Study On The Preparation Of Submicron Tetragonal Polycrystalline ZrO₂ By The Transformation Of Micro Monoclinic ZrO₂ Under High Pressure

The traditional preparation of polycrystalline bulk ceramic materials mostly rely on nanopowders as the starting materials which is consolidated into bulk form via sintering at high temperature.There exists the inevitable phenomena of agglomeration,adsorption and rapid growth of the nano-grains at high temperature,resulting in a challenge to obtain polycrystalline bulk ceramic materials with high density,excellent mechanical properties and fine grains.High-pressure phase transition is a method to fabricate nano or submicron polycrystalline bulk ceramic materials by the phase transformation under high pressure.Ceramic materials can undergo isomeric phase transition under suitable temperature and pressure conditions.The phase transformation is a process including the nucleation and the growth of crystal nucleus,and the interface of the new phase is cleaner.The diffusion mobility of the cations is suppressed and higher nucleation rate of the transformed phase under high pressure,the grain size of the new phase can be smaller than that of the starting powders.In the present work,the monoclinic ZrO₂ with the average grain size of 2?m was used as the starting material,and the monoclinic and submicron tetragonal composite polycrystalline ZrO₂ in bulk form was obtained under high pressure and high temperature.Research results indicate:1.The partial transition from monoclinic to tetragonal is realized under the condition of 5.5 GPa and 800¹700°C;2.The average grain size of tetragonal ZrO₂ fabricated under pressure of 5.5 GPa at 1200°C for 1h is?145±62?nm,the average grain size of tetragonal ZrO₂ fabricated under pressure of 5.5 GPa at 1400°C for 1h is?246±165?nm,the average grain size of tetragonal ZrO₂ fabricated under pressure of5.5 GPa at 1600°C for 30 min is?183±62?nm,and the average grain size of tetragonal ZrO₂ fabricated under pressure of 5.5 GPa at 1700°C for 20min is?245±107?nm;3.Because of the co-existence of the micro monoclinic ZrO₂ without phase transformation and submicron tetragonal ZrO₂ transformed under high pressure,the densification of the ZrO₂ bulk ceramics is not uniform.