Lecture 10 - Explosions 10 Flashcards
why is there a need for next generation explosives
current explosives are not very environmentally clean
a lot of detonations produce side products to what is expected on paper
how can we reduce the production of CO and C from explosives
use explosives with a higher nitrogen content - these are more likely to release N2 which is already in the air
how can explosives be tunes to have the properties we want
make small tweaks to the chemical structure to change the:
crystal packing
detonation products
tagging
why is tagging important
to stop explosives being used in an illicit manner
what are the two groups of chemical structures explosives are made of
energetic groups - these give us the power
stabilising groups - these are use to make explosives less shock sensitive as most energetic groups are not very stable
what are 6 examples of energetic groups seen in explosives
nitro groups = NO2
azide groups = N3
alkyne = carbon triple bond
O-O = in peroxides
high ring strain = cubes
tetrazoles =a 5 membered ring with 4 nitrogen’s and 1 carbon
what are two examples of stabilising groups seen in explosives
aromatic rings (benzene)
and amine groups (NH2)
when testing new explosives what PPE is required
helmet
face shield
leather coat
Kevlar gloves
Kevlar suit
blast shield
Kevlar = shock resistant
what is the maximum amount of a new explosive that is tested
500mg - usually a lot less is used
what class of molecules are an interest for being used as the new primary explosives and why
azidotetrazoles
these exhibit multiple spontaneous explosions = sensitive
they have a large number of nitrogen atoms per molecule = entropically favourable detonation
clean N2 gas product
how can the stability of azidotetrazoles be increased
use a base in the formation e.g LiOH or MgOH or NaOH or FeOH so a metallic salt is formed
how are azidotetrazoles formed
combine bromocyanide with azide salt
then treat with the base to create a metal salt of the azidotetrazole
what class of molecule are of interest to becoming the new secondary explosives and why
nitroiminotetrazoles
has comparable properties to RDX
more energetic than azidotetrazoles but stability comes from the aromatic ring
when can explosive salts be produced
when nitroiminotetrazoles are paired with guanidiniums
what are the conditions needed for a nitration
nitric acid and the presence of another strong acid e.g H2SO4
which analytical technique would be best to determine if oxygen balance predicted products are correct and why
FTIR - can look at small molecules and how they differ by vibrational bonds
NMR = not good for mixtures
GC = cant separate water easily
LC = we form gases so not good
what can a small change to the structure of an explosive have a big impact on
the detonation products
this is why we need to test before using explosives as the expected results aren’t always seen practically
what is a cleaner decomposition of explosives correlated with
a less negative oxygen balance
what factors affect the stability of an explosive
oxygen balance
crystal packing
presence of double and single bonds
what is the relationship between density and impact sensitivity of explosives
increase in density sees increase in sensitivity
what can be used to control the crystal packing of explosives but what is the issue with this
explosive salts
the behaviour can be hard to predict
why do the presence of more double and triple nitrogen bonds in an explosive not always work
it can be synthetically challenging
but the presence of these can be enthalpically favourable for the explosion
will adding a stabilizing group always make an explosive stable
No
what is another type of new secondary explosive developed by the US military and national labs
hexanitrohexaazowurzitane or Cl20
this has lots of ring strain
what are the desired properties to consider when making new explosives (6)
explosive power
melting point
sensitivity
tunability
safety
time and energy needed for synthesis - is this practical to scale up for larger amount
how can stereochemistry affect properties of explosives
stereoisomers need different types of synthesis
they will have different sensitivities
testing is needed to see their state at room temp - liquid or solid
melting points will be different - impacting if they can be easily casted or not
what are the effects of incorporating more nitrogen double and triple bonds into explosives
increased stability
high energy release
higher sensitivity
non toxic by products (N2 gas)
can tune molecules more easily by reacting with these bonds
hard to store safely due to increased sensitivity
how can IR spectroscopy be used to assess oxygen balance of modern explosives
can look at the ratio of the oxidiser to the fuel
analyses functional groups and identify the fuel and oxidiser
