The corrosion of etched magnox A1-80 in dry steam at approx. equal to 105 Pa pressure in the temperature range 373-573 K

The corrosion of magnox in dry steam has been studied isothermally in the temperature range 373-573 K. Within this range different products dominate the process and there are corresponding rate changes. At approx. equal to 520 K and above the product is magnesium oxide, whilst below approx. equal to 393 K magnesium hydroxide is produced, the corrosion rate increasing with temperature in both regimes. Although magnesium hydroxide remains the dominant reaction product from 395 to 497 K, the rate of corrosion passes through a maximum at approx. equal to 409 K and then falls rapidly as temperature is increased to approx. equal to 520 K. Above 440 K magnesium hydride is detectable in the corrosion product, the amount increasing with temperature. It is suggested that hydrogen is built up in traps near the metal surface to form hydride and the hydride/hydrogen slows the hydroxide production. Formation of magnesium oxide appears to be a relatively slow process compared with hydroxide formation. (orig.)