CORRESPONDENCE
Representing Delay Powder Data I
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Here is how to predict burning rate in a threeco m ponent sys te m
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SIR: In a recent publication [IND. EILG.CHEM.52, 241-4 (1960)] it was shown that burning rates of delay powder mixtures composed of gray selenium and barium peroxide could be varied and controlled, within limits, by preheating the mixtures. Practically, i t is more often necessary to be able to vary the burning properties of delay powders over much wider ranges than any pretreatment of a given mixture can accomplish. Such variation is most easily accomplished by changing the composition of the delay powder. .4 systematic representation of the eff'ects of changes in composition has been found very useful for many systems. Some data, obtained by procedures previously described in the reference, are presented to illustrate the method. As long as the system under study contains only two components (a component, in this sense? is either a metal powder, a n oxidant, or a diluent) the representation is simple. Using rectangular coordinates, composition is represented on the abscissa and the functions of Composition which are of interest on the ordinate. Heat output in calories per gram and burning time in seconds per 10 inches are shown on Figure 1 as functions of composition for the system composed of zinc and cuprous oxide. Three-component sysrems have been represented successfully on triangular composition diagrams in a manner similar to the representation of threecomponent phase systems. Each corner of the triangle represents 100% of one component. The values of the function of composition are plotted on the edges or in the body of the triangle, depending upon the composition of the sample. Lines of equal values of thc functions are then drawn. Miith a little experience, as few as 10 to 15 values are often sufficient in order to predict with a high degree of certainty the behavior of any mixture in a three-component system.
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Figure 1. Minimum burning time occurs at higher zinc percentage than maximum h e a t
Figure 2. lsocals (solid lines) and isochrones (broken roughly the same pattern
Lines of equal heat output, which we have called "isocals," and lines of equal burning times: which we have called "isochrones" are shown on Figure 2 for the system composed of iron, barium peroxide, and potassium permanganate. Heat output and burning time are most often functions which are of interest. However, other functions, such as peak
INDUSTRIAL AND ENGINEERING CHEMISTRY
lines) usually
follow
temperature and cost can be treated similarly with equal success.
L. B. JOHNSON, JR. Research Laboratories for the Engineering Sciences University of Virginia Charlottesville, Va.
