Optimization Of Preparation Parameters Of Zirconia And Construction Of Y-TZP@CeO₂ Core-shell Structure

Objective:Zirconia has been widely used in stomatology and other fields.However,it has been found in long-term observation that water molecules can destroy zirconia-oxygen bonds in oral wet environment,leading to the transformation of tetragonal to monoclinic zirconia.This phenomenon is called low-temperature degradation,which results in the decrease of mechanical properties of zirconia bioceramics.Therefore,in the first part of this paper,the effects of experimental parameters(reaction time,reaction temperature,pH value,disodium ethylenediaminetetraacetate,glycerol,Ce⁴⁺doping amount)on the grain size and tetragonal ratio of zirconia were systematically studied.In the second part,cerium oxide?CeO₂?was coated with yttrium stabilized tetragonal zirconia?Y-TZP?to form Y-TZP@CeO₂ core-shell structure,so as to slow down the aging of zirconia at low-temperature.This study is expected to have provided reference to achieve ZrO₂ crystals with reduced low-temperature degradation.Methods:Zirconium nitrate,cerium nitrate and yttrium nitrate were used as raw materials.Ethylenediaminetetraacetic acid,ethylenediaminetetraacetic acid disodium salt and glycerol were used as additives.Ammonia was used as pH regulator.Zirconia and cerium oxide powders were prepared by hydrothermal method or hydrothermal complexation method,based on that Y-TZP@CeO₂ core-shell structure was constructed by blending method.X-ray diffraction was used to characterize the crystal phase purity and grain size.Metallographic microscope,scanning electron microscopy and energy dispersive spectrometer were used to characterize morphology and element distribution of the powders.In the first part,the effects of experimental parameters on the purity and grain size of Ce-TZP,and the effects of additives on the purity and grain size of Ce-TZP and TZP were studied.In the second part,the effects of additives on the purity and grain size of Y-TZP were studied to obtain the ideal Y-TZP as the core.The effects of pH and ultrasonic time on the structure of Y-TZP@CeO₂ core-shell were studied.Results:1.In the first part of the experiment,samples were pure tetragonal zirconia and a mixture of monoclinic zirconia and tetragonal zirconia,and the content of monoclinic zirconia was less than tetragonal zirconia.The grain size of each sample was different and less than 10 nm.2.The size of Y-TZP@CeO₂ core-shell structure is about 30-60 nm.Conclusions:1.The experimental conditions for the preparation of Ce-TZP with relatively ideal tetragonal ratio and grain size are as follows:hydrothermal reaction temperature was170°C,reaction time was 16 h,pH was 11,Ce⁴⁺doping amount was 12 mol%,molar ratio of Zr⁴⁺+Ce⁴⁺:ethylenediaminetetraacetic acid:glycerol was 1:0:0,and the influence of various factors was as follows:molar ratio of Zr⁴⁺+Ce⁴⁺:ethylenediaminetetraacetic acid:glycerol>temperature>time>Ce⁴⁺doping amount>pH.Ethylenediaminetetraacetic acid disodium salt can reduce the purity of tetragonal phase,particle size and grain size of Ce-TZP;Glycerol can reduce the particle size of Ce-TZP,but can not reduce the purity and grain size of Ce-TZP;Doping Ce⁴⁺can improve the purity of tetragonal zirconia,but can not reduce its grain size;Additives can not improve the distribution uniformity of Ce⁴⁺.Ethylenediaminetetraacetic acid can reduce the purity of tetragonal phase and grain size of zirconia;Glycerol can increase the tetragonal ratio and the grain size of zirconia.2.Additives can increase the grain size of Y-TZP,but can not improve the purity of tetragonal phase;Y-TZP@CeO₂ core-shell structure was synthesized by blending method.