The Microdistribution of Copper, Chromium and Arsenic in CCA Treated Wood and Its Pyrolysis Residue Using Energy Dispersive X-Ray Analysis in Scanning Electron Microscopy

Scanning electron microscopy coupled with energy dispersive X-ray analysis is used to study the preservative distribution and the anatomical structure at the micro-level in CCA treated wood and its pyrolysis residue. The type of wood used in these analyses is Pinus sylvestris peeling and sapwood, treated with chromated copper arsenate. The sapwood was treated only once instead of twice as was done with the peeling. Examination of the peeling reveals a uniform distribution of the metals throughout the total volume of the peeling due to the porous structure, which enables the CCA solution to penetrate deep into the wood, and which explains the high retention level of CCA solution. The relative amounts of Cr, Cu and As which occur at different locations vary and differ from the ratio in the CCA treating solution. The same conclusions can be drawn for the pyrolysis residue resulting from pyrolysis of the CCA treated peeling, in which vestures and warty layers are observed. Examination of the CCA treated sapwood reveals lower metal concentrations due to the lower retention level of CCA solution during treatment. The three metals are also found at each location examined. The anatomical structure of sapwood differs from peeling in the sense that it is less porous and clusters containing predominantly copper can be observed. The pyrolysis residue of CCA treated sapwood has a more porous structure and the metals are more concentrated in the ray cells, indicating a migration of metal compounds during the pyrolysis process. Tears are also observed, probably as a result of the thermal degradation process.