Explosions 11

Question 1

What is the sensitivity to friction testing process?

Answer 1

• place a small quantity of explosive onto sliding block (beneficial as don’t know properties of explosives)
• apply a load with known weight (has frictional surface on it)
• hit the sliding block using a pendulum and observe any evidence of initiation
• repeat 100 times to ensure reproducibility
• do using different frictional surfaces

Question 2

What other properties can be explored in the sensitivity to friction process?

Answer 2

type of cleavage of explosive (even to a specific miller plane)

effect of environmental conditions e.g. moisture and temperature (as need explosive device to be able to operate within lots of environmental conditions

Question 3

What is the sensitivity to impact testing process?

Answer 3

carried out using drop towers

• a known weight is dropped from increasing heights onto plate with small amount of explosive on it
• high speed camera used to monitor ignition event
• ensure to use new sample for every drop height to prevent impact-induced sensitiveness (can cause cracking/morphological changes)
• plot height vs ignition event using median drop heigh(relative to arbitrary value of TNT)

Question 4

What is the sensitivity to sparks and discharge testing process?

What other properties of sample are considered?

Answer 4

• a capacitor is charged using a high potential source
• electrode is charged with potential source – stored in capacitor
• a small quantity of explosive is placed on a roller
• the sample is gradually wound upwards toward the discharge electrode
• at a critical distance energy is released via a spark (called arcing) and initiation is monitored
• measure this critical distance and potential source
• testing starts with a high spark energy and repeat measurements are made gradually reducing the spark energy until no initiation events occur
• the levels assessed are the average static shock from a human (don’t want this to be able to detonate explosive) and the maximum energy from initiation devices

the mass, shape and size of sample are considered as they can change the result due to change in arcing

environmental conditions can also be examined e.g. humidity and temperature

Question 5

Why does testing in a sensitivity to sparks and discharge process start with a high spark energy?

Answer 5

it is difficult to predict relative energy in terms of spark to initiate the explosive so best to start high and get lower

Question 6

What is the sensitivity to sparks and discharge testing process?

Answer 6

• small quantities of explosive are placed in holes which have a conductive base within a metal block (to to 12)
• the block is heated slowly at a fixed temperature gradient set by regulators
• the temperature of ignition is monitored using a high-speed camera
• experiment repeated 10 times to ensure reproducibility of sample
• external environmental conditions are carefully controlled (ambient heat, humidity)

Question 7

what can heating also be used to examine?

Answer 7

chemical stability of certain explosives

Question 8

What does Abel test test for?

What compounds is it used for?

How is it carried out?

What is Abel test paper composed of?

What is downside of this test?

Answer 8

measures the decomposition of energetic materials into NOx gases

nitrocellulose, smokeless powders, rocket fuels and nitro-containing compounds

• apparatus is very similar to normal heating test but includes standardised Abel test paper (white) which exhibits a colour change (brown) when exposed to NOx gases
• temperatures used are typically between 65 and 80 degrees
• the time required for the onset of colour change is compared to standards

primarily composed of starch coated with potassium iodide (KI)

it is not quantitative

Question 9

What is differential scanning calorimetry?

How does it work?

What is it used to examine?

What is a real life application?

Answer 9

controlled detection and quantification of deflagration/detonation

compare the heat flow between the sample (small amount) and reference (empty vial) as temperature increases
- peak area shows amount of heat associated with phase change
- positive heat flow - melting phase change (endothermic)
- negative heat flow - decomposition phase change (exothermic)

used to examine exothermic (e.g. detonation) and endothermic (e.g. melting) processes

used for pharmaceutical analyses of accidental explosive intermediate synthesis