Nanocrystalline zirconia（ZrO） was synthesized using a microwave-hydrothermal process.The effect of pH on the crystallization of the ZrO2 powders was investigated.The phase and microstructure of ZrO2 powders were exa...Nanocrystalline zirconia（ZrO） was synthesized using a microwave-hydrothermal process.The effect of pH on the crystallization of the ZrO2 powders was investigated.The phase and microstructure of ZrO2 powders were examined using X-ray diffraction（XRD）,Raman spectroscopy,and transmission electron microscopy（TEM）.Results show that pure m-ZrO2 can be obtained at low pH（pH＆lt;2）.Pure t-ZrO2 is formed at pH = 7 and 14.The size of the ZrO2 crystals is in the range of 8-26 nm and decreases with increasing pH.The formation of m-ZrO2 results from the precipitation of ZrO2 from solution.The t-ZrO2 is formed through the in-situ structural rearrangement of amorphous Zr（OH）xOy.The stabilization of t-ZrO2 is attributed to the small crystal size and the adsorption of hydroxy ions on the surfaces of the crystals.展开更多
Nanocrystalline zirconia powder with high surface area and high tetragonal phase percentage is prepared by the precipitation method using ammonium hydroxide as a precipitating agent. The pH of precipitation, preparati...Nanocrystalline zirconia powder with high surface area and high tetragonal phase percentage is prepared by the precipitation method using ammonium hydroxide as a precipitating agent. The pH of precipitation, preparation temperature and calcinations＇ temperature are optimized.Crystallite size, specific surface area, tetragonal phase percentage and the thermal stability of the prepared samples are identified by diferent characterization tools such as X-ray difraction（XRD）, thermo gravimetric analysis（TGA）, diferential scanning calorimetry（DSC）, BET surface area, scanning electron microscopy（SEM） and transmission electron microscopy（TEM）. The optimum preparation parameters for obtaining nanocrystalline zirconia with high percentage of tetragonal phase and high surface area are pH 9, preparation temperature of 80℃ and calcinations＇ temperature of 400℃. The sample prepared under optimized conditions showed a high specific surface area of 179.2 m2/g, high tetragonal phase percentage of 81% and high catalytic activity（60%） for synthesis of butyl acetate ester.展开更多
基金Funded by National Natural Science Foundation of China(No.51302160)Natural Science Foundation of Shaanxi Province(Nos.2014JQ6226 and 2014JQ6213)+1 种基金China Postdoctoral Science Foundation(No.2015M570808)the Doctoral Scientific Research Foundation of Shaanxi University of Science&Technology(No.BJ14-20)
文摘Nanocrystalline zirconia（ZrO） was synthesized using a microwave-hydrothermal process.The effect of pH on the crystallization of the ZrO2 powders was investigated.The phase and microstructure of ZrO2 powders were examined using X-ray diffraction（XRD）,Raman spectroscopy,and transmission electron microscopy（TEM）.Results show that pure m-ZrO2 can be obtained at low pH（pH＆lt;2）.Pure t-ZrO2 is formed at pH = 7 and 14.The size of the ZrO2 crystals is in the range of 8-26 nm and decreases with increasing pH.The formation of m-ZrO2 results from the precipitation of ZrO2 from solution.The t-ZrO2 is formed through the in-situ structural rearrangement of amorphous Zr（OH）xOy.The stabilization of t-ZrO2 is attributed to the small crystal size and the adsorption of hydroxy ions on the surfaces of the crystals.
文摘Nanocrystalline zirconia powder with high surface area and high tetragonal phase percentage is prepared by the precipitation method using ammonium hydroxide as a precipitating agent. The pH of precipitation, preparation temperature and calcinations＇ temperature are optimized.Crystallite size, specific surface area, tetragonal phase percentage and the thermal stability of the prepared samples are identified by diferent characterization tools such as X-ray difraction（XRD）, thermo gravimetric analysis（TGA）, diferential scanning calorimetry（DSC）, BET surface area, scanning electron microscopy（SEM） and transmission electron microscopy（TEM）. The optimum preparation parameters for obtaining nanocrystalline zirconia with high percentage of tetragonal phase and high surface area are pH 9, preparation temperature of 80℃ and calcinations＇ temperature of 400℃. The sample prepared under optimized conditions showed a high specific surface area of 179.2 m2/g, high tetragonal phase percentage of 81% and high catalytic activity（60%） for synthesis of butyl acetate ester.
