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The thermal dehydration kinetics of crystalline powders of (COOH)2 · 2 H2O was examined by thermogravimetry both at constant and linearly increasing temperatures. An Avrami-Erofeyev law is found to hold with a possibility that a phase-boundary controlled reaction proceeds simultaneously. This is supported by the particle size effect on the rate constant. The activation energyE for the dehydration is estimated as around 80 kJ mol−1. It is likely that the effects of particle size and temperature onE are compensated by those on the frequency factorA.

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Thomsonite with ideal chemical composition and with an ordered framework structure was synthesised hydrothermally from zeolite Na−A, which was ground to X-ray amorphous, with 0.05 mol dm−3 CaCl2 solution at 200°C. The dehydration behaviour of the prepared thomsonite was examined by TG-DTA. It was revealed that thomsonite lost most of zeolitic water below 450°C in three steps at about 180°, 340° and 390°C. The peak profiles of, the two higher-temperature endotherms were sharp and similar, and the weight loss at each step was approximately equal.

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Thermal and structural changes of lanthanum hexacyanocobaltate(III) pentahydrate, La[Co(CN)6]⋅5H2O were investigated by means of thermal analysis, visible electronic spectra, IR, powder X-ray diffraction, EXAFS and TG-MS. The dehydration of La[Co(CN)6]⋅5H2O proceeded reversibly through three steps and steps corresponded to the losses of H2O, 3H2O and H2O, and the enthalpy changes for these steps were 51.3, 211.0 and 38.7 kJ mol−1, respectively. After the dehydration, the colour of the anhydride changed from white to blue around 290C and an abrupt mass loss occurred at 350C. The colour change seems to be attributable to the change of coordination geometry around the Co ions from an octahedral structure to a tetrahedral one. LnCoO3 was obtained as a final product by heating the sample to 1000C.

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The thermal decomposition of gallium nitrate hydrate (Ga(NO3)3 · xH2O) to gallium oxide has been studied by TG/DTG and DSC measurements performed at different heating rates. It is concluded that 8 water molecules are present in the hydrate compound. The anhydrous gallium nitrate does not form at any temperature as the reaction consists of coupled dehydration/decomposition processes that occur with a mechanism dependent on heating rate. TG measurements performed with isothermal steps (between 31 and 115°C) indicate that Ga(OH)2NO3 forms in the first stage of the reaction. Such a compound undergoes further decomposition to Ga(OH)3 and Ga(NO3)O, compounds that then decompose respectively to Ga(OH)O and finally to Ga2O3 and directly to Ga2O3. Diffuse reflectance Fourier transform IR spectroscopy (DRIFTIR) has been of help in assessing that the reaction consists of parallel dehydration/decomposition processes.

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The dehydration of Ca(H2PO4)2·H2O was examined with simultaneous DTA and TG. This dehydration permitted clearly the apparation of the following phases: Ca(H2PO4)2·0.5H2O, Ca(H2PO4)2, Ca3(HP2O7)2, Ca2HP3O10 et Ca(PO3)2. The reaction of Ca(H2PO4)2·H2O and CaSO4 was also examined with the same technics. It was found that the decomposition of CaSO4 takes place for relatively low temperature (between 600°C and 800°C).

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The conditions of thermal decomposition of hydrated scandium(III) chlorobenzoates were studied. On heating, the carboxylates decompose in many steps. The hydrated complexes first lose water of crystallization in one or two steps and then anhydrous compounds are transformed to Sc2O3 with formation of Sc2O(CO3)2 intermediate. The dehydration of the complexes is accompanied by an endothermic effect and the decomposition of anhydrous complexes by strong endothermic effects. The anhydrous complexes are melted at 255–300°C.

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The thermal decomposition of cadmium acetate dihydrate in helium and in air atmosphere has been investigated by means of a coupled TG-DTA-MS method combined with X-ray diffraction analysis. Dehydration of Cd(CH3COO)2·2H2O is a two-stage process with Cd(CH3COO)2·H2O as intermediate. The way of Cd(CH3COO)2 decomposition strongly depends on the surrounding gas atmosphere and the rate of heating. CdO, acetone and CO2 are the primary products of decomposition in air. In helium decomposition goes by two parallel and consecutive reactions in which intermediates, Cd and CdCO3, are formed. Metallic cadmium oxidizes and cadmium carbonate decomposes giving CdO. Some of the metallic cadmium, depending on the heating rate and the concentration of oxygen, evaporates. Acetone is partially oxidized in secondary reactions with oxygen.

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The thermal decomposition of FeSO46H2O was studied by mass spectroscopy coupled with DTA/TG thermal analysis under inert atmosphere. On the ground of TG measurements, the mechanism of decomposition of FeSO46H2O is: i) three dehydration steps FeSO46H2O FeSO44H2O+2H2O FeSO44H2O FeSO4H2O+3H2O FeSO4H2O FeSO4+H2O ii) two decomposition steps 6FeSO4 Fe2(SO4)3+2Fe2O3+2SO2 Fe2(SO4)3 Fe2O3+3SO2+3/2O2 The intermediate compound was identified as Fe2(SO4)3 and the final product as the hematite Fe2O3.

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The dehydration process of the fibrillar potassium, rubidium and cesium isopolytrimolybdates was investigated by thermogravimetry and X-ray diffractometry. The dehydration took place in one step and the trimolybdates of general formula X2Mo3O10 (whereX=K, Rb or Cs) were obtained.

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Summary A comparative study of the non-isothermal decomposition of the dl-lactate hydrates of magnesium, calcium and strontium has been made with that of the dl-lactate hydrates chromium(III), manganese(II), iron(II), cobalt(II), nickel(II), copper(II) and zinc(II) keeping dry air as the purge gas and the heating rate maintained at 10 K min-1. While the dl-lactates of manganese(II), cobalt(II) and copper(II) followed single step decomposition scheme suggesting that dehydration and decomposition steps overlapped, the dehydration steps of the other compounds were distinct. &-T plots of none of the dehydration steps showed any induction period, indicating no physical desorption, nucleation or branching. Neither the & max-values nor the onset temperatures of the dehydration steps did show any pattern. The TG data of the dehydration steps have also been analyzed using the Freeman-Carroll, Horowitz-Metzger, Coats-Redfern, Zsakó, Fuoss-Salyer-Wilson and Karkhanavala-Dharwadkar methods. Values of order of reaction, activation energy and Arrhenius factor have been approximated and compared. There are similarities in the activation energy values for the dehydration steps (< 60 kJ mol-1 in general). It is higher with group 2 metals and lower in transition metals (maximum in magnesium and lowest in chromium and iron lactates). In cases of overlapping of dehydration and decomposition steps, the activation energy values are on the lower side with the same trend (lower in cobalt and copper cases).

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