Lecture 2 Flashcards
What is black powder used for?
it is a type of gunpowder used to accelerate small things very fast
What are some peaceful uses for explosives?
- Mining / Quarrying
- To increase efficiency
- Excavation (for construction)
- To make some space
- Cladding (explosion welding)
- Forensic Investigations
- Research
What is the deflagration process for the gunpowder invented in China around 142 AD
10 KNO3 + 3 S + 8 C → 2 K2CO3 + 3 K2SO4 + 6 CO2 + 5 N2
What was the problem with the gunpowder invented in 142 AD in China?
There would be residual carbon which isn’t always consumed so there’s black powder left over.
What components were used in traditional gunpowder?
- Potassium Nitrate
- Sulfur
- Carbon
What is carbon usually used for?
Fuel
What is KNO3 usually used for?
It contains oxygen so it’s likely a good oxidizer
If an element/compound decreases in oxidation state is it an oxidizer or fuel?
It’s likely a fuel
Black Powder
Generally deflagrates incompletely
Gun cotton
- Made of nitrocellulose
- Low explosive so it deflagrates
- It’s still used in firearms today
How effective is nitrocellulose?
It deflagrates very effectively
How is nitrocellulose formed?
- Nitric acid is added to cellulose
- Nitric acid to add nitro groups is common in explosive chemistry
- Nitration of cellulose is very effective
How was black powder made more dangerous in the early 1800’s?
- Exploding shells that contained gunpowder and had fuses were created
- This meant the black powder was enclosed and subjected to a higher pressure making the detonation more likely.
- This led to the development of exploding shells for modern artillery
What was the first commonly used high explosive?
Picric acid
What’s the problem with heavy metal salts?
- They are very unstable
- This is why Fe (Iron) shells are used over Pb (lead) but there are still very sensitive to shock
What’s the advantage of using picric acid?
- It is mostly stable
- As it relies on a phenol base, it is readily available due to the coal industry
How is picric acid created?
- A phenol is treated with nitric acid in the presence of another strong acid (Sulfuric acid for example).
- This is done as we need to generate an effective electrophile to get the nitro groups
What was TNT originally invented as?
Yellow dye in 1863
What’s the benefit of TNT?
It’s much more stable compared to picric acid and almost impossible to prematurely detonate which is preferable.
How can we reduce the activation energy?
If we can make stable intermediates this it will reduce the activation energy, this is to do with the ability to push around electrons
What are lone pairs good for?
Lone pairs are good for detonating into the ring?
What is RDX synthesised from?
Ammonia and formaldehyde
What does high brisance mean?
A good shattering power that is able to get through tanks and penetrate armour
What brisance does RDX/HMX have?
High brisance
When was nitroglycerine invented?
It was invented in 1846 for a vasodilator
What are the features of nitroglycerine?
- It’s volatile which makes it easy to detect
- It-s quite unstable so it’s less useful initially
How is nitroglycerine created?
Treat glycerol, which is high available, with nitric acid
How can you stabilise nitroglycerine?
You can adsorb it onto diatomaceous earth so you get a stable environment but you can still detonate it relatively easily.
How is ANFO made?
Ammonium Nitrate is combined with fuel oil and used as a quarrying material.
What kind of explosive is ANFO?
Tertiary so it is even less sensitive than a secondary explosive.
What are the problems with ANFO?
Ammonium nitrate is a fertiliser si there were concerns regarding terrorism
- As it’s a tertiary explosive it is hard to detonate a requires blasting cap of a ore controlled high explosive
What has been done to reduce the amount of terrorism via bombs?
Restrictions have been placed on the volumes of materials you’re able to buy.
Why is ammonium nitrate used in ANFO?
Ammonium nitrate is a fertilizer and it’s very explosive alone.
How are plastic explosives designed to be?
They are designed to be formable which gives them a bigger range of applications
What are plastic explosives?
They are a mixture of mostly explosive and a bit of plasticiser
What is a plasticiser?
A plasticiser is an additive which makes a substance mouldable
What is an example of plastic explosives?
C4s and Semtexes
What are plastic polymer bonded explosives?
- They are 95% explosive with a polymer binder which is useful as it means you can alter the properties
- They are essentially explosive encapsulated in a matrix of polymer
- What are the advantages of plastic polymer-bonded explosives?
- They are much less sensitive than cast explosives
- You can adapt the properties to what you desire based on the chain length and branching
What is the purpose of the polymer binder in plastic polymer bonded explosives (PBX)?
Polymer binder reduces the sensitivity of the explosive which is useful when you have a really sensitive explosive.
Other than PBX, how else can you change an explosive?
You can design a polymer that has an explosive on it but this is synthetically challenging to achieve
How sensitive are polymer bonded explosives?
- They are extremely insensitive
- The polymeric binder acts as a ‘cushion’ and protects (captures) much of the blast overpressure, this is known as the integral sacrificial barrier
What are the benefits of the integral sacrificial barrier?
- We can transport explosives without accidental detonation
- When we detonate explosives we have much better control as to where the energy goes
What is the figure of insensitivity?
The figure of insensitivity is an arbitrary metric of explosive stability
How is the safety of explosives measured?
Using a drop tower test
What is done during a drop tower test?
- An impact is dropped onto the explosive over a progressing distance of 1m
- Only small quantities of the explosive is required
- We look at how much force is needed to detonate the explosive
- The scale is relative and compared to other explosives
- CONO2 groups are slightly easier to detonate than N-NO2 and then the sample applies to C NO2
What is the initiation correlation for the different N groups?
Initiation correlation: C-ONO2 > N-NO2 > C-NO2
What nitro group is harder is hardest to initiate?
C-NO2 is the hardest to initiate as it is the most stable
What nitro group is the easiest to initiate?
C-ONO2 is the least stable so it is the easiest to initiate
What is the figure of insensitivity usually normalised to?
- TNT = 100 for the old system
- RDX = 100 for the new system
What is the figure of insensitivity proportional to?
The figure of insensitivity is proportional to enthalpy
What is enthalpy?
The heat of detonation
What affects enthalpy?
- Bond strength
- Ring strain
- Lattice strength is particularly important when you have mixed explosives or crystal structure
What effect does ring strain have on enthalpy?
A high degree of ring strain will likely result in extra chemical potential energy so when it detonates more heat is generated.
