Powder, explosions

In the absence of air, TEE disproportionates violently to give carbon and carbon tetrafluoride the same amount of energy is generated as in black powder explosions. This type of decomposition is initiated thermally and equipment hot spots must be avoided. The flammability limits of TEE are 14—43% it bums when mixed with air and forms explosive mixtures with air and oxygen. It can be stored in steel cylinders under controlled conditions inhibited with a suitable stabilizer. The oxygen content of the vapor phase should not exceed 10 ppm. Although TEE is nontoxic, it may be contaminated by highly toxic fluorocarbon compounds. 

In commercial practice, powdered explosives on an ammonium nitrate basis are used in most cases. Typical detonation velocities are between 1800 and 3500 m/s depending on the metal system to be bonded. The lower detonation velocity range is preferred for many metal systems in order to minimize the quantity of solidified melt associated with the bond-zone waves (12). In addition, subsonic detonation velocity explosives are required for the parallel cladding technique in order to avoid attached shock waves in the coUision region, which preclude formation of a good bond. 

Powder Explosions. See under Coal Dust Explosion Hazards from its Uses in Vol 3, C359-R Dust Explosions in Vol 5, D1578-R and Powder-Air Explosions and Detonations in this Vol... 

Ballistic Properties of Black Powder , Explosives and Pyrotechnics (The Franklin Institute Research Laboratories) 4, No 1-3 (Jan-Mar 1971)... 

The preparation of powder explosives is in essence simple. In the case of mixtures of ammonium nitrate and fuel oil in particular, the only requirement is a method of mixing which does not cause undue breakdown of the absorbent grains of ammonium nitrate. Hand mixing is employed for small quantities, otherwise some form of rotating container or gently stirred vessel. 

Semi-gelatine explosives (see p. 49) are manufactured and cartridged as powder explosives, although the presence of a thickened nitroglycerine base gives them properties which can approach those of gelatines. 

Explosives are fired in coal on the face, in the stable holes and sometimes in the making of roads. The commonest practice, as stated above, is to undercut the coal mechanically. Often a single row of holes with a permitted P3 explosive is then sufficient to bring down the coal. Powder explosives are most commonly used for this purpose, waterproofed when necessary. 

Figure 14.10 illustrates the method of seismic prospecting on land by what is known as reflection shooting. A hole usually 10 to 12 cm in diameter is drilled to a depth of 15 to 30 m. The charge of explosive is likely to be 5 to 12-5 kg and the stemming used is usually water. As the explosive must fire under a depth of water which may exceed 45 m, special varieties of gelatines are employed (see p. 53). Alternatively, a powder explosive can be sealed into pressure-resistant metal containers. Special detonators are also employed, not only to withstand the possible head of water, but also to have a specially short bursting time (see p. 113). 

Experimental investigation of poly(ethylene) powder explosions. 

For experimental investigation of aspirin powder explosions, See entry dust explosion incidents (reference 18)... 

Charcoal impregnated with the nitrate exploded lightly during sieving. Possibly a dust or black powder explosion. 

Mix equal parts of explosive and thermate incendiary. A powdered explosive is easiest to use, and TNT may be safely crushed with a wooden implement in a wooden container. Plastic explosive or dynamite also may be used, although in this case the explosive should be placed under the thermate so that the thermate will be directed upward. The thermate can be obtained from the AN M-14 incendiary grenade or homemade as described in the section on improvised incendiaries. ... 

Preliminaries. The combustion of suspended dusts and powders is quite complex and only imperfectly understood. The complexity stems from both fundamental and practical considerations. On the fundamental side, the ignition of suspensions of finely divided solids is influenced by hard-to-quantify factors such as the time-varying concentration of solids, the chemical activity and morphology of the particulate, and the degree of confinement provided by the vessel. On the practical side, industrial conditions are seldom sufficiently well-controlled or characterized to justify application of existing theoretical models. For all the above reasons, this chapter can provide only a very abbreviated coverage of ignition basics. The reader is referred to other sources for in-depth treatment of dust and powder explosions (Bodurtha, 1980 Bartknecht, 1981 Bartknecht, 1987). 

Figure 6.13. Experimental arrangement of the hot-explosive compaction method for the preparation of consolidated Ni-Al alloys (after Kecskes etal. 2004). (a) Precursor powder sample inside a steel-tube container placed in, (b) an asbestos thermal insulation sheet (c) a concentric card-box filled with the powdered explosive (80% NH4NO3 + 20% TNT) (d) threaded steel plugs serving as contacts for the preliminary heating and to be lifted off just before detonating the explosive (e) detonating cords.

Caution. Metal hexafluorides should not be condensed directly onto dry silicon powder. Explosions can occur. 

Deflagration, Development (Transition) from Combustion (Burning) in Powdered Explosives. 

CA 44, 7539(1950) (Character of the detonation break in powdered explosives) 7) Yu.B. Khariton, "On Detonating Capacity of Explosives A.F. Belyaev, "Influence of Physical Factors on Stability of Detonation in Ammonium Nitrate Explosives Ya.I. Leitman, "Influence of Fineness of Brisant Explosives on Sensitivity to Initiation . Series of papers in Russian, Vol 1 of the book "Problems of Theory of Explosives , IzdAkadNauk, Moscow(1947)... 

Same investigators (Ref 5) observed photographically behavior in detonation of powdered explosives solid NG (stable form), PETN, RDX PA. In all the expls tested a detonation "break was found which appeared... 

Ibid, DoklAkadN 58, 241-44(1947) CA 44, 7539(1950) (Cessation of detonation in powdered explosives) 6) O.A. Gurton, PrRoySoc 204A, 31-33(1950) (Fading ofde-tonation in solid expls) 6a) D.W. Woodhead R. Wilson, Nature 167, 561(1951) (Fading... 

Detonation, Cessation of (in Powdered Explosives) was discussed by A.Ya. Apin ... 

Accdg to Dunkle (Ref 2, p 284), explosive No 2 used by Deffet belongs to Class 3 of W. Taylor, (powdered explosive compositions containing a liquid sensitizer such as NG) in which a multiplicity of reaction centers may have an accelerating effect. 

K.K. Andreev S.V. Chuyko, ZhFizich-Khim 37, 1304-10(1963) ("Studies in the Deflagration to Explosion Transition of Explosives 1 . "Burning of Powdered Explosives at Constant Elevated Pressures )... 

Ibid, DoklAkadN 58, 241(1947) (On the nature of detonating conversion of powdered explosives) 5) Cook (1958) -not found 6) Zel dovich Kompaneets (I960), 218-19... 

Deflagration, Development (Transition) from Combustion (Burning) in Powdered Explosives , Section 1 DETONATION (AND EXPLOSION), DEVELOPMENT (TRANSITION) FROM BURNING (COMBUSTION) OR DEFLAGRATION , Section 2... 

Haid, Becker and Dittmar Stability Test (Designed for high explosives). 42g of powdered explosive, previously dried over phosphorous pentoxide, is introduced through a side tube into a glass vessel connected with a manometer which is in the form of a U-tube and contains mercury covered with a layer of paraffin oil. The glass vessel is also fitted with a side tap. The ensemble is heated at 75° for several hours and pressures are recorded in mm of Hg as a function of time. The steeper the pressure-time curve the less stable is the explosive... 

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