ANALYSIS OF VOLUMETRIC CHANGES OF COMPOSITE MATERIALS BASED ON THE MgO – Al2O3 – FeO – TiO2 SYSTEM DURING PHASE FORMATION

During firing, as well as operation, various chemical transformations occur in composite materials, which are accompanied by volumetric changes that affect the physical, mechanical and operational characteristics of refractories. The paper analyses the volumetric changes of composite materials based on the MgO – Al2O3 – FeO – TiO2 system during phase formation in different temperature ranges. It was found that various volumetric changes occur in composite materials during temperature changes. Significant volumetric changes occur during the formation of spinels of different compositions. Also, when working with materials that include tialite, significant volumetric changes should be taken into account. That is, to obtain a material of a certain composition, it is necessary to take into account not only phase transitions and possible solid-phase reactions, but also volumetric changes that occur in this case. The phase transformations that occur during firing and operation of periclase spinel refractories, which in turn depends on the type and amount of raw materials, are considered in more detail. During operation, phase transformations in a material become more complex due to the influence of mechanical loads, thermal fluctuations, chemical reactions and microstructural changes. Constant heating and cooling change the phase equilibrium, causing the formation of new structures or the degradation of existing ones. Diffusion processes, corrosion and oxidation can change the chemical composition of the material, and recrystallization, grain growth and the separation of secondary phases affect its mechanical properties, which makes it difficult to predict the behaviour of the material. Thus, in order to obtain a material of a certain composition and predict its behaviour during operation, it is necessary to take into account not only phase transitions and possible solid-phase reactions, but also the volume changes that occur in this case