Yttrium 화합물로 표면처리 된 BaTiO3 입자의 제조와 특성 조사

화학공학의 이론과 응용 제8권 제1호 2002년

Theories and Applications of Chem. Eng., 2002, Vol. 8, No. 1

이영호, 오성근, 이상규*, 백운규*

한양대학교 화학공학과, 한양대학교 세라믹 공학과*

Preparation and Characterization of BaTiO3 particles coated with Yttrium compound

Young-Ho Lee, Seong-Geun Oh, Sang-Gyu Lee*, Un-Gyu Paik*

Department of Chemical Engineering and CUPS, Hanyang University.

Department of Ceramic Engineering* , Hanyang University

1. Introduction

BaTiO3 is a ferroelectric material and widely used in the electronic applications, such as high-capacitance capacitors, thermistors, and piezoelectric and humidity sensors. Some additives(SiO2, MgO, Y2O3, and etc.) are used in the industrial process. The additives affect the sintering behavior, the surface charge, the grain growth, and etc. Y2O3 additives inhibits the grain growth of BaTiO3 coinciding with the loss of semiconductivity.

Many workers studied the synthesis of BaTiO3 coated with yttrium compounds. Usually, the surface of the BaTiO3 was treated with yttrium compounds by the milling of the mixtures of BaTiO3 and Y2O3 particles or by the adsorption of the Y3+ ions. But in these methods BaTiO3 was not coated with yttrium compounds uniformly.

Park and his co-workers(1) synthesized zinc sulfide phosphors coated with yttrium oxide using sol-gel process. In this process, yttrium isopropoxide was used as the precursor materials in toluene/isopropanol solution. However, this process have the problem that yttrium isopropoxide was too expensive. Matijevic and his co-workers(2)-(5) synthesized various oxide-coated particles such as hematite coated with zirconium hydrous oxide or chromium hydrous oxide, and etc. They have showed that the synthesis of the core-shell composite particles in the controlled conditions(the size of shape of the obtained colloids and the thickness of the coating) is possible for various systems, including core particles like hematite, chromium hydroxide, or titania and shell particles aluminum, zirconium, and yttrium compounds. In this method, chloride or nitrate salts are used as the precursors, so this method has the advantage that these precursors are cheap. Recently, Plaza and his co-workers(6)-(9) synthesized hematite particles coated with yttrium oxide and characterized their physical and chemical properties on the basis of the method described by Matijevic and his co-workers.

In the present work, we prepared BaTiO3 particles coated with yttrium basic carbonate by the method described by Aiken and Matijevic(5) for the obtention of elongated hematite particles coated with yttrium carbonate or oxide. Nucleation and growth of yttrium basic carbonates occurred at the surface of the BaTiO3 particle. First, yttrium ions were adsorbed on the BaTiO3 surface, because the surface of BaTiO3 was charged negatively(the isoelectric point of the BaTiO3 is pH 3~5). Then urea decomposed at 80□ and yttrium basic carbonates are formed on the surface of BaTiO3 particles. Yttrium basic carbonates were converted to yttrium oxides at 800□ for 3h.

2. Expermental

Materials

BaTiO3 powder(D=0.4□m) as core particle, urea(99+%, Aldrich) as the source of the hydroxyl and carbonate ion, polyvinypyrrolidone(Mw=40,000, Kanto) and yttrium nitrate hexahydrate(99.9%, Aldrich) as coatings were used as received. Water(18.2M□/cm) was purified with Rios and Milli-Q system (Millipore).

Preparation of the coated particles

A 250mL round-bottom flask was charged with urea, yttrium nitrate hexahydrate, polyvinylpyrrolidone and 200 mL of water. After yttrium nitrate hexahydrate, urea and polyvinylpyrrolidone were dissoved in the water completely, BaTiO3 powder was added into the mixture and sonificated for 5 mins to disperse the aggregated BaTiO3 particles. The compositions of the mixture were specified in Table 1. The reaction mixtures were aged at 6h at 80□.

Obtained suspension was precipitated after centrifugation at 3,000 rpm for 20 min. Yttrium basic carbonate particles that were formed in the bulk solution were not precipitated because those were stabilized by PVP. For removal of the unreacted materials and yttrium compounds that were formed in the bulk solution, the obtained materials were washed three times with ethanol. The suspensions were dried at 50□ in the vacuum oven and then calcined at 800□ for 3h in the presence of air.

Characterizations

The size and morphology of the core particles and the coated particles were analyzed by Transmission Electron Microscopy(JEOL model, JEM2000-EX II) and Field Emission Scanning Electron Spectroscopy(JEOL model, JSM-6340F). For analyzing TEM images, the dried particles were redispersed in ethanol. Surface chemical composition of coated particles was analyzed by EDS(Energy Dispersive X-ray Spectrophotometer) attached to SEM. For analyzing the structure of the coated particles, X-ray diffractometry measurements were performed on a Rigaku D/MAX RINT 2500 X-ray diffractometer. The contact angle and surface energy of the BaTiO3 particles and coated particles were measured by a surface tensiometer (KR□SS Co. K-12). Both the calcined and the non-calcined particles were characterized by above measurements

3. Results & Discussion

The diameter of BaTiO3 core particles was about 0.4□m and the shapes of particles were irregular (Figure 1-(a)). In case of adding PVP, the formation of particle-like coatings occurred (Figure 1-(b)).  When PVP was not added, BaTiO3 was coated with yttrium basic carbonate, but the yttrium basic carbonate particles were formed in the bulk solution and its diameter was about 100~150 nm. The diameter of the coated particles was above 0.5□m and the shapes were more spherical than that of the BaTiO3 particles. When the chemical composition of the surface was analyzed by EDS, It was found that the ratio of yttrium to barium was about 3:1(Figure 2).

3. Acknowledgement

This reaserch was funded by Center for Ultramicrochemical Process Systems

화학공학의 이론과 응용 제8권 제1호 2002년

4. References

(1) Park W., Yasuda K., Wagner B.K., Summers C.J., Do Y.R., Yang H.G., Material Science Engineering B76, 122 (2000)

(2) Gherardi, P., Matijevic, E., J. Colloid Interface Sci. 109, 57 (1986)

(3) Kratohvil, S., Matijevic, E., Adv. Ceram. Mater. 118, 506 (1987)

(4) Garg, A., and Matijevic, E., Langmuir 4, 38 (1988)

(5) Aiken B., and Matijevic, E., J. Colloid Interface Sci. 126, 645 (1998)

(6) Plaza R.C., Duran J.D.G., Quirantes A., Ariza M.J., and Delgado A.V., J. Colloid Interface Sci. 194, 398 (1997)

(7) Plaza R.C., Gomez-Lopera S.A., and Delgado A,V., J. Colloid Interface Sci. 240, 48 (2001)

(8) Plaza R.C., Zurita L., Duran J.D.G., Gonzalez-Caballero F., and Delgado A.V., Langmuir 14, 6850 (1998)

(9) Plaza R.C., Zurita L., Gonzalez-Caballero F., and Delgado A.V., Colloid Polym. Sci. 279, 1206 (2001)

화학공학의 이론과 응용 제8권 제1호 2002년

	BaTiO3	Y(NO3)3□6H2O	Urea	PVP
Sample 1	0.0466g (1mM)	0.0766g (1mM)	1.2g (0.1M)	-
Sample 2	0.0466g (1mM)	0.0766g (1mM)	1.2g (0.1M)	2g
Sample 3	0.0466g (1mM)	0.1532g (2mM)	1.2g (0.1M)	-
Smaple 4	0.0466g (1mM)	0.1532g (2mM)	1.2g (0.1M)	2g

Table 1. Samples of BaTiO3-Yttrium Basic Carbonate Composite Particles

Figure 1. SEM image; (a) BaTiO3 particles , (b) Sample 4(Y/BaTiO3 molar ratio=2/1)

(a)	(b)

Figure 2. EDS image; Sample 4