Plasma Enhanced Chemical Vapor Deposition on Particulate Solid-State Materials for Improved Powder Processing

The surface of fine lactose powder particulates was modified by direct-plasma exposure in a radio frequency (RF) discharge, in a mixture of oxygen and hexamethyldisiloxane (HMDSO) diluted in argon. Besides, the RF power (100–500 W) and the HMDSO flow rate (0–68 sccm) at constant oxygen-to-HMDSO flow rate ratio of 10 was varied in this study. Apart from the relatively high pressure of 2 mbar, the plasma process adopted is very much alike the plasma enhanced chemical vapor deposition of silica-like material descending from the plasma-chemical reaction of oxygen and HMDSO. With respect to the processability of powders in production lines to be solely gravity-driven, as for instance in the event of dye-filling, compression ratios (based on the powder bulk and mass density) were measured for solely gravity-driven filling of a graduated glass. A jolting volumeter was used to provide the compressibility of the compacted powder bulk. Higher compressibility of about 20% (improvement rate) was found for both experimental series: variation of HMDSO flow rate and variation of the discharge power. In both cases, an enhancement of the flowability of the powder was found to cause the compressibility improvement.