Dextrinated Colloidal

DCLA Dextrinated Colloidal Lead Azide (See Vol 1, p A558)... 

Of the many types of lead azide—pure or basic, dextrinated, colloidal. Service, polyvinyl alcohol. Special Purpose, RD1333, RD1343, RD1352, and dextrinated colloidal—the types which have been used for military or commercial... 

Dextrinated Colloidal Lead Azide (DCLA) Is essentially DLA with a very small particle size. The particle size Is In the range of one to two microns. 

Lead azide is not readily dead-pressed, ie, pressed to a point where it can no longer be initiated. However, this condition is somewhat dependent on the output of the mixture used to ignite the lead azide and the degree of confinement of the system. Because lead azide is a nonconductor, it may be mixed with flaked graphite to form a conductive mix for use in low energy electric detonators. A number of different types of lead azide have been prepared to improve its handling characteristics and performance and to decrease sensitivity. In addition to the dextrinated lead azide commonly used in the United States, service lead azide, which contains a minimum of 97% lead azide and no protective colloid, is used in the United Kingdom. Other varieties include colloidal lead azide (3—4 pm), poly(vinyl alcohol)-coated lead azide, and British RE) 1333 and RE) 1343 lead azide which is precipitated in the presence of carboxymethyl cellulose (88—92). 

Semenova, M., Belyakova, L., Antipova, A., Jubanova, M. (1999b). Influence of malto-dextrins with different dextrose equivalent on the thermodynamic properties of legumin in a bulk and at the air-water interface. Colloids and Surfaces B Biointerfaces, 12, 287-297. 

The presence of dextrin in the solution favours the precipitation of tiny, equal sized, rounded crystals. In Fig. 47 magnified crystals of dextrinated lead azide are shown and in Fig. 48 crystals of ordinary lead azide are shown for comparison. According to Sudo [96] gelatine exerts an influence similar to that of dextrin. In this author s opinion when precipitated from a solution containing gelatine lead azide is less sensitive to friction than that from solutions without added colloids. 

The most efficient colloids are pure Acacia gums. For reasons of economy, mixtures of Acacia gums and dextrin may be used. As in the preparation of concentrates for beverages, the oil phase to be protected will be added to the aqueous phase and the coating will be formed during homogenization. The emulsion will then be dried by atomization with air temperature at the inlet of l60 or 180 C and a powder temperature at the outlet of 85 to 90 C. 

Lead azide crystals should be spherical in shape, opaque in appearance and less than 0.07 mm in diameter. Dextrin is added as a colloiding agent, which prevents the formation of large, sensitive crystals of lead azide and regulates, to some extent, the shape of the crystals. 

The hazards involved in the manuf of the pure crystalline material delayed its practical use for many years. Although manufd and used in foreign countries since 1920, its military and coml uses in the USA, since 1931, have been restricted to an impure colloidal form or "dextrinated LA (Ref 122a). The prepn of colloidal LA has been described by Rintoul Weir (Ref 21), Snelling (Ref 23), Lowndes (Ref 24), Rinkenbach (Ref 51), Fleischer Burtle (Ref 108), Moskovich (Ref 74), Bostrom et al (Ref 145) and Fonda Fonda (Ref 125). In these procedures the objective was to obtain rounded aggregates of... 

Walcr-peptizable colloidal substances such as gelatin, dextrin, gum arable, and soap peptize many precipitates, and are often culled protective colloids. Gelatin in the solution prevents the precipitation of silver dichromatc upon mixing silver nitrate and potassium dichroinalc solutions. (See Condensation Processes, below.)... 

RDX, etc) are too sensitive to be used per se and must be desensitized. For example LA may be desensitized by coating its crysts either with dextrin (See Dextrinated Lead Azide in Vol 1, pp A 46 to A548) or with PVAlc (polyvinyl alcohol) (See Vol 1, p A558-R). It can also be desensitized by controlling the size and shape of its crysts [See Service Lead Azide (Brit) in Vol 1, p A557-R], or by pptg it in colloidal form (See Vol 1, p A558-L)... 

Bulk powders are made in considerable variety, but they consist always of nitrocellulose fibers which are stuck together but are not completely colloided. Some contain little else but nitrocellulose others contain, in addition to potassium and barium nitrates, camphor, vaseline, paraffin, lampblack, starch, dextrine, potassium dichromate or other oxidizing or deterrent salts, and diphenylamine for stabilization, and are colored in a variety of brilliant hues by means of coal-tar dyes. In the United States bulk powders are manufactured by one or the other of two processes, either one of which, however, may be modified considerably the materials are incorporated under wooden wheels, grained, and partially gelatinized, or the grains arc formed in a still where a water suspension of ptdped nitrocellulose is stirred and heated with a second liquid, a solvent for nitrocellulose which is volatile and immiscible with water. 

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