sol-gel titania - cheric · fig. 6. nitrogen adsorption isotherms of sol-gel derived titania...

7
617 HWAHAK KONGHAK Vol. 41, No. 5, October, 2003, pp. 617-623 Sol-Gel Titania * * 305-764 220 * 320-711 26 (2003 3 27 , 2003 7 8 ) Preparation of Nano Size Titania Powders with Monomodal Pore Distribution by the Sol-Gel Method and Hydrothermal Treatment Hyun-Tae Kim, Sang-Il Shin*, Ki-Chang Song* and Yong Kang School of Chemical Engineering, Institute of Nano-Technology and Advanced Materials, Chungnam National University, 220 Gung-dong, Yuseong-gu, Daejeon 305-764, Korea *Department of Chemical Engineering, Konyang University, 26 Nae-dong, Nonsan, Chungnam 320-711, Korea (Received 27 March 2003; accepted 8 July 2003) Sol-gel TTIP(titanium tetra-isopropoxide) titania , autoclave !. "#$ % &% ’()* + ,-, .’/ 01 2 ’/3!. Sol-gel 4 5 400 o C 2 "#$ titania % 1 6 789 )*(intra- particle pores) : 2 6 789 )*(inter-aggregated pores) *;< bimodal )*= >< ?@, 200 o C 4 % 1 6 789 )*A ;B< monomodal )*= ’/C-, D)E FG H.I(40-50 nm), JK@L MN(50-100%) O PQE RS(30-40%) T UVW A4 X2 NYZ!. Abstract - Titania powders were prepared from titanium tetra-isopropoxide (TTIP) by a sequence of sol-gel method and hydrothermal treatment. The powders made by sol-gel method followed by hydrothermal treatment exhibited an anatase crys- talline phase with numerous nano-size pores. The pore size distribution of the powders prepared by sol-gel method and calci- nation above 400 o C was bimodal with fine intra-particle pores (space between primary particles) and larger inter-aggregated pores (space between secondary particles). The powders by the hydrothermal treatment at 200 o C showed a monomodal pore size distribution with only intra-particle pores. The properties of titania powders could be improved by means of hydrothermal treatment considerably; the size could be reduced to 40-50 nm, specific surface area could be increased by 50-100% and the ratio of agglomeration could be reduced by 30-40%. Key words: Nano Size Titania Powder, Sol-Gel Method, Hydrothermal Treatment, Pore Size Distribution 1. titania ! "#$% &, ’( & ) *+ ,-./0 12[1-5]. Titania 3-4,56(brookite), -76(rutile), 89:6(anatase) % ; 3 / << 2= >+? @ AB /0 1C[5], 3-4,56 DE FGHI, 0JK L MBNO H .PQ RS T :U, V0, -76 W XY% Z GB [ RS \]G^_‘^,8 ab KL Xc0 12. $, 89:6 -76d2 e W fgh /0 1 RS i(@ j>M kl, e 0, m) no ) pD qjLr Xc0 12[6-8]. st N uBv i(@ ,H pD >w, >( &, "#$% ; ! AB xHyL titania pDzB /{H |}) }qZ , ~) AB w } 1C, ,~) B ! : ? % | J‘, o, B", % [ ?KLr H2. :Z w MBZ sol-gel N 0‘ B n +6’( t 1/[9-11], , N wJ :?v ! "™ !,yL >w N H qH % 1 ’( KL Z) "#$ q@ ; B™  N ¡2[10-11]. sol-gel N MB To whom correspondence should be addressed. E-mail: [email protected]

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HWAHAK KONGHAK Vol. 41, No. 5, October, 2003, pp. 617-623

Sol-Gel�� ����� � � � ��� �� Titania �� �� ��

�������*��*�� �†

����� �����305-764 � �� �� 220

*����� �����320-711 �� �� �� 26

(2003� 3� 27� ��, 2003� 7� 8� ��)

Preparation of Nano Size Titania Powders with Monomodal Pore Distribution by theSol-Gel Method and Hydrothermal Treatment

Hyun-Tae Kim, Sang-Il Shin*, Ki-Chang Song* and Yong Kang†

School of Chemical Engineering, Institute of Nano-Technology and Advanced Materials, Chungnam National University,220 Gung-dong, Yuseong-gu, Daejeon 305-764, Korea

*Department of Chemical Engineering, Konyang University, 26 Nae-dong, Nonsan, Chungnam 320-711, Korea(Received 27 March 2003; accepted 8 July 2003)

� �

Sol-gel�� �� ���� TTIP(titanium tetra-isopropoxide) �� � titania ��� �� ���, � ��� autoclave

�� ���� � � ��� � �!. ����� �� "#$ ��% &% '()*� +� ,-��, .'/�� 01

2� '/3!. Sol-gel�� �� ��4 5 400oC �2�� ��� � "#$ titania ��% 16 789 ��� )*(intra-

particle pores): 26 789 ��� )*(inter-aggregated pores)� *; < bimodal� )*�= >�< ?@, 200oC��

����4 ��% 16 789 ��� )*A ;B < monomodal� )*�= '/C-��, D)E FG H.I�(40-50 nm),

JK@L� MN(50-100%)O ��� PQE RS(30-40%)T ��� UVW A4 X2� NYZ!.

Abstract − Titania powders were prepared from titanium tetra-isopropoxide (TTIP) by a sequence of sol-gel method andhydrothermal treatment. The powders made by sol-gel method followed by hydrothermal treatment exhibited an anatase crys-

talline phase with numerous nano-size pores. The pore size distribution of the powders prepared by sol-gel method and calci-

nation above 400oC was bimodal with fine intra-particle pores (space between primary particles) and larger inter-aggregated

pores (space between secondary particles). The powders by the hydrothermal treatment at 200oC showed a monomodal poresize distribution with only intra-particle pores. The properties of titania powders could be improved by means of hydrothermal

treatment considerably; the size could be reduced to 40-50 nm, specific surface area could be increased by 50-100% and the

ratio of agglomeration could be reduced by 30-40%.

Key words: Nano Size Titania Powder, Sol-Gel Method, Hydrothermal Treatment, Pore Size Distribution

1. � �

�� titania� �� ��� ��� � ��� ���� ��

��� ��� ��� �� !� "#$�% � &�, '(� &��

�) � *+� ,-./0 12[1-5]. Titania� 3-4,56(brookite),

-76(rutile), �89:6(anatase)% ;� 3�/� << 2= >+?

@ AB� �/0 1�C[5], 3-4,56� DE FGHI, 0JK

L MBNO H� .PQ RS� T��� :U, �V0, -76� W

� �XY% ���Z GB [ RS� \]G _̂̀ ^�,8 �ab

KL X�c0 12. �$, �89:6� -76d2 e W� fgh�

�/0 1� RS� i(@ j>M kl, e �0, m) n�o� �)

�pD qjLr X�c0 12[6-8]. �st� �N uBv i(@

� ,�H� �pD ��� >w, >( &�, "#$�% ;� !

� AB� �xHyL titania� �pDzB� /{H� |}) }qZ ,

~) AB�� �w�� �}� 1�C, ,~) �B� ��� ! :

? % | J`, �o, B ", ��� % [� ?��KLr ��H2.

�:�Z �w MB�Z sol-gel�� �N�� 0�`� ��� ��

B� �� � n� +6'(� �� t 1/�[9-11], , ��� �N

wJ�� :?v !� "�� !,yL >w� �� �N H

qH� %�� 1� '(� ��KL Z) "#$�� �q@ ;� �

�� B�� ��� � N ¡2[10-11]. ��� sol-gel�� �N MB†To whom correspondence should be addressed.E-mail: [email protected]

617

618 ����������� �

v titania !� d2 �:�,I ¢%�Z >� %� £�, �

t�KL }¤v2. ��� 0J0�� H2O� ��� ¥¦H� t��

�� ,�) *+�, §¨c.¡2. ©, Ougri [[12]� titanium

tetraethoxide� ª���LH¦ autoclave@ reflux� ,�H¦ J`@

���«� �= '(� AB� "¬H­KI, Cheng [[13]� titanium

tetrachloride� ª���LH¦ pH, J`, ���«, ��:� ���®

'(� 6¯@ &�AB� *+H­0, Kondo [[14]� titanium

tetraethoxide� ª���LH¦ �N-°i�±� >Ba,²� :�

H­2. Yanagisawa [[15]� titanium tetraethoxide� ª���LH¦

�� ³� �w� �L "�� titania� :?H­KI, t���%

�� >w� Ba� ´= 0w �� Ba, �.8� �µ@ �N-°

¶� �) ·¸ >Ba �µL + H­2. ¹) Wang% Ying[16]�

titanium isopropoxide� ª���LH¦ º»¼½X,g@ �� ¾"

([Ti]/[H 20]=3-170)� �� sol-gel�� ,�H¦ �t N) ¿ "��

t��� Hq8 pH� ���® t���(T=80-240oC)H¦ �� '(

� &�@ >w� *+H­2. À~8 ,� *+��� t���� Á

) uB'(� >&�, >w, "#$�, ��AB� �) *+� �

� ,-0 12. '(� ���_��� B�� &à ��� �� �

Ä� �) *+� Ås) T,2. ��� Æ *+��� "¬�

� J`�� "� titania !� >�HI, >� %�� ,�

!� �B� �w�� t 1� t������ X�H¦ sol-gel��

�N MBv !� >�H­KI >�v !� ��� AB� 2

= q>��� �N >�v titania !� AB% "¬, ÈÉH­2.

2. � �

2-1. Sol-gel� � ����� � titania � � ��

Æ TÊ��� ª���L� TTIP(titanium tetra-isopropoxide, Adlrich,

97%)@ �DL� ethanol(Dongyang Chemical, 99.5%)� X�H­2.

Æ TÊ� �Ë�Z TÊ%� Fig. 1� 89ÌÍ2. TTIP@ �%�

��B� ?�H� �H¦ TTIP� ÎÏ � ¾t� ethanol(C2H5OH/

TTIP ¾" 5)� �N) ¿ (Ð ¬��� X�H¦ 30 ÑG ÒMH

­2. , ÒM��� ¾"� ?�v(R=H2O/TTIP=5, 20, 100, 200) ÓÂ

t� Ô�H¦ 30 ÑG �t N ��� wJ�� §¨H­2. ,ÕÃ

�.§ °i�� autoclave�� 6oC/min� ÖJ »`L 200oC×/ �

�) ¿ 50 rpmKL 3�« ÑG ��� §¨H� t���� H­2. t

���� ØÙ ¿ °i�� ÚÛ ��� X�H¦ !� tÜ) ¿ Ý

?Þß�� 100oCL 24�« Ý?) ¿ àH¦ Å !� H­2.

2-2. ���� � �� ��

uBv !� � N % á |â�q� ãH� �H¦ � Ð

aä(TA Instrument, SDT2960)� X�H¦ wJ�� 1,000oC×/ 5oC/min

� ÖJ »`L ��H¦ ãH­2. :?v !� +? Ð� �N

�� 400-4,000 cm−1� å��� FT-IR � Ð�(FTS 155, Bio-Rad)�

X�H­2. !� 6w� �Xi(�Å�(SEM, XL30SFEG, Philips)

� ,�H¦ æçH­KI, :?v titania !� >w Ð% è�

>'`� Xé ê� Ð�(XRD, Siemens D5000, Germany)� X�

H¦ ÐH­2. >w Ð� �E, ëa 1.5406ì� CuKα target,

45 kV, 40 mA� ?Ý�� ê�< 20-60o å�×/ ÐH­0, è� >

'`� ã� �N �89:w� �í&(101)� �<î� ãH¦

Scherrerï� �'H¦ µnH­2[17]. !� "#$�% �AB

� Brunauer - Emmett - Teller(BET, Micromeritics, ASAP 2400)� �q

sð�� ,�H¦ ãH­KI, , "#$�KLñò !, +6,

�� � H� 2ó� ï� X�H¦ !� è�'`� µnH­2.

(1)

¦�� D� !� è�'(&�(nm), S� "#$�(nm2/g),0, ρ�titania !� ô`(�89:w: 3.84õ10−21 g/nm3)I, 6� '(� +6

,�0 �ö� R �� shape factor÷,2. !� ��w¯� BET

@ XRDL << µn) !'`@ >'`� "(DBET/DXRD)L 89

ÌÍ2.

3. �� �

3-1. � ��

Sol-gel�� �N !MB� ª���Z TTIP� �t N� �N Ô

�c� �� ¾t� "� ���® :?) ¿ autoclave�� t���

D 6S ρ⋅---------=

Fig. 1. Flow chart for preparation of sol-gel derived titania powders withhydrothermal treatment.

Fig. 2. XRD patterns of the sol-gel derived powders with hydrothermaltreatment. The powders were dried at 100oC for 24 hr.

R5 R20 R100 R200Ratio of H2O/TTIP: 5 20 100 200

���� �41� �5� 2003� 10�

���� Titania �� �� 619

� Üø �.§ !� XRD Ð >%� Fig. 2� 89ÌÍ2. Fig. 2�

� ù t 1ú, >w� �t N� Ô�v �â� ��� wæû,

Ñ�) ³w� d­2. ©, 200oC�� 3�« ÑG t���� �N�

:?v titania !�� �ü �89:� >w, dý� ¼ t 1Í

2. ,� t��� |� TTIP� �t N� �N �.§ "�w, �

89:wKL� w��� �.þó� �Å)2.

Fig. 3� H2O/TTIP� "� 100� R sol-gel�� �N TTIP� �t

N �ÿ ¿ 100oC�� 24�« ÑG Ý?�ÿ titania !% ,� 400oC

�� 1�« ÑG ����® �.§ !�� XRD Ð >%,2. Fig.

3�� ù t 1ú, 100oC�� Ý?v !� "�w� 89Ì8,

400oCL ���v !� �89:w� 89�� ¼ t 12.

Fig. 4� TTIP� �t N % | �â� ���®(R=5, 20, 100,

200) :?) ¿ 200oC�� 3�« ÑG t���H¦ �.§ !��

FT-IR Ð >%,2. Fig. 4�� ù t 1ú, ëa, 3,380 cm−1 ñ�

�� H-OH@ Ti-OH >M� OH� �) ��§Ñ, 1,630 cm−1 ñ��

� H-O-H@ Ti-OH >M� OH� �) ��§Ñ% 530 cm−1 ñ���

� Ti-O >M� �) �<§Ñ [, 89�� ¼ t 12[5]. ¹), �

89:6 TiO2 tn��� ��5�, 1,415 cm−1 ñ��� æçcÍ

2[18]. ëa, 3,380 cm−1� �� stí&@ 1,630 cm−1 ñ�� st

fg� tq>M� H0 1� � (@ >M) Ti-OH >M� OH ��

§Ñ% *æc� KL �t N % | �, , Ô� t� fg

� � � ¼ t 12.

Fig. 5� H2O/TTIP� "� 100Z � ?ÝKL �t N v ¿ ¦

~ J`�� ���v sol-gel !�% �t N v !� t���H

¦ �.§ !� TG Ð >%,2. Fig. 5�� ù t 1ú, sol-gel

�� �N :?v ¿ 100oC�� Ý?v !� U 12%� |â�q�

d¦ ! |� �� [, , � c. 1ó� ¼ t 12[11]. �

$� sol-gel�� �N :?v ¿ 200oC�� t���� �) !,8

400oC�� ���v !�� |â �qâ` 4-5%L �� � ¼ t

1. ! |� ��� [� � â, �� � ¼ t 12.

3-2. ����� �� ��

Fig. 6� TTIP� �t N�� H2O/TTIP� "(R)� ���® :?)

¿ 200oC�� 3�« ÑG t���H¦ �.§ !�� �q s�ð

[Jé� 89� ,2. Fig. 6�� dú, �� R÷� �E� �N

BDDT� Â) 5�/� �#�Z sð[Jé| mesopore(2 nm

< diameter < 50 nm) AB� 89Ì� type IV� sð[Jé, 89þ

ó� ¼ t 12. H/� Ç� �o��� U) sð�é� 89Ì. i

6�Z type IV@� 2q 2= 6¯� 89ÌÍ2. ,� MBv '(�

, �� t� micropore� �0 1� RSKL N� t 12[18]. Fig. 6

�� R5@ R20� ?Ý% ;� �t N | Ô�v �� ³, �� ?

Ý�é de Boer� Â) �#�Z 5�/� hysteresis� 6 ̄| type A

Fig. 3. XRD patterns of titania powders made by sol-gel method.A: Powder calcined at 400oC for 1 hr, B: Powder dried at 100oC for24 hr.

Fig. 4. FT-IR spectra of sol-gel derived powders with hydrothermaltreatment. The powders were dried at 100oC for 24 hr.

Fig. 5. TG curves of titania powders made by sol-gel method and hydrother-mal treatment (R100).A: Sol-gel method, dried at 100oC for 24 hB: Sol-gel method, calcined at 400oC for 1 hrC: Sol-gel method, hydrothermal treatment at 200oC for 3 hr

HWAHAK KONGHAK Vol. 41, No. 5, October, 2003

620 ����������� �

L "¬� � '(�� ��� �N u�� �¸ T¸e �³� �,

uBv � ¼ t 1KI, ¹) R100, R200� �E�� �t N |

Ô�c� �� ³, � ?Ý�� uBv !� type EL "¬� �

� '(�� äô) �§� �) «,8 9Ú� �$� �N� uB

c� �&� �³� �� 89�2[19]. A� R200� �E�� �ð

é, �ëVà 898� � � ñ � ��, ��Hà ÄH0 1

ó� 89�2.

Fig. 7� sol-gel�� �N R100� ?ÝKL :?v ¿ 400oC��

Fig. 6. Nitrogen adsorption isotherms of sol-gel derived titania powders with hydrothermal treatment. The powders were dried at 100oC for 24 hr.R5 R20 R100 R200

Ratio of H2O/TTIP: 5 20 100 200

Fig. 7. Nitrogen adsorption isotherms of titania powders made by sol-gel method (R100) and calcined at 400oC for 1 hr.

Fig. 8. Pore size distribution curves of sol-gel derived titania powderswith hydrothermal treatment. The powders were dried at 100oCfor 24 hr.

���� �41� �5� 2003� 10�

���� Titania �� �� 621

1 hr ÑG ���v !� �q sð[JéKL type IV� 6¯� 8

9�� ¼ t 12. ¹) hysteresis 6¯��� t���� �N :?v

!� type E� 89� �$ sol-gel�� �N :?c. 400oC��

Hqv !� �&� �³% �¸ T¸e6 �, xjH� type B

� 89�� ¼ t 12[19].

TTIP� �t N % | <� �â� ��H¦ :?v ¿ t���

v !�� pore size distribution� Fig. 8� 89ÌÍ2. Fig. 8�� ù

t 1ú, �� !�, 6-10 nm� è��� �� mesopore� 8

9�� ¼ t 12. ¹) �� Ô�â, �a �� R5?Ý�� :?v

!� è� �, 12 nmL �a �� ¼ t 12. ,� �� sol-gel

MB�µ�� Ô�c� �� ³, �� �E �uB »`� DE ·¸

�$ '(Ba� z�� �.8� RS� >&�� Ó�H¦ è��

` Ó�H� ,I, e�, t���%��` �� ³, �ñH/

HyL �N-°i�w, �à �.8 �, &à 6Bc� RS,�

0 � t 12.

Fig. 9��� R100� ?ÝKL sol-gel�� �N MBv ¿ 400oC�

� 1�« ÑG ���v !% 200oC�� 3�« ÑG t��� v

!�� pore size distribution� "¬H¦ 89ÌÍ2. Fig. 9�� ù t

1ú, sol-gel�� �N MBv ¿ 400oC�� ���) !� è��

, 3 nmZ 1� '(� X,� �(intra-particle pore)% �,

60 nmZ 2� '(� X,� �(inter-aggregated pore), xH�

bimodal pore size distribution[9-11]� 89� �$, 200oC�� t�

��� �N :?v !� 7 nmñ�� è� �� �� 1� '(�

X,� �(intra-particle pore)�, xjH� monomodal pore size

distribution� d¦�Í2. , �w� �N-°i �±� �N, t���

� �� �uB� �»��!I, ,� �N 2� '(�, �Nc$� 2

� '(� X,� �, û./� KL "#� t 12[14]. ¦��

1� '(� �, uBv ¿ Ba) ��'(� 89ÌI, 2� '(� 1

� '(�� ��� �N uBv '(�� 89�2[20, 21]. ,@ ;�

�w� :?v !� 6w� 89� Fig. 10� SEM >%��` k

Z� t 12. Fig. 10�� d� $@ ;, sol-gel�� �N :?v ¿

Fig. 9. Pore size distribution curves of titania powders made by sol-gelmethod and hydrothermal treatment (R100).-�- Sol-gel method, calcined, at 400oC for 1 hr-����- Sol-gel method, hydrothermal treatment at 200oC for 3 hr

Fig. 10. Comparison of SEM images of sol-gel derived titania powdersbetween calcination and hydrothermal treatment (R100).(a) Sol-gel method, calcined, at 400oC for 1 hr(b) sol-gel method, hydrothermal treatment at 200oC for 3 hr

Fig. 11. Specific surface area of titania powders made by sol-gel methodand hydrothermal treatment.-�- Sol-gel method, hydrothermal treatment at 200oC for 3 hr-�- Sol-gel method, calcined, at 400oC for 1 hr-�- Sol-gel method, calcined, at 500oC for 1 hr-�- Sol-gel method, calcined, at 600 oC for 1 hr

HWAHAK KONGHAK Vol. 41, No. 5, October, 2003

622 ����������� �

in

ruc-

he

aces

-

ed

ce

nal

ish-

re of

400oC�� ���v titania !� 1� '(� �L ��H¦ �Ë 200-

300 nm &�� 2� '(� 6BH� Å%+?� 89Ì� �$, sol-gel

�� �N :`v ¿ 200oC�� t� ��v titania !� �N-°i

%� ÁN 2� '(�� ��, û./0 Å%+? �� &�`

40-50 nm `L �qH­2.

Fig. 11��� sol-gel�� �N :?v titania !� 200oC�� 3�

« ÑG t���� �N :?v !�% sol-gel�� �N :?v ¿

d2 W� J`�� ���v !�� "#$�� "¬H­2. Fig. 11

�� ù t 1ú, t���� �N :?v !�, sol-gel�� �N

:?v ¿ d2 W� J`L ���v !�� "N �� R÷(H2O/

TTIP ratio)�� "#$�, 50-100% ,w &à 89�� ¼ t 12.

Fig. 12��� sol-gel�� �N :?v titania !� ¦~ J`��

���) �% t��� ) !�� ��w¯� BET@ XRDL <

< µn) !&�@ >'`� ", DBET/DXRDL 89ÌÍ2. ���

KL DBET/DXRD, ÷, &$ !�� ��, ÛHà �.�� �Å)

2[22]. BETL ã) titania !� '`� XRDL ãv >'`

@ �,� d,� � ã ��� �,�� �ZH� KL X^v

2. ©, XRDL ãv >'`� Xé ê� í&� �<îKLñò

ãc� �$, BETL ãv !'`� �q sð�� �N ãv

!� "#$�KLñò µnc� RS,2. Fig. 12�� d� $@

;, sol-gel�� �N :?v ¿ d2 W� J`�� ���) !�

� ��`� t���� �N :?v !�� "N 30-40%,w &Ã

89�� ¼ t 1KI, ,� Fig. 10� SEM >%@` & �äH0

12.

4. � �

TTIP� ª���LH¦ sol-gel�� �N :?v !� autoclave�

� t� ���® �� !� AB� �N 2ó% ;� >²� ��

t 1Í2.

(1) Sol-gel�� �N :?c. 100oC�� Ý?v !� "�w�

dZ�$ 200oC�� t���� �N :?v !� � 8' �

� �0 1ÍKI �89: >w� d­2.

(2) Sol-gel�� �N :?v ¿ 400oC,w� J`�� ���H¦ >

�) �E uBv titania '(� &�� 200-300 nm `,ÍK8

200oC�� t��� ) �E�� titania '(� &�� 40-50 nm `

L &Ã �qH­2.

(3) Sol-gel�� �N :?c. 400oC�� ���v titania !� 1

�'(�X,� �(intra-particle pore)% 2� '(�X,� �(inter-

aggregated pore), xH� bimodal� � � 89� �$, 200oC

�� t���� �N �� !� 1� '(�X,� ��� ��

monomodal� 8' � � 89(KI, H2O/TTIP� "Y, 5-200 nm

� å��� , "Y, Ó��� �� è� �� &�� 6 nm×/ �

qH­2.

(4) Sol-gel�� �N :?v ¿ 400oC,w�� ���v !d2

200oC t� ��) titania !� "#$�� 50-100%×/ Ó���

t 1ÍKI, !� ��`� 30-40% ,w �q�� t 1Í2.

� ��

D : particle size [nm]

R : molar ratio of H20 to TTIP

S : specific suface area [nm2/g]

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ρ : density [g/nm3]

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���� �41� �5� 2003� 10�

���� Titania �� �� 623

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s

uc-

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ss

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HWAHAK KONGHAK Vol. 41, No. 5, October, 2003