Properties_of_explosions Explosion

1 properties of explosions

1.1 force
1.2 velocity
1.3 evolution of heat
1.4 initiation of reaction
1.5 fragmentation

properties of explosions
force

explosive force released in direction perpendicular surface of explosive. if grenade in mid air during explosion, direction of blast 360°. in contrast, in shaped charge explosive forces focused produce greater local effect.

velocity

the speed of reaction distinguishes explosive reaction ordinary combustion reaction. unless reaction occurs rapidly, thermally expanding gases moderately dissipated in medium, no large differential in pressure , there no explosion. consider wood fire. fire burns, there evolution of heat , formation of gases, neither liberated rapidly enough build sudden substantial pressure differential , cause explosion. can likened difference between energy discharge of battery, slow, , of flash capacitor in camera flash, releases energy @ once.

evolution of heat

the generation of heat in large quantities accompanies explosive chemical reactions. exceptions called entropic explosives , include organic peroxides such acetone peroxide rapid liberation of heat causes gaseous products of explosive reactions expand , generate high pressures. rapid generation of high pressures of released gas constitutes explosion. liberation of heat insufficient rapidity not cause explosion. example, although unit mass of coal yields 5 times heat unit mass of nitroglycerin, coal cannot used explosive (except in form of coal dust) because rate @ yields heat quite slow. in fact, substance burns less rapidly (i.e. slow combustion) may evolve more total heat explosive detonates rapidly (i.e. fast combustion). in former, slow combustion converts more of internal energy (i.e. chemical potential) of burning substance heat released surroundings, while in latter, fast combustion (i.e. detonation) instead converts more internal energy work on surroundings (i.e. less internal energy converted heat); c.f. heat , work (thermodynamics) equivalent forms of energy. see heat of combustion more thorough treatment of topic.

when chemical compound formed constituents, heat may either absorbed or released. quantity of heat absorbed or given off during transformation called heat of formation. heats of formations solids , gases found in explosive reactions have been determined temperature of 25 °c , atmospheric pressure, , given in units of kilojoules per gram-molecule. positive value indicates heat absorbed during formation of compound elements; such reaction called endothermic reaction. in explosive technology materials exothermic—that have net liberation of heat , have negative heat of formation—are of interest. reaction heat measured under conditions either of constant pressure or constant volume. heat of reaction may expressed heat of explosion.

initiation of reaction

a chemical explosive compound or mixture which, upon application of heat or shock, decomposes or rearranges extreme rapidity, yielding gas , heat. many substances not ordinarily classed explosives may one, or two, of these things.

a reaction must capable of being initiated application of shock, heat, or catalyst (in case of explosive chemical reactions) small portion of mass of explosive material. material in first 3 factors exist cannot accepted explosive unless reaction can made occur when needed.

fragmentation

fragmentation accumulation , projection of particles result of high explosives detonation. fragments part of structure such magazine. high velocity, low angle fragments can travel hundreds or thousands of feet enough energy initiate other surrounding high explosive items, injure or kill personnel , damage vehicles or structures.