Solid Solution And Phase Relations In SiC-Al₂O₃/AlN-Pr₂O₃ System

SiC is widely used because of its good comprehensive performance.However,SiC is hardly to densification without suitable sintering aids owing to its low diffusion coefficient,so selections of the additives is very critical.At present,there are many researches on SiC-Al₂O₃-RE₂O₃（Rare Earth Oxide,RE: Nd,Gd,Yb,Y）systems,both of Pr₂O₃ and Nd₂O₃ are light rare earth oxides,and Pr₂O₃ not only has a high surface activity but also can prevent grain growth,while its reasearches related is little reported.Besides,R₂Al（Si）O₃N（C）solid solution is detected in SiC-AlN-Nd₂O₃ system,whether a similar solid solution can be formed is unclear,and the performance of SiC ceramics basing on the two phase relations investigated deserves exploring.Commercial praseodymium oxide usually is Pr₆O₁₁,whose lattice oxygen can oxidate SiC when temperature raising.So it is essential to transform Pr₆O₁₁ into Pr₂O₃ before experiment.The present work firstly investigated the feasible methods of preparation and storage of Pr₂O₃ with the existing experiment condition.The ternary phase relations of the above systems were investigated by XRD phase analyses.The solid-state reacted samples were propared by using SiC,Al₂O₃,Pr₂O₃ and AlN powders as starting materials.Liquid phase sintering of SiC ceramics with Al₂O₃/AlN-Pr₂O₃ additives and the preparation of their composite ceramics was proposed respectively.Main contents of present work are as follows:（1）Pure Pr₂O₃ can be prepared in muffle furnace with continuous flowing Ar at1200℃ for 2h,while calcination without protecting atmosphere can only produce Pr₆O₁₁.Deterioration of Pr₂O₃ can be prevented effectively by sealing the powder with sample sack and storing in a dryer.（2）Existence of PrAlO₃（PrAP）and Pr_0.833Al_11.833O₁₉（β（Pr））were verified,and both of them are compatible with SiC,while the controversial Pr4Al2O9（PrAM）is never detected.Accordingly,phase relations in Al₂O₃-SiC-Pr₂O₃ ternary system were eatablished.Finally,SiC-Al₂O₃-Pr₂O₃-SiO₂ quaternary system were also proposed owing to presence of the SiO₂ impurity in the SiC powder.（3）Existence of Pr2AlO₃N（1:1 compound）was verified,and formation of Pr2Al（Si）O₃N（C）solid solution was discovered due to Al-N in the Pr2AlO₃ N were partly substituted by Si-C,and its solid solubility and general formula was determined.Biesides,phase relations in SiC-AlN-Pr₂O₃ ternary system were established according to the coexistence of SiC,Pr₂O₃,AlN and 1:1ss.Finally,subsolidus phase diagrams in SiC-AlN-Pr₂O₃-Al₂O₃ quaternary system were established,considering the possible influence of Al₂O₃ impurity on the original system.（4）The influence of Al₂O₃-Pr₂O₃ and AlN-Pr₂O₃ sintering additives on the densification and performance of SiC ceramics were investigated separately,basing on the two phase relations above.