Formation of glass synthesized by sol-gel technology

Abstract

The process of glass synthesis by the sol-gel method is studied using analysis of EPR spectra. The gelation process and formation of xerogels are considered depending on the temperature-time parameters and the type of initial components. It is established that the glass phase starts to be formed at 800°C.The expanded use of glass in developing a new generation of instruments requires high-quality homogeneous glass materials. The improvement of all stages of glass production, including the melting process, is of great importance.A promising method for producing homogeneous glasses is the sol-gel method.Analysis of published sources suggests two directions in the technology of sol-gel synthesis of glasses.Production of amorphous batches from gels and their subsequent melting according to the traditional technology. This direction is mainly focused on the synthesis of extra pure multicomponent glasses, primarily optical glasses, including glass for fiber optics. This technology includes preparation of solutions based on extra pure soluble materials (salts, metal hydroxides, organometallic compounds, SiO 2 sol), transition from the solution to a sol, then to a gel, its drying, and formation of an amorphous powder batch achieving a perfect (at the molecular level) mixing of the components [1].Apart from the high purity and homogeneity of the glass, the use of such batch decreased (by 150 -200°C) the vitrification temperature due to the high dispersion of the batch particles, its amorphous nature, and the emergence of chemical bonds typical of glass. At the same time, the high gas-saturation of the batch complicates the clarification process and in the case of high-viscosity melts sometimes prevents lowering the general melting temperature.Production of glass by polycondensation (polymerization) of gel and its subsequent consolidation under heat treatment (without melting), i.e., the method implementing a gradual sol ® gel ® glass transition.The purpose of our study is the investigation of sol-gel synthesis of alkali-free aluminocalcium silicate glass and stage-by-stage analysis of the structure of resulting materials depending on their temperature-time parameters and the type of initial material.In the traditional technology such glass is melted in tank furnaces at 1560°C, the clarification temperature is 1520°C, and the working temperature 1450°C. The annealed samples contain bubbles and plenty of "fly-like" defects.One can single out the following stages in sol-gel technology [2 -4]:-preparing solutions by mixing alkoxides or salts of the elements comprising glass with water and alcohol at a certain pH level and temperature;-primary structurization of the solution, which is defined in [5] as complex formation; sol formation occurs at this stage [4,6]; -gel formation, i.e., the formation of a 3D lattice as a result of hydrolysis and polycondensation reactions; a gel is formed from the solution and its structure determines subsequent processes; the processes of complex formation, hydrolysis, and polycondensation are s...

Use of Electron Paramagnetic Resonance for Investigating Glasses and Raw Materials (Review)

“…The evolution of the EPR spectra of the ion Cu 2+ at different stages of obtaining glass is studied in [14]: solution ® gel ® dried gel ® heat-treated gel ® glass. A solution (sol) was prepared for obtaining a multicomponent glass with the following composition (weight content, %): 54 SiO 2 , 18.5 Al 2 O 3 , 13.5 CaO; 6 ZnO; and, 8 BaO.…”

Tetraethyl orthosilicate (TEOS)-based sol–gel process monitored by EPR spectroscopy with VO(II) cations as a spin-probe

“…xerogel ? glass [3][4][5]. Since the silica solgel reaction mixture, and the sol-gel products (sols, gels and xerogels), are EPR-silent, a small concentration of paramagnetic centres (e.g.…”

“…xerogel transformation [3,4,7,8]. It is well documented that Cu(II) and Mn(II) ions are very sensitive as spin-probes to monitor the structural changes that occur in silica xerogels during the process of calcination, or in general, the properties of the sol-gel process products, and numerous EPR experiments, have been devised for this purpose [5,. However, there have been far fewer systematic EPR studies made of Cu(II) and Mn(II) cations with which to explore the earlier stages of the silica sol-gel process [55][56][57][58][59], while VO(II) ions have been employed relatively rarely to investigate the silica sol-gel process at all [57][58][59][60][61][62][63][64][65].…”

Glass Binder in Thick Film Metallization Paste for AlN

“…Their production environment is relatively poor and a higher melting temperature results in more serious volatilization of boron. In recent years, a promising method for producing homogeneous glasses is the sol-gel method [7]. Prepare the glass powder by sol-gel method has unparalleled advantages: availability of homogeneous high-purity materials; better control of composition, especially suitable for the preparation of multi-component materials; much lower preparation temperature than traditional methods.…”