Explosives Flashcards
What are the some of the uses of explosives other than military purposes?
Mining/Quarrying - used to excavate sites
Excavation - for construction
Cladding (explosion welding)
Forensic investigation
Research
How was smokeless powder developed in the 1800s?
It was known as “gun cotton” made of nitrocellulose
low explosive which deflagrates effectively
occasionally used in firearms today due to the cost
this was done by using the fibre “cellulose” and treated with nitric acids to form the nitro groups
The use of nitric acid to add nitro groups is very common in explosives chemistry
2 KNO3 + S + 3C = K2S + N2 + 3CO2
what is the oxidiser and what is the fuel?
Sulphur starts at an oxidation state of 0 and becomes 2-
S and KNO3 are oxidisers, C is the fuel
How was safe detonation developed?
Making secondary explosives
Why was the development of exploding shells with fuses containing gun powder dangerous?
The containing of black powder and pressurising them would eventually lead to detonation
What was the first commonly used high explosive?
Picric acid
synthesis of phenol to picric acid by treating with nitric acid and sulphuric acid
the use of another acid is vital for the generating an effective electrophile
What was the next major development of a high explosive?
the synthesis of toluene to trinitrotoluene (TNT) by treating with nitric acid and sulphuric acid
used in armour-ships shells for tanks, warships.
Why was TNT not discovered earlier?
Almost impossible to prematurely detonate (less sensitive than picric acid)
Why does the nitration of TNT take longer than the synthesis of picric acid?
Phenol is more electron rich and is able to make stable intermediates. Hence the OH group has the ability to move the electrons around and lower the activation barrier so that nitration can occur.
What was the next high explosive?
RDX/HMX
synthesised from ammonia and formaldehyde
High brisance = shattering power
What are some high explosives found in mixtures?
Torpex - made of RDX, TNT and Al
What are the explosives used for non-military use?
Nitroglycerin = glycerol treated with nitric acid
originally use as a vasodilator
volatile - relatively easy to detect
Quite unstable so less useful
How was nitroglycerin stabilised?
Nobel used diatomaceous earth
nitroglycerin was adsorbed onto a mineral making dynamite
What was ANFO?
Ammonium nitrate made from nitrogen and hydrogen via the Haber-Bosch process and then combined with fuel oil
ANFO was used in quarrying
less sensitive than secondary explosives
Why are plastic explosive useful?
They are designed to be formable
a mixture of an explosive and plasticiser
What is a plasticiser?
An additive that makes a substance mouldable
familiar plastic explosives are like C4 and Semtex
What are polymer bonded explosives and what are their use?
PBX are 95% of explosive material mixed with a polymer binder
you can adapt their properties based on their chain length
They may use HMX as the explosive and poly butadiene as the polymer component.
What is the underlying chemistry of energetic polymers for PBX applications?
When treated with nitric acid, it will only nitrate the ends. The nitric process has to be pushed to fully nitrate.
it then undergoes polymerisation
Why is PBX insensitive?
The polymer binder acts as a cushion and protects much of the blast overpressure = elastic/plastic response or deformation
an integral sacrificial barrier
What is the FIGURE OF INSENSITIVITY?
The FOI is the arbitrary metric of explosive stability
How does FOI it work?
A drop tower is used to test the safety of explosives.
Typically a 1kg weight is dropped from a height and the likelihood of initiation is measured
What functional groups are helpful for predicting the likelihood of initiation?
C-ONO2 = MOST LIKELY TO INITIATE
N-NO2 = SLIGHTY EASIER TO INITIATE
C-NO2 = HARDEST TO INITIATE/MOST STABLE
What is FOI proportional to?
Enthalpy (heat of detonation)
