Phase Relations In Si-Al-O-C-N-RE(RE=Nd,Eu) System

Silicon carbide is one of the structural ceramics with excellent high-temperature properties, such as good high-temperature flexural strength, good creep resistance and good oxidation resistance. However, low diffusion coefficient at high temperatures in association with the strong covalence bond causes Si C ceramic hard to densify. Rare-earth oxides（RE₂O₃） are usually added to the Si C ceramics as sintering aids, among which Y₂O₃ is the most commonly used. The Si C compound, like Si O2, is acidic in chemistry while the light rare-earth oxides（such as Nd₂O₃, Eu₂O₃） are more alkaline than Y₂O₃. Therefore,reactions between Si C and the light rare-earth oxides at high temperatures will be favored,according to the acid-base reaction theory. The phenomanon, which Al N of R2 Al O3N is partilly occupied by Si C with the formation of R2Al（Si）O3N（C） solid solution, was only found in light rare earth Nd by the past work. For the research of adavanced Si C ceramic and perspective of providing more sintering aids of Si C-liquid-sintering, it is necessary to research the ternary phase relionships of Si C-Al₂O₃-Nd₂O₃, Si C-Al₂O₃-Eu₂O₃ and Si C-Al N-Eu₂O₃.Several samples of these phase relationship were designed and sintered in this paper.XRD, DSC methods were used to research three ternary phase relionships. Some experimental phase diagrams were achieved. Then Al₂O₃-Nd₂O₃ liquid sintering aids and Si C-Eu Al12O19 composite ceramic method were determined. The main content of this article is as follows:1、Phase relations in the Si C–Al₂O₃–Nd₂O₃ and Si C–Nd₂O₃–SiO₂ ternary systems and the Si C–Nd₂O₃–Al₂O₃–Si O₂ quaternary system were determined by systematically experimental research.2、Three compounds, Eu AlO₃ 、 Eu₄Al₂O₉ and Eu Al₁₂O₁₉ were emerged in Al₂O₃-Eu₂O₃ binary subsystem with the temperature increasing. +3 europium aluminate Eu Al O3 、 Eu4Al2O9 can be reduced +2 europium silicate by Si C in vacuum furnace.Eu Al O3、Eu4Al2O9 can be stable in flowing protective atmosphere, while Si C is completely oxidized to Si O2.3、Eu₂O₃ can be reduced by Si C, this caused Eu₂ Al O₃N phase changed into +2europium silicate in Al N-Eu₂O₃ binary subsystem. The transform temperature was decreased with addition of Si C or Al N. That is, it is hard to form Si C-Eu2 Al O3N tie lineand Eu2Al（Si）O3N（C） solid solution.4、Al₂O₃-Nd₂O₃ liquid sintering aid was used to sinter Si C by hot press method.When T=1850℃, Al₂O₃:Nd₂O₃=23:3（mol%） and the liquid aid contain is 10 wt%, the highest ralative density is 96.47%.5、Hot press method was used to sinter Si C-Eu Al₁₂O₁₉ composite ceramic. When T=1880℃, the Eu Al₁₂O₁₉ contain is 10wt%, the highest bending strength is 348.3_-13.47^+13.47MPa,fracture toughness is 2.2.9_-0.16^+0.12MPa. The highest electrical conductivity is2.664×10^-4s.cm^-1 when Eu Al₁₂O₁₉ contain is 15 wt%, and the highest relative density is 96.77% when 20 wt%.