Clay Minerals (1967) 7, 33.
ENERGY
CHANGES
PROCESSES
IN DEHYDRATION
OF C L A Y M I N E R A L S
TOSHIO SUDO*, SUSUMU SHIMODA*, SHIGERU
AND M A S A H A R U
NISHIGAKIt
AOKI t
*Geological and Mineralogical Institute, Faculty of Science, Tokyo University of Education,
and tRigaku Denki Company, Tokyo, Japan
(Received ~8 July 1966)
ABSTRACT: Using the adiabatic calorimeter which has been developed by
Nagasaki & Takagi (1948) and manufactured by the Rigaku Denki Company, the
energy changes associated with the dehydration and dehydroxylation processes
of clay minerals were measured at room pressure. The samples studied were montmorillonite, chlorite (trioctahedral type), and three kinds of interstratified minerals
with component layers such as mica, dioctahedral chlorite, and montmorillonite.
AH-values due to the dehydration of the interlayer region were 9-8 keal/H20
mole for montmorillonite and 12"4---13"4 kcal/HzO mole for interstratified
minerals mica-montmoriIlonite and dioctahedral chlorite-montmorillonite. The
values due to dehydroxylation of the silicate layer were 17-7 kcal/H20 mole
for montmorillonite, 16"8-17"5 kcal/H20 mole for the interstratified micamontmorillonite, and 19"3 kcal/HzO mole for chlorite. The value for the
dehydroxylation of the hydroxyl layer of chlorite was 19"3 kcal/H20 mole.
For the sake of comparison, the heat of transition a<--->flof quartz was found to
be 140 cal]mole. The reproducibility of these values was in the range of -----5%.
INTRODUCTION
In the field of clay mineralogy, thermal analysis has been widely used mostly for
the purpose of qualitative identification, and the necessity for a more quantitative
approach in future research has become evident. The purpose of the present paper
is to report the data on the energy changes in the dehydration and dehydroxylation processes in clay minerals which can now be studied by more quantitative
methods. The data obtained include specific heat (SH) curves recorded by the
adiabatic calorimeter developed by Nagasaki & Takagi (1948). Thermogravimetric
(TG) and differential thermal analysis (DTA) curves were also recorded with this
calorimeter either simultaneously or successively, and the data obtained from these
curves are discussed along with AH-values measured from SH-curves.
34
T. Sudo, S. Shimoda, S. Nishigaki and M. Aoki
Several problems are left for future study, such as discussion of detailed constructional features of the apparatus and strict control of the experimental conditions.
APPARATUS
AND EXPERIMENTS
The most important feature of the adiabatic calorimeter is the part of the furnace
including the sample holder (Fig. 1). The sample holder (1) is a cylindrical bottle
of silica glass, about 4"265 g in weight, having three holes in its base; one (a) is
along the axis of the cylinder and the other two, (b) and (c), are located symmetrically on either side of the middle hole. This sample holder is set on a silica
(1)
(2)
(6)
(3)
a
FIG. 1. Schematic diagram of the sample holder and the furnace of the adiabatic
calorimeter (Nagasaki & Takagi, 1948).
glass frame and placed in the middle of a spherical nickel container (2) which is
called the adiabatic container. The sample is heated uniformly by supplying constant wattage to the internal heater (3) which is set in the middle hole (a) of the
sample holder. The temperature of the sample is measured by a thermocouple (4)
which is set in hole (c) of the sample holder. One junction of a differential thermocouple (5) is set in hole (b) and the other junction is in contact with the wall of the
adiabatic container. The adiabatic container is covered by three-fold metal shield
plates and set in the middle of the spherical furnace (6), the temperature of which
is controlled automatically so as to eliminate any temperature difference between
the sample holder and the adiabatic container.
Under these conditions, it is possible to measure the time interval At (sec) to raise
the temperature of a sample of M g by A0 ~ C by supplying constant wattage (W)
to the internal heater.
Dehydration of clay minerals
35
The specific heat (SH) is obtained from
SH =
0-239 W At
M s
cal/g
The specific heat of most materials gradually increases as the temperature rises.
Hence the base-line usually shows a slight rise with rising temperature. Phase
transition usually causes deflection of the base-line to such an extent as to form a
peak. The total energy change is calculated from the total time given by the peak
area on the specific heat (SH) curve (Fig. 2).
r
F
IF
j - - F-
F
\
F
._f
620 ~
FFFT1 i I I t [TFTR
Lt... -
610 ~
600 ~
590 ~
580 ~
570 ~
SH
560"
I I / 1 FTTT-T} ! I I I I-TT-T-lq ~ J J J FTFFFL
FIG. 2. Specific heat curve of the dehydroxylation of chlorite from Wanibuchi. Initial
weight, 5.60 g; vessel, fused quartz; wattage, 0.606 W; time full scale, 1000 sec; thermocouple, C-A; atmosphere, air.
SAMPLES
1. Montmorillonite from Aterazawa, Yamagata Prefecture
It occurs as thick beds intercalated within Tertiary tuffaceous sediments and
has been used as drilling mud in Japan. The original sample contained quartz,
which was removed as completely as possible by repeated elutriation; a small
amount of it remained, and this was estimated as 3"84% by the X-ray method.
T. Sudo, S. Shimoda, S. Nishigaki and M. Aoki
36
TnBL~ 1. Chemical analysis of the samples (%)
1
SiO~
TiO2
A1203
F~Oa
FcO
MnO
MgO
CaO
Na~O
K~O
51.04
0"21
17"42
1.37
0-72
0.02
2-86
0.62
2-54
0-13
HzO(+)
6.44
HsO(-)
P~Os
S
S:O
16.53
0"01
Total
99.91
2
28-67
0"29
19"98
1-82
2-26
3
44"80
/
J
33"88
0.39
4
5
43"17
0"51
33"54
0.26
0.13
39"94
0"74
33"17
1-34
0.18
31.15
0.40
0.13
0.27
10.96
4-24
1.24
0.97
1.88
0.65
0-52
0.38
6.44
1-30
0.52
1.13
2.84
6.91
8.13
7.75
10.48
0.24
11.64
100.17
99.33
100.23
4-39
0"08
0.69
-0.26
100.41
1. Montmorillonite from Aterazawa, Yamagata Prefecture. c.e.c, value: 107 m-eq/100 g. Exchangeable cations are Na (84 m-eq/100 g) and Ca > Mg > K, etc. The chemical composition and e.e.c, value refer to the original sample including about 3"84% quartz.
2. Chlorite (leuchtenbergite--sheridanite) from Wanibuchi mine, Shimane Prefecture.
3. Hydrous complex of mica clay mineral from Goto mine, Nagasaki Prefecture.
4. Hydrous complex of mica clay mineral from Yonago mine, Nagano Prefecture.
5. Regularly interstratified mineral of dioctahedral chlorite-montmorillonite from Kamikita
mine, Aomori Prefecture.
The chemical composition, c.e.c, value, and the kinds of the exchangeable cations
of the original sample are shown in Table 1, column 1. The structural formula was
calculated from the chemical composition after subtracting 3-84% SiO2 as follows:
(Nao.4oMgo.osKo.olCao.os) (All.51Mgo.s~Fe'"o.ogCao.osTio.ol) (Sis.s4Alo.x6) Os0 (OH)~
The ion ratio in the first brackets agrees fairly well with that calculated from the
analysis of the exchangeable cations, and shows the mineral to be a sodium-montmorillonite. Actually, the basal spacing is quite sensitive to room humidity showing
fluctuations in the range of 12-14 A. The first dehydration reaction gives a single
peak. The final endothermic peak in the DTA-curve does not accompany weight
loss as revealed by the TG-curves (Fig. 3a).
2. Chlorite (leuchtenbergite-sheridanite) #om the Wanibuchi mine, Shimane
Prefecture (Sakamoto & Sudo, 1965)
This chlorite occurs in hydrothermal alteration areas around gypsum deposits
in Tertiary sediments and volcanic rocks. It is pale greenish grey, compact and
massive like bentonite clays. In the innermost fringe of the alteration area, it
(a)
-•300oc
OoC
OOC
TG
"x~O0 ~
".,kBO0~
"~O0oC
~l~O00~
OoC
OoC
Ooc
(c)
(b)
/
-~30~'c
ooc
"ITG
-~~TG
~176
DTA
-
~
]~DTA
600~
/
OoC
OoC
"~ O0~
G
200~
200~ rkk
DTA
300~ ]~
"l~O0~
_.j
~ 9 0 `'C
~
OoC
FIG. 3. Differential thermal analysis curves (DTA) and thermogravimetric analysis
curves (TG) of the samples. (a) Montmorillonite (Aterazawa). (b) Chlorite (leuchtenbergite-sheridanite, Wanibuchi). (c) and (d) Hydrous complexes of mica clay minerals
from Goto and Yonago respectively. (e) Regularly interstratitied mineral of dioctahedral chlorite (sudoite)-montmorillonite (Kamikita).
38
T. Sudo, S. Shimoda, S. Nishigaki and M . A o k i
occurs as chlorite clay free from impurities. The chemical composition is given in
Table 1, column 2. On going outward montmorillonite layers are usually interstratified with chlorite layers. The sample used is from material which predominates
in the area, and it contains a small amount of montmorillonite layers as revealed
by a small endothermic peak at 100-200 ~ C in its DTA-curve (Fig. 3b). The peaks
at about 600 ~ and 800 ~ C, are due to the brucite and talc layers respectively. The
second peak is followed by an exothermic peak due to recrystallization, and it is
doubtful whether the energy change for the second dehydroxylation peak is influenced by the energy change due to recrystallization. Effects of heat were just
visible on X-ray powder reflections after heating at 800 ~ C for I hr, and the reflections
were modified after heating at 850 ~ C for 1 hr, the occurrence of forsterite was
clearly observed by the X-ray method after heating at 1000 ~ C.
3. Hydrous complex o] mica clay mineral ]rom the Goto mine, Nagasaki Pre]ecture.
4. Hydrous complex of mica clay mineral from the Yonago mine, Nagano
Pre]ecture.
Both are associated with hydrothermal deposits of diaspore and pyrophyllite
(Sudo, Hayashi & Shimoda, 1962). The Goto material (Table 1, column 3) is nearly
regular and may be called rectorite ( = allevardite), but it is doubtful whether its
hydrated layers agree with those in the original 'allevardite'. The Yonago material
(Table 1, column 4) may be defined as a partially random type of mica and hydrated
layers. In both cases the basal spacings are extremely sensitive to changes in room
humidity. The small endothermic peak in DTA-curves above 900 ~ C is related to
montmorillonite layers because of no deflection in TG-curves (Figs. 3c and 3d).
5. Regularly interstratified dioctahedral chlorite (sudoite)-montmorillonite (Sudo
& Kodama, 1957) [rom the Kamikita mine, Aomori Prefecture (Table 1, column 5)
It occurs in the alteration area of the hydrothermal pyrite deposit in Tertiary
volcanic rocks and tuffaceous sediments. The name 'dioctahedral chlorite' is used
here for a mixed-type of dioctahedral and trioctahedral sites. Although the mineral
described first by Sudo and his collaborators (Sudo, Takahashi & Matsui, 1954;
Sudo & Hayashi, 1956) was almost free from magnesium, the present mineral
contains an appreciable amount of this element. The way in which the magnesium
is distributed has not been clarified. In the earlier report (Suda & Kodama, 1959)
the structural formula was derived assuming that the silicate layer is completely
dioctahedral and the whole of the magnesium is in the hydroxyl layer, making it
approximately trioctahedral. The recent study of dioctahedral chlorite (Sudo & Sato,
1966) has revealed that the observed X-ray powder intensities are close to the calculated values of the model in which the silicate layer is completely dioctahedral, hence
it may be said, referring to the data on dioctahedral chlorite, that the abovementioned description of the present mixed-layer mineral may be a proper one.
Recently, Frank-Kamenetsky et al. (1963) found a similar mineral from U.S.S.R.
and named it tosudite.
Dehydration of clay minerals
39
It is noteworthy that a large endothermic peak occurs at about 600 ~ C and a
smaller endothermic peak followed by a small exothermic peak occurs between
900 and 1000~ C (Fig. 3e). The thermogravimetric (TG) curve reveals a gradual
weight loss after the peak at about 600 ~ C, but there is no weight loss associated
with the small endothermic peak at about 900 ~ C. This fact suggests that the thermal
peaks due to dehydroxylation of the silicate layer and hydroxyl layer do not occur
as two discrete peaks.
X-ray analysis of the pre-heated sample revealed that the structure of this mineral
has been disintegrated after heating at about 600 ~ C. From these facts, it is doubtful
whether the peak at 600 ~ C is solely due to dehydroxylation of the hydroxyl layer.
It is inferred that the effect of dehydroxylation of the silicate layer is partly present
in the peak at about 600 ~ C.
RESULTS
(a) Heat of transition o] quartz
The sample was pulverized to a particle size of 200-300 mesh. The peak temperature obtained was 573 ~ C, and AH was 140 cal/mole. The mean heating rate
was 1-5~ C/min at the base line, and about 0.6 ~ C/min in the peak range. The
deflection of the base-line starts from 50-100 ~ C before the transition. The value
obtained here includes all of the heat which caused the change of the base-line in
the pre-transition region. The heat of transition for ~-fl quartz has been reported
as follows: 166 cal/mole (Nagasaki et al., 1961), 290 cal/mole (Kelley, 1960),
0"15 kcal/mole ( = 150 cal/mole) (Wagman, 1957), 4.5 cal/g ( = 270 cal/mole)
(Grimshaw & Roberts, 1957), 14"6 J/g ( = 209 cal/mole) (Birch, 1942). These discrepancies may be explained by a disordered state near the transition temperature.
Actually the value depends upon the mean heating rate, and it is usually difficult
to choose the correct background extrapolation.
(b) Energy changes in dehydration or dehydroxylation processes on some clay
minerals
In Table 2, the values of energy changes in dehydration and dehydroxylation
processes of some clay minerals are shown in two ways; one is the value per gram of
the sample before heating and the other is the value per mole of water evaporated.
CONSIDERATIONS
The energy changes (heat changes) associated with the dehydration and dehydroxylation processes of clay minerals may be influenced by the following factors:
1. Atmospheric conditions.
2. Static conditions.
(a) Kind and concentration of ions associated with water molecules or
hydroxyl ions.
(b) Geometrical features of structure such as polytype or degree of regularity.
40
T. S u d o , S . S h i m o d a , S . N i s h i g a k i a n d M . A o k i
3. D y n a m i c conditions
D e h y d r a t i o n or d e h y d r o x y l a t i o n agency.
It is considered that these c o n d i t i o n s m a y be m u t u a l l y related to o n e another, h en ce
it is very difficult to d i s c r i m i n a t e each effect as will be discussed below.
1. T h e present e x p e r i m e n ts gave no i n f o r m a t i o n concerning this c o n d i t i o n except
the following c o m m e n ts . T h e w a t e r c o n te n t sh o w n in c h e m i c a l analysis is usually
useless as the basis of the c a l c u la ti o n of A H - v a l u e s , because the u su al selection of
the b o u n d a r y of the chemical analysis of w at er as H 2 0 (+) an d H 2 0 c-) is n o t
TABLE2. Energy changes in the dehydration or dehydroxylation processes of
some clay minerals measured by the adiabatic calorimeter
E(kcal/H~O)+AE H~OI" (.%o)
T1
To
T2
E(cal/g)
Montmorillonite
(Aterazawa)
62
620
102
652
154
690
89-4
35.4
9.8
17.7 _ 0"7
Chlorite
(Wanibuchi)
550
802
592
832
630
850
88-8
32"9
19"3 + 1"0
20"1
8"28
2"95
106
160 }
210
43"4*
12"4" 4- 0.3
6"33
498
560
47"3
17-5 4- 0-2
4-87
110 }
198
228
49"4*
13"4" + 0.3
6"66
450
530
578
44.2
16"8 +__0.7
4'72
70
180
502
125
202
542
180
230
588
45-5 I
5.3 J
76'3
12-5"
7-25
20"3 + 0"3
6.76
Mixed-layer mineral
(Yonago)
Mixed-layer mineral
(Goto)
Mixed-layer mineral
(Kamikita)
40
425
60
16"4
3.6
Notes: (1) Mean heating rate is 2-3 ~ C/rain, which is slower than that in usual DTA-curves. Consequently, peak temperatures in SH-curves are lower. It may be said that SH-curves are the record
of thermal states closer to the thermal equilibrium condition than in the case of the recording of
DTA-curves.
(2) /'1 temperature at the time when the deflection of the base-line starts; To, temperature of
peaks; T~, temperature at the time when the curves returned to the base-line; AE, probable error.
This may include errors being due to such factors as the sensitivity of the instrument, experimental
conditions, and measurements on the recording charts. The instrumental system is grouped into
two: one is the thermobalance (the sensitivity of the chemical balance, the detection ability of
the recorder), and the circuit of the specific heat measurement (sensitivities of the potentiometer,
ammeter voltmeter and time-circuit, etc.). Errors being due to the sensitivity of the instrument
used can be maintained to be 5 % in maximum.
*Double peak. Because of broadness of the peaks, it was difficult to measure the energy change
for each peak separately, hence the values were obtained as the total.
"~The amount of weight loss (water loss in the present samples) measured by TG-curves which were
recorded by this calorimetry simultaneously and successively.
Dehydration of clay minerals
41
necessarily in accord with dehydration ranges of clay minerals. Further, it should
be noticed that the content of moisture varies with room humidity, particularly in
clay minerals having strong dehydration capacity.
2. (a) Dehydration of the interlayer water molecules
In Table 3, kind and concentration of interlayer cations are compared with
AH-values. It is difficult to come to any conclusion on the effect of the kind of
cations, because these natural samples are usually not homoionic.
TABLE3. Interlayer cations* and H-values
Interlayer cations
Montmorillonite (Aterazawa)
Interstratified mineral (I)
(II)
(III)
Nao.4o Ko.ot Mgo.os Cao.os
Nao.5o Ko.ao Cao.14
Nao.lo Ko.6o Cao.os
Nao.a, Ko.ot Cao.,6
AH (kcal/H,,Omole)
9.8
13-4
12.4
12"5
*Assignedin the process of construction of the structural formulae.
Dehydroxylation o] the silicate layer
In the cases of montmorillonite and mixed-layer minerals (I) and (II), the
octahedral cations in the silicate layer are mostly aluminium, and they show very
close values, 17-18 kcal/H20 mole. In the case of the chlorite (trioctahedral type)
AH-value was obtained as 20-1 kcal/H20 mole, which is slightly larger probably
due to more predominant magnesium.
Dehydroxylation o/the hydroxyl layer
In the case of chlorite, the value 19"3 kcal/H20 mole was obtained from the
second endothermic peak which is clearly separate from the thermal peak due to
dehydroxylation of the silicate layer. In the case of the mixed-layer mineral (III),
as mentioned above, it is doubtful whether the peak at about 600 ~ C is solely due
to dehydroxylation of the hydroxyl layer. It shows 20 kcal/H20 mole.
2. (b) Effects of 2(b) are not so distinct in thermal data as in X-ray patterns,
as discussed in the following: qualitatively speaking, the crystallinity of the present
samples may be put in the following order: montmorillonite~mixed-layer minerals
(I) and (II)~chlorite. There is, however, no correlation between this order and the
AH-values. The mixed-layer minerals (I) and (II) belong to the same group but
are different from each other in the stacking behaviour of the component layers;
their AH-values are very close to each other. The mixed-layer mineral (III) is quite
different from (I) and (II) in the crystallochemical properties as well as in the
stacking behaviour, but AH-values due to dehydration of the interlayer region are
very close to those of the mixed-layer minerals (I) and (II). In relation to the
42
T. Sudo, S. Shimoda, S. Nishigaki and M. Aoki
discussion in the preceding paragraph the following fact may be mentioned. The
thermal peaks of the mixed-layer minerals (I) and (II) are relatively broader than
that of montmorillonite but sharper than that of fine micas.
Probably subtle differences in crystallite size distribution and also in crystal
disorder may be reflected in differences in breadth of thermal peaks. Fine micas
(hydromuscovite) usually show thermal peaks which are too broad to enable precise
measurement of heat change.
It is anticipated that some silicate layers of the random type and all layers
of the completely regular type are facing different interlayer regions. However,
it is noticed that the dehydroxylation peak of the silicate layer does not have any
indication of a double peak.
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GRIMSI-IAWR.W. & ROBERTSA.L. (1957) The Differential Thermal Investigation of Clays (R. C.
Mackenzie, editor), Chap. XI, pp. 275-298. Mineralogical Society, London.
KELLEY K.K. (1960) Contribution to the data on the theoretical metallurgy, XIII. High temperature heat content, heat capacity and entropy data on the elements and inorganic
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NAGASAKIS. & TAKAGIU. (1948) Appl. Phys. 17, 104.
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SUDOT., HAYASmH. & SmMODAS. (1962) Clays Clay Miner. 8, 378.
SUDOT. & KODAMAH~ (1957) Z. Kristallogr. Kristallgeom. 109, 406.
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SuDo T., TAr~AHASHIH. & MATSUIH. (1954) Nature, Lond. 173, 261.
WAGMAtqD.D. (1957) American Institute o/Physics Handbook, Chap. 4, J, p. 155.