Combustion synthesis of high-temperature ZrB2-SiC ceramics

The work is dedicated to researching into combustion kinetics and mechanism as well as the stages of the chemical transformations during self-propagating high-temperature synthesis of ZrB2-SiC based ceramics. Dependences of the combustion temperature and rate on the initial temperature (T-0) have been studied. It has been shown that the stages of the chemical reactions of ZrB2 diboride and SiC carbide formation do not change within the range of T-0 = 298-700 K. The effective activation energy of the combustion process amounted to 170-270 kJ/mol, from which it has been concluded that chemical interaction through the melt plays a leading role. The stages of the chemical transformations in the combustion wave have been studied by dynamic X-ray diffraction. First, ZrB2 phase forms from Zr-Si melt saturated with boron, and SiC phase is registered later. The SHS method has successfully been used in order to obtain ZrB2-SiC composite powders and compact ceramics with a silicon carbide content of 25-75%. The ceramics are characterized by a residual porosity of 1.5%, hardness up to 25 GPa, the elastic modulus of 318 +/- 21 GPa, elastic recovery of 36% and thermal conductivity of 54.9 W/(m x K) at T-room.