Thermal reaction behavior of ZrSiO4 and CaCO3 mixtures for high-temperature refractory applications

The effects of the mixing ratio of zircon (ZrSiO4) and calcium carbonate (CaCO3) powders on the synthesis and thermal reaction of their composites were investigated in the composition range, 5ZrSiO4–xCaCO3, where x=7, 13, and 19, using progressive additions of CaCO3 to the ternary CaO:ZrO2:SiO2 composition. The thermal reaction behavior of ZrSiO4 and xCaCO3 was evaluated using thermal analysis, X-ray diffraction (XRD), density measurement, and surface morphological observation. The chemical component was evaluated using energy dispersive X-ray spectrometry. The calcium oxide (xCaO) decomposed from the xCaCO3 in the temperature range 600–800 °C reacted with the ZrSiO4, forming the final stable compounds of m-ZrO2, Ca2SiO4, CaZrO3, and Ca3Zr(Si2O9)O2, depending on the CaCO3 ratio for ZrSiO4 in the mixture. The reaction temperature decreased with increasing CaCO3 content. The composites consisted of m-ZrO2–Ca2SiO4 for the 5ZrSiO4−7CaCO3 mixture, CaZrO3–Ca2SiO4–Ca3Zr(Si2O9)O2 for the 5ZrSiO4−13CaCO3 mixture, and CaZrO3–Ca2SiO4 for the 5ZrSiO4−19CaCO3 mixture. It was found that the composites showing different thermal reaction behavior could be synthesized from two different sources of ZrSiO4 and CaCO3, due to the different CaO:ZrO2:SiO2 ratio.