Kinetics and High-Temperature Oxidation Mechanism of Ceramic Materials in the ZrB2–SiC–MoSi2 System

详细

This study is devoted to the fabrication of the ZrB₂–SiC–(MoSi₂) compact ceramics according to hybrid technology (self-propagating high-temperature synthesis (SHS) + hot pressing), as well as to investigating its phase composition, structure, and high-temperature oxidation kinetics. Reaction mixtures are prepared according to the following scheme: mechanical activation (MA) of Si + C powders; wet admixing of Zr, B, and Si + C MA-mixture powders; and drying mixtures in a drying oven. The ZrB₂–SiC SHS composite powder is formed in a reactor in a combustion mode by elemental synthesis. Compact samples with a homogeneous structure and low residual porosity not exceeding 1.3% are formed by hot pressing the SHS powder. Two compositions are selected for testing, notably, the first one calculated for the formation of ZrB₂ + 25% SiC; the second composition is similar to the first one, but with the addition of 5% of the MoSi₂ commercial powder. The microstructure of the samples is presented by dispersed dark gray rounded SiC grains distributed among light faceted ZrB₂ grains. The sample with the MoSi₂ additive has a more finely dispersed structure. The high-temperature oxidation of the samples at 1200°C results in the formation of SiO₂‒ZrB₂–(B₂O₃) complex oxide films on their surface with a thickness on the order of 20–30 μm, which serve as an efficient diffusion barrier and lower the oxidation rate. Their structure also contains ZrSiO₄ complex oxide after prolonged holding (longer than 10 h). In addition, an insignificant weight loss of the samples is observed after 10 h testing, which is caused by the volatilization of gaseous oxidation products (B₂O₂, CO/CO₂, MoO₃). The sample with the MoSi₂ additive shows better resistance to oxidation.