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Experimental studies are reported on the initiation-deflagration process occurring in nitroglycerin and nitroglycerin solutions as a result of impact. The instrumented apparatus used permitted determination of the pressure/time relationships due to the momentum of the impacting weight and to the resulting deflagration. As a result, impact sensitivity testing of liquids is placed on a sounder basis. A gradual decrease in impact sensitivity is observed as desensitizer concentration is increased up to 16 per cent by weight; a more rapid decrease in sensitivity is found beyond this point.

Using the thermal initiation apparatus and an instrumented modification of the O-M drop-weight impact tester, the relationship between chemical structure of liquid nitrate esters and their sensitivity has been investigated. The expected decrease in sensitivity with decreasing degree of nitration was found, and the effect of increasing viscosity, which decreases sensitivity to impact but not to thermal surge, was confirmed. Isomeric nitrate esters show the same sensitivity; there is apparently no difference in stability of primary and secondary nitrate groups under the test conditions. Dissolved water proved a very effective desensitizer.

Minol II (40% ammonium nitrate, 20% aluminum) is useful as an explosive fill for bombs, because its use substitutes cheap, and abundant, ammonium nitrate (AN) for more expensive, and sometimes scarce, TNT. However, Minol II exhibits poor dimensional stability when exposed to temperature cycles during storage. It has been shown that growth of Minol II charges during temperature cycling is caused by the polymorphic phase transition which occurs in AN above 32C. Review of the literature suggested that this phase transition could be prevented by substitution of a solid solution of potassium nitrate (KN) in AN for AN in explosive compositions. Some of the reported properties of such solid solutions (KN-AN-III or AN-KN) have been confirmed. Charges containing 40% TNT, 40% AN-KN and 20% aluminum (now designated Minol IV) showed better dimensional stability during temperature cycling than either TNT or TNT/ aluminum (67/33).

Instrumentation of a standard drop-weight tester to give pressure- time records and further modification to permit high speed photography have allowed intimate study of the impact initiation explosion process in nitroglycerin. A plot of peak impact pressure versus concentration of conventional desensitizer (in nitroglycerin) gives a continuous, nearly linear relationship. The ratio of peak impact pressure to initial pressure is a most significant factor in determining probability of explosions of nitroglycerin. This is consistent with quasi-adiabatic compression of air bubbles as a step in the mechanism of initiation. The photographic studies support this mechanism, showing compression, breakdown of bubble structure (thereby causing more efficient heat transfer to the surrounding liquid), an induction period, and ignition starting in hot spots at the site of the bubble.