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Fires and Explosions > Lecture 2 - Explosions 2 > Flashcards

Lecture 2 - Explosions 2 Flashcards

1
Q

give 5 peaceful used of explosive

A

mining or quarrying
excavation (make space for construction)
cladding
forensic investigation
research

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2
Q

gun powder is a tradition low explosive used as a propellant - what is it made of

A

potassium nitrate, sulphur and carbon

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3
Q

what was a common side product seen in the use of gunpowder

A

soot - left over black powder/carbon

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4
Q

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?

A

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

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5
Q

gunpowder often incompletely deflagrated so what was made to replace it

A

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

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6
Q

what is a common way to add nitro groups to compounds

A

nitrate a compound using nitric acid (HNO3) with the presence of another strong acid e.g H2SO4

nitrate something = add nitro groups

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7
Q

why were the development of gun powder bombs very dangerous

A

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

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8
Q

what was the first commonly used high explosive

A

picric acid = phenol with NO2 groups on carbon 2,4,6 and OH on carbon 1

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9
Q

what was the problem with using heavy metals to as the shells to encapsulate explosive

A

they were very sensitive to shock - iron shells less so than lead shells

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10
Q

why is TNT more stable than picric acid and why is this useful in a military sense

A

it is less sensitive

less prone to accidental detonation

good for transportation and storage of a high explosive

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11
Q

the nitration of toluene to form TNT is slower than the nitration of a phenol to form picric acid, why?

A

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

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12
Q

what are the conditions for forming RDX/HMX

A

ammonia and formaldehyde in the presence of:
HNO3
NH4NO3
Ac2O

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13
Q

RDX/HMX have a high brisance/shattering power - what is meant by this?

A

the ability to break something - hence why it was used in armour piercing chemical warfare

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14
Q

how does the structure of RDX differ to TNT

A

the NO2 groups in TNT are bonded to a carbon, in RDX they are bonded to a nitrogen

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15
Q

how is nitroglycerin formed

A

from glycerol in the presence of HNO3

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16
Q

why was the discovery of nitroglycerin as a high explosive a worry

A

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

17
Q

how was nitroglycerin made more stable and what is this more commonly know as

A

by coating it with diatomaceous earth adsorbed onto its surface = dynamite

18
Q

nitroglycerin was found to be volatile, what is one advantage and one disadvantage of this

A

adv = important for its detection

disadv = makes it unstable

19
Q

what is ANFO

A

A HIGH EXPLOSIVE made of ammonium nitrate combined with fuel oil

20
Q

is ANFO a primary, secondary or tertiary explosive

A

tertiary

not very sensitive and hard to detonate so it needs a blasting cap

21
Q

what did the discovery of ANFO lead to a restriction of

A

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

22
Q

what are plastic explosives designed to be

A

formable = allowing for a broader range of applications - good for demolition

a mixture of mostly explosive and a bit of plasticiser

23
Q

what is a plasticiser

A

an additive making substances mouldable

24
Q

what are two examples of plastic explosives

A

C4 = mostly RDX

Semtex = mostly RDX and PETN

25
Q

what are PBX explosives

A

plastic polymer bonded explosives

an explosive encapsulated in a polymer matrix

explosive and a polymer binder

26
Q

why are PBX explosive beneficial

A

can make explosives less sensitive by altering the properties of the polymer used to encapsulate it

done by changing the chain length and branching

27
Q

what are many PBX explosives made of

A

HMX as the explosive component
and
polybutadiene (a synthetic rubber) or Viton (fluoropolymer) as the polymer component

28
Q

despite it being difficult what can the use of PBX explosive produce

A

polymers with explosive functional groups

29
Q

PBX explosives very insensitive and can give more controlled explosions why?

why can this be beneficial

A

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

30
Q

what are some application of PBX explosives

A

nuclear weapons
cruise missiles
any other high performance application

31
Q

how is the stability of an explosive quantified

A

using the figure of insensitivity

32
Q

how is the figure of insensitivity of an explosive typically measured

A

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

33
Q

what explosive are the most stable based of their functional group present

A

most stable/hardest to initiate
C-NO2
N-NO2
C-ONO2
least stable/easiest to initiate

34
Q

what is the figure of sensitivity proportional to and why is this relationship not completely linear

A

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

35
Q

what is a non military use of a)nitroglycerin
b) ammonium nitrate

A

a) a vasodilator for people with coronary heart disease

b) fertiliser

Fires and Explosions (20 decks)

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