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A mathematical model is suggested for heating and igniting of a powder material under frictional action. A simulation is carried out for various thermophysical and geometrical characteristics of the rubbing body, the supporter, and the powder material. Consideration of the results and comparison with those of previous experiments demonstrate the applicability of the model.

It is shown that ignition may occur under light frictional pressure. In the case of friction applied to a powder, there are two limits of ignition in terms of the frictional pressure. A frictional approach permits a high degree of compaction of powder at low frictional pressure (∼10 kg/cm2). The influence of the material of the frictional body on sample heating and ignition is investigated. Activation of chemically active powder under the action of friction is observed. A discussion of the results is presented.

We have experimentally investigated the process of propagation of the burning front along the surface of powders of titanium, magnesium, and mixtures of magnesium with diluents in an air atmosphere. We have determined the dependence of the velocity of propagation of the burning front along the surface of bulk metallic powders on the angle of inclination of the test bed of powder, and also the effect of additives introduced into the powders. We used several types of additives: free-burning in an air atmosphere, inert with high melting point, and low-melting-point inert powdered materials not burning in air but reacting exothermically with the metallic powders. In addition to our purely scientific interest, we also pursued a practical goal: solving problems of reducing fire and explosion hazards for production processes using or manufacturing metallic powders and mixtures based on such powders.

This article discusses the possible intensification of metal powder ignition and combustion processes during their mechanical treatment. The defectivity of the structure and diffusion permeability is examined. Tests were conducted on electrolytic titanium powders of mark TP-6 and TU 48-0561-4/0-80. Powder samples were selected after specific time intervals and their ignition and combustion characteristics were determined. The titanium powder was placed in a 16-mm-diameter capsule from brass mesh which does not obstruct gas supply to the specimen, and was then inserted in a metal module heated to a definite temperature in a muffle furnace. It is shown that treatment of the powder results in significant facilitation of its flammability. The electron exoemission was measured on the primary and treated titanium powders. The data on titanium powder ignition and combustion and the results of studying the exoemission indicate that the intensification observed for combustion and ignition is related to the origin of defects on the powder grain surface during its mechanical treatment.

The study of the ignition characteristics of powders of the refractory transition metals is of scientific and practical importance. It is of interest to investigate the effect on the ignition process of such parameters as the composition of the gaseous oxidizer, the heat transfer conditions, the specimen dimensions, and the grade of metal powder. The article is devoted to the question of the ignition of transition metal powders, with titanium serving as an example. On the basis of the experimental data, several conclusions may be drawn. First, it was found that nitrogen has a chemical effect on the ignition of titanium powder in air only in the presence of an oxygen deficit. Second, a gas flow has a significant effect on the critical ignition temperature, reducing it at low and increasing it at high gas flow rates. It was further found that the titanium powder ignition process can develop in the autoignition and external ignition regimes. Generally good agreement was found between the theoretical and experimental values of the critical ignition temperature for titanium powder.

Formulation of the Problem The following model is used to study theoretically the laws of ignition of bulk metal powders by an internal source in terms of such parameters as temperature, the size of the source, the pressure and concentrationof the oxidizer in the gas phase, the porosity of the powder, the filtration and diffusion coefficients, etc. At the center of the layer of metal powder there is a hot spot of size Rm which at the initial instant is at temperature To. The hot spot is surrounded by alayer of metal powder of radius ~ at the initial temperature T1o. The system (hot spot-powder) is in a gaseous medium, characterized by the constant pressure p2o and the relative mass oxidizer concentration a2o, at a temperature equal to the initial temperature of the metal powder. We are given the coefficient of heat transfer from the surface of the powder to the surrounding medium. During the reaction initiated by the internal source and proceeding at the surface of the metal particles, the oxidizer is consumed, and the temperature in the layer of powder increases, which leads to a mass flow of gas. At the center of the system (r = 0) we have adiabatic temperature conditions, at the hot spot-metal powder boundary (r = R ) adjoint boundary conditions, and at the metal powder-gas boundary (r = ~) boundary conditions of the third kind with allowance for heat transfer due to gas filtration. The system of equations describing this model takes the form: energy equation for the hot spot at 0 < r < R m