| Since the dawn of the industrial age,glass research has gradually intensified and demand has grown.In particular,high-performance glass is one of them and is widely used in military,aerospace,microelectronics and other high-end fields.However,the traditional method of bonding quartz glass can easily cause damage to the quartz glass or limit the environment in which it can be used.Therefore,there is a need for a new bonding method that can be used without damaging the quartz glass and without limiting the environment in which it can be used.This new bonding method has important applications and is currently an important research direction in the field of quartz glass.The purpose of this thesis is to investigate an effective method for sealing quartz glass and to perform some optimization of the sealing.For this purpose,a sealing glass is used to join the quartz glass and a Li2O-Al2O3-SiO2(LAS)system microcrystalline glass is selected as the sealing material.The precrystallization kinetics of the LAS microcrystalline glass and some of the properties associated with the sealing quartz glass were investigated and modified to overcome their shortcomings.The modification was carried out by external doping with WO3,and the fit of the samples to the quartz glass before and after modification was investigated by sinter imaging,thermal expansion performance testing,differential scanning calorimetry(DSC),X-ray diffraction(XRD),and scanning electron microscopy(SEM).The changes and mechanism of the sealing quartz glass before and after the modification of LAS microcrystalline glass were also investigated.The conclusions were as follows:(1)The crystallization kinetics of LAS glass ceramics prepared in this thesis was studied.Through DSC test,the normalized heat release of LAS glass ceramics at different heating rates was obtained.It was determined that the most appropriate heating rate in the crystallization process was 10℃/min.By combining with Ozawa equation,the crystallization activation energy of the glass ceramics was Ea=189.1 KJ/mol,and the average crystallization index was n=3.3,which could be used for better crystallization to reduce the thermal expansion coefficient.(2)The crystals after precrystallization were obtained by XRD test as βlithium chalcopyrite,which has a unique negative expansion property and can effectively reduce the thermal expansion coefficient of microcrystalline glass.The thermal expansion test was carried out on samples with different precrystallization times,and it was found that the longer the precrystallization time was,the smaller the thermal expansion coefficient was,and the thermal expansion coefficient α=4.73×10-7/℃ after 150 min of precrystallization.Sealing tests were conducted with quartz glass and other types of sealing glass,and it was found that none of them could seal quartz glass,mainly due to the mismatch of thermal expansion and insufficient wettability.In contrast,LAS microcrystalline glass was able to seal with quartz glass better.By analyzing the sealing force of quartz glass,it is concluded that the coefficient of thermal expansion of sealing material should be in the range of α=(-1～11)×10-7/℃.The wetting angle of LAS microcrystalline glass and quartz glass at the sealing temperature θ=30°,and the wetting property as sealing material needs to be improved.(3)The modification was carried out by adding WO3.XRD,SEM,FT-IR and Raman studies showed that the addition of WO3 had an effect on the crystallisation of the glass-ceramics,which was first strengthened and then weakened.The enhancement was due to the role of WO3 as a nucleating agent,and the weakening was due to the bonding between[WO4]and[SiO4],which strengthened the glass network and hindered the crystallisation to some extent.Through the sintering imager test,it is found that the addition of WO3 can greatly improve the wettability,flowability and sintering performance of LAS glass ceramic on quartz glass.At the sealing temperature,the wetting angle decreases by 30.0%,the spreading area increases by 36.2%and the sintering activation energy decreases by 15.6%.As a surfactant,WO3 reduces the surface tension of the solid/liquid interface.(4)The thermal expansion coefficient of the samples was significantly altered with the increase of the WO3 doping content,changing from negative expansion to a value close to that of quartz glass.When the mass fraction of external WO3 doping reached 5%the thermal expansion coefficient wasα=5.69×10-7/℃.This led to a reduction of thermal stress after sealing,as the coefficient was similar to that of the quartz glass.(5)The samples before and after modification were sealed with quartz glass.The tensile strength and flexural strength tests showed that LAS glass ceramic as a sealing material had good sealing strength after sealing with quartz glass.With the increase of WO3 content,the strength gradually increased,which also proved that the modified.sealing material had better compatibility with quartz glass.After several thermal cycles,although the connection strength of the sealing element decreases,the strength can still be maintained above 60 MPa,and will remains stable after dropping to a certain level,indicating that the sealing element has a long service life.(6)In studying the sealing mechanism,through SEM and EDS tests on the seals prepared with W0 and W5 as sealing materials,it was found that the interface bonding was mainly by chemical element migration and physical interlocking.The interface bonding of the gaskets prepared with W5 was better,and WO3 as an active agent enhanced the element diffusion and mechanical interlocking structure.Fick’s law is introduced to deduce the migration and diffusion of elements,and the ion content in unit area of quartz glass can be calculated. |
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