Surface modification and coating of powders by ion beam techniques

Powdered materials are widely used in industry. Many of the properties of powders are determined by their surface. Therefore, surface modification techniques such as those based on ion beams are promising techniques for powder modification. Ion beam techniques are typical line-of-sight processes. Only that part of a powder particle which is turned directly towards the source of the ion beam and is not shaded is treated properly. This renders uniform surface treatment of powders difficult. More or less sophisticated facilities for agitating the powder in the ion beam have to be used. In the present paper, a set-up is described for ion beam treatment of powders based on a rotating drum with wings which move the powder grains through the ion beam line. The features of this facility and the processes which take place in it during ion irradiation of powders are discussed. As an example, results of ion implantation and ion beam sputter deposition of gold onto alumina powder are presented. The amount of implanted or deposited gold, depending on rotation speed of the drum and number and type of ions, was determined using neutron activation analysis. The powder grain surfaces with deposited gold atoms were inspected with electron microscopy in combination with X-ray analysis.