Effect Of Precipitation/Filtration/Calcination Process Control On Particle Size Scale Of ZrO₂ Powder

ZrO2 has a widespread application prospect due to its excellent property of high temperature resistance,thermo stability,anti-corrosion,such as in military industry,nuclear energy,aerospace,chemical industry,environment etc.area.In this paper,the effect of production process control of ZrO2 applied at fluidized bed chlorination on powder particle size scale is studied.This paper is focused on mechanism of precipitation/filtration/calcination process control to produce the targeted powder size scale.It's paid high attention on parameters in continuous plug flow process of precipitation,such as raw material mol ratio,especially effect of sulfate/zirconyl and pH on crystallization process and calcination powder.Meantime,the deviation from normal mechanism of precipitation was revealed,the big issue or great impact of upstream zirconium slurry extra generated as crystal nuclear effect or particle generated due to zirconyl chloride with ammonia sulfate pre-mixing or high sulfate zirconium salt over growth,this resulted the barrier of zirconium slurry discharging from the kettle not synchronized as flow,so called "trapping&settlement and accumulation" effect.Oppositely,another type of deviation of "early-overflowing and delayed reaction" effect was also identified,this resulted subsequent growing of particle because sulfate zirconium salt was immatured in first precipitation kettle.The root cause has been analyzed and the tactics also developed to cover and ensure the homogenization of ZrO2 powder size scale.For filtration,the belt type membrane press filter is used for cake preparation,briefly discuss on effect of different parameters on moisture and residual salt content,such as SO42-,Cl-,NH4+(w/w%).The impurities of cake are ammonia chloride,ammonia sulfate,methyl-iso-butyl-ketone(MIBK),etc.The majority of impurities will be decomposed in calcinator,and a little residual after calcination will impact the particle size scale.The calcination process is also studied on cake processing in the horizontal calcinator by 1400-1600 `C natural gas generated hot gas,test the different temperature at hot end and cold end effect on powder characteristic measure.Actually it's suitable and simplified method to evaluate powder size scale by sieving way.Base on this measure,relevant process control is set up.Elsewise,the external factors is also investigated for effect on precipitation particle size scale,such as residule MIBK content,defect of original agitator blade type and orientation of rotating,mother liquid re-usage,dilution water,and temperature,slurry content of precipitation kettle,feeding flow which impact on duration time,the interval of re-start up.It's indicated that the primary particle size is determined by precipitation factors,as optimization,the most important is to control sulfate/zirconyl mol ratio within 2.5-2.9:5 range,the slurry content of precipitation is control at 17%-20%by ZrO2 content of ZrOCl2 at 110-140 g/L,agitation speed 50-52 r.p.m,and appropriate diluted water to adjust once the ZrO2 content of ZrOCl2 is too high and with higher flow.It's also important to set up stable thermal regulation to eliminate "sulfate circle forming" or over heating.Thus the ideal powder size scale is realized to meet chlorination requirements.