I Quesada-Peñate

C Julcour-Lebigue

U J Jáuregui-Haza

A M Wilhelm

H Delmas

† Deceased

St

Degradation of paracetamol by catalytic wet air oxidation and sequential adsorption -catalytic wet air oxidation on activated carbons

Keywords: Catalytic oxidation, Adsorption, Activated carbon, Biodegradability, Paracetamol

The concern about the fate of pharmaceutical products has raised owing to the increasing contamination of rivers, lakes and groundwater. The aim of this paper is to evaluate two different processes for paracetamol removal. The catalytic wet air oxidation (CWAO) of paracetamol on activated carbon was investigated both as a water treatment technique using an autoclave reactor and as a regenerative treatment of the carbon after adsorption in a sequential fixed bed process. Three activated carbons (ACs) from different source materials were used as catalysts: two microporous basic ACs (S23 and C1) and a meso-and micro-porous acidic one (L27). During the first CWAO experiment the adsorption capacity and catalytic performance of fresh S23 and C1 were higher than those of fresh L27 despite its higher surface area. This situation changed after AC reuse, as finally L27 gave the best results after five CWAO cycles. Respirometry tests with activated sludge revealed that in the studied conditions the use of CWAO enhanced the aerobic biodegradability of the effluent. In the ADOX process L27 also showed better oxidation performances and regeneration efficiency. This different ageing was examined through AC physicochemical properties.

Introduction

Numerous studies around the world have demonstrated the presence of pharmaceutical compounds in waterways [START_REF] Ternes | Occurrence of drugs in German sewage treatment plants and rivers[END_REF][START_REF] Alighardashi | Occurrence and fate of pharmaceutical substances in urban wastewater, a literature mini-review[END_REF][START_REF] Grunga | Environmental assessment of Norwegian priority pharmaceuticals based on the EMEA guideline[END_REF][START_REF] Snyder | Occurrence, treatment, and toxicological relevance of EDCs and pharmaceuticals in water[END_REF][START_REF] Mompelat | Occurrence and fate of pharmaceutical products and byproducts, from resource to drinking water[END_REF][START_REF] Onesios | Biodegradation and removal of pharmaceuticals and personal care products in treatment systems: a review[END_REF][START_REF] Rahman | Occurrences of endocrine disrupting compounds and pharmaceuticals in the aquatic environment and their removal from drinking water: Challenges in the context of the developing world[END_REF], as they are found resistant to biological degradation and usually escape conventional WWTPs [START_REF] Klavarioti | Removal of residual pharmaceuticals from aqueous systems by advanced oxidation processes[END_REF]. In particular, paracetamol (N-acetyl-4-aminophenol), a common analgesic and anti-inflammatory used for humans and animals, has been reported as the pharmaceutical compound present in largest concentration in French rivers [9]. Considering the potential impacts of pharmaceutical products on environment and human health, additional treatments have to be applied to drastically reduce the load of such molecules in discharged effluents and best achieve non-detectable concentrations. Several technologies have already proven to be effective for this purpose. Among the most cited appear activated carbon adsorption [START_REF] Ternes | Removal of pharmaceuticals during drinking water treatment[END_REF][START_REF] Westerhoff | Fate of endocrine-disruptor, pharmaceutical, and personal care product chemicals during simulated drinking water treatment processes[END_REF][START_REF] Snyder | Role of membranes and activated carbon in the removal of endocrine disruptors and pharmaceuticals[END_REF][START_REF] Yu | Adsorption characteristics of selected pharmaceuticals and an endocrine disrupting compound -naproxen, carbamazepine and nonylphenol -on activated carbon[END_REF][START_REF] Quesada-Peñate | Comparative adsorption of levodopa from aqueous solution on different activated carbons[END_REF], as well as advanced oxidation processes like ultrasound [START_REF] Naddeo | Fate of pharmaceuticals in contaminated urban wastewater effluent under ultrasonic irradiation[END_REF][START_REF] Quesada-Peñate | Sonolysis of levodopa and paracetamol in aqueous solutions[END_REF][START_REF] Bel | Sonolysis of ciprofloxacin in aqueous solution: Influence of operational parameters[END_REF], ozonation [START_REF] Andreozzia | Paracetamol oxidation from aqueous solutions by means of ozonation and H 2 O 2 /UV system[END_REF][START_REF] Ternes | Ozonation: a tool for removal of pharmaceuticals, contrast media and musk fragrances from wastewater?[END_REF][START_REF] Esplugas | Ozonation and advanced oxidation technologies to remove endocrine disrupting chemicals (EDCs) and pharmaceuticals and personal care products (PPCPs) in water effluents[END_REF][START_REF] Kim | Classification of the degradability of 30 pharmaceuticals in water with ozone, UV and H 2 O 2[END_REF], photocatalysis [START_REF] Zhang | Photodegradation of estrone and 17β-estradiol in water[END_REF][START_REF] Yang | Photocatalytic degradation kinetics and mechanism of environmental pharmaceuticals in aqueous suspension of TiO 2 : A case of β-blockers[END_REF], (photo)Fenton oxidation [START_REF] Perez-Estrada | Photo-Fenton degradation of diclofenac: identification of main intermediates and degradation pathway[END_REF][START_REF] Gonzalez | Sulfamethoxazole abatement by photo-Fenton. Toxicity, inhibition and biodegradability assessment of intermediates[END_REF][START_REF] Trovo | Photodegradation of the pharmaceuticals amoxicillin, bezafibrate and paracetamol by the photo-Fenton process -Application to sewage treatment plant effluent[END_REF], and hybrid configurations [START_REF] Skoumal | Mineralization of paracetamol by ozonation catalyzed with Fe 2+ , Cu 2+ and UVA light[END_REF][START_REF] Madhavan | Combined advanced oxidation processes for the synergistic degradation of ibuprofen in aqueous environments[END_REF][START_REF] Güyer | Degradation of diclofenac in water by homogeneous and heterogeneous sonolysis[END_REF]. More examples can be found in the review of Klavarioti et al. [START_REF] Klavarioti | Removal of residual pharmaceuticals from aqueous systems by advanced oxidation processes[END_REF]. On the other hand, catalytic wet air oxidation (CWAO) -in particular with cheap activated carbon (AC)has been extensively studied for the degradation of organics compounds [START_REF] Stüber | Carbon materials and catalytic wet air oxidation of organic pollutants in wastewater[END_REF][START_REF] Suárez-Ojeda | Catalytic wet air oxidation of substituted phenols using active carbon catalyst[END_REF][START_REF] Santos | Wet oxidation of phenol, cresols and nitrophenols catalyzed by activated carbon in acid and basic media[END_REF][START_REF] Quintanilla | Catalytic wet air oxidation of phenol with modified activated carbons and Fe/activated carbon catalysts[END_REF], but not yet applied to pharmaceutical products. Recently, an hybrid process (AD-OX) of classical adsorption of pollutants on a fixed bed of activated carbon followed by batch wet catalytic oxidation at higher temperature and pressure on the same bed of AC, which is then regenerated in situ, has been also evaluated for the remediation of phenols [START_REF] Delmas | Sequential process of adsorption and catalytic oxidation on activated carbon for (pre)treatment of water polluted by nonbiodegradable organic products[END_REF][START_REF] Polaert | Phenol wastewater treatment by a two-step adsorptionoxidation process on activated carbon[END_REF][START_REF] Delmas | AD-OX: A sequential oxidative process for water treatment-adsorption and batch CWAO regeneration of activated carbon[END_REF]. The basic idea is to take advantage of both operations: 1) efficient and cheap water purification at room temperature by adsorption, 2) effective pollutant degradation by catalytic air oxidation achieving simultaneously AC regeneration for the next adsorption. Despite the oxidative treatments have to be evaluated in the view of an integrated process with biological degradation (usually as a pre-treatment), only a few studies have assessed the biodegradability, toxicity or inhibitory effects of the intermediates resulting from partial oxidation, [START_REF] Quintanilla | Catalytic wet air oxidation of phenol with modified activated carbons and Fe/activated carbon catalysts[END_REF][START_REF] Arslan-Alaton | Advanced oxidation of commercial textile biocides in aqueous solution: effects on acute toxicity and biomass inhibition[END_REF][START_REF] Rubalcaba | Biodegradability enhancement of phenolic compounds by Hydrogen Peroxide Promoted Catalytic Wet Air Oxidation[END_REF][START_REF] Suárez-Ojeda | Catalytic wet air oxidation of substituted phenols: Temperature and pressure effect on the pollutant removal, the catalyst preservation and the biodegradability enhancement[END_REF][START_REF] Goi | Treatment of Landfill Leachate by H 2 O 2 Promoted Wet Air Oxidation[END_REF][START_REF] Reungoat | Removal of micropollutants and reduction of biological activity in a full scale reclamation plant using ozonation and activated carbon filtration[END_REF]. Chemical analysis of a limited suite of compounds does not assess the potential biological adverse effects of the wastewater as it does not reflect possible cumulative and interaction effects. Therefore bioassays have to be used as complementary monitoring tools. To this end, respirometry has emerged as a particularly significant analysis because the oxygen uptake rate represents a direct measurement of the correct activity and viability of the microorganisms present in an aerobic activated sludge [START_REF] Oller | Combination of Advanced Oxidation Processes and biological treatments for wastewater decontamination-A review[END_REF]. In this context, the present paper has two objectives related to the remediation of paracetamol: first, to study the CWAO of the molecule on different activated carbons, including the biodegradability assessment of the oxidation effluent; second, to study the feasibility of the sequential adsorptionoxidation process in which water quality is provided by the adsorption step.

Materials and methods

Physico-chemical characterization of activated carbons

Three ACs were used in both the batch autoclave and fixed bed experiments: carbon L27 from wood, S23 from coconut shell (Pica, Veolia group) and C1 from casuarina (CIPIMM, Havana). The surface area and pore volume of the carbons were measured from nitrogen adsorption isotherms at 77K, using an ASAP 2010 analyzer (Micromeritics). Specific surface area was calculated from BET plot for relative pressures between 0.01 and 0.2. Thermogravimetric analysis (TGA) was performed under nitrogen flow from room temperature to 700°C at a heating rate of 10°C/min (Q600 SDT, TA Instrument) in order to compare the amount of functional groups on the three carbons. Their acid/base properties were determined using the procedure proposed by Boehm [START_REF] Boehm | Some aspects of the surface chemistry of carbon blacks and other carbons[END_REF]. 70 mL of 0.05 N NaOH or 0.05 N HCl solutions were added to 1 g of AC in a glass bottle. The bottles were degassed under N 2 , sealed and let to equilibrate for three days in a rotatory shaker. Then, the carbon was separated from the solution and 3 mL of each filtrate were titrated (DL 50, Mettler Toledo) using HCl or NaOH (0.05 N), as required. Each experiment was triplicated under identical conditions. The pH at the point of zero charge (pH PZC ) was measured by the pH drift method. 0.1 g of carbon was added to 20 mL of 0.1 mol/L NaCl solution, whose initial pH was adjusted with NaOH or HCl. The containers were flushed with N 2 , sealed and placed in a shaker for 24 h, after which the pH was measured. The PZC occurred when there was no change in the pH after contact with the carbon. Elemental analysis of the ACs was carried out using Thermo Finnigan Flash EA111 for CHNSO and lixiviation/ICP-AES (Jobin Yvon -Ultima 2R) for metals. The room temperature adsorption isotherms of paracetamol were also measured on the three carbons: 100 mL of a paracetamol solution (initial concentration between 0.041 g/L and 1.3 g/L) and a fixed amount of activated carbon (0.1 g for L27 and 0.05 g for S23 and C1) were mixed during 24 hours in a thermostated bath at 25 o C. The equilibrium concentration of paracetamol on solid phase was calculated from initial and final concentrations in aqueous solution measured by liquid chromatography (see § 2.2.1.2.). Each experiment was repeated threefold under identical conditions. Five different models were used to fit single component isotherms and the best one was selected using statistical regression criteria as described by Quesada et al. [START_REF] Quesada-Peñate | Comparative adsorption of levodopa from aqueous solution on different activated carbons[END_REF].

Experimental set-ups and analytical procedures

CWAO experiments

The first step of the study was the selection of suitable oxidation catalysts among the three ACs using a batch stirred autoclave (Parr Instruments).

Operating conditions

In a typical experimental run, 200 mL of 1 g/L paracetamol aqueous solution and 1 g of AC were added to the reactor, operating at 150°C and 3.2 bar of oxygen partial pressure (total pressure 20 bar). The experiments were performed batchwise for the liquid phase and were continuous for air, circulating with a flow rate of 60 L/h STP to ensure constant oxygen pressure. Prior to oxidation reactions, the ACs (0.8-1.0 mm) were equilibrated with paracetamol at 150°C under nitrogen atmosphere. The stirrer speed was set at 800 rpm to avoid catalyst attrition and prevent external mass transfer limitations. Five oxidation cycles were completed in each case in order to evaluate the catalyst efficiency and the biodegradability of resulting effluents.

Chemical analyses

Liquid samples were characterized using a HPLC equipped with a UV/Vis detector (Varian ProStar 310). Paracetamol was separated from oxidation intermediates on a Prontosil C 18 reversed phase column using a 90:10 mixture of acidified water (pH 2.2) and acetonitrile as isocratic mobile phase (flow rate of 0.25 mL.min -1 ). The detection of the compound was achieved at a wavelength of 254 nm. The closed reflux colorimetric method was used to determine COD values. 2 mL of sample, diluted or not, was introduced into a commercially available digestion tube and the mixture was then heated 120 min at 150°C. The amount of oxidizing agent reduced was subsequently determined colorimetrically using a UV spectrophotometer (Hach Odyssey DR/2500) operating at 620 nm and expressed as COD.

Bioassays

Respirometry tests were performed with activated sludge to assess the aerobic biodegradability and the possible inhibitory effect of paracetamol and its oxidation products. The apparatus consisted in a glass respirometry cell maintained at 26°C. Dissolved oxygen concentration and temperature were monitored continuously throughout the experiments. The respirometer was inoculated with biomass from the aeration tank of the Brax wastewater treatment plant (Toulouse, France). Sodium acetate was used as a biodegradable substrate and added before and after the injection of paracetamol or final effluents from batch CWAO. The procedure was as follows: a pulse of 98 mg COD/L of sodium acetate was first added. After the control substrate was consumed, a pulse of effluent with equivalent COD was injected. The last step consisted in the addition of the same pulse of acetate as in the first run. From integration of the Oxygen Uptake Rate (OUR) profiles, oxygen consumptions (OC) obtained with sodium acetate at the first run (sdt1) and with reaction mixture were compared. A biodegradability index was subsequently calculated according to equation 1. The toxicity of the effluent (equation 2) was determined from the maximum values of the OUR curves (OUR max ) corresponding to the two additions of sodium acetate (std1 and std2).

100 OC OC OC 1 (%) index radability deg Bio 1 std effluent 1 std ×         - - = (1) 100 OUR OUR OUR (%) index Toxicity 1 std max, 2 std max, 1 std max, ×         - = (2)

AD-OX fixed bed process

A sequential process consisting in continuous adsorption on AC followed by batch CWAO was conducted on the same fixed bed set-up, oxidation achieving AC regeneration in mild conditions. The experimental setup (Figure 1) was previously described by Suwanprasop et al. [START_REF] Suwanprasop | Scale up and modelling of fixed bed reactors for the catalytic phenol oxidation over adsorptive active carbon[END_REF]. The reactor (1.2 m high, 2.54 cm internal diameter) was successively packed with 168 g of L27 and 340 g of S23 AC particles (1.25-1.40 mm sieved fraction). The adsorption step was operated at ambient conditions (25°C, atmospheric pressure). Solutions of 1 g/L and 2 g/L of paracetamol for L27 and S23 respectively were continuously introduced into the column by a dosing pump.

The same pump was used to feed the column by recycling the reaction mixture from a pressurized tank during the oxidative regeneration step. The wall temperature was here set to 150 °C, and the oxygen partial pressure (P O2 ) was adjusted to 3.2 bar. The gas flow rate (50:50 O 2 :N 2 mixture) was 100 L/h STP and the liquid flow rate was 2 L/h. Gas and liquid circulated cocurrently upward through the fixed bed. Three adsorption-oxidation cycles were completed for each AC. Liquid samples were characterized using the chemical analyses described in § 2.2.1.2.

Results and discussion

Textural, chemical and adsorptive properties of fresh activated carbons

The physico-chemical properties of the carbons are listed in Table 1. Among the investigated ACs, L27 has the highest surface area. S23 and C1 have very similar surface area but S23 is essentially a microporous carbon. The quantification of the carbon surface groups by Boehm titration reveals that L27 has also the greatest content of acidic and total surface groups. On the other hand, C1 has the greatest content of basic groups. TGA spectra confirm the results of Boehm titration with an increasing weight loss from S23 to C1 and from C1 to L27. In accordance with previous results, L27 is also found to have the lowest pH PZC and the highest oxygen content. Finally, the elemental analysis shows that all ACs have low metal contents, with a larger amount of Fe for C1. Figure 2 compares the paracetamol isotherms measured on the three carbons (with corresponding best fit adsorption model), showing a lower capacity for L27 despite a higher surface area. This conclusion is in accordance with those reported for phenol and some aromatic molecules for which a clear decrease in adsorption capacity is found when there are more acidic groups on the carbon surface [START_REF] Quesada-Peñate | Comparative adsorption of levodopa from aqueous solution on different activated carbons[END_REF][START_REF] Coughlin | Role of surface acidity in the adsorption of organic pollutants on the surface of carbon[END_REF][START_REF] Franz | Effect of chemical surface heterogeneity on the adsorption mechanism of dissolved aromatics on activated carbon[END_REF]]. An accepted mechanism for this phenomenon is the formation of water clusters through H-bonding with acidic (carboxylic) surface groups, which reduces AC adsorption capacity [START_REF] Franz | Effect of chemical surface heterogeneity on the adsorption mechanism of dissolved aromatics on activated carbon[END_REF].

CWAO of paracetamol: activated carbon screening and biodegradability assessment

Initial performance of the carbons

Figure 3 shows the time concentration profiles during preliminary adsorption and oxidation using fresh ACs.

The adsorption equilibrium at 150°C was approximately reached after 2 hours when 86.7, 134.5 and 126.1 mg of paracetamol per g of AC were adsorbed on L27, S23 and C1 respectively. The adsorption results at 150°C were in agreement with the isotherms obtained at 25°C, lower paracetamol uptake being observed for the acidic carbon. Then, after adsorption equilibrium under nitrogen, the CWAO reaction was started. The highest initial oxidation rate was obtained with fresh C1 carbon (3 mg/min) and the lowest one with L27 (1.6 mg/min).

Table 2 shows the comparison of paracetamol adsorption, conversion and COD removal for the three fresh ACs. It is obvious that although a high conversion was obtained for all the ACs, the presence of acidic groups on L27 surface affected both the adsorption and the COD removal.

Catalytic stability upon recycling

The stability of AC catalytic activity was tested by completing a series of five consecutive experiments (Figures 4a and4b). For S23 and C1 a large decrease of paracetamol conversion was observed after two oxidations, but it was rather constant for the last three cycles. For L27, paracetamol conversion was quite stable and only a slightly decrease was observed in the last cycle (Figure 4a). After five cycles the COD removal was only of 20 % or less for all the three ACs (Figure 4b).

Characterization of the spent carbons

At the end of the experimental series, the analysis of aged ACs (Table 3) showed that the BET surface area decreased by a factor of 3, 26 and 14 for L27, S23 and C1 respectively. Pore volume decreased too. The observed catalyst deactivation can thus be related to the loss of surface area, especially strong for the basic and microporous carbon. Such a change in AC porous structure has already been reported during the CWAO of phenol and some of its derivatives, which has been attributed to the deposition of condensation products, blocking the access to micropores [START_REF] Suárez-Ojeda | Catalytic wet air oxidation of substituted phenols using active carbon catalyst[END_REF][START_REF] Santos | Wet oxidation of phenol, cresols and nitrophenols catalyzed by activated carbon in acid and basic media[END_REF][START_REF] Suwanprasop | Scale up and modelling of fixed bed reactors for the catalytic phenol oxidation over adsorptive active carbon[END_REF]. Thermogravimetric analysis also reveals a higher weight loss between 200°C and 700°C for all spent carbons (Table 3) as compared to fresh ones (Table 1). This increase should correspond not only to the calcination of new surface groups, but also probably to the decomposition of these chemisorbed oligomers formed by oxidative coupling reactions. Such a phenomenon is found to be hindered by the presence of acidic surface groups [START_REF] Quintanilla | Catalytic wet air oxidation of phenol with modified activated carbons and Fe/activated carbon catalysts[END_REF], which might explain this better stability of L27.

Biodegradability assessment

In order to compare the biodegradability of paracetamol and that of the effluent from batch oxidation on L27, a pulse equivalent to 98 mg COD/L of each was successively introduced into the respirometer (this COD value corresponds to 50 mg/L of paracetamol). Figure 5 shows the OUR profiles obtained for each experiment. After paracetamol had been added to the system (Figure 5a), the oxygen consumption corresponding to sodium acetate was unchanged compared to the first run (19 mg/L). Same values of OUR max were also obtained for the two additions of control substrate.

Those results indicate that up to 50 mg/L, paracetamol is not toxic for the investigated biomass. On the other hand, the OUR profile corresponding to paracetamol is very flat, leading to an OC value equal to 2 mg/L. From equation 1, short term biodegradability of paracetamol is then estimated at 10% relative to that of sodium acetate. Figure 5b exhibits a significant improvement of the biodegradability index by CWAO (B.I.= 85%).

No sign of toxic or inhibitory effect is detected with this reaction mixture. Although a detailed study of the reaction intermediates is not presented in this paper, it is obvious that the by-products formed during the oxidation process are readily biodegradable substances.

Evolution of paracetamol uptake during preliminary adsorption

In order to evaluate the role of the adsorption capacity of the ACs on their catalytic performance and to select the most suitable activated carbons for the AD-OX process, the adsorbed amount of paracetamol at equilibrium after the preliminary adsorption step was calculated for each catalyst and each cycle (Figure 6). The adsorption capacity of L27 was more stable and it was only reduced by a factor 1.5 after five cycles. On the opposite, for S23 and C1 ACs the adsorption capacity strongly diminished during four or five cycles. There is thus some correspondence between the catalyst activity and the adsorption capacity of the carbons as proved by the similarity of Figures 4a and6. This seems to apply not only for fresh carbons, but also during their recycling.

Based on this long term performance, L27 was readily selected for the AD-OX fixed bed process; S23 was also used as microporous catalyst for comparison purposes.

Hybrid AD-OX process (fixed bed operation)

Room temperature adsorption step

Contrary to an efficient application of the AD-OX sequential process for water treatment, the complete breakthrough curve was derived, in order to have a better knowledge of the adsorption behaviour of the carbons and to estimate regeneration efficiency by CWAO. After the breakthrough, the storage tank connected to the reactor outlet was filled with 2 L of the paracetamol solution circulating through the fixed bed. With L27 (Figure 7), equilibrium conditions could be achieved within one day: the adsorption capacity calculated by numerical integration of the first breakthrough curve (385 mg/g AC ) was comparable to that obtained from the isotherm. The difference (about 20%) might be attributed to the flowing of water prior to paracetamol solution which might have slightly modified the carbon surface property. After about 15 hours of batch oxidation to destroy absorbed pollutant, a 43% recovery of the initial adsorption capacity could be achieved for L27. The next cycle gave reproducible breakthrough curve, which proved the activated carbon to be stabilized both as adsorbent and oxidation catalyst after first cycle. The analysis of spent AC also showed an important loss of surface area and microporous volume (by 84%), even more than what was observed in the autoclave reactor despite a higher solid to liquid ratio. The adsorption dynamics on fresh S23 (Figure 8) was rather different from that on L27. Only three fourth of the theoretical capacity of S23 was obtained after three days when outlet concentration already reached 95% of feed concentration. Moreover, adsorption being performed with stops during nights, the breakthrough curve of S23 showed a sharp decrease when starting solution feed again owing to the slow diffusion of the molecule inside the microporous structure of the carbon. As expected, after 15 hours of oxidation, a lower recovery of the initial adsorption capacity was obtained for S23 (only 13%). However, as shown in the third experiment, increasing oxidation time could significantly improve regeneration yield (up to 39% after 30 hours of oxidation). After the successive cycles, the BET surface area of S23 was reduced by 87%.

Oxidation step

Figure 9a compares for the two carbons the evolution of the normalized paracetamol concentration measured in the 2 liters of solution which are circulated through the bed during the first oxidation step. The experimental procedure included a heating period under nitrogen resulting in a preliminary significant desorption of the pollutant. Therefore the oxidation started with higher concentrations of paracetamol in the liquid phase than the respective feed concentrations during adsorption: 3753 and 5884 mg/L respectively for L27 and S23.

Although an initially faster decrease of paracetamol concentration was observed with S23, full conversion of the molecule was only achieved within 12 hours compared to 4 hours for L27. This was also in accordance with the CWAO results measured in batch autoclave, showing L27 to be less efficient during the first oxidation, but giving better results after five oxidation cycles. More surprisingly, time-evolution of liquid phase COD, Figure 9b, exhibited a minimum, COD increasing after paracetamol was depleted. Such behaviour was not observed with phenol as the model pollutant and much lower solid to liquid ratio [START_REF] Julcour Lebigue | Application of sludge-based carbonaceous materials in a hybrid water treatment process based on adsorption and catalytic wet air oxidation[END_REF]. It would result from the slow desorption and slower degradation of oxidation intermediates, main part of the pollutant (more than 95%) being originally adsorbed on AC in this high solid loading recycle reactor. Nevertheless the final COD in solution represented for L27 and S23 about 15 and 5% respectively of the whole initial pollution.

Conclusions

A sequential adsorption-batch CWAO process was investigated for the treatment of a paracetamol solution. Three activated carbons were compared both as adsorbents and catalysts of CWAO for their own regeneration. The initial catalyst activity seemed to be tied to the adsorption capacity of the ACs. The reuse of catalyst in consecutive runs showed a rapid deterioration in both BET surface area and catalyst performance. This is due to the formation of oligomers irreversibly adsorbed on the AC surface and minimally oxidized, which block the access to the micropores, as confirmed by TGA before and after oxidation. This preliminary investigation allowed the selection of the acidic and mesoporous AC (L27) for the sequential AD-OX process in fixed bed reactor, due to better ageing and despite lower initial performances. Three successive AD-OX cycles with L27 were carried out showing quasi stabilisation between runs 3 and 2 after an initial strong adsorption loss.

Nomenclature

List of tables

Figure 1 .

 1 Figure 1. AD-OX experimental set up 1 jacketed packed bed column, 2 gas-liquid separator, 3 pressurized liquid storage tank, 4 condenser, 5 gas mass-flow controllers, 6 feed tank, 7 balance, 8 dosing pump, 9 sampling device, 10 liquid sample valves, 11 pneumatic valve, 12 expansion vase, 13 gear pump, 14 heater, 15 cooling exchanger, 16* cooling exchanger, 17* anti-pulsatory vessel, 18* flowmeter, V1-V5 three-way valves for up-or down-flow mode.

Figure 2 .

 2 Figure 2. Adsorption isotherms of paracetamol on L27, S23 and C1 carbons at 25°C.

Figure 3 .

 3 Figure 3. Batch adsorption and CWAO of paracetamol on fresh ACs (T = 150°C, C 0 = 1000 mg/L, w ac = 1 g, adsorption: P N2 = 10 bar, oxidation: P O2 = 3.2 bar).

Figure 4 .

 4 Figure 4. Evolution of (a) paracetamol conversion and (b) COD removal, using recycled ACs (T = 150°C, C 0 = 1000 mg/L, w ac = 1 g, t oxidation = 2 h with P O2 = 3.2 bar).

Figure 5 .

 5 Figure 5. OUR profiles obtained with (a) 50 mg/L paracetamol solution, before batch oxidation; (b) effluent resulting from catalytic oxidation of paracetamol on L27.

Figure 6 .

 6 Figure 6. Adsorbed amount of paracetamol on recycled ACs.

Figure 7 .

 7 Figure 7. Successive breakthrough curves on L27 (C in = 1 g/L, Q L = 6.5 L/h, w ac = 168 g, T = 25°C).

Figure 8 .

 8 Figure 8. Successive breakthrough curves on S23 (C in = 2 g/L, Q L = 6.5 L/h, w AC = 340 g, T = 25°C).

Figure 9 .

 9 Figure 9. Evolution of concentration profiles during the first oxidation (T=150°C, P O2 = 3.2 bar, Q L = 2 L/h (recycle), Q G = 100 L/h STP, C 0 , ox = 3753 mg/L (L27) / 5884 mg/L (S23), V L = 2 L): (a) normalized concentration of paracetamol, (b) chemical oxygen demand.

Table 1 . Physico-chemical properties of fresh ACs.Table 2 . Paracetamol adsorption, conversion and COD removal with fresh ACs

 12 (T = 150 °C, C 0 = 1000 mg/L, w cat = 1 g, t oxidation = 2 h with P O2 = 3.2 bar).

Table 3 . Textural properties and thermogravimetric analysis of aged ACs after 5 oxidations in batch autoclave.

 3

Table 1 AC

 1 calculated from initial and final concentrations (respectively COD values) of oxidation step

		L27 S23 C1
	BET surface area, m 2 /g	1860 1180 1230
	Microporous volume, cm³/g	0.77 0.47 0.53
	Mesoporous volume, cm³/g	0.48 0.05 0.26
	Mesoporous/microporous volume ratio 0.62 0.11 0.49
	Average pore diameter, Å	25	17	22
	Apparent density (g/L)	552 1024 799
	Acid groups, mmol/g	1.85 0.30 0.12
	Basic groups, mmol/g	0.59 0.98 2.13
	Total surface groups, mmol/g	2.44 1.28 2.25
	pH PZC	6.2	9.7	11
	%weight loss between 200 and 700ºC 16.0 4.2	6.6
	%C	71.1 92.3 86.5
	%H	2.5	0.6	0.8
	%N	0.3	0.3	0.3
	%O	19.3 2.3	3.4
	%Ash	8.3	3.2 n.a.
	%Fe	0.008 0.012 0.064
	%Cu	0.011 0.007 0.005

*

Acknowledgements

The authors express their gratitude to the European Community through ALFA and 6 th Framework Programmes (6 th FP "REMOVALS"), the Embassy of France in Cuba, Agence Nationale de la Recherche (Precodd "PHARE" project) and INP-ENSIACET for financial support. They also thank PICA (Veolia group) for supplying S23 and L27 ACs, CIPIMM for supplying C1 AC, L. Le Coq, C. Gerente (GEPEA, Nantes), C. Rouch, M. Auriol and S. Mouysset (SAP, LGC Toulouse) for AC characterization, A. Zarragoitia and C. Albasi (BioSYM, LGC Toulouse) for respirometry tests.


Cansu Akpinar-Sposito
email: cansu.akpinar3@univ-lyon3.fr

Career barriers for women executives and the Glass Ceiling Syndrome: the case study comparison between French and Turkish women executives

Keywords: Glass Ceiling, Carrier Barriers, Women in Leadership

The situation where gender pay gaps are typically wider at the top of the wage distribution is known as the "glass ceiling". It is one of the most compelling metaphors recently used for analyzing inequality between men and women in the workplace, in order to describe a barrier to further advancement once women have attained a certain level. The general-case glass ceiling hypothesis states that not only is it more difficult for women than for men to be promoted up levels of authority hierarchies within workplaces but also that the obstacles women face relative to men become greater as they move up the hierarchy.

)), inequality (David J. Maume Jr.) and sex segregation (Mia Hultin 2003).

Introduction

In today"s world, more women than ever are entering the labour force but the majority of top management positions in almost all countries are primarily held by men. Female managers generally tend to be concentrated in lower management positions and have less authority than men. And in the same time women are still concentrated in traditionally "female" functional areas of companies such as; human resources, corporate communications, community and governmental relations marketing and finance (Catalyst, 1991;U.S. Department of Labor, 1991). Although women as a whole may place less emphasis on career success than men, there are a considerable number of women who strive for top management positions and are unable to attain them. "Women at work" has been an important topic of conversation and organizational strategy for 100 years, and certainly in the last two or three decades. There has been several strategies show that US corporations have decided to improve the work experience of women. This strategy has focused on breaking through the glass ceiling. The situation where gender pay gaps are typically wider at the top of the wage distribution is known as the "glass ceiling". It is one of the most compelling metaphors recently used for analyzing inequality between men and women in the workplace, in order to describe a barrier to further advancement once women have attained a certain level. "The glass ceiling argument suggests that gender and race differentials are largest at higher organizational levels" [START_REF] Yap | Gender and Racial Differentials in Promotions: Is There a Sticky Floor, a Mid-Level Bottleneck, or a Glass Ceiling? Département des relations industrielles[END_REF] The objective of this work is to summarize the Glass Ceiling Phenomenon and make a comparison of different arguments of researchers. In particular with this study, It has been pointed out that most past research has been relied on the glass ceiling effect who have investigated a variety of labour market outcomes such as promotions (Powell andButterfield 1994, Yap and[START_REF] Yap | Gender and Racial Differentials in Promotions: Is There a Sticky Floor, a Mid-Level Bottleneck, or a Glass Ceiling? Département des relations industrielles[END_REF]), women carrier (Belgihiti Kartochian, [START_REF] Laufer | La Revue Française de Gestion : « Femmes et carrières : la question du plafond de verre[END_REF]), inequality (David J. Maume Jr.) and sex segregation (Mia Hultin 2003). This work is divided into four parts. The first part offers a presentation of the definitions of Glass ceiling. The second part refers a synthesis of the promotion effect in the labor market. The third part presents the most common measures of chose of the women and work/family decision. Finally, the last part provides an overview of the overall situation in Europe and the sector and activity. It presents crosscountry comparisons for glass ceiling on the labor market.

Literature Review

General Definition of Glass Ceiling

The glass ceiling is a term which symbolizes a variety of barriers faced by women and by minorities as they seek to improve their employment status. Many studies confirmed the glass ceiling hypothesis and indicated that women in their early lives experienced a number of barriers during their decision of their career path (Phillips & Imhoff, 1997); and also invisible barriers, which continued to prevent women from moving up to a higher position in organizations (Adair, 1999;Baxter & Wright, 2000;Lyness & Thompson, 2000). Lyness and Thompson (2000) were curious about whether women and men executives followed similar routes in climbing the corporate ladder. In fact they found that women face greater barriers and they need different strategies to succeed than do men. In order to be a successful executive, women have to overcome isolation, sex-stereotyping and performance pressures.

Moreover, the term "Glass ceiling" was coined in a 1986 issue of The Wall Street Journal on corporate women by Hymowitz and Schellhardt. The glass ceiling is a concept that most frequently refers to barriers faced by women who attempt, to attain senior positions (as well as higher salary levels) in corporations, government, education and nonprofit organizations. Just five years after in 1991, as part of the Civil Rights Act, a Glass Ceiling Commission was appointed by the executive branch and chaired by the Secretary of Labour*. This 21-member group was established to discover blockages and broaden career possibilities and progression options for women and minorities (The Glass Ceiling Commission, 2003). To target these obstructions the commission members agreed on a common definition would help them identify the barriers. They agreed the glass ceiling was melded from, "invisible, artificial barriers that prevent qualified individuals from advancing within their organization and reaching full potential" (2003).

*The United States Secretary of Labour is the head of the Department of Labour who exercises control over the department and enforces and suggests laws involving unions, the workplace, and all other issues involving any form of business-person controversies.

The Federal Glass Ceiling Commission* described three classes of barriers for women and people of colour in top level management. The first class of barriers is Societal Barriers describe the availability and quantity of educated women and people of colour for particular positions and the differences that can be attributed to different groups of individuals as they relate to desired leadership characteristics. The second class of barriers is Internal Structural Barriers. These barriers include a lack of outreach efforts on behalf of businesses to underrepresented populations, corporate climates that may not be tolerant of difference and pipeline barriers which include a resistance to training and mentoring members of underrepresented groups for future promotions. The third class of barriers is described as Government Barriers. These barriers include a lack of monitoring and law enforcement on behalf of the government, weaknesses in data collection for descriptive analyses, and discussion and inadequate reporting on the existence of a glass ceiling.

Cotter and colleagues (2001), they examine three remaining criteria for discerning the effects of a glass ceiling (2001). First, a glass ceiling exists when artificial barriers impede the advancement of women and minorities. In measuring discrimination, analysts often control for education, work experience, tenure with the current employer, and familial factors affecting productivity (e.g., marital /parental status). A second criterion for investigating the concept of a glass ceiling is that one must use longitudinal data to examine job transitions over time. A third criterion for the existence of a glass ceiling is that inequality grows over the life course; this implies that the barriers to mobility existing early in a career become more severe later in the career.

Yet in addition, a glass ceiling is often invoked to explain disparate treatment of women and minorities in lowerlevel and blue-collar jobs. Cotter and colleagues (2001) contended that the glass-ceiling concept is increasingly equated with generic forms of racial and gender inequality, and is losing its power to describe a unique form of inequality at the apex of organizations. They conceded the point that immobility can occur in all occupations, but contended that if job limits are the same at all levels of the occupational hierarchy, and then one is describing racial or gender inequality, not a glass ceiling.

The glass ceiling exits when discrimination increases in severity with movement up the occupational hierarchy. This time, Cotter and colleagues define four specific criteria that must be met to conclude that a glass ceiling exists in a workplace: 1.

"A gender or racial difference that is not explained by other job-relevant characteristics of the employee." 2.

"A gender or racial difference that is greater at higher levels of an outcome than at lower levels of an outcome."

3. "A gender or racial inequality in the chances of advancement into higher levels, not merely the proportions of each gender or race currently at those higher levels." 4. "A gender or racial inequality that increases over the course of a career."

They find evidence of a glass ceiling for women, but racial inequalities among men do not follow a similar pattern Thus, we should not describe all systems of differential work rewards as "glass ceilings." They appear to be a distinctively gender phenomenon. The popular notion of glass ceiling effects implies that gender disadvantages are stronger at the top of the hierarchy than at lower levels and that these disadvantages become worse later in a person's career.

On the other hand, the glass ceiling is a controversial subject that' is constantly in hot pursuit. There are many statistics and theories that come into play; so many, in fact, that people may find it difficult to reach a solid conclusion. Morrison and colleagues (1991) described the glass ceiling as a transparent barrier that keeps women from rising above a certain level in corporations. They even considered it a barrier for women as a group, barring individuals" advancement simply because they are women rather than because they lack the ability to handle jobs at higher levels. Belgihiti and Kartochian (2008) support with an idea which explains that "women have some barriers when they reach a level where they become executive: in the same time men have the same barriers as well, but the question is that women have more than twice as many barriers than men at the same level".

For Powell and Butterfield (2003), "glass ceiling could exist at different levels in different organizations or industries; the term is typically used to suggest a barrier to entry into top-level management positions. No field studies to date have investigated whether actual promotion decisions for top management positions reflect the glass ceiling phenomenon." From the other side Jaqueline [START_REF] Laufer | La Revue Française de Gestion : « Femmes et carrières : la question du plafond de verre[END_REF]; «The glass ceiling phenomenon is that a strategy of the women and the strategy of the challenge».

In summary, all these ideas show that glass ceiling is visible and invisible obstacle which separates the professional and organisational hierarchical level for women. In particular, women who believe that glass ceiling phenomenon will operate to their disadvantage may be less likely to apply for open positions than equally qualified men. However, a smaller number of female applicants may also lead to a smaller number of promotions of women to top management positions. Thus, to truly avert the glass ceiling phenomenon, organizations need to address perceptions about how promotion decisions are made as well as the reality.

Promotion Effect

Some evidence suggests that gender and race effects on promotion are more prevalent in some parts of the organizational hierarchy than in others. To illustrate, [START_REF] Powell | Investigating The 'Glass Ceiling' Phenomenon: An Empirical Study Of Actual Promotions To Top Management[END_REF] found that for promotions to the highest organizational levels, women experienced an advantage over equivalent male counterparts and they add that in the same organization, race had no impact, either positive or negative, on promotions at the highest organizational levels. Other evidence suggests that women experience large promotion disadvantages in occupations that are located at the lowest organizational levels (Bihagen and Ohls, 2006;Pekkarinen and Vartiainen, 2006).

Most studies of decisions about management positions have focused on selection rather than promotion decisions (Hitt & Barr, 1989) or have examined criteria for decisions made about hypothetical rather than real applicants. Indeed, [START_REF] Lyness Karen | When Fit Is Fundamental: Performance Evaluations and Promotions of Upper-Level Female and Male Managers[END_REF] found to the same level. Findings that race discrimination is attenuated (Powell and Butterfield, 1997), and that women have a promotion advantage at the tops of large organizations support the notion that in order to be seriously considered for top management positions, women and members of racial minority groups must be extremely well-qualified for promotion. Individuals who move quickly up the middle management ranks are the most likely to eventually attain senior management positions (Hurley and Sonnenfeld, 1998). In the research of [START_REF] Powell | Investigating The 'Glass Ceiling' Phenomenon: An Empirical Study Of Actual Promotions To Top Management[END_REF], they have proposed that the applicant gender may have both direct and indirect effects on promotion decisions. In addition, the gender of decision makers may have a moderating effect on the relationship between applicant gender and promotion decisions for top management positions. Stumpf and London (1981) identified the criteria, on how actual promotion decisions are made for top management positions, which are commonly used when decisions are made about management promotions. They specified both job-irrelevant criteria, such as gender, race, and appearance, and job-relevant criteria, such as related work experience, being a current member of the organization offering the position, past performance, education, and seniority.

According to [START_REF] Yap | Gender and Racial Differentials in Promotions: Is There a Sticky Floor, a Mid-Level Bottleneck, or a Glass Ceiling? Département des relations industrielles[END_REF], promotions are linked to so many important outputs, gender and race effects on promotion outcomes that mention differential access to an important source of resources, benefits and satisfaction. Gender discrimination may have been directly influenced by past personnel decisions about women, making it more difficult for them than for men to obtain the necessary preparation for top management positions. Also, there could be gender differences in the distribution of job market skills such as education and work experience. Women consistently report to have lower salaries and lower levels of satisfaction than their male colleagues, and in academia they are less likely to be tenured or on the tenure track. Although respondents from both sexes respond positively to their work, indicating that it is intellectually challenging and provide a desirable level of autonomy in decision making, women report fewer opportunities for promotion and indicate more often than men that they would not recommend their career path to younger students.

As can be imagined that good performance ratings usually increase the chance of promotion or career advancement. A low proportion of women at the highest level of company resulted in a business women"s higher intent of leaving and reduced their satisfaction at work (Burke et McKeen 1996). This means that they don"t see themselves to become executive women in the future explains Bender (2001). A woman manager may be demotivated by the lack of promotion prospects and would be less involved (Belghiti and Kartochian 2008). However, promotions result in increased job satisfaction, opportunities to do more complex work, and greater ability to exercise authority, many employees" value promotions (Pekkarinen andVartiainen, 2006, Hultin, 2003). But "To have good promotions, women need to have a strong human capital background, Given that women are more tied to a specific geographic location for family reasons than men are" says Bielby and Bielby (1992) and that employers might prefer men over women due to actual or perceived supervisor, co-worker, or client discrimination adds Hultin (2003), men are likely to have more outside offers, which results in increases in their pay. This argument implies that gender and race do not necessarily affect the probability of promotion itself.

Human capital theory is the investment of the educational background and the job experiences. Women who anticipate a career interruption due to maternity would invest less in education and formation (Mincer and Polacheck, 1974). They accumulate less human capital than men which could prevent them from having access to occupations up the professional hierarchy. Human capital theory is in this sense no longer powerful given that women have caught up with men and even surpassed them in terms of educational attainments. Becker (1971) suggests that workers make rational choices regarding investment in their own education and careers. If women create less human capital over time than men, then their career development, including ascendancy to top management positions, would be more restricted (Stroh et al., 1992). Finally, "gender discrimination may have influenced prior evaluations of employees' human capital, with women given less credit for their education, work experience, and so on than men" says [START_REF] Powell | Investigating The 'Glass Ceiling' Phenomenon: An Empirical Study Of Actual Promotions To Top Management[END_REF].

Based on the human capital theory, not only the general gender-specific pay differentials, but also the different proportions of women and men in certain occupations and fields of work and thus the gender-specific labor market segregation is explained with the so-called self-selection (Polachek 1981). The gender-specific occupational choice is also a result of a rational cost-utility calculation; women choose in particular jobs that can be combined with family responsibilities, for example, those that allow part-time work and breaks in employment and those with a low obsolescence risk. The different level of integration into the labor market can, in accordance with this approach of self-selection, explain gender-specific career mobility to a large extent.

In summary, in this part, it has been argued that the existence of a glass ceiling should be applied to the analysis of managerial attainment. Granting control over the firm"s human and fiscal resources is an important symbolic display of trust in the worker. As Maume (1999) explains that "If firms are more willing to promote men to managerial status than women and minorities, then a significant mechanism by which inequality is created and sustained has been identified. This can be called a glass ceiling if racial and gender inequality is observed after controlling for productivity-relevant factors, and inequality grows over the course of a person"s career".

Women in workplace: Work and family balance

Work and life balance challenges can impact women's advancement and, if not dealt with, may contribute to the glass-ceiling phenomenon. Women are typically the primary family caregivers for children and/or the elderly. Assumptions are often made regarding women's availability to do a job without interference from family responsibilities. Further, some organizations may not offer work/life programs that support outside commitments, particularly for senior-level positions. As a possible solution, perhaps, women could choose to work fewer hours than men in order to spend more time with their families. Women also measure success in the workplace differently than men. Men tend to measure success by high salaries and important job titles whereas women place a higher value on their relationships with colleagues and community service. Therefore, many women are at a disadvantage to take steps that would increase the likelihood of advancing up the corporate ladder.

Having children brings a lot of responsibilities to a family life and this is the reason why many women decide to leave their careers prematurely so as to raise their children sufficiently. For this reason, employers occasionally hesitate to promote women because they are afraid that women will choose their families first. Nonetheless, an increasing number of companies are realizing the fact that women need some time out and have undertaken attempts to encourage women to remain longer in their careers as the participation of women is vital to the diversity and to the successes of corporations (George, 2005) Laufer (2003) indicates that the "different needs" of women lead them to create a self-imposed glass ceiling, in this manner only artificially seeming as if a glass ceiling would block their careers. Confronted with the ever-present glass ceiling, it is no longer possible, as has often been the case, to talk of the "choice of women for family" in explaining the absence of women in applying for certain vacancies, whilst at present many women uphold both a successful career and children. It is therefore necessary to "shift the focus" so as to give more weight to the organizational obstacles outlined here.

Many women who are at senior management positions seem to be not quite willing to climb for upper management positions because they cannot take the risk of bringing political conflicts, polemics and ambition into their family lives. Additionally, women often do not see their own personal skills and talent sufficient for those kinds of roles. However, the idea that women are not interested in high hierarchical positions because of the difficulty of reconciliation is increasingly challenged. Thus, the 2004 Catalyst study, "corporate leadership: same workplace, different realities" shows that women executives who aim at reaching the CEO position are as much as men and women with children at home desire it even more (55% against 46%).

Finally, the realization of organizational work-family initiatives is perceived to pave the way for women to make it to the top. Especially as programs such as child care support services, maternity leave arrangements or part-time working enables women to balance their family needs without sacrificing work (Straub, 2007). Powell (1999) mentioned that the "typical executive job has enormous responsibilities, time demands and pressures, which eventually calls for considerable sacrifices in personal life". As a consequence, women are often less willing than men to make such substantial sacrifices as many want to have children, spent time with family or simply do not want such a huge responsibility in their daily work.

A French research into young female executives has led to the observation of just how many of them prepare, at around their 30"s, for the future limitations imposed by family life. Mainiero and Sullivan (2006) have studied the phenomenon of opting out that woman executive who leaves the companies massively after their 35"s -40"s. Their reason to leave did not differ significantly from those of men, except with respect to the time to spend with their families.

Deemer and Fredericks (1999) retain that there are 4 mental behaviors which block the career progress of women managers and these are: a sense of victimization, limiting personal convictions, single-mindedness, paying attention to the status quo. Research shows that in societies where gender based roles are imposed, a working women perceives her in a different position than men. Initially, since being a wife and mother is prior for women they choose not to travel and work for long hours which affect their career progress. [START_REF] Laufer | La Revue Française de Gestion : « Femmes et carrières : la question du plafond de verre[END_REF] explains that some professional women give up the opportunities because of travel involved in their jobs.

Basically, for all sectors; travelling could be a real barrier for women who would like to become an executive. One of the requirements for advancement in many corporations is the mobility of the executives. Women, according to the glass ceiling commission"s report (1991), are assumed by their superiors not to be willing to relocate, thus hindering their career advancement This phenomenon was verified by a study, quoted in the report, done by the Kellog Graduated School of Management and Loyola university, of the career progressions of male and female managers with similar education, positions, ability to relocate, and career orientation. The study showed that the females had been transferred less often than their male colleagues, resulting in slower advancement and income. The study calls this practice discriminatory. It is true that many women managers would choose not to relocate, if asked to, because of their children"s education and social support systems.

In general, women are less available for geographic mobility and are mostly "followers" of their spouse (Pochic, 2005). On the research of [START_REF] Bender A.F -Pigeyre F | GRH et genre -Les défis de l"égalité hommes-femmes, chapitre 5, Carrières des femmes entre opportunités, contraintes et choix[END_REF], they mentioned the Dual career. Dual career households therefore impact on traditional family roles; the problem of such households is a female problem, however, as women have greater difficulty in making their husbands and partners accept any professional mobility. It is typically the woman who has to interrupt her career to follow the male (Laufer and Pigeyre, 2000). To meet (to satisfy) the educational needs of children, dual-career couples can develop different carrier strategies: differentiation or division of roles, sequentially or simultaneously say Sekaran and Hall, 1989. In the other side, Merignac and Falcoz, (2000) have proposed that the acceptance or not of mobility by the partner can be influenced by the support proposed by the company. If there is a dual career situation, for the double career couple, the mobilization of men can be a problem for his conjoint. Before men accept to move to another country, the company, who proposes a high level of job for men, needs to look for a job for his conditions. It will be the responsibility of the company or, otherwise, it will become a big decision for the couple who will make a decision for their future. For a professional couple with dual career, juggling work and home responsibilities has never been easy. However, in today"s global economy, where local job opportunities may be harder to find, new challenges are emerging. May be, it is possible to have a successful career without sacrificing personal satisfaction, life balance, or relationships.

Finally, opportunities for promotion often favor men due to developmental prospects, such as mentoring and networks. Women may not have full access to informal networks men use to develop work relationships in the company, and these networks often tend to exclude women due to the nature of their activities or the perception that these are "male activities", thus contributing to gender barriers in the workplace.

Sector and activity-(Organizational Influences)

Many other researchers have been interested in the magnitude and determinants of racial and gender inequality in the labor market. In 1990s, the concept of a glass ceiling pervaded the literature to describe the paucity of women and minorities heading public and private sector organizations. Several small-scale studies conducted at different times point to the scarcity of top women managers in the private sector. Studies conducted in last five decades show that the ratio of women employed in executive positions in the private sector does not surpass 4% and that there has been no increase in their representation levels in the past 30 years in the manufacturing sector. Even in sectors like banking or insurance, that traditionally employs high numbers of women; the percent of top women managers is close to 3% or 4%. There is a sharp decrease in women"s presence as the position gets to be more strategic and involves decisionmaking responsibility for large groups of people and significant amount of resources. [START_REF] Bender A.F -Pigeyre F | GRH et genre -Les défis de l"égalité hommes-femmes, chapitre 5, Carrières des femmes entre opportunités, contraintes et choix[END_REF] explain that in public sector, supposedly more equal; women additionally struggle to occupy all posts and to reach the highest hierarchical level. In three of the public sector employment areas (State, local authorities, hospital), women are concentrated in the lower qualified positions. There is also a large degree of segmentation in terms of careers. At university, for instance, whilst there appears to be a large degree of parity in senior lecturer posts, women only represent 15% of professors, across all disciplines. In France : in the case of the disciplines studied, the rate of passage of women Assistant professor (maître-assistant) to the rank of Professor, is not related to their numbers in the category and remains lower than men of the numbers involved says [START_REF] Laufer | La Revue Française de Gestion : « Femmes et carrières : la question du plafond de verre[END_REF].

As demonstrated here, the growth in the number of female graduates and those occupying executive posts, which stands at a high proportion in many countries, has not been followed by proportional increase in females in such posts in higher education (senior management position). This degree of segmentation which can additionally be observed in French universities: in the case of those disciplines which form the focus of this study, the rate of moving from assistant lecturers to professors is not linked to their total representation across the entire sector and remains much lower than that of males, irrespective of the number of employees concerned.

The research performed by Bagues & Esteve-Volart (2007) found an extremely low percentage of women in supervisory and management positions, at both the private and public sector. For instance, in Italy and France, 3% and 4% respectively, of the 50 largest companies" board directors are women. In the US, women only made up 3, 4% of the top level management back in 1997. Finally, in Europe, none of the 25 highest earning CEOs are female (Emerald, 2006). These numbers already indicate that women are faced with treatment discrimination in terms of promotion possibilities, especially likely to occur into management and further extending to pay disparities between men and women across occupational categories.

Cultural and social attitudes towards what constitutes "male" or "female" jobs result in occupational segregation, although the extent of the problem varies from country to country and from job to job. It is important to keep in mind that there are important institutional differences between countries regarding their educational and academic systems. This makes comparisons difficult. In United States, according to Adams study (2007), women, for instance, held less than 16 percent of the corporate officer positions in the United States (US) Fortune 500 companies in 2002 and less than 15 percent of Canada s FP500 corporate officer positions in 2004. Females also represented less than 2 percent of all Chief Executive Officer (CEO) positions at major US corporations in 2004. Similar to this result, Stuart s (2008) research indicated that there were only fourteen females in the CEO position at firms in the S&P 500. Catalyst released some interesting statistics about women in business in the United States. The research shows that:

Percentage of women in the U.S. labor force: 46.3% Percentage of women in management, professional and related occupations: 50.6% Percentage of female Fortune 500 corporate officers: 15.4% Percentage of female Fortune 500 board seats: 14.8% Percentage of female Fortune 500 top earners: 6.7% Percentage of female Fortune 500 CEOs: 2.4%

In France, the majority of the women executives in the companies, in the public sectors, in the universities, au CNRS will be marked. Thereby, there are just: 7% of women, who work as an executive, 31% are in administration and commercial, 12, 5 % work in function public and 49% are in state. In French universities, there is totally 16% among professor and 38% of senior lecturer posts. For instance, in Italy and France, 3% and 4% respectively, of the 50 largest companies" board of directors are women. In the US, women only made up 3, 4% of the top level management back in 1997. In Europe, none of the 25 highest earning CEOs are female (Emerald, 2006). The number of the population is 46% women,) 30 % of women work on sector of education, health and action social (INSEE* Enquête Emploi 2003 In Turkey, the glass ceiling exists in all sectors as with all around the world, including the public and private sectors as well as nongovernmental organizations. Women -52% of the 70 million populationsearn 40% less than men and provide just a quarter of the registered labour force, while 42% of them work unpaid for their familiesmainly in the fields. They hold just 4% of seats in the Ankara parliament. Of the 550 members in the Turkish Parliament, 48 are women. In the financial sector alone the percentage of women working in the top jobs is higher than in France. Turkish women are underrepresented in managerial positions like in all countries. The problem is not lost on many of the high-ranking women executives in Turkey, where 12 percent of chief executive positions are held by women, about the same as in Germany according to the World Economic Forum. Furthermore, women"s representation in management positions falls sharply at the upper echelons of the hierarchy. Studies conducted by H. [START_REF] Kabasakal | Women in Management Worldwide[END_REF], most executive women in Turkey are married and have either one or two children. Several studies conducted in western societies show that given the immense household demands on married women, most women feel the need to make a choice between their careers and private life. On the other hand, the availability of low-paid maids in Turkey allows women managers to delegate the housework and child-rearing responsibilities to the fulltime employed maids.

The other point of view explained by Laufer (1999) is that women are mainly concentrated in the "feminized" professions such as nursing and teaching, where at the same time they remain in lower job categories than men. However, women continue to make small inroads into non-traditional fields such as law, information and communication technology and computer science, engineering, so there is evidence that employers are beginning to promote women more systematically and to introduce family-friendly policies in order to retain them. Additionally, they are also less presented for the sector of Industry and Construction. [START_REF] Bender A.F -Pigeyre F | GRH et genre -Les défis de l"égalité hommes-femmes, chapitre 5, Carrières des femmes entre opportunités, contraintes et choix[END_REF] describe that women choose more and more the juridical sector; the number of lawyer women in 1992 was 32%, in 2002 it was 52%. And they add; "Women work often some certain jobs as communication 70%, function personnel 62%, finance and accountable 47% , commerce and sales 11%. Belgihiti and Kartochain (2008) explain that for the sector of engineering, women with a good level of certificate, after graduating from the best schools, have more unemployment problem than men have. This sentence proposes an idea; the glass ceiling can be have high probability in the engineering sectors or it depends of the personality or "the look" of the employer. But in the other side, this observation actually brings a further issue to light. An interesting question is asked by [START_REF] Bender A.F -Pigeyre F | GRH et genre -Les défis de l"égalité hommes-femmes, chapitre 5, Carrières des femmes entre opportunités, contraintes et choix[END_REF]; why men often have science bachelor degrees twice more than women while they come from a same technological background? A survey conducted amongst 15-25 year olds on their opinions concerning sciences confirms that females are less likely to study science than their male counterparts and that they are much more successful than boys. Girls stated that they find science boring and they prefer humanities than pure sciences [START_REF] Bender A.F -Pigeyre F | GRH et genre -Les défis de l"égalité hommes-femmes, chapitre 5, Carrières des femmes entre opportunités, contraintes et choix[END_REF].

Of course, other factors are also likely to be at work. Many labor markets are hierarchical, and promotions and appointments procedures can exacerbate gender pay gaps across the pay distribution. While promotions are typically subject to well-defined procedures, especially in larger organizations, exactly where in the rank-specific salary scale a successful candidate is appointed can depend on individual negotiation skills or employer discretion, in addition to experience. After all the statistics are stripped away, though, one naked truth persists: Women are just as capable as men. "Great ideas have no gender, race, ethnic background or age," DiRusso says. Women may have to work a little harder to reach the top, but it can and does happen. In the not-so-distant future, with a little extra effort on everyone's part, more women could be buttoning up their suits and heading into that corner office.

Methodology

3.1Research Goal

This review takes a well-documented concept, the ""glass ceiling"" and seeks to enrich our scholarly understanding of the term by analyzing the historical context, the contemporaneous uses of the term, and the ways in which this term has infiltrated research literature. By comparing and contrasting the work from multiple areas and culture (all grounded in the belief that they are discussing glass ceiling effects), we hope to aid in building a scholarly consensus on what a glass ceiling is and how it operates.

This paper is an exploratory study. The research will be focused on mid-level women managers in French and Turkish organizations and the samples will be selected from similar or same sector and same industry in France and Turkey. This approach seems particularly well suited to women in leadership and management. In this project, I will explore how the women become a leader with their social and cultural influences (e.g., organizational culture, national/ethnic culture, and gender).In particular, I will focus on the glass ceiling and what kind of barriers they can have when they climb the steps? Why do so few women become business leaders? Also, the study will test the usefulness of a perspective (the situational approach) that is underdeveloped in the leadership literature. This has been broken into the following sub-objectives:

•

Can women who live in a developing country have the same possibility to become a leader then women live in a developed country?

• Are the possibilities of the life style in a country, where he/she comes from, can make the way easier to become a leader?

• How they break the glass ceiling to be in an executive suite?

3.2 Methods 1. Data collection; Conduct a literature review on leadership and management. Data collection will comprise documents (school magazines, bulletins, newsletters, policy statements, prospectuses and more informal artefacts…etc.) and responses in interviews. There were approx. 45 documents that met the criteria for inclusion at the time of this review. A two stage process resulted in this sample for review. First, some electronic databases were used to conduct searches as such ERIC database, RDS Contemporary Women"s Issues, Academic Search/EBSCO…etc. These databases were searched using the following terms: (a) glass ceiling and (b) glass ceiling effect(s), (c) carriers barriers for women, (d) women in business. Second, abstracts were printed and screened by the researchers using the required inclusion criteria (i.e., document used glass ceiling to describe some form of workplace discrimination). At this stage, we were only concerned with documents that actually used the term glass ceiling 2. Interviews and questionnaires; All the interviews will be conducted over a 3 years period, during which the researcher will make repeated visits to the companies, to the homes of interviewees in the metropolitan and country areas. I will make depth interviews with the mid-level women managers (Women Executives) in France and in Turkey.

3. Write a research report; that combines my understanding of the relevant theory and previous research with the results of my empirical research.

Conclusion

In today"s modern world, it is known that a glass ceiling exists for women in management and it is being studied and remedied from varying perspectives. A few women have moved beyond the glass ceiling into the executive suite, yet their number is not proportionate to their representation at middle management levels and is far below that of their similarly qualified male counterparts. Both domestically and globally, women represent a relatively untapped source of talent for leadership in the workplace. While progress has been made across the globe, barriers to women"s advancement continue to exist, including cultural norms, stereotypes, and employer policies and practices.

The glass-ceiling barriers are evidenced worldwide, often compounded by cultural values and traditional gender roles and explained the differences in management/leadership styles between men and women. To illustrate, styles of management and leadership in the corporate world that are typically most valued are those often used by men (e.g., being direct and factual), rather than the interpersonal style women often use. Therefore, women who use the more direct communication style may be more likely to advance in the corporate world than women who do not. In summary; all these ideas show that glass ceiling is the visible and invisible obstacle which separates the professional and organizational hierarchical level for the women. In particular, women who believe that glass ceiling phenomenon will operate to their disadvantage may be less likely to apply for open positions than equally qualified men.

  The INSEE code is a numerical indexing code used by the French National Institute for Statistics and Economic Studies (INSEE) to identify various entities, including communes, departments.

*


S Msolli
email: smsolli@enit.fr

O Dalverny

J Alexis
email: cjoel.alexis@enit.fr

M Karama

Experimental and mechanical characterizations of a lead free solder alloy for electronic devices

Keywords: viscoplastic models, SnAgCu solder, FEM, electronic packaging, thermomechanical behavior

Electronic power modules devices are paramount components in the aeronautical, automotive and military applications. The solder layers are the most critical parts of the module and are usually subjected in their whole life to complex loading conditions. To improve the design task, realistic thermoelastoviscoplastic and lifetime prediction models which can describe efficiently the deformation-damage of the electrical device must be chosen carefully. Some of the most common behavior models are based on the separation between creep and plasticity deformations such as power law, Garofalo, Darveaux… So, to take into account the creep-plasticity interaction, the thermal cycling as well as the hardening-softening effects, unified viscoplastic models are increasingly being used to describe more efficiently the physical state of the material. We propose in this framework a survey of some unified viscoplastic models used in the electronic applications for the viscoplastic modeling of the solder as well as creep-fatigue life prediction rules. The models are used for the characterization of a SnAgCu solder and are briefly compared within tensile, creep data and stabilized responses.

Introduction

Nowadays, electronic power modules give promising perspectives for entirely electric engines with less fuel-dependent systems in aeronautic industry. Typical power module is composed of three major components: a semi-conductor chip which may be an IGBT and/or a diode, a metalized ceramic substrate and a base plate. These components are soldered to each other's and positioned over a heat sink for thermal management (Fig . 1). The dielectric ceramic substrate is double bonded with thick copper or aluminum metallization for improving heat spreading. The base plate is made also of high thermally conductive material such as AlSiC, copper or aluminum. The brazing is achieved using solder alloys considered as one of the principal failure causes in the module due to its weaker thermomechanical properties as compared to the other constitutive materials. So, regardless of their advantages, the design of the electronic power module devices represents a great challenge due to the extreme environmental and operational conditions which involve creep, fatigue as well as creep-fatigue interaction and high thermal variation. The high reliability of such components is then related to the optimized choice of the constitutive materials of the devices which consists basically on the microstructure properties, material compatibility and thermomechanical characteristics. Once the components materials are chosen, the experimental data becomes necessary for the modeling task in order to reproduce the material behavior in its real environmental and assembled state. As indicated earlier, the solder alloy is subjected to a viscoplastic deformation due to high temperature levels; the solder behavior must be described by appropriate viscoplastic models and lifetime prediction rules. There are in the literature a wide range of models which can be classified within the formulation nature of the constitutive equations i.e. coupled or uncoupled deformations. Uncoupled models are based on the summation between the plastic and creep deformations considering that there is no interaction between them [1]. The plastic deformation follows generally an isotropic-plasticity as Ramberg-Osgood model [2] or also a Drucker-Prager plasticity model [3]. The creep deformation evolves according to a creep model such as Norton [4], Garofalo [5], Darveaux [6],…The uncoupled deformation models are characterized by a simple formulation so they can be easily integrated and identified. In the other side, work-hardened solders show creep-plasticity interaction especially in the case of cyclic loading and thermal variations i.e. high-to-low or low-to-high temperatures. In this case, some kinds of unified thermoelastoviscoplastic models which consider that the plasticity and creep effects may be represented by only one time-dependent deformation are suitable for the modeling under complex loading conditions. The concept of state variables is also introduced in these models [START_REF] Krausz | Unified constitutive laws of plastic deformation[END_REF] in order to reproduce some other physical phenomena such as isotropic or kinematic hardening, dynamic and thermal static recovery, ratcheting, aging,… In despite of their complex formulation based on stiff, highly coupled first order differential equations, unified models are frequently used and are more integrated in the finite element codes. Anand's unified viscoplastic model is usually employed for the deformation modeling of the solder alloys [START_REF] Qu | Constitutive Modeling of Lead-Free Solders[END_REF][9][10]. It's integrated in a uniaxial form and has a unique scalar state variable which represents the resistance to plastic deformation. However, Bauschinger effects and cyclic hardening couldn't be well described [11]. Other authors such as Krempl, tried to incorporate on its own overstress-based viscoplastic model a kinematic state variable. Busso et al, introduced a stress-dependent Arrhenius term to describe more efficiently the thermal variation effects [12]. Basaran and Chandaroy formulate a dependency of the material viscoplastic behavior with its microstructure changes by introducing a grain size variable [13]. McDowell et al, included in their model temperature rate terms in both isotropic and kinematic hardening variables for the thermomechanical cycling [14]. Thermodynamical restrictions are also demonstrated for thermoplasticity and thermoelastoviscoplasticity cases [15]. Chaboche's used a power law term to describe the plastic flow and may contains several kinematic and isotropic hardening variables as well as a plastic strain memory for the saturation state [START_REF] Lemaitre | Mechanics of solid materials[END_REF]. The model proved to be thermodynamically consistent.

McDowell and Chaboche's viscoplastic models appear to include the most features that the solder joints material can exhibit and to match well with the thermomechanical responses of several materials references [START_REF] Moosbrugger | [END_REF][START_REF] Chellapandi | Transaction of the 14th International Conference on Structural Mechanics in Reactor Technology[END_REF]. We propose in this framework, (i) a description of the formulation of these unified models (ii) an integration of the first order differential constitutive equations and its implementation in a FE code ABAQUS ® (iii) a comparison of the viscoplastic models compared to the experimental data and the numerical simulations.

Formulation of the viscoplastic constitutive equations

The unification of the inelastic deformations and the description of several physical material states are inducing in nature a huge number of material parameters and a coupled set of stiff and first order [START_REF] Stolkarts | [END_REF]. The temperature dependency of the model is written as a function of the Arrhenius term in the flow law.

Flow Law

The inelastic strain rate is determined by the following rate equation:

    2 3 ,, 2 ij ij in ij v ij ij s A F S D J       (1)
With,

  2 v ij ij S J R     (2)
Where

      ij ij ij ij ij ij s s J         : 3 2 2 denotes the second invariant of the reduced stress   ij ij s  
. ij s is the deviatoric stress tensor, ij  the backstress tensor, and  is a thermal diffusivity parameter expressed as an Arrhenius function. A is a temperature independent material parameter.

                                          2 for 1 2 ln 2 exp 2 for exp m m m m T T T T kT Q T T kT Q (3) m
T is the melting temperature, Q the activation energy, and k the Boltzmann's constant. . is defined as

g g  if 0  g else 0  g .
The function F is the Zener-Holloman parameter expressed as follows

  1 exp   N N B F   (4) Knowing that  D S v     1 (5)
 is a factor which represents the sensibility partition of the strain rate and mainly varied between 0 and 1. D is an isotropic resistance which is usually constant for solder alloys or proportional to the yield stress for copper  

R A D 0  [20]
. N is a temperature-dependent and 0 A temperature- independent material parameters. In the case of 0   , the flow law is expressed as:

    1 2 3 exp 2 N N ij ij v v in ij ij ij s S S A B T D DJ                             (6
                                      s ij s s ij s ij s ij s ij in ij s ij Cb T T b b T C C T b p b C b b C                    0 ' ' / / (7) * * * * * * * * ij ij in ij ij H T T H H H               (8) Defining   2 / 1 : in ij in ij in ij p          and s ij ij ij ij s s b        
. T is the absolute temperature.

We see that the evolution equation is defined as the sum of a hardening term which is proportional to in ij  , dynamic recovery terms which are proportional to p  and T  and finally a static thermal recovery term which depends on both T  and s ij  and acts considerably when time-dependent mechanisms are dominant (creep, relaxation, recovery,…). The isotropic hardening variable  is decomposed into two parts: iso R corresponds to the variation of the yield stress and iso b corresponds to the saturation of the kinematic hardening

       1 2 3 iso R ( 9
) iso b   (10)                         T T p    ' ' (11)
 is a temperature dependent parameter which represents the saturation value of  .

The thermal static recovery terms are expressed in the following forms:

  2 / s M s ij s ij s s C     ,   2 / * * * * * M ij ij C     ,   2 /        M ij ij C  
The yield stress R and the kinematic hardening saturation b are written respectively as

  iso R T R R   0 and   iso b T b b   0 0 R is the initial yield stress. * H , s C , s M , * C , * M , 
C and  M are material parameters. In the case of initially isotropic materials, the stress is written as a function of the total strain and the inelastic strain tensors respectively ij e and in ij 

1 2 2 ij in ij ij ij s G s G e T T              (12)
And  

0 12 3 3 1 2 3 T T kk kk kk E T T T T T E T                                     ( 13
)
T  is the coefficient of thermal expansion and 0 T is the reference temperature. In the isothermal loading case, temperature rate terms are not considered. Chaboche's viscoplastic model. Thanks to its capability to reproduce a realistic behavior of the material under complex loading, the Chaboche's Model becomes one of the most known unified viscoplastic model used usually for thermomechanical fatigue behavior of nickel based superalloys for turbines blades and other materials with high performance [21]. We present here a formulation of the Chaboche's model with combined kinematic and isotropic hardening variables. The model contains also static thermal recovery terms.

Flow Law

The inelastic strain rate is determined as follows

    0 2 2 3 2 n ij ij ij ij in ij ij ij J R R s D J           (14)
Let's see that F takes the form

N F   knowing that   0 2 v ij ij S J R R      and D S v  

Evolution equations

The evolution equations of the state variables s ij  and * ij  are written in the following forms

s in s s s ij ij ij ij Cb C p         (15) * * * * * ij ij in ij ij p H H            ( 16
)
H is a temperature dependent material parameter.

For the isotropic hardening equations, R corresponds to  thus, for notations equivalence, we can write adopt equation (11) as the equation of evolution of the isotropic hardening variable R.

Integration and implementation

Time integration of the constitutive equations. Due to the strong coupling of the first order differential equations in the two models, a great care must be taken for the choice of the appropriate integration algorithm. The method must show a good accuracy and approved stability. Thus, satisfying numerical results may be obtained when semi-implicit Euler method is used with a Newton-Raphson iteration scheme [20] or when a fully implicit Euler method is combined with Regula Falsi (Pegasus method) and fixed point iteration schemes [22]. So, we've adopted these methods respectively for McDowell's and Chaboche's models. Let's just remember that for the Euler method and for a first order differential equation such as,

  , ij ij y f y t 
, the unknown function y(t) can be calculated knowing that :

    t t t ij y y t y            1 ( 17
)
For a fully implicit Euler scheme, is equal to 1. So, the incremental solution depends on the evaluated quantities at t + t. In the semi-implicit Euler scheme, all the incremental forms of the state variables and stress are expressed with respect to the known variables at t, such as

t dt t t t ij ij ij ij t y y y y ty        (18)
But the incremental cumulated inelastic deformation p  is expressed as function of the calculated variables at t + dt and the aim is to obtain

      , , : 0
t dt t dt in in ij ij F R p t            (19)
As indicated before,  

t dt in ij



 is calculated using the variable at time t + dt. For McDowell's model, the variable p  is updated by Newton-Raphson scheme as follows

    1 , , , ' , , , ij ij k k ij ij F p R pp F p R          (20)
As a result, if

1 1 kk tol k pp p        
, the solution is then retained else the calculation is repeated for the next iteration step k + 1. In this exercise, tol  is equal to 10 -4 . In spite of the lack on the predefined viscoplastic models available in Abaqus®, this software offers to the user the possibility to work with its own deformation behavior model. The integration algorithms for both Chaboche's and McDowell's viscoplastic models are then coded in FORTRAN language and implemented as UMAT subroutine formats. In the FE code, an asymmetric solver is used with a full newton-Raphson iteration scheme for finite element computations. This is due to the asymmetric aspect of the jacobian matrix in both two models. Identification of the material parameters. Cyclic and asymmetric displacement controlled tests are performed at 50°C, 125°C and 180°C under various displacement rates 10-2, 10-3 and 10-4mm/s. Creep tests are also achieved at 180°C and 125°C with respectively 120 N and 180 N. The shear specimen considered (fig. 2(a)) consists of three Ni coated copper plates which are connected to each other by means of copper bumps. The copper bumps are brazed to the plates using a SnAgCu solder alloy. This specimen is designed to be mounted on an Electroforce® machine test, which is rated up to 450 N and can perform precision materials tests including tension/compression loading, fatigue and dynamic material characterization. The apparatus is equipped with a furnace which can reach temperatures up to 300°C. Displacements are measured by means of an axial extensometer The Least square procedure for the parametric identification was applied as a Python script in combination with the FE code Abaqus® and the UMAT subroutine. The figure 2 125°C. Figure 3 shows the evolution of the displacement as a function of the time for different creep tests at 125 and 180°C. The two identified laws are in good agreement with the experimental data. For more complex cyclic loading, we can see the load-displacement curves (figures 4), where the assembled specimen tends to softens under. It saturates quickly whatever the imposed displacement rate but keep a nearly constant hardening behavior. Viscoplastic behavior of SnAgCu doesn't vary so much and still stable even when temperature changes. Moreover, in low temperature ranges and in comparison with McDowell's model, Chaboche's model appears to fit well the asymmetric data at 25°C in spite of the error at the end of loading. But at high temperatures, numerical results from McDowell's model correlate well with experimental data at 125°C and 180°C which is approved by the use of an activation energy term. In fact, this term intervenes in the flow and the evolution equations as well which is not the case in the Chaboche's model.

Summary

Thermoviscoplastic behavior of a lead-free solder SnAgCu is characterized using several mechanical tests at three different temperatures. The mechanical responses are used to identify two unified viscoplastic models. Numerical results of the viscoplastic models show mainly good correlation with experimental data especially at high temperature, when recovery terms dominate. In the high temperature range, the use of activation energy term appears to produce more accurate results but this fact had to be verified by thermomechanical fatigue tests when the influence of temperature rate is not negligible too. Also, SnAgCu cyclic behavior must be investigated using fatigue tests to understand the softening behavior and to quantify the damage in the material for the lifetime prediction as well.

Fig. 1 :

 1 Fig. 1: Internal architecture of a typical electronic power module.

  evolution equations of the state variables s ij  and * ij  are written in the following forms

2 :

 2 Shear specimen used for identification procedure (a) experimental configuration (b) corresponding FE model. Thermal properties Thermal conductivity (W/m.K) 33 Density (Kg/mm 3 ) 7.36×10 -6 Specific heat C p (J.K -1 ) 200 Coefficient of thermal expansion (ppm/K) 3×10 -5 Table1: Thermal properties for SnAgCu.

Fig. 3 :Fig. 4 :

 34 (b) shows a half symmetric model of the specimen considered in the finite element computations. Copper plates are considered as an elastoplastic material modeled with a combined hardening elastoplastic Chaboche model. Elastic modulus and Poisson ratio of SnAgCu are taken respectively as E (MPa) = 41632 -19.4 T (°C) and v = 0.33. Thermal properties of the solder are given in table 1. The identified material parameters of the SnAgCu solder alloy are given in the table 2 for Chaboche's and McDowell's models. Contrarily to the Chaboche's model where all parameters are temperature-dependent, McDowell model contains only six temperature-dependent coefficients i.e. E, v, C, H * , b 0 , R 0 , ' and . All the temperature dependent parameters may be expressed as functions of temperature. Numerical results and discussions. Experimental displacement profiles are used in the FE code as imposed loading to extract the SnAgCu mechanical responses. Following all the displacement imposed profiles, the displacement rate is not constant during the tests and varies from 10 -2 to 10 -5 mm/s. a) b) Creep tests (a) 180N at 125°C (b) 120N at 180°C a) b) Displacement controlled tests (a) Symmetric 10 -2 mm/s at 180°C (b) Asymmetric 10 -3 mm/s at

Chip (Diode or IGBT) Metallization s Solder alloys Base plate Heat sink Wire bonding Insulant ceramic substrate differential

  equations which couldn't be integrated without accurate and stable numerical methods. It's the case for the McDowell and Chaboche's viscoplastic models. McDowell viscoplastic model. Contrary to Anand's model based on Garofalo hyperbolic sine function, McDowell's model contains a Zener-Hollowman exponential parameter with respect to the power law term


HUNOSA N Canto

J L Fuentes-Cantillana

A Leynet
email: a.leynet@brgm.fr

BRGM), S. Lafortune (INERIS J Skiba

GIG S Vidal-Gilbert

Maximum 500

Therefore, the CARBOLAB project is working at an intermediate scale between laboratory and industrial pilot, studying an in-situ injection to test and upscale laboratory experiments (for example the CHARCO project) before further pilot-size injections. Our aim is to inject a significant, though not pilot-related, quantity of CO2 into a coal seam lying at the bottom of the Monsacro mine in Asturias, Spain.

Putting devices in the near vicinity of the CO2 plume, only a few metres away, will allow data of much higher quality and density to be collected, and to adapt the injection and monitoring protocols accordingly. Data acquisition includes geophysics (both active and passive seismic and electrical methods) and geochemistry (chemical and isotopic measurements). These and other methods also provide an initial characterization of the coal seam and its surroundings.

The injection and acquisition phase is to occur this summer. The in-situ work will be complemented by parallel laboratory experiments to provide intrinsic properties and characterisation of relationships between water, gases and coal. Afterwards, the data will be compared with results from simulations using existing analytical means as well as new developed ones.

Until now, common reservoir simulators did not represent the adsorption process, which is a key point for explaining the gas storage and migration through coal seams. CO2 sorption onto coal and the exchange with sorbed CH4 are associated with mechanical processes like swelling/shrinkage. Two models are developed, a coupling between TOUGH2/EOS7C and ASTER_CODE (by BRGM), and a COMSOL-based tool (by INERIS). Their intercomparison and their validation with in-situ data have yet to be realised; they will give opportunities for long-term behaviour simulations, in order to provide a basis for the definition of safety criteria for undertaking enhanced coal bed methane projects associated with CO2 injection. The overall aim is to make the impact on Man and the environment close to zero in the short, medium and long terms. However, site selection, risk analysis, storage security management, implementation and eventual remediation need to be studied.

The CARBOLAB project is supported by the European Fund for Coal and Steel, involving partners from three European states: the leader Hunosa, owner of the mine, and Aitemin from Spain, BRGM and Ineris from France, GIG from Poland, and the company Total. It started in 2009 and will end in 2013.

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