NON-DESTRUCTIVE DETERMINATION AND QUANTIFICATION OF DIFFUSION PROCESSES IN WOOD BY MEANS OF NEUTRON IMAGING

David MANNES
Dr. - Department of Civil, Environmental and Geomatic Engineering, Institute for Building Materials (ETH) Address: 8093 Zurich, Switzerland
Tel: +41 44 632 3228. Fax: +41 44 632 1174.
E-mail:dmannes@ethz.ch

Walter SONDEREGGER
Eng. - Department of Civil, Environmental and Geomatic Engineering, Institute for Building Materials (ETH)
E-mail: wsonderegger@ethz.ch

Stefan HERING
Eng. - Department of Civil, Environmental and Geomatic Engineering, Institute for Building Materials (ETH)
E-mail: shering@ethz.ch

Eberhard LEHMANN
Dr. - Spallation Neutron Source (ASQ), Paul Scherrer Institute (PSI)
Address: 5232 Villigen, Switzerland
E-mail: eberhard.lehmann@psi.ch

Peter NIEMZ
Prof.Dr. - Dept. of Civil, Environmental and Geomatic Engineering - Institute for Building Materials (ETH)
E-mail: niemzp@ethz.ch

Abstract: Diffusion processes in samples of European beech (Fagus sylvatica L.) and Norway spruce (Picea abies [L.] Karst.) were determined and quantified by means of neutron imaging (NI). The experiments were carried out at the neutron imaging facility NEUTRA at the Paul Scherrer Institute (PSI) in Villigen (Switzerland) using a thermal neutron spectrum.
      NI is a non-destructive and non-invasive testing method with a very high sensitivity for hydrogen and thus water. Within the scope of this study, diffusion processes in the longitudinal direction were ascertained for solid wood samples exposed to a differentiating climate (dry side / wet side). With NI it was possible to determine the local distribution and consequently the total amount of water absorbed by the samples. The calculated values differ scarcely from those ascertained by weighing (= 3%). The method yields profiles of the water content over the whole sample, thus allowing the local and temporal resolution of diffusion processes within the sample in the main transport direction (longitudinal). On the basis of these profiles, it was possible to calculate the diffusion coefficients along the fibre direction according to Fick's second law.

Key words: diffusion, diffusion coefficient, moisture content, neutron imaging, non-destructive testing, wood.

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