Study On The Low-temperature Opacified Glaze And Its Opacifying Mechanism

Opacified glaze is the thin opaque glassy layer formed on the surface of a ceramic body, which can cover the body color and defect. At present, the expensive zircon is often used as opacifying agent to prepare zircon opaque glaze, then the production cost was also increased. In this paper, ceramic body was made from the Yellow River silt, and the cheaper apatite replacing zircon as opacifying agent was used to prepare phosphate opaque glaze and zircon and phosphate opaque glaze.The Yellow River silt body was formed by slip casting, and fired during 1080-1180℃. The Water absorption (Wa), Porosity (Pa) and Bulk density (D) have been tested. The modern testing techniques such as XRD, SEM and EPMA were used to analyze the crystal phase composition and the microstructures. The results indicated that the main crystal phase of the fired body is columnar mullite(Al₆Si₂O₁₃) and granular quartz (SiO₂).For the deep color of fired body, research developed a low temperature opacified glaze which could cover it. The optimal formula and the appropriate preparation technology were researched, the whiteness and the microhardness were tested. The microstructures and properties of the glaze were discussed, as well as the opaque mechanism and the reaction mechanism. The excellent apatite glaze recipe is C-4, the glaze microhardness is 630.8MPa, the whiteness is 66.9, the phase composition of glaze are diopside and apatite which make the best opacifying effect. The excellent apatite and zircon glaze recipe is E-6, its glaze microhardness is 676.8MPa, the whiteness is 68.7, after sintered, there are abundant sphericity microlite and some flaky and columnar crystal grain in the glaze, the flaky and columnar crystal is zirconium silicate(ZrSiO₄) and the sphericity microlite is quartz(SiO₂) , which also has the good opacifying effect. Excepting apatite, zirconium silicate and quartz crystals, there is some calcium phosphate crystal appeared in the opaque glaze of zircon, zinc and calcium phosphate. The microlite diameter which approach the visible light wavelength and the coming opacifying effect of the glaze is caused by the light scatter of microlites in it. Its mechanism is that the alkali oxides in the glaze penetrate into the body and crystal composed of Al, Si grows into the glaze, then the interlayer formed. The element distribute evenly in the interlayer in which there is no large grains and pores but mostly microlites and glass that combined the glaze and body closely and endow them with excellent associativity.Apatite glaze and the compound opaque glaze of zircon, zinc and calcium phosphate can be fired at 1120℃as 30 percent Frit 707 was added. Some kinds of pigments were added to that glazes to prepare color glaze, which has good flat surface and the best chromophore effect, as well as the nice hiding power to the body and the fine aesthetic feeling to the Yellow River silt ceramic.