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E L S E V I E R Journal o f Electrostatics 42 (1997) 93-105Journal ot

ELECTROSTATICS

R a d i c a l f o r m a t i o n d u e t o d i s c h a r g e i n s i d e b u b b l e i n l i q u i d

M a s a t o K u r a h a s h i , S h i n ji K a t s u r a a n d A k i r a M i z u n o

D e p a r t m e n t o f E c o l o g i c a l E n g in e e r in g , T o y o h a s h i U n i v e r si ty o f T e c h n o l o g yT e n p a k u - c h o , T o y o h a s h i - s h i , A i c h i , 4 4 1 J a p a n

S t e ri li z a ti o n , d e c o l o r i z a t i o n o r d e o d o r i z a t i o n o f w a t e r u s i n g a c t i v e o x y g e n s p e c i e s h a v eb e e n o f i n t er e s t b e c a u s e o f th e i r s t ro n g o x i d a t i o n p e r f o r m a n c e a n d t h e y d e c o m p o s e i n t oo x y g e n m o l e c u l e s w h i c h d o n o t p o l l u t e t h e e n v i r o n m e n t . I n t h i s p a p e r , s t u d i e s h a v e b e e nm a d e o n g e n e r a t i o n a n d c h a r a c t e r is t ic s o f a n e l e c tr ic a l d i s c h a r g e i n a b u b b l e f o r m e d b ye l ec t ro ly s i s . R ad i ca l fo rm a t i on and app l i ca t ion o f t he d i s cha rge i n w a t e r t r ea t m en t a r e a l sorepo r t ed u s i ng a pos i t i ve s t a i n l e s s - s t ee l need l e and a nega t i ve a l um i num p l a t e . T he need l ee l ec t rode w as su r rounded w i t h an i n su l a t i ng g l a s s t ube . T he e l ec t rode sy s t em w as pu t i n a l owp r e s s u r e v e s s e l a n d e n e r g i z e d w i t h d c h i g h v o l t a g e . E l e c t r o l y s i s t o o k p l a c e a n d f i n e o x y g e nbubb l e s w e re fo rm ed f rom t he pos i t i ve need l e e l ec t rode . S eve ra l m i nu t e s l a t e r t he e l ec t r i c a ld i s c h a r g e b e g a n i n a n o x y g e n b u b b le . A n i n t e n s e l ig h t e m i s s io n d u e t o t h e g e n e r a t io n o f O Hr a d i c a l c o u l d b e o b s e r v e d . T h e s p e c t r o s c o p i c s t u d y i n d i c a t e d t h a t h y d r o g e n p e r o x i d e w a sf o r m e d w i t h o u t o z o n e g e n e r a t io n b y t h e d i s c h a rg e . T h e d i s c h a r g e i n b u b b l e c a n b e a p p l ie d i ns t e r i l i za t ion .

1. I N T R O D U C T I O N

F or w a t e r t r ea t m en t such a s s t e r i l i z a t i on , deco l o r i za t i on o r deodo r i za t i on , ox i d i z i ngs p e c i e s , s u c h a s o z o n e o r h y d r o g e n p e r o x id e , a r e u s e f ul . O z o n i z e d w a t e r c a n b e m a d e e i th e r

* e - m a i l : m i z u n o @ e c o . t u t . a c . jp ( A k i r a M i z u n o )0304-3886/97/$17.00 Elsevier Science B.V. All rights reserved.PII S0304-3886(97)00146-0


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94 M . K u r a h a s h i e t a l . / J o u r n a l o f E l e c t r o s ta t i c s 4 2 ( 1 9 9 7 ) 9 3 - 1 0 5

b y d i lu t i o n o f o z o n e g a s [ 1 ] o r b y e le c t ro l y s is w i t h P t o r F e - P b O 2 e l e c t r o d e [ 2 ]. H y d r o g e npe r ox i de i s u s ua l l y p r oduced i n chem i ca l p l an t s . Fo r w a t e r t r ea t m en t , how ever , on - s i t ep r o d u c t i o n o f h y d r o g e n p e r o x i d e i s p r e fe r a bl e . O n e p o s s i b le m e t h o d o f h y d r o g e n p e r o x i d ep r od uc t i on i s t he u se o f a g l ow d i s cha r ge i n am bi en t p r e s s u r e be t w e en a need l e e l ec t r ode andw a t e r s u r f ace [ 3 ,4 , 5 ].

I n t h i s s t udy , w e t r i ed t o p r oduce ox i d i z i ng s pec i e s ( ac t i ve oxygen s pec i e s ) u s i ng ad i s cha r ge i n s i de bubb l e i n w a t e r . I n th i s m e t hod , 0 2 gas o r o t he r m a t e r i a ls a r e no t neces s a r y ,a n d O H r a d ic a l s p r o d u c e d b y t h e d i s c h a r g e c a n e a s i ly d i s s o lv e d i n w a te r . E l e c t r o ly s i s c a n b eus ed t o gen e r a t e s m a l l bubb l e s o f 0 2 gas . I n o r de r t o i n it ia t e an e l ec t ri ca l d i s cha r ge i n a s m a l lbubb l e , t he i n t ens i t y o f the e l ec t r ic f i e l d s hou l d be r a is ed . W e us ed a need l e e l ec t r ode co ve r e dw i t h a g l a s s t ube t o co nv e r ge t he e l ec t ri c f i e ld t o i nc r eas e t he i n t ens i t y [ 6 ] . Th i s p ape r r epo r t sc h a r a c t e ri s ti c s o f t h e d i s c h a r g e i n s i d e b u b b l e a n d f o r m a t i o n o f h y d r o g e n p e r o x i d e .

2 . E X P E R I M E N T A L M E T H O D

2 . 1 E l e c t r o d e s y s t e mA need l e t o p l a t e e l ec t r ode s y s t em w a s us ed a s s how n i n F i g . 1 . Th e need l e e l ec t r ode

w as m ade o f s t a in l e s s s tee l w i r e ( d iam e t e r : 0 . 51 m m ) . Th e need l e e l ec t r ode w as con t a i ned i na g l a s s tube ( i nne r d iam e t e r : 2 r am , o u t e r d i am e t e r : 3 m m ) t o i nc r eas e s t r eng t h o f t he e l ec t ri cf i e ld a t t he op en and i n f r on t o f t he need l e t ip . D i s t ance f r om t he t i p o f the need l e e l ec t r ode t ot h e e n d o f th e g l a s s t u b e w a s 3 m m A n o t h e r d i st a n c e f r o m t h e g l a s s t u b e t o t h e p la t ee l e c t ro d e , G [ m m ] , w a s c h a n g e d f r o m 2 5 t o 4 0 m m . T h e p l a te e l e c t ro d e w a s m a d e o f a na l u m i n u m p l a t e ( d i a m e t e r : 7 1 m m ) . T h e n e e d l e t o p l a t e e l e c t r o d e w a s i m m e r s e d i n acy l i nd r i ca l p l a s t ic con t a i ne r o f 71 m m d i am e t e r w i t h 20 0 m g o f de i on i zed w a t e r ( r e s is t iv i t y :4 . 2 kg2 cm ) . The r e s i s t iv i t y w a s m eas u r ed each t i m e b e f o r e and a f t e r t he expe r i m en t u s i ng ac o n d u c t i v i t y m e t e r ( T O A C M - 7 B ) . T h e e l e c tr o d e s y s t e m w a s p u t i n a v a c u u m v e ss e l. T h eP r e s s u re w a s s e t a p p r o x i m a t e l y a t 1 5 0 T o r r ( 1 9 k P a ) .


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2 .3 M e a s u r e m e n t o f t h e d i s c h a r g e f r e q u e n c yT o o b s e r v e t h e f r e q u e n c y o f t h e d i s c h a rg e , t h e n u m b e r o f p u ls iv e l i g h t e m i s s i o n

as s oc i a t ed w i t h t he d i s cha r ge w as m eas u r ed w i t h a pho t om ul t i p l i e r . The s i gna l w as p r oces s edb y a c o m p a r a t o r w h i c h h a d a b a n d w i d t h o f 1 0 k H z . T h e o u t p u t o f t h e c o m p a r a t o r w a s f u r th e rp r o c e s se d b y a c o u n te r ( K E N W O O D F G - 2 7 3 ) . T h e n u m b e r o f d i sc h a r g e fo r e v e r y 1 0s e c o n d s w e r e c o u n t e d a n d a v e r a g e d t o d e te r m i n e.

2 . 4 M e a s u r e m e n t o f h y d r o g e n p e r o x i d eA f t e r t h e d i s c h a rg e t r e a tm e n t , t h e w a t e r w a s s a m p l e d . T h e c o n c e n t r a t i o n o f H 2 0 2 a n do z o n e w a s m e a s u r e d . T h e c o n c e n t r a t io n o f H 2 0 2 w a s d e t e r m i n e d b y s o d i u m t h i o s u lf a te

t i t r a t i on . The t i t r a t i on l i m i t w as de t ec t ed co l o r i m e t r i ca l l y . To d i s t i ngu i s h be t w een hydr ogenp e r o x i d e a n d o z o n e , a n a b s o r p t i o n s p e c t r u m w a s m e a s u r e d b y a u l tr a -v i o le t a b s o r p t io ns p e c tr o p h ot o m e te r ( U V - 1 2 0 0 S H I M A D Z U ) .

2 .5 E m i ss i o n s p e c tr u m m e a s u r e m e n tF i g .3 s h o w s s c h e m a t i c d i a g r a m o f th e m e a s u r i n g s y s t e m u s i n g a m o n o c h r o m a t o r f o r

obs e r v i ng t he l i gh t em i s s i on s pec t r um f r om t he d i s cha r ge i n u l t r a - v i o l e t and v i s i b l e r ange( 2 0 0 - 9 5 0 n m ) . T h e e m i s s i o n w a s re s o lv e d u s i ng a m o n o c h r o m a t o r (C T - 2 5 C P & S M D - 2 5 C

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N : need le e l ec to rode A M P : am p l if e rM . M . & C . U . :m o n o c h r o m e t o r A / D : A I D c o n v e r te r& con to ro l un i t C O M : com pu to rP.M.: photo mul t ip l ier


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J A S C O C o . ) w i th a p h o t o m u l ti p li e r (R 3 7 4 H A M A M A T S U C o . ). T h e si g na l w a s r e c o rd e d b ya c o m p u t e r ( P C - 9 8 0 1 N E C ) t h r o u g h A / D c o n v e r t e r ( A Z I - 3 1 2 3 I n t e r f a c e ) . S a m p l i n gf r e q u e n c y o f th e A / D c o n v e r t e r w a s 1 k H z , a n d e a c h d a t a p o i n t (1 n m a p a r t) w a s o b t a i n e d a sa n a v e r a g e d v a l u e f o r 2 s e c s a m p l in g p e r io d . T o m e a s u r e t h e s p e c t r u m , i n n e r d i a m e t e r o f t h eg l a s s t ube cov e r i ng t he need l e e l ec t r od e w as r educe d t o 1 m m . Th i s i s t o i n it ia t e t he d i s cha r gem or e eas i ly .

2 . 6 S t e r i l i z a t i o n e f f e c tSt e r i li za t ion e f f ec t o f the d i s cha r ge i n s i de bu bb l e w as i nves t i ga t ed u s i ng f i s s ion yea s t

ce l l . The yeas t ce l l w as s us pended i n de i on i zed w a t e r i n t he con t a i ne r . A pos i t i ve dc h i ghvo l t age w as app l i ed f o r 5 , 10 , 15 m i nu t e s . 20 , u o f t he w a t e r w as s am pl ed and cu l t u r ed ona g a r c u lt u re . T h e n u m b e r o f c o l o n i e s o n t h e a g a r c u l tu r e w a s c o u n t e d a f t er 4 8 h o u r s o fi ncuba t i on t o eva l ua t e t he s t e r il i za ti on r a te .

3 . E X P E R I M E N T A L R E S U L T S & D IS C U S S I O N

3 .1 E l e c t r ic a l c h a r a c t e r is t i c s o f t h e d i s c h a r g e i n s i d e b u b b l e in w a t e rW h e n p o s i ti v e d c v o l t a g e o f a b o u t 2 . 5 k V ( ' + '0 . 3 k V ) w a s a p p l ie d t o t h e n e e d l e e l e c tr o d e

( G = 4 0 m m a n d p = 1 5 0 T o r r ) , e le c t r o ly s i s t o o k p l a c e o n t h e ti p o f t h e n e e d le e l e c t ro d e a n df o r m a t i o n o f 0 2 b u b b l e s w a s o b s e r v e d . T h e a m b i e n t p r e ss u r e w a s s e t a t p = 1 5 0 T o r r in th ef o l l ow i ng expe r i m en t , becaus e a s t ab l e d i s cha r ge cou l d be ob t a i ned .

A t t = l m i n ( t: t r ea t m en t t i m e , ti m e o f the H . V . app l i ca t i on e l aps ed f r om t he beg i nn i ng ) ,t he e l ec t ri ca l d i s cha r ge occ u r r ed i n a bubb l e . A pho t og r ap h o f the d i s cha r ge an d i tsi l lu s t r a ti on a r e s ho w n i n F i g .4 . Th e vo l t age and cu r r en t o f t he d i s cha r ge a r e s h ow n i n F ig . 5 .T h e d i s c h a r g e p r o c e s s p r o c e e d s a s f o l l o w s :I ) A t fi rs t , an 02 bubb l e , d i am e t e r abou t t he s am e as t he need l e d i am e t e r , w as s tuck on t he

tip.


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2 ) T h e b u b b l e g r a d u a l l y e x p a n d e d a n d b l o c k e d t h e p as s o f t h e c u r r en t , re s u lt in g i n a ni nc r eas e o f t he app l ied vo l t age .

3 ) W h e n t h e a p p li e d v o l t a g e r e a c h e d a b o u t 5 k V , th e d i s c h a r g e in s i d e t h e b u b b l e to o kp l a c e , a n d p u l s i v e l a r g e c u r r e n t c o u l d b e o b s e r v e d . S t r e a m e r s w e r e p r o d u c e d b e t w e e n t h eneed l e t i p and t he inne r s u r f ace o f t he bubb l e . The co l o r o f the l i gh t em i s s i on w as pu r p l e.T h e d i s c h a r g e c a u s e d f u r th e r e x p a n s i o n o f t h e b u b b l e [ F ig . 4 ( a) ].

4 ) Th e bubb l e w as then expe l l ed f r om the g l a s s t ube and w a t e r en t e r ed i n t o t he t ube . Th ed i s c h a r g e w a s q u e n c h e d a n d t h e v o l t a g e d e c re a s e d d u e t o a n i n c r e a se o f t h e c u rr e n t.E l e c t r o l y s is b e g a n a g a i n a n d t h e a b o v e p r o c e s s w a s r e p e a te d .

i i i i i ! ~~i ~::~::~:::N~ l e i i i i~ lu t ione lec t rdei i i ~ i i ~ ! i~ ia s su b ei i ~ l i ii~bblei ! i i i i. . . i i i ! ! ! i i i ! ! i i i i! ! ! i l J ! i l i l J i il( a ) ( b )

F i g . 4 T h e d i s c h a r g e i n a b u b b l e( a ) P h o t o g r a p h o f d i s c h a r g e in a b u b b l e( b ) I l l u s t r a t i o n

A t t = 1 0 m i n , d u r a ti o n a n d f r e q u e n c y o f th e d i s c h a r g e i n b u b b l e i n cr e a se d . C o m p a r i s o nof F i g . 5 ( a ) and ( c ) s how s t ha t an i n t e rva l o f the d i s cha r ge bec am e s ho r t e r w i t h i nc r eas e i nt h e t r e a t m e n t t i m e . A d i s c h a r g e w i th l o n g d u r a ti o n ( m o r e t h a n 2 0 0 m s ) c o u l d b e o b s e r v e d a tt = 5 1 0 s e c a n d t = 1 0 4 0 s e c ( m a r k e d A a n d 13) a n d t h e v o l t a g e d r o p p e d t o a r o u n d 2 k V .

F i g . 6 s h o w s r e l a ti o n b e t w e e n t h e d i s c h a r g e f r e q u e n c y a n d t h e t re a t m e n t t im e , t , w i th t h egap d i s t ance , G , a s a pa r am e t e r . I n th i s ca s e t he s upp l i ed po w e r w as P i n= 42W . W hen t hea m b i e n t p r e s s u re w a s d e c r e a s e d f r o m 7 6 0 T o r r t o 1 5 0 T o r r , a n a ir b u b b l e w a s l e ft in s id e t h e


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g l a s s t u b e a n d t h e d i s c h a r g e o c c u r r e d s o t h a t t h e l a r g e v a l u e o f th e d i s c h a r g e f r e q u e n c y w e r eo b s e r v e d u n t i l 1 m i n u t e a f t e r t h e b e g i n n i n g o f t h e v o l t a g e a p p l i c a t io n . T h e a i r b u b b l e w a st h e n e x p e l l e d a n d t h e e l e c t r o l y s i s b e g a n . I n th e c a s e s o f G = 2 5 a n d 3 3 m m , t h e d i s c h a r g ef r e q u e n c y f o r t = 3 - 5 m i n w a s l o w e r a n d d u r a t i o n o f th e d i s c h a r g e w a s s h o r t e r t h a n t h o s e a f te rt = 5 m i n . I n t h e c a s e o f G = 4 0 m m , t h e d i s c h a r g e f r e q u e n c y d e c r e a s e d r a p i d l y ( F i g 6 a r r o w )a f t e r t = 1 0 m i n .

F i g . 7 s h o w s t h e c o m p a r i s o n o f t h e d i s c h a r g e f re q u e n c y a t Pin = 2 0 W a n d P in = 4 2 W .T h e f r e q u e n c y o f t h e d i s c h a r g e a t Pi n = 2 0 W w a s l e s s th a n t h a t a t P in = 4 2 W . T h e a m b i e n tp r e s s u r e w a s s e t a t p = 1 5 0 T o r r i n t h e f o l l o w i n g e x p e r i m e n t , b e c a u s e a s t a b l e d is c h a r g e c o u l db e o b t a i n e d .

A f t e r th i s e x p e r i m e n t a t G = 4 0 m m , P i n = 4 2 W , t= 1 5 m i n , r e s i s ta n c e o f t h e s a m p l e( d e i o n i z e d w a t e r ) d e c r e a s e d f r o m 4 .2 k Q c m t o 2. 1 k Q c m .


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3 . 2 E f f e c t o f t h e a m b i e n t p r e s s u r eE f f e c t o f t h e a m b i e n t p r e s s u r e o n t h e d i s c h a r g e i n s i d e b u b b l e w a s s h o w n i n F ig . 8 . A t

f ir s t, t h e a m b i e n t p r e s s u r e w a s s e t a t p = l l 0 T o r r ( 1 4 k P a ) , a n d t h e d c v o l t a g e w a s a p p l i e d .


9/13

M . K u r a h a s h i e t a l . / J o u r n a l o f E l e c t r o s ta t i c s 4 2 ( 1 9 9 7 ) 9 3 - 1 0 5 101

W h e n P i n = 4 2 W a n d t= 1 0 m i n , th e f r e q u e n c y a n d d u r a t io n o f t h e d is c h a r g e i n cr e a se d . T h e nt h e p re s s u re w a s r a is e d w i t h t h e in c r e a s in g r a t e o f 1 2 T o r r / s e c f r o m p = 1 1 0 T o r t . T h ef r e q u e n c y w a s d e c r e a se d . I n th e c a s e o f G = 2 5 m m , t h e d is c h a r g e w a s q u e n c h e d a t p = 3 0 0T o r r ( 4 0 k P a ) . W h e n G = -4 0 m m , t h e d is c h a r g e w a s q u e n c h e d a t p = 2 3 0 T o r r ( 3 1 k P a ) . T h ed i s cha r ge can be i n i t ia t ed eas i l y a t l ow er am bi en t p r e s s u re .

1 2 0OI1 ) 1 0 0o 8 0-g 6o 4 0

x : 2 0 o ,

, , . , , i , , ,P i n = 4 2 W | G = 2 5 m m I---~>.-- G = 40 m m I

1 5 0 3 0 0 4 5 0 6 0 0 7 5 0P r e s s u r e [ T o r r]

F i g .8 E f f e c t o f t h e a m b ie n t p r e s s u r eo n t h e d i s c h a r g e f r e q u e n c y

3 . 3 P r o d u c t s o f t h e d i s c h a r g e i n s i d e b u b b l e i n w a t e rA c t i v e o x y g e n s p e c i e s li k e O H * a n d O * a r e g e n e r a te d i n th e d is c h a rg e . H y d r o g e n

p e r o x i d e c o u l d b e p ro d u c e d f r o m O H r a d i ca l s. T h e r e l a ti o n b e tw e e n c o n c e n t r a t i o n o f H 2 0 2and t he t r ea t m en t t i m e , t , w i t h pa r am e t e r s G and P i n i s s how n i n F i g . 9 . A t t = 15 m i n , t hec o n c e n t r a t i o n o f H 2 0 2 w a s s a tu r a te d r e g a r d l e ss o f G. W i t h i n th e e x p e r i m e n t a l c o n d i t i o n s , t h eh i g h e s t c o n c e n t r a t i o n o f I -I 20 2 w a s a b o u t 5 0 p p m . A c o m p a r i s o n o f F i g . 9 ( a ) a n d ( c ), o r ( b)and ( d ) s how s t ha t , a s t he i npu t pow er i nc r eas ed f r om 20 W t o 42 W , t he r e w as s i gn i f i can ti n c re a s e i n H 2 0 2 g e n e r a ti o n . A t t = 1 5 m i n , t h e c o n c e n t r a t io n o f H 2 0"2 w a s a r o u n d 1 0 p p m f o rb o th G = 2 5 a n 4 0 m m a t p = 2 0 W , a n d w a s a r o u n d 5 0 p p m f o r G = 2 5 a n d 4 0 m m a t p -- 42 W .T h e g a p d i s t a n c e , G , d i d n o t a f f e c t t h e H 2 0 2 c o n c e n t r a t i o n w h e n t h e i n p u t p o w e r r e m a i n e dcons t an t .


10/13


5 0 [ G = 2 5 m m,_ 40 Pin=20 WO ~

~ O0 ' 1 0 '00 ~ Treatment t im e t [min ]

a )

~- 50 4 0"O

~" 30,,i,-o ~ 2 0~ . ~ . 1 0

2 0 g , o '0 o _

G = 4 0 mmPin=20W

t a J ~10 20Treatment t im e t [min ]b)

t -100"O

t "o ~ 5 0

~-~, - O~O ~

G = 2 5 m mPin=42W

0 ~ 10Treatment t im e t [min ]

( c )

c "

l o ot- "o N 5 0

8 " ~ 0 '20 = G )

.~=40mmPin=42W

r10 20Treatment t im e t [min ]

( d )Fig.9 Concen tration of hydrog en perox ide

3 .4 U V a b s o r p t io n s p e c t r u m o f t h e s a m p l eT h e u l t r a -v i o l e t a b s o r p t i o n s p e c t r u m o f t h e s a m p l e a f t e r t h e d i s c h a r g e t r e a t m e n t w a s

m e a s u r e d a s s h o w n i n F i g . 1 0 . A b s o r p t i o n p e a k w a s f o u n d a t a b o u t 2 1 0 n m , w h i c hc o r r e s p o n d e d t o t h a t o f H 2 0 2 . P e a k o f n i tr i c a c i d a n d n i t r o u s a c i d a r e a l s o a r o u n d 2 1 0 n m [ 7] ,a n d c a n n o t b e s e p a r a t e d f ro m t h e p e a k o f H 2 0 2 . I n t h i s e x p e r i m e n t , h o w e v e r , n i t r o g e n is n o tc o n t a i n e d i n w a t e r. T h e 2 1 0 n m p e a k w a s , t h e re f o r e , c o n s i d e r e d t o b e c a u s e d b y f o r m a t i o n o fH 2 0 2 . C o n c e n t r a t i o n o f o z o n e w a s a l s o c h e c k e d b y t h e s p e c t r o p h o t o m e t e r , b u t o z o n e c o u l dn o t b e d e t e c t e d .


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M. Kurah ashi e t a l . /Jo urn al of E lec tros tat ics 42 (1997) 93 -105 103

0.050

.~ 0.025

0.000200 350 500wavelength [nm]

Fig. 10 UV Spectrum of sample3 .5 L ig h t e m i s s i o n s p e c t r o s c o p y

S p e c t r u m o f l ig h t e m i s s i o n o f t h e d i s c h a rg e i n si d e b u b b l e w a s s h o w n i n F i g .1 1 .H o r i z o n t a l a n d v e r ti c al a x i s o f t h e f i g u re d e n o t e w a v e l e n g t h a n d t h e a v e r a g e d i n te n s i ty o f th el i gh t em i s s i on r e s pec t i ve l y . Th e obs e r v ed peak s i nd i ca t ed t he ex i s tence o f t he r ad ica l s . Peakso f 3 0 9 n m a n d 6 5 6 .3 n m w e r e f o u n d , w h i c h w e r e c o r re s p o n d i n g t o e m i s s i o n f r o m O H r a d ic a land H o , r e s pec t i ve l y [ 8 ] . O r ad i ca l s s hou l d be gene r a t ed i n t he d i s cha r ge , bu t no no t i ceab l ee m i s s i o n d u e t o O r a d ic a l s ( a r o u n d 7 7 7 n m ) c o u l d b e o b s e r v e d .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . L . . . . . . . . . , . . . . . . . . . . . . . . . . . L . . . . . . . . . , . . . . . . . . . J . . . . . . . . . , . . . . . . . . . . . . . . . . . J . . . . . . . . . . . . . . . . . . J . . . . . . . . . ~ . . . . . . . . .200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950wave length [nm]

Fig.11 Spectrum of discharge in bubble with pos it ive needle electrodep=110 - 220T orr(1 .4x 104 - 2.9 X 104 P a) , g lass tube inner d iameter1 mm

3 . 6 P h y s ic a l P h e n o m e n aA t f i r s t , e l ec t r o l ys i s s t a r t s on t he need l e t i p and s m a l l 02 bubb l e i s gene r a t ed . The 02

b u b b l e b e c o m e s l a r g e r a s t i m e e l a p s e s . A t t h e s a m e t i m e o h m i c h e a t i n g t a k e s p l a c e a n dt em p er a t u r e o f w a t e r i n s ide t he g l a s s tube i nc r eas es . V apo r p r e s su r e o f t he bubb l e i s l ow s o


12/13

104 M . K u r a h a s h i e t a l . / J o u r n a l o f E le c t r o s ta t i c s 4 2 ( 1 9 9 7 ) 9 3 - 1 0 5

t h a t H 2 0 e v a p o r a t e i n t o th e b u b b l e. W h e n d i a m e t e r o f t h e b u b b l e b e c o m e s t h e s a m e a s th a t o ft he g l a s s t ube , t he cu r r en t i s b l ocked , and t he app l i ed vo l t age i nc r eas es becaus e o f r educedv o l t a g e d r o p d u e t o o u t p u t i m p e d a n c e o f th e v o l t a g e s o u r c e . M o s t o f th e v o l t a g e d r o p is th e nde l i ve r ed t o t he bubb l e , and t he d i s cha r ge t ake p l ace . The l i gh t em i s s i on s pec t r um o f thes t re a m e r o f th e d i s c h a r g e i n c lu d e d H a ( 6 5 6 . 3 n m ) a n d O H r a d i c a ls ( 3 0 9 n m ) , i n d ic a t in gf o r m a t io n o f h y d r o g e n a t o m a n d O H .

W e c o n s i d e r e d t h a t O H r a d ic a l s c h a n g e d i n to H 2 0 2 . T h e h i g h e r th e f r e q u e n c y a n d t h el o n g e r t h e d u r a t io n t i m e o f t h e d i sc h a r g e i n s id e b u b b l e , c o n c e n t r a t i o n o f H 2 0 2 s h o u l d b ehigher .

3 . 7 S t e r i l i z a t io n e f f e c tY eas t ce l l s w er e u s ed t o s t udy t he e f f i c i ency o f s t e r i l i za t i on , becaus e o f t he i r ea s y

ava i l ab i l i t y . The s t e r i l i za t i on r a t e w as ca l cu l a t ed a s t he r a t i o o f num ber o f co l on i e s a f t e r andbe f o r e t he t r ea t m en t . T he r e s u l ts a r e s ho w n i n F ig . 12. A s t he t r ea t m en t t i m e w as i nc r eas ed ,s t er i l i za t ion r a t e increased .

4 . C O N C L U S I O N S

~ " 1 0 0e 8 0~ 6o-ON 4 0N

= 2 0r"

1 0 2 0T r e a t m e n t t i m e t [ m i n ]F i g . 1 2 S t e r i li z a t io n e f f e c t

( 1 ) A d i s cha r ge i n a sm a l l bubb l e f o r m ed by e l ec t r o l ys i s can be gene r a t ed i n t he need l e t op l a t e e l ec t r ode s ys t em . The need l e e l ec t r ode w as s u r r ounded by an i n s u l a t i ng g l a s s t ube


13/13

M . K u r a h a s h i e t a l . / J o u r n a l o f E l e c t r o st a t ic s 4 2 ( 1 9 9 7) 9 3 - 1 0 5 105

to inc rease the e lec t r ic f ie ld and pos i t ive dc vo l tage was app l ied . The ambien t p ressureshould be reduc ed to a round 150 Torr .

(2) L ig h t e mis s io n a s s o c iate d w i th OH ra d ic al s c o u ld b e o b s e rv e d , b u t n o n o t i ce a b lee mis s io n f ro m O ra d ica l s c o u ld b e o b s e rv e d . Th e o b s e rv a t io n in d ic ate d th a t th e b u b b le ,fo rm e d b y e le c t ro ly s i s a t th e p o s i t iv e n e ed le e l e c t ro d e , c o n tain e d m a in ly wa te r mo le c u le .

(3) Hy d ro g e n p e ro x id e c o u ld b e fo rme d b y th e d i sc h a rg e , a n d 5 0 p p m m a x im u mc o n c e n t ra t io n c o u ld b e o b ta in e d in the e x p e r ime n ta l c o n d i tio n .

(4) A m o d e ra te k i ll in g e f fe c t o f th e d i s ch a rg e t re a tme n t c a n b e c o n f i rme d u s in g fi s s io n y e a s tcell.

REFERENCES1. M. S a to , K . Mu ra i , T . Os hima : P re l imin a ry In v e s t ig a t io n o f P re b re a k d o w n P h e n o m e n a

a n d Ch e mic a l Re a c t io n s Us in g a P u l s e d H ig h -Vo l ta g e D is c h a rg e in Wa te r , P ro c . IEJAn n u a l Me e t in g (1 9 9 3 ) 2 2 5

2 . J ianren Feng , Dennis C. Johnson , S tephen N. Lo uery and Jam es J . ca rey :E le c t ro c a ta ly s i s o f An o d ic Ox y g e n -T ra n s fe r Re a c t io n s , J . E le c t ro c h e m S o c . , Vo l. 1 41 ,No .1 0 , Oc to b e r (1 9 9 4 ) 2 7 0 8

3 . A .R .De n a ro a n d A .Hic k l in g : G lo w -Dis c h a rg e E le c tro ly s is in Aq u e o u s S o lut io ns , J .E lec t rochem. Soc . 105 (1958) 265

4 . Ya s u s h i Ka n z a k i , No r im ic h i N is h imu ra , J u n ta ro To b a , M i t s u h a ru K o n u m a a n d Os a m uM a ts u mo to : In f lu e n c e o f A tmo s p h e r ic G a s e s o n th e Ox id a t io n Y ie ld s o f G lo w D is c h a rg eElec t ro lys is in Aqueous So lu t ion , Denki Kagaku 57 , No.2 (1984) 126

5 . H .L e w a n d I .He ib e r : S p e c t ru m o f H2 0 ~, J .chem .Phys .5 8 (1973) 12466 . T . Te n m a , M. Ha y a m iz u , A . Miz un o : D e s t ru c tio n o f y e a s t c e l ls b y p u l s e d h ig h v o lt a g e ,

Proc. IEJ, 13, (1989) 2237 . Bu n s e k ik a g a k u b in ra n , N ih o n b u n s e k ik a g a k u g a k k a i8. R .W . B P ea se , A . G . G ay d o n, T H E I D E N T I F I C A T I O N O F M O L E C U L A R S P E C T R A ,

C h a p m a n A n d H a l l, L o n d o n ( 1 9 7 6)

Oh Radicals in Bubble

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