A COMPARISON BETWEEN ANALYTICAL METHODS FOR ZINC SPECIMENS EXPOSED IN A RURAL ATMOSPHERE

The aim of this work is to explore the possible use of different methods for analyzing corroded zinc specimens exposed under sheltered and unsheltered conditions in a rural environment for 5 years. X-ray powder diffraction with a Guinier-Hagg camera showed the presence of (Zn, Cu)4SO4(OH)6.4H2O (naumwite) and SiO2 (low quartz) on the sheltered sample and Zn5(CO3)2(OH)6 (hydrozincite) on the unsheltered sample. Naumwite has not previously been reported as a corrosion product on zinc, whereas hydrozincite commonly occurs in different kinds of atmospheres. To provide further information a number of other methods were used for analysis of corrosion products on the same zinc specimens. The methods included in this work are: (i) x-ray powder diffraction, Fourier transform infrared spectrometry and thermogravimetry for phase analysis, (ii) glow discharge optical spectroscopy, scanning electron microscopy with x-ray microanalysis, x-ray fluorescence spectroscopy, x-ray photoelectron spectroscopy, and secondary ion mass spectroscopy for elemental analysis, and finally (iv) ion chromatography for analysis of water soluble anions. Among less-established analytical methods in the field of atmospheric corrosion this comparison shows that glow discharge optical spectroscopy and ion chromatography can provide valuable complementary information to more established methods such as x-ray powder diffraction and scanning electron microscopy.