ARTICLE IN PRESS
J. Yu et al. / Journal of Solid State Chemistry 179 (2006) 800–803
801
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2
. Experimental
can be easily found. At [PSMA] ¼ 0.02 g L , the ends of
the dumbbells became large (as shown in Fig. 1c). When
the concentration of PSMA was further increased to
2
.1. Preparation
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0.1 g L , spherical particles with concave surfaces were
prepared (as shown in Fig. 1d). When the concentration of
PSMA (sodium salt, 30 wt% solution in water, average
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1
molecular weight ꢀ120,000) was obtained from Aldrich.
All other chemicals were of A.R. grade and used without
further purification. The water used in the experiment was
distilled water. In a typical synthesis, a solution of Na CO
PSMA reached 0.3 g L , perfect spherical particles were
obtained (Fig. 1e). Lots of investigations carried out in our
group have shown that when the concentration of organic
additives, acted as shape modifier, reached a critical value,
the final shape of the controlled particles tended to become
a sphere [4,5,15,21–23]. This might be due to the fact that,
when the concentration of additives reached an enough
amount, the oriented adsorption of additives would
disappear, which resulted in the formation of a sphere
[22–24]. It could be seen from Fig. 1a to e that the size of
the spherical particles was obviously larger than that of
those obtained in other conditions. This might be ascribed
to the decrease of the number of nucleation at a high
PSMA concentration due to the fact that most of the ions
for nucleation or growth were adsorbed by PSMA, which
resulted in the formation of big spherical particles.
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3
(
0.5 M, 0.4 mL) was added into an aqueous solution of
PSMA (100 mL, containing different amount of PSMA
according to the needs of experiments), and the pH value of
the solution was adjusted to 10 by adding HCl (1 M) or
NaOH (1 M) solution. Then a solution of Sr(NO ) (0.5 M,
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0
.4 mL) was added quickly into the pH-adjusted solution
under vigorous stirring by using a magnetic stirrer. The
mixture was stirred for another 5 min, and then the
solution was kept under static conditions for 24 h to ensure
reaction equilibration.
2
.2. Characterization
In order to investigate the influence of PSMA on the
phase structures of SrCO particles, three samples were
The resulting SrCO precipitates were characterized by
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scanning electron microscopy (SEM) (type JSM-5610LV,
Japan) with an accelerating voltage of 20 kV. The powder
X-ray diffraction (XRD) patterns obtained on an
HZG41B-PC X-ray diffractometer using CuKa radiation
at a scan rate of 0.051 2y S were used to determine the
identity of any phase present and their crystallite size. The
accelerating voltage and the applied current were 35 kV
and 20 mA, respectively.
selected for XRD characterization and the XRD results
were shown in Fig. 2. It could be seen that XRD patterns
of SrCO products prepared at different PSMA concentra-
tion had the same diffraction patterns. This was due to the
fact that strontium carbonate is single-phase crystal.
Further observation showed that with increasing the
amount of PSMA, the intensity of diffraction peaks
decreased and the crystallization became weak. This could
be attributed to the fact that PSMA inhibited the crystal-
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3
. Results and discussion
lization and growth of SrCO particles by adsorbing on the
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crystal faces. We measured the amount of SrCO3
precipitates obtained in the presence of 0, 0.01 and
Fig. 1 shows SEM micrographs of SrCO3 particles
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obtained from aqueous solution in the absence and
presence of PSMA at room temperature. It could be seen
from Fig. 1a that, in the absence of PSMA, the as-obtained
particles appeared bundle-like aggregates consisting of
0.3 g L
found that their mass was 0.285, 0.250 and 0.120 g L
PSMA by using a mass analysis method and
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,
respectively. This also showed that PSMA could inhibit the
formation and crystallization of SrCO particles due to
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many small SrCO needles aligned radially towards both
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PSMA adsorbing Ca
methods and Scherrer’s equation [25], the average crystal-
ions [11]. Using line-broadening
ends. Further observation showed that there existed many
fragments ruptured at the middle parts of the bundles.
Therefore, it could be inferred that the middle parts of the
bundles were more fragile than their radial branches. When
lite sizes of SrCO particles were calculated. It was found
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that those of SrCO particles obtained in the presence of 0,
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0.01 and 0.3 g L
respectively. This also indicated that with increasing the
PSMA were 63, 36 and 11 nm,
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a small amount of PSMA (0.01 g L ) was added into the
reaction system, the morphology of SrCO particles was
amount of PSMA, the crystallite size of SrCO particles
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3
obviously changed (as shown in Fig. 1b). Compared with
the above-mentioned bundle-like aggregates, the morphol-
ogy of the as-obtained particles was more homogeneous
whatever in shape or in size, which looked like a dumbbell.
Such monodispersed morphology was a bit different from
that observed by Qi and coworkers [20]. The formation of
such a shape in our work might be due to the oriented
adsorption of PSMA on some specific crystal faces
perpendicular to the growth direction of the needle-like
branches, which inhibited the growth of the needles.
Moreover, some projections at the both ends of particles
decreased.
Qi et al. has ever proposed a schematic growth
mechanism for the formation of oval-, peanut-, and
peach-like BaSO particles [10], but this mechanism does
not coincide well with our experimental results, probably
due to the difference in crystal habit between BaSO and
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SrCO . Fig. 3 shows a schematic mechanism of formation
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of SrCO particles obtained in the presence of PSMA. At
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first, amorphous nanoparticles were formed in the presence
of PSMA. Then the nanoparticles aggregated and evolved
into small crystals with high surface energy marked by
Yu, Jiaguo
