Nanocrystalline hydrous zirconia from zirconium tungstate

Article abstract of DOI:10.1111/j.1551-2916.2011.04394.x

Crystalline hydrous zirconia (ZrO₂·2H₂O) with volume-weighted average domain size of 1.5 nm was obtained by soaking zirconium tungstate (α-ZrW₂O₈) in boiling 1M NaOH solution for 5 h. The selected area electron diffraction pattern of hydrous zirconia particles could be indexed according to a tetragonal lattice with a=1.463(4) A and c=2.535(6) A. Upon heating to 60°C under a vacuum of 10^-5 mbar, hydrous zirconia dehydrates reversibly. Further heating to 850° and 1000°C resulted in the formation of tetragonal and monoclinic zirconia, respectively. Some of the nanocrystalline hydrous zirconia produced from zirconium tungstate coalesced into transparent, nearly pore-free aggregates. The formation of these almost fully densified aggregates of hydrous zirconia, and the observed dehydration under very mild conditions, suggests that it could be possible to obtain transparent bodies of zirconia, with unprecedented small crystallite size, with the controlled deposition of the extremely small hydrous zirconia nanoparticles from a water-based suspension.

Full text of DOI:10.1111/j.1551-2916.2011.04394.x

J. Am. Ceram. Soc., 94 [8] 2640–2645 (2011)
DOI: 10.1111/j.1551-2916.2011.04394.x
r 2011 The American Ceramic Society
ournal
J
Nanocrystalline Hydrous Zirconia from Zirconium Tungstate
Luciana M. Somavilla,z,y Janete E. Zorzi,w,z Giovanna Machado,z Gustavo R. Ramos,z
Cintia L. G. de Amorim,z and Claudio A. Perottoniz,y
´
zUniversidade de Caxias do Sul, 95070-560, Caxias do Sul, RS, Brazil
yPGCIMAT-Universidade Federal do Rio Grande do Sul, 91501-970, Porto Alegre, RS, Brazil
zCentro de Tecnologias Estrate
´
gicas do Nordeste—CETENE, 50740-540, Recife, PE, Brazil
.
Crystalline hydrous zirconia (ZrO2 2H2O) with volume-
weighted average domain size of 1.5 nm was obtained by soak-
ing zirconium tungstate (a-ZrW2O8) in boiling 1M NaOH
solution for 5 h. The selected area electron diffraction pattern
of hydrous zirconia particles could be indexed according to a
Because of the low concentration of Lewis acid sites, zirconia
has found application as catalyst, for instance, in the isomer-
ization of olefins and epoxides, dehydration of alcohols, and
hydrogenation of olefins and carboxylic acids.11,12
The surface area of zirconia powder is affected by the prep-
aration conditions and is highly dependent on the precursors.6
Amorphous zirconia with specific surface area of 200–300 m2/g
has been obtained by different methods.12 Indeed, several differ-
ent methods have been investigated as routes for the synthesis of
nanometer-sized zirconia, including sol–gel process, spray
pyrolysis, chemical precipitation, mechanochemical processing,
gas-phase reaction, hydrothermal synthesis, and salt-assisted
aerosol decomposition.1,2,6,7,16 Among these methods, aqueous
precipitation of zirconium hydroxide or hydrous zirconia con-
stitutes an interesting route for the preparation of precursors to
make ultra fine zirconia powder.1 Nanocrystalline tetragonal
zirconia produced by some of these methods has been reported
with mean crystallite size in the 2.9–6 nm range.2,17–21
˚
˚
tetragonal lattice with a 5 1.463(4) A and c 5 2.535(6) A. Upon
heating to 601C under a vacuum of 10ꢀ5 mbar, hydrous zirconia
dehydrates reversibly. Further heating to 8501 and 10001C
resulted in the formation of tetragonal and monoclinic zircon-
ia, respectively. Some of the nanocrystalline hydrous zirconia
produced from zirconium tungstate coalesced into transparent,
nearly pore-free aggregates. The formation of these almost fully
densified aggregates of hydrous zirconia, and the observed de-
hydration under very mild conditions, suggests that it could be
possible to obtain transparent bodies of zirconia, with unprec-
edented small crystallite size, with the controlled deposition
of the extremely small hydrous zirconia nanoparticles from a
water-based suspension.
Zirconia produced from amorphous precursors (gel,
precipitated, etc.) usually begin to crystallizes at around
4001–6001C.17,19–21 The amorphous precursors usually begin
crystallizing into the metastable tetragonal phase, not the ther-
modynamically stable monoclinic phase. The tetragonal phase
thus obtained can be retained at high temperatures. For instance,
the crystallization of zirconia gel into the t-phase begins at 4001C
and the t-m conversion occurs at 10001C.19–22 The crystalliza-
tion into the metastable t-ZrO2 phase has been explained in terms
of the similarity between the structures of the amorphous and the
t-phase, crystallite size, and deformation effects, as well as the
presence of ionic impurities.18,19–22 Recent results, however, sug-
gest that nanocrystalline t-ZrO2 is not just kinetically metastable,
but can be truly thermodynamically more stable than monoclinic
zirconia below 12001C, as long as coarsening is precluded.18
Hydrous zirconia is very often found among the intermediate
products in the preparation of nanocrystalline zirconia. Hy-
drous zirconia is also used as catalyst for the reduction of alde-
hydes and ketones and the oxidation of secondary alcohols with
ketones.6
In this work, we report on the production of very small and
narrow size distribution hydrous zirconia nanoparticles, starting
from zirconium tungstate powder (ZrW2O8). The evolution of
hydrous zirconia toward t-ZrO2 and m-ZrO2 was followed by
successive thermal treatments. The product obtained from zir-
conium tungstate was characterized by transmission electron
microscopy (TEM), scanning electronic microscopy (SEM),
semiquantitative elemental analysis by energy-dispersive X-ray
spectroscopy (EDS), thermogravimetric analysis (TGA), X-ray
diffraction (XRD), and diffuse reflectance infrared Fourier-
transform spectroscopy (DRIFTS). Selected area electron
diffraction (SAED) patterns and high-resolution transmission
electron microscopy (HRTEM) images allowed to confirm the
crystalline nature of the hydrous zirconia nanoparticles and also
to determine their Bravais lattice and to estimate their lattice
parameters.
I. Introduction
IRCONIA (ZrO2) is an outstanding ceramic material, with ap-
plications that span from high performance transformation-
Z
toughened structural engineering ceramics to catalysts, solid
electrolytes, and oxygen sensors, to cite just a few.1–3 Such di-
verse applications rely on the unique properties of zirconia,
which include high fracture toughness, relatively high hardness,
wear resistance, low coefficient of friction, high melting point,
good ionic conductivity, and low thermal conductivity.4–7
Three polymorphs of zirconia are widely known which adopt
monoclinic, tetragonal, and cubic crystalline structures.2,4,5
Other crystalline polymorphs of zirconia were obtained at
high pressure and high temperature and also by fast cooling
to liquid nitrogen temperature.3,8
Many properties of nanocrystalline materials are fundamen-
tally different from those of bulk materials. Some specific ad-
vantages of nanocrystalline ceramic materials include superior
phase homogeneity and the possibility of low-temperature
sintering.9 Besides structural applications, nanocrystalline
ceramics have found application in areas such as electronics,
optics, and catalysis.10 In fact, the reduced size of nanosized
particulate materials, and the presence of edges and corners, of-
ten leads to an increased catalyst activity.11,12
Zirconia has been used in heterogeneous catalysis both as a
support for the catalyst as well as the catalyst in itself.6,13–15
W.-C. Wei—contributing editor
Manuscript No. 28665. Received September 25, 2010; approved December 13, 2010.
This work was supported by Conselho Nacional de Desenvolvimento Cientı
Tecnologico (CNPq, Brazil).
wAuthor to whom correspondence should be addressed. e-mail: jezorzi@ucs.br
´
fico e
´
2640

August 2011
Nanocrystalline Hydrous Zirconia from Zirconium Tungstate
2641
II. Experimental Procedure
(1) Sample Preparation
A white precipitate was obtained by soaking micrometer-sized
zirconium tungstate (a-ZrW2O8) powder (Wah Chang, Albany,
OR), with boiling NaOH 1M solution for 5 h, with magnetic
stirring. The precipitate was washed with water several times,
filtered (or centrifuged) and dried overnight in a oven at
1201C.23 The white precipitate powder was characterized as
obtained and after being submitted to successive 24 h thermal
treatments in a tubular furnace, in air, at increasing tempera-
tures from 5001 up to 13001C. Amorphous zirconium tungstate
was prepared by pressing a-ZrW2O8 at 7.7 GPa for 15 min, fol-
lowing a procedure described previously.24
(2) Materials Characterization
X-ray powder diffraction analysis at room temperature was per-
formed with a XRD 6000 diffractometer (Shimadzu, Shimadzu
Corp., Tokyo, Japan) using CuKa radiation (l 5 0.15418 nm),
in the angular range from 51 to 801 (2y), with a step size of 0.051
and 2 s integration time. The diffractometer was equipped with
Soller slits both in the primary and secondary beams, a 11 di-
vergence slit, a 0.15 mm receiving slit, and a graphite mono-
chromator in the secondary beam. Peak positions and intensities
were determined by fitting a pseudo-Voigt peak profile to indi-
vidual Bragg peaks using Winplotr software, taking into ac-
count CuKa1,2 contributions.25 The volume-weighted average
domain size was estimated from the integral width of individual
Bragg peaks according to Young.26 The instrumental contribu-
tion to the peak width was estimated using high-purity silicon
powder (Shimadzu).
TGA was performed using a TGA-50 thermobalance (Shim-
adzu). Heating rate was 201C/min and all the runs were carried
out under a flow of 50 ml/min of high-purity nitrogen. DRIFTS
analysis was performed on a Spectrum 400 spectrometer (Per-
kin-Elmer, Waltham, MA), using KBr as dispersant and 32
scans. The measurements were carried out with samples as ob-
tained and after thermal treatment at 13001C during 24 h.
SEM images and semiquantitative elemental analysis by EDS
were carried out using a SSX-550 scanning electron microscope
(Shimadzu) operating at 15 kV. Integral peak areas were used in
the elemental semiquantitative analysis, in which matrix effects
were corrected using the ZAF method.27 For the SEM analysis,
samples were coated either with carbon (SEM imaging) or gold
thin films (EDS).
Individual nanoparticles were observed using a transmission
electron microscope JEM2010 (JEOL, Tokyo, Japan) operating at
200 kV and equipped with an EDS system. Samples for TEM
analysis were prepared by dispersion of the powder in is-
opropanol. A small amount of this suspension was dispersed on
a holey carbon grid. Particle size distribution was determined from
the analysis of TEM images showing well-defined individual nano-
particles. The crystalline nature of the hydrous zirconia was con-
firmed by HRTEM micrographs and SAED patterns. Indexing of
the diffraction spots in the SAED patterns was performed on the
basis of the corresponding interplanar distances as obtained with
ProcessDiffraction.28 Lattice parameters were calculated using
XRDA.29 Optical microscopy images of micrometer-sized aggre-
gates were obtained with a Axioscope A1 microscope (Carl Zeiss,
Fig. 1. X-ray powder diffraction patterns of (a) the white precipitate
obtained after soaking zirconium tungstate in boiling 1M NaOH solu-
tion for 5 h and (b) pristine zirconium tungstate (a–ZrW2O8).
soaking of zirconium tungstate was accompanied by a 85%
weight loss and, according to EDS semiquantitative elemental
analysis, the tungsten content was reduced from 24%mol in zir-
conium tungstate to o0.6%mol in the white precipitate.
The selective leaching of tungsten by soaking of ZrW2O8 in
boiling NaOH solution was further confirmed by chemical anal-
ysis of the filtered solution, which revealed the presence of the
WOꢀ4 2 ion by reacting it with hydrochloric acid and a small pel-
let of zinc, giving a blue coloration (tungsten blue).30 A second
test with tin chloride also confirmed the presence of the tung-
state ion in solution.30 Accordingly, the reaction taking place
upon soaking of zirconium tungstate with sodium hydroxide
solution should produce either hydrous zirconia
ZrW2O8 þ 4NaOH ! ZrO2 ꢁ 2H2O þ 2Na2WO4
or anhydrous zirconium hydroxide
ZrW2O8 þ 4 NaOH ! ZrðOHÞ4 þ 2Na2WO4
the latter probably getting some water from the solution to give
Zr(OH)4 ꢁ nH2O. After neutralizing the waste solution with HCl,
tungsten can be recovered in the form of calcium tungstate by
precipiting it with calcium chloride.
Gottingen, Germany) in transmitted-light mode.
¨
III. Results and Discussion
The X-ray powder diffraction pattern from the white precipitate
obtained after soaking zirconium tungstate in boiling 1M
NaOH solution is typical of an amorphous or nanocrystalline
material (Fig. 1). EDS semiquantitative elemental analysis
obtained by SEM (Fig. 2) revealed that the white precipitate is
almost completely depleted of W, thus suggesting that soaking
of a-ZrW2O8 in hot sodium hydroxide solution is a selective
process in which part of the structure is leached. In fact, the
Fig. 2. Energy-dispersive spectroscopy analysis of (a) a-ZrW2O8 and
(b) the white precipitate obtained from soaking zirconium tungstate in
boiling NaOH solution.

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Journal of the American Ceramic Society—Somavilla et al.
Vol. 94, No. 8
Fig. 3. TGA analysis of the white precipitate dried overnight in a oven
at 1201C and them exposed to air before the measurement.
Fig. 4. DRIFTS analysis of (—) the white precipitate obtained by
soaking of zirconium tungstate with sodium hydroxide solution (dried
overnight in a oven at 1201C and them exposed to air before the mea-
surement) and (- - - -) m-ZrO2 obtained from the white precipitate by
thermal treatment at 13001C/24 h.
Zirconium hydroxide Zr(OH)4 ꢁ nH2O and hydrous zirconia
ZrO2 ꢁ nH2O are structurally very similar and have been often
treated as a single compound in the literature. In fact, according
to the literature the probable structure of hydrous zirconia
differs slightly from that of zirconium hydroxide, with Zr at-
oms bonded by an oxygen atom instead of a pair of hydroxo
bridges.1 Despite of the great similarity, there are some differ-
ences between hydrous zirconia and zirconium hydroxide that
may help to clarify the nature of the white precipitate obtained
from zirconium tungstate. For instance, zirconium hydroxide
readily dissolves into hydrochloric acid 1M solution, while hy-
drous zirconia is relatively impervious to acid digestion.1,31
The white precipitate obtained from ZrW2O8 resisted to treat-
ment with hydrochloric acid 1M solution for ten minutes with a
weight loss inferior to 9%.31 Moreover, upon heating, the white
precipitate obtained by soaking zirconium tungstate in hot
sodium hydroxide solution undergone a weight loss around
23%, as can be seen in Fig. 3. The weight loss upon heating is
reported to be around 22% and 32% for hydrous zirconia and
hydrated zirconium hydroxide (Zr(OH)4 ꢁ 2H2O), respectively.1
The weight loss upon heating and the resistance to acid digestion
both indicate that the white powder obtained by soaking zirco-
nium tungstate in boiling NaOH solution is, at least, mainly
composed of hydrous zirconia, ZrO2 ꢁ 2H2O. Furthermore, the
weight loss of the sample in the soaking process (about 85%, by
measuring the weight of the dehydrated precipitate) is also con-
sistent with the formation of hydrous zirconia (79% weight loss
considering the dehydrated product), especially considering the
losses during the process and that some zirconia may be well
dissolving into the boiling NaOH solution. For comparison, the
weight loss for the formation of anhydrous zirconium hydroxide
should be of 74%.
Noteworthy, the 23% weight loss that the sample of hydrous
zirconia exhibits upon heating to 6001C is also observed under
very mild conditions, when the sample is submitted to a thermal
treatment at 601C, in a vacuum of 10ꢀ5 mbar during 5 h. Upon
exposure to ambient conditions, samples of dehydrated hydrous
zirconia absorb water until fully recovering its initial mass. Also,
the precise weight loss exhibited by the samples of hydrous zir-
conia may vary according to the conditions under which the
sample was storaged.
The presence of water in the white precipitate is also evident
in the DRIFTS results (Fig. 4). Infrared bands assigned to O–H
stretching and to the water scissoring mode, at around 3500 and
1640 cmꢀ1, respectively, are clearly seem in the DRIFTS spec-
trum of the white precipitate. These bands are absent (or are
very weak) in the spectrum of the sample heated to 13001C/24 h.
Besides that, the DRIFTS spectrum of the white precipitate
clearly exhibits an infrared band at 1340 cmꢀ1, which has been
assigned to coordinated hydroxyl groups (dZr–O–H) in hydrous
zirconia.32
The findings so far described strongly suggest that the white
precipitate obtained by soaking zirconium tungstate with so-
dium hydroxide solution can be identified as mainly composed
of hydrous zirconia, ZrO2 ꢁ 2H2O. However, it is not possible to
tell, solely on the basis of XRD analysis, whether the hydrous
zirconia obtained from zirconium tungstate is truly amorphous
or just nanocrystalline. TEM analysis was thus performed and
some results are presented in Fig. 5.
TEM images show agglomerates of nanoparticles o2 nm. In
fact, the nanoparticle size distribution histogram (inset on
Fig. 5a) obtained from the analysis of TEM images reveals a
monomodal distribution with an average diameter of 1.8 nm
and a full-width at half-maximum of only 0.6 nm. Furthermore,
the HRTEM image in Fig. 5(b) clearly exhibits crystalline
planes, giving strong evidence that the hydrous zirconia nano-
particles are actually nanocrystalline instead of truly amor-
phous. This has been corroborated by the SAED pattern
shown as an inset in Fig. 5(b), which exhibits well-defined
diffraction spots. The SAED pattern was analyzed using Pro-
cessDiffraction,28 yielding a set of four interplanar distances
˚
(2.535, 1.465, 0.957, and 0.702 A) which could be indexed ac-
cording to a tetragonal Bravais lattice, as the (001), (100), (111),
˚
˚
and (201) lattice planes, with a 5 1.463(4) A and c 5 2.535(6) A.
The actual lattice parameters should vary according to the water
content of the sample under the vacuum conditions during the
TEM analysis.
The evolution of the sample of hydrous zirconia upon suc-
cessive 24 h thermal treatments at increasing temperatures was
followed by XRD. Figure 6 shows XRD patterns taken at am-
bient temperature for a hydrous zirconia sample as prepared,
and after successive thermal treatments from 5001 up to 13001C.
The pristine sample exhibit broad peaks, characteristic of a
material with very small coherent domain size. Those broad
peaks remain almost unaltered even after prolonged thermal
treatments up to 6001C. Coarsening begins at 6001C, but rea-
sonably well-defined t-ZrO2 Bragg peaks appear only after a
8001C/24 h thermal treatment. Bragg peaks from m-ZrO2 be-
came more evident in the pattern taken from the sample heated
to 10001C. The tetragonal and monoclinic phases of zirconia
coexist in samples heated up to 12001C. Above this temperature,
only Bragg peaks from m-ZrO2 are seen in the XRD pattern of
the sample.
The high temperature needed to promote crystallization of
nanocrystalline hydrous zirconia into t-ZrO2 is noteworthy. In-
deed, while amorphous precursors usually start to crystallize
into t-ZrO2 at temperatures between 4001 and 6001C, the hy-
drous zirconia obtained by soaking zirconium tungstate with

August 2011
Nanocrystalline Hydrous Zirconia from Zirconium Tungstate
2643
Fig. 6. Room temperature X-ray powder diffraction patterns of hy-
drous zirconia previously submitted to successive 24 h thermal treat-
ments at increasing temperatures. The tick marks below the patterns
taken with the samples previously heated to 9001 and 13001C indicate
the expected positions of the Bragg peaks for t-ZrO2 and m-ZrO2,
respectively.
prolonged thermal treatment at 6001C. This is a key observation
for future work aiming to obtain ceramic bodies made of nano-
crystalline zirconia, as will be further discussed below.
Some experiments were also conducted with amorphous
zirconium tungstate to determine the influence of particular
features of the a-ZrW2O8 structure on the production of
hydrous zirconia by soaking with sodium hydroxide solution.
a-ZrW2O8 exhibits an open framework structure consisting of a
tridimensional arrangement of corner-shared ZrO6 and WO4
polyhedra. For each WO4 unit, three oxygen atoms are shared
Fig. 5. (a) TEM image of hydrous zirconia nanoparticles. The inset
shows the particle size distribution. (b) HRTEM image exhibiting indi-
vidual hydrous zirconia nanoparticles with clearly distinct crystalline
planes. The inset shows the SAED pattern of hydrous zirconia
nanoparticles.
sodium hydroxide solution has to be heated to 8501C for 24 h to
begin exhibiting reasonably well-defined t-ZrO2 Bragg peaks.
Whether this is a consequence of a hindered kinetics or the result
of a greater thermodynamic stability due to the extremely small
coherent domain size of the hydrous zirconia remains to be fur-
ther explored.
The XRD patterns exhibited in Fig. 6 were used to evaluate
the temperature dependence of the volume-weighted coherent
domain size (crystallite size) of hydrous zirconia and the t-ZrO2
and m-ZrO2 obtained from it.26 The calculations were
performed using the peaks around 2y 5 30.21 for hydrous
zirconia and t-ZrO2 and 2y 5 28.21 for m-ZrO2. The results
are shown in Fig. 7.
For the sample as prepared, the coherent domain size is ex-
tremely small (1.5 nm) and is very similar to the particle size as
determined from the analysis of TEM images of individual hy-
drous zirconia nanoparticles. It is noteworthy that the volume-
weighted average crystallite size remains o3.5 nm even after a
Fig. 7. Volume-weighted average domain size versus temperature of
thermal treatment of hydrous zirconia, t-ZrO2 and m-ZrO2. Dotted line
is just a guide to the eye.

2644
Journal of the American Ceramic Society—Somavilla et al.
Vol. 94, No. 8
light. These images were taken from the white precipitate ob-
tained after soaking zirconium tungstate with hot NaOH solu-
tion, dried overnight in a oven at 1201C, i.e., without any further
heating that could promote sintering. Indeed, given the ex-
tremely small crystallite size of the hydrous zirconia reported
in this work, the reduction of surface energy should be a very
effective driven force for sintering, even at temperatures only
slightly above room temperature. This observation, along with
the fact that hydrous zirconia dehydrates under very mild con-
ditions (for instance, by heating to 601C under a vacuum of 10ꢀ5
mbar), suggests the possibility that fully densified, transparent
ceramic bodies made of very small crystallite size anhydrous
zirconia may be obtained under controlled conditions. With this
aim in mind, further studies are being conducting trying to sta-
bilize the hydrous zirconia nanoparticles in suspension.
IV. Conclusions
Hydrous zirconia nanoparticles were produced by soaking zir-
conium tungstate in boiling 1M NaOH solution for 5 h. The
crystalline nature of the hydrous zirconia nanoparticles was
investigated by TEM and XRD. Individual nanoparticles
exhibited a narrow size distribution centered at 1.8 nm, in ac-
cordance with the volume-weighted coherent domain size of 1.5
nm, as determined by XRD. The extremely small crystalline
domain size is probably responsible for the unusually high tem-
peratures needed to promote the conversion from hydrous zir-
conia, ZrO2 ꢁ 2H2O, into t-ZrO2 (8501C) and m-ZrO2 (10001C)
and, also, for the formation of nearly pore-free, micrometer-sized
agglomerates. Further studies are needed in order to control the
aggregation of the hydrous zirconia nanoparticles. Once a suc-
cessful strategy has been devised, nanocrystalline hydrous zir-
conia suspensions could be used, among others possible
applications, to prepare polymer–ceramic nanocomposites with
high refraction index. Incorporation of phase stabilizers (such as
yttrium) depends on finding a suitable precursor. Furthermore,
controlled deposition from nanocrystalline hydrous zirconia sus-
pensions by ultracentrifuging, followed by removal of hydratat-
ion water under very mild conditions could allow obtaining cold
sintered bodies of anhydrous zirconia without coarsening, with
mean crystallite size in the range of a few nanometers.
Acknowledgments
We thank Jim Walker, from Wah Chang Co. (Albany, OR), for the sample of
zirconium tungstate. TEM analysis was performed in the Centro de Microscopia
Fig. 8. SEM images of hydrous zirconia agglomerates at (a) low and
(b) high magnification, and (c) optical microscopy image showing trans-
parent, nearly fully densified polycrystalline agglomerates of nanocrys-
talline hydrous zirconia.
Eletro
Alegre, Brazil. Thanks are due to Ca
Marcia R. Gallas (Laboratorio de Altas Presso
ˆ
nica (CME) at the Universidade Federal do Rio Grande do Sul, Porto
ssio R. de Almeida for his assistance and to
es e Materiais Avan@ados, Univ-
´
´
´
˜
ersidade Federal do Rio Grande do Sul) for the sample of amorphous zirconium
tungstate.
with Zr, while the fourth atom is bonded only to W and is re-
ferred to as terminal oxygen. Zirconium tungstate undergoes
pressure-induced amorphization and previous results from O1s
X-ray photoelectron spectroscopy give strong evidence that
the amount of terminal oxygen atoms is greatly reduced in the
amorphous phase.24,33 Accordingly, to verify to what extent the
presence of terminal oxygen in a-ZrW2O8 may be determinant
for the obtainment of hydrous zirconia by soaking zirconium
tungstate with sodium hydroxide solution, the same experiment
was performed with a sample of amorphous zirconium tungstate
prepared at 7.7 GPa. Tungsten was lixiviated from amorphous
ZrW2O8 the same way as with a-ZrW2O8, leading to the con-
clusion that the presence of terminal oxygen atoms in a-ZrW2O8
is not determinant for the successful production of hydrous
zirconia.
References
1C. Huang, Z. Tang, and Z. Zhang, ‘‘Differences between Zirconium Hydroxide
(Zr(OH)4 ꢁ nH2O) and Hydrous Zirconia (ZrO2 ꢁ nH2O),’’ J. Am. Ceram. Soc., 84
[7] 1637–8 (2001).
2J. Joo, T. Yu, Y. W. Kim, H. M. Park, F. Wu, J. Z. Zhang, and T. Hyeon,
‘‘Multigram Scale Synthesis and Characterization of Monodisperse Tetragonal
Zirconia Nanocrystals,’’ J. Am. Chem. Soc., 125 [21] 6553–7 (2003).
3P. Li, I. W. Chen, and J. E. Penner-Hahn, ‘‘X-Ray-Absorption Studies of Zir-
conia Polymorphs. 1. Characteristic Local Structures,’’ Phys. Rev. B, 48 [14]
10063–73 (1993).
4R. H. J. Hannink, P. M. Kelly, and B. C. Muddle, ‘‘Transformation Tough-
ening in Zirconia-Containing Ceramics,’’ J. Am. Ceram. Soc., 83 [3] 461–87 (2000).
5R. Stevens., Zirconia and Zirconia Ceramics;, 2nd edition, Magnesium Elekt-
ron Ltd., Manchester, U.K., 1986.
6S. Jaenicke, G. K. Chuah, V. Raju, and Y. T. Nie, ‘‘Structural and Morpho-
logical Control in the Preparation of High Surface Area Zirconia,’’ Catal. Surv.
Asiac., 12, 153–69 (2008).
7S. So
ˆ miya, F. Aldinger, N. Claussen, R. M. Spriggs, K. Uchino, K. Koumoto,
Hydrous zirconia produced from zirconium tungstate exhib-
its a tendency to form micrometer-sized agglomerates of nano-
crystalline particles. This can be seen in images obtained by
SEM and optical microscopy, as shown in Fig. 8. The images
shown in Fig. 8 exhibit what seem to be fully densified, nearly
pore-free agglomerates, some of them even transparent to visible
and M. Kaneno, Handbook of Advanced Ceramics, Vol. 1, pp. 471–513. Elsevier
Academic Press, London, U.K., 2003.
8J. Haines, J. M. Le
´
ger, S. Hull, J. P. Petitet, A. S. Pereira, C. A. Perottoni, and
J. A. H. da Jornada, ‘‘Characterization of the Catunnite-Type Phases of Zirconia
and Hafnia by Neutron Diffraction and Raman Spectroscopy,’’ J. Am. Ceram.
Soc., 80 [7] 1910–4 (1997).

August 2011
Nanocrystalline Hydrous Zirconia from Zirconium Tungstate
2645
9S. Wang, Y. Zhai, X. Li, Y. Li, and K. Wang, ‘‘Coprecipitation Synthesis
of MgO-Doped ZrO2 Nano Powder,’’ J. Am. Ceram. Soc., 89 [11] 3577–81
(2006).
22D. A. Zyuzin, E. M. Moroz, A. S. Ivanova, and A. N. Shmakov, ‘‘Structure
Characteristics of Disordered Zirconium Hydroxoxides,’’ Cryst. Rep., 48 [3] 413–5
(2003).
10M. Trunec and K. J. Maca, ‘‘Compaction and Pressureless Sintering of Zir-
conia Nanoparticles,’’ J. Am. Ceram. Soc., 90 [9] 2735–40 (2007).
11M. Rezaei, S. M. Alavi, S. Sahebdelfar, and Z. F. Yan, ‘‘Mesoporous Nano-
crystalline Zirconia Powders: A Promising Support for Nickel Catalyst in CH4
Reforming with CO2,’’ Mater. Lett., 61, 2628–31 (2007).
23C. A. Perottoni, ‘‘Transi@o
altas pressoes’’; Ph.D. Thesis, Instituto de Fı
2000.
˜
es de fase em compostos de estrutura aberta sob
sica-UFRGS, Porto Alegre, Brazil,
˜
´
24C. A. Perottoni and J. A. H. da Jornada, ‘‘Pressure-Induced Amorphization
and Negative Thermal Expansion in ZrW2O8,’’ Science, 280 [5365] 886–9
(1998).
12M. Inoue, K. Sato, T. Nakamura, and T. Inui, ‘‘Glycothermal Synthesis of
Zirconia-Rare Earth Oxide Solid Solutions,’’ Catal. Lett., 65, 79–83 (2000).
13T. Yamaguchi, ‘‘Application of ZrO2 as a Catalyst and a Catalyst Support,’’
Catal. Today, 20 [2] 199–217 (1994).
25T. Roisnel and J. Rodriguez-Carvajal, ‘‘WinPLOTR: A Windows Tool for
Powder Diffraction Pattern Analysis,’’ Mater. Sci. Forum, 378–381, 118–23 (2001).
26R. Delhez, T. H. de Keijser, J. I. Langford, D. Louer, J. Mittemeijer, and
¨
14K. Tanabe, ‘‘Surface and Catalytic Properties of ZrO2,’’ Mater. Chem. Phys.,
13 [3–4] 347–64 (1985).
E. J. Sonneved, ‘‘The Rietveld Method’’; pp. 146–52 in IUCr Monographs on
Crystallography, Edited by R. A. Young. Oxford University Press, Oxford, U.K.,
1993.
15K. Tanabe and T. Yamaguchi, ‘‘Acid-Base Bifunctional Catalysis by ZrO2 and
its Mixed Oxides,’’ Catal. Today, 20 [2] 185–97 (1994).
27J. I. Goldstein, D. E. Newbury, P. Echlin, D. C. Joy, A. D. Romig Jr., C. E.
Lyman, C. Fiori, and E. Lifshin, Scanning Electron Microscopy and X-Ray
Microanalysis, 2nd edition, pp. 404–20. Plenum Press, New York, 1992.
16K. G. Kanade, J. O. Baeg, S. K. Apte, T. L. Prakash, and B. B. Kale, ‘‘Syn-
thesis and Characterization of Nanocrystallined Zirconia by Hydrothermal
Method,’’ Mater. Res. Bull., 43, 723–9 (2008).
28J. L. La
bar, ‘‘Consistent Indexing of a (Set of) Single Crystal SAED Pattern(s)
´ ´
17V. F. Petrunin, V. V. Popov, Z. Hongzhi, and S. A. Korovin, ‘‘Stability of
High-Temperature Phases of Ultrafine Zirconia,’’ Glass Phys. Chem., 31 [4] 459–64
(2005).
with the ProcessDiffraction Program,’’ Ultramicroscopy, 103, 237–49 (2005).
29S. Desgreniers and K. Lagarec, ‘‘XRDA—A Program for Energy-Dispersive
X-Ray-Diffraction Analysis on a PC,’’ J. Appl. Crystallogr., 27, 432–4 (1994).
30S. Svehla, Vogel’s Textbook of Macro and Semimicro Qualitative Inorganic
Analysis, 5th edition, Longman Group Limited, New York, 1979, 510pp.
31C. Huang, Z. Tang, Z. Zhang, and J. Gong, ‘‘Study on a New, Environmen-
tally Benign Method and its Feasibility of Preparing Nanometer Zirconia Pow-
der,’’ Mater. Res. Bull., 35 [9] 1503–8 (2000).
18M. W. Pitcher, S. V. Ushakov, A. Navrotsky, B. F. Woodfield, G. Li, J. Boe-
rio-Goates, and B. M. Tissue, ‘‘Energy Crossovers in Nanocrystalline Zirconia,’’
J. Am. Ceram. Soc., 88 [1] 160–7 (2005).
19E. Torres-Garcia, A. Pela
iz-Barranco, C. Vasquez-Ramos, and G. A. Fuentes,
´ ´
‘‘Thermal and Structural Characterization of the ZrO2ꢀx(OH)2x to ZrO2 Transi-
tion,’’ J. Mater. Res., 16 [8] 2209–12 (2001).
32G. Davidson, Spectroscopic Properties of Inorganic and Organometallic Com-
pounds, Vol. 35. RSC, Manchester, U.K., 2002, 243pp.
20H. Wang, G. Li, Y. Xue, and L. Li, ‘‘Hydrates Surface Structure and its Im-
pacts on the Stabilization of t-ZrO2,’’ J. Solid State Chem., 180, 2790–7 (2007).
21M. K. Naskar and D. J. Ganguli, ‘‘Range of Metastability of Tetragonal Zir-
conia in Some Rare Earth Doped Zirconia Fibers,’’ J. Mater. Sci. Lett., 17 [23]
1971–3 (1998).
33C. A. Figueire
ˆ do, J. Catafesta, J. E. Zorzi, L. Salvador, I. J. R. Baumvol, M.
R. Gallas, J. A. H. da Jornada, and C. A. Perottoni, ‘‘Compression Mech-
anism and Pressure-Induced Amorphization of g-ZrW2O8,’’ Phys. Rev. B, 76
[18] 184201–7 (2007).
&