Explosions 1

Question 1

Give 3 examples of explosions.
Give an example of each.

Answer 1

1. physical (overpressure pV = nRT)
2. nuclear (E = mc^2)
3. chemical (ΔG = ΔH – TΔS)

Question 2

Define energetic material.

Answer 2

contains its own oxidant and doesn’t rely on an external oxidant

it’s explosion is more efficient and powerful

Question 3

Energetic materials can be what 2 things…

Answer 3

mixtures
compounds

Question 4

Give an example of a mixture energetic material.
Define the fuel and oxidiser of this.
How does this mixture energetic material work?

Answer 4

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

Question 5

Give an example of a compound energetic material.
Define the fuel and oxidiser.

Answer 5

TNT - trinitrotoluene

fuel - toluene
oxidiser - nitro groups

Question 6

What are typical properties of fuels and oxidisers?

Answer 6

fuels - carbon e.g. hydrocarbons
oxidisers - has oxygen

Question 7

What is an external oxidant?

Answer 7

when rely on oxygen from atmosphere

Question 8

What state are the products of detonation typically?
Give 4 examples.

Answer 8

just gases

CO, CO2, N2 and H2O

Question 9

What are the 5 labels that can be given to explosives?

Answer 9

primary
secondary
tertiary
low
high

Question 10

Define primary explosives.

Answer 10

• sensitive to some kind of stimuli: shock, heat, light and electricity
• dangerous to user and not generally synthesised on large scale

Question 11

Define secondary explosives.

Answer 11

• more difficult to detonate as they are contact insensitive
• typically detonated by small amount of primary explosive

Question 12

Define tertiary explosives.

Answer 12

even less sensitive than secondary explosives

Question 13

Define low explosives.
Give an exception to this definition.
What are their uses and why?
Give three examples.

Answer 13

they typically deflagrate (burn)

when pressurised they detonate

typically used as propellants as generate a lot of gas

(gunpowder, fuels, fireworks)

Question 14

Define high explosives.
Where is oxidiser contained?
Give three examples.

Answer 14

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

Question 15

Define the concept of deflagration.

Answer 15

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

Question 16

Why is speed of sound different in dense material?

Answer 16

in dense material around 1000ms-1 - less than speed of sound in air

Question 17

What is the equation for the rate of burning?

Answer 17

da/dt = rAρ

where:
r = burn rate constant of explosive
A = surface area of explosive
ρ = density of explosive

Question 18

What is the equation for the burn rate constant of explosive?

Answer 18

r= βP^α

where:
β = burn rate coefficient (constant)
P = pressure
α = pressure index (constant)

Question 19

What is burn rate proportional to?

Answer 19

area and pressure
directly proportional relationship

area and pressure increase = burn rate increase

Question 20

Define the concept of detonation.

Answer 20

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

Question 21

Describe the process of detonation and draw this.

Answer 21

1. explosion initiated on edge of reaction zone (at detonation shock front) through detonation
2. gases are being expanded out of end of reaction zone
3. as the one part detonates, shock wave propagates through unreacted explosive and detonates unreactive explosive

Question 22

What are two properties of RDX?

Answer 22

entropically favourable - one mole of RDX generates nine moles of gas

enthalpically favourable - heat of explosion is 5100 kJ kG-1