Synthesis and characterization of submicron-to-micron scale, monodisperse, spherical, and nonporous zirconia particles

Article abstract of DOI:10.1111/j.1551-2916.2005.00133.x

Monodisperse, spherical, and nonporous zirconia particles ranging from submicrons to microns for use as supports for capillary electrophoresis and chromatography were synthesized by the controlled hydrolysis of zirconium tetra-alkoxides in alcohol solutions in the presence of long-chain organic acids. Particle characteristics varied as a function of water concentration, the chain length of the organic acid, aging time, temperature, and extent of stirring. Changing these experimental parameters affected particle size, particle size distribution, and the degree of particle aggregation. Submicron particles were made by increasing the water concentration and decreasing aging time. Particle size increases as temperature during the aging period increases. Most importantly, large monodisperse particles (4 μm) could be made by extended stirring. In general, we found that particle size increases as the chain length of the organic acid increases. We also found that gentle rotation during the aging period prevented both particle settling and secondary nucleation. This allowed the production of large particles. BET nitrogen adsorption uptake measurements demonstrate that the particles could be sintered, without aggregating them, to remove virtually all internal porosity.

Full text of DOI:10.1111/j.1551-2916.2005.00133.x

J. Am. Ceram. Soc., 88 [3] 707–713 (2005)
DOI: 10.1111/j.1551-2916.2005.00133.x
ournal
J
Synthesis and Characterization of Submicron-to-Micron Scale,
Monodisperse, Spherical, and Nonporous Zirconia Particles
w
Bingwen Yan and Clayton V. McNeff
ZirChrom Separations, Inc., Anoka, Minnesota 55303
Peter W. Carr
Department of Chemistry, University of Minnesota, Minneapolis, Minnesota 55455
Alon V. McCormick
Department of Chemical Engineering and Material Science, University of Minnesota, Minneapolis, Minnesota 55455
Monodisperse, spherical, and nonporous zirconia particles rang-
ing from submicrons to microns for use as supports for capillary
electrophoresis and chromatography were synthesized by the
controlled hydrolysis of zirconium tetra-alkoxides in alcohol
solutions in the presence of long-chain organic acids. Particle
characteristics varied as a function of water concentration, the
chain length of the organic acid, aging time, temperature, and
extent of stirring. Changing these experimental parameters af-
fected particle size, particle size distribution, and the degree of
particle aggregation. Submicron particles were made by increas-
ing the water concentration and decreasing aging time. Particle
size increases as temperature during the aging period increases.
Most importantly, large monodisperse particles (4 lm) could be
made by extended stirring. In general, we found that particle
size increases as the chain length of the organic acid increases.
We also found that gentle rotation during the aging period
prevented both particle settling and secondary nucleation. This
allowed the production of large particles. BET nitrogen
adsorption uptake measurements demonstrate that the particles
could be sintered, without aggregating them, to remove virtually
all internal porosity.
cally have efficiencies that are five-folder greater than conven-
tional HPLC columns, and that can provide ultrafast separa-
tions. CE columns packed with submicron particles can also
5
generate extremely high efficiency and superfast separations.
Radko and Chrambach reviewed the use of submicron- and
6
micron-sized organic and inorganic particles for CE and re-
ported that the particles used were submicron to micron in size.
The use of short liquid chromatographic columns (1–5 cm)
packed with micron-size nonporous silica particles can signifi-
cantly speed up chromatographic analysis times compared with
4
,7
standard, porous silica columns owing to faster interphase
mass transfer kinetics (because of the absence of intraparticle
8
,9
pore diffusion). Several authors compared a 7-mm nonporous
column with three porous columns of the same type of chemical
support and found that the nonporous packings provide supe-
rior resolution when both higher flow-rates and shorter gradient
times were used. Several researchers described applications for
micron-size nonporous packings, including both native and
modified silicas, mainly for ultrafast chromatography of bio-
7
,10,11
12
polymers.
Recently, Oostervink et al. described submi-
cron nonporous silica particles used in applications for the sep-
aration of macromolecules in hydrodynamic chromatography.
1
3
Reynolds and Colon synthesized spherical, nonporous submi-
cron silica particles for CEC and demonstrated that high
efficiencies can be achieved in CEC.
I. Introduction
ECENT advances in capillary electrophoresis (CE), capillary
electrochromatography (CEC), and ultrafast liquid chro-
Methods for synthesizing unaggregated, nonporous silica
particles suitable for CE, CEC, and HPLC are widely known.
Such particles can be made either by the hydrolysis and con-
R
matography have greatly increased interest in the synthesis and
use of monodisperse ceramic particles ranging in size from sub-
microns to microns and having a narrow particle size distribu-
tion. The monodisperse particles for chromatographic use are
defined herein as those that have less than 10% variation in the
distribution of particle size; to date, silica is the ceramic used
1
1–18
densation of alkoxysilanes to yield nonporous particles
by depositing silica to fill the void volume within conventional
or
1
9
porous silica particles.
Porous zirconia (ZrO
stationary phase support for liquid chromatography.
conia is chemically (pH 5 1–14) and thermally much more stable
2
) has only recently been developed as a
20–23
1
–4
1
Zir-
most commonly. Unger et al. demonstrated that the gain in
total plate number when using 1–2 mm porous silica particles in
short columns is minimal in high-performance liquid chroma-
tography (HPLC) as compared with longer columns packed
2
0–23
(
of porous zirconia spheres has been investigated.
up to 2001C) than silica-based supports,
and the synthesis
Recently,
2
4–28
2
9
1
Van Canfort et al. prepared monodisperse and spherical zir-
conia particles (0.7 and 2.6 mm) by hydrolysis of zirconium
propoxide in 2-methoxylethanol in the presence of decanoic
with 5 mm particles. Unger et al. described CEC as a hybrid
method that enables the use of either submicron- or micron-size
particles. CEC columns packed with submicron particles typi-
3
0
acid. Lerot et al. reported that monodisperse spherical zirconia
particles can be made by the hydrolysis of zirconium alkoxide in
an alcoholic solution using long-chain carboxylic acids as stab-
lizers. By varying the reactant concentrations, and changing the
type of alcohols and carboxylic acids, particles ranging in size
K. Bowman—contributing editor
3
1
from 0.1 to 2.5 mm were obtained. Brinker and Scherer re-
ported that silica particle growth depends on the temperature.
Higher temperatures produce larger particles because of greater
silica solubility.
Unfortunately, the particles synthesized by Lerot et al. were
aggregated. Furthermore, the effect on particle size by using
Manuscript No 10051. Received March 18, 2003; approved June 7, 2004.
Supported by the National Science Foundation under grant SBIR PHASE I (Grant No.
9761543) and II (Grant No. 9901750), by the National Institute of Health, and by ZirChrom
Separations, Inc.
30
wAuthor to whom correspondence should be addressed. e-mail: bingwenyan@
zirchrom.com
7
07

7
08
Journal of the American Ceramic Society—Yan et al.
Vol. 88, No. 3
longer chain organic acids (e.g., eicosanoic acid), by changing
temperature, and by extended stirring (e.g., continuous stirring
after induction time) has not been investigated. Extended stir-
ring is of interest because stirring has a significant effect on the
particle formation. For example, in the synthesis of sterically
stabilized polyaniline dispersions using poly(vinyl alcohol) or
via a Millipore Q water purifier (Millipore Corp., Bedford,
MA).
SEM using a JEOL 8401 instrument (Hertfordshire, U.K.)
(ca. 100 A resolution) was used to characterize particle size,
shape, and state of aggregation. The particles were sputter-coat-
˚
ed with a 50 A layer of platinum prior to viewing.
Nitrogen sorptometry was performed on 10 g samples of the
synthesized particles using a Micromeritics ASAP 2000 (Nor-
cross, GA) sorptometer. Such large samples are required to en-
sure accurate surface area determination of our low surface area
materials.
˚
3
2
poly(N-vinylpyrolidone) stabilizers, Stejskal and Kratochvil
report that stirring is detrimental to colloid formation.
In previous work, we showed that reproducible, unaggre-
3
2
gated, and monodisperse 1.7 mm diameter zirconia particles can
3
3
be made by a modified ‘‘Lerot method’’ and demonstrated
that the product is nonporous. However, the process for making
unaggregated, nonporous submicron-size and micron-size zir-
conia particles designed for CE and chromatography has not yet
been reported.
(2) Preparation of Monodisperse Zirconia Particles
A 0.96 g portion of stearic acid was weighed into a 250 mL po-
lyethylene wide-mouth bottle, 80.6 g of anhydrous butanol was
added, and the bottle was tightly closed. When the effect of
chain length of organic acid was studied, the portions of acids
varied as follows: 0.55 g decanoic acid, 0.64 g lauric acid, 0.82 g
palmitic acid, and 1.00 g eicosanoic acid. The solution was
stirred for 30 min to allow for full dissolution. Then 12.20 g of
the zirconium propoxide solution was slowly added with stirring,
and the mixture was stirred for an additional 30 min (this is re-
ferred to in Lerot’s description as the ‘‘exchange’’ time). We have
found that a longer exchange time does not yield substantially
different particles, but exchange times much shorter than 30 min
can cause significant differences from the results shown below.
A fresh solution consisting of 70.1 g of anhydrous butanol
and 1.51 g deionized water was then slowly added with stirring
to the zirconium-containing solution over a period of 1 min;
when the water concentration effect was studied the amount of
water was changed to the following amounts: 1.62, 1.73, and
In this paper a general sol–gel procedure is presented that
describes the synthesis of monodisperse, spherical, and nonpo-
rous zirconia particles and the control of their average particle
size within the range of 0.8–4 mm. We show that particle sizes
ranging from submicron to micron can be obtained by varying
water concentration, aging time, chain length of organic acids,
temperature, and the extent of stirring. Furthermore, we report
that gentle rotation during the aging time can prevent particle
settling and resulting polydispersity in the synthesis of larger
particles. Using scanning electron microscopy (SEM), we con-
firm that the particles synthesized by our method are monodis-
perse and spherical. We also show here that the synthesized
particles of varying sizes are indeed nonporous as measured by
both nitrogen sorptometry.
II. Experimental Procedures
(
1) Materials
1
.80 g. The bottle was tightly closed and the mixture was vig-
n
Reagent grade zirconium propoxide (Zr(OPr )
4
, 70% (w/w) so-
orously stirred by a magnetic stirrer. The total amount of time
that the solution is stirred after water addition is defined as the
‘‘induction time’’. At the end of the induction time, the solution
becomes cloudy. Under the aforementioned conditions, in the
present case, the induction time was 26 min.
lution in n-propanol) was purchased from Aldrich (Milwaukee,
WI) and was stored in a desiccator with phosphorus pentoxide
as the desiccant after the bottle was opened. ACS grade n-but-
anol was purchased from Fisher Scientific Co. (Pittsburgh, PA).
Stearic acid (495%) and acetone (analytical grade) were pur-
chased from Aldrich. Distilled water was deionized prior to use
At the end of the induction time, stirring was stopped and
the suspension was allowed to age without agitation at room
n
Fig. 1. Scanning electron microscopy of final zirconia particles synthesized at different water concentrations. Synthesis conditions: [Zr(OPr )
4
] 5 0.1M,
[
2
stearic acid]5 0.016M, induction time 5 26 min, aging time5 30 min and (a) [H O]5 0.42M, particle size5 1.24 mm, standard deviation5 0.15 mm; (b)
[
described in text.
2
H O] 5 0.48M, particles size 5 0.84 mm, standard deviation5 0.17 mm. Postsynthetic treatment: dilution, filtration, washing, and heating schedule as

March 2005
Synthesis and Characterization of Nonporous Zirconia Particles
709
2.5
2.0
1.5
1.0
0.5
0.0
agglomeration. The following procedure was found to be satis-
factory for the particles prepared here: the particles were trans-
ferred to a crucible with a spatula and dried in a vacuum oven at
1201C for 3 h. The crucible was then transferred to a combustion
oven, and the temperature was ramped up at 51C/min to 4501C.
The particles were held at 4501C for 3 h in order to burn off any
remaining organic compounds. Then the temperature was raised
to 7501C at 51C/min and held at 7501C for 5 h to allow complete
densification. Finally, the temperature was decreased at 51C/min
to room temperature.
Using this procedure and range of variables discussed above,
we were able to reproducibly synthesize monodisperse, and
spherical nonporous zirconia within a size range of 0.8–4 mm.
0
100
200
300
400
Aging time (min)
III. Results and Discussion
Fig. 2. Effect of aging time on the mean particle size of final zirconia
(
1) Effect of Water Concentration
n
particles. Synthesis conditions: [Zr(OPr )
stearic acid]50.016M, induction time 5 26 min. Aging time varies as
indicated.
4 2
] 5 0.1M, [H O] 5 0.42M,
Figure 1 shows that the average particle size decreases as the
water concentration increases for a fixed aging time of 30 min.
At high concentrations of water, the hydrolysis of zirconium
propoxide is rapid, thus leading to a large number of nuclei and
small particles formed after complete precipitation. As can be
seen in Fig. 1, monodiperse zirconia particles are produced at
the given concentration range of water without aggregates or
secondary nuclei formation.
Most importantly, submicron (0.8 mm) monodisperse zirconia
particles can be made at a water concentration of 0.48M and at
an aging time of 30 min, which should be especially useful in
CEC and CE separations. It is noteworthy that aggregates and
wide particle size distributions will likely result if the hydrolysis
is too fast (at high water concentration). Although higher yields
can be attained at the target particle size, the colloid appearance
time (induction time) can become so short that reagent mixing
becomes difficult to achieve before colloid appearance. In such
situations we encountered significant particle polydispersity, and
batch-to-batch irreproducibility unless special measures were
taken to improve mixing. Thus in general we found that the
optimum water concentration should be controlled to less than
0.51M to produce submicron spheres reproducibly.
[
temperature. As described later, when the effect of temperature
was studied, the temperature was varied between À51 and 501C
during aging time. Also, when the duration of stirring was stud-
ied, the total induction times were 28, 32, and 38 min. In this
instance, the aging time was 150 min. The reaction was then
quenched by gently adding an additional 200 mL of anhydrous
butanol to the mixture. The suspension was then vacuum-fil-
tered through a 60M glass sintered Bu
cles were washed three times by gently resuspending them in
0 mL of anhydrous butanol and refiltering. Lastly, the particles
¨
chner funnel. The parti-
5
were washed with three 50 mL aliquots of acetone. This filtering
and washing procedure allowed for the collection of the still soft
(gel-like) and reactive particles without significant sticking to-
gether of particles or inter-particle growth.
After washing, the particles were subjected to a heating pro-
tocol; this protocol was designed to avoid rupture of the parti-
cles, and to allow the particles to densify while avoiding particle
Fig. 3. Scanning electron microscopy of final zirconia particles. Synthetic conditions: All chemicals as in Fig. 2. Induction time5 26 min, (a) aging
time5 30 min; (b) aging time5 390 min. Postsynthetic treatment as in Fig. 1.

7
10
Journal of the American Ceramic Society—Yan et al.
Vol. 88, No. 3
Fig. 4. Scanning electron microscopy of final zirconia particles synthesized by rotation during aging time. Synthesis conditions: All chemicals as in Fig.
. Induction time5 26 min, (a) Aging time5 360 min, rotation speed5 2 rpm, particle size 5 2.3 mm, standard deviation 5 0.25 mm; (b) aging
time5 1440 min, rotation speed 5 0.25 rpm, particle size5 2.5 mm, standard deviation50.92 mm. Postsynthetic treatment as in Fig. 1.
2
(
2) Effect of Aging Time
simply by increasing the aging time in combination with reac-
tion vessel rotation.
Figure 2 shows that the size of the zirconia particles increased
from 1.1 to 2.1 mm as aging time was increased from 30 to 390
min. Under the synthetic conditions described in Fig. 3, the
largest particles that could be produced are approximately
(
3) Effect of Alkyl Chain of Organic Acid
As shown in Fig. 5, the induction time decreases from 37 to 18
min as the chain length of the organic acid used increases from
nine carbons to nineteen carbons. Obviously, the zirconium
propoxide first reacts with the organic acid to form a metal–
carboxyl bond during the exchange time. In the presence of wa-
ter, the hydrolysis of the metal–alkoxy bond increases as the
chain length of organic acid increases. As a result, nucleation
and precipitation are accelerated, thus leading to shortened in-
2
.1 mm. Larger sizes are not possible because the degree of par-
ticle settling increases as the aging time increases. At an aging
time of 390 min, the particles have settled to the bottom of the
reaction container. As can be seen in Fig. 3, the resulting par-
ticles are monodisperse and spherical without smaller secondary
particles or aggregates.
Severe particle settling can result in polydispersity, especially
at long aging times. If settling can be prevented during the aging
time, so that the particles can still remain in contact with the
hydrolyzed species in the system, then the particles continue to
grow. Under these conditions we observed no secondary nucle-
ation or significant polydispersity. One explanation for this
might be that the concentration of the hydrolyzed species was
so low that secondary nuclei could not form. Alternatively, the
aging time may not have been long enough for the hydrolyzed
species to form new nuclei. In any event, our work strongly
suggests that particles larger than 2.1 mm cannot be produced
simply by increasing the aging time.
3
0
duction time, which is consistent with Lerot’s results.
Figure 6 shows the effect of increasing the chain length of the
organic acid from nine carbons (e.g., decanoic acid) to nineteen
carbons (e.g., eicosanoic acid) on particle size (from 1.2 to
2.7 mm). In this series of experiments, the particle size increases
40
1 (C9H20 COOH)
2
(C11 H23 COOH)
35
The key to making larger particles and preventing particle
settling is to gently rotate the reaction bottle during the particle
growth period. Figure 4(a) shows that 2.4 mm monodisperse,
spherical particles can be made by rotation of the reaction bottle
at a speed of 1 rpm over 200 min of aging time. Although larger
particles can be made by increasing aging time during rotation,
particle aggregation still occurs. This is likely caused by the par-
ticles being very ‘‘sticky’’, and as particles collide they become
aggregated. Rotation forces the particles together, thus leading
to particle aggregation. In order to minimize this problem, we
tried to reduce the rotation speed but, as shown in Fig. 4(b), the
particles grow larger, but have a wider size distribution. This
likely occurs because the aging time is so long that secondary
nucleation occurs, thereby causing a wider size distribution. We
conclude that it is difficult to make larger than 2.4 mm mono-
disperse particles with concomitant narrow size distribution
3
2
2
1
0
5
0
5
3 (C15 H31 COOH)
4 (C17 H35 COOH)
5 (C19 H39 COOH)
8
10
12
14
16
18
20
Carbon number of alkyl group
Fig. 5. Effect of chain length of organic acids on the induction. The
synthetic conditions as in Fig. 2 except organic acids as indicated.

March 2005
Synthesis and Characterization of Nonporous Zirconia Particles
711
Fig. 6. Scanning electron microscopy of final zirconia particles synthesized by different organic acids. Synthesis conditions: All chemicals as in Fig. 2.
a) [decanoic acid]5 0.016M, particle size 5 1.14 mm, standard deviation5 0.32 mm; (b) [eicosanoic acid] 5 0.016M, particle size5 2.7 mm, and standard
(
deviation5 0.15 mm. Postsynthetic treatment as in Fig. 1.
as the chain length of the organic acid increases. Figure 6 illus-
trates that the use of a short chain acid leads to small polydis-
perse, nonspherical particles with a wide size distribution. For
example, the standard deviation for decanoic acid is 0.32 mm. In
contrast, monodisperse, spherical 2.7 mm zirconia particles made
with eicosanoic acid have a size standard deviation of only
of different alcohols (e.g., pentanol and hexanol), and possibly
using elevated temperatures to help dissolve them. Further re-
search into the use of long-chain organic acids and elevated
temperature is underway.
(4) Effect of Temperature
0
.15 mm. It is also noteworthy that it is difficult to dissolve a 20-
Figure 7 clearly shows that temperature has a profound effect on
particle formation (nucleation and growth) during aging time.
Increasing the temperature from À51 to 501C during the aging
period increases particle size from 0.9 to 2.6 mm. We believe that
carbon chain organic acid in butanol. However, particles larger
than 2.7 mm should be possible to synthesize by using organic
acids with chain lengths longer than 20-carbon in the presence
Fig. 7. Scanning electron microscopy of final zirconia particles synthesized at different water concentrations. The synthetic conditions as in Fig. 2 except
temperature during aging time. (a) Temperature5 501C, particle size 52.6 mm, standard deviation5 0.17 mm; (b) Temperature5 À51C, particle
size 5 0.9 mm, and standard deviation5 0.10 mm.

7
12
Journal of the American Ceramic Society—Yan et al.
Vol. 88, No. 3
Fig. 8. Scanning electron microscopy photograph of final zirconia particles synthesized by extended stirring after the solution becomes cloudy. Syn-
thesis conditions: All chemicals as in Fig. 2. Induction time526 min, aging time5 150 min. Postsynthetic treatment as in Fig. 1. Total stirring times are:
(a) 28 min; (b) 38 min.
temperature affects the reaction in two ways: (1) hydrolysis rate:
the higher the temperature, the faster the hydrolysis rate;
proximately 4.5 mm as extended stirring time increases from 2 to
12 min. Unfortunately, Fig. 8 also shows that secondary nucle-
ation and aggregation occurs during this extended stirring peri-
od. This effect of extended stirring on particle size and shape was
very reproducible. We believe that extended stirring forces nano-
meter size colloids together to form aggregates because the col-
loids are very reactive and sticky at this stage. In addition,
extended stirring may accelerate the hydrolysis of zirconium
propoxide and the formation of new nuclei, thus leading to sec-
ondary nucleation during particle settling.
(2) Dissolution of the hydrolyzed species: the higher the tem-
perature, the greater the solubility. These two factors work
counter-current to each other when the temperature changes.
For example, increasing the temperature from À51 to 501C
makes the hydrolysis rate faster, thus leading to an increase in
particle size. However, if temperature increases too much, the
solubility of the hydrolyzed species is so great that the nuclei
formation is inhibited, thereby slowing particle formation and
growth.
Decreasing the temperature to À51C during the aging period
slows down the hydrolysis rate. As the solution becomes super-
saturated and the nuclei start to form, it is expected that fewer
nuclei will be formed than at room temperature. These nuclei
should grow more slowly at lower temperatures and consume
less hydrolyzed specie because of both the fewer number of par-
ticles and the slower growth rate. Thus, submicron particles can
be made by decreasing temperature during the aging period.
(5) Effect of Extended Stirring Time
We found that it is very important to stop stirring after the in-
3
2
duction time. Stirring that lasts for the entire aging period
perturbs the stability of the colloid system and leads to agglom-
eration and the formation of irregularly shaped particles. The
particle size distribution deteriorates if stirring is continued
(
called extended stirring) during the aging period after the mix-
ture becomes cloudy. During the extended stirring period, the
particles are on the order of several hundred nanometers in size.
The external force coming from the stirring is much higher than
the potential barrier at the first minimum of the interaction po-
tential, thus causing irreversible coagulation of the tiny particles.
Thus we believe that the small particles agglomerate, and then
settle quickly to the bottom of the vessel. At this point the
growth of the particles halts because the source of hydrolysis
species is depleted.
Surprisingly, we discovered that extended stirring at 2 and 12
min at early aging time has a dramatic effect on the particle size.
Figure 8 shows the effect of extended stirring on particle shape
and size. Particle size increases significantly from 2.3 mm to ap-
Fig. 9. Scanning electron microscopy of final zirconia particles synthe-
sized by extended stirring for 6 min and rotation at a speed of 0.25 rpm.
Synthesis conditions: All chemicals as in Fig. 2. Particle size5 3.61 mm,
standard deviation5 0.21 mm. Postsynthetic treatment as in Fig. 1.

March 2005
Synthesis and Characterization of Nonporous Zirconia Particles
713
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2
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4
2
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1
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1
0
2
3
.24 (Fig. 1 (a))
.84 (Fig. 1 (b))
.72 (Fig. 6 (b))
.61 (Fig. 9)
0.83
1.23
0.38
0.29
1.03
1.38
0.55
0.44
5
for Capillary Electroendosmotic Chromatogrpahy (CEC),’’ Chromatographia, 49
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As previously mentioned, a method to prevent secondary nu-
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on particle shape and size under rotation during the aging time.
The mean diameter of the particles is 3.61 mm with a standard
deviation of 0.21 mm. These synthesized particles are monodis-
perse and spherical. Figure 9 shows that secondary nucleation is
no longer apparent.
9
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7
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11
G. J. Opiteck, J. W. Jorgenson, and R. J. Anderegg, ‘‘Two-Dimensional SEC/
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In order to verify that the synthesized particles were nonporous,
we examined them using accurate BET nitrogen adsorption
measurements of the surface area. Table I gives the surface ar-
eas of the synthesized particles. For example, the surface areas
of the 0.84 mm particles shown in Fig. 1(b), and the 2.7 mm par-
ticles shown in Fig. 6(b) are 1.23 and 0.38 m /g, respectively,
which are quite close to the theoretical surface areas of dense
zirconia spheres of 0.84 and 2.7 mm —1.38 and 0.55 m /g, re-
spectively. The experimental surface areas are likely greater than
the theoretical surface areas because the surface of the synthe-
sized particles is slightly rough because of the growth of the
particles being surface reaction (nucleation) limited. We con-
clude that all particles synthesized in this work are indeed
nonporous.
12
of Soluble Macromolecules of Columns Packed with Submicron Nonporous
Spheres,’’ Am. Lab., 30 [6] C 24 ff (1998).
13
K. J. Reynolds and L. A. Colon, ‘‘Submicron Sized Organo-Silica Spheres
for Capillary Electrochromatography,’’ J. Liq. Relat. Technol., 23 [1] 161–73
2
(
2000).
14
J. Th. G. Overbeek, ‘‘Monodisperse Colloidal System, Fascinating and Use-
ful,’’ Adv Colloid Interf. Sci., 15, 251–77 (1982).
2
15
K. K. Unger, J. N. Kinkel, B. Anspach, and H. Gieche, ‘‘Evaluation of Ad-
vanced Silica Packing for the Separation of Biopolymers by High-Performance
Liquid Chromatography,’’ J. Chromatogr., 296, 3–14 (1984).
A. K. van Helden, J. W. Jansen, and A. Vrij, ‘‘Preparation and Characteri-
16
zation of Spherical Monodisperse Silica Dispersions in Nonaqueous Solvents,’’
J. Colloid Interf. Sci., 81, 354–68 (1981).
3
3
17
W. Stober, A. Fink, and E. Bohn, ‘‘Controlled Growth of Monodisperse Silica
Spheres in the Micron Size Range,’’ J. Colloid Interf. Sci., 26, 62–9 (1968).
18
K. K. Unger, H. Giesche, and J. N. Kinkel, ‘‘Spherical Silica Particles.’’
German Patent, DE 3,534,143, 1985.
19
L. F. Colwell and R. Hartwick, ‘‘Synthesis of Nonporous Silica Supports for
HPLC from Porous Silica Gels,’’ J. High Resolut. Chromatogr., 9, 304–5 (1986).
M. J. Annen, R. Kizhappali, P. W. Carr, and A. V. McCormick, ‘‘Develop-
IV. Conclusions and Perspectives
20
Synthetic methods for making monodisperse, spherical nonpo-
rous zirconia have been developed to reproducibly make parti-
cles within a size range of 0.8–4 mm. Submicron particles (0.84
mm) can be produced by increasing the water concentration and
decreasing the aging time. A maximum particle size of 2.1 mm
was achieved by increasing the aging time. Larger particles (e.g.,
ment of Porous Zirconia Spheres by Polymerization-Induced Colloid Aggrega-
tion-Effect of Polymerization Rate,’’ J. Mater. Sci., 29, 6123–30 (1994).
P. W. Carr, E. F. Funkenbusch, M. P. Rigney, P. L. Coleman, D. A. Hanggi,
21
and W. A. Schafer, ‘‘High Stability Porous Zirconium Oxide Spherule.’’ US Pat-
ent, US 5,015,373, 1991.
M. P. Rigney, T. P. Weber, and P. W. Carr, ‘‘Preparation and Evaluation of
22
a Polymer-Coated Zirconia Reversed-Phase Chromatography,’’ J. Chromatogr.,
484, 273–91 (1989).
C. F. Lorenzano Porras, P. W., Carr, and A. V. McCormick, ‘‘Relationship
2
.7 mm) can be produced by increasing the organic acid chain
length and by rigorously controlling the total stirring time.
.9–2.6 mm particles were produced by varying the reaction
23
2
Between Pore Structure and Diffusion Tortuosity of ZrO Colloidal Aggregates,’’
0
J. Colloid Interf. Sci., 164, 1–8 (1994).
24
temperature from À51 to 501C during the aging period. Gentle
rotation of the reaction vessel was found to help prevent sec-
ondary nucleation and help reduce particle settling.
R. K. Iler, H. J. McQueston, and J. Herbert, ‘‘Preparation of Microparticles
Composed from Many Small Particles.’’ German Patent, DE 2,317,454, 1972.
L. Sun, M. J. Annen, F. Lorenzano-Porras, P. W. Carr, and A. V. McCor-
25
mick, ‘‘Synthesis of Porous Zirconia Spheres for HPLC by Polymeriza-
tion-Induced Colloid Aggregation (PICA),’’ J. Colloid Interf. Sci., 163, 464–73
(1994).
In future work, we will focus on controlling the surface
roughness of particles as well as imparting both a carbon and
polymer coating on these submicron- and micron-size nonpo-
rous zirconia particles. We believe that these coated nonporous
zirconia particles will have considerable utility for CE, and
capillary liquid chromatography. We also plan to extend this
methodology to make other monodisperse, spherical nonporous
metal oxides such as titania.
26
C. M. A. Stuart, ‘‘Absorbed Polymers in Colloidal System: From Statics to
Dynamics,’’ Polym. J., 23, 669–82 (1991).
G. J. Fleer and J. M. H. M. Scheutjens, ‘‘Effect of Adsorbing and Nonadsor-
27
bing Polymer on the Interaction Between Colloidal Particles,’’ Croat. Chem. Acta.,
60, 477–94 (1987).
28
K. Muhle, ‘‘Particle Adhesion in Coagulation and Bridging Flocculation,’’
Colloid Polym. Sci., 263, 660–72 (1985).
O. Van Canfort, B. Michaux, R. Pirard, J. Pirard, and A. J. Lecloux, ‘‘Syn-
29
thesis and Characterization of Monodisperse Spherical Zirconia Particles,’’ J. Sol–
Gel Sci. Tech., 8, 207–11 (1997).
30
Acknowledgments
L. Lerot, F. Legrand, and P. D. Bruycker, ‘‘Chemical Control in Precipitation
of Spherical Particles,’’ J. Mater. Sci., 26, 2353–8 (1991).
31
We are grateful to Dr. John Nelson from the surface characterization facility of
the Center of Interfacial Engineering at University of Minnesota for his help.
C. J. Brinker and G. W. Scherer, Sol–Gel Science, pp. 105–7. Academic Press,
Inc., San Diego, 1990.
32
J. Stejskal and P. Kratochvil, ‘‘Polyaniline Dispersion. 5. Poly(Vinyl Alcohol)
and Poly(N-Vinylpyrrolidone) as Steric Stabilizers,’’ Langmuir, 12, 3389–92
1996).
(
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