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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.

An experimental study of the effect of foreign inclusions of both chemically active materials, capable of burning in an air atmosphere and inert oxide materials on the propagation of a combustion front over the surface of titanium powders was carried out. It has been established how the character and the rate of surface combustion Vc of titanium powders change upon their dilution, depending on diluent concentration, melting temperature, disperse composition, and chemical activity.

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.