Encapsulation of hematite in zircon by microemulsion and sol-gel methods

Microemulsion method has been applied and compared with sol-gel, coprecipitation and ceramic route with the purpose of encapsulating hematite into zircon crystals used as ceramic pigment. In the commercial synthesis of pink coral pigment, NaF flux agent is usually added in order to improve the reactivity of the system; therefore, the addition of flux agents (NaF or NaF . 2NaCl) has been investigated. Likewise, the effect of precipitating agent (NH3 or NaOH) has been studied. Sol-gel becomes the more reactive method and produces the best red colours without fluorides addition, but does not give red colour in the presence of halides fired at 1000degreesC. Ammonia microemulsioned and coprecipitated powders give similar orange-brown colours without fluorides, and red colours with fluorides addition. The addition of NaF produces higher inclusion effectiveness than NaF . 2NaCl. The stabilization of sodium silicozirconate crystalline phases in NaOH coprecipitated or emulsioned samples avoids the zircon crystallization and then the hematite encapsulation.