Determination of Boron Diffusion Coefficients in Wood
Keywords:Boron, boric acid equivalent, dip-diffusion treatment, diffusion coefficients, Egner's solution, Timbor®, solution, unsteady-state diffusion
The unsteady-state diffusion of boron through southern pine (Pinus spp.) was investigated at various moisture contents, temperatures, and treatment conditions. The fastest rates of diffusion were observed in the longitudinal direction, followed by the radial and the tangential directions. The diffusion rate increased with time in all directions. The longitudinal diffusion rate increased rapidly with moisture content (MC), while a slow increase in the radial diffusion rate was observed at MCs above 90%. Moisture conlent did not affect the rate of tangential diffusion within the range of MCs in this study (70-110%). The effect of temperature on boron diffusion rates was more pronounced than the effect of MC. The diffusion rate increased with temperature, although slight direction-dependent differences were observed. A repeated dip-treatment increased the rate of diffusion in the tangential direction, but only small differences were found in the longitudinal and the radial directions. No other data were found in the literature for comparison.
Average values of the diffusion coefficients were calculated to predict the concentration profile of boron in wood under various conditions. The longitudinal diffusion coefficients were 10 to 20 times larger than the radial diffusion coefficients, and the radial diffusion coefficients were two to four times larger than the tangential diffusion coefficients. The use of the average boron diffusion coefficients caused some differences between real and predicted values in the early stages of diffusion, but the potential for practical use was demonstrated.
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