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Abstract  

The silica waste originating from a geothermal power plant in Mexico was investigated with the aim of finding its applicability as a raw secondary material for ceramics production. The thermal behaviour of the original silica waste (containing NaCl and KCl from marine brine) and of the purified silica was characterized by means of DTA/TG, emanation thermal analysis (ETA) and thermodilatometry (TD). The reactivity of the purified silica waste mixed with CaCO3 (1.8 mass%) was characterized by means of ETA, DTA and TG. The microstructures and phase compositions of the final products prepared by heating in air were tested by means of X-ray diffraction and of scanning electron microscopy coupled with electron probe X-ray microanalysis. The thermal analysis methods allowed determination of the optimal conditions for thermal treatment of the silica waste in order to obtain partly sintered porous materials for use as refractory bricks.

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Abstract  

Two different samples of amorphous calcium carbonate (ACC) hydrates were prepared respectively by mixing aqueous solutions of CaCl2 and Na2CO3-NaOH and by allowing the diffusion of (NH4)2CO3 sublimate into ethanol solution of CaCl2. Thermal behaviors of the synthetic ACCs were investigated comparatively by means of thermoanalytical techniques complimented by powder X-ray diffraction, FTIR spectrometry and microscopic observations. The anhydrous ACCs produced by the thermal dehydration of the respective samples were crystallized to calcite in different ways. The sample prepared in aqueous medium was crystallized at around 600 K in a single step. Crystallization in two separated steps at around 600 and 825 K was observed for the sample prepared in ethanol medium. Characteristics of the crystallization processes were discussed from thermodynamic and kinetic points of view.

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Summary Several Fe-Ni-P-Si alloys were produced in an amorphous state by mechanical alloying and rapid solidification. Thermal behavior of the as prepared alloys was analyzed and compared with identical alloys stored during 1 and 2 years. During annealing time, several exothermic processes related to the structural relaxation were detected at low temperature and with further crystallization at high temperature. As increasing the storage time, the powdered samples were relaxed at lower temperatures. The activation energy, E, of the main crystallization process varies between 2.7 and 4.7 eV at.-1. The E values obtained remains similar with the storage time. Small contamination from the milling tools was found. Furthermore, powdered alloys are more sensible to oxidation processes than as quenched ribbons.

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Abstract  

Synthesis, characterization and thermal behavior of four compounds that have the general formula [Cu{Pd(CN)4}(L)x]n, in which en=1,2-diaminoethane and pn=1,3-diaminopropane (L=en, x=1 (I); L=pn, x=1 (II); L=en, x=2 (III); L=pn, x=2 (IV)) were described in this work. The complexes were studied by elemental analysis, infrared spectroscopy (IR), differential thermal analysis (DTA) and thermogravimetry (TG) and the residues of the thermal decomposition were characterized by X-ray powder diffraction and found as a mixture of CuO and PdO. The stoichiometry of the compounds was established via thermogravimetric and elemental analyses and their structures were proposed as coordination polymers based on their infrared spectra. The following thermal stability sequence was found: IV<I=II<III.

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Abstract  

Samples of an organic–inorganic hybrid were prepared by solvolysis and polycondensation in formic acid of tetraethoxysilane and diethylbenzyl phosphonate, simultaneous with the oxidative polymerization of aniline. The thermal behavior of the samples in dynamic air atmosphere and non-isothermal conditions was determined by a coupled thermogravimetric/evolved gas analysis. Two significant thermal events were established: the elimination from the polymeric matrix of low mass molecules, respectively the thermooxidative degradation of the organic part of the matrix. The kinetic analysis was performed with the Flynn-Wall-Ozawa, Friedman and modified Non-Parametric-Kinetic methods. Only the last one allowed an objective analysis of the first process as a process of two simultaneous thermally induced phenomena with the kinetic functions of the type αm(1 − α)n.

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Abstract  

The effect of CuO on the thermal behaviour of Zr/KClO4 primer mixtures was studied by thermoanalytical techniques, and the Bruceton method and its related calculation. It was found that the CuO catalytically promoted the decomposition of Zr/KClO4 primer mixtures and shifted the exothermic peak of DSC curves to lower temperatures. In addition, the Zr/KClO4 primer mixture containing CuO had a significant effect on the firing characteristics of electro-explosive devices.

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Abstract  

The thermal behavior of chitosan (CS)/natural rubber latex (NRL) blends has been studied by thermogravimetry (TG) and differential scanning calorimetry (DSC). Decomposition behavior of CS changes with the addition of NRL. The effect of blend composition on the amount of residue remaining at various temperatures has been studied. Activation energies of degradation have been calculated using Horowitz-Metzger equation. From the activation energy values, it is found that among the series of the blend compositions, CS15NRL85 exhibits better thermal stability. DSC studies reveals that the CS/NRL blends are thermodynamically incompatible. This is evident from the presence of two glass transitions, corresponding to CS and NRL phases in the blend.

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The thermal behaviours of polystyrene (PS), polymethylacrylate (PMA), polyacrylonitrile (PAN), polystyrene-co-methylacrylate [P(S: MA)](alternate and random), polystyrene-co-acrylonitrile [P(S: AN)] (alternate) and a terpolymer of styrene, methylacrylate and acrylonitrile [P(S: MA: AN)] are discussed on the basis of non-isothermal thermogravimetric studies. The thermal stabilities of the copolymers have been found to be intermediate between of those of the individual homopolymers. The stability of the [P(S: AN)] copolymer is higher than those of the individual homopolymers. The activation energy values are also in accordance with the thermal behaviours of these polymers.

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Abstract  

Ammonium nitrate (AN) is one of the main nitrogen fertilizers used in fertilization programs. However, AN has some serious disadvantages — being well soluble in water hardly 50% of the N-species contained are assimilated by plants. The second disadvantage of AN is associated with its explosive properties. The aim of this paper was to clarify the influence of different lime-containing substances — mainly Estonian limestone and dolomite — as internal additives on thermal behaviour of AN. Commercial fertilizer grade AN was under investigation. The amount of additives used was 5, 10 or 20 mass%, or calculated on the mole ratio of AN/(CaO, MgO)=2:1 in the blends. Experiments were carried out under dynamic heating condition up to 900°C (10°C min−1) in a stream of dry air or N2 by using Setaram Labsys 2000 equipment coupled to Fourier transform infrared spectrometer (FTIR). The results of analyses of the gaseous compounds evolved at thermal treatment of neat AN indicated some differences in the decomposition of AN in air or in N2. At the thermal treatment of AN’s blends with CaCO3, MgCO3, limestone and dolomite samples the decomposition of AN proceeds through a completely different mechanism — depending on the origin and the content of additives, partially or completely, through the formation of Mg(NO3)2 and Ca(NO3)2.

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