Explosions 10 Flashcards
What are the three reasons as to why we need new explosive materials?
What four properties associated with tunability might we like to manipulate?
1 - many current explosives aren’t very clean and do not give environmentally friendly products
2 - explosives with higher nitrogen content generally reduce the production of CO and C (gives more nitrogen gas which is abundant in air already)
3 - increased tunability over particular properties is preferable - can make small tweaks to molecular structure or way in which different FGs are used
1 - crystal packing
2 - stability
3 - detonation products
4 - tagging (stop being used in illicit manner
What energetic groups can be used as design principles for explosive materials?
- nitro group
- azide group
- alkyne - current interest due to all chemical energy in triple bond (good for heat or detonation generated)
- O-O bonds
- high ring strain molecules (when broken get lot of energy out)
- aromatic ring structures with nitrogen
What other type of group is needed in design principles for explosive materials?
stabilising groups to make it stable e.g.
- aromatic rings
- amine groups (NH2) - make less shock sensitive
What are the safety principles for novel explosives?
considerable amount of PPE required for < 500 mg of explosive
- helmet
- face shield
- leather coat
- kevlar gloves and suit
- blast shield
What are azidotetrazoles? and how do they work?
What is their possible interest?
How are they formed?
compounds with a large number of N atoms that exhibit multiple spontaneous explosions
large number of N = entropically favourable detonation as it forms a lot of gas per molecule of azidotetrazoles (entropy contributes to explosive power)
quite sensitive so possible interest as primary explosives
Bromocyanide treated with sodium azide salt.
Intermediate (with 7 nitrogen’s, 1 carbon and 1 hydrogen) treated with base in presence of some kind of salt (MOH) to make metallic salt of azidotetrazoles.
Changing M in MOH can tune properties and if done in presence of base increases stability.
What are nitroiminotetrazoles?
What type of explosives are they?
nitroiminotetrazoles are nitrated by nitric acid in presence of a strong acid to give NO2 group (energetic group so this gives us a bit of explosive power)
secondary explosives:
not that sensitive despite having two energetic groups next to each other because stabilisation due to aromaticity in ring.
Which analytical technique would be the best to determine if the oxygen balance predicted products are correct?
gas phase FTIR is good as looking at small molecules and can differentiate between small molecules from different vibrational bands
Not suitable:
NMR (would need to do some reconstruction)
GC-MS (good for volatiles but GC column won’t be able to separate CO CO2 and H2O)
LC-MS (forming gases so not useful)
Ion chromatography (not forming ions and not in condensed phase)
Why are detonation products more complex than we previously modelled?
the correlation between a less negative oxygen balance and a clean decomposition is not always there as connectivity is also important (two compounds with identical oxygen balance have different products)
What can changing the methyl group in an explosive do?
can change both the oxygen balance and the sensitivity of the explosive
How does oxygen balance affect explosive stability?
What other factor determines explosive stability?
it affects it
relationship between crystal packing (in terms of density and how much we can pack in) and impact sensitivity
lower density = higher impact sensitivity = higher explosive stability
What can be used as explosive materials?
inorganic complexes
What can be used to control crystal packing in explosives?
Why is this confusing?
explosive salts
hard to predict
What might be a useful technique to predict impact sensitivity?
XRD - can infer about crystal packing
When it comes to nitrogen based explosives, what is there a limit for?
a limit to stability achievable with nitrogen based explosives
we want to maximise the number of N=N and NN bonds (entropically favourable) but synthetically challenging
What is hexanitrohexaazowurzitane (CL20)?
Why is it a potentially good explosive?
How is it stabilised?
secondary explosive developed by US military and national labs
lots of ring strain so lots of chemical potential energy
stabilised as 1:1 cocrystal with TNT
not stabilised by cocrystallisation with 98% H2O2
