Burning Rate and Grain Size of Component Materials of Pyrotechnic Mixtures

Dr Takeo Shimizu


It has been generally believed that the finer the grain size, the faster the burning when we select the component materials of a pyrotechnic mixture. It is not always true because a small explosion occurred in the past when we tested a smoke mixture, although it contained a dye of very coarse grains. The purpose of this paper is to make clear the general mechanism of the burning rate of pyrotechnic mixtures on the standpoint of the grain size of component materials of pyrotechnic mixtures. Experiments on burning rate were carried out with four types of mixtures changing the grain size of the component materials:

(a) base mixtures of oxidizer (conventional materials as potassium chlorate, potassium perchlorate or ammonium perchlorate) and fuel (accroides resin),
(b) mixtures of the base and an inert material (clay),
(c) mixtures of the base and a semi-inert material (barium nitrate),
(d) mixtures of an explosive of synthesized simple substance (potassium picrate) and an inert material (clay).

All the materials except potassium picrate were sieved to obtain grains of six class sizes. With decreasing the grain size of the component materials, some mixtures increased and some decreased the burning rate. In other cases there were grain sizes which gave the smallest burning rate: the burning rate at first decreased and then increased. In general, the burning reaction seemed to be stabilized as the grain size decreased. These effects will help the designing of pyrotechnic mixtures for various purposes.


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