF][START_REF] Young | High Temperature Oxidation and Corrosion of Metals[END_REF]. The mass transport processes discussed here are summarized in Fig. 9. In the later stage of the reaction, although NiO is, intrinsically, a cation diffuser, oxide growth occurs predominantly at the sulfide/oxide interface because inward molecular oxygen transport is faster than the outward ionic diffusion of nickel.

Role of the environment in the oxidation-sulfidation process

As discussed above, the presence of an interconnected sulfate solution in the scale has an influence on the boundary conditions governing the oxidation-sulfidation process. This in turn affects the constitution and growth rate of the corrosion product. A similar observation is arrived at when comparing the results of the "Na 2 SO 4 /O 2 -0.1SO 2 ", "no deposit/O 2 -0.1SO 2 " and "Na 2 SO 4 /dry air" experiments (Fig. 7). The roles of the sulfate deposit and gas atmosphere are now examined further. To do so, reaction paths for the three experiments are constructed by reporting the activities prevailing at the metal/scale and scale/gas (or scale/deposit) interfaces on the stability diagram of Fig. 11.

The thermodynamic conditions at the scale/gas interface during the "no deposit/O 2 -0.1SO 2 " experiment are simply defined by the equilibrium gas composition; these are marked as point 1 in Fig. 11. In the "Na 2 SO 4 /dry air" experiment, sulfur could only be obtained from dissociation of the sulfate. The absence of a significant p SO 3 in the flowing gas has two implications: no liquid Na 2 SO 4 -NiSO 4 solution can be stabilized, and gas-solid equilibrium indeed requires that reaction (3) proceeds to the right, i.e., that the sulfate releases some SO 3 . Incidentally, SO 3 removal from the sulfate further precludes any liquid formation as it reduces Ni 2+ solubility; indeed, the deposit appeared to have remained solid, and it was found by SEM-EDS to contain only traces of nickel, corresponding to a solid Na 2 SO 4 -NiSO 4 solution. Despite remaining solid, the deposit must have effectively sealed the oxide in order for sulfidizing conditions to develop. Based on these observations, it is concluded that the p O 2 and the p SO 3 at the oxide/sulfate interface were lower than in the O 2 -0.1SO 2 atmosphere; estimated values are indicated as point 2 in Fig. 11. In the "Na 2 SO 4 /O 2 -0.1SO 2 " experiment, again boundary conditions are estimated relative to those prevailing in the two other experiments. As discussed in Section 4.1, oxidation and sulfidation of the nickel produced activity gradients across the sulfate, resulting in both p SO 3 and p O 2 lower below the sulfate than in the flowing gas. The infiltrated sulfate was saturated with nickel, so the p SO 3 at the oxide/sulfate interface was most likely higher than in the "Na 2 SO 4 /dry air" experiment, where Na 2 SO 4 contained only traces of nickel. The p O 2 also was presumably higher, since mass transport would have been faster in a partially molten sulfate than in a solid form. An estimated gas composition is shown as point 3 in Fig. 11.

We now turn to the conditions prevailing at the metal/scale interface. In the "no deposit/O 2 -0.1SO 2 " experiment, sulfidation was localized and limited in extent, which suggests that the sulfur supersaturation with respect to Ni (s) was small, i.e., that the (p O 2 , p SO 3 ) couple was relatively close to the Ni/NiO/Ni-S (l) triple point. In the "Na 2 SO 4 /dry air" experiment, sulfidation was also local but occurred to a greater extent; finally, in the "Na 2 SO 4 /O 2 -0.1SO 2 " experiment, the continuous sulfide layer indicates that the reaction path crossed the NiO/Ni-S (l) phase boundary.

Based on these observations, tentative reaction paths are plotted in Fig. 11 for the three experiments. The orientation of these paths depends on the way the gas composition evolves across the porous NiO layer. Since the oxide scales formed in the three situations present similar microstructures, the paths are plotted parallel to one another. This graphical construction shows that the experimental results are consistent with an evolution of the gas composition following SO 2 isobars, rather than SO 3 isobars. We conclude that in O 2 -0.1SO 2 , the main influence of adding a sulfate deposit is to lower both p SO 3 and p O 2 at the oxide surface, in a ratio which generates an increased sulfur activity and eventually leads to enhanced sulfidation. When a deposit is present, adding SO 2 -SO 3 to the gas leads to an increased p SO 3 below the deposit, which also favors sulfidation. Another effect of the presence of sulfur is the formation of a porous NiO; this is discussed next.

Role of sulfur in the NiO microstructures

All three corrosion tests involving sulfur, in the form of Na 2 SO 4 deposits, O 2 -0.1SO 2 gas or both, resulted in the fast growth (i.e., faster than in air) of porous NiO scales. It is noted that the NiO scale grown in air also presented some, much smaller, degree of porosity (Fig. 7). Scales grown in air or oxygen at temperatures lower than 1000 • C usually consist of two layers, with the porous inner layer growing by inward oxygen transport [START_REF] Peraldi | Correlations between growth kinetics and microstructure for scales formed by high-temperature oxidation of pure nickel. I. Morphologies and microstructures[END_REF]. In the extensive study of nickel oxidation in oxygen by Peraldi et al. [START_REF] Peraldi | Correlations between growth kinetics and microstructure for scales formed by high-temperature oxidation of pure nickel. I. Morphologies and microstructures[END_REF], scales grown at 700 • C were described to present an extensive open porosity. Yet, even though oxidation involved molecular oxygen transport inward, oxidation kinetics were controlled by solid-state nickel diffusion, along short-circuits (e.g., grain boundaries, dislocations pipes or pore surfaces) at this relatively low temperature. This is also the case in the present study, where the measured oxide thickness after reaction in air with no deposit, 5 ± 1 µm, is consistent with reported growth rates based on short-circuit nickel diffusion [START_REF] Peraldi | Correlations between growth kinetics and microstructure for scales formed by high-temperature oxidation of pure nickel. II. Growth kinetics[END_REF]. As is evident in Figs. 7 and8, both the porosity and the growth rate of the NiO scales formed in the presence of sulfur were significantly greater. As discussed earlier, this fast growth is due to inward transport of SO 2 -SO 3 , which also provided the sulfur for sulfidation.

A question of interest, then, is how the presence of sulfur in the system led to an extensively porous microstructure. Goebel and Pettit [START_REF] Goebel | Na 2 SO 4 -induced accelerated oxidation (hot corrosion) of nickel[END_REF] argued that porous NiO scales could be obtained by oxidation of nickel sulfide: for a sufficiently high sulfur activity in the sulfide, p SO 2 at the sulfide/oxide interface would exceed 1 atm, such that gas evolution would mechanically rupture the oxide and yield a porous scale. A comparison of the tests conducted here with Na 2 SO 4 or O 2 -0.1SO 2 in Fig. 7 shows that the oxide scales formed in these conditions all had a similar microstructure, including similar degrees of porosity, despite the sulfide being only present locally in the "no deposit/O 2 -0.1SO 2 " and "Na 2 SO 4 /dry air" experiments. Thus the porosity in this case was not specifically due to the displacement reaction, and must have involved sulfur in some other way. Smialek [START_REF] Smialek | Non-protective alumina growth in sulfur-doped NiAl(Zr)[END_REF] reported the fast growth of porous Al 2 O 3 on highly S-and Zr-doped NiAl in air at 1200 • C. The NiAl/Al 2 O 3 and Ni/NiO systems are obviously very different, but Smialek argued that an open network of submicron microchannels served as paths for rapid gas transport, and also concluded that the widespread porosity was due to SO 2 evolution. A similar mechanism might be operating here. Alternatively, or in addition, sulfur is known to segregate at metal/oxide interfaces, where it is thought to stabilize interfacial pores by reducing their surface energy, which can have the effect of lessening the oxide adherence [START_REF] Gheno | Characterization of sulfur distribution in Ni-based superalloy and thermal barrier coatings after high temperature oxidation: a SIMS analysis[END_REF]. Preferential sulfur adsorption at pore surfaces may also hinder kinetic processes to the extent that a porous NiO scale results, although this remains to be investigated in more detail.

Conclusions

The reaction of nickel with Na 2 SO 4 in O 2 -0.1SO 2 at 700 • C was analyzed in terms of two processes: [START_REF] Goebel | Na 2 SO 4 -induced accelerated oxidation (hot corrosion) of nickel[END_REF] the interaction between the thermally grown NiO scale and the sulfate deposit; and (2) the simultaneous oxidation-sulfidation of the nickel. The acidic dissolution of NiO in the Na 2 SO 4 produced a liquid sulfate solution, which infiltrated the porous oxide. In the absence of a negative solubility gradient, the liquid sulfate was rapidly saturated with nickel. Eventually, oxygen and sulfur consumption led to the precipitation of NiO and a solid sulfate solution, which dispersed throughout the growing scale. The reaction was then reduced to an oxidation-sulfidation process.

Sulfidation was also found to occur with no deposit in O 2 -0.1SO 2 , and with Na 2 SO 4 in air. The role of the deposit and atmosphere on the boundary conditions relative to the oxidation-sulfidation process was studied by analyzing the reaction path associated with each environment. In O 2 -0.1SO 2 , adding Na 2 SO 4 led to lower p O 2 and p SO 3 levels at the oxide surface due to slow mass transport, in a ratio which corresponded to an increased sulfur activity, which led to enhanced sulfidation. When a deposit was present, adding SO 2 -SO 3 to the gas led to a greater sulfur activity at the oxide/sulfate interface, and also promoted sulfidation.

Finally, although NiO scales grown in air with no sulfate deposit tend to develop some degree of porosity, the extent is much greater in the presence of sulfur, whether added as Na 2 SO 4 or as SO 2 -SO 3 (g). This phenomenon may be associated with the tendency of sulfur to preferentially adsorb on internal surfaces and poison reaction processes (e.g., oxidation and sintering).

Figure 1 :

 1 Figure 1: Superimposed stability diagrams of Ni-O-S and Na-O-S systems at 700• C, plotted with log p SO3 -log p O2 coordinates from data in Refs.[START_REF] Barin | Thermochemical Data of Pure Substances[END_REF][START_REF] Waldner | Thermodynamic modeling of the Ni-S system[END_REF], making the assumption of unit activity for all compounds. The mixed compounds Na 2 NiO 2 and NaNiO 2 are missing by lack of reliable data. Iso-p S2 , iso-p SO2 and iso-a NiSO4 directions are indicated with dashed lines (values of log p S2 and log p SO2 are indicated). The p SO3 at equilibrium between solid and liquid Na 2 SO 4 -NiSO 4 solutions is from Misra et al.[START_REF] Misra | Thermodynamics of molten sulfate mixtures[END_REF]. The cross marks the equilibrium composition of a gas mixture of initial composition O 2 -0.1SO 2 at 700 • C.

Figure 2 :

 2 Figure 2: Cross-section of nickel specimen after 6.5 h reaction with Na 2 SO 4 in O 2 -0.1SO 2 at 700 • C. The oxide scale on the bottom face (i.e., the side which was not coated with Na 2 SO 4 prior to exposure) is infiltrated with Na 2 SO 4 -NiSO 4 , which indicates that the sulfate mixture was liquid at temperature.

Figure 3 :

 3 Figure 3: XRD analysis (Co radiation) of reaction products formed during exposure of nickel to O 2 -0.1SO 2 at 700 • C, with and without Na 2 SO 4 deposit.

Figure 4 :

 4 Figure 4: Corrosion product formed on nickel after 0.5 h reaction with Na 2 SO 4 in O 2 -0.1SO 2 at 700 • C. Observations with the salt retained showed that the NiO was infiltrated with Na 2 SO 4 -NiSO 4 . This image was obtained after washing the sulfate off, and shows that NiO is also wetted with liquid sulfide.

Figure 5 :

 5 Figure 5: Back-scattered electron images and WDS maps of corrosion product formed after 6.5 h reaction of nickel with Na 2 SO 4 in O 2 -0.1SO 2 at 700 • C. The two regions come from the same specimen but reflect different stages of the reaction process: (a) in an earlier stage, the porous NiO scale is infiltrated with a Na 2 SO 4 -NiSO 4 solution in its top half (inset shows fine porosity in outer part); (b) in a later stage, the scale mostly contains a NiO + Ni 3 S 2 mixture.

Figure 6 :

 6 Figure 6: Back-scattered electron image and WDS maps of corrosion product formed after 20 h reaction of nickel with Na 2 SO 4 in O 2 -0.1SO 2 at 700 • C. The scale consists of a porous NiO layer, and a nickel sulfide layer in contact with the metal.

Figure 7 :Figure 8 :

 78 Figure 7: Corrosion product observed after 20 h reaction of nickel at 700 • C in air and O 2 -0.1SO 2 , with and without Na 2 SO 4 deposit. The Ni-Ni 3 S 2 mixture is formed upon cooling of liquid Ni-S.

Figure 9 :Figure 10 :

 910 Figure 9: Schematic representation of microstructural evolution and transport processes during reaction of nickel with Na 2 SO 4 in O 2 -0.1SO 2 at 700 • C. Successive steps represent: (a) NiO dissolution in Na 2 SO 4 and infiltration of the mixed sulfate in the oxide layer; (b) sulfide development within the oxide layer; (c) growth of porous NiO (details given in text).

Figure 11 :

 11 Figure 11: Tentative reaction paths for the reaction of nickel with Na 2 SO 4 in O 2 -0.1SO 2 , with no deposit in O 2 -0.1SO 2 , and with Na 2 SO 4 in dry air. The crosses mark the thermodynamic conditions estimated at the scale surface for each environment (see text).

  by the Na 2 SO 4 -NiSO 4 vertical line. The equilibrium gas p SO 3 in the present work is seen by the cross in Fig.1to be sufficiently high for liquid Na 2 SO 4 -NiSO 4 formation, but lower than that required for solid NiSO 4 to be stable. The reaction of Ni with Na 2 SO 4 in this gas is thus expected to produce a liquid Na 2 SO 4 -NiSO 4 solution in equilibrium with NiO.

Oxid Met 84 (2015) 567-584

Acknowledgements

This work was supported by the Department of Energy through the University Turbine Systems Research Program run by the National Energy Technology Laboratory, award number DE-FE0007271, Dr. Seth Lawson, project manager. The authors thank Prof. G.H. Meier at the University of Pittsburgh for useful discussions, as well as the reviewers for useful suggestions.


Union. Since then, research on Iraqis refugees has been largely policy driven, by or from the perspective of humanitarian aid agencies or refugee advocacy organizations. There are many justifications in favour of the policy bias in refugee research. v There are also several shortcomings. In 2008, at a time when scholars were still mostly focusing on refugees in formal camps, and often limited their interest to refugee policy issues, Oliver Bakewell made a plea for researching forced migrants without using preconceptions. vi He convincingly argued for considering the large number of self-settled refugees and aspects of their lives other than their interaction with aid programs, which tended to remain invisible to scholars. vii The new academic interest in self-settled refugees had in fact emerged in the early 2000s, inspired by the policy concerns of UNHCR which, in 1997, had issued its first policy on refugees in urban areas. However, scholarly publications on the belated recognition of the presence of refugees in cities only started to be available during the mid-2000s. This new area of refugee research has flourished in recent years due to the realization by a number of ground-breaking scholars that, in developing countries, the number of refugees found in non-camp settings, and particularly in urban areas, has increased considerably and that the paradigms used to understand the predicament of encamped refugees are not applicable to urban contexts. Beyond creating knowledge that reflects more closely the variegated experience of refugees, this approach also responds to the ethical imperative of better informing humanitarian policy to make it more relevant and likely to promote durable solutions for refugees.

1 Editorial Essay: Iraqi Refugees, Beyond the Urban Refugee Paradigm GÉRALDINE CHATELARD AND TIM MORRIS Displacement and exile have been recurrent and durable phenomena affecting Iraqi society for the last 90 years. The process of forming an Iraqi state from the ruins of the Ottoman empire, which Aristide Zolberg has analyzed as a prime factor generating refugee flows, i has been ongoing since 1920. Unfinished endeavours to build a state and nation have been characterized by almost incessant antagonistic claims over the nature of the state and national identity, the exercise of and access to political power, control of natural resources and border sovereignty. Political repression, violent regime change, redefinition of national identity, demographic engineering, and domestic or international armed conflicts have resulted in eviction, deportation, denaturalization, political emigration, and flight from violence. A large part of displacement in Iraq has been internal. But vast numbers of refugees and exiles have also formed a regional and global diaspora extending from Iran, Jordan, Israel, Syria, all the way to such distant emigration countries as New Zealand.

Belated Recognition of Iraqi Displacement

Despite their massive scale, displacement and other forms of involuntary migration from Iraq have so far largely escaped academic interest as topics in their own right. This is in sharp contrast with the large body of research devoted to Palestinian refugees. References to displacement within and from Iraq do exist, but they are scarce and scattered: they generally document displacement in relation to particular ethnicities or sects, episodes of conflicts, or political struggles. ii So far, there has been little attempt to conceptualize Iraqi displacement as a political and social phenomenon or reflect on its historical depth and global scope. iii The displacement that resulted, directly or indirectly, from the toppling of Saddam Hussein's regime by a US-led coalition in April 2003 has appeared to most scholars as a crisis of unprecedented scale. Although many Iraqis started leaving the country as early as 2003, it was only in 2007, at the height of sectarian tensions and generalized insecurity, that advocacy and humanitarian organizations started releasing reports on Iraqi refugees in neighbouring countries. They particularly focused on Syria and Jordan, where the majority had fled, generating media coverage, especially in the US and UK, and a new interest from the part of mostly young scholars. The corpus of academic publications focusing on the post-2003 displacement trend has since been growing. iv It will come as no surprise that the 2007 surge of interest in Iraqi refugees closely corresponded with the beginning of humanitarian and policy engagement from the office of the UN High Commissioner for Refugees (UNHCR) and large donors, particularly the US and the European

Urban Refugee Studies Rises Up Agenda

Most humans now live in towns and cities. As the world urbanizes, so too do patterns of displacement. Increasingly, refugees, asylum seekers, returnees and internally displaced persons (IDPs) are not living in camps and rural areas but in towns and cities. They usually reside in impoverished neighbourhoods where governments are already struggling to provide their own citizens with basic services.

In recent years the growing attention to the phenomenon of displacement to urban areas is reflected in a spate of special issues of displacement-focused publications. viii In part, this interest has been fuelled by the decision of the High Commissioner to focus on the subject for the annual dialogue convened by UNHCR in 2009. Urban refugee studies has gained traction and legitimacy as a subfield of refugee and forced-migration research, structured around a number of established scholars, and a growing bulk of literature. The field has developed analytical paradigms to reach a sociological understanding of specific refugee situations.

In urban areas most governments of host countries leave the management of refugees to UNHCR. The refugee agency often finds itself unable to provide the degree of protection and assistance it commonly provides in camps. Refugees may be hard to access. As their presence is often unauthorized, many keep a low profile and remain unregistered. Many host governments continue to regard camps as the only legitimate space for refugees, and UNHCR has tended, at least de facto, to adhere to this view. Often it has had little choice except to do so in the face of determined governments.

Many refugees, like IDPs, find urban settings attractive, offering better livelihood, social and self-sufficiency opportunities than rural or camp settings. Outside of the physical and legal space of camps, refugees in cities are often not granted a legal status under international or domestic law, thus remaining unprotected. For many the main consequence of lack of protection is having to pay bribes to government officials to move about cities, to trade, or to seek work. In urban areas, governments and political parties may frame refugees (as well as migrants and IDPs) as security threats to the existing social and economic fabric and strive to maintain their segregation to prevent their long-term settlement and integration. By implying that urban refugees should be contained, and that their stay is temporary, governments deny the possibility of accession to citizenship. Deemed a burden on national resources and often demonized, urban and other outof-camp refugees may be faced with arbitrary state action and a hostile environment that creates xenophobia and fear among the refugees. This forces the refugees to seek anonymity, generally in urban slums, and adopt strategies of identity or physical concealment. As a result, refugees are prevented from access to existing services and decent livelihoods. Jacobsen ix and others have stressed that urban refugees could be an asset to regional economies if legal avenues were opened to allow them to pursue productive lives within formal frameworks. Fábos and Kibreab x point to the development of transnational spaces within which refugees may rely on, or contribute to, remittances and other forms of support from social networks, often family based. They further note that refugees are often part of mixed-migration movements.

The urban turn in refugee studies, but also in advocacy, has had a strong impact on policy. In recent years, international emergency NGOs, together with UNHCR, have strived to adapt protection and assistance, the two pillars of their actions, to the challenges of operating in an urban environment. They have found it difficult to assess the needs of refugees intermixed among the population of the host country, to distinguish refugees, IDPs and migrants, and to deliver aid to those who either do not necessarily want to be identified or are extremely hard to identify as they live on urban peripheries far from UNHCR offices.

Iraq Displacement Hastens Policy Change

UNHCR recognized that the Iraqi refugee crisis was the biggest urban refugee crisis it had ever been obliged to address. The agency's reports of its operations in the main host countries of the Middle East, namely Syria, Jordan, and Lebanon, have also made it abundantly apparent that the crisis is different from previous urban refugee situations. The profile of the refugees, in their majority from the urban middle class, and the operational environment resulting from the development levels of Iraq and regional host states, together with the latter's reception policies for Iraqis, have presented humanitarian actors with some unprecedented challenges to existing protection and assistance models. Furthermore, the high political profile of the crisis, particularly in the US, has generated a donor response significantly greater than for other UNHCR caseload of urban refugees and IDPs. All these factors have allowed the agency to test new and costly approaches for delivering assistance, such as systematic outreach efforts, the provision of services to refugees and nationals alike on the basis of vulnerabilities, partnership with local NGOs, xi informing refugees via SMS or delivering cash through ATMs and employing refugees as outreach workers and counsellors. xii It is unlikely that these new models will be easily replicable in other urban refugee situations where funding levels for assistance are lower, the operational context in host countries is less favourable, and refugees have a more typical thirdworld profile.

Operations in favour of Iraqi refugees have also prompted UNHCR to revise its much-criticized urban policy, launching a new Policy on Refugee Protection and Solutions in Urban Areas in September 2009. Its roll-out correlated with the expansion of the refugee agency's activities in favour of Iraqi refugees. However, the Iraqi refugee crisis poses a question of the universality of the new urban refugee policy. The document acknowledges the need to adapt to the specific context and the circumstances, capacities, and vulnerabilities of different groups and individuals within the refugee population. It provides a checklist to assess protection risks and vulnerabilities, describing in detail what these risks can be in extreme circumstances. On the other hand, very little guidance is given on how to identify and assess risks and vulnerabilities in situations where refugees are moving between middle-income countries, and where the protection environment is more favourable yet far from guaranteeing local durable solutions for refugees.

Cumulative Causes of Displacement

A consideration of the causes of displacement, which are extremely varied, helps understand the untypical profile of Iraqi refugees. As early as 2003, several thousands of political émigrés who were close associates of the Saddam Hussein regime left with their families and assets to find refuge in Arab countries, particularly Syria and Yemen, which welcomed them and offered them a stable status. That same year, the dismantlement of the Iraqi army and the order, passed by the US-led Coalition Provisional Authority, to remove all public sector employees who had been members in the Baath party left over half a million Iraqis without an income and disenfranchised. Among them were large numbers of professionals, such as medical doctors, engineers, teachers, and university professors. Furthermore, the lifting of the international embargo, imposed on Iraq by the UN-Security Council in 1990, gave way to a neo-liberal order which made the professional conversion of former civil servants difficult. xiii This situation was compounded by an assassination campaign targeting secular intellectuals and professionals. Factors have therefore combined to force or convince tens of thousands of middle-class Iraqis to seek security and employment abroad, particularly in other Arab countries, from Jordan and Egypt all the way to the Gulf.

The major impetus for displacement was however the sectarian killings and cleansing affecting several areas of Iraq, particularly Baghdad, in 2006-8. During those years, Syria, the only country of the region with borders still universally open to Iraqis, received the largest number of refugees. Within this group, socio-economic and geographical backgrounds have been more varied than among political émigrés and professionals; however, the majority still originates from the Baghdad middle class. Less economically or socially privileged Iraqis forced into displacement have remained inside the country as IDPs.

Further factors convincing many Iraqis to take the decision to leave are the constant deterioration of public services (at the time of writing, Baghdad only receives four hours of electricity a day) and the growing rate of unemployment (close to 30 percent). For many, it is a combination of various types of insecurityphysical, social, and economictogether with a sense of alienation from the new political and religious order now prevalent in Iraq that has prompted their departure and still prevents them from considering return a viable option.

The pattern of displacement has not been a sudden and vast movement of people across borders, limited in time. Rather, it has been a constant out-migration since 2003, with a peak in 2006-7. Entire family groups have left with children and, at times, aging parents. Most did not flee abroad reactively, but after pondering their decision and making preparations, including selling properties. In several cases, the decision to leave Iraq came after an initial episode of internal displacement.

Mixed Migration and Patterns of Mobility

Iraqi refugees have to be understood as part of a large flow of mixed migration created by the major geopolitical and economic reconfiguration of Iraq which the US intervention has prompted. The integration of Iraq within the global free market, the war and reconstruction economy, and the possibility of travelling outside the country, strictly controlled under the Baath, afforded new opportunities for Iraqis with capital to invest in real estate and the private sector of neighbouring states, and in cross-border trade. This capital flow has benefitted the economies of countries hosting refugees from Iraq. Already in 2004-5, Iraqi businesses and community organizations started becoming highly visible in Damascus and Amman, the two major urban centres where refugees from Iraq have moved. Many of those Iraqis who left with financial and/or professional assets were able to successfully invest in other Arab countries, in some cases creating employment opportunities for less affluent refugees, generally in the informal sector. This has particularly been the case in areas of Damascus where Iraqis have gathered.

Not all Iraqi capital holders with a foothold in another Arab country are refugees. Many business entrepreneurs operate between Iraq, a base in the region, and the international market, and keep their families in security in Beirut, Amman, Cairo, the Gulf, or even a Western country. Dual residence is also a common feature of the Iraqi political class with duties carried out in Iraq, and family life lived elsewhere, including in the more affluent Arab capitals that also host refugees. Furthermore, Damascus, Amman, and Beirut play hub to activities for large numbers of temporary visitors from Iraq: patients seeking high quality medical care, university students pursuing an education, pilgrims to Shiite shrines in the Syrian capital, holiday visitors escaping the summer heat at home, and so on. xiv

Migration Regimes Sharpen Socio-economic Differences

Overwhelmingly from the middle and upper classes, and with urban backgrounds, Iraqi refugees originate from a middle-income, oil-producing country with what were, at one time, good social and education services, which progressively deteriorated over several decades due to the Iran-Iraq war of the 1980s, the international sanctions applied between1990 and 2003, and the US-led invasion. The refugees have first-world expectations in terms of living standards, medical care, and quality of education for their children. Exile has sharpened social stratification between those who have maintained socio-economic status and those who have not, creating anxieties and uncertainty among the latter.

The Arab states receiving Iraqi refugees are themselves middle-income countries generally experiencing a crisis of the welfare state and increasingly adopting neo-liberal policies. They have a vested interest in offering privileged access and status to Iraqis with capital to invest or to spend on the local market and services, regardless of the reasons why they have come to stay. Each of these countries, particularly those sharing a border with Iraq, also envision their policy vis-à-vis Iraqis willing to enter or stay on their territory within specific geopolitical and domestic agendas. None of the main host countries receives Iraqis within a refugee regime. Rather, Iraqis are fitted within migration regimes that tend to favour those with financial, professional, or political assets.

Syria has been the most inclusive host facilitating the near universal entry of Iraqis, and the delivery and renewal of one-year residence. The government has also offered Syrian passports to high-level Iraqi Baathists. By contrast, Lebanon only allows entry to Iraqis with financial means, and has requested that those who want to stay long-term find a local sponsor to be granted residence permits. Many Iraqis who entered illegally or remained without a sponsor have been detained. Jordan and Egypt restrict entry based on financial means or professional guarantees. They grant one-year residence to holders of financial capital or legal work contracts. The authorities however apply a tolerance regime to Iraqis inside the country who fail to meet residence requirements, and they refrain from systematic detention or deportation.

In all cases, because Iraqis are treated as migrants, their access to the work market is governed by labour laws applying to foreigners. The general trend has been to deny work permits to Iraqis except in professions where skills are in demand. Since labour markets in host countries are already congested, and unemployment high in sectors where educated Iraqis have competences, vast numbers of refugees have been left without employment or forced to seek informal jobs below their qualifications. This has greatly contributed to the sense of insecurity and anxiety of Iraqi individuals and families who have used their savings and survive on remittances from relatives in Iraq or the diaspora to strive to maintain living standards, particularly quality education for their children.

As migrants, Iraqis are free to settle where they wish, in urban or rural areas, and to rent or even buy properties when then can so afford. Residential patterns reflect socio-economic status, real or aspired, as many Iraqis make desperate financial efforts not to move to less affluent areas in large Arab cities. Iraqi neighbourhoods have developed in the centre or the periphery of Damascus, Amman and Cairo with ethnic businesses catering for the needs of the new residents. xv In Amman, for example, Iraqis are known to be scattered across the city. The most affluent ones cluster in a number of residential neighbourhoods in the west part of the capital where a high-end Iraqi business area has also developed. Less well-off Iraqis have regrouped alongside poorer Jordanians, Palestinian refugees, and labour migrants in the eastern part of Amman. This is also where local and international NGOs have concentrated their social services.

Refugee Policy and Assistance

UNHCR operates through agreements or memorandums of understanding with Arab host governments whereby responsibilities for refugee assistance and protection are shared. Michael Kagan provides an in-depth analysis of the modalities and implications of UNHCR's role as a "surrogate state' in the Middle East." xvi He also sees the Iraqi refugee crisis as exemplifying the "grant compromise" of global refugee policy, namely burden sharing: high donor interest has allowed UNHCR to mobilize considerable resources channelled to services for refugees delivered by the UN refugee agency, international NGOs, or host governments.

However, there are marked differences between host countries in their willingness to open staterun services to Iraqis. Syria and Jordan allow Iraqis to use government medical facilities and schools regardless of their residence status and situation vis-à-vis UNHCR. In Jordan and, to a lesser extent, Syria, the vast amount of international aid generated by the Iraqi refugee crisis has served to upgrade public facilities that benefit host-country nationals more than the refugees from Iraq. xvii By contrast, Lebanon has opened public schools and medical facilities only to Iraqis registered with the UN refugee agency, whereas Egypt has closed access for all Iraqis to public services and has impeded alternative service provision by NGOs. UNHCR also directly operates programs such as the delivery of cash assistance to needy refugees, and has set up mechanisms to coordinate between different assistance providers.

Syria does not fit neatly into Kagan's analysis. The country's almost constant open-door policy to Iraqi refugees, and the universal access it grants them to public facilities while receiving much less donors' assistance than Jordan, require a consideration of the country's regional and international political agendas. In general, it can be argued that the relative favourable "protection space" afforded underprivileged Iraqi refugees by host countries is as much the result of economic and geopolitical calculations by host governments as the effect of international assistance and UNHCR's assumption of the role of a surrogate state.

Resettlement and Asylum

The high interest of resettlement states is the second pillar of the "grand compromise" between regional host states and Northern donors. All Arab host countries envision the stay of Iraqis, particularly those dependant on assistance, as temporary and rule out naturalization. xviii Even Iraqis with assets and a residence permit share with their less advantaged co-nationals a feeling of uncertainty about the future because there is no guarantee that host states will not shift policy and force them to return to Iraq. The current instability in the region, particularly in Syria and Egypt, exacerbates this feeling and it appears that refugees have returned to Iraq in unprecedented numbers over the first quarter of 2012. xix In this context, probably the main reason why Iraqis register with UNHCR is to access third-country resettlement.

The resettlement program has taken up a large amount of UNHCR staff time and financial resources. In 2010, Iraqis were the largest group of beneficiaries of UNHCR-facilitated thirdcountry resettlement programs (26,700). xx The US has accepted far more Iraqis than the other developed country (including Canada, the Nordic countries, Australia and New Zealand) that each year participates in the program. xxi As of April 2012, 58,810 Iraqi refugees had arrived in the US. Numbers have been declining since arrivals peaked in 2009. xxii The process has been extremely slow with a large number of Iraqis waiting well over a year between admission and actual resettlement because of several levels of security screening. xxiii This delay maintains Iraqi individuals and families in an unbearable situation of uncertainty, keeping them dependent on humanitarian assistance or depletion of personal resources, thwarts their efforts to plan for their future and, often, that of their children, and forces an increasing number to return to Iraq where insecurity still prevails.

While the US has been the main resettlement country, Western European states have received the 9 largest number of in-country asylum applications from Iraqis, with Sweden topping the list. Another unusual aspect of the ongoing crisis of Iraqi displacement is that there are considerable numbers of Iraqi asylum seekers whose claims have been refused but who are in a legal limbo as European states seek to enforce decisions to forcibly return them to Iraqdespite UNHCR advocacy. Judgments in 2010 by the European Court of Human Rights blocking forced returns were followed by a resolution of the Iraqi parliament in June 2012 banning the forced return of tens of thousands of failed asylum seekers and threatening to fine airlines that take part in deportation programs. There appears to be no precedent for the post-crisis legislature of a refugee-producing state to refuse to take back its own nationals.

Assumptions about Refugees' Needs

The unusual profile and first-world expectations of the refugees, the desire of governments to assert control and sovereignty over humanitarian intervention, and the role UNHCR has come to assume as a "surrogate state" for non-Palestinian refugees in the region have rendered models developed to respond to the needs of urban refugees in extremely different circumstances illfitted to the situation of the Iraqis.

Interventions initially proceeded from a series of assumptions about the needs and vulnerability of the refugees. In its early stages, programming was emergency-oriented and aimed at meeting such needs as access to primary health care and basic education. Refugees were thought to be at threat of arrest and detention, refoulement, harassment, exploitation, discrimination, and vulnerability to sexual and gender-based violence. Over the last two years, UNHCR and its implementing partners have made considerable progress in refining their approach, responding to Iraqi refugees' actual needs: secondary and tertiary health-care psychosocial programs (particularly mental health for survivors of torture), remedial and higher education, skills maintenance and development.

"Guesstimating" Numbers

Arguably, the most difficult assumption to dislodge has been that there are vast numbers of unregistered Iraqi refugees, fearful and in hiding among the host population. Indeed, the original estimates of the number of Iraqi refugees put forward by host countries at the April 2007 donor conference organized in Geneva by UNHCR were above two million. In 2009, the number of registrations with UNHCR peaked at just above 310,000 throughout the Middle East, with 220,000 in Syria and 52,000 in Jordan. When the expected number of refugees failed to register, humanitarian actors, advocacy organizations, the international media, and refugee scholars all concurred that uncounted numbers of Iraqis were in hiding in the cities, fearing arrest and deportation.

UNHCR and NGOs inaugurated outreach programs that considerably stretched their human and financial resources to try to locate these "invisible" refugees and convince them to register. However, after a couple of years of these costly efforts, concerned agencies came to admit that, at least in Syria and Jordan, over 90 percent of those Iraqis in need of protection and/or assistance were already registered. This is not to say that the figure of 310,000 represents 90 percent of Iraqis who left to escape political or criminal violence, or the new social, moral, and economic order brought about by the change of regime, which for many has proven disorientating. However, it is likely that other Iraqis who have relocated from Iraq without seeking registration with refugee or asylum agencies have to be approached in terms different from those offered by both the international refugee regime and refugee studies.

Difficulty in estimating numbers of refuges is compounded by the mixed nature of Iraqi migration to neighbouring countries and the circulation of refugees between a host country and Iraq. xxiv This situation is not unlike that of other refugee crises worldwide after the intensity of conflict decreases. Afghanistan provides another major example of the phenomenon.

Policy Effects of Inflated Numbers

There has been much discussion about the size of the Iraqi refugee population as well as a tendency among practitioners and scholars to base accounts, assessments, narratives, and analysis on the highest figures publicized by host governments. xxv There has also been much debate behind closed humanitarian doors and academic institutions about the relevance of speculating on the number of refugees when what mattered was the amount of suffering the displacement experience was inflicting.

There are at least some reasons for arguing that inflating the number of refugees has had direct detrimental effects on their immediate well-being and future. Kate Washington and Harriet Dodd, xxvi reflecting on their experience working with a large international NGO in Jordan since 2007, concur that the adherence of large donors and UNHCR to very high figuresup to 750,000 Iraqis in Jordan at some pointnegatively impacted the capacity of operational aid agencies to plan, tailor, and implement programs in the best interest of the refugees. The disproportionately large amount of funding flowing from donors, particularly the US government, also had negative consequences: the rapid expansion of agencies applying readymade models and the resistance to change in approach even as it became obvious that the Iraqi refugee situation was not, except maybe in its very early stage, a humanitarian crisis; competition between NGOs for, and retention of Iraqi beneficiaries; agencies focusing on meeting predeveloped targets rather than on quality and goal of the services; the difficulty of developing a sustainable strategy focused on a realistic number of beneficiaries; and the development of an assistance-seeking behaviour in the Iraqi community. With some nuances, these remarks are equally valid for Syria. xxvii The perception of the Iraqi refugees by host communities has also been affected by their representation in official discourse, in the media, and by many international NGOs as hordes of people preying on scarce national resources or as potential exporters of the kind of sectarian conflict which raged in Iraq in 2006-7. xxviii These representations have, in several cases, created xenophobia and tensions between nationals and refugees. They have also provided justification for authoritarian governments to enhance their security apparatus and restrict the entry of Iraqis fleeing violence. xxix Unfortunately, at the time of writing, these patterns are being reproduced in relation to Syrians seeking refuge in neighbouring countries while fleeing massacres and repression at home. These misconceptions have also undermined advocacy efforts by UNHCR and international NGOs to encourage host governments to support refugees' self-sufficiency through allocation of work permits, vocational training, or credit schemes for small businesses. Which government, anywhere in the world, would willingly open its formal labour market to a foreign work force thought to represent up to 10 percent of the national workforce?

Another distorting effect of inflated numbers has been sidelining of UNHCR resettlement endeavours and the fact that the program has provided ammunition to critics of the US intervention in Iraq. In January 2011, UN High Commissioner for Refugees António Guterres stated that 60,000 Iraqi refugees had departed to resettlement countries while another 60,000 were still in need of resettlement. In statistical terms, there are at least two contrasting ways of measuring the overall resettlement efforts. One is to look at the ratio of resettled refugees to the numbers of Iraqi refugeesaccording to host governments about two million. This would represent 3 percent of the total estimated refugees already resettled, and another 3 percent in need of resettlement. The other way is to take as a basis the number of Iraqi refugees registered with UNHCR throughout the region. If and when the target of 120,000 is met, 40 percent of the total number of Iraqi refugees registered in 2009, or 46 percent of those registered in early 2011, will have been resettled. Considering the unreliability of the estimates used by host governments, the second set of figures is more likely to reflect the size of the efforts and the remaining needs. Here too, it may make a difference for policy makers and public opinion in resettlement countries to be informed by refugee advocates and the media that 60,000, and not two million, refugees are desperately waiting to be granted the safety and stability which they hope resettlement will provide them.

Towards Improved Understanding of Iraqi Displacement

Social scientists have tended to see those displaced from Iraq almost exclusively through paradigms developed to account for the experience of urban refugees facing extremely different circumstances. The caseload of Iraqi refugees has not been typical urban refugees of the kind now found throughout the world. Arguably, the category of urban refugees has been too rigid, unable to adequately describe either the situation of displaced Iraqis or to analyze the universal applicability of programs to assist them. This has prompted several contributors in this issue, particularly those with a strong ethnographic insight, to engage with Iraqi refugees on a different plane. Distancing themselves from policyinformed analytical frameworks, they anchor their discussions within current social science debates, exploring the nexus between gender and citizenship among women refugees; the dialectic of provisional return and place-making; social stratification, class, and the effects of neo-liberalism on refugees; the production and reproduction of state sovereignty by international NGOs; the impact of exile on relations within the nuclear family and rebuilding of roles and meaning; or migrant's social capital and its role in information sharing about the resettlement process.

Essays in this issue also aim to contribute to some crucial policy issues: the effect on refugees of irregular migration and refugee containment measures adopted by the more wealthy states; the politics of resettlement, particularly in the US and EU; the process of accommodation taking place between refugees and host societies and governments in countries of the Middle East; the necessity for humanitarian actors to recognize regional and international mobility as legitimate coping mechanisms for refugees; and finally the urgency to look beyond conventional approaches to durable solutions to the plight of the refugees.

The three opening contributions examine the legacy of previous trends of refugee migration from Iraq, so far largely disregarded by scholars and the humanitarian community. Thousands of Iraqis aspiring to reach safety from the regime of Saddam Hussein in Australia, which they expected to be a liberal asylum country, have spent years stranded in transit countries in Southeast Asia with no durable solution in sight: they are now joined by new arrivals from Iraq. In Middle Eastern host countries, where no stable legal status is available to poor refugees, UNHCR has fitted the pre-2003 Iraqi caseload into resettlement programs that would force some of these long-term refugees to sever the family ties they have built in the host country. More fortunate escapees from the Baathist regime, who managed to rebuild a secure life in exile, have taken advantage of post-2003 opportunities to go back to Iraq, only to then realize how much home, and their sense of it, had changed, making permanent return impossible.

Iraqis Stranded in Indonesia

Sue Hoffman addresses the experience of Iraqi asylum seekers stranded in Indonesia after failing to reach Australia through irregular migration in the late 1990s. Often experiencing multiple traumasfrom persecution at home to unsuccessful boat journeys trying to reach the coast of Australia, in several cases resulting in the death of loved onesthese refugees are difficult to resettle, because they represent the old caseload of pre-2003 refugees from Iraq. They have fallen through the gaps of the international refugee protection system and their experience of "wasted lives" is poignant. This significant group is at the core of recent policy debates in Australia, not least because of the continuous furor over boat arrivals and the centrality of anti-refugee rhetoric in political discourse (blaming Iraqis, and other asylum seekers, as "queue-jumpers"). The contribution documents the action of UNHCR and the International Organization for Migration (IOM) in Indonesia and highlights the essential problem with Australian demonizationthat there is, effectively, no regional queue for them to "jump." The paper also accounts for arrival, along the same routes, of new Iraqis fleeing the Middle East after 2003, and the reasons behind the refugees' choice of this migratory route.

Iraqi Women Returning from Australia

Katie Vasey examines the experience of Iraqi women who relocated to Australia as part of Australia's Refugee and Humanitarian Program during the years of international sanctions against Iraq, and who returned to visit their homeland after the fall of Saddam Hussein. The author explores these women's experiences of provisional return to Iraq, and questions how their return influences their "home" making in Australia. Through narratives of longing, belonging, return to Iraq and return to Australia, Vasey interrogates the complex, contradictory, and ambivalent relationships that Iraqi women developed with both their host and home countries and how this impacted upon their well-being. Iraqi women expected to experience a feeling of well-being upon return to Iraq, as they stepped back into the "home country," an idealized place that had allowed them to cope with the anxieties of exile. Such feelings of well-being, security, and being "at home" crumbled with the realization that the social environment had irreversibly changed, and that returning permanently to Iraq was impossible. This realization was not only based on the fact that the country had, in their absence, been subjected to ongoing destruction and devastation, but also related to the transformations they had undergone in Australia.

Divorced Iraqi Women in Jordan

Susan MacDougall explores the nexus between divorce, immigration laws, and refugee status for Iraqi women in Jordan who had arrived in the country before 2003 and were previously married to Jordanian men. The legal systems effectively fence off divorced women in Jordan, with child custody laws preventing them from leaving and citizenship laws denying them the possibility of naturalization, reinforcing their vulnerability and social exclusion. These women register with UNHCR as an alternative to their lack of status but are funnelled into a refugee management regime that envisions Jordan merely as a place of transit for refugees. This is inappropriate for women who have lived in the country for over a decade and have children with Jordanian citizenship. Central to the discussion are issues of gender and citizenship, or rather how citizenship is gendered in particular ways in countries of the Middle East, and how the refugee regime is ill-suited to provide durable solutions to women whose situation does not fit neatly into existing legal categories.

Class and Rejection of the "Refugee" Label

By introducing the class variable, Elisa Pascucci offers a complex view of what displacement means to those who do not want to be called "refugee." The author challenges typical portrayals of Iraqis in the Middle East while prompting the reader to consider the ways in which vulnerability and class statute may coexist. Her informants underplay ethnic and religious differences, and emphasize rather social stratification, past or created by displacement, as the most divisive factor among Iraqis. Class divides in exile between those who can maintain stability and security through financial capital, taking advantage of neo-liberal investment policies and unconcerned by the regime of international refugee assistance, and those who cannot, or who cannot any more after a slow process of downward social mobility during which they strived to maintain social status through remittances and/or savings. What Pascucci deems "middle-class anxieties" about children's education and standards of living pose challenges to international assistance providers used to dealing with other types of refugee vulnerabilities. Pascucci reminds us that, beyond the focus of humanitarian agencies and legal scholars on the legal and policy context of reception in host countries, social and economic factors are strong determinants of the refugee experience. She also argues that neo-liberal policies and the political economy of bilateral relations (such as trade and investment linking countries of origin and settlement of the displaced) need to be factored into any meaningful analysis of the refugee experience and context of vulnerability.

INGOs and State Sovereignty

Sophia Hoffmann takes the reader to a different planethat of humanitarianismunveiling the underlying tendency among mainstream INGOs to work within social relations established by and, in essence, reproducing the hegemonic power of state sovereignty. INGO practices towards Iraqi refugees in Damascus reveal how the "sovereign ideal" of territory, nation, and government informs techniques of migration management, which in turn reproduces this ideal. The author makes a point crucial to an understanding of how the humanitarian regimewhose perspective has dominated the literature on Iraqi refugees --has also blurred an appreciation of the variety of Iraqi experiences in exile and in migration. She notes that professional INGOs were prevented by the Syrian government from amassing knowledge about the Iraqi population and could not conduct the needs assessments that usually form the basis of aid-projects. INGOs in Damascus thus based their interventions largely on assumptions about the Iraqi population, which flowed from established ideas and tropes about refugees, intimately connected to sovereignty and sovereign exclusions. INGO rhetoric, and the academic production that adheres to this rhetoric, reduce the extremely varied existence of Iraqis in exile, which also includes successes, opportunities, strength, health, and self-help, to that of suffering and weakness, and in this contribute to the construction of sovereignty. Yet, as the author notes, refugees negotiate, experience, and subvert in multiple ways the sovereignties projected by the state and the INGOs.

Rebuilding Roles and Meaning within the Family

The contribution by Muriel Génottogether with Muath Asfoor, and Hala Hammad who assisted her in her therapeutic engagement with Iraqi refugee children and their fathers as part of the activities of the NGO Center for Victims of Torture (CVT)brings to the fore the crucial question of how exile affects relations within the nuclear family. The authors account for an innovative experience of psychological counselling with Iraqi refugees in Jordan responding to a request from fathers who had seen their protecting role shattered by violence and displacement. CVT offered to organize regular meetings of small groups where fathers and children worked together with counsellors on rebuilding roles and re-establishing communication though endowing violence and exile with meanings children could access and fathers could utter. One of the key contributions of the paper is that humanitarian intervention does not necessarily reproduce existing models as long as practitioners are ready to listen, propose, engage on par with refugees, and take the risk of innovating. Beyond its disciplinary underpinnings, and its value for practitioners, the paper makes a particularly strong contribution to the literature on refugees' agency. It demonstrates in a powerful yet moving way how, during periods of uncertainty and temporariness, such as between flight and resettlement, refugees can productively engage at the family level to act upon their own future.

Information Sharing among Refugees

Adam Saltsman's focus remains with Iraqi refugees in Jordan. He provides insight into the effects of information sharing (or lack thereof) between international organizations (especially UNHCR) and displaced populations. The author argues that information campaigns by international refugee agencies often falter for two crucial reasons beyond resource scarcity. First, agencies disseminating information are often under pressure to curb the outflow of migrants from the Global South, and as a result, information provision has tended to be coloured by efforts to control or protect against forced migrants' movement or desires. Second, these agencies do not typically consider or engage with migratory capital, including migrants' informal networks for sharing knowledge about the migratory process, often based on transnational relations. As a case study, the author explores the lived experiences of refugees vis-à-vis both the official information from humanitarian agencies and their informal networks that are transnational in nature. Saltsman makes a compelling case in favour of initiatives contributing to migratory capital, a set of resources on which forced migrants often depend just as much as on the protection of international agencies. He argues that, rather than relying on a model of universal protocol, UNHCR and other agencies should both increase their transparency vis-à-vis the refugee and engage the sorts of local and transnational initiatives that spring up as survival mechanisms in contexts of displacement.

Local Accommodation

Dawn Chatty and Nisrine Mansour offer a more policy-oriented contribution to this issue based on a study of perception among refugees and policy makers in the three main host countries of the Middle East, who are found to be more pragmatic than the international aid community and to broaden the scope for durable solutions. The authors identify an ongoing process of local accommodation that takes please in Syria, Lebanon, and Jordan in lieu of official integration, a term widely rejected because of the sensitivity to the protracted Palestinian refugee situation. Accommodation is the outcome of new patterns of inter-and intra-social relations between host and refugee communities and within Iraqi communities, and is not problem-free as mutual recriminations and competing claims between local and refugee communities are reported. Another important element the authors highlight is the fluid movement of Iraqis back and forth to Iraq as an important mechanism for improving life opportunities and reducing family risk. Mobility is also a common feature of Iraqi exiles' transnational networks, built over decades of displacement from Iraq and linking family members scattered on several continents. The authors make a case for recognizing regional and transnational mobility as a risk-management strategy for refugees for whom the three classic durable solutions are largely inapplicable. They also regret that this mobility is often looked at sceptically by many in the humanitarian aid regime as it raises questions regarding how well Iraqis fit into the "category" of refugee.

Return and Remigration

Echoing and complementing Chatty and Mansour's paper, Vanessa Iaria's essay provides an overview of the complex political and economic context within which Iraqis who fled to Syria or Jordan after 2003 make decisions regarding return and remigration. She found that Iraqi refugees' decision to return is driven less by improvements in Iraq than by their desire to rebuild their lives back home and overcome the difficult legal and socio-economic conditions in neighbouring countries. However, the micro and macro transformations occurring in post-Saddam Iraq also have a strong bearing on refugees' return and reintegration in their home communities. In the absence of security at home and durable perspectives in a neighbouring country, several of the Iraqis Iaria interviewed engage in transnational mobility and livelihoods as a survival mechanism. The article makes two notable contributions to refugee policy. One is that the voluntary repatriation of refugees cannot be interpreted solely as an evidence of progress in a series of post-conflict issues, including restoration of security and political stability. The other is that the international refugee regime's concern with governing refugees' movements after repatriation by stopping remigration may hamper the natural transnational practices that refugees have developed as alternative livelihood strategies in the absence of other, durable solutions.

Limits of Third-Country Resettlement

Chantal Berman's closing contribution stands as a counterpoint, illustrating the inadequacy of third-country resettlement as the main durable solution envisioned so far by the humanitarian regime for Iraqi refugees. The rationale for resettlement policies is to be found elsewhere than in the humanitarian needs of the refugees. Using a detailed comparative policy focus, the author examines US and EU policies regulating the selection and admission of Iraqi refugees since 2003, focusing on the divergent political priorities and structural considerations underpinning variations in resettlement levels during this time. The author argues that US resettlement of Iraqi refugees is primarily an element of foreign policy, defined by strategic objectives in Iraq and the surrounding region, whereas admissions to the EU reflect ongoing intra-European debates surrounding the construction and modification of the Common European Asylum System(CEAS). While Europeans opposed to Iraqi resettlement have argued for sole US responsibility for Iraqis' humanitarian needs, Bush Administration officials justified policies of minimal resettlement through a causational de-linking of the US invasion and the ensuing refugee crisis. Refugee resettlement (or a calculated lack thereof) remains one tool among many in the diplomatic and strategic arsenal of the United States on a global scale. Finally, comparing US and EU policies vis-à-vis Iraqi refugees raises questions about states' accountability for refugee-producing policies, and about the corresponding levels of aid and resettlement required to offset this "responsibility."

Géraldine Chatelard is an independent researcher (http://independent.academia.edu/GéraldineChatelard). Tim Morris is an independent consultant (www.timmorris.info).

i Aristide Zolberg, "The Formation of New States as a Refugee-Generating Process," Annals of the American Academy of Social and Political Science 467 (1983).

ii

  Major references providing direct or indirect account of this long history of displacement are: Abbas Shiblak, The Lure of Zion: The Case of the Iraqi Jews (London: Saqi Books, 1986); Yitzhak Nakash, The Shi'ites of Iraq (Princeton: Princeton University Press, 1994); Pierre-Jean Luizard, "Iraniens d'Irak, une élite religieuse chiite face à un état Sunnite," Cahiers du Cemoti 22 (1996); Nelida Fuccaro, "Ethnicity, State Formation, and Conscription in Postcolonial Iraq: The Case of the Yazidi Kurds of Jabal Sinjar," International Journal of Middle East Studies 29, no. 4 (1997); Maarten Michiel Leezenberg, "Between Assimilation and Deportation: History of the Shabak and the Kakais in Northern Iraq," in Syncretistic Religious Communities in the Near East, ed. Krisztina Kehl-Bodrogi, Barbara Kellner-Heinkele, and Anke Otter-Beaujean (Leiden: Brill, 1997); Madawi Al-Rasheed, Iraqi Assyrian Christians in London: The Construction of Ethnicity (Lewiston, NY: The Edwin Mellen Press, 1998); Ismet Cheriff Vanly, "The Forgotten Feili Kurds of Iraq," in Kurdish Exodus: From Internal Displacement to Diaspora,

accessed 20/06/2012, http://ceriscope.sciences-po.fr/content/part2/les-irakiens-en-syrie-et-en-jordanie.