Sandrine Gomes

Elodie Petit

Lawrence Frézet

Jean-Marie Nedelec

Ameni Gharzouni

Sylvie Rossignol

Guillaume Renaudin
email: guillaumerenaudin@sigma-clermont.fr

Lawrence Frezet

Temperature stability of a pure metakaolin based K-geopolymer: Part 2. Variations in the mesoporous network and its rehydration stability

Keywords: Geopolymers, Characterization, Thermal treatment, Densification

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1-Introduction

Geopolymers, the usual name for the more conventional denomination of alkali aluminosilicate gels, are inorganic solids obtained by the alkaline activation of an aluminosilicate precursor.

The precursor can be either a calcined clay (usually metakaolin, a dehydroxylated natural kaolin) or low-calcium aluminosilicate industrial by-products (fly ashes or ground blast furnace slag). In most cases these precursors are activated with an alkaline aqueous solution based on sodium or potassium, which induces the dissolution of the precursors followed by the polymerization of [AlO4] 5-and [SiO4] 4-tetrahedra into a three-dimensional network. The solid obtained is completely amorphous [START_REF] Provis | Geopolymers: Structures, Processing, Properties and Industrial Applications[END_REF][START_REF] Provis | The role of mathematical modelling and gel chemistry in advancing geopolymer technology[END_REF][START_REF] Duxson | Geopolymer technology: the current state of the art[END_REF][START_REF] Chlique | XRD analysis of the role of cesium in sodium-based geopolymer[END_REF] and porous, [START_REF] Provis | Geopolymers: Structures, Processing, Properties and Industrial Applications[END_REF][START_REF] Kriven | Microstructure and nanoporosity of as-set geopolymers[END_REF][START_REF] Kong | Comparative performance of geopolymers made with metakaolin and fly ash after exposure to elevated temperatures[END_REF] and presents interesting mechanical properties. [START_REF] Li | Utilization of chitosan biopolymer to enhance fly ash-based geopolymer[END_REF][START_REF] Palomo | Chemical stability of cementitious materials based on metakaolin[END_REF] Geopolymers belong to the family of inorganic binders, however their setting mechanism and setting productslinked to the geopolymerization reaction [START_REF] Duxson | Geopolymer technology: the current state of the art[END_REF][START_REF] Babushkin | Thermodynamics of Silicates[END_REF][START_REF] Xu | The geopolymerisation of alumino-silicate minerals[END_REF][START_REF] Dimas | Polymerization in sodium silicate solutions: a fundamental process in geopolymerization technology[END_REF] are fundamentally different from the hydration process of conventional Portland cements.

Geopolymer binders generate a significant improvement in CO2 emissions (compare to Portland cement production), [START_REF] Duxson | The role of inorganic polymer technology in the development of 'green concrete[END_REF][START_REF] Weil | Life-cycle analysis of geopolymers in geopolymers[END_REF][START_REF] Mclellan | Costs and carbon emissions for geopolymer pastes in comparison to ordinary portland cement[END_REF][START_REF] Habert | Recent Update on the Environmental Impact of Geopolymers[END_REF] present unusual thermal and acid resistance, [START_REF] Li | Utilization of chitosan biopolymer to enhance fly ash-based geopolymer[END_REF][START_REF] Pacheco-Torgal | Durability of alkaliactivated binders: a clear advantage over portland cement or an unproven issue?[END_REF][START_REF] Barbosa | Thermal behaviour of inorganic geopolymers and composites derived from sodium polysialate[END_REF][START_REF] Fernández-Jiménez | New cementitious materials based on alkali activated fly ash: performance at high temperatures[END_REF][START_REF] Malviya | Durability of fly ash based geopolymer concrete using alkaline solutions (NaOH and Na2SiO3)[END_REF] as well as the ability to stabilize various kinds of wastes (including nuclear wastes). [START_REF] Pacheco-Torgal | Bond strength between concrete substance and repair materials: comparisons between tungsten mine waste geopolymeric binder versus current commercial repair products[END_REF][START_REF] Palomo | Alkali-activated cementitous materials: Alternative matrices for the immobilisation of hazardous wastes: Part I. Stabilisation of boron[END_REF][START_REF] Lambertin | Corrosion behaviour of Mg alloys in various basic media: Application of waste encapsulation of fuel decanning from UNGG nuclear reactor[END_REF][START_REF] Cantarel | Solidification/stabilisation of liquid oil waste in metakaolin-based geopolymer[END_REF] Geopolymers are characterized by high thermal stability, which makes them promising candidates for various applications. Many authors have investigated the thermal behavior of metakaolin-based geopolymers. For instance, Duxson et al. [START_REF] Duxson | Evolution of gel structure during thermal processing of Na-geopolymer gels[END_REF][START_REF] Duxson | Physical evolution of Na-geopolymer derived from metakaolin up to 1000 °C[END_REF] studied the structural variations in sodium-based geopolymers at temperatures up to 1000 °C using DTA, quantitative XRD and FTIR. They found that phase stability is Si/Al ratio-dependent, with two different densification mechanisms: viscous flow and the collapse of the pore network. Both are responsible to a large extent for thermal shrinkage. It has been demonstrated that the beginning of the crystallization process, corresponding to the loss of the amorphous characteristic of the geopolymer, is also Si/Al ratio-dependent and alkaline dependent, with the formation of (Na,K)AlSiO4 above 850°C. [START_REF] Duxson | Evolution of gel structure during thermal processing of Na-geopolymer gels[END_REF][START_REF] Rahier | Reaction mechanism, kinetics and high temperature transformation of geoplymers[END_REF][START_REF] Buchwald | Geopolymeric binders with different fine fillers -Phase transformations at high temperatures[END_REF][START_REF] Barbosa | Synthesis and thermal behaviour of potassium sialate geopolymers[END_REF] In parallel with these physicochemical transformations, mechanical properties are also affected by the temperature. [START_REF] Tchakouté | Thermal behavior of metakaolin-based geopolymer cements using sodium waterglass from rice husk ash and waste glass as alternative activators[END_REF] Despite the advanced research concerning the thermal behavior of metakaolin-based geopolymers, further fundamental knowledge is required in order to understand the chemical and structural variations in the geoplymer network as a function of the temperature, and therefore to evaluate their potential for high-temperature applications as refractories and in fire-retardant or fireproof applications.

In the first part of this study, the thermal stability of the mineral matrix of a potassium-based geopolymer was highlighted up to a temperature of 900 °C, before crystalizing into kalsilite and leucite. [START_REF] Gomes | Temperature stability of a pure metakaolin based K-geopolymer: Part 1. Variations in the amorphous mineral network[END_REF] In order to complete our investigations on the refractory potential of such a geopolymer, we are focusing in the present paper on the behavior of the porous part of the material when subjected to a temperature increase: the pore dimensions in volume and radius, and also its ability for rehydration. It is well accepted that the polycondensation of silicate and aluminate species, at the origin of the formation mechanism of geopolymers, enables a porous material to be obtained with an alkaline residual solution contained in the pores. Mercury intrusion and gas adsorption-desorption isotherm techniques are in favor of a monomodal open mesoporosity for geopolymers. [START_REF] Kriven | Microstructure and nanoporosity of as-set geopolymers[END_REF][START_REF] Jämstorp | Modeling structure-function relationships for diffusive drug transport in inert porous geopolymer matrices[END_REF][START_REF] Boher | Experimental investigation of gas diffusion through monomodal materials. Application to geopolymers and Vycor® glasses[END_REF][START_REF] Maitland | Characterization of the pore structure of metakaolin-derived geopolymers by neutron scattering and electron microscopy[END_REF][START_REF] Metroke | Effect of curing conditions on the porosity characteristics of metakaolin-fly ash geopolymers[END_REF][START_REF] Sindhunata | Structural evolution of fly ash based geopolymers in alkaline environments[END_REF] Nevertheless, direct observations made by transmission electronic microscopy are in favor of a poorly-definedin size and in shapeporous network, [START_REF] Kriven | Geopolymers: nanoparticulate, nanoporous ceramics made under ambient conditions[END_REF] implying the notion of an "ink-bottle" effect. Other studies have also evidenced the presence of macroporosity in combination with the mesoporous network. [START_REF] Duxson | Understanding the relationship between geopolymer composition, microstructure and mechanical properties[END_REF][START_REF] Lloyd | Spatial distribution of pores in fly ashbased inorganic polymer gels visualised by Wood's metal intrusion[END_REF][START_REF] Provis | X-ray microtomography shows pore structure and tortuosity in alkali-activated binders[END_REF][START_REF] Benavent | Effect of composition and aging on the porous structure of metakaolin-based geopolymers[END_REF] The purpose of our work is to determine not so much the fine characteristics of the porous network as its variations with temperature, always with the aim of probing the potential of geopolymers for high-temperature applications because the water contained in the pores, of the order of 25 weigh percent, [START_REF] Melar | The porous network and its interface inside geopolymers as a function of alkali cation and aging[END_REF] provides interesting fire-resistant properties.

The precise characterisation of both geopolymer sub-networks will then be decisive in understanding the fire-resistant properties of the material. Thus, our fundamental studies aim to help in the formulation of a thermally resistant geopolymer composition with the aim of developing a mineral binder with fireproof properties. The targeted material could be used to protect nuclear waste containers and drifts for the planned construction of a geological disposal centre for radioactive waste (Cigeo project carried out by The National Agency for the Management of Radioactive Waste -Andra).

2-Materials and methods

geopolymer synthesis, thermal treatments and storage conditions

The samples used in this paper were exactly those previously prepared and characterized in Part 1 of this study. [START_REF] Gomes | Temperature stability of a pure metakaolin based K-geopolymer: Part 1. Variations in the amorphous mineral network[END_REF] As a summary, the geopolymer was obtained by the potassium silicate activation of a metakaolin of high puritynon-commercial productsupplied by Imerys (AGS quarrying, F-17270 Clérac, France). The samples were called T RH with T the heat treatment temperature after geopolymer preparation (25, 100, 200, 300, 450, 600, 700, 800, 900, 1000, 1100, 1250 or 1400) and RH the storing conditions after heat treatment ('95' for 95 % RH, '30' for 30 % RH or 'bak' for the baked powders), making a total of 37 samples. The interest of these three series was to have different water filling levels for the porous network; from watersaturated (T 95 series) to dry geopolymers (T bak series), with an intermediate water filling level (T 30 series). Figure S1 in the supplemental material superimposes the thirteen heat treatments used with a thermogravimetric analysis of the geopolymer.

1 H solid-state NMR spectroscopy

1 H solid-state NMR experiments were performed using a 300 MHz Bruker spectrometer operating at 7.04 T, the Larmor frequency being 300.1 MHz. [START_REF] Provis | Geopolymers: Structures, Processing, Properties and Industrial Applications[END_REF] H solid-state NMR experiments were carried out using MAS at 30 kHz and a 2.5 mm-diameter zirconia rotor. Static measurements were systematically performed. [START_REF] Provis | Geopolymers: Structures, Processing, Properties and Industrial Applications[END_REF] H MAS spectra were recorded using one pulse sequence and a recycling time of 5 s; chemical shifts were calibrated using adamantane at 1.7 ppm.

DSC measurements and TPM analyses

For thermoporosimetry (TPM) analyses, the water inside the geopolymer was chosen as a probe solvent. TPM analyses were performed by differential scanning calorimetry (DSC) measurements using a Mettler-Toledo DSC 823e apparatus, with STARe software. The DSC apparatus was calibrated (both for temperature and enthalpy) with metallic standards (In, Pb) and water. About 70 mg of the crushed geopolymer sample was introduced into an aluminium DSC crucible of 160 μl. The measurement procedure, under compressed air in airtight crucibles without adding external water, included the four following segments: cooling from room temperature to -60 °C at a rate of 10 °C/min; heating from -60 °C to -1 °C at a rate of 0.7 °C/min; renewed cooling from -1 °C to -60 °C at a rate of 0.7 °C/min; and finally heating to 25 °C at a rate of 10 °C/min to return to room temperature (Figure 1). This procedure enables the characterization of only the porous volume saturated with water under the different storage conditions. A slow rate of 0.7 °C/min was chosen to allow continuous thermal equilibrium inside the DSC cell. Crystallization curves (segment 3) were mainly used for calculation purposes, but corresponding events in the melting curve (segment 2) were systematically checked to avoid artefacts and to determine pore geometry. The calibration of water as a thermoporosimetric probe has been already published by Brun and co-workers. [START_REF] Brun | A new method for the simultaneous determination of the size and shape of pores: the thermoporometry[END_REF] The following empirical relationships were used:

        T T Jg W a
where ΔT is the shift of the thermal transition temperature, Rp the pore radius and Wa is the apparent energy of crystallization for water. The application of TPM formalism beyond the mesoporous domain has been already validated and applied on geopolymer samples, [START_REF] Melar | The porous network and its interface inside geopolymers as a function of alkali cation and aging[END_REF] but for the first time we used internal water to probe only the saturated porous volume.

Gas absorption isotherms

Nitrogen adsorption-desorption isotherms were obtained using a Micromeritics ASAP 2020 instrument at 77 K. The geopolymer degassing process was carried out under two vacuum stages at different temperatures depending on the temperature of the heat treatment applied to the geopolymers. The first step was performed under primary vacuum during at least 24 hours at room temperature for the as-synthesized geopolymer (25 30 sample), 100 °C for the 100 [START_REF] Gomes | Temperature stability of a pure metakaolin based K-geopolymer: Part 1. Variations in the amorphous mineral network[END_REF] sample, and 200 °C for all the other T 30 samples (with T  200). Then a secondary vacuum was applied without modifying the temperature. The second degassing process was controlled by checking the back pressure increase rate after 5 min and 10 min of equilibration. This controlled back pressure was judged satisfactory for values below 10 µm Hg/min. The second degassing duration was sample-dependent to achieve this condition. The average pore size was calculated using the Barrett, Joyner and Halenda (BJH) method [START_REF] Rouquerol | Recommendations for the characterization of porous solids (Technical Report)[END_REF] and the specific area was determined using the Brunauer, Emmet and Teller (BET) theory. [START_REF] Brunauer | Adsorption of gases in multimolecular layers[END_REF]

3-Results

1 H NMR spectroscopy

1 H NMR static spectra on samples stored at 95% RH

First, 1 H NMR static measurements were performed on samples stored at 95% RH in order to evidence the liquid nature of the water present in the geopolymer. As-prepared samples presented a well-defined signal with a single component close to 4.5 ppm, corresponding to free water molecules located in the porous network. For heat-treated samples (stored at 95% RH) the same signal was still observed. This signal became finer when the temperature increased to 700 °C, then decreased in intensity toward 900 °C before disappearing at 1000 °C.

Above 900 °C, the recorded signal corresponded to that of the rotor only (Figure 2a). These results clearly evidence the liquid nature of the water located in the pores of the geopolymer, its reversible departure indicating the open feature of the porous network. The modeling of these signals by a Lorentzian component indicated the sharpening of the signal without modification of its chemical shift (Figure 3b). The Full Width at Half Maximum (FWHM; Figure 3c) of this signal, centred at about 4.5 ppm, is divided by two between room temperature (FWHM = 5.0 ppm) and 600 °C (FWHM = 2.5 ppm), indicating an increase in the 'liquid nature' of the pore wateri.e. an increase in the water dynamic parameterswhich could be due either to a decrease in its containment (increase in pore diameter), to a change in the nature of the interface (wall between the mineral and porous networks), or to a decrease in water salinity (i.e. decrease in its alkalinity). [START_REF] Bellissent-Funel | Single-particle dynamics of water molecules in confined space[END_REF][START_REF] Floquet | Structural and dynamic properties of confined water in nanometric model porous materials (8 Å ≤  ≤ 40 Å)[END_REF][START_REF] Takahara | Neutron scattering study on dynamics of water molecules confined in MCM-41[END_REF][START_REF] Takahara | Neutron scattering study on dynamics of water molecules in MCM-41.2. Determination of translational diffusion coefficient[END_REF][START_REF] Mitra | Dynamics of water in confined space (porous alumina): QENS study[END_REF][START_REF] Shen | Effect of pore size and salt doping on the protonic conductivity of mesoporous alumina[END_REF][START_REF] Briman | Impact of pore size and pore surface composition on the Dynamics of confined water in highly ordered porous silica[END_REF][START_REF] Mamontov | Quasielastic neutron scattering study of dynamics of CaCl2 aqueous solution confined in Vycor glass[END_REF][START_REF] Mamontov | Dynamics of water in LiCl and CaCl2 aqueous solutions confined in silica matrices: A backscattering neutron spectroscopy study[END_REF]

1 H NMR MAS spectra for samples stored at 95% RH

The results from 1 H MAS NMR measurements were very close to the previous ones, again with a single Lorentzian component centered around 4.5 ppm (more precisely around 4.6 ppm for static measurements, slightly shifted to around 4.4 ppm for dynamic measurements; Figures 2b and3b). The 30 MHz rotation speed enabled an increase in the 'aqueous nature' of the probed hydrogen atoms, leading to a general refinement of the signals, which still presented a decrease in their FWHM as the heat treatment temperature rose (from FWHM = 4.0 ppm at room temperature to FWHM = 1.0 ppm at 600 °C; Figure 3c). The same general trends observed simultaneously in static and dynamic measurements indicated that overall the hydrogen atoms from geopolymers belong exclusively to free water molecules located in the porous network. Similar results have been observed for liquid water molecules filling the mesopores in silica glass. [START_REF] Vyalikh | Hydrogen bonding of water confined in controlled-pore glass 10-75 studied by 1 H-solid state NMR[END_REF] The relatively weak value of our 1 H MAS NMR chemical shift (4.5 ppm compared to a value of 5.5 ppm in the case of the Vyalikh study [START_REF] Vyalikh | Hydrogen bonding of water confined in controlled-pore glass 10-75 studied by 1 H-solid state NMR[END_REF] ) could be explained by the strong confinement in a porous network of diameter of the order of 4 nm, which decreases the average number of hydrogen bonds compared to free water. [START_REF] Hartnig | Modification of the hydrogen bond network of liquid water in a cylindrical SiO2 pore[END_REF][START_REF] Thompson | The three-dimensional structure of water confined in nanoporous Vycor glass[END_REF]

1 H NMR spectra for samples stored at 30% RH and for baked samples

Similar measurements were performed on samples stored at 30% RH (Figures 2c and2d), and also on baked samples (spectra not shown here). These last spectra show a significant decrease in the intensity of the signal centred at 4.5 ppm for samples stored at 30% HR, and its disappearance for baked samples. Additional sharp and weak signals were observed at 1 ppm and 0 ppm, which can be attributed to small numbers of hydrogen atoms belonging to hydroxyl groups from silanol and/or Al-OH. [START_REF] Stepanov | Chapter 4 -Basics of solid-state NMR for application in zeolite science: material and reaction characterization[END_REF] Baked samples (at 200 °C for samples previously heat treated at and above 200 °C) showed almost nothing but the fine components from silanols.

Quantitative analyses can be deduced from 1 H NMR spectra when the signals come from liquid water. Thus the spectra were calibrated using the rotor signal (the same rotor having been systematically used for each measurement) and quantitative analyses were performed using the data. The 100 % value was attributed to the amount of water in the as-prepared sample stored at 95% RH, and the results are shown in Figure 3a. Variations observed from static and MAS measurements gave similar results. At 95% RH the amount of water is quite unchanged from room temperature up to a heat treatment temperature of 600 °C, and then decreases continuously to reach about 10 weight percent (wt %) at 900 °C and 0 wt % at 1000 °C, indicating the collapse of the porous structure. The water content in the as-prepared sample decreases to about 45 wt % when stored at 30 % RH, and this amount linearly decreases with temperature. Finally, we can note that 200 °C baked samples contained only a few wt % of water, whatever the temperature of the heat treatment. The FWHM of signals measured from samples stored at 30 % RH, although larger, still decreased with temperature (from FWHM = 9 ppm at room temperature to FWHM = 4 ppm at 600 °C; Figure 3c). At the same time, the chemical shift for these samples was now temperature-dependent, with a decrease in the iso value from 4.8 ppm to 4.0 ppm for both the samples stored at 30 % RH and the baked samples (Figure 3b). Similar results have been observed by Vyalikh et al., with a 1 H MAS NMR chemical shift decreasing from 5.5 ppm to 3.5 ppm when emptying the water from the porous network of silica glass. [START_REF] Vyalikh | Hydrogen bonding of water confined in controlled-pore glass 10-75 studied by 1 H-solid state NMR[END_REF][START_REF] Grünberg | Hydrogen bonding of water confined in mesoporous silica MCM-41 and SBA-15 studied by 1 H solid-state NMR[END_REF] This decrease in chemical shift is attributed to the fact that free water molecules become hydrogen-bonded to surface hydroxyls.

DSC analyses

Thermoporosimetry

DSC measurements were performed on samples taken from their wet storage chamber, without adding water. Only the water-filled pores were probed, which can be far from the total porosity of the sample. Several measurements were performed on the as-synthesized sample stored in wet conditions with a relative humidity of between 90% RH and 98% RH (Figure 4a). Three distinct signals were observed; two of themlabelled 1 and 2 in Figure 4 and corresponding to mesoporositywere not humidity-dependent, whereas a third, temperature-dependent signal (observed for higher crystallization temperatures and labelled 3 in Figure 4) was attributed to incompletely-filled macropores. Analysis of the invariant signals at around -25 °C and -40 °C indicates that they correspond to an apparent pore radius of 2.7 nm and 1.9 nm respectively (Figure 4b). At the same time, comparison with the fusion temperature observed for the third measurement ramp indicated an almost perfect cylindrical feature for the 2.7 nm mesopores (Figure 4c), explaining the large hysteresis observed between fusion and crystallisation signals for confined water. [START_REF] Briman | Impact of pore size and pore surface composition on the Dynamics of confined water in highly ordered porous silica[END_REF] The signal corresponding to the 1.9 nm mesopores was not observed on the crystallisation ramp. The interpretation of this signal close to -40 °C had already been discussed in the literature, and attributed to water homogenous nucleation, which is observed for cylindrical pores below a critical radius. [START_REF] Morishige | Pore-blocking-controlled freezing of water in cagelike pores of KIT-5[END_REF][START_REF] Khokhlov | Freezing and melting transitions of liquids in mesopores with ink-bottle geometry[END_REF] The variations in DSC signals for thermally treated geopolymer are shown on Figure 5. Both temperature-independent signals (N°1 and 2) evolved only very partially. The signal close to -40 °C split into two components at 200 °C and 300 °C before coming back to a single component up to 800 °C (Figure 5a). The modification of this signal with the temperature of the heat treatment was not in favour of a homogeneous nucleation origin (which excludes any interference from the porous surface); however, the differences observed had no significant repercussions in terms of water containment (the pore radius varying between 1.85 and 2.00 nm; Figure 5b). The second mesopore signal varied between -20 °C and -25 °C, and the corresponding calculated pore radii were a little impacted, with variations between 2.4 nm and 2.9 nm (Figure 5c). And finally, the variation in the third, humidity-dependant signal has no interest here because it corresponds to macroporosity. The collapse of the porous network was evidenced for thermal treatments above 900 °C, then its complete closure above 1000 °C, illustrated by the absence of any signal on the DSC curve, reflecting the impossibility for the heat-treated material to exchange water with the environment. Measurements performed on samples stored at 30% RH and on samples baked at 200°C demonstrated the absence of free water in the mesopores: the absence of any signal on the DSC curves for all samples from both series (an example from geopolymer heat-treated at 300°C is shown in Figure 5d) indicating the absence, or a very small amount, of water in closed pores.

Thermal weight loss

The airtight aluminum crucibles used for the DSC measurements were then used to quantitatively determine the free water amount contained in the pores as a function of the heat treatment temperature and the storage conditions. All crucibles were pierced before making fire loss measurements at 400 °C. The water weight amount variations determined in samples stored at 95% RH, at 30% RH and in baked samples were in perfect agreement with the previouslymentioned variations in 1 H NMR intensities (Figure 6). To compare both sets of results on the same scale, 1 H NMR intensities (from Figure 3a) were normalized by considering the amount of 26 wt % of water for sample 25 95 (i.e. its determined weight loss). The absence of signal on DSC curves for both the 30% RH and baked series was surely due to the emptying of the mesopores only, with water still present in the macropores for the 30% RH samples. The 200 °C baked samples should be considered as anhydrous, or more precisely as dry. The few weight percent of observed water were certainly only physisorbed water molecules inherent to the manipulations outside the storage chamber required for the preparation of the samples before NMR or DSC experiments.

Nitrogen adsorption-desorption isotherms

Figure 7 shows nitrogen adsorption-desorption isotherms at 77 K for selected samples. The general shape of the isotherms changed drastically between 800 °C and 900 °C. As-prepared geopolymer (i.e. the measured 25 [START_REF] Gomes | Temperature stability of a pure metakaolin based K-geopolymer: Part 1. Variations in the amorphous mineral network[END_REF] sample) and samples heat-treated up to 800 °C showed an adsorption isotherm of type IV related to mesoporous materials (according to the IUPAC classification [START_REF] Rouquerol | Recommendations for the characterization of porous solids (Technical Report)[END_REF] ). The renewal of adsorption at capillary condensation (for P/P0 > 0.95), is characteristic of either a combined macroporous network or the presence of an ink-bottle effect in the mesoporous network. During heating, the hysteresis loop changed from type IVb to type IVa, with adsorption and desorption branches that became more and more parallel. The IVb type for the as-prepared geopolymer is certainly due to the presence of ink-bottle mesopores [START_REF] Sing | Reporting physisorption data for solid/gas systems[END_REF] in which desorption is controlled by the narrow necks. Thermal treatments tend to homogenize the cylindrical shape and size of the mesopores. [START_REF] Huo | Surfactant control of phases in the synthesis of mesoporous silica-based materials[END_REF][START_REF] Kruk | Application of large pore MCM-41 molecular sieves to improve pore size analysis using nitrogen adsorption measurements[END_REF] However, this variation in the mesoporous network did not affect the calculated pore radius, which stayed close to ~4 nm (see RBJH in Table 1). On the other hand, the shape of the adsorption branch remained almost unchanged up to 800 °C, with a gentle slope due to capillary condensation into the cylindrical mesoporous channels. Finally, from 900 °C upward, we observed a type III isotherm corresponding to non-porous solids and indicating the complete collapse of the geopolymer porous network.

Table 1 summarizes the main physicochemical parameters of the samples used in the present study and compares results extracted from gas adsorption isotherms, 400 °C weight losses and thermoporismetry. As previously observed for the RBJH average pore size, there is only very little change in the specific surface area up to 800 °C, with a value of around SBET = 80 m 2 /g. The only significate variation is observed between the 25 [START_REF] Gomes | Temperature stability of a pure metakaolin based K-geopolymer: Part 1. Variations in the amorphous mineral network[END_REF] and 100 [START_REF] Gomes | Temperature stability of a pure metakaolin based K-geopolymer: Part 1. Variations in the amorphous mineral network[END_REF] samples (SBET = 112 m 2 /g), with potentially erroneous calculated values for the as-prepared 25 [START_REF] Gomes | Temperature stability of a pure metakaolin based K-geopolymer: Part 1. Variations in the amorphous mineral network[END_REF] geopolymer due to an incomplete evacuation of water from the porous network. Indeed, in order not to misrepresent the porous characteristics of this untreated sample, degassing was performed at room temperature. Concerning the Vp pore volume (calculated by using the BJH theory, and corresponding to mesopores), we can notice a gradual decrease in the value, from 0.28 cm 3 /g for the 25 [START_REF] Gomes | Temperature stability of a pure metakaolin based K-geopolymer: Part 1. Variations in the amorphous mineral network[END_REF] sample to 0.18 cm 3 /g for the 800 [START_REF] Gomes | Temperature stability of a pure metakaolin based K-geopolymer: Part 1. Variations in the amorphous mineral network[END_REF] sample.

4-Discussion

In this study we focused our investigation on mesopore-type porosity because it is the type that is likely to rehydrate easily by capillary condensation, depending on the surrounding humidity, and therefore likely to provide interest in terms of fire resistance. According to the classification by the International Union of Pure and Applied Chemistry 43 mesoporosity concerns pore widths ranging from 2 nm to 50 nm; with pore widths corresponding to their diameter in the case of cylindrical pores. Results obtained by thermoporosimetry and nitrogen adsorptiondesorption isotherms for our geopolymer (Table 1), in agreement with previously published values, enable us to characterize the geopolymer as a mesoporous material. Furthermore, the observation of our material in different ambient humidity conditions makes it possible to highlight the ability for geopolymers to rehydrate easily.

Thermal variations in the porous network

The determined physicochemical characteristics of pores having a cylindrical shape, a pore radius of about 5 nm and a specific surface area of around 100 m 2 /g agree with previously published characteristics for K-based geopolymers. [START_REF] Kriven | Geopolymers: nanoparticulate, nanoporous ceramics made under ambient conditions[END_REF][START_REF] Benavent | Effect of composition and aging on the porous structure of metakaolin-based geopolymers[END_REF] The difference between pore radius values provided by DSC measurements (thermoporosimetry treatment) and nitrogen sorption isotherms, although in a proportion of one to two (Table 1 and Figure 8a), is in fact not aberrant.

The strong ink-bottle effect mentioned by Benavant 40 affects the two techniques differently.

For DSC measurements, the presence of narrow necks in the mesoporous network separates the zones of water crystallisation, which is no longer continuous. This can also be at the origin of the phenomenon of homogenous nucleation, toward -40 °C, already mentioned in the literature. [START_REF] Morishige | Pore-blocking-controlled freezing of water in cagelike pores of KIT-5[END_REF][START_REF] Khokhlov | Freezing and melting transitions of liquids in mesopores with ink-bottle geometry[END_REF] At the same time, such narrow necks impact the hysteresis loop on N2 adsorption desorption isotherms, and potentially also affect the renewal of adsorption for P/P0 > 0.95.

We have also to indicate that thermoporosimetry was conducted considering water as a probing solvent. It is known that interstitial liquid in geopolymers is far from being pure water, containing in particular large amounts of solvated alkaline cations (potentially 1 mol/L). [START_REF] Lloyd | Pore solution composition and alkali diffusion in inorganic polymer cement[END_REF] We have shown that the presence of ions in the solvent (unpublished results using a simulated cementitious interstitial solution for TPM analyses) resulted in a smaller apparent pore radius.

It seems, therefore, that the pore size values determined by the BJH method are more accurate.

The TPM results remain, however, interesting for the characterization of the morphology of the mesoporous network, with a clearly marked cylindrical aspect (Figure 4c). Both techniques show a limited variation in the mesoporous characteristics from ambient temperature to 800 °C.

We simply note a slight decrease in the apparent porous radius, as well as in the specific surface area (from about 100 m 2 /g at room temperature to about 80 m 2 /g at 800 °C). By contrast, at a temperature of 900 °C these characteristics change significantly and reflect the collapse of the porous network (with SBET less than 5 m 2 /g and the impossibility to evidence porosity) resulting in a condensate ceramic. These findings complete our previously reported results concerning the mineral matrix of this geopolymer, which preserves its intrinsic characteristics up to 900 °C. [START_REF] Gomes | Temperature stability of a pure metakaolin based K-geopolymer: Part 1. Variations in the amorphous mineral network[END_REF] In the light of these latest results, considering the two porous and mineral sub-networks, we can now say that the geopolymer material is preserved up to a temperature of 800 °C.

The pore volume was determined using three techniques: weight losses at 400 °C on samples hermetically enclosed in DSC crucibles, intensities of the 1 H NMR signal and BJH treatment of the nitrogen adsorption branch. Results from weight losses and 1 H NMR are very close (Figure 6) and illustrate the ability of the geopolymer to rehydrate when stored at 95% RH, even after substantial thermal treatments. The different water amounts determined in samples stored at 30% RH and 95% RH led us to attribute the difference between the two series to capillary condensation, only possible in high humidity conditions. Therefore, the difference between 30% and 95 % RH in Figure 6 corresponds to mesoporosity, and consequently water already present in the samples stored at 30% RH partially fills the macropores. The porous volumes Vp and Vmes in Table 1 thus express approximately the same value, corresponding to the mesopore volume. In Figure 8b, their averages were fitted and a constant mesoporous volume of 0.23 cm 3 /g emerges from room temperature to 600 °C, followed by a slight drop to 0.17 cm 3 /g at 800 °C, before the collapse at 900 °C. Still in Figure 8b, the difference between the merged fitted line for mesopores and the hollow symbols for the total probed pores remains approximately constant up to 600 °C with a volume of about 0.10 cm 3 /g, corresponding to macroporosity.

Thermal variation in water status

Static and MAS 1 H NMR experiments were carried out in order to discriminate between hydrogen atoms belonging to 'free' liquid water and bonded hydroxyls or water molecules. The comparison of spectra from samples stored at 95% RH (Figures 2a and2b) simply shows a sharpening of the signal, with the 30 kHz rotor spin indicating that the vast majority of the protons present in the geopolymer correspond to liquid water molecules filling the porous network. Again, the intensity of the signals from the heat-treated samples shows the ability of the material to rehydrate when stored in a humid atmosphere, and therefore illustrates the fact that the porous network is open and traversing. Figure 3a highlights that this is particularly true up to a temperature of 700 °C. At 800 °C the signal intensity is approximately halved, then almost nonexistent beyond this temperature, in agreement with previous results on pore volume determination and its variation with temperature. Spectra recorded for samples stored at 30% RH complete these observations (Figure 2c and2d) with additional signals (close to 0 ppm) of low intensity in MAS spectra. These additional signals, related to non-mobile hydrogen atoms, were attributed to silanol Si-OH (or aluminol Al-OH) entities present in limited quantity. The low number of -OH entities in the geopolymer agrees with the TGA curve, [START_REF] Gomes | Temperature stability of a pure metakaolin based K-geopolymer: Part 1. Variations in the amorphous mineral network[END_REF] showing a weak dehydroxylation around 400 °C. In addition to the sharpening of the signal with magic angle spinning, there is also a sharpening associated with the temperature of the heat treatment for both series: FWHM varies from 5.5 to 2.5 ppm for the static series and from 4 to 1 ppm for the MAS series (Figure 3c). Moreover, we can observe that this FWHM sharpening is performed without any variation in the isotropic chemical shift when the material is saturated with water (figure 3b). This allows us to conclude that the status of the water has not changed as a result of heat treatments. In high humidity, we are always in the presence of liquid water which fills the pores. It appears more and more 'free' during the increase in temperature, which can be explained either by a decrease in its confinement (i.e. an increase in the size of the mesopore), or by a decrease in its salinity (i.e. a decrease in its alkalinity). Findings from the previous paragraph indicate a minimal variation in mesopore size, which would not explain a variation in the FWHM. On the other hand, a reduction in interstitial water alkalinity would mean that following the heat treatments the pore-filling liquid would be increasingly pure water. This is then in agreement with the observations made on the variations in the mineral matrix in the previous study, [START_REF] Gomes | Temperature stability of a pure metakaolin based K-geopolymer: Part 1. Variations in the amorphous mineral network[END_REF] which concluded that the potassium cations in the pore solution pass through the mineral sub-network during the rise in temperature. There would be a variation in the pore surface chemistry that could explain the variation in the chemical shift for the 30% RH and baked series. For the samples from these two series the pores are not filled; water molecules are physisorbed to the porous interface, which evolves with the fixation of potassium. This nonliquid water status explains the absence of a DSC signal for these two series of samples (Figure 5d).

5-Conclusion

The combination of several complementary techniques for the characterisation of the porous network ( 1 H static and MAS NMR, DSC with TPM treatment, thermal weight loss, nitrogen adsorption-desorption isotherms) led to a precise description of the mesoporosity of a geopolymer. The porosity of our investigated K-based geopolymer agrees very well with the porous structure of metakaolin-based geopolymers detailed by Benavent, 40 including the strong 'ink-bottle' effect due to a two-level pore structure composed of interlinked meso-and macroporous networks. Almost the entire porous network is accessible to water, thus translating the fact that the closed pore volume is very low. Water from the porous network can easily and without damage leave the geopolymer during a rise in temperature. This water flow is totally reversible (for heat treatments up to 700 °C) in the presence of significant relative humidity.

For heat treatment at 800 °C, half of the pore volume has disappeared, and at 900 °C the material is no longer porous. By combining the results from parts 1 and 2 on the temperature stability of our K-based geopolymer we can confirm, without any ambiguity, that the geopolymer retains its whole mineral and porous characteristics up to a temperature of 700 °C. At 800 °C we are still the presence of a geopolymer-type material, with half the original pore volume. At 900 °C the mineral network is still amorphous with a 3D connection of the aluminate and silicate tetrahedra, but with the disappearance of the porous nature specificity of geopolymers which is becoming a dense ceramic. Finally, at 1000 °C, there is the beginning of crystallization, and the disappearance of any characteristics of a geopolymer.

Thus it can be concluded that a high-temperature application (refractory, up to 700-800 °C for a potassium geopolymer) is absolutely conceivable. Furthermore, the rehydration ability of the material gives it interesting fireproof properties, with about 25 weight percent of easily available liquid water.

FiguresFigure 1 .

 1 Figures

Figure 2 .

 2 Figure 2. 1 H NMR measurementsstatic (a and c) and MAS (b and d)for heat-treated

Figure 3 .

 3 Figure 3. Results from the Lorentzian modeling of the 1 H NMR spectra (a: signal intensities,

Figure 4 .

 4 Figure 4. Thermoporosimetry realized on the as-synthesized geopolymerwithout heat

Figure 5 .

 5 Figure 5. Thermoporosimetry performed on the heat-treated geopolymers: a. the third

Figure 6 .

 6 Figure 6. Water amount quantification determined by weight losses at 400 °C (hollow symbols, labeled DSC in the key) and comparison with the variations previously observed by 1 H NMR

Figure 7 .

 7 Figure 7. Adsorptiondesorption isotherms of nitrogen at 77 K for heat-treated geopolymers.

Figure 8 .

 8 Figure 8. Physicochemical characteristics of the mesoporous network determined using several

Acknowledgements

Project supported by Andra under the "Investing in the Future" Programme ("Investissement d'Avenir") -Selected under the Andra Call for Projects: "Optimisation of post-dismantling radioactive waste management", organised in cooperation with the French National Research Agency (ANR).


Charlotte Hauser
email: charlotte.hauser@live.fr

Carlo Geraci
email: carlo.geraci76@gmail.com

Relative clauses in French Sign Language (LSF): some preliminary results

Keywords: LSF, relative clauses, internal head, external head, head-matching derivation 2

We report preliminary findings on the morpho-syntactic structure of relative constructions in French Sign Language (LSF). We describe two manual markers that are analyzed as d-like relative pronouns and we show that LSF has both internally and externally headed relative clauses. We offer a unified derivation for both types of relative clauses.

Introduction

The syntax of relative clauses is a well studied topic in sign language (see [START_REF] Cecchetto | Strategies of relativization in Italian Sign Language[END_REF], [START_REF] Branchini | Relatively different: Italian Sign Language relative clauses in a typological perspective[END_REF], [START_REF] Brunelli | Antisymmetry and sign languages: A Comparison between NGT and LIS[END_REF] for LIS, [START_REF] Wilbur | Internally-headed relative clauses in sign languages[END_REF] for a recent review on ASL, [START_REF] Pfau | Relative clauses in German Sign Language: Extraposition and reconstruction[END_REF] for DGS and [START_REF] Li | Relative constructions in Hong Kong Sign The Chinese University of Hong Kong[END_REF] for HKSL among others). All these studies showed that the main relativization strategies found in spoken languages are also attested in sign languages, namely externally headed, internally headed and correlatives.

In this paper we present some preliminary results on the main strategies of relativization used in French Sign Language (LSF). We show that LSF has genuine cases of relative clauses and that they can be both internally and externally headed. Relative clauses can be marked in three different ways: by using prosodic cues only (i.e., facial expressions and body postures), or by using two manual signs. One is the classifier for person, which is specific to human referents, the other is a particular kind of pointing sign and it is available for all kinds of referents. Most of the discussion will be based on relative clauses marked with this particular pointing sign that we glossed as PI.

The rest of the paper is organized as follow: Section 2 illustrates the methodology adopted to collect the data. Section 3 presents some basic facts about LSF. Section 4 contains the empirical part of the paper, while a formal implementation is offered in Section 5.

Data have been collected in two steps using various fieldwork techniques. In the first step we obtained the baseline examples by adapting tasks commonly used in language acquisition [START_REF] Stegenwallner-Schütz | Accessibility effects through contrasts in the development of referential choices in german[END_REF]; [START_REF] Belletti | The Acquisition of Italian: Morphosyntax and its interfaces in different modes of acquisition[END_REF]). In the second step we manipulated word order and syntactic positions to investigate more complex structures. All data have been recorded in various sessions. Cross-validation was done by letting the informants judge each other's recordings. We always worked with one informant at a time and during all the phases of data collection LSF was the only mean of communication between the informants and the researchers.

The image in Figure 1 illustrates the various steps and substeps of the procedure. At the top left corner of Figure 1 there is an example of elicitation material displaying two girls with two different pets. After presenting the picture, we asked our informants which girl do they prefer (a similar technique has been used to elicit relative clauses in Israeli Sign Language, [START_REF] Dachkovsky | The development of a RC marker from a deictic gesture in Israeli Sign Language[END_REF]). In the second step of the procedure, we manipulated word order and syntactic complexity, by asking our informants for instance to displace the relative marker in various positions in the sentence, or to add more lexical material to the sentence (e.g., temporal adverbs). At the end of each stage, we collected acceptability and felicity judgments on our baselines using the playback method [START_REF] Schlenker | Donkey anaphora: the view from sign language (ASL and LSF)[END_REF].

Figure 1: Elicitation procedure's pattern

To offer a concrete example of our procedure, consider a relative clause on the subject in object position like the one in (1) (e.g., I prefer the girl who is petting the dog.). We obtained that sentence by asking our informants which girl do they prefer, after the presentation of the picture in Figure 1. In order to investigate the syntactic position of PI, we then asked our informants to simply displace PI in various parts of the sentence. The examples in (1a)-(1e) are the result of this word order manipulation. Once we recorded the video examples for each of the sentences in (1) acceptability and felicity judgments on a 7-point scale have been collected by playing back the videos to our informants. The data included in this section will be useful to frame some aspects of the internal structure of relative clauses provided in the following sections. For space reasons, we cannot offer a detailed overview about the structure of LSF and we only focus on word order and whquestions. For word order facts, we partially replicated previous findings (see below), while for wh-questions there is no previous documentation that we know of.

Like in many other sign languages, word order is quite free in LSF. [START_REF] Bouvet | Approche polyphonique d'un récit produit en Langue des Signes Française[END_REF] reports SVO as the base order, while De Langhe et al. ( 2004) reports SOV as the basic one, although other orders are also attested. The preferred word order for our informants is SVO, as shown in (2a). OSV is also frequently attested, however, it requires at least the raising of the eyebrows over the object which is a clear mark of topic as shown in (2b) (on the OSV order in LSF see also De Langhe et al. ( 2004)). The SOV order is marginally possible, with the condition that, if no particular non-manuals are used on either the first or the second nominal element, the most natural reading is that of a coordinated subject with an implicit object, as indicated in the translation offered for the example (2c).

(2) a. MAN The most preferred strategy for asking wh-questions is to leave the wh-sign in situ (Geraci (in prep.)), a property shared with ASL [START_REF] Neidle | The Syntax of Americain Sign Language : Functional Categories and Hierarchical Structure[END_REF]). This is shown by the examples in (3a)-(3b).

(3) a. DOG SCRATCH WHO 'Who did the dog scratch?' b. WHO SCRATCH CAT 'Who scratched the cat?'

Wh-questions will be used as a test for island [START_REF] Ross | Constraints on variables in syntax[END_REF]).

Finally, temporal adverbs are normally found either at the beginning or at the end of the clause, as shown in (4). The position of temporal adverbs is normally used as a reliable cue to determine the edges of a clause. This is also true for sign languages (see among others [START_REF] Neidle | The Syntax of Americain Sign Language : Functional Categories and Hierarchical Structure[END_REF] and [START_REF] Cecchetto | Strategies of relativization in Italian Sign Language[END_REF]). In the next section, we will use the position of temporal adverbs to show that LSF has clear cases of externally headed relative clauses.

FEAST vol. 1, 2018

The data

There are three different ways of producing relative clauses in LSF, at least when the head of the relative clause refers to humans. All of them involve some eyebrow raising, two of them involve the use of an overt marker, the classifier for person, glossed as PERSON-CL or a kind of pointing sign glossed as PI (see Section 4.2 for a detailed description). The relevant examples are illustrated in (5):

(5) a. 'I prefer the vet who is curing the dog.'

In the next sections we first look into the macroscopic properties of these constructions, and then into some fine-grained aspects of the morphological and prosodic makeup of relative clauses. For concreteness, we present only cases of relative clauses marked with PI as this marker allows a more direct identification of the properties of LSF relative clauses.

Macroscopic properties

At the macroscopic level, we have evidence that the examples in ( 5) involve subordination of a sentence modifying a nominal element because these constructions are wh-islands [START_REF] Ross | Constraints on variables in syntax[END_REF]). The examples in (6) illustrate that it is possible to have matrix wh-questions with sentential complements embedded in bridge verbs. Crucially, when the wh-sign is inside the sentential nominal modifier, as in (7), neither matrix nor embedded wh-questions are possible. We take this as evidence that the constructions in (5) are genuine cases of relative clauses.

(6) a. Intended meaning: 'What is the animal such that you prefer the woman that is petting it?'

In terms of macroscopic structure, the pattern in (5) excludes the possibility that we are dealing with correlatives, as there is no obligatory fronting of the relative clause (see [START_REF] Cecchetto | Strategies of relativization in Italian Sign Language[END_REF]). However, several languages allow for both externally and internally headed relative clauses, like Japanese [START_REF] Shimoyama | Internally headed relative clauses in japanese and e-type anaphora[END_REF]) and ASL [START_REF] Liddell | American Sign Language syntax[END_REF]). This is the case of LSF too. For sake of clarity, in the next examples we also include the gap corresponding to the syntactic position of the head inside the relative clause and when needed also the relevant bracketing. In the example in (8a), the relative clause is extraposed to the right of the temporal adverb which refers to the time of the event described in the matrix clause. The head of the relative clause VET along with the marker PI is left inside the matrix clause. The example FEAST vol. 1, 2018 in (8b) is a case where the head is internal since it is found to the right of the temporal adverb along with the relative marker. In this specific case, the temporal adverb refers to the event of the relative clause (prosodic and spatial information is used to determine to which event the temporal adverb refers). The examples in (8) display subject relative clauses, while those in (9) display object relative clauses. 'Today I prefer the dog which the man is petting.'

Overall, our informants have a clear preference for externally headed relative clauses, although internally headed are more or less equally fine. This is particularly evident in the case of object relative clauses where word order automatically disambiguates between the two options. Both are equally acceptable but signers have a preference for the externally headed version. The examples in (5) are subject relative clauses in object position. However, relative clauses can also modify subjects as shown in ( 10). The example in (12a) illustrates one particular case in which the head corresponds to the entire event described by the relative clause. The relative marker PI occurs at the end of the sentence, crucially after the temporal adverb which is used to mark the right edge of the relative clause. The example in (12b) illustrates the relative clause with the overt head. 'I prefer those situations in which a vet is curing a dog today.'

Microscopic properties

At the microsopic level, LSF relative clauses are either juxtaposed or marked with the sign PI or the classifier for person, PERSON-CL. The use of PERSON-CL is limited to cases where the head of the relative clause refers to humans, as shown in (13).

FEAST The examples in ( 14) are also helpful in determining the morpho-syntactic status of the relative markers. The fact that they can occur inside and outside the relative clause can be taken as evidence that they are not complementizer-like elements. Furthermore, both markers can be used as independent pronominal elements, as shown in ( 15), strongly suggesting that even when used in relative clauses they are pronominal/d-like elements as well. For further semantic properties of PERSON-CL in LSF see [START_REF] Kuhn | Low referentiality in LSF and LIS[END_REF] and for PI see [START_REF] Schlenker | Strong Pronominals in ASL and LSF (Squib)[END_REF].

(15) a. IX-1 PREFER PI 'I prefer that.' b. PERSON-CL ENTER 'Someone entered (the room).'

At the prosodic level, relative clauses normally come with a cluster of non-manuals, the most salient of which are raised eyebrows and a slight head tilt. Although we did not conduct a deep study of these prosodic features, we observed that the spreading of the non-manuals is quite limited in our examples. It co-occurs with the relative marker and sometimes spreads over the head. In the case of juxtaposed relative clauses it occurs on the head, as illustrated in the images on Table 1.

FEAST vol. 1, 2018

Analysis

LSF has both internally and externally headed relative clauses which are marked by a d-like relative pronoun and can relativize virtually any constituent. The fact that the same lexical material is used to generate both kinds of relatives calls for a unified analysis. Indeed LSF data support theories of relative clauses where the head is generated inside the relative clause. The Head-Raising Analysis [START_REF] Bianchi | Headed relative clauses in generative syntax[END_REF][START_REF] De Vries | The Syntax of Relativization[END_REF] and [START_REF] Kayne | The Antisymmetry of Syntax[END_REF]) and the Head-Matching Analysis [START_REF] Carlson | Amount relatives[END_REF], [START_REF] Cinque | The prenominal origin of relative clauses[END_REF], [START_REF] Heim | Where does the definiteness restriction apply? evidence from the definiteness of variables[END_REF] and [START_REF] Sauerland | Unpronounced Heads in Relative Clauses[END_REF]) are two of the most influential proposals of this kind. The LSF data we introduced in Section 4 are compatible with both approaches modulo some assumptions which are independently needed.

We implement here an account based on the Head-Matching Analysis. Under this approach the head and the relative pronoun are generated inside the relative clause and then moved to its edge to create the operator-variable chain. Then a DP identical to the head + relative pronoun is merged in the derivation and forces deletion under identity of the head and the relative pronoun at the edge of the relative clause. For illustration purposes, we provide the main steps of the derivation of the sentence in (5c), repeated here as (16). The step of the derivation in (17a) shows that the head and the relative marker PI are merged as part of the TP/vP complex of the relative clause. The step in (17b) illustrates the movement to spec,CP and deletion of the lower copy in spec,TP. The "match" DP is externally merged in (17c) and the head noun gets deleted under identity, as in (17d). The derivation further continues by merging the syntactic object created in (17d) in the complement position of the matrix verb PREFER. The derivation of internally headed relative clauses can be done by assuming covert movement to the edge of the relative CP and then deletion of the match rather than the head (similar assumptions would be needed in order to derive internally headed relative clauses with the head-raising approach). We provide here the derivation for the example in (18). The temporal adverb now refers to the event of the relative clause and is used as evidence that the head is inside the relative clause itself.

(18) IX-1 PREFER [ TODAY VET PI CURE DOG ] 'I prefer the vet who is curing the dog today.'

The relevant steps of the derivation are offered in ( 19). The step of the derivation in (19a) shows that the head and the relative marker PI are merged as part of the TP/vP complex of the relative clause, just like in (17a Further research is needed to establish the fine-grained structure of the head DP and whether head and relative marker have a fixed order (especially in the case of internally headed relative clauses). Nonetheless, the derivations we offered here also account for the distribution of the relative marker. Indeed, it is introduced as part of the head DP (possibly its head) and it moves with the head along the structure. This last fact determines its spell-out position within the CP of the relative clause in externally headed relative clauses.

Conclusions

Relativization is one of the most widespread phenomena of the syntax of human language. It raised the attention of many researchers working both in sign and spoken languages. In this paper we provided preliminary results from LSF showing that this language has two main strategies to create relative clauses. One involves external heads, the other involves internal heads. In both cases we clearly have evidence that we are dealing with subordinate constructions, rather than juxtaposed clauses. We also described the main properties of the relative FEAST vol. 1, 2018 marker PI. The data coming from LSF support theories of relative clauses in which the head is generated inside the relative clause. We implemented our analysis using one of them, namely the head-matching analysis.

These preliminary findings open the door for further research, both at syntactic and the semantic level. It is still to be determined what the role of spatial agreement is and how it interacts with the structure of internally and externally headed relative clauses. More data are also needed to clarify the structure of relative clauses built on the event. Another domain which we didn't cover is whether the relativization process is sensitive to the morphological nature of the head. In particular, whether classifiers nouns have a special morpho-syntactic behavior in relative clauses. We hope to address all these issues in our future works.

( 1 )FEAST

 1 Elicited sentence: IX-1 PREFER GIRL PI PET DOG a. Directly asked alternatives : PI IX-1 PREFER GIRL PET DOG b. IX-1 PI PREFER GIRL PET DOG c. IX-1 PREFER PI GIRL PET DOG

  the dog, the man is petting it.' c. MAN DOG PET 'The man and the dog are petting something.' ?? Intended reading: 'The man is petting the dog.'

  (4) a. YESTERDAY DOG SCRATCH CAT b. DOG SCRATCH CAT YESTERDAY 'A dog scratched a cat yesterday.'

  (8) a. IX-1 PREFER VET PI TODAY [ g ap CURE DOG ] 'Today I prefer the vet who is curing the dog.' (. . . Yesterday I preferred the vet who was curing the cat.) b. IX-1 PREFER [ TODAY VET PI CURE DOG ] 'I prefer the vet who is curing the dog today.' (. . . not the one that is curing the cat.) (9) a. IX-1 PREFER DOG PI [ MAN PET g ap ] 'Today I prefer the dog which the man is petting.' b. IX-1 PREFER [ MAN DOG PI PET ]

  who is curing the dog eats fries.' Relative clauses can be built virtually out of any constituents. We illustrate here object and adjunct relative clauses. (11) a. IX-1 PREFER re DOG PI MAN PET g ap 'I prefer the dog which the man is petting.' b. IX-1 PREFER re TOOTHBRUSH PI LITTLE GIRL PAINT g ap 'I prefer the toothbrush with which the little girl is painting.'

(

  12) a. IX-1 PREFER [ VET CURE DOG TODAY ] PI b. IX-1 PREFER SITUATION PI [ VET CURE DOG TODAY ]

FEAST

  the vet who is curing the dog.'

( 17 )

 17 Derivation of Externally Headed Relative Clauses in LSF: Head-Matching Analysis a. Head inside the RelCl TP RelC l [. . . [ vP VET PI CURE DOG ]]

  Both markers can be used with internally headed relative clauses and show spatial agreement with the head of the relative clause. The subscript in the examples in (14) indicates that the vet's location in the signing space is used to realize both PI and PERSON-CL. (14) a. IX-1 PREFER TODAY VET PI vet CURE DOG b. IX-1 PREFER TODAY VET PERSON-CL vet CURE DOG 'I prefer the vet which today is curing the dog.'

	b. IX-1 PREFER VET PERSON-CL CURE DOG 'I prefer the vet who is curing the dog.' c. IX-1 PREFER DOG PI VET CURE g ap d. * IX-1 PREFER DOG PERSON-CL VET CURE vol. 1, 2018 (13) a. IX-1 PREFER VET PI CURE DOG 'I prefer the dog which the vet is curing.'	g ap

Table 1 :

 1 Manual and non-manual morpho-phonological properties of each strategy.

	Beginning

of PI End of PI sign Beginning of PERSON-CL End of PERSON-CL Sign for VET (the head) Sign for CURE (the verb)