1.Metallurgical -IJMMSE - Structural - B

International Journal of Metallurgical & Materials

Science and Engineering (IJMMSE)

ISSN 2278-2516

Vol. 3, Issue 2, Jun 2013, 1-12

© TJPRC Pvt. Ltd.

STRUCTURAL, THERMAL AND DIELECTRIC STUDIES ON SELENITE MINERAL

B. PRAMEENA1, G. ANBALAGAN

2 & S. GUNASEKARAN

3

1,2PG and Research Department of Physics, Presidency College, Tamil Nadu, Chennai, India 3PG and Research Department of Physics, Pachaiyappa’s College, Tamil Nadu, Chennai, India

ABSTRACT

The mineral Selenite has been investigated by X-ray diffraction, infrared, FT-Raman, optical absorption and

Thermo gravimetric analysis (TGA). In X-ray diffraction structure has been determined as monoclinic. In FTIR the

fundamental stretching and bending vibrations observed in the infrared region for Ca and SO4. In FT-Raman, the Selenite

mineral is characterized by the position of the symmetric stretching mode which is observed at higher wavenumbers than

the anti-symmetric stretching mode. The optical absorption spectrum indicates the presence of ferric and ferrous ions in the

mineral. The thermal decomposition behaviour and degradation characteristics of selenite were also studied. Dielectric

study has also been carried out and it is found that both dielectric constant and dielectric loss decreases with increase in

frequency.

KEYWORDS: X-ray Diffraction, FTIR & FT-Raman, Optical Absorption, Thermal Analysis, Selenite, Dielectric

Studies

INTRODUCTION

Selenite, satin spar, desert rose, and gypsum flower are four varieties of the mineral gypsum; all four varieties

show obvious crystalline structure. The four "crystalline" varieties of gypsum are sometimes grouped together and called

selenite. All varieties of gypsum, including selenite and alabaster, are composed of calcium sulfate dihydrate (meaning has

two molecules of water), with the chemical formula CaSO4·2H2O. Selenite contains no significant selenium; the similarity

of names comes from both substances being named from the Ancient Greek word for the Moon. Selenite has a layered

structure and it is easily cleaved along the (010) plane, which in turn reveals the y-axis in the crystal structure.

The atomic arrangement in the crystal structure composes two sheets of sulphate ions (SO42-) that are closely bond

together by calcium ions (Ca2+) to form strong double sheets in a repetitive mode. These sheets, in turn, are held together

by water molecules that share the two oxygen atoms with calcium in an octahedral structure. The water molecules hold the

sheets together through hydrogen bonding, which allows for the perfect cleavage along the (010) plane. Each sulphate ion

is tetrahedrally bonded to calcium ions, though a distinct distortion of the shape commonly occur, which in turn gives rise

to band splitting in Raman spectroscopy (University of Warwick, UK, 2010-11-30, Sarma et al., 1998).

Infrared and Raman spectroscopy has proven very useful for the study of minerals. Indeed, Raman spectroscopy

has proven most useful for the study of diagenetically related minerals, as often occurs with many minerals. Some previous

studies have been undertaken by the authors, in which Raman spectroscopy was used to study complex secondary minerals

formed by crystallization from concentrated sulphate solutions [1-5]. The aim of this paper is to present to predict XRD,

IR, Raman spectra, optical absorption and TGA of a natural selected selenite and to discuss the spectra from a structural

point of view. It is a part of systematic studies on the vibrational spectra of minerals of secondary origin in the oxide

supergene zone and their synthetic analogs.

2 B. Prameena, G. Anbalagan & S. Gunasekaran

EXPERIMENTAL METHODS

Selenite minerals were ground with an agate mortar and pestle. The powder sample was sieved, and particles with

diameter smaller than 50 micrometer were submitted to XRD, FTIR, FT-Raman, UV and TGA. XRD analysis were

performed with a SEIFERT X-ray diffractometer with Cu Kα radiation (λ=1.54 A), Cu filter on secondary optics, 45 kV

voltage and 20 mZ current. The powdered sample was mounted on a quartz support to minimize background. A Perkin-

Elmer Spectrum one FTIR spectrometer was used, and the samples were analyzed in KBr pellets. Spectrum were traced in

the range 4000 –400 cm-1, and the band intensities were expressed in transmittance (%). FT-Raman spectrum was

recorded using 1064 nm line of Nd: YAG laser as excitation wavelength in the region 4000-10 cm-1 on Bruker IFS 66V

spectrometer equipped with FRA 106 Raman module was used as an accessory.

The optical absorption spectrum of the sample was recorded using Varian Cary 5E UV-Visible-NIR

spectrophotometer in the range 200 – 2500 nm by employing mull technique. The thermal analysis were performed in a

simultaneous TG (SDT Q600 V8.3 BUILD101) procedure. The experimental conditions were: (1) continuous heating

from room temperature to 1200°C at a heating rate of 10° C min-1 ; (2) N2 – gas dynamic atmosphere (90 cm3 min-1); (3)

alumina, crucible; sample mass: 3 mg approximately. TG curves were obtained. The thermal analysis resulted in the

following data: (1) reactions peak temperature and main effect (endothermic or exothermic) and (2) content of bound

water, which is the weight loss in the temperature 142-1041°C.

THEORY: KINETIC METHODS

TGA kinetics analysis is determined by measurement of fractional mass loss and degradation rate according to

temperature change. The fraction of conversion α, is defined as:

α = (Wo-W) / (Wo-Wf)

Where, W is the actual weight at any degradation time, Wo is the initial weight, and Wf is the final weight at the

end of thermal degradation process. The rate of degradation, dα/dt, can be expressed as the product of the function of

temperature and the function of conversion:

dα/dt =β dα/dT = k(T).f(α)

where β=dT/dt is the heating rate.

For experiments, the reaction rate at all times depends on both f(α) and k(T), Hence generally f(α), k(T) and ln A

are known as kinetic triplet.

The temperature dependent function is generally assumed to follow an Arrehenius type dependency ln k= ln A

Ea/RT. The multiple heating methods used in the present study were the Flynnwall, Kissinger and Kim-Park method.

Flynn-Wall Method

This is the simplest method for determining activation energies directly from weight loss against temperature

obtained at several heating rates. This technique assumes that A, (1-α)n and Ea are independent of T, A and Ea are

independent of α. Flynn-Wall plot is obtained by using the following expression

ln β= ln (AEa/R) = ln F(α) - Ea/RT

The value of the activation energy (Ea) can be calculated from the slope of the plot between ln β vs 1/T for a fixed

weight loss. This method cannot give the other kinetic parameters except for the activation energy.

Structural, Thermal and Dielectric Studies on Selenite Mineral 3

Kissinger Method

The activation energy for the non-isothermal decomposition of selenite was calculated from the TG data by using

Kissinger expression

ln (β/Tp2) =ln [n(1-αm)n-1AR/Ea] - Ea/RTp

where β is the heating rate , A is the pre-exponential factor, Ea is the energy of activation, R is the gas constant,

Tp is the absolute temperature at the maximum rate of thermal decomposition and αm is the weight loss at the maximum

decomposition rate. The Kissinger method [23] assumes that ln(1-αm)n-1 is independent on the heating rate. It also assumes

that the reaction order remains constant, and is very nearly equal to unity. The value of the activation energy can be

calculated from the slope of the plot of ln (β/Tp2) vs 1/Tp at the maximum weight loss.

Kim-Park Method

ln β= ln Z + (Ea/R) + ln [ 1-n+(n/0.944)]

The Kim-Park method [8] assumes that αm is independent of the heating rate β, activation energy Ea, and a pre-

exponential factor A. The activation energy can be obtained by plotting ln β against 1/Tp. Since the conversion factor is

taken as unity, this method can be considered as more accurate than the other methods.

RESULTS AND DISCUSSIONS

X-Ray Diffraction Analysis

The room temperature powder X-ray diffraction pattern of the Selenite is given in Figure 1 which shows quite

sharp peaks with little background absorption. It has a monoclinic structure. A complete structure [9] was carried out with

the choice of the simpler cell with is A- centered, space group (A2/a) and contains 4 (CaSO4. 2H2O). In the structure of

selenite, determined two sheets of SO4 ions parallel to (010) are bonded together by Ca ions and these double sheets are

separated by layers of water molecules. Each Ca ion is coordinated by eight oxygen’s, six belonging to SO4 tetrahedra and

two to water molecules. The Ca-O distances range from 2.552 to 2.366 Å. The water molecules lie near the centers of

triangles formed by a calcium ion and two oxygen’s (of sulphate groups) to which they are hydrogen bonded. Each water

molecule links a Ca ion with an oxygen in the same double sheet at 2.81Å and to an oxygen in a neighboring sheet at

2.88Å. The relatively weak hydrogen bonding between layers explains the perfect (010) cleavage of mineral. Also, the

direction [001] is that in which Ca and O ions are closest together; this corresponds approximately with the direction of

fibrous cleavage, small expansion co-efficient and high refractive index.

Vibrational Analysis

The symmetry of the selenite should be similar to that of sulphite which has a tetrahedral symmetry with one

vacant orbital thus making C3v symmetry. The fundamental vibrational modes of selenite mineral were assigned to the

peaks in FTIR and FT-Raman spectra are shown in Figures 2 & 3 and Table 1 are presented. Our assignments for most

peaks are consistent with those in previous literature [10-12]. In Raman spectra of gypsum [13], and selenite, the strongest

peaks were found at 1019 and 1008 cm-1 respectively, up-shifted following the decrease of the hydration degree. These are

υ1 symmetric stretch vibration modes of SO4 tetrahedra. Variations in the structure of covalent bonded ionic group and its

chemical environment are the general cause for the variations in Raman spectral patterns and for the systematic shift of

Raman peaks. In addition, hydrogen bonding affects the coordinating oxygen of SO4 tetrahedra. Gypsum and selenite all

exhibit doublet for υ2 symmetric bending of SO4 tetrahedra, as (427, 506 cm-1) and (415, 494 cm-1) respectively. The other

peaks of SO4 tetrahedra are much weaker. The peak at 1143 cm-1 in selenite mineral is assigned to υ3 anti-symmetric


stretching vibration mode whereas no peaks are present around 1100 cm-1 in gypsum mineral, which confirms that selenite

is one of the variety of gypsum. The peaks at 631 and 682 cm-1 in gypsum and 620 and 670 cm-1 in selenite are υ4

antisymmetric bending vibration modes.

In FTIR spectra, the strongest peaks were found at 1143 cm-1, for the both samples, which are υ3 anti-symmetric

stretch vibration modes of SO4 tetrahedra. The gypsum [13] and selenite exhibit two (669, 600 cm-1) and two (669, 602

cm-1) which are anti-symmetric bending vibrations, respectively, in FTIR spectra. The frequency 672 cm-1 in selenite

indicates that the sulfate ions in selenite are linked with water molecules by hydrogen bonding, because in general the

hydrogen bonding will lower the frequency of the absorption band. In addition, there is a very weak peak at 1003 cm-1 in

selenite mineral, which should be the υ1 symmetric stretching vibration modes of SO4 tetrahedra whereas no peak is

present at 1000 cm-1 in gypsum mineral. This also indicates the selenite is a variety of gypsum, because of the selection

rules, these peaks are very weak in the infrared spectra, but very strong in Raman spectra. The presence of water in the

gypsum and selenite can be detected and characterized by peaks in spectral region near 3500 cm-1 and 1600 cm-1. In the

high frequency Raman spectra, the peaks around 3500 cm-1 in the gypsum and selenite are caused by stretching vibration

modes of water, and no peaks for υ2 bending vibration modes of water were observed in the two samples. In FTIR spectra,

the peaks at 3540 cm-1 in gypsum and 3544 cm-1 in selenite are υ1 symmetric stretch vibration modes of water, and the

peaks at 3400 cm-1 in gypsum and 3403 cm-1 in selenite are υ3 anti-symmetric stretching vibration modes of water. There

are two IR peaks for OH bending vibration modes (1682, 1620 cm-1) in the gypsum spectrum, one peak (1685, 1620 cm-1)

in selenite. The presence of two peaks in selenite indicates that there are two crystallographic distinct types of water. One

type of water is linked with sulfate ions by hydrogen bonding, and the corresponding peak has lower frequency (also due to

the hydrogen bonding) and high intensity. The other one is directly linked to calcium ions.

Optical Absorption Spectrum

The optical absorption spectrum (Figure 4) exhibits features similar to those of Fe2+ and Fe3+ impurities in

different iron bearing minerals [14-17]. There are six bands observed in the spectrum and all are attributed to different

transitions arising from isolated Fe2+ and Fe3+ as well as by pairs of iron ions. The bands observed at 360 nm (27778 cm-1)

are assigned to 6A1→4E(4D) transitions. The band at 423 nm (23640 cm-1) is ascribed to 6A1→

4T2(4D) transition. With the

help of Tanabe-Sugano diagram the bands at 480, 620 nm (20833, 16130 cm-1) are then identified as 6A1→4T2(G) and

6A1→4T2(

4G) transitions, respectively [18]. The energy matrices for the d5 configurations are solved and band data of Fe3+

is given Table 2. The following crystal field parameter (Dq) and inter electronic parameters (B, C) are determined. The

weak band at 950 nm (10526 cm-1) attests the presence of Fe3+ in the sample [19]. However, Halenius et al. [20] assigned

this band to a process involving ferrous as well as ferric ion.

The nature of Fe(II) ion associated absorption bands in sulfates. Comparison of the spectra with that reported by

Cloutis et al. [21] indicates that prominent Fe2+ associated absorption bands occur near 0.8 – 1.2 µm. The appearance of

the two absorption bands in the 0.8-1.2 µm region attributes Lamporte forbidden transition [22, 23]. Spectra of the mineral

where the Fe2+ is coordinated by H2O exhibit two bands near 0.9 – 0.95 and 1.19 whereas other exhibit a single band near

0.9 µm [18]. For the ferrous ion, the band at 676 nm (14792 cm-1) 5T2→3T2 and the bands at 876, 1174 nm (11415, 8517

cm-1) are attributed to 5T2→5E2. The average 9966 cm-1 of these two bands gives approximate value of 10Dq [24]. The

separation (11415, 8517 cm-1) of these two components is 2898 cm-1. The order of splitting indicates the tetragonal

distortion of the ferrous ion in the mineral. The energy matrices for d6 configuration are solved for different values of Dq,

B and C. The position of the 10Dq band observed for Fe(II) ion in the sample indicates that Fe(II) is situated in a


tetragonally distorted octahedral site. The crystal field parameters derived in the present case agree well with those

reported for Fe(II) in a tetragonally distorted octahedral environment [25-27].

Thermal Analysis

The thermal behavior of selenite was studied at 10, 15 and 20°C/min by using a SDTQ600V8.3 Build 101

instruments. The experimental conditions were: (a) continuous heating from room temperature to 1187°C for 10, 15 and

20°C/min.; (b) Nitrogen gas dynamic atmosphere (90cm3/min); (c) alumina, crucible; (d) sample of mass: 3.0440, 3.1170

and 2.3990 for 10,15 and 20°C/min respectively. TG-DTA curves of selelnite at three different heating rates 10, 15 and

20°C/min are depicted in Fig. 5.

The TG curve exhibit weight losses. For 10°C/min, the initial mass is taken as 3.0440 mg. The decomposition

takes place in the temperature range of 105.51°C to 124.99°C with a weight loss of 14.42% and is due to the liberation of

one water molecule. The corresponding exothermic peak is seen at 119.83°C. A gradual weight loss starts at 139.47°C and

continues up to 367.62°C with a weight loss of 7.35%. This mass loss is attributed to the decomposition of sulphate

molecules from the structure of the compound. It is exactly matches with an exothermic peak at 350.19°C in DTA curve

which is assigned as the melting point of selenite. And the remaining 1.84% of weight loss occurs in the range 398.80°C-

520.23°C and it is due to the decomposition of calcium with a final residue of 2.100 mg. This is accompanied by an

exothermic peak at 497.74°C. There is a good agreement between the expected and observed mass loss for the loss of one

water molecule, sulphate and calcium molecule. From this it is identified that the title compound have more thermal

stability and this enables the suitability of the mineral for thermal applications. When the heating rate is increased to 15 and

20°C/min, all exothermic peaks in DTA curve are shifted to higher temperatures which is clearly seen in Figure 5. Thus the

heating rate has influence on the thermal decomposition of selenite.

A typical plot of α versus temperature as shown in Figure 6. It is seen that all α-T curves have same shapes. From

the slope, the activation energy (Ea) were calculated and listed in Table 3. Activation energies of the decomposition

complex were also calculated by Kissinger and Kim-Park shown in Figures 7 & 8. Both methods yield similar calculation

results, which are therefore reasonable (Table 3). In Flynn-Wall plots for three different heating rates against the

temperature as shown in Figure 9. Activation energy (Ea) is calculated from the slope of ln β versus 1/T for a fixed mass

loss. The calculated values of the activation energy in the Flynn-Wall method fairly agree with the Kissinger method.

Dielectric Studies

Frequency dependent dielectric constant and dielectric loss values of the studied minerals are depicted in Figures

10 & 11. The Figure shows the dielectric constant decreases with increasing frequency and attain saturation in the range 50

Hz–5 MHz. The low frequency dispersion of dry samples is believed to be due to polarization associated with charge build

up at grain boundaries or at grain imperfections of the sample heterogeneous particles of different value dielectric constant.

Further, the contribution of grain sizes and their distribution are also important factors in controlling the dielectric constant

[28,29]. The dielectric constant of the mineral has been calculated using the relations,

ε = Cd/A εo

where d is the thickness and A is the area of the sample. The response of dielectric constant as a function of

frequency is shown in Figure. Dielectric studies furnish a great deal of information regarding the dielectric constant that

arises from the contribution of different polarizations, namely electronic, ionic, atomic, space charge, etc., developed in the

material subjected to the electric field variations. The large dielectric constant at low frequency for the selenite mineral in


the present study is due to the presence of space charge polarization arising at the grain boundary interfaces [30]. The low

values of dielectric constant at higher frequencies reveal the good quality of the mineral, which is the desirable property of

the materials to be used for various optical and communication devices. The dielectric constant measured at different

temperatures almost remains the same at higher frequencies. It indicates the temperature variation has no influence on the

dielectric property of the material. The electronic exchange of a number of ions in the selenite mineral gives local

displacement of electrons in the direction of the applied field, which in turn gives rise to polarization. At higher

frequencies, the measure of dielectric loss is relatively low since the electric wave frequency is not equal to that of natural

frequency of the bounded charge, and hence the radiation is very weak. At low frequencies the dipoles can easily switch

alignment with the changing field. As the frequency increases the dipoles are less able to rotate and maintain phase with

the applied field, thus they reduce their contribution to the polarization.

CONCLUSIONS

In X-ray diffraction confirms it has a monoclinic structure and space group (A2/a). In this study, the assignments

of fundamental vibrational modes were made in FT-Raman and FTIR spectra. Hence from FTIR and FT-RAMAN spectra

it is concluded that the mineral selenite is a variety of gypsum. Our results can be used for the interpretation of the data

from current exploration. In optical absorption, Calcium and silicon bearing sulfates can display absorption bands when the

atoms are linked through shared oxygen’s or hydroxide ions. In TGA at 188°C the material gets decomposed and the

residue left out was only 69.47% of the taken mass. Since the mineral shows notably high thermal stability it can be used

as an application for high temperature studies. From the dielectric study, it can be concluded that both dielectric constant

and dielectric loss of the crystal decreases with increase in frequency attaining a constant value beyond 1000 Hz.

REFERENCES

1. Frost, RL, Cejka, J, Ayoko, Raman. G. (2008). J Spec. 39: 495.

2. Frost, RL, Cejka, J, Ayoko, GA, Dickfos, Raman.MJ. (2008). J Spec. 39: 374.

3. Frost, RL, Dickfos, MJ, Cejka, Raman.J. (2008). J Spec. 39: 582.

4. Frost, RL, Hales, MC, Wain, Raman.DL. (2008). J Spec. 39: 108.

5. Frost, RL, Keeffe, Raman.EC. (2008). J Spec. 40(5), 509-512.

6. Flynn.J.H, Wall.L.A. (1966). A quick direct method for the determination of activation energy from

thermogravimetric data, J. Polym.Sci B Polym Lett., 4, 323-328.

7. Kissinger.H.E. (1957). Reaction kinetics in differential thermal analysis, Anal. Chem., 27, 1702-1716.

8. Kim.S , Park.J.K. (1995). Characterization of thermal reaction by peak temperature and height of DTG curve,

Thermochim. Acta 264 137-156.

9. Wooster, W. A., Kristallogr.Z. (1936). 94, 375.

10. Hass et al. (1956). Pro Roy Soc London, 236, 427-445.

11. Berenblut et al. (1971). Spectrochimica, 27, 1849-1863.

12. Takaha-shi et al. (1983). Spectrochimica, 39, 449-455.


13. Anbalagan.G, Mukundakumar.S, Sakthi Murugesan.K and Gunasekaran.S. (2009). “Infrared, optical absorption

and EPR spectroscopic studies on natural gypsum”, Vibrational Spectroscopy, 50, 226-230.

14. Sherman.GD.M, Waite.T.D. (1985). Electronic spectra of Fe3+ oxides and oxide hydroxides in the near IR to near

Uv. Am. Mineral. 70, 1262-1269.

15. Reece.J.J, Redfem.S.A.T, Welch.M.D, Henderson,.C.M.B C.A. Mc Cammon. (2002). Temperature-dependent

Fe2+ - Mn2+ order-disorder behavior in amphiboles. Phys. Chem. Miner, 29, 562-570.

16. Grygar.T, Dedeck.J, Kruiver.P.P, Dekkers.M.J, Bezdicka.P, Schnceweiss.O. (2003). Iron oxide mineralogy inlate

Miocene red beds from La Gloria, Spain; rock-magnetic, voltammetric and divisible spectroscopy analyses,

Catena 53, 115-132.

17. Taran.M.N, Monika, Koch-Muller, Langer, Klaus. (2005). Electronic absorption spectroscopy of natural (Fe2+,

Fe3+)-bearing spinels of spinel S.S. – hercynite and gahnite solid solutions at different temperatures and high

pressures, Phys. Chem. Miner, 32, 175-188.

18. Tanabe.T, Sugano.S. (1954). Phys.. J Soc. Jpn. 9, 753.

19. Johnson.J.R, Horz.F. (2003). Geophys.J. Res. 108, 5120.

20. Halenius.U, .Skogby.H, Andreozzi.G.B. (2002). Phys. Chem. Miner, 29, 319.

21. Cloutis.E.D, Hawthorne.F.C, Mertzman.S.A, Krenn.K, Craig.M.A, Marcino.D, Methot.M, Strong.J, Mustard.J.F,

Blaney.D.L, Bell.J.R III, Vilas.F. (2006). ICARUS, 184, 121.

22. Cloutis.E.A, Gaffey.M.J. (1991). Geophys.J. Res. 96, 22809.

23. Burns.R.G. (1993). Mineralogical Applications of Crystal Field Theory, second ed., Cambridge Univ. Press,

Cambridge, UK, 551.

24. Faye.G.H. (1971). Am. Miner., 56, 344.

25. Jones.J.D. (1967). Phys. Rev. 155, 259.

26. Lakshman.S.V.J, Jaganatha Reddy.B. (1970). Spectrochim. Acta 26A, 2230.

27. Chandrasekar.A.V, Venkata Ramanaiah.M, Reddy.B.J, Reddy.Y.P, Rao.P.S, Ravikumar.R.V.S.S.N. (2003).

Spectrochim. Acta 59A, 2115.

28. Lesmes.D.P and Morgan.F.D, Dielectric spectroscopoy of sedimentary rocks. (2001). J Geophys Res (USA). 106,

13329.

29. Sen.P.N, Chew.W.C and Wilkinson.D, Dielectric enchancement due to geometrical and electrochemical effects in

Physics and Chemistry of Porous Media, Eds DL Johnson and P.N. Sen. (1984). AIP Conference Proc. 107, 52.

30. Ishwar Bhat.S, Mohan Rao.P, A.P. Ganesh Bhat.A.P, Avasthi.D.K. (2002). Surf. Coat. Technol. 158 725-728


APPENDICES

Figure 1: X-Ray Diffraction of Selenite

Figure 2: FTIR Spectrum of Selenite

Figure 3: FT-Raman Spectrum of Selenite

Figure 4: Optical Absorption of Selenite


Figure 5: TG-DTA Curves of Selenite in Nitrogen; Heating Rate of 10, 15, and 20°C/min

Figure 6: α Versus Temperature at Three Heating Rates of Selenite

Figure 7: Kissinger Method

Figure 8: Kim-Park Method


Figure 9: Flynn-Wall Method

Figure 10: Plot of Log Frequency vs Dielectric Constant of Selenite

Figure 11: Plot of Log Frequency vs Dielectric Loss of Selenite

Table 1: Vibrational Assignments of Selenite Mineral

Sl.No. FTIR FT-Raman Assignment

1 3544

ν2OH 2 3403

ν1OH

3 2923

ν3 SO4 4 2853

ν3 SO4

5 2239 2148 ν3 SO4 6 1685

ν2OH

7 1620

ν2OH 8 1143 1135 ν3 SO4 9 - 1008 ν1 SO4 10 669 670 ν4 SO4 11 602 620 ν4 SO4 12 470 494 ν4 SO4 13 - 415 ν2 SO4

symmetric stretching vibration mode (ν1) symmetric bending vibration mode (ν2)

antisymmetric stretching vibration mode (ν3) antisymmetric bending vibration mode (ν4)


Table 2: Optical Absorption of Selenite Mineral

Transition Observed Calculated

Wavenumber (cm-1) Wavelength(nm) Wavenumber (cm-1

)

For Fe(III) ion 6A1→

4T1(4G) 876 11415 11248

6A1→4T2(

4G) 630 16130 16100 6A1→

4E(4D) 360 27778 27800 6A1→

4T2(4D) 423 23640 24390

For Fe(II) ion 5T2→

3T2 676 14792 5T2→

5E2 876 11415 11248 5T2→

4E(G) 1174 8517 8610

Table 3: Activation Energies of Thermal Degradation of Selenite by Flynn Wall, Kissinger & Kim-Park Method

Method Ea R2

Flynn wall 62 0.9989 Kissinger 56 0.9942 Kim-park 82 0.9968

1.Metallurgical -IJMMSE - Structural - B

Documents

Transcript of 1.Metallurgical -IJMMSE - Structural - B