Synthesis of MgAl2O4 nanopowders

Article abstract of DOI:10.1134/S0020168511080231

A procedure has been developed for the synthesis of MgAl₂O ₄ nanopowders with a characteristic particle size of 10-40 nm. Translucent hydrous xerogels have been synthesized as precursors to MgAl ₂O₄. The synthesized magnesium aluminum spinel nanopowders are promising for the fabrication of optical ceramics.

Full text of DOI:10.1134/S0020168511080231

ISSN 0020ꢀ1685, Inorganic Materials, 2011, Vol. 47, No. 8, pp. 895–898. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © S.V. Kuznetsov, P.P. Fedorov, V.V. Voronov, V.V. Osiko, 2011, published in Neorganicheskie Materialy, 2011, Vol. 47, No. 8, pp. 988–991.
Synthesis of MgAl O Nanopowders
2
4
S. V. Kuznetsov, P. P. Fedorov, V. V. Voronov, and V. V. Osiko
Prokhorov General Physics Institute, Russian Academy of Sciences, ul. Vavilova 38, Moscow, 119991 Russia
eꢀmail: kouznetzovsv@gmail.com
Received January 31, 2011
Abstract—A procedure has been developed for the synthesis of MgAl O nanopowders with a characteristic
2
4
particle size of 10–40 nm. Translucent hydrous xerogels have been synthesized as precursors to MgAl O . The
2
4
synthesized magnesium aluminum spinel nanopowders are promising for the fabrication of optical ceramics.
DOI: 10.1134/S0020168511080231
INTRODUCTION
EXPERIMENTAL AND RESULTS
Interest in the synthesis of magnesium aluminum
The starting chemicals used were analyticalꢀgrade
spinel, MgAl O4, stems from its unique physicochemꢀ magnesium oxide, OSCh 17ꢀ3 aluminum nitrate nonꢀ
2
ahydrate, analyticalꢀgrade nitric acid, a concentrated
solution of analyticalꢀgrade NH OH, and distilled
ical properties: high hardness (13.5 GPa), high meltꢀ
ing point (2135 ), high thermal conductivity
15 W/(m K)), and chemical stability. Owing to this, it water. The synthesized powders were characterized by
finds application in metallurgy, nuclear engineering, Xꢀray diffraction (XRD) (DRONꢀ4 diffractometer,
photonics, and other areas [1]. A number of applicaꢀ pyrolytic graphite monochromator, Cu radiation),
°
С
4
(
K
α
tions require optically transparent ceramics. Various thermal analysis (MOM Qꢀ1500 D thermoanalytical
methods for the synthesis of MgAl O powders have system), and scanning electron microscopy (JEOL
2
4
been reported in the literature: decomposition of preꢀ JSMꢀ5910). The crystallite size
cursors obtained by hydroxide coprecipitation from were determined by XRD on a URDꢀ63 diffractomeꢀ
aqueous solutions of nitrates [1, 2] and chlorides [3]; ter. and were calculated as described elsewhere [9].
D
and lattice strain
ε
D
ε
reaction of a Mg(NO3)2 solution with a solid sodium Lattice parameters were determined using the Powder
2
.0 program.
aluminum hydroxide carbonate [4]; reactions of aluꢀ
minum salts with ammonia solutions containing magꢀ
An extensive analysis of the literature prompted us
nesium cations [3]; crystallization of MgSO4
⋅
to use coprecipitation from aqueous nitrate solutions
Al (SO )
2
⋅
22H O from a solution of magnesium and with aqueous ammonia as the precipitant. This
4 3
2
method offers the advantages of simplified apparatus,
high reaction rates, and low cost. First, we prepared a
aluminum sulfates [3]; and mixing of hydrous magneꢀ
sium and aluminum nitrates, followed by melting and
decomposition [5].
0.2 M magnesium nitrate solution and a 0.28 M aluꢀ
minum nitrate solution, which were then mixed on a
magnetic stirrer. To the resultant nitrate solution was
The powders thus obtained were used to fabricate
ceramics [2, 3]. The fabrication of ceramics using preꢀ
cursors allows one to reduce the process temperature
added dropwise a 25% NH OH solution until precipiꢀ
4
tation. The curve describing the mixing process is preꢀ
sented in Fig. 1. As seen, precipitation begins at pH 4
and reaches completion near pH 9. The latter pH
value fits well with the conclusion drawn by Sokol et al.
[3] that, at pH 9, the precipitate has the stoichiometric
cation composition.
in comparison with the sintering of Al O
– Mg(OH)2
2
3
mixtures [6].
Even though a variety of approaches have been proꢀ
posed for the fabrication of optical MgAl O ceramics,
2
4
process parameters have not yet been optimized.
This paper presents a continuation of our studies
The precipitates were characterized by thermoꢀ
concerned with the synthesis of nanopowders of variꢀ gravimetry at a heating rate of 10 C/min in the temꢀ
°
ous compounds from aqueous solutions. Previously, perature range 20–1000 (Fig. 2). The temperature
°
С
we reported syntheses of magnesium, aluminum, and was monitored with a 5 С accuracy. The differential
°
yttrium oxides from precipitates obtained by a similar thermal analysis (DTA) curve in Fig. 2 shows a numꢀ
technique [7, 8]. ber of exoꢀ and endothermic peaks in the range 200–
895

896
KUZNETSOV et al.
400
°
С, which are attributable to dehydration of the
pH
1
0
9
8
7
6
5
4
3
2
1
precipitate and MgAl O4 crystallization. The sample
2
weight stabilizes near 560
°
С. The total weight loss is
51.8%.
Based on the thermogravimetry data, we selected
annealing temperatures for identifying phase transforꢀ
mations and evaluating the particle size and lattice
strain of the powders. The samples were heated to the
intended temperature at a rate of 10 C/min. The XRD
°
0
20
40
60
80
100
data are presented in Fig. 3. Figure 3a shows the XRD
pattern of the unannealed precipitate, which comꢀ
prises amorphous and crystalline components. Heatꢀ
ing leads to amorphization of the material (Figs. 3b–
Volume, ml
Fig. 1. Solution pH as a function of the added volume of
NH OH solution.
4
3
e). Starting at 565
spinel phase. The lattice parameter of the powder
heated to 1000 was determined to be = 8.077(8) Å.
This lattice parameter is close to the value given in the
ICDD PDF database (#84ꢀ0377, = 8.080 Å), sugꢀ
°
С, we observe formation of a cubic
°
С
а
а
TG
gesting that we obtained MgAl O4. XRD data were
2
used to evaluate the crystallite size and lattice strain of
the samples heated to 565, 800, and 1000°С (table).
DTG
It can be seen from the table that, at the temperaꢀ
ture where the sample weight stabilizes, the particle
size is 11 nm and there is high lattice strain. Further
heating markedly increases the particle size (by a facꢀ
561°С
DTA
tor of 4). At still higher temperatures, both
D
and
ε
drop sharply. This is accompanied by changes in the
shape of XRD peaks. Similar behavior of the crystalꢀ
lite size and lattice strain was reported for yttrium
oxide [8] and solid solutions between barium and rareꢀ
earth fluorides [10].
4
40°С
3
74°С
3
30°С
2
35
00°С
75
°
°
С
2
С
2
Working out the synthesis procedure, we obtained,
like Ledovskaya et al. [1], translucent xerogels with a
characteristic size of 3–5 mm. Their photographs are
presented in Fig. 4. The translucent xerogels were simꢀ
ilar in appearance to materials synthesized in an earꢀ
lier study [10].
Fig. 2. Thermal analysis results for the precipitate used as
a precursor to magnesium aluminum spinel.
To determine the morphology and size of the synꢀ
thesized particles, the translucent xerogels were examꢀ
ined by scanning electron microscopy (Fig. 5). Prior
Parameters of MgAl O nanoparticles
2
4
to examination, the samples were dried at 150 С (priꢀ
°
10 3
mary dehydration). In the micrograph in Fig. 5a, one
can discern agglomerated particles about 20 nm in
size, which are aligned to form chains.
tann
,
°
C
D
, nm
ε
×
5
65
00
11
41
13
20.3
20.0
5.7
In the micrograph of the MgAl O4 sample heated to
2
1
000 С (Fig. 5b) and then furnaceꢀcooled, one can
°
8
discern agglomerates of particles about 50 nm in size.
The discrepancy between the scanning electron
microscopy and XRD data (table) for 1000
°
С
is most
1
000
likely due to nanoparticle relaxation processes.
INORGANIC MATERIALS Vol. 47
No. 8
2011

SYNTHESIS OF MgAl O NANOPOWDERS
897
2
4
1
5
00
0
0
1
(
а)
b)
0
0
20
20
20
20
20
20
20
20
30
30
30
30
30
30
30
30
40
40
40
50
50
50
50
50
50
50
50
60
60
60
60
60
60
60
60
70
70
70
70
70
70
70
70
100
(
5
0
0
1
100
(c)
(d)
(e)
5
0
0
1
0
0
0
0
0
0
1
00
50
0
1
00
40
40
40
40
40
1
50
0
1
00
1
(f)
50
0
1
100
(j)
5
0
0
1
100
(h)
5
0
0
1
2θ, deg
Fig. 3. XRD patterns of samples heated to (b) 220, (c) 235, (d) 275, (e) 330, (f) 565, (g) 800, and (h) 1000°C; (a) precipitate.
Fig. 4. Photographs of translucent xerogels used as precursors to magnesium aluminum spinel. The mean sample thickness is
.3 mm.
2
INORGANIC MATERIALS Vol. 47
No. 8 2011

898
KUZNETSOV et al.
ACKNOWLEDGMENTS
We are grateful to S.V. Lavrishchev for performing
the electronꢀmicroscopic work.
REFERENCES
1
. Ledovskaya, E.G., Gabelkov, S.V., Litvinenko, L.M.,
et al., LowꢀTemperature Synthesis of Magnesium Aluꢀ
minum Spinel, Vopr. At. Nauki Tekh., 2006, no. 1,
pp. 160–162.
2. JiꢀGuang Li, Takayasu Ikegami, JongꢀHeun Lee, and
Toshiyuki Mori, Fabrication of Translucent Magneꢀ
sium Aluminum Spinel Ceramics, J. Am. Ceram. Soc.
000, vol. 83, no. 11, pp. 2866–2868.
,
2
0.1
μ
m
3. Sokol, V.A., Rokhlenko, D.A., Kononova, L.I., and
Bromberg, A.V., Magnesium Aluminum Spinel for
Transparent Ceramics, Izv. Akad. Nauk SSSR, Neorg.
Mater., 1981, vol. 17, no. 5, pp. 896–901.
(а)
4
. Tomilov, N.P. and Devyatkina, E.T., Synthesis of
MgAl O from Coprecipitated Hydroxides, Izv. Akad.
2
4
Nauk SSSR, Neorg. Mater., 1990, vol. 26, no. 12,
pp. 2556–2561.
5
. Messier, D.R. and Gazza, G.E., Synthesis of MgAl O
2
4
and Y Al O by Thermal Decomposition of Hydrated
3
5 12
Nitrate Mixtures, Ceram. Bull., 1972, vol. 51, no. 9,
pp. 692–697.
6
. Cambaz, G. and Timucin, M., Compositional Modifiꢀ
cations in Humidity Sensing MgAl O Ceramics, Key
2
4
Eng. Mater., 2004, vols. 264–268, pp. 1265–1268.
7
. Fedorov, P.P., Tkachenko, E.A., Kuznetsov, S.V., et al.,
Preparation of MgO Nanoparticles, Neorg. Mater.,
2
007, vol. 43, no. 5, pp. 574–576 [Inorg. Mater. (Engl.
0.5 μm
(
b)
Transl.), vol. 43, no. 5, pp. 502–504].
Fig. 5. Micrographs of powders heated to (a) 150 and
b) 1000 C.
8. Fedorov, P.P., Voronov, V.V., Ivanov, V.K., et al., Evoluꢀ
tion of Yttria Nanoparticle Ensembles, Ross. Nanotekhꢀ
nol., 2010, vol. 5, nos. 9–10, pp. 37–44.
(
°
9
. De Keijser, Th.H., Landford, J.I., Mittemeijr, E.J., and
Vogels, A.B.P., Use of the Voigt Function in a Singleꢀ
Line Method for the Analysis of XꢀRay Diffraction
Line Broadening, J. Appl. Crystallogr., 1982, vol. 15,
pp. 308–314.
CONCLUSIONS
MgAl O nanopowders have been synthesized via
precipitation from aqueous solutions. The present
results demonstrate the possibility of producing transꢀ
2
4
10. Kuznetsov, S.V., Fedorov, P.P., Voronov, V.V., et al.,
lucent hydrous xerogels as precursors to MgAl O4. The
2
Synthesis of Ba R F (R = RareꢀEarth Element) from
4
3 17
synthesized nanopowders are promising for the fabriꢀ
Aqueous Solutions, Zh. Neorg. Khim., 2010, vol. 55,
no. 4, pp. 536–545.
cation of optical MgAl O nanoceramics.
2
4
INORGANIC MATERIALS Vol. 47
No. 8
2011