Processing Fundamentals of Fine Aluminum Foam Production from Liquid Metals

摘要

This paper reviews the fundamentals of fine aluminum foam production from liquid metals based on a physical and chemical model, namely the influence of the surface tension and viscosity of the liquid, and the nucleus materials of bubbles on the foamability. The collapse of a liquid bubble has been mainly discussed using an aqua solution model for the stability of the bubble film as a function of the surface tension and the viscosity based on a simple experiment, because in this model, we cannot take into account the solidification. As is well known, the low surface tension and high viscosity of a liquid is recommended for the production of foams, nevertheless, the surface tension of liquid metals is significantly higher than that of water or organic materials such as plastics. Moreover, the viscosity of liquid metals is much lower than that of these materials. The reduction of the surface tension of liquid metals can be done by the addition of surfactant elements such as oxygen and sulfur for iron and bismuth, lithium and oxygen for aluminum. The reduction ratio is only half of the base metal. This half value is still much higher than that of water and organic materials. The viscosity of liquid metals is much lower than that of water. The influence of alloying elements on the viscosity is very low. Therefore, we have to discuss the influence of a fine powder addition on the viscosity using an aqueous solution. We discuss the influence of viscosity-increasing agents such as polyvinyl and fine powders, and surfactants on the bubble film stability of the aqueous solution.