Journal of Sol-Gel Science and Technology 19, 409–412, 2000 c 2000 Kluwer Academic Publishers. Manufactured in The Netherlands. °
Sol-Gel Poly-Component Nano-Sized Oxide Powders MARIA CRISAN∗, MARIA ZAHARESCU, A. JITIANU AND D. CRISAN Romanian Academy, Institute of Physical Chemistry, 202, Splaiul Independentei, 77208, Bucharest, Romania m
[email protected];
[email protected]
MARIA PREDA University “Politehnica”, Faculty of Industrial Chemistry, 1 Polizu Street, Bucharest, Romania
Abstract. Nano-sized, amorphous and monodispersed poly-component powders in the Al2 O3 TiO2 MgO and Al2 O3 TiO2 SiO2 systems have been obtained by the sol-gel method. These powders have been characterized by XRD, IR spectroscopy, DTA/TGA and EDAX spectrometry. This last method confirmed the composition of the ternary powders, which are formed during the gelation process. The powders were tested as precursors for obtaining advanced ceramics, as tialite, Al2 TiO5 . The samples prepared with powders obtained by sol-gel method have shown a high reactivity, and the formation of tialite was improved. Keywords: tialite 1.
Al2 O3 TiO2 MgO sol-gel system, Al2 O3 TiO2 SiO2 sol-gel system, poly-component powders,
Introduction
The design of advanced ceramics depends on the availability of powders with outstanding properties in terms of composition, purity, size, and size distribution. Solgel processes allow synthesis powders to have a more elaborate structure. Preparation of nano-sized oxide powders by sol-gel method represents, for the time being, an important goal for the scientists working in the field. Many attempts to obtain individual and polycomponent oxide powders in several systems were achieved. Some of them are presented below: Al2 O3 SiO2 [1], Al2 O3 TiO2 [2, 3], Al2 O3 MgO [4], Al2 O3 SiO2 MgO [5]. In the present work, ternary reactive powders in the Al2 O3 TiO2 MgO and Al2 O3 TiO2 SiO2 systems have been obtained using the sol-gel method, by the simultaneous gelation of all cations. The powders were tested as precursors for obtaining advanced ceramics, as tialite, Al2 TiO5 . Due to the difficulties noticed at the ∗ To
whom all correspondence should be addressed.
obtaining of the tialite based materials, the researches have been directed to use powders with different additives such as MgO and SiO2 which stabilize the tialite structure. Results concerning of tialite preparation from monocomponent sol-gel oxide powders or binary sol-gel oxide powders (corresponding to tialite and magnesium spinel compositions or tialite and mullite compositions) were presented in previous papers [3, 6–8]. 2. 2.1.
Experimental Synthesis of the Reactive Powders
The composition of the starting solutions and the experimental conditions used for ternary powders are listed in Table 1. Base catalysis was used in the case of magnesium powders. All solutions were prepared at high temperature in nitrogen atmosphere. The starting oxide powders, as well as thermally treated samples were characterised by XRD (using Co Kα radiation), IR spectroscopy in the 3800–200 cm−1 range, DTA/TGA analysis up to 1400◦ C with
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Table 1.
Composition of starting solutions and experimental conditions for ternary powders preparation. Molar ratio ROH + (R0 OH)
H2 O
Metal precursors
metal 6precursors
metal 6precursors
metal 6precursors
Al(O i C3 H7 )3 + Ti(O i C3 H7 )4 + Mg(NO3 )2 ·6H2 O
72.5a
13.94
2.23
7
70 80
1.5 1 in N2
Al(O i C3 H7 )3 + Ti(O i C3 H7 )4 + Mg(NO3 )2 ·6H2 O
70a
20.33
4.47
8
70 80
1.5 1 in N2
Al(O i C3 H7 )3 + Ti(O i C3 H7 )4 + Si(O C2 H5 )4
75b
12.33
–
4.5
70
3 in N2
Al(O i C3 H7 )3 + Ti(O i C3 H7 )4 + Si(O C2 H5 )4
75b
16.37
–
4.5–5.0
70
3 in N2
Sample (% weight) T1 (90AT + 10MA)
T2 (80AT + 20MA)
T3 (50AT + 50A3 S2 )
T4 (75AT + 50A3 S2 )
AT = Al2 TiO5 —Tialite; MA = MgAl2 O4 ; a R= i C H . 3 7 b R= C H ; R0 = i C3 H7 . 2 5
NH4 OH
Conditions of reaction pH of the mixture
T (◦ C)
t (h)
A3 S2 = 3Al2 O3 ·2SiO2 —Mullite.
a heating rate of 7,5◦ C/min., and EDAX spectrometry using an EDAX spectrometer attached to Phillips CM 30 TEM.
The amount of tialite formed at different temperatures was determined by the relation: Tialite (%)
2.2.
=
Synthesis of the Ceramic Masses
The powders prepared according to the experimental conditions are presented in Table 1. This corresponds to the oxide and theoretical mineralogical compositions presented in Table 2. For obtaining ceramic masses before pressing, the sol-gel powders were thermally treated 2 h at 450◦ C with 1◦ C/min. for removal of organic matter. By uniaxial pressing at 400 dN/cm2 , 10 mm high samples have been obtained, which were fired at temperature between 1250–1450◦ C, with a 2 hour plateau at the highest temperature and then oven cooled.
Table 2.
where I represents the intensity of following lines: (113) for α-Al2 O3 ; (101) for TiO2 —rutile; (110) for mullite; (311) for MgAl2 O4 and (020) for tialite. 3. 3.1.
Results and Discussion Reactive Powders
The powders obtained in experimental conditions presented in Table 1 are all amorphous as determined
Oxide and theoretical mineralogical composition of the synthesised masses. Oxide composition (% weight)
Sample
100 · ITialite IAl2 O3 + ITiO2 + 2 · IMullite + 2.38 · ITialite + IMgAl2 O4
Mineralogical composition (%)
SiO2
MgO
Al2 O3
TiO2
AT
MA
A3 S2 –
T1
–
2.89
57.63
39.54
90
10
T2
–
5.67
59.18
35.15
80
20
–
T3
14.10
–
63.93
21.97
50
–
50
T4
7.05
–
60.00
32.95
75
–
25
Sol-Gel Poly-Component Nano-Sized Oxide Powders
Figure 1.
EDAX spectra of T1 sample.
Figure 2.
EDAX spectra of T4 sample.
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Figure 3. IR spectra of the ternary powders thermally treated 2 h at 450◦ C.
by XRD, and have a great value of BET surface area (>200 m2 /g) according to the small size of particles. The presence of the additives, Mg and Si, in T1 and T4 powders, (with the smallest content of additive) were confirmed by EDAX spectra (Figs. 1 and 2). The thermal analysis of powders, obtained by DTA/TGA, emphasized in all cases that the thermal effects below 450◦ C are assigned to the evolution of adsorbed water and alcohol and the burning out of organic residues. Phase composition established by XRD on the DTA/TGA residues at 1400◦ C shows in all samples the presence of a high amount of tialite. This fact pointed out the high reactivity of the sol-gel powders. The amorphous character and the high values of BET surface area >200 m2 /g are maintained also after thermal treatment at 450◦ C, 2 h. The IR spectra of the ternary powders are presented in Fig. 3. The characteristic vibrations due to the presence of molecular water and structural OH are observed. In the range corresponding to the M O vibration, broad
bands were recorded which are an uncommon overlapping of the bands corresponding to the monocomponent oxides: Al O (780, 570, 380 cm−1 ), Ti O (670, 540, 360 cm−1 ), Si O (1050, 450 cm−1 ) and MgO (430 cm−1 ) [9]. No vibration band is recorded at about 1050 cm−1 in the ternary samples containing SiO2 (T3 and T4 samples). Thus, the formation of Al O Ti and Al O Si (or Al O Ti O Si) bonds is not excluded. In a similar way, in the case of the samples that contain MgO (T1 and T2 samples) the Al O Ti and Al O Mg (or Al O Ti O Mg) bonds could be formed.
3.2.
Ceramic Masses
The evolution of tialite content of the ternary ceramic masses thermally treated at 1250–1450◦ C is presented in Fig. 4. For all samples, the tialite formation can be
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4.
Conclusions
Nano-sized, monodisperse and amorphous powders prepared in the Al2 O3 TiO2 MgO and Al2 O3 TiO2 SiO2 systems using sol-gel method, by the simultaneous gelation of all cations, were tested as precursors for obtaining an advanced ceramic, in this case tialite. The ternary sol-gel powders show high reactivity for tialite formation. MgO and SiO2 were used as additives only in low concentration (1–10% weight) and improved tialite syntheses by solid state reactions. References
Figure 4.
Variation of tialite content versus annealing temperature.
observed starting with 1250◦ C and slowly increases with temperature. Sample T3 has the smallest amount of tialite because the high content of SiO2 in its composition. In the case of sample T2 containing ∼6% MgO, besides tialite, a low quantity of MgAl2 O4 was noticed (∼7.5% at 1400◦ C). For the sample T3 , the low content of tialite is correlated with the formation of high quantity of mullite (∼28% at 1400◦ C).
1. B.E. Yoldas, in Ceramic Transactions, edited by S. Somiya, R.F. Davis, and J.A. Pask (American Ceramic Society, Westerville, 1990), p. 255. 2. E. Kato, K. Daimon, and Y. Takahashi, J. Amer. Ceram. Soc. 63, 355 (1990). 3. M. Zaharescu, M. Crisan, D. Crisan, N. Dragan, A. Jitianu, and M. Preda, J. Eur. Ceram. Soc. 18, 1257 (1998). 4. C. Pommier, K. Chor, J.F. Bocquet, and M. Bary, Mat. Res. Bull. 25, 213 (1990). 5. S. Komarneni, J. Sol-Gel Sci.Technol. 6, 127 (1996). 6. M. Zaharescu, M. Preda, M. Crisan, D. Crisan, E. Vasile, and A. Jitianu, Key Engineering Materials 132–136, 852 (1997). 7. M. Zaharescu, M. Preda, M. Crisan, D. Crisan, E. Vasile, and A. Jitianu, in Ceramics: Getting into the 2000’s, edited by P. Vincenzini (Techna Srl, Faenza, 1999), p. 89. 8. M. Crisan, M. Preda, D. Crisan, A. Jitianu, and M. Zaharescu, J. Sintering Science, in press. 9. P. Tarte, in Physics of Non-Crystalline Solids, edited by J.A. Prins (North Holland, Amsterdam, 1965), p. 549.
