Preparation Of Yttria Stabilized Zirconia Ultra-fine Powder In Submerged Circulative Impinging Stream Reactor

Zirconium dioxide contains of monoclinal zirconium dioxide（m-Zr O2）, tetragonal zirconium dioxide（t-ZrO₂） and cubic zirconium dioxide（c-ZrO₂）, which can be transformed into each other. The pure zirconium dioxide products easily to crack and even to fragment in cooling process from high temperature to room temperature because of inevitable phase transformation. Adding a certain amount of stabilizer in zirconium dioxide, such as Y₂O₃, CeO₂, CaO, MgO, BaO and Al₂O₃, to restrict the phase transition which can cause volume changes in the sintering process is an effective method to obtain stabilized zirconium dioxide or partially stabilized zirconium dioxide. Currently, the Yttrium stabilized zirconium dioxide（YSZ） is one of the most widely investigated ceramic materials which is extensivly used in oxygen sensors and solid oxide fuel cells（SOFC） because of its excellent properties. The zirconium dioxide powder with the properties of small particle, narrow size distribution and excellent surface morphology is essential to obtain stable performance and compact zirconium dioxide ceramic body. The impinging stream reactor with a significant enhancement of phase transfer and micro-mixing characteristics, which can provide high and uniform super saturation, and have an advantage in preparation of inorganic nanometer or submicron materials.The 5% yttrium stabilized zirconium dioxide was synthesized by impinging stream reaction-precipitation method, and ZrOCl2?8H2O as Zr source, Y（NO3）3?6H2O as yttrium source, PEG4000 as dispersing agent and ammonium bicarbonate as precipitant in this paper. The yttrium stabilized zirconium dioxide ultrafine powder was prepared by filtering, washing, drying, grinding and sintering processes. The influence of PEG4000 addition, propeller speed, zirconium ion concentration, reaction time, roasting temperature and roasting time on the particle size of yttrium stabilized zirconium dioxide ultrafine powder was investigated by orthogonal and single factor experiments. The particle size and morphology of yttrium stabilized zirconium dioxide ultrafine powder were investigated by laser particle size analyzer（WJL）, scanning electron microscopy（SEM）, X-ray diffraction（XRD）, respectively. The optimal process conditions of preparing yttrium stabilized zirconium dioxide ultrafine powder were acquired as follow: PEG4000 addition is 1.4 g/L, propeller speed is 900 r/min, zirconium ion concentration is 0.08 mol/L, reaction time is 70 min, roasting temperature is 800℃, roasting time is 2 h, and the particle size of yttrium stabilized zirconium dioxide ultrafine powders is 0.5 μm.The kinetics of thermal decomposition of 5% yttrium stabilized zirconium dioxide precursor were studied and the apparent activation energy was calculated by combining thermo-gravimetric analysis（TG） and differential scanning calorimetry（DSC） analyzing with model free methods proposed by Kissinger method, Kissinger-Akahira-Sunose（KAS） and Flynn-Wall-Ozawa（FWO） method. The research results show that there are three weight losses occurs in the thermal decomposition process. The first weight loss stage proceeds in a range from approximately 30 to 216℃ ℃for low heating rate and 230 for high heating rate. ℃The location of maximum endothermic peak is 119 as showed in the DSC curves ℃and the weight loss rate is about 16.61% due to lost absorbed water and crystallization water. The second weight loss stage occurrs in a range from approximately 221 to ℃355 for low heating rate and 416℃ ℃for high heating rate. The location of maximum exothermic peak is 290 ℃as showed in the DSC curves and the weight loss rate is 4.73% due to the residual organic matter polyethylene glycol decomposition. The third weight loss stage proceeds in a range from approximately 408 to 521℃ for ℃low heating rate and 534 ℃for high heating rate. The location of maximum exothermic peak is 477 ℃as showed in the DSC curves and the weight loss rate is 65.33% due to zirconium carbonate and yttrium carbonate decompose to zirconium oxide and yttrium oxide respectively, and carbon dioxide releasing at the same time. The amorphous crystallization phenomenon occurs and stable zirconium dioxide with cubic phase structure is also obtained in this stage. The apparent activation energy was calculated by Kissinger method, KAS method and FWO method. The apparent activation energy values in first weight loss stage are 63.33 kJ/mol, 63.71 kJ/mol and 60.65 kJ/mol, respectively. The apparent activation energy values in the second stage are 97.12 kJ/mol, 95.65 kJ/mol and 91.32 kJ/mol, respectively. And the apparent activation energy values in the third stage are 237.87 kJ/mol, 215.53 kJ/mol and 215.63 kJ/mol, respectively. The values of apparent activation energy obtained from Kissinger method are consistent with the range of average values obtained by the FWO method and the KAS method.