1. Magnetised by things that matter
Introducing Transport in Permeable Media
Department of Applied Physics
Eindhoven University of Technology

2. colophon
October 2013
TPM Transport in Permeable Media
Department of Applied Physics
Eindhoven University of Technology
P.O. Box 513, 5600 MB Eindhoven
The Netherlands
T: +31 40 247 4248
E: secretariaat.tpm@tue.nl
Graphic design:
Rob Samson
Photography:
Bart van Overbeeke (page 1; 4-5; 6-7; 8-9;
14-15; 18)
Timo Nijland (page 10, right)
AkzoNobel (page 11, left; 12)
TU/e Multi-Scale Lab Mechanics of
Materials (page 11, right)
Photographic design:
Melanie Rijkers (page 10-11)

3. It is our pleasure to introduce the Group Transport in Permeable Media TPM, a group
embedded in the research cluster Flow of the Department of Applied Physics, Eindhoven
University of Technology.
Who we are
October 2013, TPM offers a dynamic habitat to a group of 15 PhD students and 3
post-doc positions with a scientific staff consisting of 1 professor (prof.dr. Olaf Adan),
1 associate professor (dr. Leo Pel), 1 assistant professor (dr. Henk Huinink), and 3
supporting staff members (Jef Noijen, Hans Dalderop and our secretary Wendy van
Gangelen). Three industrial fellows, seconded by TNO (dr. Bart Erich), AkzoNobel (Leo
van der Ven) and Océ (dr. Nicolae Tomozeiu) respectively, expand the scientific staff,
reflecting our use-inspired research approach.
In the past decade, the group exposed its vitality, not only reflected in a steep increase
in our project portfolio and, correspondingly, group size, but also in expansion of our
experimental infrastructure that ultimately developed into a new state-of-the-art lab at
the TU/e campus in 2013.
Our mission
Our mission is to advance materials technology through an in-depth understanding of
transport physics in permeable media, in support of various technology domains, such as
high tech materials, petro physics and thermal energy storage. The interaction between
transport of fluids and solutes, phase changes and material response on different scale
levels -typically in the micrometer to millimeter range- forms the core of our research
activities. Inherently, interdisciplinarity is in TPMs genes, encompassing transport
physics, materials science, chemistry and biology. This booklet contains some of our
research highlights.
Our unique position
The experiment is at the heart of the group, which is due to the unique opportunities of
our MRI infrastructure, consisting of nine home-built or -modified scanners operating
at fields ranging from 0.7 – 4.7 T. As the group has the know-how to develop dedicated
NMR equipment, fitted to a particular research question, it has been able to achieve
a position at the interface of materials science and NMR imaging. The hardware and
software of our equipment enable studies of a large variety of technologically relevant
materials. These often contain magnetic impurities, which precludes the use of standard
NMR techniques that are applied by most other groups that study porous materials.
Our infrastructure covers a wide range of length and time scales. The group owns two
of the three GARField set-ups in the world that are able to visualise processes with a
resolution down to a micrometer scale. Our project portfolio points out the potential
industrial added value of these unique features.
Welcome

4. TPM is positioned at the crossroad of materials science, porous media, and experimental
physics. In the area of porous media, progress in fundamental understanding is highly
accelerated by advanced experimental tools enabling non-invasive monitoring. This is
where the TPM group brings added value through the combination of NMR imaging
with physical modelling. Our experimental strength enables us to bridge the gap between
model systems and real materials, creating a beneficial position in view of valorisation.
Our approach
TPMs research profile is based on use-inspired basic research. Consequently, interaction
with industrial players forms a cornerstone in our approach. We believe that industrial
cooperation should preferably be embedded in partnerships to create a real breeding
ground for our contribution to industrial innovation. For this reason, fruitful
partnerships exist with TNO, AkzoNobel and Océ, via secondment of employees in our
staff. Next to that, our project portfolio is a balance of funding flows (i.e. so-called 2nd
and 3rd indirect funding flows), containing project-based ventures with a wide range of
industrial players.
Cooperation with academic partners forms a prerequisite to deal with the complexity
and multidisciplinarity of use-inspired challenges. Next to obvious departmental
interaction with groups like Mesoscopic Transport Phenomena, TPM cooperates with
the Departments of Chemical Engineering (coatings and thin films), Mechanical
Engineering (thermal storage and conversion) and Mathematics and Computer Science.

5. Joint projects are carried out with Delft University, Utrecht University and CBS-KNAW
Fungal Biodiversity Centre. TPM is embedded in the J.M. Burgers Center - Research
School for Fluid Mechanics - and has a solid international network with academic
partners, such as Princeton University USA.
Our vision
TPM widens its research scope to thermal energy storage materials, anticipating the
industrial and societal priorities identified in the national (i.e. High Tech and Energy
Sectors) and the European (i.e. Horizon2020) innovation agendas. Our dream is to
contribute to the thermal battery, a breakthrough solution to realise the 2050 energy
targets, efficiently using low temperature solar heat. We are well positioned. The step
towards the next generation of high energy density materials deals with transport
phenomena and phase transitions. This is in line with our core expertise and our high
field NMR infrastructure will facilitate a leap in understanding.
Such ambitions cannot be realised alone. We aim for a joint TU/e effort, bringing
Departmental Groups and key industrial players together in a cooperative research
approach, fully embedded in the Strategic Area Energy of Eindhoven University of
Technology.
TPM: magnetised by things that matter. Magnetised by energy.

7. Transport in permeable media
The migration of water and ions in a variety of permeable media, encompassing
concrete, organic coatings, biofilms and paper, is the main topic of research in the group
TPM. Modelling of such transport phenomena goes hand in hand with adequate and
quantitative measuring. We use Nuclear Magnetic Resonance (NMR), allowing us to
monitor transport in non-transparent material.
Imaging with NMR
NMR imaging uses the fact that nuclei resonate in a magnetic field with a certain
frequency. By varying the field with position, nuclei will resonate with different
frequencies corresponding to their position. Images (3D) or profiles (1D) can be
obtained through analysis of the frequency spectrum.
Standard NMR techniques cannot be used to study technologically relevant materials
considering that many of them may include magnetic impurities, apart from the fact that
such techniques can hardly be used to acquire quantitative data. E.g. iron oxides, causing
the red colour of fired-clay brick, mess up the magnetic field, so high static field gradients
are needed to get significant resolution.
Building our own NMR devices
Therefore, in the early 90’s the group started to develop its own dedicated NMR setups
for quantitative measuring in a wide range of length and time scales. Large continuous
gradients from 0.3 T/m up to about 40 T/m characterize the equipment, giving a
spatial resolution range in the order of 1 millimeter down to 6 micrometer. To obtain
quantitative data, we use a so-called Faraday shield in the LC circuit.
More than just water transport
TPM was amongst the first to develop a setup for simultaneous measurement of
hydrogen atoms (water) and ions like Na, Li and Cl, allowing the coupled study of
components in porous media. We use a specially designed RF circuit of which the
tuned LC circuit of the NMR setup can be toggled between the resonance frequencies.
Furthermore, dedicated set-ups are available now for accurately controlled humidity and
temperature loads of sample, including extreme conditions mimicking fire loads. Further,
we use in many cases NMR imaging in combination with NMR relaxometry to clarify
how water changes the state of a material during transport.
Unique NMR imaging infrastructure

11. porous media

13. It is without any doubt that the future will be based on renewable energy. Europe and
many of its member states individually -amongst which the Netherlands- have set
ambitious goals, targeting energy and CO2 neutrality in 2050, and intermediate goals of
a substantial reduction (16-20%) in the short term (i.e. 2020).
Need for seasonal thermal energy storage
This transition of fossil based into renewable energy supply requires more than energy
sources. Energy storage plays a pivotal role in large scale implementation of renewables,
tuning non-synchronised energy supply and demand. For the short term, i.e. diurnal
fluctuations, electrical batteries are a proven concept of energy storage. For long
term storage, i.e. seasonal heat storage, storage into electrical batteries is not suitable,
considering the relatively high energy losses within such time scales.
A promising candidate
Presently, the most promising candidate for seasonal and high density heat storage is
Thermo Chemical Energy Storage (TCES). Typical examples of a class of TCES material
are salt hydrates, based on the reversible sorption of water vapour in the crystalline
structure. While a salt crystal hydrates, energy is released, and when heat is added the
crystal is forced to dehydrate under influence of dry air. This is known for several decades.
Findings underline the immaturity of nowadays technology, pointing out main challenges
with respect to stable long term performance, kinetics and operation temperatures.
Multiscale, material and flow
The usual core of a storage device using the TCES concept consists of packed beds of
particles. Phase transformations are triggered in these particles by changing the humidity
of the air that flows through the reactor. On atomic scales, the lattice structure of the
particles changes due to incorporation or disappearance of water molecules. These
processes manifest themselves as morphological and volume changes of the particles,
leading to structural changes in the particle packing and/or arrangement. This interacts
with the flow paths through the particle beds and thereby influences the reactor efficiency.
Our entry point
The group TPM is well positioned to play a role in the area of TCES technology. It has a
long tradition in studying transport processes and phase transformations in porous media.
The group has unique NMR facilities to investigate the molecular behaviour of water in
TCES materials. A first PhD project is exploring (de)hydration of salts and experimental
and computational projects will be initiated to study processes down to molecular length
scales together with the group Mesoscopic Transport Phenomena, Applied Physics, and
the Energy Technology group, Mechanical Engineering.
Moving into energy storage

15. highlights

17. Salt crystals may damage
Crystallization of salts (i.e. NaCl, Na2
SO4
) is a common cause of porous material
degradation. When water enters the pore system, salts in the material dissolve. Due to
temperature drops or evaporation, the salt recrystallizes given that the solubility limit is
exceeded. For decades it was speculated that the exert pressure of growing crystals on the
pore surface causes structural damage. This hypothesis could not be verified due to the
lack of experimental data on the time evolution of salt and water distributions.
Measuring of salt crystallization
TPM developed a NMR set-up to image 23
Na and 1
H simultaneously, enabling
monitoring of the time evolution of Na+
concentration profiles in water. As the sodium
signal per nuclei is a factor of ten lower, imaging sodium profiles required far more
sensitive equipment. We proved experimentally that certain salts supersaturate, which is a
signature of crystallization pressure.
The key: crystal phases
Furthermore, apparently, expected crystal phases are not always formed. Na2
SO4
crystallized in the so-called heptahydrate form, whereas normally this salt crystallizes in
the decahydrate form (mirabilite). This finding was key for understanding why Na2
SO4
is such a damaging salt. The heptahydrate has a higher solubility than mirabilite and
therefore a high supersaturation with respect to mirabilite is maintained given that
initially heptahydrate crystals are formed. Consequently, stress of the porous matrix
sustains for a longer period.
[1] L. Pel, H.P. Huinink, K. Kopinga; Ion transport and crystallization in inorganic building materials as
studied by nuclear magnetic resonance; Applied Physics Letters, 81, 2893 (2002).
[2] L.A. Rijniers, H.P. Huinink, L. Pel, K. Kopinga, Experimental Evidence of Crystallization Pressure
inside Porous Media, Physical Review Letters, 94, 75503 (2005).
[3] L.A. Rijniers, H.P. Huinink, L. Pel, K. Kopinga, Salt crystallization as damage mechanism in porous
building materials - a nuclear magnetic resonance study, Magnetic Resonance Imaging, 23, 273 (2005).
Crystals in pores

19. Coatings protect materials, e.g. to prevent wood rot in case of wood, or to inhibit
corrosion in case of metals. Such coatings are often cross-linked polymer layers.
Understanding and improving its protective function requires a profound insight in its
barrier properties. Considering a common layer thickness of 10-100 micrometer, imaging
processes in its initial (film formation) and final state are a real challenge.
New opportunities due to our GARField NMR
NMR imaging has become possible with the introduction of the GARField concept in
1999. By adapting the shape of the magnet pole tips, depth profiling with resolutions
below 10 micrometer became possible. TPM built two GARField set-ups, making it one
of the two groups in the world capable of depth profiling in coatings with micrometer
resolution. This opened the door for studying chemical reactions and water transport in
coatings.
The impact of catalysts on alkyd curing
An important class of coatings are the so-called alkyd systems. Alkyd paint hardens under
influence of oxygen. With NMR depth profiling we were able to follow the motion of
the reaction front and the hardening of the coating in presence of a cobalt catalyst. We
showed that a manganese catalyst promotes a more homogeneous cross-linking reaction
in the coating.
What attracts water in coatings
Coatings should protect a substrate against water. With our combination of NMR depth
profiling and relaxometry, simultaneously monitoring of water uptake by a coating and
tracing the molecules in the coating responsible for attracting water was possible for the
first time.
[1] S.J.F. Erich, J. Laven, L. Pel, H.P. Huinink, K. Kopinga, Dynamics of cross linking fronts in alkyd
coatings, Applied Physics Letters, 86, 134105 (2005).
[2] S.J.F. Erich, J. Laven, L. Pel, H.P. Huinink, K. Kopinga; Influence of catalyst type on the curing process
and network structure of alkyd coatings, Polymer, 47, 1141 (2006).
[3] V. Baukh, H.P. Huinink, O.C.G. Adan, S.J.F. Erich, L.G.J. van der Ven, Water -Polymer Interaction
during Water Uptake, Macromolecules, 44, 4863 (2011).
[4] N. Reuvers, H. Huinink, O.C.G. Adan, Water Plasticizes Only a Small Part of the Amorphous Phase in
Nylon-6, Macromolecular Rapid Communications, 34, 94 (2013).
Inside coatings

21. Concrete is globally the most used material, only exceeded by the usage of naturally
occurring water. It is widely used to shape the infrastructure of our society, and its
fire safety has become a major societal issue. Under fire loads, concrete structures may
suddenly show thermal instability, so-called fire-spalling, which may seriously jeopardise
the structure stability. During the Channel tunnel fire in 1996 the concrete lining at
several spots was reduced from its original 40 to only 2 centimeter.
Violently boiling water
The fundamental understanding of this phenomenon is lacking, and particularly the
role of water is questioned. During fire, the pore matrix temperature quickly rises to
1200 °C or more, causing water in concrete to be superheated and to boil violently. The
consequent pressure rise due to steam generation is considered to induce stress generation
that causes explosive cracking. Verifying this hypothesis is a challenge as water transport
has to be monitored real time under extreme thermal conditions.
Extreme heating in the NMR
TPM built a set-up for mimicking fire loads of concrete within a medical NMR scanner.
The whole set-up, using focussed halogen lamps, was placed in safety cage in a super-
cooled 1.5 T magnet. For the first time ever, water transport inside porous material could
be monitored real time under such extreme conditions.
Moisture peaks associate with pressure localization
For a long time, it was assumed that moisture peaks and pressure localization go hand in
hand under elevated temperatures. For the first time our measurements prove that these
moisture peaks indeed develop at the boiling front and that pressure runs up at this front.
It remains a question whether the stress generated is sufficient to induce cracking.
[1] G.H.A. van der Heijden, R.M.W. van Bijnen, L. Pel, H.P. Huinink, Moisture transport in heated
concrete, as studied by NMR, and its consequences for fire spalling, Cement and Concrete Research,
37, 894 (2007).
[2] G.H.A. van der Heijden, L. Pel, O.C.G. Adan, Fire spalling of concrete, as studied by NMR, Cement
and Concrete Research 42 , 265 (2012).
Concrete under fire

23. homebuilt

24. TPM: magnetised by things that matter !