Nano- and microagglomeration processes in the thermolysis of titanium and zirconium oxyhydrates

Article abstract of DOI:10.1134/S0020168510050134

Titanium and zirconium oxyhydrates have been prepared using various additives and synthesis procedures, and the heating kinetics of polyacids and the mechanism of nanoparticle agglomeration during the thermolysis process have been studied. The resultant m

Full text of DOI:10.1134/S0020168510050134

ISSN 0020ꢀ1685, Inorganic Materials, 2010, Vol. 46, No. 5, pp. 510–516. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © G.P. Shveikin, I.V. Nikolaenko, 2010, published in Neorganicheskie Materialy, 2010, Vol. 46, No. 5, pp. 579–585.
Nanoꢀ and Microagglomeration Processes in the Thermolysis
of Titanium and Zirconium Oxyhydrates
G. P. Shveikin and I. V. Nikolaenko
Institute of SolidꢀState Chemistry, Ural Division, Russian Academy of Sciences,
Pervomaiskaya ul. 91, Yekaterinburg, 620041 Russia
eꢀmail: nikolaenko@ihim.uran.ru
Received March 2, 2009
Abstract—Titanium and zirconium oxyhydrates have been prepared using various additives and synthesis
procedures, and the heating kinetics of polyacids and the mechanism of nanoparticle agglomeration during
the thermolysis process have been studied. The resultant materials have been characterized by thermogravimꢀ
etry, Xꢀray diffraction, microstructural analysis, and specific surface area measurements.
DOI: 10.1134/S0020168510050134
INTRODUCTION
protons was determined according to the reaction, e.g.,
for metatitanic acid:
In earlier studies [1–3], adsorption of oxyhydrates on
a solid adsorbent (carbon black) was used to synthesize
nanooxides and nanocomposites. The precipitate
obtained by neutralizing acid solutions of titanium and
zirconium in the presence of a sorbent was shown to conꢀ
sist mainly of a mixture of metal oxyhydrate and sorbent
nanoparticles. The first step was to determine the main
composition of the metal hydrates resulting from adsorpꢀ
tion precipitation with an inert carrier (carbon black) and
with no adsorbent. Heating was shown to cause the therꢀ
molysis of the adsorbed oxyhydrates and the formation of
a powder mixture consisting of agglomerates of titania or
zirconia with black. This made it possible to identify the
agglomerates forming during hydrolysis, which had an
adsorption character and their size and growth showed
hierarchical behavior.
M TiO + xHNO = M H TiO + х
MNO3,
3 2 – x x 3
2
3
but no analysis for alkali metals was carried out. It is,
therefore, cannot be ruled out that the titanium
hydrates contained Mn – xH TiO3 alkaliꢀmetal titanates
x
as impurities. Consequently, various ordered strucꢀ
tures of the titanate homologous series, such as Н TiO
2
3
and Н Ti O7, may be stabilized by alkalineꢀearth metal
2
3
impurities. The synthesized compounds of this series
were similar in structure to alkaliꢀmetal titanates, and
some of them were used as precursors for the preparaꢀ
tion of anatase nanopowders [7–10].
Despite the large number of studies concerned with
the synthesis of nanostructures using metal hydrates as
precursors, the kinetics and mechanism of the formation
of hydrate intermediates, their conversion to the final
semiproducts, and the agglomeration process during
water removal have not yet been studied in sufficient
detail. The resultant structures and particle size were
determined incompletely. This paper addresses the above
issues.
In recent years, interesting and important results were
obtained by studying reaction intermediates in the synꢀ
thesis of nanoparticulate compounds and composites
with the use of metal hydrates, which enabled the syntheꢀ
sis of organic and inorganic precursors for the preparaꢀ
tion of nanoparticulate compounds.
As shown by Denisova et al. [4], the TiO –H O and
x
2
EXPERIMENTAL
ZrO –H O systems contain, in addition to the standard
x
2
titanium and zirconium oxyhydrates TiО(OH)2 and
Titanium and zirconium hydroxides were prepared by
ZrО(OH)2, acids such as H TiO and H ZrO3. Feist and precipitation from acid solutions of titanyl sulfate and
2
3
2
Daviest [5] and Wang et al. [6] determined the composiꢀ zirconium nitrate (18–19 g/l), which were adjusted to
tions of the acids, identified a homologous series of titaꢀ pH 7–7.5 with 12% aqueous ammonia. Carbon black
nium compounds with the general formula H Ti O + 1,, was added to the acid salt solutions before precipitation in
2
n
2n
and proposed a crystalꢀchemical model for structural an МО2 : C molar ratio of 1 : 3–5. The precipitation proꢀ
transitions between the homologues. Note that the comꢀ cess was run with constant stirring. Salt impurities were
pounds of this series were prepared using М Ti O
removed from the resultant suspensions by decantation.
) titanates, in which an alkaꢀ The residual impurities were removed by washing on a filꢀ
lineꢀearth metal atom was replaced by a hydrogen ion to ter. The hydrated titanium and zirconium precipitates
give М2 – хН Ti O solid solutions. The amount of obtained from pure salt solutions, with no adsorbent,
2
n
2n + 1
+
alkalineꢀearth metal (
М
х
n
2n +1
510

NANOꢀ AND MICROAGGLOMERATION PROCESSES IN THE THERMOLYSIS
511
Table 1. Effect of precipitation and heatꢀtreatment conditions on the specific surface area of the samples
S
,
m2
200
/g
Sample no.
Composition, preparation procedure (air drying)
H TiO , precipitated with NH OH
2
0
°
C
°
C
250°C
2
79.3
585.1
591.9
1
2
3
4
5
6
2
3
4
H TiO , precipitated with NH OH, treated with HNO3 at pH 3
348.25
94.6
426.8
519.2
282.45
692.9
458.6
741.3
654.2
376.45
734.8
476.5
675.2
630.4
369.2
2
3
4
H TiO , precipitated with NH OH, treated with H O (red precipitate
)
2
3
4
2 2
H TiO /3C, precipitated with NH OH
2
3
4
H TiO /3C, precipitated with NH OH under sonication
2
3
4
H ZrO /3C, precipitated with NH OH
2
3
4
Table 2. Experimental and calculated weight loss data
Weight loss, mg
oxyhydrates
Chemical composition
calculation
experiment
composites with black
H TiO = TiO + H O
18.38
9.18
6.12
4.62
12.77
14.6
15.00
13.44
16.52
–
14.23
16.27
15.46
–
2
3
2
2
H Ti O = 2TiO + H O
2
2
3
2
2
H Ti O = 3TiO + H O
2
3
7
2
2
H Ti O = 4TiO + H O
2
4
9
2
2
Average
H ZrO = ZrO + H O
15.02
–
15.32
10.88
2
3
2
2
were white, and those obtained using a sorbent (carbon lated weight loss data for the vaporization of the water of
black) were black. All of the precipitates were amorꢀ hydration during heating of the titanic and zirconic acids.
phous. They were dried in air at room temperature.
It can be seen that, in the H Ti O
homologous series,
2
n
2n
+ 1
water of crystallization is released most rapidly by
H TiO3 (pseudocubic structure) and H Ti O (monoꢀ
The dry powder samples were characterized on a Shiꢀ
madzu DTGꢀ60/60H thermal analyzer and a QMS 403
Aeolos quadrupole mass spectrometer, with a new conꢀ
cept for a capillary coupling to a thermogravimeter and
simultaneous thermal analyzers (TG + DSC).
Specific surface area was determined by a standard
argon desorption technique [11].
2
2
3
7
clinic structure) at comparable heating rates. The calcuꢀ
lation results for the H МO3 (M = Ti, Zr) acids correlate
2
well with the weight loss curves obtained during thermolꢀ
ysis.
The thermal analysis results obtained with the QMS
Microstructures were examined on a JEOL JSMꢀ 403 Aeolos during heating to 1000
С point to a number
900LV generalꢀpurpose scanning electron microscope. of distinctions between pure titanium hydrate and the
°
5
material adsorbed on black. It can be seen from the DSC
curves of H TiO3 (Table 1, sample 1) that, at the beginꢀ
ning of thermolysis, at temperatures from 80 to 200 С,
2
RESULTS AND DISCUSSION
°
Table 1 presents the surface area data for the titanium there is an endothermic process, which involves release of
and zirconium oxyhydrate samples prepared using differꢀ a large amount of water vapor and a small amount of
ent precipitation and heatꢀtreatment procedures. The ammonia (Fig. 2a). This process gradually gives way to an
thermal analysis results for the titanium and zirconium exothermic process with a peak at 450 С and a heat effect
°
oxyhydrates and their mixtures with black are presented of 84.23 J/g, followed by a broad exotherm, which seems
in Fig. 1. The DTA and TG curves of all the samples are to arise from the formation of the brookite structure durꢀ
seen to be similar in shape. The minimum temperature of ing slow formation of rutile TiO2. Note that the release of
the dehydration endotherm is roughly the same for the the large amount of water vapor during heating is readily
pure titanic acid and the acid adsorbed on black: 80 and accounted for by the vaporization of free water, followed
7
5.5
°
С
, respectively. For the pure zirconic acid and its by the decomposition of the titanic acid and the release of
composite, we obtained 78
°
С. The TG curves show that the water of hydration. The presence of ammonia vapor
the salt precipitating upon neutralization begins to in the gas phase is most likely due to partial substitution
decompose at nearly the same temperature, which sugꢀ of ammonium ions for protons of the titanic acid, which
gests that the titanic and zirconic acids have the same stoꢀ leads to the formation of (NH ) H xTiO3. It is of great
4
x
2 –
ichiometry. Table 2 presents the experimental and calcuꢀ interest to verify this assumption because H O and NH3
2
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512
SHVEIKIN, NIKOLAENKO
ture endothermic process gradually gives way to an exoꢀ
thermic process, which can only be accounted for by the
presence of black: some of the heat released by the titaꢀ
nium particles is scattered by the black, and no sharp heat
release occurs.
DTA,
μ
V
t, °C
TG, mg
H TiO
2
3
1
40
20
00
–20
–40
–60
–80
2
2
1
2
0
8
1
1
The titanic acid, Н TiO3, prepared by direct synꢀ
2
thesis from a pure titanium sulfate solution, followed
by air drying at room temperature, has a relatively
large specific surface area. Raising the temperature to
80
60
2
00 С, sharply increases the specific surface area:
°
2
from 279 to 585.1 m /g (Table 1). During heating, the
irregularly shaped, loose agglomerates in sample 1
break down into small titania (anatase) particles
–100
16
spherical in shape and
Ӎ100–200 nm in size, but
DTA, μV
remain loose (Fig. 3). This suggests that there are two
main processes: decomposition of the solid titanic acid
and agglomeration of the particles. The former process
t
,
°
C
TG, mg
H TiO /3C
2
3
140
reaches completion by 250 C, and the specific surface
°
–
–
–
20
40
60
2
1
1
2
0
8
6
2
area stabilizes. The micrograph of sample 4, prepared
by the coprecipitation of a titanium salt and acetylene
black, shows a number of interesting features (Fig. 4).
The sample is seen to consist of spherical agglomerates,
which are, in turn, composed of smaller particles. The
titanium oxyhydrate prepared by precipitation on an
1
1
8
6
20
00
0
2
inert carrier had a large specific surface area (426.8 m /g)
even at room temperature (20
200 , its specific surface area increased to an abnorꢀ
mally high level: 741 m /g
°
С). On heating to
–80
0
°
С
2
2
S
(black) = 20 m /g).
DTA,
μ
V
The samples were found to consist of 80ꢀ to 200ꢀnm
Ӎ
TG, mg
t
,
°
C
agglomerates of titania adsorbed on the surface of the
carbon black. It is reasonable to assume that the agglomꢀ
eration process involves two steps. The first step is
agglomeration proper, due to sol adsorption. The second
step is secondary adsorption of particles on the surface of
the inert carrier (adsorbent). The first step plays a key role
in determining the formation of small pertitanic acid parꢀ
ticles. This step strongly depends on the pH of the
medium, temperature, additives, and solution viscosity.
In the second step, larger particles are formed on the
adsorbent surface owing to their own size and the sol–gel
derived particles adsorbed on their surface. This step fixes
the sol–gel derived agglomerates, and their dimensions
in the particular medium remain unchanged. The
agglomeration process is governed by the diffusion of sols
in solution: the lower their mobility, the smaller is the
number of sol–gel collisions. With decreasing temperaꢀ
ture, solution density, and concentration, the rate of
encounter of titanium hydrate particles drops. The comꢀ
3
3
2
2
2
2
0
8
6
4
H ZrO /3C
2 3
140
–40
–60
–80
120
1
8
6
00
0
–100
0
–120
0
5
10
Time, min
15
20
Fig. 1. Thermal analysis results for titanium and zirconium
oxyhydrates; heating rate, 5 C/min.
°
peting process, sol–sol
→
gel, then leads to the formaꢀ
tion of an agglomerate with the inert carrier in solution,
with precipitation of both the sol and the forming gel
are close in molecular weight (18 and 17, respectively).
The TG curve clearly indicates the presence of both
phases, and qualitative analysis of the sample during
heating confirmed the presence of ammonia in the gas
phase (characteristic odor and litmus test).
(
sol–sol associates). For this reason, adsorbed particles in
a heterogeneous process typically differ in size. It cannot
be ruled out that the distribution of the sols in the
agglomerate depends on the amount of sol particles,
The DSC curve of the titanium hydrate on black which favors the formation of different agglomerates and
corresponds to an hierarchy of the sol particle distribuꢀ
tion in these agglomerates.
(
Table 1, sample 4) is similar to that of sample 1, but there
is no exothermic peak at 450 , and the lowꢀtemperaꢀ
°
С
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NANOꢀ AND MICROAGGLOMERATION PROCESSES IN THE THERMOLYSIS
513
TG, %
00
DSC,
μ
V/mg
Iion
×
109,
Å
(
а)
1
EXO
4.0
3.5
0
0
0
.15
DSC
95
.10
.05
3.0
Area: 43.64 mVs/mg
Heat effect: 84.23 J/g
2.5
9
0
5
2
.0
.5
Weight change: –19.64%
0
NH
3
1
H O
2
–0.05
8
1.0
0.5
0
–
–
0.10
0.15
TG
8
0
(b)
EXO
100
9
DSC
0.8
8
7
6
5
4
3
2
1
0
90
80
70
60
TG
0.6
0
0
0
.4
H O
2
Weight change: –49.01%
.2
100
200
300
400
500
600
700
800
900
Temperature, C
°
Fig. 2. Thermal analysis results for (a) H TiO and (b) H TiO /3C (QMS 403 Aeolos quadrupole mass spectrometer).
2
3
2
3
Using in situ Xꢀray diffraction analysis during therꢀ
molysis, we detected anatase formation (Fig. 5) both on treated with strong oxidants. Treatment with nitric acid
the pure salt and in the presence of the adsorbent. markedly changed the specific surface area of sample 2
The asꢀprecipitated titanium oxyhydrates were
INORGANIC MATERIALS Vol. 46
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514
SHVEIKIN, NIKOLAENKO
0.1
μ
m
0.1 μm
(а)
(b)
Fig. 3. Micrographs of H TiO (sample 1): (a) room temperature, (b) heating to 200°С.
2
3
0.2 μm
Fig. 4. Micrograph of titania with carbon black: heating to 200°С.
(
Fig. 6). It can be seen that the agglomeration process in duced no drastic changes in specific surface area. Thereꢀ
the sample is pronounced even in the first step: some fore, sonication promotes the deagglomeration process.
agglomerates reach 0.5 nm in size. At the same time, the The samples prepared under sonication and heated to
total specific surface area of the sample is substantially 200
°
C consisted mainly of agglomerated spherical partiꢀ
greater than that of the asꢀprepared titanium hydroxide
cles with sharp boundaries (Fig. 7). This is attributable to
the more rapid and more complete decomposition of the
titanic acid salt and, more importantly, is accompanied
by a reduction in agglomerate size.
2
(sample 1), reaching 348.25 m /g.
Interesting results were obtained by treating samples
of the same type in hydrogen peroxide (sample 3). Here,
the titanic acid aggregates grew in the same time by
almost one order of magnitude and, accordingly, the speꢀ
cific surface area dropped (
molysis of the salt treated with H O , agglomeration proꢀ
cesses were again active, and the specific surface area of
the sample increased to 458.6 m /g.
Similar studies were performed for zirconium
hydroxide (sample 6). A distinctive feature of the zircoꢀ
nium hydrate powder and H ZrO /3C composite is the
relatively large agglomerate size, exceeding that in the
titanium hydroxide by a factor of 2–3. We believe that
this is due to the larger atomic radius of zirconium.
2
S
= 94.6 m /g). During therꢀ
2
3
2
2
2
Sonication may have a strong effect on nanoparticle
synthesis. The H TiO /3C sample prepared by precipitaꢀ
The nanoparticle size in the agglomerates was deterꢀ
mined as
2
3
tion in a UZUꢀ0.25 ultrasonic processor in the presence
of carbon black as a sorbent (sample 5) had a higher
−6
2
roomꢀtemperature specific surface area (519.2 m /g) in
3×10
r =
,
comparison with the other samples. Thermolysis proꢀ
Sd
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NANOꢀ AND MICROAGGLOMERATION PROCESSES IN THE THERMOLYSIS
515
2
1
2
50
°
C
20°
C
0°
C
5
10
15
20
25
30
35
2
40 45
, deg
50
55
60
65
70
θ
Fig. 5. Xꢀray diffraction patterns illustrating titania formation.
0.5
μ
m
0.1 μm
Fig. 6. Micrograph of titanium oxyhydrate treated with nitric
acid at pH 3 (sample 2).
Fig. 7. Micrograph of the titanium oxyhydrate–black sample
prepared under sonication (sample 5).
2
where
S
is the specific surface area (m /g) and
d
is the
CONCLUSIONS
3
density of the particles (cm /g).
We examined the agglomeration of titanium and zirꢀ
conium oxyhydrates precipitated from acid salt solutions
by adding ammonia. In the case of titanium, the resulting
amorphous precipitate consists predominantly of titanic
The particle size in sample 4, prepared by coprecipiꢀ
tation with black at room temperature, was determined
to be 28 nm.
INORGANIC MATERIALS Vol. 46
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516
SHVEIKIN, NIKOLAENKO
acid (H TiO3) particles with partial substitution of
2. Polyakov, E.V., Denisova, T.A., Grigorov, I.G., and
Shtin, A.P., Hierarchy of Sizes and Sorption Selectivity of
Ultrafine Particles of Hydrated Titania, Int. J. Nanotechꢀ
nol., 2006, vol. 3, no. 1, pp. 39–46.
2
ammonium ions for hydrogen atoms: (NH ) H xTiO3
.
4
x
2 –
The titanic and zirconic acids are unstable and begin
to decompose at 80 to form titania (zirconia) and
Ӎ
°
С
3
. Nikolaenko, I.V., Shtin, A.P., and Shveikin, G.P., Microvꢀ
wave Synthesis of Titania and Zirconia from Titanium
and Zirconium Hydroxides, Fizika ekstremal’nykh sostoyꢀ
anii veshchestva ꢀ 2007 (Physics of Extreme States of Matꢀ
ter 2007), Fortov, V.E., Ed., Chernogolovka: Inst. Problem
Khimicheskoi Fiziki Ross. Akad. Nauk, 2007, pp. 87–89.
water. Thermolysis leads to the formation of loose
rounded agglomerates with an anomalously large specific
surface area.
According to our results, the agglomeration process
and specific surface area of the hydrate powders are influꢀ
enced by the precipitation procedure (mechanical agitaꢀ
tion, sonication), inert additives (carbon black), treatꢀ
ment with strong oxidants (HNO , H O2), and temperꢀ
4. Denisova, T.A., Maksimova, L.G., Polyakov, E.V., et al.,
Synthesis and Physicochemical Properties of Metatitanic
Acid, Zh. Neorg. Khim., 2006, vol. 51, no. 5, pp. 1–10 .
3
2
5
. Feist, T.P. and Daviest, P.K., The Soft Chemical Synthesis
of TiO (B) from Layered Titanates, J. Solid State Chem.
ature. The specific surface area of the samples increases
as the temperature is raised from 20 to 200 , stabilizes
at 250 , and falls off at higher temperatures and longer
heatꢀtreatment times.
,
°
С
2
1
992, vol. 101, pp. 275–295.
. Wang, J., Yin, S., and Sato, T., Characterization of
H Ti O with High Specific Surface Area Prepared by a
°
С
6
2
4 9
The addition of acetylene black as an inert sorbent
and sonication hinder agglomerate growth and increase
the specific surface area of the samples for both titanic
and zirconic acids.
The agglomeration process is shown to precede selfꢀ
organization of the ultrafine particles.
Delamination/Reassembling Process, Mater. Sci. Eng., B
006, vol. 126, pp. 53–58.
. Wang, N., Lin, H., Li, J., et al., Crystalline Transition
from H Ti O Nanotubes to Anatase Nanocrystallites
under LowꢀTemperature Hydrothermal Conditions, J.
Am. Ceram. Soc., 2006, vol. 89, no. 11, pp. 3504–3566.
,
2
7
8
9
2
3 7
. Wing, Z.N., Halloran, J.W., Gong, X., et al., Fabrication
and Properties of an Anisotropic TiO Dielectric Comꢀ
2
ACKNOWLEDGMENTS
posite, J. Am. Ceram. Soc., 2006, vol. 89, no. 9, pp. 2812–
1815.
This work was sponsored by the RF President’s
Grants Council for Support to Leading Scientific
Schools, grant no. NSHꢀ752.2009.3, contract no. 117.
. Kotani, Y., Matsuda, A., Tatsumisago, M., et al., Formaꢀ
tion of Anatase Nanocrystals in Sol–Gel Derived TiO –
2
SiO Thin Films with Hot Water Treatment, J. Sol–Gel
2
Sci. Technol., 2000, no. 19, pp. 585–588.
1
0. Shveikin, G.P., Preparation of UltrafineꢀParticle Titaꢀ
nium Compounds by Carbon Reduction of Titania,
Neorg. Mater., 1999, vol. 35, no. 5, pp. 587–590 [Inorg.
Mater. (Engl. Transl.), vol. 35, no. 5, pp. 485–488].
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INORGANIC MATERIALS Vol. 46
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