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Over our Christmas barbecue 鈥� it was 35 掳C in Perth, Western Australia on 25 December 鈥� we started an argument. If it was raining (which it wasn鈥檛), which would rust faster, a scalding hot barbecue or a cold one, presuming they were made out of an iron-containing material?
鈥� If 鈥渞ust鈥� is taken to mean the oxides of iron commonly seen on exposed iron and steel surfaces, rather than the oxides which form at several hundred degrees Celsius (unlikely to be attained in a barbecue), then water must be present for rust to develop. A scalding hot barbecue will thus rust far less than a cool one, as rain landing on the former will evaporate instantly.
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For the hot barbecue to be moist, the air would have to be saturated at the temperature of the barbecue 鈥� a practical impossibility unless the atmospheric pressure could be increased as well.
I really hope no one will try this at home.
Neil Fairweather, Risley, Cheshire, UK
鈥� My partner, a blacksmith, says that a barbecue that is scalding hot and remains that way will not rust. If it gets wet while hot and then cools down, however, it will rust faster than a barbecue that gets wet when cold.
Barbecues are generally made of steel, which consists of iron plus a small amount of carbon. If the barbecue is heated to dark red heat 鈥� around 600 掳C, a temperature easily reached with charcoal 鈥� and cools down, some of the carbon burns off. The pure iron left behind rusts easily; rusting can be very quick when the iron is cooled by rain.
A cold barbecue, however, rusts when water gets into cracks in the steel and corrodes the iron, leaving the carbon behind. This is a slow process.
Sarah Lewis-Morgan, T眉ngeda, Germany