INTRODUCTION Casings/Ammunitions of Small Calibre Shoulder-Fired Rockets4

Defenc.: Scienc.: Journal. Vol 45, No I, January 1995, pp ()1-63 @ 1995. DESIDOC

SHORT COMMUN]CAT]ON

J.S. G~aria, C.G. Mudkanna and S.V. Shirwalkar

E.t"plosives Research & Development Laboratory, Pune-411021

ABSTRACT

Incendiaries are chemical agents which on suitable initiation cause destructive damage due to fire on combustible targets. A solid pyrophoric incendiary composition has been developed and evaluated for its effectiveness, storage life and applications in different devices. This paper describes the method of preparation and compares the properties of the developed composition with a number of other solid incendiary compositions.

INTRODUCTION casings/ammunitions of small calibre shoulder-fired rockets4. The Jiqui.d incendiaries, however, suffer from Incendiary devices are used to initiate destruct~ve drawbacks, such as limited storage life arid poor fires for causing damage to various combustible targets, incendiary effect, and are not suitable for spinning type like fuel and ammunition dumps, base camps, tents, industrial installations. refineries, camouflages, wide projectiles. area of grass/paddy fields. Incendiary devices can be The mechanical strength and performance of liquid delivered to the target end by aircraft, artillery guns or incendiaries can be improved by the addition of suitable missiles in the form of bombs, shells and warheads. The thickening/gelling agents (metal soaps, rubber and tactical use of such devices is to create psychological polymers). A notable development of such ~ "ystem fear of mass fires and destruction amongst troops during was the Napalm-based incendiaries, which were found operations. The efficacy of the incendiary compositions to be very effective in Korean, Vietnam and Gulf wars4-f1. to ignite combustible targets depends on factors, such The original Napalm was a mixture of aluminium soaps as total heat output. burning temperature, duration of (12 per cent) of naphthenic or palmitic acids with burning and spread area. The dispersion of incendiary gasoline7. Napalm 'B' is a viscous mass obtained by composition is achieved either by bursting or by base mixing 50 per cent polystyrene, 25 per cent gasoline ejection of the ammunition/shell. and 25 per cent benzene. It gives longer duration of In general, the incendiaries are categorised as liquid, burning, higher heat output and better sticking gel and solid incendiaries (based on metal powders). propertyX. However" these gels are suitable for Liquid hydrocarbons. like benzene, gasoline, non-spinning projectiles, like bombs, mortars and toluene, xylene, etc. are reported to be used through rockets, and have short storage life. A number of flame throwers. Other types of promising liquids for thermite incendiaries and metal powder bombs a. e also incendiary applications are triethyl aluminium (TEA), reported as incendiary agents (AJ. Mg alloys and trimethyl magnesium, diethyl zinc. etcl-3. But their thermite compositions). These compositions are application in the armament system has not been much pyrophoric of a low order and cannot be ignited on reported so far. In US, TEA is filled in the bursting; -and a separate pyrotechnic device is needed

Received ]5 September ]994

61 DEF SCI J, VOL 45, NO JANUARY 1995 for ignition9-14. Aluminised, high explosives and 3. RESULTS AND DISCUSSION fuel-air-explosives (F AE) also have been claimed to be The results on the incendiary effect of the incendiary agents. These systems, on bursting, produce compositions studied are given in Table 2. The results fireballs above the ground for a few miIliseconds6. The obtained indicate that solid incendiary composition advantages and disadvantages of different incendiaries based on Zr and rubber is the best in view of better are indicated in Table 1. pick-up and longer burning duration. Further, optimum

Table I. Comparison or different incendiary systems proportion of rubber for Zr-based solid incendiary composition is 7 per cent to achieve optimum compromise on incendiary effect and mechanical Property Solid Ge1/liquld incendiaries incendiaries strength. The temperature of the burning incendiary pieces, as measured using WIRe thermocouple, was Heat output (caVcc) 18100 800! . observed to be of the order of 2000 °C. The results of Temperature (OC) 2(XX) 670 Duration of burning (s) 150 60 static trial with stimulated targets clearly indicated that

Stickiness Non-sticky Sticky the composition is capable of igniting all combustible Storage life (yrs) 10 0.5 targets. The composition studied is suitable for Suitability Suitable for Not suitable spinning and non. for spinning production, filling and application.

spinning projectiles. projectiles Table 2. Incendiary effect or various compositions

In view of the numerous advantages of solid Composition Observal. (%) Spread Duration of incendiary compositions for spinning-type projectiles, diameter burning pyrophoric metal (Zrrrl) powders-based compositions (m) (min) with suitable binders (natural rubber) were studied. The Zr (J} 40 0.25 use of the pyrophoric metal powders facilitates the Thermite 33 ignition of incendiary compound on bursting. The use Rubber 07 of binder provides mechanical strength to the Zr 95 40 1.0 composition, which in turn, makes it suitable for Rubber 05 spinning-type projectiles. This communication reports Zr 95 40 0.5 the results of various Zrrri powders-based incendiary Teflon 05 compositions studied and developed at ERDL. Zr 95 30 0.25 EP4 05

Ti(fine) 93 30 0.1 2. EXPERIMENTAL DETAILS Rubber 1"17

Zirconium powder of 98 per cent purity, received Zr 93 50 3.0 Rubber 07 from the Yashoda Special Metals Pvt Ltd, Hyderabad and having average partical size of 5-8 micron, was used. Note: 1. Weight of the compositions: 1.5 kg Unvulcanised natural rubber was used as binder . 2. Thenniteconstitutes Al- 25 percent, F~O3 -75 percent The compositions were prepared by dissolving rubber in benzene. The gel thus formed and metal powder (ZrITI) were mixed in the Sigma mixer REFERENCES thorougly. The mixed mass was then poured into trays and cured at 60 °C for 24 h. The cured sheet was broken Burns, W. Incendiary compositions containing into pieces, which were then consolidated into pellets triethyl aluminium. Chem. Abstr. , 1972, 76, of required size and geometry by pressing technique, 74450n. followed by assembly of pellets in projectile casings. 2, Lehikoinen, U .A. Tracer incendiary materials The compositions thus obtained were evaluated in a including liquid alkylaluminium and compatible number of devices and subjected to static as well as inorganic oxidizer. Chem. Abstr. , 1974, 80, dynamic tests, for their efficiency. 110527m.

62 .GHARIA, et al: SOLID INCENDIARY coMPosmoNs

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