Thermal and physical properties of ZrO2–AlO(OH) nanopowders synthesised by microwave hydrothermal method
J Therm Anal Calorim
Thermal and physical properties of ZrO2-AlO(OH) nanopowders synthesised by microwave hydrothermal method
Iwona Koltsov 0 1 2
Marta Przes´niak-Welenc 0 1 2
Jacek Wojnarowicz 0 1 2
Anna Rogowska 0 1 2
Jan Mizeracki 0 1 2
Maria Malysa 0 1 2
Giora Kimmel 0 1 2
0 Ben-Gurion University of the Negev , 8410501 Beersheba , Israel
1 Faculty of Applied Physics and Mathematics, Gdansk University of Technology , Narutowicza 11/12, 80-233 Gdan ́sk , Poland
2 & Iwona Koltsov
Industrially relevant nanopowder was synthesised by microwave hydrothermal synthesis to obtain wellcontrolled composition (ZrO2-AlO(OH) system) which was found to determine a number of physical and thermal characteristics. This study reports variation of particle size, density, specific surface area (SSABET), as well as thermal behaviour of nanopowder mixtures of ZrO2-AlO(OH) in the whole range of compositions. It was found that the onset temperature (Ton) of physically and chemically bounded water desorption depends on the Al3?/or AlO(OH) content. The lower content of Al3? in the ZrO2AlO(OH) system, the higher Ton of physically bound water desorption. There are three distinct temperature regions for water decomposition for nanomaterials investigated in air (at approximately 50, 250 and 450 C). These temperature ranges depend on particle size and chemical composition of ZrO2-AlO(OH) nanopowders. Materials were divided into three groups characterised by different properties: (1) ZrO2 with 2-12% of Al3?, where particle sizes are from 4 to 8 nm, (2) ZrO2 with 30-67% of AlO(OH), where particle sizes are from 10 to 13 nm, and (3) ZrO2 with 80-99% of AlO(OH), where particle sizes are from 13 to 23 nm. AlO(OH) content determines thermal and physico-chemical properties of synthesised ZrO2-AlO(OH) nanopowders.
Low-temperature DSC; Microwave hydrothermal synthesis; ZrO2-AlO(OH) nanopowders; Thermal stability; Water decomposition; High-temperature DSC-MS
Institute of High Pressure Physics, Polish Academy of
Sciences, Sokolowska 29/37, 01-142 Warsaw, Poland
It is well known that nanoparticle size, shape, surface
chemistry, dispersibility or sinterability are dependent on
external factors such as temperature, humidity or level of
contamination as well as being time dependent. This has
implications for industry, standardisation community and
regulators. Fundamental questions of sell-by date for
nanomaterial, environmental fate, toxicology and usability
in applications are being asked. It is known that
nanomaterials have a large specific surface area and that their
properties are often governed by surface processes. The
dynamics of such processes (agglomeration, dispersion or
sintering) are determined by external factors as well as
internal energy transitions. This presents a complex
problem where chemistry of material as well as its surface,
particle size and shape affect dynamics and practical
applications. One of such commercial applications is the
use of sintered ZrO2-based ceramics which are industrially
relevant nanomaterials in medical implants and dentistry.
Amongst other factors, thermal behaviour of nanopowders
is one of the most influential factor in this material system
governing material parameters. Chemical bonding of –OH
groups and physisorption of H2O on the surface depend on
material composition and its particle size. Their presence
may influence densification and sintering processes [
Nanomaterials used in biomedical applications,
especially the ones in implant and prosthetics applications area
received a lot of attention in recent years [
]. One of the
most promising bio-compatible materials systems is a
ceramic based on ZrO2. Synthesis of such ceramics
presents a number of challenges [
]. For a good sinterability,
synthesis of ZrO2-based ceramic powders with narrow
particle size distribution is of considerable interest [
Relative to their conventional micron-sized crystalline
counterparts, nano-ZrO2-based ceramics demonstrate better
materials properties and superplastic behaviour [
Therefore, nanograined ceramics hold promise of unique
mechanical properties that are not commonly found in
coarse-grained counterparts .
Generally, ZrO2 in the equilibrium state exists in three
polymorphic forms: monoclinic (m-ZrO2), tetragonal
(tZrO2) and cubic (c-ZrO2) [
]. The amount and type of
dopant and the synthesis route may determine the phases of
the crystalline product [
]. From existing crystallographic
forms of ZrO2, the tetragonal phase is the most demanded
phase because of its mechanical properties. From
crystallographic X-ray studies, it is not possible to distinguish
t-ZrO2 and c-ZrO2 phases [
] due to the overlap of their
characteristic diffraction lines.
The required t-ZrO2 phase is very often stabilised by
additional compounds such as yttria (Y2O3) [
it was found that t-ZrO2 can be stabilised at room
temperature by doping divalent or trivalent cations such as
Ca2? or Al3? which are much less expensive than Yttrium
]. The XRD studies show that the structure
remains unaltered even after 10 mol% of Al3? doping,
confirming the stability of such crystalline structure .
This opens a perspective for cost-effective synthesis and
sintering of bulk materials made from zirconia–alumina
alloys. Zirconia–alumina nanomaterials amongst other
advanced ceramics show superior mechanical properties,
chemical inertness and biocompatibility. They are used for
a wide range of applications such as biomedical implants
] and structural ceramics [
The production process of ZrO2–Al2O3 (ZrO2–
AlO(OH)) nanopowders follows various chemical routes,
such as sol–gel method [
], hydrothermal synthesis
] or co-precipitation method [
]. It was found
 that the main benefit of hydrothermal synthesis is the
generation of weakly agglomerated nanopowder. However,
some research suggests difficulties in reproducing and
controlling properties of these nanopowders [
is because the synthesis of ZrO2–Al2O3 ceramics is highly
sensitive to synthesis parameters, including concentration,
temperature, pH and drying method . Also, synthesis
conditions influence density, specific surface area, phase
composition of ZrO2–Al2O3 [
] and the amount of
On the other hand, sintering properties of nanomaterials
depend on the green body micro- and nanostructure [
is also required that the pores are in the nanometre size
range, since large pores may grow during synthesis [
The green body nanostructure depends strongly on the
viscosity of the slurry used for its production, which in turn
depends on the amount of water physically or chemically
bounded to the nanoparticles. Cinar et al. [
] showed that
nanopowder suspensions based on ZrO2–Al2O3 are
characterised by higher viscosities compared to micron size
powders. The lower viscosity indicates poor dispersion of
nanopowder with a lot of aggregates. Higher viscosity
indicates that all particles are contributing to the dynamics
of the liquid due to the increased solid–liquid contact
around particles [
]. Cinar et al. [
] also showed that
high viscosity of powders is linked to the bound water on
particle surface. It was explained that bound water, which
exists around the nanoparticles, does not function as a
solvent in the system, but behaves as a part of the powder.
This fact leads to the change of viscosity. Thus, for optimal
green body formation technology, it is required to control
existence and amount of bound water around the
This work evaluates the impact of composition (in
ZrO2–AlO(OH)) on physical and thermal parameters such
as water decomposition, onset temperature of ZrO2–
AlO(OH) phase transformations, as well as zeta potential,
density, particle size, and SSABET.
The novelty of this paper is the discussion of
characterisation results and thermal behaviour of ZrO2–AlO(OH)
nanopowders (synthesised by MHS method) with different
amounts of AlO(OH) in a whole range of compositions
(from 2 to 99% of Al3?). Pure ZrO2 and v-AlO(OH) were
used as a references. The boehmite (v-AlO(OH)) phase
transforms into Al2O3 after annealing which we already
]. However, in this work we describe results
Fig. 1 XRD patterns for as-synthesised ZrO2, AlO(OH) and ZrO2
with chosen Al3? or AlO(OH) additive, where M, T and B represent
m-ZrO2, t-ZrO2 and Boehmite phases, respectively
obtained only for as-synthesised powders in order to
preserve water content and analyse it in detail. Applied
synthesis method allows to create fully crystalline product in
contrary to the traditional sol–gel synthesis. Our results
demonstrate the complexity of processes taking place in
nanomaterials. This work may be helpful to track
nanomaterials ageing process and material selection for various
Nanopowders synthesis and characterisation
Various compositions of ZrO2–v-AlO(OH) nanopowders
were synthesised using microwave- hydrothermal
synthesis. The reagents used in the process were: zirconyl
chloride octahydrate [ZrOCl2 8H2O Sigma-Aldrich
(C 99.5%)], sodium hydroxide (CHEMPUR, analytically
pure) and aluminium nitrate non-ahydrate [Al(NO3)3 9H2O
CHEMPUR, analytically pure]. The reagents were used
without additional purification. Deionised water with
specific conductance below 0.1 lS cm-1 was obtained
using a deioniser (HLP 20UV, Hydrolab, Poland).
Microwave reactions took part in a MAGNUM II ERTEC
microwave reactor (2.45 GHz, 600 W). The reaction
parameters were set as follows: T = 258–263 C,
P = 50–56 atm, heating time = 20 min. The details of the
hydrothermal synthesis method were reported previously
]. Calculations for all compositions were done for
mass% of AlO(OH) needed to obtain such amount of
Al2O3 (in ZrO2–Al2O3) after annealing.
Scanning electron microscopy (SEM) analysis for ZrO2–
AlO(OH) nanopowders was performed on carbon-coated
samples using Zeiss Ultra Plus scanning electron
The low-temperature differential scanning calorimetry
and thermogravimetry (LT-TG–DSC) experiments were
carried out on a STA 449 F1 Jupiter by Netzsch using
stainless steel furnace. The experiments were performed
with a heating rate of 10 C min-1 from - 150 C up to
/m15 4–8.5 nm
Fig. 3 Dependence of SSABET values, particle size (D) obtained
from SSABET, and density (d) for ZrO2 on different AlO(OH) content,
where A = 100% ZrO2 phase, B = 100% AlO(OH) phase. a SSABET
as a function of composition, b D as a function of composition and
c d as a function of composition
800 C. Constant flow of helium at 60 mL min-1 was
applied. For each experiment, we used approximately
30 mg fine (previously mortared) powder which was
pressed into crucible prior each measurement. In order to
obtain reproducible results, samples were outgassed
without heating before the start of each experiment.
The high-temperature differential scanning calorimetry
and mass spectrometry (HT-DSC–MS) analyses were
performed using a STA 449 F1 Jupiter by Netzsch equipped
with SiC furnace. The experiments were carried out with a
heating rate of 10 C min-1 from ambient temperature up
to 1450 C, where a constant flow of air (60 mL min-1)
was applied. The volatile products emitted during heating
were detected with a mass spectrometer (QMS 403C
Aeolos) coupled in line with the STA instrument.
X-ray diffraction patterns of nanopowders were
obtained on X’Pert PRO, PANalytical diffractometer
equipped with a copper anode (CuKa1) and an ultra-fast
PIXcel1D detector. The analysis was performed at room
temperature in the 2h range 10 –100 with a step of 0.03 .
The Scherrer equation was used to calculate the average
crystallite diameter for selected nanopowders [
Density measurements were taken using the helium
pycnometer (AccuPyc II 1340, FoamPyc V1.06,
Micromeritics, USA). The measurements were taken in
accordance with ISO 12154:2014 at temperature of
25 ± 2 C.
Specific surface area (SSA) of nanopowders was
determined using the surface analyser (Gemini 2360, V 2.01,
Micromeritics, USA) by gas (nitrogen) adsorption method
based on the linear form of the BET (Brunauer–Emmett–
Teller) isotherm equation in accordance with ISO
9277:2010. Prior to performing measurements of density
and specific surface area, the samples were subject to 2-h
desorption in a desorption station (FlowPrep 060,
Micromeritics, USA), at temperature of 220 C with the
flow of helium. Based on the determined specific surface
area and pycnometric density, an average equivalent
spherical particle diameter was determined. In this case, the
assumption was that all particles are spherical and
identical. The following equation was used for calculating the
average particle size:
D ¼ SSABET d ð1Þ
where D—average size (diameter) of particles/nm, N—
shape coefficient being 6 for the sphere, SSABET—specific
surface area/m2 g-1, d—density/g cm-3.
The zeta potentials (f) of samples were measured at
23 C using laser Doppler electrophoresis analyser
[Zetasizer Nano ZS (ZEN3600), Malvern Instruments Ltd]. Each
sample powder (10 mg) was dispersed in 50 mL of
deionised water (0.07 lS cm-1, HLP 20UV, Hydrolab, Poland)
by ultrasonication for 10 min in ultrasonic washer (30 W,
Elma Schmidbauer GmbH, Germany). In order to obtain
the isoelectric point (IEP), the pH of the suspension was
first adjusted to pH 11 by adding 0.2 M NaOH solution and
changed several times to pH 2 by adding 0.2 M HCl
solution using an automated titration system (titrator
0 10 20 30 40 50 60 70 80 90 100
A Composition/% B
Fig. 6 Onset temperature (Ton1) dependence on the composition (a),
and the onset temperature (Ton1) as a function of SSABET, where
A = 100% ZrO2 phase, B = 100% AlO(OH) phase
between 5 and 15% of Al3? addition show diffraction
patterns for only t-ZrO2. Higher amount of AlO(OH)
(between 30 and 90%) besides t-ZrO2 phase also contains
Our previous results [
] confirmed that boehmite phase
appears in as-synthesised ZrO2 samples from 30% of
AlO(OH) additive. Below this value (up to 25% of Al3?),
ZrO2–Al3? creates solid solution (Al3? doped ZrO2) [
The temperature of microwave synthesis conducted by us
was in the range from 258 to 263 C, which was not high
enough to obtain Al2O3 phase. a-Al2O3 is formed in a
reactor with minimum crystallisation temperatures of
380 C or higher [
]. In this work, microwave synthesis
conditions (T = 80–270 C) could only form v-AlO(OH)
] phase. However, according to hydrothermal Al2O3–
H2O phase diagram in the temperature range 310–380 C,
and after applying pressure higher than 17 MPa,
] is formed. It was mentioned above that
100 200 300 400 500 600 700 800
boehmite phase transforms into Al2O3 after annealing in at
least 800 C, which was shown in [
] and [
Figure 2 shows SEM images for selected compositions
in order to demonstrate the change of powders’
morphology. It can be seen that all samples are rather uniform.
With the higher content of AlO(OH) particles became more
elongated. This fact is due to presence of Boehmite which
is characterised by plate-like, elongated morphology [
Figure 3a shows SSABET results for all synthesised
nanopowders. The spread of the values is from
approximately 80 up to 326 m2 g-1. However, the biggest
differences are observed for ZrO2 with 12% Al3? and 90% of
vAlO(OH) (Table 1). Higher SSABET from 90% of
AlO(OH) is due to apparent non-sphericity of particles as
shown in Fig. 2. The increase in the specific surface area
for the ZrO2 and ZrO2 with 2–12% of Al3? is due to
Fig. 9 HT-DSC curves for ZrO2 with different AlO(OH) content,
where a shows 100% ZrO2, and ZrO2 with 5–12% of Al3?, b ZrO2
with 30–67% of AlO(OH) additive, and c represents AlO(OH), and
ZrO2 with 80–96% of AlO(OH) additive
increasing amount of aluminium ions. Stable t-ZrO2 is
leading to the formation of smaller particles [
]. For the
compositions ranging from 30 to 67% of AlO(OH),
SSABET values are relatively constant declining slowly
from 30 to 67% of AlO(OH). The SSABET decline could be
attributed to an increased amount of non-outgassed water
in the v-AlO(OH) which remains in the system during the
BET outgassing procedures. We think that it results in a
small reduction in apparent surface of the sample as –OH
groups occupy some available sites. Change in SSABET is
also visible when shape of the particles changes ]with the
composition of ZrO2 from 80% AlO(OH) to the pure
As it was described above, the SSABET values show 3
different regions approximately 0–12% Al3?, 30–67 and
80–100% of AlO(OH) addition. Based on the combined
measurements of SSABET and density (1) it was possible to
report the variation of mean equivalent sphere size of
particles in the nanopowder for all compositions
investigated (Fig. 3b) [
]. It should be noted that particle density
was found to monotonically decrease with % AlO(OH) in
the system (Fig. 3c). This is as expected from the
compound composition. It is possible to distinguish
nanopowders with 3 different particle size ranges: form 4 to 8.5 nm,
from 10 to 13 nm and from 13 up to 23 nm (Fig. 3b). The
particle size increases, while the amount of Al3? in the
composition increases. Interestingly, for 0–12%
compositions the SSABET increased sharply due to the rapid
decrease in particle equivalent diameter. From 30 to 67%
of AlO(OH), particle size increases slowly. However, for
particles of 80% or higher the SSABET increases rapidly
leading to a steep decrease in the equivalent particle
diameter. From the SEM images of these samples (Fig. 2e,
f), it is evident that the particle shape is not spherical.
Particle aspect ratio or the non-sphericity increases with
increasing AlO(OH) content for this composition range
(from 80 to 100%). In order to test the assumption of
particle size evaluation using SSABET, another method
(Scherrer method) was used [
]. The particle size
range for selected compositions was following: 80% of
AlO(OH): 18–25 nm, 90% of AlO(OH): 17–33 nm, 96%
of AlO(OH): 9–17 nm, 99% of AlO(OH): 7–13 nm, and
AlO(OH): 6–12 nm. Obtained results from Scherrer
equations are in agreement with particle size calculated using
Variation of density with composition is shown in
Fig. 3c. The theoretical density of m-ZrO2 and v-AlO(OH)
is 5.68 g cm-3 [
] and 3.01 g cm-3 [
respectively. Pycnometric density of nano-ZrO2, measured
as a reference sample, is 5.17 g cm-3. The difference
between literature value, and that obtained in our
examination maybe due to nanosized particles. At the same time,
that difference could be caused by surface defects and
]. The density value of v-AlO(OH) is very
close to the literature (Table 1; Fig. 3c). As it could have
been predicted, values decrease when Al content in
synthesised powder increases.
The isoelectric point (IEP) for ZrO2 is 6.0 (Table 1;
Fig. 4), which is in agreement with previously reported
]. The IEP value for v-AlO(OH) is 9.5 and is
slightly higher than reported in the literature (9.1–9.2
]). The difference may be caused by specific
features of nanomaterials obtained by MHS. In case of ZrO2
and v-AlO(OH), the positive charge on the surface exists
for pH \ pH(IEP) while the negative charge appears in
pH [ pH(IEP) range. The increase of Al3? content in ZrO2
causes an increase in IEP values. This result is due to
changes in nanopowder composition.
Figure 5 presents results of low-temperature DSC
(conducted from - 100 up to 800 C) for all synthesised
nanopowders. We chose such a low starting temperature in
order to observe clearly the onset temperature of released
water. It is known that for this type of system the first
endothermic transition is located at approximately 100 C
which corresponds to the evaporation of the physically
adsorbed water [
]. The second one, between 200 and
500 C, takes place due to the loss of chemically bonded
water (hydroxides transformation) together with carbon
]. It can be seen that nano-ZrO2 and ZrO2
with AlO(OH) content below * 30% are characterised by
only one endothermic transition due to releasing of
physically absorbed water (Fig. 5a). There is no signal from
chemically bonded water. The reason for such behaviour is
the increasing amount of v-AlO(OH) in the ZrO2–
AlO(OH) . These findings are in agreement with results
described above. It should be noted that such behaviour is
very sensitive to composition. We found that the limit for
the presence of chemically bonded water for ZrO2–
AlO(OH) materials investigated in helium is between
approximately 12 and 30% of AlO(OH). Above 30% both
physically bound and chemically bonded water is present.
The type of released gasses during ZrO2–AlO(OH) thermal
treatment will be discussed further.
Obtained onset temperature (Ton) from DSC experiment
for ZrO2–AlO(OH) nanopowders is shown in Fig. 6 and
Table 1. Figure 6a presents change in the onset
temperature for the first endothermic event as a function of
composition. Taking into account that estimation of starting
point of the transition (Ton1) is quite difficult, we use the
same approach and software (Proteus, Netzsch) in order to
extract these values. Analysis of Fig. 6a shows that onset
temperature for the evaporation of the physically adsorbed
water differs for samples with lower content of Al. One
possible explanation of such behaviour might be a reduced
particle size. Figure 6b confirms a dependence of Ton1 on
the particle size. The smaller the average particle size, the
higher the Ton1. Therefore, we would expect to obtain the
lowest onset temperature for the powders with the smallest
particle size and the highest specific surface area,
especially while we are referring to the physically adsorbed
200 400 600 800 1000 1200 1400
200 400 600 800 1000 1200 1400
200 400 600 800 1000 1200 1400
b Fig. 10 HT-DSC–MS curves for ZrO2 with different Al3? or
AlO(OH) content: a 12%, b 30%, c 67% and d 80%
On the other hand, Ton2 for chemically bonded water
shows rather linear dependence on composition (Table 1).
The higher amount of AlO(OH), the lower onset
temperature, which is most likely due to slower kinetics. There is
clear exception for ZrO2 nanopowder with 90% of AlO(OH)
additive. Analysis of data collected in Table 1 shows such a
high onset temperature for chemically bonded water
desorption may be due to particle size and SSABET. The ZrO2–
90%-AlO(OH) sample is characterised by very small
SSABET * 78 m2 g-1 (compared to other samples) and
relatively big particles size (* 24 nm). These values differ
from other compositions by nearly 200%. Grabis et al. [
have characterised ZrO2–Al2O3 nanopowders produced by
plasma techniques. They synthesised materials with very
small SSABET (29–46 m2 g-1) which increased with
alumina content. Authors suggest that the described behaviour
is coupled with the reduction in m-ZrO2 present.
Figure 7 shows sample mass loss (TG) during thermal
treatment which is attributed to water and carbon dioxide
release as we discussed above. In addition, Fig. 8 shows
correlations between compositions and sample mass losses
during the first (Fig. 8a) and second event (Fig. 8b). The
desorption of physically absorbed water is the highest for
the compositions at the ends of composition range [up to
approximately 12% of Al3? and AlO(OH)-10% ZrO2].
Sample mass loss during second transition increases, while
the content of AlO(OH) in the composition increases
(Fig. 8b). This fact confirms our previous findings [
The high-temperature DSC was prepared in air in order to
analyse thermal stability in broader temperature range
(Fig. 9). Experiment curves were split into 3 figures:
Fig. 9a: ZrO2 with 5–12% Al3?, Fig. 9b: ZrO2 with 30–67%
of AlO(OH) and Fig. 9c: ZrO2 with 80–96% of AlO(OH). In
this way, it is highlighted how particle size and materials’
chemical composition change thermal characteristic of
ZrO2–AlO(OH). The onset temperatures for event 2, 3 and 4
are listed in Table 2. Transitions from RT up to
approximately 450 C are associated with the H2O and CO2 release
(Fig. 10) [
1, 41, 42
], while the following endothermic
transition is due to v-AlO(OH) transformation and water
]. The forth, weak endothermic event above
1000 C is related to particle growth and/or further
(t ? m) ZrO2 phase transformation [
200 400 600 800 1000 1200 1400
The interdependence of composition, particle size, specific
surface and thermal properties due to water adsorption has
been demonstrated on an industrially relevant nanomaterial.
We showed how density, particle size and SSABET
values are changing for ZrO2–AlO(OH) nanomaterials
synthesised by MHS method in the whole range of
compositions. The chosen synthesis method allowed to create
crystalline ZrO2–AlO(OH) nanopowders in simple and
repeatable way. Obtained results, especially investigation
of thermal behaviour, allow to establish suitable conditions
for densification and sintering process of ZrO2–AlO(OH)
Our research showed that nano-ZrO2 and nano-ZrO2
with 2–12% of Al3? are characterised by only one
endothermic transition due to releasing of physically
adsorbed water (Ton1). There is no signal from chemically
bonded water. The onset temperature for the evaporation of
the physically adsorbed water was found to be relatively
low and varied between the samples with lower content of
AlO(OH). We found that Ton1 depends on the particle size
and boehmite presence. The smaller the particle size, the
higher the Ton1. Specific surface area SSABET has a direct
influence on Ton1. The composition limit for the presence
of only chemically bonded water was found to be between
approximately 12 and 30% of Al3?. Above 30% of
AlO(OH) both physically bound and chemically bonded
water is present. Experimental results show that ZrO2–
AlO(OH) nanopowders properties change above 30% of
AlO(OH). For the composition below this value, Al3?
exists in solid solution (Al3? doped ZrO2).
Presented results allow to distinguish 3 groups of ZrO2–
AlO(OH) nanopowders, with distinct properties and
thermal behaviour. The first group (I) of materials is ZrO2 with
Al3? content up to 12% characterised by very small
particles size (* 4–10 nm), relatively high Ton1, and a visible
endothermic transition at approximately 1050 C.
As-synthesised powders from group (I) indicate m ? t-ZrO2
phase composition. DSC–MS of these nanopowders
conducted in air shows that water is release in Ton1 and Ton2
The second group (II) of materials is placed in the
30–67% range of AlO(OH) additive. This group is
characterised by particles size in the range 10–13 nm, lower
than (I) group value of Ton1, and lack of or shift of Ton4 to
the * 1320 C. As-synthesised powders of group (II)
show AlO(OH) and m ? t-ZrO2 phases. DSC–MS of these
nanopowders conducted in air is characterised by water
release in Ton1, Ton2 and Ton3 regions.
The third group (III) of ZrO2–AlO(OH) materials
contains from 80 to 99% of AlO(OH). This group is
characterised by larger particles size up to 23 nm, lower than
(I) group value of Ton1, and shift of Ton4 to the * 1320 C.
As-synthesised powders of group (III) show AlO(OH) and
m ? t-ZrO2 phases. DSC–MS of these nanopowders
conducted in air is characterised by water release in Ton1 and
Acknowledgements Authors are grateful to the Polish National
Science Centre for financial support under Contract No. UMO-2013/
11/D/ST8/03429-‘‘Sonata 6’’. The research subject was partly carried
out with the use of equipment funded by the Project CePT, reference:
POIG.02.02.00-14-024/08, financed by the European Regional
Development Fund within the Operational Programme ‘‘Innovative
Economy’’ for 2007–2013.
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