Effect Of Ultrasonic Oscillation On The Properties Of Nano-zirconia Ceramics

Zirconic ceramics have been used in dental clinic for decades,for its' high strength,high toughness and excellent aesthetic effect,it's popular between clinicians and patients.Zirconic's indications cover the single crown,the combined crowns,the fixed partial denture and the upper structures of the implant denture.But at present,there are some failures limit the application of zirconia,like fractures of crowns and breaks of pontics.These failures are mainly due to the features of high hardness and brittleness.After toughening and modification the zirconia ceramics to a certain extent,more peoples have turned the attention to the material's processing technology,hoping to improve the material's performance by improving the processing technology.In order to make zirconia have excellent physical and chemical properties,how to improve the density and uniformity of powders is the key point.In the past years,more researchers improved the properties of materials by sintering process,and neglected the preparation of powders and molding process.In our study,ultrasonic was used to improve the properties of materials in the stage preparation of powders and molding process,we discussed the mechanism of ultrasonic in preparation of nano-zirconia powder,and confirmed the technological parameters of ultrasonic oscillation.The results of our study are as follows:1.The preparation of nano-zirconia powders by ultrasonic assisted chemical precipitation has a good effect.And the anti-agglomeration effect of ultrasonic oscillation has been confirmed.The results of XRD and SEM showed that the product of our study is a spherical nano-zirconia precursor whose particle size up to 12 nm,the stable tetragonal nanometer zirconia can be obtained after sintering.2.The density and uniformity of the zirconia can be effectively improved by applying ultrasonic oscillation before pressing,and the physical properties of the material can be improved obviously.Under the condition of constant time,when the ultrasonic oscillation of zirconia powder with moderate vibration,the flexural strength,hardness and fracture toughness of the zirconia can be improved.3.The mechanical properties of zirconia prepared under ultrasonic oscillation are better than those of non-oscillating group.The SEM results show that the zirconia crystal size of the oscillating group is small and the grain distribution is uniform and compact.The mechanical properties of zirconia added with 3%mol yttrium oxide are superior to those of 5%mol yttrium oxide group.Zirconia crystal phase in 3%mol yttrium oxide group consists of tetragonal phase and a small amount of monoclinic phase,5mol yttrium oxide stabilized zirconia contains tetragonal phase,monoclinic phase and cubic phase.Compared with the non-oscillating group,the surface roughness of the zirconia prepared under ultrasonic vibration is lower and more compact,however the difficulty of grinding and bonding is increased too.4.There was a positive correlation between the two group in the m phase precipitation and the LDT time,but it was no significant difference between the two groups in the early aging period,and the m phase precipitation in the experimental group was lower than that in the control group at the later stage.Zirconia ceramics prepared under ultrasonic oscillation condition can delay the aging process to some extent,but can not prevent its' occurrence.