Undoped And Doped Strontium Oxalate

Published Date: 02 Nov 2017

5.1 Introduction

In the present work, undoped and doped strontium oxalate was grown. However, there are very few reports in the literature on the growth of doped strontium oxalate crystals by agar-agar gel. Undoped strontium oxalate crystals were grown by gel method using single diffusion and double diffusion techniques and doped strontium oxalate crystals were grown by single diffusion technique. These growth procedures and different parameters affecting the growth of these crystals are discussed in details in chapters III and IV respectively. This chapter deals with comparative study of these crystals regarding their growth, characterization and results at a glance.

5.2 Growth

For undoped strontium oxalate crystals single diffusion technique is found more suitable for growth of these crystals. Also instead of hydro-silica gel, agar-agar gel is found to be more suitable for growing the crystals since the size and shape of the crystals were increased.

The cobalt doped strontium oxalate crystals are pinkish in colour, transparent, more shining and large in size. The copper doped strontium oxalate crystals are greenish in colour, transparent, more shining and large in size. The silver doped strontium oxalate crystals are yellowish in colour, transparent, more shining and large in size. From the comparative study with undoped strontium oxalate crystals, the size, shape, shining and transparency in the doped strontium oxalate crystals were increased and colour also changed due to impurity elements incorporated in strontium oxalate crystals. This means that cobalt, copper and silver doping has enhanced the growth of crystals. The details about type, method, chemical used, quality of crystals, size, etc. are as shown in table- 5.1.

Table - 5.1 Undoped and doped strontium oxalate crystals

Type

Method

Chemical used

Crystal quality

Size

Undoped strontium oxalate crystals

Gel method by using single diffusion technique

Na2SiO3,5H2O

SrCl2,6H2O

H2C2O4

Transparent, well shining

Micro crystals

Undoped strontium oxalate crystals

Gel method by using single diffusion technique

Agar-agar powder, SrCl2,6H2O

H2C2O4

Tiny, opaque, lustrous, crowded

Nearly

1mm × 1mm

Undoped strontium oxalate crystals

Gel method by using double diffusion technique

Agar-agar powder, SrCl2,6H2O

H2C2O4

Transparent, few opaque

Micro crystals

Cobalt doped strontium oxalate crystals

Gel method by using single diffusion technique

Agar-agar powder, CoCl2 SrCl2, 6H2O

H2C2O4

Pinkish colour, transparent, shining

Larger size 1mm × 1mm

Copper doped strontium oxalate crystals

Gel method by using single diffusion technique

Agar-agar powder, CuCl2 SrCl2, 6H2O

H2C2O4

Greenish colour, transparent, shining

Larger size 1mm × 1mm

Silver doped strontium oxalate crystals

Gel method by using single diffusion technique

Agar-agar powder,AgNO3

SrCl2, 6H2O

H2C2O4

Yellowish colour, transparent, shining

Larger size 1mm × 1mm

Optimum growth conditions for gel grown undoped and doped strontium oxalate crystals by varying various parameters such as gel density, pH of gel, gel setting time, gel aging time, etc. Various concentrations of reactants and supernatant were tried. Experiments by changing the positions of reactants were also carried out. Once the optimum values of concentration of reactants were obtained, experiments of concentration programming were also carried out. All these parameters have more or less effect on growth and habit of these crystals.

Gel setting time and gel aging time is less in agar-agar gel as compared to hydro-silica gel. Gel aging period reduces the nucleation centers without affecting the quality of crystals.

Nucleation density was increased with the concentration of reactants. Concentration of reactants has pronounced effect on the habit, quality and size of the crystals. Rate of diffusion of supernatant has great effect on the quality of crystals. Crystal growth period is less in agar-agar gel as compared to hydro-silica gel.

Table -- 5.2 Optimum growth conditions for gel grown undoped and doped

strontium oxalate crystals

Parameter

Undoped strontium oxalate

Undoped strontium oxalate

Cobalt doped strontium oxalate

Copper doped strontium oxalate

Silver

doped strontium oxalate

Density of sodium meta-silicate solution

1.04 gm/cc

-

-

-

-

Concentration of agar-agar gel

-

3%

3%

3%

3%

Concentration of reactant H2C2O4 (Incorporated)

0.5M

-

-

-

-

Concentration of supernatant SrCl2

1M

-

-

-

-

Concentration of reactant SrCl2 (Incorporated)

-

1M

1M

1M

1M

Concentration of supernatant H2C2O4

-

1M

1M

1M

1M

Temperature

30oC

30oC

30oC

30oC

30oC

Gel setting time

25 days

4 days

4 days

4 days

4 days

Gel aging time

4 days

2 days

2 days

2 days

2 days

Growth period

70 days

30 to 45 days

30 to 45 days

30 to 45 days

30 to 45 days

5.3 XRD analysis

Undoped and doped strontium oxalate crystals were characterized by XRD analysis. X-ray diffractogram is useful in the analysis of crystal structure. Unit cell parameters, ‘d’ values, volume and lattice system etc. can be evaluated by using x-ray diffractogram.

X-ray diffractogram of gel grown undoped strontium oxalate crystals were recorded using powder rotated diffraction on ‘Miniflex Rigaku’ X-ray diffractometer at Department of Physical Sciences, North Maharashtra University, Jalgaon, (M. S.). Table- 5.3 represents unit cell parameters, volume and system of grown crystals.

Table - 5.3 Unit cell parameters, volume and system of undoped and doped

strontium oxalate crystals

Parameters

Undoped strontium oxalate

(Hydro silica gel)

Undoped strontium oxalate (Agar-agar gel)

Cobalt doped strontium oxalate

Copper doped strontium oxalate

Silver doped strontium oxalate

a

16.7505 Ao

2.7219 Ao

4.1951 Ao

10.7393 Ao

7.5980 Ao

b

3.4772 Ao

3.2973 Ao

2.880 Ao

3.5952 Ao

4.4930 Ao

c

2.5623 Ao

11.0085 Ao

3.053 Ao

3.1260 Ao

3.6381Ao

α

111.393o

116.524o

91.146o

106.951o

108.126o

β

90.441o

108.889o

103.107o

98.348o

91.208o

γ

100.384o

95.492o

96.12o

95.893o

91.726o

V

136.41Ao3

80.20 Ao3

115.73Ao3

112.88Ao3

117.92Ao3

System

Triclinic

Triclinic

Triclinic

Triclinic

Triclinic

From the comparative study of XRD of undoped and doped strontium oxalate crystals following conclusions can be predicated

1) The respective peaks of the undoped sample have been shifted to slightly at lower side where as the intensity of the same peak of doped samples have been increased by large amount.

2) The slight shifting in the XRD peak and large increase in the intensity may be attributed to cobalt, copper and silver doping. If the lattice parameter i.e. c is compared, it has been observed that c has been reduced and volume of doped sample have been increased as compared with undoped strontium oxalate by agar-agar gel. This manifested that change in shift in peaks, change in lattice parameters and increase in the height of respective peaks due to cobalt, copper, silver doping had not affected the structure of strontium oxalate i.e. the structure remained triclinic with small doping of cobalt, copper, silver which is expected. However cobalt doping has induced pink colour, copper doping has induced green colour and silver doping has induced yellow colour to the grown crystals.

5.4 Infrared spectroscopy

IR spectra is the characteristics of the entire molecule, it means that certain groups of atoms give rise to bands at or near the same frequency regardless of the structure of the rest of the molecule. Mostly IR spectra are used in conjunction with other spectral data to determine molecular structure of the sample under study.

In the present work IR spectra of Strontium Oxalate sample was recorded on JASCO instrument, Model 460 Plus at AISSMS College of Pharmacy, Pune, (M. S.) and University Department of Chemical Technology, North Maharashtra University, Jalgaon, (M. S.) on SHIMADZU FT-IR 8400 spectrophotometer. The spectral assignment of IR peaks are represented in table- 5.4

From IR spectra first four bands of undoped strontium oxalate crystals grown in agar-agar gel are on lower wave number, metal-oxygen bond and water of crystallization on higher wave number as compared to wave number for crystals grown in hydro-silica gel.

The IR study of undoped sample by agar- agar gel and cobalt doped sample suggested that the bands in all cases except present at the water of crystallization have been shifted to lower wavelength side where as band due to O-H stretching in both samples remain at the same wavelength i.e. 1316.18 cm-1 . In copper doped and silver doped strontium oxalate crystals the first two bands are on lower wave number while last three bands are on higher wave number as compared to undoped strontium oxalate crystals.

Table -- 5.4 Spectral assignments of the IR peaks

Assignment

Wave number (cm-1)

Undoped strontium oxalate (Hydro silica gel)

Undoped strontium oxalate (Agar-agar gel)

Cobalt doped strontium oxalate

Copper doped strontium oxalate

Silver doped strontium oxalate

O-H stretching

3428.81

3301.54

3292.86

3294.53

3289.70

C=O stretching

1788.65

1608.34

1602.56

1605.79

1604.83

O-H bending

1351.86

1316.18

1316.18

1317.43

1316.46

C-O bond

1071.26

1009.55

1006.66

1018.45

1016.52

Sr-O bond

719.318

740.317

736.674

714.65

757.09

Water of crystallization

610.36

668.214

673.035

671.25

669.32

5.5 Thermal analysis

5.5.1 Thermo-Gravimetric Analysis

TGA was carried out on Diamond TG / DTA Perkin Elmer instrument at National Chemical Laboratory, Pune, (M. S.) and at University Department of Chemical Technology, North Maharashtra University, Jalgaon, (M. S.) on SHIMADZU DSC 600, Japan. The comparisons of kinetic data analysis of undoped and doped strontium oxalate crystals are shown in table- 5.5.

Table -- 5.5 Kinetic data of TG Analysis

Compound

Step

Temperature range (oC)

% weight loss

Undoped strontium oxalate crystals (Hydro silica gel)

I

130.88 to 191.28

8.887

II

261.21 to 301.56

18.253

III

365.98 to 498.55

12.260

Undoped strontium oxalate crystals (Agar-agar gel)

I

121.00 to 240.47

7.933

II

251.19 to 256.87

18.795

III

359.94 to 497.74

11.830

Cobalt doped strontium oxalate crystals

I

114.00 to 226.74

7.828

II

239.08 to 356.31

18.717

III

368.64 to 498.84

12.379

Copper doped strontium oxalate crystals

I

114.00 to 187.29

8.961

II

245.08 to 319.69

17.461

III

365.64 to 516.84

11.648

Silver doped strontium oxalate crystals

I

115.13 to 187.20

8.633

II

240.08 to 319.94

19.149

III

369.64 to 510.84

11.941

From comparative study of TGA of undoped and doped strontium oxalate crystals predicated the following conclusion

a. All three doped strontium oxalates started deposition at less temperature comparative to undoped strontium oxalates.

b. The loss CO in doped strontium oxalates took place at lower temperature as that as undoped strontium oxalates.

c. But the loss of CO2 of doped strontium oxalates took place at higher temperature i.e. undoped strontium oxalate becomes stable at 498.55oC and 498.74oC while doped sample becomes stable at 498.84oC, 516.84oC and 510.84oC respectively.

The loss of CO2 at higher temperature and increase of stability of strontium oxalate at high temperature may be due to presence of cobalt, copper and silver impurity incorporated in the crystals.

5.5.2 Differential Thermal Analysis

DTA was carried out on Diamond TG / DTA Perkin Elmer instrument at National Chemical Laboratory, Pune, (M. S.). The comparisons of DTA of undoped and doped strontium oxalate crystals are shown in table- 5.6.

Table -- 5.6 DTA data of undoped and doped strontium oxalate crystals

Compound

Peaks Recorded

(oC)

Peak Height

(v)

Area

(v.s)

Nature

Undoped strontium oxalate crystals

(Hydro-silica gel)

185.99

-23.029

5058.205

Endothermic

293.44

10.773

-22840.144

Exothermic

505.53

20.350

-7846.491

Exothermic

Undoped strontium oxalate crystals (Agar-agar gel)

172.47

-99.791

19241.244

Endothermic

315.91

37.272

-1023.200

Exothermic

481.36

519.138

-34084.412

Exothermic

Cobalt doped strontium oxalate crystals

170.50

-86.359

15829.018

Endothermic

313.15

97.623

-7615.824

Exothermic

472.33

414.161

-33204.932

Exothermic

Copper doped strontium oxalate crystals

187.41

-25.840

12756.749

Endothermic

318.15

97.623

-7615.824

Exothermic

428.69

38.535

-16915.456

Exothermic

Silver doped strontium oxalate crystals

167.53

-65.056

10165.989

Endothermic

308.19

53.553

-6184.164

Exothermic

464.65

317.079

-20932.599

Exothermic

The above comparisons shows undoped and doped strontium oxalate crystals have a same peak that means one endothermic and other two exothermic peaks.

5.5.3 Differential Scanning Calorimetry

DSC was carried out on Perkin Elmer instrument Pyris 6 DSC at National Chemical Laboratory, Pune, (M. S.) and at University Department of Chemical Technology, North Maharashtra University, Jalgaon, (M. S.) on SHIMADZU DSC 600, Japan instrument. The comparisons of DSC measurement of undoped and doped strontium oxalate crystals are shown in table- 5.7.

Table -- 5.7 DSC measurement of undoped and doped strontium oxalate crystals

Sample

Wt. of the sample

Change in enthalpy

Transition temperature

Undoped strontium oxalate crystals (Hydro-silica gel)

7.900 mg

0.2201 KJ/mole

169.45oC

Undoped strontium oxalate crystals (Agar-agar gel)

20.800 mg

0.2141 KJ/mole

171.56oC

0.1906 KJ/mole

304.26oC

Cobalt doped strontium oxalate crystals

7.900 mg

0.2301 KJ/mole

165.92oC

0.2022 KJ/mole

298.87oC

Copper doped strontium oxalate crystals

15.700 mg

0.2545 KJ/mole

170.53oC

0.1848 KJ/mole

304.75oC

Silver doped strontium oxalate crystals

12.400 mg

0.2082 KJ/mole

165.56oC

0.1638 KJ/mole

303.85oC

From above comparisons it can be concluded that change in enthalpy and transition temperature are practically same in case of both undoped and doped samples (strontium oxalate).

5.6 Energy Dispersive Analysis by X-rays (EDAX)

Elemental analysis was carried out at Sophisticated Instrumentation Centre for

Applied Research and Testing (SICART), Sardar Patel Centre for Science and Technology, Aanand, Gujarat.

The data obtained of the undoped and doped strontium oxalate crystals grown in agar- agar gel obtained after EDAX is given in table- 5.8, which shows mass (wt) % of different elements in the sample. The presence of Sr metal is confirmed from EDAX. The observed mass (wt) % is in agreement with calculated one.

Table -- 5.8 EDAX data of undoped and doped strontium oxalate crystals

Sample

Element

Content as measured by EDAX

wt %

at %

Undoped strontium oxalate crystals

(Hydro silica gel)

C

7.83

23.85

O

20.13

46.05

Sr

72.05

30.10

Undoped strontium oxalate crystals

(Agar-agar gel)

C

12.28

32.57

O

21.84

43.48

Sr

65.88

23.95

Cobalt doped strontium oxalate crystals

C

12.88

35.33

O

18.95

39.03

Sr

68.18

25.64

Copper doped strontium oxalate crystals

C

13.01

34.37

O

21.04

41.74

Sr

65.96

23.89

Silver doped strontium oxalate crystals

C

14.80

41.69

O

14.71

31.10

Sr

70.49

27.21

5.7 Chemical Analysis

Chemical analysis of undoped and doped strontium oxalate crystals was carried out at Department of chemistry, Shri Shivaji Vidya Prasarak Santhas’s Bapusaheb Shivajirao Deore College of Engineering, Dhule, (M. S.).

The comparison of amount of strontium was found in undoped strontium oxalate crystals and cobalt, copper, silver doped strontium oxalate crystals by gravimetric and volumetric method is shown in table- 5.9.

Table -- 5.9 Chemical analysis data of undoped and doped strontium oxalate crystals

Sample

Method

Amount of Strontium in %

Estimated

Calculated

Undoped Strontium Oxalate

Gravimetric

65.45

64.40

Volumetric

64.13

Cobalt doped Strontium Oxalate

Gravimetric

66.15

Volumetric

66.08

Copper doped Strontium Oxalate

Gravimetric

66.15

Volumetric

65.33

Silver doped Strontium Oxalate

Gravimetric

67.45

Volumetric

66.27

The data obtained of the grown undoped and doped strontium oxalate crystals, which shows mass (wt) % of strontium. The presence of Sr metal is confirmed from chemical analysis. The observed mass (wt) % is in agreement with calculated one.

From the comparative study by chemical analysis and EDAX of the grown undoped and doped strontium oxalate crystals, which shows mass (wt) % of strontium. The presence of Sr metal is confirmed from chemical analysis EDAX. The observed mass (wt) % by chemical analysis means gravimetric and volumetric analysis is in agreement with EDAX as shown in table- 5.10.

Table -- 5.10 Chemical analysis and EDAX data of undoped and doped strontium oxalate crystals

Sample

Amount of Strontium in % by

Gravimetric

Volumetric

EDAX

Undoped Strontium Oxalate (Hydro silica gel)

65.45

64.13

72.05

Undoped Strontium Oxalate (Agar-agar gel)

65.45

64.13

65.88

Cobalt doped Strontium Oxalate

66.45

66.08

68.18

Copper doped Strontium Oxalate

66.15

65.33

65.96

Silver doped Strontium Oxalate

67.45

66.27

70.49

CHAPTER- VI

SCOPE FOR FUTURE WORK

Growth of the crystals has become the heart of the research due to various applications of the crystals. The development of newer and better techniques of growing large crystals and control of nucleation remains an open field to research, a lot of work remains to be done to explain the detailed nature of the gel structure.

Oxalate crystals have wide applications in electro, acousto-optical devices, synthesis of super conducting compounds. As far as strontium oxalate is concern, it is used in formation of SrTiO3, preparation of strontium salts, pyrotechnic compositions, solid state field, etc. Doping of other different metals in the growth of strontium oxalate is also another area to study the changing properties of doped grown crystals compared to undoped grown crystals. Instead of doping mixed crystals of oxalate of strontium cobalt oxalate, strontium copper oxalate, strontium silver oxalate can be grown is also another area to study.

An attempt should be made to micro topographical and etching studies using high power microscope to learn the kinetics of etching and to determine the activation energy.

The research on growth of crystals is highly interdisciplinary, since it is concerned with various branches of physics, chemistry, material sciences, etc. Also it is expected to extend future studies in the context of other properties of crystals such as electrical conductivity, magnetic properties, and change in susceptibility, which will be helpful for fulfilling the electronics engineering, mechanical engineering and industrial requirements. Research on crystal growth is industry oriented. There are two slogans, which all concerned and unconcerned with science, talk that our research should be interdisciplinary and industry oriented. Thus, research on crystal meets both the ends.