Use and manufacture of improvised explosives Flashcards
Clandestine explosives
frequently used in terrorist attacks
manufacture is uncontrolled
minimal temperature control in exothermic syntheses
No quality control (will not have have high degrees of crystallinity)
Can lead to accidental detonations due to increased shock sensitivity
Acetone peroxide
Known as TATP
A common clandestine explosive
Produced in both a dimer and trimer form
incredibly oxygen deficient = -151
Hence, it cannot form CO and H2O without using O2 from the environment
How does TATP detonate?
The actual products do not conform to the KW rules at all
It reforms acetone and ozone
Why is the heat of explosion positive for TATP?
TATP defies the rules of an explosive of generating a lot of heat and a lot of gas.
This is an endothermic reaction and it takes energy in, getting colder during the explosion.
Known as an entropic explosive, taking in heat and releasing any energy.
What do entropic explosions look like?
A large volume of gas is generated but no fireball or loud bang is heard
What makes the detection of TATP challenging?
It is a white powder which makes it hard to detect.
if TATP has no strong UV signature, then HPLC/UV-VIS techniques will not be useful
GC-MS is possible but not appropriate for field tests because a standard GC-MS is not portable
How do we detect TATP?
One method is by using a peroxidase enzyme.
When we shine UV light of 254nm on to the TATP, it decomposes back into hydrogen peroxide and acetone. Then the test for hydrogen peroxide is performed.
Start with colourless substance of enzyme and mix with substance of interest.
a colour change of colourless to green should occur as the hydrogen peroxide interacts with the colourless enzyme, it invokes a change in the electronic structure which changes the colour.
What is the drawback of the detection of TATP?
The method is not very sensitive, not suitable in situations where you have trace amounts
Use of TATP and related explosives
Tiny explosives pf acetone peroxide used in bread whitening
Used in suicide bombings - 2005 London underground
2017 Manchester attack
How can you manufacture a failed explosive?
FLOUR is very fine powder and has a large surface area allowing for efficient detonation. However it can take in residual water and get damp = causing the explosive to fizzle out.
What is a taggant and what is it used for?
Additives that provide a traceable signature to the explosive.
Used to deal with the illicit and military use of plastic explosives.
Taggants are preventative and diagnostic = they have properties that means they are easy to detect
What kind of properties would we want a taggant to have?
volatile = if they are readily volatile they are much easier to detect in the gas phase
not used in other applications = if they are found everywhere this removes the context
How are taggants designed?
Sensitive and specific detection before and after explosive use
they are designed to be chemically related to the explosive materials
what are pre-detonation taggants?
These are used to prevent attacks
typically detected by sniffer dogs (ppm levels) or mass spectrometry based systems
How does ion mobility spectrometry work?
Ionises volatile molecules by an electric field.
resulting ions are fired through a tube against the action of a drift gas, which is inert (unreactive)
the drift gas goes in the opposite direction of the electric field, preventing the molecules
the drift gas will affect the larger molecules more than smaller molecule, allowing for separation
