J. Am. Ceram. Soc., 85 [5] 1107–13 (2002)
journal
New Process for the Preparation of
Monodispersed, Spherical Silica Particles
†
Ki Do Kim and Hee Taik Kim
Department of Chemical Engineering, Hanyang University, 1271 Sa 1-Dong, Ansan Kyunggi-do, 425–791 Korea
A new method is presented for preparing highly monodis-
persed silica particles using a two-stage semibatch/batch hy-
drolysis reaction of Si(OC H ) . The slower rate of hydrolysis
The controlled hydrolysis and condensation of tetraethylortho-
silicate (TEOS) in dilute alcohol solution using a batch precipita-
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tion technique gives fine particles of SiO . Typically, small-scale
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of the tetraethylorthosilicate (TEOS) that occurred during the
semibatch process resulted in larger silica particles with a
higher yield and narrower size distribution. This was in direct
contrast to the batch process. In addition, the ability of four
different mixed processes to produce silica particles with good
packing density, narrower particle-size distribution, and
higher yield were evaluated. These were batch/batch (B-B),
batch/semibatch (B-S), semibatch/batch (S-B), and semibatch/
semibatch (S-S) processes. The S-S system produced the
largest particles with the highest yields. The size of the silica
particles obtained by the S-B method decreased with increas-
ing reaction time, while the particles obtained by the B-S
process had the best particle-size distribution and packing
density. In conclusion, a mixed batch/semibatch system was
the best way to produce an extremely narrow particle-size
distribution and a good packing density.
batch hydrolysis is done under a nitrogen atmosphere in a vessel
fitted with a magnetic stirrer. Precipitation parameters, such as
reactant concentration, the concentration ratio of water and TEOS,
reaction temperature, and aging conditions, affect the resulting
particle size, size distribution, morphology, and state of particle
agglomeration. However, the batch process does not give SiO
particles with a narrow size distribution. A semibatch process, in
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which the system reactants feed into a reactor at a constant flow
rate gives greater control over the resulting particle size, shape,
and size distribution, because of the system’s short nucleation time
and the slow rate of reaction of hydrolysis.
In the first part of this study SiO particles were prepared using
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both semibatch and batch processes. The properties of the SiO2
particles prepared by each process were compared.
In the second part of the study, four mixed two-stage methods
combining the merits of the semibatch and batch methods were
used to obtain spherical silica particles with a narrower size
distribution, higher yield, and better packing density than either the
batch or semibatch systems.
I. Introduction
The objectives of this work were (i) to suggest a new method for
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synthesizing highly monosized SiO particles by hydrolysis of an
alkoxide, (ii) to establish the conditions for preparing monodis-
persed particles, and (iii) to determine the conditions that affect the
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INE metal-oxide particles such as Al O , SiO , Ta O , TiO ,
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F
and ZrO , are widely used in industrial applications as cata-
lysts, ceramics, pigments, etc. Of these metal oxide particles, SiO
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properties of monodispersed SiO particles.
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particles are used industrially in electronic and thin film substrates,
electrical and thermal insulators, humidity sensors, etc. The silica
particles play a different role in each of these applications. In
particular, spherical SiO2 particles of uniform size have wide
application, not only in the field of physical chemistry involving
dynamic behavior and the stability of particle systems, but also in
industries involving catalysts, chromatography, ceramics, pig-
ments, photographic emulsion, etc. Therefore, a great deal of effort
has been directed at producing SiO particles with controlled size,
shape, and porosity, for use in these applications.
The most common procedures for preparing submicrometer-
sized SiO2 particles reported in the literature are based on
liquid-phase reaction methods, such as those involving sol–gels,
II. Experimental Procedure
In this work, TEOS (Si(OC H ) , 99%, Aldrich Chemical Co.,
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Milwaukee, WI), ethanol (99.9%, Sigma Chemical Co., St. Louis,
MO), and ammonia water (28%, Junsei Chemical Co., Tokyo,
Japan) were used as starting materials without any purification.
The solutions were prepared in a glove box at room temperature
under dry air. The humidity in the glove box was kept below a few
percent.
The apparatus consisted of a reservoir for each starting solution,
a micro-feed pump to supply the solutions, a water bath, and a
reactor with a magnetic stirrer (which typically stirred at 150 rpm).
Monodispersed, spherical silica particles were prepared by both
single- and two-stage alkoxide hydrolysis reactions. A single-stage
consisted of either a batch or semibatch process. The method for
the semibatch process was as follows: the micro-feed pump fed
starting solution A (TEOS and ethanol) into the reactor containing
solution B (water, ammonia, and ethanol) at a constant rate; the
experiment was done under dry nitrogen. The apparatus used for
the semibatch and the batch system is shown in Fig. 1(a).
The four mixed processes, i.e., batch/batch (B-B), batch/semi-
batch (B-S), semibatch/batch (S-B), and semibatch/semibatch
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alkoxides, and emulsions. Stober et al. first showed that mono-
disperse silica particles could be derived from silicon alkoxides.
Processes that result in a narrow size distribution have a strong
effect on the final properties of products. Therefore, more recently,
many methods of preparation that result in a uniform particle size
have been studied. The size of silica particles synthesized from
the liquid phase—unlike that of particles such as TiO and ZrO —
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is easy to control due to the slow rate of hydrolysis of TEOS.
(
S-S), were tested in a two-stage mixed reaction method. Solutions
C. J. Brinker—contributing editor
A and B described above for the single- stage methods were
also used in the two-stage reactions. The mixed types of
operating systems used to form fine silica particles are summa-
rized in Fig. 1(b).
Particle size, particle-size distribution, and the shape of the
powders were determined by scanning electron microscopy (SEM,
Manuscript No. 188764. Received February 1, 2000; approved January 14, 2002.
Supported by the research fund of Hanyang University, Korea.
†
Author to whom correspondence should be addressed.
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