Research On The Compositions And Processing Properties Of Non-alkali Aluminoborosilicate Glasses

Non-alkali aluminoborosilicate glass is the most ideal substrate material for thin film transistor liquid crystal display?TFT-LCD?because of its excellent thermal stability,chemical stability,mechanical properties and dielectric properties.However,it also has many difficulties in producing,such as high melting temperature,high viscosity,hard to be refining and so on.In this paper,FTIR,thermal dilatometer and high temperature rotary viscosimeter were used to study the effects of basic components RO,Al₂O₃ and B₂O₃ on the structure and properties of non-alkali aluminoborosilicate glass.We aim to find the compositions of alkali-free aluminoborosilicate glass which is suitable for float processingThe nominal compositions of the glass were xRO-8B₂O₃-11Al₂O₃-?70-x?SiO₂?x=10²0 mol%?.The relationship between viscosity and temperature of the prepared glass in the temperature range from transition temperature to melting temperature were fitted by VFT,AG,AM and Mauro-Yue equations,respectively.And fitting results possessing smallest error were obtained by using Mauro-Yue equation.When 10²0mol%RO substituted for SiO₂,the high temperature viscosity of glass decreased,thus the melting temperature decreased from 1717?to 1554?,and the workability of glasses were shortened,which was conducive to rapid forming.The thermal expansion coefficient?25-300??increased from 27.8×10^-7/K to 42.3×10^-7/K,and the strain point Tst decreased from 683?to 633?.The resistivity at 1600?of glass melt was reduced from 72.0?·cm to 21.1?·cm,and the conductivity was improved.We fixed the RO?SrO/CaO/MgO?content at¹6 mol%.When only one kind of RO in the glass compositons,the effects of RO on high temperature viscosity,high temperature resistivity and thermal expansion coefficient follow this order,SrO>CaO>MgO.The accumulation of R²⁺ions with different radius,resulting in the effect of mixed alkaline soil,made the structure of the glass network more compact,which led to the increase of viscosity,the decrease of thermal expansion coefficient,the increase of resistivity,and the enhancement of chemical stability.There was a minimum of the thermal expansion coefficient at CaO/SrO=1:1.The highest temperature viscosity was found when the ratios of MgO/CaO=1:3,MgO/SrO=1:3 and CaO/SrO=1:3,and the high temperature resistivity was found at MgO/CaO=1:3 and MgO/SrO=1:3.The glass possessed the best chemical stability when MgO/SrO=1:3.The mixing alkali earth effects was more obvious when the difference of ionic radius was larger.The nominal compositions of the glass were yRO-8B₂O₃-?27-y?Al₂O₃-65SiO₂(?y=13.5¹9.5 mol%?.When the substitution content of RO for Al₂O₃ increased from 13.5 mol%to 15.5 mol%,the number of[AlO₄]reduced,and the network connection was broken,which lead to the increasing of the thermal expansion coefficient from 23.0×10^-7/K to 36.2×10^-7/K.When RO concentration increased from15.5 to 19.5 mol%,Q⁴ transformed into Q³,and the structure of silicon oxygen skeleton was gradually depolymerization.While the ratio of[BO3]to[BO4]increased from 5.9%to 16.4%,which is suggested a well connection of network structure.The thermal expansion coefficient of all the glasses were at 36³8×10^-7/K.As 13.5¹9.5mol%RO substituted for Al₂O₃,the strain point T_st decreased from 685?to 630?,and the resistivity at 1600?of glass melt reduced from 52.3?·cm to 28.9?·cm.The V-T relationship of the glasses were fitting using the Arrhenius and Mauro-Yue equations,and the results showed that the melting temperature decreased from 1631?to 1546?,the workability of glasses were gradually shortened,and kinetic fragility index m increased from 22.58 to 23.98.