OXIDATION RESISTANCE OF SILICON TETRA BORIDE POWDER

The oxidation of silicon boride (SiB4) powder at high temperatures was investigated in order to determine the possibility of its high-temper ature utility, SiB4 powder with an average particle size of about 10 m u m was used in this experiment, The sample oxidized at 200 to 1100 de grees C for 5 min to 50h in air; the weight changes were measured to e stimate the oxidation resistance. The oxidation of sample, at the shor t oxidation time of 5 min, started at 500 to 600 degrees C, and weight gain changes with increasing oxidation temperature. The sample at the oxidation time of 0.5 to 1h, exhibited weight gain change with increa sing oxidation temperature, and then the oxidation saturated at 900 de grees C. On the other hand, at the oxidation time of 10h, it had the m aximum value of the weight gain at 600 degrees C, after that the weigh t gain monotonically decreased with increasing oxidation temperature. SiB4 is oxidized to vitreous SiO2 and B2O3 at about 700 degrees C. The B2O9 of oxidation product vaporized above at 900 degrees C. The vitre ous SiO2 transformed into the cristobalite.