Synthesis of ultrafine particles of intermetallic compounds by the vapor-phase magnesium reduction of chloride mixtures: Part I. Titanium aluminides

Abstract

A new chemical synthesis process for the preparation of intermetallic compounds has been developed. It involves the vapor-phase reduction of mixtures of constituent metal chlorides by magnesium vapor to produce intermetallic compounds in the form of fine powder. The advantages of the process include (a) the use of inexpensive raw materials, (b) low reaction temperatures, and (c) products in the form of fine particles. Part I describes the synthesis of titanium aluminide particles by this method, whereas Part II presents the synthesis of nickel aluminides particles. Although nickel aluminides can also be prepared by the hydrogen reduction of nickel chloride and aluminum chloride vapor mixtures, titanium aluminides cannot be produced by hydrogen reduction because of unfavorable thermodynamics. The effect of AlCl₃/TiCl₃ partial pressure ratio on the formation of different titanium aluminides was studied. A two-phase mixture containing 80 mol pct of TiAl+20 mol pct of TiAl₃ formed at an AlCl₃/TiCl₃ ratio of 10. The amount of TiAl₃ was maximized to 72 mol pct at an AlCl₃/TiCl₃ ratio of 16. The maximum conversion of the limiting chloride TiCl₃ was 94 pct. The product particles were very fine in the size range of 0.2 to 0.3 µm.