Manufacture lead azide

THE CONTINUOUS METHOD OF LEAD AZIDE MANUFACTURE (ACCORDING TO MEISSNER [110, 111])... 

Neutral azide Basic azides Lead azide manufacture... 

The continuous method of lead azide manufacture (according to Meissner) Lead azide with a purity under 95%... 

Destruction of lead azide Manufacture of sodium azides Sodium azide formation in liquid ammonia retrazene (Tetracene) retrazolc derivatives and their salts Azotetruzole Furoxanc derivatives Nitro derivatives of phenols... 

Avrami and Jackson [38] investigating dextrinated lead azide manufactured during World War II and repackaged in 1953, concluded that 25-year-old azide did not differ from recently manufactured dextrinated lead azide with respect to its sensitivity to impact. 

In the United States, lead azide manufactured for military use is packaged in steel drums under 50 50 water-ethanol solution however, isopropanol may be substituted for the ethanol. The drums are stored in above-ground magazines, and surveillance consists of periodic checks of the drum exterior and a yearly inspection of the liquid level. The top of each drum is fitted with a clear plastic plug to allow a more stringent control of the liquid level. 

Only relatively few compounds can act as primary explosives and still meet the restrictive military and industrial requirements for reflabiUty, ease of manufacture, low cost, compatibiUty, and long-term storage stabiUty under adverse environmental conditions. Most initiator explosives are dense, metaHoorganic compounds. In the United States, the most commonly used explosives for detonators include lead azide, PETN, and HMX. 2,4,6-Triamino-l,3,5-triuitrobenzene (TATB) is also used in electric detonators specially designed for use where stabiUty at elevated temperatures is essential. 

Lead Azide. The azides belong to a class of very few useflil explosive compounds that do not contain oxygen. Lead azide is the primary explosive used in military detonators in the United States, and has been intensively studied (see also Lead compounds). However, lead azide is being phased out as an ignition compound in commercial detonators by substances such as diazodinitrophenol (DDNP) or PETN-based mixtures because of health concerns over the lead content in the fumes and the explosion risks and environmental impact of the manufacturing process. 

Lead azide is manufactured by reaction of sodium azide with either lead nitrate or lead acetate. It is a white crystalline solid, insoluble in cold water and stable on storage. It is very sensitive to friction and impact and has a velocity of detonation, when pressed to a density of 3-8, of4500 ms 1. 

Two crystallographic forms of lead azide are important, the ordinary alpha form which is orthorhombic and the beta form which is monoclinic. The densities of these forms are 4-71 and 4-93 respectively. It was for many years believed that the beta form is the more sensitive to friction and impact and accounted for detonations which have occurred in the manufacture and handling of the substance. It is now known that the beta form is in fact no more sensitive than the alpha. Even the alpha form, when present as large crystals, is very sensitive and conditions can arise (particularly when the formation of the lead azide is controlled by diffusion effects) where spontaneous detonation occurs. Although with modern knowledge these hazards can be avoided, pure lead azide is nevertheless a dangerous compound and is now made only for military purposes. 

Commercially, lead azide is usually manufactured by precipitation in the presence of dextrine, which considerably modifies the crystalline nature of the product. The procedure adopted is to add a solution of dextrine to the reaction vessel, often with a proportion of the lead nitrate or lead acetate required in the reaction. The bulk solutions of lead nitrate and of sodium azide are, for safety reasons, usually in vessels on the opposite sides of a blast barrier. They are run into the reaction vessel at a controlled rate, the whole process being conducted remotely under conditions of safety for the operator. When precipitation is complete, the stirring is stopped and the precipitate allowed to settle the mother liquor is then decanted. The precipitate is washed several times with water until pure. The product contains about 95% lead azide and consists of rounded granules composed of small lead azide crystals it is as safe as most initiating explosives and can readily be handled with due care. 

The original initiating explosive used by Nobel and all manufacturers for many years was mercury fulminate. This had the disadvantage of decomposing slowly in hot climates, particularly under moist conditions. For this reason mercury fulminate is no longer widely used. In most countries it has been replaced by a mixture of dextrinated lead azide and lead styphnate. In the U.S.A. some detonators are made containing diazodinitrophenol. 

Although the requirement for flame sensitiveness is the main consideration for initiating explosives for plain detonators, others are important in manufacture. The explosive must be capable of compression into a coherent mass and at the same time leave the equipment free from adhesions. Lead azide can be somewhat deficient in cohesion, and to improve this a small proportion of tetryl is sometimes added to the... 

The introduction of LA into commercial detonators resulted in an unacceptably high level of explosions during manufacture and use and hence its use was discontinued until it could be prepared in less sensitive form. A number of methods have been used to prepare LA in a less sensitive form. The main control of properties is by synthesis rather than by any other approach. Lead azide compositions RD 1343 (improved CMC co-precipitated LA), RD 1352 (improved dextrinated LA) and Service lead azide (SLA) illustrate some modified LAs which are used depending on the requirements. Different processes developed for the modification of LA may be summarized as follows ... 

When manufacturing lead azide, efforts should be made to precipitate small, highly regular, free flowing crystals of a length not exceeding 0.1 mm. 

Considerable progress in the manufacture and application of lead azide was achieved by the addition of dextrin to the solution in which it was produced, as mentioned above. 

Lead azide is manufactured on a technical scale by the action of sodium azide on an aqueous solution of lead nitrate. According to a description of manufacture in the Wolfratshausen factory in Germany [109], the reaction is conducted in an open reactor of stainless steel, provided with a jacket warmed by hot water and a stirrer which may be lifted out of the reactor (Fig. 49). The reactor is emptied by tilting. Its upper edge is therefore fitted with a spout so that the contents pour easily. The size of the reactor is such that 4.5 kg of lead nitrate in the form of a 9-10% solution can be used in each batch. This solution is poured into the reactor, warmed to 50°C and neutralized with sodium hydroxide to a pH of about 4.0 (in the presence of methyl orange) and 150 g of dextrin mixed with a small amount of water, is added. The suspension or solution of dextrin in water should be decanted before use to separate mechanical impurities, such as sand. 

Fig. 49. Diagram of the design and operation of a reactor for the manufacture of lead azide and other primary explosives (tetrazene, lead styphnate and lead picrate).

Pure lead azide may be produced in the same equipment, but instead of lead nitrate and dextrin lead acetate is employed. The precipitation temperature is lower than in the manufacture of technical-grade lead azide (having a purity of less than 95%). All other operations are the same as already described. 

Silver azide, AgN3, is manufactured in the same way as lead azide, in aqueous solution, by action of sodium azide on silver nitrate. 

Into a reactor of the type used for the manufacture of lead azide (cf. Fig. 49) 501. of a solution of sodium nitrite (4 kg of NaNOz) were introduced and heated to a temperature of 50-55°C. To the warm solution 401. of a solution of aminoguanidine sulphate, containing 5 kg of the dry substance, was added during a period of 1-2 hr. The rate at which the solution was introduced influences the dimensions of the crystals formed. If the solution was introduced rapidly, small crystals resulted, if it was introduced slowly, the crystals were large. 

The lead picrate for this purpose was produced in the following way [42]. Into a stainless-steel reactor equipped with a stirrer of the type used for the manufacture of lead azide and other initiators (cf. Fig. 49) 8 1. of a solution containing 1.44 kg of lead nitrate and 151. of ice water were poured. Fifteen litres of a solution containing 1.5 kg of picric acid were then added. During the reaction the temperature should be maintained between 6 and 10°C. Since the temperature rises with the precipitation of lead picrate, 7-8 more litres of ice water must be poured into the reactor, usually a few minutes after the picrate has begun to precipitate. After 4 hr the liquid was decanted from above the precipitate the latter was transferred to a cloth filter and washed with alcohol (101.) to which an aqueous solution of lead, nitrate (500 ml of a 30% solution) has been added to avoid the dissolution of lead picrate during washing. 2.2 kg of product was obtainable from one batch. 

The continuous preparation of lead styphnate can be carried out in the same equipment as for the manufacture of lead azide (Fig. 50) after previous cleaning of the apparatus and exchanging the flowmeters. 

The precipitating temperature is, in this production, somewhat higher than in the manufacture of technical-grade lead azide. 

Curtius added lead acetate to a solution of sodium or ammonium azide resulting in the formation of lead azide. In 1893, the Prussian Government carried out an investigation into using lead azide as an explosive in detonators, when a fatal accident occurred and stopped all experimental work in this area. No further work was carried out on lead azide until 1907 when Wohler suggested that lead azide could replace mercury fulminate as a detonator. The manufacture of lead azide for military and commercial primary explosives did not commence until 1920 because of the hazardous nature of the pure crystalline material. 

Uses of Sodium Azide. The principal use of NaN, in the expl ind is in the prepn of alkali alkaline earth and other azides (Refs 37,38, 42,96,113,201,% others) (See Lead Azide, Plant Manufacture, etc). Meissner (Ref 44) used equiv quants of NaN, and a heavy metal salt, such as Pb acetate, for the continuous prepn of LA. Matter (Ref 33) found that NaN, was freed from carbonates by the addn of aq... 

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