Solid Wood Products Predicting Boron Diffusion in Wood from Surface Sorption

Constant radial diffusion coefficients of boron through southern pine (Pinus spp.) were determined from the total amount of boron diffusing through wood and the amount of boron remaining o n the wood surface after different diffusion periods. The concentration profiles of the treated samples were measured using a slicing technique. Another coefficient representing the effect unexplained by the diffusion coefficients at the given conditions was calculated by comparing the real values of boron concentration through the wood with the predicted values calculated using the diffusion coeftcients. This method shows a potential way to easily predict the boron diffusion coeftcients for dip-diffusion treatment. If the coefficients represent the difference among species characteristics, they might be useful as species indices. Future research is needed to determine additional coefficients of different species at various conditions. B . . . oron diffusion in wood is dependent on factors such as wood moisture content (MC). temperature, diffusion period, solution strength and temperature, diffusion direction, and treatment method (Puettmann and Schmidt 1997, Morrell et al. 1990, U.S. Borax 1986, Smith and Williams 1969). Research has been performed to predict boron behavior in wood, but only a few trials have been performed to mathematically quantify the boron diffusion. One approach to predict the boron behavior in wood is to determine the boron diffusion coefficients. Ra and others (Ra et al. 2001, Ra and Barnes 1999) determined the radial boron diffusion coeftcients of southern pine (Pinus spp.) using Egner’s solution, a modified form of Fick’s second law for diffusion. Egner’s solution can be used for any diffusible system because it has no cumbersome assumptions (Skaar 1954). Although various diffusion coefficients can be obtained from Egner’s solution, the method has some disadvantages for practical application. If the calculated diffusion coefficients are not expressed as a function of MC, temperature, or thickness, it is very difficult to apply Egner’s solution for predictive purposes. Constant diffusion coefficients should be calculated from the various diffusion coefficients to predict the boron movement in wood using Egner’s solution. In this research, constant radial boron diffusion coefficients were determined from the total amount of boron diffusing through wood and the amount of boron remaining on the wood surface at varous diffusion periods. Applications for predicting boron diffusion in wood are also discussed. MATERIALS AND METHODS