Study On Soil Corrosion Of Archaeological Iron

The electrochemical methods of polarization curves, electrochemical impedance were used to study the corrosion of the archaeological iron caused by the variation of salt(Cl^-,SO₄^2-,HCO₃^-)that was in the soil. The results showed: the more the content of Cl^-, SO₄^2- in the soil, the severer the corrosion of archaeological iron. However, HCO₃^- induced the fluctuation of corrosion velocity because of its participation in the formation, cracking, and repairing of corrosion product.The electrochemical methods of polarization curves and weight loss experiment were employed to study the corrosion of the archaeological iron in soil with different water content and pH. The results showed: corrosion of archaeological iron was in the highest severity when the water content came to the range of 15%-20% in the soil. In the same water content, the lower the pH of the soil, the higher corrosion rate of archaeological iron had.The corrosion products at different phase on archaeological iron were investigated through immersion corrosion, scanning electron microscope (SEM), X-ray diffraction(XRD), infrared ray(IR) and X-ray photoelectron spectroscopy(XPS).The appearance and phase composition were presented, as was compared with the corrosion products that was on the surface of iron coin from Song Dynasty. The results showed: the corrosion products were mainly composed of FeOOH and Green rust. With the increasing of salt content and moisture content in simulating soil water, the corrosion products became more compact.Phosphate treatment is one of the processing technics for chemical stabilization. A kind of phosphate dispensation was developed to convert the active rust on the surface of archaeological iron into a layer of crystal indissolvable phosphate film. The method of phosphorise in protecting archaeological iron was discussed though the experiment of dropping of CuSO₄ and scanning electron microscope (SEM).