Study On The Preparation Of Nano-zirconia And Its Application In Nano-ceramics

Zirconia has excellent properties such as large thermal expansion coefficient,low thermal conductivity,strong oxidation resistance,high temperature resistance,and corrosion resistance,and is widely used in nano-ceramic materials.Zirconia has three structures:monoclinic crystal phase,tetragonal crystal phase,and cubic crystal phase.With temperature changes,a reversible phase transition process is formed between the three crystal phases.The phase transition is accompanied by large shear strain and volume change,which is also conducive to improving the strength and toughness of nano-zirconia ceramics.The preparation of nano zirconia ceramics mainly includes three parts:preparation of nano zirconia powder raw materials,press molding,and high temperature sintering.Among them,the preparation of raw materials is extremely important.Nano zirconia ceramics with excellent preparation properties require nano zirconia powder with small particle size,narrow distribution,good morphology and uniform distribution.In this paper,a liquid-phase precipitation method is used to prepare nano-zirconia powder with zirconium oxychloride,yttrium oxide,aluminum nitrate as raw materials,and sodium hydroxide as a precipitating agent.Committed to solving the problems of large particle size,serious agglomeration,and low purity of zirconia powder prepared in the traditional precipitation method.In this paper,the preparation of nanometer zirconia powder was firstly studied in a stirred reactor.The results showed that with the increase of sodium hydroxide concentration,Al³⁺content,and aging time,the particle size of zirconia powder showed a trend of first decreasing and then increasing.With the increase of p H value,the particle size of zirconia powder shows a trend of first increasing and then decreasing.With the increase of sodium hydroxide concentration and aging time,the particle size distribution first narrows and then widens.With the increase of Al³⁺content and p H value,the particle size distribution becomes wider and narrower.The suitable process conditions are:the concentration of reaction raw material zirconium oxychloride is 0.2mol/L,the addition amount of Y³⁺and Al³⁺is 3%of the mass of zirconium oxychloride,and the reaction raw material Na OH concentration is 0.4 mol/L.The amount of dispersant PEG400 is 2%of the mass of sodium hydroxide,the reaction temperature is 60°C,the end point of the reaction is p H=9,the aging time is 60min,the calcination temperature is 500°C,and the calcination time is 4 h.The powder prepared under optimal conditions has a particle size distribution between 14-34 nm,an average particle size of 23 nm,and a minimum of 14 nm.When using an impinging stream-rotating packed bed(IS-RPB)reactor to prepare nano-zirconia powder,the influence of different feed rates and rotation speeds on the particle size and morphology of the zirconia powder was investigated.The experiment found that with the increase of the feeding speed and rotation speed,the particle size of the nano-zirconia powder showed a decreasing trend.The optimal reaction conditions were the feeding speed of 60 L/h and the rotation speed of 1000 r/min.Compared with the nano zirconia powder prepared by the stirred reactor,the zirconia prepared by the IS-RPB reactor also exists in a tetragonal phase.However,the particle size of the zirconia nano-powder particles is smaller,the smallest is 8nm,and the particle size distribution is more uniform,in the range of 8-28nm,and there is no obvious agglomeration.It shows that the IS-RPB reactor has a better micro-mixing effect.When using the same quality raw materials,more small crystal nuclei can be formed,and the particle size of zirconia particles is smaller.In addition,the precursor of zirconia powder was measured by TG-DSC,and the activation energy Ea of the sample was calculated as 261.67 k J/mol.The zirconia nanopowder prepared by IS-RPB was used to prepare a simple nano zirconia ceramic,and compared with the nano zirconia ceramic prepared by the powder prepared by a stirred reactor.It was found that the nanometer zirconia ceramics prepared by using IS-RPB nanopowders had high volume density,high shrinkage,smaller porosity,and improved ceramic properties.At the same time,the effects of different polyvinyl alcohol concentration,molding pressure,sintering temperature,and alumina content on the relative density,shrinkage rate,porosity and other properties of nano-zirconia ceramics were investigated through experiments.It was found that as the concentration of polyvinyl alcohol increased,the volume density,porosity and shrinkage of the ceramic showed an overall increasing trend.With the increase of pressure and sintering temperature,the volume density and shrinkage rate of nano-zirconia ceramics increase,and the porosity decreases.