Sulphur segregation

This work has been carried out by Marcus and his co-workersand deals with the influence of sulphur on the passivation of Ni-Fe alloys. For sulphur-containing Ni-Fe alloys, sulphur segregates on the surface during anodic dissolution. Above a critical sulphur content a non-protective thin sulphide film is formed on the surface instead of the passive oxide film. 

Once more, the presence of reactive elements allows protective oxide scales to form, even in the presence of sulphur. It is generally proposed that the reactive elements react with S and form sulphides, then stopping their detrimental effect on the oxide scale adherence [208,209]. However, very few studies were able to identify such compounds [210,211], even if S was detected [212], The role played by the RE then is preventing sulphur segregation at the oxide scale-metal interface [213]. 

Like sulphur, phosphorus appears to have little effect on the overall scaling of iron alloys in air. It may, however, play a role in suppressing breakaway oxidation in carbon steels in CO/CO2 environments. Donati and Garaud " found that the tendency for breakaway was lower over ferrite, where P segregates. To confirm this, the authors doped pure Fe with P and found that... 

SALlt KTRR and sulphur, for fireworks, 147 Segregation lesut for explosives, 65... 

Phosphate and sulphate modifiers were incorporated by the addition of appropriate amounts of 0.01 M sulphuric or phosphoric acid to a pre-calcined aerogel followed by further calcination at 873 K. Samples are labeled as X-SiZr (y) where X refers to either sulphated (S) or phosphated (P) samples, and y refers to the mole ratio of sulphate/phosphate relative to zirconium in the preparation method. For comparison purposes, samples of zirconia and sulphated zirconia were also prepared. This was achieved via precipitation from zirconium isopropoxide (Aldrich 70 wt.%). The same H2O Zr propanol ratios were employed as used during the preparation of the mixed oxides. A sulphated zirconia, prepared by the use of sulphuric acid as hydrolysis catalyst was prepared for comparative purposes and had a nominal S Zr ratio of 0.30 1. A further sample was prepared where segregation of components was induced by thermal treatment by calcination at 1373 K for 6 h.of the non-treated SiZr (0)... 

Figure (2), and, therefore, it can be concluded that no sulphur did segregate from the bulk of the material towards the surface. Ra values were In the order of 0.1... 

Typical segregation pattern for sulphur in a killed-steel ingot. 

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