Initiatory explosives

These explosives are characterized by very high rates of reaction and generation of high pressures on explosion. They are usually sub-divided into (i) primary or initiatory explosives, (ii) secondary explosives and (iii) tertiary explosives. 

Different types of initiatory explosives essentially developed for military applications have also been used for commercial detonators and cap compositions. Service lead azide (SLA) has been extensively used as an initiatory explosive for detonators. However, it has the limitation that hydrazoic acid forms on ageing and ultimately forms sensitive copper azide with copper tube-based detonators (responsible for many unfortunate accidents all over the globe) therefore SLA has been replaced by a new and safe initiatory explosive known as basic lead azide (BLA). 

Mercury fulminate (MF) is the oldest initiatory explosive known. 

Normal lead styphnate (LS) [Structure (2.10)] was first reported by Von Herze in 1914, although its basic salt, that is, basic LS was prepared by Griess [7] way back in 1874, by the reaction of acidified magnesium styphnate with lead nitrate/acetate in hot aqueous solution. It is precipitated as mono hydrate and consists of reddish-brown rhombic crystals. It is filtered off, washed with water, sieved through a stainless steel sieve and dried. Like other initiatory explosives, it is kept in wet conditions until used. 

Despite the fact that LA, LS and tetrazene suffer from serious drawbacks, they are still being used in detonators and cap compositions for military and civil applications. Thus LA, LS and tetrazene are the most commonly used primary explosives at present and research is in progress in order to find out suitable substitutes free from such drawbacks. The aim of research in initiatory explosives has all along been to get less sensitive, more compatible, more stable and more efficient material so that safety in manufacture and handing is ensured. 

The erstwhile Explosives Research and Development Laboratory (ERDL), now High Energy Materials Research Laboratory (HEMRL), Pune, had undertaken a study on primary explosives with a view to synthesizing a series of new explosives, which are safer, powerful and free from the drawbacks of lead azide and MF. As a result of these sustained efforts, HEMRL has successfully synthesized and developed a new and safer initiatory explosive called basic lead azide (BLA). 

The detonator is considered as the first fire-device of key importance in any explosive train and contains a small quantity of a very sensitive explosive as a means of initiation of inorganic salts of weak acids, that is, M F, LA and LS. However, they all suffer from some shortcoming and are not eco-friendly. In order to overcome these shortcomings of the existing initiatories, use of nickel hydrazine nitrate (NHN) [ Ni(N2H4)3 (N03)2], which has better storage stability and is also eco-friendly, has been reported in the literature [262, 263]. 

Bahadur, K. (1972) Ph.D. Thesis entitled, Preparation of New Initiatory Compounds and Study of Their Explosive, Physical and Chemical Properties, University of Poona. 

Lead azide is not used in primers where it is desired to produce fire or flame from impact. Fulminate mixtures and certain mixtures which contain no fulminate are preferred for this purpose. Lead azide is used where it is desired to produce, either from flame or from impact, an initiatory shock for the detonation of a high explosive—in compound detonators as already described, and in the detonators of artillery fuzes. For the latter purpose, caps containing azide and tctryl (or other booster explosive) are... 

Clark found that the initiatory power of diazodinitrophenol is about twice that of mercury fulminate and slightly less than that of lead aside. His experiments were made with 0.5-gram charges of the high explosives in No. 8 detonator capsules, with reenforcing caps, and with charges compressed under a pressure of 3400 pounds per square inch. He reported the results which are tabulated below. 

Commonly, mercury fulminate, lead azide, and lead styphnate (lead 2,4,6-trinitrobenzene- 1,3-diolate) have been used as primary explosives. These compounds are very good initiatory explosives, however they also suffer from some drawbacks, such as [28,20] ... 

Bahadur, K. Study of some double salts of lead useful as initiatory explosives by thermo gravimetry and thermometric titration. In Hansson, J. (ed.) Proceedings of Symposium on Chemical Problems Connected with the Stability of Explosives, pp. 1-15. Ystad, Sweden (1973)... 

---