What are some examples of peaceful uses of explosives?
- Mining/quarrying
- Excavation (for construction)
- Cladding (explosion welding)
- Forensic investigations
- Research
What are the traditional reactants in gun powder deflagration?
KNO3, S and C
What does changing the relative proportions of the reactants in the deflagration process of gun powder do?
Changes what products are formed
What is the deflagration process?
2 KNO3 + S + 3 C –> K2S + N2 + 3 CO2
What is the oxidiser and fuel in the deflagation process?
KNO3 is an oxidiser, S and C are fuels
* KNO3 contains oxygen = oxidiser
* Carbon is usually a fuel
* Look at the oxidation state changes to know if Sulphur is a fuel or oxidiser
Fact about black powder
- Generally deflagrates incompletely
How is ‘gun cotton’ made?
Nitration of cellulose fibres to produce nitrocellulose
Gunpowder bombs
Gunpowder bombs
* Very dangerous
* Enclosed black powder (causing it to be pressurised) can detonate easily
Picric Acid
- First commonly used high explosive
- Stable(ish)
- Made from phenol (found in coal tar), treated with nitric acid in the presence of another acid
Why do you need the presence of another acid when forming an explosive with nitric acid?
To generate an effective electrophile to get the nitro groups to be added effectively
TNT
- Less sensitive than picric acid (almost impossible to prematurely detonate)
- Nitration of toluene in the presence of H2SO4
Nitration of toluene is much slower than for phenol, why?
Phenol is electron rich
* Lower activiation barrier
RDX/HMX
- Research and Development explosive
- Her Majesty’s explosive
- High brisance - shattering power (can pierce armour)
Nitroglycerin
- High explosive - non-military use
- Nitration of glycerol
- Very unstable on its own (volatile)
- Adsorb nitroglycerin onto the surface of diatomaceous earch to stabilise it (dynamite)
Ammonium nitrate (NH4NO3) as a high explosive
- Combined with fuel oil (C11-20 alkanes) makes ‘ANFO’ - high explosive used in quarrying
- ANFO is a tertiary explosive - even less sensitive than a secondary explosive
- Hard to detonate - needs a blasting cap of more controlled high explosive
- Restrictions on the amount of NH4NO3 that people can buy because it is easy to make into a ‘fertiliser bomb’
Plastic explosives
- Designed to be formable
- A mixture of mostly explosive and a bit of plasticiser
- Broader range of applications because it is formable
What is a plasticiser?
An additive which makes a substance mouldable
Polymer bonded explosives (PBX)
- ~ 95% explosive with a polyer binder
- Explosive is encapsulated in a matrix of polymer
- Can reduce the sensitivity of an explosive because polymers are less sensitive
- Can adapt properties like chain length or branching to optimise the explosive
- Can make a polymer with an explosive functional group
What are some applications of polymer bonded explosives?
- Nuclear weapons
- Cruise missiles
- Any high performance application
What is an integral sacrificial barrier in PBX’s?
The polymeric binder acts as a cushion and protects (captures) much of the blast overpressure - elastic/plastic response or deformation so all the gas/energy goes in one direction
What is a drop tower and how is it used?
Used to test the safety/stability of explosives
* Impactor is dropped onto the explosive, look to see how much force is required for detonation
What is the order of initiation?
C-ONO2 > N-NO2 > C-NO2
* C-ONO2 is more likley to detonate than N-NO2
