Gasless delay formulations

Casless Delay Formulations Gasless delay formulations were introduced around 1929 to replace the old fuse formulation based on gunpowder which used to give erratic results under conditions of low ambient pressure at higher altitudes. 

The basic reaction underlying the combustion of many gasless delay formulations is the Goldschmidt or thermite reaction where a metal powder and a metallic oxide interact in an oxidation-reduction reaction manner with the evolution of a large amount of heat but very little or no gas. Consequently, these formulations are used where no vent or very little vent is provided in the ammunition. Gasless delay formulations tend to burn faster under higher consolidation as the points of contact of fuel and oxidizer increase. This is because the reaction in this case is a solid state reaction by diffusion. 

The fuels are finely powdered metals (2.0-10.0 g) among which titanium, zirconium, manganese, tungsten, molybdenum and antimony are very common. Sometimes, non-metal powders such as boron and silicon (for fast burning delays), binary alloy powders such as ferrosilicon, zirconium-nickel, aluminum-palladium and metal compounds such as antimony sulfide, calcium silicide etc. are also used. 

The oxidizers include heavy metal oxides such as red lead (Pb304), lead dioxide (Pb02), iron oxide (Fe203), bismuth oxide (Bi203), lead and barium chromates etc., peroxides (barium peroxide) and various oxysalts of potassium and barium. 

The most important characteristic of a delay formulation is its IBR. In addition, other important characteristics are sensitivity to impact, friction and electric spark, ignition temperature, heat output and gas output. Therefore, before static evaluation of delays, the delay formulation must be characterized thoroughly for these properties. 

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