Diffusion of D₂O in archaeological wood measured by 1-D NMR profiles

Abstract

1-D¹H nuclear magnetic resonance profiles have been used to image the penetration of D₂O into waterlogged archaeological wood. A series of well characterised plugs were sampled from different depths, reflecting different degrees of degradation and orientation with respect to the wood structure, of an oak timber from the Mary Rose. The ingress of D₂O was Fickian in character and the diffusion coefficients,D, are reported as a function of depth into the timber for each orientation. The behaviour ofD could be approximated by a surface layer, with a higher diffusion coefficient, and a lower diffusion core region. The differences in the values ofD in the different orientations are rationalised in terms of the known structure of decayed wood. Theoretical uptake curves were calculated from a numerical evaluation of the analytical solution for diffusion into a multiple-layer model. Saturation of the surface layer was predicted to occur prior to diffusion into the core, with a characteristic change of gradient displayed in the uptake curve. Good agreement was achieved with experiments that sampled the different decay environments. Concentration distributions, and uptake curves, were calculated using these models for a typical archaeological timber.