Processing of Ceramic Powder using High Energy Milling

Abstract

High Energy Milling (HEM) is a well known and commercially used technique [1-3]. Today the applications are limited to the range of metal based materials, alloys and composites where the methods are described as Mechanical Alloying [3-5], HEM and Reactive Milling [5]. Since the high kinetic energy transfer represents the performance of these techniques [2-7], up to now it has not been possible to apply them for pure ceramic materials. This is simply caused by the contamination problem, as milling tools e.g. made by ceramic usually do either not show a suitable shock-resistibility or hardness. The present paper is the report of a study and development of suitable milling tools to be used in the well known Simoloyer-mill or in other high kinetic systems. The goal is to be able to use the high kinetic processing technique and approach the existing range of ceramics processing. Most important is the high potential of new materials, composites and applications. The majority of today’s applications are the production of fine powders, thus the main route is described as particle size reduction. The traditional milling-devices used for this are the drum-ball-mills which are characterized as low energetic systems with a specific energy of 0.01-0.03 kW/l [9]. The terminal size in dry milling condition refers to a diameter d = 15-20 μm, in wet milling condition d = 10 μm. Usually a long duration of the milling procedure of up to a few days is required, a real continuously processing is not considerable. As e.g. the consolidation behavior of metallic and ceramic powders is considerably influenced by their particle size, there is a high potential for fine ceramic powders with a particle size of a few microns or less one micron which is required to improve the mechanical properties [10] of products and/or facilitate following processing, e.g. a better fluidity of the powder by injection and thermal spray or a better sintering activity due to their large free surface with an elevated particle contact density. Another very interesting application is the ultrafine distribution of a ceramic hard-phase in a ceramic matrix in nanometer-scale [9-12]. Always a dry milling process is in principle to be preferred as any fluid process control agent (PCA), such as water or alcohol, is required to brake the milling intensity unnecessarily.