Explosions 4 Flashcards
What is wrong with the manufacture of clandestine explosives?
it is dangerous
Where are clandestine explosives frequently used?
terrorist attacks
What are the limitations in the manufacture of clandestine explosives?
Explain reasoning.
- uncontrolled and undertaken by less experienced personnel
- minimal temperature control in exothermic syntheses - runaway chemical chain reactions
- no quality control (e.g. crystallinity/polymorph control)
- no control of starting material impurity profile - increase shock sensitivity
- often unaware of exact products made as no access to good analytical equipment - requires trial and error
- whatever they can get hold of determines what they will make - often not safest/most stable
What is the problem with the common manufacturing materials of clandestine explosives?
can’t buy large quantities of them but still can buy them and build them up over time
What is a common clandestine explosive?
What are two forms it is produced in?
acetone peroxide
dimer (DATP) and trimer (TATP)
trimer most common modern form
What is weird about TATP?
calculated oxygen balance is -151% so in theory can’t even form CO and H2O without O2 from environment
shouldn’t work well as explosive in terms of efficiency - should have to use oxygen from atmosphere
What are the products of TATP detonation? and why is this weird?
acetone and ozone
would never see these as products of explosives
doesn’t obey K-W rules at all
What is the heat of explosion of detonation of TATP?
What does this mean? Why is this weird?
ΔHr = +10.8 kcal mol-1 (45.2 kJ mol-1 or 203.6 kJ kg-1)
positive so endothermic - explosive gets colder during detonation and takes in heat from surroundings
weird as most explosives want to generate lots of heat and gas
What is explosive like in terms of amounts of gas generated?
not perfect but still used widely as materials needed to make this are readily available (hydrogen peroxide and acetone)
What can detonation of TATP be referred to as? and why?
entropic explosion
because of large volumes of gas produced without producing heat
Can we quantitatively define an explosive power for TATP?
no as rules don’t work
doesn’t make sense to multiply enthalpy value by gas as we are taking in heat
Why can’t TATP be detected by HPLC/UV-vis techniques?
TATP doesn’t produce a strong UV or visible absorption
Can TATP be detected by GC-MS?
yes because it is volatile
challenging due to decomposition and it is not appropriate for field tests
What is the method for onsite detection of TATP?
when shine UV light of around 254nm onto TATP, it decomposes back into hydrogen peroxide and acetone again so can do a test for hydrogen peroxide and acetone
start with colourless substance, mix with potential containing TATP, shine UV light on it, see decomposition, then look for colour change
when hydrogen peroxide interacts with horseradish peroxidase enzyme, invokes a change in electronic structure of this which changes its colour from colourless to green
What is problem with chemical tests for explosives?
When are they good/bad?
they are not very sensitive:
if have trace amounts of TATP will be difficult to conclusively say we have TATP
if have unexploded TATP, will be large quantities of TATP so will be able to detect it.
Are there any legitimate uses of TATP?
no
acetone peroxide used in tiny quantities in bread whitening
When was TATP discovered and when was it used in explosives?
Why was it started to be used in explosives?
1890’s - discovered
1980’s - used in explosives
people started to look for alternatives that could easily be made when restrictions were made on actual explosives
What are global uses of TATP?
What are UK uses of TATP?
early 2000’s - suicide bombings on Israeli side of Green (Armistice) Line
July 2005 - London underground and bus bombings
2017 - Manchester arena bombing
What does low quality TATP-like material lead to?
leads to ‘fizzled’ explosives not ideal in terms of quality
When/where was copycat tube bombings?
What did they use? (state fuel and oxidiser)
Why was this supposed to be a good explosive but failed?
2017 Parsons’ Green
H2O2 + chapatti flour
fuel - amylase (chapatti flour)
oxidiser - hydrogen peroxide (readily breaks down into oxygen radicals)
potentially powerful explosive due to high surface area of explosive
flour is hygroscopic so took in residual moisture from atmosphere and when explosive materials get damp, they do not detonate properly or work effectively
How can you accidentally make TATP in the lab?
by adding nitric acid (strong oxidant) to acetone
What is sometimes added to ANFO?
aluminium to increase length of blast
What are ‘Annie’ bombs?
ANFO and nitrobenzene
used by IRA in 1980-1990
What are improvised explosive mixtures often based on?
what is obtainable e.g. raw materials that are not regulated like fertiliser
What is the issue with plastic explosives?
insecure storage in relatively large quantities – people would steal them for illicit purposes
Define taggants.
What is their purpose?
additives that provide a traceable signature to the explosive
used primarily to deal with the illicit use of military or industrial grade plastic explosives
What are two properties of taggants and what does this mean for it?
preventative and diagnostic
can be detected easily and use them to trace back
What 2 qualities do we want taggants to have any why?
volatile
so can detect it in gas phase without having to mess about with unexploded IED
not used in other common applications
don’t want taggant that we can find anywhere as we won’t know if it is just at scene normally or come from an explosive
How are taggants usually designed?
to be chemically related to explosive materials
What is being looked for when using a taggant?
sensitive and specific detection before and after explosive use
Define pre-detonation taggants.
Where are these used? and what detects them?
used to prevent attacks
used in high security settings e.g. airport, government building
sniffer dogs to ppm level
mass spec to ppb level
what are the illicit purpose advantages of using plastic explosives?
easy to store, people didn’t know what they looked like and easier to detonate
How does ion mobility spectrometry work?
volatile molecules we want to detect are ionised
ions are generated
ions enter drift tube
molecules are accelerated from left to right by electric field
at same time we are pumping a drift gas (inert so no chemical reactions) that goes in opposite direction to electric field
this is preventing our molecules from going really fast
drift gas will affect larger molecules more than our smaller or lighter molecules, so we get pretty good separation of differing molecules
What is the advantage of ion mobility spectrometry over other chromatographic techniques like GC or LC?
gives considerably faster separation of components
What is ion mobility spectrometry often paired with?
What does this do?
a mass spectrometer - TOF or quadrupole-MS
automated software will flag up anything that comes up as a substance that shouldn’t be there (taggant)
if mass spectrum good enough match with traditional mass spectrum they would expect of taggant then investigate bag
What is mobility of ions related to?
What is the equation?
velocity of gas and strength of electric field
K = vd/E
where
K = ion mobility
vd = drift velocity
E = electric field
What 4 factors affect ion mobility?
What is the equation?
K = 3/16 √(2π/μkT x Q/nσ)
where
μ = reduced mass of the ion
n = number density of drift gas (molecules/volume)
σ = collision cross section (probability of collision with drift gas)
Q = charge on the ion
What is an example of a homemade nitrocellulose-like materials?
What is it’s use and how is it made?
What is the nature of its deflagration?
gun cotton
often used as propellant
made from nitration of cellulose (fibres)
homemade nitrocellulose deflagration is very dangerous and rapid - produces lots of gas
What is danger of homemade nitrocellulose-like materials?
hard to stop deflagration once started as very difficult to remove oxygen
