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  • Author or Editor: V. B. Lazarev x
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Low temperature heat capacity of ammonium, rubidium and cesium perbromates has been studied by method of adiabatic calorimetry. Anomaly of the heat capacity of cesium perbromate has been found, which corresponds to a structural phase transition. The separation of heat capacity into components has been carried out by the additive scheme. The torsion oscillation of BrO4 anions in solid perbromates at low temperatures has been found. Ammonium ions retardedly rotate aroundC 2 axes in the crystal lattice of NH4BrO4.

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The thermal decompositions of the acetates of Pr, Nd, Sm, Gd and Ho have been investigated using thermogravimetry and differential thermal analysis, together with infrared spectroscopy and X-ray diffraction. The thermal decompositions of the acetates of the rare earth elements exhibit several stages, depending upon both the number of crystal water molecules in the acetates and the rare earth element behaviour. Experiments with the benzoates and abietates of Pr, Nd, Sm, Gd and Ho indicate some correlations in the thermal decompositions of carboxylates of the rare earth elements.

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Several commercial and laboratory-synthesized specimens of silica gel have been studied, using thermogravimetry. Two forms of adsorbed water have been found: the first form, which evaporates in the temperature range 100–200°, is polymolecular water layer in open pores and loosely-bonded molecules on the surface and in the bulk of the globules; the second form, which evaporates in the temperature range 200–700°, comprises water molecules hydrogen-bonded to silanol groups, and evidently coordinated to silicon atoms. The dehydration heat of the first form, determined from the DTA curves, depends on the ratio of the two forms, and varies from 3.7±0.6 kcal/mole H2O for coarse-grain silica gel produced at pH=7 to 12±1 kcal/mole H2O for fine-grain silica gel of commercial “chromatography” grade.

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To determine the role of the forms of fixed water in the relaxation of the silica structure, silica as treated with hot water vapour in an autoclave, and the kinetics of its dehydration were studied by thermogravimetry. Five successive stages of relaxation were established:1.Flocculation of globules, accompanied by evaporation of the polymolecular water layer situated in the interglobular space.2.Formation of a glassy structure, accompanied by further water evaporation.3.Transition of the glassy structure to cristobalite with the formation of large particles.4.Formation of quartz seeds within each particle.5.Aggregation of oriented seeds into monocrystals of quartz.

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