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International audience; Alteration experiments involving intermediate level nuclear waste (ILW) glass in contact with hardened cement paste (HCP) were performed to assess its behavior under simulated repository conditions. Batch experiments were conducted at 20 °C and 50 °C in several artificial cement pore water (ACW) samples (pH from 10 to 13), in the presence of HCP (CEM-I, CEM-V and low pH), with a ratio of glass surface to volume of solution of 8000 m−1 and a ratio of mass of HCP to volume of solution of 10 g L−1. Glass alteration rates increase up to ∼4 × 10−2 g m−2 d−1 with pH in contact with HCP, notably with CEM-I. This value decreases by 2 orders of magnitude in low pH cement solution and also for residual alteration rates. The effect of calcium on glass alteration was observed, mainly in Ca(OH)2 saturated solution, with an incubation effect on the release of Si in solution. Experimental data were successfully modeled with the PhreeqC geochemical code. Glass and HCP samples were characterized via SEM/EDX and micro-Raman studies. This work showed that vitrified glass exhibits good performance in terms of low alteration rates (∼10−4 g m−2 d−1), the absence of secondary phases, and the formation of a gel layer at the surface, when in contact with low pH conditions (in the presence or absence of low pH HCP).

Vapor hydration of a simulated typical French nuclear intermediate-level waste (ILW) glass in unsaturated conditions has been studied in order to simulate its behaviour under repository conditions before complete saturation of the disposal site. The experiments were conducted for one year at 50 °C and 90 °C and the relative humidity (RH) was maintained at 92% and 95%. The glass hydration was followed by Fourier Transform Infra-Red spectroscopy (FTIR). The surface of the reacted glass was characterised by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The chemical and mineralogical composition of the alteration products were studied by Energy Dispersive X-ray Spectroscopy (EDX) and μ-Raman spectroscopy, respectively. The glass hydration increased with temperature and RH and led to the formation of a depolymerized gel layer depleted in alkalis. The glass hydration rate decreased with time and remained almost unchanged for the last three months of exposure. Overall, the ILW glass hydration rate was similar to that obtained with the SON68 high-level waste glass.

We investigated the role of pH in the vapor hydration at 175oC of the French SON68 glass using controlled atmospheres. Hence, experiments were conducted under ammonia and hydrogen sulfide to respectively simulate high and low pH conditions. Results were compared with those obtained under air. Glass hydration and surface analysis were conducted by FTIR, SEM and μ-Raman spectrometry. The glass hydration is ten times higher under NH3 than under H2S. Under ammonia the main corrosion products were analcime and a smectite, and incidentally calcite, apatite and tobermorite while under hydrogen sulfide only a gel-like phase was identified. The precipitation of silica-consuming secondary phases at high pH involves high hydration rates under ammonia atmosphere.

The equilibrium phase diagram of the Ce-Zr-Au system was studied by differential thermal analysis, X-ray diffraction and electron probe microanalysis along the isopletic section at 50 at. % Au. Our main result concerns the discovery of a new ternary phase and a ternary invariant. The polymorphic transitions of the ZrAu phase, previously reported, was confirmed and we precised the melting and the polymorphic transition temperatures of the CeAu phase. A schematic representation of the isopletic section is given.

The polar fractions of various transformer petroleum oils (one new and two used oils) were extracted from the neat oils using silica as solid support. We found that the amount of the polar fraction adsorbed on the silica was higher for the used oils as compared to the new one. Such oil polar fractions are insoluble in low molecular weight paraffins (n-hexane and n-heptane) and are soluble in ethanol. The analysis of the diffuse reflectance infrared Fourier transform (DRIFT) spectra of the silica samples coated with oil polar components indicate the presence of oil polar functional groups such as hydroxyl, aromatic and carboxyl groups resembling asphaltenes or resins. In addition, we studied the electrical properties of the oil polar fraction by determining the ζ potential, in water, of the coated silica. In order to compare the modified and the non-modified silica surface properties, we made blank experiments by measuring the surface charge in water of the bare SiO2 particles. The negative surface charge at the water/oil–silica interface was found to increase with pH, resulting from the increase in ionisation of the oil polar fraction acidic surface groups. The objective of varying the pH was to analyse the possible acid–base interactions at the water–oil interface for substrates having various oil polar fraction contents. The polar components in the neat oil adsorb on the silica surface and increase its surface charge and stabilisation in water. We found a good correlation between the amounts of the oil polar fractions, the surface concentration of their functional groups (carboxylic and phenolic groups) and the magnitude of their ζ potential at the water/oil–silica interface.

Since the ability to provide lattice oxygen should be an important factor dictating the catalytic activity of supported gold catalysts, we synthesized, simply by oxidation of the primary AuCe, AuZr, AuCeZr alloys, intimate mixtures of nanostructured Au with CeO 2 , ZrO 2 or Ce–Zr mixed oxides which have unique redox properties and high mobility of lattice oxygen. This makes it possible to accurately study the influence of the support identity on the catalytic activity. A detailed investigation of the preferential oxidation of CO (PrOx) in the presence of H 2 was undertaken also with the oxidation of CO and the oxidation of H 2 . For CO oxidation, it immediately appears that the nature of the oxide affects significantly the activity of gold, ceria being the best whereas for H 2 oxidation no or only slight support effect has been observed. Catalytic performances in the PROX reaction were compared with those in the oxidation of CO. A change in the conversion of CO was observed in the presence of H 2 at low temperature for all system, the effect depending on the support identity. A boost is clearly observed on Au/ZrO 2 whereas the samples containing ceria present an opposite effect: when H 2 is introduced in the reactive mixture, the CO conversion rate is drastically decreased. According to a Mars–van Krevelen mechanism, implying lattice oxygens of the cerium oxide it was suggested that the presence of H atoms in the vicinity of gold should reduce considerably the oxygen spillover activity. At higher temperature, hydrogen can desorb from ceria and the opposite trend is observed. Whereas the rate of CO’s oxidation decreases in a regular and fast way with the temperature for AuZr, it decreases more slowly when ceria is present. This could explain the better selectivity obtained with ceria containing gold catalysts as compared to gold–zirconia material in the high temperature range. Indeed when H 2 is no longer present on the support, oxygen spillover activity should be recovered and CO oxidation favored. In any case we showed that Au/CeO 2 , in our conditions, is not active in the WGS reaction.

We investigated the role of temperature on the carbon steel corrosion under simulated geological conditions. To simulate the effect of temperature increase due to radioactive decay, we conducted batch experiments using Callovo-Oxfordian (COx) claystone and synthetic water formation with steel coupons at 30 °C and 90 °C for 6 months. The corrosion products have been studied by scanning electron microscope/energy dispersive X-ray spectroscopy, X-ray diffraction and micro-Raman spectroscopy. At 30 °C, experiments showed the formation of magnetite and iron sulphide, indicating the activation of sulphate-reducing bacteria. At 90 °C a continuous iron sulphide layer was identified on steel surface due to the reduction by hydrogen of pyrite originating from claystone into pyrrhotite and hydrogen sulphide. Thus, sulphide production may occur even in the absence of microbial activity at high temperature and must be taken into consideration regarding the near-field geochemical evolution.

In the power transformer, the presence of polar or charged species in the insulating oil can cause failure and electric discharges. Solid substrates such as silica can be used to extract the polar species and to refine the oil in order to prevent future failure in the power transformer. However, the use of silica for petroleum oil separation and refining will depend on the silica characteristics such as surface charge, surface composition, specific surface area and particle size. Various pyrogenic silicas having various specific surface areas (49–200 m 2 g −1 ) and particle sizes (207–500 nm) were used to extract the polar fractions from the neat transformer insulating oils (a new, NO, and used, UO2, oils). The oil covered silica samples were investigated by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy in the range 4000–600 cm −1 . The bare silica surfaces present two main hydroxyl components, a sharper peak at 3745 cm −1 , I 3745 , due to isolated silanols and a second broad, which spreads over 3745–3000 cm −1 , I 3745–3000 , due to H-bonded silanols. The relative intensities of the two components, I 3745 / I 3745–3000, varied for the bare and the oil covered silicas depending on the solid surface characteristics. The adsorption of the NO polar fraction onto silica leads to strong reduction in intensity of the sharper peak in favour of the broad one. However, the adsorption of the UO2 polar fraction onto silica leads in all cases to the decrease in the intensity of the both silica OH components. Further, the UO2 adsorption on the silica leads to the apparition of a broad peak at low frequency in the region 3250–3300 cm −1 which, is due to the associated phenolic groups of UO2 oil polar fraction. The analysis of the DRIFT spectra for various samples indicates that the oil polar fraction resembles to asphaltenes compounds. The microelectrophoresis method used to investigate the surface charge at the water/oil polar fraction covered silica interface, indicates negatively charged particles. Further, the negative charge increased with the pH, as resulting from the increase of the ionisation and/or the amount of the oil polar carboxylic and phenolic groups. The oil polar fraction, i.e. the asphaltene components, in contact with both the silica surface and water at high pH values rearrange, due to their amphiphilic character. Finally, the use of the silica substrates seems to be suited to extract and analyse polar species present in petroleum oil. A correlation is found between the nature of the oil, its functionalities, and the magnitude of its zeta potential value at the water/oil covered silica interface.

The presence of polar species in transformer insulating oil may cause degradation and electric discharges in the power transformer. Such oil polar fraction can originate either from the neat oil and/or from its oxidative degradation in the power transformer. The aim of this study is to examine the relation between the insulating oil and the electrical properties of its polar fraction in order to predict eventual failure in the power transformer. We investigate at ambient temperature the adsorption of the polar fractions of various transformers insulating oils (a new and two used oils) from the neat oils onto silica particles. The adsorbed amount was higher for the used oils as compared to the new one. Infrared spectra of the polar fraction indicate the presence of hydroxyl, aromatic and carboxyl functional groups that are found in the asphaltenes compounds. Microelectrophoresis study of the oil polar fraction covered silica particles gives negatively charged oil polar fraction. Such oil surface charge depends on the pH and results from the ionisation of the oil acidic surface groups. Finally, we obtain a good correlation between the amount of the oil polar fraction and the magnitude of the zeta potential at the water/oil–silica interface.

During the geological disposal of high-level waste, the nuclear glass is expected to be first hydrated in water vapor prior to liquid alteration. In the present work, we investigated the vapor hydration of the International simple glass (ISG) at 175°C and different relative humidities (60%, 80% and 98%). The glass hydration was investigated by nuclear reaction analysis (NRA) and Fourier transform infra-red spectroscopy. The chemical and mineralogical compositions of the alteration products were studied using scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM-EDS) and l-Raman spectroscopy, respectively. The NRA results gave water diffusion coefficients of 2.31–7.34 9 10 � 21 m 2 /s, in good agreement with the literature data on borosilicate glasses altered in aqueous media. The glass hydration increased with relative humidity percentage and the SEM-EDS analysis showed a slight enrichment in Si and loss of Na in the hydrated glass layer compared with the pristine glass. The hydration rate of the ISG glass was little higher than that of the French SON68 glass hydrated using water vapor. The corrosion products were analcime, tobermorite, and calcite, which were typical of the SON68 glass hydrated in similar conditions.

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International audience; The intimate mixture of a skeletal gold structure with ZrO2 nanoparticles obtained simply by oxidation of Au0.5Zr0.5 alloy at room temperature turns out to be an efficient catalyst for the selective oxidation of CO in the presence of hydrogen.