Crystal Growth Has Given New Dimension

Published Date: 02 Nov 2017

4.1 Introduction

Crystal growth has given new dimension to fulfill the need of modern technology. Natural crystals are not available in adequate quantities and also having imperfection and low purity. Synthetic crystals, prepared in the laboratory can replace these natural crystals. These synthetic crystals are pure having less imperfection and can be grown of desirable size.

With the help of gel method a lot of work has been done [35]. Afterwards several investigators have used gel method to grow various types of undoped, doped crystals and also different oxalates and characterized it, due to its simplicity of the process it can be successfully used to grow the crystals at room temperature with good control over nucleation [92-107].

For getting detail information about growing crystals, they are characterized by various techniques.

In this work, the grown strontium oxalate crystals were characterized by

X-ray diffraction (XRD)

Fourier Transform Infrared Spectroscopy (FT-IR)

Thermal analysis

Thermal Gravimetric Analysis (TGA)

Differential Thermal Analysis (DTA)

iii) Differential Scanning Calorimetry (DSC)

Chemical Analysis

i) Gravimetric

ii) Volumetric

5) Energy Dispersive Analysis by X-ray (EDAX)

6) Scanning Electron Microscope (SEM)

The present chapter describes growth of crystals of doped strontium oxalate by establishing optimum conditions and their characterization.

4.2 Gel technique

The growth of crystal in the gel method is based on the diffusion of reactant in gel. Following two techniques for the process of diffusion in gel media were employed.

Single diffusion technique.

Double diffusion technique.

These techniques are discussed in chapter I as shown in fig. 1.1 and fig. 1.2.

Both techniques were used in the present work but single diffusion technique was found to be most suitable for the growth of good quality crystals in present work. Requirements and procedure of both techniques are discussed below.

4.3 Apparatus used

Corning glass test tube

Corning glass U shape tube

Magnetic stirrer

Burette and pipette

Beaker, measuring cylinder

Specific gravity bottle, Electronic Balance

Gas (for heating), funnel, stand, glass rod, filter paper, wire gauge, cotton plug etc.

4.4 Chemical used

All are A.R. Grade as follows

Agar-agar powder

Strontium Chloride (SrCl2, 6H2O)

Strontium Nitrate [Sr(NO3)2 ]

Oxalic acid (H2C2O4)

Cobalt Chloride (CoCl2)

Silver Nitrate (AgNO3)

Copper Chloride (CuCl2)

Double Distilled Water

4.5 Chemical reaction

Strontium chloride reacts with oxalic acid and it forms strontium oxalate,

SrCl2 + H2C2O4 ï‚® SrC2O4 + 2HCl

Strontium Nitrate reacts with oxalic acid and it forms strontium oxalate,

Sr(NO3)2 + H2C2O4 ï‚® SrC2O4 + 2HNO3

4.6 Doping of different metals in the growth of strontium oxalate

Doping is done by some transition metals or metal ions by using common ion property. In order to study effect of impurity with respect to size of crystal, transparency and habit on grown crystals, the crystals of strontium oxalate were doped with some transition element as impurity.

PART-A

Growth and characterization of cobalt doped strontium oxalate crystals

4.6.1 Experimental procedure

3 to 5 gm of agar-agar powder was dissolved in to hot double distilled water mixed with 0.5 M to 1 M strontium chloride solution and measured small quantity of cobalt chloride solution was incorporated then again the mixture was stirred to make homogenous mixture. The crystallizing vessel were used essentially consist of standard glass tube of 2.5 cm inner diameter and 20 cm in length. Gelling mixture poured in glass test tubes. These tubes were hermitically sealed to prevent evaporation and contamination of the exposed surface by dust particles of atmosphere or atmospheric impurities and were kept undisturbed. The gel was usually found to set 3 to 4 days, depending on the environmental temperature. It was observed that the mixture in a glass tube was initially transparent and slowly turned light yellowish. The water slowly evaporated and gel was completely set. After ensuring firm gel setting, it was kept for aging for 3 to 4 days. After that 0.5 M to 1 M solution of oxalic acid was added as a supernatant over the set get. Nucleation was observed after 5 to 6 days and crystals started to grow. Pinkish colour, larger size, transparent and shining crystals were obtained in the gel, as shown in fig. 4.1.

4.7 Results and discussion

A series of experiments were conducted by varying the concentrations of incorporated and other reactants as well as gel setting time and gel aging time. In single diffusion, after a few days’ pinkish colour, larger size, transparent and shining crystals were obtained in the gel, as shown in fig. 4.1.

Doping leads to

Growth of better quality of crystals

Crystals were more shining and somewhat hexagonal

The grown crystals were pinkish in colour.

The colour itself indicated that the cobalt had been incorporated in the strontium oxalate crystals. More over size of the crystals had been also increased with the cobalt doping as shown in fig. 4.1. This means that cobalt doping has enhanced the growth of crystal. Hence it had been decided to grow strontium oxalate crystals with cobalt doping.

4.7.1 Optimum conditions

i) Concentration of agar-agar gel -- 3 %

ii) Concentration of reactant, strontium chloride -- 1 M

iii) Concentration of supernatant, oxalic acid -- 1 M

iv) Room temperature -- 30oC

v) Gel setting period -- 4 days

vi) Gel aging period -- 2 days

vii) Growth period -- 30 - 45 days

ix) Quality of crystals -- Pinkish colour, Larger size (1mm × 1mm) transparent, shining crystals

4.8 Characterization

4.8.1 X-ray Diffraction (XRD)

X-ray diffractogram is useful in the analysis of crystal structure. Cell parameters,‘d’ values, unit cell, volume and lattice system etc. can be evaluated by using x-ray diffractogram.

X-ray diffractogram of gel grown 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.).

CuK radiation ( = 1.54051 Ao) was used as a target material. The sample rotated in the range 5o to 80o (2). The recorded X-ray diffractogram of doped sample is shown in fig. 4.2. From these diffractogram, intensity ratio I/Io,‘d’ spacing, corresponding miller indices (h k l) of doped sample were computed as shown in table- 4.1. These calculated‘d’ values are well matched with the reported ones. (h k l) and (a b c) and system calculated by the computer program POWD (Integrative Powder Diffraction and Indexing program).These unit cell parameters and system of doped sample are shown in table- 4.1.1.These parameters satisfy the conditions for triclinic system, i.e. the grown crystals have triclinic structure with a ≠ b ≠ c and  ≠  ≠.

Table -- 4.1 XRD data of cobalt doped strontium oxalate crystals

Peak

No.

2

Deg.

FWHM

d value

Intensity

I/Io

Indices

h k l

1

31.20

0.176

2.8643

224

13

0 1 0

2

36.40

0.059

2.4661

234

13

-1 1 0

3

41.45

0.118

2.1766

218

12

1 0 1

4

43.75

0.118

2.0673

288

16

0 -1 1

5

43.95

0.118

2.0584

206

12

0 1 1

6

44.45

0.059

2.0364

211

12

-1 1 1

7

44.55

0.059

2.0321

342

19

2 0 0

11

47.60

0.118

1.9087

1859

100

-1 -1 1

13

68.80

0.118

1.3634

465

26

-1 -1 2

14

69.05

0.118

1.3590

320

18

-1 1 2

Table - 4.1.1 Unit Cells Parameters and System

Parameters

Strontium Oxalate

System

Triclinic

a

4.1951 Ao

b

2.880 Ao

c

3.053 Ao



91.146o



103.107o



96.12o

V

115.73 Ao3

4.8.2 Fourier Transform Infrared Spectroscopy (FT-IR)

Nearly all–academic and industrial laboratories make use of infrared spectroscopy as a bench tool for structural analysis. Although the IR spectra is the characteristics of the entire molecule, it turns out 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.).

The IR spectra of these gel grown Strontium Oxalate crystals were obtained in the wave number range 400-4000 cm-1 for KBr line, accumulation 70, resolution 4 cm-1, gain–auto (128), scanning speed –auto (2mm/sec.), apodization – cosine. The IR spectra obtained for the grown crystals in is shown in fig. 4.3.

IR studies on various oxalates have been carried out by several investigators [94-99].

For Cobalt Doped Strontium Oxalate

In the IR spectrum of strontium oxalate crystals, the absorption at 3292.86 cm-1 is due to O-H stretching mode and water stretch. Few bands on the small wave number side of these bands represent overtones and combination tones occurring at smaller wave number.

A strong asymmetrical band at 1602.56 cm-1 is attributed to the C=O stretch of carbonyl group.

The peak 1316.18 cm-1 is due to of plane bending O-H stretch.

The peak 1006.66 cm-1 is due to C-O stretching.

The sharp IR band observed at 857.204 cm-1 contains absorptions caused by C-C stretching.

The sharp IR peak at 736.674 cm-1 may be attributed to presence of strontium-oxygen (Sr-O mode) bond.

The absorption from 673.035 cm-1 is due to presence of water of crystallization.

Table -- 4.2 Spectral assignment of the IR peaks

Wave number (cm-1)

Assignment

3292.86

O-H Stretching

1602.56

C=O Stretching

1316.18

O-H bending

1006.66

C-O bond

736.674

metal – oxygen bond

673.035

Water of crystallization

Therefore from above discussion the structure of doped strontium oxalate may

be

O = C – O

Sr xH2O (x – unknown)

O = C – O

4.8.3 Thermal analysis

Thermal studies of certain oxalates have been reported by several investigators [27, 102, 103].

In the present work, TGA and DTA of cobalt doped strontium oxalate was carried out 30oC to 1000oC at a heating rate of 10oC / min in an atmosphere of air and the sample doped strontium oxalate hold for 1 minute at 30oC. DSC of cobalt doped strontium oxalate was carried out 30oC to 400oC at a heating rate of 10oC / min and cooled from 400oC to 30oC at the rate of 10oC / min in nitrogen. The sample cobalt doped strontium oxalate was hold for 1 minute at 30oC.

4.8.3.1 Thermo-Gravimetric Analysis (TGA)

TGA was carried out on Diamond TG / DTA Perkin Elmer instrument at National Chemical Laboratory, Pune, (M. S.).

TGA curve for cobalt doped strontium oxalate is shown in fig. 4.4.

From the thermo gram of cobalt doped strontium oxalate one can observe that

i) The compound is stable up to 114oC.

ii) 7.828% weight loss in temperature range 114oC to 226.74oC may be due to dehydration of 0.85 water molecule and there is no further weight loss up to 239.08oC

iii) 18.717% weight loss in temperature range 239.08oC to 356.31oC from the dehydrated compound corresponds to loss of CO.

iv) 12.379% weight loss in temperature range 368.64oC to 498.84oC corresponds to loss of CO2.

v) The residue remains stable from 498.84oC.

TGA data indicates that the grown crystals contains 0.85 water molecule, which is lost up to 226.74oC and dehydrated compound decomposed by loosing CO up to 356.31oC . Again the compound decomposed by loosing CO2 up to 498.84oC and after that the remaining compound remains stable. These results can be interpreted by the following thermo chemical reactions.

114oC-226.74oC

SrC2O4, 0.85 H2O SrC2O4 + 0.85H2O

Stage –I

239.08oC-356.31oC

SrC2O4 SrCO3 + CO

Stage –II

368.64oC-498.84oC

SrCO3 SrO + CO2

Stage –III

Percentage of weight loss in the different stages of decomposition of cobalt doped strontium oxalate crystals are observed as mention in table- 4.3.

Table -- 4.3 Percentage of weight loss of cobalt doped strontium oxalate crystals

Stage

Temperature

(oC)

Loss of material

Observed weight loss (%)

Calculated weight loss (%)

I

114.00 to 226.74

0.85 H2O

7.828

7.827

II

239.08 to 356.31

CO

18.717

18.711

III

368.64 to 498.84

CO2

12.379

12.361

Thus the strontium carbonate finally turns into strontium oxide at 498.84oC for doped sample which is confirmed by residual weight up to end of analysis 61.076% of SrO, which is in agreement with calculated residual weight 61.101%.

4.8.3.2 Differential Thermal Analysis (DTA)

DTA was carried out on Diamond TG / DTA Perkin Elmer instrument at National Chemical Laboratory, Pune, (M. S.).

DTA curve for cobalt doped strontium oxalate is shown in fig. 4.5.

From DTA curve of cobalt doped strontium oxalate one can observe that the loss of bulk of water of crystallization in a single peaked endothermic at 170.50oC. Complete dehydration is only on the onset of oxalate decomposition as observed. DTA curve at the peak 313.15oC and 472.33oC are characterized by an exothermic peak which shows the oxalate decomposition.

Loss of weight at the temperature relates to the loss of water of crystallization (endothermic reaction) at the range 108.36oC to 241.29oC.

Loss of weight at the temperature 313.15oC relates to release of CO and loss of weight at the temperature 472.33oC relates to release of CO2 which are exothermic in character. That means the weight loss with respect to temperature of the grown crystals was further supported by DTA results. DTA data is shown in table- 4.4.

Table -- 4.4 DTA data of cobalt doped strontium oxalate crystals

On set

(oC)

Peaks Recorded

(oC)

Peak Height (v)

Area

(v.s)

Nature

161.25

170.50

-86.359

15829.018

Endothermic

299.15

313.15

97.623

-7615.824

Exothermic

428.13

472.33

414.161

-33204.932

Exothermic

4.8.3.3 Differential Scanning Calorimetry (DSC)

DSC was carried out on Perkin Elmer instrument Pyris 6 DSC at National Chemical Laboratory, Pune and at UDCT, North Maharashtra University, Jalgaon on SHIMADZU DSC 600, Japan.

DSC curves are shown in fig. 4.6 for cobalt doped strontium oxalate by agar-agar gel.

From DSC curve of cobalt doped strontium oxalate by agar-agar gel one can

observe that:

Step-I

The initiation temperature is 125.04oC and equilibrium temperature is 224.21oC. At 125.04oC initiation of phase change start and phase change is completed at peak endo-down temperature 165.92oC. The temperature at which the sample and reference come to the thermal equilibrium by thermal diffusion appears to be at 224.21oC.

Area under the curve is 1817.697 mJ.

Heat of transition ΔH i.e. enthalpy change of transition is 230.0882 J/gm; this is 0.2301 KJ/mole. Since molecular weight is 1 gm/mole.

Therefore, ΔHtr = ΔHf

Hence heat of phase formation is also 0.2301 KJ/mole.

Where ΔHf is enthalpy change of new phase formation or it is called heat of phase formation.

Step-II

The initiation temperature is 232.98oC and equilibrium temperature is 358.89oC. At 232.98oC initiation of phase change start and phase change is completed at peak endo-down temperature 298.87oC. The temperature at which the sample and reference come to the thermal equilibrium by thermal diffusion appears to be at 358.89oC.

Area under the curve is 1597.553 mJ.

Heat of transition ΔH i.e. enthalpy change of transition is 202.2218 J/gm; this is 0.2202 KJ/mole. Since molecular weight is 1 gm/mole.

Therefore, ΔHtr = ΔHf

Hence heat of phase formation is also 0.2202 KJ/mole.

Where ΔHf is enthalpy change of new phase formation or it is called heat of phase formation.

In the DSC study the two endothermic stages were obtained at 165.92oC and 298.87oC respectively. The result of DSC measurement is presented in the table- 4.5.

Table -- 4.5 DSC measurement of cobalt doped strontium oxalate crystals

Sample

Wt of the sample

Change in enthalpy ΔHf

Transition temperature

Cobalt doped Strontium Oxalate

7.900 mg

0.2301 KJ/mole

165.92oC

0.2022 KJ/mole

298.87oC

4.8.4 Chemical analysis

Chemical analysis was carried out at Department of chemistry, Shri Shivaji Vidya Prasarak Santhas’s Bapusaheb Shivajirao Deore College of Engineering, Dhule.

1. Gravimetric method

Strontium is quantitatively estimated as strontium sulphate, from the grown crystals of strontium oxalate. 1gm of crystals were dissolved in hydrochloric acid and diluted to 100 ml with distilled water. In a boiling solution slight excess of hot 0.5 M sulphuric acid solution was added slowly with constant stirring and precipitate was filtered in a weighted porcelain- filter crucible, washed with hot acidified water and then with warm distilled water . It was dried in electric muffle furnace at 600oC and allowed to cool and take the weight.

The estimated amount of strontium was found 66.45 % in the grown crystals by gravimetric analysis is in agreement with the calculated amount of strontium, (64.40%) in SrC2O4, 0.85H2O.

2. Volumetric Analysis

Strontium is quantitatively estimated volumetrically using standard EDTA solutions. 0.0130 gm of strontium oxalate crystals were dissolved in 100 ml de-ionized water with few drops of HCL (0.01N solution). 25 ml of this solution was pipette in a titration flask, 12.1 pH was adjusted by the addition of 1 M sodium hydroxide solution in it and Eriochrome black T was added as an indicator. It was titrated with 0.01 N (standard) EDTA solutions until the colour changed from blue to gray.

1mole EDTA = 1 mole Sr2+

i.e. 1000 ml 1 mole EDTA contain 87.63 gm strontium

As 25 ml pipette solution required 24.5 ml 0.01N, EDTA

100 ml solution required = 98.0, 0.01 N EDTA

As 1000 ml 0.01N EDTA = 0.08763 gm Sr2+

98.0, 0.01N EDTA = 0.008588 gm Sr2+

As 0.0130 gm of strontium oxalate solution = 0.008588 gm strontium

100 gm of strontium oxalate solution contains = 66.08 gm strontium

Thus the volumetric estimation of strontium in the grown crystals was found to be 66.08%. This is matched with the calculated amount (64.40%) of strontium in SrC2O4, 0.85 H2O.

4.8.5 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 graph of the sample cobalt doped strontium oxalate grown in agar-agar

gel obtained after EDAX is shown in fig.4.7 and the data obtained is given in table- 4.6, 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 -- 4.6 EDAX data of cobalt doped strontium oxalate crystals

Element

Content as measured by EDAX

wt %

at %

C

12.88

35.33

O

18.95

39.03

Sr

68.18

25.64

4.8.6 Scanning Electron Microscope (SEM)

In present work Scanning Electron Microscope (SEM) studies of gel grown cobalt doped strontium oxalate crystals by agar-agar gel are done by using latest computerized scanning electron microscope Quanta 200 3D at National Chemical Laboratory, Pune, (M. S.). The successive photographs were taken at magnification of 250×, 1000×, 2500× and 5000× at width 14.0 mm, 14.1 mm respectively and at high voltage 20 KV as shown in fig. 4.8 (a, b, c, d).

The surface of the crystals of gel grown strontium oxalate doped with cobalt is shown by fig. (a). The figure shows the presence of triangular growth hillocks at the edges and pentagonal growth hillocks at the middle of the surface. The growth layers forming the triangular growth hillocks at the edges are clearly visible. The growth layers forming the growth hillocks are sharp and parallel to each other of the respective edges.

The magnified version of some portion of fig. (a) is shown in fig. (b) at 1000×. The magnified version of the portion of fig. (b) at 2500× is shown by A1 in fig. (c) and the magnified version of the portion B of fig. (c) is shown by portion B1 in fig. (d) at 5000×. Fig. (c) and (d) shows the presence of well defined oriented triangular edge pits at the various portion. The formation of edge pits indicates controlled etching during the growth.

4.9 Experimental procedure

3 to 5 gm of agar-agar powder was dissolved in to hot double distilled water mixed with 0.5 M to 1 M strontium chloride solution and measured small quantity of copper chloride solution was incorporated then again the mixture was stirred to make homogenous mixture. The crystallizing vessel were used essentially consist of standard glass tube of 2.5 cm inner diameter and 20 cm in length. Gelling mixture poured in glass test tubes. These tubes were hermitically sealed to prevent evaporation and contamination of the exposed surface by dust particles of atmosphere or atmospheric impurities and were kept undisturbed. The gel was usually found to set 3 to 4 days, depending on the environmental temperature. It was observed that the mixture in a glass tube was initially transparent and slowly turned light greenish. The water slowly evaporated and gel was completely set. After ensuring firm gel setting, it was kept for aging for 3 to 4 days. After that 0.5 M to 1 M solution of oxalic acid was added as a supernatant over the set get. Nucleation was observed after 5 to 6 days and crystals started to grow. Greenish colour, larger size, transparent, shining crystals were obtained in the gel, as shown in fig. 4.9.

4.10 Results and discussion

A series of experiments were conducted by varying the concentrations of incorporated and other reactants as well as gel setting time and gel aging time. In single diffusion, after a few days’ greenish colour, larger size, transparent and shining crystals were obtained in the gel, as shown in fig. 4.9.

Doping leads to

Growth of better quality of crystals

Crystals were more shining

The grown crystals were greenish in colour.

The colour itself indicated that the copper had been incorporated in the strontium oxalate crystals. More over size of the crystals had been also increased with the copper doping as shown in fig. 4.9. This means that copper doping has enhanced the growth of crystal. Hence it had been decided to grow strontium oxalate crystals with copper doping.

4.10.1 Optimum conditions

i) Concentration of agar-agar gel -- 3 %

ii) Concentration of reactant, strontium chloride -- 1 M

iii) Concentration of supernatant, oxalic acid -- 1 M

iv) Room temperature -- 30oC

v) Gel setting period -- 4 days

vi) Gel aging period -- 2 days

vii) Growth period -- 30 - 45 days

ix) Quality of crystals -- Greenish colour, Larger size (1mm×1mm) transparent, shining crystals

4.11 Characterization

4.11.1 X-ray Diffraction (XRD)

X-ray diffractogram is useful in the analysis of crystal structure. Cell parameters, ‘d’ values, unit cell, volume and lattice system etc. can be evaluated by using x-ray diffractogram.

X-ray diffractogram of gel grown 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.).

CuKa radiation (l = 1.54051 Ao) was used as a target material. The sample rotated in the range 5o to 80o (2q). The recorded X-ray diffractogram of doped sample is shown in fig. 4.10. From these diffractogram, intensity ratio I/Io, ‘d’ spacing, corresponding miller indices (h k l) of doped sample were computed as shown in table- 4.7. These calculated ‘d’ values are matched with the reported ones. (h k l) and (a b c) and system calculated by the computer program POWD (Integrative Powder Diffraction and Indexing program).

These unit cell parameters and system of doped sample are shown in table- 4.7.1.

These parameters satisfy the conditions for triclinic system, i.e. the grown crystals have triclinic structure with a ≠ b ≠ c and a ≠ b ≠g.

Table – 4.7 XRD data of copper doped strontium oxalate crystals

Peak

No.

2q

Deg.

FWHM

d value

Intensity

I/Io

Indices

h k l

1

26.20

0.235

3.3984

65

30

0 1 0

2

28.80

0.235

3.0973

65

30

1 1 0

3

30.00

0.235

2.9760

218

100

-1 0 1

4

33.10

0.235

2.7041

52

24

1 0 1

5

34.20

0.235

2.6196

57

26

-1 -1 1

6

35.00

0.235

2.5615

51

24

1 -1 1

8

37.00

0.235

2.4275

58

27

-2 -1 1

9

37.60

0.235

2.3901

72

34

2 0 1

10

43.10

0.235

2.0970

60

28

5 0 0

18

50.70

0.235

1.7990

90

42

4 0 1

20

54.40

0.235

1.6851

69

32

-1 -2 1

23

56.10

0.235

1.6380

94

44

1 2 0

26

58.60

0.235

1.5739

72

33

3 -2 1

Table – 4.7.1 Unit Cells Parameters and System

Parameters

Strontium Oxalate

System

Triclinic

a

10.7393 Ao

b

3.5952 Ao

c

3.1260 Ao

a

106.951 o

b

98.348 o

g

95.893 o

V

112.88 Ao3

4.11.2 Fourier Transform Infrared Spectroscopy (FT-IR)

Nearly all–academic and industrial laboratories make use of infrared spectroscopy as a bench tool for structural analysis. Although the IR spectra is the characteristics of the entire molecule, it turns out 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. An IR spectrum in conjunction with other spectral data is to determine molecular structure of the sample under study.

In the present work IR spectra of Strontium Oxalate sample was recorded on SHIMADZU FT-IR 8400 spectrophotometer at University Department of Chemical Technology, North Maharashtra University, Jalgaon, (M. S.).

The IR spectra of these gel grown Strontium Oxalate crystals were obtained in the wave number range 400 – 4000 cm-1 for KBr line, accumulation 70, resolution 4 cm-1, gain–auto (128), scanning speed –auto (2mm/sec.), apodization – cosine. The IR spectra obtained for the grown crystal is as shown in fig. 4.11.

IR studies on various oxalates have been carried out by several investigators [94-99].

For Copper Doped Strontium Oxalate

In the IR spectrum of strontium oxalate crystals, the absorption at 3294.53 cm-1 is due to O-H stretching mode and water stretch. Few bands on the small wave number side of these bands represent overtones and combination tones occurring at smaller wave number.

A strong asymmetrical band at 1605.79 cm-1 is attributed to the C=O

stretch of carbonyl group.

The peak 1317.43 cm-1 is due to of plane bending O-H stretch.

The peak 1018.45 cm-1 is due to C-O stretching.

The sharp IR band observed at 800.49 cm-1 contains absorptions caused by C-C stretching.

The sharp IR peak at 714.65 cm-1 may be attributed to presence of strontium-oxygen (Sr-O mode) bond.

The absorption from 671.25 cm-1 is due to presence of water of crystallization.

Table – 4.8 Spectral assignment of the IR peaks

Wave number (cm-1)

Assignment

3294.53

O-H Stretching

1605.79

C=O Stretching

1317.43

O-H bending

1018.45

C-O bond

714.65

metal – oxygen bond

671.25

Water of crystallization

Therefore from above discussion the structure of doped strontium oxalate may be

O = C – O

Sr xH2O (x – unknown)

O = C – O

4.11.3 Thermal analysis

Thermal studies of certain oxalates have been reported by several investigators [27, 102, 103].

In the present work, TGA of copper doped strontium oxalate was carried out 30oC to 600oC and DTA was carried out 30oC to 1000oC at a heating rate of 10oC / min in an atmosphere of air and the sample copper doped strontium oxalate hold for 1 minute at 30oC. DSC of copper doped strontium oxalate was carried out 30oC to 400oC at a heating rate of 10oC / min and cooled from 400oC to 30oC at the rate of 10oC / min in nitrogen. The sample copper doped strontium oxalate was hold for 1 minute at 30oC.

4.11.3.1 Thermo-Gravimetric Analysis (TGA)

TGA was carried out on SHIMADZU DSC 600, Japan instrument at University Department of Chemical Technology, North Maharashtra University, Jalgaon, (M. S.).

TGA curve for copper doped strontium oxalate is shown in fig. 4.12.

From the thermogram of copper doped strontium oxalate one can observe that

i) The compound is stable up to 114.00oC.

ii) 7.828% weight loss in temperature range 114.00oC to 187.29oC may be due to dehydration of 0.85 water molecule and there is no further weight loss up to 245.08oC

18.717% weight loss in temperature range 245.08oC to 319.69oC from the dehydrated compound corresponds to loss of CO.

iv) 12.379% weight loss in temperature range 365.64oC to 516.84oC corresponds to loss of CO2.

The residue remains stable from 516.84oC.

TGA data indicates that the grown crystals contains 0.85 water molecule, which is lost up to 187.29oC and dehydrated compound decomposed by loosing CO up to 319.69oC. Again the compound decomposed by loosing CO2 up to 516.84oC and after that the remaining compound remains stable. These results can be interpreted by the following thermo chemical reactions.

114.00oC-187.29oC

SrC2O4, 0.85 H2O SrC2O4 + 0.85H2O

Stage -I

245.08oC-319.69oC

SrC2O4 SrCO3 + CO

Stage –II

365.64oC-516.84oC

SrCO3 SrO + CO2

Stage –III

Percentage of weight loss in the different stages of decomposition of doped strontium oxalate crystals are observed as mention in table- 4.9.

Table - 4.9 Percentage of weight loss of copper doped strontium oxalate crystals

Stage

Temperature

(oC)

Loss of material

Observed weight loss (%)

Calculated weight loss (%)

I

114.00 to 187.29

0.85 H2O

8.961

7.827

II

245.08 to 319.69

CO

17.461

18.711

III

365.64 to 516.84

CO2

11.648

12.361

Thus the strontium carbonate finally turns into strontium oxide at 516.84oC for doped sample which is confirmed by residual weight up to end of analysis 61.930% of SrO, which is in good agreement with calculated residual weight 61.101%.

4.11.3.2 Differential Thermal Analysis (DTA)

DTA was carried out on Diamond TG / DTA Perkin Elmer instrument at National Chemical Laboratory, Pune, (M. S.)

DTA curve for copper doped strontium oxalate is shown in fig. 4.13.

From DTA curve of copper doped strontium oxalate one can observe that the loss of bulk of water of crystallization in a single peaked endothermic at 187.41oC. Complete dehydration is only on the onset of oxalate decomposition as observed. DTA curve at the peak 318.15oC and 428.69oC are characterized by an exothermic peak which shows the oxalate decomposition.

Loss of weight at the temperature relates to the loss of water of crystallization (endothermic reaction) at the range 104.67oC to 241.41oC.

Loss of weight at the temperature 318.15oC relates to release of CO and loss of weight at the temperature 428.69oC relates to release of CO2 which are exothermic in character. That means the weight loss with respect to temperature of the grown crystals was further supported by DTA results. DTA data is shown in table- 4.10.

Table - 4.10 DTA data of copper doped strontium oxalate crystals

On set

(oC)

Peaks Recorded

(oC)

Peak Height (mv)

Area

(mv.s)

Nature

132.60

187.41

-25.840

12756.749

Endothermic

290.15

318.15

97.623

-7615.824

Exothermic

377.89

428.69

38.535

-16915.456

Exothermic

4.11.3.3 Differential Scanning Calorimetry (DSC)

DSC was carried out on Perkin Elmer instrument Pyris 6 DSC at

National Chemical Laboratory, Pune, (M. S.).

DSC curves are shown in fig. 4.14 for copper doped strontium oxalate by agar-agar gel.

From DSC curve of copper doped strontium oxalate by agar-agar gel one

can observe that:

Step-I

The initiation temperature is 138.80oC and equilibrium temperature is 223.83oC. At 138.80oC initiation of phase change start and phase change is completed at peak endo-down temperature 170.53oC. The temperature at which the sample and reference come to the thermal equilibrium by thermal diffusion appears to be at 223.83oC.

Area under the curve is 3995.665 mJ.

Heat of transition ΔH i.e. enthalpy change of transition is 254.5010 J/gm; this is 0.2545 KJ/mole. Since molecular weight is 1 gm/mole.

Therefore, ΔHtr = ΔHf

Hence heat of phase formation is also 0.2545 KJ/mole.

Where ΔHf is enthalpy change of new phase formation or it is called heat of phase formation.

Step-II

The initiation temperature is 248.21oC and equilibrium temperature is 361.19oC. At 248.21oC initiation of phase change start and phase change is completed at peak endo-down temperature 304.75oC. The temperature at which the sample and reference come to the thermal equilibrium by thermal diffusion appears to be at 361.19oC.

Area under the curve is 2900.849 mJ.

Heat of transition ΔH i.e. enthalpy change of transition is 184.7675 J/gm; this is 0.1848 KJ/mole. Since molecular weight is 1 gm/mole.

Therefore, ΔHtr = ΔHf

Hence heat of phase formation is also 0.1848 KJ/mole.

Where ΔHf is enthalpy change of new phase formation or it is called heat of phase formation.

In the DSC study the two endothermic stages were obtained at 170.53oC and 304.75oC respectively. The result of DSC measurement is presented in the table- 4.11.

Table - 4.11 DSC measurements of copper doped strontium oxalate crystals

Sample

Wt of the sample

Change in enthalpy ΔHf

Transition temperature

Copper doped Strontium Oxalate

15.700 mg

0.2545 KJ/mole

170.53oC

0.1848 KJ/mole

304.75oC

4.11.4 Chemical analysis

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

1. Gravimetric method

Strontium is quantitatively estimated as strontium sulphate, from the grown crystals of strontium oxalate. 1gm of crystals were dissolved in hydrochloric acid and diluted to 100 ml with distilled water. In a boiling solution slight excess of hot 0.5 M sulphuric acid solution was added slowly with constant stirring and precipitate was filtered in a weighted porcelain- filter crucible, washed with hot acidified water and then with warm distilled water . It was dried in electric muffle furnace at 600oC and allowed to cool and take the weight.

The estimated amount of strontium was found 65.15 % in the grown crystals by gravimetric analysis is in agreement with the calculated amount of strontium, (64.40%) in SrC2O4, 0.85H2O.

2. Volumetric Analysis

Strontium is quantitatively estimated volumetrically using standard EDTA solutions. 0.0132 gm of strontium oxalate crystals were dissolved in 100 ml de-ionized water with few drops of HCL (0.01N solution). 25 ml of this solution was pipette in a titration flask, 12.1 pH was adjusted by the addition of 1M sodium hydroxide solution in it and Eriochrome black T was added as an indicator. It was titrated with 0.01 N (standard) EDTA solutions until the colour changed from blue to gray.

1mole EDTA = 1 mole Sr2+

i.e. 1000 ml 1 mole EDTA contain 87.63 gm strontium

As 25 ml pipette solution required 24.6 ml 0.01N, EDTA

\100 ml solution required = 98.4, 0.01 N EDTA

As 1000 ml 0.01N EDTA = 0.08763 gm Sr2+

\98.4, 0.01N EDTA = 0.008623 gm Sr2+

As 0.0132 gm of strontium oxalate solution = 0.008623 gm strontium

\100 gm of strontium oxalate solution contains = 64.13 gm strontium

Thus the volumetric estimation of strontium in the grown crystals was found to be 65.33%. This is matched with the calculated amount (64.40%) of strontium in SrC2O4, 0.85 H2O.

4.11.5 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 graph of the sample copper doped strontium oxalate grown in agar-agar

gel obtained after EDAX is shown in fig.4.15 and the data obtained is given in table- 4.6, 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 -- 4.12 EDAX data of copper doped strontium oxalate crystals

Element

Content as measured by EDAX

wt %

at %

C

13.01

34.37

O

21.04

41.74

Sr

65.96

23.89

4.11.6 Scanning Electron Microscope (SEM)

In present work Scanning Electron Microscope (SEM) studies of gel grown copper doped strontium oxalate crystals by agar-agar gel are done by using latest computerized scanning electron microscope Quanta 200 3D at National Chemical Laboratory, Pune, (M. S.). The successive photographs were taken at magnification of 1000×, 2000×, 5000× and 10000× at common width 15.0 mm and at high voltage 20 KV as shown in fig. 4.16 (a, b, c, d).

In fig. (a), the whole surface of gel grown strontium oxalate crystals doped with copper is dark but in within the surface white irregular geometrical images are seen. No particular shape can be assigned to any white patch at magnification 1000×. But if the portion A in fig. (a) is examined at higher magnification 2000× as shown in fig. (b), the magnified version of A of fig. (a) is shown by A1 in fig. (b). They are seem to be two small portion of A are seem to be pentagon in the portion A1 in Fig. (b). In fig. (a) and (b) no difference in intensities if the portion is dark or white that means the surface is optically uniform. If the portion B in fig. (a) is magnified it is shown by portion B1 in fug. (b). It also shows better geometrical shape comparative to B.

If the portion B1 in fig. (b) is successively magnified it represented by portion B2 and B3 in fig. (c) and (d) respectively. Both fig. (c) and (d) shows better geometrical shapes compare to B1. It is also seen that the figures have well defined boundaries with irregular shapes even at magnification 5000× and 10000× shown in fig. (c) and (d). There is no attachment of microcrystal’s on the figures shown by portion B2 and B3. This manifest that the growth condition of copper doped strontium oxalate crystals are somewhat controlled.

4.12 Experimental procedure

3 to 5 gm of agar-agar powder was dissolved in to hot double distilled water mixed with 0.5 M to 1 M strontium nitrate solution and measured small quantity of silver nitrate solution was incorporated then again the mixture was stirred to make homogenous mixture. The crystallizing vessel were used essentially consist of standard glass tube of 2.5 cm inner diameter and 20 cm in length. Gelling mixture poured in glass test tubes. These tubes were hermitically sealed to prevent evaporation and contamination of the exposed surface by dust particles of atmosphere or atmospheric impurities and were kept undisturbed. The gel was usually found to set 3 to 4 days, depending on the environmental temperature. It was observed that the mixture in a glass tube was initially transparent and slowly turned light yellowish. The water slowly evaporated and gel was completely set. After ensuring firm gel setting, it was kept for aging for 3 to 4 days. After that 0.5 M to 1 M solution of oxalic acid was added as a supernatant over the set get. Nucleation was observed after 5 to 6 days and crystals started to grow. Yellowish colour, larger size, transparent and shining crystals were obtained in the gel, as shown in fig. 4.17.

4.13 Results and discussion

A series of experiments were conducted by varying the concentrations of incorporated and other reactants as well as gel setting time and gel aging time. In single diffusion, after a few days’ yellowish colour, larger size, transparent and shining crystals were obtained in the gel, as shown in fig. 4.17.

Doping leads to

Growth of better quality of crystals

Crystals were more shining and somewhat hexagonal

The grown crystals were yellowish in colour.

The colour itself indicated that the silver had been incorporated in the strontium oxalate crystals. More over size of the crystals had been also increased with the silver doping as shown in fig. 4.17. This means that silver doping has enhanced the growth of crystal. Hence it had been decided to grow strontium oxalate crystals with silver doping.

4.13.1 Optimum conditions

i) Concentration of agar-agar gel -- 3 %

ii) Concentration of reactant, strontium nitrate -- 1 M

iii) Concentration of supernatant, oxalic acid -- 1 M

iv) Room temperature -- 30oC

v) Gel setting period -- 4 days

vi) Gel aging period -- 2 days

vii) Growth period -- 30 - 45 days

ix) Quality of crystals -- Yellowish colour, larger size (1mm × 1mm) transparent, shining crystals

4.14 Characterization

4.14.1 X-ray Diffraction (XRD)

X-ray diffractogram is useful in the analysis of crystal structure. Cell parameters, ‘d’ values, unit cell, volume and lattice system etc. can be evaluated by using x-ray diffractogram.

X-ray diffractogram of gel grown 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.).

CuK radiation ( = 1.54051 Ao) was used as a target material. The sample rotated in the range 5o to 80o (2). The recorded X-ray diffractogram of doped sample is shown in fig. 4.18. From these diffractogram, intensity ratio I/Io, ‘d’ spacing, corresponding miller indices (h k l) were computed as shown in table- 4.13.

These calculated‘d’ values are well matched with the reported ones. (h k l ) and (a b c) and system calculated by the computer program POWD (Integrative Powder Diffraction and Indexing program).

These unit cell parameters and system of doped sample are shown in table- 4.13.1.

These parameters satisfy the conditions for triclinic system, i.e. the grown crystals have triclinic structure with a ≠ b ≠ c and  ≠  ≠ .

Table – 4.13 XRD data of silver doped strontium oxalate crystals

Peak

No.

2

Deg.

FWHM

d value

Intensity

I/Io

Indices

h k l

1

20.80

0.353

4.2669

40

30

0 1 0

2

23.50

0.353

3.7824

43

33

-1 1 0

3

24.30

0.353

3.6597

41

31

1 1 0

4

28.00

0.471

3.1839

49

37

-1 0 1

5

28.70

0.353

3.1078

47

35

1 0 1

6

30.10

0.353

2.9664

124

92

-1 -1 1

9

35.70

0.353

2.5129

59

44

2 0 1

10

36.60

0.353

2.4531

135

100

2 -1 1

15

42.30

0.353

2.1348

74

55

0 2 0

17

45.60

0.471

1.9877

50

71

3 -1 1

19

52.10

0.588

1.7539

102

76

1 -1 2

20

53.60

0.353

1.7083

73

54

4 1 0

26

59.40

0.353

1.5546

54

40

2 0 2

Table – 4.13.1 Unit Cells Parameters and System

Parameters

Strontium Oxalate

System

Triclinic

a

7.5980 Ao

b

4.4930 Ao

c

3.6381Ao



108.126 o



91.208 o



91.726 o

V

117.92 Ao3

4.14.2 Fourier Transform Infrared Spectroscopy (FT-IR)

Nearly all–academic and industrial laboratories make use of infrared spectroscopy as a bench tool for structural analysis. Although the IR spectra is the characteristics of the entire molecule, it turns out 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. An IR spectrum in conjunction with other spectral data is to determine molecular structure of the sample under study.

In the present work IR spectra of Strontium Oxalate sample was recorded on SHIMADZU FT-IR 8400 spectrophotometer at University Department of Chemical Technology, North Maharashtra University, Jalgaon, (M. S.).

The IR spectra of these gel grown Strontium Oxalate crystals were obtained in the wave number range 400 – 4000 cm-1 for KBr line, accumulation 70, resolution 4 cm-1, gain–auto (128), scanning speed –auto (2mm/sec.), apodization – cosine. The IR spectra obtained for the grown crystal is as shown in fig. 4.19.

IR studies on various oxalates have been carried out by several investigators [94-99].

For Silver Doped Strontium Oxalate

In the IR spectrum of strontium oxalate crystals, the absorption at 3289.70 cm-1 is due to O-H stretching mode and water stretch. Few bands on the small wave number side of these bands represent overtones and combination tones occurring at smaller wave number.

A strong asymmetrical band at 1604.83 cm-1 is attributed to the C=O stretch of carbonyl group.

The peak 1316.46 cm-1 is due to of plane bending O-H stretch.

The peak 1016.52 cm-1 is due to C-O stretching.

The sharp IR band observed at 857.204 cm-1 contains absorptions caused

by C-C stretching.

The sharp IR peak at 757.09 cm-1 may be attributed to presence of strontium-oxygen (Sr-O mode) bond.

The absorption from 669.32 cm-1 is due to presence of water of crystallization.

Table – 4.14 Spectral assignments of the IR peaks

Wave number (cm-1)

Assignment

3289.70

O-H Stretching

1604.83

C=O Stretching

1316.46

O-H bending

1016.52

C-O bond

757.09

metal – oxygen bond

669.32

Water of crystallization

Therefore from above discussion the structure of doped strontium oxalate may be

O = C – O

Sr xH2O (x – unknown)

O = C – O

4.14.3 Thermal analysis

Thermal studies of certain oxalates have been reported by several investigators [27, 102, 103].

In the present work, TGA of silver doped strontium oxalate was carried out 30oC to 600oC and DTA was carried out 30oC to 1000oC at a heating rate of 10oC / min in an atmosphere of air and the sample silver doped strontium oxalate hold for 1 minute at 30oC. DSC of silver doped strontium oxalate was carried out 30oC to 400oC at a heating rate of 10oC / min and cooled from 400oC to 30oC at the rate of 10oC / min in nitrogen. The silver doped strontium oxalate was hold for 1 minute at 30oC.

4.14.3.1 Thermo-Gravimetric Analysis (TGA)

TGA was carried out on SHIMADZU DSC 600, Japan instrument at University Department of Chemical Technology, North Maharashtra University, Jalgaon, (M. S).

TGA curve for silver doped strontium oxalate shown in fig. 4.20.

From the thermogram of silver doped strontium oxalate one can observe that

i) The compound is stable up to 115.13oC.

ii) 7.828% weight loss in temperature range 115.13oC to 187.20oC may be

due to dehydration of 0.85 water molecule and there is no further weight

loss up to 240.08oC.

iii) 18.717% weight loss in temperature range 240.08oC to 319.94oC from the

dehydrated compound corresponds to loss of CO.

iv) 12.379% weight loss in temperature range 369.64oC to 510.84oC

corresponds to loss of CO2.

v) The residue remains stable from 510.84oC.

TGA data indicates that the grown crystals contains 0.85 water molecule, which is lost up to 187.20oC and dehydrated compound decomposed by loosing CO up to 319.94oC. Again the compound decomposed by loosing CO2 up to 510.84oC and after that the remaining compound remains stable. These results can be interpreted by the following thermo chemical reactions.

115.13oC-187.20oC

SrC2O4, 0.85 H2O SrC2O4 + 0.85H2O

Stage -I

240.08oC-319.94oC

SrC2O4 SrCO3 + CO

Stage –II

369.64oC-510.84oC

SrCO3 SrO + CO2

Stage –III

Percentage of weight loss in the different stages of decomposition of doped strontium oxalate crystals are observed as mention in table- 4.15.

Table - 4.15 Percentage of weight loss of silver doped strontium oxalate crystals

Stage

Temperature

(oC)

Loss of material

Observed weight loss (%)

Calculated weight loss (%)

I

115.13 to 187.20

0.85 H2O

8.633

7.827

II

240.08 to 319.94

CO

19.149

18.711

III

369.64 to 510.84

CO2

11.941

12.361

Thus the strontium carbonate finally turns into strontium oxide at 510.84oC for doped sample which is confirmed by residual weight up to end of analysis 60.277% of SrO, which is in good agreement with calculated residual weight 61.101%.

4.14.3.2 Differential Thermal Analysis (DTA)

DTA was carried out on Diamond TG / DTA Perkin Elmer instrument at National Chemical Laboratory, Pune, (M. S.).

DTA curve for silver doped strontium oxalate is shown in fig.4.21.

From DTA curve of silver doped strontium oxalate one can observe that the loss of bulk of water of crystallization in a single peaked endothermic at 167.53oC. Complete dehydration is only on the onset of oxalate decomposition as observed. DTA curve at the peak 308.19oC and 464.65oC are characterized by an exothermic peak which shows the oxalate decomposition.

Loss of weight at the temperature relates to the loss of water of crystallization (endothermic reaction) at the range 111.55oC to 242.39oC.

Loss of weight at the temperature 308.19oC relates to release of CO and loss of weight at the temperature 464.65oC relates to release of CO2 which are exothermic in character. That means the weight loss with respect to temperature of the grown crystals was further supported by DTA results. DTA data is shown in table- 4.16.

Table - 4.16 DTA data of silver doped strontium oxalate crystals

On set

(oC)

Peaks Recorded

(oC)

Peak Height (v)

Area

(v.s)

Nature

158.24

167.53

-65.056

10165.989

Endothermic

291.67

308.19

53.553

-6184.164

Exothermic

414.28

464.65

317.079

-20932.599

Exothermic

4.14.3.3 Differential Scanning Calorimetry (DSC)

DSC was carried out on Perkin Elmer instrument Pyris 6 DSC at National Chemical Laboratory, Pune, (M. S.).

DSC curves are shown in fig. 4.22 for silver doped strontium oxalate by agar-agar gel.

From DSC curve of silver doped strontium oxalate by agar-agar gel one can

observe that:

Step-I

The initiation temperature is 109.22oC and equilibrium temperature is 218.03oC. At 109.22oC initiation of phase change start and phase change is completed at peak endo-down temperature 165.56oC. The temperature at which the sample and reference come to the thermal equilibrium by thermal diffusion appears to be at 218.03oC.

Area under the curve is 2581.086 mJ.

Heat of transition ΔH i.e. enthalpy change of transition is 208.1521 J/gm; this is 0.2082 KJ/mole. Since molecular weight is 1 gm/mole.

Therefore, ΔHtr = ΔHf

Hence heat of phase formation is also 0.2082 KJ/mole.

Where ΔHf is enthalpy change of new phase formation or it is called heat of phase formation.

Step-II

The initiation temperature is 245.83oC and equilibrium temperature is 367.06oC. At 245.83oC initiation of phase change start and phase change is completed at peak endo-down temperature 303.85oC. The temperature at which the sample and reference come to the thermal equilibrium by thermal diffusion appears to be at 367.06oC.

Area under the curve is 2031.542 mJ.

Heat of transition ΔH i.e. enthalpy change of transition is 163.8340 J/gm; this is 0.1638 KJ/mole. Since molecular weight is 1 gm/mole.

Therefore, ΔHtr = ΔHf

Hence heat of phase formation is also 0.1638 KJ/mole.

Where ΔHf is enthalpy change of new phase formation or it is called heat of phase formation.

In the DSC study the two endothermic stages were obtained at 165.56oC and 303.85oC respectively. The result of DSC measurement is presented in the table- 4.17.

Table -- 4.17 DSC measurement of silver doped strontium oxalate crystals

Sample

Wt of the sample

Change in enthalpy ΔHf

Transition temperature

Silver doped Strontium Oxalate

12.400 mg

0.2082 KJ/mole

165.56oC

0.1638 KJ/mole

303.85oC

4.14.4 Chemical analysis

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

1. Gravimetric method

Strontium is quantitatively estimated as strontium sulphate, from the grown crystals of strontium oxalate. 1 gm of crystals were dissolved in hydrochloric acid and diluted to 100 ml with distilled water. In a boiling solution slight excess of hot 0.5 M sulphuric acid solution was added slowly with constant stirring and precipitate was filtered in a weighted porcelain- filter crucible, washed with hot acidified water and then with warm distilled water . It was dried in electric muffle furnace at 600oC and allowed to cool and take the weight.

The estimated amount of strontium was found 67.45 % in the grown crystals by gravimetric analysis is in agreement with the calculated amount of strontium, (64.40%) in SrC2O4, 0.85H2O.

2. Volumetric Analysis

Strontium is quantitatively estimated volumetrically using standard EDTA solutions. 0.0128 gm of strontium oxalate crystals were dissolved in 100 ml de-ionized water with few drops of HCL (0.01N solution). 25 ml of this solution was pipette in a titration flask, 12.1 pH was adjusted by the addition of 1M sodium hydroxide solution in it and Eriochrome black T was added as an indicator. It was titrated with 0.01 N (standard) EDTA solutions until the colour changed from blue to gray.

1mole EDTA = 1 mole Sr2+

i.e. 1000 ml 1 mole EDTA contain 87.63 gm strontium

As 25 ml pipette solution required 24.2 ml 0.01N, EDTA

100 ml solution required = 96.8, 0.01 N EDTA

As 1000 ml 0.01N EDTA = 0.08763 gm Sr2+

96.8, 0.01N EDTA = 0.008483 gm Sr2+

As 0.0128 gm of strontium oxalate solution = 0.008483 gm strontium

100 gm of strontium oxalate solution contains = 66.27 gm strontium

Thus the volumetric estimation of strontium in the grown crystals was found to be 66.27%. This is matched with the calculated amount (64.40%) of strontium in SrC2O4, 0.85 H2O.

4.14.5 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 graph of the sample silver doped strontium oxalate grown in agar-agar

gel obtained after EDAX is shown in fig. 4.23 and the data obtained is given in table- 4.18, 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 - 4.18 EDAX data of silver doped strontium oxalate crystals

Element

Content as measured by EDAX

wt %

at %

C

14.80

41.69

O

14.71

31.10

Sr

70.49

27.21

4.14.6 Scanning Electron Microscope (SEM)

In present work Scanning Electron Microscope (SEM) studies of gel grown silver doped strontium oxalate crystals by agar-agar gel are done by using latest computerized scanning electron microscope Quanta 200 3D at National Chemical Laboratory, Pune, (M. S.). The successive photographs were taken at magnification of 250×, 500×, 2000× and 5000× at width 14.0 mm and 14.2 mm respectively and at high voltage 20 KV as shown in fig. 4.24 (a, b, c, d).

The surface of strontium oxalate crystals doped with silver is shown in fig. (a). The fig. shows the presence of pentagonal growth hillocks. The edges of the growth hillocks are clear but they are not sharp. The view portion A of fig. (a) at higher magnification 500× is shown by A1 in fig. (b). It also shows the presence of small grains on the surface. The view portion B which is a part of A1 of fig. (b) is further magnified at 2000× as a portion B1 of fig. (c). The portion B1 shows the presence of small irregulated triangular and rectangular edge pits which shows etching during the growth. Again it is magnified at 5000× as shown in fig. (d). The formation of the edge pits indicates controlled etching during the growth.

Conclusions

From the above discussion, the following conclusions can be derived:

Gel technique can be successfully employed for growth of doped strontium oxalate crystals. Single diffusion method is convenient for growth of the crystals. Size of the crystals improved with small amount of impurity added in agar- agar 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.

From the study of XRD, IR, TGA, DTA, DSC, EDAX and SEM of doped sample of strontium oxalate following conclusions can be predicated:

From XRD the unit cell parameters of grown doped strontium oxalate crystals satisfy the conditions for triclinic system. The size of all three doped strontium oxalate crystals and volume are approximately same that means dopant cannot change unit cell volume and structure of unit cell. The slight shifting in the XRD peak and large increase in the intensity may be attributed to cobalt, copper and silver doping.

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.

Chemical compositions of the grown crystals by EDAX are approximately same with the theoretical calculation.