THERMOPHYSICAL PROPERTIES OF A GLASS-CRYSTAL MATERIAL DEPENDING ON THE RELATIVE CONTENT OF PHASES

Abstract

The study and search for the patterns of the relationship between the properties of glass and glass-ceramic materials, which are composite materials from glass and crystalline phases, and their composition is a very important task of modern materials science. The thermal expansion of multicomponent crystalline and glass materials is related to the nonlinearity of vibrations of atoms, ions, structural groups. Currently, many works have been completed in which the goal was to develop methods for calculating the properties of glasses with different compositions. However, the identification of the most general patterns of changes in the thermal expansion of bodies of complex composition and structure, such as glass crystalline materials (glass ceramics), remains a topical issue now. As the system cools, microstresses occur at the crystal-glass interface which are proportional in magnitude to the free compression of crystals in a glassy matrix. The thermal expansion of a glass crystal body can be calculated by assuming that the microstresses in the crystal-glass transition layer are purely hydrostatic compression or tension.

The crystallization process of glasses of cordierite composition containing B2O3 by a single-stage heat treatment of glasses at 1000⁰C and 1200⁰C, the nature of crystallization, the thermal properties of glasses and glass crystalline materials of the system (MgO·Al2O3)- B2O3-SiO2 are studied. It is revealed that, depending on the composition of the glass and the heat treatment mode, solid solutions 2MgO·2Al2O3·5SiO2 cordierite, spinel MgO·Al2O3, sapphirine 4MgO·5Al2O3·2SiO2, and solid solutions described by the formula 2MgO·2Al2O·5[(SiO2)1-X(B2O3)X] are released, where 0,05  х  0,2. It is revealed that during the isolation of boron-containing cordierite, the residual glass phase is enriched in MgO and Al2O3, leading to an increase in the thermal expansion coefficient of the glass phase of glass ceramics. It is shown that the research results make it possible to synthesize heat-resistant glass materials for electronics with certain thermophysical parameters by stopping the further crystallization of glass at the stage of formation of a certain amount and ratio of the necessary crystalline phases.