Explosions 1 Flashcards
Give 3 examples of explosions.
Give an example of each.
- physical (overpressure pV = nRT)
- nuclear (E = mc^2)
- chemical (ΔG = ΔH – TΔS)
Define energetic material.
contains its own oxidant and doesn’t rely on an external oxidant
it’s explosion is more efficient and powerful
Energetic materials can be what 2 things…
mixtures
compounds
Give an example of a mixture energetic material.
Define the fuel and oxidiser of this.
How does this mixture energetic material work?
ANFO - ammonium nitrate oxidiser, fuel oil reductant
fuel - fuel oil
oxidiser - ammonium nitrate
ammonium nitrate on own is fertiliser (not explosive) - needs addition of fuel to become energetic material
Give an example of a compound energetic material.
Define the fuel and oxidiser.
TNT - trinitrotoluene
fuel - toluene
oxidiser - nitro groups
What are typical properties of fuels and oxidisers?
fuels - carbon e.g. hydrocarbons
oxidisers - has oxygen
What is an external oxidant?
when rely on oxygen from atmosphere
What state are the products of detonation typically?
Give 4 examples.
just gases
CO, CO2, N2 and H2O
What are the 5 labels that can be given to explosives?
primary
secondary
tertiary
low
high
Define primary explosives.
- sensitive to some kind of stimuli: shock, heat, light and electricity
- dangerous to user and not generally synthesised on large scale
Define secondary explosives.
- more difficult to detonate as they are contact insensitive
- typically detonated by small amount of primary explosive
Define tertiary explosives.
even less sensitive than secondary explosives
Define low explosives.
Give an exception to this definition.
What are their uses and why?
Give three examples.
they typically deflagrate (burn)
when pressurised they detonate
typically used as propellants as generate a lot of gas
(gunpowder, fuels, fireworks)
Define high explosives.
Where is oxidiser contained?
Give three examples.
they typically detonate efficiently.
chemical reaction yields a supersonic shock wave that propagates through the material
oxidiser contained in one molecule
TNT, nitro-glycerine, RDC
Define the concept of deflagration.
a rapid oxidation reaction generating a low intensity pressure wave of moving gases
propagation of the reaction takes place at the surface of the material and is subsonic (slower than speed of sound in dense material - 1000 ms-1)
rate of deflagration is proportional to SA of explosive and external pressure
Why is speed of sound different in dense material?
in dense material around 1000ms-1 - less than speed of sound in air
What is the equation for the rate of burning?
da/dt = rAρ
where:
r = burn rate constant of explosive
A = surface area of explosive
ρ = density of explosive
What is the equation for the burn rate constant of explosive?
r= βP^α
where:
β = burn rate coefficient (constant)
P = pressure
α = pressure index (constant)
What is burn rate proportional to?
area and pressure
directly proportional relationship
area and pressure increase = burn rate increase
Define the concept of detonation.
a process of supersonic combustion in which a shockwave is propagated forward due to energy release in a reaction zone behind it
the high speed shock wave (1500 to 9000 ms-1) causes a violent disruptive effect
Describe the process of detonation and draw this.
- explosion initiated on edge of reaction zone (at detonation shock front) through detonation
- gases are being expanded out of end of reaction zone
- as the one part detonates, shock wave propagates through unreacted explosive and detonates unreactive explosive
What are two properties of RDX?
entropically favourable - one mole of RDX generates nine moles of gas
enthalpically favourable - heat of explosion is 5100 kJ kG-1
