Micropyretic synthesis of MoSi 2 powders through an aluminothermic reaction
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Micropyretic synthesis of MoSi2 powders through an aluminothermic reaction Ming Fu and S. Penumella Micropyretics Heaters International (MHI), Inc., 613 Redna Terrace, Cincinnati, Ohio 45215
J. A. Sekhar International Center for Micropyretics, Department of Materials Science and Engineering, University of Cincinnati, Cincinnati, Ohio 45221 (Received 1 July 1998; accepted 3 November 1998)
An aluminothermic reaction starting with inexpensive MoO3 , SiO2 , and Al powders was utilized to prepare molybdenum disilicide (MoSi2 ) powders by the micropyretic/combustion synthesis process and leaching. The combustion-synthesized product was porous and could readily be crushed into powders. X-ray diffraction (XRD) analysis revealed that the product of such a reaction consisted of a –Al2 O3 , MoSi2 , and a small amount of Mo(Si,Al)2 and Mo5 Si3 . The reason for the formation of Mo(Si, Al)2 phase is discussed. MoSi2 powders were obtained by leaching out the Al2 O3 from the synthesized powder mixtures in boiling phosphoric acid solution. The synthesized MoSi2 powders, including a small amount of Mo(Si, Al)2 and Mo5 Si3 , were very fine with an average particle size of about 1 mm.
I. INTRODUCTION
Molybdenum disilicide, MoSi2 , has drawn considerable research attention in recent years due to its potential to meet the demands of advanced high temperature structural applications.1–3 In the manufacture of MoSi2 bulk parts, it is usual to employ powder metallurgy techniques and therefore MoSi2 powders are required. In recent years, micropyretic synthesis, also referred to as combustion synthesis or SHS, has been developed as a cost-effective technique for synthesis and processing of numerous high-temperature materials in both powdered forms and dense bodies.4,5 There are numerous chemical reactions that may be utilized in a combustion synthesis process. These reactions can generally be divided into elemental and thermite reactions. Thermite reactions are based on the reduction of one or more oxides by a metal such as Al (aluminothermic) or Mg (magnesiothermic), and therefore have the advantages over elemental reactions in that they start with naturally occurring oxides which are less expensive and more readily available. A number of in situ composite powders, such as carbideoxide,6–9 boride-oxide,10 and silicide-oxide,9,11 have been synthesized by utilizing thermite reactions. These composite powders either can be directly used as precursor powders for subsequent fabrication of dense composite bodies,6 or can be used to obtain single phase powders providing that product phases can be separated.6–8 Leaching is an effective method for removing undesirable product phase(s). By leaching out magnesia (MgO) from the micropyretic synthesized products, single phase powders like SiC,6 B4 C,7,8 and MoSi2 11 have been obtained through a number of magnesiothermic reactions. J. Mater. Res., Vol. 14, No. 5, May 1999
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