Table Of ContentDEVELOPMENTS IN SEDIMENTOLOGY 34
ADVANCED TECHNIQUES
FOR
CLAY MINERAL ANALYSIS
Invited contributions from the Symposium held at the 7th International
Clay Conference, September 6-12,1981, Bologna and Pavia, Italy
edited by
JmJm FRlPlAT
Centre National de la Recherche Scientifique, Centre de Recherche sur les
Solides 6 Organisation Cristalline Imparfaite, Orl6ans Cedex (France)
ELSEVIER SCIENTIFIC PUBLISHING COMPANY
Amsterdam - Oxford - New York 1982
ELSEVIER SCIENTIFIC PUBLISHING COMPANY
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Library 01 Congress Cataloging in Publication Data
Main entry under title:
Advanced techniques for clay mineral analysis.
(Developments in sedimentology ; v. 34)
Bibliography: p.
Includes index.
1. Clay minerals--Analysis--Congresses. I. Fripiat,
J. J. 11. International Clay Conference (7th : 1981 :
Bologna and Pavia, Italy) 111. Series.
~~389.6.2A 38 553.6'1'028 81-9881
ISBN O-d4-420@-9 (U.S.) M C W
0 Elsevier Scientific Publishing Company, 1982
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1
PREFACE
One of the important aims of an international congress devoted to natural or
synthetic materials is to inform the researcher about the potential use of new
physical techniques employed for characterizing these materials. This specific
task is becoming more and more urgent because the number of physical techniques
and their new applications are increasing very rapidly.
The organizing committee of the 7th International Clay Conference has thought
that a special symposium on Advanced Methods in Clay Minerals Research should
be of great interest for many participants and I have been asked to take the
responsibility for its organization.
The first difficulty of that task was to select the methods to be reviewed.
There are techniques which have been known for many years but,because of the
recent instrumentation progress,there are new results which are worthwhile to
summarize. There are also techniques which are not of general use in the field
of clay research but which can provide important supplementary information. Fi-
nally, there are recent techniques which have not yet developped or demonstrated
their full capacity. A review of preliminary results obtained by these new tech-
niques can stimulate other scientists to use them more broadly.
Thus the choice is not easy and, in addition, the space and time allotted for
that type of review are necessarily limited. Nine techniques have been selected
for one or several of the reasons explained above; they constitute the nine chap-
ters of this monograph.
The authors have been asked to avoid as much as possible theoretical discussions
and to concentrate-their presentation on experimental results and their physical
meaning. There was a good reason to operate in that way. Indeed in 1979, at Urbana
(Illinois), J.W. Stucki and W.L. Banwart organized a Nato School devoted to Ad-
vanced Chemical Methods for Soil and Clay Mineral Research (Nato advanced study
institutes : Series C: Mathematical and Physical Sciences, D. Reidel Publish. Co,
1980). The objective of that school was to teach a limited number of participants
the basic principles of Mossbauer spectroscopy, Neutron Scattering, X-Ray Photo-
electron Spectroscopy, Nuclear Magnetic Resonance, Electron Spin Resonance and
Photo Acoustic Spectroscopy, and to show the way to apply their basic principles
to the study of clay minerals. Thus a recent book containing the theories dealing
with several chapters of the present monograph is available.
The present monograph has as goal to reach a larger community of scien-
tists and to disseminate information about applications of physical techniques on
2
a more general basis. It is why modern developments of Thermal Methods Ana-
lysis and of Electron Microscopy have been included together with chapters dea-
ling with MGssbauer Spectroscopy, Nuclear Magnetic Resonance, Electron Spin Re-
sonance, Neutron Scattering and X-Ray Photoelectron Spectroscopy. It appeared
also desirable to have a chapter on UV and Visible Spectroscopy for which, to
my best knowledge, no review on their application to the study of clay minerals
exists. The same is true for far infrared spectroscopy.
All criticisms concerning the choice of the topics have to be adressed to the
editor. The authors of individual chapte,rs should be given all credit for making
the reader aware of the new exciting developments in the physical techniques
used in clay minerals research.
J. FRIPIAT.
5
Chapter 1
THERMOANALYTICAL METHODS IN CLAY STUDIES
Robert C. MACKENZIE
The Macaulay Institute for Soi Research, Craigiebuc kl er , Aberdeen , Scot1 and , UK.
1.1 INTRODUCTION
There is nothing new in the thermal study of clays. Indeed, as early as about
315 BC, Theophrastus refers to the effect of "fire" (i.e. heat) on talc (as
steatite) and on palygorskite (as "mountain wood") (Eichholz, 1965) and
development in the use of heat as a discriminator can be traced from that time
on (Mackenzie, 1981a). Even evolved gas analysis, which would be considered by
some as a relatively recent technique for clays, has its roots in the eighteenth
century, when the Rev. Stephen Hales (1727) found that "a cubick inch of fresh
untried earth" (his italics) yielded "43 cubick inches of air" on heating and
Josiah Wedgwood (1782) detected only carbon dioxide on firing china clay in a
closed system, the evolved water having condensed and gone unnoticed.
The first thermoanalytical study of clays was performed in 1887, when Henri
Le Chatelier recorded what were essentially heating-rate curves for halloysite,
allophane, kaolinite, pyrophyllite and montmoril lonite, over the approximate
temperature range 20-llOO°C, in an attempt to use their behaviour on heating as
a classificational criterion. His results suggest that the samples used were
remarkably authentic - surely a tribute to the mineralogists of the time who had
none of the modern methods of diagnosis available to them. Despite the
differences observed, 1 ittle advance, apart from the pub1 ication of some so-called
"dehydration curves" (Samoilov, 1909) and some heating curves (e.g. Mellor and
Holdcroft, 1911; Ashley, 1911; Brown and Montgomery, 1912), occurred until Wallach
in 1913 first applied differential thermal analysis (DTA) to clays. Even this,
however, seems to have elicited little response and, although the OTA studies of
Satoh (1918, 1921) aroused more attention, it was not until the early 19405,
subsequent to the detailed studies of Norton (1939) and Hendricks and Alexander
(1939), that DTA blossomed forth as an investigational technique. The reason is
simple: at that period clays excited much interest as the general structure of
the clay minerals had been establisned and the species collected into groups, with
the reLult that methods of identification and estimation additional or complementary
to X-ray diffraction were being sought. Unfortunately, the indiscriminate
application of DTA to problems that it could not possible solve,and even the use
of unsuitable equipment and technique, led to the method being discarded by some
as useless in clay mineralogy. However, by no means all clay mineralogists were
6
so disillusioned and much painstaking work over the years (by e.g. Ralph E. Grim,
Paul F. Kerr, Toshio Sudo and others) gradually demonstrated that DTA did have a
place in clay mineralogical studies.
At this point the reader might well ask why thermoanalytical studies (discussed
in the paragraph above) should be separated from purely thermal studies (referred
to in the first paragraph). The reason is that thermal methods have to satisfy
certain criteria before they can be termed thermoanalytical. These criteria,
some of the thermoanalytical techniques currently available and their application
and/or applicability in clay investigations are the subject of the remainder of
this paper.
1.2 THERMAL ANALYSIS
Over the past fifteen years much attention has been devoted to nomenclature,
definition and classification of thermoanalytical techniques with the result that
the methods included can now be clearly recognized and named.
According to the International Confederation for Thermal Analysis (ICTA),
thermal analysis covers (Lombardi, 1980):
"A group of techniques in which a physical property of a substance and/or its
reaction products is measured as a function of temperature, whilst the substance
is subjected to a control led temperature programme".
The three criteria that distinguish a thermoanalytical method are, therefore,
that a physical property is measured as a function of temperature under a
controlled temperature programme. Thus, a single isothermal determination is not
thermoanalytical but assessment of the results of a series of isothermal
determinations at different temperatures as a function of temperature is.
Similarly, non-thermal methods, such as X-ray diffraction, performed under a
control led temperature programme become thermoanalytical determinations. In the
account that follows, however, only those methods normally included in thermal
analysis will be considered: it should be observed that classical calorimetry is
excluded, despite its close relationship to some thermoanalytical methods.
1.2.1 Available thermoanalytical techniques.
A general classification of methods currently recognized as thermoanalytical
is given in Table 1.1 along with the physical property on which they depend and,
'for common methods where it is generally in use, the acceptable abbreviation
(Lombardi, 1980). Most of the techniques can be defined in exactly the same way
-
as thermal analysis, the physical property itself "mass" for thermogravimetry,
"an electrical characteristic" for "thermoelectrometry': etc. - replacing the words
"a physical property" in the definition. In some instances, however, more precise
wording is necessary. For example, six methods are listed as being dependent on
change in mass, but only two are so dependent directly: isobaric mass-change
7
TABLE 1.1
Classification of thermoanalytical techniques
Physical property Derived techniques Abbreviation
Mass Isobaric mass-change determination
Thermogravimetry TG
Evolved gas detection EGD
Evolved gas analysis EGA
Emanation thermal analysis
Thermoparticulate analysis
Temp era tu r e Heating-curve determination*
Differential thermal analysis DTA
En tha 1 py Differential scanning calorimetry? osc
Dimensions Thermodi latometry
Mechanical characteristics Thermomechanical measurement+
Acoustic characteristics Thermosonimetry5
Thermoacoustimetryg
Optical characteristics Thermoptometry
Electrical characteristics Thermoel ectrometry
Magnetic characteristics Thermomagnetometry
*
In the cooling mode this becomes Cooling-curve determination.
t Two types, Power-compensation DSC and Heat-flux DSC, can be distinguished.
? Tests under oscillatory load come under the heading Dynamic thermomechanical
measurement.
5 Thermosonimetry refers to sound emitted by the sample whereas
Thermoacoustimetry involves measurement of changes in the characteristics of
imposed acoustic waves passing through the sample.
determination, which covers equilibrium techniques, such as the once common
"dehydration curves" under a constant partial pressure of water vapour, and
thermogravimetry- (TG), which uses a dynamic temperature programme. Evolved gas
detection (EGO) and evolved gas analysis (EGA) are secondary techniques whereby
materials evolved during heating are detected or analysed, respectively, and the
remaining two, emanation thermal analysis and thermoparticulate analysis, are
tertiary techniques, being special instances of EGA related to radioactive
emanation and particulate matter, respectively. A common method that is not
listed in Table 1.1 is derivative thermogravimetry (DTG), the reason being that
derivative curves can be calculated for most measurements and it would be invidious
to include only one. Attention should also be drawn to the distinction between
derivative and differential, the former applying to the mathematical process and
the latter being used only as the adjectival form of "difference" (Lombardi, 1980).
Thus, in "differential thermal analysis" (and "differential scanning calorimetry")
the "difference in temperature between" (and "the difference in energy inputs
into"), "a substance and a reference material is measured". Moreover, heating
a
- -
curves i.e. curves for sample temperature against tlme give rise to two
-
derivatives "heating-rate curves", where dT/dt is plotted against temperature
(T) or time (t),a nd "inverse heating-rate curves" where dt/dT is plotted against
T or t: both these have been extensively used in the past.
The information given above, together with that in Table 1.1, is probably
adequate to allow appreciation of the enormous strides that have been made over
the past decade or so in obtaining international agreement on a general nomen-
clature and classification system for thermoanalytical techniques. This effort,
however, has covered not only nomenclature of methods but also that of components
of equipment, of aspects of experimental" technique, of critical points on curves
and of symbols (Lombardi, 1980) and has been fortunate enough to receive the
backing of national and international standards institutions, such as AFNOR, ASTM
and ISO, as well as of major international bodies such as IUPAC (1974, 1980).
Moreover, the recommendations in English have been converted into forms acceptable
in many other language-speaking areas (Lombardi, 1980; Mackenzie, 1981b), since
direct translation is not always possible because of already accepted conventions
in other languages.
1.2.2 Simultaneous techniques
It is often convenient to make two or more measurements on one sample at the
same time, leading to "simultaneous determinations" such as DTA-EGA, TG-EGA,
DTA-TG-DTG, etc. This has advantages and disadvantages, and one has to study not
only the bases of the techniques themselves but also the nature of the samples
involved before deciding on their use. For example, EGA is most profitably
employed in conjunction with DTA or TG, as one can then relate the evolved
volatiles to specific changes in the sample; similarly, by comparing simultaneous
DTA and DTG curves one can readily relate reactions involving mass change with
specific enthalpy changes. And, of course, there is a considerable saving in
both time and material. The major disadvantage is that optimum conditions for
one technique may not necessarily be those for another. However, this can be
-
minimized by careful selection of experimental conditions for example, in
simultaneous DTA-TG, by using a small sample and/or employing a slow heating rate.
1.2.3 Standardization of techniques
Since thermoanalytical results can vary with experimental technique, the
Standardization Committee of ICTA have published a code of practice listing the
information that should be supplied with every curve published: they have also
been instrumental in providing materials for temperature calibration of apparatus
(Lombardi, 1980). These aspects should be thoroughly studied by anyone considering
application of thermal analysis.
9
1.3 APPLICATIONS TO CLAYS
Emphasis in this article I's, quite deliberately, on the applications or
potential applications of the various techniques now available to clays. It is,
therefore, impossible to deal adequately with Instrumentation, experimental
technique, or even with some basic principles, although all these are critical in
determining the quality of thermoanalytical results. To overcome this deficiency
the reader is referred to the books of Daniels (1973) and Wendlandt (1974) and to
the excellent reviews that have appeared biennially in Analytical Chemistry
Fundamental Reviews (e.g. Murphy, 1978) for a considerable period.
In the account that follows, clay mineralogical applications take priority,
but due consideration must also be given to the wider field of applications to
clays and clay rocks of technological or industrial importance and to accessory
minerals, since the presence or absence of these may well determine the suitability
of a clay for a particular application. With this wide field in mind, it will be
appreciated that the references given are illustrative only: an exhaustive study
of all published work would be inordinately long.
1.3.1 IIsobaric) mass-change determination
In isobaric mass-change determination the sample is heated at each selected
temperature until there is no further mass change and the equilibrium mass is
plotted against the temperature: the partial pressure of the evolved volatile
(e.g. water or carbon dioxide) is maintained constant throughout the determination
An excellent description of the technique has been given by Weiser and Milligan
(1939).
In the past this technique, although not perhaps in an isobaric mode, was
widely applied to clays in the derivation of so-called "dehydration curves". An
excellent collection of these was given by Nutting (1943) and the technique was
still employed for characterization purposes in the 1950s (see e.g., Mackenzie,
1957a). It is rather time-consuming and with the advent of thermogravimetry
seems to have fallen into disuse. However, families of isothermal mass-change
curves, particularly in their isobaric mode, can probably yield more reliable
information on the kinetics of reactions than the TG curves so commonly in use
(see below).
1.3.2 Thermogravirnetry (TG)
Although DTA has been the most widely used technique in clay mineralogy, the
use of TG and DTG has grown markedly, particularly since the introduction of the
Derivatograph, which provided simultaneous DTA-TG-DTG curves, and its commercial
production in Hungary in the mid-1950s. This instrument, which is by far the
most widely used, and apparently the only one comnercially produced in eastern
Europe, has been upgraded several times and now has various optional additional
i 0
attachments for thermodilatometry, EGA, etc. (Paulik and Paulik, 1978). Its value
in clay mineralogy is readily assessed from the simultaneous curves for a large
number of clays and clay minerals published by Langier-Kuzniarowa (1967). Out-
side eastern Europe, thermogravimetry was stimulated by the commercial production
of the robust Stanton thermobalance in 1954 and simultaneous techniques by the
introduction of the Mettler Thermoanalyzer (Wiedemann, 1964). A wide range of
thermobalances and simultaneous DTA-TG instruments suitable for clay studies can
now be purchased (e.g. Dunn, 1980). the number of the latter tending to increase
as available sensitivity has increased. Of the various types of balance system
used (Keattch and Dollimore, 1975), the null-point electrobalance now seems the
most common. When simultaneous equipment is not used and a comparison is made
between DTA and DTG curves, great care must be taken to ensure that all experimental
-
variables are identical for both determinations for example, use of a different
heating rate can displace peaks and even alter peak shape appreciably (Alietti,
Brigatti and Poppi, 1979).
The main uses of TG add DTG (which must be considered together) in clay
mineralogy have been in determining the reasons for DTA peaks, assessing the range
over which reactions occur and obtaining quantitative information. The methods
are not particularly suitable for identification studies, although the occurrence
of one or two peaks on a DTG curve, and the relative sizes of the two peaks when
they appear, can apparently be employed in characterizing serpentine minerals
(Morandi and Felice, 1979) and the disappearance of the hygroscopic moisture peak
after K-saturation can be used to distinguish hydrobiotite from montmorillonite
in some soils (Ryzhova, 1980). These must be regarded as rather isolated instances
and the main use of the techniques has undoubtedly been to obtain quantitative
information on evolved volatiles, etc. In such applications, however, great care
must be exercised, as the mass change, during, for example, a dehydroxylation
reaction, could be seriously affected iff errous iron in the lattice were
simultaneously oxidized to ferric. For this reason too, quantitative determina-
tion of minerals by DTG (Smalley and Xidakis, 1979) should be undertaken only
when sufficient confirmatory evidence that nothing likely to interfere with the
DTG peak area is present and when comparison can be made with a mineral that is
identical with that in the clay. It is noteworthy in this respect that even the
saturating cation of montmorillonite affects the character and temperature of
the DTG dehydroxylation peak (Schomburg and Stbrr, 1978a). TG has proved
valuable in elucidating the nature of DTA peaks for palygorskite and sepiolite
(Fernandez Alvarez, 1978) and for montmorillonite (Iliuta, Drimus and Preda, 1978)
and OTG in revealing multiple reactions not obvious on the TG curve (e.g. Mifsud,
Rautureau and Fornes, 1978). Changes in the temperature range and magnitude of
the step on the TG, or peak on the DTG, curve can provide valuable confirmatory
evidence for a particular phenomenon, such as the occurrence of NH,+ in some
