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W.-y. Jo et al. / Journal of Physics and Chemistry of Solids 67 (2006) 1071–1074
ZBS-nitrate was dispersed in aqueous solution containing
ammonium acetate and sodium dodecylsulfate. The amount of
ammonium acetate and sodium dodecylsulfate corresponds to
throughout the long-range diffusion of dissolved zinc species,
but throughout the short-range transchelation reaction.
The crystallization kinetics is studied by the Avrami
equation that is an empirical rate equation describing the
kinetics of crystallization and mechanism of nucleation for
heterogeneous reaction system [10]. In accordance with the
Avrami equation, time-dependent relative crystallinity func-
2
-fold excess to anion exchange capacity (AEC), respectively.
These solid precursors such as ZBS-nitrate, ZBS-acetate and
ZBS-dodecylsulfate were reacted with a stoichiometric amount
of 3.5 M sodium pyrithione (aq), respectively. Sodium
pyrithione aqueous solution was titrated with glacial acetic
acid to adjust the final pH of solution around 6.5, and then ZBS
were added immediately, the resulting off-white suspension
was stirred vigorously for 5, 10, 15, 30, and 60, 90, 120 min at
room temperature under ambient pressure. All the reactions
were quenched at a given time to prevent further reactions, and
the products were collected by centrifugation, washed with
ethanol and deionized water (1:1,v:v) and air-dried at 65 8C for
about 1 day, and then analyzed.
n
tion X(t) can be expressed as X(t)Z1Kexp (KKt ), where KZ
dX(t)/dt is the rate constant including the nucleation and the
growth parameter, n is an Avrami exponent being dependent on
the mechanism of nucleation and on growth of crystals, and t is
reaction time. This equation can be rearranged in the double
logarithmic form as ln{Kln(1KX(t))}ZlnKCn ln t. By
plotting ln{Kln(1K X(t))} versus ln t, so that we obtain the
straight line whose slope gives an Avrami exponent (n), and
the intercept is equal to lnK. Fig. 2B demonstrates plots on
ln(Kln(1KX(t)) versus ln t extracted from normalized inten-
sities of the discrete XRD peaks for zinc pyrithione at (110) and
3
. Results and discussion
(
111). In case of ZBS-nitrate, ZBS-acetate and ZBS-
dodecylsulfate, the n values are 1.10, 1.06, and 1.87,
respectively. Such low n values give support to the fact that
the crystallization has involved with negligible amount of
intermediate amorphous phase, and even if any amorphous
phase exists, small amount of fraction of the starting materials
might go through amorphous phases [11,12]. According to the
amount of normalized XRD peak intensity of ZBS precursor
Zinc basic salts show characteristic (00l) diffraction peaks
indicating intrinsic layered structures, and the typical 2q values
indexed as (001) are 9.18 for Zn (OH) (NO ) $2H O, 6.78
5
8
3 2
2
for Zn (OH) (CH COO) $2H O, and 2.88 for Zn (OH) (CH
3
5
8
3
2
2
5
8
(
CH ) CH OSO ) $2H O [9]. Fig. 1A represents the XRD
2 10 2 3 2 2
patterns for the reaction products prepared from ZBS-acetate as
a function of reaction time. As seen in Fig. 1A, new diffraction
peaks corresponding to zinc pyrithione are shown, and
characteristic reflections of ZBS-acetate gradually disappear.
As the reaction proceeds, the reflections of the zinc pyrithione
are dominant at the expense of ZBS-nitrate, and the single-
phase zinc pyrithione is finally obtained after 120 min. The
XRD patterns of the reaction products synthesized from ZBS-
nitrate are also shown in Fig. 1B, which have the similar
tendency to those of ZBS-nitrate precursor. In comparison with
those from ZBS-nitrate and ZBS-acetate precursors, zinc
pyrithione prepared from ZBS-dodecylsulfate precursor has
an outstanding difference in the reaction rate (Fig. 1C). Only
after 5 min, all the diffraction peaks of ZBS-dodecylsulfate
disappear, which suggests that the transchelation has not arisen
(001) and zinc pyrithione (110 and 111), the integrated value
turned out to be nearly constant for all cases, which also
suggests that crystallization might not involve formation of
significant amounts of amorphous phase.
Fig. 2A illustrates the evolution of relative crystallinity upon
the reaction time for zinc pyrithione synthesized from various zinc
precursors. The half-time of the crystallization (t ), which is
1/2
defined as the time when the 50% of initial materials transformed
into final products, can be obtained from the diagram of relative
crystallinity against crystallization time. Generally, the half-time
of the crystallization is adopted to describe the rate of
crystallization [13]. The t1/2 values are found to be 4.6 min for
the zinc pyrithione synthesized from ZBS-dodecylsulfate, which
*
•
ZBS-Acetate
ZBS-Nitrate
A
* ZBS-Acetate
20 min
0 min
B
C
1
20 min
1
1
20 min
9
0 min
0 min
9
6
90 min
60 min
30 min
15 min
6
0 min
0 min
3
0 min
5 min
0 min
min
3
1
1
5 min
0 min
1
1
1
0 min
5 min
5
5
min
*
•
*
ZBS-Nitrate
ZBS-Acetate
30
ZBS-Dodecylsulfate
20 30
0
10
20
40
10
40
10
20
30 40
Two theta (degrees)
Two theta (degrees)
Two theta (degrees)
Fig. 1. X-ray patterns for reaction products synthesized from A, ZBS-acetate; B, ZBS-dodecylsulfate; C, ZBS-nitrate by solid transchelation reaction under reaction
time variation.
Jo, Won-young
