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CHAPTER 8

CHARACTERIZATION OF PURE AND COPPER DOPED IRON

TARTRATE CRYSTALS GROWN IN SILICA GEL

8.1 Introduction

Many of the tartrate compounds including pure and doped iron tartrate

deserve special attention due to their medical, pharmaceutical and industrial

applications. For example, injections of Na-Cr tartrate increase the susceptibility

of the transplanted sarcoma to the effect of X-rays, calciphylatic responses of

various ferrous tartrate compounds to prevent anemia in animals, ferrous tartrate as

a catalyst in manufacture of champagne, tanning action of ferrous tartrate to tan

skin and the use of manganese tartrate crystals in chemical temperature indicators.

A series of pure and mixed crystals have been grown by several researchers with

the aim of identifying new materials for practical and industrial pruposes (Shenoy

et al.2010; Sushma Bhat et al. 1994; John et al.2001; Parekh et al.2009;Pan Gao et

al.2008). Pure and doped iron tartrate crystals find several practical applications in

science and technology because of their interesting physical properties such as

dielectric, ferroelectric, piezoelectric and non-linear optical properties. The present

work describes the growth of pure and mixed crystals of copper –iron tartrate

grown in silica gel.

8.2 Experimental method of crystal growth

The test tube single diffusion method (Henisch 1996) was employed to grow

pure and copper doped iron tartrate single crystals in gel medium. 0.5M sodium

metasilicate (Na2SiO3 9H2O) was titrated with 0.5M tartaric acid till the mixture

attained the pH of 4.5. This gelling mixture was allowed to set in glass tubes of

length, 200 mm and diameter 25 mm. The gel was set in about 24 hr. The gel

setting was found to be strongly dependent on pH, high pH value gel takes lower

 

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time to set than low pH value. After confirming the gel setting an aqueous

solution of iron sulphate of required concentration is poured slowly along the sides

of the test tubes, to avoid breaking of the gel surface. Similarly, for growing

copper doped iron tartrate crystals an aqueous solution of FeSO4 and CuSO4 of

required concentration has been used. Slow diffusion of the upper reactant ions

through the narrow pores of the silica gel leads to reaction between these ions and

the ions present in the gel as lower reactant.

Fig 8.1 Crystals of (a) pure iron tartrate (b) Cu2+ doped iron tartrate

 

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The following reaction was expected to occur:

FeSO4 + C4H6O6 → FeC4H4O6 + H2SO4

(pure iron tartrate)

(1-x) FeSO4 +x CuSO4 +C4H6O6 → Cux Fe (1-x) C4H4O6 + H2SO4

where x = 0.07,0.06,0.05,0.04,0.03 (copper doped iron tartrate)

The crystals of pure and Cu2+ doped iron tartrate crystals are shown in Fig 8.1.

Spherulitic crystals of pure and Cu-Fe tartrate crystals exhibit slight variation in

colour.

8.3 Results and discussion

8.3.1 Energy Dispersive X-ray analysis

The elemental analysis of Cu2+ doped iron tartrate crystals are shown in Fig

8.2. Table 8.1 gives the theoretical and experimental atomic and weight % of pure

and Cu2+ doped iron tartrate crystals.

Fig 8.2 EDAX spectrum of Cu2+ doped iron tartrate

 

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Table 8.1

Elemental analysis of pure and Cu2+ doped iron tartrate crystals

Element calculated observed

Atomic % Weight% Atomic % Weight % FeC4H4O6 Fe 100 100 100 100

Cu0.07Fe 0.93 C4H4O6 Fe 94 Cu 6

85.08 14.92

93 7

86.09 13.91

Cu0.06 Fe 0.94 C4H4O6 Fe 95 Cu 5

86.88 13.12

94 6

87.95 12.05

Cu0.05 Fe 0.95 C4H4O6 Fe 96 Cu 4

87.99 12.01

95 5

89.85 10.15

Cu0.04 Fe 0.96 C4H4O6 Fe 97 Cu 3

90.12 9.88

96 4

91.80 8.20

Cu0.03 Fe 0.97 C4H4O6 Fe 98 Cu 2

92.66 7.34

97 3

93.78 6.22

8.3.2 Fourier Transform Infrared spectroscopy

The infrared radiation promotes transition in a molecule between rotational

and vibrational energy levels of the ground electronic energy state. The FTIR

spectra of pure and Cu2+ doped iron tartrate crystals are shown in Fig 8.3. The

observed bands with intensity and their vibrational assignment are given in Table

8.2. Several authors have reported the vibrational spectra of metal tartrate crystals

(Quasim et al.2009; .Arora et al.2006; Firdous et al.2009).It is observed that the

transmittance percentage of Cu2+ doped iron tartrate is more than the pure iron

tartrate crystals. The peaks observed at 3356.90 cm-1 and 3453.07 cm-1 are due to

OH stretching mode. The band at 2360.68 cm-1 is attributed to CH stretching

mode of tartaric acid. The strong peaks at 1612.01 cm-1 and 1610.91 cm-1 are due

to C=O stretching mode of vibration. The bands at 1373.78 cm-1 and 1378.08 cm-1

are attributed to λ (C=O) + δ (O-C=O). The obsorption peaks at 1237.63 cm-1 and

1286.78 cm-1 are assigned to OH plane bending. The strong peaks at 1119.65 cm-1

 

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and 1119.11 cm-1 are attributed to δ (C-H)+π (C-H) modes of vibration. The

bands at 1081.94 cm-1 and 1082.38 cm-1 are assigned to γ C(OH) mode.

Fig 8.3 FTIR spectra of (a) pure and (b) Cu2+ doped iron tartrate crystals

 

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Table 8.2

FTIR assignments for pure and Cu2+ doped iron tartrate crystals

Absorption in wavenumber (cm-1) Assignments

Pure Iron tartrate Cu2+ doped Iron tartrate

3356.90 3453.07 OH stretching - 2360.68 CH stretch

1612.01 1610.91 C=O stretch 1373.78 1378.08 λ (C=O) + δ (O-C=O) 1237.63 1286.78 OH plane bending 1119.65 1119.11 δ (C-H)+π (C-H) 1081.94 1082.38 γ C(OH) 1049.96 1047.24 C-O stretching 930.49 931.33 γ CC 628.08 628.39 CO2 deformation

Below 500 Below 500 metal-oxygen stretching

The absorption peaks at 1049.96 cm-1 and 1047.24cm-1 are attributed to C-

O stretching. The bands at 930.49cm-1 and 931.33cm-1 are due to stretching modes

of carbonyl group γ CC. The bands observed at 628.08cm-1 and 628.39cm-1 are

attributed for CO2 deformation. The absorption wavenumbers below 500cm-1 are

assigned for Fe Cu O mode or metal-oxygen stretching.

8.3.3 Powder X-ray diffraction studies

The powder XRD patterns of pure and Cu2+ doped Iron tartrate crystals are

given in Fig 8.4. There are slight variations between the pure and doped crystals

(Joseph et al.1997;Joshi et al.2008).

 

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Fig 8.4 Powder XRD spectrum of (a) pure iron tartrate and

(b) Cu2+ doped iron tartrate crystals

Table 8.3

Indexed XRD data for pure and Cu2+ doped iron tartrate

Pure Iron tartrate Cu2+ doped Iron tartrate hkl 2θ (°) hkl 2θ (°) 101 14.68 101 14.56 020 16.68 020 16.53 302 19.20 301 19.04 210 23.75 210 23.59 211 24.89 211 24.81 122 29.15 221 27.26 310 30.80 310 30.69 041 33.12 410 33.71

 

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Table 8.4

Comparative unit cell parameters for pure and Cu2+ doped

iron tartrate crystals

Chemical formula Interaxial angle

Unit cell dimensions

Å

Unit cell volume Å3

Pure FeC4H4O6 α = β = γ = 90˚ a = 9.8845 b = 7.4420 c = 8.8480

650.96

Cu0.05 Fe 0.95 C4H4O6

α = β = γ = 90˚ a = 9.9832 b = 8.9142 c = 7.8892

702.07

The indexed XRD of the pure and doped crystals are given in Table 8.3.

The data observed from powder diffraction is well correlated with the data

available in the JCPDS file (v.2.3,26-0282). The peaks observed from the X-ray

diffraction spectrum were analysed and the lattice parameters were calculated by

the unit cell software program. The calculated lattice parameter and unit cell

volume are shown in Table 8.4. Hence, the grown crystals belong to orthorhombic

structure with α = β = γ = 90˚ and a ≠ b ≠ c.

8.3.4 Magnetic properties

The pure and Cu2+ doped FeC4H4O6 crystals are finely ground, crushed and

the resulting powders were packed in a Gouy tube of known magnetic

susceptibility. These experiments were repeated five times and the change in

weight was calculated for the given magnetic field. The readings of Gouy balance

was recorded when the values became steady. These values are given in Table 8.5.

The magnetic susceptibility of the samples are found out by using the equation

mg = χ H2, where ‘m’ is the mass of the substance; ‘A’ is the area of cross

section of the glass tube; ‘H’ is the magnetic field between the pole- pieces and

 

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‘χ’ magnetic susceptibility of the substance. A graph is drawn between m and H2

and the slope gives A χ /2g. Hence the susceptibility ‘χ’ is calculated. This is

shown in Fig 8.5. The slope is found out at the linear region of the graph. The

magnetic moment ‘µ’ of pure and doped FeC4H4O6 crystals are found out by

using the formula µ = 2.828 (χ x T )1/2 BM, where ‘T’ is the room temperature

in terms of Kelvin. The susceptibility and magnetic moment of the pure and

doped crystals are given in Table 8.6.

Table 8.5

Change in mass with respect to applied magnetic field for (a) pure FeC4H4O6

(b) Cu2+ doped FeC4H4O6

Name of the crystal Magnetic field in Kilogauss

Mass in Kilograms

Pure FeC4H4O6

1 0.0690 2 0.0688 3 0.0685 4 0.0681 5 0.0677

Cu2+ doped FeC4H4O6

1 0.0395 2 0.0397 3 0.0399 4 0.0401 5 0.0403

 

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Fig 8.5 Graph between ‘m’ and ‘H2’ for (a) pure iron tartrate and (b) Cu2+ doped iron tartrate crystals

Table 8.6

Susceptibility ‘χ’ and magnetic moment ‘µ’ for pure and Cu2+ doped FeC4H4O6

8.3.5 Thermal analysis

The TGA analysis of pure and copper doped Iron tartrate crystals are

shown in Fig 8.6. The TGA analysis is done between 40˚C to 500˚C at a heating

Name of the crystal Magnetic susceptibility

( χ ) x10-6 emu

Magnetic moment (µ) BM

Pure FeC4H4O6 crystals 27.59 2.572

Cu2+ doped FeC4H4O6 16.98 2.01

 

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rate of 20˚min-1 in nitrogen atmosphere. In the case of pure iron tartrate crystals

(shown in Fig 8.6(a)), the first stage of decomposition is due to water of hydration.

This starts at 50.42˚C and continues upto 325.5˚C with an observed weight loss of

about 25%. The second stage of decomposition starts from 325.56˚C and

continues upto 368.45˚C with an observed weight loss of about 14.95%. The

observed and calculated weight percentage losses suggests chemical formula for

the given crystal to be FeC4H4O6 2H2O. Similarly, in the copper doped iron tartrate

crystal (shown Fig 8.6(b)), the first stage of decomposition starts from 50.45˚C

and continues up to 123.45˚C with a weight loss of about 20%. The second stage

of decomposition starts from 320.05˚C and continues upto 360˚C with a weight

loss of about 22%. The observed and calculated weight percentage losses suggests

chemical formula for the given crystal to be Fe0.95 Cu0.05C4H4O6 2H2O. The TGA

results of pure and copper doped iron tartrate crystals are shown in Table 8.7.

DSC is a thermoanalytical technique in which the difference in the amount

of heat required to increase the temperature of a sample and reference is measured

as a function of temperature. Both the sample and reference are maintained at

nearly the same temperature throughout the experiment.

The result of a DSC experiment is a curve of heat flux versus temperature.

These curves may be exothermic or endothermic used to calculate enthalpies of

transition. The DSC curves for pure and copper doped iron tartrate crystals are

shown in Fig 8.7. The endothermic peaks at 118.95˚C and 120.45˚C shows the

decomposition temperature for pure and Cu2+ doped Iron tartrate crystals

respectively.

 

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Fig 8.6 TGA data of (a) pure and (b) Cu2+ doped iron tartrate crystals

Table 8.7

TG results of Pure and Cu2+ doped iron tartrate crystals

Name of the

crystal Stage

Temperature

range (˚C)

Weight Loss% Reaction

Observed Calculated

Pure Iron

tartrate

I 50.42 to

325.56 25 24.5

FeC4H4O6 2H2O FeC2H4O2

II 325.56 to 368.45 14.95 15.08 FeC2H4O2 FeO

Cu2+ doped

Iron tartrate

I 50.45 to 123.45 20 19.58 Fe0.95 Cu0.05C4H4O6 2H2O

Fe0.95 Cu0.05C2H4O2

II 320.05 to 360 22 22.05 Fe0.95 Cu0.05C2H4O2 Fe0.95 Cu0.05 O

 

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Fig 8.7 DSC curves of (a) pure and (b) Cu2+ doped iron tartrate crystals

8.4 Conclusion

Single crystal of pure and copper doped iron tartrate are grown successfully

by single diffusion method from gel. The EDAX analysis confirms that the dopant

Cu2+ has entered into the lattice of iron tartrate crystals. The presence of

O-H, C=O, C-O, C-H and metal oxygen bonds were confirmed from FTIR

spectroscopy. From XRD analysis the unit cell volume of pure iron tartrate is

found to be 650.86Å3 and Cu2+ doped iron tartrate is found to be 702.07 Å3. The

magnetic moment of pure and copper doped iron tartrate crystals are found to be

2.572 BM and 2.01 BM respectively. The thermal analysis of the samples

revealed that there is water of hydration for both samples and the chemical

formula for the given samples are FeC4H4O6 2H2O and Fe0.95 Cu0.05C4H4O6 2H2O

respectively.