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Fires & Explosions > Lecture 2 > Flashcards

Lecture 2 Flashcards

1
Q

What is black powder used for?

A

it is a type of gunpowder used to accelerate small things very fast

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2
Q

What are some peaceful uses for explosives?

A
  • Mining / Quarrying
  • To increase efficiency
  • Excavation (for construction)
  • To make some space
  • Cladding (explosion welding)
  • Forensic Investigations
  • Research
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3
Q

What is the deflagration process for the gunpowder invented in China around 142 AD

A

10 KNO3 + 3 S + 8 C → 2 K2CO3 + 3 K2SO4 + 6 CO2 + 5 N2

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4
Q

What was the problem with the gunpowder invented in 142 AD in China?

A

There would be residual carbon which isn’t always consumed so there’s black powder left over.

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5
Q

What components were used in traditional gunpowder?

A
  • Potassium Nitrate
  • Sulfur
  • Carbon
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6
Q

What is carbon usually used for?

A

Fuel

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7
Q

What is KNO3 usually used for?

A

It contains oxygen so it’s likely a good oxidizer

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8
Q

If an element/compound decreases in oxidation state is it an oxidizer or fuel?

A

It’s likely a fuel

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9
Q

Black Powder

A

Generally deflagrates incompletely

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10
Q

Gun cotton

A
  • Made of nitrocellulose
  • Low explosive so it deflagrates
  • It’s still used in firearms today
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11
Q

How effective is nitrocellulose?

A

It deflagrates very effectively

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12
Q

How is nitrocellulose formed?

A
  • Nitric acid is added to cellulose
  • Nitric acid to add nitro groups is common in explosive chemistry
  • Nitration of cellulose is very effective
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13
Q

How was black powder made more dangerous in the early 1800’s?

A
  • 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
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14
Q

What was the first commonly used high explosive?

A

Picric acid

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15
Q

What’s the problem with heavy metal salts?

A
  • They are very unstable
  • This is why Fe (Iron) shells are used over Pb (lead) but there are still very sensitive to shock
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16
Q

What’s the advantage of using picric acid?

A
  • It is mostly stable
  • As it relies on a phenol base, it is readily available due to the coal industry
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17
Q

How is picric acid created?

A
  • 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
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18
Q

What was TNT originally invented as?

A

Yellow dye in 1863

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19
Q

What’s the benefit of TNT?

A

It’s much more stable compared to picric acid and almost impossible to prematurely detonate which is preferable.

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20
Q

How can we reduce the activation energy?

A

If we can make stable intermediates this it will reduce the activation energy, this is to do with the ability to push around electrons

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21
Q

What are lone pairs good for?

A

Lone pairs are good for detonating into the ring?

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22
Q

What is RDX synthesised from?

A

Ammonia and formaldehyde

23
Q

What does high brisance mean?

A

A good shattering power that is able to get through tanks and penetrate armour

24
Q

What brisance does RDX/HMX have?

A

High brisance

25
Q

When was nitroglycerine invented?

A

It was invented in 1846 for a vasodilator

26
Q

What are the features of nitroglycerine?

A
  • It’s volatile which makes it easy to detect
  • It-s quite unstable so it’s less useful initially
27
Q

How is nitroglycerine created?

A

Treat glycerol, which is high available, with nitric acid

28
Q

How can you stabilise nitroglycerine?

A

You can adsorb it onto diatomaceous earth so you get a stable environment but you can still detonate it relatively easily.

29
Q

How is ANFO made?

A

Ammonium Nitrate is combined with fuel oil and used as a quarrying material.

30
Q

What kind of explosive is ANFO?

A

Tertiary so it is even less sensitive than a secondary explosive.

31
Q

What are the problems with ANFO?

A

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

32
Q

What has been done to reduce the amount of terrorism via bombs?

A

Restrictions have been placed on the volumes of materials you’re able to buy.

33
Q

Why is ammonium nitrate used in ANFO?

A

Ammonium nitrate is a fertilizer and it’s very explosive alone.

34
Q

How are plastic explosives designed to be?

A

They are designed to be formable which gives them a bigger range of applications

35
Q

What are plastic explosives?

A

They are a mixture of mostly explosive and a bit of plasticiser

36
Q

What is a plasticiser?

A

A plasticiser is an additive which makes a substance mouldable

37
Q

What is an example of plastic explosives?

A

C4s and Semtexes

38
Q

What are plastic polymer bonded explosives?

A
  • 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
39
Q
  • What are the advantages of plastic polymer-bonded explosives?
A
  • They are much less sensitive than cast explosives
  • You can adapt the properties to what you desire based on the chain length and branching
40
Q

What is the purpose of the polymer binder in plastic polymer bonded explosives (PBX)?

A

Polymer binder reduces the sensitivity of the explosive which is useful when you have a really sensitive explosive.

41
Q

Other than PBX, how else can you change an explosive?

A

You can design a polymer that has an explosive on it but this is synthetically challenging to achieve

42
Q

How sensitive are polymer bonded explosives?

A
  • 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
43
Q

What are the benefits of the integral sacrificial barrier?

A
  • We can transport explosives without accidental detonation
  • When we detonate explosives we have much better control as to where the energy goes
44
Q

What is the figure of insensitivity?

A

The figure of insensitivity is an arbitrary metric of explosive stability

45
Q

How is the safety of explosives measured?

A

Using a drop tower test

46
Q

What is done during a drop tower test?

A
  • 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
47
Q

What is the initiation correlation for the different N groups?

A

Initiation correlation: C-ONO2 > N-NO2 > C-NO2

48
Q

What nitro group is harder is hardest to initiate?

A

C-NO2 is the hardest to initiate as it is the most stable

49
Q

What nitro group is the easiest to initiate?

A

C-ONO2 is the least stable so it is the easiest to initiate

50
Q

What is the figure of insensitivity usually normalised to?

A
  • TNT = 100 for the old system
  • RDX = 100 for the new system
51
Q

What is the figure of insensitivity proportional to?

A

The figure of insensitivity is proportional to enthalpy

52
Q

What is enthalpy?

A

The heat of detonation

53
Q

What affects enthalpy?

A
  • Bond strength
  • Ring strain
  • Lattice strength is particularly important when you have mixed explosives or crystal structure
54
Q

What effect does ring strain have on enthalpy?

A

A high degree of ring strain will likely result in extra chemical potential energy so when it detonates more heat is generated.

Fires & Explosions (18 decks)

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