Preparation And Properties Of Silicon Carbide Ceramics With Small Dielectric Constant And Small Thermal Expansion Coefficient

In this paper,the effects of different proportioning of YOCl,NdOCl and YbOCl with MgO,CaO and Al2O3 on the properties of SiC Composite ceramics were prepared by the method of pressure-free liquid phase sintering,in order to prepare SiC composite ceramic materials with small thermal expansion coefficients of small permittivity.It is found that the compound doping of rare earth chloride oxides and metal oxides has a certain effect on the properties of SiC,and it is found that the grain structure of all the samples is even more uniform when we study the influence of different ratios of YOCl-MgO-Al₂O₃ and NdOCl-MgO-Al₂O₃ composite SiC ceramics.The grains are smaller and the compactness is similar.However,the results of contrast phase analysis showed that the samples doped with YOCl formed the second phase after sintering at high temperature,such as MgSiO₃,YAlO₃,SiO2,C and Y4Al2O9.It is indicated that the YOCl-MgO-Al2O3 of SiC and sintering additive in sintering process produces liquid phase at high temperature,and some reactions occur,and some compounds are substituted for Cl element and O element,in addition,the YOCl-MgO-Al₂O₃ system at room temperature and frequency conversion?10²Hz¹0⁶Hz?,the Dielectric property is better,wherein the ratio of YOCl:MgO=6:3 specimen is lower than the relative dielectric constant?_r=0.5096 The frequency is 10⁶Hz.The second phase of NdOCl-MgO-Al₂O₃system sample is mostly silicate,such as MgSiO₃,Mg₂SiO₄,15R-SiC and C.The compactness is relatively YOCl-MgO-Al2O3,but the dielectric property is poor under the condition of room temperature and frequency conversion?10²Hz¹0⁶Hz?,the relative dielectric constant?_r between 169¹7072.In the process of preparing SiC composite ceramic materials with CaO as metal oxide sintering auxiliaries doped with different ratios of ReOCl?Y,Yb?,it was found that the grain size distribution of each sample was uniform and probably distributed between 2⁶?m.The phase analysis of YOCl-CaO system specimen shows that the main crystal phase of each sample is 6H-SiC,and the second phase is in addition to Y₂O₃,SiO₂ phase,and some yttrium compounds such as YC₂,Ca₂SiO₃Cl₂ and YSi are produced,It is indicated that the replacement and reduction reaction of YOCl-CaO with SiC and carbon heating elements under high temperature conditions.In addition,the dielectric property of YOCl-CaO system specimen is better under the condition of room temperature and frequency conversion?10²Hz¹0⁶Hz?,the relative dielectric constant?_r between 50.48²21.71.It is found that the thermal expansion coefficient of the YOCl:CaO=4:5 specimen is close to the thermal expansion coefficient of pure SiC prepared by atmospheric sintering,while the thermal expansion coefficient of the other samples is relatively small,and the thermal expansion coefficient of the-150?⁵00?is close to that of the monocrystalline silicon.The results of the YbOCl-CaO system sintering showed that the second phase had SiO2 and YbCl2,except the main crystal phase 6H-SiC,and no crystallization phase of complex compounds was found.In addition,under the condition of room temperature and frequency conversion?10²Hz¹0⁶Hz?,the dielectric constant of YbOCl-CaO system is larger.The coefficient of thermal expansion is close to that of pure SiC in-150?⁵00?.