Titanium powder production by TiCl 4 gas injection into magnesium through molten salts
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INTRODUCTION
TWO processes for titanium production have been applied industrially: the Kroll and the Hunter process. Both are batch-type operations. The Kroll process is based on the chemical reaction of TiCl4 reduction by liquid metallic magnesium.[1,2] Industrial application of the Hunter process (sodium reduction) was stopped in 1993.[3] Numerous reactions, ideas, and projects have been reviewed.[4,5] Previous studies on continuous Ti reduction are classified roughly into two categories: those on electrolysis of Ti-containing molten salts and those on pyrometallurgical processes. Serious problems in electrolysis include the morphology control of Ti deposits and the low current efficiency caused by multivalent Ti ions. Pyrometallurgical processes to produce Ti liquid also have difficulties for industrial application because of the high chemical reactivity of molten Ti with the reactor materials. Consequently, none of these proposals have been applied industrially. The Kroll process has been applied to Ti mass production, where liquid TiCl4 is dropped onto the Mg molten surface in a sealed vessel. Metallic titanium is produced as TiCl4 1 2Mg 5 Ti 1 2MgCl2
[1]
at around 1173 K in an Ar gas atmosphere. Porous aggregates known as ‘‘sponge titanium’’ form in a vessel of stainless steel or mild steel. Sponge titanium consists of tightly connected Ti particles about 20 mm in size. The byproduct, MgCl2 and the residual reductant, Mg, are con-
TETSUSHI N. DEURA, formerly Doctor of Engineering with the Department of Energy Science and Technology, Graduate School of Energy Science, Kyoto University, is with KOBE Steel, Ltd., Kobe, 6512271 Japan. MASAHIRO WAKINO, formerly Master of Engineering with the Department of Energy Science and Technology, Graduate School of Energy Science, Kyoto University, is with SANYO Electric Co., Ltd., Tokushima, 771-0213 Japan. TOMOYA MATSUNAGA, Graduate Student, RYOSUKE O. SUZUKI, Associate Professor, and KATSUTOSHI ONO, Professor, are with the Department of Energy Science and Technology, Graduate School of Energy Science, Kyoto University, Kyoto 606-8501, Japan. Manuscript submitted September 8, 1997. METALLURGICAL AND MATERIALS TRANSACTIONS B
tained in the fine porosity inside this sponge titanium and arc removed after reduction, by evacuation at 1273 K for a few days. One problem with the Kroll process is the costly and time-consuming batch operation for the reduction of TiCl4 and the separation of MgCl2. An important advantage, however, is that the combination of chlorination of TiO2 and the successive TiCl4 distillation allow one to remove many metallic impurities in addition to oxygen[6] prior to the reduction to metallic Ti. We hope to utilize this distilled TiCl4, as the starting material for reduction, in the design of an alternative Ti production process. The purpose of this work is to propose an alternative continuous reduction process for the mass production of titanium and to examine experimentally the fundamental behavior of the chemical reaction. We are interested in wh
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