Characterization of protective rust on ancient Indian iron using microprobe analyses

Local compositional and structural information was obtained from an ancient 1500-yearold Indian iron and its protective scale utilizing microprobe techniques (lXRD and lPIXE). Different locations in the iron matrix and in the entrapped slag inclusions were also analyzed for P contents. The P content of the metallic iron matrix was very heterogeneous. Lower P contents were observed in the regions near slag inclusions. The surface oxide scales was layered. Enrichment of P in the metal–scale interface and in the scale adjacent to the interface was determined. The P content in the scale decreased on moving away from the interface. Microdiffraction patterns obtained at different locations in the oxide scale indicated that at locations where the P content was high (i.e. nearer the interface), the oxide was amorphous while at locations where P was low, crystalline phases were identified. The presence of crystalline phosphates was also confirmed at some regions in the scale, where the P content was relatively very high. The probable reasons for the presence of the identified phases in the atmospheric corrosion product have been discussed. 2002 Elsevier Science Ltd. All rights reserved.