Lecture 3 - Explosions 3

Question 1

what are the issues with using drop tests/towers to measure stability of explosives

Answer 1

semi-quantitative

arbitrary scale of sensitivity

doesn’t take into account explosive power of the material

Question 2

what does the volume of gas produced by an explosive correlate to

Answer 2

its explosive power

Question 3

what 3 factors are important when considering the power of an explosive

Answer 3

the detonation products

the volume of gas produced

the energy released

Question 4

what is the power equation

Answer 4

power = heat x volume of gas

Question 5

what are the Kistiakowsky-Wilson rules used for

Answer 5

predicting the products of an explosion

Question 6

what is the oxygen balance used for

Answer 6

Seeing if the explosive needs oxygen from the surrounding environment to detonate

Question 7

what are the products of a complete combustion

Answer 7

CO2 + H2O

Question 8

what does a lack of oxygen in combustion result in the production of

Answer 8

CO or C (soot)

Question 9

what is the equation used to calculate oxygen balance

Answer 9

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

Question 10

what is the molecular weight in calculating oxygen balance used to (decimal place wise)

Answer 10

nearest whole number as this is an approximation anyway

Question 11

what would the oxygen balance of an oxygen deficient molecule be

Answer 11

a negative value

the carbon and hydrogen can not be fully oxidised

Question 12

what would an oxygen balance of 0 mean

Answer 12

that we have the correct amount of oxygen

Question 13

when are the Kistiakowsky-Wilson rules applied

Answer 13

when the oxygen balance is negative but not less than -40%

Question 14

what are the Kistiakowsky-Wilson rules

Answer 14

1. C atoms to form CO
2. H atoms to form H20
3. CO molecules to form CO2
4. N atoms to form N2

Question 15

in practical experiments why are you likely to see different products to those predicted using the kistiakowsky rules

Answer 15

as oxygen is present from the atmosphere and other reactions can also occur

Question 16

what gaseous product of a detonation indicate a nearer neutral oxygen balance

Answer 16

CO2 as this is only produced when there is some oxygen left over from CO and H20 formation

Question 17

how is the enthalpy of detonation calculated and what unit is used for this

Answer 17

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

Question 18

what does the enthalpy of detonation mean

Answer 18

the energy released per mole of explosive

Question 19

what does the volume of detonation depend on and what is it a measure of

Answer 19

depends on the moles of gas released

is a measure of entropy change

Question 20

how do you calculate volume of detonation

Answer 20

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

Question 21

what is the explosive power a measure of

Answer 21

both enthalpic and entropic components of an explosion

Question 22

how do we calculate explosive power

Answer 22

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

Question 23

do secondary explosive tend to have higher or lower heats of explosion and volume of detonation compared to primary

Answer 23

higher

Question 24

why is aluminium added to mixed explosives

Answer 24

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

Question 25

why is adding too much aluminium not good

Answer 25

it reduces to volume of gas formed

Question 26

what is thermite

Answer 26

a mixed explosive incorporating aluminium and iron oxide used in incendiary weapons

Question 27

what is important to get right in mixed explosives

Answer 27

the proportion of each component so the effects can be optimised

Question 28

is the oxygen balance if more negative than -40% what rules do we use ands what are these rules

Answer 28

the modified kistiakowsky-wilson rules

1. H atoms form H2O
2. C form CO
3. C remaining forms solid C
4. N forms N2