Researches On The Microwave Dielectric Properties And Breakdown Strength Of Alumina Ceramics

Al₂O₃-based ceramics were chosen as the research objective in this article,and its microwave dielectric properties and the breakdown strength were adjusted by adding CaO-SiO₂-MgO,ZrO₂ and other sintering aids.Meanwhile,the effect of cold isostatic pressing on density,pressure resistance and microwave properties of ceramics were studied.By adjusting the ratio of the oxide content in CaO-SiO₂-MgO,the sintering characteristics and electrical properties of alumina ceramics were studied.The study found that when SiO₂/CaO=1.8,MgO content is 20wt%in CaO-SiO₂-MgO,a ceramic with good microwave dielectric properties and breakdown strength properties sintered at 1550?can be obtained:Eb=48.24kV/mm?1mm??20kV/mm?3mm?,relative density 95.62%,?_r=9.23,Q×f=17580?The incorporation of ZrO₂ can reduce the grain size of ceramics and significantly improve the relative density of samples.The samples doped with ZrO₂ can obtain higher breakdown strength properties sintered at 1500?and 1550?,and can increase the dielectric constant slightly,but the microwave properties are poor.When the doping amount of ZrO₂ is 3wt%,a ceramic with higher relative density,breakdown strength properties can be obtained by sintering at 1550?:Eb=42.52 kV/mm?1mm??20 kV/mm?3mm?,relativedensity98.57%,?_r=10.22,Q×f=12023 GHz?When we fixed the doping amount of ZrO₂ is 3wt%and the doping amount of MgO is 1wt%,it is found that the ceramic can obtain higher relative density and compressive breakdown strength under the addition of 0.5wt%CaO-SiO₂,and the quality factor of ceramics is increased remarkably,Q×f increased to 40977.Then we choose the best formula for cold isostatic pressing.It is found that the pressure and the holding time have little effect on the performance of the samples,but the properties of the samples are slightly decreased after the isostatic pressing.After cold isostatic pressing,the glue discharging process has a great influence on the final performance.When the samples were discharged in air and the heating rate is 0.5/min,the best breakdown strength properties can be obtained:Eb=38.38 kV/mm?1mm??19.23 kV/mm?3mm?.When the samples were discharged in oxygen,the heating rate had little effect,and the best breakdown strength properties can be obtained when the heating rate is 0.5/min:Eb=41.63 kV/mm?1mm??20 kV/mm?3mm?.