Abstract

Hollow metal microspheres are made by forming a liquid film of molten film forming metal composition across a coaxial blowing nozzle and applying a blowing gas at a positive pressure on the inner surface of the metal film to blow the film and form an elongated cylinder shaped liquid film of molten metal. An inert entraining fluid is directed over and around the blowing nozzle at an angle to the axis of the blowing nozzle so that the entraining fluid dynamically induces a pulsating or fluctuating pressure field at the opposite side of the blowing nozzle in the wake of the coaxial blowing nozzle. The continued movement of the entraining fluid produces asymmetric fluid drag forces on the cylinder and closes and detaches the elongated cylinder from the coaxial blowing nozzle. Surface tension forces acting on the detached cylinder form the latter into a spherical shape which is rapidly cooled and solidified by cooling means to form a hard, smooth hollow metal microsphere. A thin metal coating can be deposited on the inner wall surface of the microspheres by using a metal vapor as the blowing gas or by adding to the blowing gas small dispersed metal particles and/or gases of organometallic compounds which are decomposed. The metal microspheres can be used to make insulation materials systems and as filler materials in plastics, plastic foam compositions, rubber and rubber compositions and in metal compositions. Filamented hollow metal microspheres with a thin metal filament connecting adjacent metal microspheres are also disclosed.

Other References

• Kendal et al., J. Vac. Sci Tech, 20 (4), Apr. 1982, pp. 1091-1093