Study Of The Microstructure And Defects Of MgO/ZrO₂ Nanocrystals

Nano MgO and ZrO2 have been widely investigated because of their excellent performances,such as mechanical property,corrosion resistance,oxidizing and so on.Comparing with traditional bulk materials,volume fraction of grain boundaries in nano-ceramics is meaningful and thus open volume defects in grain boundaries play an important role.Because the grain boundaries could absorb defects,they were used in nuclear reactors.However,ZrO2 exhibited a high thermal stability and good mechanical properties,but low thermal conductivity;while MgO had high thermal and electronic conductivity,but pure MgO was easy to hydrolysis reaction,which would cause nuclear reactor breaking down.Therefore,it is important to develop MgO/ZrO2 composite nano-ceramics having better potential properties,such as high thermal conductivity and stability.Detailed investigation of microstructure and defects is a great importance for understanding the physical properties of these nano-ceramics as well as for their impact of application in industries.Pure MgO,ZrO2 and mixture MgO/ZrO2 nanocrystals were annealed in air from 100 to 1200?.Variation of the microstructure and defects was investigated by positron lifetime spectroscopy,X-ray diffraction and transmission electron microscope.The experiment results showed that there are not found phase transition and new phase in MgO/ZrO2.The average positron lifetime(i.e.total defect density)of mixture MgO/ZrO2 was larger than that of single phase MgO and ZrO2,and decreased with increasing annealing temperature.Thermal annealing below 600?,the movement of grain boundaries mainly led a reduce of the number of microvoids,and vacancy defects began to recover due to the growth of MgO nanoparticles after annealing between 600 to 900 ?.Furthermore,ZrO2 nanoparticles began to grow above 900?,meanwhile the recovery of vacancy and vacancy clusters in MgO/ZrO2 nanoparticles are restrained because of synergic effect between MgO and ZrO2 nanoparticles.