Electron beam technique and its application to electrolysis of solid salts and ceramic

Brenner, A.

Sligh, J.

English

NASA Technical Reports Server

3120463 June 1, 1966 
ELP,CTRO$? SEAM ELECTRQLYSIS 
by 
Abner Brenner and John Sl igh  
9331 
SECOND QUARTERLY STATUS REPORT 
February 15 - May 15, 1966 
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 
Contract No. R-09-022-052 
November 15, 1965 - _  - _  
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ELECTRON BEAM ELECTROLYSIS 
I. INTRODUCTION 
This period w a s  spent i n  dealing with various problems encoun- 
te red  i n  the  attempt t o  apply the technique t o  the  e l e c t r o l y s i s  of 
s o l i d  salts and ceramics. The earlier experiments w e r e  made with 
mainly a few salts (fused and then so l id i f i ed )  which, because of 
t h e i r  exce l len t  conductivity and ce r t a in  other  physical  propert ies  
(such as t h e - p l a s t i c i t y  of s i l v e r  chlor ide) ,  enabled them t o  be  
e lectrolyzed by the  e lec t ron  beam method without d i f f i c u l t y .  
I 
The d i f f i c u l t i e s  encountered in  the  attempts t o  e lec t ro lyze  
the  ceramics and o the r  s o l i d  salts  showed t h a t  the technique needed 
t o  be developed fur ther .  
leakage, lack  of conductivity,  arcing-through, sho r t  c i r c u i t i n g  
through cracks, poor electrical contact of the anode lead, and 
cas t ing  fused salts (which m e l t  a t  a high temperature) i n t o  a-crack- - 
f r e e  p l a t e  s u i t a b l e  f o r  e lec t ro lys i s .  
Some of the problems were electrical 
4 
11. ELECTRICAL LEAKAGE 
The first problem encountered w a s  electrical leakage between 
t h e  heated tungsten filament and the anode lead,  which usual ly  w a s  
a platinum w i r e .  This amounted t o  a shor t -c i rcu i t ,  since the  cur- 
’ 
r en t  took t h i s  path instead of flowing through the more poorly 
conductive s o l i d  fused salt or ceramic. The d i f f i c u l t y  w a s  reme- 
died by placing a ceramic tube over the  lead-wire up t o  the  point 
, 
where t h e  lat ter contacted the electrolyzable  material. Further- 
more, t h e  la t ter  w a s  surrounded by a ceramic tube which extended 
beyond the  point  where the  lead wire w a s  connected t o  it. 
I 
1x1 OBTAINING PLATES OF SOLID SALTS 
For t h e  e l e c t r o l y s i s  experiments, it would be i d e a l  t o  have a 
p l a t e  of t h e  e lec t ro lyzable  material about 1 mm i n  thickness and 
4 c m  i n  area. These w e r e  d i f f i c u l t  t o  prepare from fused sal ts  2 
t because of t h e i r  contract ion on cooling. For example, t he  cas t ing  
of t h e  fused salt  around a platinum p l a t e ,  which w a s  t o  serve as 
anode connection, usual ly  r e su l t ed  i n  numerous cracks in t h e  sal t .  
Casting around a platinum w i r e  o r  dipping the  w i r e  a number of times 
in t h e  molten m e l t  t o  bu i ld  up a deposit  did not  y i e ld  a sound ma- 
terial. 
The ex is tence  of cracks i n  t h e  e l e c t r o l y t e  w a s  indicated by 
the  immediate flow of current  t h a t  resu l ted  i n  the  e l ec t ron  beam 
apparatus while the  specimen w a s  still  cold and, hence, not conduc- 
tive. 
d i t ions .  As t h i s  specimen gradually became heated by the fi lament 
A sound specimen allowed no current  t o  flow under these  con- 
4 
(or an aux i l i a ry  hea ter )  i t  gradually became conductive and i n  a 
f e w  minutes a small cur ren t  began to  flow and increased up t o  a 
value of from 50 t o  100 ma.  
The b e s t  procedure f o r  obtaining sound specimens of a sa l t  w a s  
t o  cast the  molten sa l t  i n t o  an evaporating dish o r  cassero le  l ined  
with a t h i n  sheet  of metal ( for  example. s t a i n l e s s  steel 0.02 mm 
2 
thick)  and allow the  sa l t  t o  cool slowly i n  the  furnace. 
shee t  of metal deformed with the  salt and prevented the  la t ter  from 
developing tension-cracks. 
sawed from t h e  mass. 
IV. HEATING THE ELECTROLYTE 
The t h i n  
A specimen f o r  e l ec t ro lys j s  was then 
i 
To obta in  e l e c t r o l y s i s  of so l id  e l ec t ro ly t e s ,  t h e  lat ter m u s t  
be  heated up t o  a temperature a t  which they become a t  least moder- 
a t e l y  conductive. For example, glass  needed t o  be heated t o  400' 
o r  500OC. I n  t h e  earlier experiments, t he  heating w a s  derived from 
t h e  fi lament which w a s  placed about 1 c m  d i s t a n t  from the  e lec t ro-  
l y t e .  
s u f f i c i e n t l y  conductive, and t h e  temperature a t ta ined  was about 40O0C. 
About f i v e  minutes w e r e  required f o r  the  e l e c t r o l y t e  t o  become 
However, ceramics need a higher temperature than a sal t  t o  be- 
come conductive and an independent source of hea t  w a s  necessary. 
F i r s t ,  induction heating with a cy l ind r i ca l  susceptor of graphi te  
w a s  t r i e d ,  but  t h e  magnetic f i e l d  of t h e  c o i l  d i ss ipa ted  the  elec- 
t r o n  beam, and cur ren t  ceased t o  flow as soon as the  induction u n i t  
w a s  act ivated.  A wire-wound res i s tance  hea ter  with the  axis of 
t h e  c o i l  p a r a l l e l  t o  the  d i r ec t ion  of t h e  beam had t h e  same e f f e c t  
of d i s s ipa t ing  t h e  e l ec t ron  beam. Awire-wound resistance element * 
which d id  not i n t e r f e r e  with t h e  e lec t ron  beam w a s  produced by wind- 
4 
i ng  t h e  w i r e  on a cyl inder  with the w i r e s  p a r a l l e l  t o  t he  axis of 
t h e  cyl inder  and, hence, t o  the  e lec t ron  beam. Nichrome w i r e  w a s  
used for temperature up to 100O'C. Higher temperatures w e r e  obta ined  
3 
, 
i 
I 
I 1 
by winding t h e  hea ter  with tungsten w i r e .  
employing a noninductive winding, w i l l  be t r i e d  on ceramic cyl inders  
provided with a double thread. 
Another type of hea te r ,  
V. ARCING THROUGH 
I n  experiments with the  less conductive e l ec t ro ly t e s  and 
ceramics, a t  f i r s t  no current  flowed, but as the  specimen became 
heated a gradually increasing current developed. After  a period 
of a few minutes t o  10  minutes a sudden heavy current  flowed and 
a sparking w a s  observed, ind ica t ing  t h e  per fora t ion  of the  electro4 
ly t e .  W e  be l ieve  t h a t  t h e  a rc ing  through is owing t o  the  poor 
electrical contact  t o  the  anode lead. W e  envision t h a t  t h e  anode 
lead  made electrical contact with the  e l e c t r o l y t e  at  perhaps only 
one point. 
l o c a l  overheating which s t i l l  fur ther  increased t h e  cur ren t ,  which 
later formed an arc through the  e l e c t r o l y t e  as a r e s u l t  of the  h'igh cur- 
r a n t  dens i ty  and high vol tage applied between the  conducting poin t  
and t h e  filament. 
The flow of a l l  t h e  current  a t  t h i s  one point  caused 
VI. ELECT~CAL CONNECTION OF ELECTROLYTE TO ANODE LEAD 
The experience with arcing-through indicated t h a t  the  connec- 
t i o n  of t h e  e l e c t r o l y t e  with the  anode lead  w a s  t h e  most important 
problem t o  be solved. I n  t h e  earlier experiments with ch lor ide  
salts which had low melting poin ts  and, hence, a f a i r  conductivity 
a t  t h e  temperature obtained with the tungsten fi lament alone, a 
corrodible  w i r e ,  such as copper o r  n icke l ,  served as anode lead. 
* 
4 
But the  d i r e c t  metallic connection did not s e e m  t o  be adequate 
with e l ec t ro ly t e s  of high melting point o r  ceramics. 
Some experiments with attempted e l e c t r o l y s i s  of a glass test 
tube indicated t h e  importance of the contact  of the anode lead. 
The i n t e r i o r  of the tube was metall ized with a gold f r i t  i n  one ex- 
periment and with silver f r i t  i n  another and connection made t o  the  
b 
m e t a l  f i lms with a platinum w i r e .  
through occurred with the gold film, which sloughed from the g lass  
Poor conduction and arcing- 
i n  a few minutes. Some conduction f o r  f i v e  minutes w a s  obtained 
with the  s i l v e r  fi lm, but  the current gradually dropped t o  zero and 
f i n a l l y  arcing-through occurred. 
r e s u l t s  is the forxuation,of highly resistive l aye r  of s i l i c o n  next 
The probable explanation of these 
t o  t h e  m e t a l .  This is known t o  occur i n  t h e  e l e c t r o l y s i s  of g lass  
by conventional m e a n s .  
W e  in tend t o  check t h i s  hypothesis by e lec t ro lyz ing  the  g lass  
while i n  contact with a molten salt ,  which is t he  technique t h a t  
w a s  described i n  the  l i t e r a t u r e  i n  connection with the  well-known 
light-bulb experiment. 
-4 
If t h i s  experiment confirms the  hypothesis, 
then electrical connections t o  t h e  high melting point  ceramics and 
s o l i d  salts w i l l  be  made via a molten e l ec t ro ly t e ,  or a s o l i d  elec- 
t r o l y t e  which is eas i ly  cast on the specimen of i n t e r e s t ,  o r  a low- 
melting glass .  
5 


Electron beam electrolysis Second quarterly status report, Feb. 15 - May 15, 1966

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