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Synchrotron Based X-Ray Fluorescence Microscopy Confirms Copper in the Corrosion Products of Metals

X-ray fluorescence microscopy (XFM) maps of corrosion products removed from corroded fasteners that had been in contact with preservative treated wood clearly show the presence of copper and confirm the mechanism of corrosion in treated wood.

Product Number: 51317--9017-SG
ISBN: 9017 2017 CP
Author: Samuel Zelinka
Publication Date: 2017
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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 this under almost all conditions copper has not been detected in the corrosion products as the proposed mechanism would imply.  Recently synchrotron based X-ray fluorescence microscopy (XFM) was used to examine the wood that had been in direct contact with metal fasteners in a corrosion test. These measurements showed a copper depleted region in the wood directly adjacent to the metal fastener. Based on the size of the region and the copper concentration the amount of copper in the corrosion products was calculated to be on the order of 1 part per million. This low concentration explains why previous attempts to find copper in the corrosion products using scanning electron microscopy energy dispersive X-ray spectroscopy and powder X-ray diffraction were unsuccessful.  Here we present XFM maps of corrosion products removed from corroded fasteners that had been in contact with preservative treated wood. The XFM maps of the corrosion products clearly show the presence of copper. These measurements definitively confirm the mechanism of corrosion in treated wood and give further insights into where and how the cathodic reaction takes place.  

Key words: preservative treated wood, steel, cupric ions, corrosion mechanisms.

 

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 this under almost all conditions copper has not been detected in the corrosion products as the proposed mechanism would imply.  Recently synchrotron based X-ray fluorescence microscopy (XFM) was used to examine the wood that had been in direct contact with metal fasteners in a corrosion test. These measurements showed a copper depleted region in the wood directly adjacent to the metal fastener. Based on the size of the region and the copper concentration the amount of copper in the corrosion products was calculated to be on the order of 1 part per million. This low concentration explains why previous attempts to find copper in the corrosion products using scanning electron microscopy energy dispersive X-ray spectroscopy and powder X-ray diffraction were unsuccessful.  Here we present XFM maps of corrosion products removed from corroded fasteners that had been in contact with preservative treated wood. The XFM maps of the corrosion products clearly show the presence of copper. These measurements definitively confirm the mechanism of corrosion in treated wood and give further insights into where and how the cathodic reaction takes place.  

Key words: preservative treated wood, steel, cupric ions, corrosion mechanisms.

 

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