a nmr study of the moisture and ion transport in two- and three-layer porous building materials
TRANSCRIPT
time-dependent diffusion coefficient in the short time region. The shape of
the clay particle is layered structure about 1 Am in length, and the card-house
structure is expected in clay gel. In this situation, it may be difficult to satisfy
smooth boundary conditions for pore space, i.e., sharp corners on the clay
surface contribute to diffusion coefficient. Therefore, applying the relation
between D0 and S/Vp to clay saturated porous media becomes difficult.
[1] Mitra PP, Sen PN, Schwartz LM. Phys Rev B 1993;47:8565.
[2] Cotts RM, Hoch MJR, Sun T, Markert JT. J Magn Reson 1989;83:252.
doi:10.1016/j.mri.2007.01.084
Study of a porous media: NMR parameters distribution and
structural heterogeneity
P. Palmasa, J.-F. Kuntza, V. Levela, D. Canetb
aLaboratoire de Physico Chimie, CEA le Ripault, 37260 Monts, France,bMethodologie RMN, Universite Henri Poincare, 54506 VandKuvre-les-
Nancy, France
Since the pioneering works of Stejskal and Tanner [1] in the 1960s, pulsed
field gradient NMR (PFG-NMR) has become one of the most suitable
method for measurements of self-diffusion coefficient of liquids. Very early,
it has been shown that NMR diffusion experiments can also be used to
probe the local geometry (pore size, connectivity, etc.) of a porous media. It
is well known that structural heterogeneities inside a porous material (i.e.,
distribution in pore sizes) can lead to multiexponential decays in a CPMG
experiment. The inverse Laplace transformation (ILT) is now a common
approach in NMR which can be used to extract T2 relaxation times
distribution [2]. We performed several DOSY experiments on a porous
polymer (cross-linked polystyrene embedded with water) at different
evolution times D (between 10 and 500 ms) using a conventional stimulated
echo with two pairs of bipolar B0 gradients (STE_BP) at 400 MHz. We
showed that the observed apparent coefficient diffusion is not unique and a
distribution of this parameter can be resolved in the frequency domain. This
distribution, which is clearly visible at short D values, is progressively
damped as D increases. To validate this approach, we started a similar study
on more or less monodisperse systems of beads embedded with water. A
way of investigation will be to compare the distribution of apparent
diffusion coefficient with data obtained using classical granulometry
measurement and scanning emission microscopy for those systems.
[1] Stejskal EO, Tanner JE. J Chem Phys 1965;42:288–92.
[2] Fantazzini P, Brown RJS, Borgia GC. Magn Res Imaging 2003;21:
227–34.
doi:10.1016/j.mri.2007.01.085
Multi-scale proton dynamics in acid colloids
L. Pautrot-d’Alencon, D. Petit, P. Barboux
Laboratoire de Physique de la Matiere Condensee, UMR 7643 du CNRS,
Ecole Polytechnique, 91128 Palaiseau Cedex, France
Introduction: Due to their large specific area, colloidal oxides can yield
large concentrations of ionizable OH groups and exchangeable protons
equivalent to a concentrated acid solution. These acid functions, anchored
to the solid particles, are stable during operation in electrochemical
devices such as fuel cells (FCs). These nanoparticles can be used as
membrane components or as additive fillers increasing the conductivity
of polymer exchange membranes (PEM) [1]. To better understand this
effect, we have synthesized nanoparticles and grafted different acid groups
[2]. In this work, large timescale proton dynamics is investigated in
membrane built with colloidal zircon and sulfofluorophosphonic acid
(SFPA) grafts.
Experiments: Colloidal zircon particles were first prepared by hydro-
thermal decomposition of zirconium acetate and purified. These particles
are 60-nm aggregates of 5-nm primary grains with the monoclinic
ZrO2 structure. They present a large specific area (450 m2 g�1 before
drying) which is accessible to chemical species from the surrounding
solvent [3].Their surface was functionalized by grafting SFPA synthesized
in the laboratory. The different experiments were carried out with a relative
humidity (RH) varying from 0% to 90%. The grafted species were
studied through static and MAS NMR of 31P at 145 MHz and 1H at
360 MHz. The fast proton dynamics was studied by 1H NMR T1
relaxation time at 360 MHz between �908C and 908C. The slow proton
dynamics was characterized at different temperatures (�208C to 908C)by longitudinal relaxation rate dispersion NMRD using a Stelar relaxo-
meter in the frequency range of 10 kHz to 20 MHz. The macroscopic
proton diffusion was studied by impedance spectroscopy between �408Cand 908C.Results and discussion: Grafting of phosphonic acids reverses the surface
charge of the colloids from positive to negative, due to the ionization of
the grafted species. The grafted species are strongly attached to the surface
through covalent bonds as shown by 31P MAS-NMR. At �1208C, thestatic proton NMR line exhibits a super-Lorentzian shape characteristic of
a surface rigid lattice [4]. A motional narrowing of the super-Lorentzian
line from 8.5 to 1.4 kHz occurs when the temperature increases from
�1208C to 258C. This kind of narrowing is consistent with an
exchangeable proton motion near the surface. This is explained both by
the acidity and by the high degree of rotational freedom of the species
grafted at the surface of the colloids. The proton T1 temperature
dependence at 360 MHz is activated with an energy of 7 kJ/mol, typical
of water mobility. The frequency dependence following a power law a(x�1/2) is the main feature of 1H NMRD curves. A proton dynamics
model compatible with this frequency dependence could be a 1D diffusive
motion model [5] or a reorientation mediated by translation model [6].
NMRD experiments with D2O are under investigation to evaluate the
relevant model. Nevertheless, this feature proves a proton dynamics
involving the surface. Conductivity was measured on pressed powders
and is proportional to the surface area of the powders, proving the
surface conduction.
Conclusion: This study shows that the grafting of phosphonic acids to
reverse the surface charge of the zircon colloids is very efficient to maintain
the dynamics of the proton near the surface in a very large timescale.
So these grafted colloids are good candidates for PEM FC.
[1] Jones D, Rozieres J. J Membr Sci 2001;185:41.
[2] Carriere D, Moreau M, Lahlil K, Barboux P, Boilot JP. Solid State Ionics
2003;162:185.
[3] Carriere D, Moreau M, Barboux P, Boilot JP, Spalla O, Langmuir.
2004;20:3449.
[4] Korb JP, Torney DC, McConnell HM. J Chem Phys 1983;78:5782.
[5] Korb JP, Whaley Hodges M, Gobron Th, Bryant RG. Phys Rev E
1999;60:3097.
[6] Kimmich R, Weber HW. Phys Rev B 1993;47:11788.
doi:10.1016/j.mri.2007.01.086
A NMR study of the moisture and ion transport in two- and three-layer
porous building materials
J. Petkovica, L. Pelb, H.P. Huininkb, K. Kopingab
aInstitut Navier, LMSGC (LCPC-ENPC-CNRS), 2 Allee Kepler, 77420
Champs sur Marne, France, bEindhoven University of Technology, Den
Dolech 2, 5600 MB Eindhoven, The Netherlands
Moisture and salt decay processes are amongst the most recurrent causes of
damage of buildings and monuments. Knowledge about the transport of
water and ions and salt crystallization in porous building materials is
needed to explain salt-induced damage and to develop durable materials.
NMR, a nondestructive technique, is used for the quasi-simultaneous
measurement of the time evolution of the profiles of hydrogen and
dissolved sodium, which enables monitoring the moisture and salt transport.
Abstracts / Magnetic Resonance Imaging 25 (2007) 544 – 591578
The investigated two-layer materials consisted of the same plaster applied
on two different types of bricks: Bentheimer sandstone and calcium–silicate
brick. The calcium–silicate brick contains the pores which are of the order
of magnitude smaller than the pores of the plaster, while the Bentheimer
sandstone has pores in the order of magnitude bigger than that of plaster.
It was shown that the moisture transport in the plaster layer was largely
influenced by the pore-size distribution of the brick. The layer with the
largest pores dried first. This has important implications for the transport
and accumulation of salt in plaster/brick systems. When the plaster was
applied on a brick with larger pores, salt tended to accumulate in the
plaster layer, because this layer remained wet for a longer time than the
brick. When the plaster was applied on a brick with smaller pores, some
salt crystallized in the plaster layer, but a significant amount of salt
crystallized within the brick itself. In both cases, salt was accumulated at
the drying surface, as an efflorescence.
These results are used to design the three-layer materials which have the
desired transport properties allowing salt to accumulate inside the plaster
layer and not as an efflorescence. These systems consisted of two plaster
layers of different pore sizes applied on the Bentheimer sandstone. In the
case of uniformly salt-loaded system, the salt efflorescence at the drying
surface is observed. If salt is initially present only in the Bentheimer
sandstone, after the drying process salt was accumulated mainly in the
middle plaster layer which has the smallest pores.
The drying process, transport and accumulation of salt are firstly
determined by the pore sizes in the various layers. During drying, air
first invades the largest pores with the lowest capillary pressure. Secondly,
the presence of salt strongly influences the drying process by suppressing
the formation of a receding drying front and by reducing the drying rate.
The effect of the drying rate on the salt transport is described by a Peclet
number which characterizes the competition between advective and
diffusive ion transport.
doi:10.1016/j.mri.2007.01.087
Characterizing porous materials through the melting and freezing
behaviour of pore-filling fluids
O. Petrov, I. Furo
Industrial NMR Centre, Royal Institute of Technology, SE-100 44
Stockholm, Sweden
We demonstrate a joint use of melting and freezing curves obtained in nuclear
magnetic resonance (NMR) cryoporometry experiments for characterising
porous materials. A benefit of such a combination follows from the finding
[1] that freezing (DTf) and melting (DTm) temperature shifts in pores are
determined by different parameters of pore morphology, namely, DTf by the
surface-to-volume ratio (S/V) and DTm by the integral curvature (j) of thepore surface. In particular, this makes it possible to apply NMR
cryoporometry to the pore shape analysis. We measured DTm and DTf for
four different liquids — water, benzene, cyclohexane and cyclooctane —
confined in controlled pore glasses (CPG) with the nominal pore diameter
varying from 7.5 to 73 nm. All liquids were found to exhibit a linear
correlation between DTm and DTf, with the ratio DTm/DTf gradually
decreasing from 0.67 to 0.57 when going from 7.5- to 73-nm pores. Within
a framework of our approach, this indicates a change in pore shape from
spherical one for the smallest pores towards cylindrical or channel-like one
for bigger pores.
We also exploited the freezing curves to calculate model-free constants K in
the Gibbs-Thomson equation for the pore-filling fluids under investigation,
using S/V obtained by gas adsorption methods. The Ks so evaluated are
somewhat higher than those that follow from nominal pore radius of CPGs in
the commonly used cylindrical pore model. The inadequacy of cylindrical
pore model for CPGs is also indicated by the difference between pore radius
distributions obtained from freezing and melting curves of confined liquids
(Fig. 1). Yet, distributions of S/Vand j shifted according to the experimental
ratios DTm/DTf, coincide. The latter finding indicates that freezing and
melting processes probe the same pore length scale in CPGs.
[1] Petrov O, Furo I. Phys Rev E 2006;73:011608.
doi:10.1016/j.mri.2007.01.089
Investigation of water content and dynamics of a Ricinus root system in
unsaturated sand by means of SPRITE and CISS: correlation of root
architecture and water content change
A. Pohlmeiera, A.M. Oros-Peusquensb, M. Javauxa, M.I. Menzelc
H. Vereeckena, N.J. Shahb
aAgrosphere Institute, Forschungszentrum Julich, Germany, bInstitute for
Medicine, Forschungszentrum Julich, Germany, cPhytosphere Institute,
Forschungszentrum Julich, Germany
The water uptake by a Ricinus root system in an artificial soil (99.5% fine
sand, 0.5% clay) is investigated by magnetic resonance imaging. Ricinus
was planted in a container, which was initially water-saturated, and then
sealed so that transpiration could take place only through the leaves, and the
change of water content was only caused by suction of the roots. The water
content was imaged by SPRITE, which was first applied here on a plant/soil
system, at four different dates (1, 12, 15 and 20 days after implantation).
The SPRITE signal I(tp) was recorded between tp=0.08–5.0 ms, with an
isotropic resolution of 0.625 mm, and the amplitude, which is proportional
to M0(T2*), was calculated by fitting exponential functions to the I(tp)
curves. Next, the amplitudes were calibrated by a 100% water standard. The
reliability of the technique and the evaluation procedure is proven by the
linear correlation of the soil volume integrated amplitude with the
gravimetric water content.
A parallel study of the root system with high resolution (0.6 mm) was
performed by CISS and FLASH in order to correlate the water content
changes with the architecture of the root system. Since water in the root
Fig. 1 (A) Melting and freezing curves for water in CPG with 11.9 nm
pores. (B) Pore radius distributions calculated from (A), using relationships
(DTm=�K/r and DTf =�2K/r in the cylindrical pore model with
K=25K�nm.
Abstracts / Magnetic Resonance Imaging 25 (2007) 544 – 591 579