Determination of Diffusion Coefficients of Boron from Borate Rods in Wood Using Boltzmann's Transformation

This research was performed to investigate the diffusivity of borate rods in radiata pine (Pinus radiata D. Don) conditioned to 40 percent moisture content (MC). The deepest penetration of boron were observed in the longitudinal direction, followed by the radial and the tangential directions. The boron loading on the wood face adjacent to the borate rod tended to increase with diffusion time in all directions. To mathematically quantify boron diffusion, the diffusion coefficient of boron was determined using Boltzmann's transformation by assuming that it was a function of concentration only. The values of the longitudinal diffusion coefficients were between 1.3×10^-8 cm²/sec and 9.2×10^-8 cm²/sec. The radial diffusion coefficients were between 1.4×10^-8 cm²/sec and 9.5×10^-8 cm²/sec, and the tangential diffusion coefficients were between 5.2×10^-9 cm²/sec and 1.3×10^-8 cm²/sec. The differences of diffusion coefficients between the longitudinal direction and the radial direction were slight, although their concentration profiles were markedly different. This indicates that the amount of boron loading on the wood face adjacent the borate rod is one of the most important factor for boron penetration in wood with low MC.