The kinetics of the establishment of the oxidation-reduction potential of a titanium electrode upon contact with hydrazine was studied in different media: H2SO4, NaOH, and Na2SO4. It was found that the nature of the potential shift depends little on the medium. The initial potential determines the rate of potential displacement upon contact with hydrazine, which is explained by the different condition of the electrode's surface

Bogdanovich, V. B.

Korolev, A. K.

Kuznetsov, G. A.

Levchenko, A. K.

English

NASA Technical Reports Server

NASA TECHNICAL MEMORANDUM NASA TM-88538/ 
ELECTROCHEMICAL BEHAVIOR OF A TITANIUM ELECTRODE 
IN HYDRAZINE SOLUTIONS 
A. K. Levchenko, G. A. Kuznetsov, V. B. Bogdanovich, 
A. K. Korolev 
Translation of "Elektrokhimicheskoye povedeniye titanovogo elektroda 
v rastvorakh gidrazina," Nekotoryye voprosy sovremennogo elektro- 
khimiya kinetika, vol. 1, pp. 107-113. 
(N A S A-TH - 8 8 5 3 E) E LEC 3EOC HE M IC R L E E H AVI 0 R OF N87-14464 i A 4 I ' I A N I U H  E I E C ' I l i C C E  IE H Y C E A Z I N E  SOLUTIONS 
{ N a t i c n a l  Aercnautics and Space 
A d m i n i s t r a t i o n )  f p LSCL 9 9 P  Unclas 
G3/25 43652 
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 
WASHINGTON, D.C. 20546 DECEMBER 1986 
https://ntrs.nasa.gov/search.jsp?R=19870005031 2020-03-20T12:18:56+00:00Z
1. Report No. 
NASA TM-88538 
7. Author(s) 
A. K. Levchenko, G. A. Kuznetsov, V. B. Bogdano- 
vich, A. K. Korolev 
2. Government Accession No. 
9. Performing Organization Name and Address 
Leo Kanner Associates 
P.O. Box 5187, Redwood City CA 94063 
19. Security Classif.(of this report) 
Unclassified 
12. Sponsoring Agency Name and Address 
National Aeronautics and Space Administration 
Washington, D.C. 20546 
20. Security Classif. 
Unclassified. 
s T n N m R D ~ P A G E  
3. Recipient's Catalog No. 
(of this page) 
5. Report Date 
December 1986 
6. Performing Organization Code 
21. No. of pages 22. 
8. Performing Organization Report No. 
10. Work Unit No. 
11. Contract or Grant No. 
NASW- 4 0 0 5 
13. Type of Report and Period Covered 
Translation 
14. Sponsoring Agency Code 
15. Supplementary Notes 
Translation of "Elektrokhimicheskoyepovedeniye titanovogo elektroda 
v rastvorakh gidrazina," Nekotoryye voprosy sovremennogo elektrokhimiya 
kinetika, vol. 1, pp. 107-113. 
16. Abstract 
The kinetics of the establishment of the oxidation-reduction potential 
of a titanium electrode upon contact with hydrazine was studied in 
different media: H2S04, NaOH, and Na2S04. 
It was found that the nature of the potential shift depends little 
on the medium. The initialpotential determines the rate of potential 
displacement upon contact with hydrazine, which is explained by the 
different condition of the electrode's surface. 
17. Key Words [Selected by Author(s)] 18. Distribution Statement 
Unclassified-Unlimited 
8 
ELECTROCHEMICAL BEHAVIOR OF A TITANIUM ELECTRODE 
IN HYDRAZINE SOLUTIONS 
A. K. Levchenko, G. A .  Kuznetsov, V. B. Bogdanovich, 
A. K. Korolev 
The electrochemical behavior of hydrazine on platinum-group metals/l07* 
is examined rather thoroughly in the current literature. Processes in 
the "double-layer region" in the absence of electrochemically active 
gases -- oxygen and hydrogen -- can be studied on these metals. 
At the same time, the electrochemical interaction between hydra- /lo8 
zine and oxidized surfaces possessing semiconductor properties is of 
some interest. From this standpoint, we chose a titanium electrode. 
Hydrazine hydrate of "ch. d. a." [analytical] grade was used in 
our work, and the purity of the titanium electrode was 99.985; all 
solutions were prepared from twice-distilled products. 
Since the purpose of this work was to investigate the interaction 
of an electrode-hydrazine system relative to the thickness of the 
oxide film, it proved necessary to choose a method of electrode prep- 
aration so that at the initial moment the surface was as close as 
possible to a metal surface free of oxide film. 
The electrodes were subjected to mechanical trimming and chemical 
treatment in hat solutions of 1 N  sodium hydroxide (10 min) and 2 N  
sulfuric acid (2 min) [l]. Then the electrode was smoothed off with 
powdered glass, transfered to a cell, and subjected to electrochemical 
treatment in 0 . 1 N  sodium hydroxide by a 20 mA cathode current with 
simultaneous passage of argon. 
The study was conducted using the familiar method, described in [ 2 ] .  
*Numbers in the margin indicate pagination in the foreign text. 
1 
T o  s tudy  t h e  processes  t a k i n g  p l a c e  w i t h  anode and cathode po la r -  
i z a t i o n ,  charg ing  cu rves  of a t i t an ium e l e c t r o d e  i n  0.1N s o l u t i o n s  of 
sodium hydroxide,  s u l f u r i c  a c i d ,  and sodium s u l f a t e w e r e p l o t t e d  (F ig .  1). 
These e l e c t r o l y t e s  have a 
t i t a n i u m  [ 3 ] .  
very  small d i s s o l v i n g  power r e l a t i v e  t o  
Fig.  1. Charging cu rves  
of t i t a n i u m  e l e c t r o d e  
i n  v a r i o u s  media: 
1 -- Na2.504; 2 -- H2SO4; 
3 -- N a O H .  
The  i n i t i a l  anode branch of t h e  char-  
g ing  curve i s  c h a r a c t e r i z e d  by a r a p i d  
s h i f t  of p o t e n t i a l  i n  t i m e .  This  i s  e v i -  
dence t h a t  i n  t h i s  s e c t i o n  t h e r e  i s  only  
su r face  charge t r a n s f e r .  A s l o w  change 
i n  p o t e n t i a l  i s  c h a r a c t e r i s t i c  of  t h e  nex t  
s ec t ion .  This  change of  p o t e n t i a l  can be 
explained by t h e  f a c t  t h a t  p rocesses  of  
both oxide-fi lm growth and formation o f  /lo9 
oxides  of  d i f f e r e n t  composi t ions are 
t ak ing  p l a c e .  
The a u t h o r s  of [ 4 ,  51 suggest  t h a t  i n  t h i s  i n t e r v a l  of p o t e n t i a l s  
t h e r e  i s  formation of T i 2 0 3  ox ide  and i t s  f u r t h e r  o x i d a t i o n ,  according 
t o  r e a c t i o n :  
Ti&+R$ 7 T i % + 2 @ + l . I  
A "p la t eau"  appears  a t  a p o t e n t i a l  of  2 V ,  i . e . ,  t h e  p o t e n t i a l  
no longe r  degends on t h e  amount of e l e c t r i c i t y  passed through,  b u t  
no release of molecular  oxygen was observed.  This  d e l a y  is expla ined  
by t h e  p rocess  of  anodiza t ion  -- accumulation of an  oxide f i l m .  
An ab rup t  p o t e n t i a l  change i s  i n i t i a l l y  observed when t h e  cathode 
charg ing  curve i s  p l o t t e d .  I n  t h i s  p o t e n t i a l  r eg ion  t h e  oxide  f i l m  
i s  reduced a t  h i g h e r  cathode p o t e n t i a l s .  
A s  F ig .  1 shows, t h e  charging cu rves  of t h e  t i t a n i u m  e l e c t r o d e  
i n  d i f f e r e n t  media are no t  s u b s t a n t i a l l y  d i f f e r e n t .  This  a l lows  t h e  
sugges t ion  t h a t  t h e  medium's pH has no s i g n i f i c a n t  e f f e c t  on t h e  pro- 
cess of ox ide  l a y e r  formation w i t h  anode p o l a r i z a t i o n .  
2 
The value of the initial electrode potential at which hydrazine /110 
was put on the electrode to study electron-adsorption interaction was 
chosen through 200 mV on the charging curve. By changing the initial 
potential by 200 mV we changed the strength of the oxide film on the 
electrode and the surface charge. 
When hydrazine was introduced on the titanium electrode in an 
acid medium, we observed a sharp displacement of potential toward 
the cathode side. As shown by oscillographic study, the rate of poten- 
tial displacement is not a constant value and depends on the initial 
potential (Fig. 2). 
Fig. 2. Effect of Eo 
on the kinetics of 
potential displace- 
ment upon contact 
between hydrazine and 
titanium electrode 
in 0.1N H2S04. 
As Fig. 2 shows, upon contact with 
hydrazine the electrode potential shifts 
fairly abruptly toward the cathode side, and 
in 2-3  min an oxidation-reduction potential 
is established. The final value of the poten- 
tial of the titanium electrode in hydrazine 
solutions is approximately the same in 
different solutions, -0.21 - 0.24 V, and does 
not depend on the initial electrode potential. 
When studying the kinetics of oxidation- /111 
reduction potential establishment on a titanium 
electrode in hydrazine solutions, we have to 
note a fairly good convergence of the adsorp- 
tion parts of the potential displacement curves when the substance 
comes in contact with the electrode. This phenomenon is not observed 
with potential displacement produced by electrochemical interaction 
between alcohols and a platinum electrode. 
It seemed interesting to study the behavior of hydrazine at initial 
potentials whose values were more cathodal than the establishlng poten- 
tial. When the potential displacement was found using a potentiometer, 
the potential was found to shlft toward the anode side. But use of 
the oscillographic method revealed that the potential shifts toward 
3 
. 
the cathode side, with oscillographic return to the anode region. 
Thus, at any initial potential values, there is hydrazine oxidation, 
the electrode potential shifts to the cathode side, and the final po- 
tential is determined by the relationship of the oxidized to the 
reduced form of hydrazine. Experiments performed in decinormal solu- 
tions of sodium sulfate and sodium hydroxide produced similar results. 
Oscillographic study of the kinetics of potential shift revealed 
that when the initial electrode potential shifts toward the anode side 
we observe an increase in 
3 )  - 
t.V . 
Fig. 3 .  Effect of Eo 
on rate of potential 
shift upon contact of 
hydrazine with titanium 
electrode in different 
media: 
1 -- NaOH; 2 -- Na2S04; 
3 -- H SO 2 4 '  
the rate of electrochemical interaction (Fig. 
When the initial potential is increased, 
an oxide film of variable composition accumu- 
lates on the electrode. Furthermore, there 
is adsorbed oxygen on the metal's surface. 
Potential displacement toward the cathode 
side may be explained by electrochemical 
removal of oxygen from the electrode's sur- 
face [6] and chemical interaction between 
hydrazine and surface oxygen compounds, since 
hydrazine solutions have reducing properties 
[ 7 1 .  
The presence on the surface of the elec-/112 
trode of non-stoichiometric oxides that are 
n-type semiconductors [8], which do not block the surface of the elec- 
trode, may lead to electronexchangebetween the molecules of hydrazine 
and the electrode. The increase in the potential displacement rate 
is explained by different energy-level differentials in the molecule 
and in the metal. 
In this case a phenomenon occurs where the increase in the rate 
of electrochemical interaction is determined by the accumulation of 
film on the electrode's surface. But in this case it is impossible 
4 
to decide the question in favor of merely electrochemical interaction. 
As mentioned above, the nature of the titanium electrode's poten- 
tial shift upon contact with hydrazine depends very little on the 
medium. The increase in the rate of potential fall-off with shift in 
the initial potential to the anode region is similar in acid and neutral 
media (Fig. 3). The slope of the curve for an alkaline medium is more 
abrupt. The obtained data confirm the stated hypothesis of the formed 
oxide film's lack of dependence on medium pH. The rate increase upon /113 
transition to an alkaline medium can be explained by a parallel reac- 
tion -- oxidation by OH- radicals. 
Conclusions 
The kinetics of the establishment of the oxidation-reduction 
potential of a titanium electrode upon contact with hydrazine was 
studied in different media. 
It was revealed that the nature of the potential displacement 
depends little on the medium. The initial potential determines the 
rate of potential displacement upon contact with hydrazine, which is 
explained by the different condition of the electrode's surface. 
5 
REFERENCES 
1. Kolotyrkin, Ya. M., and T. S. Petrov, Zh. fiz. khimii 31, 659 (1957). - 
2. Korolev, A. K., in Nekotoryye problemy sovremennoy elektrokhimii. 
Uchen. zap. DVGU [Some Topics in Modern Flectrochemistry. Scien- 
tific Inquiries of the Far East State Universitvl. vol. 15. ..-. 
Vladivostok, 1968, p. 39. 
3. Speranskaya, Ye. F., Ye. F. Mertsalova, I. I. Kulev, Uspekhi khimii 
- 3 9 ,  2129 (1966). 
4. Kuznetsova, Ye. G.,G. I. Borisova, V. I. Veselovskiy, Elektrokhimiya 
- 4 ,  167 (1968). 
5. Shub, D. M., A .  A. Remneyev, V. I. Veselovskiy, Elektrokhimiya 9, - 
676 (1973). 
6. Kuznetsov, G. A., A. A. Levchenko, A. K. Korolev, in Sovremennyye 
aspekty elektrodnykh protsessov [Modern Aspects of Electrode 
Processes], vol. 103, Vladivostok, 1975, p. 41. 
7. Korovin, V. N., and A. G. Kicheyev, Elektrokhimiya 6, 1330 (1970). 
8. Krylov, 0 .  V., Kataliz nemetallami [Catalysis by Non-metals], 
- 
"Khimiya" Press, Leningrad, 1967, p.  4 4 .  
6 


Electrochemical behavior of a titanium electrode in hydrazine solutions

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