for rh>54%: two peaks 2 well-defined families of pore sizes osmotic swelling occurs at rh >...
TRANSCRIPT
For RH>54%:
•Two peaks 2 well-defined families of
pore sizes
•Osmotic swelling occurs at RH > 80% in
interlayer space compared to RH ~ 54% in
mesopores
HYDRATION SEQUENCE of SWELLING CLAYS EXCHANGED with ALKALI and ALKALI-EARTH CATIONS
F. Salles1, O. Bildstein2, J.M. Douillard1, B. Prelot1, J. Zajac1, M. Jullien3 and H. Van Damme4
(1) ICGM, Université Montpellier – France (2) CEA, DEN, LMTE – Cadarache – 13108 St Paul lez Durance – France (3) Ecogeosafe – Aix-en-Provence – France (4) ESPCI – 75231 Paris -France
Material and Method
Introduction and Principle
Aim of this study : determination of the cation dependence of the hydration process for samples saturated with alkaline cations and the resulting distribution of water molecules in the interlayer space and mesopores
Hydration sequence depends on the nature of the interlayer cation
Osmotic swelling in mesopores is evidenced by original use of thermoporometry + free water observed in mesopores only at RH>90%
Osmotic swelling occurs in mesopores before crystalline swelling is finished in the interlayer space
The interlayer spaces are never completely filled in montmorillonites, except for Cs-sample, but interlayer space water > mesopore water for all cations
References: (a) F. Salles, I. Beurroies, O. Bildstein, M. Jullien, J. Raynal, R. Denoyel, H. Van Damme, Appl. Clay Sci., 2008, 39, 186 and (b) F. Salles, O. Bildstein, J.M. Douillard, M. Jullien, J. Raynal, H. Van Damme, Langmuir, 2010, 26, 5028
•Purified powder of montmo-
rillonites (Mont) from the MX-80
bentonite saturated with a large
majority of Na+ and Ca2+ as
interlayer cations
•Exchanged powders of MX-80
bentonites saturated by alkaline
or Ca2+ cations: Li+, Na+, K+, Cs+
Upon hydration, the structure of the swelling clays is strongly modified due to interactions between water molecules and the multi-scale clay structure (layers and extra-framework cations, particles and aggregates) induce a multi-scale swelling: interlayer swelling and and osmotic swelling in the mesopores. In this study, from an original use of the thermoporometry on unsaturated clay samples, the mesopore size distribution is investigated for samples saturated with alkali and alkali-earth compensating cations as a function of the relative humidity. The results are validated by comparison with the pore sizes estimated from N2 adsorption. The impact of the interlayer cation is thus evidenced and the hydration processes can finally be elucidated by distinguishing the impact of
the swelling of the various scales. we determine the distribution of water (interlayer water and mesopore water) present in our samples by the original combination of (1) X-ray diffraction data, (2) the pore size distribution obtained by thermoporometry and (3) recent adsorption isotherm results.
Material Thermoporometry
Results and Interpretation Evolution of the mesopore size
•Li and Na-Montmorillonites
•At RH< 54% no interpretable signal
(mesopores not filled or not enough
water?)
At RH= 54%
•1 peak corresponding to a size of 2.5 nm
•Good agreement with BJH calculations (N2
adsorption)
• Impact of Rp dominant compared to the
effect of ions for the phase of water
Towards a step by step model for hydration
minterlayer water = mwater in clay – mwater in mesopore
mwater in clay from water adsorption isothermmwater in mesopore from thermoporometry data
mtheoretical interlayer water=d001 * (SH2O –SN2)
with SH2O and SN2 specific surface area as a function of RH* (see poster MR/CI/7) and d001 the interlayer space opening
•Thermoporometry = calorimetric technique sensitive to phase transitions of fluid confined in the porosity 2 nm < Pore radius < 50 nm (mesoporosity)
Original practice : DSC on unsaturated and swelling samples (powder / 10-20 mg) but saturation of studied porosity is necessary
Theoretical equation Brun et Quinson Model
• fusion-solidification-fusion cycles (2°C/min for a range of temperatures between -80°C and 0°C)
• RH conditions: 11%, 33%, 54%, 75%, 90%, saturated material• Hydration vapour or liquid water for saturated samples
T
T
fslp o
v
dTS
tR 2
1
)(
1
T
BARp
-500
-400
-300
-200
-100
0
100
200
300
400
500
-100 -80 -60 -40 -20 0 20
Temperature (°C)
Hea
t (m
W)
fusion
solidification
Rp estimated from solidification
RH = 54%
2.5 nm
No free water
FREE WATER
Osmoticswelling
RH = 75%
RH = 90%
RH = saturated
Evolution of interlamellar space
0
2
4
6
8
10
12
14
16
18
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
Relative humidity
Inte
rla
ye
r d
ista
nc
e
Osmotic swelling in interlayer space
Crystalline swelling (2 layers
of water)
Osmotic swelling in mesopores
•In the case of K-, Rb-, Cs- and Ca-montmorillonites no mesopore swelling except at
saturation in the case of Ca-montmorillonite
Conclusions
Na
LiCa
Cs
K
20%<RH<60%
Na
Li
Li-60% Li-80% Na-60% Na-80% K Cs Ca0
200
400
600
800
1000
1200
1400
Wat
er u
ptak
e (m
g/g
of c
lay)
Samples
• Maximal water amount in interlayer space- Water present in interlayer space- Water present in mesopore space