RESEARCH OF HIGH-TEMPERATURE CORROSION OF SiC-COATING ON GRAPHITE

The relevance of this work is caused by possible prospect of creating a Kazakhstani high-temperature gas-cooled reactor, in which a number of new materials science solutions will be applied regarding the graphite matrix and fuel cells. Silicon carbide (SiC) coatings will be used on reactor fuel cells, in which graphite is the main constituent material. The aim of the research is to evaluate the corrosion rate of reactor graphite with SiC-coating in the temperature range from 750 to 1400 °C at the initial pressure of water vapor in the chamber 100 Pa. Object: isotropic fine-grained graphite of IG-110 brand with a protective SiC-coating thickness of 200 microns. Methods: programmable thermal desorption of samples in the presence of water vapor, mass spectrometric recording of the gas composition in the working chamber, microstructural studies, Raman spectroscopy, energy-dispersed X-ray spectroscopy. Results. It is shown that at pressures of water vapor of 100 Pa, the SiC-coating interacts with steam through a passive (forming an additional protective layer of amorphous silicon dioxide) mechanism. Corrosion of SiC in water vapor at temperatures of 1100–1400 °C occurs by orders of magnitude more intense than at 750–900 °C. A model for analytical description of the experimental results was developed and the parameters of the rate constant for water vapor interaction with a SiC-coating were calculated for sample temperatures of 1400, 1300, 1200, 1100, and 1000 °C. Microstructural studies of the samples before and after corrosion tests were carried out, which showed that a protective SiO2 film is formed on the surface with a SiC carbide coating during passive corrosion. The research results allow us to conclude that the prototype of a fuel with a SiC-coating has improved anti-corrosion properties and can be successfully used to reduce carbon chemical activity in fuel cells and fuel assemblies of high-temperature gas-cooled reactor without deteriorating their mechanical and temperature properties.