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Journal of Minerals & Materials Characterization & Engineering, Vol. 8, No.6, pp 439-453, 2009
jmmce.org Printed in the USA. All rights reserved
Nucleation Reduction Strategy of SrNH4MgHPO4 (Strontium Ammonium
Magnesium Hydrogen Phosphate) Crystal Growth
in Silica Gel Medium and Its Characterization Studies
J. Kishore Kumar1, R. Ramesh1, G. Kanchana2, P. Suresh1
and P. Sundaramoorthi1*
1Department of Physics, Thiruvalluvar Govt. Arts College, Rasipuram, Namakkal, India-
2Department of Biochemistry, Muthayammal College of Arts and Science, Rasipuram,
*Corresponding Author: E-mail: firstname.lastname@example.org, Ph-04287-252785,
Kidney stones consist of various chemical compounds. Mineral oxalate monohydrate and di-
hydrate is the main inorganic constituent of kidney stones. However, the mechanisms for the
formation of crystal mineral oxalate are not clear. In this field of study, there are many theories
including nucleation, crystal growth and or aggregation of formation of crystals .The effect of
some urinary species such as ammonium oxalates, calcium, citrate, proteins and trace mineral
elements have been previously reported by the author. The kidney stone constituents are grown
in the kidney environments, the sodium meta silica gel medium (SMS) provides the necessary
growth simulation (in-vitro). In the artificial urinary stone growth process, growth parameters
within the different chemical environments are identified. The author has reported the growth of
urinary crystals such as CHP, SHP, BHP and AHP. In the present study, SrNH4MgHPO4
(Strontium Ammonium Magnesium Hydrogen Phosphate) crystals have been grown in three
different growth faces to attain the total nucleation reductions. As an extension of this research,
many characterization studies have been carried out such as FTIR, XRD, TGA/DTA, SEM and
etching and the results are reported.
Key words: Trace element, Strontium, MHP, AHP, SMS gel and renal stone.
440 J. Kishore Kumar, R. Ramesh, G. Kanchana, P. Suresh and P. Sundaramoorthi Vol.8, No.6
All kidney stones consist of a complex matrix with bio-minerals. The organic matrix has a
composition that remains constant regardless of the type of crystals that make up the stone [1, 2].
The urinary stone matrix accounts for approximately 3% of weight of a calculus . From the
analysis, the matrix compounds are soluble . The most recent knowledge of the matrix has
been described as a heterogeneous material composed of organic, inorganic and semi organic
compounds like protein, lipids, carbohydrates and cellular minerals etc. . Proteins are the
major constituents of stone matrices and the principle macromolecule in the urine . Urinary
proteins with the potential to adjust crystallization of mineral oxalates and calcium phosphate are
Tamm-Horsfall protein, nepheromineralin, osteopontin, calprotectin, human serum albumin and
urinary prothrombin fragment . The kidney, chiefly by the renal tubular epithelial cells,
produces most of the proteins. Other protein such as calprotectin, which is produced by
granulocytes are commonly released at the sites of inflammation, has also been of concern in
stone formation. The bio-minerals contain hard minerals like Ca, Ba, Sr, Mg and phosphates or
its mixtures. The most common and important human body element of all the stones is calcium.
Naturally calcium is found at concentrations of 8.9-10.1 mg/ml in the plasma .
Hypermineraluria is a biological syndrome defined as excretion in the urine of more than 0.1
mmol / kg / 24 hours of major minerals. Hypermineraluria is the most common metabolic
abnormality in patients with nephrolithiasis .
Hypermineraluria raises urine supersaturation with respect to the solid phase of mineral complex
with phosphate, enhancing the probability of self-nucleation and growth in to clinically
significant stones. Urinary mineral excretion is continuously influenced by dietary intakes of
calcium, sodium, protein, carbohydrates, alcohol, ammonium, trace element and potassium .
A mineral has been shown to bind to oxalate to form mineral oxalate monohydrate. Thus,
mineral has been shown to affect the concentration of oxalate. In addition, oxalate is a major
component of urinary stones and its urinary concentration plays an important role in stone
formation. Even a small increase in urinary oxalate has a significant impact on mineral oxalate
saturation. Although primary hyperoxaluria is relatively uncommon, patients with mineral
oxalate stones have some degree of hyperoxaluria . More amounts of oxalate can be
obtained from foods such as nuts, chocolate, and dark green leafy vegetables . A citrate
concentration of plasma ranges from 0.05-0.03 mmol / liter and it exits as an alkaline citrate .
Citrate inhibits crystallization of mineral oxalate and mineral phosphate by several mechanisms.
(a) It decreases urinary saturation of mineral salts by complexion minerals and reducing ionic
minerals concentration . (b) Citrate directly inhibits spontaneous precipitation of mineral
oxalate , agglomeration of mineral oxalate , crystal growth of mineral phosphate 
and heterogeneous nucleation of mineral oxalate by monosodium urate . (c) Citrate converts
glycoproteins to an active disaggregated state probably by enhancing their inhibitor activity
Vol.8, No.6 Nucleation Reduction Strategy of SrNH4MgHPO4 441
against the crystallization of calcium salts [17-18]. Due to the inhibitory role of citrate mentioned
above, patients with hypocitraturia would be at a higher risk of minerals containing renal stones.
The kinetic process of AOMH (Ammonium Oxalate Monohydrate) nucleation and crystal
growth requires super saturation , which can be obtained by excretion of the reactants in the
urine (ammonium ion, calcium, trace elemental oxalate and water). A few molecules are
combined together to form clusters. In the early step, clusters do not show a high degree of
internal ordering. The longer time they exist, however, their degree of ordering increases by
replacing internal salvation bonds by solid ion-ion bonds. Gradually, clusters become crystal
embryos [20-21]. Above a critical size, embryos will grow into stable nuclei, and below some
critical size, crystal embryos are too small and will reduce over all free energy by dissolving. The
size of the nuclei is usually 100A° or less . Once a crystal nucleus has reached its critical size
and super saturation ratio remains above one, the overall free energy is decreased by adding new
crystal components to the nucleolus (self/spontaneous growth). This process is technically
referred to as crystal growth.
2. MATERIALS AND METHODS
The silica gel also known as water glass was used in the present work as an intermediate growth
medium. SMS (ARG-sodium meta silicate powder) was added to the double distilled water, in
the ratio of 1:1, mixed, stirred well and kept undisturbed for few days to allow sedimentation.
Then the clear top solution was filtered and stored in a light protected glass container. This is
known as a stock solution . Gel densities of 1.03-1.06 gm/cc were used. Simple test tubes of
25 mm diameter and 150 mm length were used as growth apparatus. The concentration of
orthophosphoric acid used in this experiment was 0.5N, 1N and 2N. The concentration of
supernatant solution [SrCl2+NH4Cl2+MgCl2] varied from 0.5:0.5:0.5 M to 2:2:2 M [23-24]. One
of the reactants orthophosphoric acid was mixed within the gel solution. The gel solution was
taken as one third of its volume of the test tubes and after the gel set, the supernatant solution
was added slowly along the sides of the test tubes. The mixture diffuses through the gel medium,
which contains orthophorphoric acid and the self nucleation starts which in turn leads to the
growth of SrNH4MgHPO4 crystal.
The chemical reaction is
Sr2++NH42+ +Mg2++HPO42-+2H2O => SrNH4MgHPO4. 2H2O +Waste
The crystal growth processes were carried out in three different environments, one within
laboratory environment, second one was sunlight exposed environment (day time only-7 hours
per day) and another one was continuous (with suitable SMPS arrangement) semiconductor laser
light exposed environment.
442 J. Kishore Kumar, R. Ramesh, G. Kanchana, P. Suresh and P. Sundaramoorthi Vol.8, No.6
Table -1 Growth parameters of SrNH4MgHPO4 crystals (SDP)
N- Normality, M- Molarity
3. RESULTS AND DISCUSSION
The SrNH4MgHPO4 crystals are grown in three different growth faces by applying various
growth parameters. Figures 1-3 shows the growth of SrNH4MgHPO4 crystals at different growth
environments and Figure-4 shows the harvested SrNH4MgHPO4 crystal. Table-1 gives the
growth parameters of SrNH4MgHPO4 crystals and the bold letters represents the optimum
growth parameters. Among them, the laser exposed (4 mW, 7800Å of continues semiconductor
laser light power and wave length are used) growth medium shows better nucleation reduction
and no crystals were formed, because of the inability to attain super saturation. In sun light
exposed medium partial nucleation was observed, since exposure of sunlight to the growth
medium was only in the day time, that is seven hours per day and the growth period was six
on in N
] in M
Vol.8, No.6 Nucleation Reduction Strategy of SrNH4MgHPO4 443
Fig.1 Growth of SrNH4MgHPO4 crystals within the laboratory environment
Fig. 2 Growth of SrNH4MgHPO4 crystals within sunlight exposed medium
444 J. Kishore Kumar, R. Ramesh, G. Kanchana, P. Suresh and P. Sundaramoorthi Vol.8, No.6
Fig. 3 Growth of SrNH4MgHPO4 crystals in laser light exposed medium
Fig. 4 Harvested SrNH4MgHPO4 crystal
3.1. FTIR Spectral Analysis of SrNH4MgHPO4 Crystals
SrNH4MgHPO4-FTIR spectrum was recorded by using SHIMADZU FTIR-435 instrument. The
FTIR spectrometer has KBr pellets sample holder and a KBr detector. The KBr pellet samples
were used and the absorption frequencies start in the range from 400 cm-1 to 4000 cm-1. The
Vol.8, No.6 Nucleation Reduction Strategy of SrNH4MgHPO4 445
spectrum was interpreted with the earlier reported values [25-27]. The absorption bonds,
absorption frequencies and percentage of transmittance are tabulated in Table-2.
Table-2 Comparative study of the FTIR-Spectrum of SrNH4MgHPO4 crystal
S.No. Bonds/vibrations Reported
% of absorption
NH in plane stretching
1000 - 1100
3.2. Thermo Gravimetric (TGA and DTA) Analysis of SrNH4MgHPO4 Crystals
The TGA and DTA of SrNH4MgHPO4 crystals were carried out by STA 11500-PLTS
instruments. The SrNH4MgHPO4 crystal, a 5.976 mg sample, was used for the TGA process.
The TGA was ramped from room temperature to 9000C by heating at a constant rate. The
percentages of weight loss of the SrNH4MgHPO4 sample at a particular temperature are
tabulated in Table-3.
The expected thermo-chemical reactions are
SrNH4MgHPO4.2H2O Δ SrMgHPO4 + NH3 ↑+ 2H2O ↑
2SrMgHPO4 Δ 2Sr Mg + (PO4.H2O) ↑ + 2
3O2 ↑ up to 900ºC
Beyond 100ºC, the sample becomes anhydrous and after that it is hydrous along with ammonia
up to 365ºC and 59% of the sample remained stable at the end of the analysis. Sr and Mg
(Strontium and Magnesium) are stable up to 950 ºC.
446 J. Kishore Kumar, R. Ramesh, G. Kanchana, P. Suresh and P. Sundaramoorthi Vol.8, No.6
Table-3 TGA and DTA of SrNH4MgHPO4 crystal
DTA in 0C
3.3. Etching Studies of SrNH4MgHPO4 Crystal
A well-grown SrNH4MgHPO4 crystal was immersed in HCl solution at a desired concentration.
The dissolution of the SrNH4MgHPO4 crystal depends on the etchant concentration, temperature,
crystal morphology, etching time etc. Fig-5 shows the etch pits of SrNH4MgHPO4 crystal [28-
31]. The etch pit patterns are observed as spirals, dendrites, vallies of ups, downs and straights.
Fig. 5. Etch pit pattern of SrNH4MgHPO4 crystal.
Vol.8, No.6 Nucleation Reduction Strategy of SrNH4MgHPO4 447
3.4. Scanning Electron Microscopic Studies of SrNH4MgHPO4 Crystal
A well-grown SrNH4MgHPO4 single crystal was selected for the investigation of surface
morphology of the grown crystal by using SEM. The SEM photograph was obtained in a version
S-300-I instrument. The sample named as VCA-600 was kept in lobe middle; the data size was
640 x 480 µm. The difference between the minor and major magnification of SEM was about
500 times. SEM acceleration voltage was 25000 volts and the sample was kept in high vacuum
state. A 18200- µm work distance was maintained and monochromatic color modes were
employed. Fig-6 shows the SEM pattern of the SrNH4MgHPO4 crystal of 200 µm magnification
Fig. 6 SEM photo of SrNH4MgHPO4 crystal
3.5. X-ray Diffraction
The XRD results revealed that the grown crystal was in single phase of SrNH4MgHPO4. The
XRD pattern and diffraction indices of the grown crystals are calculated. Using the treor program
crystal cell parameters are calculated. The unit cell parameters of SrNH4MgHPO4 crystals are a
=18.06 Å, b=18.57 Å, c=22.72 Å and α=β=γ=90o. The crystal system is identified as
orthorhombic. The volume of the SrNH4MgHPO4 unit cell is 7619.702 (Å)3 .
The SrNH4MgHPO4 (Strontium Ammonium Magnesium Hydrogen Phosphate) crystals were
grown at room temperature, and exposed to sunlight and laser medium. It was found that the
SrNH4MgHPO4 crystal nucleation rate has been reduced more in the laser exposed medium than
448 J. Kishore Kumar, R. Ramesh, G. Kanchana, P. Suresh and P. Sundaramoorthi Vol.8, No.6
the sunlight-exposed medium, which is due to a variation of super saturations. The FTIR-
spectrum recorded the functional group frequencies of SrNH4MgHPO4 crystal constituents.
These results are recorded and compared with the reported values. Chemical etchings have been
done at room temperature, which revealed the grown crystal defects. SEM analyses were also
done and it reveals the surface morphology of SrNH4MgHPO4 crystal. The decomposition
temperature and percentage of weight loss of the grown crystal are recorded by TGA and DTA
analysis. XRPD data provides the SrNH4MgHPO4 grown crystal cell parameters and its
structure. This investigation results can be discussed with nephrologists and the results can be
applied to the human physiological system in stepwise manner to avoid the renal stone
formation. The crystal can be further investigated by atomic forced microscopy (AFM) to study
the atomic orientation of renal stones with in the human physiological system.
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