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molybdenum disilicide (MoSi2
High oxidation-resistant MoSi2-based materials are useful for the oxidation-resistant coating of ceramic components, which are often used in furnaces at high temperatures and in an oxidizing atmosphere. They are also suitable for sintering and other high-temperature processing of metal components, glass, and ceramics.
Typical microstructures of bulk Hf(C,N)-MoSi2 samples obtained by spark plasma sintering are shown in Figure 1. The SEM images reveal that the MoSi2 content contributes to the formation of different phase components, namely, monoclinic and tetragonal HfO2 and refractory MoSi2, with a grain size varying from 2 to 15 um.
The presence of MoSi2 increases the oxidation resistance of Hf(C,N) by preventing the diffusion interaction between the monoclinic HfO2 layer and oxygen, thereby accelerating the oxidation reaction. The TG curves of the samples with 10 and 20 vol% MoSi2 reveal a pronounced exothermic peak at temperatures of 800 degC and 820 degC, respectively.
In addition, the oxidation rate of Hf(C,N) is decreased by the presence of MoSi2 at lower concentrations, due to the formation of dense oxide layers on the Hf(C,N) surface that prevent oxygen diffusion to the substrate. This decrease in the rate of Hf(C,N) oxidation appears to be related to the presence of a high pressure of MoO3 vapor at 800 degC, which may explain the presence of this exothermic peak.