The Study And Preparation Of Low-Expansion Transparent LAS Glass-Ceramics

Li₂O-Al₂O₃-SiO₂ glass-ceramics have attracted the attention of many researchers due to their unique thermal,optical,and mechanical properties.At present,it has been widely used in civil or aerospace fields such as cooking utensils,high-temperature observation windows,astronomical telescopes,and laser gyroscopes.This paper aims to prepare low-expansion and high-transparency glass-ceramics,whose main crystal phase isβ-quartz solid solution.And the Australian spodumene was used as the main raw material.At the same time,the composition of glass-ceramic and the heat treatment were studied.In terms of the composition of glass-ceramic,mainly from the perspective of crystal phase composition and crystal nucleating agent,the two-step method was used to study the change of Al₂O₃ content and the substitution of different oxides for Ti O₂ on properties of glass-ceramics.As for heat treatment system,the relationship between crystallization temperature and nucleation temperature and the structure together with properties of glass-ceramics is mainly studied,and low-expansion transparent glass-ceramics are tried to prepared by one-step method.XRD,FTIR and MAS-NMR were used to characterize the structure of lithium-aluminosilicate glass and glass-ceramic,and the thermal expansion coefficient,visible light transmittance,and flexural strength of the samples were measured to study the effect of different factors on thermal,optical and mechanical properties of glass-ceramics.Finally,the glass composition that is conducive to the precipitation of the target crystal phase,as well as a suitable heat treatment system were obtained.The main findings are listed as followed:（1）The increase of Al₂O₃ content was beneficial to obtainβ-quartz solid solution with smaller grain size,thereby improving the visible light transmittance of glass-ceramics.When the Al₂O₃ content was 21.00 wt.%,the comprehensive performance of glass-ceramic was the best,the thermal expansion coefficient in the temperature range of 30～500℃was 0.5823×10^-6 K^-1,and the visible light transmittance can reach 84%,the average flexural strength is 173.45 MPa.（2）The decrease of TiO₂ content is not conducive to the precipitation ofβ-quartz solid solution phase,but it can improve the visible light transmittance of glass-ceramic to a certain extent.When the Zr O₂ content was 3.00 wt.%and the Ti O₂ content was1.20 wt.%,the comprehensive performance of the glass-ceramic was the best.The CTE of this sample is-0.0028×10^-6K^-1 in the temperature range of 30～700℃,the visible light transmittance can reach 87%,and the average flexural strength is as high as231.80 MPa.（3）In the study of heat treatment schedule,the crystallization temperature can affect the structure and properties of glass-ceramics more than the nucleation temperature.Glass-ceramics with excellent properties can also be prepared by one-step heat treatment.The thermal expansion coefficient of this sample is 0.1105×10^-6 K^-1 in the temperature range of 30～700°C,the visible light transmittance reaches 89%,and the average flexural strength is 164.32 MPa.In this paper,low thermal expansion,high transparency,and high strength LAS glass-ceramics have been successfully prepared as the main raw material was Australian spodumene.In addition,through the optimization of the heat treatment,the glass-ceramics with excellent performance are obtained,and the process flow is shortened,which is of great significance in reducing production costs.