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Journal of the Korean Ceramic Society Vol. 44, No. 10, pp. 574~579, 2007. Processing of Al 2 O 3 Ceramics with a Porous Cellular Structure Byong Gu Lim, Lak-Hyoung Lee, and Jung-Soo Ha School of Advanced Materials Engineering, Andong National University, Andong, 760-749, Korea (Received August 22, 2007; Accepted August 31, 2007) œ Al 2 O 3 Á xáw w œw (2007 8 22 ; 2007 8 31 ) ABSTRACT Porous Al 2 O 3 ceramics were prepared by the gelcasting foams method (a slurry foaming process) with acrylamide monomer. The foaming and gelation behavior was investigated with the parameters such as the type and concentration of surfactant, solid loading of slurry, and the concentrations of initiator and catalyst. Density, porosity, microstructure, and strength of the green and sintered samples were characterized. Of the four kinds of surfactants tested, Triton X-114 showed the highest foaming ability for the solid loading of 55-30 vol%. The gelation condition giving the idle time of 3 min was found to set the foamed structure without significant bubble enlargement and liquid lamella thinning. The green samples were fairly strong and machinable and showed maximum strength of 2.4 MPa in diametral compression. The sintered samples showed densities of 10-36% theoretical (i.e. porosity 90-64%) with a highly interconnected network of spherical pores with sizes ranging from 30 to 600 µm. The pore size and connectivity increased but the cell strut thickness decreased with decreasing the solid loading. Flexural strength of 37.8-1.7 MPa was obtained for the sintered samples. Key words : Porous Al 2 O 3, Slurry foaming, Gelcasting, Cellular structure 1. œ n, t, üy, ƒyw y ¼ yw» w,,,, k,»ƒ y vl w.»œ j»,,»œ š» p w,,, y, y š. 1,2) œ»œ p w ww kw w. œ ƒ»œ 50 nm macropore ƒ, š s 3,4)»œ 5,6) š.»œx ƒ»»y š û ƒ»œ û w»œ w w,»œ y w. Corresponding author : Jung-Soo Ha E-mail : jsha@andong.ac.kr Tel : +82-54-820-5637 Fax : +82-54-820-6211 ù»œx g w œ ³» p w š. w š s»œ w s œ (slurry foaming process) š. 7-12) y (foaming agent w) s ù gelling agentƒ ƒ» ù» w s w z š w, 10-2000 µm» œj» e w ³ w œ (porous cellular structure). s š w gelcasting z š gelcasting foams š w. 8-11) Gelcasting x š w w»» monomer yww ü» ƒ ƒ monomer k û ùküš, x ƒw polymer network x w šy x. gelcasting 13,14) acrylamide monomerƒ acrylic( acrylate) monomer w Al 2 O 3 9) hydroxyapatite œ 10,11) gelcasting foams w ƒ š 574

. s œ w gelcasting foams» ƒ x ƒ û šxw. šxw y ƒ s foam p w, w gelation w idle time( ƒw z gelation ¾ ) j» s strut Ì w. gelcasting acrylamide monomer ƒ š gelcasting foams w œ Al 2 O 3 w. y, š xw, ƒ s gelation w š, w x r,»œ,, p w. 2. x 2.1. s³ ƒ 0.5 µm α-al 2 O 3 (99.8%, AES-11, Sumitomo Chemical Co., Japan) w š, w Darvan C(R.T. Vanderbilt Co., Inc., Norwalk, CT, USA) w.» monomer 1 x acrylamide (AM; C 2 H 3 CONH 2 ; Sigma Chemical Co., St. Louis, MO, USA) 2 x ƒ methylenebisacrylamide (MBAM; (C 2 H 3 CONH) 2 CH 2 ; Sigma) w. š w ammonium persulfate (APS; (NH 4 ) 2 S 2 O 8 ; Sigma) N,N,N',N'-tetramethylethylendiamide (TEMED; C 6 H 16 N 2 ; Sigma) ƒƒ w. y w»»s w 15) 4 ƒ y w : Tween 80 (polyoxyethylenesorbitan monooleate; Aldrich, USA), Tergitol TMN 10 (polyethylene glycol trimethylnonyl ether; Fluka, Switzerland), M-OP 1019 (polyoxyethylene octylphenyl ether; Dongnam Chemical, Korea), Triton X-114 (polyethylene glycol-terc-octylfenyl ether ; Sigma). 2.2. r p x œ Fig. 1 ùkü. AM MBAM 14 : 0.6 wt% w 85.4 wt% w g monomer w. 16) Al 2 O 3 monomer 30 min ball milling w 30-55 vol% šxw w. Darvan C w 0.67 wt% w. 20-50 ml ƒ š v p f(250 ml) y ƒw triple blade mixer (700 œ Al 2 O 3 575 Fig. 1. Experimental procedure for preparation of porous Al 2 O 3 samples by the gelcasting foams method. rpm, 5 min)w»s g. Monomer š w w APS(1 wt% xk) TEMED» ƒ. s s v d w f gelation g. w monomer free-radical w ww» w» ü. Gelation x kx 72 h, 60 o C 24 h z 1600 o C 2h œ»» w. wr, monomer, ƒ ƒ ƒ š y s p w. w šxw 55 vol% 4 ƒ y (M-OP 1019, Triton X-114, Tregitol TMN 10, Tween 80) ƒƒ 0.1-1.5 wt% ƒ w z» 5 w v y d w. w y ƒ (0.32 wt%) š jš šxw y(55, 40, 30 vol%) wì s v d w y s w. w, y ƒ ƒ (, s ) ƒ š ƒ idle time 44«10y(2007)

576 Á xáw y w. Idle time sœ ƒ w p. w (šxw 55, 50, 45, 40 vol%) 32, 38, 45 g/l 2.93, 4.31 g/l ƒƒ ƒw ³ w yww z gelation y d w. x j» d w w š j xk r( 38 mm, Ì 10 mm) ƒ š diametral compression test 17) w d w. r Archimedes d w š l»œ w. š SEM(scanning electron microscope, JSM 6300, JEOL, Japan) w q w, x»(h10k- S, Hounsfield, UK) w 3-point flexural test( r 20 mm, Ì 10 mm; span 20 mm) mw d w. 3. š 3.1 s p Fig. 2 55 vol% Al 2 O 3 y foam v y.» y ƒ foam v ƒ. ƒ y ƒ» ƒ yw w t û». z foam v yƒ ù w w š, y 0.32 wt% ƒ foam vƒ y w Triton X-114 ƒ ƒ foam v. 55 vol% 0.32 wt% y ƒƒ ƒ foam v» y 0.32 wt% š wš šx w y(55, 40, 30 vol%) g Fig. 2. Variation of foam volume with surfactant type and concentration. Fig. 3. Variation of foam volume with surfactant type and solid loading. foam v y w Fig. 3 ùkü. š xw foam v j ƒ w 40, 30 vol% Triton X-114ƒ ƒ foam v ùkþ. l Triton X-114 0.32 wt% ƒw w r wš p w. 3.2. šy p Fig. 4 ƒ s y. w» idle time ƒw š l d. Fig. 4 ƒ ƒw idle time w. w ƒw y y g e ƒ š, ƒw e ƒ w C=C w ƒ š monomer w j». Gelation w w ƒ w w ƒ». s šy» ¾»sƒ yw šyƒ. idle time š š w (, gelation»¾ ) v w. Fig. 4 38 g/l, 4.31 g/l w w š, idle time 3min. y ƒ w s g»s y liquid lamella thinning foam ƒ œ šy. Fig. 5 ( 38 g/l, 4.31 g/l) w wz

셀 다공구조를 갖는 Al O 세라믹스의 제조 2 3 Fig. 4. Variation of the temperature of non-foamed slurry with time during gelation for different additions of catalyst and initiator at solid loadings of 55-40 vol%. 고형함량(55, 50, 45, 40 vol%)에 따른 슬러리의 온도 변 화를 보여준다. Idle time은 슬러리의 고형함량이 낮아질 수록 다소 짧아짐을 알 수 있는데 이는 고형함량이 줄어 Fig. 5. 577 Variation of the temperature of non-foamed slurry with time during gelation for different solid loadings at optimum additions of catalyst (4.31 g/l) and initiator (38 g/l). 들수록 상대적으로 더 많은 monomer, 개시제와 촉매량으 로 인해 중합반응이 더욱 가속되기 때문인 것으로 생각된다. Fig. 6. Photograph of green bodies prepared using Triton X114 with different solid loadings of slurry, comparing the foam volumes. 제 44 권 제 10호(2007)

임병구 이락형 하정수 578 ral compression으로 측정한 강도는 50, 45 vol%에서 각각 2.4, 1.1 MPa이었다. 40과 35 vol% 경우엔 시편이 너무 약 해서 강도 측정을 할 수 없었다. 소결체의 경우 밀도는 1.45-0.38 g/cm3(즉, 36-10% 이론밀도와 64-90% 기공률) 를 보였으며, flexural로 측정한 강도는 37.8-1.7 MPa이었 다. 시편의 매우 높은 기공률을 고려하면 상당히 우수한 강도가 얻어졌음을 알 수 있다. 4. 결 Fig. 7. SEM micrographs of sintered samples prepared using Triton X-114 with different solid loadings of slurry. Density, Porosity, and Strength of Green and Sintered Samples Green samples Sintered samples Solid loading 50 45 40 35 50 45 40 35 (vol%) Density (g/cm3) 1.15 0.75 0.31 0.27 1.45 0.78 0.43 0.38 (%) 36 19 11 10 Porosity (%) 64 81 89 90 Strength (MPa) 2.4 1.1 * * 37.8 11.1 2.3 1.7 *Samples too weak to measure the strength. Table 1. 성형체 및 소결체 특성 Fig. 6은 슬러리의 고형함량에 따른 foam 성형체의 부 피 변화를 확실하게 보여주는 사진이다. 35 vol%의 경우 발포되지 않은 경우와 비교했을 때 매우 크게 팽창되었 음을 알 수 있으며 그 부피증가는 14배나 되었다. 이러한 결과는 발포된 기공 구조가 효과적으로 잘 고화되었음을 말해준다. Fig. 7은 소결된 시편들의 파단면 미세구조를 보여준다. 상호 연결된 네트워크를 갖는 구형의 기공들로 이루어졌 으며, 기공크기는 30-600 µm 범위였다. 발포된 기공 구조 는 이웃 하고 있는 구형의 셀들과 이 셀들을 연결하는 windows들과 셀을 분리하는 strut들로 되어있다. 슬러리의 고형함량은 기공의 미세구조를 결정하는데 중요한 역할 을 하는데 고형함량이 감소함에 따라 기공크기와 연결성 은 증가 했지만, strut 두께는 감소하였다. 성형체와 소결체 시편들의 밀도, 기공률, 강도 특성을 Table 1에 정리하였다. 슬러리 고형함량 50-35 vol%에 대 해 성형체의 경우 밀도는 1.15-0.27 g/cm 이었으며, diamet- 4가지 계면활성제중에 Triton X-114가 가장 높은 foaming 능력(슬러리 고형함량이 35 vol%일 경우 부피 14 배 증가)을 보였다. Idle time이 3 min인 gelation 조건은 기포 확대와 liquid lamella thinning이 거의 없이 foam 구 조를 성공적으로 고화시켰다. 성형체는 기계가공이 가능 할 정도로 충분히 강하였다. 소결된 시편은 슬러리 고형 함량(50-35 vol%)에 따라 36-10%의 이론밀도(기공률 6490%)를 보였고, 상호 연결된 네트워크를 갖는 구형의 기 공들로 이루어졌으며 기공크기는 30-600 µm 범위였다. 고 형 함량이 감소함에 따라 기공크기와 연결성은 증가했지 만 strut 두께는 감소하였다. 소결체의 강도는 37.8-1.7 MPa이었으며 기공률이 매우 높은 것을 감안하면 상당히 우수한 강도가 얻어졌다. Acknowledgment 이 논문은 2005학년도 안동대학교 학술연구지원사업에 의하여 연구되었음. REFERENCES 3.3. 3 한국세라믹학회지 론 1. K. Ishizaki, S. Komarneni, and M. Nanko, Porous Materials: Process technology and applications; pp. 181, Kluwer Academic Publishers, Dordrecht/Boston/London, 1998. 2. S.-H. Kim, Y.-W. Kim, J.-Y. Yun, and H.-D. Kim, Fabrication of Porous SiC Ceramics by Partial Sintering and their Properties, J. Kor. Ceram. Soc., [7] 541-47 (2004). 3. F. F. Lange and K. T. Miller, Open-Cell, Low-Density Ceramics Fabricated from Reticulated Polymer Substrates, Adv. Ceram. Mater., [4] 827-31 (1987). 4. J. Saggio-Woyansky, C. E. Scott, and W. P. Minnear, Processing of Porous Ceramics, Am. Ceram. Soc. Bull., [11] 1674-82 (1992). 5. J.-S. Ha and C.-S. Kim, Processing of Porous Ceramics with a Cellular Structure Using Polymer Beads, J. Kor. Ceram. Soc., [12] 1159-64 (2003). 6. S.-J. Lee and H.-D. Kim, Fabrication of Porous Al2O3 Ceramics Using Thermoplastic Polymer, J. Kor. Ceram. Soc., [7] 513-17 (2004). 7. S. J. Powell and J. R. G. Evans, The Structure of Ceramic Foams Prepared from Polyurethane-Ceramic Suspensions, 41 2 71 40 41

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