Research On The Preparation And Performances Of 0.9Al₂O₃-0.1TiO₂ Microwave Dielectric Ceramics Via Novel Direct Coagulation Casting

Low-permittivity microwave dielectric ceramic,which can reduce the delay problem of signal,is widely used in military,satellite communications and other fields.However,the dry pressing-degreasing-sintering-machining process used generally is complex with a long cycle,through which only simple shape device can be compared,and the processing cost accounts for more than 70%of the total cost due to the characteristics of hard and brittle of ceramics.Direct coagulation casting can not only in-situ solidificate complex shape ceramic green bodies with homogeneous microstructure but avoid binder removal process,simplifing the process.Thus the DCC process has great potential for the application of forming microwave dielectric ceramics.Based on the situation above,0.9Al₂O₃-0.1TiO₂ was selected as the research object in this paper and High valence counter ion forming?DCC-HVCI?and Dispersant reaction method?DCC-DRM?were applied to its forming.Then the microstructure,phase composition and microwave dielectric properties were systematically studied by means of field emission scanning electron microscopy?SEM?,X-ray analysis?XRD?and network analyzer.The results are summarized as follows:?1?On the aspect of molding 0.9Al₂O₃-0.1TiO₂ ceramic in DCC-HVCI:0.3 wt%Ammonium citrate was used as dispersant,and stable suspensions with solid loadings of more than 50 vol%and viscosity of less than 1 Pa·s were prepared.The DCC-HVCI forming of 0.9Al₂O₃-0.1TiO₂ suspension was realized by temperature controlled release of Ca²⁺from calcium iodate.When the addition amount of calcium iodate was 8 g/L,green bodies with complete shape and smooth surface were obtained after taking a 70?water bath for 1 h.After sintering at 1500?for 4 h,0.9Al₂O₃-0.1TiO₂ ceramics of 3.62±0.02g/cm³ in density were obtained.After annealing,the Al₂TiO₅ phase is completely eliminated and the ceramics exhibits the microwave dielectric properties with?_r=11.26±0.06,Q×f=11569±629 GHz,?_f=-33.60±0.20 ppm/?.The propreties were lower than that of dry pressing after annealing:?2?On the aspect of molding 0.9Al₂O₃-0.1TiO₂ ceramic in DCC-DRM:0.5 wt%Tetramethylammonium hydroxide?TMAOH?was used as dispersant to prepare stable suspensions with solid loadings of up to 60 vol%and viscosity of less than 1 Pa·s.In-situ solidification of 0.9Al₂O₃-0.1TiO₂ suspensions were achieved when 2 vol%Glycerol diacetate was added and a 60?water bath were taken for 1 h,Green samples with smooth surface were obtained with no pores and cracks.The best microwave dielectric properties were gained after samples of 60 vol%in solid loading were sintered at 1550?:?_r=10.70±0.04,Q×f=27640±446 GHz,?_f=-19.33±0.05 ppm/?.The performance were better than that of dry pressing after annealing and the quality factor was improved by around 24%than that of annealed dry pressing samples,and approximately 36%decreased of the temperature coefficient.