Effect of hydrotalcites in tannate conversion coatings for iron artefacts

The surface treatment of iron artefacts requires an application of the proper conservation coating to prevent further corrosion deterioration. Tannate coating is preferred as a conservation agent of iron/steel with the desired black appearance of the surface. In this work, the modification of the tannate coating with hydrotalcites to improve conservation ability was studied. Methodology of the surface treatment was developed, and process parameters: hydrotalcite addition, applied layers, immersion time and pH of the stock solution were studied. The treated surface was characterised by various methods e.g. Raman spectroscopy, EDX measurements and electrochemical characterisation, and the quality of the surface treatment was evaluated with respect to cyclic QUV test. Effect of hydrotalcite addition on quality of the conversion coating was confirmed and explained by incorporation of Al in the coating. Mechanism of the modified conversion coating was proposed.