Crystallization,thermal Expansion And Wetting Behavior Of Nd₂O₃-Al₂O₃-SiO₂ Glass Ceramic

Glass ceramic materials have good chemical compatibility with ceramic materials,excellent high temperature resistance and oxidation resistance.They are often used as solder to join ceramic materials.However,from the point of view of matching the thermal expansion coefficient of base metal and solder,it is necessary to choose glass solder of different systems to join different ceramic materials.In this paper,the thermal expansion coefficient of glass ceramics is adjusted by controlling the type and content of precipitates in glass ceramics,so that it can meet the joint requirements of a variety of ceramics.In view of the excellent mechanical properties and high temperature resistance of rare earth glass,this paper takes Nd₂O₃-Al₂O₃-Si O₂（NAS）glass as the basic glass system,adds Ti O₂ as nucleating agent to promote its crystallization,and adds Li₂O to change the type of crystallization phase.The effects of the content of Ti O₂ and Li₂O on the crystallization behavior,microstructure and phase composition,thermal expansion coefficient,softening temperature and wetting behavior of NAS glass ceramics were deeply studied.The crystallization behavior,microstructure,crystalline phases,microhardness,coefficient of thermal expansion（CTE）,and wetting behavior of Nd₂O₃-Al₂O₃-Si O₂（NAS）glass ceramics with different Ti O₂ content were investigated.The results show that the content of crystals increases and the size of crystals decreases with the increase of Ti O₂content.Moreover,the formation of Nd₂Si O₅ leads to the increase and the precipitation of Al₆Si₂O₁₃ results in the decrease in the CTE value of NAS glass ceramics.As a result,the CTE of NAS glass ceramics can be controlled in the range of 4.2-9.2×10^-6/℃.These values are suitable for matching bonding to most ceramics with different CTE.Indeed,contact angle measurement demonstrates that the NAS glasses with 3%,6%and 9%Ti O₂ possess excellent wettability on the Al₂O₃,Zr O₂ and zirconia toughened alumina（ZTA）ceramic,respectively.However,the coefficient of thermal expansion of NAS glass ceramics is still too large for ceramics with low coefficient of expansion such as Si C and Si₃N₄.The crystallization behavior,microstructure,crystalline phases,microhardness,coefficient of thermal expansion（CTE）,and wetting behavior of Nd₂O₃-Al₂O₃-Si O₂（NAS）glass ceramics with different Li₂O content were investigated.The results show that Nd₂O₃-Al₂O₃-Si O₂（NAS）glass-ceramics with Li₂O will form Nd₂Si O₅ and Li Al Si₂O₆ crystals after crystallization and the content of Li Al Si₂O₆ increases with the increase of Li₂O.Moreover,the formation of Li Al Si₂O₆ results in the decrease in the CTE value of NAS glass ceramics.As a result,the CTE of NAS glass ceramics can be controlled in the range of 2.9-7.1×10^-6/℃.Indeed,contact angle measurement demonstrates that the NAS glasses with 4%and 6%Li₂O possess excellent wettability on the Si C and Si₃N₄ ceramic,respectively.