Papers by Keyword: Specific Electrical Resistance

Abstract: The readiness of coal coke is a necessary condition for ensuring its high quality, which ultimately depends on the degree of orderliness of the macromolecular structure in the form of graphite-like blocks. Coke then acquires semiconductor properties. According to the zone theory of solid-state physics, the dependence of the specific electrical resistance of coke on the final coking temperature has an exponential form. The pre-exponential factor characterizes the properties of the original coal, including its caking ability, the content of mineral impurities, and their ability to form free current carriers (electrons or holes). The coefficient in the exponent indicates the rate of decrease of the logarithm of resistance with increasing temperature. These two quantities can be determined experimentally. For each blend composition, they determine the final coking temperature required to form the appropriate coke readiness, taking into account its intended use.

Abstract: Thermoelectric oxide Bi1.5Pb0.5Sr1.7Y0.5Co2O9- δ is produced by sintering method. Uniaxial compression deformation is performed on the oxide under various strain rates at 1113K, close to the melting temperature. After deformation, density, microstructure, texture and thermoelectric characteristics such as specific electric resistance and Seebeck coefficient, are experimentally studied. Deformation mechanism is examined by stress change test. It is found that the oxide plastically deforms mainly by the motion of dislocations at the present temperature, resulting in an increase in density as well as the development of texture. It is concluded that the specific electric resistance extensively decreases by the high temperature compression deformation through densification and texture development.

Abstract: In this work severe plastic deformation (SPD) was applied to magnesium base alloys of the Mg-Sm system (2.8-5.5 mass %Sm). These alloys are characterized by high strength at elevated temperatures and high strengthening effect during aging. SPD was performed by torsion under pressure of 4 GPa at 20 and 200°C to ε ∼ 6. SPD results in significant strengthening of the Mg-Sm alloys due to the formation of submicrocrystalline structure. In all cases SPD accelerates the solid solution decomposition upon subsequent aging. The highest strengthening can be obtained if the solution treated alloy is aged at 200°C after SPD at room temperature. The state of high strength can be also reached if the following sequence of the operations is used: solution treatment + aging at 200 °C up to maximum hardness + SPD at 20°C + aging at 200°C accompanied by Sm –rich phase precipitation in the submicrocrystalline matrix.