Surface coating of natural wollastonite fibers with colloidal rutile

Surface coating of natural wollastonite fiber with colloidal rutile was per formed in order to produce antibacterial inorganic filters for ventilators of buildings, The wollastonite surface in suspensions was made sufficiently negative to electric charge by adding chelating reagents, such as disodium salt of the ethylenediaminetetraacetic acid (EDTA) and sodium citrate for masking Ca2+ which dissolves from the ran materials acting as counter ion i n the electric double layer. Rutile particles with positive charge adsorbed quantitatively onto the wollastonite surface by electrostatic force of att raction at pH6, Detaching of rutile particles from the wollastonite surface during filtration and drying processes due to aggregation by large surface tension of water was avoided by replacing water by acetone. As a result, w ollastonite fibers were covered with a homogeneous layer of colloidal rutil e, and the rutile particles firmly adhered on the surface by heating at 500 degrees C for 2h.