Clay Science 7, 129-138 (1988)

EXPANSION CHARACTERISTICS OF MONTMORILLONITE AND SAPONITE UNDER VARIOUS RELATIVE HUMIDITY CONDITIONS

TAKASHI WATANABE and TSUTOMU SATO Department of Geoscience, Joetsu University of Education,

Joetsu, Niigata Pre f, 943 Japan

(Accepted July 3, 1988)

ABSTRACT

The basal spacings of the homoionic (Na+, K+ and Ca2+) montmorillonite (T1)

and saponite (SapCa-1) were examined by X-ray powder diffraction (XRD) analysis

under the atmospheres of relative humidity (RH). RH was controlled by ReCX

(Relative humidity Control system for X-ray diffractometer) precisely in the range of 0 to 100% RH.

The variations of basal spacing were almost similar in both minerals at the range

of 0 to 80% RH. However, noticeable differences between the hydration state of T1

and SapCa-1 were observed at 100% RH. It was explained that the differences were

caused by charge localization and hydroxyl orientation in silicate layer because of

these specimens having similar layer charge.

In the region between 2 hydration states, irrational and asymmetrical reflections were observed. These reflections indicated interstratified structure of 2 hydration

states. Especially at 60% RH, that the segregation structure was recognized. The existence of 2 phases indicates that there is heterogeneity in its charge density of

layer.

Key words: Expansion Characteristics, Relative Humidity, Charge Localization, Hydroxyl Orientation, Segregation.

INTRODUCTION

The expandability of smectites has been studied by a number of workers and the factor to influence the expandability have been discussed. Hendricks et al. (1940) and Mooney et al. (1952) showed that the water content was effected by the kind of interlayer cations. Schultz (1969) claimed that the value of layer charge was the controlling factor to influence the expandability of smectites. Suquet et al. (1975) examined montmorillonites, beidellites, saponites, and vermiculites systematically, and estimated the respective influence of the nature of the cation, the surface charge density and the charge localization (octahedrally or tetrahedrally charged) as factor of the expandability.

Recently, the basal reflections of montmorillonites were analysed in detail under various relative humidity (RH) (Moore and Hower, 1986; Iwasaki and Watanabe, 1988). They concluded that interstratified structure was formed in the intermediate stage of

130 T. Watanabe and T. Sato

hydration. However, about the type of interstratification, both workers have got the different conclusion. The interstratified structure in hydration stage has attracted special interest recently. In order to get more precise information of expandable clay minerals, it is necessary to control the condition of RH precisely and to accumulate data about other expandable clay minerals. Then we have developed the system which can control RH for X-ray diffractometer.

In this study, dioctahedral montmorillonite and trioctahedral saponite are examined by X-ray diffraction (XRD) analyses under the atmospheres of precisely controlled RH, in order to clarify their expansion characteristics.

EXPERIMENTAL

The < 0.2 ƒÊm fraction of natural montmorillonite and saponite were used in this

study. Montmorillonite (T1) produced by Tsukinuno mine, Yamagata Pref., Japan.

Saponite (SapCa-1), from Ballarat, California, was obtained from the Source Clay

Repository of The Clay Minerals Society. The layer charge of T1 and SapCa-1 are 0.40

and 0.38 (e.s.u./half u.c.) respectively, but the charge localization is different. T1

apparently possess both tetrahedral and octahedral charge, and SapCa-1 is superior in

tetrahedral charge localization after Greene-Kelley test.

Interlayer cation of each sample was exchanged with K+, Na+ and Ca2+ . K- and

Na-exchange were achieved by adding 1N solutions of the chloride salts, in the case of

Ca-exchange, by adding 1N solution of the acetate. The homoionic materials placed on

glass slides and were dried in air, and were used for XRD. XRD carried out under the

atmospheres controlled by ReCX (Relative humidity Control system for X-ray

diffractometer).

The ReCX consists of the three parts that are the humidity generator, the specimen

chamber and its controller (Fig. 1).

FIG. 1. Schematic figure of ReCX. A, B and C parts are the humidity

generator, the controller and the specimen chamber, respectively. a, b: flowmeter; c: saturated air (100% RH); d: mixture of saturated and dry air (0% RH)

Expansion Characteristics of Smectites 131

The Accurate Humidity Generator (made by Shinyei Co. Ltd., Japan) was used as

the humidity generator, which can be simply operated, and set up the atmosphere of

aimed RH (0-100% RH) rapidly.

The specimen chamber was designed to be set on a goniometer of X-ray

diffractometer (Fig. 2). This chamber has two path (A and B). Controlled air passes into

the inside through the A, and comes out through the B. It also has two windows that

covered by polyethylene terephthalate film (Mylar film) in the path of X-ray.

Controller part can control temperature and check RH in specimen chamber

simultaneously. Temperature and RH were checked by the sensor, and RH was

controlled by personal computer using A/D converter and parallel I/O unit. By this

controller part, it was guaranteed experimentally that atmosphere in chamber was

controlled within •}0.5•Ž and •} 3% RH at 25•Ž.

Using this system, the following experiment was performed. The orientate samples

were kept in the specimen chamber at 0% RH for 6 hours. Then, XRD was carried out

after confirming that the position and intensity of 001 reflection became constant. The

X-ray line profile was measured at intervals of 10% RH between 0 to 100%. It tooks

about 10 minutes to reach equilibrium after raising of 10% RH.

XRD patterns were obtained by Rigaku diffractometer using monochromatized

CuKa radiation, and was recorded from 2•‹ to 50•‹ in 2 ƒÆ. The basal spacing of specimen

was calculated from all basal reflections in this range.

FIG. 2. Photograph of the specimen chamber. A and B are paths of controlled air. A: entrance;

B; exit.

132 T. Watanabe and T Sato

RESULTS AND DISCUSSION

Hydration of montmorillonite (T1) Fig. 3 shows the variations of basal spacing obtained for T1 saturated with different

cations (Na+, K+ and Ca2+) at 0 to 100% RH. Their basal spacings gradually varied with increasing RH. Several homogeneous states of hydration were observed and their XRD patterns were characterized by rational series of reflections.

Na-saturated gave a collapsed phase with the basal spacing of about 10.0A at 0% RH. With increasing RH, rational reflections of about 12.4A appeared at 40 to 50% RH, those of about 15.6A appeared at 70 to 90% RH. At 100% RH, the basal spacing of expanded to 18.8A and its rational reflections can observed. Bradley (1937) has reported that the 10.0A, 12.4A, 15.6A and 18.8A phases was the 0, 1, 2 and 3-layer hydration states respectively. Therefore, it was concluded that there were four phases of 0, 1, 2, and 3 water layers in Na-saturated at 0 to 100% RH.

Though the variations of basal spacing of K-saturated were generally similar to Na-saturated below 50% RH, 12.4A phase retained at 60 to 100% RH. In the case of K-saturated, two phases were observed at 0 to 100% RH.

In the case of Ca-saturated, almost rational reflections were obtained under the condition of 20 to 80% RH. The clear horizontal but slightly inclined lines were observed in hydration curves of Na- and K-saturated. The basal spacing increased from 15.0 to 15.8A gradually. The basal reflections at 0% RH formed rational series, and basal spacing was about 11.6A. This spacing agreed with that of one-water hydrated

FIG. 3. Variations of basal spacing in Na-saturated (•¡, •  ), K-

saturated (A, A) and Ca-saturated (•Ÿ, •ž) montmorillonite at

various relative humidity. Black symbols: rational basal reflec-

tions. Open symbols: irrational basal reflections.

Expansion Characteristics of Smectites 133

Mg-vermiculite (Walker, 1956). In the case of Ca-saturated, there were three phases of 1, 2, and 3 water layers at 0 to 100% RH.

Hydration of saponite (SapCa-1) Fig. 4 shows the variations of basal spacing obtained for SapCa-1 saturated with

different cations (Na+, K+ and Ca2+) at 0 to 100% RH. Several homogeneous states of hydration were similar to T1 . Their XRD pattern were characterized by a rational series of reflections.

In the case of Na-saturated, the variations of basal spacing of SapCa-1 were generally similar to T1 below 90% RH. At 100% RH, SapCa-1 kept 2 layer hydrate state T1 expanded to the 3 layer hydrate state (18.82k). In the case of Na-saturated SapCa-1, there were three phases of 0, 1 and 2 water layers at 0 to 100% RH.

In the case of K-saturated, the variations of basal spacing of SapCa-1 were generally similar to T1 below 80% RH. SapCa-1 expanded to 2 layer hydrate state (15.6A) at 100% RH. On the contrary, T1 kept 12.4A phase at 40 to 100% RH. In the case of K-saturated SapCa-1, three phases were observed at 0 to 100% RH.

In the case of Ca-saturated, 2 water layer hydrate was predominant over a wide range of RH. But Ca-saturated differed from T1 in showing irrational reflection at 100% RH. This reflection indicates an interstratified structure with the layer of 15.6A and 18.8A phases. In the case of Ca-saturated SapCa-1, there were completely two phases of 1 and 2 water layers at 0 to 100% RH.

FIG. 4. Variations of basal spacing in Na-saturated (•¡, •  ), K-

saturated (A, i) and Ca-saturated (•Ÿ •ž) saponite at various

relative humidity. Black symbols: rational basal reflections. Open

symbols: irrational basal reflections.

134 T. Watanabe and T Saw

Comparison between hydration of Ti and SapCa-1 Fig. 5 to 7 show the comparison of variations in basal spacing of homoionic

specimens. The variations of basal spacing were similar in both minerals at the range of 0-80% RH, though a little differences were observed in the transition of two hydration states. However, noticeable differences between both of hydration state were observed at 100% RH and summed up as follows:

FIG. 5. Variations of basal spacing in Na-saturated montmorillonite

(•£ , •¢ ) and saponite (•¡, • ) at various relative humidity. Each

open symbols: irrational basal reflections.

FIG. 6. Variations of basal spacing in K-saturated montmorillonite

(A , A) and saponite (U, 0) at various relative humidity. Each open symbols: irrational basal reflections.

Expansion Characteristics of Smectites 135

FIG. 7. Variations of basal spacing in Ca-saturated montmorillonite

(•£, •¢) and saponite (•¡, • ) at various relative humidity. Each

open symbols: irrational basal reflections.

(1) In the case of Na- and Ca-saturated, T1 gave completely 3 water layer hydration with the basal spacing of 18.8A phase (rational reflections), whereas SapCa-1 didn't.

(2) In the case of K-saturated, SapCa-1 had completely 2 water layer hydration with the basal spacing of 15.6A phase (rational refractions), whereas T1 didn't, and a spacing of 12.4A phase remained.

Suquet et al. (1975) summarized the expansion characteristics of smectites and vermiculites. They suggested that factors to influence the expandability were the nature of the exchangeable cation, the surface charge density and charge localization. The

phenomena pointed out in (1) is mainly caused by charge localization, because of both minerals having similar layer charge. The tetrahedrally charge of SapCa-1 is superior to T1, and the electrostatic energy between interlayer cation and silicate layer in SapCa-1 is larger than Ti. Consequently, it was difficult to insert water molecules into interlayer in the case of SapCa-1.

The fact of (2) pointed out that SapCa-1 showed higher expandability than T1 . However, this fact contradicted result in (1). In order to explain this contradiction, it can be considered that there is some effect of the interaction of interlayer cation and the hydroxyl ions of octahedral sheet. In the case of micas, it has been known that

phlogopite tends to leach the interlayer cation more than muscovite. The fact has been explained in terms of hydroxyl orientations which, in a trioctahedral mica, results in a much shorter proton-interlayer cation distance and a greater repulsion between the silicate layer and the potassium (Giese, 1975). The phenomenon described above can be explained in the some way as the case of micas. Namely, the hydrogen end of the hydroxyl axis in dioctahedral montmorillonite orients toward the empty octahedral site, and that is trioctahedral saponite orients toward interlayer cation. Therefore, the insert of water molecule becomes more easy for the reason that the repulsion force of SapCa-1 to interlayer cation is greater than Ti.

136 T. Watanabe and T. Sato

Though the ethylene glycol method is not useful to distinguish montmorillonite with saponite, the comparison of behavior of hydration could distinguish them .

Interstratified structure in hydration During the transition of 2 hydration states, irrational and asymmetrical reflections

were observed. In Fig. 8 and 9, these examples were shown in the patterns at 20% and 60% RH. It was regarded that these reflections indicated an interstratified structure of two hydration states. Especially at 60% RH, it was recognized that segregation structure was formed, because that the 001 reflection was dablet and their higher reflection also spilled into two peaks belonging to 12.4A and 15.6A phases as pointed out by Iwasaki and Watanabe (1988). The existence of two phases indicates that there is some differences in its charge density of layer. The heterogeneity of the charge distribution in the layers was recognized under the atmospheres of controlled RH, in the same as the results obtained by the alkylammonium method (Lagaly and Weiss, 1969).

FIG. 8. X-ray basal reflection patterns of Na-saturated mont-morillonite at 0, 20, 40, 60 and 80% relative humidity. The reflection at 60% RH is explained to be consist of the one (at 40% RH) and two (at 80% RH) water hydration.

Expansion Characteristics of Smectites 137

FIG. 9. X-ray basal reflection patterns of Na-saturated saponite at 0,

20, 40, 60 and 80% relative humidity. The reflection at 60% RH is

explained to be consist of the one (at 40% RH) and two (at 80%

RH) waer hydration.

ACKNOWLEDGEMENTS

The authors are grateful to Dr. T. Iwasaki of Government Industrial Research Institute, Tohoku

for valuable discussions and suggestions.

REFERENCES

BRADLEY, W.F., GRIM, R.E. and CLARK, G.F. (1937) Z. Kristallogr. Kristallgeom., 97, 260-270. GIESE, R.F. (1975) Z. Kristallogr., 141, 138-144. HENDRICKS, S.B., NELSON, R.A. and ALEXANDER, L.T. (1940) J. Amer. Chem. Soc., 62,

1457-1464. IWASAKI, T. and WATANABE, T. (1988) Clays and Clay Minerals, 36, 73-82. LAGALY, G. and WEISS, A. (1969) Proc. Mt. Clay Conf. Tokyo, 1, 61-80.

138 T. Watanabe and T. Sato

MOONEY, R.W., KEENAN, A.G., and WOOD, L.A. (1952)1. Amer. Chem. Soc., 74, 1371-1374. MOORE, D.M. and HOWER, J. (1986) Clays and Clay Minerals, 34, 379-384. SCHULTZ, L.G. (1969) Clays and Clay Minerals, 17, 115-149. SUQUET, H., DE LA CALLE, C. and PEZERAT, H. (1975) Clays and Clay Minerals, 23, 1-9.