Physics
Scientific paper
Aug 1948
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1948rspta.241..204u&link_type=abstract
Philosophical Transactions of the Royal Society of London. Series A. Mathematical and Physical Sciences, Volume 241, Issue 831,
Physics
Scientific paper
In section (a), details are given of a method of determining the delay to ignition at various temperatures, for initiators. The heat sensitiveness of an initiator can be characterized by an equation log Y = E/4 \cdot 57T + B, where Y is the induction period before ignition, E is the activation energy of the physico-chemical process controlling it, in kcal./mol., and B is a constant. T is the absolute temperature. Values of E and B are listed for lead azide, mercury fulminate, basic lead di-nitroresorcinate (L.D.N.R.), lead styphnate and barium styphnate. From an extrapolation, ignition temperatures have been calculated corresponding with delays of 10-3 and 10-5 sec., to link these up with certain aspects of sensitiveness and detonation. Experiments are described which show that initiators such as lead azide can be more or less permanently sensitized by heat treatment, and by photochemical action. In section (b), experiments are described on the failure to detonate below a certain temperature, and on the ignition times, of lead azide, lead styphnate and mercury fulminate. The behaviour of mixed initiators, and of simple initiators admixed with inert diluents, has also been investigated. The results show that detonation is built up from the co-operation of a number of centres of reactivity. It is shown that in the mixed composition 'A.S.A.' the lead styphnate plays the predominant role in the heat sensitiveness, improving the thermal pick-up and lessening the tendency of lead azide to fail to detonate on heating. In section (c), X-ray measurements and determinations of the heat sensitiveness are described for Service and dextrin azides. It is shown that the grains of Service azide consist largely of single crystals, whereas the grains of dextrinated azide each contain about 106 crystallites. The lattice crystal structure in the two azides is the same. With the samples investigated, the activation energy controlling the length of the induction period is about 41 \cdot 3 kcal./mol. for Service azide and 23 \cdot 4 kcal./mol. for dextrinated azide. The large difference between these values is correlated with the difference in initiating power of the two types of azide. In section (d), sensitiveness to heat, percussion and friction are compared for Service and dextrin azides. General sensitiveness of Service azide is somewhat greater. Particular attention is drawn to the grit sensitiveness of Service azide.
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