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Toughened metal

Metallurgists are always trying to make stronger metals. One of their tricks is to mix molten metal with tiny solid particles, say of ceramic, to give a tough composite. The result is limited by poor adhesion between metal matrix and suspended particles; it also blunts cutting tools. Daedalus has a new plan.

Suppose, he says, you were to burn metal vapour, not in excess air or oxygen as a chemist would normally do it, but in excess metal vapour. The usual branched dendritic oxide particles would form; but on cooling they would get covered with metal from the surrounding excess vapour. Solid surfaces adhere strongly unless air or water vapour has coated them first (which is why solids hold together in the first place). So burning in excess metal vapour should give metal oxide particles pre-coated with metal.

DREADCO chemists are now trying it. They are burning metal vapours — aluminium, magnesium, zinc — in as little oxygen as possible; an inert-gas diluent may help. The cooled oxide particles should be superficially covered and wetted with metal.

This novel oxide should be easy to mix with melted metal. Unlike powdered ceramic, it should not float on top but, being already wetted with metal, will just seem to dissolve in the melt. The resulting 'Metox' composite will be greatly strengthened by its loading of fine oxide particles. Aluminium toughened by its own oxide should be more inextensible and much stronger than the metal itself. Magnesium and zinc should tell the same story. The chemists have many other metals to try — notably titanium. Sadly, metal oxide particles blunt the cutting tools used on metal. Metox composite will be best cast from the melt into its final form.

DREADCO's new Metox composites should be ideal for superchargers and turbine blades. Zinc binds conveniently firmly to iron (hence 'galvanized' zinc-plated steel sheets), so zinc-coated zinc oxide particles should mix readily with melted iron alloys. Daedalus also recalls how the graphite inclusions in cast iron make it remarkably silent. Silent Metox composites, or at least highly damped ones without the 'ring' of steel, would be a splendid contribution to our noisy civilization. But Daedalus's ultimate goal is a Metox with so much oxide that it is compatible with ceramics. It would be ideal for the pistons and cylinder-blocks of adiabatic engines, with no cooling system. They just run hot.

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