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The thermal decompositions of Ca-bentonites (CaB) from Santai, Shichuan Province, China, over the temperature range of 30-1,100 °C were investigated by simultaneous thermal analyzer. Non-isothermal kinetic analysis was employed to study the thermal decomposition mechanism by using Netzsch Thermokinetics software. Flynn-Wall-Ozawa and Friedman isoconversional methods were used to calculate the activation energy and analyze the reaction steps. The probable mechanism and the corresponding kinetic parameters were determined by multivariate non-linear regression program. The results show that the thermal decomposition process of CaB over the temperature range of 30-800 °C is a kind of six-step, competitive reaction ( F D F C F F model). The dehydration reaction is controlled by two consecutive mechanisms, nucleation and growth, followed by a diffusion-controlled reaction ( F D model), the first step: E = 61.68 kJ mol, log A = 6.75 s; the second step: E = 50.73 kJ mol, log A = 3.11 s. The dehydroxylation reaction is controlled by three-step competitive mechanisms, an autocatalytically activated, initial reaction followed by n-order competitive reaction ( C F F model), the first step: E = 124.74 kJ mol, log A = 5.67 s; the second step: E = 245.29 kJ mol, log A = 11.69 s; the third step : E = 261.73 kJ mol, log A = 11.23 s. A combination reaction of the dehydration and dehydroxylation is observed, and controlled by one n-order reaction ( F model), E = 8.99 kJ mol, log A = 1.91 s. [ABSTRACT FROM AUTHOR]

The single-phase La(CO)·3.4HO with the orthorhombic type was synthesized by hydrothermal method. The results characterized by XRD, FTIR and DTA-TG showed that the thermal decompositions of La(CO)·3.4HO below 1,273 K experience four steps, which involve a two-stage dehydration and formation of anhydrous La(CO) at first, and then the formation of LaOCO and LaO, respectively. An additional intermediate product assigned to LaO(CO) was observed in the third step. Thermal decomposition kinetics of La(CO) to LaOCO was investigated under nonisothermal conditions. The dependence of the activation energy on the reaction degree was estimated by Ozawa and Friedman isoconversional methods, which confirm that the step is a multistage kinetic process. The reaction mechanism determined by a multivariate nonlinear regression program is a kind of two-stage consecutive reaction ( A- A model), f( α) = n(ln(1 − α)(1 − α)). The first stage: E = 435 ± 9 kJ mol, lg A = 28.7 ± 0.8, Dimension1 = 0.28; the second stage: E = 234 ± 4 kJ mol, lg A = 13.5 ± 0.3, Dimension2 = 1.22. [ABSTRACT FROM AUTHOR]