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FSCI6010 - Fires and Explosions > Explosions 2 > Flashcards

Explosions 2 Flashcards

1
Q

List 5 peaceful uses of explosives.

A
  1. mining/quarrying
  2. excavation (for construction)
  3. cladding (explosion welding)
  4. forensic investigation (replicate controlled explosion)
  5. research
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2
Q

What has driven considerable development in explosives?

A

war

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3
Q

What type of explosive is gunpowder?
When was it invented and where?
What can KNO3 also be called?

A

low explosive so deflagrates

142 AD in china

Saltpetre

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4
Q

Why is gunpowder deflagration process complex?

A

not all carbon is consumed
form carbon monoxide and black powder (carbon - soot)

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5
Q

What are two deflagration processes of gunpowder?
What are fuel and oxidiser in first one?

A

Depending on proportions:
2 KNO3 + S + 3 C –> K2S + N2 + 3 CO2

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

fuel - S and C
oxidiser - KNO3

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5
Q

Give 3 examples in the history of explosives.

A

black powder - deflagrates incompletely (causes health issues and impractical as forms soot)

smokeless powder - 1800’s

gun cotton - made of nitrocellulose (nitration of cellulose)
low explosive and still used today because cheap and easy to make

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6
Q

What is common with nitric acid in explosives chemistry?

A

use of nitric acid to add nitro groups

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7
Q

What did most cannon fire use in early 1800’s?

A

used solid lead shot (cannonballs) or grapeshot (clusters of small lead projectiles)

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8
Q

What were gunpowder bombs and why were they dangerous to use and transport?

A

exploding shells containing gunpowder with fuses

gunpowder being kept under pressure so can detonate

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9
Q

What did safe detonation require the use of?

A

secondary explosives

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10
Q

What did gunpowder bombs lead to the development of?

A

exploding shells for more modern artillery

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11
Q

What was first commonly used high explosive that detonates rather than deflagrates?
What is another name for this and why?

A

picric acid

Lyddite, named after Lydd in Kent

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12
Q

What is process of production of picric acid?
Give reasoning for conditions.

A

phenol treated with nitric acid in presence of another strong acid (sulphuric acid)

in presence of strong acid - to force nitro groups to go to 2,4,6- positions

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13
Q

What was availability of phenol like?

A

readily available in coal tar due to coal industry

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14
Q

What is stability of picric acid like?

A

stable-ish in isolation
when make heavy metal salts, these are unstable and shock sensitive
iron shells better than lead but still shock sensitive

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15
Q

What was invented in 1863 but wasn’t used as explosive until early 20th century?

A

TNT as a yellow dye

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16
Q

What is process of production of TNT?
Give reasoning for conditions.

A

toluene treated with nitric acid (nitration) in presence of strong acid (sulphuric acid)

presence of sulphuric acid - to get correct substitution of nitro groups at positions 2.4.6-

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17
Q

Compared to picric acid, what is sensitivity and stability of TNT like?

A

TNT much less sensitive and more stable than picric acid (almost impossible to prematurely detonate)

preferable for example in transfer

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18
Q

What are some uses of TNT?

A

Used in armour-piercing shells for tanks, warships, etc.

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19
Q

Is nitration of toluene (TNT) or phenol (picric acid) slower?
Why?

A

nitration of toluene is much slower than nitration of phenol

phenol is more electron rich = has lone pairs = good at donating into ring

(activation barrier can be lowered by making stable intermediates = to do with the ability to move electrons and push them around)

20
Q

What does RDX/HMX stand for supposedly?

A

RDX - research and development explosive
HMX - her majesty’s explosive

21
Q

What are some high explosives used in military and non-military uses?

A

military:
picric acid
TNT
RDX/HMX

non-military:
nitroglycerine
ANFO

22
Q

What is a property of RDX and HMX?
Why is this good for a specific application?

A

high brisance - high shattering power
good at war - penetrating to armour

23
Q

Define Torpex mixture.

A

42% RDX, 40% TNT and 18% Al (metal)

24
Q

What explosive was formed in 1846 but used for a medical purpose?

A

nitroglycerine
used as vasodilator for people with coronary artery disease

25
Q

What is process of production of nitroglycerine?

A

glycerol is treated with nitric acid

26
Q

What was the problem with nitroglycerine as an explosive?

A

glycerol was attainable by anyone and could quite easily make potent explosive with nitric acid

27
Q

What are 2 properties of nitroglycerine?
How was one of these improved?

A

volatile - small molecule so easy to detect
unstable - initially less useful

stabilised by coating onto surface of diatomaceous earth (mineral) - formed dynamite

28
Q

What is applications of ANFO?

A

high explosive used in quarrying (also illicit purposes)

29
Q

What was problem with ANFO as an explosive?
Why was it not the most major problem?

A

serious terrorism concern for fertiliser bomb

ammonium nitrate was a fertiliser so could be bought - farmers now require a license to buy ammonium nitrate

ANFO is tertiary explosive so very hard to detonate and needs a blasting cap of more controlled high explosive - not as much of a concern as not everyone can access high explosive

30
Q

What was plastic explosives designed to be?

A

formable - broader range of applications

31
Q

What are the constituents of a lot of plastic explosives?
What are their purposes?

A

a mixture of mostly explosive and a bit of plasticiser

plasticiser - makes substance mouldable and usable in more different applications

32
Q

Name 2 familiar plastic explosives.

A

C4 - mostly RDX
Semtex - mostly RDX and PETN

33
Q

Define polymer bonded explosives (PBX).
Why are these useful?

A

95% explosive with polymer binder
(explosive is encapsulated in polymer matrix)

useful as can alter properties based on polymer chain length/branching

34
Q

What is sensitivity of PBX like compared to cast explosives?

Why is this good for sensitive explosives?

Compare to cast explosives.

A

PBX are extremely insensitive - no need to worry about transport and accidental detonation

If have sensitive explosive can incorporate it into plastic matrix to reduce sensitivity

much better than cast explosives with metal shells

35
Q

What are the common components of PBX’s?

A

explosive - RDX or HMX
polymer - polybutadiene (synthetic rubber) or Viton (fluoropolymer)

36
Q

What is a harder alternative to PBX?
Why is this harder?

A

make a polymer with an explosive FG

synthetically challenging to get exact properties

37
Q

Why do energetic polymers for PBX applications have interesting chemistry?

A

when glycerol is nitrated with nitric acid, only the ends are nitrated.

treat this with base to form epoxide (how epoxide forms is not well understood)

then work in presence of another base to polymerise it

not well understood and still an area of development

38
Q

What is purpose of polymeric binder?

Why is this beneficial?

A

integral sacrificial barrier - acts as a ‘cushion’ and protects (captures) much of the blast overpressure through elastic/plastic response or deformation rather than cracking

get lot more control in way in which it is detonated

39
Q

List 3 applications of PBX’s.

A

Nuclear weapons (control in detonation)
Cruise missiles
Any high-performance application (get control which is often needed)

40
Q

Define figure of insensitivity.

A

an arbitrary metric of explosive stability

41
Q

How is the safety of explosives tested?

A

using a drop tower

small amount of explosive material put on platform and impactor is dropped onto explosive.
see how much force is needed to cause detonation
can change load from impactor or force being applied

42
Q

What is scale used to measure FOI?

A

arbitrary scale so normalised to TNT = 100 (old) or RDX = 100 (new)

43
Q

Predict the relative stability of explosives containing C-ONO2, N-NO2 and C-NO2 groups.

A

easiest to initiate - least stable
C-ONO2 (nitroglycerine)
N-NO2 (RDX)
C-NO2 (TNT)
hardest to initiate - most stable

44
Q

What are the key factors that determine the FOI?

A

enthalpy (heat of detonation)
ring strain
lattice strength

45
Q

What is correlation between FOI and enthalpy (heat of detonation)?

Why is this trend not perfect?

A

as enthalpy increases, FOI decreases

got linear trend but this is not perfect so measured volumetric enthalpy of detonation

due to effects of ring strain and lattice strength

46
Q

How does ring strain affect trend?

A

ring strain causes chemical potential energy so when make detonation products there is extra heat

47
Q

When do we consider the effect of lattice strength on trend?

A

When have mixed explosives or with particular crystal structures

e.g. how crystal lattices and density can affect relative sensitivity and entropy of explosives

FSCI6010 - Fires and Explosions (20 decks)

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