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Due to the reactive nature of aluminium powder it is used as a reactant in rocket fuels and explosives, this can however lead to concern about the safe handling of these powders from many other potential users. During production the powders develop a 2-5nm impervious oxide film which prevents reactions in normal environments, so that with care they can be handled with safety in most applications. Precautions do need to be taken however to ensure safe handling. These include:
-- Avoid generating dust clouds in air – the energy required to ignite a dust cloud can be quite low for fine powders in the presence of oxygen.
-- Keep the powders dry – they will react exothermically with moisture and liberate hydrogen gas.
As with many powders if they are fine and dispersed into a dust cloud in the presence of a source of ignition in air they have the capability to explode. However the influence of particle size is great because fine powders form dust clouds more easily and the reactive surface area of particles in the cloud will be much higher.
Compare the results below on demonstrations carried out with different grades of powder and on a common household powder. These excerpts are from a training video produced for the European Aluminium Particulate Association (EAPA) by John W Wright and based on powders produced by Alpoco.
The demonstrations are carried out in a non-qualitative and non-quantitative way using a demonstrator which incorporates a vertical tube into which a small sample of powder is dispersed in air whilst a high energy spark is applied.
Video |
The first video shows common household icing sugar to demonstrate the explosive potential of everyday powders. This shows that even domestic powders have unexpected hazards.
The second video shows aluminium granules. These are generally a coarse product (greater than 100 micron) which is difficult to disperse into a dust cloud and as seen here there is no ignition.
The third video shows fines extracted from the above granules which shows that when concentrated and dispersed into a dust cloud there is a hazard. This shows the importance of good housekeeping since depending on how the powders are handled it is possible for fines to build up over an extended time period.
The fourth video shows a standard aluminium powder. This is much finer than aluminium granules (less than 75 micron) and as such is easier to disperse into a dust cloud and a vigorous reaction occurs.
The last video shows the same powder but with removal of the 15 micron size fraction, this is still reactive but the intensity is much reduced.
The lesson to be learnt from the above is that aluminium powders can be hazardous if not treated correctly. Appreciation must be given to the way all aluminium powders are handled and treated. If you follow the following rules then any potential hazards can be minimised:
-- Avoid generation of dust clouds in air.
-- Keep work areas clean.
-- Remove any source of sparks or ignition i.e. no grinding, naked flames, smoking etc.
-- Protect against static electricity.
-- Use electrically conductive materials when possible and earth all equipment.
-- Avoid accidental contact with reactive materials - acids or chemicals - oxidisers etc.
-- If the explosion potential cannot be removed, consider inerting.
For more information consult our safety data sheets or contact: