Application of a Multi-Analytical Toolset to Characterize

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*Corresponding author: Email: [email protected];

International Research Journal of Pure &Applied Chemistry

3(3): 210-219, 2013

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Application of a Multi-Analytical Toolset toCharacterize the Ancient Pottery fromKottapalayam, Tamilnadu, India Using

Spectroscopic Techniques

R. Ravisankar1*, G. Raja Annamalai2, A. Naseerutheen3

and A. Chandrasekaran4

1Post Graduate and Research Department of Physics, Government Arts College,Thiruvannamalai-606603, Tamilnadu, India.

2Department of Physics, Shri Krishnaa College of Engineering & Technology, Mannadipet,Puducherry-605501, India.

3Department of Physics, C. Abdul Hakeem College, Melvisharam-632509, Tamilnadu, India.4Department of Physics, Global Institute of Engineering & Technology, Vellore-632509,

Tamilnadu, India.

Authors’ contributions

This work was carried out in collaboration between all authors. Author GRA performedexperimental work, collected the literature survey and drafted the manuscript, Author AN

took part in the discussions and versioned the paper. Author AC done overall technical anddiscussions of this work. Author RR supervised and authenticated in the final work.

Received 31st March 2013Accepted 31st May 2013

Published 15th June 2013

ABSTRACT

The aim of this paper is to assess the full potentialities of spectroscopy techniques inthe art work investigation and to explore the capabilities in the determination of thechemical and mineralogical composition of ancient pottery excavated fromKottapalayam village, Karur district, Tamilnadu. Spectroscopic techniques such as FT-IR. X-ray diffraction, thermal gravimetric analysis and scanning electron microcopy(SEM) coupled with energy dispersive X-ray spectrometer (EDX) are utilized in thiswork. The constituent of the minerals is identified with help of FTIR and compared with

Research Article

International Research Journal of Pure & Applied Chemistry, 3(3): 210-219, 2013

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XRD. The combined mineralogical results showed that the pottery samples fromKottapalayam were fired in between 800ºC-850ºC. The microstructure and elementalcomposition of the pottery sample were evaluated from their microphotograph byScanning Electron Microscope (SEM) along with energy dispersive X-ray spectrometer(EDX). The results are discussed and the conclusion is drawn.

Keywords: Ancient pottery; firing temperature; FT-IR; XRD; TG-DTA; SEM-EDX.

1. INTRODUCTION

Each age and region has its own peculiar thought and customs that influence every human.In particular, the artistic works on pottery reflect and emphasize the culture of thegeographical area and of a historical period [1]. Potteries were made from clay as rawmaterial. It consists of different minerals which are formed by weathering of rocks andsediments. The study performed on pottery objects is relevant within several research fieldsand many questions have to be solved. Kaolinite and montormorlinite are the most widelyused clay mixtures in the manufacturing of pottery. In the unfired matrix, it is possible to find,as major components, clay minerals mixed with quartz, feldspar and firing producedifferences in the products as a result of the initial composition and of the different operativeconditions [2]. These minerals change their structure, decompose and finally, new mineralsare formed during firing process. For instance, hematite is produced during pottery firing onlyif the process is carried out in oxidizing conditions [3].

The minerals in archaeological artifacts can be classified as primary minerals and secondaryminerals. The primary minerals scuch as quartz, which does not undergo reactions in a widerange of temperatures. But the secondary minerals are formed after the production of wares,during their use and mainly their burial, as a result of either transformation of metastablefiring minerals. Spectroscopic technique, such as FTIR transmittance is a very powerful toolto investigate the chemical composition of unknown minerals. Mineralogical investigationswere generally performed by using X-ray powder diffraction (XPRD), often combination withother analytical techniques, like TG-DTA and SEM-EDX [4].

In the present paper, we report spectroscopic measurements performed by FTIR, XPRD,SEM-EDX and TG-DTA on potteries collected from Kottapalayam (Tamilnadu), provide goodinformation for the mineral composition and estimation of firing temperature and firingconditions.

2. MATERIALS AND METHODS

2.1 Excavation Site

The pottery samples were recently excavated from the site Kottapalayam (77º 55' 23" E; 10º48' 24" N), Tamilnadu, India, by the Department of History, Pondicherry University,Puducherry, India. The pottery shreds of Kottapalayam belonging to Iron Age grave century.Black and Red ware, Red slipped ware and Red ware were collected in the site. The typicalcollection of pottery samples is shown in Fig. 1. The samples are labeled as KMP 1, 2 & 3.


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Fig. 1. Visual characteristics of ancient potteries from Kottapalayam

2.2 FTIR Technique

The major and minor minerals were qualitatively determined by FT-IR technique. The KBrpellet technique was followed for the mineral analysis. A grounded sample of 2 mg wasmixed with 40 mg KBr in the ratio 1:20 using a mortar and pestle and pressed to 5 tons forone minute in preparing the disc. Before mixing, necessary amount of KBr powder was driedat 120ºC for 6hours in an oven. Otherwise the broad spectral peak due to free OH willseriously affect the interpretation on the bound hydroxyls associated with any of theminerals. The Bruker Alpha FT-IR spectrometer was made use of in the present work forrecording the IR spectra of the samples at room temperature. For each of the samples, thespectra were taken in the mid region of 4000-400cm-1. The instrument scans the spectra 16times in 1 minute and the resolution is ±5 cm-1. A typical FT-IR spectrum is shown in Fig. 2.

Fig. 2. A typical FT-IR spectrums of potsherds of Kottapalayam

2.3 PXRD Technique

Samples for X-ray powder diffraction (XRD) studies were packed in shallow cavities in glassslides to minimize preferred orientation. The X-ray patterns of pottery samples were


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recorded at room temperature by using X-ray diffractometer (D500, Siemens) having acurved graphite crystal diffracted monochromator, with a source of CuKα radiation andNaI(Tl) scintillation detector. Diffraction patterns were obtained by continuous scanning from10º to 70º. Qualitative mineralogy of the studied samples is determined with the standardinterpretation procedures of XRD. A typical XRD is shown in Fig. 3.

Fig. 3. A typical PXRD spectrums of Kottapalayam potsherd

2.4 TG - DTA Technique

Thermo gravimetric analysis and Differential thermal analysis (TG-DTA) was carried out witha SDT Q 600 V. 8.3 thermal analyzer with thermal advantage software. The experiment wascarried out by heating the samples up to 800ºC with heating rate of 10ºC min-1 under highpurity atmosphere. A typical TG-DTA is shown in Fig. 4.

Fig. 4. A typical TG-DTA Spectrum of Kottapalayam potsherds


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2.5 SEM-EDX Technique

The microphotographs of the samples were recorded using SEM Quanta FEI, Netherland.The maximum magnification possible in the equipment is 3,00,000 times with the resolutionof 3nm. The elemental analysis was done using the Oxford INCA Energy Dispersive X-raySpectrometer (EDX). The samples were coated with a thin layer of platinum was examinedusing SEM, typically setting at a magnification of X 4000 for all the samples of the study. Atypical SEM and EDX is shown in Figs. 5 & 6 respectively.

Fig. 5. A typical SEM Spectrum of Kottapalayam potsherd

Fig. 6. A typical EDX spectrum of Kottapalayam potsherd

3. RESULTS AND DISCUSSIONS

3.1 Mineral Analysis Using FT-IR Study

The FTIR spectrum of KMP1, KMP2 and KMP3 are shown in Fig. 2. Table.1 lists theconstituent minerals identified in the pottery by the IR absorption bands. The two weak


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peaks observed at 2852 cm-1 and 2922 cm-1 reveal the presence of some organiccontribution this is due to CH stretching mode [5]. These peaks are observed in all thesamples. Russell [6], reported that the presence of bands at 775 cm-1, 695 cm-1 along with460 cm-1 indicate the pottery fragments are due to quartz. According to Elsass and Oliver[7], the presence of the sharp band at 695 cm-1 indicates thin particles. The peak at 695 cm-

1 in the sample KMP2 indicates thin particle size.

The presence of absorption bands around 465 cm-1 and 585 cm-1 are due to the presence ofmicrocline [8]. The presence of the peaks at 640 and 730 cm-1 indicates albite. Theabsorption band at 1632 cm-1 is due to the H-O-H bending of water molecule [9]. This peakin received samples owing to the absorption of moisture present in the samples. The peakcentered and broad at 1034 cm-1 is kaolinite. All the samples showed this peak (1034 cm-1)with the strong intensity indicating the type of the clay is red clay origin of kaolinite and it isused for making of potteries.

Table 1. Observed absorption frequency in the region of 400 – 4000 cm-1of the ancientpotteries of Kottapalayam together with minerals identification

Sam

ple

No

Silicatemineral

Feldspar mineral Clay minerals Iron oxidemineral

Organiccarbon

Qua

rtz

Mic

rocl

ine

Ort

hocl

ase

Alb

ite

Kao

linite

Mon

torm

orili

nte

Hem

atite

Mag

netit

eKMP1 777 465 646 - 1035 1636 542 - 2926,2854KMP2 779,460,695 - 652 - 1039 1638 536 - 2920,2849

KMP3 777,469 586 - 641,734 1038 1636 539 581 2920,2849

The bands at 540 and 580 cm-1 were due to hematite and magnetite. Hematite is observedin all the samples and magnetite was observed only in KMP3. The appearance of peak at540 cm-1 in all the samples indicates that the potteries were fired in an oxidizing condition[10].

3.2 Firing Temperature Analysis by FT-IR Spectroscopy

Potteries are made up of clay minerals which are found in sheet structure, when the potteryis fired, the structure gets collapsed depending on the level of temperature of firing andconditions, which can be monitored by FTIR study. When the clay is fired between 300ºCand 500ºC dehydroxylation of octahedral layers of most clay minerals takes place [11]. At600ºC silicate structure collapses and a broad symmetry band observed at 1030 cm-1 for redclay and 1080 cm-1 for white clay [12]. In all the samples abroad symmetry band is observedaround 1030 cm-1. Red clay was used for making of the pottery samples. Ramasamy andKamalakannan [13], studied the effect of temperature on various clay and concluded that thedisappearance of Al-O-(O4) band at 910 cm-1 with the appearance of band at 635 cm-1

around 600ºC is the indication of the formation of Al2O3.


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Maritin et al. [5] stated that magnetite is formed at a temperature 800-850ºC. The iron oxidemineral magnetite originate from chemical reaction between quartz and carbonates when thetemperature 900ºC. The presence of magnetite and absence of calcite in the samples KMP1and KMP3 indicate that the sample was fired above 800ºC. According to Yariv andMendelovici [14], a shoulder band at 875 cm-1 indicates that dehydroxylation of kaolinitemineral which is completed at 800ºC and octahedral sheet structure in the clay mineraldisappeared. None of the samples show the presence of the peak at 875 cm-1 indicating thatsamples were fired above 800ºC.

The peak around 540 cm-1 is observed in all the samples indicate that the presence ofhematite which also confirms the firing temperature above 800ºC. The color of the potteriesis due to hematite which is red brown solid and decides the atmospheric conditions(oxidizing/reducing) where the artifacts were fired. The potteries collected from theKottapalayam were Red slipped, Red and Red and black ware in color and shows that thepresence of hematite and hence fired in the oxidizing atmosphere.

3.3 PXRD Analysis

XRD is one of the most direct techniques for the identification of the mineral composition ofpottery. X-ray diffraction spectra have been recorded for the powdered pottery samples. Thepresence of minerals is identified by comparing the JCPDS file [15]. Table 2 lists the mineralcomposition in the samples. The XRD analysis shows the potsherds very rich of quartz andalso traces of feldspar minerals [16]. Feldspars were the other phases always present in theall the samples. Calcite was identified only in KMP3. The presence magnetite is observed inKMP1 which indicates reducing kiln atmosphere conditions whereas hematite is identified inKMP1 and KMP2 would confirm oxidizing kiln conditions. The absence of appreciable calcitesignals in the spectra recorded on the shred samples, suggesting a firing temperature higherthan 800ºC-850ºC, but lower than 950ºC [17].

The absence of calcite in the fired samples KMP1 and KMP3 indicate that the samples havebeen fired above 800ºC. Kottapalayam potteries are characterized by the presence of quartzas main phase is evidenced the firing temperate above 800ºC [18]. The secondary phases,such as feldspars could be also identified. The presence of hematite in KMP1 and KMP2and magnetite is noticed in KMP1 indicates the firing temperature of pottery above 800ºC.The hematite is one of the most intense coloring material and to give reddish color to thepottery [19]. The reddish color observed in samples KMP1 and KMP2 support the statement.

Table 2. Mineralogical composition of Potsherds from Kottapalayam

S. No. Minerals KMP1 KMP2 KMP31. Quartz +++ +++ +++2. Microcline - ++ -3. Albite ++ - ++4. Hematite + + -5. Magnetite + - -6. Calcite - - tr

Very abundant = +++, abundant = ++, present = +, trace = tr, absent = - .


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3.4 Thermal Analysis

DTA and TG analysis reveal changes in sample weight as well as in thermodynamicproperties. The endothermic peaks were observed at 377ºC due to water and at 446ºC dueto combustion of organic material in it [20]. In lower temperatures the most probable reasonfor mass loss is evaporation of water and in the temperatures 200–560ºC [21] all the organicremains originating from ceramic use are being destroyed. The organic material might beadded intestinally as a binder in the preparation of pottery or raw material itself containedorganic material. The endothermic peak at 450 to 650ºC is due to dehydroxylation ofkaolinite. The presence of dehydroxylation of kaolinite peak indicates that the pottery has notfired above this temperature. The absence of this peak in this endothermic peak in thissample KMP1 indicates that this shred would has been fired between the temperature range650 and 900ºC.

The weight loss of the pottery in thermal analysis can be explained in three steps based onthe work done by Drebushchak et al. [22]. (i) The dehydration occurs from room temperatureto 100ºC, (ii) The decomposition of hydroxyls occurs from the temperature 400ºC to 500ºC,(iii) The decomposition of minerals occurs above 700ºC. The shred shows larger mass lossat dehydration and less is at dehydroxylation.

3.5 SEM-EDX Analysis

The Scanning Electron Microscope is extremely in valuable in providing information on thepore structure and the and the glassy phase development used to study systematically theinternal morphology changes occurring when fired at a temperature range 600ºC to 1300ºC.

The SEM micrograph shows that particles are irregularly shaped and varied in sizes. Thesurface of the pottery comprises of volumetric plate like grains with different crystalline sizesranging from 10 µm to 20 µm. The careful examinations of micrograph of KMP1 reveal thatthe particles were heterogeneously shaped with a lot of incisions. In some parts of itsmicrograph horizontally aligned pores were present which may be attributed to coiling ofpottery [23]. The vitrification stage of the sample KMP1 was initial vitrification stage of noncalcareous type and might have been fired in the temperature range 800-850ºC in theoxidizing atmosphere in accordance with reports of Russell [6]. The sample KMP1 was initialstage and made of non-calcareous clay. The sample may be fired in the oxidizingatmosphere between temperature range 800-850ºC.

The chemical composition of the sample was obtained by EDX analysis and its spectrum isshown in Fig. 6. From the analysis, silica is enriching in the samples. The chemicalcomposition of the potsherds is strong related to the source of clay and other materials usedfor production. From the EDX analysis, the abundant amount of Si, Al, Fe, K and Ca wasfound and it supports vibrational spectroscopic findings; the presence of quartz, feldspar andiron oxides (hematite and magnetite) [24].

4. CONCLUSION

The present work was addressed to the characterization of pottery fragments, fromKottapalayam of Tamilnadu, India by spectroscopic techniques. The mineralogicalcharacterization was obtained from FTIR and PXRD techniques. The combined methodconfirmed quartz is enriching in all the samples. The presence of hematite and magnetite


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reveal that potsherds have been fired the temperature greater than 800ºC and alsoindicating the firing conditions. Thermal analysis results showed that larger mass loss atlower temperature than the higher temperature. The Scanning Electron Microscope isextremely valuable in providing information on the size and structure of the particle of thesample. From all the above four analysis, one can say that the artisans have fired thesamples to a temperature greater than 800ºC in an oxidizing atmosphere and also red claywas used for making of the pottery samples.

The analytical results achieved in this study allowed us to estimate the firing temperatureand manufacturing techniques. The methodological approach was successfully applied tothe complete characterization of the potsherds.

COMPETING INTERESTS

Authors have declared that no competing interests exist.

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Application of a Multi-Analytical Toolset to Characterize