Effect of the surfactant and precipitant on the synthesis of pink coral by a microemulsion method

The use of hematite and other iron oxides as a natural red ceramic pigment has been known since prehistoric times and, probably, is the first ceramic pigment to have been employed by humanity. However, hematite crystals grow with temperature and the colour shade becomes unstable. The best red shades are obtained by the inclusion of hematite in silica or in zircon (pink coral) casings. A microemulsion method has been applied in order to improve the inclusion efficiency of hematite into zircon crystals; the effects of several parameters on the synthesis, such as the precipitating agent (ammonia or alkaline hydroxides), the surfactant (anionic or cationic) and the flux agent (NaF or NaF.2NaCl), have been studied.