Diffusion of boron from borate rods in radiata pine

The diffusivity of borate rods was investigated in three anisotropic directions using radiata pine (Pinus radiata D. Don) sapwood samples conditioned to 40 and 60 percent moisture content (MC) for 60 days. Varying diffusion coefficients were graphically determined using the measured boron concentration profile of each sample except the longitudinal diffusion at 60 percent MC because the boundary conditions were completely changed during diffusion periods. Wetter samples showed deeper penetration and higher concentration of boron at the wood face adjacent to the borate rod. The deepest penetration of boron was observed in the longitudinal direction, followed by the radial and the tangential directions. But the values of the determined boron diffusion coefficients showed only slight differences. The results indicate that the limiting factor for boron diffusion rates at the given conditions was the diffusion through bound water.