Limits in Composite Explosives

This subject was discussed in detail by Gordon (Ref 3) and to a lesser degree by Jost (Ref 1) and Cook (Ref 2) 

The composite explosives are usually those consisting of powdered mixtures of an oxidizer and an organic fuel. Dynamites are composite expls contg some NG. The composite expls examined by Gordon consisted of AN-fuel or Ammonium Perchlorate-fuel and their properties were compared with those of TNT, RRX and pure Amm Perchlorate 

Most striking feature is the difference in behavior toward a change in the initial density pQ. Increase in density of TNT, RDX or Amm Perchlorate causes continuous increase in detonation velocity D, while for composite expls increase of D follows increase in density only to some limiting value and then D sharply decreases. This unusual behavior of composite expls is caused, accdg to Cook (Ref 2, pp 140-41), by slowing down of the diffusion reaction between fuel and oxidizer with increase in density 

The paper of Gordon describes a model for diffusion-controlled reaction based on the hole concept in liquids of Jost (Ref 1, p 459). in which the activation energy for diffusion is equated simply to pV. The marked effect of density, therefore, results from the strong dependence of pressure on density (p varying about as the density cubed) and the appearance of this factor in an exponential term. On this basis, Gordon derived an approximate expression for dependence of detonation velocity D on explosive density pQ. This equation is given on pp 833 and 836 of Gordon s paper. From this expression the critical diameter dc for composite explosives is related to an exponential function of density by  

Experimental evidence to support this behavior is given and the implications of these results for the problem of determining critical diameter in composite solid propellants are discussed in the paper of Gordon Refs 1) W. Jost, Diffusion , Academic Press, NY (1952), p 459 2) Cook (1958), 

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W.E. Gordon, "Detonation Limits in Composite Explosives , 10thSympCombstn(l964), 833-38 9) R.C. Mitchell N.W. Ryan,... 

Critical diameter-critical density relationship lor composite explosives given by Gordon in Ref 13, pp 837-38 is abstracted in this Vol under "Detonation Limits in Composite Explosives", Critical diameter-critical density relationship in condensed explosives, given by Gordon in Ref 14, pp 180-85 8t 193-96 is abstracted in this Vol under "Detonation Limits in Condensed Explosives . The resume of paper by Price (Ref 15) is given in this Vol under the title "Contrasting Patterns in the Behavior of High Explosives ... 

The explosion limits have been determined for liquid systems containing hydrogen peroxide, water and acetaldehyde, acetic acid, acetone, ethanol, formaldehyde, formic acid, methanol, 2-propanol or propionaldehyde, under various types of initiation [1], In general, explosive behaviour is noted where the ratio of hydrogen peroxide to water is >1, and if the overall fuel-peroxide composition is stoicheiometric, the explosive power and sensitivity may be equivalent to those of glyceryl nitrate [2],... 

A 2-value smaller than 1 means that there is an excess of fuel in the mixture. In this case the air/fuel mixture is called rich. If more air is in the mixture than needed for a complete fuel combustion (2 > 1) the term lean mixture is used. Ideally the combustion is complete at 2 = 1. Real fuel cannot be combusted without an increase in CO and soot at 2-values smaller than 1.05. Due to changing operation conditions, for example a soiled burner, wear of the nozzle or leaky flaps, change of gas quality or changes of temperature and air pressure in the ambient atmosphere, the air/fuel ratio and thus flue gas composition can change over time. In order to minimize the risk of intoxication (see also chapter 5333), explosion and pollution real (uncontrolled) fuel burners are adjusted to operate far beyond this limit in the excess (lean mixture) region. However, unfortunately effi-... 

Amongst the earliest experiments carried out with a view to the quantitative determination of the limits of inflammability of combustible gases were those of Davy with fire damp, wfliich is mainly methane, CH4. Owing to the importance of this gas m connection with gob fires and explosions in coal mines, several other workers have also investigated it. The value of the results, however, is restricted by the fact that firedamp, like most natural products, is subject to very considerable variation in composition.3 Even Davy recognised that it was not pure methane indeed, perfectly pure methane is not easy to prepare in quantity. The gas, as obtained from sodium acetate, may contain as much as 8 per cent, of hydrogen, as well as ethylene.4 No doubt this variation m composition is one contributory cause of the very varied results listed in the table on p. 93. 

There have been a number of measurements of the effects of mixture composition and temperature on the hydrogen—oxygen second limits in potassium chloride coated vessels (e.g. refs. 28,14, 23, 25, 30). Typical of the results are the explosion regions shown in Figs. 3 and 4. They all... 

This classification limits the combinatorial explosion encountered in conventional computer-aided synthesis approaches, because composite operators know a priori when they apply. For example, the application of bimolecular operators to a list of chemical species results in the selective application of radical-operator to radicals contained in the list and molecule-operator to species that are molecules. 

DATB is a lemon-yellow coloured crystalline substance, it is fairly stable when close to its melting point (286 C) decomposing at a rate of less than IT per hour at 260 ( but it is transformed into crystal form of lower density at 216 "C. which temperature, therefore, represents the limit of its utility. The use of DATB in higlily explosive compositions has been described in several patents (14,151... 

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