Тheoretical bases of milling and mechanical activation of materials forsurfaces and gas-term sprays

Abstract

One of the new directions in the production of composite materials is the use of mechanical activation of the components of the mixture before the SHS process. This operation allows you to make mutual grinding of the initial powders and form composite particles with a uniform distribution of initial reagent volume, and reduces heat loss during the synthesis, increases the activity of the system and the homogeneity of the product of combustion, contributes to the formation of synthesized nanoscale inclusions in the volume of the matrix.The grinding process is considered in the physics of destruction, as the destruction of solids by a series of mechanical actions. The aim of the grinding theory is to establish the relationship between the dispersion of the powder, physical,chemical and mechanical properties of particles, energy costs and parameters of mills. The ultimate goal of research in the field of fine grinding is to predict the result of dispersion of materials of different properties, that is, the creation of fine particles with a high specific surface area with a minimum amount of experimental work on their grinding. The kinetic concept of strength of solids, which proved that the destruction is a thermodynamic process, and allowed to predict the destruction at the micro-and macro-level, as well as a two-stage model of destruction of heterogeneous materials, based on the kinetic model of strength.The problems of grinding - the process of destruction of pieces of solid material at critical internal stresses generated as a result of any load and exceeding the corresponding strength parameters. Grinding is divided into crushing and grinding, and the machines that are used for this purpose are called crushers and mills. The main characteristic of the grinding process is the degree of grinding. The physics of the process of mechanical activation of inorganic materials is analyzed.Mechanoactivation is the process of formation of a chemically active substance by mechanical grinding. Mechanochemical activation of solids studies a complex of interrelated phenomena and processes occurring during mechanical action on a solid body, both at the time of machining and as a result. Bowden and Tabor proposed a "hot spot" model to explain the mechanical initiation of chemical reactions. They found that in the process of friction by 10-3 - 10-4s. the temperature rises to 1000 K, and this is the cause of mechanical induction of chemical reactions. In the process of mechanical activation, the properties of the materials themselves play a significant role.Amorphization of the surface is primarily observed for materials with high hardness and brittleness, such as corundum, quartz, etc. the Energy that is supplied to them does not have time to dissipate. The system is forced to accumulate a significant part of it to create internal defects. For mechanical activation of materials for surfacing and spraying, ball mills, which are a cylindrical drum closed from the ends, inside which the balls and the processed material are placed, are most used.Currently, the method of mechanoactivated self-propagating high-temperature synthesis is actively developed in which at the first stage the reaction mixture is treated for a relatively short time in the activator apparatus and then used as a precursor for SHS. It is established that mechanoactivation extends the possibility of reactions in the self-propagating mode in the concentration areas where the traditional SHS could not be implemented under any conditions.The process of mechanical activation is necessary to initiate combustion reactions of low-calorie systems in which it can be used instead of preheating. Based on the analysis of modern ideas about the mechanism of destruction of solid materials, the laws of grinding mixtures of different materials, the process of mechanical activation of materials, the relevance of research on the creation of composite materials using SHS-process.