Strontium oxalate crystals are grown by the gel method using hydro - silica gel as media of growth at ambient temperature. Strontium chloride is allowed diffuse into a gel in which oxalic acid is incorporated. Strontium oxalate crystals are formed by chemical reaction and the growth process is observed. The optimum conditions are established by varying various parameters such as concentration of gel, concentration of reactant, pH of gel, gel setting time, aging period and density of gel. The grown crystals are characterized by powder x-ray diffraction (XRD) & Fourier transform infrared (FT-IR) spectroscope studies.
Crystal growth is a chemical process and in the field of crystal growth, gel technique has become more popular and has been used by several investigators [1-3]. Due to its simplicity it can be used at room temperature or at low temperature conveniently to suppress nucleation at centers  and is suitable for crystals having low solubility. Number of investigators have been utilized the technique in various manner to grow crystals of different materials [5-7]. Some investigators have grown and studied characterization of some oxalate crystals [8-12].
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Oxalate crystals are insoluble in water and they decompose before the melting point. Hence single crystals of such type of compounds can not be grown by either melt or slow evaporation techniques. In this situation gel method is most convenient and the appropriate one for their growth. There are not many efforts in the literature on the growth of strontium oxalate by gel method. However M.A. Gabal et; al.  have reported thermal decomposition kinetics of Strontium oxalate. J Bera and P.K. Roy have reported formation of SrTiO3 from strontium oxalate and TiO2 . Also G. Vanhoyland et; al. reported Kinetics of Consecutive reactions in the solid state: Thermal decomposition of oxalates . The present paper deals with the growth of strontium oxalate in hydro-silica gel by single diffusion technique at ambient temperature.
Good quality, white coloured crystals of strontium oxalate were prepared by employing single tube diffusion technique in gel. The crystallizing vessel were used essentially consist of standard glass tube of 2.5 cm inner diameter and 20 cm in length. Initially, reactants used for the same were sodium meta silicate (Na2SiO3, 5H2O), oxalic acid and strontium chloride. All the chemicals (reactants) used were of AR grade. All the chemicals (reactants) were prepared in double distilled water throughout the study.
The process of preparation was as follows: Initially, silica gel was prepared by titrating sodium meta silicate with oxalic acid. Oxalic acid solution of particular quantity was taken in a beaker and sodium meta silicate solution of suitable specific gravity was added drop by drop using burette under continuous stirring by magnetic stirrer. Stirring is done to avoid the excessive local ion concentration, which may otherwise cause premature gelling and make the final medium inhomogeneous and turbid. The solution was continuously stirred till the pH of the resulting solution has reached a specific value. Gelling mixture, after noting pH was allowed to set 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. After ensuring proper, firm gelation, supernatant strontium chloride solution was introduced carefully over the set gel with the help of pipette. Tubes were again kept idle for further processes to occur.
The following reaction took place.
SrCl2 + H2C2O4 à SrC2O4 + 2HCl
III. Results and discussion
A series of experiments were conducted by varying the concentrations of inner and other reactants as well as the pH of the medium. In single diffusion, after a few days a large, better quality, well shining, transparent micro crystals were observed as shown in figure 1
Figure 1 - Growth of strontium oxalate crystals by single diffusion technique.
The optimum conditions for gel setting and for better quality growing crystals are found as follows
1) Density of Sodium Meta silicate solution 1.04 gm/c.c
2) Concentration of oxalic acid 0.5 ml
3) Volume of oxalic acid 12 ml
4) Concentration of supernatant (SrCl2) 1M
5) Volume of sodium meta silicate 20.2 ml
6) pH of the mixture (gel) 4.0
7) Room temperature 300 C
Always on Time
Marked to Standard
8) Gel Setting period 25 days
9) Gel aging period 4 days
10) Growth period 70 days
11) Quality of crystals Micro crystals
The powder XRD pattern of grown crystals was obtained using a Miniflex, Rigaku X-ray diffractometer with CuKa radiation with wavelength l = 1.54051 AÂ°, scan range 20Â° to 80Â°, scan speed is 5Â° / min. and scan mode continuous at Department of Physical Sciences NMU Jalgaon.
The FT-IR spectra of the grown crystals in the frequency range of 400 - 4000 cm-1 was recorded on JASCO, model 460 plus at AISSMS COP, Pune.
A. X-ray diffraction - The recorded x-ray diffractogram of strontium oxalate is as shown in figure 2. The computer program, POWD, as Interactive powder Diffraction Data Interpretation and Indexing Program, Version 2.2 was used to calculate 'd' values. Calculated d values matched. with the reported values. Table-1 provides the corresponding 'd' spacing of observed lines together with their relative intensities and (hkl) values.
Table - 2 shows calculated unit cell parameters.
The powder XRD pattern reveals the strong crystalline nature of the sample. X-ray crystal analysis for the exact determination of the structure is in progress.
Figure 2- X-ray diffractogram of strontium oxalate crystal
Table 1 - X-ray powder data of strontium oxalate crystal.
Table 2 Unit cell parameters and system of strontium oxalate crystal.
Parameters Strontium oxalate
a 16.7505 AÂ°
b 3.4772 AÂ°
c 2.5623 AÂ°
V 136.41 AÂ°3
These parameters satisfy the conditions for Triclinic System i.e. a Â¹ b Â¹ c and aÂ¹bÂ¹gÂ¹90Â°
B. FT-IR spectroscope analysis
Figure 3 Shows FT-IR spectrum of strontium oxalate crystals grown in hydro silica gel. The observed infrared bands and their assignments are shown in table 3. The infrared spectrum in the range 400-4000 cm-1 shows intense peak at 3428.81 cm-1 attributed to O-H stretching mode and the peak 1788.65 cm-1 at attributed to C=O stretch of carbonyl group. The peak 1351.86 cm-1 is related to O-H bending vibration, which established the presence of water molecule associated with crystal. The band around 1071.26 cm-1 corresponds to the asymmetric stretching mode of C-O bond. The peak of 719.318 cm-1 has been assigned to metal - oxygen bond. The absorption between 610.36 to 562.148 cm-1 are due to presence of water of crystallization.
Figure 3 - FT-IR of strontium oxalate crystal
Table 3 - Spectral assignment of the IR peaks
Wave number (cm-1) Assignment
3428.81 O-H Stretching
1788.65 C=O Stretching
1351.86 O-H bending
1071.26 C-O bond
719.318 metal - oxygen bond
610.36 to 562.148 Water of crystallization
From systematic investigation on the gel growth of the strontium oxalate crystals, best conditions have been established to get better crystals.
Following points are observed,
1. Gel growth technique is suitable for growing crystals of strontium oxalate.
2. Gel requires appropriate condition of pH.
3. Formation of crystals, in all parts of the test-tube suggesting that diffusion of heavier strontium ions occur in all directions.
4. The 'd' Values of the grown material obtained from the XRD are well matched with the JCPDS data, which confirming crystalline nature of grown strontium oxalate.
5. The IR spectrum revealed the presence of water molecules, O-H bond, C-O bond, Carbonyl C=O bonds and metal - oxygen bond. It is obvious that the band assignments are in conformity with the structure proposed for the compound.