Zinc precipitates and thermogravimetric studies of silver oxide for zinc-silver and cadmium-zinc batterie

Arcand, G. M.

English

NASA Technical Reports Server

FiRST QGiiiiTERiY REPORT 
THE REACTIONS PERTAINING TO ZINC-SO LVER AND CADHRUEE.S!&VER BATTERgES 
JPL 951458 
This work was performed f o r  the Jet Propulsion Laboratory, Cal Efornia 
l n s t i  tu te  o f  Technology, sponsored by the National Aeronautics and 
Space Administration under Contract NAS7-100. 
G. Myron Arcand 
Department o f  Chemistry 
Idaho State Unlversi t y  
Pocatello, Idaho 
https://ntrs.nasa.gov/search.jsp?R=19660020465 2020-03-16T20:57:56+00:00Z
f 
Zn(l I )  was prec ip i  teted from t s i  t i a t e d  solut ions w i t h  KOH and "3. 
Precipi tates formed w i t h  KOH contained l i t t l e  a c t i v i t y  whi l e  those 
formed w i t h  NH3 conta'ined considerable a c t i v i t y .  
combined w i t h  the resul ts  of  thermgravimetric experiments, suggest 
that  ZnO i s  formed by KOH and Zn(OH)2 by NH3. 
These observations, 
Thermgravimetric behavior o f  Ago depends on whether the oxide i s  
formed chemically o r  electrochemically. 
composes rap id ly  a t  14OoC. 
These i s  evidence that Ago de- 
OBJECT! VES 
The objectives o f  the contract are three-fold: 
( 1 )  The characterization of cadmium and zinc anodic reaction 
products. 
The thermal decomposition o f  s i  lver  oxide and the measurement 
of the ra te  of decomposi t i  on o f  Ago and Ag20 a t  various temp- 
eratures between 110' and 200°C. 
(3)  The deposition o f  s i  l v e r  cathode material on zinc anodes. 
This report deals w i t h  parts o f  the f i r s t  two Objectives and w i l l  
(2) 
be divided into: 
when formed by the addi t ion o f  a lka l ine solut ions and (B) a prel iminary 
thermogravi met ri c i nvest i gat i on o f  Ago. 
(A) the invest igat ion of  the precipi tates o f  Zn(BI) 
A. PRECIPITATION OF ZSNC OXIDE 
Introduction. 
The reaction occurring a t  the zinc electrode during the discharge 
o f  a Ag-Zn c e l l  i s  usual ly expressed i n  one o f  two ways: 
Zn(s) + 2 OH' = ZnO(,) + H20 + 2 e' 
zn(S) 
+ 2 OH' + 2 e- 
I n  e i t he r  case, the pH i n  the v i c i n i t y  o f  the electrode should de- 
crease; 
water formed would d l  lu te  the solution. 
produce a greater change i n  electrode potent ia l .  
however, react ion (1) would produce the greater change since the 
The greater change i n  pH should 
The physical nature o f  a metal hydroxide i s  qu i te  d i f f e r e n t  from 
that  of an oxide, the former being more gelatinous and less eas i ly  caused 
t o  s e t t l e  i n  a f l u i d .  One would expect s ign i f i can t  differences i n  mechan- 
i c a l  and e l e c t r i c a l  behavior of the electrode i f  the hydroxide rather than 
the oxide were formed during discharge. 
- 2 -  
0 
The l i t e r a t u r e  i s  not consistent On characterizing the zinc prec ip i -  
Papers by Chalyi and co-workers ( I ,  2) appear t o  be contradictory. tate. 
Duval (3) presents thermgravimetric evidence which suggests d i f f e r e n t  
types o f  p rec ip i t a te  depending on the method o f  preparation, yet  he refers 
t o  a l l  as being hydroxides. On the other hand, he states that many metals 
form only hydroxides when precipi tated by KOH. Sneed (4) states that  the 
hydroxide can be prepared oniy under careful  i y  controi  ied cond'i tions. 
I f  t r i t i a t e d  water i s  added t o  an a l ka l i ne  solut ion, there should be 
a rapid exchange o f  t r i t i u m  between water and hydroxide. Any metal hydrox- 
ide prec ip i ta ted from such a solut ion should contain a c t i v i t y  proport ional 
t o  the amount o f  hydroxide i n  the sol id;  an oxide should contain no ac t i v -  
i t y .  
the zinc p rec ip i t a te  formed i n  a lka l ine solution. 
used t o  support the f indings made by t racer techniques. 
This technique should provide a mans o f  determining the nature of  
Thermgravimetry may be 
Experimenta 1.  
Concentrated Zn(N03)2 stock solut ions were prepared from d. T. Bakes 
Reagent Grade materials and were standardized iodometrical ly (5). 
Baker Reagent Grade 45% KOH solut ion was standardized against HCB and 
stored under n i  trogen. 
w i thou t s tanda rd  i r a t  0 on. 
J. T. 
Concentrated DuPont Reagent Grade amnonia was used 
Liquid s c i n t i l l a t i o n  solutions contained 7 g / l  PPO, 0.3 g / l  dlmethyl 
POPOP, and 100 g / l  reagent grade naphthalene i n  J. T. Baker Reagent Grade 
p-dioxane stabi l i zed  w i t h  sodium d ie thy ld i  thiocarbamate. The f l u o r s  were 
obtained from the Packard Instrument Company. 
p-dioxane were stored under nitrogen. 
The solut ions and the stock 
- 4 -  
3 Stock H,O was added t o  known volumes o f  supernatant and redissolved 
L 
prec ip i t a te  obtained from the system o r i g i n a l l y  contain9ng no a c t i v i t y .  
From the measured count ra te and the known a c t i v i t y ,  the cownting e f f i -  
ciency was calculated i n  each case, these values being used t o  calculate 
the ac t ' i v i t ies  i n  the tagged systems. 
Zn(O SI was prec lp i  tated wi th  NH3 i n  the same manner except that  NH3 
was added u n t i l  the pH o f  the mixture was approximately 8 as measured 
w i t h  a pH meter. 
p l e t e  p rec ip i t a t i on  o f  the z inc but s u f f i c i e n t l y  low t o  prevent re-solut ion 
as Z ~ ( N H ~ ) ~  . 
This pH value should be s u f f i c i e n t l y  high t o  ensure c o w  
2+ 
The prec lp i  tates from the f l  r s t  two experiments were Incompletelly 
washed. Subsequently, washing was continued u n t i l  the washings showed no 
ind icat ion o f  n i t r a t e  (6). 
p-dioxane followed by absolute ethanol. 
exposed t o  room a% r f o r  severa 1 days. 
The precipt tates were dr ied by washing w i th  
The sol ids were allowed t o  stand 
Potassium n l  t r a t e  tended t o  form supersaturated solutions; therefore, 
the precipi tates from the las t  experiment were allowed t o  stand On contact 
w i t h  the supernatant f o r  a t  least 24 hours before separation. 
A l l  s c i n t i  I l a t i o n  samples were placed 'in the refs lgerator chamber a t  
Counting time was adjusted t o  provide a t  least 12 hours before counting. 
least 10,000 counts per sample. Data were taken manlsaII%y. 
A thermogram o f  a sample of p rec ip i t a te  formed by each of the two 
procedures was made. The i n i t i a l  sample weights from the WM3 and KOH 
prec ip i ta t ions were 15.75 mg and 24.84 mg, respectively. The heating 
ra te  was 5 O ~ / r n i  nute. 
- 5 -  
Results and Discussion. 
The resul ts  of the experiments w i th  KOH are sunmarlzed i n  Table 1. 
A I  1 values reported are averages o f  three or  more precipi  tatfons. 
prec ip i ta tes i n  experiments 1 and 2 contained considerable amounts o f  
W03, which accounts for the high weights. 
;sent 3 was washed thorough?y and d r fed  I n  a i r .  
4 was not separated untOl the supernatant was no longer supersaturated 
w i t h  KN03. 
The 
The p r e c l p i t a t e .  On experl- 
The mixture In experintent 
The supernatant a c t i v i t y  i s  reported i n  dpm/A because i t  i s  d i f f i -  
c u l t  t o  determine the Forrect to ta l  volume o f  the Supernatant', a quant i ty 
necessary i n  the ca lcu lat ion of t o t a l  a c t i v i t y .  Calculations were made 
assuming that: 
applicable, and (3) the volurae could be calculated from the changes i n  
( I )  a l l  o f  the KNO3 had prec8p%tated, (2) reaction ( I )  is 
densities whose valuer could be graphi ta l ly  determined. 
showed the t o t a l  a c t i v i t y  i n  the supernatant to be about 1-2% higher than 
the t o t a l  added t o  the system or ig ina l ly .  
volume could e a s i  l y  account f o r  the discrepancy. 
The resul ts  
A small e r ro r  I n  the calculated 
I f  we assume that a l l  of  the Zn(UU) i s  recovered i n  the prec ip i ta te,  
the prec ip i  t a t e  Is we can calculate how much a c t i v i t y  should be present I f  
Zn(OH) 2. 
Assume the f o l  low0 ng densities determined graphica 
p = 1.565 g/m 4.000 VF Zn(NOg)2 - 
10.00 VF KOH f3 = 1.400 g/ml - 
Then, the weight of water i n  the system is :  
12.50 m l  Zn(N03)2 contains 10.09 g H20 
10.00 m l  KOH contains 8.39 g H20 
Total H20 = 18.48 9 H20 
l Y  (7): 
- 6 -  
Since there are 2 moles of H i n  every m l e  of H,O and 0.100 mole o f  KOH 
i n  that  solut ion, 
- 
H = 2(18.48)/(18.02) + 0.100 P 2.152 moles H 
The t o t a l  a c t i v i t y  i n  the system i s  8.470 x I O 7  dpm which can be expressed 
as 3.936 x IO7 dpm/mole H. 
mi 1i:moies of Zn{OH)2 i s  io0 m i i i i m i e s .  
Ap, i s  
The least amount of hydrogen expected i n  50 
Therefore, the expected a c t i v i t y ,  
6 Ap = 0.100 mole H x 3.936 x I O 7  dpm/mole H = 3.936 x 10 dpm 
The maximum found was 1.066 x IO5 dpm, about 2.7% o f  that  expected, which 
suggests that  the prec ip i ta te  formed i s  ZnO rather than Zn(OH)2. 
The p o s s i b i l i t y  that  t r i t i u m  I n  Z ~ I I O H ) ~  might exchange rap id ly  w i th  
water and thus be l o s t  during the washing process was considered. 
fore, an experiment which might produce another form o f  the precip t a t e  
was desirable. Duval's thermogravimetric data showed considerable d i f f e r -  
mces i n  the mater3als formed, dependrng on wAet5cer they were prec p i ta ted  
by KOH or by NH3$ a d e f i n i t e  break i n  the thesmogram of the l a t t e r  suggest- 
ing loss of  bonded water or hydroxide. The resul ts  o f  the experime3t wOth 
NPI3 are s u m r i  zed: 
There- 
Quanti t y  o f  Zn( B 1 )  
Tota 1 act! vi  t y  
Supernatant a c t i v i  t y  
50.00 mi 1 l imoles 
8,470 x lo7 dpm 
3.545 x 103 dpm/h 
Precipi ta te  weight 2.838 g 
1.815 x 10 6 dpm Precipi ta te  a c t i v i t y  
There i s  much more a c t i v i t y  i n  th is  p rec ip i ta te  than appeared i n  those 
from KOH prec ip i ta t ions,  which suggests that  a considerable por t ion  o f  
the prec ip i ta te  i s  Zn(0H)q. The weighed matet la l  corresponds t o  57.1% 
o f  the t o t a l  which should have been col lected i f  one assumes that  the 
- 7 -  
prec ip i t a te  i s  Zn(OHl2. 
t ha t expected . 
O n  t h i s  bas is ,  the a c t i v i t y  found i s  72% of  
The thermograms for the two types o f  p rec ip i t a te  are rhown i n  
Figure 1. 
i s  essent ia l ly  constant whi le the cuwe i n  Figure I b  shows a d i s t i n c t  
break beginning about 10OoC. 
corresponding t o  about 60% Zn(0H)g I n  the prec ip i ta te.  
The rate o f  weight loss w i t h  temperature shown i n  Figure l a  
The span of the break i s  about 1.7; mg 
Ht' t t ig (8) reports that Zn(OM)2 i s  unstable above 39°C. The temp- 
erature o f  the mixtures during precipl t a t i o n  rose t o  maxima of  52-54OC. 
While these temperatures may prevent complete formation o f  Zn(OH)2, they 
cannct be the cause o f  the observed differences i n  the BehavSsrs o f  the 
sol ids. 
eratures being held around 2soC. 
However, experiments presently 3re be! ng performed w i t h  temp- 
Thermgravimetric and tracer experiments indicate that  ZnO I s  the 
predominant product when KOH 3s added t o  an equivalent amount o f  Zn(N03)2, 
whi l e  Zn(0H)p i s  the predomgnant species when peec!pitaa%on i s  accomplished 
w i t h  MHg. Exchange between Zn(OH)g and water is s u f f i c i e n t l y  slaw that  i t  
rannot be completed during a n o m 1  washing procedure a t  room temperature. 
As yet, there i s  l i t t l e  t o  indicate that  temperature a f fec ts  the charac- 
t e r  of the precipi tate.  
The data show that the character of the p rec ip i t a te  i s  strongly de- 
pendent on the conditions of  formation. Therefore, the experiments re- 
ported here can throw no l i g h t  on the electrochem?cal react ion even though 
one might be induced t o  favor reaction (1). 
Proposed Work. 
Precipi tat ions of ZnO or  Zn(O#j2  ~ : l l  be csntlnucd a t  &owes tempsea- 
tures. Zn(Oktj2 samples w %  1 1  be stF rued :n  water t o  t r y  t o  deaermS ne the 
ra te  ob exchange ab hydroxide between the ss4rd and water. ZnO w i l l  be 
rnSxzd wi th  tr3tis:ed water ta try to detasmYne t 5e  r a t e  o f  hydtmticn of  
the oxide, I f  any. Precipi tat ions w8 8 1  be made I n  concentrated base t o  
determine what specfes is formed under these condEti0ns. Exchange experi- 
ments w %  1 1  be p e r f o m d  i n  conceqtrated base. 
8. THERMAL. DEX%POS3$6QN O i  AgO 
Argentic oxide decomposes a t  h;gn cempepatures ? n  a manner which may 
be descrybed by the equations: 
2 AgO p A920 + 1/2 02 (3) 
Ag2Q = 2 Ag + i / 2  02 (4) 
Reaction f3 )  apparently begins tc be s?gn?f:iant a t  a b u t  ;20% and may 
be qu l rc  rapid a t  84O-85O0C,  depmd"g on cond:tions. 
Crude experiments done a t  jPL shmed that  bath reactions (3 )  and (4) 
occur t o  some extent I n  the v i c i n i t y  of 835OC. 
seemed dependent on very sFSght exposure t o  Eight o r  very small var ia t ions 
i n  oxygen pressure or  both. Al ien (91 reps'rts several d iscont inu i t ies i n  
themgrams made i n  vacuum belm 20OoC. 
invest igat ion 1s required. 
The ear ly  work a t  JPL was done by heating samples i n  3 cruc ib le  i n  a 
drying oven. Ut was necessary to  cool the samples i n  a desiccator before 
weighing; thus drast ic,  periodic temperature changes occurred through- 
out each experiment and the samples were disturbed during the transfers. 
Use of a thermobalance W E  1 1  perm! t control  o f  exposure t o  Bight, cont ro l  
o f  the atmosphere over the solid, end continuous recording o f  weight changes. 
The ra te  of  react ion (3)  
i€v!dently, a care fu l l y  cont ro l led 
- 9 -  
Experimental . 
Ago was prepared by a modif icat ion o f  the method described by Rai lar  
(!O)* 
weighed material was analyzed by heating i t  t o  600°C for 20 minutes, 
cooling, and weighlng. 
loss i n  weight agreed w i t h  that  calculated. 
Ago was prepared e l e c t r o l y t i c a l l y  by a m d i f l c a t i o n  o f  the method 
The mshed prcc?p!tate w s  dried mer P,a5 s t  about f 5  torr. The 
The prec ip i ta te was considered dry Of the observed 
described by J o l l y  (11). 
smooth p l a t i  num. 
Electrodes were platinum screen instead o f  
Samples o f  Ago prepared by both methods were investigated on the 
thennobalance without temperature control;  the temperature probably In- 
creased a t  40-50°C/minute. 
investigated a t  a programed teaperature increase of  5'C/alnute. 
One sample o f  chemically prepared Ago was 
Results and Discussion. 
Argentic oxide samples prepared by the dsfferent methods were d ? f f e r -  
ent On appearance; the chemically prepared material was dark gray i n  
co lor  and consisted o f  very small c r ys ta l s  (less than 5p i n  diameter) 
whi l e  the e l e c t r o l y t i c a l l y  prepared material was almost black and consist- 
ed o f  crysta ls  as large as SO> i n  diameter. 
prepared Ago slowly turned dark gray on standing f o r  about one month i n  a 
dark conta i net . 
However, the e l e c t r o l y t i c a l l y  
Figure 2 shows thermograms f o r  the two d i f f e r e n t  materials. The 
curves have been normalized t o  percsi t bet ter  conparison. 
a time scale since the heating rate i s  unknown, though f a i r l y  reproducible. 
The abscissa i s  
Both curves shaw breaks a t  about 3.5 and 12 minutes. This was ex- 
pected I n  s p i t e  o f  par t ic le-s ize differences. The po r t i on  o f  the curve 
f o r  the e l e c t r o l y t i c a l l y  prepared Ago between the breaks i s  f a i  r l y  f l a t  
and corresponds we l l  w i th  the expected 50% loss of  avai lable oxygen 
wh l le  that  region on the curve for chemically prepared material i s  
much steeper and f a l l s  below the po in t  corresponding to  a 50% loss o f  
oxygen. I n  no case was the total  weight change such as t o  suggest slg- 
n i  f 6 cant i mpu r i t i  es . 
The small break a t  the beginning of  curve (1) i s  probably caused 
by a s;nal! amount of  moisture. 
The chemically prepared powder tended t o  cake so that, during 
s ieving operations, small, hard b a l l s  formed. 
were about the same s ize as those found i n  the powder. Bal l ing d id  not 
af fect  the rough thermogram s ign i f i can t ly ;  t h i s  suggests that  p a r t i c l e  
size, I t s e l f ,  may not be too Important. 
Crystals w i th in  the b a l l s  
The trace f o r  the one programed thermogram i s  not shown because 
an equipment malfunction destroyed pa r t  of  it. 
rap id ly  around 14OoC and decomposition was cemplete a t  440°C. 
temperatures are somewhat lower than expected, especial Iy since e a r l i e r  
experiments d3d not ind icate such a rapld decomposltion o f  Ago a t  such 
a low temperature. However, i t  must be emphaslzed that  these experf- 
ments were done uvder cond2 t ions considerably d i f f e ren t  from those i n  
the pree im5 nary study. 
The sample los t  weight 
These 
Conc 1 us i ons . 
The method o f  preparation of Ago a f fec ts  the physical propert ies 
o f  the material. No proof o f  chemical dif ferences i s  avai lab le yet. 
Rough thermograms suggest that the decomposition o f  A920 begins a t  
lower temperature i f  the pa r t i c l e  s ize  i s  small. However, the curves 
a lso  suggest that decomposition o f  Ago i s  retarded uader those condi- 
t i m s ;  t h i s  seems improbable. 
- 11 0 
Rapid decomposition of Ago seemingly occurs near 14OoC. Ohis i s  
a serious consideratfon i f  charged Ag-Zn batter ies are t o  be heat s t e r i -  
l ized. 
0 
Al te ra t i on  o f  experimental conditions may a f f e c t  t h i s  value. 
Proposed Work. 
Further programed thermograms wf 11 be made W B  t h  both types o f  Ago. 
Constant-tensperatuse thermograms w0 1 1  be made f n  room l i g h t  and wl th 
l l g h t  excluded. Constant temperatures w i  11 be adjusted a t  appropriate 
values between lW0C and 2OO0C, the values depending somewhat on the re- 
s u l t s  o f  the programed thermograms. Particle-sHze d l s t r l b u t f o n  w i  11 be 
determi ned m i  croscopi ca 1 ly. 
S 
0 s 
- 
B 
0 c 
N 
y. 
0 .  
E: 
Q - 
U 
(B 
44 
Q. 
6) 
a 
- - 
t 
Q U E  
86)h 
In 
S A  
8 E- E- m a o  
- z E  
4 3 -  
> 6  
P c u  
0 e - m  
P 
0 
0 
E.? 
8 
0 
v\ 
N 
0 
0 
2 
8 
L A  
9 
N - 
0 
0 
9 - 
8 
0 
0 
P 
L 
Y 
O N  
6 ) -  m 
x d‘ 
o x  
0 -  
U C  
v ) N  
9 
hl 4 
. * 
24 
23 
16 
14 
- 13 - 
I I I I I 
F:gu+e la, Thermogram of " Z r W  
I I I I I 
40 80 120 160 200 
Temperature (OC) 
1 .o 
0.9 
0.8 
0.7 
0.6 
u) 
a 
0 
N - 0.5 
8 
0 .3  
0.2 
0.1 
I I I 1 I I 
f 
E 1 ect roehemi ca 1 Ago 
79 
I 1 1 I I 
2 4 6 8 10 12 14 
Heating time (min.) 
Fi gure 2. Themgrams of Ago 
REF ER ENC ES 
V. P. Chalyi, V .  T. Zorya, and Z. Ya. Makarova, Zh, Meorgan. Khlm. 
- 10, 265 (1965) 
S. P. Rozhenko and V. P. Chalyi , Ukr. Khfm. Zh. a, 900 (1964) 
C. Duval, "inorganic Thermogravimetrfc Analysist8, Elsevles Publishing 
Co., New York, N.Y. 1953, pp. 275-6. 
M. C. Sneed, J. L. Maynard, and R. C. Brasted, "Comprehensive 
inorganic Chemistry", 1 V ,  D. van Nostrand Lo., 3nc., N e w  York, N.Y. 
E. K. Mun and E. W. S w i f t ,  Anal. Chm. 219 798 (1949) 
F. F e i g l ,  "Spot Tests I n  lnorgenlc Analysis", Elsevier Publishing Go., 
dew York, N. Y., 1958, p. 326 
"Handbook of  Chemistry and Phys3crI8, 13th ed., Chemical Rubber Pub- 
l i sh ing  C O . ~  Cleveland, Ohio. 1954, pp. 1369, 1871, 1913 
G. F. Hutr ig and H. Miildner, Z. anorg. :hem, Go 368 (1933) 
(9) J. A. Allen, Proc. Austral ian Cod. Electrochem., I s t ,  Sydney, Hobart, 
AustFalia 1963, 72 (Pub. 196s) 
J. C. Bai ler, Jr., "lnorganie Syntheses, a W ,  MeG~aw-HTll Book Co., 
New York, ld. Y., 1953, p. '12 
(10) 
(1Y) W. i. Jol ly,  W n t h e t i c  inorganic Chemlstay"', Paentice-Hall, Dnc., 
Englewood C l i f f s ,  M. J., 1960, p ~ .  148-9 


The reactions pertaining to zinc-silver and cadmium-silver batteries First quarterly report

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server