Pyrotechnic delay mixture

Despite this study not being on the nanoscale, it does show the dramatic effect particle size has on combustion rate, since doubling the particle size causes the combustion rate to be more than halved. The Si / Pb304 mixture has found use as a pyrotechnic delay mixture (slow burning mixture used for timing in pyrotechnics) as its combustion rate is easily tailored. 

Four pyrotechnic delay compositions given in 1961 edition of Ellern (Ref 44a) are listed in Vol 3 of Encycl, p D50. In regard to Exotic" Delay Mixtures, Dr Ellern remarks in the 1968 ed of his book (Ref 57, p 415), that these formulations were actually prepd and tested in his laboratory, but the limited investigation was not further pursued by him or by others. At the time of development of Nb(Cb)-Ta - Ba Chromate mixts, the delay mixts with Cr, Mo W(Tungsten) were classified in US. That is why Dr Ellern develops his own mixts which were not classified, although their components Niobium and Tantalum were rather expensive... 

Figure 2.15 shows a schematic representation of the construction of a 12.7 mm multipurpose projectile with a pyrotechnic mixture (incendiary) and secondary explosive. Figure 2.16 schematically shows the construction of a hand grenade with a pyrotechnic delay composition. Bombs such as, for example, the MK 80 series, where approx. 45 % of the total mass is the explosive, usually contain pyrotechnic ( nose or tail ) fuses. 

Another matter to consider is whether or not pyrotechnic compositions will bum, and at what rate, at very low pressure. For reactions that nse oxygen from the air as an important part of their functioning, a substantial drop in performance is expected at low pressure. Mixtures high in fuel (such as the magnesium-rich illuminating compositions) will not bum well at low pressures. Stoichiometric mixtures, in which all oxygen needed to burn is provided by the oxidizer, shonld be the least affected by pressure variations. Data for bum rate of a delay mixture as the ambient pressure is reduced below 1 atmosphere are given in Table 5.10, and the bum rate is observed to slow up, as predicted, at lower pressures. 

With the possible exception of delay fuses, any pyrotechnic mixture represents a hazard worthy of report. Although the cause of frequent accidents reviewed in [2], compositions intended to explode or deflagrate are generally outside the field of this work and few are listed. Numerous reviews and specialist texts exist and hundreds of patents appear yearly. The account [1] of the theory and practice of pyrotechnics contains much useful information on the performance and potential hazards of a great variety of oxidant-fuel combinations which burn very rapidly or explosively. Safety measures are found in [2], Other reviews written from a functional viewpoint are found in [3] and [4], Some hazardously incompatible pyrotechnic mixes are reported [5], Detonability of pyrotechnic compositions has... 

Low-Explosive (LE). An explosive which when used in its normal manner deflagrates or burns rather than detonates that is the rate of advance of the reaction zone into the unreacted material is less than the velocity of sound in the unreacted material. LE s include propellants, certain primer mixtures, BkPdr, blasting explosives (See Ref 44, p B202-L), pyrotechnic compositions and delay compositions. Whether an explosive reacts as a high explosive or a low explosive depends on the manner in which it is initiated and confined. For example, a double base propellant when initiated in the usual manner acts as a LE. However, this material can be made to detonate if it is initiated by an intense shock. Conversely, a HE like TNT, can, under certain conditions be ignited by flame and will burn without detonation (Ref 40a, p 97)... 

Delay elements consisting of a pyrotechnic mixture that burns without production of gases. 

The primary source of perchlorate is the ammonium salt. Ammonium perchlorate is the oxidizer ingredient in solid propellant mixtures for rockets, missiles, and munitions. Other uses of perchlorate salts include medicine, matches, metal cation chemistry, and pyrotechnics (illuminating and signaling flares, colored and white smoke generators, tracers, incendiary delays, fuses, photo-flash compounds, and... 

Useful for pyrotechnical fire transfer are the A/39 (Army) mixture, Formula 7 mixture PA-lOl, Formula 8, said to be particularly well-suited for the ignition of delay compositions FA-70, Formula 9, used in numerous pyro primers such as the M19 and in commercial small arms ammunition primers, e.g. Winchester 8-1/2 NOL-60, Formula 10 and FA-959, Formula M. Red phosphorus in combination with barium nitrate and other materials has been used in several formulas in percussion primer mixtures and is also the subject of a patent. ... 

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