Atmospheric pressure plasma enhanced chemical vapor deposition on fine powders in a circulating fluidized bed reactor

Abstract

Silicon oxide deposition on fine alumina powders (100 ㎛) by plasma-enhanced chemical vapor deposition (PECVD) at atmospheric pressure was carried out in a circulating fluidized bed reactor (18 mm-ID x 1000 mm-high). A stable glow discharge under atmospheric pressure was successfully attained at a source frequency of 13.56 MHz with an insertion of a dielectric quartz tube into the inner part of the ring shaped electrodes. To deposit silicon species on alumina powders, a mixture of tetraethoxysilane (TEOS) or hexamethyldisiloxane (HMDSO) and oxygen was used as the reactant gases. Helium and argon gases were used as the carrier gases. The characteristics of deposited films were analyzed by the dynamic wicking meter, FTIR with ATR, XPS, SEM-EDS, and ICP-MS. Chemically deposited silicon species was evenly distributed on the surface of alumina particles. The surface energy of plasma treated alumina powder is varied from hydrophobic to hydrophilic in the surface composition with variation of the applied power (150-350W). In oxygen-containing atmospheres, the chemical composition of the deposited film is similar to that of inorganic $SiO_2$ with increasing the applied power and the flow rate ratio of $O_2/monomer$ (TEOS or HMDSO). The deposition efficiency was improved by increasing the solid concentration or holdup in the plasma treatment rime. The glow discharge was stable at solid holdup less than $5×10^{-3}$ in the plasma volume. For sufficiently high discharge power and $O_2/precursor$ ratios, the structure of the deposited films was very similar whatever the organosilicon precursor (TEOS or HMDSO) was employed. The effect of discharge power on deposited film onto the powders from HMDSO is less pronounced to the chemical composition of deposited film.