The Influence of Physical Properties on Black Powder Combustion

Abstract
It has been observed that black powder made from ingredients of the same lot and fabricated using the same manufacturing procedure results in material exhibiting different burning rates. The current study was undertaken to determine if the physical properties of black powder affected burning rate and established if these properties varied from one production batch to another. Physical properties of black powder were measured including surface area, pore size distribution, and internal free volume. Black powder derived from oak and maple charcoals was compared, and the effects of processing the material by a jet mill or ball mill were contrasted. Scanning electron microscopy revealed that applied pressure, a manufacturing step used in making black powder, induced considerable plastic flow that resulted in a fused conglomerate, cohesive mass containing interconnecting passageways of about 0.1 micron diameter. Density, free volume, and surface area were found to be functions of burning rate. Based on these relationships, the conclusion was offered that the degree of openness of a grain of black powder is a significant factor affecting its burning rate.

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