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Hydrolyses of 1-halo-2,2,2-trifluoroethanes (HCFC 133a, 133b, 134) in 2,2,2-trifluoroethanol (TFE) were studied in the presence of modified lanthanum phosphates. Thermodynamic equilibrium could be achieved when the reactions were carried out in the vapour phase. The order of reactivity and selectivity of the various catalysts seemed to be governed by impregnation of the lanthanum phosphate with the desired alkaline earth salt.

International audience; The influence of the gaseous atmosphere and the Ba/Ti ratio on the decrease in specific surface area in a BaTiO3 powder was studied at 850 °C. A model involving elementary steps and the BaTiO3 point defects was proposed to quantitatively account for the accelerating effect of the water vapour pressure and the Ba/Ti ratio.

International audience; Adsorption of polymers on mineral surfaces allowing colloidal stability have widespread applications in industrial processes. The binding mechanism has been quite well described on oxide surfaces. Mainly in terms of hydrogen bonds and electrostatic interactions between charged sites and polymer segments. This phenomenon has been modelized and the influence of pH. Ionic strentgh, and molecular weight can be calculated or predicted. In the case of sparingly soluble substrates such as BaSO4, CaCO3 or CaSO4, several problems arise : the difficulty for the identification of surface sites and the interference of ions coming from the material's solubility. In the case of calcite, the solubility imposes dissolved calcium ions in solution which could complex the polyelectrolyte and reduce its solubility. For that purpose, we have measured the binding energy using microcalorimetry. Microcalorimetric measurements have shown that the adsorption enthalpy is weakly enclothermic: about + 2 kj/mol. Interestingly, this value is very closed to that of calcium complexation with PANa. It is suggested that the driving force for adsorption is the net gain in entropy of the system. The microcalorimetric adsorption isotherm does not show any evidence for a strongly exothermic interaction between positive edges and negative segment of the polyion. Practically, in most cases, adsorption of polymers is calculated from the decrease of its concentration in the solution after separation of the solid by centrifugation. This procedure does not discriminate therefore between real adsorption and phase separation. To answer the question, we have performed adsorption experiments using a dialysis membrane to separate the solid particles from the solution. It has been established that in some circumstances, depending on the relative amount of calcite, calcium ions and polyelectrolyte, precipitation takes place rather than adsorption. This is especially the case at low polymer concentration (less than 2 g/l). Adsorption isotherms were correctly reproduced, taking into account all solution equilibria, including calcium and sodium binding constants and a solubility limit for the calcium polymer complex : the latter was determined by turbidimetric titration for various polymer molecular weights. Our conclusion is that in the presence of divalent ions which is often the case with sparingly soluble minerals, the surface binding of the polyelectrolyte results from a precipitation rather than an adsorption phenomenon.

Solutions of cellulose diacetate (CDA) from two sources (cotton linters and wood pulp Floranier) were analysed in various solvents by size exclusion chromatography (SEC). Without special precautions, the SEC chromatograms presented three peaks — or prehumps — before the main polymer peak. The first prehump which could be eliminated by ultracentrifugation corresponded to microgels whose sugar composition was determined. These microgels were also investigated by electron microscopy, X-ray and electron diffraction analysis. They corresponded mainly to cellulose triacetate (CTA-II) in the case of CDA from cotton linters and a mixture of CTA-II and xylan diacetate (XDA) in the case of CDA from the wood pulp Floranier. The second and third prehumps could be attributed to ionic effects corresponding to the association of remaining sulfate groups on the CDA molecules with residual calcium. It was found that these ionic effects could be eliminated by the addition of LiBr or LiCl to the elution solvents. This led to chromatograms devoid of prehumps.

Carbonyl compounds are converted into polyethylenic aldehydes in a one pot reaction with the anions of phosphonates 1. followed by a mild acidic hydrolysis.

International audience; The influence of surface area and additives on the transformation of transition aluminas into alpha alumina was studied using differential thermal analysis and by measuring the rate of transformation by X-ray diffraction of samples calcined at numerous intervals during a 50 hour period. Four transition alumina samples of different specific surface area ranging from 80 to 130 m2g-1 were used. The transformation was found to be facilitated by a high surface area of the initial transition alumina. Initially the surface area decreased very rapidly from its starting value until about 60 m2g-1 then more slowly and also linearly with respect to the amount of alpha phase in the sample. The influence of additives was followed by adding Mg2+, Ca2+, Ga3+, In3+, La3+, Zr4+ and Th4+ cations by the dry impregnation method with nitrate salts. The influence of the method of preparation was determined by using the same procedure for aluminium nitrate. By comparison with pure alumina and in order of increasing effect. In3+, Ga3+, Al3+ and Mg2+ were found to be accelerators, whereas Zr4+, Ca2+, Th4+ and La3+ were found to be inhibitors. The influence of adding an ion to different initial aluminas was investigated in the case of Mg2+.