DETERMINACION DE LA CONDUCTIVIDAD TERMICA EN POLVOS AISLANTES TÉRMICOS DE MgO A ALTA TEMPERATURA: EFECTO DE LA DISTRIBUCION DEL TAMAÑO DE GRANO E IMPUREZAS

Abstract

This thesis work reports the determination of the thermal conductivity K, at high temperatures values (100 to 870 ° C), in electric grade MgO powders with different grain measurements were performed using the technique of radial heat flow in steady state, according to the Standard American Society for Testing and Materials (ASTM) 2858-90, and an analysis complementary of composition by EDS and XRD. There was a significant increase in K for samples with smaller grain size, which reached more than 1000% in samples of higher purity and up to 500% for samples with higher concentrations of impurities. The rate of change of K with T also increased significantly with a smaller grain size, up to 240% in samples of higher purity and up to 110% for samples with higher concentrations of impurities. The measured values of K with grain size (T constant) showed a dependence as a logistic of Boltzmann type, in all cases, revealing a sharp drop in K with the increasing of grain size, and reaching a constant value of saturation. Samples with higher concentration of impurities showed a notable increase in the width of characteristic curve and a shift in its center to higher values of grain size, which did not occur in samples of higher purity.