Research in the Field of Composite Materials Based on HCBS and Refractory Materials Based on the System Al.sub.2O.sub.3-SiO.sub.2-SiC. Part 4.sup.1

The effect of prolonged heat treatment (single- and two-stage firing in a tunnel kiln) of specimens based on HCBS in the Al.sub.2O.sub.3-SiO.sub.2 -SiC system on their indices is studied. Specimens containing 15% SiC and 1 and 2% Si are characterized by a significant increase (up to 9%) in porosity and a reduction in strength compared with original specimens (without SiC) after prolonged heat treatment (120 hours in the range 1300 - 1400°C). significant increase in specimen volume is due not only to oxidation of SiC or Si, but also due to additional mullite formation. It is assumed that subsequently during oxidation of SiC at a certain stage of heat treatment there is mullitization due to the interaction of newly formed SiO.sub.2 in the form of cristobalite with bauxite Al.sub.2O.sub.3.