Research On Fabrication And Properties Of Al₂O₃-based Microwave Window Materials

With the rapid development of high power microwave technology,developing a ceramic microwave window,which is suitable for high power microwave materials,is a urgent issue of the moment.Al2O3 is the most widely used microwave window material due to the advantages of thermal shock,low dielectric loss,low cost and so on.Therefore,it's important to study Al2O3-based microwave ceramic.Alumina powders were prepared by sol-gel process.The sintering characteristics and dielectric properties of Al2O3 ceramics with Ca O-Si O2-Ti O2,Mg O-Cu O-Ti O2,Mg O-Cu OTi O2-Eu2O3 as doping agent were investigated.The crystal morphology and particle size of Al2O3 were studied by XRD,SEM and TEM and the dielectric properties were investigated by using network analyzer.The results show that the alumina xerogels are successfully prepared by sol-gel method with aluminium nitrate and citric acid as raw materials at p H=7 and Al2O3 powders with a diameter of 50~80 nm are obtained after calcining 2 h at 1000?.The sintering temperature of Al2O3 ceramic with Ca O as doping agent is decreased to 1450?,but the second phase(Ca Al12O19)has a negative effect on the Q·f values.When the sintering temperature is 1450? and the content of Ca O is 0.4 wt.%,the materials show superior properties: the relative density of the sample is 98.61%,?r=9.88,Q·f =21957 GHz,?f=-21.353 ppm/?.The addition of Mg O effectively increases Q·f value of Al2O3 ceramics and the ?f value of Al2O3 ceramics with Ti O2 as doping agent is increased to-15.635 ppm/?significantly.When the sintering temperature is 1500? for 4 h,the content of Mg O is 1.0wt.% and that of Ti O2 is 0.8 wt.%,the materials show superior properties: the relative density of the sample is 98.83%,?r=9.89,Q·f =38028 GHz.Eu2O3 makes the dielectric constant of Al2O3 ceramics more stable,and the dielectric constant is about 9.90 smoothly with the change of Eu2O3.When the sintering temperature is 1450? and the content of Eu2O3 is 0.25 wt.%,the materials show superior properties: the relative density is 98.21%,Q·f =37984 GHz,?f=-29.548 ppm/?.