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1 Jurnal f the Krean Ceramic Sciety Vl. 44, N. 3, pp. 182~187, Micrwave Sintering f Gd-Dped CeO 2 Pwder Yung Gun Kim and Seuk-Bum Kim Department f Materials Science and Engineering, Gyenggi University, Suwn , Krea (Received February 14, 2007; Accepted March 13, 2007) Gd-Dped CeO 2 j q ½ ³Á½» w œw ( ; ) ABSTRACT 10 ml% Gd 2 -CeO 2 pwder was sintered by micrwave in a 2.45 GHz multimde cavity t develp a dense electrlyte layer fr intermediate temperature slid xide fuel cells (IT-SOFCs). Samples were sintered frm 1100 C upt 1500 C by 50 C difference and kept fr 10 min and 30 min at the maximum temperature respectively. Theretical density f the sample sintered at 1200 C fr 10 min was 95.4% and increased gradually upt 99% in the sample sintered at 1500 C fr 30 min. All f sintered samples shwed very fine micrstructures and the maximum average grain size f the sintered sample at 1500 C fr 30 min was (0.87 ±0.42) µm. Inic cnductivity f the samples were measured by DC 4 prbe methd. Key wrds : SOFC, Gd-dped, CeO 2, Micrwave prcess, Ceramic electrlyte, Sintering SOFC, Gd-dped, CeO 2, Micrwave prcess, Ceramic electrlyte, Sintering 1. 3 š y (SOFC : slid xide fuel cell) w š w w z 50~ 60%. ƒ w wù š w» ƒ, kƒ w xk ƒ w. 1,2) ù x ¾ š y 800 C š. w, w, q w g SOFC y j. 3,4) ƒ 800 C w x (Intermediate Temperature-SOFC) w ƒ y w š. w 5,6) š w w k s œ rw š ƒ». ù š y û ü Crrespnding authr : Seuk-Bum Kim sbkim@kynggi.ac.kr Tel : Fax : w ƒ w. w w» w ZrO 2 w ƒ Bi 2, CeO 2, LaGa w ƒ w. 7,8) x SOFC w wù Ce y e, 9) œe, 10) w 11), Ce y Gd ù Sm y ƒw j ƒ. w 12,13) w w Gd š Ce (GDC) 14)ù C Mn 15) y (transitin metal xides) ƒ w ù ù j» 16) w û ƒ w, ƒ r s³ j» w š š. wr œ» w»¾ v w ù t v w w w» w š ƒ. ù ƒ œ k ù ƒ w ùš j q û y y e yƒ w 182

2 ƒ š d p j ƒ š. w mw ³ w ùkü j q r j q w ü v w r ü ù kù. w p w jš w r š ³ w w g ³ w ) p ƒ j q w ƒ w š 10 ml% Gd 2 - CeO 2 w j q w œ ƒ w w. 2. x ƒƒ 99.9% ƒ CeO 2 Gd 2 (Kjund Chemical Lab. C. Ltd., Japan) yw Ce 0.90 Gd 0.10 O 1.95 (GDC10, 0.5~1 µm) w ³ w yw w k ü Al 2 w 24 z w. 18 mm w 70 MPa 1 xw z 140 MPa x w x r. j q r Fig. 1 ùkù j q e w w r ƒ w» w e š insulatin bx w z SiC susceptr w 2.45 GHz multimde j q ƒ (3 kw) 30 C/min w w C 1500 C¾ 50 C d w t ƒƒ w š œ» ww. Fig. 2 w insulatin bx ü j q pwer level r ƒ xk š ùkü. j q Fig. 1. A schematic diagram f the micrwave furnace. Gd-Dped CeO 2 j q 183 Fig. 2. Temperature prfile and the pwer level f the micrwave during the sintering prcess. Eurtherm Cntrller(Eurtherm- 2404) w r d insulatin bx mw R-type w d w. z r Archimedes w» w, y yƒ w» w X- z»(x-ray diffractmeter, SIEMENS D5005) w w r w y w. r x (SEM, JEOL, JSM-6300, Japan) w w š, r j» line intercept w SEM l d w. d w w r diamnd cutter mm š sand paper w w z ƒ w r z 600~1000 C DC C 3C þ ƒw d w. 3. š 10 Fig. 3 j q 1100 C w r 1500 C 30 w r XRD w GDC r 2 sw w š. r s³ y Fig. 4 x j q w 1100 C w r 90% ùkù x x w š q C 10 w w r 91.6% ùkü 1200 C 10 w 95.4% ùkù 1200 C e yƒ 44«3y(2007)

3 184 ½ ³Á½ Fig. 3. XRD diffractin patterns f the samples sintered by micrwave; (a) 1500 C fr 30 min and (b) 1100 C fr 10 min. Fig. 5. Average grain size f samples sintered by micrwave as a functin f temperature. Fig. 4. Relative density f sintered samples by micrwave as a functin f temperature. w. z 50 C ƒ w w 1500 C 10 w 98.5% ùkü. 30 w w 1350 C l 10 w w ƒw ù w 30 w ƒ w ƒ f 1500 C 30 w 99% 1350 C ƒ j ùkû. s³ j» ùkü Fig C 10 w s³ (0.17 ±0.42) µm ù j» w x ƒ 1500 C 10 w s³ (0.57 ±0.42) µm ƒ j ùkû. r ƒ j ùkù 1500 C 30 w w r s³ (0.87 ±0.42) µm ùkù j q w œ r s ³ j» 1µm w j». Zhang œe 20) GDC10» 1550 C 5 w j» ~14 µm ~97%, Han 21) w w GDC C 4 w r 97.8%, s³ 0.73 µm šwš, x j q 1300 C 10 w r 97.2% s³ (0.24 ± 0.08) µm ùkù w š ù j». y yw ~0.55 µm (CeO 2 ) ~0.5 µm (Gd 2 O 2 ) w GDC20 r 1500 C 5 w Ma ~92% 22) ~4 µm, Park x 15) w GDC10 w 1600 C 12 w s³ (4.2 ±1.1) µm 99% ùkü šwš. j q w 99% ùkü 1500 C 30 w w Park 15) w 100 C ûš j» ~1/5 1/24, j q ¾ 1 sww œ w w j. w wz

4 Gd-Dped CeO 2 Fig. 6. 분말의 마이크로파 소결 185 SEM micrgraphs f sintered samples by micrwave at (a) 1200 C, (b) 1250 C, (c) 1450 C, (d) 1500 C fr 10 min, and (e) 1500 C fr 30 min hlding time. Fig. 6은 마이크로파로 1200~1500 C의 온도 범위에서 유지시간에 따른 시편의 파단면의 미세구조 사진을 나타 내었다. Fig. 6(a)는 1200 C에서 10분간 소결한 미세조직으 로서 밀도가 95.4%이며 기공이 불균일하게 입계에 존재하 는 것을 볼 수 있으나, 1250 C에서 소결한 시편인 Fig. 6(b) 의 경우부터는 1200 C 보다는 기공이 많이 줄어든 것으 로 관찰되었고, 밀도가 98%인 1450 C에서 10분 유지한 경우인 Fig. 6(c)에서는 기공이 거의 보이지 않으며 치밀 하며 균일한 형태의 결정립을 가진 미세구조를 관찰할 수 있었다. 각각 1450 C와 1500 C에서 10분 유지한 경우인 Fig. 6(d)와 6(c)의 두 경우 사이에는 밀도 값은 약간 증 가하였으나 입자의 성장이 별로 크지 않아 비슷한 크기의 입경을 나타내고 있는 것을 볼 수 있다. 그러나 Fig. 6(d) 와 1500 C에서 30분 유지한 경우인 Fig. 6(e)에서는 밀도 가 각각 98.5%와 99%로써 치밀화된 미세구조를 보이고 있으며 Fig. 6(e)의 경우에는 입성장이 빨라져 Fig. 6(d)의 경우보다 평균입경이 커진 모습을 볼 수 있다. Fig. 7에는 마이크로파로 1200 C에서 10분 유지하여 소 결한 시편과 1500 C에서 30분 유지한 시편의 온도에 따른 이온전도도를 DC 4단자법으로 측정한 값을 아래 Arrhenius 식을 이용하여 나타내었다. σ α- σin Scm 1 = exp E T (1) kt 고온인 1000 C 근처에서는 1500 C에서 30분을 유지하 Fig. 7. Electrical cnductivity f the 10 ml% Gd O -CeO samples sintered by micrwave 여 소결한 경우가 1200 C에서 10분간 유지한 시편의 이 온전도도 값보다 약간 높은 값을 나타내지만 온도가 낮 아질수록 차이가 커져서 600 C 근처에서는 그 차이가 더 크게 나타나고 있다. Table 1에 있는 이 시편들의 이온전도도와 활성화에너 지 값(Ea)을 비교하여 보면 1500 C의 경우가 1200 C 경 우에 비하여 더 낮은 활성화에너지 값을 가지고 있기 때 문이며, 그 이유는 온도가 높은 1000 C 근처에서는 grain bundary effect가 크게 영향을 나타내지 않으나 온도가 낮아지면서는 그 영향이 크게 나타나는 것으로 판단되며, 제 44 권 제 3호(2007)

5 186 ½ ³Á½ Table 1. Inic Cnductivity and Activatin Energy Data f the Samples by Micrwave Sintering Micrwave sintering 1200 C-10 min 1500 C-30 min Ea 0.70±0.1 ev 0.59±0.04 ev σ 1.4 ± ± C 10 w w s³ (0.17 ±0.04) µm 1500 C w 1/5 j» d ƒw û ùküù 1500 C ƒ w r f w d w û ùkü ) 4. w ƒ 10 ml% Gd 2 -CeO GHz j q w 30 C ƒ w 1100~1500 C t ¾ k z ƒƒ w w 1.5 ü j w, r w w w ù s³ ùkû. r 90% s³ 1 µm w, 1200 C 10 w r 95.4% (0.17 ±0.42) µm s³ 1500 C 30 w ƒ ƒ 99% (0.87 ±0.42) µm ³ e w ùkü C 30 w r ƒ 1200 C 10 w r w w ùkü d, r j» d ƒ ù w. w j q w 1500 C¾ 50 t w ƒ ƒ 98.5% 99% ùkü š e» w w». l j q w w ƒ w w wì œ w z SOFC w Gd š Ce (GDC) w ƒ ƒ q. Acknwledgment 2004w» w w ( ) w w. REFERENCES 1. O. Yamamt, Slid Oxide Fuel Cell: Fundamental Aspects and Prspects, Electrchimica Acta., (2000). 2. E. I. Tiffee, A. Weber, and D. Herbstritt, Materials and Technlgies fr SOFC-Cmpnents, J. Eur. Ceram. Sc., (2001). 3. N. Q. Minh and T. Takahashi, Science and Technlgy f Ceramic Fuel Cell, pp. 1-14, Elsevier Science, Amsterdam, B. C. H. Steele, Science and Technlgy f Zircnia:, vl, V, pp. 713, J. Am. Ceram. Sc., Clumbus (1993). 5. T. Tsai, E. Perry, and S. Barnett, Lw-Temperature Slid Oxide Fuel Cells Utilizing Thin Bilayer Electrlyte, J. Electrchem. Sc., (1997). 6. P. K. Srivastava, T. Quach, Y. Y. Duan, R. Dnelsn, S. P. Jiang, F. T. Ciacch, and S. P. S. Badwal, Electrde Supprted Slid Oxide Fuel Cells: Electrlyte Films Prepared by DC Magnetrn Sputtering, Slid State Inics, (1997). 7. K. Huang, M. Feng, and J. B. Gdenugh, Synthesis and Electrical Prperties f Dense Ce 0.9 Gd 0.1 O 1.95 Ceramics, J. Am. Ceram. Sc., (1998). 8. T. T. Sai and S. A. Barnett, Bias Sputter Depsitin f Dense Yttria-Stabilized Zircnia Films n Prus Substrates, J. Electrchem. Sc., (1995). 9. T. S. Zhang, J. Ma, L. B. Kng, P. Hing, and J. A. Kilner, Reparatin and Mechanical Prperties f Dense Ce 0.8 Gd 0.2 O 2-δ Ceramics, Slid State Inics, (2004). 10. K. Higashi, K. Snda, H. On, S. Sameshima, and Y. Hrata, Synthesis and Sintering f Rare-Earth-Dped Ceria Pwder by Oxalate Cprecipitatin Methd, J. Mater. Res., (1999). 11. K. Yamashita, K. V. Ramanujachary, and M. Greenblatt, Hydrthermal Synthesis and Lw Temperature Cnductin Prperties f Substituted Ceria Ceramics, Slid State Inics, (1995). 12. C. Keinlgel and L. J. Gauckler, Sintering and Prperties f Nansized Ceria Slid Slutins, Slid State Inics, (2000). 13. C. Keinlgel and L. J. Gauckler, Sintering f Nancrystalline CeO 2 Ceramics, Adv. Mater., (2001). 14. D. P. Fagg, J. C. C. Abrantes, D. Pérez-Cll, P. Núñez, V. V. Khartn, and J. R. Frade, The Effect f Cbalt Oxide Sintering Aid n Electrnic Transprt in Ce 0.8 Gd 0.2 O 2-δ Elec- w wz

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