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We used a finite element method for the computer simulation of the temperature field in the apparatus of hot vacuum pressing (HVP) of alumina powder blanks. We considered the temperature dependence of the properties of the materials of the apparatus elements and the contact thermal and electrical resistances. The results of the calculations agreed to the laboratory temperature measurements, which confirms the reliability of the model. The results of computer experiments show that by selecting the materials of the HVP apparatus elements, we can create a practically uniform temperature field in the sample at the final stage of the sintering process and decrease significantly energy consumption in the entire sintering process. Depending on the arrangement of the equipment of the working cell of the HVP apparatus, the consideration of contact resistances can significantly affect the results of predicting the homogeneity of the temperature field of the sample during HVP. [ABSTRACT FROM AUTHOR]

A computer model is developed on the basis of the finite-element method for the temperature field formed during the sintering of large-size boron carbide products in the working cell of a high-pressure apparatus at a pressure of 0.5–1.0 GPa and temperatures of 1700–1750°C. The dependence of the thermophysical properties of a sample on the porosity and temperature in the process of sintering is taken into account. It is shown that the selection of geometric parameters for the constructional elements of the working cell of a high-pressure apparatus makes it possible to find such a cell structure, whose application may provide a nearly uniform temperature field in a large-size sample under sintering and uniformity of the density and physicomechanical properties of the sintered sample. [ABSTRACT FROM AUTHOR]

The reaction of sulfoxides with peroxy acids in various organic media was studied. The reaction mechanism involves the rapid formation of a sulfoxide-–peroxy acid intermediate which decomposes in the second stage to form carboxylic acid and the corresponding sulfone. The second stage is the rate-limiting step. The reaction medium significantly affects the rate of oxidation. The calculated activation parameters of the oxidation process indicate a compensation effect in the investigated reaction. Correlations between the main physicochemical parameters of solvents and the effective rate constants (k) of dimethyl sulfoxide oxidation with peroxy acids were found. Depending on the reaction conditions, the main factors affecting the k values are specific and nonspecific solvation of the reactants and structural factors. [ABSTRACT FROM AUTHOR]

We study the influence of temperature of a working medium and loading frequency on the contact fatigue of 20KhN3A and ShKh15 steels in oil and in a 3% NaCl aqueous solution. It is shown that, as the loading frequency increases, the contact fatigue of steels increases in a 3% NaCl aqueous solution but does not change in oil. At the same time, as temperature increases, the contact fatigue decreases in a 3% NaCl aqueous solution but remains almost constant in oil. It is shown that the outlined behaviors of the analyzed steels is explained by the action of the components of working media and their concentrations in the surface layers in the course of the tests. [ABSTRACT FROM AUTHOR]

The computer simulation of the temperature field in the working cell of the production unit during high-speed sintering under pressure of boron carbide powder samples is performed by the finite elements method. Consideration is given to the dependence of the thermophysical properties of a powder sample on the porosity and temperature. In order to minimize the temperature drop in the powder sample, the effect of the working cell design on the temperature drop in the sample is studied by computational modeling. Based on the computational experiments, the working cell design of the unit for high-speed sintering under pressure has been optimized and the heating conditions have been selected such that the sample sintering temperature of 2000°C is reached within 80 to 150 s and the temperature drop in the sample during the holding period for 100–150 s is within 50–30 deg. The laboratory experiments have revealed that the optimized working cell design provides an almost uniform distribution of microhardness in the sintered product. [ABSTRACT FROM AUTHOR]

The kinetics of thermal decomposition of didecanoyl diperoxyadipate in different organic solvents have been studied. The primary homolytic dissociation of the peroxide bond (O-O) is accompanied by secondary induced chain decomposition processes. The reaction medium affects both the rate of primary homolytic decomposition and secondary decomposition processes. Correlation equations have been proposed for the rate constants of the reactions under study and physicochemical parameters of the solvents. [ABSTRACT FROM AUTHOR]

Thermal decomposition of peroxydecanoic acid has been investigated in various organic solvents. The reaction medium significantly affects the rate of peroxydecanoic acid thermal decomposition. It has been shown that primary homolytic decomposition of peroxy group is followed by induced radical chain decomposition reactions. The solvent nature influences both primary homolytic decomposition and secondary induced reactions. The correlation equations relating kinetic parameters of peroxydecanoic acid thermolysis and basic solvent properties have been derived. [ABSTRACT FROM AUTHOR]