Note: Descriptions are shown in the official language in which they were submitted.
~5~371
This invention relstes to 1nethods ntilized in the reduction of
corrosion nnd gns3ing in aqueous electrochemical cells particularly in
slkaline type cells haviug zinc anodes.
~ problem in nqueous electrochemical cells bss been the evolntion of
hydrogen gas in the sealed cell container. Such g&ssing hns resulted in
corrosion, lesknge of the electrolyte $rom the cell, cell container
deformation and rupture, and a possible hazard ~hen the cell is disposed
of in a fire. Vsrious e~cpedients hsve been ntilized in preventing,
minimi~ing llud controlling snch hydrogen 8a8 evolntion and its
conseqnences, Such espedients have included mechanical mesua snch a8 vents
snd sdditional volume for storing the hydrogen without ~ceDsive pressnre
build up. Chemical e~cpedients hsve inclnded: corrosion and gallsing
inhibitors such as lesd, indinm, tin, cadmium, bismuth, thallium, and
gallinm; hydrogen getters such as rare raetala ~lupported ou o~idos ~uch a8
plstimm snpported on alnminum oxide or palladinm or finely di~p2rsed
nickel mixed with pol~tetrsflnoroethylene and manganeae dioxide, and
hydrides l~nch a8 Lalli'd; hydrogen recombination with oxygen particulsrly
ntilized in nickel cadmium cells; and removsl of chemicsls 3uch as
chlorides fro~ the snrface of the nnode metal vhich tend to accelerate
torrosion. The st conmlon, ~o~t effective snd the oldest e~pedient
(particnlnrly in slkaline electrolyte cells) hss been the utili~ation of
~ercnry to 3malgsmate the anode metal such as zinc to increase the
norrdally high h~drogen overpotentisl and to psovide for a nniform
equipotentisl surface on the anode metal. B.ecently, ~ith the incresse of
environmental concerna, rednction or elimination~of rdercnrv without
~ubstantial concomitant incresse in cell corrosion or ga~sing hns been
vigorously pursued.
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~L2~937~
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It is en object of the pre~ent inveDtion to provide ~eaD~ for
reduction or eli~iu-tion of mercurg in cell uodec vithout lo~- of
corrosiou protection Ird ircre-ee in cell g-s-iDg.
Thi- and other object~, feature~ aDd advautage- of the pre~ent
inveDtiou vill beco~e Dore evideDt fro~ th~ follo~iDg ti~CU~3ioD.
GeDerllly the pre~ent invention eo~pri~e~ ~ethod for ou~iDg an
electrocherqical cell eubject to reduced ga--iDg by me-ua of utiliz-tion of
~pecific o teri-lo iD apecific ~t-tee; ~uch ~gteri~ nd the cell it~elf.
~he method i~ pgrticulorly epplic-ble to ~ cell hnviDg n anode comprieed
of a r~ercury a2alg~0ated povdered ~etal ~ueh a- rinc. In tbe oethod of the
pre~eDt~iDvention the po~dered ~et-l ia oubet-nti~ formed into
individu-1 siDgle cry~t~19 erd a a~11 amouDt of or~e or Dore of indiu~,
c-drqiur~, g-llium, tballiurq, biuruth, tin, nd le-d ia added to the anodic
terial i e. the povdered ~et~l (amalgar~ted or un~ulgss~ed) or to
~ercury vhich i~ then ~ulga~eted vith the po~dered r~etal. The mercur~ Dd
the additive, in thi~ latter procedure, geuerally form a ~urace allag OD
each of the particles
Though the u~ of ~ingle cry~e~1 aDOde ~uterial r~t tbe u-e of a~
iudiu~ snd/or other adtiti~e~ have aep-rately been ~no~n to effec~ivelg
per2it 70~e redUCtioD of ~ercury content in the auode vithout aetri~eDtal
incres~e iu ga~iDg, the effect of the ~o~biD~tioD h~- uDe~p~ctedl7 ~e~u
discovered to be coD-iderehl~ ~ore teun ~dditive. Thu~, in cell~ h-vin~
~alga~ated 3ingle cry~tal riDc ~node~ the ~ount of nercury in the
: .
ar~algsm csn be effeceively reduced frorq bout 6-72 to about 42. Similarly
the utili~stion oS aD intiu~ additiv~ vith polycr~t-lliDe ~iDC a~algaD
nodes permie- the retuction of ~ercury from ~bout 6-72 to ~bout 3.5Y.
~o~ever, in accordance ~ith the pre-ent invention, a corqbiD~tioD of the
t~o, i e ~ siDgle cry~t~l zinc er~ lg~ h an indiun ~ddi~ive
u~e2pectedly pernit~ ~he effective reduction of tbe w rcury to gbout 1.52.
Aa a nstter of course, conbinstion of cher~ical gas reduction e~pedients
does oot usually provide an 9dditiv~ effect nor doe~ e~ceB~i~o utili~stion
of addit ives .
~ ` ~
~5~ 3~
The single crystnls of zinc are preferably prepsred 88 described in
copending application llo. 448,306 . Such procedure involves the
formstion of a thin ~kin crucible on esch of the zinc particles by
oxidation in air at a temperature just below the melting point (419~C) of
the zinc, heating of the skin encloJsd zinc particles in an inert
atmosphere sbove the melting point of tbe zinc snd 810~ cooling thereafter
with removal of the oxide skins. Zinc particle sizes generally range
between 80 and 600 microns for ntility in electroches~ical cells and such
~ethod provideD an effective means for makiug single crystal particles of
such smsll dinensions.
Generally the amounts of indium or other additive added to the snode
metal amslgAm may range between ~5-5000 ppm and preferably bet~een
lOO-lOOO ppm. 8uch ~terial may be directlg added to the marcury itself.
For e~a~ple indium is highly solnble in mercury snd can be directly ~Idded
tbereto in the form of powder or grsnules. ~lternatively, the additive mav
oe plated on the ~urface of the anode metal from ~alts of the ~Idditive
prior to amalgamation with mercury. Such balts include the halides,
particularly chlorides, o~l:ides and acetates of the ~aterials Dnch as
indinm. It has been discovered that the addit*e~ ~uch a~ indium whether
by addition to the mercury or by platiog on the single crystsl anode 1Detsl
particles do not in fact disrupt the ~ingle crystsl nsture thereof to any
detrimental extent ss msy have been expected.
The ~Dount of mercury in the anode llmalgam may range from O - 4%
depending upon the cell utilizstion snd the degree of gas~ing to be
tolerated.
The amalgamated single crystal ~etal particles with sdditives ~uch as
indium are then formed into anodes for electrochemical cells particulsrly
slkaline electrochemical cells. Such cells generally have snodes of zinc
and cathode~ of materisls ~uch as msngauese dioxide, oilver oxide,
nercuric oxide and the li!ce. Electrolytes in such cells sre generally
alkaline and u~ually comprise hydroxide solutions such as of sodius~ or
potassium hydroxide. Other anode metals capable of being formed into
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~;~593~71
single crystal po~ders and vhich are u~eful in electrochcmicsl cells
.include Al, Cd, Ca, Cu, Pb,.~g, Ni, and Sn. It is uuderstood that with
~nodes of these metals th additive is not the ~sme as the nnode act *e
r~aterial but is less-electrochemically-nctive.
.Tbe effects of the present ineention csn be ~ore clesrly evidenced by
consideration:of co~psrative gas~ing rates and dischArge-capRcities-ss
-sho7n in the follo~iug e~ples. It is understood that ~uch 2~a~ples are
for illustrstive purpo~es And re not to be con~trued a8 a limitstion OD
the present invention. In the e~mples a8 vell as throughout this
discus~ion all pArts are pArts by ~eight-unless other~ise indicated.
.~3A~PLE 1
Zinc po~der.dmalg~ms contaiDing.1.5Z mercury-are ~ade ~ith
:polycrystalline ZiDC alone, polycrystalline zinc:~ith O.lZ.indium as aD
additi~e element-with the ~ercury, single crystAl:zinc,:and single crystAl
zinc with O.lZ indium a8 an additive ele~ent with the ~ercury. LquAl
AmOUUts of.the amalgAm po~dera arz theu plac~d.in equal a~ounts of 37Z XO'd
~lkaline colution (typical electrolyte.oolutiou of alk~line cells) and
tested for ga~sing st 8 te~perature of 71~C. The amouut of gassing,
meAsured in-microliters/gram-per day tuL¦g-day) and the rste reduction
fActors (~ith the polvcrystAlline zinc:control beiug 1) are szt:forth iu
Table 1:
T~BL~ 1
~NODE ~AT~BI~LGA5SING B~TERATE B3D~CTION F~CTOR
PolycrystalliDe zinc, 1.5%.~g 295
PolycrgstAlline riDc, 1.5Z ~g 105 .2.8
O.lZ indium
Single crystal zinc, 1.5~ 'dS 140 2.1
Siugle crystnl zinc, 1.5% ~g 30 9.8
0.1% indium
~ rate reduction factoT (if auy~ ~ould at ~ost ba~e b~en e~ected to
be ~bout 5.9 (2.8 x 2.1~ for 8 co~bined utilizatioo of ~Lngle cry~tal zinc
:and indiu~ vith a gas~ing rate reduction to about 50 uL/g-day. Tbe
` ~5~37~
co~bination ho~vcr ryDer~i~ticallJ rhducr- tbe gae-isg ~o about double
tbe ~xp~ct2d reduction
E~PL~ 2
FifeeeD ~ ~u of aingle cry~eal ~inc particlce ~ith ~rioue
co2bin-tion~ of atditi~r ~ter h le of indiu~, tb~lliuA~ g-lliu~ ~nd lc-d
~re prep~rad 1st t-ot d for cDrroeion. Th- ~dtiti~c r~teri lJ rc pl~ed
on tb- ~inc plrticl-- frn~ ~-lta tboroof. All eh~ a~ulga~ cont-i~ 1 5~ by
veigbt of ~rcury rb- aoounta of ~c~ of tbo tditiv~ r~terial~
(deri~n~t~d bg ~Jaud ~-~ if not pr-- nt) aro 0 12 in~iu~ t~n~ 0.0lg
t~alliu~ ~TI~0.005X ~-lliu~ (C ), ~n~ 0.042 lc d (~o). T~o ~r~DJ of c~cb
of tho 2alg~rt~ re pl~ced in 372 ~O~ trolyt- aolution ~it~ g~-~ing
t tbe nt of 24 and 48 bourr b-in~ ~q~ur d at 90-C ~ ~ein~
r~pre~entativ2 of corro~ion ~J controls t~o ~ lg~-u re ~ d- Yitb one
cont~ining no Idditiv~ ~rerial but vith 1.5~ u-rcur~ ~nd th~ otb~r
~ont~iing pol~er~et~lline rinc ~itb 77 ~rcury cimilar to tb~t co D only
u-~d in ~lk~lin~ typ- c-llo. ~eault~ of Juch t~cta re ~iv~n in T~ble 2.
I~nL~ 2
ADDITIVE BLE~E~T VOL~E OP C~S (2L), 90 C
In Tl G- Pb 24 aour~ 48 3Our~
Z0 + - - - 0.17 0.51
~ 0.13 0 49
- - ~ - 0 42 1.35
_ _ _ ~ 0.40 1.15
0.13 0.36
_ ~ _ 0 l~ 0 47
~ ~ + 0.15 0.4~
~ ~ ~ ~ 0.12 0 40
- ~ + 0.12 0 56
~ + 0 40 1.13
30 ~ ~ ~ - 0.13 0 42
I + - l 0.1l 0.32
- + I ~ 0 15 0.60
0.14 0.44
~ ~ + + 0 lO 0 28
- - - - (control) 0 41 1 39
Concrol 72 ~g-polycsy~t~llin~ Zn 0.16 0 43
Indiu~ ~nd/or thalliu~ aa ho~n in tbe abovr t-bl~ provide the ~o-
~efficaciou- reduction of gA-~ing and ~re thuc pref~rred r~hodir~nr~ of che
pre~ent invention aoYever incre-~e ir percen~age of g~lliur or le-d i-
~g3~7~ i
expected to provide similcr effects Oeh~r materiala imil~r i2 effecc toiDdium such as c-dmiu~ ein ~nd bi~muth m~y be ~imil-rly eIpected to
provide the enhsnc~d effe~t of th~ preoeoe inventior
E~A~PLE 3
~ even zinc malgams CODt~iniDg 1 57. ag ~re prep-red ~icb three beiag
comprised of Dingle crystal zinc (~dde ~c dercribed bove) ~Dd four bein8
comprised of polycry~talline zinc The armilg~mJ containing ~intle cry~tal
ZiDC coQprise tvo h~viug 0 12 i~dium tone dded to the ~ercury prior to
amdigamation ~nd the other beiD8 plated on che ZiDc particle urf-ces
prior to amalg~r~dtion) dDd ore having DO indiun The polycry~t-lline zinc
~r~ Ig-ms iDclude three vithout lead for direct cor~p-riaon vitb tbe ~ingle
crystal zinc whicù cont-iD~ Do le-t Dd on~ polycry~t~lline r~alg~r~ vi~b
le-d ~ commooly utilized in electrocbemicel cella Sbe lead free
polycrysc-lline ~rJdlg-~s are directly ~r-l~gou~ to tbe tbree ~ingle
cryDt~l zinc ~m lg~mD The polycry~tilliDe le-d~d zin~ ~m31~-~ cont-in-
0 022 indiun A control of polycry~t-lliDe ZiDC vitb le-d and 77 rDercury
~as commonly utilized in Ik~line c~ o pr~p~red Tvo gram
samples of each of the sbove a~algama sre te~t~d for ga~aing t elevDted
temperdtures (71 C and 90'C) for varying time ptriod~ vitb total gar
volume and 8asaiD8 r~tes ùeirlg cor~par~tively deterriiDed la Cet forth in
lable 3 below
E~AHPLE 4
Cells are 3~de vith tbe 4mDlgar~ de~crib~d iD ~-r~ple 3 of ~iDgle
crystal zirlc vith 0 lY indium ~both typea), polycryatallirle ziuc vith 0 1
indium plated OD th~ zinc p~rticle~ polycry4t-11iDe ZiDC vitbD 0.02~
indium added to the ~ercury, Dd a control of polycry~t~lline ZiDC vitb Do
iDdium and 7~ r~ercury ~- typicAl alk-lioe cell) E-cb of tbe cell~ of AA
standdrd size ~oDtaiD~ a 2 7 grdr~ ~Dode ~1 75~ 4t2rch graft copoly~er
gelling agene) 2 6 grars of a 37~ 80~ ~lectrolyte Dd a r~Dg~e3e diolide
rathode vith the cell beiDg aoode limited Five cellr~ ~re te~ted for
gassing for varyiDg periods at 71 C vitbout diDch~rge aod five are
similarly tes~cd but after partial disch~rge at 3 9 ohm for ODe bour
lo~al gas volu~e aDd gassiog rates are set forth in Table 3 belo~
i
Ç~
12593~7~
lo o~l ~ 1 ~ 1~ ~ c ~ o~ 0
_ C D ,_
~o ~ ~ ~
O ~ V~ ~_
~a
~W~ 00 1-OOO 0000 ~1-00 ~'~
OOO.pO~ oo~ 0~i~ O~ 1:~ ~;;
~0 1~~ _ ~
q~ ~
n~ 00 000 0 0000 ~~00
oOO~O~ O Co~oco ~1~ .
Z ~: ~
W
""~ w 1"" ~ 0~O 0~ 1I11 0 1111~ ~0~0 ~ ~C a~z
O :~ ?~C~
P
O ~1--00 td 1--OO ~ ~ C _
ooo~ ~3 ~ o V10C~ ~ oo~o ~ _
,
O~ Do~ . . ~ ..1~,,. ~W~1~ C ~
a
b w
~~ ww~www~ oo ~-ooo oooo ~ oo ~ Zn
~n~ o~o~n\n~JW~I~ 0~00 _~jW~~ o ~ ~C
., n e
~ ~2~3~
E~PLF 5
Cells are m~de a6 iD EYa~ple 4 nd re e-ch di~charged to v-riou~
cutoff-volt~ea vith 3 9 oh~ lo-d ~ith ehe capscitiea in ~er~ic~ hours
et oreh iD T3ble 4 belov.
IABLE 4 (Diacharge Ch~r-cteri~tic-)
(Service ~oura t 3.9 oh~s)
SINGLE C8YSTAL ZINC PCLYCRYSTALLIN~ Z~NC
CDT-OFF 0 1~ In 0.1Z In 0 022 In 0 lZ Ia aO In
~OLTAGES 1 5% 'd4 in 1 5Z ~ 1.5Z ~g tl,5Z dc 72 a~ Ctrl
1 2 0 660 0 668 0 533 0 688 0 bZ3
1 1 1 616 1 638 1.457 1.712 1 553
1 0 i 826 2 859 2.480 2.926 2.598
0 9 3 535 3 652 3 235 3 619 3 295
0.8 3 800 3 967 3.498 3.883 3 599
0.65 3 986 4 179 3.594 4.020 3 684
It i~ evident ro~ the bove el~ple- nd table- th~t th~ gle
crys~sl ~inc ~ith o~e or ~ore ~dditive~ of tho pre~eot iuvention h
~arkedly effective in permittine larEe'nercury reduction~ vithout increase
iD cell g~s-ing uhile at the ~r~ e enhADciDg cell diich-rge
characteristics ~hen such cell- ~re co~pared to the current co~rcial
alkaline cells having higb r~ercury aw-lga~ content
It is understood that the above e~arlples are for illu~tr~tive purpose~
only and detail~ contained therein are not to be conatrued a~ limitatioD6
on tbe preaent in~eDtioD Changea in cell coDctruction, materialc, ratio~
aDd tbe like ~ay iD fact be made vithout departiDg fro~ the ~cope of ~he
pre6ent invention a~ defiD~d iD the folloviDg clai~
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