The powder melting sponge made of thorium or thorium Th dense ingot process. The method of smelting casting includes vacuum induction melting (see induction melting), non-consumable electrode resistance-arc casting, consumable electrode resistance-arc casting (see resistance-arc smelting), and electron beam melting (see electron beam melting). . The crucible can be further purified by casting. The purity of the cast ingot is generally 99.8%, and the Brinell hardness is 36. It can be processed into various materials for nuclear fuel testing.
The research and industrialization of tantalum casting was developed after the discovery of the nuclear use of tantalum. The former Soviet Union, the United States, and the United Kingdom began large-scale experimental research work in the 1950s and industrialized in the 1960s. China cast a nuclear pure ingot in 1973.
Vacuum induction casting sponge is placed thorium oxide, beryllium oxide crucible in a vacuum induction melted and heated to 2173K, and then flows from the bottom of the graphite ingot mold.
Non-consumable electrode resistance - tungsten arc electrode is cast in water-cooled copper crucible typically used for casting a small amount of thorium and thorium metal alloy.
Self-consumption electrode resistance-arc casting is a consumable electrode made of cold-pressed tantalum powder. The electrode is melted with an appropriate power arc under an argon pressure of 1333 Pa to obtain a casting without shrinkage and good surface. After two resistance-arc casting, a 50.8 mm × 50.8 mm crucible consumable electrode can be cast into a crucible having a diameter of 101.6 to 127 mm. The white current electrode resistance-arc casting method can remove some volatile metal impurities in the crucible, for example, the calcium content is reduced to 30×10 -4 %, and the magnesium content is reduced to 8×10 -4 %. The zinc content after two castings can be reduced to 128 × 10 -4 %. Calcium, magnesium and volatilized in casting. 228 Ra, 224 Ra, etc., 232 Th decay daughters are often deposited on the inner wall of the furnace. In the production process, attention should be paid to fire prevention and prevention of the spread of radioactive materials.
The vapor pressure at the melting point is very low, and the evaporation loss is not significant, and is suitable for electron beam melting. During the casting process, enthalpy is remarkably purified by the volatilization of impurities and the overheating of hydrazine. The electron beam melting operation of the crucible is smooth, and the obtained crucible has high purity and smooth sidewalls.
The impurity content and hardness of the antimony ingots which are self-consumed electrode resistance-arc casting and electron beam melting are listed in the table.
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