Abstract: Using fly ash as the matrix material and aluminum powder as the phase change medium, the spherical high temperature composite fixed phase change material with diameter of 15 mm was prepared by the mixed sintering method. The surface coating of low temperature black glaze was prepared by dipping glaze method and four sintering systems, and its waterproof property was evaluated by water permeability and microscopic characterization. Researches show that the sintering temperature of glaze layer and glaze concentration have significant influence on glaze layer properties. When the sintering temperature of glaze layer is 950 ℃, the glaze volume concentration is higher than 90%, the glaze layer cracks and coking are caused by the large difference in expansion coefficient between the blank glazes and the incomplete release of organic decomposition products before the glaze power melting; the volume concentration is more than 80% and less than 90%, the surface density of glaze layer increases and the waterproof property is enhanced, but there is the flow phenomenon of glaze. When the sintering temperature is 870 ℃ and 810 ℃, and the glaze volume concentration is 85% to 95%, the glaze gloss is good, the flow glaze is reduced, and the waterproof property is enhanced. When the sintering temperature of glaze layer is 750 ℃, because the temperature is too low, the gas between glaze layers cannot be discharged in time, it leads to the increase of pinholes in glaze surface and the decline of waterproof property. Compared the properties of glaze layer under four sintering systems, when the highest sintering temperature of glaze layer is 810 ℃ and slurry volume concentration is 88% to 92%, the coating has high density, good tightness with the surface of spherical phase change material, outstanding waterproof property, and good experiment repeatability.

Key words: spherical phase change material, low temperature black glaze, coating, water permeability, preparation technology