Production of Willemite Pigments Suitable for The Ceramic Industry by Utilization of Rice Husk Ash (RHA)
In this study willemite ceramic pigments, doped with Co, Ni, Fe or Mn were synthesized. The optimal parameters of the synthesis process have been determined. The willemite is a mineral - zinc silicate Zn2SiO4. For the production of willemite ceramic pigments in the system CoO.ZnO.SiO2 we used the following main materials: CoO, ZnO, SiO2.nH2O) and NaF as a mineralizer. In our work, as a source of SiO2, we used SiO2.nH2O or white rice husk ash. The use of industrial bio-waste as raw materials in the ceramic industry has been studied for decades due to the economic, energy and environmental advantages. The present study was carried out with rice husks obtained during processing of the Krasnodarski 424 variety grown in Bulgaria. This type of rice contains 17.8% husk. They are arc-shaped and size approximately: 8 mm long, 2-3 mm wide and 0.10 to0.15 mm thick. The shell contains 74.5% organic matter (cellulose, hemicellulose and lignin) and water, and the rest is an inorganic matter containing 20% SiO2 and 5.5% of the following oxides: CaO, Fe2O3, MgO, Al2O3, Na2O, K2O, MnO2, as well as traces of Cu and Pb. The willemite ceramic pigments and rice husk ash were studied by X-ray analysis, infrared (IR) spectroscopy, differential thermal analysis (DTA) and scanning electron microscopy (SEM). The color of the pigments was determined using a Lovibont Tintometer RT 100 Color tintometer. It was proved that the synthesized pigments are suitable and can be successfully applied in glaze tiles and sanitary ceramics.