Study of contact interaction between metalline borides and graphite at high temperatures in a vacuum

Abstract

We studied the contact interaction between compacted boride specimens and boride powders: TiB2, ZrB2, HfB2, NbB2, TaB2, Mo2B5, and W2B5 and graphite powder and graphite at temperatures up to 2200°C in a vacuum. It was established by metallographic and chemical analyses together with microhardness test that the borides of hafnium, niobium, tantalum, and tungsten were stable in contact with graphite right up to 2200°C, and that molybdenum boride was stable up to its melting point, after a contact period of up to 5 h. In the case of titanium boride, we observed a slight interaction with graphite at 2200°, as a result of which the boride loses up to 1% boron, which transfers to the graphite charge. At 2200° after 5 h soaking, clear signs of interaction with graphite are detected in zirconium boride; during contact between compacted boride and graphite powder, the weight of the boride specimen and its microhardness decline, and traces of zirconium and boron are detected in the graphite charge. When compacted graphite is in contact with ZrB2 powder, we observe a change in the chemical composition of the boride, an increase in the microhardness of the graphite, and a transition layer is detected on the contact boundary.