117
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
118
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
119
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
120
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
121
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
122
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).
123
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
124
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
125
‘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
126
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
127
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.
128
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
129
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.