The Synthesis And Coloring Mechanism Of Low-cost Chromite Based Stain

Accompanying the increasing demand of metal minerals, the price of metal-oxides has been growing, which increases the cost of building sanitary ware stain. As a result, related companies who supply assistant raw materials or produce building sanitary ware are searching ways to reduce cost, including improving producing technics, adopting inferior or substitute materials etc.Chromite is the only raw for producing Cr2O3 and generally used as coloring material for black polished tiles. The coloring effect of using chromite separately and the influence of chromite mixing quantity on body's quality have been studied in this paper. Results show that the mixing quantity of chromite should be much more than 6% to reach lower brightness value, however, under the circumstances kiln shrinkage ratio is higher while water absorption ratio, cross-breaking strength, firing temperature and over-burn temperature are evidently lower. Therefore, the mixing quantity of chromite stain should be reduced.By adding Cr2O3 and Fe2O3 to chromite, we can synthesize satisfactory chromite based black stain, when the raw stain contains 20 wt.% chromite, 40% Cr2O3, and 40% Fe2O3 with calcined temperature at 1230℃and soaking time of 30min. The a* value can be lowered through ways of increasing calcined temperature or prolonging soaking time which will weaken the coloring ability of synthesized stain. Therefore, we tried to add suitable quantity of H3BO3, WO3, V2O5 and NH4VO3 to solve the problem. Results show that V2O5 is the most suitable mineralizer. Through analyzing XRD result of stain powder we found that: raising the calcined temperature or prolonging the soaking time will improve the solubility of hematite solid solution; adding mineralizer to the raw stain will not only improve the solubility of hematite solid solution but also change the composition of compound spinel phase by which the coloring ability of stain is improved.Through adding ZnO, Cr2O3, Al2O3 and Fe2O3 in different proportions to the chromite, we can synthesize series of brown stain, when the calcined temperature is at 1250℃and soaking time of 30min.This synthesized stain works well in low melting lead glaze, intermediate fritted glaze and calcium sub-shine glaze, but fails in magnesium sub-shine glaze and body.The coloring ability of chromite based stain depends on its stability in the body and glaze. Synthesis and solution mechanisms of spinel have also been explored through thermodynamics calculation and geothermometer model in this paper firstly which constitutes theoretical backups for the synthesis and application of chromite based stain.