Preparation And Properties Of Transparent And Microwaves Ceramics With Low Dielectric Constant

As a transparent polycrystalline ceramics, spinel ceramics have a seriesof excellent properties, such as favourable chemical stability, excellentmechanical property, good thermal shock resistance and high thermalexpansion coefficient and high transmittance from ultraviolet to infraredlight.The spinel-based MAl2O4(M=Zn or Mg) transparent ceramics wereselected as the research objects. Using the high-temperature calcinationsmethod, the nano-sized powder of MAl2O4were synthesized by using highpurity primary salts (NH4Al(SO4)2·12H2O and MgSO4·7H2O orZnSO4·7H2O with a molar ratio of2:1) as the raw materials. The resultsshowed that spinel powders with an average grain size of20nm and haveglobular and vermicular shape.The optical process to fabricate the MgAl2O4transparent ceramics byspark plasma sintering (SPS) was explored. The effects of sintering processeson the the morphology, microstructure and components were studied byX-ray diffraction (XRD), scanning electron microscope (SEM), transmissionelectron microscope (TEM). The optical properties and resistance to erosionability of MgAl2O4transparent ceramics were analyzed by double-beamspectrophotometer (UV-Vis), FTIR/Raman spectrometer (FT-IR) and SEM.The results indicated that MgAl2O4transparent ceramics had the high in–line transmission in infrared wavelength. The Tin,2000was above80%andthe highest value of Tin,550was66.6%. MgAl2O4transparent ceramics had abad corrosion resistance in85%H3PO4solution at180℃even for20seconds while it was good for the molten NaOH at340℃. MgAl2O4transparent ceramics had a good hot-corrosion resistance below1200℃. The orthogonal experiment method was applied to study the effects ofSPS parameters including Zn additive amount, sintering temperature andholding time on the optical properties of Zn:MgAl2O4transparent ceramics.And the optimal process parameters of SPS were as follows:1.5at%Znadditive amount, sintered at1325℃for10min. The in-line transmission atthe wavelength of550nm and2000nm can be reached61.8%and80%,respectively. The most significant factors on in-line transmission wassintering temperature, and the second was doping concentration and holdingtime.In the last, ZnAl2O4transparent ceramics with the high transparencywere prepared by SPS. The influence of tetraethyl orthosilicate (TEOS) assintering aids on the in-line transmission of ZnAl2O4transparent ceramicswere studied. The results showed that Tin,550of ZnAl2O4transparent ceramicswas improved about26.4%and reached63.5%, Tin,2000was84.7%by using0.5wt%TEOS as sintering aids.