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Abstract: Montmorillonite (MMT) is a layered silicate clay which belongs to the smectite clay group with a wide range of applications in medicine, polymer industry, ceramic industry and nano materials. This research is focused on the use of Fourier Transform Infrared Spectroscopy (FTIR) technique to identify and characterize Montmorillonite clay deposits available in the dry zone of Sri Lanka. Apart from identification, FTIR can be used to discover the family of minerals to which the specimen belongs, the nature of isomorphic substituent and the distinction of molecular water from constitutional hydroxyl. Clay samples obtained from several locations within the dry zone of Sri Lanka were purified, treated and subjected to FTIR, X-ray Diffraction (XRD) and Differential Thermal Analysis (DTA). To further strengthen the findings, specimens of commercially available MMT and Bentonite were subjected to the same tests. Peaks of the resultant spectrum were analyzed and compared with published literature. Results revealed that the specimens subjected to the tests contained MMT with Kaolinite. In-depth study of absorbance level of each specimen was useful in identifying the exchangeable cations present in MMT. Further study of the spectrum could pave the way for quantitative analysis of these clay minerals.

Keywords: Montmorillonite, FTIR, Clay minerals, Smectite clay

1. Introduction

Montmorillonite is the well-known smectites which is most commonly used in the preparation of polymer nanocomposites. Raw

formula of MMT is

(Na,Ca)0.3(Al,Mg)2Si4O10(OH)2,nH2O. MMT has the wider acceptability for use in polymer nanocomposites because of its ease availability, well known intercalation/ exfoliation chemistry, high surface area and high surface reactivity. Polymer-clay composites synthesized with MMT are known to have superior mechanical, thermal and gas-barrier properties (Olad, [5]). Recently there has been a growing interest for the development of polymer-clay nano composites due to their improved properties compared to the conventional polymer composites. Polymer clay nano composites received intense attention because of their unique properties which can never be attained by micro size fillers or by other nano fillers. The enhancement of properties by the addition of Montmorillonite clay, without sacrificing the pure polymer processability, mechanical properties and light weight, make this clay more and more important in modern polymer industry (www.sigmaaldrich.com, [10]).

Fourier Transform Infrared Spectroscopy (FTIR) has a long and successful history as an analytical technique. It is mainly a complementary method to X-ray diffraction

(XRD) and other methods used to investigate clays and clay minerals. It is an economical, rapid and common technique because a spectrum can be obtained in a few minutes and the instruments are sufficiently inexpensive (Madejova et al., [9]). A FTIR spectrum can serve as a fingerprint for mineral identification, but it can also give unique information about the mineral structure, including the family of minerals to which the specimen belongs and the degree of regularity within the structure, the nature of isomorphic substituents, the distinction of molecular water from constitutional hydroxyl, and the presence of both crystalline and non-crystalline impurities (Madejova, [4]).

Published literature has shown the presence of MMT in clay deposits located mainly in the dry zone of Sri Lanka (Herath, [3]). The identification of MMT from deposits has been conducted extensively using XRD analysis. The growing interest in MMT in the nano engineering applications has given the need of a rapid and user-friendly identification and

Eng. (Dr.) S.U. Adikary, B.Sc. Eng (Hons) (Moratuwa),

M.Sc., PhD. (Hong Kong), AMIE (Sri Lanka), Senior Lecturer, Department of Materials Science and Engineering, University of Moratuwa.

Eng. D.D. Wanasinghe, B.Sc. Eng (Hons) (Moratuwa),

AMIE (Sri Lanka), Research Assistant, Department of Materials Science and Engineering, University of Moratuwa.

characterization technique which can be used repeatedly. FTIR technique has the ability to fulfill these requirements adequately.

Therefore this research was focused on the use of FTIR to identify and characterize MMT from locally available clay deposits which are known to be rich in MMT.

2. Methodology

Studies done previously revealed MMT is abundant in the dry zone of Sri Lanka (Herath, [3]). Therefore, the selection of sites to obtain specimens was done in that region. Clay samples were collected from four sites located in Anuradhapura region. Exact locations of these sites are as follows,

Clay 1 - Kalathirappane Tank Clay 2 - Galkulama Tank Clay 3 - Illanthagahawewa Tank Clay 4 - Pallankulama Tank

Collection of samples was done at a depth of 3 ft from the surface. Collected samples were then wet sieved from 53 μm to remove any organic and coarse particles present in clay. Then, each specimen were dried in the oven at 1200_{C, ground using mortar and pestle to make} them powder again and sieved again from 53 μm sieve. In order to remove organic materials, the specimens were heated up to 3000_{C for a}

period of one hour. Resultant powder is then subjected to FTIR, XRD and DTA.

FTIR tests were carried out by using Bruker alpha-T instrument employing KBr pellet method for frequency range of 4000-500 cm-1_. Specimens were subjected to XRD using Siemens D5000 X-ray diffractometer to ensure the presence of MMT and to verify the results of FTIR. Specimens were first spread on a flat surface in a desiccator and ethylene glycol was added to the bottom of the desiccators. The entire desiccator was then put into the oven and heated to 600_{C and kept at that temperature for} one hour. Then it was kept for 24 hours before being subjected to XRD analysis. DTA and TGA test were done by Differential Thermal Analyzer, Rigaku Thermoflex TG 8110, by heating the specimens from room temperature to 9900_C.

3. Results and Discussion

Resultant FTIR spectrums for specimens tested are given in Figure 1. In addition to the four specimens, MMT, Bentonite (BT) and Kaolinite were tested using the FTIR technique, since Kaolinite is found in almost all the clay deposits in Sri Lanka.

The FTIR spectrums reveal a vast similarity between the clays analyzed and the commercial MMT and BT. Table 1 summarizes the absorption bands found in the spectrum.

Absorption bands that are common to tested specimens are as follows,

1 - OH stretching of structural hydroxyl groups 2 - OH stretching of structural hydroxyl groups 3 - OH stretching of water

5 - OH deformation of water 7 - Si–O stretching of cristobalite 8 - Si–O stretching

10 - AlAlOH deformation

11 - Si–O stretching of quartz and silica

14 - Coupled Al–O and Si–O, out-of-plane

15 - Al–O–Si deformation

The presence of band 1 can be seen for all the tested specimens except in MMT and bentonite. Comparison with values from literature indicates that this band is a result of presence of kaolinte in the specimen.

The deposits used in this study are known to be a mixture of kaolinite and MMT. Band 7 indicates the presence of cristobalite and its stretching due to the absorption of infrared radiation indicating that the commercial grade of

MMT has different phases of SiO2 (Madejova, et al. [9]).

Band 13 is again present in all the specimens