Lecture 2 - Explosions 2 Flashcards
give 5 peaceful used of explosive
mining or quarrying
excavation (make space for construction)
cladding
forensic investigation
research
gun powder is a tradition low explosive used as a propellant - what is it made of
potassium nitrate, sulphur and carbon
what was a common side product seen in the use of gunpowder
soot - left over black powder/carbon
in the use of gunpowder (equation below)
2KNO3 + S + 3C —> K2S + N2 + 3CO2
what is the oxidiser and what is the fuel
what is the purpose of the sulphur?
fuels = carbon
oxidiser = KNO3 and sulphur
sulphur is normally a stabiliser or fuel but here is reduced so acts as an oxidiser (oxidation state decreases)
fuel = carbon containing compound
oxidiser normally has oxygen
gunpowder often incompletely deflagrated so what was made to replace it
a ‘smokeless’ powder called gun cotton which is made of nitrocellulose
nitrocellulose = cellulose undergone a reaction in presence of HNO3 to add NO2 groups on all the oxygens
what is a common way to add nitro groups to compounds
nitrate a compound using nitric acid (HNO3) with the presence of another strong acid e.g H2SO4
nitrate something = add nitro groups
why were the development of gun powder bombs very dangerous
the shells were made of lead encapsulating the gun powder - as this is a low explosive it will deflagrate but as it was enclosed it become pressurised and could detonate
= dangerous to transport and have in possession
what was the first commonly used high explosive
picric acid = phenol with NO2 groups on carbon 2,4,6 and OH on carbon 1
what was the problem with using heavy metals to as the shells to encapsulate explosive
they were very sensitive to shock - iron shells less so than lead shells
why is TNT more stable than picric acid and why is this useful in a military sense
it is less sensitive
less prone to accidental detonation
good for transportation and storage of a high explosive
the nitration of toluene to form TNT is slower than the nitration of a phenol to form picric acid, why?
because phenol is more electron rich than toluene - the lone pairs on the oxygen can donate into the ring
the OH group can push electrons around and lower the activation energy of the reaction
but TNT is more stable than picric acid
what are the conditions for forming RDX/HMX
ammonia and formaldehyde in the presence of:
HNO3
NH4NO3
Ac2O
RDX/HMX have a high brisance/shattering power - what is meant by this?
the ability to break something - hence why it was used in armour piercing chemical warfare
how does the structure of RDX differ to TNT
the NO2 groups in TNT are bonded to a carbon, in RDX they are bonded to a nitrogen
how is nitroglycerin formed
from glycerol in the presence of HNO3
why was the discovery of nitroglycerin as a high explosive a worry
glycerol (used to make nitroglycerin) was readily available so if people could get hold of HNO3 too then a high explosive could easily be made
it was also very unstable by itself
how was nitroglycerin made more stable and what is this more commonly know as
by coating it with diatomaceous earth adsorbed onto its surface = dynamite
nitroglycerin was found to be volatile, what is one advantage and one disadvantage of this
adv = important for its detection
disadv = makes it unstable
what is ANFO
A HIGH EXPLOSIVE made of ammonium nitrate combined with fuel oil
is ANFO a primary, secondary or tertiary explosive
tertiary
not very sensitive and hard to detonate so it needs a blasting cap
what did the discovery of ANFO lead to a restriction of
the purchase of ammonium nitrate as a terrorism was a concern
but there couldnt be restrictions for the use of it as fertiliser or for quarrying so licences were introduced
what are plastic explosives designed to be
formable = allowing for a broader range of applications - good for demolition
a mixture of mostly explosive and a bit of plasticiser
what is a plasticiser
an additive making substances mouldable
what are two examples of plastic explosives
C4 = mostly RDX
Semtex = mostly RDX and PETN
what are PBX explosives
plastic polymer bonded explosives
an explosive encapsulated in a polymer matrix
explosive and a polymer binder
why are PBX explosive beneficial
can make explosives less sensitive by altering the properties of the polymer used to encapsulate it
done by changing the chain length and branching
what are many PBX explosives made of
HMX as the explosive component
and
polybutadiene (a synthetic rubber) or Viton (fluoropolymer) as the polymer component
despite it being difficult what can the use of PBX explosive produce
polymers with explosive functional groups
PBX explosives very insensitive and can give more controlled explosions why?
why can this be beneficial
the polymer binder acts as a barrier to cushion the overpressure affects from the blast - the elastic/plastic properties of polymers allow it to deform rather than crack
can be beneficial for transportation and we have more control over where the energy from the explosion goes
what are some application of PBX explosives
nuclear weapons
cruise missiles
any other high performance application
how is the stability of an explosive quantified
using the figure of insensitivity
how is the figure of insensitivity of an explosive typically measured
using a drop tower
- a small amount of explosive is used
- tests the force required to cause detonation
- tower = a metre or so big
the scale is relative to a known explosive e.g TNT or RDX - these are given the value of 100
what explosive are the most stable based of their functional group present
most stable/hardest to initiate
C-NO2
N-NO2
C-ONO2
least stable/easiest to initiate
what is the figure of sensitivity proportional to and why is this relationship not completely linear
enthalpy
as other factors can impact enthalpy other than bond strength for example ring strain, conjugation, lattice strength
high ring strain = higher internal energy = more energy released upon detonation than expected based on bond enthalpies
what is a non military use of a)nitroglycerin
b) ammonium nitrate
a) a vasodilator for people with coronary heart disease
b) fertiliser
