a nmr study of the moisture and ion transport in two- and three-layer porous building materials

2
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 D 0 and S/V p 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. Palmas a , J.-F. Kuntz a , V. Level a , D. Canet b a Laboratoire de Physico Chimie, CEA le Ripault, 37260 Monts, France, b Me ´thodologie RMN, Universite ´ Henri Poincare ´, 54506 Vand Kuvre-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 T 2 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 B 0 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’Alenc ¸on, D. Petit, P. Barboux Laboratoire de Physique de la Matie `re Condense ´e, 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 ZrO 2 structure. They present a large specific area (450 m 2 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 31 P at 145 MHz and 1 H at 360 MHz. The fast proton dynamics was studied by 1 H NMR T 1 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 408C and 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 31 P MAS-NMR. At 1208C, the static 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 T 1 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 1 H 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 D 2 O 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, Rozie `res J. J Membr Sci 2001;185:41. [2] Carrie `re D, Moreau M, Lahlil K, Barboux P, Boilot JP. Solid State Ionics 2003;162:185. [3] Carrie `re 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. Petkovic ´ a , L. Pel b , H.P. Huinink b , K. Kopinga b a Institut Navier, LMSGC (LCPC-ENPC-CNRS), 2 Alle ´e Kepler, 77420 Champs sur Marne, France, b Eindhoven 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 – 591 578

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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