Synthesis of nanocrystalline ZrO2 with tailored phase composition and microstructure under high-power sonication

Article abstract of DOI:10.1134/S0020168512050214

The effect of sonication on the composition and properties of zirconia precipitated from aqueous zirconyl nitrate solutions at various pH values has been studied using thermal analysis, X-ray diffraction, and low-temperature nitrogen adsorption measuremen

Full text of DOI:10.1134/S0020168512050214

ISSN 0020ꢀ1685, Inorganic Materials, 2012, Vol. 48, No. 5, pp. 494–499. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © A.D. Yapryntsev, A.E. Baranchikov, N.N. Gubanova, V.K. Ivanov, Yu.D. Tret’yakov, 2012, published in Neorganicheskie Materialy, 2012, Vol. 48, No. 5,
pp. 576–582.
Synthesis of Nanocrystalline ZrO with Tailored Phase Composition
2
and Microstructure under HighꢀPower Sonication
a
b
c
b
a
A. D. Yapryntsev , A. E. Baranchikov , N. N. Gubanova , V. K. Ivanov , and Yu. D. Tret’yakov
a
Moscow State University, Moscow, 119899 Russia
b
Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences,
Leninskii pr. 31, Moscow, 119991 Russia
Konstantinov Institute of Nuclear Physics, Russian Academy of Sciences,
c
Orlova Roshcha, Gatchina, Leningrad oblast, 188300 Russia
Received November 9, 2011
Abstract—The effect of sonication on the composition and properties of zirconia precipitated from aqueous
zirconyl nitrate solutions at various pH values has been studied using thermal analysis, Xꢀray diffraction, and
lowꢀtemperature nitrogen adsorption measurements. The results demonstrate that acoustic processing conꢀ
siderably reduces the content of sorbed ions in amorphous ZrO2 ⋅ xH O gels and allows one to control the
2
composition and microstructure of the nanocrystalline zirconia produced through thermal decomposition of
the gels.
DOI: 10.1134/S0020168512050214
INTRODUCTION
EXPERIMENTAL
Hydrous zirconia was prepared by slowly adding
aqueous ammonia (2.7 M) to an aqueous 0.25 M soluꢀ
tion of zirconyl nitrate, ZrO(NO3)2, with constant
stirring, until the pH of the solution was 5.26, 7.17, or
One of the most promising approaches to the synꢀ
thesis of inorganic materials in highly dispersed and
nanoparticulate states is highꢀpower sonication. In
recent years, a number of studies have been concerned
with the use of sonochemical techniques for the prepꢀ
aration of simple and complex nanoparticulate subꢀ
stances with tailored properties [1–3].
8
.99. The solution pH was monitored with a Crison
GLPꢀ22 pH meter, equipped with a multipurpose
measuring electrode and thermocompensator. Precipꢀ
itations were carried out in a thermostated cell. The
temperature was maintained at 20
ZrO2 H O was precipitated in the same conditions
The mechanisms of sonochemical reactions in
homogeneous liquids have been studied in sufficient
detail. The results were systematized in terms of two
main theories: hot spot theory [4] and local electrizaꢀ
tion of the surface of cavitation bubbles [5]. At the
same time, the specifics of the physicochemical proꢀ
cesses that take place in heterogeneous systems under
highꢀpower acoustic processing conditions are far less
well understood. In particular, the effect of sonication
on heterogeneous systems containing nanoparticles
±
1°С. In addition,
⋅
x
2
but under sonication. The ultrasound source used was
a Bandelin Sonopuls HD 3200 generator equipped
with a submerged titanium waveguide. The ultrasound
frequency was 20 kHz, and the effective acoustic
2
power density was 35 W/cm .
After the precipitation, the resultant suspensions
were vigorously stirred for an additional 15 min. The
suspensions prepared under sonication were stirred in
an ultrasonic field. Next, the precipitates were washed
with distilled water several times, separated by centrifꢀ
(
e.g., sols) and on amorphous gels that result from the
aggregation of colloidal particles has been studied litꢀ
tle. The evolution of such systems in an acoustic field
was studied using amorphous silica [6] and iron(III)
hydroxide [7] as examples. The results indicate that
ugation (8000 rpm), and airꢀdried at 50°С for 24 h.
The hydrous zirconia xerogels prepared at pH 5.26,
ultrasonic processing increases the gelation rate and 7.17, and 8.99 without sonication will be referred to as
changes the mesostructure of the resulting gel (in parꢀ Zꢀ5C, Zꢀ7C, and Zꢀ9C. The samples prepared under
ticular, the density, particle size, aggregate size, and sonication will be designated Zꢀ5US, Zꢀ7US, and
fractal characteristics of the surface).
Zꢀ9US.
The xerogels were annealed in air in a muffle furꢀ
nace at 400, 500, 600, 700, and 800 for 5 h.
The samples were characterized by thermogravimꢀ
The purpose of this work was to study the effect of
sonication at various pH values of the medium on the
thermal characteristics of amorphous hydrous zirconia
°С
and on the phase composition and microstructure of etry (TG) and differential thermal analysis (DTA) in
nanocrystalline zirconia hydrolysis products. air at temperatures from 20 to 1000° using a Pyris
С
494

SYNTHESIS OF NANOCRYSTALLINE ZrO WITH TAILORED PHASE COMPOSITION
495
2
Diamond thermal analyzer (PerkinElmer). The heatꢀ
ing rate was 10° /min.
The phase composition of the samples was deterꢀ
mined by Xꢀray diffraction (XRD) on a Rigaku
Consider now the TG curves of the samples preꢀ
pared in the acid and neutral solutions (pH 5.26 and
.17) under sonication (Fig. 1b). The key feature of
these curves is that there is little or no weight loss durꢀ
ing zirconia crystallization. This indicates that the
amount of nitrate ions adsorbed on the surface of the
particles forming in an ultrasonic field is considerably
smaller than that in the control experiments.
С
7
D/MAX 2500 diffractometer (Cu
K radiation, scan
α
rate of
2
°
2 /min). Diffraction peaks were indexed
θ
using JCPDS PDF data. The crystallite size of zircoꢀ
nia was determined by the Scherrer formula:
The TG curves of the samples prepared in an alkaꢀ
line solution (pH 8.99) with or without ultrasonic proꢀ
cessing differ significantly from those of the samples
obtained in the acid and neutral solutions. The DTA
curve of the control sample shows no highꢀtemperaꢀ
ture nitrate decomposition step and is very similar to
the DTA curve of the sample precipitated in the same
conditions but under sonication. Also, there is no lowꢀ
temperature ammonium nitrate decomposition step.
Kλ
Dhkl
=
,
(1)
[
β
(
2θ
)
− s
]
cos θ
hkl
where
θ
is the peak position,
λ
is the Cu
K
Xꢀray waveꢀ
is the true physical
s is the instrumental
α
length (0.154056 nm),
β
hkl(2
θ
)
broadening of the peak, and
broadening (0.1
taken to be unity. To determine
°
). The Scherrer constant (
K) was
, backgroundꢀsubꢀ
β
tracted 111 and 111 diffraction line profiles of monoꢀ These features lead us to conclude that there are few or
clinic and 101 of tetragonal ZrO2 were fitted with no adsorbed nitrate ions in the corresponding samples,
pseudoꢀVoigt functions.
The contents of the monoclinic (MꢀZrO2) and tetꢀ
ragonal (TꢀZrO2) zirconia polymorphs in our samples
were evaluated from XRD data using relations
reported by Toraya et al. [8].
Specific surface areas were determined by lowꢀ
temperature nitrogen adsorption measurements with
an ATXꢀ6 analyzer (KATAKON, Russia). Prior to
which fits well with the data on the variation of the
phase composition of ZrO2 xH O with pH during
⋅
2
synthesis [9].
Consider the phase compositions of the hydrous
zirconia xerogels annealed at temperatures from 400
to 800°
С
. Heat treatment of ZrO2 nH O leads to zirꢀ
⋅
2
conia crystallization in the form of the tetragonal and
monoclinic phases. The phase composition of the
annealing products is determined by the ZrO2 xH O
⋅
2
measurements, the samples were outgassed at 150°С
xerogel preparation conditions. Figure 2 plots the perꢀ
centage of tetragonal zirconia against annealing temꢀ
perature. It can be seen that, at relatively low temperꢀ
in flowing dry helium for 30 min. The specific surface
of the powders was evaluated using BET analysis (six
points).
atures (up to 600°С), heat treatment of the xerogel
precipitated in the alkaline solution without sonicaꢀ
tion produces no monoclinic ZrO2, and the annealing
product is phaseꢀpure tꢀZrO2. Heat treatment of samꢀ
ples Zꢀ5C and Zꢀ7C, precipitated in the acid and neuꢀ
tral solutions leads to the formation of a mixture of
RESULTS AND DISCUSSION
The TG curves of the hydrous zirconia xerogels are
presented in Fig. 1.
The weight loss curves of the control samples are tꢀZrO2 and mꢀZrO2 (containing 10–15% mꢀZrO2).
seen to differ markedly in shape. In particular, the The formation of monoclinic ZrO2 during heat treatꢀ
weight loss of the samples prepared in acid and neutral ment of these samples and the absence of mꢀZrO2 in
solutions (Zꢀ5C and Zꢀ7C) occurs in several steps. the annealing products of sample Zꢀ9C (in the range
The first step (below 200°С
) is the removal of sorbed 400–600°С) are consistent with a model for size stabiꢀ
water. The second step (200–400
°С
) is probably the lization of tꢀZrO2 [10–12], according to which metaꢀ
decomposition of trace amounts of ammonium nitrate stable tetragonal zirconia can be obtained under ordiꢀ
and nitrateꢀcontaining zirconium hydroxy comꢀ nary conditions when its particle size is below 30 nm.
pounds through highꢀtemperature hydrolysis. The Indeed, the particle sizes of the tꢀZrO2 produced by
third decomposition step, with the highest rate at annealing samples Zꢀ5C and Zꢀ7C [evaluated using
440–445°С
, is the complete removal of nitrates relation (1)] differ little and lie in the range 31–36 nm,
through pyrolysis in parallel with zirconia crystallizaꢀ whereas the particle size of the tꢀZrO2 obtained by
tion. Note that the decomposition of the nitrateꢀconꢀ annealing sample Zꢀ9C at temperatures from 400 to
taining zirconium compounds is accompanied by an 600°
С
is 24–25 nm (Fig. 3).
appreciable heat absorption.
At the same time, all of the samples precipitated
The pyrolytic character of the highꢀtemperature under sonication and heatꢀtreated at temperatures
nitrate decomposition step is supported by the DTA from 400 to 600° contain insignificant amounts of
curves in this temperature range (Fig. 1c). It can be monoclinic ZrO
С
.
2
seen that the exothermic zirconia crystallization proꢀ
cess occurs concurrently with the endothermic 800
Increasing the heatꢀtreatment temperature to 700–
markedly increases the rate of the tꢀZrO2
°С
→
decomposition process. As a result, the net heat effect mꢀZrO2 phase transition in the xerogels precipitated at
of the process is insignificant in magnitude. pH 8.99 (Fig. 2). The monoclinicꢀZrO2 content of the
INORGANIC MATERIALS Vol. 48
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496
YAPRYNTSEV et al.
Δ
m/m0
1.0
0.9
0.8
0.7
0.6
0.5
0.4
(а)
(b)
1
2
3
4
5
6
(d)
(c)
1
4
2
3
5
6
100
200
300
400
°
500
600 100
200
300
400
500
600
Temperature
,
C
Temperature, °C
Fig. 1. (a, b) TG and (c, d) DTA curves of samples (1) Zꢀ5C, (2) Zꢀ7C, (3) Zꢀ9C, (4) Zꢀ5US, (5) Zꢀ7US, and (6) Zꢀ9US.
samples prepared under sonication considerably mation in samples Zꢀ5US and Zꢀ7US was much lower
exceeds that of the control samples. In particular, after than that in sample Zꢀ9US. It seems likely that this
heat treatment of the asꢀprepared xerogels at 800
°С
was mainly due to the stabilization of the tetragonal
for 5 h the degree of conversion was 33 and 12%, phase by impurity ions and not to the size effect: the
respectively. Note that the rate of the phase transforꢀ tꢀZrO2 particles in the samples prepared from xerogels
INORGANIC MATERIALS Vol. 48
No. 5
2012

SYNTHESIS OF NANOCRYSTALLINE ZrO WITH TAILORED PHASE COMPOSITION
497
2
ω
(t
ꢀZrO2)
v
(а)
(
b)
100
90
80
70
60
1
2
3
400
500
600
700
800
400
500
600
700
800
Temperature
,
°
C
Temperature, °C
Fig. 2. Volume percent of tetragonal ZrO2 as a function of annealing temperature for (a) the control samples precipitated at pH
(1) 5.26, (2) 7.17, and (3) 8.99 and (b) the samples precipitated at the same solution pH values but under sonication.
(
а)
(b)
45
40
35
30
25
20
1
2
3
400
500
600
Temperature
700
800 400
500
600
Temperature, °C
700
800
,
°
C
Fig. 3. Particle size of
t
ꢀZrO2 as a function of annealing temperature for (a) the control samples precipitated at pH (
1) 5.26,
(2
) 7.17, and ( ) 8.99 and (b) the samples precipitated at the same solution pH values but under sonication.
3
INORGANIC MATERIALS Vol. 48
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498
YAPRYNTSEV et al.
2
SBET, m /g
150
(а)
(b)
1
2
3
100
50
0
1
00 200 300 400 500 600 700 800 100 200 300 400 500 600 700 800
Temperature Temperature
,
°
C
, °C
Fig. 4. Specific surface area as a function of annealing temperature for (a) the control zirconia samples precipitated at pH (
1) 5.26,
(2
) 7.17, and ( ) 8.99 and (b) the samples precipitated at the same solution pH values but under sonication.
3
Zꢀ5US and Zꢀ7US were larger than those in the samꢀ forming gels typically have a linear structure. With
ples obtained by annealing Zꢀ9US (Fig. 3).
increasing pH, the polycondensation rate increases
relative to the hydrolysis rate. As a consequence, the
hydrous zirconia gels synthesized under alkaline conꢀ
ditions have a branched structure and large specific
surface area.
The experimental data presented in Fig. 4 also lead
us to conclude that sonication ensures a considerable
increase in the specific surface area of the asꢀprepared
xerogels. Clearly, this effect is related to the distinctive
features of gel structure formation in an ultrasonic
field: under active cavitation conditions, intense local
liquid microflows and shock waves lead to the formaꢀ
tion of gels with a looser structure, which have a larger
specific surface area. Note also that the use of ultraꢀ
sonic processing allows one to obtain hydrous zirconia
gels with a larger specific surface area in acid solutions,
in contrast to other techniques.
Consider now the lowꢀtemperature nitrogen
adsorption data for the asꢀprepared hydrous zirconia
xerogels and heatꢀtreatment products (Fig. 4).
These data indicate that the specific surface area of
the unannealed zirconia xerogels increases considerꢀ
ably with increasing solution pH. This correlates well
with previous data of other groups [13–15] and ours
[
9]. In particular, it has been shown [16, 17] that the
structure of solid zirconyl chloride corresponds to the
formula [Zr (OH) Cl 16H O]4Cl 12H O. Accordꢀ
⋅
⋅
4
8
4
2
2
ing to smallꢀangle Xꢀray scattering results, solutions
also contain tetrameric planar complexes. In
Clearfield’s model [18], the interaction between the
tetramers in the early stages of polymerization leads to
the formation of an OH bridge pair in the plane of the
zirconium atoms. Precipitation of gels from zirconium
salt solutions by strong bases results in the formation of
With increasing annealing temperature, the speꢀ
a soꢀcalled Aꢀphase, which is commonly thought of as cific surface area of the powders decreases systematiꢀ
a twoꢀdimensional disordered structure formed by tetꢀ cally, and the distinctions between the samples preꢀ
ramers. It is well known that acid hydrolysis has a pared from the xerogels precipitated with and without
higher rate in comparison with condensation, so the sonication vanish. Clearly, this is due to the collapse of
INORGANIC MATERIALS Vol. 48
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SYNTHESIS OF NANOCRYSTALLINE ZrO WITH TAILORED PHASE COMPOSITION
499
2
pores through particle growth and coalescence of crysꢀ
tallites with the formation of monolithic structures.
Phys. Rev. B: Condens. Matter Mater. Phys., 2010, vol. 81,
paper 174 201.
. Toraya, H., Yoshimura, M., and Somiya, S., Calibration
Curve for Quantitative Analysis of the Monoclinic–Tetꢀ
8
Thus, the present results demonstrate that highꢀ
power sonication during hydrous zirconia precipitaꢀ
tion allows one to tune the composition and microꢀ
structure of the resulting material. In particular,
acoustic processing enables the preparation of xeroꢀ
gels containing much less impurities and having a conꢀ
siderably larger specific surface area (especially when
synthesis is conducted at a relatively low solution pH).
ragonal ZrO System by XꢀRay Diffraction, J. Am.
2
Ceram. Soc., 1984, vol. 67, pp. C119–C121.
9
. Ivanov, V.K., Kopitsa, G.P., Baranchikov, A.Ye., et al.,
Mesostructure, Fractal Properties and Thermal Decomꢀ
position of Hydrous Zirconia and Hafnia, Russ. J. Inorg.
Chem., 2009, vol. 54, no. 14, pp. 2091–2106.
1
0. Garvie, R.C., The Occurrence of Metastable Tetragonal
Zirconia As a Crystallite Size Effect, J. Phys. Chem.,
1
965, vol. 69, pp. 1238–1243.
ACKNOWLEDGMENTS
1
1. Djurado, E., Bouvier, P., and Lucazeau, G., Crystallite
Size Effect on the Tetragonal–Monoclinic Transition of
Undoped Nanocrystalline Zirconia Studied by XRD and
Raman Spectrometry, J. Solid State Chem., 2000,
vol. 149, pp. 399–407.
2. Shukla, S. and Seal, S., Thermodynamic Tetragonal
Phase Stability in Sol–Gel Derived Nanodomains of
Pure Zirconia, J. Phys. Chem. B, 2004, vol. 108,
pp. 3395–3399.
3. Gavrilov, V.Yu. and Zenkovets, G.A., Formation of the
Pore Structure of Zirconium Dioxide at the Stage of Gel
Aging, Kinet. Catal., 2000, vol. 41, pp. 561–565.
4. Stenina, I.A., Voropaeva, E.Yu., Veresov, A.G., et al.,
Effect of Precipitation pH and Heat Treatment on the
Properties of Hydrous Zirconium Dioxide, Russ. J.
Inorg. Chem., 2008, vol. 53, p. 350.
5. Stenina, I.A., Voropaeva, E.Yu., Brueva, T.R., et al.,
HeatꢀTreatment Induced Evolution of the Morphology
and Microstructure of Zirconia Prepared from Chloride
Solutions, Russ. J. Inorg. Chem., 2008, vol. 53, pp. 842–
848.
6. Clearfield, A. and Vaughan, P.A., The Crystal Structure
of Zirconyl Chloride Octahydrate and Zirconyl Bromide
Octahydrate, Acta Crystallogr., 1956, vol. 9, pp. 555–558.
This work was supported by the Russian Foundaꢀ
tion for Basic Research (grant no. 09ꢀ03ꢀ01067) and
the RF Ministry of Education and Science (grant
no. 14.740.11.0281).
1
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