Thermodynamic aspects of explosives Flashcards
What is meant by the power of an explosive?
This is related to the thermodynamic considerations such as enthalpy and entropy
What is oxygen balance?
Dictates whether a detonation consumes external O2
The Kistikowsky rules is used to predict the products of the explosion
What can be calculated once the relative proportions of the products are known?
Heat (enthalpy) of explosive
Volume (moles) of gas
Explosive power (QV)
When are the standard KW rules applied?
When the oxygen balance is greater than -40%
The KW rules
C to CO
H to H2O
CO to CO2
N to N2
What gaseous product would qualitatively indicate near-neutral or positive oxygen balance?
CO2 - we only form carbon dioxide if we have lots of oxygen left over so we can get very close to the ideal oxygen balance
How do we calculate explosive power of an explosive?
Calculate the oxygen balance
Apply KW rules to determine detonation products
Calculate enthalpy of detonation
Calculate the volume of detonation
Calculate the explosive power (QV)
Which explosives have a higher heat of explosion?
Secondary explosives have a higher heat of explosion
Why are mixed explosives utilised?
This is to optimise the performance of each component within the explosive
Why is aluminium added to Torpex, the mixed explosive?
It has a high enthalpy of combustion and increases length of blast wave.
It increases shattering power and resonance effect e.g torpedoes
Combination of aluminium and oxygen is enthalpically favourable
How does aluminium increase the enthalpy of combustion?
It scavenges oxygen atoms from the gaseous products increasing the enthalpy of detonation
However a good balance of aluminium is required to ensure not too much oxygen is taken away to reduce the volume of the gas formed.
What is another mixed explosive which uses aluminium?
Thermite usually aluminium and iron oxide used for incendiary weapons
When do we use the modified KW rules?
When the oxygen balance is more negative than -40%
works for RDX and PETN
What are the modified KW rules?
H atoms to H2O
C atoms to CO
if C atoms remaining (and no O) for solid C
N to N2
