Lecture 11 - Explosions 11 Flashcards
what are the 4 ways we can test the performance of a modern explosive
tests its sensitivity to
1 = friction
2 = impact
3 = sparks and discharge ‘
4 = heat
how do we test an explosives sensitivity to friction
put a small amount on a sliding block
apply a known weight
hit the sliding block with a pendulum and look for evidence of initiation
repeat 100 times for reproducibility
can also look at the effect of temp and moisture of surrounding here or the type of cleavage of the explosive - done using XRD
what are things to look for as evidence of initiation
bang
flash of light
why is looking at the effect of environment temp and moisture good when testing an explosive
different regions of the world have different climates
how do we test an explosives sensitivity to impact
using a drop tower
known weight is dropped from increasing height onto small amount of explosive
use of high speed cameras to monitor ignition
compare to a standard and plot height vs ignition event
if it didn’t initiate need to use a new sample
how do we test an explosives sensitivity to sparks and discharge
charge a capacitor using a high potential source
place small amount of explosive on a roller
sample is gradually wound up to the discharge electrode
at a certain distance between sample and electrode a spark will be seen
start with higher energy and decrease it = repeat measurements until no spark is seen
compared to a standard
in the testing of sensitivity to friction sparks and discharge why do we start with a higher energy and lower it down
it is hard to predict the energy needed for a spark so this could take forever if starting with lower energy
hard to know what incrimants to go up in aswell so if you start with high you can go up or down
what other factors can be considered in the testing of sensitivity to friction sparks and discharge
mass, shape and size of explosive
environmental conditions
average static shock of a human can be tested
max energy of initiation devices can be tested
how is reproducibility achieved in testing of sensitivity to friction sparks and discharge
testing multiple samples at each energy level
how do we test an explosives sensitivity to heat
place small amount of it into a metal block that has holes in it
heat it slowly at a fixed temp gradient
monitor ignition temp using high speed camera
repeat 10 times to ensure reproducibility
must control external conditions well i.e heat and humidity
what other thing can be tested when examining the sensitivity of heat of an explosive
how is this achieved
the chemical stability
using the Abel Test which measures the decomposition energy of the energetic materials into NOx gases
briefly describe the Abel Test
use metal block with holes for small amount of explosive
heat using a fixed temp gradient slowly
use standardised Abel test paper which exhibits a colour change from white to brown when exposed to NOx gases
temp used normally between 65 and 80 degrees as don’t want explosive to detonate
compare time taken of colour change onset to a standard
why is the Abel test not the best method
simple but not quantitative
colour change can be slightly subjective
what is the name of a technique used to control the detection and quantification of deflagration/detonation
differential scanning calorimetry
how does differential scanning calorimetry work
compare the heat flow between a sample and a standard as the temperature increases
here standard = an empty vial
can examine exothermic and endothermic processes
+ve heat flow = phase change = melting
-ve heat flow = decomposition
look at peak areas to get amount of heat
