Why do we need new explosive materials?
- Many current explosives aren’t very ‘clean’ - give detonation products that arent environmentally friendly
- Can get more complicated products in true detonations
- Explosives with a higher nitrogen content generally reduce the production of CO/C
What properties can we change to make different properties?
- Crsytal packing - can manipulate the sability by changing this
- Stability
- Detonation products
- Tagging - stop them being used in an illicit manner
What are some examples of energetic groups and what do they do?
Give the explosive more power - more sensitive
* Nitro groups
* Azide groups
* Alkine groups
* High ring strain (lots of chemical energy)
* Aromatic ring with lots of nitrogens
What are some examples of stabilising groups and what do they do?
Stabilise the explosive so that it doesnt detonate accidentally
* Benzene ring/aromatic rings
* Amine groups
What is the PPE required for explosive reseach labs?
- Helmet
- Face Shield
- Leather coat
- Kevlar gloves
- Kevlar suit
- Blast shield
Why is a small amount of explosive tested on in research labs and what is this amount?
< 500 mg of explosive
* Dont know how it will expload
* Dont know the detonation products
Which of these analytical techniques would be the best to determine if the oxygen balance predicted products are correct?
a) FTIR
b) NMR
c) GC-MS
d) LC-MS
e) Ion Chromatography
FTIR in the gas phase because it looks at small molecules and can differentiate those (CO, H2O, CO2, N2)
* NMR - too complex preparation to use
* GC-MS - cant separate those types of products easily (MS is good for giving molecular ion but GC isnt)
* LC-MS - not useful when we are forming gases
* Ion Chromatography - not forming ions or in a condensed phase
What can be seen from FTIR spectras about slightly reactants?
- Detonation products are more complex than modelled with the oxygen balance
- Correlation between less negative oxygen balances and a more clean decomposition
- Two compounds with identical oxygen balances have different products
- Further supporting that testing needs to be done to know the products and how they behave
Influence of oxygen balance on stability
- Less negative oxygen balance the more sensitive
- Crystal packing (density) is also a factor as two compounds could have the same oxygen balance but if one is less dense it will be less sensitive
- Most sensitive has a higher density
How does crystal packing affect stability?
- The use of explosive salts can control the crystal packing (hard to predict however)
- e.g. Ag+ can easily pack to make the compound more dense and so less sensitive
- However changing to a NH2+ salt creates loads of space (lower density) and much more sensitive
- XRD is useful to look at the crystal packing
How does the stability of nitrogen containing compounds change?
- There is a limit to the stability achievable with nitrogen based explosives
- N-N are the least stable, then N=N and then N≡N being the most stable (enthalpically favourable)
- Want to maximise the number of N=N and N≡N but this is synthetically challenging
- Combination of kinetic and thermodynamic stability
What is stereochemsitry and regiochemsitry?
Stereochemsitry: each of two or more compounds differing only in the spatial arrangement of their atoms.
Regiochemsitry: same molecular chemsitry but different connectivity
How does Stereochemistry/Regiochemistry affect explosives?
- Changes the properties
- Have different sensitivites and melting points
What are the desired properties for new explosives?
- Melting point
- Sensitivity
- Explosive power
- Tunability
