What test is used to look at the sensitivity to friction for explosions?
- Place a small quantity of explosive onto a sliding block
- Apply a load with known weight
- Hit the sliding block using a pendulum and observe any evidence of initiation
- Repeat 100 times to ensure reproducibility - quick experiment so this can be done easily
What are the signs of initiation to look for when assessing an explosive performance?
Noise or light
What other properties can be explored when looking at the sensitivity to friction of explosives?
- Type of cleavage of explosive (even to a specific miller plane)
- Effect of environmental conditions (e.g. humidity, temperature)
- Different frictional surfaces
What test is used to look at the sensitivity of an explosive by impact?
- Use drop towers
- A known weight is dropped from increasing heights (increases the force)
- High speed camera used to monitor ignition event
- Use new sample for every drop height to prevent impact-induced sensitiveness
- Compare to standards (TNT) also tested on the same drop tower
What is the test to look at the sensitivity of explosives to sparks and discharge?
- A capacitor is charged using a high potential source
- A small quantity of explosive is placed on a roller with a conductive material below it
- The sample is gradually wound upwards towards the discharge electrode
- At a critical distance energy is released via a spark and initiation is monitored
- Repeat measurments are made by gradually reducing the spark energy until no initiation events occur
- Tests starts at a high spark energy and decreases with each test
- Repeated many times to get reproducible results
Why does testing start at a high spark energy when assessing the sensitivity to sparks and discharge?
It is difficult to predict the relative energy to intiate a spark so we start high as we know it will detonate, if we started low it might take a long time to get to a high enough energy to cause a spark
What are some important levels that are assessed when looking at the sensitivty to sparks and discharge of explosives?
- Average static shock from a human - humans can produce static shocks and need to make sure that an explosive wont detonate due to this
- The maximum energy from intiation devices - usually electrical type detonators
- Mass/shape/size of a sample - these can significantly change the result due tot he aring of the spark changing a lot
- Environmental conditions - temperature/humidity
What is the test to look at the sensitivity to heat of explosives?
- Small quantities of explosive are placed in holes within a metal block (usually 6 to 12)
- The block is heated slowly at a fixed temperature gradient set by regulations
- The temperature of ignition is monitored using a high-speed camera
- Repeated around 10 times - lower than other tests because more than one sample can be tested at once
What needs to be carefully controlled when assessing the sensitivity to heat of explosives?
External environmental conditions (ambient heat, humidity)
What is the Abel Test?
- Measures the decomposition of energetic materials into NOx gases
- Used for nitrocellulose, smokeless powders, rocket fuels, and nitro containing compounds
- Very similar to normal heating test but includes standardised Abel test paper
- Brown colour change from white is a positive reaction to NOx gases
What is the Abel test paper made from?
Starch with a coating of postassium iodide
What are the advantages and disadvantages of the Abel Test?
- Simple method
- Not quantitative - can show colour change but doesnt say how much NOx gases are produced
- Not very precise - colour change is subjective
What is differential Scanning Calorimetry?
- Used for the controlled detection and quantification of deflagration/detonation
- Compare heat flow between sample and reference as temperature increases
- Used to examine exothermic (detonation) and endothermic (melting) processes
What can the area of the peak be used for in Differential Scanning Calorimetry?
- Know the amount of heat that is associated with the phase change
- Negative heat flow = decomposition (exothermic changes)
- Positive heat flow = Phase changes (melting)
What standards do we have to apply to be credible?
- Laboratory conditions and protocols
- Codes of Practice and SOPs
