Study On The Preparation Process Of (ZrTiCoNiNb)O_x High-entropy Oxide By Microwave Heating

High-entropy ceramics,as a new type of structurally functional integrated material,have attracted widespread attention and exploration by scholars in the fields of thermoelectric materials,catalysts,electrode materials,thermal barrier coatings,wear and corrosion resistant coatings,etc.At present,the preparation process of high entropy ceramics has the disadvantages of complicated operation process,long process cycle time and high energy consumption.Microwave synthesis technology,as a new field-assisted heating method,is increasingly being applied in the field of material manufacturing.The method has the advantages of uniform thermal field,high efficiency and short process cycle,which helps to improve the deficiencies of existing methods for the preparation of high-entropy materials.In this paper,high-entropy oxide powders were synthesized from Zr O₂,Ti O₂,Co O,Ni O and Nb₂O₅by microwave heating in the temperature range of 700°C to900°C.The thermal field modulation mechanism was explored and the temperature field distribution was simulated by COMSOL software.The effects of sintering temperature and heating rate on the density of products during the microwave preparation of high-entropy oxide ceramics were also investigated.The results are as follows:（Zr Ti Co Ni Nb）O_xhigh-entropy oxide powder was successfully prepared by microwave synthesis technology.Stable high-entropy phases can be formed by microwave heating at a lower temperature（700°C）.The synthesis of high-entropy oxide powder by microwave is divided into four reaction stages,namely,thermal accumulation stage,local solid phase reaction stage,synchronous reaction stage and grain growth stage.According to the different loss capacity of the raw material medium,microwave and its reaction will have a sequential progression,guiding the reaction between raw materials from local to synchronous reaction.The thermal field modulation mechanism of microwave heating is explored to reduce the temperature gradient and improve the heating efficiency.The problem of uneven temperature field during microwave heating was effectively improved.The thermal field distribution of the sample in the microwave field is simulated by COMSOL Multiphysics 5.6,which more intuitively shows the effectiveness of the thermal field modulation mechanism.The higher temperature（1100°C）and suitable heating rate（15°C/min）help to increase the hardness of the product and reduce the thermal stress.When the temperature is 1100°C and the heating rate is 15°C/min,the hardness of the sample can be increased from 6.712 GPa to 7.165 GPa.The higher sintering temperature and heating rate help to improve the response of the elements in the product to the microwave and their own diffusion ability.However,the faster heating rate（20°C/min）can significantly increase the internal thermal stress of the product.The slower heating rate（10°C/min）is not enough to excite the ability of the group elements in the product to respond to the microwave electric field and the coupling ability to the microwave thermal field,which is not conducive to the densification of the material.And by comparing with the conventional sintering method,the mechanism of microwave thermal and non-thermal effects on ceramic performance enhancement is revealed.