Lecture 1 - Explosions 1

Question 1

what at the 2 definitions of an explosion

Answer 1

1 = a sudden and violent release of physical or chemical energy often accompanied by the emission of light, heat and sound

2 = a rapid increase in pressure in a confined space… generally caused by the occurrence of exothermic chemical reactions where gases are produced in relatively large amounts

Question 2

what two types of changes are seen within explosions

Answer 2

chemical and physical changes

chemical - relate to thermodynamics (Gibbs free energy equation)

physical - relate to pressure

Question 3

do all explosions cause loud sounds

Answer 3

no

Question 4

what does the volume of gas release during an explosion relate to

Answer 4

the power of the explosion

Question 5

explosive are known as energetic materials what does this mean?

but can are all explosions caused by energetic materials

Answer 5

energetic material contain their own fuel and oxidant so don’t rely on other sources = more efficient and powerful explosive

no, as some fuels can react with external oxidant such as oxygen in the air to create an explosion

Question 6

what is a fuel-air explosion

Answer 6

an explosion that relies on an external oxidant for example oxygen

Question 7

are energetic materials elements, mixtures or compound

Answer 7

mixtures or compounds

Question 8

give two examples of energetic materials

Answer 8

TNT - trinitrotoluene
ANFO - ammonium nitrate and fuel oil mix

ammonium nitrate is not explosive on its own it is a fertiliser but when combined with fuel oil it can be explosive

Question 9

what are the products of detonations generally

Answer 9

gases but side products are possible

Question 10

in TNT what parts act as the fuel and what parts as the oxdiant/oxidiser

Answer 10

fuel = the hydrocarbon (toluene part)

oxidiser = nitro groups (NO2 here)

Question 11

what 4 gases could be produced by an explosion of TNT

what 2 gases could also be produced but are not favourable thermodynamically

Answer 11

CO - if oxygen deficient reaction
CO2 - if enough oxygen
H2O - as a vapour not liquid (enough energy to convert it to a gas)
N2

methane and NOx gases

Question 12

what categorises a primary explosive

Answer 12

sensitive to shock, heat, light and electricity

very dangerous to the user

not synthesised on a large scale as easy to accidantally go off

Question 13

what categorises a secondary explosive

Answer 13

harder to detonate (not as sensitive)

contact insensitive

normally detonated by a small amount of a primary explosive

(tertiary explosive even less sensitive)

Question 14

what categorises a high explosive

give three examples

Answer 14

generally detonate

chemical reaction yields a supersonic shock wave that propagates through the material

contain the oxidiser within them normally

e.g TNT, nitroglycerin, rdx

Question 15

what categorises a low explosive

give three examples

Answer 15

they generally deflagrate

burn when pressurised so they eventually can detonate due to a pressure build up

used as propellants normally

e.g gunpowder, fuels (propane, methane, hydrogen), fireworks

Question 16

in deflagration, where does the propagation of the reaction take place and what is the reaction speed

Answer 16

takes place at the surface of the material

is subsonic expanding wave (slower than speed of sound (1000m/s))

Question 16

is one big explosive or lots of little ones at key point generally better

Answer 16

little ones at key points

if big one fails then problem
the energy from the big one if not confined properly could go into another material rather than the job intended

Question 17

what is deflagration

Answer 17

a rapid oxidation reaction generating a low intensity pressure wave of moving gases

Question 18

in deflagration what is the burn rate proportional to

Answer 18

the surface area and the pressure

higher surface area is better hence why explosives are normally powders

higher pressure = more powder

Question 18

what does confining a low explosive in a small space do

Answer 18

increase the burn rate as it stops gases escaping - can lead to detonation

Question 19

what type of speed does the wave travel in a detonation and what destruction effect does this have

Answer 19

a high-speed shock wave (typically 1500m/s to 9000m/s)

causes a violent disruptive effect

Question 20

what is detonation

Answer 20

a supersonic combustion where a shock wave is propagated forward due to the energy release in something called a ‘reaction zone’ behind it

Question 21

what equipment can be used to monitor explosions

Answer 21

high speed cameras

Question 21

if there is not enough oxygen initially for a high explosive to produce CO2 what is produced and what can this go on to react with

Answer 21

carbon monoxide (CO)

this can then go onto react with oxygen in the atmosphere to form CO2

Question 22

what results in an explosion being enthalpically favourable

Answer 22

production/release of heat

Question 23

what is seen in the pressure initially during a detonation

Answer 23

a sharp increase in the pressure of the system followed by a decrease

Question 24

why is RDX considered a good high explosive

Answer 24

entropic and enthalpically favourable reaction

generates lots of heat and gas
generate a huge amount of energy

Question 24

what does entropy relate to and what results in an explosion being entropically favourable

Answer 24

the moles of gas on either side of the equation

if more moles of gas are in the products compared to the reactant = favourable