Oxidation behavior of a silicon boride composite

Abstract

The oxidation resistance of a silicon hexaboride (SiB6) composite at high temperature was investigated in order to determine the possibility of its use as an advanced high temperature structural material. Fortunately, monolithic SiB6 and its composites were known to be chemically stable up to high temperatures. To date, there have been few reports regarding the properties of SiB6 ceramics. In this study, the oxidation resistance at high temperature of a dense SiB6 composite prepared from SiB6 with the addition of 10 mass% C as starting powders has been studied. The samples were oxidized at room temperature up to 1173 K for 25 h in air. The weight changes were measured to estimate the oxidation resistance. The oxidation of samples oxidized for a short oxidation time of 5 minutes started at 973 K, and the weight gain increased with increasing oxidation temperature. On the other hand, at oxidation times of above 1 h, a maximum weight gain value at 973 K was observed. After that a SiB6 composite oxidized at 973 to 1073 K for 25 h exhibited increased weight gain with increasing oxidation temperature; the oxidation changed in accordance with the parabolic law during the initial oxidation stage. However, even if the oxidation temperature was increased only a slight additional weight change occurred. The weight gain of the sample oxidized at 1173 K for 25 h was approximately 2.5%. Finally, the SiB6 composite showed a good oxidation resistance at high temperature, because the surface oxide film formed by oxidation acted as an oxidation-resistant layer.