Clay Minerals (1993) 28, 25-31
This paper is dedicated to Professor Lisa Heller-Kallai on the occasion of her 65th birthday.
THE EFFECT
OF TEMPERATURE
ON THE SWELLING
OF MONTMORILLONITE
F. ZHANG,
Z. Z. ZHANG,
P. F . L O W ArqO C. B . R O T H
Agronomy Department, Purdue University, WestLafayette, Indiana 47907, USA
(Received27 February 1992; revised29 September1992)
A B ST R A C T : The effect of temperature on the swellingof clay was studied by determining (1) the
relation between the interlayer spacing, 2, and the swelling pressure,/7, at different values of the
temperature, T, using the method of Viani et al. (1983) as modified by Wu et al. (1989); (2) the
relation between ,~and T at different values of/7; and (3) the relationship between Hand row~me,the
mass ratio of water to clay, at different values of T using the method of Low (1980). The results
showed that )~was essentially independent of T but that mw/mcdecreased slightlywith T at any value
of/7. Such results are not consistent with electric double-layer theory. Therefore, it was concluded
that the decrease in m~/mc with increasing T was due primarily to the thermal breakdown and
consequent loss of water from the larger pores outside of the interlayer region.
Swelling is one of the most important of all the processes that occur in soils. It affects their
strength, structure, permeability and erodibility, yet we have only limited knowledge of
how different factors affect swelling. In particular, very little is known about the effect of
t e m p e r a t u r e . Kolaian & Low (1962) observed that the swelling p r e s s u r e , / 7 , of a relatively
dilute suspension of N a - m o n t m o r i l l o n i t e decreased with increasing t e m p e r a t u r e , T, when
mw/mc, the mass ratio of water to clay, was held constant. H o w e v e r , Yong et al. (1963)
observed contrary results for a m o r e concentrated suspension of the same montmorillonite.
M o r e recently, Oliphant & Low (1983) used m e a s u r e d t h e r m o d y n a m i c data to calculate
(6H/6T) for Na-montmorillonite at different values of m J m ~ . Their calculations showed
that (6/7/6T) rose rapidly from negative to positive values, passed through a m a x i m u m and
then fell gradually toward zero as row~m,, increased from 0.25 to 8.0. H o w e v e r , the absolute
values of (617/67) were always <0.02 atm/deg. In view of the paucity of experimental
results, the a p p a r e n t inconsistency of the results that have b e e n obtained, and the
importance of swelling in nature, we decided to conduct the present study.
MATERIALS
AND METHODS
The <2/~m, Na-saturated fraction of the montmorillonite from U p t o n , W y o m i n g was used
and p r e p a r e d as described by Low (1980).
To measure the distance, )t, between the layers of the montmorillonite at any value of the
swelling pressure, H, the p r o c e d u r e of Viani et al. (1983, 1985) was used with the
environmental c h a m b e r of Wu etal. (1989). In this p r o c e d u r e , a suspension of
montmorillonite is deposited on a m e m b r a n e s u p p o r t e d by a ceramic filter enclosed in an
environmental c h a m b e r with Be windows for the transmission of X-rays. Then solution is
9 1993 The Mineralogical Society
26
F. Zhang et al.
expressed from the suspension by admitting nitrogen gas at an elevated pressure to the
chamber. Thus a filter cake of oriented montmorillonite particles is formed. Additional
solution is subsequently expressed from the filter cake by increasing the pressure of the
nitrogen gas in successive increments. Immediately below the filter is a reservoir with a
connection to the outside atmosphere. The reservoir catches the expressed solution and
allows it to remain at atmospheric pressure while it equilibrates with the montmorillonite on
the other side of the filter. After equilibrium is achieved at each of the successive gas
pressures, the surface of the filter cake is positioned so that it is tangent to the focusing circle
of an X-ray diffractometer and an X-ray diffraction (XRD) pattern is obtained from which
the basal spacing of the montmorillonite is determined. Subtraction of the thickness of an
individual layer (0.93 nm) from the basal spacing yields the value of Z. The value o f / / e q u a l s
the applied pressure. Hence, the relation between Z a n d / 7 can be obtained.
The locations of the diffraction peaks in the diffraction patterns were determined by using
a curve-fitting program (Fraser & Suzuki, 1966, 1969) with an IBM PC computer. In this
program, the intensity of diffraction is described by a linear combination of three functions,
namely, a quadratic function representing the base-line and two Gaussian functions
representing diffraction peaks of first and second order. The Gaussian functions are in the
form
,--,oeX I
where ! is the intensity of the diffracted X-rays at x ~20, Io is the amplitude of the diffraction
peak, and Xo and Ax are the centre and width, respectively, of the diffraction peak in ~ By
repeatedly adjusting the parameters in these functions, the computed diffraction pattern is
made to fit the observed diffraction pattern. Then the locations of the diffraction peaks are
determined from the values OfXo required to achieve this fit. Generally, the results obtained
in this way agree with those obtained by other methods described by Klug & Alexander
(1974). However, they have the advantage of being more objective.
For the present purpose, it was necessary to control T and this was achieved by enclosing
the environmental chamber, goniometer, X-ray generator and X-ray detector in an air bath
as shown in Fig. 1. Temperature control was +0-5~
To prepare a sample of Na-montmorillonite for X-ray analysis at any value of T, - 2 0 0 mg
of the montmorillonite were suspended in 40 ml of a solution of 10 4 M NaC1. Then the
suspension was deposited on the membrane in the environmental chamber and nitrogen gas
at a pressure of - 0 . 7 atm was admitted to the chamber to express solution from the
suspension and form a filter cake. Thereafter, the effect of T on the relation between ~ and
/ / w a s determined in either of two ways, namely, by holding//constant and changing T, or
by changing/7 in successive increments at each of several values of T.
The value of mJmc was also determined as a function o f / 7 at different values of T. This
determination was accomplished as described by Low (1980) with the miniature pressuremembrane apparatus enclosed in a water bath controlled to within +0.1~
RESULTS AND DISCUSSION
X-ray diffraction patterns for Na-montmorillonite at several values of T and H = 6-1 atm
are presented in Fig. 2, (a) showing the original data and (b) the corresponding data
computed as described above. These patterns are typical of those obtained at other values
Effect of t e m p e r a t u r e
on
montmorillonite swelling
27
Water Bath
Circulator
Beryllium Window
Copper Coil
s _
Wall
Goniometer
M
x_ra,
Generator
x-r.
Detector
Lead to N 2
Gas Tank
Drained Solution Collector
I
=
I
Environmental
Chamber
Water Reservoir
FI6.1. Cutawaytop view of the apparatusfor measuringthe c-axisspacingof the clay crystalsin a clay
paste under a given pressure and temperature.
.
~,
.
.
.
.
I
)'/C~'---30
O
x 20
.
12
.
.
39 oc
25
W2-
.
.
.
.
.
.
39 oc
~
13=6.1
'2
atm
o.c
10
/A-~-5 o ~
x
"0
c
0
o.c
o<r
O
o15
6
69
L.
19
c~
4
gO
2
~10
c
0
o
5
i
I
2
J
3
4
28
5
6
0
2
3
4
5
6
2e
F16. 2. X-ray diffractionpatterns of Na-Upton montmorillonitein equilibriumwith a 10-4 MNaCl
solution at four temperaturesand/7 = 6.1 atm. The data were: (a) originallyrecorded; (b) obtained
by using a Gaussian function to fit the original data.
o f / 7 . N o t e that the intensity of the first and second order X R D peaks increased with
increasing temperature. This change in intensity was reversible, i.e., the intensity was
restored to its original value when the temperature was restored to its original value. In a
supplementary experiment, it was found that the X R D intensity for cholesterol also rose
and fell reversibly with increasing and decreasing temperature. A s cholesterol is used as a
standard for the alignment of X-ray diffractometers because it has a non-swelling crystalline
structure, the change in X R D intensity with temperature cannot be attributed to
corresponding changes in the sample. It is possible that the X-ray beam was attenuated by
films of adsorbed water on the Be windows of the environmental chamber and that its
F. Zhang et al.
28
intensity rose and fell as the thickness of these films decreased with rising temperature, and
increased with falling temperature.
Plotted in Fig. 3 are data showing the relation between H a n d X for Na-montmorillonite at
three temperatures. The data in Fig. 4 were obtained from Fig. 3 and show the relation
between X and T at different values o f / 7 . From these two figures, it is evident that the
relation between /7 and X is essentially independent of temperature in the temperature
range of the experiments. Changes in this relation from one temperature to another were
within experimental error. These results are entirely consistent with the results of Pashley
(1981) who observed that the force between mica sheets was unaltered by changing the
temperature from 21~ to 65~
The effect of temperature on the relation between H and row~me for the Namontmorillonite is shown in Fig. 5 and Fig. 6 was constructed from the data in Fig. 5. Note
from these figures that /7 decreased with T at any value of mw/mc, i.e., (6H/6T) was
negative, and that mJmr decreased with increasing T at any value of/7. These results do not
agree with those of Yong et al. (1963). The reason for the discrepancy is not clear. We used
gaseous nitrogen to express water from the clay and measured the loss of water
gravimetrically, whereas Yong et al. used a solid piston for this purpose and measured the
loss of volume by the change in height of a column of mercury that also transmitted the
applied pressure to the piston. For a water-saturated, plastic clay, the loss of water should
equal the loss of volume. However, it should be noted that a gaseous piston exerts pressure
uniformly on the clay particles and the interparticle water, but a solid piston will do the
same only if there is no interparticle stress, i.e., only if the piston is not supported by a
matrix of particles in contact with each other. The results in Figs. 5 and 6 also disagree with
those of Oliphant & Low (1982) who reported very small positive values of (6/7/6T) at most
values of mw/mr However, their values of (6/7/6T) were calculated by substituting
experimental data from three different sources into the relevant equation and small errors
in any of these data could have changed the value of (6/7/6T) from slightly negative to
I
I
I
[1=1.7
5
E 4
E
12
C
i-i=4.0 9
4
r- 3
FI=6.0
3
9
F1=8.2
I
I
I
I
3
4
5
6
2
7
), ( n m )
FIG. 3. Relation between H and ,~ for Namontmorillonite in equilibrium with a 10-4 M
NaC1 solution at three temperatures.
10
I
I
I
20
50
40
T (~
FIG. 4. Relation between X and T for Namontmorillonite in equilibrium with a 10 4 M
NaCI solution at four values of H.
Effect of temperature on montmorillonite swelling
7
l
f
i
i
29
i
i
i
FI
i
(otm)---~
6
5
E
o
4
a
10~
9
25
~
9
50
~
9
75
~
3
2
r-
2
4
1
@---
- ......
"-t
........
5
0- ....
9
0
i
i
i
2
3
4
5
6.5
i
i
l
i
i
20
40
60
80
100
T (~
mw/mc
Fie. 5. Relation between Hand m~/mcfor Namontmorillonite in equilibrium with a 10-4 rd
NaC1 solution at five temperatures.
row~m,,a n d T f o r N a montmorillonite in equilibrium with a 10 4 M
NaC1 solution at different values of/7.
F16.6.
Relation
between
slightly positive. Therefore, we regard the data on (611/670 in this paper as being more
reliable.
In aqueous systems, the layers of montmorillonite can co-exist in two phases, namely, a
partially expanded phase with a fixed value of A and a fully expanded phase with a value of A
that varies w i t h / 7 (e.g., Viani et al., 1983, 1985; Wu et al., 1989). Hence, we can write
7(mw/mc) = 1/2pwS[fpAp + feAe]
(2)
where 7 is the fraction of the total water in interlayer regions, Pw is the density of the water,
S is the specific surface area of the montmorillonite, fp and f~ are the fractions of the layers in
the partially and fully expanded states, respectively, and Zp and Ae are the corresponding
distances between the layers in these states, Now,
fp + f~ = 1-0
(3)
(mw/mc) = 112 pwS [(Ae _ Ap)fe + Ap].
(4)
and so eqn. (2) can be reduced to
7
As indicated in Figs. 3 and 4, Ae does not change with T. If partially expanded layers are
present, their value of Ap should also be constant with T. Therefore, differentiation of
eqn. (4) with respect to T yields
d(mw/mc)/dT = -112 ~ 2 ~ [(At - Ap)f~ + Ap]dT/dT + 112 pwS7 (A~ - Ap) dfffdT.
(5)
It is evident, therefore, that mJm,. can decrease with rising temperature while Ae remains
constant if dT/dT is positive or if dfeldT is negative.
In order to determine the approximate magnitudes of dy/dT and dfffdT that would
satisfy eqn. (5) under the conditions of our experiments, we will let Pw = 1-0 g/cm 3,
S - 8 • 106 cmZ/g and f,, = 1 at T = 286~ (13~
Then we will consider two cases: (1) the
F. Zhang et al.
30
i
6
i
i
____-----
2
-
F1 (atrn)
5
I
______-- 3
E
r
----------
4
4
5
--------3
10
i
20
,
30
6
,
40
T (~
FIG.7. Relation between ;~and Tfor Na-montmorillonite in equilibrium with a 10-4 MNaCI solution
at different values of/7 as predicted by electrical double-layer theory.
case when fe is constant and dffldT = 0 and (2) the case when y is constant and dv/dT = O.
F r o m Fig. 6 it can be seen that d(mw/mc)/dT = - 5 x 10 3 g of water per degree per g of
montmorillonite. A n d from Fig. 4 it can be seen that ,~ = 4 nm when H = 4.0 bars.
M o r e o v e r , a reasonable value of ),is 0.7 (Low, 1987) and a reasonable value of ,~p is 1.0 nm
(Viani et al., 1983). By using the above values in eqn. (5), d),/dT = 1-5 x 10-3/deg when
dffldT = 0; and dfe/dT = - 2 ' 9 x 10 3/deg when d),/dT is zero. This means that, over a
t e m p e r a t u r e range of 26~ (from 13-39~
A), would be 0.039 and Afe would be - 0 . 0 7 5 .
Consequently, neither ), nor fe would change appreciably as a result of the change in mw/mc
with T. A t the present time, it is not known whether one or both of these factors changed
with mw/m~.
To determine whether or not electrical double-layer theory could account for our
observations, it was assumed that all of the exchangeable cations were in the diffuse layer
and, therefore, that the surface charge density of the montmorillonite was calculable from
its cation exchange capacity and specific surface area. A l t h o u g h this assumption is not valid
(e.g., see Miller & Low, 1990), the results obtained by using it should indicate the sign, if
not the absolute magnitude, of (6216T)17. Then the conventional equations of this theory
(van O l p h e n , 1963; Viani et al., 1983; Miller & Low, 1990) were used to calculate ). at
different values of T and constant values o f / 7 . The results are shown in Fig. 7. Note that
double-layer theory predicts that ~. will increase with T at any value o f / 7 . Reference to
Fig. 4 shows that this prediction is not fulfilled and it is clear, therefore, that the theory is not
consistent with the experimental observations.
F r o m the results r e p o r t e d , the following conclusions are drawn: (1))~ is essentially
i n d e p e n d e n t of T, (2) /7 decreases slightly with T at any value of mw/mc, and (3) rnw/rnc
decreases slightly with T at any value o f / 7 .
ACKNOWLEDGMENT
The authors wish to thank the US-DOE, Office of Health and Environmental Research, for support under Grant
DE-FG02-85ER60310. Journal Paper 13375, Purdue University, Agricultural Experiment Station, West Lafayette,
Indiana 47907.
Effect o f temperature on montmorillonite swelling
31
REFERENCES
FRASERR.D.B. & SUZUI(IE. (1966) Resolution of overlapping absorption bands by least squares procedures. Anal.
Chem. 38, 1770-1773.
FRASERR.D.B. & SVZUKlE. (1969) Resolution of overlapping bands: functions for simulating band shapes. Anal.
Chem. 41, 37-39.
KLW H.P. & ALEXANDERL.E. (1974) X-ray Diffraction Proceduresfor Polyerystallineand Amorphous Materials.
John Wiley & Sons, New York.
KOLAIANJ.H. & Low P.F. (1962) Thermodynamic properties of water in suspensions of montmorillonite. Clays
Clay Miner. 9, 71-84.
Low P.F. (1980) The swelling of clay: II. Montmorillonites. Soil Sci. Amer. J. 44, 667-676.
Low P.F. (1987) Structural component of the swelling pressure of Clays. Langmuir 3, 18-25.
MILLER S.E. & Low P.F. (1990) Characterization of the electrical double layer of montmorillonite. Langmuir 6,
572-578.
OLWnANTJ.L. & Low P.F. (1982) The relative partial specific enthalpy of water in montmorillonite-water systems
and its relation to the swelling of these systems. J. Coll. lnterf. Sci. 89, 366-373.
PASHLEYR.M. (1981) Hydration forces between mica surfaces in aqueous electrolyte solutions. J. Coll. Interf. Sci.
80, 153-162.
VAN OLPHEN H. (1963) An Introduction to Clay Colloid Chemistry. Interscienee, London.
VIANI B.E., Low P.F. & ROTH C.B. (1983) Direct measurement of the relation between interlayer force and
interlayer distance in the swelling of montmorillonite. J. Coll. Interf. ScL 96, 229-244.
VIANI B.E., RoTn C.B. & Low P.F. (1985) Direct measurement of the relation between swelling pressure and
interlayer distance in Li-vermiculite. Clays Clay Miner. 33, 224-250.
Wv J., Low P.F. & ROTH C.B. (1989) Effects of octahedral-iron reduction and swelling pressure on interlayer
distances in Na-montmorillonite. Clays Clay Miner. 37, 211-218.
YONC~R., TAYLORL.O. & WARKENT~NB.P. (1963) Swelling pressures of sodium montmorillonite at depressed
temperatures. Clays Clay Miner. 11, 268--281.