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Abstract  

The results of theoretical analysis of the properties of crystal structure and bonding in relation to thermal decomposition process in chosen anhydrous metal oxalates (Cd, Co, Zn) are presented. The methods used in this analysis — the Bader’s quantum theory of atoms in molecules and bond order model (as defined by Cioslowski and Mixon), applied to topological properties of the electron density, obtained from DFT calculations performed by Wien2k package (full potential linearized augmented plane wave method), as well as Brown’s bond valence model (bonds valences and strengths, and bond and crystal strains, calculated from crystal structure and bonds lengths data) are described. Presented results allow us to state, that these methods, when used simultaneously, make possible the description and analysis of the crystal structure and bonding properties and give us the additional insight into its behavior during thermal decomposition process. The proposed theoretical approach can be considered as promising and reliable tool for theoretical analysis, allowing explanation and prediction of the properties of the structure and bonding and hence the most probable way of thermal decomposition process to take place in such structure.

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Abstract  

Thermal conductivity, specific heat capacity, thermal diffusivity and linear thermal expansion coefficient of two types of carbon fiber reinforced cement composites are measured in the temperature range up to 800�C. Thermal conductivity and thermal diffusivity are also determined for the specimens exposed to thermal load up to 800�C before the measurement. Differential thermal analysis (DTA), mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD) are utilized for the assessment of thermal decomposition processes taking place in the high temperature range under consideration. The high temperature thermal properties of the studied materials are found to be positively affected by the application of the high alumina cement and in the case of the Portland cement based composite also by using the autoclaving procedure in the production process. Also, the randomly distributed carbon fibers that can reduce the damage of the pore structure by the thermal decomposition processes are identified as a positive factor in this respect. A comparison of thermal conductivity vs. temperature curves obtained for the specimens pre-heated to different temperatures is found to be a useful tool in the identification of major dynamic effects in the specimens due to the thermal decomposition reactions. The results are in a good agreement with the DTA, MIP, SEM and XRD analyses. The character of the thermal conductivity measurements that in fact includes the effects of convection and radiation into the thermal conductivity coefficient can be beneficial for a simple assessment of the influence of the fire on a dividing structure.

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Abstract  

The thermal decomposition of several lanthanide salts Ln(CF3COO)33H2O (Ln=La, Gd, Tb) was studied under quasi-equilibrium conditions and under linear heating. According to mass spectral data, H2O is the single product of thermal decomposition up to 120-140C. Thermogravimetric data were processed with 'Netzsch Thermokinetics' computer program. Kinetics parameters of the first decomposition step (as the simple dehydration process, not complicated by the water hydrolysis with the liberation or the decomposition of the organic ligand) were calculated.

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Some possible elementary reactions are not included in the classical mathematical models of thermal decomposition. For example, we can assume that in the thermal decompositions of simple carbonates a proportion of the O2− ions produced on the reaction interface can migrate into the interior of the reactant phase, since at this temperature there is some probability of CO2 exchange between an O2− and a neighbouring CO3 2− ion. A similar diffusion-type process can be assumed in a wide class of decomposition reactions. The present state of computer science makes it possible to show by mathematical modelling how this migration influences the TG curves of the simplest contracting-sphere-type reactions. The resulting extended contracting-sphere model can provide the induction and the acceleration period of the TG curves.

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The decompositions of the clathrate compounds [M(NCS)2(4-MePy)4]·nG (whereM=Mn, Co, Ni or Cd;G=4-methylpyridine (4-MePy), benzene or xylenes) were studied on a Q-derivatograph under quasi-equilibrium conditions and with linear heating. These clathrates can be divided into two groups, in which the loss of guest is either (I) accompanied by destruction of the host complex, or (II) occurs before decomposition of the host complex. Kinetic parameters were obtained.

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Separate stages of mathematical processing of thermogravimetric data, the difficulties most often encountered, and typical error sources are considered. A complex procedure of automatic acquisition and editing of experimental data, including calculation of effective kinetic parameters, is described and an appropriate algorithm for the 15 BCM-5 microcomputer is presented. The computer calculation of the kinetic parameters of the multistage thermal decomposition of a polyamide fibre is given as an example.

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Journal of Thermal Analysis and Calorimetry
Authors: Luiz Carlos Machado, Marcos Tadeu D’Orlando de Azeredo, Hamilton Perez Soares Corrêa, Jivaldo do Rosário Matos, and Ítalo Odone Mazali

Abstract

This study investigates two lanthanide compounds (La3+ and Sm3+) obtained in water/ethyl alcohol solutions employing the anionic surfactant diphenyl-4-amine sulfonate (DAS) as ligand. Both sulfonates were characterized through IR, TG/DTG (O2 and N2). The thermal treatment of both compounds at 1273 K under air leaves residues containing variable percentages of lanthanide oxysulfide/oxysulfate phases shown by synchrotron high-resolution XRD pattern including the Rietveld analysis. The phase distributions found in the residues evidence the differences in the relative stability of the precursors.

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