PREPARATION OF 10 KG INGOT OF ULTRA-PURE IRON

A new induction melting furnace with a cold-copper crucible has been d esigned and constructed using ultra-high vacuum technology. The main c hamber can be evacuated to 6.7 x 10(-8) Pa as the base pressure. The f urnace can melt high-purity iron of 10 kg, at most, within 300 s. The total pressure becomes less than 4 x 10(-6) Pa during melting of iron under the best condition. As starting materials for melting, high-puri ty electrolytic iron containing impurities of 25.2 massppm which is de termined after the analysis of 18 elements was prepared. The content o f gaseous impurities such as carbon, nitrogen, oxygen, sulfur and hydr ogen is 19.6 massppm in total. It is concluded that ultra-high vacuum melting of iron is quite useful to increase the purity of iron. The to tal content of impurities in iron is reduced from 25.2 to 12.6 massppm by melting under the atmosphere of 7.5 x 10(-6) Pa. The amount of gas eous impurities can be reduced from 19.6 to 10.1 massppm in total. Esp ecially, the amount of oxygen is reduced from 14.1 to 7.5 massppm. The se amounts of gaseous impurities are almost the limit of detection by conventional methods of analysis.