A Study of Solid State Phase Transformation of Biogenic Aragonite into Calcite Crystals

Transcription

1 Proc. of Int. Conf. on Emerging Trends in Engineering and Technology A Study of Solid State Phase Transformation of Biogenic Aragonite into Calcite Crystals R.Manikandan 1, P.Martin 2, and S.Devashankar 3* 1 Research scholar, Department of Advanced Zoology, Govt. Arts College, Nandanam, Chennai, India mailmrithunjayan@gmail.com 2 P.G and Research Department of Advanced Biology and Biotechnology, Govt. Arts college, Nandanam, Chennai, India- dr.martinjayakumar@gmail.com 3* Department of Physics, Velammal Engineering College, Chennai, India devashankar.srinivasan@gmail.com Abstract Biogenic calcium carbonate obtained from Pearl oyster subjected to FTIR, FT- Raman and Powder X-ray diffraction studies. It is in the polymorphic form of aragonite. The analysis of calcined aragonite reveals that it undergoes solid state phase transformation in to calcite a thermodynamically more stable polymorphic form of calcium carbonate. Index Terms Calcite, Aragonite, Biogenic, Phase transformation I. INTRODUCTION Calcium carbonate (CaCO 3 ) is a ubiquitous inorganic component of the near-surface environment, occurring aqueous systems, sediments and aerosols. It precipitates in both fresh and saline water and can form by biogenic or abiotic means [1]. CaCO 3 has three anhydrous forms namely calcite, aragonite and vaterite and three hydrated forms, amorphous CaCO 3, monohydro calcite (CaCO 3.H 2 O) and ikatite (CaCO 3.H 2 O) [2]. The phase diagram of CaCO 3 shows that calcite is thermodynamically most stable and most abundant phase under ambient conditions, aragonite is the high-pressure polymorph and vaterite is thermodynamically unstable [3]. Many sea shells and corals are composed either totally or in part of aragonite [4]. Calcite has the ability to fix or structurally incorporate biologically active elements such as phosphorous, calcium, magnesium, zinc, iron [5]. Due to its metastability under earth s surface condition, aragonite tends to transform into calcite by reaction with aqueous solutions[2]. Sequential polymorphic transformation of CaCO 3 in the presence of DTPA was reported [6]. Structural transformation from aragonite to vaterite and calcite by the assistance of SDBS in the temperature range 9 to 15 o C was reported [7]. In traditional Indian medicine CaCO 3 obtained from various biogenic sources such as Pearl oyster, Conch shell, Snail shell and Cowry shell are mixed with other organic/inorganic compounds and calcined. The resultant powder is being used for the treatment of many diseases like piles, fistula, tuberculosis, bronchial asthma, gastric ulcers, skin diseases, renal calculus. There are very few reports on the study of initial and final products. The aim of the paper is to find in what polymorphic form CaCO 3 exists as obtained from biogenic sources and in the calcined final products which are used as medicine. In this regard calcium carbonate obtained from four biogenic sources such as Pearl oyster, Conch shell, Snail shell and Cowry shell are studied using Fourier Transform Infrared (FTIR), FT Raman spectroscopy and Powder X-ray diffraction techniques. The results of one of the species are presented. DOI: 3.AETS Association of Computer Electronics and Electrical Engineers, 213

2 II. EXPERIMENTAL A. Sample preparation The biogenic species Pearl oyster (common name) called as Muthuchippiparpam (Indian Medicinal name) known as Pinctada species by zoological name is purified by boiling it a solution mixed with fullers earth for 18 min and the same process was repeated for five times. The purified sample is powdered in a mortar and subjected to tituration with Justicaadhatoda leaf juice and calcined. The calcined product is again titurated with Vitexnegundo leaf juice and calcined. The calcined product is again titurated with Curculigoorchoides juice and calcined. This is the end product and used as a medicine for the treatment of diseases such as piles, tuberculosis and bronchial asthma. B. Characterization The initial compound pearl oyster and the finally obtained compound are subjected to FTIR spectral analysis in the wavelength range 45 to 4 cm -1, FT Raman spectra analysis in the range 4 to 1 cm -1. The initial and final compounds are subjected to powder X-ray diffraction in the 2theta range 1 to 8. II. RESULTS AND DISCUSSIONS A.FTIR Spectrum The initial compound pearl oyster and the finally obtained compound after various steps of calcinations are subjected to FTIR spectral analysis in the wavelength range 45 to 4 cm -1. Fig. 1 shows the combined FTIR spectrum of as prepared compound and the final product. 1 8 I F % T ra n s m itta n c e ARAGONITE CALCITE wavenumber (cm -1 ) Figure 1.FTIR spectra of the initial and final compounds The absorption bands observed around 147, 182, 864 and 699 cm -1 for the initial compound are attributed to the vibrations of carbon-oxygen double bond in the carbonate ion present in aragonite. The absorption bands observed around 1436, 875 and 712 cm -1 in the final product are due to the vibrations of carbonoxygen double bond in the carbonate ion present in calcite [2]. From the FTIR spectral analysis it can be concluded that the pearl oyster contains calcium carbonate in the form of aragonite crystal and after calcinations it undergoes phase transformation to thermodynamically stable calcite crystalline phase 537

3 B.FT-Raman Spectrum The initial compound pearl oyster and the finally obtained compound are subjected to FT-Raman spectral analysis in the range 5 to 2 cm -1. Fig. 2 and 3show the FT-Raman spectra of the initial and final compound respectively. Figure 2.FT-Raman spectra of the initial compound From Fig.2, the peaks observed around 185.3, 73, 27 and 153 cm -1 is characteristics to that of aragonite form of calcium carbonate and the peaks observed around 185, 78 and 285 cm -1 in the Fig.3 are characteristics to that of calcite form of calcium carbonate [2]. Figure 3.FT-Raman spectra of the final compound Raman spectral analysis conforms once again that the calcium carbonate present in the pearl oyster compound undergoes solid state phase transformation from aragonite to calcite phase. 538

4 C. Powder X-ray diffraction analysis Finely ground powder of the initial compound and final compound are subjected to powder X-ray diffraction analysis in the 2 theta range 1 to 8 degree. The powder X-ray diffraction spectra of the initial and final compounds are shown in the Fig. 4 and 5 respectively. Sharp and well defined peaks at specific 2 theta values show the crystalline nature of the initial and final compounds. INTENSITY(cps) INITIAL (radian) Figure 4.Powder X-ray diffraction of the initial compound The peaks observed in Fig.4 are in accordance to the peaks observed to that of aragonite and the peaks observed in Fig.5 are characteristics to that of calcite. The observations are in accordance with that of JCPDS values numbers and Intensity (CPS) FINAL (degree) Figure 5.Powder X-ray diffraction of the final compound III. CONCLUSIONS From the FTIR, FT-Raman ad Powder X-ray diffraction studies it can be concluded that the calcium carbonate present in the form of less stable aragonite crystals and upon calcinations it is undergoing irreversible solid state phase transformation in to stable calcite crystals. Further work is in progress to elucidate the role of other compounds added to the pearl oyster and the mechanism of phase transformations. 539

5 ACKNOWLEDGMENT The authors wish to thank their respective College authorities for the encouragement and kind permission to carry out this work. REFERENCES [1] Tori Z. Forbes, A.V. Radha, and Alexandra Navrotsky, The energetics of nanophase calcite, Geochimicaet Cosmochimica Acta, vol.75, 211, pp [2] ShanmukhaprasadGopi, V.K. Subramanian, K. Palanisamy, Aragonite calcite vaterite: A temperature influenced sequential polymorphic transformation of CaCO3 in the presence of DTPA, Materials Research Bulletin, vol.48, 213,pp [3] Christina Perdikouri, ArgyriosKasioptas, Thorsten Geisler,Burkhard C. Schmidt and Andrew Putnis, Experimental study of the aragonite to calcite transition in aqueous solution, Geochimica et Cosmochimica Acta, vol.75, 211,pp [4] Marko Ukrainczyk, Jan Stelling,MarijanVuc ˇak, and Thomas Neumann, Influence of etidronic acid and tartaric acid on the growth of different calcite morphologies, Journal of Crystal Growth, vol.369,213,pp [5] Manuel AnuelPrieto, Pablo Cubillas, and Angeles Fern Andez-Gonzalez, Uptake of dissolved Cd by biogenic and abiogenic aragonite: a comparison with sorption onto calcite, Geochimica et Cosmochimica Acta, Vol. 67, No. 2, 23,pp [6] Jonas Baltrusaitis and Vicki H. Grassian, Calcite ð114þ surface in humid environments, Surface Science, vol.63, 29, pp. L99 L14. [7] ZhaodongNan,Xiangna Chen, Qianqian Yang,XiuzhenWang,ZuoyiShi and WanguoHou, Structure transition from aragonite to vaterite and calcite by the assistance of SDBS, Journal of Colloid and Interface Science, vol.325, 28,pp