Explosions 2 Flashcards
List 5 peaceful uses of explosives.
- mining/quarrying
- excavation (for construction)
- cladding (explosion welding)
- forensic investigation (replicate controlled explosion)
- research
What has driven considerable development in explosives?
war
What type of explosive is gunpowder?
When was it invented and where?
What can KNO3 also be called?
low explosive so deflagrates
142 AD in china
Saltpetre
Why is gunpowder deflagration process complex?
not all carbon is consumed
form carbon monoxide and black powder (carbon - soot)
What are two deflagration processes of gunpowder?
What are fuel and oxidiser in first one?
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
Give 3 examples in the history of explosives.
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
What is common with nitric acid in explosives chemistry?
use of nitric acid to add nitro groups
What did most cannon fire use in early 1800’s?
used solid lead shot (cannonballs) or grapeshot (clusters of small lead projectiles)
What were gunpowder bombs and why were they dangerous to use and transport?
exploding shells containing gunpowder with fuses
gunpowder being kept under pressure so can detonate
What did safe detonation require the use of?
secondary explosives
What did gunpowder bombs lead to the development of?
exploding shells for more modern artillery
What was first commonly used high explosive that detonates rather than deflagrates?
What is another name for this and why?
picric acid
Lyddite, named after Lydd in Kent
What is process of production of picric acid?
Give reasoning for conditions.
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
What was availability of phenol like?
readily available in coal tar due to coal industry
What is stability of picric acid like?
stable-ish in isolation
when make heavy metal salts, these are unstable and shock sensitive
iron shells better than lead but still shock sensitive
What was invented in 1863 but wasn’t used as explosive until early 20th century?
TNT as a yellow dye
What is process of production of TNT?
Give reasoning for conditions.
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-
Compared to picric acid, what is sensitivity and stability of TNT like?
TNT much less sensitive and more stable than picric acid (almost impossible to prematurely detonate)
preferable for example in transfer
What are some uses of TNT?
Used in armour-piercing shells for tanks, warships, etc.
Is nitration of toluene (TNT) or phenol (picric acid) slower?
Why?
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)
What does RDX/HMX stand for supposedly?
RDX - research and development explosive
HMX - her majesty’s explosive
What are some high explosives used in military and non-military uses?
military:
picric acid
TNT
RDX/HMX
non-military:
nitroglycerine
ANFO
What is a property of RDX and HMX?
Why is this good for a specific application?
high brisance - high shattering power
good at war - penetrating to armour
Define Torpex mixture.
42% RDX, 40% TNT and 18% Al (metal)
What explosive was formed in 1846 but used for a medical purpose?
nitroglycerine
used as vasodilator for people with coronary artery disease
What is process of production of nitroglycerine?
glycerol is treated with nitric acid
What was the problem with nitroglycerine as an explosive?
glycerol was attainable by anyone and could quite easily make potent explosive with nitric acid
What are 2 properties of nitroglycerine?
How was one of these improved?
volatile - small molecule so easy to detect
unstable - initially less useful
stabilised by coating onto surface of diatomaceous earth (mineral) - formed dynamite
What is applications of ANFO?
high explosive used in quarrying (also illicit purposes)
What was problem with ANFO as an explosive?
Why was it not the most major problem?
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
What was plastic explosives designed to be?
formable - broader range of applications
What are the constituents of a lot of plastic explosives?
What are their purposes?
a mixture of mostly explosive and a bit of plasticiser
plasticiser - makes substance mouldable and usable in more different applications
Name 2 familiar plastic explosives.
C4 - mostly RDX
Semtex - mostly RDX and PETN
Define polymer bonded explosives (PBX).
Why are these useful?
95% explosive with polymer binder
(explosive is encapsulated in polymer matrix)
useful as can alter properties based on polymer chain length/branching
What is sensitivity of PBX like compared to cast explosives?
Why is this good for sensitive explosives?
Compare to cast explosives.
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
What are the common components of PBX’s?
explosive - RDX or HMX
polymer - polybutadiene (synthetic rubber) or Viton (fluoropolymer)
What is a harder alternative to PBX?
Why is this harder?
make a polymer with an explosive FG
synthetically challenging to get exact properties
Why do energetic polymers for PBX applications have interesting chemistry?
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
What is purpose of polymeric binder?
Why is this beneficial?
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
List 3 applications of PBX’s.
Nuclear weapons (control in detonation)
Cruise missiles
Any high-performance application (get control which is often needed)
Define figure of insensitivity.
an arbitrary metric of explosive stability
How is the safety of explosives tested?
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
What is scale used to measure FOI?
arbitrary scale so normalised to TNT = 100 (old) or RDX = 100 (new)
Predict the relative stability of explosives containing C-ONO2, N-NO2 and C-NO2 groups.
easiest to initiate - least stable
C-ONO2 (nitroglycerine)
N-NO2 (RDX)
C-NO2 (TNT)
hardest to initiate - most stable
What are the key factors that determine the FOI?
enthalpy (heat of detonation)
ring strain
lattice strength
What is correlation between FOI and enthalpy (heat of detonation)?
Why is this trend not perfect?
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
How does ring strain affect trend?
ring strain causes chemical potential energy so when make detonation products there is extra heat
When do we consider the effect of lattice strength on trend?
When have mixed explosives or with particular crystal structures
e.g. how crystal lattices and density can affect relative sensitivity and entropy of explosives
