Kinetics and high-temperature oxidation mechanism of ceramic materials in ZrB2–SiC–MoSi2 system

Abstract

The paper focuses on the production of compact ceramics ZrB2–SiC–(MoSi2) using the hybrid SHS + HP technology, as well as on its phase composition, structure and high-temperature oxidation kinetics. Reaction mixtures were obtained according to the following scheme: mechanical activation of Si + C powders; wet admixing of Zr, B and MA powders of Si + C mixture; drying of mixtures in a drying cabinet. The composite SHS powder ZrB2–SiC was obtained in the SHS-reactor in combustion mode by element synthesis. Compact samples were produced using the hot pressing method by SHS powder consolidation. Resulting samples characterized by a homogeneous structure and low residual porosity not exceeding 1,3 %. In total, two compositions were chosen for tests: the first one rated for ZrB2 + 25 % SiC formation, the second one similar to the first one, but with the addition of 5 % commercial MoSi2 powder. The microstructure of samples is represented by dispersed dark gray rounded SiC grains distributed among the light faceted ZrB2 grains. The sample with the MoSi2 additive has a more finely dispersed structure. High-temperature oxidation of samples at 1200 °С forms complex oxide films SiO2–ZrO2–(B2O3) about 20–30 μm in thickness on their surface, which serve as an effective diffusion barrier and reduce oxidation rate. The complex ZrSiO4 oxide is also present in the oxide film structure after long holding times (more than 10 hours). In addition, after 10 hours of testing, a slight decrease in the mass of the samples is observed, which is due to the volatilization of B2O2, CO/CO2, MoO3 gaseous oxidation products. The sample with MoSi2 added demonstrates better resistance to oxidation.