POSSIBILITY OF APPLICATION OF ZrO2-MgO-CaO CRUCIBLES FOR PRODUCING ALLOY U-10 % Zr

Abstract

It is known that the thermal shock resistance of ceramic crucibles is insufficient for melting uranium alloys in them. Typically, crucibles withstand one or more heats and then break down. The possibility of using nanostructured ceramic crucibles based on ZrO2-MgO-CaO to obtain a U-10 % Zr alloy in an induction electric furnace has been substantiated at IPPE. Crucibles were made in JSC “ONPP “Tekhnologiya” named after A.G. Romashin” from a mixture of zirconium dioxide powders, partially stabilized with nanocrystalline CaO and MgO in a ratio of 30 and 70 wt. %, using two-stage sintering. Such crucibles have a sufficiently high resistance to thermal shock in contact with melts of metals and alloys and withstand 1-3 melts without destruction. Crucibles with various densities (from 5.206 to 5.29 g/cm3) and porosity (from 5 to 9 %) were tested under conditions of heating the melt at a rate of 12 to 19 °C/min to a maximum temperature of 1455 to 1560 °C. The tested crucible ZrO2-MgO-CaO was inserted into a graphite crucible to prevent leakage of the melt in the electric furnace in case of destruction of the ceramic crucible. There was no complete destruction of the crucibles; some crucibles with small cracks could be reused. The best result (three melts) was obtained when using such a crucible with a porosity of about 5 % for melting a charge containing uranium and zirconium. In order to determine the degree of interaction of a uranium-zirconium melt with a crucible based on ZrO2-MgO-CaO, the microstructure and microhardness of the crucible surface in contact with the melt were studied at an elevated temperature of 1600 °C. The surface of all tested crucibles is not wetted by liquid uranium-zirconium melt, and there is no chemical interaction. Nanostructured ceramic crucibles based on ZrO2-MgO-CaO are suitable for melting uranium-containing materials in an electric induction furnace.