For example, a coating of resins such as polytetrafluoroethylene, perfluoroalkoxide, polyfluoroethylene propylene or that for which metallic powder, inorganic oxide, etc. are mixed and dispersed in those resins, or LURON (manufactured by Dinox) on a material of aluminum, stainless steel, etc. or an impregnation of a porous material treated with hard almite with Teflon may bring a satisfactory re