Shigekazu Kato

Thin film coating of photocatalytics on ultra light ceramic tile by use of supercritical fluid

Abstract Although sol-gel method is an easy procedure to form a thin film, its extremely difficult to coat on the surface of small size particles, fibers, and fiber ceramics, because concentration occurs by capillary phenomena and causes peeling or breakage of film. In order to solve this problem, we use supercritical CO2 rapid expansion from supercritical solution (RESS), nano-sized particles of TiO2 with high intensity can be sprayed out of a nozzle, then collected on the surface of substrates, but can be absorbed into fibers or porous materials, being not interfered by viscosity of a solution. TiO2 sol made by hydrolysis process is set in a pressure cell and mixed together with super-critical CO2. Controlling the pressure and the temperature, we could obtain TiO2 sol and super critical fluid mixture, and then discharge to the substrate. At this point, Titania sol viscosity is so low that a surface wettability of the substrate becomes negligible. By the use of the characteristics of the supercritical fluid, without constraint condition of viscosity or capillarity, this sol can penetrate into the interstices of the substances structure. Thus, clearing obstruction of capillary phenomena, supercritical fluid coating method shows its capability to penetrate deep into inside of entangled fiber of the three-dimensional structure so as considered to be a heat resistant filter with 95% porosity.