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Encapsulation of nano hematite into zircon-silica matrix as a non toxic red ceramic pigment

Maryam Hosseini Zori

The hematite as a natural and non toxic red ceramic pigment has been known since prehistoric times but color shade of hematite becomes unstable with temperature and need to protect with a suitable matrix. The best red shades are obtained by the inclusion of hematite in silica casings. Zircon has the best thermal and chemical stability but it is more rare and expensive than silica, so in this research a fraction of zircon is substituted with silica crystals. A Sol-Gel method has been applied in order to improve the inclusion efficiency of hematite into silica and zircon crystals; Iron sulfate was used as Fe precursor and matrix agents were zirconium chloride and colloidal silica. Continuous changes in color were measured by comparing L*-a*-b* values of the heated samples. TEM analysis on calcined powders shows hematite single crystals with spherical morphology and diameter of 5-10nm that were occluded with silica-zircon crystals successfully. Due to its chemical and thermal stability, the pigment of hematite-silica-zircon system may be considered as a suitable red pigment for ceramic manufacturing by fast firing cycles.