CORROSION RESISTANT ALUMINUM ABOVE 200 C

At elevated temperatures most aluminum alloys in water suffer severe penetrating attack, resulting in relatively rapid destruction of the material.This penetrating attack is explained in terms of mechanical damage as a result of diffusion of corrosion-product hydrogen into the metal.It is prevented by adding to the water cations which are reduced on the aluminum to form deposits of low hydrogen overvoltage metals.It is also prevented in untreated water by using alloys of aluminiim with the same metals.Alloying metals observed to be beneficial are nickel, copper, cobalt, iron, platinum, with nickel probably the most effective.There has been developed an alloy, containing approximately 1% nickel in 2S alviminiim, which appears to be completely safe against the penetrating attack.It is easy to make and is workable.It probably can be used, from a corrosionresistant point of view, wherever its normal reaction rate with water or a solution is tolerable.Penetration rates in static distilled water are approximately 1, 1-1/2, 3 and 9 nails per year at 250°, 290°, 315° and 350°C, respectively.They are higher where there is significant flow velocity of water past metal.