Initiation hot wire

Ignition by Hot Wires. Now we turn to a discussion of ignition by hot wires, but we purposely exclude studies on EED s (See Vol 5, pp E63-E68) or initiation of detonation by hot wires (See Initiation, Hot Wire in this Vol). We quote Lewis Von Elbe ... 

Type of Initiation Catalytic Cr Ni Metal Rings Spark Hot Wire Inert Shock... 

Type of Initiation Catalytic (Ni Cr oxides in coke granules) Spark Hot Wire Expl Shock... 

It could not be detonated by hot wire initiation, but a sample exploded during distillation at ambient pressure at 102°C. 

Metathesis reaction to prepare crystalline transition and B metal oxides from halides and sodium peroxide is initiated by a hot wire and can be highly exothermic and explosive in some instances. 

Pentanitroaniline (PNA) has five neighboring nitro groups and is destabilized even more than the tetranitro compound by repulsive steric interactions. The 3- and 5-nitro groups are easily hydrolyzed as observed earlier for HNB. PNA was studied as an initiating explosive (a sensitive explosive that will decompose to hot gaseous products explosively by a hot wire or weak shock)98. 

Initiation by Primers (and Boosters) is the standard method of initiating secondary explosives. Thus hot wires (or other means) are used to initiate the primer charge (Lead Azide, Mercuric Fulminate etc) explosive whose detonation then initiates the main charge of PETN,... 

Initial mixt composition ranges of knallgas and w vapor in a detonation tube were varied by controlling temps at 100, 200 300°, for knallgas densities of 0.64-1.8, 8.5—16 46-62g/liter, respectively. Ignition was by hot wire. The threshold composition decreased as initial mixt density increased. Threshold compositions were 62, 44 V36% knallgas at 100, 200 300°, or initial mixt densities... 

The explosive was exhaustively characterized for thermal behavior, impact sensitivity and electrostatic discharge sensitivity etc. Based on this data, CP has been described as much less sensitive to accidental initiation than primary explosives such as LA but at the same time, initiation grows rapidly to detonation when properly confined. Its performance evaluation in a test detonator or hardware indicates that CP can replace primary explosives in many hot wire detonator applications especially if safety considerations are of prime importance [239]. 

While it sublimes below 250° at press 0 to 150 mm Hg, it shows slow decompn between 250-450° at 70 mm and betw 250°-310° at 150 mm. Amm azide is one of the more stable azides (Ref 20). According to Gray Wad-dington it vaporizes and dissociates into NH3 HNa and then the HN3 explodes. A hot wire causes Amm azide to burn quietly in air rather than detonate (Ref 20). This azide detonates violently when properly initiated, heared rapidly or heated under confinement (Refs 2 10). Temp of expln is 1400° and specific energy 7102 kg/1 (Ref 9). It is considered a non-brisant expl as it decomposes in an ideal manner producing only innocuous gases (1148 1/kg at 0° and 760 mm) (Ref 6). The toxicity of Amm azide is unknown (Ref 22). Ephraim (Ref 19) states that this salt may be regarded as a polymer of imide(NH). ... 

Detonation Rate, 1500 m/sec (unconfined and initiated by hot wire), 1700 m/sec (unconfined and initiated by impact with grit particle), and... 

To measure the rate of burning, fine wires of some low-melting metal (fuze wire) were threaded thru holes drilled diametrically thru the strand at accurately measured intervals (eg, 1r ). Two or more wires were used. Each wire was attached in series with an electric timer. The strand was mounted in a holder and placed vertically inside a dosed chamber. A given initial pressure was established in the chamber by using high, pressure N2. The initial temp was controlled by means of a constant-temp bath, and ignition of the strand was accomplished by means of a hot wire wrapped around it at one end... 

Temperature Upon Initiation Times of Four Primary Explosives , NOLTR 72-123 (1972) [Leopold reports that when the induction time to hot wire ignition is compared between Ag Azide, LA, n-L Styphnate and basic L Styphnate at temps ranging from 550° to 3400°, the latter two always have the longest initiation times. Also, that pulsed hot wire initiation of both n-L Styphnate and basic L Styphnate gives a linear relationship between the log of the induction time and the reciprocal of the absolute temp (Arrhenius relationship)]... 

We can put known amounts of methane and chlorine into a bomb calorimeter and use a hot wire to initiate the reaction. The temperature rise in the calorimeter is used to calculate the precise value of the heat of reaction, AH°. This measurement shows that 105 kJ (25 kcal) of heat is evolved (exothermic) for each mole of methane converted to chloromethane. Thus, AH° for the reaction is negative, and the heat of reaction is given as... 

Future work requires optimization of the system in order for K2DNABT to be considered as a replacement for lead azide in detonators. From the initial results, K2DNABT appears to be a good possible replacement for lead styphnate when initiated via a hot-wire or electric bridgewire. Formulations will also need to be optimized in the future, with respect to finding the correct particle size. 

Another method similar to flame as an impulse is to ignite the explosive by heat (Figure 5.3, B + C). A bridgewire which is heated by an electric current is either in direct contact with the primary explosive (hot-wire initiator), or first it is in contact with a pyrotechnical composition which then initiates the primary explosive by flame. This second type, called an electric match, is the most common initiation method in blasting caps worldwide. However, there is also a type of detonator known which achieves detonation without a primary explosive. This type of deto-... 

Fig. 5.3 Schematic representation of common initiation and ignition methods of energetic materials. A) Fuse type. B) Electric match type. C) Hot-wire type. D) Percussion / Stab type. E) Exploding-bridgewire type.

While Region II can be compared with the hot-wire initiation of primary explosives or pyrotechnic compositions, the laser power densities in region IV also make it possible to directly shock initiate secondary explosives by laser irradiation. The laser power densities of Region IV are achieved by solid-state lasers with laser powers of at least 100 W. In contrast, laser diodes ( 1-10 W) only provide power densities which fall into the regions II and III. However, more powerful laser diodes have been gradually developed and therefore, laser diode initiators (LDI) have be-... 

Concluding, based on these aspects, the laser initiation of explosives by laser diode radiation seems to be a very attractive and initiation method of the future. However, due to the limited power of laser diodes, the explosives might be thermally ignited and undergo a DDT, in contrast to the shock initiation which results by high-power solid-state laser radiation. The operating mode of laser diode initiators can be compared to that of electric hot-wires but with faster function times as has been demonstrated in the literature. 

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