Ultrafine powder materials, particularly ceramic and metal powders, are advantageous for forming sintered products for use in high temperature applications. Accordingly, an inexpensive and reliable method for producing ultrafine powder materials is desired. Thermal plasma methods are known for preparing ultrafine powder materials as set forth in "Thermal Plasma Chemical Synthesis of Powders", Vogt et al, presented at 168th Meeting of the Electrochemical Society, Oct. 13-18, 1985. Generally, the high temperature thermal plasma methods employ high powder levels, for example, 1 to 10.sup.3 kW, and temperatures of at least several thousand degrees Kelvin (.degree.K.), and usually of about 5000.degree. K. The Ogawa et al U.S. Pat. No. 4,610,857 discloses a modified thermal plasma method for forming ultrafine ceramic particles wherein a metal powder is vaporized and mixed with a reactive gas to form the ultrafine particles. The Niwa U.S. Pat. No. 4,138,306 discloses a film forming method wherein reaction gases are subjected to a high temperature microwave plasma. However, the high temperature and high power requirements of the thermal plasma methods place limitations on the physical and chemical properties of the powders produced.
On the other hand, glow discharge apparatus employ lower energy and temperature requirements as compared with the high temperature thermal plasma powder generating apparatus. Glow discharge has been used in various applications, for example, for gas phase reaction chemistry as disclosed in the Dickson, Jr. U.S. Pat. No. 4,568,437 and the Hellund U.S. Pat. No. 3,444,061, for the deposition of film layers as disclosed in the Kubacki U.S. Pat. No. 4,262,631, and for treatment of solid materials as disclosed in the Gorin U.S. Pat. No. 3,775,621. The Weissfloch et al U.S. Pat. No. 3,814,983 discloses a further method for treating materials using microwave generated plasmas. However, no methods are known for the production of ultrafine powders using glow discharge.
Thus, a need exists for a method of producing ultrafine powder materials economically and in large quantities.
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