Ceramics and Composite Materials

Biography

Biography: Mahdi Ghassemi Kakroudi

Abstract

Because of strong covalent bonding, low bulk and grain boundary diffusion rates, high melting point and high vapor pressure, the sintering of ZrB2 usually needs high temperature and external applied pressure. At the first stage of this research, monolithic ZrB2 was hot pressed without using any sintering aid or secondary phase as the obtained relative density was about 92%. In this case, the final microstructure of ceramic faced with a fanatic grain growth. Hence, SiC particles were used to increase the density and improve the sinterability which is the most common additive in ZrB2-based composites. Due to the presence of SiC, some densification mechanisms such as mechanical interweaving, particles fragmentation and rearrangement, plastic deformation of grains and diffusion processes were activated and resulted in a higher density at 1850 °C. Using 200-nm SiC particles increased the driving force of the sintering as the theoretical density was obtained at 1850°C. The addition of 200-nm ZrO2 particles caused to an increased density through the reaction of ZrO2 and SiC which led to the formation of dense ZrC. The addition of carbon additives (graphite and graphene) led to achieving the full density at 1850°C via the chemical reactions with the surface oxide impurities on the starting powders.