Diffusion in porous
with high internal
Measuring of water diffusivity with NMR in building materials is
by the presence of internal magnetic fields originating from the
impurities (Fe). To investigate the diffusion of water and ions in
materials, a stimulated echo NMR technique is applied. A new analytical
equation for the long time decay in the presence of spatially varying
field gradients is derived. This equation is experimentally confirmed
applied to stimulated echo decay in the materials with high internal
(sintered crushed glass and fired-clay brick) and a standard material
internal gradients (glass filter). In figure 1 the measured stimulated
spin-echo as a function of interpulse time and for various gradients
for fired-clay brick.
Figure 1. Ratio between the
stimulated echo and primary echo in fired
clay brick plotted against the spin-echo time.
a) interpulse time t
is varied at constant gradient strength G = 188 mT/m.
b) G is varied at
t = 410 ms. The solid lines reflects
the decay due to longitudinal relaxation only.
Dashed lines are fits of
a mono-exponential decay.
The diffusivity is determined from the slopes of the
decay in the long time limit. The diffusivity is constant and limited
the tortuosity of the pore structure. Tortuosities of different samples
are calculated, showing the excellent agreement with the macroscopic
measured by electrochemical impedance spectroscopy method (see table
Sintered crushed glass
T1 (s) (SE)
T1 (s) (SR)
D (10-9 m2/s)
Table 1. Comparison of the
stimulated echo (SE) results with the
values of T1 obtained by saturation recovery method (SR)
the electrolytically (EL) determined tortuosity a
. The tickness of the glass filter sample was insufficient to perform
- An extensive description can be found in:
J. Petkovic, H.P. Huinink, L.Pel and K.Kopinga, Diffusion in
building materials with high internal magnetic field gradients, J.
Mag. Reson.167, 97-106 (2004).
R.M.E. Valckenborg, J. Petkovic, H.P. Huinink, L. Pel, K.Kopinga,
NMR relaxation and diffusion in a porous building material during
drying, Magn. Reson. Imaging 21, 448 (2003) .
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