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HAL Id: jpa-00219256

https://hal.archives-ouvertes.fr/jpa-00219256

Submitted on 1 Jan 1979

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DISSOCIATION OF WATER VAPOUR IN THE HOLLOW CATHODE GLOW DISCHARGE

B. Nehmzow, A. Rutscher, H.E. Wagner

To cite this version:

B. Nehmzow, A. Rutscher, H.E. Wagner. DISSOCIATION OF WATER VAPOUR IN THE HOLLOW CATHODE GLOW DISCHARGE. Journal de Physique Colloques, 1979, 40 (C7), pp.C7-55-C7-56.

�10.1051/jphyscol:1979727�. �jpa-00219256�

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JOURNAL DE PHYSIQUE CoZZoque C7, s u p p l d m e n t a u n07, Tome 40, J u i Z l e t 1979, page c7- 55

DISSOCIATION OF WATER VAPOUR IN THE HOLLOW C A M O D E GLOW DISCHARGE

13. Nehrnzow,A. Rutscher, H.E. Wagner.

S e k t i o n P h y s i k / E Z e k t o n i k , E.M. A r n d t - U n i v e r s i t a t G r e i f s w a Z d , D. D. R.

1NTRODUCTION:During t h e l a s t y e a r s much a t t e n t i o n was g i v e n t o t h e q u a l i f i c a t i o n of d i f f e r e n t t y p e s o f e l e c t r i c a l d i s c h a r - g e s f o r plasma chemical reactions.To r e a l - i z e e . g . d i s s o c i a t i o n p r o c e s s e s under non- i s o t h e r m a l c o n d i t i o n s t h e well-known hol- low cathode glow d i s c h a r g e (BcGD) shows some f a v o u r a b l e p r o p e r t ies.Mainly t h e s e p r o p e r t i e s can be a t t r i b u t e d t o f a s t beam e l e c t r o n s a c c e l e r a t e d i n t h e cathode dark space. Some new p a p e r s / l / / 2 / / 3 / h a d a l r e a d y proved t h e f a c i l i t i e s of t h e HCGD f o r t h e decomposition of d i f f e r e n t s u b s t a n c e s . I n t h e f o l l o w i n g more s y s t e m a t i c r e s u l t s on t h e p r o d u c t i o n of hydrogen o r i g e n a t e d from w a t e r vapour a r e given/4/.

EXIiERIl<IENTAL ARPcAIIGEXENT (Fig. I ) :The v ~ a t e r vapour produced by a c a l i b r a t e d evapora- t o r flows through t h e HCGD(diameter 8mm) and i s a n a l y s e d by a g a s chromatograph, A s p e c i a l p i s t o n compressor p r o v i d e s f o r t h e r e q u i r e d h i g h p r e s s u r e a t t h e e n t r y of t h e g a s chroffiatograph.To s t u d y t h e i n f l u e n c e of t h e cathode w a l l v a r i o u s m a t e r i a l s could be i n s e r t e d i n t h e device.

RESULTS AXD DISCUSSI0N:In dependence on t h e e s s e n t i a l o p e r a t i o n parameters ( p r e s - s u r e p / t o r r ; p o w e r U/W;!gas flow r a t e v/lh'l a t normal c o n d i t i o n s ) t h e H2-portion xHI behind t h e HCGD was measured s y s t e m a t i c - ally.Some r e s u l t s ( o b t a i n e d w i t h a copper c a t h o d e ) a r e shown i n Figs.2...5.It could be n o t i c e d t h a t h i g h decomposition r a t e s can be achieved.According t o t h e g r o s s r e a c t i o n : 2H20

+

2H2+02 t h e maximum p o r t - i o n of H2 could be 66.7 v o l , % a t t h e

- out l e t .

O f c o n s i d e r a b l e i n t e r e s t i s t h e f a c t t h a t w i t h r e g a r d t o t h e r e c i p r o c a l flow r a t e l / v ( F i g . 2 ) a n d t h e power U(Ffg.3) a t h i g h p a r a m e t e r s l i m b a l v a l u e s a r e reached.In- dependent of t h e flow r a t e a t h i g h d i s - charge powers an e q u i l i b r i u m s t a t e a p p e a r s which i s i n t h e c a s e of Fig.3 about 3 0 ~ 0 1 % ~ The adjustment of such an e q u i l i b r i u m

s t a t e seems very t y p i c a l f o r a wide c l a s s

of non-isothermal plasma chemical r e a c t - i o n s and should g i v e some h i n t s t o under- s t a n d t h e k i n e t i c background of t h e con- v e r s i o n . 0 f c o u r s e t h e e x a c t k i n e t i c me- chanism(the t o t a l i t y of a l l elementary p r o c e s s e s ) i s very complicated,even in t h e c a s e o f simple substances. A s u i t a b l e k i n e t i c d e s c r i p t i o n should c o l l e c t many of t h e s e d i f f e r e n t elementary p r o c e s s e s and should f i n a l l y r e s u l t i n a c l e a r - f o r m u l a f o r t h e c a l c u l a t i o n of t h e q u a s i e q u i l i b - rium s t a t e mentioned l i k e a mass a c t i o n law.

I n t h e frame of an o v e r a l l o r wmacroscop- i c m k i n e t i c s E.N.EREXIR d e s c r i b e d plasma chemical r e a c t i o n s by t h e model of t h e so- c a l l e d " k i n e t i c curveu/5/.The governing d i s c h a r g e parameter in t h i s model i s t h e s p e c i f i c energy U/v.But f r e q u e n t l y t h e o t h e r parameters of t h e a n a l y t i c k i n e t i c c u r v e ( t h e r a t e c o n s t a n t s of t h e g r o s s re- a c t i o n l a r e f u n c t i o n s of U/v,too and no g e n e r a l i z a t i o n i s p o s s i b l e i n such a c a s e .

We s t a r t from a b a l a n c e e q u a t i o n of t h e H2 g e n e r a t i o n which t a k e s i n t o account one p r o d u c t i o n t e r m ( d i r e c t 1 y p r o p o r t i o n a l t o U) and t h r e e l o s s terms(one independent of U, one d i r e c t l y p r o p o r t i o n a l t o U, and one r e l a t i n g t o t h e l o s s due t o t h e f l o w r a t e >

kEU

-

kVoxH3.

-

kV, UxH1 -vxH% = 0

The s o l u t i o n i s : xH,/xHlm = z / l + z w i t h z=k v4 U/(k vo +v) and xHHLIJD=

kE/kv..

f he s y s t emat i c a n a l y s i s of t h e experiment- a l v a l u e s shows t h a t t h i s c l e a r formula is i n t h e p o s i t i o n t o comprise a n a l y t i c a l a l l t h e measuring points.The parameters kE,kvo' kV4 a r e r e a l c o n s t a n t s ( f o r c o n s t a n t p r e s s - u r e l a l t h o u g h t h e power U changes by t h e f a c t o r 250 and t h e flow r a t e v by t h e

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979727

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factor 25.The curves in Fig.2...5 are cal- culated ones using the k-values shown.That the power U can act as a governing para- meter is indicated by some results belong- ing to other discharge operations. Fig.5 relates to an impulse operation of the HCGD(W :duration of the current impulse 1.

Decisive for the rate of the H2 production is the (meanlpower of the discharge again.

This was also the case for a condensed discharge as some preliminary experiments ahowed

,

Fig. 6 contains the influence of different cathode materials on the H2 production.

There is a distinctly marked effect which can be understood if the essential process of the H2 production is the recombination of H atoms at the cathode surface. Large recombination coefficients(e.g.~l/Al~O~:

0,3/0,45) give high port ions of H2, smaller ones (e.g.Cu:O,l and Cu-net on glass) act inversely.

REF'EREHCES :

/ I / B U T Y L I ( I N , I . P . ~ ~ . ~ ~ . ~ ~ ~ ~ ICPIG,Berlin 1977,p.377.

/E/METYEL, A.S., NASTYKHA,A.I., 13th ICPIG, Berlin 1977, p.379.

/3/ld&K, T.D., Acta Physica Austria 49(1978)67.

/~/NEHMZOW, B., WAGNER, H A , Report 1977/78, Greif swald, p.41,

/5/EREMIN, E.N., Elementy gazovoj electro- chimi, Moskau 1 968.

goschromotogroph

m

volve for

device compres-

I

p - 1 torr

1

v - ' l h l l

-

Fig. 2 Fig. 6

p - I torr o v-0.12 I l h A 0.24 "

v 0.39 1:

0.71 Fig. 3

0 1.75 "

3.03 "

kE'l.l L/Wh k,=0.45 I l h kv,-0.037IlWh

p -1 torr stationary HCGD v-3 ... 0.12 1/h

r 2 "

A 4.1 "

X 8.2 "

21 "

0 43 "

p-1 torr pulsed HCGD V - 3 ... 0.12L/h

f-500 s-l r.103~ u . 2 ~ 5 ~

250 12.3

+ 125 loJ 6.1

v 50 2.5

o 50 24.5

A 25 1.2

X 8 lo5 039

Fig. 1

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