Effect of ZrO2 particle size on morphology and synthesis temperature of nano CaZrO3 synthesized via molten salt method

Abstract

Well crystallized pure calcium zirconate (CaZrO3) nanopowder was successfully synthesized using the molten-salt method. CaCl2, Na2CO3, micro-ZrO2 and nano-ZrO2 were used as starting materials. On heating, Na2CO3 reacted with CaCl2 to form NaCl and CaCO3. Nano CaZrO3 was formed by reacting equimolar amounts of in situ-formed CaCO3 (or CaO) and ZrO2 in molten Na2CO3–NaCl eutectic mixture. CaZrO3 particle size and synthesis temperature was tailored as a function of ZrO2 particle size. Due to the usage of nano-ZrO2, the molten salt synthesis (MSS) temperature was decreased and possible impurity phases in the final product were suppressed. The synthesis temperature was lowered to 800 °C and soaking time of the optimal synthesis condition was reduced to 3 h. After washing with hot-distilled water, the n-ZrO2 sample heated at 800 °C for 3 h, was single phase CaZrO3 with 70–90 nm in particle size, while the m-ZrO2 sample heated at 1000 °C for 3 h, was single phase CaZrO3 with 250–400 nm in particle size. Based on the TEM observation and thermodynamic analysis, the synthesized CaZrO3 grains retained the morphology of the ZrO2 nanopowders, which indicated that a template formation mechanism plays a dominant role in synthesis process.