Study On Preparation Of Low Thermal Expansion And High Strength Glass-Ceramics Of The Li₂O-MgO-Al₂O₃-SiO₂ System By Sintering Method

Li2O-MgO-Al2O3-SiO2(LMAS)system glass-ceramics has been prepared by sintering method,using chemically pure Li2CO3,MgO,Al2O3,SiO2 as main raw materials,adding Ti02,Zr02,P2O5 as nucleating agents.The effect of glass composition,heat treatment schedule,nucleating agents on the phase composition,microstructure and properties of LMAS system glass-ceramics has been investigated by DTA,XRD,SEM and orthogonal test.Reasonable composition of glass ceramics,the amount of nucleating agents and heat treatment schedule have been confirmed.Based on above researchs,the effect of fluorides on the microstructure and properties of glass-ceramics has been further studied,low expansion glass-ceramics with relatively high mechanical properties has been prepared.The results show that there is granular and acicular ?-spodumene solid solution on glass-ceramics when the molar ratio of SiO2/Al2O3 is 9.5:1.The thermal expansion coefficient is 1.32×10-6/? and the flexural strength is 75.84MPa.When the molar ratio of Li2O/MgO is 0.53:1,glass-ceramics precipitate lots of granular and fibrous ?-spodumene solid solution.The thermal expansion coefficient and the flexural strength are 1.12×10-6/?and 85.15MPa.The heat treatment system has been optimized.The optimal heat treatment is as follows:the nucleation at 700? for 0.5h,the crystallization at 810? for 1.5h respectively.At this time,the thermal expansion coefficient and the flexural strength of glass-ceramics are 0.54×10-6/? and 104.41MPa.The main crystal phase of glass-ceramics without nucleating agents is?-quartz solid solution.The kinds of nucleating agents(TiO2,ZrO2,P2O5)have effects on the main crystal phase and crystal morphology of glass-ceramics.Composite nucleating agents(3wt%TiO2?3wt%Zr02+1wt%P2O5)could be favorable to the precipitation of a short rod-like ?-spodumene solid solution.The thermal expansion coefficient and the flexural strength are 0.86×10-6/?and 95MPa.The amounts of nucleating agents have changed crystal morphology of galss-ceramics.When the optimal compound amount of TiO2,Zr02 and P2O5 is determined to be 2wt%,2wt%and 3wt%respectively,the thermal expansion coefficient and the flexural strength of glass-ceramics are0.75×10-6/? and 99.35MPa.The effects of fluorides(LiF,MgF2,AlF3,CaF2)and composite fluorides on the microstructure and properties of glass-ceramics has been furtherly studied.Composite fluorides(2wt%MgF2+2wt%CaF2)added are beneficial to the precipitation of granular/?-spodumene solid solution.And the thermal expansion coefficient and the flexural strength of glass-ceramics are 1.10×10-6/? and 112.83MPa.Glass-ceramics are mainly composed of granular and fibrous/?-spodumene crystal phase when the content of single MgF2 added is 2wt%.The thermal expansion coefficient and the flexural strength of glass-ceramics are 0.99×10-6/? and 130.36MPa.