Research On Separative-phase Glaze And Its Structural Color

Glaze coloring from phase separation and structural color is an important decorative technique, which can increase varieties and color stability of ceramic glazes. With increasing environmental pollutions, it is of significance to develop low-cost and green materials. The aim of this paper is to develop new environmentally friendly phase separated glazes. Firstly, two kinds of basic glazes in R2O-RO-Al2O3-SiO2-P2O5 and R2O-RO-Al2O3-SiO2-P2O5-B2O3 systems showing excellent opaque properties were obtained by melting quartz, talc, calcite, calcium phosphate (Ca3(PO4)2), etc and cooling the high-temperature melt. And then the phase separated glazes were prepared by adding the colorants of Fe2O3, Cu powders, CuO and iron-ore slag to the basic glaze systems. The phase compositions and microstructure of the glazes were studied by X-ray diffraction and scanning electron microscopy, respectively. The coloring mechanism of phase separation and structure were investigated by analyzing the effects of sintering system, composition, microstructure, etc on the color-producing performances of the phase separated glazes on the basis of physical and optical theories, which is quite important and practical for improving the updating of the ceramic industries and glaze decoration and additional value.(1) The opaque glaze of R2O-RO-Al2O3-SiO2-P2O5 system with high whiteness was prepared by "four-corner coding" batching at 1180-1230 ℃ with a cooling velocity of 25-35 ℃/min above 850 ℃ (natural cooling from furnace temperature to room temperature below 850 ℃). The results show that the glaze owns higher whiteness with increasing Ca3(PO4)2, and phase separation and crystallization are the main opacity mechanism. The mass ratio of B2O3/P2O5 has important effect on the opaque properties of the glaze including opacifier agents of B2O3 and P2O5. The glazes with 2.5-15 wt% Ca3(PO4)2 and a B2O3/P2O5 mass ratio value of 1/3-3 show high whiteness, high glossiness, and no cracks. The sintering temperature plays an important part in the size, content and distribution of the melting droplet, which determines the glaze opacity. The glaze opacification is mainly contributed to the phase separation during cooling.(2) The phase separated glazes with good colors were prepared at different temperatures by adding Fe2O3 to basic glazes in R2O-RO-Al2O3-SiO2-P2O5 and systems. The coloring mechanism of the separated glaze was investigated by analyzing the effects of sintering temperatures and composition on the color-producing performances of the phase separated glazes on the basis of physical and optical theories. The results show that the colors of the phase separated glazes are determined by the Rayleigh scattering or the Mie scattering. The glaze shows a color of light blue, which is predominantly caused by Rayleigh scattering from the phase separated droplets less than 100 nm in size. The glaze is ivory white when phase separated droplets are higher than 100 nm in size, and Mie scattering is the main coloring mechanism. Therefore, the colorful phase separated glazes containing Fe2O3 can be prepared by adjusting the composition and sintering temperature of the basic glaze to control the size and distribution of the phase separated droplets.(3) The copper glazes were prepared by introducing copper and its oxide powders into the basic glaze in R2O-RO-Al2O3-SiO2-P2O5 system at (weak) oxidation atmosphere. The glazes show different colors such as lunar white, azure, patina and so on, which is attributed to the sizes and distribution of the phase separated droplets, depending on the mole ratios of SiO2/Al2O3 and SiO2/CaO (the content of Ca3(PO4)2 keeps constant). The glazes become sea-blue from ivory white and azure, and opacity of the glaze rises with the increase of copper powders. The color of the glaze become lunar white from light green and azure, and glossiness of the glaze changes from translucence to half opalescence and opalescence. The glaze with different mole ratio of Cu+/Cu2+ prepared at different temperatures and atmospheres, resulting in the difference in the size and distribution of the phase separated droplets, and the glazes show various colors.(4) The phase separated glaze containing iron was obtained by introducing iron-ore slag into the basic glazes in R2O-RO-Al2O3-SiO2-P2O5 system, and the color of the glaze is mainly from the coupling of the structural color related to the phase separation and the chemical color from the coloring ion. The glaze surfaces with various colors and arabesquitic are smooth and glossy when the content of iron-ore slag is 25 wt % and the sintering temperature of the glaze is in the range of 1190-1250 ℃, which results from the composition, microstructure and sintering temperature of the glaze. The arabesquitic on the surface of glaze sintered at 1160 or 1220 ℃ results from the un-melted calcium phosphate. Calcium phosphate in the glaze melts completely at 1280℃, and becomes the major phase from the second phase, which resulting in the formation of arabesquitic on the glaze surface. The content of Fe2O3 melted in the glaze rises with the increasing iron-ore slag, which deepens the glaze. Redundant Fe2O3 precipitates in the form of hematite appear when excess iron-ore slag is added and the glaze has metallic luster.(5) The structural color of the phase separated glaze results from the photonic crystal, Rayleigh scattering and phase separation. The structural color from phase separation is too light and weak to see because two glass phases in the glaze have the similar refractive indexes. The phase separated glaze can show various colors by introducing the elements of Fe and Cu into the separated phase from the main phase, further improving the coloring of ceramic glazes and changing the views:the colorful glaze can be obtained by changing the sintering atmosphere of the glaze.