The Preparation And Thermal Stability Study Of Encapsulated Cd(S_xSe_1-x) Pigment

Cadmium selenide sulfide Cd(SxSe1-x) is the only ceramic pigment that shows scarlet colour. For its poor high temperature performance─beginning to oxidize at 550°C and to decompose at 800°C, it cannot be directly used as a pigment in ceramics which are commonly fired at the temperature higher than 1000°C. Therefore, coprecipitation method is employed to prepare ZrSiO4 encapsulated Cd(SxSe1-x) pigment to keep the red color at the temperature higher than 1200°C. However, the traditional methods usually have low pigment encapsulation efficiency and the products have low colour stability. Thus, developing a new way to synthesis the red pigment is of great significance.Firstly, we studied the dispersivity of Cd(SxSe1-x) in aqueous solution. The result showed that 15% PVP or 20% CTAB of pigment led to good dispersion of 2% Cd(SxSe1-x) slurry. The dispersion performance of PVP was found to be independent of pH values. We also studied the dispersion mechanism through Zeta potential analysis.Secondly, encapsulated Cd(SxSe1-x) pigment was prepared by sol-gel method and the formation mechanism was discussed. Using ZrOCl2·8H2O, Na2SiO3·9H2O, NaAC as raw material and MgF2 as mineralizer, the initial formation temperature of ZrSiO4 decreased from 1100°C to 700°C. Adding 25% Cd(SxSe1-x), pink encapsulated pigment with particle size of 1-5um could be obtained when calcined at 950°C for 0.5h.Thirdly, with TEOS as silica source, silica encrusted Cd(SxSe1-x) composite powder were synthesized. The composite powder was characterized by XRD,FTIR,SEM,colorimeter, etc. The experimental results showed 100ml alcohol-water mixture with 1g dispersive Cd(SxSe1-x), 2.6g ammonia, 2.0g TEOS led to good capsulation of the pigment and the high temperature stability of composite powder had been effectively enhanced.Finally, hydrothermal method was explored to fabricate encapsulated pigment. Lamellar crystals of ZrSiO4 were formed under hydrothermal treatment at 200°C for 4h. Unfortunately, the ZrSiO4 crystals and Cd(SxSe1-x) were completely separated and no core-shall structure was found. The results showed that the pH value of precipitation, hydrothermal temperature, holding time had little effect on the crystal form of zircon. This might be attributed to the crystal habit of lamellar structure under the hydrothermal conditions of this experiment.