From Ken Revell
Your article on the Columbia space shuttle disaster attracted a letter from David Harris of the Aluminium Federation regarding the supposed non-flammability of aluminium (19 April, p 24). He states authoritatively: “Your article raises the spectre of aluminium burning. This is a mythhellip;I have never seen aluminium burning in any formhellip;and nor do I ever expect to.”
This is contrary to my experience. Aluminium does burn, and surprisingly (with relevance to the shuttle) it can do so in near-vacuum conditions. Several years ago, against the accepted knowledge of experts in the field, I devised a process that achieves this, operating at a pressure of around 10−3 millibars (0.1 pascals).
In a large vacuum chamber, aluminium wire is continuously melted, vaporised, and burnt in a stream of oxygen, and deposits a coating of aluminium oxide onto a web of polyethylene terephthalate (PET) film moving past at high speed from reel to reel. Counter-intuitively, the process even improves the vacuum through a “getter” effect, by mopping up any traces of water vapour present.
This is not just a laboratory curiosity. It is a large-scale industrial process. The reels are more than 2 metres wide, weighing more than a tonne and holding more than 36 kilometres of PET film. Over the years, the burning of aluminium has produced thousands of tonnes of flexible, transparent, gas-barrier packaging material for the food industry (Patent GB 2246794A).
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Stowmarket, Suffolk, UK
