Assessment of Investment Process for Producing Copper Hollow Spheres

Abstract

Cellular materials and designed porous materials are a class of materials with extremely low densities and an outstanding combination of mechanical, electrical, thermal, and acoustic properties, based on nature’s way of decreasing the weight of materials such as bone or cork by incorporating cells or pores. These materials are increasingly being considered as lightweight construction, heat exchangers, passive safety and other purposes. Especially, their extraordinary property combinations make them interesting for applications where more than one function is required e.g. high stiffness and fire resistance or acoustic damping. Cellular (or porous) materials are defined as solids containing cells (or pores). They can be classified by morphology and dimensionality as well as formation mechanism, namely; by building up single cells (hollow spheres) or by incorporating cells into bulk material (foam materials). Both approaches lead to three-dimensional cellular materials but with different macroscopic properties, which are determined more by the cell formation mechanism. It is regarded that cellular materials produced by building up hollow spheres give predictable macroscopic properties, compared with those by foaming processes. 1–5) To date, hollow metallic spheres have been produced usually via the coaxial nozzle process using oxide slurry. 6, 7) Compared with the conventional coaxial nozzle process, this paper demonstrates the feasibility of investment process in producing hollow spheres from copper alloys. Optimum processing variables such as slurry viscosity and the mass ratio, hardness, and electrical conductivity of copper hollow spheres with respect to oxide reduction temperature and ZnO content are discussed. 2. Experimental Procedures