Method for producing low density porous metals or hollow metallic spheres

摘要

Disclosed are methods, utilizing electromagnetic levitation, for producing low density, porous metal structures and hollow metallic spheres, using particulate material as a starting point. As an initial step, a porous article of sufficient green strength to be substantially self-supporting is formed of a particulate material containing at least one electrically-conductive metal. The green porous article is subjected to an electromagnetic field which has a field strength and frequency sufficient to levitate the green article in space against the force of gravity, and which has a frequency sufficient to induce in the article an eddy current of such intensity to produce heat sufficient to melt the electrically conductive metal, thereby entrapping the pores of the green article and any gases or non-electrically conductive particulate material contained therein. The next steps vary, depending on whether a porous metal structure or a hollow metallic sphere is to be produced. For producing a porous metal structure, the article is cooled at a rate sufficient to solidify the molten metal and produce a low density porous metal structure containing pores which contain any entrapped gases or non- electrically conductive particulate material. For producing a hollow metallic sphere, the heating of the molten article is continued for a time sufficient to expand any gas contained in the pores to a volume such that substantially all of the entrapped pores combine to produce a hollow molten metal sphere, and then the sphere is cooled to solidify the molten metal.