High temperature oxidation of calcium hexaboride

The oxidation process of calcium hexaboride (CaB6) ceramic powder was investigated systematically in this paper. The CaB6 powder samples were heated continuously from room temperature to 1473 K at a heating rate of 10 K/min using differential scanning calorimetry (DSC). The oxidation tests were conducted at different exposure temperatures, and the phases and morphologies of the samples before and after exposure were analyzed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was pointed out that there were two reactions in the CaB6 oxidation up to 1473 K, corresponding to the formations of CaB4O7 and CaO. About 16.8% and 45% of weight gain occurred due to oxidation in the air from 940 to 1200 K and from 1200 to 1455 K, respectively. The mechanism of oxidation was analyzed. As one of the alkali-earth metal borides, calcium hexaboride (CaB6) belongs to the group of refractory non-oxide metal-like compounds characterized by high melting point, high strength, and high chemical stability, which can be used as abrasives, tools, and high-temperature structural materials. Several studies of this material have been made. Like other non-oxide ceramics, CaB6 will be oxidized at elevated temperatures, which will shorten its life and degrade its properties. However, previous investigations on the oxidation of borides have been concentrated on diborides, such as TiB2, ZrB2, and HfB2. A few papers have discussed the development of the oxidation of hexaboride materials.

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