Corrosion of metals in treated wood examined by synchrotron based xanes and XFM

Abstract

Copper based waterborne wood preservatives are frequently used to extend the service life of wood products used in outdoor environments. While these copper based treatments protect the wood from fungal decay and insect attack, they increase the corrosion of metals embedded or in contact with the treated wood. Over the past ten years, several studies have looked at the corrosion mechanisms for metals in contact with copper treated wood. These studies have concluded that the most plausible corrosion mechanism involves the migration of copper ions from the wood treatment through the wood to the metal surface, where they are then reduced. Despite the evidence for this corrosion mechanism, copper is usually not detected in corrosion products as the proposed mechanism would suggest. Here, we examine wood that was in contact with corroding metal using synchrotron based X-ray fluorescence microscopy (XFM) and X-ray Absorption Near Edge Spectroscopy (XANES) to test whether the previously proposed corrosion mechanism is correct and if so, why copper is not deposited on the metal surface. With XFM we are able to detect copper in the wood and construct a copper concentration profile map with a spatial resolution of 0.5μm down to trace (less than 0.01 μg cm^-2) concentrations. We compliment these measurements with XANES, a technique that allows us to differentiate between the different ionic states of copper in the wood. These measurements give, for the first time, an experimental method to test the previous theories of the role of copper in the corrosion metals in treated wood.

Citation

Zelinka, Samuel L.; Jakes, Joseph E.; Kirker, Grant T.; Passarini, Leandro; Lai, Barry. 2016. Corrosion of metals in treated wood examined by synchrotron based XANES and XFM. NACE International, Corrosion 2016 Conference and Expo. Paper No. 7038. 10 pp.