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www.elsevier.com/locate/ceramintThermal and chemical treatments of montmorillonite clay
Tharsia Cristiany de Carvalho Costa*, José Daniel Diniz Melo, Carlos Alberto Paskocimas
Federal University of Rio Grande do Norte, Department of Materials Engineering, Natal, RN, CEP 59072-970, Brazil
Received 28 November 2012; received in revised form 29 November 2012; accepted 30 November 2012Abstract
Montmorillonite clay from a natural deposit was processed to remove impurities and later submitted for thermal and chemical
treatments. The sample was first subjected to a thermal treatment at 400 1C, for 1 h, to remove organic components. The chemical
treatment was conducted first by using an acid attack with nitric acid and sulfuric acid, then, adding sodium acetate in ethylene glycol
clay dispersion, and finally the clay was dispersed in xylene with subsequent addition of silane, N-(b-aminoethyl)-g-aminopropyil-
trimethylsilane. The combined thermal and chemical treatment was found to have a significant effect on the final chemical composition
of the nanoclay. X-ray diffraction patterns suggested that the combined thermal and chemical treatment resulted in increased
interplanar distances, thus favoring exfoliation of the clay lamellae, which was also confirmed by SEM images. Fourier transform
infrared (FTIR) spectroscopy analysis suggested that the combined thermal and chemical treatment resulted in removal of water from
the montmorillonite, without any modification or destruction of the clay structure. Thus, the combination of thermal and chemical
treatments proposed in this work may be a promising approach to process montmorillonite intended for the production of advanced
materials.
& 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Keywords: B. Impurities; C. Chemical properties; D. Clays; Raw materials1. Introduction
Some materials are used as fillers for polymers to obtain
composite materials, being applied from macro- to nano-
scale. Some forms such as nanotubes, nanoparticles and
nanoplatelets stand out among them. For example, carbon
nanotubes display exceptional properties for specific
applications. Nanotubes, however, have the disadvantage
of being produced on a limited industrial scale at high
prices. The addition of nanoparticles to polymers is
already employed with beneficial results to their mechan-
ical and physical properties.
Clays have been the most widely studied material
used as nanofillers. This is partly due to the large natural
reserves of these minerals and to many studies aiming at
obtaining nanosized clays, which are increasingly mastered
by researchers.
One major problem in studying and obtaining polymer/
clay nanocomposites is the difficulty to achieve a highng author.
ess: tharsia@gmail.com (T.C.C. Costa).
e front matter & 2012 Elsevier Ltd and Techna Group S.r.l. A
g/10.1016/j.ceramint.2012.11.105
s article as: T.C.C. Costa, et al., Thermal and chemical treatmen
ceramint.2012.11.105degree of exfoliation of the clay lamellae, which allows
greater interaction with polymer matrices. In recent years,
universities and industries have worked with various
unconventional methods to facilitate the exfoliation of
clays [1–9]. A strategy frequently adopted is to use organic
additives to modify the clay surface, in an attempt to
improve the compatibility between the hydrophobic poly-
mer and hydrophilic clay, thereby facilitating clay exfolia-
tion [10].
Among nanoclays, montmorillonite stands out, being
classified as mineral clay, with lamellar structure of the
smectite group belonging to family 2:1. It has elementary
crystal forming structures consisting of layers of octahe-
dra, with aluminum at the center and oxygen or hydroxyl
at the vertices, between two tetrahedral layers, with silicon
at the center and oxygen at the vertices [11].
Isomorphic substitutions of Al3þ by Mg2þ or Fe2þ can
be observed in the octahedral structure, which generate a
negative effective charge on their surface. This negative
charge is compensated by the presence of cations in the
interlayer space. Smectites are capable of accommodating
water molecules or other polar molecules in the interlayerll rights reserved.
ts of montmorillonite clay, Ceramics International (2012), http://dx.doi.
2 T.C.C. Costa et al. / Ceramics International ] (]]]]) ]]]–]]]region, causing variation of the basal spacing, depending
on the type of cation intercalated [12].
For better control of the intercalation of cations or
molecules between layers, it is necessary to treat the mon-
tmorillonite clay with an attack of acids, thus promoting the
removal of impurities from the clay surface and morphologi-
cal changes in the montmorillonite structure [13]. These
changes must not alter the crystalline structure of the mineral.2. Experimental
2.1. Clay preparation procedure
A montmorillonite sample was initially screened on a
200 mesh sieve. After clay deagglomeration, a thermal
treatment was performed, consisting of heating the sample
up to 400 1C, at a heating rate of 5 1C/min, for 1 h. After
this thermal treatment, the clay was submitted to a
chemical attack with sulfuric and nitric acid, where 100 g
of clay was dispersed in 800 ml of distilled water at 70 1C
until complete dispersion occurred, adding 100 ml of
sulfuric acid 98 wt%, stirring and controlling the tempera-
ture for 3 h, and then adding 100 ml of nitric acid 65 wt%
under the same time and temperature conditions.
The solution was kept at rest for 24 h. After this period,
the clay sample was subjected to successive washes with
distilled water until it reached pH 4. At the end of this
process, the top and bottom phases were discarded,
keeping only the clay between these two phases. The
process of adding sodium to the clay was carried out by
dispersing the clay in ethylene glycol with sodium acetate
until homogenization, maintaining the temperature at
90 1C under magnetic stirring for 2 h. Soon after, the
clay was dried in an oven with circulating air at 100 1C for
24 h, deagglomerated and heated again under magnetic
stirring and the clay was dispersed in xylene. Then, silane,
N-(b-aminoethyl)-g-aminopropyiltrimethylsilane was added
under heating and magnetic stirring until total xylene
evaporation occurred, leaving in the oven for more than
24 h. The resulting clay samples are described in Table 1.
The physical, chemical and morphological characteriza-
tions were carried out using X-ray diffraction (XRD),
thermal analysis (TG), X-ray fluorescence (FRX), Fourier
transform infrared (FTIR) spectroscopy and scanning
electron microscopy (SEM).Table 1
Nomenclature adopted for clay samples according to the process used.
Nomenclature Treatments
Mont. Nat. Natural montmorillonite
Mont. AA 400 Acid montmorillonite heated at 400 1C
Mont. AA 400 Acid montmorillonite heated at 400 1C with sodium
Na acetate
Mont. AA 400 Acid montmorillonite heated at 400 1C with sodium
Na Si acetate and silane
Please cite this article as: T.C.C. Costa, et al., Thermal and chemical treatmen
org/10.1016/j.ceramint.2012.11.1052.2. X-ray diffraction
X-ray diffraction experiments were conducted using a
Shimadzu equipment model XRD-6000. Intensity vs.
scattering angle (2y) were recorded at room temperature
in the range 2–75 (2y), with a step size of 0.021 and
scanning rate of 21/min. X-ray diffraction experiments
were conducted to evaluate the effects of treatments on
the montmorillonite structure.
2.3. Thermal analysis
Thermogravimetric analyses were conducted on samples
in various stages of the preparation procedure. Measure-
ments were carried out with a BP model RB-3000, using a
scan rate of 10 1C/min, over a temperature range from 25
to 1000 1C. Mass loss (in %) was calculated from the TG
curve, based on the initial mass of the sample.
2.4. Chemical composition
Samples collected in the various stages of the prepara-
tion procedure were analyzed for chemical composition
determination. Silicon content was determined using gravi-
metric analysis, while the content of other elements was
determined by inductively coupled plasma optical emission
spectrometry (ICP OES). The X-ray fluorescence analysis
was performed by a semi-quantitative method. The equip-
ment used was a Shimadzu model EDX 700.
2.5. FTIR
Fourier transform infrared (FTIR) spectroscopy analysis
was performed on a Shimadzu equipment model IR Prestige-
21 using absorbance mode, in the region of 400–4000 1/cm
in KBr medium, and a proportion of 100 mg of 1% KBr
sample.
2.6. SEM
Samples for scanning electron microscopy (SEM) were
prepared and analyzed with a Shimadzu equipment model
SSX-550, using an accelerating voltage VA of 20 kV.
3. Results and discussion
Fig. 1 shows X-ray diffraction results in accordance with
the nomenclature previously mentioned in Table 1. This
figure illustrates the changes promoted at each stage of the
treatment, as well as treatment efficiency. Changes intro-
duced by the treatment are observed by the main diffraction
peak at 5.7711, corresponding to the interplanar spacing of
15.314 Å (Fig. 1a and Table 2). When the chemical and
thermal processes are combined (AA Mont. 400), it was
observed that with the removal of organic matter, there was
an approximation of the montmorillonite lamellae, shifting
the main peak to 9.2121 corresponding to an interplanarts of montmorillonite clay, Ceramics International (2012), http://dx.doi.
T.C.C. Costa et al. / Ceramics International ] (]]]]) ]]]–]]] 3
1000
1000
900
900
800
800
700
700
600 600
500 500
4 6 8 10
400 400 4 6 8 10
300 300
200 200
100 100
0 0
0 10 20 30 40 50 60 70 0 10 20 30 40 50 60 70
2 2
1000 1000
900 900
800 800
700 700
600 600
500 500
400 4004 6 8 10
4 6 8 10
300 300
200 200
100 100
0 0
0 10 20 30 40 50 60 70 0 10 20 30 40 50 60 70
2 2
Fig. 1. XRD of clay samples: (a) natural montmorillonite, (b) acid montmorillonite heated at 400 1C, (c) acid montmorillonite heated at 400 1C with
sodium acetate and (d) acid montmorillonite heated at 400 1C with sodium acetate and silane.
0
 MontNat
Table 2  Mont AA 400
 Mont AA 400 Na
Angles and changes of interplanar spacings of clays, both natural and -5  Mont AA 400 Na Si
chemically treated.
-10
Samples 2h (deg.) Interplanar
spacing d (Å) -15
Mont. Nat 5.771 15.314 -20
Mont. AA 400 9.212 9.913
Mont. AA 400 Na 7.090 12.469
-25
Mont. AA 400 Na Si 4.820 18.333
-30
-35
0 200 400 600 800 1000
Temperature (°C)
Fig. 2. TG analysis of clay samples, both natural and treated.
Intensity Intensity
Intensity Intensity
% Loss massspacing of 9.913 Å (Fig. 1b and Table 2), suggesting an
elimination of organic matter and water from the montmor-
illonite structure. When sodium acetate is added to the
sample for combined treatment (Mont. AA 400 Na), the
opposing phenomenon was observed, and the main peak
shifted to 7.0901, reaching an interplanar spacing value of
12.469 Å (Fig. 1c and Table 2). After the incorporation of
silane to the sample (Mont. AA 400 Na Si), the best result
was obtained with the shift of the main peak to 4.8201 and
interplanar spacing of 18.333 Å (Fig. 1d and Table 2).
Although the chemical attack promoted the elimination
of organic matter from Mont. Natural sample, the water
existing in its structure was not removed by this treatment, asPlease cite this article as: T.C.C. Costa, et al., Thermal and chemical treatmen
org/10.1016/j.ceramint.2012.11.105observed by thermogravimetry with 13% mass loss over the
temperature range of 25–165 1C (Fig. 2). However, when
chemical and thermal attacks are combined, the removal of
water existing in the montmorillonite structure was clearly
observed, with mass loss over the same temperature range
dropping to a value lower than 4%. In the clay sample
modified with silane (Mont. AA 400 Na Si), there was massts of montmorillonite clay, Ceramics International (2012), http://dx.doi.
4 T.C.C. Costa et al. / Ceramics International ] (]]]]) ]]]–]]]
Table 3
Chemical composition of samples after each treatment.
Al-Si Si-O-Si
Mont. Nat Mont. AA 400 Mont. AA 400 Na Mont. AA 400 Na Si H2O H2O
Comp. % Comp. % Comp. % Comp. % Mont AA  400 Na Si
SiO2 61.60 SiO2 51.94 SiO2 49.75 SiO2 47.21
Al2O3 20.96 Al2O3 33.35 Al2O3 30.9 Al2O3 22.61 Mont AA  400 Na
Fe2O3 4.33 Fe2O3 2.58 Fe2O3 2.72 Fe2O3 2.55 Mont AA  400
CaO 1.38 CaO 0.18 CaO 0.15 CaO 0.12
MgO 2.44 MgO 2.79 MgO 2.36 MgO 1.60
Na2O 1.25 Na2O – Na2O 1.07 Na2O 0.88
SO3 0.96 SO3 0.73 SO3 0.62 SO3 0.50
K2O 0.46 K2O 0.33 K2O 0.26 K2O – Mont Nat
TiO2 0.36 TiO2 0.26 TiO2 0.27 TiO2 0.22
ZrO2 0.05 ZrO2 0.05 ZrO2 0.04 ZrO2 0.03
LOI 6.07 7.12 11.86 24.04 500 1000 1500 2000 2500 3000 3500 4000
wavelengths (cm-1)
LOI—loss-on-ignition.
Fig. 3. FTIR analysis of clay samples both natural and treated.
Absorbance
loss over the temperature range of 200–600 1C, correspond-
ing to the initial silane decomposition and another mass loss
over the range of 610–1000 1C, corresponding to the final
silane decomposition (Fig. 2).
Table 3 shows the results of the chemical analyses of
the samples studied. Through comparison between Mont.
Nat. and Mont. AA 400 samples, significant changes in the
chemical composition of the Mont. AA 400 sample were
observed such as reduction of SiO2, confirming the elimination
of quartz from the samples, reduction of Fe2O3 and CaO and
complete elimination of Na2O. In the Mont. AA 400 Na
sample, the efficiency of this part of the process could be
confirmed by introducing Na2O in the clay. In Mont. AA 400
Na Si sample, despite a high reduction of SiO2, the Si/Al ratio
remained almost constant as compared with the Mont. Nat.
sample, which confirmed the silane intercalation in the clay
structure. The increased mass loss in all samples could be
related to the elimination of organic matter. The loss on
ignition (LOI) represents loss of water, hydroxyl groups from
mineral clays, organic matter and carbonates [13]. For the
samples studied, LOI showed values of 6.07% for Mont. Nat
clay, 7.12% for Mont. AA 400 clay, 11.86% for Mont. AA
400 Na clay, and 24.04% for Mont. AA 400 Na Si clay. The
highest LOI value was observed in the organically modified
clay, indicating that silane was incorporated into the clay
structure.
The spectrum infrared spectroscopy (FTIR ) in Fig. 3
corresponds to pure clay and shows a typical band of OH
stretching (3634 cm1) absorbance. The broad bands at
3447 and 1640 cm1 can be attributed to water molecules
adsorbed on the clay structure [15]. Bands of 1116, 1035
and 914 cm1 may be collectively allocated to the stretch-
ing and vibration of Si–O bonds [16]. The spectrum of the
clay modified with thermal and chemical treatments shows
the removal of water existing in the montmorillonite
structure, without any modification or destruction of the
clay structure, maintaining the same crystallographic
pattern of the natural clay [10].Please cite this article as: T.C.C. Costa, et al., Thermal and chemical treatmen
org/10.1016/j.ceramint.2012.11.105Fig. 4 shows the scanning electron microscopy (SEM)
analyses performed on samples with magnification of
10,000 . The micrograph of the Mont. Nat sample
suggests a very cohesive clay, confirming that the material
consists of micrometer-sized agglomerates composed of
individual lamellae (Fig. 4a). The micrograph of the Mont.
AA 400 sample shows the separation of some of these
lamellae (Fig. 4b). This is due to the removal of organic
matter and water existing within the clay structure, which
contributes to reduce the effect of agglomeration. The
micrograph of Mont. AA 400 Na sample confirms the
X-ray diffraction of this sample, showing that the addition
of sodium acetate in the clay structure promoted a new
approximation in the clay lamellae (Fig. 4c). The micro-
graph of Mont. AA 400 Na Si sample confirms that the
combination of thermal and chemical treatments, com-
bined with the dispersion of silane into the clay, promoted
a more refined exfoliation of the clay lamellae (Fig. 4d).4. Conclusions
In this investigation, montmorillonite clay from a natural
deposit was processed to remove impurities and later
subjected to thermal and chemical treatments. The thermal
treatment was conducted at 400 1C, for 1 h, followed by the
chemical treatment which was conducted first by using an
acid attack with nitric acid and sulfuric acid, then, adding
sodium acetate with subsequent incorporation of silane. The
characterization of the clay in various stages of the treat-
ments was conducted by X-ray diffraction, thermogravime-
try, Fourier transform infrared (FTIR) spectroscopy and X-
ray fluorescence analysis. The results suggested that the
chemical and thermal processes combined promoted the
elimination of organic matter and water from the montmor-
illonite structure and resulted in increased interplanar spa-
cing when compared to the natural montmorillonite clay,
without any modification or destruction of the clay struc-
ture. Moreover, the elimination of quartz and incorporationts of montmorillonite clay, Ceramics International (2012), http://dx.doi.
T.C.C. Costa et al. / Ceramics International ] (]]]]) ]]]–]]] 5
Fig. 4. SEM images of samples: a) Mont. Nat; b) Mont AA. 400; c) Mont. AA 400 Na; d) Mont. AA 400 Na Si.of silane in the clay structure were confirmed. Therefore, the
combination of thermal and chemical treatments of mon-
tmorillonite was found effective in removing impurities and
promoting exfoliation of the clay lamellae.
Acknowledgments
The authors gratefully acknowledge the financial support
of the Brazilian research council—CNPq.
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