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Journal of the Korean Ceramic Society Vol. 46, No. 2, pp. 137~145, 2009. Preparation of Ultrafine Barium Titanate Powder by Slurry Spray Pyrolysis Jong Ho Lee, Kang Heon Hur, and Jung Soo Lee LCR Division, Samsung Electro-Mechanics Co., Ltd., Suwon 443-743, Korea (Received November 14, 2008; Accepted December 8, 2008) w w pk y Áx xá» z LCR (2008 11 14 ; 2008 12 8 ) ABSTRACT A remarkable improvement of the productivity in barium titanate by slurry spray pyrolysis process was realized by supplying solid source slurry into the rector. The produced barium titanate powders showed uniform powder properties, and reproducibility with higher tetragonality in the range of 80 ~ 200 nm, case by case. The secondary calcination experiments of the as-prepared powders by spray pyrolysis revealed that the powders as-prepared over 700 o C showed perfectly different behavior with the lower temperature s ones and the solid state reaction s case. The result was discussed in terms of the reaction mechanism based on the activation energy analysis. Key words : Spray pyrolysis, Barium titanate, MLCC, Tetragonality, Reaction mechanism 1. t w, p k w š w j w., e t xy, š» y w dy š dyƒ v w j» š. 1) w dx g (MLCC) ƒ, d ƒ š, core-shell xw» w ƒ wì y w» t w ƒ» w v. y w p y w» w w p ƒ ƒ y w ƒ MLCC ƒ. yw, w ³ w s, ³ w x, y, yw š, yw ³ Corresponding author : Jong Ho Lee E-mail : jh205.lee@samsung.com Tel : +82-31-210-3187 Fax : +82-31-300-7900(1854). BaTiO 3 ƒ, t š, œe, sol-gel, w. 2-5), š d w ƒ ù s³ y w ƒ yw ³ ƒ û,»w j». œe ƒ y e j, ù k y w yw k j., wì œe, w w ù t ƒ. w mw w»ƒ» x ù t w e. Sol-gel w w» yw y š ù, šƒ w». w, w ³ w ù xk, w w. w w k, w w, x ü sz y» w ü»œ w 137

138 yáx xá Fig. 1. Two types and new type of preparation of barium titanate powder by spray pyrolysis. ƒ š. w w q ù» w yw š» ü m g w. w k w w, w ƒ w ³ ³ w v š, œ ƒ z œ œ ƒ š. w» w w œ w x» x ³. w w œ w w» w, ù j» šx k w z» w jš w. Fig. 1 w w pk w w w. Fig. 1 type I w œ w, wù l wù., j»., 1/3 w, j» 1 w.,» w û ù q w k e w w., nm w» 1 ~ g/h û. Type II type I w,» ƒ ƒw w w w w, w œ ù Ì shell l j. 6) wù l w» j»ƒ j»ù j w., w j e w v ƒ, w w j e w ƒ w, type I {. w, w ƒ w Ti ƒ g ù y w š š ƒ œ» wš, w w w ƒ.» 1 100 g/h. Type III w û w» w, w» kvw ù j» š w w» w., š w w w w., w yw, ù»» ù yw ƒ, ü w» type I, II w.» 1 1~1.5 kg/h type II w 10 ~15 y ƒ ƒ w. 2. x Barium titanate w Ba Ti ƒƒ BaCO 3, TiO 2 w, ƒƒ Table 1. Sannop 5468C w wz

w w pk 139 Table 1. Raw Materials for Preparation of Barium Titanate Powder Raw material Supplier Purity Specific surface area BaCO 3 Solvay 99.9% 20 m 2 /g TiO 2 Showa denko 99.7% 45 m 2 /g (Sannop Co.) q 3wt% w, yw Netzsch(LMZ10) w yw w. Ba m TiO 3 m =1.005 š w, 8 yw w XRF(Rigaku, ZSX) mw w. yw yw w Fig. 2 w w» mw q w w z, w œ mw w ƒ barium tatanate w. w œ» air(100 L/min) w š,» ( φ0.3 mm) w. w, 4.5 L/h š w,» 500 ~1000 o C y g ƒ w. w» 250 mm ¼ 1500 mm. w barium titanate š» m w w barium carbonate w, y w œ v w. w œ box furnace 800 o C ww, 5 o C/min, 1 š w. w w œ barium titanate FE-SEM(Jeol, JSM-6700F) w x j» w š, XRD(Rigaku, Rint2200HF+) mw sƒw, BET(Mircromeritics, Tristar3000) w t d w. w TGA (TA Instrument, DSC2010) w mw e ³ wš w. 3. š 3.1. w w w w» mw w w 30 nm µm j» k (Fig. 3(a)). mw 10 µm», wù sw ƒ š, sw wù x w., ƒƒ y ƒ ³ w w j»,» m w, TiO 2 w w š ³ w ù Fig. 2. Schematic diagram of spray pyrolysis reactor. 46«2y(2009)

이종호 허강헌 이정수 140 Fig. 3. FE-SEM micrographs of as-prepared barium titanate powder and calcined powders at various temperature by slurry spray pyrolysis (T = 900 C, Air 100 L/min; 50,000(left), 20,000(right)). o reactor 다. Fig. 3에는 분무열분해 반응기의 온도가 900oC일 때 합성된 분말과, 이 분말의 하소온도에 따른 하소 후 분말 의 형상을 나타내고 있다. 하소 전 분말은 수 µm 단위로 응집되어 있으나, 하소 후에는 액적 단위의 응집이 깨어 지는 것을 알 수 있다. 또한, 하소 온도가 높아질수록 일 o 차입자의 성장이 이루어져, 800~1000 C의 하소에 의해 일 차입자의 크기가 60~200 nm로 변화됨을 알 수 있다. 이 는 최종 요구되는 입경에 상관없이 분무열분해에 의해 동 한국세라믹학회지 Fig. 4. XRD pattern of as-prepared barium titanate powder and calcined powder at various temperature by slurry spray pyrolysis (T = 900 C, Air 100 L/min). o reactor 일 조건으로 파우더를 합성한 후, 요구되는 입경에 따라 하소 공정에 의해 입경을 제어할 수 있다는 것을 의미하 며, 입경에 따른 생산성의 차이가 없다는 장점 또한 가짐 을 의미한다. Fig. 4와 Fig. 5에는 900oC에서 합성된 분말의 하소 온 도에 따른 결정상 및 결정성과, FE-SEM 사진으로부터 측 정된 일차 입자의 크기에 따른 정방화도를 나타내었다. 하소 전 분말의 XRD 결과에는 미반응된 barium carbonate 상이 미량 존재하는 것을 알 수 있으나, 하소 분말에서는 모두 barium titanate로 전환됨을 알 수 있다. 또한, 850oC

w w pk 141 Fig. 5. Tetragonality with changing primary particle size of barium titanate by slurry spray pyrolysis(t reactor = 900 o C, Air 100 L/min). w l cubic tetragonal y» w. Fig. 5 ùkü 80 nm y» w, 130 nm c/aƒ 1.01. f ³ w w» y g ƒ w w q w.» 500 ~1000 o C y j w w w XRD 950 o C w w Fig. 6 w. 600 o C w w barium titanate w š barium carbonate š ù, 700 o C w l barium titanate» w 1000 o C w. w ƒ w 950 o C w w, Fig. 6 600 o C w w w cubic, 700 o C w w tetragonal. 600 o C w w w w» m w ù š k, w œ š w barium titanate w œ w š. l š w ƒ ù œ w z z mw š y j œ w š w, š w œ w k,» š w w w ƒ wš. Fig. 6. XRD spectra with changing the reactor temperature for (a) as-prepared and (b) calcined at 950 o C. 46«2y(2009)

142 yáx xá Fig. 8. Effect of calcination temperature on BET surface area (solid line: BET, dot line: c/a). Fig. 7. (a) Crystallinity v.s. BET surface area and (b) K factor v.s. BET with temperature of reactor. w ƒ ƒ» 800 ~1020 o C w w, ƒ w BET t c/a k factor w Fig. 7 w w ù. 600 o C w w 6m 2 /g BET t q c/aƒ y w, BET t k factorƒ û, 700 o C w 9m 2 /g BET t q y, k factor w. w d, w w k z w w y w, w BET t ( ) û Fig. 8 š. ù 600 o C w w w BET t»» w w, barium titanate y ù 700 o C w w w BET t»» w ù küš. 600 o C w w w BET t w, w ƒ 950 o C w û y w. w t w œ ƒ w, w œ w (kiln) r ƒ w, w w lot ü ³ w ù p r ƒ š, lot p w r ƒ w. 3.2. w kinetics w Fig. 9 k z, yw TGA š ùküš. 200 ~ 300 C o w, Region I Region II j s ƒ BaCO 3 w w ù. w ƒ ù, BaCO 3 TiO 2 l BaTiO 3 y ƒ mechanism w w. Region I II w ƒƒ Table 2 kinetic equation w Arrhenius plot w ùkü reaction model, mechanism ³ w. š w txw. w wz

w w pk 143 Table 2 ƒ w (4) l f(α) w z, (3) w ùkü Arrhenius plot Fig. 10., Region I random nucleation (Erofeev equation:a 3 ) model, Region II Three dimensional diffusion (Ginstling-Brounshtein equation: D 4 ) model.», BaCO 3 TiO 2 l BaTiO 3 x w š. 9,10) BaCO 3 BaO+ CO 2 (5) BaO+ TiO 2 BaTiO 3 (6) Fig. 9. TGA curve of powder mixture of BaCO 3 -TiO 2. dα ------ = kf( α) dt», α» w, k Arrhenius tx. k = Ae E/RT β(= dt/dt) w, (1) t x. β dα ------ = Ae E/RT dt ( ) f α Table 2 F(α) (3) f(a). (1) (2) (3) f ( α) 1 = -------- df( α) -------------- dα (4) Table 2. Kinetic Equations Examined in This Work 7,8) Reaction model F(α) Symbol One-dimensional diffusion α 2 D 1 Two-dimensional diffusion α+(1 α)ln(1 α) D 2 Jander equation, three-dimensional diffusion Ginstling-Brounshtein equation, three-dimensional diffusion Two-dimensional phase boundary reaction Three-dimensional phase boundary reaction [1 (1 α) 1/3 ] 2 D 3 (1 2/3α) (1 α) 2/3 D 4 [1 (1 α) 1/2 ] R 2 [1 (1 α) 1/3 ] R 3 First-order kinetics [ ln(1 α)] F 1 Random nucleation: Avrami equation Random nucleation: Erofeev equation [ ln(1 α)] 1/2 A 2 [ ln(1 α)] 1/3 A 3 Fig. 10. Arrhenius plot of (a) region I and (b) II. 46«2y(2009)

144 yáx xá Fig. 11. Model of thermal decomposition reaction of BaCO 3 and TiO 2, (a) Region I and (b) Region II. BaTiO 3 + BaO Ba 2 TiO 4 Ba 2 TiO 4 + TiO 2 2BaTiO 3 Fig. 10 w ³ mechanism w, Region I BaOƒ TiO 2 ù BaTiO 3 w barium titanate x wƒ w w (6), (7) ƒ, Region II t d barium titanateƒ sy y (6), (7) ù wš, (8) w barium titanate x t d l TiO 2 core Ba š y (6), (7) ù, diffusion-controlled step. w BaTiO 3 x Fig. 11 w w. w» w y gƒ Fig. 12. TGA curves of as-prepared powder with changing temperature of reactor by slurry spray pyrolysis. (7) (8) w TGA š Fig. 12 w. 600 o C w w Fig. 9 region I II ùkù, 700 o C w w region I ùkù., 700 o C w w œ w diffusion-controlled process w. w w e, ù w d j w ùkù wù j ƒ ù, w œ ù w š w yw w ƒ w. 4. š w w œ wš l š barium titanate w» w l. - w w 10 ~15 ƒ š barium titanate ƒ ƒ w. - w w 700 o C, w w diffusion-controlled process w, y. - w w w œ š w w p x û. ww, š w w wz

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