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A video on the combustion of double-base propellant produced by the Explosive Research and Development Establishment (ERDE).
A possible correlation between burning rates and the appearance of the burning surface in a number of platinized propellants.
Each propellant strand was three millimetres in diameter and the film records are shown 8 times slower than real time. These ingredients were present in all the examples to be shown. Any additives to the basic composition are included on the graph prior to the film record of the experiment.
Composition one contained no ballistic modifier. The burning rate increased smoothly with pressure.
At a combustion pressure of two megapascals some carbonaceous material can be seen in the surface of the burning propellant, but beneath this a clear decomposing melt covers the propellant.
In this experiment, the same composition was burned at a combustion pressure of five megapascals. The char was thinner at the higher pressure and underneath it a clear melt covered the whole of the burning surface. The presents of red lead oxide as a ballistic modifier in composition two resulted in the familiar plateau in the burning rate curve.
At two megapascals large beads of molten lead and a quantity of char completely covered the surface.
As the combustion pressure was increased, the lead globules became smaller and the amount of char on the surface also decreased.
At four megapascals near the end of the plateau region of the burning rate curve, the lead beads became very small and the char which remained on the surface glowed red hot.
Above the plateau at 5 megapascals, no lead or char could be seen on the surface.
The same was true at 6 megapascals.
When copper oxide was present as a ballistic modifier instead of red lead oxide, the maximum in the burning rate curve shifted to higher pressures. Metallic beads could still be seen on the propellant surface at 10 megapascals.
When lead and copper were both present, the burning rate resembled those obtained when lead oxide was the only ballistic modifier.
Carbonaceous char and metallic beads could be seen at two megapascals when combustion occured in the catalytic region.
However, at 6 megapascals, beyond the plateau, there was no metal or char, but only clear melt.
Inclusion of ammonium perchlorate completely remove the effect of lead oxide in the burning rate. It also removed the visible signs of the catalytic burning that had become associated with platinization.
RDX also removed platinization. But this case proved to be the exception that always seems to occur if too many experiments are carried out.