0001_j. electrochem. soc.-1964-threadgill-1408-11.pdf

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1408

JO U RN A L O F T H E E L E CT RO CH E M I CA L SO CI E T Y

December 1964

C U B IC U C 2 + C ~ C + C U B IC G d C2

T E T R A G O N A L

UC2+C ~ ~ /

A O O

*C

TETRAGONALUC2--~ ;A ~ \ / L ~ ~ / J \ \ \

~oo~ ~ / / / ~ ~ ~ \ ~ o o

( UO.glGdo.09)2C5+ (UO.12Gdo,8s) 2+ C

1300 (; ISOTHER MAL SECTION

Fig. S. P erspective draw ing of the h igh carbo n portion of the

U Gd C tern ary system.

position curve intersects the 1300~ isoth ermal plane

(Fig. 5) the tie-triangles connect the phases (U0.91

Gd0.09 2C3 t- cubic (U,Gd)C 2 + C. Fro m Fig. 2 it is

seen that the cubic (Gd,U)C2 phase must also undergo

a ternary eutectoid decomposition below 1300~

Figure 5 shows a perspective view of the equil ibr iu m

phases associated with the decomposition curve. The

base represents the high carbon portion of the 1300~

isothermal section of the U-Gd-C ternary.

C o n c l u s i o n s

From this study it was found that UC2 and GdC2

form a continuous series of solid solutions above 1785~

with the solid solution solidus and carbon eutectic

temperatures decreasing in a regular manner f rom the

UC2 boun dary to the GdCs boundary. Along the line

which lies betw een UC2 (1785~ and appr oxi matel y

(U0.sGd0.2)C2 (1510~ th ere is a tw o- ph as e re gi on

that connects solid solution regions of tetragonal-

(U,Gd)Cs and cubic-( U,Gd)C2. Below 1525~ there

is a decomposition curve below which the UC2-GdC2

solid solution is unstable. The decomposition curve

progresses from the UC2 boun dary (1525~ to a com-

po si ti on of (U0.1sGd0.ss)C2 at 1300~

The tetragonal to cubic transformation curve of the

UCs-GdC2 solid solution decreases as one moves from

both boundaries indicating that

AFM ->c

is negative.

Further , the course of the To curve may be used to

make thermodynamic approximations on var ious prop-

erties of the solid solution region.

A c k n o w l e d g m e n t s

The authors gratefully acknowledge the advice and

support of Dr. Melvin G. Bowman during the course

of this work. Acknowledgment is also made of the

work of membe rs of Group CMB-1 of this Laborat ory

for the chemical analyses and Mrs. M. J. Ulery for

reading the x-ray diffraction patterns. Thanks are due

to Willard G. Witteman and Charles Radosevich for

assistance in obtaining the transformation curves.

Without the ingenuity of Mr. George N. Rupert in de-

signing and building the thermal analysis apparatus

used, the work on the transformation temperatures

could not have been performed. Finally, the help of

Dr. Allen L. Bowman and Mr. Paul McWilliams is

acknowledged for the programming and computing of

the results obtained from Eq. [2].

Manuscript received May 7, 1964. Work performed

under the auspices of the United States Atomic Energy

Commission.

Any discussion of this paper will appear in a Discus-

sion Secti on to be pub lis hed in the Ju ne 1965 JOURNAL.

REFERENCES

1. S. Langer, General Atomics Report, GA-4450, Sep-

tember 5, 1963.

2. W. G. Witteman and M. G. Bowman, To be pub-

lished.

3. F. Spedding, K. Gschneider, and A. Daane, J. Am.

Chem. Soc. 80, 4499 (1958) .

4. J.M. Leitnaker, M. G. Bowman, and P. W. Gilles,

J. Chem. Phys. 36, 350 (1962).

5. G. N. Rupert, Rev. Sci. Instr., 34, 1183 (1963).

6. G. N. Rupert, To be published.

7. O. H. Kriege, Los Alam os Scientific Laborat ory

Report LA-2306, March 1959.

8. J. B. Hess,

Acta Cryst.

4, 209 (1951).

9. A. L. Bowman, W. G. Witteman, G. P. Arnold, and

N. G. Nereson, To be published.

10. Roger Chang, Acta Cryst. 14, 1097 (1961).

11. Larr y Kauf man and Morris Cohen, Ther mod y-

namics and Kinetics of Martensit ic Transforma-

tions, in Prog ress in Metal Physic s, 7, 167,

Pergamon Press, New York (1958).

12. L. S. Levinson, J. Chem. Phys. 38, 2105 (1963).

13. K. K. Kelley,

Contribution to the data on theoretical

metallurgy XIII , High-Temperature Heat Con-

tent , Heat-Capacity, and Entropy Data for the

Elements and Inorganic Compounds, Bullet in

584 (1960).

14. Max Hansen, Consti tution of Binary Alloys, p.

387, McGraw-Hill Book Co., Inc., New York

(1958).

15. F. N. Rhines, Phas e Diagrams in Metallur gy, Their

Devel opme nt and Applications, Chap. 14, Mc-

Graw -Hil l Book Co., Inc., New York (1956).

P r e p a r a tio n o f M e t a l l ic C a l c iu m b y E le c t ro l y s is o f

C a lc i u m O x i d e D i s s o lv e d in M o l te n C a l c i u m C h l o r id e

W . D . T h r e a d g i l l

Depart ment of Chemical Engineering Vanderbilt University Nashville Tennessee

ABSTRACT

Metallic calcium was prepared by electrolysis of calcium oxide dissolved

in molten calcium chlor ide in a modif ied moving cathode-type cell . For com-

parison, control electrolyses of the chloride were made. Average cell voltage

with the oxide -bearing electrolyte ranged up to 23% less than that with the

chloride alone. The oxide content of the electrolyte decreased due to electrol-

ysis, and tests showed that chlorine was not released at the anode. This appears

to be the first demonstration that calcium oxide can be fed to a chloride elec-

trolyte for calcium production.

The first exp erime nts of record with a fused elec- commer cial prepa ratio n of man y metals. The processes

trolyt e were made by Sir Hum phr ey Davy (1) in 1802. and equi pment used show wide var iatio n because of

Subse quen t to his time, the electrolysis of fused salts depend ence on the specific characteristics of each

has been used as a metho d for either the discovery or metal and its electrolyte.

) unless CC License in place (see abstract).ecsdl.org/site/terms_useaddress. Redistribution subject to ECS terms of use (see 193.205.210.45Downloaded on 2014-09-19 to IP

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2/4

Vol . 111 No . 12 PRE PA RA T I O N O F

of the ear l ier investigations (2-8) concerned with

the electrolytic production of calcium, probably the

greatest advancement was made in 1904. At this time

Rath enau (9) described a metho d of drawi ng out the

calcium metal in the form of a rod attached to the

cathode. The follo wing year Go odwin (10) describ ed a

similar apparatus. Subsequent to this time, several in-

vestigators (11-16) have made various changes and im-

provements in the apparatus of Goodwin and Rath-

enau

The energy consumption of calcium is high compared

to other products in the fused electrolyte industry.

Mantell (17) gives the averag e energy consumption of

calcium as 23 kw hr /l b as compared to 9 for alumin um,

8 for magn esiu m (chloride process), and 5.2 for sodium.

According to Mantell (18) , var iat ion in energy con-

sumption for any one process is due to size of the cell,

details of construction and insulation of the cell, and

length of time the cell is operated before changes need

to be made either in the electrolyte, the cell proper, or

the electrical connections.

Johnson (19) lists the factors which influence the

decomposit ion voltage of the electrolyte as chemical

composition, temperatu re, natu re of the electrodes, and

their geometr ical disposit ion with respect to each

other. Lorenz (20) and Broc kma n (21) summa rize the

conditions affecting the curre nt y ield at the cathod e as

temperature, distance between electrodes, current den-

sity, secondary chemical reactions at the electrodes,

and formation of metallic fog.

Collection of the calcium metal produced is much

more difficult than that of any other metal made com-

mercially by fused salt electrolysis. Calcium metal

floats on top of the bath, is active and soluble in the

electrolyte, and cannot be protected by a film of the

melt held over it by surface tension. If allowed to re-

main in contact with the electrolyte for any length of

time, it will be converted back to the chloride or the

oxide due to the circulation of the bath which car-

ries the dispersed metal into the gas producing area

around the anode, or it will burn due to atmospheric

oxygen. Consequently, it is necessary to use a con-

tact cathode, that is, one that just touches the bath

surface. The cathode is raised gradually as the metal

is collected and a solid stick or carrot obtained.

The decomposition voltage of calcium chloride is

reported as 2.04-3.24v (14, 18, 22, 23) with the com-

monly accepted value being 3.2v. Taking the value as

3.2v, the voltag e efficiency calculated from the opera t-

ing voltages reported by various investigators is 10.3-

20%. German industr ial practice has been reported

as 25v per cell (17), which represents a voltage effi-

ciency of 12.8%.

No information was found in the l i terature on the

decomposit ion voltage of a calcium chlor ide-calcium

oxide mixture.

Investigations of calcium production by use of mixed

electrolytes have generally been l imited to mixtures of

the chloride and the fluoride. Johnson (14) and Frary

(24) both ex perien ced difficulty with such an elec-

trolyte due to its low melting point.

A p p a r a t u s

The modified movi ng cathode type cell used in this

investigation is shown in Fig. 1. The container and

anodes (not shown) were of graphite. The cathode

consisted of a 1- in. diameter water-cooled aluminum

bar with a removable 1-in. diameter iron tip. Tem-

perature measurements were made with a bare

chrome l-alum el thermocoupl e immersed in the elec-

trolyte. A direct-current welding generator was used

as the source of current.

C e l l O p e r a t io n

The electrolyte was brought to approx imately the

desired operating temperature by external heating.

The anode was immersed in the electrolyte and an arc

struck between the cathode and the electrolyte in or-

der to heat the t ip momentar i ly above the melt ing

M E T L L I C C L C I U M

1409

F i g . 1 . E l e c t r o ly t ic c e l l a n o d e s n o t s h o w n )

point of calcium metal. Without this heating, the metal

would not wet the cathode surface except in spots.

Adjustment of the cathode was then made to effect

good operation.

Generally, operation was unsteady for a period of

5-10 rain at the start of electrolysis. Current and volt-

age fluctuated, and the electrolyte temperature in-

creas ed fro m 25 ~ to 50~

During normal operation, the heating effect of the

electrol yzing curren t was sufficient to keep the tem-

perature fair ly constant (•176 The cathode was at

the center of an ir regular br ight rosette with radial

markings formed by currents of hot electrolyte moving

away from it . Normal operation was maintained by

raising or lowering the cathode in such a manner that

this rosette was kept at approximately the same size

and color. The calcium metal could be observed in a

molten condit ion just underneath the bath surface and

was drawn out in good solid form covered by a thin

film of frozen electro lyte.

When the electrolyte tempera ture arou nd the cathode

was allowed to become too low by raising the cathode

too slowly, metal was depos ited in a spongy form

with branches of much t he same appearan ce as moss

or fern. These branches were easily dislodged by con-

vection currents. A low bath temperature required

more rapid raising of the cathode in order to control

the cathode temperature, and a smaller diameter car-

rot resulted.

When the electrolyte tempera ture around the cathode

was allowed to become too high as a result of too

rapid raising of the cathode, the protecting film of

frozen ele ctrolyt e melte d and draine d off. A globule of

molten metal formed underneath the cathode and

s~metimes broke away due to the influence of convec-

tion currents. When this occurred an arc was struck

between the bath surface and the remaining st ick of

metal thereby causing the metal to melt rapidly and

to be lost or, in extreme cases, even to be ignited.

If the electrolyte contained moisture, normal opera-

tion was impossible to achieve at the start of electrol-

ysis. No metal deposited on the cathode, and there was

a continuous burning of gas at the cathode, such gas

burn ing w ith a yello w flame. This beha vior has been

explained by previous investigators as being due to

electrolysis of the water contained in the electrolyte.

Generally, the evolution of gas ceased after a few

minutes ' operation and normal operating condit ions

could then be effected.

If the graphite powder which formed a scum on the

bath surface was not removed occasionally and was

allowed to come in contact with the molten metal ,

flames at the cathode resulted, suggesting that pos-

sibly the graphite was reacting with the metal . Occa-

sionally, a f roth would also form depending on wheth er

the electrolysis contained moisture.




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1 4 1 0

J O U R N A L O F T H E E L E C T R O C H E M I C A L S O C I E T Y

December 1964

C a t h o d e c u r r e n t d e n s i t y s e e m e d t o b e o f i m p o r t a n c e

o n l y in s o f a r a s i t a f f e c te d t h e c a t h o d e t e m p e r a t u r e . I n

t h i s r e s p e c t , F r a r y ( 13 ) c o n s i d e r e d t h e a l l o w a b l e a n d

m o s t s a t i s f a c t o r y c a t h o d e c u r r e n t d e n s i t y t o b e a c o n -

s t a n t f o r a n y p a r t i c u l a r c e l l a n d n o t o f t h e p r o c e s s

i ts e lf . A n o d i c c u r r e n t d e n s i t y s e e m e d o f n o g r e a t i m -

p o r t a n c e e x c e p t w i t h a n e l e c t r o l y t e o f c a l c i u m c h l o -

r i d e a l o n e . I n t h i s c a s e , o c c u r r e n c e o f t h e s o - c a l l e d

a n o d e e ff e c t w a s p r o m o t e d b y h i g h e r c u r r e n t d e n -

s i t i e s .

D u r i n g e l e c t r o ly s i s w i t h c a l c i u m a l o n e , t h e r e w a s

v i g o r o u s e v o l u t i o n o f g a s a t t h e a n o d e . T h e s p a t t e r i n g

o f e l e c t r o l y t e c a u s e d b y t h i s e s c a p i n g g a s w a s s u f f i c i e n t

t o c o a t th e e x p o s e d p o r t i o n s o f t h e c e l l a n d p r o t e c t

i t f r o m r a p i d a t t a c k b y t h e a t m o s p h e r e . A m u c h l e ss

v i g o r o u s e v o l u t i o n o f g a s o c c u r r e d w i t h t h e o x i d e -

b e a r i n g e l e c t r o ly t e . A n o d i c a t t a c k w a s l e ss w i t h t h e

c h l o r i d e e l e c t r o l y t e a l o n e th a n w i t h t h e e l e c t r o l y t e

c o n t a i n i n g o x id e . A s i n t h e a l u m i n u m i n d u s t r y ( 2 5 ) ,

h i g h e r f u r n a c e t e m p e r a t u re s c a u s e d m o r e r a p i d c o n -

s u m p t i o n o f t h e a n o d e .

A t r o u b l e s o m e p h e n o m e n o n , k n o w n a s a n o d e e f fe c t,

c a u s e d c o n c e r n a m o n g p r a c t i c a l l y a l l p e r s o n s w h o h a v e

p r e p a r e d c a l c i u m b y e l e c tr o l y s is . T h i s p h e n o m e n o n

m a n i f e s t s i t s e l f i n a s u d d e n i n t e r r u p t i o n o f n o r m a l

o p e r a t i o n . T h e v o l t a g e i n c r e a s e s m a r k e d l y a n d t h e

c u r r e n t d e c r e a s e s t o a l m o s t z e r o . A g a s f i lm is f o r m e d

a r o u n d t h e a n o d e , a n d t h e e l e c t r o l y t e i s p r e v e n t e d

f r o m w e t t i n g t h e a n o d e s u r f a c e . T h i s f i lm g l o w s w i t h

a b l u i s h c o lo r , a n d t h e c u r r e n t s e e m s t o p a s s f r o m t h e

a n o d e t o t h e e l e c t r o l y t e b y a s e r i e s o f s m a l l a r c s. T h e

a n o d e i t s e lf s o on b e c o m e s r e d h o t. N u m e r o u s a t t e m p t s

( 13 , 20 , 2 6, 2 7 ) h a v e b e e n m a d e t o e x p l a i n t h i s p h e -

n o m e n o n .

I n t h e c o u r s e o f t h i s i n v e s t i g a t i o n , t h e a n o d e e f f ec t

o c c u r r e d q u i t e r e a d i l y w i t h c a l c i u m c h l o r i d e a l o n e .

T e m p e r a t u r e o f t h e b a t h s e e m e d t o h a v e n o e f f e c t o n

i ts o c c u r r e n ce . T h e l a r g e r t h e a n o d e s u r f a c e e x p o s e d

t o t h e e l e c t r o l y t e t h e m o r e d i f f ic u l t i t w a s t o i n d u c e

t h e e f fe c t. T h e e f f e c t c o u l d b e e l i m i n a t e d t e m p o r a r i l y

b y m o m e n t a r y i n t e r r u p t i o n o f c u r r e n t , r e d u c t i o n i n

a p p l i e d v o l t a g e , o r m e c h a n i c a l s h a k i n g o f t h e a n o d e .

N o d i f f i c u lt y w a s e x p e r i e n c e d w i t h a n o d e e f f e c t w h e n

u s i n g t h e e l e c t r o l y t e c o n t a i n i n g o x i de . A s l o n g a s

n o r m a l o p e r a t i o n h a d s t a r t e d , l a r g e c u r r e n t s w o u l d

n o t c a u s e t h e e f f e c t t o a p p e a r . O n e r e f e r e n c e ( 2 7 ) w a s

m a d e i n t h e l i t e r a t u r e t o t h e f a c t t h a t c a l c i u m o x i d e

w o u l d i n h i b i t t h i s ef f ec t . T h i s w a s a t t r i b u t e d t o a

c l e a n a n o d e s u r f a c e s in c e th e o x y g e n l i b e r a t e d c o m -

b i n e s w i t h t h e c a r b o n a n d i t i s t h u s e t c h e d a n d a

n e w s u r f a c e i s c o n t i n u a l l y b e i n g f o r m e d .

R e s u l t s

T a b l e I c o n t a i n s t h e r e s u l t s o f t h e e l e c t r o l y s i s o f

e l e c t r o l y te s o f c a l c iu m c h l o r i d e a l o n e a n d c a l c i u m

o x i d e in c a l c i u m c h l o r i d e . R u n s w e r e m a d e a t s e v e r a l

t e m p e r a t u r e s a n d w i t h v a r i o u s c u r r e n t s i n t w o s iz e s

o f c e ll s . O x i d e c o n c e n t r a t i o n s f r o m 0 .2 6 t o 2. 0 0 % b y

w e i g h t w e r e u s e d i n t h e s e r u n s . T h e r u n s w e r e o f 2 0 -6 0

r a i n d u r a t i o n .

C a t h o d e c u r r e n t d e n s i t y c o u l d n o t b e c a lc u l a t e d

a c c u r a t e l y b e c a u s e t h e c a r r o t d i a m e t e r d i d n o t r e -

m a i n u n i f o r m t h r o u g h o u t t h e e le c t r o l y s is p e r io d . A p -

p r o x i m a t e v a l u e s w e r e i n t h e r a n g e 2 0 0- 3 00 a m p / i n . 2.

N u m e r o u s a d d i t io n a l r u n s w e r e m a d e w i t h o x i d e

c o n c e n t r a t i o n s i n th e r a n g e o f 2 - 1 2 % . A l l t h e s e r u n s

w e r e u n s u c c e s s f u l i n t h a t th e te m p e r a t u r e a r o u n d t h e

c a t h o d e c o u l d n o t b e c o n t r o l l e d . T h e m e l t w a s s o f lu i d

t h a t i t w a s i m p o s s i b l e t o k e e p a p r o t e c t i v e f i l m o f

f r o z e n e l e c t r o l y t e o n t h e m e t a l a s it e m e r g e d f r o m t h e

b a t h . W i t h o u t t h i s p r o t e c t i o n , t h e c a l c i u m w o u l d i g n i t e

a n d b e l os t . F l a m e s c o n t i n u a l l y b u r n e d a r o u n d t h e

c a t h o d e , a n d i t w a s n o t p o s s i b le t o e l i m i n a t e t h e m .

I n a n a t te m p t t o e l i m i n a t e t h e e x c e s s i v e b u r n i n g

a n d h i g h c o n v e c t i o n c u r r e n t s a r o u n d t h e c a th o d e , r u n s

o f u p t o 2 h r i n d u r a t i o n w e r e m a d e w i t h l o w e l e c -

t r o l y z i n g c u r r e n t s o f 2 5 -3 5 a m p a n d m a x i m u m c o o l in g

w a t e r f lo w . W h i l e t h i s r e d u c e d t h e i n t e n s i t y o f t h e

c o n v e c t i o n c u r r e n t s , t h e b u r n i n g w a s n o t e l i m i n a t e d ,

T a b l e I E l e c tr o ly s i s d a t a

CaCl~ electrolyte

A vg

A vg ce l l vo l t age

Temp, Curre nt voltage, eff iciency,

Cell s ize range, ~ range, amp v

7 1/16 in. I.D. 774-899 90-130 16.6 19.26

Two 3/4 in .

d i a. a n o d e s

7 1/16 in I.D. 800- 843 60-12 0 18 17.78

One 3/4 in .

dia. anode

4 1/2 in. I.D. 816-857 75-110 17 18.82

One 3/4 in .

dia. anode

CaO-CaCl~ electrolyte

O x ide

cone. Temp. Curre nt Avg cel l Decrease in

range, range, range, voltage, avg cel l

wt Cell s ize ~ amp v voltage,

0.68-1.34 7 1/16 in. I.D. 774-828 50-60 13.7 17.46-23.9

One 3/4 in.

dia. anode

0.67-1.90 4 1/2 in. I.D. 800-843 40-100 14.1 15.06-17.05

One 3/4 in .

dia. anode

0.26-2.00 4 1/2 in. I.D. 788-843 45-85 15.3 No com par abl e

One 1/2 in. data for CaCle

dia. anode alone

a n d o n l y i s o l a t e d p a r t i c l e s o f c a l c i u m c o u l d b e c o l -

l e c t e d . C e l l v o l t a g e r a n g e d f r o m 1 01 /2 t o 1 8v , a n d c u r -

r e n t r a n g e d f r o m 3 0 -9 0 a m p . T e m p e r a t u r e s w e r e i n

t h e r a n g e 7 74 ~ 1 7 6 D a t a o n a n u m b e r o f t h e s e u n -

s u c c e s s f u l r u n s m a y b e f o u n d i n re f . ( 2 8 ).

N e x t , r u n s w e r e m a d e w i t h t h e c a t h o d e s h i e l d e d a s

s u g g e s t e d b y K u n i t o m i ( 2 9 ) . B u r n i n g s ti ll p e r s i s t e d ,

a n d t h e s h i e l d r e s u l t e d i n a h i g h e r t e m p e r a t u r e

a r o u n d t h e c a t h o d e a n d a n i n c r e a s e i n c e l l v o l t a g e .

O x i d e c o n c e n t r a t i o n s f r o m 2 t o 1 0 w e r e u s e d .

S i n c e i t w a s o b s e r v e d t h a t o x i d e c o n c e n t r a t i o n s i n

t h e n e i g h b o r h o o d o f 1 5 g a v e a m o r e v i s c o u s m e l t , t h e

n e x t s t e p i n a n a t t e m p t t o e l i m i n a t e t h e a f o r e m e n -

t i o n e d d i f f i c u l t y w a s t o e m p l o y a n e l e c t r o l y t e w i t h

o x i d e c o n c e n t r a t i o n s i n t h i s r a n g e . I n g e n e r a l , c e l l

v o l t a g e s w e r e s i g n i f i c a n t l y h i g h e r t h a n t h o s e o b t a i n e d

w i t h o x i d e c o n c e n t r a t i o n s l e s s t h a n 2 . 0 . B u r n i n g

a r o u n d t h e c a t h o d e a n d c o n v e c t i o n c u r r e n t s w e r e l e s s

s e v e r e , b u t o n l y i s o l a t e d b r a n c h e s o f c a l c i u m c o u l d

b e o b t a i n e d .

I n a l l i n s t a n c e s , o p e r a t i o n w a s m o r e d i f f i c u l t w i t h

t h e e l e c t r o l y t e c o n t a i n i n g o x i d e t h a n w i t h t h e c h l o -

r i d e a l o n e . E x t r e m e c a r e w a s n e c e s s a r y i n c a t h o d e a d -

j u s t m e n t t o c o n t r o l t e m p e r a t u r e a r o u n d t h e c a t h o d e .

T h e c a l c i u m w o u l d i g n i t e q u i t e r e a d i l y w h e n t h e f i l m

o f f r o z e n e l e c t r o l y t e d r a i n e d a w a y , a n d i t w a s p r a c -

t i c a l l y i m p o s s i b l e t o e x t i n g u i s h i t a n d a g a i n e f f e c t

n o r m a l o p e r a t i o n . F o r t h i s r e a s o n a n d t h e g r e a t e r

t e n d e n c y t o w a r d s t r o n g e r c o n v e c t i o n c u r r e n t s , t h e u s e

o f l o w e r e l e c t r o l y z i n g c u r r e n t s w a s n e c e s s a r y .

T h e g a s e s e v o l v e d a t t h e a n o d e d u r i n g e l e c t r o l y s i s

o f t h e c h l o r i d e - o x i d e e l e c t r o l y t e w e r e t e s t e d f o r c h l o -

r i n e w i t h s t a r c h i o d i d e p a p e r . A f t e r s t e a d y o p e r a t i o n

w a s a c h i e v e d , t h i s t e s t w a s n e g a t i v e .

I n o r d e r t o v e r i f y t h e d e c r e a s e i n o x i d e c o n t e n t a s

a r e s u l t o f e l e c t r o l y s i s , a m e l t o f k n o w n o x i d e c o n -

c e n t r a t i o n w a s s u b j e c t e d t o e l e c t r o l y s i s . S a m p l e s o f

t h e m e l t w e r e t a k e n a t i n t e r v a l s a n d a n a l y z e d f o r

o x i d e c o n t e n t . I n a l l i n s t a n c e s , t h e o x i d e c o n c e n t r a t i o n

d e c r e a s e d d u r i n g e l e c t r o l y s i s .

Cat ciu ~ ch ~oride catciu~ S~uoride ca~cium oxide as

electrolyte. I t w a s t h o u g h t p o s s i b l e t h a t a d d i t i o n o f

t h e f l u or i d e t o t h e e l e c t r o l y t e m i g h t o v e r c o m e s o m e

o f t h e o p e r a t i n g d i f f ic u l ti e s e x p e r i e n c e d w i t h t h e o x i d e -

c h l o r i d e e l e c t r o l y te a n d , i n p a r t i c u l a r , p e r m i t o p e r a -

t i o n w i t h h i g h o x i d e c o n c e n t r a t i o n s b y p o s s i b l y d e -

c r e a s i n g t h e p a s t i n e s s o f t h e m e l t . H o w e v e r , p r e l i m -

i n a r y r u n s w i t h t h i s e l e c t r o l y te i n a n e w a p p a r a t u s

w e r e u n s u c c e s s f u l d u e t o o p e r a t i n g d i ff i cu l ti e s w i t h

t h e p o w e r s o u r c e .




4/4

V o l . 1 1 1 , N o . 1 2

P R E P R T I O N O F M E T L L I C C L C I U M

4

Conclus ions

Carrots of metallic calcium may be obtained by

electrolysis of an electrolyte of calcium oxide in cal-

cium chloride containing up to 2% by weight of oxide.

With concentrat ions between 2% and approximately

14% oxide, the melt was so fluid that the metal carrot

could not be protected with a film of frozen electrolyte

as i t emerged from the melt , and severe burning re-

sulted. Convection currents were also par t icular ly

troublesome in this concentrat ion range.

The most favorable temperature range for electro]-

ysis of the o xide-bearin g electrolyte f rom the stand-

point of ease of control and good carrot formation was

788~176 The most favo rabl e oxide concent ration

range from the same standpoint was 0.5-1%, with

satisfactory operation being possible with concentra-

tions up to 2%. Operation was more difficult with the

oxide-bearing electrolyte than with chlor ide alone. No

significant temperature effect on cell voltage was noted

with either of the electrolytes. No advantage in cell

voltage was noted in using oxide concentrat ions greater

than 2% over that to be obtained with use of concen-

trations less than 2%.

Average cell voltage with the o xide-bearing elec-

trolyte ranged up to 23.9% less than that with the

chloride alone. The large cell and large anode sur-

face area were advantageous in both lower average

cell voltage and ease of operation and control.

Anode effect presented no prob lem with the oxide-

bearing electrolyte. This was probably due to the fact

that a clean surface is continually maintained by the

etching effect caused by combination of the liberated

oxygen with the anode.

This research presents the f irst known demonstra-

tion that calcium oxide can be fed to a calcium chloride

electrolyte for calcium production. This is contrary to

literature claims that calcium oxide causes the elec-

trolyte to become pasty. Such pastiness was not in

evidence except at high oxide concentrat ions, approx-

imately 14% and above.

Manuscript received Nov. 5, 1963; revised manu-

script received June 5, 1964.

Any discussion of this paper will appear in a Discus-

sion Sect ion to be pub lish ed in t he Ju ne 1965 JOURNAL.

REFERENCES

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i b i d . ,

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(1920).

12. C h e m i c a l A b s t r a c t s , 3, 1948 (1909).

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28, 84 (1906).

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17. C. L. Mantell, Indus trial Electroche mistry , 3rd

ed., p. 735, McGraw-Hill Book Co., New York

(1950).

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allur gy and Technology , p. 140, Reinho ld Pub-

lishing Corp., (1945).

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20. Richard Lorenz,

T r a n s . A m . E l e c t r o c h e m . S o c ., 6 ,

160 (1904).

21. C. J. Brockman, ib id . , 47, 245 (1925).

22. Paul Drossbach, Elek troch emie Geschm olzen er

Salze, p. 27, Edward s Brothers, Inc., Ann Arb or

(1943).

23. R. E. Kirk, Editor, E n c y c l o p e d i a o ] C h e m i c a l T e c h -

n o l o g y , 1, p. 459, The Interscience Encyclopedia,

New York (1947).

24. F. C. Frary, H. R. Bicknell, and C. A. Tronson,

T r a n s . A m . E I e c t r o c h e m . S o c . , 18, 117 (1910).

25. J. D. Edwar ds, F. C. Fra ry, and Zay Jeffries, The

Aluminum Indust ry- -Aluminum and I t s Produc-

tion, p. 80, McGr aw-H ill Book Co., New York

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El l ipsometr ic Invest iga t ion of the Opt ica l Proper t ies

o f n o d ic O x id e F i lm s o n T a n t a lu m

S K u m a g a i 1 a n d L Y o u n g

D e p a r t m e n t o f E l e c tr i ca l E n g i n e e r in g , T h e U n i v e r s i t y o f B r i t i sh C o l u m b i a , V a n c o u v e r , B r i t is h C o l u m b i a

ABSTRACT

Tantalum surfaces were examined both immersed in the electrolyte and dry.

The optical constants of the metal and of the oxide were obtaine d by com par-

ing .experimental and theo retical ellip someter curves. It was found that the

method of estimating the optical constants of the metal by neglecting.the effects

of the oxide film already present before anodization leads to serious error.

The el l ipsometr ic method gave results in agreement with those obtained using

light polarized in the plane of incidence. The advantages of the method seem

to l ie in the investigation of f i lms which are too thin or otherwise unsuitable

for the spectrophotometr ic method, and for i n s i t u measurements.

In the study of thin films and, in particular, of anodic

oxide films (1), optical techniques are important be-

cause they give accurate and absolute estimates of the

thickness. The thickness is, of course, needed to cal-

culate such quanti ties as field streng th and dielectric

constant. Several nonoptical methods give quite sensi-

t ive measurements of the thickness of anodic oxide

~Pres ent address: OKI Elect ric Company Tokyo Japan.

films in indeterminate units, but it is very desirable to

be able to determine the absolute thickness, if only to

allow comparisons to be made between the oxides of

different metals. Optical measurements may also be

used to show whether the films are homogeneous and to

detect var iat ions with formation condit ions in the na-

ture of the film material.

A complete measurement of the optical propert ies of

an isotropic homogeneous f i lm would include the deter-


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