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Ba2Ti9O20 CERAMIC FROM BaSO4 AND TiO2 POWDER SYNTHESIS
MIXTURE
Yu. Koldayeva1, M.C.A. Nono1 and P. J. Castro2
Laboratório Associado de Sensores e Materiais - LAS, Instituto Nacional de
Pesquisas Espaciais - INPE, São José dos Campos 12201-970, Brazil
2
Laboratório Associado de Plasma - LAP, Instituto Nacional de Pesquisas Espaciais
- INPE, São José dos Campos 12201-970, Brazil
[email protected]
1
Keywords: powder synthesis, processing, barium nanotitanate, barium sulphate.
Abstract: In this work the BaSO4 powder was synthesized from BaCO3 powder that was
attacked with HCl. Then BaCl2 was precipitated in (NH4)2 SO4, containing TiO2 powder.
The influences of processing and TiO2 particles presence were investigated by X-rays
diffraction and SEM. It was found that the washing of BaSO4 - TiO2 precipitated by ethanol
greatly benefited the formation of smaller size particles.
Introduction
Barium nanotitanate (Ba2Ti9O20) dense ceramic has adequate properties for use as
dielectric resonator for microwave applications [1-3]. Most of the Ba2Ti9O20 available on
the market is produced by calcinations and results in wide ranges of particle sizes that can
affect homogeneity of microstructure and dielectric properties. The average particle size of
this type of powder is in the range of a few micrometers [4]. On the other hand the
tendency for miniaturization of advanced devices demands high purity, precisely controlled
stoichiometry and fine starting powders. The alternative processes (co-precipitation,
alkoxide, hydrothermal) show commercial promise [4-9], because of the lowest
temperatures employed and lower cost of the precursors, typically TiO2 and BaCO3 ou
Ba(OH)2. As usual the BaCO3 and TiO2 powders are used to obtain dielectric dense
ceramics, but the shape anisotropy of BaCO3 particles difficulties the particle
accommodation during the compaction, chemical reactions and diffusion during sintering,
and, consequently, the formation of Ba2Ti9O20 pure crystalline phase. The classical ways of
preparing barium nanotitanate powders involve the reaction between carbonates, oxides or
hydroxides of the constituent elements at high temperatures. Using of wet chemical routes
can offer better quality powders. This was investigated in this study where the BaCO3
powder was substituted by BaSO4 one. Ceramic materials with submicron and/or nanosized
structures have attracted much interest in recent years because they often display greatly
improved performances in comparison to traditional coarse-grained materials.
Experimental Procedure
The materials used in this work were: BaCO3, HCL, ((NH4)2SO4) and TiO2 (anatase
structure), ethyl alcohol, deionized water. The process of BaSO4 obtaining is shown on
Figure 1. Aqueous solution of HCL (20% in excess) was prepared and followed by the
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dissolution of BaCO3 with the aid of a magnetic agitator. The solution of barium chloride
was put in a pulverizer and sprayed quickly in form of a fine drops on the precipitate
((NH4)2SO4). As result, was obtained a powder of white color. The precipitation was driven
under the condition of constant magnetic agitation and during this procedure the pH of the
solution was not monitored. After the precipitation and segregation of the powder it was
necessary to wash it with deionized water to remove the undesirable ions, i.e., chlorine
ions. In the following stage it was made the extraction liquid-liquid with ethyl alcohol.
Each wash was realized in a Buckner funnel with paper filter aided by vacuum. The
powders of BaSO4 obtained in this work were characterized on XRD and MEV.
BaCO3
HCl
BaCl2
(NH4)2SO4
BaSO4 or
BaSO4 +TiO2 mixture
TiO2
Figure 1. The process of BaSO4 synthesis.
The dot line shows (Fig. 1) the additional stage to obtain homogeneous mixture of
BaSO4 and TiO2. The TiO2 power was dispersed directly in the (NH4)2SO4 solution before
the BaCl2 was added. The amounts of barium sulphate and titanium oxide were mixed in
equimolar proportions. The global reaction for barium sulphate and anatase can be written
as follows:
2 BaSO4 (s) + 9 TiO2 (s) → Ba2Ti9O20 (s) + 2 SO2 (g) + O2 (s)
The dried powder mixture was compacted by an uniaxial (40 MPa) and isostatic
(300 MPa) pressings to form cylindrical test bodies. The samples were synthesized and
sintered at the same time at 1000°C and 1200°C for 3 hours. Afterwards, the ceramic
crystallographic phase composition were evaluated by the X-rays diffraction (Philips Xrays diffratometer, Model PW3710) patterns of powders. The fracture surfaces were
observed by scanning electron microscopy (SEM, JEOL, Model JSM-5310).
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Results and discussion
20
30
50
60
(160)
(422)
(330)
(410)
(411)
(123)
(213) (332)
(132)
(122)
40
(041)
(211)
(002)
(221)
(310)
(101)
10
(111)
(200)
(210)
(021)
(121)
(231)
XRD has shown that the BaSO4 powders obtained in this work had single phase and
it X-rays diffraction patterns is shown in Fig. 2.
Intensity (a.u)
Coordenação
70
2θ
Figure 2. X-rays diffraction patterns of the BaSO4 powder
The SEM image of BaSO4 powder is presented in Fig 3. Electron microscopy showed that
the powder contained predominantly submicron particles, quite homogeneously distributed
and few dense agglomerates.
Figure 3. SEM images for BaSO4 powder.
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The preparation of the BaSO4 powder is a critical step in the fabrication process. It
is necessary to control the inter-particle forces because of the tendency for agglomeration.
The liquid-liquid extraction with ethyl alcohol helped to remove the water absorbed on the
surface of the particles and pores of the powder. This procedure let to minimize the
formation of dense agglomerates during the drying stage. It can be clearly seen on the Fig.
3.
The ceramics obtained in this work have presented the barium nanotitanate as the
major phase. For those processed at 1200° C for 3 hours only Ba2Ti9O20 phase was
detected. And for others processed at 1000° C for 3 hours although this phase was detected
too it was detected the presence of unreacted BaSO4 and TiO2 powders. None of the
samples has shown formation of the BaTi4O9 phase that is the common problem in
processing of this type of ceramics [10-13].
0 - BaSO4
1 - TiO2
2 - BaTi4O9
3 - Ba2Ti9O20
Intensity (a.u.)
Coordenação
3
3
3
33
3
33 3
13
1
3 3
03
0
1 3 3
33
0 0
10
20
30
40
3
3
3 33
3
3 h, 1200 °C
1
0 3
50
3
3 h, 1000 °C
3 33
60
70
2θ
Figure 4. X-rays diffraction patterns for Ba2Ti9O20 ceramics.
The scanning electronic microscopy analyses of the ceramic fracture surfaces
showed a low densification degree of the microstructure and the presence of a lot of pores
(Fig.5). One of the reasons to these defects appear is the formation of not enough contacts
during the compaction step. This effect can be minimized when greater pressure is applied
during compactation or by using the hot pressing. It can be observed (Fig. 5) that ceramics
processed at 1200° C for 3 hours present more dense microstructure nevertheless it is not
adequate to use them as dielectric resonators.
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b
Figure 5. SEM images for Ba2Ti9O20 ceramics: a) 1000° C, 3 hrs, b) 1200° C, 3 hrs
Summary
BaSO4 powder have been prepared from BaCO3 through precipitation, and the
BaSO4 + TiO2 was used to fabricate Ba2Ti9O20 ceramics. The BaSO4 powder was found to
have agglomerates of much (submicron) particles than that of BaCO3 [14-17].
Advantages of BaSO4 powders is using of lowest temperature [13-15] and times for
it sinterization. It was homogeneous in particle size distribution and with average particle
sizes. It is necessary to carry out more experiments to solve the problem of microstructure
densification. It is important to control the densification and firing schedule. A good control
over the chemical composition and processing conditions is essential.
Acknowledgements
The authors gratefully acknowledge the financial support of CAPES (Brazil) for
carrying out this work.
References:
[1] D. Hennings; P. Schnabel, Philips J. Res., Vol.38, no. 6 (1983), p. 295.
[2] J.M. Wu; H.W. Wang,, J. Amer. Cer. Soc., Vol. 71, no. 10 (1988), p. 869.
[3] P. Tandon; J. Goyette; Y.K.Bose, J. Mater. Sci. Let., Vol. 14 (1995), p. 1373.
[4] G.A. Hutchins et al.. Am. Ceram. Soc. Bull. Vol. 66, no. 4 (1987), p. 681.
[5] F.S. Yen et al.. J. Am. Ceram. Soc. Vol. 73, no. 11 (1990), p. 3422.
[6] P.P. Phule and S.H. Risbud. Adv. Ceram. Mater. Vol. 3, no. 2 (1985), p. 183.
[7] Y. Suyama and M. Nagasawa. J. Am. Ceram. Soc. Vol. 77, no. 2 (1994), p. 603.
[8] R. Vivekanandan et al.. Mater. Res. Bull. no. 22 (1986), p. 99.
[9] M.A. Delfrate et al.. J. Mater. Sci. no. 5 (1994), p. 153.
[10] H.M. O’Bryan Jr; J. Thomson Jr, J. Amer. Cer. Soc., Vol. 66, no. 12 (1983), p. 66
[11] M.C.A. Nono; P.J. Castro, 36th Brazilian Ceramic Meeting, (1992), p. 609.
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[12] P.J. Castro; M.C.A. Nono, J. Microwave and Optoeletronics, Vol.4, n.1 (1999), p. 27.
[13] W.-Y. Lin; R.A. Gerhardt; R.F. Speyer, J. Mater. Sci., Vol. 34 (1999), p. 3021 – 3025.
[14] W.-Y. Lin; R.F. Speyer, J. Am. Ceram. Soc., Vol. 82, no. 5 (1999), p. 1207–1211.
[15] W.-Y. Lin; R.F. Speyer, J. Am. Ceram. Soc., Vol. 82, no. 2 (1999), p. 325–330.
[16] M.C.A. Nono; P.J. Castro, J. Mater. Sci. Forum,, Vols. 416-418 (2003), p. 11-16.
[17] S.-F. Wang, T. C. K. Yang, C.-C.Chiang, S. H. Y. Tsai, Cer. Inter., Vol. 29 (2003), p.
77-81.
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