Lecture 1 - Explosions 1 Flashcards
what at the 2 definitions of an explosion
1 = a sudden and violent release of physical or chemical energy often accompanied by the emission of light, heat and sound
2 = a rapid increase in pressure in a confined space… generally caused by the occurrence of exothermic chemical reactions where gases are produced in relatively large amounts
what two types of changes are seen within explosions
chemical and physical changes
chemical - relate to thermodynamics (Gibbs free energy equation)
physical - relate to pressure
do all explosions cause loud sounds
no
what does the volume of gas release during an explosion relate to
the power of the explosion
explosive are known as energetic materials what does this mean?
but can are all explosions caused by energetic materials
energetic material contain their own fuel and oxidant so don’t rely on other sources = more efficient and powerful explosive
no, as some fuels can react with external oxidant such as oxygen in the air to create an explosion
what is a fuel-air explosion
an explosion that relies on an external oxidant for example oxygen
are energetic materials elements, mixtures or compound
mixtures or compounds
give two examples of energetic materials
TNT - trinitrotoluene
ANFO - ammonium nitrate and fuel oil mix
ammonium nitrate is not explosive on its own it is a fertiliser but when combined with fuel oil it can be explosive
what are the products of detonations generally
gases but side products are possible
in TNT what parts act as the fuel and what parts as the oxdiant/oxidiser
fuel = the hydrocarbon (toluene part)
oxidiser = nitro groups (NO2 here)
what 4 gases could be produced by an explosion of TNT
what 2 gases could also be produced but are not favourable thermodynamically
CO - if oxygen deficient reaction
CO2 - if enough oxygen
H2O - as a vapour not liquid (enough energy to convert it to a gas)
N2
methane and NOx gases
what categorises a primary explosive
sensitive to shock, heat, light and electricity
very dangerous to the user
not synthesised on a large scale as easy to accidantally go off
what categorises a secondary explosive
harder to detonate (not as sensitive)
contact insensitive
normally detonated by a small amount of a primary explosive
(tertiary explosive even less sensitive)
what categorises a high explosive
give three examples
generally detonate
chemical reaction yields a supersonic shock wave that propagates through the material
contain the oxidiser within them normally
e.g TNT, nitroglycerin, rdx
what categorises a low explosive
give three examples
they generally deflagrate
burn when pressurised so they eventually can detonate due to a pressure build up
used as propellants normally
e.g gunpowder, fuels (propane, methane, hydrogen), fireworks
in deflagration, where does the propagation of the reaction take place and what is the reaction speed
takes place at the surface of the material
is subsonic expanding wave (slower than speed of sound (1000m/s))
is one big explosive or lots of little ones at key point generally better
little ones at key points
if big one fails then problem
the energy from the big one if not confined properly could go into another material rather than the job intended
what is deflagration
a rapid oxidation reaction generating a low intensity pressure wave of moving gases
in deflagration what is the burn rate proportional to
the surface area and the pressure
higher surface area is better hence why explosives are normally powders
higher pressure = more powder
what does confining a low explosive in a small space do
increase the burn rate as it stops gases escaping - can lead to detonation
what type of speed does the wave travel in a detonation and what destruction effect does this have
a high-speed shock wave (typically 1500m/s to 9000m/s)
causes a violent disruptive effect
what is detonation
a supersonic combustion where a shock wave is propagated forward due to the energy release in something called a ‘reaction zone’ behind it
what equipment can be used to monitor explosions
high speed cameras
if there is not enough oxygen initially for a high explosive to produce CO2 what is produced and what can this go on to react with
carbon monoxide (CO)
this can then go onto react with oxygen in the atmosphere to form CO2
