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Zhang X.-H.,Chengdu University of Technology | He C.,Central South University | Wang L.,Chengdu University of Technology | Liu J.,Chengdu University of Technology | And 2 more authors.
Transactions of Nonferrous Metals Society of China (English Edition) | Year: 2014

The single phase La2(CO3)3·3.4H2O was synthesized by hydrothermal method. The thermal decomposition and intermediates and final solid products of La2(CO3)3·3.4H2O from 30 to 1000 °C were characterized by XRD, FTIR and DTA-TG. The kinetics of dehydration of La2(CO3)3·3.4H2O in the temperature range of 30-366 °C was investigated under non-isothermal conditions. Flynn-Wall-Ozawa and Friedman isoconversion methods were used to calculate the activation energy and analyze the reaction steps; multivariate non-linear regression program was applied to determine the most probable mechanism and the kinetic parameters. The results show that the thermal dehydration of La2(CO3)3·3.4H2O is a kind of three-step competitive reaction, and controlled by an n-order initial reaction followed by n-order competitive reaction (FnFnFn model). The activation energy matching with the most probable model is close to value obtained by Friedman method. The fitting curves match the original TG-DTG curves very well. Source


Zhang X.-H.,Chengdu University of Technology | He C.,Central South University | Wang L.,Chengdu University of Technology | Li Z.-Q.,Chengdu University of Technology | And 4 more authors.
Mineralogy and Petrology | Year: 2015

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 (F1D3FnC1EFnFn model). The dehydration reaction is controlled by two consecutive mechanisms, nucleation and growth, followed by a diffusion-controlled reaction (F1D3 model), the first step: E = 61.68 kJ mol−1, logA = 6.75 s−1; the second step: E = 50.73 kJ mol−1, logA = 3.11 s−1. The dehydroxylation reaction is controlled by three-step competitive mechanisms, an autocatalytically activated, initial reaction followed by n-order competitive reaction (C1EFnFn model), the first step: E = 124.74 kJ mol−1, logA = 5.67 s−1; the second step: E = 245.29 kJ mol−1, logA = 11.69 s−1; the third step : E = 261.73 kJ mol−1, logA = 11.23 s−1. A combination reaction of the dehydration and dehydroxylation is observed, and controlled by one n-order reaction (Fn model), E = 8.99 kJ mol−1, logA = −1.91 s−1. © 2014, Springer-Verlag Wien. Source


Zhang X.-H.,Chengdu University of Technology | He C.,Central South University | Wang L.,Chengdu University of Technology | Li Z.-Q.,Chengdu University of Technology | Feng Q.,NETZSCH Scientific Instrument Trading Co.
Journal of Thermal Analysis and Calorimetry | Year: 2015

The single-phase La2(CO3)3·3.4H2O with the orthorhombic type was synthesized by hydrothermal method. The results characterized by XRD, FTIR and DTA-TG showed that the thermal decompositions of La2(CO3)3·3.4H2O below 1,273 K experience four steps, which involve a two-stage dehydration and formation of anhydrous La2(CO3)3 at first, and then the formation of La2O2CO3 and La2O3, respectively. An additional intermediate product assigned to La2O(CO3)2 was observed in the third step. Thermal decomposition kinetics of La2(CO3)3 to La2O2CO3 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 n-A n model), f(α) = n(ln(1 - α (1 - 1/n))(1 - α)). The first stage: E = 435 ± 9 kJ mol-1, lg A = 28.7 ± 0.8, Dimension1 = 0.28; the second stage: E = 234 ± 4 kJ mol-1, lg A = 13.5 ± 0.3, Dimension2 = 1.22. © 2015 Akadémiai Kiadó, Budapest, Hungary. Source


Zhang X.-H.,Chengdu University of Technology | Wang L.,Chengdu University of Technology | Deng M.,Chengdu University of Technology | Feng Q.,NETZSCH Scientific Instrument Trading Co.
Kuangwu Yanshi/ Journal of Mineralogy and Petrology | Year: 2010

Ca-bentonite from Santai,Shichuan Province was used to study the thermal effect of clay minerals under different heating rates by thermogravimetry analysis(TG/DTG) and differential scanning calorimetry (DSC/DDSC). Curves from TG,DTG and DSC-analyses showed that the sample decomposition consists of four stages,and represents the evolution stage of adsorbed (about 114. 1°C) and cation-coordinated water (about 181. 9°C) ,dehydroxylation stage (about 651°C), destroyed stage of crystal structure in montmorillonite (about 876.8°C), respectively. It demonstrated that the heating rate had a strong influence on the thermal effect of clay mineral as following. (1)Thermogravimetry analysis showed a relative mass change and the result was inversely proportional with the heating rate. With increase of the heating rate,the mass losses were more close to the absolute value,while the mass loss rate was the smaller. (2)When heating temperature is beyond 400°C, the resolution of the sample DTG,DSC curves was' inversely proportional with the heating rate. The low heating rate was in favor of analysis of dehydration reaction of clay mineral. Between 400°C and 900°C ,the resolution of the sample DTG,DSC curves was proportional to the heating rate,and improving the heating rate was benefit to distinguish the dehydroxylation reaction. (3)Beyond 400°C,the resolution of dehydration reaction of clay mineral was the highest. At the temperature range of 400°C - 1 100°C ,the effect of the heating rates to the dehydroxylation and phase reaction of clay mineral sample was very complex. Source

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