for rh>54%: two peaks 2 well-defined families of pore sizes osmotic swelling occurs at rh >...

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