Physicochemical characterization of the decomposition course of hydrated ytterbium nitrate: Thermoanalytical studies

Article abstract of DOI:10.1016/j.tca.2003.12.029

Yb(NO₃)₃·6H₂O was used as a parent compound for the formation of Yb₂O₃ at up to 800°C in atmosphere of air. Thermal processes occurring during the decomposition course were monitored by means of differential thermal analysis (DTA), thermogravimetry (TG), and the gaseous decomposition products were identified by mass spectrometry (GC-MS). The intermediates and final solid products were characterized by IR-spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that, Yb(NO₃) ₃·6H₂O decomposes completely through 11 endothermic mass loss processes. The dehydration occurs through the first six steps at 95, 145, 165, 175 and 200°C, forming crystalline nitrate Yb(NO₃) ₃, which decomposes to YbO_0.5(NO₃)₂ at 250°C. The latter, decomposes to non-stoichiometric unstable intermediate YbO_0.75(NO₃)_1.5 at 335°C, which decompose immediately to a stable and crystalline YbONO₃ at 365°C, then to a non-stoichiometric unstable intermediate Yb(O)_1.25(NO ₃)_0.5 at 470°C. Finally, Yb₂O₃ was formed at 510°C. The decomposition course and surface morphology were supported and followed by SEM and textural studies (S_BET).The final product Yb₂O₃ at 600°C has a large irregular sheet shaped particles containing a large pores, voids and cracks and has S _BET=45 m²/g. The gaseous decomposition products are water vapor, nitric acid and nitrogen oxides (NO, NO₂ and N ₂O₅). The activation energy (ΔE in kJ/mol) was calculated non-isothermally for each thermal processes.

Full text of DOI:10.1016/j.tca.2003.12.029

Thermochimica Acta 419 (2004) 173–179
Physicochemical characterization of the decomposition course of
hydrated ytterbium nitrate: thermoanalytical studies
∗
Basma A.A. Balboul
Chemistry Department, Faculty of Science, Minia University, El-Minia 61519, Egypt
Received 14 August 2003; received in revised form 12 December 2003; accepted 13 December 2003
Available online 14 April 2004
Abstract
Yb(NO
◦
2 2 3
OwasusedasaparentcompoundfortheformationofYb O atupto800 Cinatmosphereofair. Thermalprocessesoccurring
3
)
3
·6H
during the decomposition course were monitored by means of differential thermal analysis (DTA), thermogravimetry (TG), and the gaseous
decomposition products were identified by mass spectrometry (GC–MS). The intermediates and final solid products were characterized by
IR-spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that, Yb(NO
completelythrough11endothermicmasslossprocesses. Thedehydrationoccursthroughthefirstsixstepsat95, 145, 165, 175and200 C, form-
3
)
3
·6H
2
O decomposes
◦
◦
ing crystalline nitrate Yb(NO
mediate YbO0.75(NO
unstable intermediate Yb(O)1.25(NO
3
)
3
, which decomposes to YbO0.5(NO
3
)
2
at 250 C. The latter, decomposes to non-stoichiometric unstable inter-
◦
◦
3
)
1.5 at 335 C, which decompose immediately to a stable and crystalline YbONO
was formed at 510 C. The decomposition course and surface morphology
were supported and followed by SEM and textural studies (SBET).The final product Yb
containing a large pores, voids and cracks and has SBET = 45 m /g. The gaseous decomposition products are water vapor, nitric acid and
nitrogen oxides (NO, NO and N ). The activation energy (ꢀE in kJ/mol) was calculated non-isothermally for each thermal processes.
2004 Elsevier B.V. All rights reserved.
3
at 365 C, then to a non-stoichiometric
◦
◦
3
)
0.5 at 470 C. Finally, Yb
2
O
3
◦
2
O
3
at 600 C has a large irregular sheet shaped particles
2
2
2 5
O
©
Keywords: Yb-nitrate; Yb-oxide; Decomposition; Formation; DTA; TG; XRD; GC–MS; SBET; SEM
1
. Introduction
cursors leads to higher surface area compared with those
obtained from oxalate precursors. Patil et al. [4] reported
that, the formation of M2O3 from rare earth nitrates takes
place via the oxy-nitrate (MONO3). They also reported
the possible formation of anhydrous nitrate, while Wend-
landt and Bear [5] stated that the anhydrous nitrates are
unstable. Stewart and Wendlandt [6] studied the decom-
position of La(NO3)3·6H2O. They reported that, the de-
The sesquioxide, Yb2O3, has a cubic structure below
◦
1
870 C, at higher temperatures it exists as monoclinic and
hexagonal phase [1]. The Yb2O3 with cubic structure has
been used as catalyst in the dehydration of alkan-2-ols to
alk-1-enes and for the oxidative coupling of methane (i.e.
a petrochemical industrial catalyst [2,3]). Yb2O3 is a basic
oxide whose basicity and catalytic properties are dependent
on the method of preparation and pretreatment [3]. There
is a little information available on literature about the de-
composition course of Yb-salts compared to other rare earth
metal salts.
Several studies [4–11] and a review article [12] have
been published concerning with the thermal decomposition
of rare earth metal salts. It was reported [12] that, rare
earth metal oxides obtained from nitrate or acetate pre-
◦
hydration takes place at 105 C to give La(NO3)3·3H2O,
◦
which decomposes at 200 C to form a basic nitrate; and
◦
at 500 C, La2O3 was the final product. Recently, the de-
composition of Y(NO3)3·5H2O, was studied [7]. It was
reported that a thermally stable monohydrate was formed.
Also a mixture of Y(NO3)3 and Y(OH)(NO3)2 were ob-
◦
tained at 270 C; and YONO3 was detected by XRD as
◦
crystalline phase at 325 C. Y2O3 was the final product at
00 C. The texture analysis by nitrogen adsorption method
◦
5
[
8], revealed that Y2O3 obtained from Y(NO3)3·5H2O at
◦
2
∗
500 C has a higher surface area (SBET = 58 m /g) com-
Tel.: +20-86-345231; fax: +20-86-342601.
◦
2
E-mail address: bsma64@yahoo.com (B.A.A. Balboul).
pared with that obtained at 700 C (SBET = 20 m /g).
0
040-6031/$ – see front matter © 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.tca.2003.12.029

1
74
B.A.A. Balboul / Thermochimica Acta 419 (2004) 173–179
They attribute the lower surface area as results of sintering.
Hussein et al. [9,10] have studied the decomposition course
of Th(NO3)4·5H2O [12] and Dy(NO3)3·6H2O [10] in air
by TG, DTA, IR, XRD and SEM. They reported that,
the anhydrous nitrates are thermally unstable and the de-
From the thermoanalytical data, the temperature (Tmax)
obtained from the DTA curve, were determined as a function
of the heating rate (θ) applied. The activation energy (ꢀE in
kJ/mol) was then calculated for each process using Kissinger
equation [14].
◦
◦
compositions gave ThO2 at 300 C and Dy2O3 at 600 C,
respectively. Different intermediates of non-stoichiometric
oxy-nitrates were also detected. The DyONO3 is crystalline
and thermally stable, compared to ThO(NO3)2 which is
unstable and amorphous. Basma and Balboul [13] studied
the decomposition course of Ho(NO3)3·5H2O in air by
TG, DTA, IR, XRD and SEM. It was reported that, the
anhydrous nitrates are thermally unstable and the decom-
2.3. Gas–mass spectrometry
All the gas–mass spectra of the volatile decomposition
products were recorded with a Hewlett Packard (HP-5890
series II) gas chromatograph equipped with a 5971 mass
selective detector. An HP-vectra Q5/165F data station was
used for acquisition and processing of the spectra. Also the
data station was equipped with ATLAS software for com-
parison and identification purposes.
The spectra of the gaseous products of YbNit were
taken using a sample cell Tekmar 5 ml frit sparger (Pn
14-2337-024). Some modifications were made by heating
the sample area with additional coiled heater equipped with
temperature controller. This makes the cell to work as a
variable temperature cell.
◦
position gave Ho2O3 at 560 C. Different intermediates
of non-stoichiometric oxy-nitrates were also detected. The
HoONO3 is crystalline and thermally stable.
The present investigation is intended to characterize the
thermal decomposition course of Yb(NO3)3·6H2O to the
onset of Yb2O3 formation by means of thermogravimetric
(TG) and differential thermal analysis (DTA). The volatile
decomposition products were analyzed by means of gas
chromatography–mass spectrometry (GC–MS), while the
solid reaction products were characterized by X-ray diffrac-
tion (XRD). Scanning electron microscopy (SEM) was used
to characterize the progressive changes in the morphology
of the nitrate samples as they convert to the oxide. The ox-
The standard procedure for automated GC–MS were as
follows: powder sample (20 mg) was heated at different tem-
◦
peratures (150–450 C) for 5 min. At each temperature, the
gaseous products were trapped using Tekmar LSC2000, dy-
namic head space concentrator. The trapped products were
automatically disrobed into a HP-5890 GC, interfaced with
a 5971A mass-selective detector.
◦
ide formed at 600 C was subjected to surface area mea-
surements by N2 adsorption. The activation energy (ꢀE in
kJ/mol) was determined non-isothermally for the decompo-
sition processes involved.
The gaseous decomposition products were injected at
◦
200 C to the GC equipped with 60 m × 0.25 mm DP5 col-
◦
umn, with a 2.5 ␮m film thickness. It is held at 50 C for
0 min after injection, then programmed to 240 C. The N2
◦
1
2
. Experimental
gas was used as a carrier gas at a flow rate 1.0 ml/min.
To prepare for the next experiment (decomposition tem-
◦
2
.1. Materials
perature), the trap (LSC2000) was baked out at 250 C for
0 min under a flow of N2 gas.
1
Yb(NO3)3·6H2O, abbreviated as YbNit, was 99.9% pure
(
Aldrich, USA). It was used as received. Its calcination
2.4. Infrared spectroscopy
products were obtained by heating at various temperatures
◦
−1
,
(
200–600 C) for 1 h in static air. The calcination tempera-
IR spectra were obtained at a resolution of 4 cm
−
1
tures were chosen on bases of the thermal analysis results.
Prior to analysis, the calcination products were kept dry over
Silica Gel. For simplicity, these products are donated in the
text by YbNit, followed by the calcination temperatures.
Thus, YbNit-400 indicates decomposition products of YbNit
between 4000 and 400 cm , using a model FT/IR 410
JASCO (Japan). IR spectra of YbNit and its solid calci-
nation products were obtained from thin, lightly loaded
(<1%) KBr-supported discs.
◦
at 400 C for 1 h. The abbreviation ML stands for mass loss.
2.5. X-ray diffraction
2
.2. Thermal analysis
XRD powder patterns were obtained using JSX-60P JEOL
diffractometer equipped with Ni-filter and generates a beam
of Cu K␣ radiation (λ = 1.5418 Å). The operational set-
tings for all the XRD scans are voltage: 40 kV; current:
Thermal analysis were performed using DuPont 9900,
Model DTA 951-TG 910 (USA). Thermogravimetry and dif-
◦
◦
◦
ferential thermal analysis curves were recorded up to 700 C
30 mA; 2θ = range 4–60 ; scanning speed = 8 /min; slit
◦
◦
at different heating rates (5–50 C/min), in static air atmo-
width = 0.02 . For identification purposes the relative in-
◦
sphere. Equal weights of the test sample (ca. 15 mg) were
used in TG measurements. Highly sintered ␣-Al2O3 was the
reference material for the DTA measurements.
tensities (I/I ) and the d-spacing (Å) were compared with
standard diffraction patterns of the ASTM powder diffrac-
tion files [15].

B.A.A. Balboul / Thermochimica Acta 419 (2004) 173–179
175
2
.6. Scanning electron microscopy
Table 1
Process
(kJ/mol)
ML
observed
(%)
ML
theoretical
(%)
Composition
Activation
energy
SEM was performed using a Shimadzu (Kyoto, Japan)
electron probe microanalyzer (EPMA 8705) operated at
0 kV. Samples of YbNit and its calcination products
were mounted separately on aluminum stubs, evacuated
to 10 Torr and pre-coated (20 and 5 min for each of
the four sides) in a sputter-coater with a thin, uniform,
gold–palladium film to minimize charging in the electron
beam. The applied voltage was 1.2–1.6 kV.
2
I
II
–
3.85
7.50
Melting
6.85
7.50
Yb(NO3)3·6H2O
–
Yb(NO3)3·5H2O 45
Yb(NO3)3·4H2O 41
Yb(NO3)3·3H2O 54
Yb(NO3)3·1H2O 79
−3
III
IV
V
VI
VII
VIII
IX
X
11.56
19.27
23.40
34.30
40.80
46.20
52.10
57.70
11.56
19.27
23.12
34.68
40.47
46.25
52.03
57.8
Yb(NO3)3
YbO0.5(NO3)2
YbO0.75(NO3)1.5 136
YbONO3 97
YbO1.25(NO3)0.5 163
Yb2O3 152
42
63
2
.7. Nitrogen sorption measurements
XI
The N2 sorption isotherms were determined volumetri-
◦
cally at −196 C using a micro-apparatus based on the de-
losses processes, which maximize at 95, 145, 165, 175 and
200 C, respectively. The mass losses observed of these pro-
cesses (Table 1) are similar to that theoretically calculated
for the release of 6 mol of water, hence the dehydration pro-
cess most likely proceeds as follows:
sign of Lippens et al. [16]. The test sample (YbNit-600) was
out-gassed at 200 C for 2 h under evacuation at 10 Torr.
◦
◦
−5
3
. Results and discussion
◦
9
5 C
Yb(NO3)3 · 6H2O (II) −−→ Yb(NO3)3 · 5H2O
3
.1. Characterization of thermal processes
The DTA curve (Fig. 1) shows 11 endothermic processes.
The first endothermic weight invariant process indicates that
the material melts at 60 C. A direct visual observation of
the physical changes taking place during the decomposition
indicates that the material melts at 59 C. Therefore, process
is due to melting.
◦
1
45 C
Yb(NO3)3 · 5H2O (III) −−→ Yb(NO3)3 · 4H2O
◦
◦
165 C
Yb(NO3)3 · 4H2O (IV) −−→ Yb(NO3)3 · 3H2O
◦
175 ◦C
Yb(NO3)3 · 3H2O (V) −−→ Yb(NO3)3 · H2O
1
◦
200 C
3
.1.1. Dehydration processes
Processes II–VI: The TG and DTA curves (Fig. 1) indi-
Yb(NO3)3 · H2O (VI) −−→ Yb(NO3)3
◦
cates that processes II–VI are overlapping endothermic mass
The mass spectra up to 200 C (Fig. 2), is consistent with
the TG/DTA data. Only the mass of H2O ion (18, at a re-
tention time of 6.5 min) and its positive radicals, m/z = 19,
17 and 16 [17] were detected.
The corresponding activation energy (Table 1) has values
of 45 kJ/mol (II), 41 kJ/mol (III), 54 kJ/mol (IV), 79 kJ/mol
V) and 42 kJ/mol (VI). They are within the range charac-
teristic to the dehydration processes [18,19].
(
3.1.2. Decomposition processes
Process VII is a strong endothermic process peaking at
◦
2
50 C. The ML loss determined (Table 1) for process VII
is 34.3%, which is near to that expected 34.6% for the for-
mation of the amorphous phase YbO0.5(NO3)2.
◦
2
50 C
Yb(NO3)3 (VII) −−→ YbO0.5(NO3)2
◦
The XRD-pattern (Fig. 3) at 300 C indicates the pres-
ence of the anhydrous Yb(NO3)3 as a crystalline phase. The
IR spectrum YbNit-300 (Fig. 4) is similar to that obtained
for untreated YbNit. Except for the disappearance of bands
due to water of crystallization. It displays bands at 1500,
−
1
1
320, 1040 and 830 cm due to nitrate groups of a mainly
Fig. 1. TG and DTA curves recorded for YbNit at the heating rates
indicated, in a dynamic (10 C/min) atmosphere of air.
◦
shelving bidentate structure [20,21].

1
76
B.A.A. Balboul / Thermochimica Acta 419 (2004) 173–179
Fig. 3. X-ray powder diffractograms for the 1 h, calcination products of
YbNit at the temperatures indicated.
Fig. 2. Gas–mass spectra recorded from the gas surrounding a 20 mg
portion of YbNit at the temperatures indicated.
The low activation energy of the first decomposition pro-
cess (VII), 63 kJ/mol, indicates the unstability of the anhy-
drous YbNit.
Processes VIII and IX are strongly overlapped, endother-
◦
mic maximized at 335 and 365 C. The mass loss associated
with each process (Table 1) was close to that equivalent to
the formation of nonstiochiometric unstable form of oxyni-
trate YbO0.75(NO3)1.5 and to the thermally stable interme-
diate YbONO3, respectively.
◦
3
35 C
YbO0.75(NO3)2 (VIII) −−→ YbO0.75(NO3)1.5 + N2O5
Fig. 4. IR spectra for the 1 h calcination products of YbNit at the indicated
temperatures.
◦
3
65 C
YbO0.75(NO3)1.5 (IX) −−→ YbONO3 + N2O
5

B.A.A. Balboul / Thermochimica Acta 419 (2004) 173–179
177
The formation of non-stoichiometric oxy-nitrate has been
reported before [22], during the decomposition of Pr-nitrate,
a different forms of PrOx(NO3)y was formed as an unstable
intermediate which decomposed to the lower oxynitrate (x <
y) and finally to the oxide PrO1.83. Also, the decomposition
course of Ho-nitrate pentahydrate [13] proceeded through
the formation of the unstable intermediates Ho(OH)(NO3)2
and HoOx(NO3)y (x > y). The latter decomposes finally to
◦
the oxide Ho2O3 at 560 C.
◦
The mass spectra up to 450 C (Fig. 2), detect the masses
due to N2O (m/z = 108, 47, 46, 45, 32, 31, 30, 28, 16
5
and 14) [17]. Also, NO (m/z = 30, 16 and 15) and NO2
(
m/z = 46, 30, 16 and 15) were detected as a result of the
decomposition of N2O as follows:
5
N2O → NO + NO2 + O2
5
The activation energy values listed in (Table 1), for pro-
cesses VIII and IX are 136 and 97 kJ/mol.
The XRD pattern of YbNit-400 (Fig. 3), displayed the
pattern due to YbONO3 in addition to a pattern match well
with pattern (ASTM no. 41-1106) of the standard Yb2O3
cubic structure.
◦
The IR spectrum (Fig. 4), of solid phase at 400 C dis-
plays bands mainly due to nitrate [21,22]; the new bands at
−
1
1
(
190 and 830 cm are due to (N=O) outside of bridge and
N=O) bridge, respectively. This may suggest the formation
of bridging nitrogroup. However, the evidence for the for-
mation of oxynitrate anion YbONO3, is quite convincing.
−
1
Absorptions displayed between 600 and 400 cm are re-
lated to Yb–O lattice vibrational mode [23].
Processes X and XI: Process X is strong and endother-
◦
mic maximized at 470 C. The ML determined upon com-
pletion of this process (Table 1) was 52.1% which is close
to that theoretically calculated (52.03%) for the formation
of the non-stoichiometric YbO1.25(NO3)0.5. As the temper-
◦
ature goes up to 510 C. The later decomposes to give the
final decomposition product, Yb2O3, through process XI.
◦
4
70 C
YbONO3 (X) −−→ YbO1.25(NO3)0.5
◦
5
10 C
YbO1.25(NO3)0.5 (XI) −−→ Yb2O3
The ML determined in this process, 57.7%, is close to that
expected theoretically, 57.8%, for the over all decomposi-
tion of Yb(NO3)3·6H2O into Yb2O3. The activation energy
(ꢀE) calculated for this two processes is 163 and 152 kJ/mol.
These values are close to that reported for analogous com-
pounds [13,22].
◦
The XRD pattern at 600 C YbNit-600 (Fig. 3), was in
good agreement with both the former pattern (YbNit-400)
and with that of the standard Yb2O3 [ASTM no. 41-1106].
Fig. 5. Scanning electron micrograph obtained for YbNit calcined at
different temperatures for 1 h (magnification 7500×).
◦
Also, the IR-spectrum of the solid product at 600 C (Fig. 4),
−
1
displays only bands below 600 cm due to Yb–O lattice
vibration mode [23].

1
78
B.A.A. Balboul / Thermochimica Acta 419 (2004) 173–179
4. Conclusions
1. The thermal decomposition of hydrated YbNit in atmo-
sphere of air involves the following path way:
Yb(NO3)3 · 6H2O
◦
◦
(III) 145 C
(
II) 95 C
−
−− −→ Yb(NO3)3·5H2O −−−−−→ Yb(NO3)3 · 4H2O
◦
◦
(V) 175 C
(
IV) 165 C
−
−−−−→ Yb(NO3)3 · 3H2O −− −− −→ Yb(NO3)3·H2O
◦
◦
(VII) 250 C
(
VI) 200 C
−
−−−−→ Yb(NO3)3 −−−−−→ YbO0.5(NO3)2
◦
◦
(IX) 365 C
(
VIII) 335 C
−
−−−−−→ YbO0.75(NO3)1.5 −−−−−→ YbONO3
◦
◦
(XI) 510 C
(
X) 470 C
◦
−− −− −→ YbO1.25(NO3) −−−−−→ Yb2O3
Fig. 6. Nitrogen adsorption isotherm obtained at −195 C (using N2
0.5
adsorption volumetric method) for YbNit-600.
2
3
4
5
. The lower hydrate nitrate of Yb are stable but the anhy-
drous nitrate of Yb is unstable.
. The non-stoichiometric forms of higher and lower oxyni-
trate were detected as unstable intermediates.
. YbONO3 was detected as stable and crystalline interme-
diate.
3
.2. Scanning electron microscopy
Attempts were made to correlate structure changes accom-
panying the decomposition of YbNit, with the corresponding
physicochemical measurements. The SEM specimens were
prepared on the basis of TG curve (Fig. 1). Original YbNit
shows that the parent YbNit consists of large crystals with
well defined shape (Fig. 5).
. The Yb2O3 formed from YbNit has a large crystalline
surface with different types of pores, voids and cracks
2
and has a surface area of 45 m /g.
6. The gaseous decomposition products, detected by gas
mass spectroscopy were H O vapor, HNO , NO, NO
◦
2
3
2
The sample heated at 300 C (YbNit-300, Fig. 5) makes
and N2O5.
a complete change in the morphology, and the melt can
be seen. Also the photo shows bubbling on the surface as
a result of the evolution of water vapor as a dehydration
process. In this range of temprature the TG curve (Fig. 1),
7. The thermal behavior of Yb-nitrate is nearly the same as
other rare earth nitrate.
◦
◦
indicates melting at 60 C and dehydration at 95 C.
◦
References
When the calcination temperature goes to 400 C, the
photo shows a plate-like, irregular sheets, shape particle with
a lot of cracks and small fragments arise as a consequence of
the build up of the gas pressure (H2O and HNO3) detected
by gas mass at 200 C. At this temperature, both TG (Fig. 1)
and XRD (Fig. 3), revealed the formation of YbONO3.
[
1] P. Kofstad, Nonstoichiometry, Diffusion and Electrical Conductivity
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[
[
◦
◦
[4] K.C. Patil, R.K. Gosavi, C.N.R. Rao, Inorg. Chem. Acta 1 (1967)
155.
[
For the 600 C YbNit, both TG and XRD revealed the for-
◦
mation of Yb2O3. The SEM photo (YbNit-600 C, Fig. 5)
5] W.W. Wendlandt, J.L. Bear, J. Inorg. Nucl. Chem. 12 (1960) 276.
6] D.F. Stewart, W.W. Wendlandt, J. Phys. Chem. 63 (1959) 1330.
shows that the surface morphology of Yb2O3 is character-
ized by the presence of cracks, edges and voids with a rough
surface. The particles are irregular sheet-shaped with differ-
ent particle sizes.
[
[7] G.A.M. Hussein, Thermochim. Acta 244 (1994) 139.
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[
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[
(
[
[
[
[
[
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Testing and Materials, Philadelphia, USA, 1960.
3
.3. Nitrogen sorption and surface area measurements
◦
The N2 adsorption isotherm of YbNit-600 C is shown
in (Fig. 6). The isotherm generally belongs to type IV of
IUPAC classification [24]. The desorption isotherm closed
at p/p > 0.4, which give indication the hysteresis loop is
nearly of type H3 [24]. The loop suggested that the surface
pores are of slit-shaped or interplating [25]. This is in close
agreement with the SEM photo of YbNit-600 (Fig. 5). The
◦
[
16] B.C. Lippens, B.G. Linsen, J.H. de-Boer, J. Catal. 3 (1964) 32.
17] F.W. Mclafferty, D.B. Stauffer (Eds.), The Wiley/NBS Registry of
Mass Spectral Data, vol. 1, Masses from 2 to 198, New York, 1989.
18] M.E. Brown, D. Dollimore, A.K. Galwey, Chemical Kinetics, in:
C.H. Bamford, C.F.H. Tipper (Eds.), Reactions in the Solid State,
vol. 22, Elsevier, Amsterdam, 1980, p. 130.
[
[
2
SBET value determined was 45 m /g.

B.A.A. Balboul / Thermochimica Acta 419 (2004) 173–179
179
[
[
19] G.A.M. Hussein, J. Phys. Chem. 98 (1994) 9657.
20] K. Nakamoto, Infrared Spectra of Inorganic and Coordination Com-
pounds, Wiley, New York, 1970, p. 253.
[23] J.A. Goldsmith, S.D. Ross, Spectrochem. Acta (A) 23 (1967) 1909.
[24] S.J. Gregg, K.S.W. Sing, Adsorption, Surface Area and Porosity,
second ed., Academic Press, London, 1982.
[21] G.A. Gadsden, Infrared Spectra of Minerals and Related Inorganic
Compounds, Butterworths, London, 1975, p. 65.
[25] K.S.W. Sing, Pure Appl. Chem. 54 (1982) 2201.
[22] G.A.M. Hussein, B.A.A. Balboul, M.A.A-. Warith, A.G. Othman,
Thermochim. Acta 244 (2001) 139.