Effects Of Rare Earth Fluorides/Oxide Additives On The Thermal Conductivity Of Silicon Carbide Ceramic

Various industrial applications of SiC ceramics such as substrate materials for semiconductor devices,take advantage of its excellent thermal conductivity and thermal stability,also similar thermal expansion coefficient with Si.In this study,?-SiC is investigated as research materials,aiming at the problem of its hardly densely sintering,according to the method of liquid phase sintering with rare earth oxides,a system of rare earth fluoride/oxide was selected as sintering aids,using method of hot press sintering to fabricate SiC ceramics with different ratios and kinds of rare earth fluoride/oxide sintering additives,and density,thermal property,phase composition and microstructure of the samples were characterized.Getting the formula with best property from the comparisons of the samples'composition,property and microstructure,so as to achieve the aim of densely sintering SiC ceramic and improving its thermal property.Firstly,yttrium fluoride and oxide were chosen as sintering additives to study their effects on the properties of SiC ceramic.By studying the effects of the content of YF₃,the varieties and content of oxides on the properties of the samples,we can get that,in the system of yttrium fluoride and oxide sintering additives we studied,SiC ceramic doped with 5 wt%YF₃ and 3 wt%MgO shows the best properties.The patterns of XRD and SEM show that oxygen amount in SiC grains can be reduce by doping with moderate amounts of YF₃,the high density of sample was attributed to more liquid phase,the liquid phase can be obtained to promote the re-arrangement and of the grains by doping with moderate amounts of oxide,the improvement of thermal conductivity was attributed to more densification and less liquid phase.In this study,lanthanum fluoride and oxide were chosen as sintering additives to study their effects on the properties of SiC ceramic.the results show that,density and thermal conductivity of SiC ceramics can be improved by doping with lanthanum fluoride and oxide as sintering additives,in this system,SiC ceramic doped with 5 wt%LaF₃ and 3wt%MgO shows the best properties.From the view of improving density of SiC ceramic,both of system of yttrium fluoride/oxide and system of lanthanum fluoride/oxide contributes equally.But from the view of improving thermal conductivity of SiC ceramic,system of yttrium fluoride/oxide performs better.Finally,the sample which was hot pressed at 1900°C for 3 h under a pressure of 50MPa in nitrogen atmosphere achieves the best properties as following,the density is98.93%,the thermal diffusivity is 71.40 mm²/s,the thermal conductivity is 154.29W/?m·K?.