XRD, TEM and thermal analysis of yttrium doped boehmite nanofibres and nanosheets

Article abstract of DOI:10.1007/s10973-008-9002-6

Yttrium doped boehmite nanofibres with varying yttrium content have been prepared at low temperatures using a hydrothermal treatment in the presence of poly(ethylene oxide) surfactant (PEO). The resultant nanofibres were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). TEM images showed the resulting nanostructures are predominantly nanofibres when Y-doping is less than 5%; in contrast Y-rich phases were formed when doping was around 10%. The doped boehmite and the subsequent nanofibres/nanotubes were analyzed by thermogravimetric and controlled rate thermal analysis methods. The boehmite nanofibres produced in this research thermally transform at higher temperatures than boehmite crystals and boehmite platelets. Boehmite nanofibres decompose at higher temperatures than non-hydrothermally treated boehmite.

Full text of DOI:10.1007/s10973-008-9002-6

Journal of Thermal Analysis and Calorimetry, Vol. 94 (2008) 1, 219–226
XRD, TEM AND THERMAL ANALYSIS OF YTTRIUM DOPED
BOEHMITE NANOFIBRES AND NANOSHEETS
Y. Zhao1, R. L. Frost1*, Veronika Vágvölgyi2, E. R. Waclawik1, J. Kristóf2 and Erzsébet Horváth3
1Inorganic Materials Research Program, School of Physical and Chemical Sciences, Queensland University of Technology
2 George Street, GPO Box 2434, Brisbane, Queensland 4001, Australia
2Department of Analytical Chemistry, University of Pannonia, 8201 Veszprém, PO Box 158, Hungary
3Department of Environmental Engineering and Chemical Technology, University of Pannonia, 8201 Veszprém
PO Box 158, Hungary
Yttrium doped boehmite nanofibres with varying yttrium content have been prepared at low temperatures using a hydrothermal
treatment in the presence of poly(ethylene oxide) surfactant (PEO). The resultant nanofibres were characterized by X-ray diffrac-
tion (XRD) and transmission electron microscopy (TEM). TEM images showed the resulting nanostructures are predominantly
nanofibres when Y-doping is less than 5%; in contrast Y-rich phases were formed when doping was around 10%.
The doped boehmite and the subsequent nanofibres/nanotubes were analyzed by thermogravimetric and controlled rate ther-
mal analysis methods. The boehmite nanofibres produced in this research thermally transform at higher temperatures than boehmite
crystals and boehmite platelets. Boehmite nanofibres decompose at higher temperatures than non-hydrothermally treated boehmite.
Keywords: acicular, boehmite, nanofibre, nanomaterial, nanosheets, nanotube
Introduction
erties and mesoporous properties, alumina has been
extensively used as carrier and support for a variety of
industrial catalysts at high temperature as well as low
temperature. It is believed that the high temperature
creep deformation of alumina is related to the grain
boundary diffusion process in polycrystalline alu-
mina [17]. It has been noticed that high-temperature
creep in fine-grained alumina can be controlled by
doping with small amounts of rare-earth elements,
such as yttrium [18]. Besides, doped with yttrium, the
resulting boehmite/alumina nanostructure may have
special optical properties which will enable it to
further industrial applications.
Recently, the synthesis of inorganic nanoscale materi-
als with special properties has been of great interest in
material science [1, 2], because their intrinsic proper-
ties at the nanoscale level. Material properties are
mainly determined by their composition, structure,
crystallinity, size and morphology [3]. In particular,
one dimensional (1D) nanoscale inorganic materials
including nanofibers, nanowires and nanotubes have
attracted extensive interest due to their distinctive ge-
ometries, novel physical and chemical properties and
potential applications in numerous areas [4].
Boehmite (AlOOH), a principal oxo-hydroxide
of aluminium, is a crucial precursor in sol–gel tech-
nique for preparing high-purity and high-strength
monolithic a-alumina ceramics for use as substrates
for electronic circuits, abrasive grains, high-tempera-
ture refractory materials, fibres and thin films [5].
Alumina (Al2O3) can be obtained from AlOOH by a
simple dehydration process from a certain tempera-
ture. It has been demonstrated that AlOOH nano-
structures undergo an isomorphous transformation to
nanocrystalline alumina during heating [6–8]. There-
fore, the morphology and size of the resultant alumina
can be manipulated by controlling the growth of
boehmite. Alumina has been employed as catalyst [9],
adsorbent [10, 11], composite materials [12, 13] and
ceramics [14–16]. Due to the high surface area of alu-
mina phases, its chemical and thermally stable prop-
Thermal analysis has proved most useful for the
analysis of minerals and related materials [19–28].
In this work, a series of yttrium doped boehmite nano-
fibres with varying yttrium content have been synthe-
sised by introducing yttrium as dopant and the proper-
ties of the resultant yttrium doped boehmite nanofibres
were systematically studied using X-ray diffraction,
transmission electron microscopy and both dynamic
and controlled rate thermogravimetric techniques.
Experimental
Synthesis of Y-doped boehmite nanofibres
The detailed experimental procedure is as follows.
A total amount of 0.2 mol aluminium nitrate and
*
Author for correspondence: r.frost@qut.edu.au
1388–6150/$20.00
Akadémiai Kiadó, Budapest, Hungary
Springer, Dordrecht, The Netherlands
© 2008 Akadémiai Kiadó, Budapest

ZHAO et al.
yttrium nitrate were mixed before dissolved in ul-
and differential thermal analysis (DTA) curves simul-
taneously. The sample was heated in a ceramic
crucible in static air atmosphere at a rate of 5°C min–1.
tra-pure water. Mixtures with yttrium molar percentage
of 1, 2, 3, 4.5 and 10% were prepared separately and
then dissolved in ultra-pure water to form a solu-
tion (A) with a metal ion to H2O molar ratio of 1:100
and heated to 80°C. With stirring in solution A,
5 mol L–1 NaOH solution was then added dropwise at a
constant rate of 5 mL min–1 to form precipitate. After
that it was aged for two hours with constant stirring
at 80°C, the resulting precipitate was recovered by
centrifugation, washed with pure water several times to
remove sodium nitrate. The washed precipitate was
then mixed with water and nonionic PEO surfactant
Tergitol 15-S-7 (C12–14H25–29O(CH2CH2O)7H, Aldrich)
Controlled rate thermal analysis experiment
Thermal decomposition of the yttrium doped
boehmite was carried out in a derivatograph in static
air atmosphere (250 cm3 min–1) at a pre-set, constant
decomposition rate of 0.15 mg min–1. (Below this
threshold value the samples were heated under dy-
namic conditions at a uniform rate of 1.0°C min–1).
The samples were heated in an open ceramic crucible
at a rate of 1.0°C min–1. With the quasi-isothermal,
quasi-isobaric heating program of the instrument the
furnace temperature was regulated precisely to pro-
vide a uniform rate of decomposition in the main
decomposition stage.
with average molecular mass of ~508 at
a
metal:H2O:PEO molar ratio of 0.2:3.2:0.04. The vis-
cous mixture is stirred for 1 h at room temperature and
then transferred into an autoclave and kept in oven an
at 100°C for 6-day hydrothermal treatment. The final
product was washed by water and dried in air at 80°C.
Results and discussion
X-ray diffraction
X-ray diffraction
XRD analyses were performed on a PANalytical
X’Pert PRO X-ray diffractometer (radius: 240.0 mm).
Incident X-ray radiation was produced from a line fo-
cused PW3373/10 Cu X-ray tube, operating at 45 kV
and 35 mA, providing Ka1 wavelength of 1.540596 .
The incident beam passed through a 0.04 rad, Soller
slit, a 1/2° divergence slit, a 15 mm fixed mask and
a 1° fixed anti-scatter slit. After interaction with the
sample, the diffracted beam was detected by an
X’Celerator RTMS detector. The detector was set in
scanning mode, with an active length of 2.022 mm.
Samples were analysed utilising Bragg–Brentano ge-
ometry over a range of 3–75° 2q with a step size
of 0.02° 2q, with each step measured for 200 s.
Figure 1 shows the XRD patterns of doped samples
after 6 days hydrothermal treatment at 100°C. All the
diffraction peaks of the resultant samples with yttrium
doping of 1, 2, 3, 4 and 5% can be assigned to ortho-
rhombic boehmite (AlOOH, JCPDS 00-005-0190).
The characteristic diffraction peaks for boehmite at
around 14, 28, 38 and 48° 2q degree indicate an
excellent crystallinity of these samples. As for 10%
doped sample, yttrium peaks as well as boehmite
peaks were presented in the XRD pattern. Peak posi-
tion, FWHM, lattice parameters and crystal sizes of
samples with varying Y-content after 6 days hydro-
thermal treatment at 100°C are shown in Table 1.
Peak position at both 020 and 002 varied with the in-
crease in doped Y%. Variation in lattice parameter b
was observed whereas lattice parameter c remains
constant with the increase in Y-content when taking
account of calculation errors. Crystallite size along c
and b crystallographic directions varies with the
increase in doped Y.
TEM analysis
A Philips CM 200 transmission electron micros-
copy (TEM) at 200 kV was used to investigate the
morphology of the boehmite nanofibres. All samples
were dispersed in absolute ethanol solution and then
dropped on copper grids coated with carbon film,
dried in an oven at 60°C for 10 min for TEM studies.
Thermal analysis
Dynamic experiment
Thermal decomposition of the yttrium doped boehmite
samples was carried out in a Derivatograph PC-type
thermoanalytical instrument (Hungarian Optical
Works, Hungary) capable of recording the thermo-
gravimetric (TG), derivative thermogravimetric (DTG)
Fig. 1 Powder X-ray diffraction patterns of Y doped boehmite
samples with varying Y%
220
J. Therm. Anal. Cal., 94, 2008

YTTRIUM DOPED BOEHMITE NANOFIBRES AND NANOSHEETS
Table 1 Peak position, FWHM, lattice parameters and crystal sizes of samples with varying Y-content after 6 days hydrother-
mal treatment at 100°C
Peak position
FWHM
Added/%
h k l
Lattice parameter/
Crystal size/nm
2q/degree
0 2 0
0 0 2
13.820
49.120
2.222
0.672
12.81
3.71
3.6
1
2
13.0
0 2 0
0 0 2
13.970
49.178
2.180
0.894
12.67
3.70
3.7
9.8
0 2 0
0 0 2
13.990
49.157
1.998
0.624
12.65
3.70
4.0
3
14.0
0 2 0
0 0 2
13.754
49.192
2.400
0.726
12.87
3.70
3.3
4
12.0
0 2 0
0 0 2
13.795
49.160
2.386
0.658
12.83
3.70
3.4
5
13.3
0 2 0
0 0 2
13.816
49.115
2.551
0.883
12.81
3.71
3.1
9.9
10
Transmission electron microscopy
and 2.5 nm, respectively. It was noted that the size
of 5% Y-doped boehmite was remarkable bigger than
the other two doped samples with an average length and
width of about 100 and 3.5 nm which is close to the size
of pure boehmite synthesized under the same procedure
and conditions our early study [29]. As for 10% sample,
except for nanofibres with similar size as that formed
in 5% sample, large nanorods and square-shaped yt-
trium rich crystals were observed.
Figure 2 shows the morphology of Y-doped samples af-
ter 6 days hydrothermal treatment with Y% of 1, 3
and 5. It was noted that nanofibres, nanotubes with
small amount of nanosheets were formed in all these
three samples. The overall morphology and size of 1
and 3% doped boehmite are similar. The average length
and width of these two samples are approximately 90
Thermogravimetric analysis
The dynamic thermal analysis of boehmite is dis-
played in Fig. 3. The results of the dynamic experi-
ment are reported in Table 2. Due to a yttrium rich
phase formed in the 10% sample, samples with added
yttrium percentage of 1, 3 and 5 were selected for fur-
ther investigation by dynamic and controlled rate
thermogravimetric techniques. The dynamic thermal
analyses of the 1, 3 and 5% yttrium doped boehmite
are shown in Figs 4–6. The controlled rate thermal
analysis of boehmite is displayed in Fig. 7. The con-
trolled rate thermal analysis of 1, 3 and 5% yttrium
doped boehmite are displayed in Figs 8–10. The re-
sults of the thermal decomposition of the 1, 3 and 5%
yttrium doped boehmite are reported in Table 3.
Fig. 2 TEM images of a – 1, b – 3 and c – 5% Y-doped
boehmite nanofibres
Fig. 3 Dynamic thermal analysis patterns of boehmite
J. Therm. Anal. Cal., 94, 2008
221

ZHAO et al.
Fig. 4 Dynamic thermal analysis patterns of 1% yttrium doped
Fig. 6 Dynamic thermal analysis patterns of 5% yttrium doped
boehmite
boehmite
Fig. 5 Dynamic thermal analysis patterns of 3% yttrium doped
Fig. 7 Controlled rate thermal analysis patterns of 1% yttrium
boehmite
doped boehmite
Pure boehmite with 6 days hydrothermal treatment
at 100°C shows four decomposition steps. The step
characteristic of boehmite is the broad DTG step at
~397°C with a mass loss of 15.10% (Table 2). The first
mass loss occurs at around 83°C with a mass loss of
7.90%. This mass loss step is attributed to adsorbed and
intercalated water. The second mass loss step is ob-
served at 209°C and accounts for the major mass loss
step of 2.10% mass loss. This mass loss is attributed to
interstitial water trapped between the boehmite layers.
The theoretical mass loss based upon the equation:
composition steps. The step which is characteristic of
boehmite is the sharp DTG step at 345°C, with a mass
loss of 13.23%. The first mass loss occurs at around
50°C, with a mass loss of 1.23%. This mass loss step
is attributed to adsorbed water. The second mass loss
step is observed in the 176–241°C temperature range
and accounts for the major mass loss step with
13.24% mass loss. This mass loss is attributed to the
combustion of the surfactant [31].
The 1% Y-doped boehmite DTG curve dis-
plays 4 maxima in the DTG curves at 89, 231 (sharp),
326 and 422°C. These DTG peaks are assigned to
9a) dehydration (b) combustion of the surfactant di-
recting agent (c) dehydroxylation of boehmite and
(d) further dehydroxylation. The DTA curve for this
material shows an endotherm at 89 and around 430 and
2AlOOH®Al2O3+H2O
is 15.0% [30].
Undoped boehmite nanofibres/tubes prepared
at 100°C for 6 days show at least four separate de-
Table 2 Decomposition stages under dynamic condition for yttrium doped boehmite
Sample
Boehmite at 100°C
Boehmite 1% Y-doped
Boehmite 3% Y-doped
Boehmite 5% Y-doped
Mass loss (sample
Mass loss (sample
mass: 53.11 mg)/
Mass loss (sample
Mass loss (sample
mass: 88.85 mg)/
mass: 56.91 mg)/
range/°C
mass: 76.02 mg)/
Trange/°C
T
range/°C
T
T
range/°C
mg
%
mg
%
mg
%
mg
%
24–172
172–246
246–506
506–877
4.2
1.1
8.0
0.9
7.9
2.1
29–205
4.9
1.1
3.6
5.1
0.9
8.6
1.9
6.3
9.0
1.6
25–199
199–270
270–516
516–800
8.0
1.7
9.0
1.9
25–211
8.7
2.8
9.1
1.1
11.4
3.7
205–256
256–360
360–500
500–800
211–305
305–527
527–800
15.1
1.7
12.3
1.2
13.8
1.4
12.0
1.4
222
J. Therm. Anal. Cal., 94, 2008

YTTRIUM DOPED BOEHMITE NANOFIBRES AND NANOSHEETS
J. Therm. Anal. Cal., 94, 2008
223

ZHAO et al.
at constant heating rates show that thermally stimu-
lated transformation of nanocrystalline boehmite into
alumina can be accurately modelled by a 4-reaction
mechanism involving: (I) the loss of physisorbed wa-
ter, (II) the loss of chemisorbed water, (III) the conver-
sion of boehmite into transition alumina, (IV) the de-
hydration of transition alumina (loss of residual
hydroxyl groups) [33]. Another study of boehmite pre-
cipitates by the authors found that thermal analysis
showed five endotherms at 70, 140, 238, 351 and
445°C and these endotherms are attributed to the dehy-
dration and dehydroxylation of the hydrolyzate [34].
The calculation of the water content is given in
the appendix. For the 1% yttrium doped boehmite the
amount of water was calculated as 0.30 mol mol–1 of
AlO(OH). The values for 3 and 5% yttrium doped
boehmite are 0.36 and 0.45 moles of water per mole
of AlO(OH). The relationship between the moles of
water in the interlayer and the moles of yttrium dop-
ing of the boehmite appears linear. The relationship is
given as y=0.375x+0.2575 with R2=0.9868. In a pre-
vious study the authors proposed that water was in-
corporated into the boehmite structure through fold-
ing of the boehmite layers which resulted in changes
in the 020 reflection [34]. It was postulated that the
structure of the resultant AlO(OH) formed from cold
water hydrolysis of trisecbutoxyaluminium(III) was
one of folded boehmite structure along the 020 planes
of boehmite. This structure was then proposed to
straighten during ageing of the amorphous aluminium
oxy(hydroxide), which results in the formation of
pseudoboehmite. Such a structure showed an X-ray
diffraction pattern with the (020) peak for pseudo-
boehmite but not other peaks, which was attributed to
the disintegration of long range order but preservation
of short range order. It should be noted that the tem-
perature of hydrolysis is 75°C. The reason for the se-
lection of this temperature is that at and above this
temperature a single phase is formed. If the hydro-
lysate is formed at 25°C, an amorphous aluminium
oxy(hydroxide) is formed, which on ageing trans-
forms to boehmite and gibbsite. Thus it is proposed
that the increase in Y-content in the boehmite results
in an increase in the amount of pseudoboehmite and
thus more water is incorporated into the pseudo-
boehmite structure.
Fig. 8 Controlled rate thermal analysis patterns of 1% yttrium
doped boehmite
Fig. 9 Controlled rate thermal analysis patterns of 3% yttrium
doped boehmite
Fig. 10 Controlled rate thermal analysis patterns of 5% yttrium
doped boehmite
an exotherm at 231°C. It is proposed that at 427°C the
boehmite nanofibres transformed to g-alumina.
The DTG peak and the DTA exotherm at 231°C are as-
signed to the combustion of the PEO surfactant. In a
previous piece of research infrared emission spectros-
copy was used to study the dehydroxylation of natural
and synthetic boehmite [32]. It was found that de-
hydroxylation starts at 250 and is complete by 450°C.
The dehydroxylation is followed by the loss of inten-
sity of the hydroxyl stretching frequencies observed at
3478, 3319 and 3129 cm–1 and by the loss of intensity
of the hydroxyl deformation modes at 1140 and
1057 cm–1. A previous study made simulations of the
thermal decomposition of boehmite [33]. It was found
that the simulations of the non-isothermal experiments.
The 3% Y doped boehmite shows three DTG
peaks at 99, 255 and 427°C. The DTA curve displays
two endotherms at 99 and 427°C and an exotherm
at 255°C.
The attribution of the DTG peaks is as above.
The 5% Y-doped boehmite shows three DTG peaks at
97, 282 and 424°C. The DTA curve of the 5% Y-doped
boehmite displays two endotherms at 97 and 427°C and
an exotherm at 282°C. It appears that as the yttrium dop-
224
J. Therm. Anal. Cal., 94, 2008

YTTRIUM DOPED BOEHMITE NANOFIBRES AND NANOSHEETS
Conclusions
ing increases the DTG peak at around 427°C becomes
significantly broader. This provides an indication of the
wide range of nanofibres present in the boehmite
nanomaterial. In the work reported by Alphonse and
Courty [33] the DTG peak for the nanocrystalline
boehmite of platelets of size 10 nm was around 390°C.
It is concluded that the boehmite nanofibres produced in
this research thermally transform at higher temperatures
than boehmite crystals and boehmite platelets.
Yttrium doped boehmite nanofibres of some 250 nm
in length can be prepared at 100°C using soft chemi-
cal hydrothermal methodology using PEO as a
surfactant directing agent. The yttrium content in
boehmite nanostructures was found to be limited to a
maximum of around 5.0%. Fibres or needles were
formed at low Y-doping. With the increasing Y-con-
tent nanosheets are formed.
The CRTA of the pure boehmite (Fig. 7) shows as
for the dynamic experiment shows four decomposition
steps as per Table 3. These steps are attributed to two
dehydration steps the first of which is isothermal
at ~70°C and is assigned to adsorbed water. This ac-
counts for a 8.4% mass loss. The second mass loss
at 180°C is obviously non-isothermal and accounts for
a 1.4% mass loss. In the dynamic experiment a signifi-
cant exothermic reaction was observed at 209°C. The
third mass loss of 16.10% is also isothermal and occurs
at ~400°C. In the dynamic experiment a slow mass loss
over a wide temperature range occurs, commencing at
around 250 and is complete by 470°C.
Thermal analysis under dynamic and CRTA con-
ditions shows that the steps of dehydroxylation are
merged with the increase of the yttrium content. The
CRTA experiment revealed that the two steps of
dehydroxylation take place according to different
mechanisms.
Appendix
Calculation of water content for Y-doped boehmite
using the formula AlO(OH)×xH2O. Loss of water is calculated
The CRTA of the 1% yttrium doped boehmite
shows a quasi-isothermal dehydration step at 80°C.
Similarly to the dynamic experiment, two de-
hydroxylation stages can be separated in the 175 to
500°C range with the local minimum in the DTG
curve at 326°C. Interestingly, the second step of de-
hydroxylation is approaching a quasi-isothermal
course. The shoulder in the DTG curve at about
220°C is assigned to the combustion of traces of the
surfactant adsorbed on the surface.
according to the reaction:
AlO(OH)×xH2O®AlO(OH)+xH2O
A) 1% Y-doped boehmite
Composition: AlO(OH)×xH2O
Loss of water up to 175°C is 17.9 mg (0.993 mmol).
Mass of dehydrated mineral is 197.24 mg (3.288 mmol).
Thus, the amount of crystallization water is 0.30 mol.
The CRTA of the 3% yttrium doped boehmite
shows a quasi-isothermal step of dehydration at
around 60°C. The two-stage pattern of dehydroxyla-
tion can also be observed in the DTG curve in the 175
to 450°C range. The second (quasi-isothermal) step of
dehydroxylation is increased at the expense of the
first one. The burning of the surfactant can also be
identified at around 220°C. The CRTA of the 5% yt-
trium doped boehmite shows a quasi-isothermal de-
hydration step at about 63°C. The combustion of the
surfactant can be observed at about 250°C. Although
the second part of dehydroxylation is approaching a
quasi-isothermal pattern, the separation of the two
dehydroxylation processes can no longer be observed
in the DTG curve. This is in harmony with the dy-
namic experiments. In the dynamic experiments the
two dehydroxylation steps at 326 and 422°C gradu-
ally merged with the increase of yttrium concentra-
tion. The anomaly why the initial part of de-
hydroxylation is non-isothermal, while the second
part is getting to be an isothermal process needs
further studies on the mechanism of decomposition.
B) 3% Y-doped boehmite
Composition: AlO(OH)×xH2O
Loss of water up to 172°C is 23.5 mg (1.304 mmol).
Mass of dehydrated mineral is 214.49 mg (3.575 mmol).
Thus, the amount of crystallization water is 0.36 mol.
C) 5% Y-doped boehmite
Composition: AlO(OH)×xH2O
Loss of water up to 193°C is 22.6 mg (1.254 mmol).
Mass of dehydrated mineral is 166.43 mg (2.774 mmol).
Thus, the amount of crystallization water is 0.45 mol.
Acknowledgements
The financial and infra-structure support of the Queensland
University of Technology Inorganic Materials Research Pro-
gram of the School of Physical and Chemical Sciences is
gratefully acknowledged. The Australian Research Coun-
cil (ARC) is thanked for funding the Thermal Analysis facility
through a LIEF grant. One of the authors (YZ) is thankful for a
Queensland University of Technology international doctoral
scholarship (QIDS).
J. Therm. Anal. Cal., 94, 2008
225

ZHAO et al.
19 J. M. Bouzaid, R. L. Frost, A. W. Musumeci and
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