Abstract
Ceramics are often prepared with surface layers of different composition from the bulk, in order to impart a specific functionality to the surface or to act as a protective layer for the bulk material. Here I describe a general process by which functional surface layers with a nanometer-scale compositional gradient can be readily formed during the production of bulk ceramic components. The basis of this approach is to incorporate selected low-molecular-mass additives into either the precursor polymer from which the ceramic forms, or the binder polymer used to prepare bulk components from ceramic powders. Thermal treatment of the resulting bodies leads to controlled phase separation ('bleed out') of the additives, analogous to the normally undesirable outward loss of low-molecular-mass components from some plastics; subsequent calcination stabilizes the compositionally changed surface region, generating a functional surface layer. Using this technology, we developed a strong photocatalytic fiber (TiO2-covered SiO2 fiber), which effectively decomposed many types of organic chemicals and bacteria into CO2 and water by irradiation of UV light. Furthermore, we performed some field tests using a circulation purifier with a module composed of the cone-shaped felt material of our new fiber.
