Minerals and Metals in Ancient India v1.c27.s2.t2.12

v1.c27.s2.t2.12

The phosphorus content is very high and is less varying. While P in steel occurs as a solid solution in the ferrite (up to 1 %), a considerable part in wrought iron may appear as slag inclusions of FePO₄. Naturally, the strongly oxidized parts and the surface layer, depleted in carbon, tend to be rich in phosphorus. In accord with the above, Ghosh (1963) found that of the 0.28 per cent P in a sample from the pillar, 0.18 per cent occurred as elementary P, the remainder occurring as phosphate slag. In oxygen-consuming corrosion, as in water and in the atmosphere, high P-content actually exerts a beneficial influence, probably because phosphorus in the ferrite is oxidized to phosphate which, as an inhibitor, promotes the formation of protective oxide films.