| Zirconium oxide is one of the most important structural and functional materials,which has the excellent chemical and physical properties including the high meltingpoint, high boiling point, low thermal conductivity coefficient, large thermalexpansion coefficient, high temperature resistance, good abrasion resistance andexcellent corrosion resistance. The preparation of the nano-ceramics consists of threeprocedures: powders, molding and sintering. The good performance of ZrO2powdersis the key to the preparation of high quality zirconia ceramic materials. Therefore, inthis paper, how to prepare the high purity and ultrafine nano ZrO2powder and toexplore its formation mechanism are the key problems.In this paper, according to the amount of literature reading and exploratoryexperiments, the microwave pyrolysis of nano ZrO2powder is one simple methodthat need the few time, save energy and protect the environment. The nano ZrO2powder is obtained by the regular resistance furnace sintering and microwavepyrolysis of the precursor. The preparation of the precursor is used the oxygenzirconium chloride and ammonia water as the main raw material, yttrium nitrate asstabilizer and obtained by the solution co-precipitation method and the cross spraymethod, respectively. In this paper, the process parameters including the calcinationmethod, reaction temperature, solvent and input power are investigated to study theinfluence on the nano-ZrO2powder morphology. Meanwhile, the mechanism of thecross spray reaction and microwave pyrolysis is also analyzed. The main results arethe following:The results show that the size of ZrO2particles, obtained by the conventionalresistance furnace sintering the precursor which obtained by co-precipitation method,is larger than60nm and the size distribution is not uniform. In addition, theas-prepared particles appear the serious agglomeration phenomenon. When thetemperature is above600oC, there are some abnormal particles grew up.Comparing to the traditional resistance furnace sintering, the highly dispersed nano zirconia powder can be obtained by the co-precipitation-microwave pyrolysismethod at750oC for20min. The size of the as-prepared powder is smaller than40nmand the size distribution is uniform. Besides, there are only a few hard agglomerationsand a part of the soft agglomeration which lead to the reduction of the reunionphenomenon in a certain degree. Then, the powders that are pure, well-crystallized,uniformly size distributive is also obtained by the cross spray-microwave pyrolysismethod at750℃in a relatively short time. Therefore, the cross spray-microwavepyrolysis is superior to the co-precipitation-microwave pyrolysis to prepare the highpure and ultra-dispersed powder.The mechanism between materials and microwave was investigated, using the3Y-ZrO2as the research object. The results show that during the process ofmicrowave heating, the microwave can limit the crystal formation of the tetragonalZrO2and tend to the forming of the monoclinic phase, presenting the namely“induced transformation effect” of microwave sintering. Meanwhile, the crystals aregrowing larger after the heat treatment by the conventional method. But in thesecond heat treatment of the microwave, the size of powder particles does notincrease but decrease which indicates that in a critical nano-scale. The constanttemperature that is supported by the microwave makes particles perfect and rapidcrystallized which scatter the agglomeration, make powders dispersed better and thesize of particles uniformly distributed. The loss of microwave absorbing is below theheat diffusion of the surface of the particles. Then we present the “limited growtheffect” of the nano particles in the microwave field. |
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