Crystallogenesis in the Forming of Plates for the
Lead-Acid Storage Battery
A. C. Simon and E. L. Jones1
United States Naval Research Laboratory, Washington, D. C.
ABSTRACT
Changes in m i c r o s t r u c t u r e have been observed d u r i n g the f o r m i n g of the
positive and n e g a t i v e plates which p r o v i d e clues as to the o p t i m u m conditions
for formation. The m i c r o s t r u c t u r e p r o d u c e d was found to be d e p e n d e n t on the
conditions u n d e r w h i c h f o r m i n g took place. The conversion to lead dioxide in
the positive plate was found to be initiated on the surface of a definite t y p e of
crystal, as y e t not identified. The quantity, size, and shape of this c r y s t a l
v a r i e d w i t h the t e m p e r a t u r e and specific g r a v i t y of the e l e c t r o l y t e and w i t h the
c u r r e n t density employed. T h e indications w e r e that a basic sulfate c r y s t a l was
being c o n v e r t e d d i r e c t l y to l e a d dioxide, w i t h o u t change in e x t e r n a l form,
t h r o u g h some s o l i d - s t a t e reaction. The conversion to lead in the negative plate
was definitely b y solution of the l e a d sulfate and deposition of r e d u c e d lead.
The form and size of the l e a d crystals in the negative could also be v a r i e d
w i t h m e t h o d of forming, b u t not to the e x t e n t of those in the positive plate.
While t h e r e was indication that subsequent life of the positive p l a t e might
d e p e n d on the m i c r o s t r u c t u r e d e v e l o p e d d u r i n g forming, t h e r e was no such
correlation found for the n e g a t i v e plate.
tions c o n d u c i v e to t h e a t t a i n m e n t of m o r e c o m p l e t e
d a t a , a n d t h e r e s u l t s w i l l b e r e p o r t e d . M e a n w h i l e , in
v i e w of r e c e n t l y p u b l i s h e d w o r k b y o t h e r i n v e s t i g a tors it a p p e a r s a d v i s a b l e to r e p o r t on t h i s p h a s e of
t h e i n v e s t i g a t i o n a n d to p o i n t o u t its p o s s i b l e c o r r e lation with their data.
A s w i l l b e s h o w n in t h e d e s c r i p t i o n of t h e e x p e r i mental results and subsequent discussion, the foll o w i n g o b s e r v a t i o n s , a m o n g others, w e r e m a d e w h i c h
a r e c o n s i d e r e d of p r i m e i m p o r t a n c e in i n f l u e n c i n g
t h e c o u r s e of f u t u r e i n v e s t i g a t i o n .
1. T h e r e w e r e o b s e r v e d to b e t w o or m o r e d i s t i n c t
species of c r y s t a l p r e s e n t in t h e p o s i t i v e p l a t e . T h e s e
c o u l d b e f o r m e d e i t h e r d u r i n g m i x i n g a n d d r y i n g or
at a v e r y e a r l y s t a g e of f o r m a t i o n . T h e s e s e p a r a t e
c r y s t a l species c o u l d b e r e a d i l y d i s t i n g u i s h e d b y
m i c r o s c o p i c e x a m i n a t i o n b e c a u s e of r a d i c a l l y d i f f e r ent crystal habit and chemical reactivity. They have
not, as yet, b e e n s e p a r a t e d a n d i d e n t i f i e d w i t h a defin i t e c h e m i c a l c o m p o s i t i o n , b u t a r e a s s u m e d to b e
a m o n g t h e f o r m s of s u l f a t e w h i c h h a v e b e e n f o u n d
in u n f o r m e d b a t t e r y p a s t e b y v a r i o u s w o r k e r s . T h e s e
f o r m s are: n o r m a l l e a d s u l f a t e , PbSO4; m o n o b a s i c
l e a d s u l f a t e , P b S O , ' P b O ; t h e m o n o h y d r a t e of l e a d
t r i b a s i c s u l f a t e , PbSO~" 3PbO" H~O; a n d t e t r a b a s i c l e a d
s u l f a t e , PbSO~" 4PbO.
2. O n e of t h e s e c r y s t a l f o r m s , in t h e u n f o r m e d
p o s i t i v e p l a t e , c o n s i s t e d of n e e d l e l i k e o r r e c t a n g u l a r
crystals, usually with much greater length than
b r e a d t h . T h e c o n v e r s i o n to l e a d d i o x i d e w a s a l w a y s
o b s e r v e d to i n i t i a t e on t h e s u r f a c e of c r y s t a l s of this
t y p e , w h i c h w e r e in c o n t a c t w i t h t h e m e t a l grid, a n d
to s p r e a d f r o m o n e c r y s t a l to a n o t h e r of t h i s t y p e a t
p o i n t s of contact. T h e c r y s t a l s w e r e t h u s c o n v e r t e d
into l e a d d i o x i d e w i t h o u t c h a n g e of f o r m . C r y s t a l s of
this t y p e w i l l b e r e f e r r e d to as t y p e A in t h e s u b s e q u e n t discussion. F r o m e v i d e n c e a c c u m u l a t e d b y
P l a t e s f o r l e a d - a c i d s t o r a g e b a t t e r i e s of t h e t y p e
u s e d for a u t o m o t i v e p u r p o s e s u s u a l l y h a v e as a s u p p o r t a l e a d a l l o y g r i d i n t o w h i c h is s p r e a d a p a s t e l i k e
m a t e r i a l c o n s i s t i n g of a m i x t u r e of l e a d o x i d e s to
w h i c h sufficient d i l u t e s u l f u r i c a c i d h a s b e e n a d d e d
to p r o d u c e a w o r k a b l e p a s t e . R e a c t i o n of t h e o x i d e s
w i t h t h e s u l f u r i c a c i d p r o d u c e s a m i x t u r e of l e a d s u l f a t e a n d b a s i c l e a d s u l f a t e s t h a t sets t h e p a s t e i n t o
a c e m e n t l i k e mass. E l e c t r o l y s i s in d i l u t e s u l f u r i c a c i d
t h e n p r o d u c e s a n o x i d a t i o n to l e a d d i o x i d e a t t h e
p o s i t i v e p l a t e a n d r e d u c t i o n to a s p o n g e l i k e m a s s of
l e a d c r y s t a l s a t t h e n e g a t i v e . T h e c h e m i s t r y of t h i s
process has been very thoroughly investigated, but
the physical changes that accompany these reactions
h a v e b e e n l a r g e l y i g n o r e d , a n d l i t t l e or no a t t e m p t
h a s b e e n m a d e to d e t e r m i n e t h e c r y s t a l l o g e n e s i s in
t h e process.
Using the methods that have been described previo u s l y (1) a n a t t e m p t w a s m a d e to s t u d y t h e c h a n g e s
in m i c r o s t r u c t u r e t h a t a c c o m p a n y t h e s o - c a l l e d f o r m ing, o r c o n v e r s i o n of t h e l o w e r o x i d e s of l e a d to l e a d
d i o x i d e a n d s p o n g e lead. T h e e x p e r i m e n t a l m e t h o d s
were extremely simple, and hindsight has shown
that the microscopical observations should have been
s u p p l e m e n t e d w i t h d a t a c o n c e r n i n g single e l e c t r o d e
a n d cell p o t e n t i a l s d u r i n g o p e r a t i o n , t h e c a p a c i t i e s
d e v e l o p e d b y t h e v a r i o u s t r e a t m e n t s , etc. T h e s e d e r e l i c t i o n s w i l l b e r e m e d i e d in f u t u r e i n v e s t i g a t i o n s ,
b u t at t h e t i m e this e x p e r i m e n t w a s b e g u n it w a s i n t e n d e d o n l y to i n v e s t i g a t e t h e s u i t a b i l i t y of t h e
m e t h o d . T h e w e a l t h of i n f o r m a t i o n o b t a i n e d f r o m
t h e s t u d y of t h e f e w s a m p l e s p r e p a r e d w a s f a r b e yond expectations and produced more questions than
c o u l d be a n s w e r e d w i t h t h e l i m i t e d d a t a t h a t h a d
been recorded concerning the experimental conditions. E x p e r i m e n t a t i o n is c o n t i n u i n g u n d e r c o n d i 1 Died March
1, 1 9 6 2 .
760
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Vol. 109, No. 9
CRYSTALLOGENESIS
o t h e r s it is c o n c l u d e d t h a t t h e l a r g e t y p e A c r y s t a l s
m u s t consist of e i t h e r t h e m o n o h y d r a t e of t r i b a s i c
l e a d s u l f a t e , PbSO~. 3 P b O - H 2 0 , o r t h e t e t r a b a s i c l e a d
s u l f a t e , P b S O , - 4 P b O . A f t e r c r y s t a l s of this t y p e h a d
b e e n c o n v e r t e d to l e a d d i o x i d e t h e r e w a s a s l o w e r
b u t c o n t i n u o u s c o n v e r s i o n of a n o t h e r t y p e of c r y s t a l
also f o u n d in t h e u n f o r m e d p a s t e .
3. T h i s s e c o n d f o r m of c r y s t a l in t h e u n f o r m e d
p o s i t i v e p l a t e a l w a y s c o n s i s t e d of v e r y s m a l l , r e g u l a r
p o l y h e d r o n s of n e a r l y e q u a l size w h i c h w e r e n o t
c h a n g e d in size, s h a p e , or q u a n t i t y b y a n y m e t h o d of
f o r m i n g u s e d in t h e e x p e r i m e n t a l series. T h i s c r y s t a l f o r m , s u b s e q u e n t l y r e f e r r e d to as t y p e B, a p p e a r e d to c o n v e r t to l e a d d i o x i d e w i t h g r e a t e r difficulty than did the type A crystals, and was converted
only after a long time and after the prior oxid a t i o n of t h e t y p e A. I t is b e l i e v e d t h a t t h i s t y p e of
crystal represented either monobasic lead sulfate,
P b S O ~ . P b O , o r n o r m a l l e a d s u l f a t e , PbSO4.
4. I t w a s n o t e d t h a t t h e l e a d d i o x i d e t h a t f o r m e d
on t h e s u r f a c e of t h e l a r g e c r y s t a l s of r e c t a n g u l a r or
needlelike form (type A) was always harder and
m o r e d e n s e t h a n t h a t w h i c h f o r m e d on t h e s m a l l
regular polyhedrons (type B). Evidence accumul a t e d b y o t h e r s s u p p o r t s t h e a s s u m p t i o n t h a t ~-PbO~
is f o r m e d on t h e t y p e A c r y s t a l s w h i l e fl-PbO~ is
f o r m e d on t h e t y p e B c r y s t a l s .
5. T h e l a r g e r e c t a n g u l a r o r n e e d l e l i k e c r y s t a l s
( t y p e A ) w e r e s e n s i t i v e to t h e f o r m i n g c o n d i t i o n s ,
a n d t h e size, s h a p e , a n d q u a n t i t y of t h e s e c r y s t a l s
c o u l d b e a l t e r e d c o n s i d e r a b l y b y c h a n g e s in t e m p e r a t u r e , specific g r a v i t y of e l e c t r o l y t e , o r c u r r e n t
d e n s i t y . U n d e r c e r t a i n c o n d i t i o n s t h e size a n d s h a p e
of t h e s e c r y s t a l s b e c a m e s u c h t h a t , on f o r m a t i o n , t h e
~-PbO~ t h a t f o r m e d on t h e i r s u r f a c e s c r e a t e d a h a r d ,
d e n s e n e t w o r k or c e l l u l a r s t r u c t u r e t h r o u g h o u t t h e
active material.
6. E x a m i n a t i o n of c y c l e d a n d floated p l a t e s o b tained from commerical sources indicated that this
network remained unchanged by service conditions
w h i c h s u g g e s t e d t h a t t h e c r e a t i o n of such a c e l l u l a r
s t r u c t u r e w o u l d a i d m a t e r i a l l y in p o s i t i v e p l a t e a c t i v e m a t e r i a l r e t e n t i o n , a n d it h a s b e e n f o u n d b y e x a m i n a t i o n of a l i m i t e d n u m b e r of c o m m e r c i a l p l a t e s
t h a t a c t i v e m a t e r i a l r e t e n t i o n is i n d e e d b e t t e r in t h e
p r e s e n c e of such a s t r u c t u r e .
It s h o u l d be r e a l i z e d t h a t t h e e x p e r i m e n t a l d a t a
f r o m a m i c r o s c o p i c e x a m i n a t i o n of t h i s s o r t consist
of n u m e r o u s p h o t o m i c r o g r a p h s w h i c h a r e b e s t e x a m i n e d s i m u l t a n e o u s l y or in v a r i o u s definite c o m b i n a t i o n s to d e t e c t c r y s t a l l o g r a p h i c changes. T h e l i m i tations imposed by publication require a condensed
w r i t t e n d e s c r i p t i o n t h a t is a d m i t t e d l y c o n f u s i n g a n d
l a c k i n g in c o n v i c t i o n . F o r t h o s e sufficiently i n t e r ested, m o r e c o m p l e t e r e p o r t s w i t h a d d i t i o n a l i l l u s t r a t i o n s a r e a v a i l a b l e (1) w h i c h c o v e r v a r i o u s p h a s e s
of this w o r k .
T h e r e m i n d e r s h o u l d also b e i n c l u d e d t h a t this
s e r i e s of e x p e r i m e n t s , d e a l i n g w i t h t h e m e c h a n i s m
of f o r m i n g , w a s p e r f o r m e d on a u t o m o t i v e t y p e p l a t e s
of one c o m p o s i t i o n a n d m a n u f a c t u r e only. P r e l i m i n a r y e x a m i n a t i o n of o t h e r t y p e s of p l a t e i n d i c a t e
t h a t , in g e n e r a l , t h e i r c r y s t a l l o g e n e s i s is s o m e w h a t
d i f f e r e n t , b u t f o r m i n g b e h a v i o r is s i m i l a r to t h a t
IN
FORMING
PLATES
761
outlined for this plate. Exceptions have been found,
however, even in such a preliminary examination so
that it would be unwise to regard this behavior as
universal.
Experimental Procedure
T h e m i c r o s c o p i c a l m e t h o d w a s b a s e d on t h e i m p r e g n a t i o n of s a m p l e s , o b t a i n e d at v a r i o u s s t a g e s in
the forming process and under various controlled
c o n d i t i o n s of f o r m i n g , w i t h a n e p o x y r e s i n a n d t h e
subsequent examination at both low and high magn i f i c a t i o n of t h e m i c r o s t r u c t u r e r e v e a l e d b y s e c t i o n ing and polishing the specimens. For convenience the
e x p e r i m e n t w a s d i v i d e d into t w o p a r t s . T h e first
d e a l t w i t h a n e x a m i n a t i o n of t h e c h a n g e s in s t r u c t u r e t h a t o c c u r r e d as t h e f o r m i n g p r o c e s s p r o c e e d e d ,
the second with the changes that could be induced
by altering the forming conditions from those commonly employed by industry.
F o r t h e first p a r t of t h e e x p e r i m e n t a s e r i e s of cells
w e r e c o n s t r u c t e d e a c h c o n s i s t i n g of one p o s i t i v e a n d
one n e g a t i v e p l a t e s e p a r a t e d b y a d i s t a n c e of a p p r o x i m a t e l y 1.3 cm. T h e s e p l a t e s w e r e o b t a i n e d in a n
unformed but dried condition from a manufacturer
of s t o r a g e b a t t e r i e s . T h e e l e c t r o l y t e c o n s i s t e d of s u l f u r i c a c i d d i l u t e d w i t h w a t e r to a specific g r a v i t y of
1.05. No effort w a s m a d e to c o n t r o l t h e t e m p e r a t u r e
of this e x p e r i m e n t , b u t it r e m a i n e d f a i r l y c o n s t a n t a t
a b o u t 27 ~
Following the information given by Vinal (2), the
c u r r e n t d e n s i t y u s e d w a s 0.25 a m p / d m ~ ( a p p r o x i m a t e l y 2.5 a m p / f V ) . T h e cells w e r e c o n n e c t e d in
s e r i e s so t h a t t h e s a m e c u r r e n t p a s s e d t h r o u g h all. A
ceil w a s r e m o v e d at 1/2-hr i n t e r v a l s d u r i n g t h e first
8 hr, a t 1 - h r i n t e r v a l s f o r t h e n e x t 4 hr, a n d f i n a l l y
at 2 - h r i n t e r v a l s u n t i l no f u r t h e r c h a n g e c o u l d b e
detected. The plates were thoroughly washed immediately after removal and after drying were imp r e g n a t e d w i t h a n e p o x y resin, u s i n g v a c u u m . T h e
p l a t e s w e r e t h e n c u t in such a m a n n e r t h a t s e c t i o n s
could be obtained across the grid thickness both
h o r i z o n t a l l y a n d v e r t i c a l l y a n d also p a r a l l e l to t h e
p l a t e s u r f a c e b u t at v a r i e d d e p t h s b e n e a t h t h e s u r face. I n t h i s m a n n e r a n d a f t e r s u i t a b l e p o l i s h i n g a
r a t h e r c o m p l e t e p i c t u r e of w h a t h a d h a p p e n e d c o u l d
be o b t a i n e d .
To p r o d u c e t h e s e c o n d s e r i e s of s a m p l e s i n d i v i d u a l
cells w e r e p r e p a r e d as in t h e p r e v i o u s case. T h e cells
w e r e a r r a n g e d in g r o u p s w i t h e a c h g r o u p h a v i n g
a c i d of a d i f f e r e n t specific g r a v i t y , r a n g i n g f r o m 1.05
for t h e l o w e s t to 1.45 for t h e highest. O n e cell f r o m
e a c h a c i d g r o u p w a s t h e n p l a c e d in a c o n s t a n t t e m p e r a t u r e b a t h , a n d t h e s e cells w h e n c o n n e c t e d in
s e r i e s w e r e a l l o p e r a t e d at t h e s a m e c u r r e n t d e n s i t y .
This w a s r e p e a t e d at c u r r e n t d e n s i t i e s of 0.023, 0.23,
a n d 2.3 a m p / d m 2. T h e w a t e r b a t h w a s t h e n r a i s e d to
a higher temperature and the process repeated with
a n e w set of s a m p l e s t a k e n f r o m e a c h a c i d g r o u p as
b e f o r e . T e m p e r a t u r e s e m p l o y e d v a r i e d f r o m 4 ~ to
80~
T h e t i m e t h a t c u r r e n t flowed w a s so a d j u s t e d
t h a t r e g a r d l e s s of c u r r e n t d e n s i t y each cell r e c e i v e d
t h e s a m e t o t a l q u a n t i t y of e l e c t r i c i t y . A n a u t o m a t i c
l e v e l i n g d e v i c e a d d e d w a t e r to m a i n t a i n t h e e l e c t r o l y t e at c o n s t a n t level. I n t h i s a n d also t h e p r e v i o u s l y
d e s c r i b e d s e r i e s t h e u n f o r m e d p l a t e s w e r e a l l o w e d to
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762
JOURNAL
OF THE ELECTROCHEMICAL
stand for 30 m i n at r o o m t e m p e r a t u r e in e l e c t r o l y t e
of the same c o n c e n t r a t i o n as e m p l o y e d in t h e e x p e r i m e n t to i n s u r e t h a t the p l a t e s w e r e t h o r o u g h l y w e t
w i t h e l e c t r o l y t e a n d t h a t gas evolution, a p p a r e n t l y
f r o m c a r b o n a t e s which h a d f o r m e d in the d r i e d
plate, was finished so t h a t e l e c t r o l y t e could e n t e r the
pores of the plate. As m e n t i o n e d above all cells r e ceived t h e same t o t a l q u a n t i t y of electricity, an
a m o u n t selected so t h a t no cell w o u l d h a v e p l a t e s so
c o m p l e t e l y f o r m e d as to m a k e o b s e r v a t i o n and comparison difficult and which would r e s u l t in a p p r o x i m a t e l y o n e - t h i r d the a m o u n t r e q u i r e d for t h e o r e t i cally complete formation.
As before, t h e samples w e r e p r e p a r e d for m i c r o scopical e x a m i n a t i o n i m m e d i a t e l y on r e m o v a l from
the electrolyte. The samples w e r e c o m p a r e d for similarities and differences at v a r i o u s magnifications
r a n g i n g f r o m a low of 13 d i a m e t e r s to a high of 1000
d i a m e t e r s to avoid the p o s s i b i l i t y of overlooking a n y
f e a t u r e because of its m a g n i t u d e .
Observations
The progress of t h e f o r m i n g process, the accomp a n y i n g changes in color, and the v a r i a t i o n in the
r e l a t i v e a m o u n t of lead d i o x i d e and lead p r o d u c e d
u n d e r different conditions of f o r m i n g w e r e r e a d i l y
visible to the u n a i d e d eye on e x a m i n a t i o n of the
polished sections, b u t the~details of the process w e r e
not r e v e a l e d u n t i l microscopic e x a m i n a t i o n was
m a d e of each specimen. I n i t i a l l y the u n f o r m e d positive p l a t e was a light y e l l o w color while the u n f o r m e d n e g a t i v e a p p e a r e d gray. U n d e r the m i c r o scope, using p o l a r i z e d light, both the positive and
n e g a t i v e p l a t e s a p p e a r e d to be yellow, a l t h o u g h the
n e g a t i v e was of a much l i g h t e r hue. The i n i t i a l soaking caused c o n s i d e r a b l e i n c r e a s e in the a m o u n t of
sulfate which was m a d e e v i d e n t to the u n a i d e d eye
by a f a d i n g of the y e l l o w color in t h e positive plate,
b u t which did not become e v i d e n t in t h e n e g a t i v e
u n t i l e x a m i n a t i o n u n d e r c o n s i d e r a b l e magnification.
Under the microscope the r e s u l t i n g w h i t e or light
y e l l o w b a c k g r o u n d caused the f o r m a t i o n s of the r e d d i s h - b r o w n lead d i o x i d e or m e t a l l i c l e a d to stand out
clearly.
The Mechanism of Formation--Positive Plate
In both the positive and n e g a t i v e p l a t e the c o n v e r sion to lead dioxide and lead, r e s p e c t i v e l y , i n v a r i a b l y
began at t h e grid m e m b e r . A t low magnification the
positive p l a t e reaction was o b s e r v e d to proceed o u t w a r d f r o m t h e grid as a f a i r l y u n i f o r m c y l i n d e r of
lead dioxide w i t h the exception t h a t r e a c t i o n a p p e a r e d to slow down as the s u r f a c e of t h e p l a t e was
reached, so t h a t the c y l i n d e r b e c a m e ovoid w i t h its
g r e a t e r d i a m e t e r p a r a l l e l to the p l a t e surface. T h e r e
was a t h i n surface l a y e r in which conversion to l e a d
d i o x i d e did not t a k e p l a c e u n t i l quite l a t e in t h e p r o cess so t h a t t h e last portions of t h e p l a t e to f o r m
w e r e at the surface and at points m i d w a y b e t w e e n
grid members. The m a t e r i a l w i t h i n the c y l i n d r i c a l
a r e a of reaction was not u n i f o r m l y c o n v e r t e d to l e a d
dioxide, b u t in cross section p r e s e n t e d a f e r n l i k e a p p e a r a n c e as if the r e a c t i o n w e r e p r o c e e d i n g b y t h e
f o r m a t i o n of b r a n c h e d filaments of l e a d dioxide.
These f e a t u r e s are i l l u s t r a t e d in Fig. 1.
SOCIETY
September 1962
Fig. 1. Upper photograph: Cross section through the positive
plate. The light areas represent unformed positive paste, the dark
areas result from conversion of paste to reddish-brown PbO~. Dark
triangular area at top center is cross section of small lead alloy
horizontal grid member as is also the dark line bisecting the lower
photograph horizontally. Lower photograph: Section of same plate
parallel to surface. Formation took place at room temperature, in
t.OS sp gr electrolyte, at 0.25 amp/dm 2 current density. Total time
of formation was 6 hr. Note that cross section gives less misleading
view of total area of formation than does plane section since latter
gives widely varying areas at different depths. Magnification approximately 8X.
E x a m i n a t i o n at h i g h e r magnification r e v e a l e d t h a t
the f o r m e d portions of the positive p l a t e w e r e m a d e
up of at least two v a r i e t i e s of crystal. Most n u m e r o u s
w e r e the p o l y h e d r a l crystals of n e a r l y equal size,
h e r e i n d e s i g n a t e d as t y p e B. These w e r e i n t e r s p e r s e d
with l a r g e r crystals of a different configuration,
h e r e i n d e s i g n a t e d as t y p e A.
The small, p o l y h e d r a l crystals, t y p e B, w e r e u s u ally quite r e g u l a r in form, b u t so small (2 or 3~)
t h a t the g e n e r a l i m p r e s s i o n was of a rough sphere.
These p o l y h e d r a l crystals p r e d o m i n a t e d u n d e r all of
the conditions w h e r e f o r m a t i o n to lead dioxide h a d
occurred. Crystals i d e n t i c a l in size and shape to these
b u t consisting of sulfate w e r e found in the u n f o r m e d
portions of the same p l a t e and in the original d r i e d
paste of the plates as r e c e i v e d f r o m the m a n u f a c turer. These crystals did not v a r y significantly in
size, shape, or n u m b e r u n d e r a n y of the f o r m i n g
conditions used. It a p p e a r e d t h a t the p o l y h e d r a l
c r y s t a l s of s u l f a t e w e r e being c o n v e r t e d d i r e c t l y into
lead dioxide w i t h o u t e x t e r n a l change of form. It was
found m o r e o v e r t h a t this conversion occurred s u b sequent to and w i t h g r e a t e r a p p a r e n t difficulty t h a n
t h a t which took place on a second f o r m of sulfate
p r e s e n t in the paste.
This second f o r m of c r y s t a l ( t y p e A) a p p e a r e d
u s u a l l y in the f o r m e d areas of the p l a t e as long
n e e d l e l i k e or r e c t a n g u l a r c r y s t a l s of l e a d dioxide.
[The e x c e l l e n t electron m i c r o g r a p h s of Buskirk,
Boyd, and S m i t h (3) show t h i n p l a t e s of r e c t a n g u l a r
f o r m at the surface of f o r m e d positive plates. There
is a p o s s i b i l i t y t h a t the c r y s t a l s h e r e i n d e s c r i b e d m a y
be of a s i m i l a r f o r m and a p p e a r n e e d l e l i k e only as a
consequence of h a v i n g been sectioned edgewise.
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Vol. 109, No. 9
CRYSTALLOGENESIS IN FORMING PLATES
While the term needlelike will appear frequently in
the subsequent discussion as a description of the
actual appearance of the crystal in the section, the
above possibility should be retained in mind.] This
type A crystal varied in size, shape, uniformity, and
quantity depending on the conditions under which
forming took place, as will be discussed in a later
section. The size of these type A crystals varied with
the conditions from a m a x i m u m of about 150~ in
length when long and needlelike to a m i n i m u m of
about 10~ when short and rectangular. Crystals
similar in size, shape, and frequency of occurrence
were always found in the unformed portions of the
same plate, indicating that these crystals were being
converted directly from a sulfate to type A lead dioxide crystals without change in external form.
In the dried unformed plates as received from the
manufacturer, the small, polyhedral crystals of type
B predominated. Only a few of the type A crystals
were formed and these were all long, slender needles
with no hint of the rectangular structure seen in
some of the plates after forming under certain conditions. Examination of unformed plates from several manufacturers, however, disclosed that in some
of these the rectangular crystals of large size (type
A) predominated. Thus it appears that the presence
of the type A crystals can be induced either by
certain conditions associated with paste composition, temperature, time of drying, specific gravity
of the acid, etc., during pasting, or b y the control
of similar conditions in the forming process. In
the present experiment it was certain that crystal
structure of the crystals of type A was modified
(and, in some instances, the n u m b e r of crystals
was changed) either during the soaking prior to
passage of current or in that period at the beginning of current flow when no conversion to lead dioxide could be detected.
Fig. 2. Large needlelike crystals of what is presumed to be a
basic sulfate over~oid with hard Pb02. Each needlelike crystal is
surrounded by a slightly less dark area of soft PbO~ that formed
on crystals of a much smaller type and at a later time than the
overlay on the needlelike crystals. The white or very light areas
represent unformed paste. Compare with Fig. 3. Formed at 4oC, in
1.25 sp gr electrolyte and 0.25 amp/dm ~ current density. Photographed by polarized light. Magnification approximately 650X.
763
Fig. 3. More detailed view, of crystals s:m~lar to those shown in
Fig. 2, obtained by relief polishing. The hard dense PbO~ stands
in relief, outlining the original crystal of basic sulfate, and because
of its hardness is brightly reflecting. The softer Pb02 surrounding
these needles is featureless and dark in color wEle some as yet
unformed paste may be seen as a featured, light colored material
at upper and lower right margin. Photograph represents the type
of crystal obtained when positive plate was formed at 30~
in
1.05 sp gr electrolyte and 0.25 amp/dm ~ current density. Magnification approximately 6SOX.
It was also found that the initial oxidation always
began on the surface of the larger crystals of type A,
forming a hard dense layer of lead dioxide that
cause2 these crystals to appear much darker than
th~ small polyhedrons when illuminated by polarized
light and to stand outlined in relief when subjected
to relief polishing and oblique illumination with u n polarized light, Fig. 2 and 3. The reaction spread
promptly and rapidly from one to another of this
type A crystal wherever there were points of contact
either with the grid or other crystals on which this
lead dioxide layer had already formed. At a later
stage in the forming reaction, and much more slowly,
the small polyhedral sulfate crystals (type B) were
converted to a softer, lighter hued lead dioxide. The
fernlike appearance of the conversion b o u n d a r y observed at lower magnification was a result of the
initial stage of the reaction rapidly spreading through
a thinly dispersed mass of the large crystals to cover
a fairly large area while some of the small polyhedral grains in the spaces between these larger crystals
remained unchanged at this stage. As a consequence
an area of small polyhedrons adjacent to each large
crystal was converted to lead dioxide which was
sufficient in extent both to mask the outline of the
original large crystal and to make the area visible at
low magnification, but insufficient to completely fill
the area between the points of p r i m a r y reaction.
(Since the conversion of both the large needlelike,
and the small polyhedral crystals of lead sulfate to
lead dioxide appeared to take place without change
in external form of the crystal, the terms type A and
type B will be used to identify the corresponding
crystal shape in both its sulfate and dioxide form.)
It was also established that the presence of the
large type A crystals was not absolutely essential for
the conversion of the small polyhedral sulfate crys-
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764
JOURNAL
OF THE
ELECTROCHEMICAL
t a l s to l e a d d i o x i d e c r y s t a l s of t y p e B. H o w e v e r , in
t h e a b s e n c e of t h e f o r m e r , t h e p r o c e s s w a s e x t r e m e l y
slow a n d r e q u i r e d a m u c h g r e a t e r t o t a l q u a n t i t y of
e l e c t r i c i t y to c o n v e r t a g i v e n a r e a of p l a t e t h a n w h e n
they were present. For reasons that will be outlined
l a t e r in t h e p a p e r it is a s s u m e d t h a t t h e i n i t i a l f o r m a t i o n p r o c e s s t h a t r e s u l t e d in t h e p r o d u c t i o n of
h a r d , d e n s e l e a d d i o x i d e on t h e s u r f a c e of t h e l a r g e
c r y s t a l s p r o d u c e d t h e r h o m b i c f o r m of l e a d d i o x i d e ,
~-PbO~, w h e r e a s t h e l a t e r c o n v e r s i o n of t h e s m a l l
p o l y h e d r a l c r y s t a l s to a softer, l i g h t e r c o l o r e d l e a d
d i o x i d e p r o d u c e d t h e t e t r a g o n a l f o r m , fl-PbO~.
E f]ect of Changing the Forming Conditions-Positive Plate
A s to t h e s e c o n d p a r t of t h e e x p e r i m e n t , t h a t of
s t u d y i n g t h e effect of c h a n g e s in f o r m i n g c o n d i t i o n s ,
very definite and significant changes were noted,
e s p e c i a l l y in t h e p o s i t i v e p l a t e . I n t h e first place, a l t h o u g h a l l of t h e s a m p l e s r e c e i v e d t h e s a m e t o t a l
q u a n t i t y of e l e c t r i c i t y , t h e r e w a s a d e c i d e d d i f f e r e n c e
in t h e a m o u n t of l e a d d i o x i d e f o r m e d . It w o u l d b e
b e t t e r , p e r h a p s , to s a y t h a t t h e a r e a of l e a d d i o x i d e
in c o m p a r a b l e sections v a r i e d r a t h e r t h a n t h e a m o u n t
since s o m e d o u b t r e m a i n s w h e t h e r t h o s e p l a t e s t h a t
exhibited the greatest apparent coverage by lead dioxide would have indeed had the greatest capacity.
This is b e c a u s e u n f o r m e d m a t e r i a l r e m a i n e d in a l l
r e a c t e d a r e a s , a n d in s o m e cases r e a c t e d a r e a s of
s m a l l e x t e n t h a d also a n o t i c e a b l y l e s s e r a m o u n t of
u n r e a c t e d m a t e r i a l w i t h i n t h i s a r e a or, in o t h e r
w o r d s , a m u c h h i g h e r d e n s i t y of r e a c t e d p a r t i c l e s p e r
u n i t area. N e v e r t h e l e s s , t h e size of t h e a r e a c o n v e r t e d to l e a d d i o x i d e a p p e a r s to b e a good m e a n s of
j u d g i n g t h e efficiency of t h e p r o c e s s for s e v e r a l r e a sons. I n o r d e r to r e a c h t h e p l a t e i n t e r i o r w h e r e r e a c t i o n b e g i n s t h e e l e c t r o l y t e m u s t diffuse t h r o u g h a
r e l a t i v e l y n o n p o r o u s paste, c o n s i s t i n g l a r g e l y of l e a d
s u l f a t e w h i c h is a v e r y p o o r c o n d u c t o r of e l e c t r i c i t y
as well. T h o s e p a r t i c l e s t h a t a r e c o n v e r t e d to l e a d
dioxide immediately become a much better cond u c t o r , a n d b e c a u s e t h e l e a d d i o x i d e has a l e s s e r s p e cific v o l u m e t h a n t h e l e a d s u l f a t e t h e p l a t e b e c o m e s
m o r e p o r o u s to t h e flow of e l e c t r o l y t e . T h e g r e a t e r
t h e a r e a of f o r m a t i o n for a g i v e n t o t a l c u r r e n t , t h e
m o r e e a s i l y s h o u l d t h e b a l a n c e of t h e u n f o r m e d
i~
Fig. 4. This graph shows how the area of formed material in the
positive plate varied as the specific gravity and temperature were
changed although all samples received the same total quantity of
electricity, using a current density of 0.025 amp/dm ~.
SOCIETY
S e p t e m b e r 1962
?
o
8
~g
Fig. 5. As for Fig. 4, this graph shows variation of area of
formed material in the positive plate with variation of temperature
and specific gravity, but at a higher current density. The total
quantity of electricity that these samples received was the same
as in Fig. 4, but the much lower average area of formation was
apparently caused by the use of the higher current density of 0.25
amp/dm ~.
C:Y
Fig. 6. Graph similar to Fig. 4 and 5 but showing the lowered area
of forming in the positive plate when a current density of 2.5
amp/dm 2 was used. Comparison of Fig. 4, 5, and 6 indicates a maximum in area of formation at temperatures in the region of 40 ~
60oc, at the lowest specific gravity of 1.05 and at the lowest
current density used, 0.025 amp/dm "~.
m a t e r i a l be c o n v e r t e d to l e a d d i o x i d e b e c a u s e of t h e
more extended circuit paths and greater porosity
u n d e r t h e s e c o n d i t i o n s . A c a r e f u l s t u d y at h i g h e r
magnification indicated that even with more reacted
particles per unit area those plates with a small total
a r e a of r e a c t i o n c o u l d n o t b e as c o m p l e t e l y f o r m e d
as t h o s e w i t h a l a r g e r a r e a of r e a c t i o n .
F o r t h e p u r p o s e of e v a l u a t i n g r e s u l t s , t h e r e f o r e ,
a n e s t i m a t e w a s m a d e of t h e a r e a of t h e p l a t e s i n v o l v e d in t h e f o r m i n g r e a c t i o n , i g n o r i n g t h e a c t u a l
d e n s i t y of f o r m e d p a r t i c l e s w i t h i n t h i s a r e a . F r o m
t h e s e e s t i m a t e s , b a s e d on a n a v e r a g e d v a l u e of t h e
p l a t e surface, t h e sections p a r a l l e l to t h e s u r f a c e a n d
cross sections, t h e g r a p h s s h o w n in Fig. 4, 5, a n d 6
were prepared. Each graph represents the variation
in t h e t o t a l a r e a of f o r m e d m a t e r i a l w i t h c h a n g e s in
a c i d specific g r a v i t y a n d t e m p e r a t u r e w h e n t h e c u r rent density and total current are maintained constant. T h e s u c c e s s i v e g r a p h s s h o w t h e c h a n g e in area,
at a g i v e n a c i d specific g r a v i t y a n d t e m p e r a t u r e , w i t h
c h a n g e in c u r r e n t d e n s i t y . T h e r e s u l t s i n d i c a t e t h a t
t h e a r e a of f o r m a t i o n c o n t i n u o u s l y i n c r e a s e d w i t h
d e c r e a s i n g specific g r a v i t y of e l e c t r o l y t e a n d w i t h
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Vol. 109, No. 9
CRYSTALLOGENESIS
decreasing c u r r e n t density. In g e n e r a l the m a x i m u m
a r e a of f o r m e d lead dioxide, for a given specific g r a v ity and c u r r e n t density, a p p e a r e d b e t w e e n 40 ° and
60°C.
The m i c r o s t r u c t u r e of t h e positive p l a t e was also
found to v a r y w i t h t h e conditions used in forming.
This was not t r u e of the small p o l y h e d r a l crystals
p r e v i o u s l y r e f e r r e d to as t y p e B which a p p a r e n t l y
r e t a i n e d the same size and shape r e g a r d l e s s of conditions, b u t a p p l i e d to the l a r g e r crystals of t y p e A
on which the f o r m i n g process a p p e a r e d to initiate
and which changed shape, size, a n d f r e q u e n c y of
occurrence w i t h changes in conditions. The subsequent description of the changes in c r y s t a l form is
incomplete. There w e r e not only v a r i a t i o n s in form
t h a t are not included, but v a r i a t i o n s in size and f r e quency of occurrence for a given t y p e t h a t w o u l d be
superfluous to describe. The main point to be m a d e is
t h a t change from one f o r m to a n o t h e r of the t y p e A
c r y s t a l was r e p r o d u c i b l y o b t a i n e d and t h a t definite
c o r r e l a t i o n could be d r a w n b e t w e e n e x p e r i m e n t a l
conditions and the o b t a i n e d m i c r o s t r u c t u r e . It m i g h t
be wise to r e i t e r a t e t h a t the s u b s e q u e n t description
refers only to the changes t h a t occurred in the l a r g e r
c r y s t a l s of t y p e A t h a t p r o d u c e the i n i t i a l and h a r d e r
form of lead dioxide, and not to the small p o l y h e d r a l
crystals t h a t p r o d u c e d the subsequent softer f o r m of
lead dioxide, and which a p p a r e n t l y w e r e not influenced by t h e f o r m i n g conditions.
The large crystals of lead dioxide fell into s e v e r a l
m a i n categories, a n d as has been mentioned, v a r i e d
in size f r o m 10 to 150ft. A t t h e lowest c u r r e n t density,
t e m p e r a t u r e , and specific gravity, Fig. 4, t h e area of
f o r m e d lead dioxide was n e a r the m a x i m u m . Yet
u n d e r these conditions the lead d i o x i d e so f o r m e d did
not seem to be much h a r d e r t h a n the original lead
sulfate, because relief polishing p r o d u c e d only a u n i f o r m l y smooth section in which t h e u n f o r m e d areas
could not be d i s t i n g u i s h e d from those w h e r e f o r m a -
Fig. 7. Illustrating the very long and thin needlelike crystals produced at low specific gravity of electrolyte, 1.05, and low temperature, 4°C. Such crystals were visible only by polarlzed light.
These were produced at a current density of 2.5 amp/dm 2. At
lower current densities they are even longer, but more difficult to
see. Dark line at left is a portion of the grid. Compare these
crystals with those of Fig. 2. Magnification approximately 650X.
IN FORMING PLATES
765
tion to lead d i o x i d e h a d occurred. (Relief polishing,
done on a v e r y soft lap w i t h light pressure, tends to
p r e f e r e n t i a l l y r e m o v e the softer m a t e r i a l , l e a v i n g
the h a r d e r e x p o s e d in r e l i e f on t h e surface. A n y such
i r r e g u l a r i t y in surface can be easily d e t e c t e d b y u s ing oblique i l l u m i n a t i o n for t h e microscope.) It was
found, however, t h a t this a p p a r e n t l y soft m a t e r i a l
contained l a r g e n u m b e r s of e x t r e m e l y long a n d thin
n e e d l e l i k e c r y s t a l s of lead dioxide, Fig. 7. These only
b e c a m e visible w h e n the section was e x a m i n e d b y
p o l a r i z e d light. It is b e l i e v e d t h a t these long crystals
consisted of the hard, dense modification of l e a d d i oxide, b u t t h a t because of their thinness t h e y could
not be resolved in t h e relief polishing process. It is
significant t h a t in the as y e t u n f o r m e d portions of the
same p l a t e t h e r e w e r e found sulfate crystals of s i m i lar shape a n d size.
W h e n samples w e r e c o m p a r e d in which the t e m p e r a t u r e and c u r r e n t d e n s i t y used in the f o r m i n g h a d
been the same, b u t in which the specific g r a v i t i e s of
e l e c t r o l y t e h a d differed, the area of f o r m a t i o n w a s
found to decrease w i t h each increase in specific g r a v ity. At the same t i m e the crystals of t y p e A in the
m i c r o s t r u c t u r e w e r e found to become i n c r e a s i n g l y
shorter, thicker, and m o r e r e c t a n g u l a r in outline as
the specific g r a v i t y i n c r e a s e d to about 1.25. As the
c r y s t a l s b e c a m e s h o r t e r and more r e c t a n g u l a r in
shape t h e y also increased in thickness, and it was
found t h a t a h a r d e r l a y e r of l e a d d i o x i d e h a d f o r m e d
on the surface of the c r y s t a l t h a n on the i n t e r i o r and
t h a t this h a r d m a t e r i a l outlined the b o u n d a r i e s of the
original crystal, Fig. 8. Thus, each increase in specific
g r a v i t y of e l e c t r o l y t e p r o d u c e d s t r u c t u r e s t h a t w e r e
more c l e a r l y outlined and h a d a m o r e definite d e m a r c a t i o n b e t w e e n the outer coating and the interior.
A b o v e a specific g r a v i t y of 1.25 this d e m a r c a t i o n b e came i n c r e a s i n g l y less distinct, a n d at the highest
value of specific g r a v i t y the f o r m e d a r e a was small
Fig. 8. Illustrating the more rectangular type of crystal obtained
with increasing specific gravity of electrolyte. Compare this figure
where forming was at a specific gravity of 1.25 with Fig. 3, where
the specific gravity was 1.0S. Current density and temperature were
as in Fig. 3. A portion of the grid metal alloy with segregated
light-colored particles of antimony appears as a dark material
at the left side of the photograph. Magnification approximately
650X.
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766
JOURNAL
OF THE ELECTROCHEMICAL
and a p p e a r e d to be u n i f o r m l y soft. In this case no
large crystals could be fcund w i t h e i t h e r relief p o l ishing or p o l a r i z e d light, and it m u s t be concluded
t h a t conditions w e r e u n f a v o r a b l e to t h e i r formation.
U n d e r these conditions only t h e small p o l y h e d r o n s
w e r e detected in e i t h e r the f o r m e d or u n f o r m e d p o r tions of t h e plate.
It was found t h a t for a given specific g r a v i t y of
e l e c t r o l y t e and c u r r e n t d e n s i t y t h a t the area of f o r m a t i o n was at a m a x i m u m b e t w e e n 40~176
and
decreased at both h i g h e r and lower t e m p e r a t u r e s .
T e m p e r a t u r e also influenced the m i c r o s t r u e t u r e .
Thus, if at the lowest t e m p e r a t u r e t h e r e w e r e p r e s ent only the long n e e d l e l i k e c r y s t a l s s i m i l a r to those
shown in Fig. 7, these w e r e r e p l a c e d at a h i g h e r t e m p e r a t u r e by the shorter, h a r d e r , m o r e r e c t a n g u l a r
forms shown in Fig. 8, b u t u s u a l l y of l a r g e r size. This
l a t t c r f o r m was almost i n v a r i a b l y found at those
t e m p e r a t u r e s w h e r e the a r e a of f o r m a t i o n was at a
m a x i m u m . A t still h i g h e r t e m p e r a t u r e s the open
r e c t a n g u l a r forms w e r e r e p l a c e d b y l a r g e rough, i r regularly shaped particles that had a uniform hardness t h r o u g h o u t t h e i r cross section, Fig. 9, b u t which
w e r e not v e r y numerous. In general, the effect of a
t e m p e r a t u r e increase was to p r o d u c e shorter, t h i c k e r
crystals, w i t h a m o r e i r r e g u l a r outline t h a n those
f o r m e d u n d e r o t h e r w i s e e q u i v a l e n t conditions b u t at
a lower temperature.
Comparison of Fig. 4, 5, and 6 shows t h a t w i t h a
given t e m p e r a t u r e and specific g r a v i t y i h e r e was an
increasingly l a r g e a r e a of f o r m a t i o n as i h e c u r r e n t
density was decreased. The m i c r o c r y s t a l s f o r m e d at
the t h r e e c u r r e n t densities e m p l c y e d had r o u g h l y
the same shape w h e n c o m p a r e d at e q u i v a l e n t t e m p e r a t u r e and specific g r a v i t y of e l e c t r o l y t e except
t h a t the i n d i v i d u a l c r y s t a l s w e r e much s m a l l e r and
m o r e n u m e r o u s for each increase in c u r r e n t density.
SOCIETY
September 1962
Fig. 9. The large irregular crystals that appear at high temperature. Note that these are hard and dense throughout and are
surrounded by an area of the softer lead dioxide, which is shown as
the dark featureless material surrounding the large grains. Do not
confuse this with the dark appearing grid at the left of the picture.
Unformed paste also appears at the right. Formed at 80~
specific gravity and current density were as in Fig. 8. Magnification approximately 650X.
Mechanism of Formation--Negative Plate
The process of f o r m a t i o n in the n e g a t i v e p l a t e
followed a quite different course f r o m t h a t in the
positive. I n i t i a l l y r e d u c t i o n took place at the n e g a tive grid j u s t as o x i d a t i o n also o r i g i n a t e d at the grid
of the positive plate. But w h e r e a s t h e lead dioxide
f o r m e d a m o r e or less u n i f o r m c y l i n d e r of reaction
around the grid the n e g a t i v e p l a t e reaction p r o c e e d e d
at once to t h e surface b y t h e most d i r e c t route. This
r o u t e was u s u a l l y along both sides of a n y cracks t h a t
opened to the surface. W h e r e v e r the reaction r e a c h e d
the surface it s p r e a d r a p i d l y to cover it, so t h a t the
two surfaces of the p l a t e w e r e q u i c k l y c o n v e r t e d to
crystals of lead a l t h o u g h the i n t e r i o r of the p l a t e r e m a i n e d u n f o r m e d u n t i l long a f t e r w a r d , Fig. 10. This
was quite t h e opposite to w h a t occurred in the positive plate, and erroneous conclusions w o u l d h a v e
been o b t a i n e d if the p l a t e h a d not been sectioned.
In ~he o r i g i n a l dried, u n f o r m e d , n e g a t i v e p l a t e s
used for these e x p e r i m e n t s only the small p o l y h e d r a l
lead sulfate c r y s t a l s w e r e found. In the f o r m e d or
p a r t i a l l y f o r m e d p l a t e s this also a p p e a r e d to be t h e
case. D u r i n g the f o r m i n g these c r y s t a l s w e r e observed to become t r a n s l u c e n t and finally to dissolve
in the i m m e d i a t e v i c i n i t y of lead crystals a l r e a d y
f o r m e d or at the grid. U n d e r t h e conditions used for
the first p a r t of the e x p e r i m e n t , w h e r e a s t u d y was
Fig. 10. Upper photograph: Cross section through negative plate
after 6 hr forming time, showing how surface is formed prior to the
interior. The two oval dark areas are cross sections through grid
members as is the dark line that bisects the lower photograph
horizontally. Lower photograph: Plane section of negative plate
with 2 hr forming time. Note that formation does not proceed
uniformly from the grid, but preferentially along the sides of
cracks that allow entrance of electrolyte. Conditions of formation
the same as for Fig. 1. Magnification approximately 8X.
m a d e of sections r e m o v e d at v a r i o u s stages of the
f o r m i n g process, the lead c r y s t a l s t h a t f o r m e d at the
grid or o n . o t h e r lead c r y s t a l s in contact w i t h the
grid w e r e o b s e r v e d to h a v e long n e e d l e l i k e s t r u c t u r e
and to be so d e n s e l y i n t e r m i n g l e d as to m a k e difficult
i n d i v i d u a l e x a m i n a t i o n , Fig. 11.
Ef/ect of Changing the Forming Conditions-Negative Plate
In the n e g a t i v e p l a t e it was found t h a t the g r e a t e s t
a r e a of f o r m e d m a t e r i a l was at a specific g r a v i t y of
e l e c t r o l y t e of about 1.25, b e t w e e n 30 ~ a n d 60~ a n d
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Vol. 109, No. 9
CRYSTALLOGENESIS
IN FORMING
PLATES
767
Ii
o
~_ ~
~.o
.-
'r
c; \ oc
Fig. 13. Graph showing a very slight increase in area of formed
material over the previous figure, but here the current density was
increased to 0.25 amp/din ~.
Fig. 11. Appearance of lead crystals in the negative plate. Such
crystals are scattered fairly uniformly throughout the area where
formation has occurred. The area containing such crystals increased
with the time of forming rather than the number of crystals per
unit area. As a result the material in the area between crystals, as
shown here, would not be converted until quite late in the process.
Toward the end of the forming period, however, the number of
crystals of lead would enormously increase and would no longer
be individually distinguishable. Magnification approximately 200X.
t h a t c u r r e n t d e n s i t y d i d n o t h a v e v e r y m u c h effect
w h e n t h e t e m p e r a t u r e a n d specific g r a v i t y w a s as
s t a t e d a b o v e , Fig. 12, 13, a n d 14. A s c a n b e s e e n f r o m
Fig. 12 t h e l o w e s t c u r r e n t d e n s i t y d i d c a u s e a n i n c r e a s e of t h e a r e a of f o r m e d m a t e r i a l w h e n f o r m i n g
t o o k p l a c e in l o w specific g r a v i t y e l e c t r o l y t e , b u t t h e
a m o u n t does n o t a p p e a r to b e significant. T h e c o m b i n a t i o n of h i g h t e m p e r a t u r e a n d h i g h a c i d g r a v i t y
n o t o n l y p r o d u c e d no f o r m i n g b u t c a u s e d a c t u a l
s h e d d i n g of p l a t e m a t e r i a l .
When the negative plates were examined at high
m a g n i f i c a t i o n it w a s f o u n d t h a t c o n s i d e r a b l e c h a n g e
o c c u r r e d in t h e s t r u c t u r e of t h e l e a d c r y s t a l s w h e n
t h e c o n d i t i o n s of f o r m i n g w e r e v a r i e d . S i n c e t h e l e a d
crystals were definitely formed by deposition from
s o l u t i o n a f t e r t h e d i s s o l u t i o n of t h e n e c e s s a r y a m o u n t
of l e a d s u l f a t e t h e i r s t r u c t u r e d i d n o t d e p e n d on t h e
p r e s e n c e of a n y p a r t i c u l a r k i n d of c r y s t a l b u t o n l y
on t h e a v a i l a b i l i t y of l e a d ion.
~
\o o
ul
~o
~,~.o
-..
%,o
~sc,,\o~
Fig. 12. Graph showing that a maximum occurred in the area of
formed material of the negative plate when the electrolyte had a
specific gravity of between 1.15 and 1.25 and was used at about
40oc. The same total quantity of electricity was employed for all
samples and the current density was 0.025 amp/dm ~.
>
Q
1
/
L4~
'~os
cescj\~
Fig. 14. Graph showing the somewhat lower area of formed material obtained when the current density was further increased to
2.5 amp/dm ~. Comparison of Fig. 12, 13, and 14 with Fig. 4, 5, and
6 indicates that current density had a more pronounced effect on
positive plate formation than on that of the negative plate.
T w o m a i n t y p e s of s t r u c t u r e w e r e o b s e r v e d . D e p e n d i n g on t h e c o n d i t i o n s e m p l o y e d t h e l e a d c r y s t a l s
were either long and needlelike or roughly spherical.
I t w a s s u s p e c t e d t h a t t h e n e e d l e l i k e c r y s t a l s at t i m e s
h a d a b r a n c h e d s t r u c t u r e , b u t t h e y w e r e u s u a l l y so
c l o s e l y i n t e r m i n g l e d t h a t it w a s difficult to d e t e r m i n e
this, Fig. 15. F o r t h e s a m e r e a s o n t h e r e w a s a p o s s i b i l i t y t h a t t h e s o - c a l l e d s p h e r i c a l c r y s t a l , since it
s h o w e d no c l e a r l y d e f i n e d faces, m i g h t in r e a l i t y b e
a m a s s of n e e d l e l i k e f i l a m e n t s r a d i a t i n g f r o m a c o m m o n n u c l e u s b u t w i t h e a c h n e e d l e so fine as to b e
b e l o w t h e l i m i t of o p t i c a l m i c r o s c o p e r e s o l u t i o n t h u s
g i v i n g t h e i m p r e s s i o n of a solid s p h e r i c a l o b j e c t ,
Fig. 16.
T h e m a j o r c h a n g e in c r y s t a l a p p e a r a n c e p r o d u c e d
b y v a r y i n g t h e f o r m i n g c o n d i t i o n s w a s to a l t e r t h e
size of t h e s e c r y s t a l s a n d to c o n v e r t one t y p e i n t o t h e
other. T h e l a r g e s t c r y s t a l s of t h e n e e d l e l i k e a p p e a r a n c e w e r e p r o d u c e d w h e n t e m p e r a t u r e , specific
gravity, and current density were all at the minim u m of t h e series. T h e c r y s t a l s d i d n o t a p p e a r v e r y
s e n s i t i v e to c h a n g e s in t e m p e r a t u r e w i t h i n t h e r a n g e
investigated. There was a slight tendency, however,
for t h e a v e r a g e c r y s t a l size to b e c o m e s m a l l e r as t h e
t e m p e r a t u r e w a s i n c r e a s e d . C h a n g e in t h e specific
g r a v i t y of e l e c t r o l y t e h a d t h e m o s t effect on c r y s t a l
a p p e a r a n c e . W h e n t h e specific g r a v i t y w a s i n c r e a s e d
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768
JOURNAL
OF THE ELECTROCHEMICAL
SOCIETY
September 1962
Discussion
Fig. 15. View of the unusually large dendritic type crystals of
lead formed in the negative plate at 4~ an electrolyte specific
gravity of 1.05 and at a current density of 0.025 amp/dm ~. The
long lead filaments appear to have an irregular and porous surface
that may possibly consist of much smaller secondary filaments. Magnification approximately 650X.
Fig. 16. View of the spherical type of lead crystals formed in the
negative plate when the specific gravity of electrolyte was 1.45, the
temperature 4~ and the current density 2.5 amp/dm 2. Magnification approximately 650X.
the crystals w e r e found to become coarser, t h a t is,
the n e e d l e l i k e forms b e c a m e short and thick a n d a p p e a r e d in dense groups. A t the h i g h e r specific g r a v i ties these groups a p p e a r e d to be r e p l a c e d by the
s p h e r i c a l p a r t i c l e s of lead which, as has been said,
m i g h t possibly be composed of m a n y e x t r e m e l y
small n e e d l e l i k e forms.
At a constant t e m p e r a t u r e and specific g r a v i t y ,
f o r m i n g at an increased c u r r e n t d e n s i t y p r o d u c e d
s m a l l e r c r y s t a l s in the same m a n n e r as t h a t caused
by increasing the t e m p e r a t u r e w h e n specific g r a v i t y
and c u r r e n t d e n s i t y w e r e held constant.
The most e x t e n s i v e a r e a of f o r m a t i o n occurred
in the samples w i t h the n e e d l e l i k e c r y s t a l s and the
m i n i m u m a r e a of f o r m a t i o n in those p l a t e s cont a i n i n g the spherical p a r t i c l e s of lead. The a r e a of
f o r m a t i o n was more e x t e n s i v e w h e n the n e e d l e l i k e
c r y s t a l s w e r e of s m a l l size t h a n w h e n t h e y w e r e
large.
The d a t a o b t a i n e d are insufficient to a r r i v e at a n y
definite conclusions, but some v e r y i n t e r e s t i n g suppositions can be made, p a r t i c u l a r l y in the case of
the positive plate. There was definite evidence t h a t
a p a r t i c u l a r l a r g e t y p e of c r y s t a l was the first to
u n d e r g o reaction to f o r m the lead dioxide. A t the
same t i m e it was found t h a t f o r m i n g could t a k e place
in the absence of this t y p e of c r y s t a l b u t a p p a r e n t l y
at a much slower rate.
It t h e r e f o r e a p p e a r s obvious t h a t this t y p e of
c r y s t a l which produces a c r y s t a l s t r u c t u r e and affinity for o x y g e n so different f r o m that of the f a r more
n u m e r o u s small r e g u l a r p o l y h e d r o n s m u s t r e p r e s e n t
a different chemical compound. While d e t e r m i n a t i o n
of the i d e n t i t y of these compounds was not a t t e m p t e d
in the p r e s e n t e x p e r i m e n t it is possible to m a k e
a t e n t a t i v e identification based on p r e v i o u s l y p u b lished work.
L a n d e r (4) established the composition of t h r e e
compounds o b t a i n e d by boiling w a t e r suspensions
of lead monoxide, PbO, and lead sulfate, PbSO,, in
the p r o p e r ratios. Two of these compounds w e r e
found to be basic sulfates: t e t r a b a s i c lead sulfate,
P b S O , ' 4 P b O a n d monobasic lead sulfate, PbSO~
PbO. The t h i r d compound a p p e a r e d to be a h y d r a t e
and was t e n t a t i v e l y identified as the m o n o h y d r a t e
of tribasic lead sulfate, PbSO~'3PbO'H~O. I k a r i (5)
studied the p r e p a r a t i o n of the m o n o h y d r a t e of t r i basic lead sulfate and concluded t h a t its f o r m a t i o n
was modified b y the p a r t i c l e size of the P b O used
and by w h e t h e r the red or y e l l o w modification was
employed. The m e t h o d of d r y i n g and t h e a m o u n t
of CO... in the d r y i n g a t m o s p h e r e also influenced the
yield. T a k a g a k i (6-8) and Ikari, Yoshizawa and
O k a d a (9, 10) s t u d i e d the basic oxides t h a t w e r e
found in p a s t e d plates m a d e f r o m various ratios
of PbO and PbSO,. They found v a r i a t i o n s in the
a m o u n t of basic oxides and the points of m a x i m a
d e p e n d i n g on w h e t h e r t h e y used the r e d or y e l l o w
form of PbO and on the size of the lead monoxide
particles. They a g r e e d on the a d d i t i o n a l significant
o b s e r v a t i o n t h a t the t e t r a b a s i c l e a d sulfate was e n t i r e l y a b s e n t f r o m those pastes t h a t w e r e d r i e d at
t e m p e r a t u r e s below 60~ and was found in pastes
t h a t w e r e d r i e d above 80~ or steam dried, a p p a r e n t l y f o r m e d at the h i g h e r t e m p e r a t u r e b y the
decomposition of the h y d r a t e d t r i b a s i c salt into the
t e t r a b a s i c and monobasic forms.
The t h e o r e t i c a l points of m a x i m a in the PbO,
PbSO, m i x t u r e s should occur at a p p r o x i m a t e l y 25
w e i g h t p e r c e n t of t h e lead sulfate for the f o r m a t i o n
of t e t r a b a s i c lead sulfate, PbSO4-4PbO; at a p p r o x i m a t e l y 31% of lead sulfate for the f o r m a t i o n
of t h e m o n o h y d r a t e of tribasic lead sulfate, PbSQ,"
3PbO.H_~O; and at a p p r o x i m a t e l y 58% of lead sulfate for the f o r m a t i o n of monobasic lead sulfate,
PbSO4"PbO. None of the authors cited above r e p o r t e d a g r e e m e n t w i t h the t h e o r e t i c a l p e r c e n t a g e s
u n d e r all of t h e conditions investigated, b u t Ikari,
u
and O k a d a (9) a p p e a r e d to a t t a i n
a g r e e m e n t w i t h these v a l u e s w h e n using steam
d r i e d pastes m a d e from e i t h e r modification of the
lead monoxide w i t h m e a n p a r t i c l e size of 0.9~ or
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Vol. 109, No. 9
CRYSTALLOGENESIS
less. T a k a g a k i (6) a p p a r e n t l y r e a c h e d a g r e e m e n t
only w h e n using the y e l l o w modification and steam
drying, b u t p a r t i c l e size was not specified.
In s u m m a r i z i n g the w o r k of these v a r i o u s authors
it w o u l d a p p e a r t h a t in m i x t u r e s containing f r o m
0 to 25% PbSO~ the u n r e a c t e d P b O w i l l diminish
to insignificant amounts and the PbSO~'3PbO'H~O
will increase to a m a x i m u m at 25% PbSO4. P r o v i d e d
the t e m p e r a t u r e of m i x i n g has been m a i n t a i n e d
below 60~ no crystals of PbSO~-4PbO w o u l d be
expected. If the t e m p e r a t u r e has exceeded this v a l u e
the a m o u n t of PbSO,-3PbO'H~O found in this
region will decrease g r e a t l y and be r e p l a c e d b y i n c r e a s i n g l y l a r g e a m o u n t s of PbSO,-4H~O as the
a m o u n t of PbSO4 in the o r i g i n a l m i x t u r e increases
t o w a r d 25%. P a s t e m i x t u r e s w i t h f r o m 25 to 60%
w i l l contain i n c r e a s i n g l y large amounts of PbSO~P b O while PbSO~'3PbO.H~O in significant a m o u n t s
will d i s a p p e a r at about 45-50% and P b S O , . 4 P b O
w i l l likewise become insignificant at about 31%.
Paste m i x t u r e s above 60% PbSO4 will contain increasing amounts of u n r e a c t e d lead sulfate and d e creasing amounts of PbSO~'PbO as the PbSO~ content in the original m i x t u r e increases t o w a r d 100%.
Ikari, Yoshizawa, and O k a d a (9) and Dodson (11)
found t h a t the a m o u n t of a-PbO~ found in a f o r m e d
p a s t e d p l a t e i n c r e a s e d as the specific g r a v i t y of the
e l e c t r o l y t e used in f o r m i n g d e c r e a s e d and as the
d e n s i t y of the original paste used in f o r m i n g i n creased. They also found t h a t t h e a m o u n t of a-PbO.o
i n c r e a s e d as the t e m p e r a t u r e used in f o r m a t i o n was
increased, b u t the t e m p e r a t u r e s used in t h e i r e x p e r i ments a p p a r e n t l y did not exceed 60~ The J a p a n e s e
a u t h o r s also showed t h a t an i n c u b a t i o n period, after
e l e c t r o f o r m a t i o n began, was r e q u i r e d before PbO~
could be detected in the paste. Both Dodson and the
J a p a n e s e w o r k e r s r e p o r t e d t h a t ~-PbO~ was f o r m e d
first, followed at a l a t e r stage in the e l e c t r o f o r m i n g
by i n c r e a s i n g a m o u n t s of fl-PbO~. C o m p a r i n g these
observations w i t h those in the p r e s e n t p a p e r t h a t the
first conversion to PbO~ is at the surface of a p a r t i c u l a r species of crystal, t h a t these c r y s t a l s i n crease in n u m b e r , l e n g t h a n d r e g u l a r h a b i t w i t h d e creasing e l e c t r o l y t e specific g r a v i t y , c u r r e n t density,
and t e m p e r a t u r e , and t h a t these crystals a p p a r e n t l y
form as a first step in electrolysis, develops a strong
suspicion t h a t the h a r d dense surface l a y e r on these
crystals must be the a-PbO~ observed by the e a r l i e r
w o r k e r s e m p l o y i n g x - r a y analysis. F u r t h e r d a t a
from the cited p a p e r s indicate t h a t m a x i m u m f o r m a t i o n of a-PbO~ occurred u n d e r conditions t h a t
would cause m a x i m u m f o r m a t i o n of PbSO,-3PbOH..,O. This indicates t h a t the o b s e r v e d crystals on
which the PbO.. f o r m a t i o n first occurred w e r e p r o b a b l y the m o n o h y d r a t e of the t r i b a s i c lead sulfate.
Doubt is cast on this conclusion by T a k a g a k i ' s p h o t o m i c r o g r a p h s (7) which show c r y s t a l s s i m i l a r in size
and shape to those r e p o r t e d in the p r e s e n t p a p e r b u t
which he identified as the t e t r a b a s i c lead sulfate,
PbSO~'4PbO. However, since the f o r m a t i o n of ~PbO~ is g e n e r a l l y observed as a surface l a y e r on the
u n d e r l y i n g c r y s t a l it is p r o b a b l e t h a t in this l a y e r
of the c r y s t a l t h e r e has occurred some change p r i o r
to PbO~ formation. This m i g h t be caused b y the
IN FORMING
PLATES
769
t r a n s f o r m a t i o n of PbSO~'3PbO'H~O into PbSO,"
4PbO and PbSO4"PbO, as r e p o r t e d b y L a n d e r (4)
or the f o r m a t i o n of some as y e t unidentified, r e l a t i v e l y unstable, i n t e r m e d i a t e compound on the c r y s tal surface. It is e v i d e n t t h a t f u r t h e r i n v e s t i g a t i o n
will be r e q u i r e d to settle this.
On the basis of the foregoing some v e r y i n t e r e s t ing speculation is in o r d e r concerning the ever
p r e s e n t p r o b l e m of increasing the efficiency and
l o n g e v i t y of b a t t e r y plates. F o r if a continuous film
of h a r d dense lead dioxide is being f o r m e d on the
surface of a p a r t i c u l a r crystal, the presence of a
sufficient n u m b e r of such crystals of the p r o p e r size
and shape should ensure a continuous n e t w o r k of
such h a r d s t r u c t u r e t h r o u g h o u t the p l a t e and the
s e p a r a t i o n of the softer m a t e r i a l into small cells
held t o g e t h e r by the h a r d film, s o m e w h a t as shown
in Fig. 17. This h a r d lead d i o x i d e film should h a v e
a g r e a t e r d e n s i t y t h a n t h e s u r r o u n d i n g softer m a t e r i a l and t h e r e f o r e g r e a t e r electrical conductivity.
If it does consist of a-PbO~ then this w o u l d ass u r e d l y be t r u e because of the g r e a t e r o x y g e n d e ficiency. Less electrical resistance would t h e r e f o r e
be e n c o u n t e r e d b e t w e e n the grid and the more distant portions of the active m a t e r i a l and the electron
flow would be e x p e d i t e d .
P e r h a p s an even more i m p o r t a n t point w o u l d be
the possibility of p r o l o n g i n g p l a t e life b y the r e tention of active m a t e r i a l . I k a r i , Yoshizawa, and
O k a d a (13, 14) and Dodson (12) showed t h a t the
discharge capacity of the a-PbO~ was not as great
as t h a t of t h e B-PbO~. In e x p e r i m e n t s w i t h solid
electrodes of the two forms of l e a d d i o x i d e (13)
the J a p a n e s e w o r k e r s showed t h a t the d i s c h a r g e a b l e
thickness w h e n the p o r o s i t y of the m a t e r i a l was
zero was b e t w e e n 0.3 and 0.4tL on a-PbO,~ and about
1~ on fi-PbO_~. P r o v i d e d a sufficiently thick film of
Fig. 17. Photomicrograph illustrating a type of structure that
might ass:st in active-material retention and electrical conductance
for the positive plate. Here the original crystals have been overlaid
by a hard, dense surface layer of what is presumably a-Pb02. These
crystals are sufficiently interlaced so that this surface layer of PbO~
when envisioned in three dimensions could act as a cellular network throughout the paste. Crystals were formed at 40~
0.23
amp/dm 2 current density, and 1.05 sp gr of electrolyte. Magnification approxlmatety 650X.
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770
JOURNAL
OF THE ELECTROCHEMICAL
~-PbO~ w a s p r e s e n t i n i t i a l l y on t h e a p p r o p r i a t e c r y s t a l f o r m s , it c a n b e seen t h a t t h e s u r f a c e l a y e r of
lead sulfate formed by the initial discharge would
be c o n v e r t e d to fi-PbO.~ on t h e n e x t c h a r g e c y c l e
and that subsequent charge-discharge cycles would
t e n d to t a k e p l a c e in t h i s s u r f a c e l a y e r a n d t h a t
p e n e t r a t i o n i n t o t h e u n d e r l y i n g a - P b O 2 w o u l d occ u r v e r y s l o w l y or n o t at all. It h a s b e e n r e p o r t e d
b y I k a r i , Y o s h i z a w a , a n d O k a d a (13) t h a t w h e n
l a y e r s of ~-PbO~ w e r e p r e s e n t u n d e r t h e fl-PbO.~
t h a t d i s c h a r g e of t h e fl-PbO~ o c c u r r e d first, f o l l o w e d
b y t h e d i s c h a r g e of t h e ~-PbO... T h e s e e x p e r i m e n t e r s
h a v e also r e p o r t e d t h e i n t e r i o r of p l a t e s to b e
s t r o n g l y a l k a l i n e e v e n a f t e r l o n g i m m e r s i o n in acid,
a n d it is l i k e l y t h a t t h e i n t e r i o r of a t w o - l a y e r c o a t i n g such as h a s b e e n p r o p o s e d w o u l d r e m a i n p e r m a n e n t l y in a s t a t e of l o w h y d r o g e n ion c o n c e n t r a tion. T h e p r e s e n t a u t h o r s in t h e l i g h t of t h e f o r e g o i n g r e p o r t s see no r e a l o b s t a c l e to t h e f o r m a t i o n
of a n e t w o r k of ,~-PbO.o t h r o u g h o u t t h e m a s s of a c t i v e m a t e r i a l t h a t w o u l d s e r v e s i m u l t a n e o u s l y as a
c o n t i n u o u s c u r r e n t p a t h a n d a b i n d e r to r e t a i n a n d
s u p p o r t t h e b a l a n c e of t h e p a s t e m a d e u p of s m a l l
p o l y h e d r o n s of fl-PbO~. B y t h e m e c h a n i s m p r e v i o u s l y o u t l i n e d t h i s n e t w o r k , p r o v i d e d it h a d s u f ficient t h i c k n e s s , w o u l d be c o v e r e d b y a n o u t e r l a y e r
of ~-PbO~ w h i c h w o u l d p r o t e c t t h e u n d e r l y i n g
s t r u c t u r e a n d a l t e r n a t e f r o m PbO.~ to P b S O , w i t h
e a c h c y c l e of c h a r g e a n d d i s c h a r g e . T h e u n d e r l y i n g
a-PbO.~ w o u l d n o t c y c l e at a l l o r c o n v e r s i o n w o u l d
b e at s u c h a s l o w r a t e t h a t m a n y c y c l e s w o u l d be r e q u i r e d to d e s t r o y it.
I n a n a t t e m p t to c o n f i r m t h i s l i n e of r e a s o n i n g a n
e x a m i n a t i o n w a s m a d e of a l i m i t e d n u m b e r of p l a t e s
that were available with known performance data.
It w a s f o u n d t h a t in a l l cases of s u c c e s s f u l p e r f o r m a n c e a t y p e of s t r u c t u r e such as h a s b e e n a n t i c i p a t e d a n d d e s c r i b e d a b o v e w a s p r e s e n t a n d still
v i s i b l e , for e x a m p l e , in p l a t e s t h a t h a d b e e n on
o p e n c i r c u i t f o r f o u r y e a r s , or on float for nine. F o r
t h e cases of u n s u c c e s s f u l o p e r a t i o n it w a s f o u n d t h a t
a hard network was completely lacking although
hard isolated particles were occasionally present.
I t w a s r e p o r t e d b y B u r b a n k (15), w h o s t u d i e d t h e
x - r a y d i f f r a c t i o n p a t t e r n of s o m e of t h e s e p l a t e s ,
t h a t t h o s e p l a t e s h a v i n g t h e t y p e of s t r u c t u r e d e s c r i b e d a b o v e also g a v e e v i d e n c e of l a r g e a m o u n t s
of ~-PbO~ w h e r e a s t h o s e in w h i c h it w a s a b s e n t d i d
not. T h e a b s e n c e of t h e a b o v e d e s c r i b e d n e t w o r k
of h a r d m a t e r i a l a n d t h e s i m u l t a n e o u s a b s e n c e of
~-PbO~ in p l a t e s w i t h u n s a t i s f a c t o r y p e r f o r m a n c e
a p p e a r s significant.
F u r t h e r c o n f i r m a t i o n is s u p p l i e d b y t h e w o r k of
D o d s o n (12) in w h i c h h e r e p o r t e d t h a t on S A E
O v e r c h a r g e L i f e T e s t s t h e b a t t e r i e s c o n t a i n i n g ~PbO~ o u t l a s t e d p r o d u c t i o n b a t t e r i e s , a n d t h e s a m e
a p p e a r e d to b e t r u e of S A E C y c l e L i f e T e s t s a l t h o u g h
SOCIETY
S e p t e m b e r 1962
t h e t e s t r e s u l t s w e r e n o t as c o n c l u s i v e as in t h e
f o r m e r case.
S i n c e t h e r e p o r t s of D o d s o n a n d of t h e v a r i o u s
Japanese workers previously cited indicate the
s t e p s n e c e s s a r y to p r o d u c e a p a s t e w i t h t h e s e c h a r a c t e r i s t i c s it s h o u l d p r o v e to b e a r e l a t i v e l y s i m p l e
m a t t e r to p r o d u c e a p o s i t i v e p a s t e of g o o d r e t e n t i o n a n d l o n g life s h o u l d t h e s e s u p p o s i t i o n s p r o v e to
be c o r r e c t .
I n t h e case of t h e n e g a t i v e p l a t e t h e b a s i c c a u s e
of f a i l u r e is n o t loss of a c t i v e m a t e r i a l , b u t a p p e a r s
to b e t h r o u g h t h e f o r m a t i o n of l a r g e s u l f a t e c r y s t a l s
t h a t b l o c k t h e p o r e s of t h e p l a t e a n d t h r o u g h a
g r a d u a l c o n v e r s i o n of t h e n e e d l e l i k e l e a d c r y s t a l s
to p o l y h e d r a l f o r m s w i t h m u c h less r e a c t i v e s u r f a c e .
T h e r e w a s no i n d i c a t i o n f r o m t h e f o r e g o i n g e x p e r i m e n t t h a t a n y s o l u t i o n to t h i s p r o b l e m c o u l d b e
f o u n d in t h e m e t h o d u s e d f o r t h e f o r m i n g process.
H e r e t h e m e c h a n i c s of t h e p r o c e s s r e q u i r e t h e s o l u t i o n a n d r e p r e c i p i t a t i o n of t h e c r y s t a l s a l t e r n a t e l y
e i t h e r as l e a d or as l e a d s u l f a t e a c c o r d i n g to w h e t h e r
t h e cell is c h a r g i n g o r d i s c h a r g i n g . I t d o e s n o t a p p e a r l i k e l y t h a t t h e f o r m of c r y s t a l p r o d u c e d b y t h e
f o r m i n g p r o c e s s c o u l d e x i s t l o n g e n o u g h to h a v e
a n y p r o l o n g e d effect on p e r f o r m a n c e .
M a n u s c r i p t received Jan. 16, 1962; revised m a n u s c r i p t
r e c e i v e d M a y 18, 1962.
A n y discussion of this p a p e r will a p p e a r in a Discussion Section to be p u b l i s h e d in the J u n e 1963 JOURNAL.
REFERENCES
1. A. C. Simon and E. L. Jones, This Journal, 1@2, 279
(1955); U. S. N a v a l Research Lab. Reports No.
5149, J u n e 25, 1959; No. 5679, Oct. 2, 1961; No.
5733, Feb. 1, 1962.
2. G. W. Vinal, "Storage Batteries," p. 35, J o h n W i l e y
& Sons, Inc., N e w Y o r k (1940).
3. J. E. Buskirk, P. D. Boyd, and V. V. Smith, P a p e r
p r e s e n t e d at The Electrochemical Society M e e t ing, Houston, October 1960.
4. J. J. Lander, This J o u r n a t , 95, 174 (1949). U. S.
N a v a l Research Lab. R e p o r t No. C-3262, March
22, 1948.
5. S. Ikari, J. Electrochem. Soc. Japan, 27, 385 (1959);
overseas ed., 27, El50 (1959).
6. T. Takagaki, ibid., 26, 278 (1958); overseas ed., 26,
E87 (1958).
7. T. Takagaki, ibid., 26, 320 (1958); overseas ed., 26,
El03 (1958).
8. T. Takagaki, ibid., 26, 354 (1958); overseas ed., 26,
El18 (1958).
9. S. Ikari, S. Yoshizawa, and S. Okada, ibid., 27, 426
(1959) ; overseas ed., 27, E167 (1959).
10. S. Ikari, S. Yoshizawa, and S. Okada, ibid., 27, 487
(1959) ; overseas ed., 27, E186 (1959).
11. V. A. Dodson, This Journal, 108, 401 (1961).
12. V. A. Dodson, ibid., 108, 406 (1961).
13. S. Ikari, S. Yoshizawa, and S. Okada, J. Electrochem. Soc. Japan, 27, 552 (1959); overseas e~d.,
27, E223 (1959).
14. S. I k a r i and S. Yoshizawa, ibid., 27, 613 (1959);
overseas ed., 27, E247 (1959).
15. J e a n n e B u r b a n k , P r i v a t e communication.
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