Search Results
Abstract
Mixtures composed of amides and electrolytes exhibit interesting properties such as viscoelastic behaviour and a megavalue of the dielectric constant. In order to improve the dielectric properties, the authors are investigating a large number of molten mixtures of CF3COONa with different types of amides, including the ternary system sodium trifluoroacetate-chloroacetamide-acetamide. The experimental measurements showed that the ternary mixtures are thermally unstable. A yellow oily product is formed; this was purified and tested by means of IR and NMR techniques. The formula and the kinetic mechanism are proposed.
Abstract
Thermal reactions of polyethylene with coal were studied. Coal used exhibited an endothermal effect in the temperature range of 425-495C with a flat maximum (about 460C). In contrast, polyethylene alone was decomposed in the temperature range of 420-540C (mainly of 485-540C) with the significant DSC maximum at 510C. In the presence of coal this maximum shifted to lower temperature (483C), therefore, coal promoted the decomposition of polyethylene. As decomposition of polyethylene yields alkenes and alkadienes, the thermal reaction of polyethylene with coal under low temperature conditions can be described as two-stage process in which the first stage includes the decomposition of polyethylene giving unsaturated hydrocarbons and the second stage adsorption and hydrogenation of these products (mainly by coal hydrogen) on the inner surfaces of semicoke and coal.
Summary Thermal reactions in natural fluorapatite or fluorcarbonate apatite and ammonium sulfate mixtures with mole ratio 1:4 at calcination up to 500°C were studied by simultaneous thermogravimetry and FTIR analysis of the evolved gases. The composition of natural apatite has little impact on the release of NH3. Upon the evolution of NH3 nitrous oxides were found in minor amounts. The release of SO2 at temperatures above 400°C is more intensive and occurs at lower temperatures in the case of fluorapatite than of carbonate containing apatites. Evolution of CO2 starts at 250°C with maximum at 350-360°C.
Abstract
Selected kinetic and mechanistic studies of thermal reactions of initially solid substances are reviewed with emphasis on the evidence that some of these chemical changes proceed with the essential participation of melting. The reactions considered are classified on the extent and the role of such melting and the various types of behaviour observed are discussed with reference to solid state rate processes in crystals. It is stressed that melting is an important feature in theoretical considerations of crystal reactivity because chemical changes often proceed more rapidly in a melt than in the solid state. However, literature reports concerned with reactions of solids do not always explicitly mention the possibility of melting during discussions of reactions mechanisms. The present paper comments on methods capable of detecting liquefaction during reaction, a feature of behaviour that is not always easily identified experimentally. Also considered here is the recognition of reaction intermediates, which provide important evidence concerning the course of the chemical changes through which the reactant is transformed into product. This short review draws attention to the considerable value of chemical evidence in elucidating mechanisms of reactions of solids including the necessity for identifying intermediates and the role of any melt or liquid participating.
Abstract
The effect of mechanical activation on the structure and thermal reactions of glasses has been studied on the example of Na–Al–Fe phosphate glasses. These glasses are used in nuclear technology for immobilization of radioactive waste. The glasses were activated by grinding in a planetary mill. Mechanical activation causes a decrease of the T g temperature as well as of the glass crystallization temperature. The type of crystalline phases formed and the quantitative proportions between them are changing. Analysis of inter-atomic interactions in the structure of glass was applied to explain the observed regularities governing the crystallization of the activated glasses.
Abstract
Rebuilding reactions of the internal structure of minerals and their artificial analogues are considered. Solid products of these reactions are formed within the structure of the parent substance. This factor determines the course of the reactions and product formation. The mechanism of internal thermal dissociation and rebuilding reactions of internal structure connected with segregation of chemical components and their redistribution (crystallization of multicomponent amorphous solids) is discussed. The internal pressure of gaseous decomposition products and rate of diffusion of chemical components are critical factors influencing kinetics of these processes. Diffusional mass transfer during internal structure rebuilding reactions is directed by acid-base interaction of the parent-structure components; this determines the stages of the reaction pathway.
Thermal reactions of inorganic hydroxy-compounds under applied electric fields
IV. Dehydration of amorphous iron(III)hydroxide
The effect of electric fields on the thermal dehydration of amorphous hydrated iron(III) oxide under oxidizing, inert and reducing atmospheres was studied by X-ray diffractometry. In oxidizing and inert atmospheres, the transformation toα-Fe2O3 was enhanced by electric fields, especially at the negative electrode. The crystallite size of the product was also greatest at the negative electrode. Both results are explained in terms of the migration of protons to the negative electrode, where they subsequently form water which acts as a nucleating agent for the crystalline phase. In reducing atmospheres the formation of Fe3O4 and FeO at the expense of Fe2O3 is facilitated by electric fields, particularly at the negative electrode. Possible reaction mechanisms are considered, and the role of protons in stabilizing defect-spinel intermediates and products is discussed.
The gibbsite →χ-alumina decomposition (in air) and theχ-alumina → boehmite transformation (under hydrothermal conditions) were investigated isothermally. Reaction products were characterized by TG and X-ray diffraction.
