Incomplete fixation of chromium in the pre-treated wood with a solution of copper and arsenic compounds
J N R Ruddick, K Yamamoto, F G Herring, P C Wong, K A R Mitchell
Ponderosa pine wood thin sections were treated with a combination of chromium, copper, and arsenic chemicals. The wood sections was analyzed by electron spin resonance spectrometry (ESR) and X-ray photoelectron spectrometry (XPS) to elucidate the mechanism of fixation of the chromated-copper preservatives. The wood subjected to the two-step treatment with copper and arsenic followed by chromium exhibited a strong Cr(V) ESR signal. However both Cr(III) and weak Cr(V) signals were observed in wood subjected to the one-step treatment containing chromium, copper, and arsenic. XPS spectra also supported the Cr(V) formation in the former treatment. The further chromium reduction from Cr(V) to Cr(III) for samples treated in two steps did not proceed very well during the fixation period of 3 months. Copper arsenate formed in the wood could disturb the interaction of chromium with the wood. These results indicate that re-treatment of wood with chromium containing preservatives may result in incomplete fixation of chromium.