Lecture 3 - Explosions 3 Flashcards
what are the issues with using drop tests/towers to measure stability of explosives
semi-quantitative
arbitrary scale of sensitivity
doesn’t take into account explosive power of the material
what does the volume of gas produced by an explosive correlate to
its explosive power
what 3 factors are important when considering the power of an explosive
the detonation products
the volume of gas produced
the energy released
what is the power equation
power = heat x volume of gas
what are the Kistiakowsky-Wilson rules used for
predicting the products of an explosion
what is the oxygen balance used for
Seeing if the explosive needs oxygen from the surrounding environment to detonate
what are the products of a complete combustion
CO2 + H2O
what does a lack of oxygen in combustion result in the production of
CO or C (soot)
what is the equation used to calculate oxygen balance
OB = d - 2a - b/2
where
d = number oxygens
a = number carbons
b = number hydrogens
then (ans x16)/moleuclar weight
then ans x 100 to get a percentage
what is the molecular weight in calculating oxygen balance used to (decimal place wise)
nearest whole number as this is an approximation anyway
what would the oxygen balance of an oxygen deficient molecule be
a negative value
the carbon and hydrogen can not be fully oxidised
what would an oxygen balance of 0 mean
that we have the correct amount of oxygen
when are the Kistiakowsky-Wilson rules applied
when the oxygen balance is negative but not less than -40%
what are the Kistiakowsky-Wilson rules
- C atoms to form CO
- H atoms to form H20
- CO molecules to form CO2
- N atoms to form N2
in practical experiments why are you likely to see different products to those predicted using the kistiakowsky rules
as oxygen is present from the atmosphere and other reactions can also occur
what gaseous product of a detonation indicate a nearer neutral oxygen balance
CO2 as this is only produced when there is some oxygen left over from CO and H20 formation
how is the enthalpy of detonation calculated and what unit is used for this
delta H or Q = products - reactants
explressed a kj/mol and converted to heat per kg by doing
delta H x (1000/MW) where MW = molecular weight
what does the enthalpy of detonation mean
the energy released per mole of explosive
what does the volume of detonation depend on and what is it a measure of
depends on the moles of gas released
is a measure of entropy change
how do you calculate volume of detonation
V = moles of gas in products x 22.4 L/mol = answer in L/mol
22.4 can be used for every gas as this is again an approximation
then convert to volume per kg by doing
ans x (1000/MW) = L/Kg
MW = molecular weight
what is the explosive power a measure of
both enthalpic and entropic components of an explosion
how do we calculate explosive power
enthalpy of heat x volume of gas (Q x V) = and in kJ L kg-2
ignore the magnitude of the Q value
expect a 10^5 or 10^6
do secondary explosive tend to have higher or lower heats of explosion and volume of detonation compared to primary
higher
why is aluminium added to mixed explosives
it has high enthalpy of combustion and increases the length of the blast wave
the resonance effect allows it to do this
easy to incorporate into explosives and cheap
takes oxygen from the gaseous products increasing enthalpy of detonation
why is adding too much aluminium not good
it reduces to volume of gas formed
what is thermite
a mixed explosive incorporating aluminium and iron oxide used in incendiary weapons
what is important to get right in mixed explosives
the proportion of each component so the effects can be optimised
is the oxygen balance if more negative than -40% what rules do we use ands what are these rules
the modified kistiakowsky-wilson rules
- H atoms form H2O
- C form CO
- C remaining forms solid C
- N forms N2
