p. 1


# OAR Box 1313 Prepped by LaTeia Shed



### Document

Number: 

# 75 ) ll-B-4 9 Docket Number: 

# A-88-0 2

Printed 6/12/20089:03:30AM

Sheet 75of 99

# MRI $ P. 2 

## A-88-0 2 MIDWES TRESEARC H INSTITUT E TX - CH-ff i Suit

e 35 ( •10 1 Harriso n Oak

s Boulevar

c Cary . N.C . 275 U



## \u-* \ Date : Ma

y 20 , 198 8 (Finalize d Novembe

r 3 , 1988 ) Subject : Sit

e Visit—Engelhar

d Corporatio

n Chromiu m Electroplatin

g NESHA P \88, —•*—s\ ~..-\ \\ EP A Contrac t 68-02-3817 ; ES

D Projec t 85/(M\Kf'v * V

\^J^ MR I Projec t 7717- K\0>->-"* * From : Robi

nBarke r To : Andre

w Smit h ESD/ISB/SS S (MD-13 ) U . S . Environmenta

l Protectio

nAgenc y Researc hTriangl

e Park , N.C . 2771 1 I . Purpos

e Th e purpos e o f th e visi t wa s t o obtai ninfonnatio

no nth e manufactur

e an d us e o f th e trivalen

t chromiu

m process sol

d b y Engelhar d Corporatio

n(formall

y Harshaw/Filtro

l Partnership ) a

s a substitut

e fo r th e hexavalen

t chromiu

m process use

d fo r decorativ

e chromiu

m electroplatin

g applications . II . Plac

e an d Dat e Engelhar d Corporatio

n 2380 0 Mercantil

e Roa d Beachwood , Ohi

o 4412 2 (216 ) 464-571 0 Decembe r 2 , 198 7 III . Attendee

s Engelhar d Corporatio

n(Engelhard ) 0 . Ken t Dickie , Produc

t Manage r - Meta l Finishin

g H . Richar

d Garner , Vic

e Presiden

t an d Genera l Manage r Meta l Finishin g an d Industria

l Product

s Denni s R . Masarik , Technica l Directo

r Meta l Finishin

g an d Industria

l Product s U . S . Environmenta

l Protectio

nAqenc y (EPA ) Andre w M . Smith , IS

BP. 3

2 Midwes t Researc hInstitut e (MRI ) Robi nBarke r IV . Discussio n A meetin g wa s hel dwit hpersonne l fro m Engelhar dt o discus s th e trivalen t chromiu

m process . Th e discussio nfocuse do nth e trivalen t chromiu m proces s requirement s an dlimitations , basi c difference s betwee n th e double-cel l (Canning ) process an dth e single-cel l (Allbright-Wilson ) process , a s wel l a s Engelhard' s abilit y t o suppl y

th e trivalen t chromiu m proces s i f marke t deman dincreases . Thi s discussio nwa s followe db y a tou r o f th e productio nfacilit y i nCleveland , Ohio . A . Engelhard' s Trivalen t Chromiu m Proces s Requirement s an d Limitation s Engelhar dha s successfull y operate dthei r trivalen t chromiu m processe s sinc e 1975 . Engelhar dha s recentl y develope da trivalen t chromiu m bath , Tri-Chrome ®Plus , tha t operate s a t highe r bat htemperature s an dfaste r platin g rate s tha nth e bath s tha t wer e markete d1 nth e lat e 1970' s an

dearl y 1980's . Attachmen t 1 1 s th e produc t informatio nbrochur e supplie db

y Harshaw o nth e Tri-Chrome ®

Plu s platin g process . Th e trivalen t chromiu m proces s ca nb e use donl y fo r decorativ e chromiu m platin g applications . Decorativ e chromiu m application s requir e chromiu m plat e thicknesse s rangin g fro m 0.000 1 t o 1. 0 thousandt ho f a n inch(mils) . Th e trivalen t chromiu m proces s i s capabl e o f platin g th e ful l rang e o f thicknesse s require dfo r decorativ e applications ; however , th e process i s unabl e t o achiev e th e plat e thicknesse s require dfo r har d chromiu m platin g application s (>1. 0 t o 3 0 mils) . Th e Tri-Chrome ®

Plu s process require s goodcontro l o f meta l contamination . Metal s ente r th e bat hdu e t o dragou t fro m previou s platin g bath s o r dissolutio no f th e part . Meta l contaminant s ca nb e remove db y "dummying " th e solutio no r addin g ina purifie r solutio nt o th e bath . "Dummying " th e bat hi s performe db y placin g a nonproduc t par t i nth e bat h an dsettin g th e curren t densit y s o tha t th e contaminan t meta l wil l b e th e meta l tha t plate s ou t o f th e solutio nont o the par t andth e trivalen t chromiu m wil l remai ni nth e solution . Th e additio no f a purifie r solutio n t o th e bat hresult s i nprecipitatio no f meta l contaminant s whic har e the n remove dfro

m th e bat hsolutio nb y filtration . T o reduc e dragi no f metal s fro m othe r platin g bath s an dt o preven t solutio ncontamination , th e trivalen t chromiu m proces s require s sufficien t rinsing betwee nth e nicke l platin g bat han dthe trivalen t chromiu m bath . Following th e trivalen t chromiu m platin g bath , adequat e rinsin g als o i s require dt o remov e th e chloride s whic hca ncaus e corrosion . Engelhar d recommend s thre e counterflow rinse s befor e an

dafte r th e trivalen t chromiu m plating bath .

* * .P. 4

Al l trivalen t chromiu m processe s requir e a bas e laye r o f nicke l plat e o f a t leas t tw

o t o three-tenth s o f a mil . Thi s laye r o f nicke l i s require dbecaus e a nicke l plat e i s microporou s an da thinne r laye r o f nicke l woul dexpos e smal l portion s o f th e bas e metal . Inhexavalen t chromiu m plating , th e microporou s nicke l plat e i s "chromated " fro m th e chromat e compound s availabl e inth e bath , whic hcover s th e expose d portion s o f th e bas e meta l an dprovide s corrosio nresistance . However , in trivalen t chromiu

m plating , hexavalen t chromiu m i s a bat hcontaminan t an d a thicke r laye r o f nicke l an dchromiu

m (0.2 5 mils ) i s require dto'giv e th e par t corrosio nresistanc e tha t i s comparabl e t o a hexavalen t chromiu m plate dpart . Also , rus t inhibitin g pos t dip s ar e recommende dfo r us e wit h trivalen t chromiu

m bath s t o ai di ncorrosio nresistance . Brass , zinc , an

dtubula r (hollow ) stee l part s requir e specia l provision s whe na trivalen t chromiu m proces s i s used . Th e metal s foun d1n thes e part s (copper , zinc , an dlead ) ca ncontaminat e th e trivalen t chromiu m solutio ni f th e part s fal l of f th e rack s an dth e metal s dissolv e i nth e solutio no r i f th e coverag e i nth e nicke l bat hi s poo r s o tha t th e bas e metal s ar e expose dan ddissolv e i nth e solution . Thes e problem s ca n b e overcome b

y checkin g fo r an

dremovin g al l part s tha t ma y hav e falle n fro m th e rack s int o th e solutio nan db y ensurin g tha t th e coverag e i nth e nicke l bat hi s sufficien t t o cove r th e par t s o tha t portion s o f th e bas e meta l ar e no t exposed . Tubula r (hollow ) bras s o r stee l part s presen t uniqu e problem s becaus e th e nicke l platin g proces s doe s no t hav e th e throwin g powe r t o cove r th e interna l surface s o f tubula r parts . Th e inne r surface s o f th e tubula r part s tha t ar e no t covere dwit hnicke l ca nresul t 1 nlea do r coppe r contaminatio no f th e trivalen t chromium solution . B . Th e Double-Cel l Proces s Versu s th e Single-Cel l Proces s Bot hsingle-cel l an

ddouble-cel l processe s ar e use di ntrivalen t chromiu m plating . Th e double-cel l proces s wa s th e firs t proces s develope d tha t use dtrivalen t chromium . Th e double-cel l proces s wa s develope di n 1854 , bu t di dno t become commerciall y viabl e unti l th e mid-1980's . Th e single-cel l proces s wa s develope dinth e mid-1970's . Double-cel l processe s ar e manufacture dan dsol db

y Frederic k Gumr

nChemica l Company

an d MacDermid , Inc . Th e single-cel l processe s ar e manufacture dan dsol db

y Engelhar dan

dOMF/Udylit e Internationa l Corporation . Th e majo r difference s betwee nth e two processe s ar e discusse dbelow . Th e double-cel l proces s solutio ncontain s minima l t o no chlorides , whereas , the single-cel l proces s contain s a highconcentratio no f chlorides . Du e t o th e highchlorid e concentratio ni nth e single-cel l process , thoroughrinsin g i s require dafte r th e trivalen t chromiu m bat ht o remov e an

y chloride s lef t o nth e par t tha t ca nstar t corrosion . Thre e o r fou r counterflow

rinse s ar e deeme dsufficien t fo r remova l o f th e chlorides . Th e double-cel l proces s utilize s lea danode s tha t ar e place din anod e boxe s tha t contai na dilut e sulfuri c aci dsolutio nan dar e line d wit ha permeabl e membrance . Th e single-cel l proces s utilize s carbo no r graphit e anode s tha t ar e place di ndirec t contac t wit hth e platin gP. 5

solution . Th e anod e solutio n i n th e double-cel l proces s mus t b e treate d an d dispose d approximatel yever y2 months , and th e solutio n remad e t o enabl e th e proces s t o plat e efficiently . Also , th e anod e boxe s line d wit h th e permeabl e membrane s ar e susceptibl e t o breakag e b ypart s hittin g th e boxe s a s the yente r an d exi t th e platin g tank . Whe n th e anod e boxe s o r membrane s ar e broken , th e compartmen t mus t b e replace d an d th e bat h adjuste d t o it s norma l operatin g rang e befor e platin g ca n b e restarted . I n th e single-cel l process , i f th e anode s ar e broke n the ynee d onl yb e replace d t o maintai n th e correc t anod e t o cathod e ratio . Th e platin g rat e o f th e double-cel l an d single-cel l processe s ar e comparabl e t o th e hexavalen t chromiu mproces s a t 4 m i month s o f a n Inc h pe r minute . However , ther e i s a ne whigh-efficienc ysingle-cel l proces s tha t ha s a platin g rat e o f 1 0 millionth s o f a n inc h pe r minute . Fo r mor e detaile d informatio n o n bot h processes , refe r t o Attachmen t 2 whic h i s a n articl e writte n b yDr . Donal d L . Snyde r o f Engelhar d tha t wil l b e publishe d i n th e sprin g o f 198 8 i n "Platin g and Surfac e Finishing. " Thi s articl e compare s th e double-cel l and single-cel l trivalen t chromiu mprocesse s t o th e hexavalen t chromiu mproces s no wuse d i n th e majorit yo f decorativ e platin g facilities . C . Productio n Capacit yand Staffin g Engelhar d personne l wer e aske d wha t problem s migh t occu r i n supplyin g trivalen t chromiumprocesse s i f marke t deman d increase d significantly . Harsha wbelieve s tha t ther e woul d b e n o problem s i n th e chemica l supply , productio n capacity , o r equipmen t suppl yneede d t o mee t a n increas e i n demand . Th e majorit yo f chemical s use d i n th e manufactur e o f th e platin g bath , excep t fo r th e trivalen t chromiu mcompound , ar e commo n compound s tha t ca n b e purchase d fro ma variet yo f suppliers . Th e trivalen t chromiu mcompoun d i s bough t i n a foreig n market ; however , Engelhar d contacte d th e supplie r t o determin e i f th e deman d fo r th e compoun d coul d b e met , an d th e supplie r di d no t anticipat e anyproblems . Th e trivalen t chromiumbat h i s mad e up o f fou r componen t mixtures : (1 ) TC-stabilizer , (2 ) TC-regulator , (3 ) TC-addit1ve , an d (4 ) TC-adjuster . Th e curren t productio n fo r th e trivalen t chromiu mbat h component s i s wel l belo wth e productio n capacit yfo r th e plant . Bat h component s ar e produce d b ymixin g individua l chemica l component s i n a larg e tank prio r t o packaging . Th e limitin g componen t mixture , TC-stab1lizer , i s th e onl y chemica l componen t mixtur e tha t involve s a mil d chemica l reaction , and , therefore , require s a longe r holdin g tim e tha n th e othe r chemica l componen t mixture s t o allo wth e reactio n t o g o t o completion . Th e holdin g tim e fo r th e TC-stabilize r i s 8 hours , whic h require s th e componen t mixtur e t o b e package d durin g th e secon d shift . Wit h th e existin g mixin g tank s a t th e facility , th e productio n coul d b e increase d t o 35,96 0 i (9,50 0 gal ) pe r mont h fo r th e TC-stabilizer . Th e tota l productio n capacit yfo r th e facilit yi s 227,13 0 t o 302,84 0 %(60,00 0 t o 80,00 0 gal ) o f th e trivalen t chromiumbat h component s pe r month . A t present , th e plan t i s operatin g on e 8-hou r shif t an d a partia l second and thir d shift . Withi n 3 t o 4 months , th e plan t coul d add ne wmixin g tank s and a

#P. 6

ne w packagin g lin e t o increas e tota l productio ni f marke t demandwer e t o increas e significantly . Engelhar dpersonne l indicate dthat'th e technica l staf f require dt o mee t a significan t demandfo r trivalen t chromiu m coul db e me t b

y trainin g existin g distributors , hirin g new employees , an

dredistributin g th e curren t technica l suppor t staff . Meetin g th e deman dfo r technica l suppor t du e t o a dramati c increas e i nth e trivalen t chromiu m market would.requir e som e shiftin g o f resource s an dadditiona l training . A 6-mont" htim e frame woul dallo w

Engelhar dt o mee t th e demand . 2 Attachment s



### vi ~^ipptUS ; Chrottilut H Plalln g



# Trivalent :

Th e Secon d Decad e

By DR . DONAL D L . SNYDE R Research Directo r Harshaw/Filtro l Beachwood , Ohi o

56 PRODUCT S FINISHIN G 

# T hre e majo rhistorica l event s oc curre d i n th e developmen to f present-day trivalen tchromiu m electroplatin g processes. 1 Ove r10 0 year s passe d betwee n th e firstmajo r historical event , whe n trivalen tchro miu m electroplatin g wa s originall y observe d in th e laborator y b y Profes so rRobertBunson ' i n 1854 , an d th e second , th e introductio n o f th e first MARCH , I98 B tUnrr**- ataffl r : 

### - W li' .



### \*w |-vt»*> &

Electroplatin g fro m trivalen t chromiu m solution s was commercialize d ftior o tha n te n years ago ; I n thi s secon d decad e th e numbe r u l solution s availabl e ah d th e numbei - o f reason s t o conside r trivalen t have proliferate d *

commerciall y successfu l trivalen t chromiu m process , i n 1975. ' Professo rBunson' s trivalen tchro miu m electrowinnin g proces s re quire d th e us e o f

adouble-cel l plat in g tank , with th e anod e isolate d fro m th e catholyt e b y amembrane . Thi s double-cel l configuratio n wa s a majo rfacto rtha tretarde d th e de velopmen t"o

f trivalen tchromium . MARCH . 198

8 COLO R o f deposit s (above ) fro m today' s trivalen t chromiu m platin g solution s i s very clos e t o th e blue-whit e o f th e deposit s fro m traditiona l hexavalen t chromiu m platin g solutions . I twasn' tunti l th e single-cel l pro ces s wa s develope d in 197 5 thattriva len tchromiu m becam e acommercia l suqeess . Th e ne w trivalen tchromiu m proces s wa s simila rt o othe rprocesse s

PRODUCTS FINISHING 5 7

# 1 Chromiu m Platin g

* > ' Trivalen t processe s ar e use d toda y o n a wid e variet yo f parts..
. 

### if f plater s wer e use d to , suc h a s nickel , copper, an

d hexavalen

tchromiu

m electroplating . Abou tte n year s afte rthe introduc tio n o f th e firs tcommerciall

y success fu l decorative trivalen

tchromiu

m processes , the thir

d majo reven toc curred : th

e introduction of

severa l othe rtrivalen

tchromiu

m plating processes . These processes ca n be categorize d into two genera

l groups : those tha trequir e th e anode to b

e separate d fro m th e chromiu

m elec trolyt e b y amembran

e an d thos e tha

t d o not . I twasn' tunti

l approximatel

y two year s afte rthe origina

l discover y o f trivalentchromiu

m platin g tha

t Geuther

4 publishe d information on th e firs treporte d process fo

relec troplating chromiu

m fro m ahexava len tchromiu m electrolyte . Because his process di

d no trequir e the sepa ratio n o f th eanode fro

m th e cathode b y amembrane, an

d wa s eas y to op erate, muc h o f th echromiu m electro plating researc

h in the earl

y 1900' s wa s base d upon th e hexavalen

tchro miu m ion . Also , sulfate , on e o f the catalyst s necessar

y fo r decorative electroplating o f

chromiu m fro m a hexavalen tchromiu m electrolyte, wa

s anaturall

y occurrin

g impurit y i n 5 8 PRODUCT S FINISHING . chromicacid , permittin g chromiu

m t o b e plated easily fro

m these earl

y solutions . Becaus e th e hexavalent-chromiumio n processes wer

e easierto use tha

n trivalent-chromiu

m processes , hex avalen tchromiu m electroplating wa

s essentially the only commercia l dec orative-chromiu

m electroplating pro ces s i n use until th

e introduction of th e trivalen tchromiu m process i

n ap proximately 1975 . B y the mid-1980's , plater

s i n the United States "ha

d verifie d th e com mercia l viabilit y o f trivalen tchro miu m processes b

y operating ove

r 10 0 trivalen tchromiu

m tanks , re

presentin g wel l ove r50,000 gallon

s of installe d operatin g solution . Trivalen

t processes ar

e use d toda y on awide variet y o f part s an d assemblies , rang

in g fro m carpentertool s t o surgica l tools , a s wel l as on furniture, bumpers , an d wir e racks . Eve n thoug h th e trivalen tchro miu m introduced i

n 197 5 ha s advan tages , ther

e ar e als o limitations fo

r som e platers , i

n term s of platin g rate, thickness o f

electrodepositan

d th e colo ro f the deposit . Some o f the trivalen

tchromiu m processes introduced durin g the mid 1980' s hav e overcom e severa l of thes e limitations. ' On

e single-cell process ha s aplatin g rat

e a tleasttwo times tha tof th e oldertrivalen

tproces s an d ca n deposi tchromiu m almos tone mi l thick . Thi s single-cell process an d al l the double-cell processes produc e deposit s similari

n colo rt o thos e fro m tha to f hexavalen

tchromium . MARCH . 198 8 gftUgMj^^ttH U

TABL E I Chrnrtlliitt
. PlnllHt ) Pollutio n fcniiHnl Cos ! [Equipmen tCos ! t- 8 ••• , 8;s ; ^^^gfM^^^^M^^'55-5 > . Hexavalent Chromiu m > • Reactio

n tan k ';!. • Mixe r.._ __

. „ . i»Pump s ' ••.

• • ! i ; 8 7 i&f3&M?{»M-J « Controls and DumosrMi ' drver.*"> v: J
* • i m Reductio n ^'#ltl^#if ( Chromiu m Hydroxid e Precipitatio n j

'.Y 8' - ! ; r^l'*TfM"PrtM?iK»Pfi ' * Neutralizin g \3t\\.Y:iti\'Y' Filte rpres

s j : '' : ' ! \

l I'^^-^MH' ' SeI,lin 9 tank'*>***^
. Sludg e H 1 Control panel an

d control s - ; * 'Estimated Cost:
. $15,00

0
. [.Operatio n Cos

t !•..
. Estimate

d Annua l Cos t ( 1 gpt *
'• Hexavalen

t Chromium t • j ? j Hexavalent cnromlu m (gg^ i Tr i

Reductio n I W$,t).Am^\0^0ff^ 'reciDitatio n ; - ir-8- ;

. 255.W8 > "'. "'•'::J&S»iM;. ~ Trivalen t Chromiu m

~ • 5&5Ui•• $ 3 8 i." 1 : :=8 :.- . •Chromiu m Hydroxid

e Precipitation i\:)55 : 255.ji? ^ | ; Sludg e Disposa

l ; !^8
. ;•.-,,.;;,. ; 8jj|j ; 3.80 5 (14,200 lbs.)p&|&8 ' 53 8 (2,000 lbs. ) ^yi ! Tota l Cos t 77l!r$5.540iiLJjM^i8B ;

. ^ Proces s Comparison s Because al

l the trivalen

tchromiu m processes o n the marke

ttoda y fal l into two genera

l classes , base

d o n thei rgenera l chemistry, th

e processe s wil l b e divide d into these two group s fo rthis comparison . The firs tclassification include

s the origina l process introduce

d i n 1975 , severa l othernewe

rbu tver y simila r processes , an

d the ne w light-colored , high-speed version introduce d in 1987 . The y ar e al l simila rin chemis tr y in thatthey ar

e single-cel l processes . Th e secon d type , adouble-cel

l pro cess , require

s the separation o f

the anode fro m the chromiu

m electrolyt

e an d cathode . Eve n thoug h supplier s indicat e tha t MARCH , 198 8 ther e ar e severa l types o f hexavalent chromiu m electroplating processes , the grea tmajorit y of thos e no w use d commercially Td

rdecorative plating ar e simila renoug h t o b e groupe

d to gethe rfo r purpose s o f thi s comparison . Safer . A n increasingly important consideration whe

n comparing triva len tchromiu m wit h hexavalen

tchro miu m processes i s the safety , health , an d environmenta

l concern . Because th e trivalen tchromiu m ion i s utilized , chromicacid is no

tpresen ti n th e plating process . The trivalen tchro miu m ion i s muc

h les s toxic , yielding lowerhealt

h an d environmenta

l con trol costs an

d concerns tha

n thos e o f hexavalen tchromium . The tota l chromiu

m contento f PRODUCT S FINISHIN G 5 9Chromiu m Plating ?

T5 T T.'7'.rY"

"~VP'\ i-" s *vi *,!•-*:-" r*

f "*"•'" " ? •'•'•' ''''.' I rY..r \L5\iiti'\55.\ P H
__ _ Temperatur e • ' '••'•* 5.'•' Curren t Densit y(Cathode ) Agitatio n ''•''•<';*

Y •• 5 •:./. •'<••'. Anode s Single-Cel l Double-Cel l Chromiu m Single-Cel l Double-Cel l Filtratio n Single-Cel l Double-Cel l Rectilie r Trivalen t ' • Chromiu m 2.3-4. 0

" 80-120* F 40-10 0 AS F ; Mil d Ai r7 '"' Specia l Graphit e Lea d I n Anod e Box 15-2 0 g/liter
. ! 5-1 0 g/Nte r. ; Onl ylo rSolid s Continuou s Wit h Carbo n 6-1 2 V ' ' Hexavalen t Y Chromiu m Les s tha n 1 110-115* F 175-20 0 AS F Non e ' Lea d /Lea d Allo y
150-30 0 g/lile r
Uncommo n 6-1 2 V
trivalent chromiu msolution s i s ap proximately one-fift

hthat of hexava

len t chromiu msolutions
. Thi s i s on e reaso n wh y trivalent chromiu mpro cesse s are environmentall y easie r t o operate . Th e trivalen t

chromiu mio n i s presently no t

liste da s apotentiall y carcinogeni c agent , a s i s th e hexava

lii " lent

chromiu mion
. Trivalen t chro

miumprocesse s are als o muc heasie r t o handl e environmentally
. A s aresult

o f th e chemistr

y o f trivalen t chromium' s electrolyte , mistin g doe s no t

occur durin g plat

ing , a s i t doe s durin g hexavalent chromiu mplating
. Thu s les s ventila

tio n than wouldbe require dwit hhex

avalent solution s i s satisfactory
. Us e o f trivalent chromiu mals o re duce s waste-disposal problem s an d 6 0 PRODUCT S FINISHIN G costs . Waste treatmen t o f hexavalent chromiu mrequire s atwo-stag e treat
ment . Th e hexavalent

chromiu mio n i s first reduce dt o th e trivalent

chro

miumion ; the n i

t ca n b e precipitate d a s chromiu mhydroxide
. Trivalen t chromiu mplatin g solutions , which ar e already in th e reduce dtrivalen t state , requir e only th e chromium

hydroxide-precipitatio n step . Tabl e 1 compare s th e equipmen t an doperatin g cos t

fo r wast e treatin g atypical 1 2 oz/ga l hexavalent chro

miu mplatin g bat

hwit htha t fo r a2. 7 oz/ga l trivalent

chromiu mplatin g bath
. Th e treatmen t

procedur e an d associate dcost s greatly favor th e us e of trivalent
. Operatin g advantages
. Safet y an d waste-disposa l consideration s i n chromiu mplatin g ar

e ver y importan t MARCH . 198

8 TABL E II I

Hexavalen t fcluottilurU troubleshootin g Guid e

",
. 1 i
. • ; <

; ; '! ' r'-fr

- r'I|! f Typica

l Problom s ?p^tP^^^|Pf? ' .;••,- . 8 ;v^8^i:;-vV^. Low . Curren ,.^. f c 7W7"".""'- * •-•"• *

! Cause s Poo r: i : ! t • •••'.'••*'•""••"""•'.'";« • Low-uurreni''.*;.; : ;; • Gra y\ Coverag e "Burnin g " Whitewash ' Densit yStai n ~ ' • Deposit s * Rati o j Temperatur e High/Lo w Catalys t ; Par t ! Configuratio n Rac k Overloa d ..Metalli c I Impuritie s Nicke l Deposi t j Hig h Curren t i Densit y . . Bl-Polarit y

,' Chlorid e ; Contaminatio n Hig h Trivalen t Chromiu m ,

.. .

... . • Intermitten t t Electica l Contact X



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-,rrr--r"*" ! V."-*H"';T ! 'triv'.X ' 0;'!.*, j

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.

an dgreatly favor

trivalent chromiu m processes . Bu

t thi s fac t become s les s significan t i f the operatin g condition s d o no t als o favor trivalent chromiu m electroplating
. Tabl e II list s th e typical operatin g condition s for

trivalen t an dhexava

lent chromiu melectroplatin g pro cesses . Trivalent

chromiu mprocesse s ar e operate di

n th e p H rang e o f

2. 1 t o 4.0
. Hexavalent

chromiu mha s a muc hlowe

r pH , du e t o th e presenc e o f chromi c acid
. Hexavalent

chromiu mplatin g pro cesse s ar e operate dove

r arelativel y MARCH . 198

8 narro w temperatur e range , nea r 110F
. Th e processe s wit

hformula

tion s simila

r t o tha t o f th e origina l trivalen t chromiu mproces s operat e nea r ambien t temperatures , while tli e newer trivalen t chromiu mprocesse s generall y operat e a t

abou t 100F
. Leadanode s ar e use di

n bothth e hexavalent

chromiu man dth e double

cell trivalen t

chromiu mprocesses . Graphit e anode s ar e use di n th e •single-cel l trivalen t

chromiu m processes . On e distinctio n betwee n different trivalen t chromiu mprocesse s i s tha t PRODUCT S FINISHIN G 6 1Chromiu m Plating??-" :

-TABLE * IV ; tuvnleti l bht-oitilumltttHiblcshootln g Guid e
Cause s Typica l Proble m

Dar k Smudges Poo r Coverag e White Patches Metalli cImpuritie s Chemica l Imbalanc

e Zin cContaminatio n Caus e Solutio n Metalli cImpuritie s Purll yo r Dumm y Chemica l Imbalanc

e Chec k pH , Specifi cGravity , an d Amper e Hour s Zin cContaminatio n Purll yo rDumm y
som e o f the solutions use

d i n th e single-cel l processe s d o no thav e t o b e filtere d excep tt o remov e solid s fro

m th e bath , suc

h a s afte rchemica l purification , whil

e other s requir e mor e frequen tfiltration . Recommendation

s cal l fo rdouble cel l trivalen tchromiu m processe

s an d afe w single-cel

l processes t

o be con tinuousl y filtere d wit h carbon . Hexavalen tchromiu

m processes ar

e al mostneve rfiltered . Bot h hexavalen

tan d trivalen

t chromiu m deposition hav

e th e sam e curren trequirements . Fo

rmaximu m coverag e an d throw , a15-voI

trecti fie rca n b e use d o n som e of th e single cel l trivalen tchromiu

m processes whe n extremel y dee p recesse s nee d t o b e plated . I n general , though , asix to 12-vol trectifie ris al l tha tis neces sar y t o plat e chromiu m fro m trivalen t solutions . Ever

y are aof th e par ttha t ha s bee n nicke l plate d wil l b e covere d wit h chromium . I

n mostcases , hex avalen tchromiu m processes d o not 6 2 PRODUCT S FINISHIN G hav e th e covering orthrowin

g powe r o f trivalen tprocesses an

d ca n not plat e into th e recesse s a s wel l a s nickel . Troubleshooting . Table II I is a troubleshooting.guide fo

rhexavalen

t chromiu m electroplating, whil

e Table I V i s atroubleshooting guide for trivalen tchromiu

m electroplating . The troubleshooting guide fo rtriva len tchromiu m is simplified because trivalen tchromiu

m processes , a

s compare d wit h hexavalen

tchromiu m processes , hav

e improve

d covering power, wil l no tburn , ca n tolerat e an y levels o f curren tinterruptions an

d ripple , wil l tolerat e sulfat e an d chlo rid e drag-in , ca

n b e use d to plat e aroun d holes , an

d wil l no tproduc e hexavalent-chromiu

m staining . Productivity . Productivit y i s in crease d whe n trivalen

tchromiu

m processes ar

e use d because les s strip pin g an d replatin

g of part s is required . Chromiu

m colo rbuffing i s als o eliminated whe

n using most MARCH , 198

8 ^ trivalen tchromiu

m prpcesses . Pro duction ca

n be increase

d becaus e mor e part s ca n be place

d o n arac

k an d mor e rack s ca n b e place d on a workbar. Thi s i

s s o because ther

e i s less likelihood o f

burning, an

d cover in g powe ri s better . Because trivalen

tchromiu m plates i n lower-current-densit

y areas , platin g rack s ca n b e constructe

d of lighte r material . I n mostplating operations , th e hexavalen tchromiu m plating step i s the limiting proces s within the plating line . Wit

h the hig h covering an

d throwin g propertie

s o f trivalen tchro miu m electroplatin g solutions , how ever , typically the nicke l tan kbe comes the limiting tank . Costs . Base

d upon overte

n year s o f operating experience , mos tplater s hav e foun d tha tth e cos tof single-cell trivalen tchromiu

m plating is les s tha n tha to f hexavalen

tchromiu

m plating , even thoug

h the cos to f

so lution fo rtrivalen

tchromiu

m is highe rtha n tha tforhexavalent. Operatin g costs fo rtrivalen tchro miu m ar e als o lowerbecause main tenance costs ar

e loweran

d the iner t anodes hav

e indefinit e life . Th e lea

d anod e use d i n hexavalen

tchromiu m processes mus

tb e cleaned , condi tioned , an

d replace d a ttimes . Th e single-cel

l trivalen tchromiu m process uses graphit

e anodes tha

tar e relativel y inexpensive , requir

e littl e maintenance , an

d ar e only replace

d whe n mechanicall

y damaged . Anodes fo

rthe double-cell trivalen tchromiu m processes als o hav

e a MARCH . 198

8 . . .trivalen t chromiu m plate s i n lower-current-densit y areas. . . 

### 1 9 9 long life , bu

tthe anode compar

U ment s ar e ver y expensive to replac

e whe n mechanicall

y damaged . A

n ex tr aoperating expense is tha tthe so lution inside the anode compartmen t mus tb e change d frequently . The an od e boxes als o tak

e u p mor e roo m i n the tank , whic

h migh tincrease th

e chanc e o f mechanica

l damag e an d reduc e th e usable plating volume . Operatin g costs forbot

h hexava len tan d trivalen tchromiu

m ca n b c reduce d b y returnin g drag-outsolu tio n to the plating tank . Since the origina l trivalen tchromiu m processe

s operat e a tambien ttemperatures , little evaporation.takes place , makin g i tdifficul tt o retur n dragge d ou tplatin g solutio n to the plating tank . The new, high-efficienc

y single-cell trivalen tchromiu m proces s an d th e doublecel l trivalen tchromiu

m processes bot h operat e a tabove ambien

ttem peratures , however , increasing evap oration an

d the opportunit

y t o reuse dragged-ou

tplating solution . Atmosphericevaporators ar e routinely use d o n the dragged-outsolution s fro m th e single-cell trivalen

tchro miu m processes . Contamination . Bot

h the single and double-cell trivalen

tchromiu

m processe s ar e mor e sensitive t o metal PRODUCT S FINISHIN G 63{.Chromiu m Plating " 

## 66
Carbo n an dhydroge n peroxid e ca n b e use dt o remov e man y organi c impurities . 

### 199 lie impuritie s than ar e hexavalent chromiu mprocesses . Bu

t onc e pres en t i n th e solution , impuritie s ca n b e removedeasily
. Chemical purifyin g solution s ar e availabl e t o precipitat e metallic impurities
. Som

e of thes e pu rifiers ca n eve n b e adde ddurin g plat

ing
. B y dummyin g th e platin g solu

tio n an dusin g purifier s on e can maintai n atrivalent

chromiu mplat

in g bat hindefinitely i

f i t i s being con taminate donly by metalli c impuri

ties
. Carbo n an dhydroge n peroxid e ca n be usedt o remov e many organi c impurities
. Throwin g Power
. Trivalen t chro

miu melectroplatin g processe s hav e better throwin g powe

r than hexava

len t chromiu mprocesses . Platin g Rate
. Th e high-efficienc y single-cel l trivalent chromiu mproces s ha s areporte dplatin g rat e o f aroun d 1 0 millionth s o f

a n inchper

minut e while th e double-cel l processe s re portedl y plat e at

les s tha n fou

r mil

lionth s o f a n inc hpe r minute
. Th e other single-cell processe s plat e at abou t four millionth s per

minute
. Micro-discontinuou s Chromium
. Al l trivalent chromiu mprocesse s pro duc e micro-discontinuou s chromiu m 6 4 PRODUCT

S FINISHIN

G deposit s fro mth e bath
. Deposit s fromhexavalen

t chromiu mprocesse s mus t underg o variou s post-platin g o r pre-platin g step s t o induc e microdiscontinuity
. Fo r highl y corrosiv e environments , microdiscontinuou s chromiu mim

prove s corrosio n resistanc e o f nickel

chromiumelectroplates
. Unde r typica l conditions , th e corrosio n characteris

tic s of trivalen t chromiu melectro

deposit s plate dove

r a t leas t 0. 3 mi l of nickel compare favorabl y o r ar e better than chromiu mdeposit s pro duce dfro mhexavalen

t chromiu mplat

ing solutions. ' I

n mos t cases , a t leas t 1 0 millionth s o f

a n inc hof chromiu m i s specifiedfo

r corrosio n protection
. Color . Historically , th e colo r o f trivalent chromiu melectrodeposit s i s different than that

produce dfrom hexavalent

chromiu melectrolytes
. Hexavalent

chromiu melectrolyte s produc e deposit s tha

t ar e slightly blu e i n color , makin g themappear white t o th e human eye . Deposit s fromth e origina l trivalen t chromiumprocesse s d o no t contai n thi s blu e coloration , makin g themappea

r darke r i n color
. I n contrast , the ne

w double-cell triva

len t chromiu mprocesse s andthe high

efficiency single-cell trivalen t chro

miumproces s produc e chromiu mde

posit s tha t

ar e ver y simila r i n colo r t o that of hexavalent

chromium
. Many plater s an dmos t

consumer s canno t distinguis hbetween th e colo r of th e deposit s fro

mthes e ne

w triva

len t processe s an dthat

fromhexava

lent processes . Th e "pewter " or

"stainles s steel " MARCH
. 198

8 

# fc look o f deposit s fromth e original trivalen t chromiu mproces s is , t o many people , ver

y appealing
. I

t ha s been specifie dfor

som e application s becaus e o f

it s richappearance . Deposit Thickness
. A majo r

dis

tinctio n between hexavalent chro

miuman dtrivalent

chromiu mi s tha t chromiu mcan b e plate dt o almos t an y thicknes s fromahexavalent chromiumplatin g bath , while deposi t thicknes s fromtrivalen t

solution s i s limited
. Th e original single-cell triva

len t chromiu mproces s allow s platin g amaximumchromiu mthicknes s o f approximatel y 5 0 millionth s o f a n inch
. Th e double-cel l trivalen t chro

miumprocess , i

n fieldexperience , plate s amaximu mthicknes s o f les s tha n 1 0 millionth s o f

a n inch
. Th e high-efficienc y single-cell trivalen t chromiu mproces s allow s platin g u p t o approximatel y on e mil
. Fo r thi s reason , hexavalen

t chromiu mplatin g processe s are favore dfor tru e har d chrom e applications
. Wear . In mos t

cases , th e wea

r resistanc e o f

trivalen t chromiu mde

posit s i s th e same a s that o f chro

miumdeposit s fromhexavalent so lutions
. Mos t

studie s als o report

that th e hardnes s o f

the deposit s i s als o es sentiall y identical
. The Secon d Decad e Th e original , an dver

y successful , single-cel l trivalent chromiu mproces s ha s now been usedcommerciall y for more than ten years . Withi n th e sec on ddecad e o f

trivalen t chromiu m electroplating , a

n improvement

i n th e original commercial proces s wa s MARCH . 198

8 made , whichha s increase dit s platin g efficienc y an dmad e th e colo r o f it s deposi t simila r t o that o f hexavalen t chromiu mdeposits
. Th e commercial

izatio n o f

a . numbe r

o f single-cell trivalent chromiu mprocesse s an dth e introductio n o f

th e double-cel l triva

lent chromiu mproces s cam e abou t during the seconddecade
. Th e double

cell processe s als o produc e deposit s simila r i n colo r t o tha t obtainedfro

m hexavalen t

chromiu mplatin g processes . Wit hth e increas e in platin g effi

ciency , higher

deposi t thickness , an d colo r simila r t o hexavalent

chromiu m deposits , trivalent

chromiu mdeposit s can no w b e introduce dt o new mar kets
. Also , wit

hth e stricte r

safety , health , an denvironmenta l regula

tions , trivalen t

chromiu mprocesse s become eve

n more desirabl e than hexavalen t

chromiu mprocesses . Trivalent processe s present

fewe r air , water an dhealth/safet y problems
. Bot hth e first

- ari dsecond-decad e trivalen t chromiu mprocesse s are ready fo r th e challenge s o f

th e future o f chromiu mplating
. P F For more data circle 292 on Postpaid Card REFERENCES I.D
. L
. Snyder , AES FChromiu mCollo

quium , Feb
. 1987
. Also , an articl e o n ih c his

tor y o f Irivalen t chromiu melectroplatin g is to b e publishe di

n Plating and

Surface Finishing in Ihe sprin g o f

1988
. 2
. R.JV
. Bunson , Pogg , An n 1854 , 91 , 619-25
. 3
. USP : 3.954,574 ; 4,038,160 ; 4,053,374 ; 4,093,521 ; an d4,184.929
. 4
. A
. Ceuther , Liebig
. Ann 1856 , 99,314
. 5
. D.L
. Snyder , Plating and Surface Finishing. 1979 , 66 , 60-65
.

PRODUCT

S FINISHIN

G6 5P.1 2 TCRLC-0387 R 

# HARSHA WPLATINGPRODUCT S

OPERATIN G INSTRUCTION S HARSHA W TRI-CHROME ®L C TRIVALEN T CHROMIU M PLATIN G PROCES S
INTRODUCTIO N ® Harsha wTRI-CHROM E L C i s a ne wtechnolog ychromiu m platin g proces s usin g n o chromi c aci d an d offerin g th e followin g advantages : 1 . Reduce d effluen t problem s - n o need

- t o reduc e toxi c hexavalen t chromium . Reduce d sludg e volume . 2 . N o toxi c hexchromiu m - n o mis t suppressant s needed . 3 . Improve d coverin g power . 4 . Complet e absenc e o f "burnin g a t hig h curren t density . Note : Du e t o th e hig h platin g spee d o f L C a t lowe r pH' s som e microcracke d deposit s ca n b e detected . Thes e deposit s ca n giv e th e appearanc e o f burning . 5 . On e formulatio n fo r bot h decorativ e an d haze

fre e microdiscontinuou s deposits . 6 . Improve d meta l distribution : mor e unifor m thicknes s acros s curren t densities . Simplifie s rac k design . 7 . Tolerate s curren t interruption , sulfat e an d chlorid e drag-in . 8 . Bette r evaporatio n - reducin g cost . 9 . Anode s wil l las t indefinitely . Harsha wTri-Chrom e ca n replac e conventiona l o r proprietar y chromi c aci d base d electrolyte s withou t chang e o f process in g sequences . Timin g sequence s o n presen t equipmen t nee d little , i f any , alteration . Harsha wTri-Chrom e L C wil l hel p provid e a lighte r colo r deposi t tha n firs t generatio n trivalen t chromiums .



## KLCEIVE P '"' " ^ 

# HARSHAW/FILTRO L ^ 3 58 7 HARSHAW/FILTRO L PARTNERSHI P • 3010 0 CHAGRI N BOULEVAR D • CLEVELAND
. OHI O 4412 4 • (216 ) 292-920 0 

# u- 2 -

HARSHA W TRI-CHROME ®L C PLATIN G PROCES S
SOLUTIO NCOMPOSITIO N Materia l
T C Additiv e T C Stabilize r T C Regulato r Chromiu m

(Cr +3 ) Bori c Aci d (H3BO3 )
OPERATIN G CONDITION S 360-42 0 g/ L 55-7 5 g/ L 2.0-5. 0 ml/ L 20-2 3 g/ L 60-6 5 g/ L

2.3-2. 9 P H Temperatur e Cathod e Curren t Densit y Agitatio n Anode s Anod e Curren t Densit y Specifi c Gravit y1.2.0-1.2 4 Rang e (48-5 6 oz/gal ) 40 0 g/ L (5.5-7. 5 %/vol ) 6 5 ml/ L (2- 5 gal/100 0 gal ) 3. 0 ml/ L (2.7-3. 0 oz/gal ) 2 2 g/ L 6 3 g/ L Optimu m

2.5-2. 7 (80-110°F ) 85-90° F 860-108 0 A/m 2 (80-10 0 ASF ) Mil d Ai r Agitatio n Harsha wSpecia l Graphit e Maximu m5 4 0 A/m 2 (5 0 ASF ) 1.2 2 (53. 3 oz/gal )

(6. 5 %/vol ) ( 3 gal/1000 ) (2. 9 oz/gal )



# fcP. M

- 3 - PROCES S CONTRO L Genera l Al l constituent s shoul d b e maintaine d withi n th e range s specifie d unde r "Solutio n Composition" . Addition s o f al l constituent s sho.ul d b e mad e n o les s ofte n tha n ever y 5 amp-hours/litr e (2 0 A/ h gal. ) o r eac h eigh t hour s o f accumulate d operation . Extensio n o f th e foregoin g current-tim e relationship s wil l resul t i n imbalanc e o f th e solutio n an d th e necessit yt o mak e larg e addition s whic h wil l requir e additiona l electrolyzin g t o restor e th e bat h t o operatin g condition . Additio n schedule s shoul d b e establishe d fo r eac h installatio n t o adjus t fo r varyin g amount s o f drag-out . Al l addition s shoul d b e mad e durin g o r jus t precedin g electrolysis . T C Additiv e TRI-CHROM E T C Additiv e i s use d fo r makeu p an d replen

ishment . I t provide s conductivit yt o th e bat h an d als o replace s chromiu mlos t throug h drag-out . T C Additiv e ma ydissolv e wit h difficult yunles s specia l precaution s ar e used . Fas t additio n rate s ma yresul t i n th e formatio n o f wet
- lump s o f additiv e whic h ma yno t dissolve . Th e T C Additiv e i s preferabl ydistribute d slowl yan d evenl y ove r th e surfac e o f th e solution , givin g mos t o f th e materia l tim e t o dissolv e befor e furthe r addition s ar e made . Smal l frequen t addition s ar e therefor e preferred . Th e concentratio n o f T C Additiv e shoul d b e maintaine d b ykeepin g th e specifi c gravit yo f th e solutio n a t a minimu mvalu e o f 1.18 . A n additio n o f 22. 5 g/ L ( 3 oz/gal ) o f T C Additiv e wil l rais e th e specifi c gravit yapproxi

matel y0.0 1 units . I t i s preferre d t o mak e thi s additio n subsequen t t o addition s o f T C Chrom e Adjuste r (se e Specifi c Gravity) . Hig h concentration s o f T C Additiv e ma yresul t i n th e formatio n o f som e crystals , especiall yi f th e solutio n temperatur e i s low . Th e presenc e o f crystal s ma yresul t i n plugge d ai r agitatio n line s o r coate d anodes . Th e latte r ma yresul t i n reduce d current . I f th e crystal s pos e a problem , th e affecte d equipmen t an d anode s shoul d b e remove d an d cleane d (scrubbed) . Lo wconcentration s o f T C Additiv e wil l reduc e conductivit yo f th e bat h resultin g i n reduce d curren t o r th e nee d fo r increase d voltag e t o maintai n cathod e curren t density . TRI-CHROM E T C Additiv e i s a ligh t gree n powde r an d wil l ten d t o dus t easily . Prope r safet yprocedure s shoul d b e use d whic h ar e suitabl e fo r th e handlin g o f powdere d materia l tha t ca n produc e dusting .•- 4 -

T C Chrom e Adjuste r TRI-CHROM E T C Chrom e Adjuste r i s use d t o replenis h th e chromiu m

plate d fro mth e solutio n an d i s adde d o n th e basi s o f ampere-hours . T C Chxbm e Adjuste r mus t b e dis

tribute d slowl yan d evenl yove r th e surfac e o f th e solu

tio n i n th e sam e manne r a s T C Additiv e discusse d above . T C Chrom e Adjuste r wil l hav e a consumptio n rat e o f 22,5-34 0 g/10.0 0 amp-hour s (8-1 2 oz/100 0 A-h ) an d shoul d "b e adde d a t leas t afte r eac h eigh t hour s o f accumulate d actua l platin g time . TRI-CHROM E T C Chrom e Adjuste r i s a dar k gree n powde r an d wil l ten d t o dus t easily . Prope r safet yprocedure s shoul d b e use d whic h ar e suitabl e fo r th e handlin g o f powdere d materia l tha t ca n produc e dusting . T C Stabilize r TRI-CHROM E T C Stabilize r form s a stabl e compoun d wit h th e chromiu mallowin g i t t o plat e ou t fro mth e trivalen t state . Hig h concentratio n o f T C Stabilize r ma yresul t i n som e precipitatio n o f chromiu msalt s especiall yi f th e solutio n i s unbalance d i n othe r respects , suc h a s hig h pH , an d hig h temperature . Lo wstabilize r reduce s platin g rate . I t i s therefor e importan t tha t T C Stabilize r b e maintaine d withi n th e rang e specified . T C Stabilize r i s consume d b ydrag-ou t an d electrolysis . Aconsumptio n rat e o f 100 0 mL/100 0 amp-hour s (3 5 fl . oz/100 0 A-h ) ma yb e use d unti l a specifi c consumptio n rat e fo r th e individua l installatio n ca n b e establishe d base d o n analysis . T C Regulato r TRI-CHROM E T C Regulato r function s t o clea r th e deposi t o f dar k smudge s an d provid e satisfactor ymeta l distribu

tion . Lo wT C Regulato r ma yresul t i n dar k smudge s i n th e deposi t an d decreas e chromiu mthicknes s i n mid-curren t densit yareas . Hig h concentration s ar e no t especiall y harmful , however , amount s greate r tha n 1 0 mL/ L (1 0 gal/100 0 gal ) ma yresul t i n reduce d cove r and/o r haz y whit e patche s i n th e deposits . T C Regulato r i s consume d mainl yb yelectrolysi s an d shoul d b e adde d base d o n a n averag e consumptio n o f 2 5-5 0 m L (1- 2 f l oz ) pe r 100 0 amp hours . T C Correcto r T C Correcto r i s use d a t th e tim e o f make-up , 3 mL/ L ( 3 gal/100 0 gal) . Furthe r addition s ma yb e require d i n som e installation s bu t shoul d b e adde d onl yo n th e advic e o f a Harsha wRepresentative . Harsha wT C Cor
recto r help s improve s throw . 

### /J*P.1 6

- 5 - 

### £ H Optimu moperatin g p H i s i n th e rang e o f 2.5-2. 7 p H value s betwee n 2.3-2. 9 ca n b e used , however , a t hig h p H (2.9 ) coverag e i s improve d a t th e expens e o f platin g speed . p H shoul d b e measure d wit h a p H mete r fitte d wit h a sleev e typ e calome l electrod e (se e Analytica l Method s fo r measur e o f pH) . Du e t o th e dar k colo r o f th e solution , mos t p H paper s wil l produc e unsatisfactor y result s an d thei r us e i s no t recommended . p H adjustment s shoul d b e mad e o n th e basi s o f 2 mL/ L ( 2 gal/100 0 gal ) concentrate d hydrochlori c aci d t o lowe r th e p H 0. 1 unit s o r 2 mL/ L ( 2 gal/100 0 gal ) o f concentrate d ammoniu m hydroxid e (Sp . Gr . 0.89 ) t o rais e th e p H 0. 1 units . Addition s o f hydrochlori c aci d o r ammoni a wil l initiall y produc e larg e temporar ychange s i n p H whic h wil l the n reac h equilibriu move r a perio d o f time . Becaus e o f this , p H canno t b e accuratel ymeasure d fo r abou t 8-1 2 hour s followin g a n additio n o f aci d o r ammonia . p H adjustment s shoul d b e limite d t o 0. 2 p H unit s a t on e time . p H adjustment s greate r tha n 0. 2 p H unit s ar e preferabl ymad e i n step s ove r a perio d o f severa l hours , e.g. , a desire d adjustmen t o f 0. 4 p H uhi t shoul d b e mad e b yadditio n o f enoug h hydrochlori c aci d (o r ammonia ) t o chang e 0. 2 p H unit , waitin g severa l hours , an d the n addin g th e additiona l requirement . Temperatur e Optimu m

temperatur e rang e i s 80°-110°F . A t lowe r tempera
ture s ther e i s som e dange r o f crystallizatio n whil e highe r temperature s wil l reduc e coverin g power . Coolin g ma yb e require d whe n operatin g continuousl ya t mor e tha n 0. 5 amp/litr e ( 2 amp/gal ) (se e Equipment-Cooling) . Consultatio n wit h Harsha wfo r appropriat e coolin g rec ommendation s i s suggested . Operatin g a t temperature s belo w80° F ma ycaus e precipitation . Heatin g abov e 110° F wil l redissolv e precipitate . Cathod e Curren t Density/Platin g Rat e I t i s suggeste d tha t a n averag e cathod e curren t densit y o f 860-108 0 A/m 2 (80-10 0 ASF ) b e use d t o provid e a balanc e betwee n consumptio n o f additives , depositio n rate , recti

fie r requirement s an d coolin g capacity . Increasin g curren t densit ywil l resul t i n decreasin g cathod e efficienc yresultin g i n increase d coverin g powe r bu t a t th e sam e tim e decreasin g depositio n rat e (especiall y in ' hig h curren t densit yareas) , increasin g consumptio n o f additive s an d possibl yover-heatin g (requirin g addi

tiona l cooling) . I n extrem e case s wher e th e utmos t- 6 -

i n coverag e i s require d a s wel l a s uniformit yo f meta l thickness , i t ma yb e advantageou s t o strik e a t highe r curren t density , e.g. , 1600-210 0 A/m 2 (150-20 0 ASF ) fo r thirt yseconds . .. . f Unde r optimu m

conditions , (6-1 0 yin. ) o f chromiu mwil l b e deposite d pe r minut e a t 108 0 A/m 2 (10 0 ASF) . In
creasin g curren t densit ywil l no t significantl yincreas e th e platin g rat e du e t o a decreas e i n cathod e efficiency . Ai r Agitatio n Th e rol e o f ai r agitatio n i s t o insur e uniformit yo f meta l distributio n rathe r tha n t o sto p hig h curren t densit yburning . Th e agitatio n shoul d b e mil d and . a s unifor ma s possible . (Se e Equipment ) To o muc h agitatio n result s i n • a sligh t los s o f coverag e an d to o littl e result s i n uneve n meta l distribution . Ai r Agitatio n shoul d b e turne d of f durin g idl e periods . Specifi c Gravit y Specifi c Gravit yshoul d b e measure d wit h a suitabl e hydromete r (se e Analysi s Bulletin) . Th e specifi c gravit y o f th e solutio n shoul d b e maintaine d a t a minimu mo f 1.18 . Operatio n o f th e bat h a t specifi c gravit yo f 1.2 2 wil l produc e bes t result s wit h greate r toleranc e t o th e effect s o f metalli c impurities . Operatio n o f th e bat h a t specifi c gravit ygreate r tha n 1.2 4 ma yresul t i n som e crystallizatio n especiall yi f th e solutio n i s allowe d t o coo l belo w27° C (80°F) . Warmin g th e solutio n t o operatin g temperature , 27-43° C (80-110°F) , wil l usuall y redissolv e th e crystals . (se e Equipment-Anodes ) Specifi c gravit yi s maintaine d byadditio n o f T C Additiv e followin g adjustmen t .o f th e bat h (i f necessary ) wit h T C Chrom e Adjuster . Th e followin g tabl e provide s conversio n informatio n fro m specifi c gravit yt o Baum e i n th e even t thi s typ e o f hydromete r i s available : Specifi c Gravit y°Baum e 1.19 0 23. 2 1.20 0 24. 2 1.21 0 25. 2 1.22 0 26. 2 1.23 0 27. 1 1.24 0 28. 1



# MP.1 8

- 7 - SOLUTIO NMAINTENANC E Th e Tri-Chrom e solutio n i s maintaine d byadditio n o f T C Additive , T C Chrom e Adjuster , T C Stabilizer , T C Regulato r an d contro l o f p H a s describe d unde r "Proces s Control" . Th e informatio n give n shoul d allo wfo r nea r optimu m

performanc e fo r mos t installations . Occasionally , th e solutio n shoul d b e analyze d an d adjustment s mad e t o optimiz e th e solution . Larg e addition s o f T C Additive , 22. 5 g/ L ( 3 oz/gal ) o r greater , T C Chrom e Adjuster , 7. 5 g/ L ( 1 oz/gal ) o r greater , o r smalle r quantitie s i f bot h ar e added , ma y unbalanc e th e chromiu mcomple x requirin g re-electrolysi s (30-6 0 minutes ) t o avoi d plat e defects . T o avoi d re electrolysis , addition s shoul d b e broke n u p an d sprea d ou t ove r 2 4 operatin g hours , alon g wit h th e regula r maintenanc e additions . SOLUTIO NPREPARATIO N Th e sequenc e outline d belo wshoul d b e followe d a s closel y a s possible . Suitabl e precaution s shoul d b e take n wher e note d t o insur e prope r make-u p an d agin g o f th e solution . 1 ) Rea d "Equipment " sectio n t o insur e tha t th e tan k ha s bee n cleane d ou t properl yan d th e prope r equip

men t i s i n place . 2 ) Fil l th e properl yprepare d platin g tan k one-hal f ful l wit h clea n cit ywater . Tur n o n th e ai r agi

tatio n an d hea t th e solutio n t o 60-65° C (140-150°F) . Disconnec t hea t afte r reachin g thi s temperature . 3 ) Ad d (1. 3 oz/gal ) 1 0 g/ L Bori c Acid . Le t mi x unti l dissolved . 4 ) Usin g ai r agitation , slowl yad d th e Tri-Chrom e T C Additiv e (40 0 g/ L o r 3.3 3 lbs/gal ) makin g sur e tha t th e materia l i s dissolvin g a s fas t a s i t i s bein g added . (Se e Proces s Control-T C Additive ) Undissolve d materia l o n th e botto mo f th e tan k ma ydissolv e wit h difficult yan d seriousl yaffec t prope r break-i n o f th e solution . Th e temperatur e o f th e solutio n wil l fal l durin g th e additio n du e t o th e solutio n o f th e T C Additive . I t wil l b e helpfu l t o rehea t th e solutio n t o 35° C (95°F ) t o facilitat e dissolvin g th e T C Additive . 5 ) Instal l anode s a t thi s tim e (se e Equipment-Anodes) . 6 ) Fil l th e tan k to . abou t 85 % o f it s fina l volum e wit h col d water . A t thi s tim e th e solutio n temper
atur e shoul d b e "abou t 25-30° C (77-86°F) . Continu eP.1 9

- 8 -
t o agitat e th e solutio n (us e mechanica l agitatio n i f necessary ) t o insur e /complet e solutio n o f th e T C Additive . I t i s preferre d t o agitat e th e solu

tio n fo r 16-2 4 hour s t o insur e complet e solution . 7 ) Wit h goo d agitation , ad d 6. 5 %/vo l (6 5 mL/ L o r 6. 5 gal/100 0 gal ) T C Stabilizer . Ad d T C Stabilize r onl ya s fas t a s thoroug h mixin g o f previou s addi

tion s o f T C Stabilize r wil l allo wt o avoi d local

ize d hig h concentrations . 8) Mi x fo r a fe wminute s an d ad d 3. 0 Ml/ L (3. 0 gal/100 0 gal ) T C Regulator . Adjus t temperatur e t o 29° C (85°F) . 9 ) Ad d 8 gal/100 0 gal . Hydrochlori c Aci d an d chec k p H afte r 8-1 0 hours . 10 ) Ad d 3 mL/ L ( 3 gal./100 0 gal. ) T C Corrector . 11 ) Inser t previousl ynicke l plate d corrugate d stee l dummycathodes . Atota l are a o f abou t 25-100m 2 / 100 0 litre s (1- 4 ft 2 /10 0 gal ) shoul d b e used . Ad d wate r t o th e workin g leve l a t thi s tim e an d begi n electrolyzing . 12 ) Th e solutio n mus t b e electrolyze d a t thi s poin t t o comple x bat h constituent s properly . Electrolysi s shoul d b e performe d a t 108 0 A/m 2 (10 0 ASF ) usin g 0.25-1. 0 amp/litr e (1- 4 amp/gal ) fo r on e hou r a t operatin g temperature . 13 ) Afte r th e on e hou r electrolysi s period , th e solutio n ca n b e pu t int o operation . Defect s i n th e deposit , especiall ya t hig h curren t densit yareas , ca n b e eliminate d b yfurthe r electrolysis . METALLI C CONTAMINATIO N Du e t o th e ver ymil d acidit yo f th e solutio n (p H 2.3-2.9 ) an d th e continuou s remova l o f trac e metalli c contaminatio n b yplating , ther e shoul d b e n o excessiv e buildu p o f impuritie s unles s part s ar e frequentl ylos t fro mrack s o r i f post-nicke l rinsin g i s inadequate . I n som e cases , electrolyti c purificatio n ma yb e recommende d t o insur e tha t trac e element s ar e kep t withi n th e tolerabl e levels , an d thi s i s bes t achieve d byplatin g periodicall yfo r a fe whour s a t 108-324 A/m 2 (15-4 5 ASF ) usin g nicke l plate d corrugate d stee l cathodes . Th e informatio n belo wgive s a guid e t o maximu mlevel s o f trac e element s whe n presen t alon e an d show s tha t coppe r an d zin c mus t b e maintaine d a t a lo wlevel . 

## JJP.2 0

- 9 -
I n practice , contaminant s ar e foun d together , an d unde r thes e condition s ma yreinforc e on e another.

- Fo r example , 0.0 5 g/ L zinc , 0.1 0 g/ L iro n an d 0.0 1 g/ L coppe r ma y wel l b e mor e harmfu l tha n 0.20 . g/ L nicke l alone , eve n thoug h al l element s ar e present/ ' withi n thei r toleranc e limits . Occasiona l difficultie s hav e arise n i n practic e du e t o siphonin g o f nicke l solutio n alon g compresse d -ai r lines . T o avoi d this , ai r line s shoul d b e fitte d wit h anti-sipho n device s (e.g. , th e drillin g o f a smal l hol e a t th e highes t point) . I n case s o f gros s contamination , method s ar e availabl e fo r remova l o f metalli c impuritie s b yprecipitatio n wit h T C Purifier , (se e Harsha wPlatin g Processe s Bulletin , "Purificatio n o f Tri-Chrom e Trivalen t Chromiu mPlatin g Solutions". ) Importan t Note : Imbalanc e i n solutio n compositio n ma ylea d t o brown/blac k mark s whic h ca n b e confuse d wit h nicke l o r iro n contamin

ation . Poorl ymaintaine d solutions , especiall ythos e deficien t i n T C Stabilize r and/o r T C Chrom e Adjuster , o r to o hig h i n p H o r temperature , wil l als o b e mor e susceptibl e t o th e effect s o f metalli c contamination . I f a n analysi s i s available , th e solutio n shoul d alway s b e optimize d befor e attributin g th e defec t t o metalli c contamination . I n man ycase s readjustmen t o f th e solu

tio n wil l cur e th e proble mwithou t us e o f T C Purifier . 1 . Coppe r - maximu m0.0 2 g/ L Thi s i s rarel yfoun d i n practic e unles s solutio n i s allowe d t o com e int o contac t wit h expose d coppe r structure s (e.g. , bu s bars ) o r brass/coppe r part s ar e allowe d t o dissolv e i n th e bath . Symptom s Firs t show n bya grayin g a t hig h curren t density , extendin g t o lowe r curren t densitie s a s th e con centratio n increases . A t ver yhig h concentrations , mid-curren t densit yarea s ca n appea r blac k an d expose d nicke l i s staine d brow n (b yimmersio n plat e o f copper) . Remova l I f coppe r i s th e onl ycontaminan t i t i s bes t t o plat e ou t o n nicke l plate d corrugate d meta l cathode s a t lo wcurren t densit yo f 108-32 4 A/m 2 , (15-4 5 ASF) . I f othe r contaminant s nee d t o b e removed , T C Purifie r wil l remov e coppe r a t th e sam e tim e a s othe r metalli c contaminants .P.2 1

- 1 0 - Zin c - maximu m0. 0 5 g/ L Zin c contaminatio n ca n * occu r i n plant s platin g zin c di e casting s especiall ywhe n part s ar e s o shape d tha t the ycanno t b e full ycopper/nicke l plated . Symptom s Lo wlevel s o f zin c contaminatio n resul t i n a re ductio n i n coverag e an d a characteristi c shar p whit e edg e a t th e chromiu mcut-off . (Norma l Tri

Chrom e deposit s hav e a diffus e blue/brow n cut-of f i n lo wcurren t densit yareas. ) Hig h level s o f zin c contaminatio n sho wa whit e iridescen t stai n a t lo wcurren t densit yarea s an d thi s ca n sprea d int o mid-curren t densit yregion s i n th e presenc e o f othe r contaminants . Remova l I f zin c i s th e onl ycontaminan t an d i s presen t a t a lo wleve l i t ca n bes t b e remove d b yplatin g ou t a s fo r copper . Hig h level s o f contaminatio n usuall yrequir e treatmen t wit h T C Purifier . Nicke l - maximu m0.2 0 g/ L Som e nicke l contaminatio n i s foun d i n al l baths , du e t o drag-i n an d dissolutio n fro mnicke l plate d part s los t fro mracks . Th e leve l o f nicke l contam
inatio n i s foun d whe n post-nicke l rinsin g i s poo r o r part s retainin g nicke l solutio n ar e processed . Th e presenc e o f nicke l tend s t o reduc e th e toleranc e t o othe r contaminant s suc h a s coppe r an d iron . Symptom s Contaminatio n i s indicate d b ydar k brow n o r blac k mark s a t mid-curren t densities . Thes e ten d t o b e streak yan d sharp-edged , unlik e thos e resultin g fro m iro n contamination . Nicke l contaminatio n ca n als o b e recognize d b yth e reductio n i n stainin g belo wth e cut-of f althoug h coverag e i s no t reduce d a s wit h zinc . I n combinatio n wit h iro n th e regio n belo wth e cut-of f become s golde n (se e Iron ) an d th e mark s black . Remova l Nicke l plate s ou t ver yslowl yan d i s no t normall y remove d whil e platin g ou t zin c o r copper . Th e recommende d metho d o f remova l i s t o us e T C Purifier .

/ *P.2 2

- 1 1 "

Iro n - maximu m0 . 5 g/ L • , Iro n contaminatio n ca n aris e i n tw o ways , b ydis

solutio n o f part s los t fro mrack s o r bybipolarit y effect s whe n usin g plai n unplate d stee l dummysheets . Tri-Chrom e i s toleran t t o iron , whic h whe n presen t alon e ca n b e detecte d b yth e golde n yello wstai n presen t belo wth e chromiu mcut-off . Symptom s Iro n alon e ca n caus e brow n fluff ymark s a t mediu m curren t density , togethe r wit h obviou s iro n dep

ositio n (se e above ) i n ver ylo wcurren t densit y areas . Asmal l amoun t o f iro n (0.05-0.1 0 g/L ) i s beneficia l i n extendin g cove r an d minimizin g th e effect s o f sligh t zin c contamination . Remova l Iro n plate s ou t slowl ya t 108-32 4 A/m 2 (15-4 5 ASF ) o n nicke l plate d corrugate d stee l cathode s bu t car e shoul d b e take n no t t o introduc e iro n b yth e us e o f unplate d cathodes . Fo r large r concentration s o f iro n th e us e o f T C Purifie r i s recommended . Lea d - maximu m0. 0 2 g/ L Lea d contaminatio n ma yaris e a s a consequenc e p f inadequat e cleanin g o f tank s whic h hav e bee n use d fo r hexavalen t chromiu msolutions . Remova l o f lea d i s no t alway s complet e eve n wit h hydrochlori c aci d leachin g an d lea d contaminatio n manifest s itsel f usuall yafte r th e firs t overnigh t standin g period . Symptom s Whit e patche s i n lo wcurren t densit yareas , spreadin g aroun d th e bac k o f part s a s a whit e haze . Som e hig h curren t densit yadhesio n failur e ma yals o b e note d whe n hig h level s o f lea d ar e present . Remova l Lea d plate s ou t readil ya t lo wcurren t densitie s o f 108-21 6 A/ 2 (10-2 0 ASF ) an d i s bes t remove d bythi s means .P.2 3

- 1 2 - TROUBLESHOOTIN G SUMMAR Y I . Poo r Coverag e

ai r agitatio n to o hig h T C Additiv e o r specifi c gravit yto o lo w need s plating , i f addition s hav e jus t bee n mad e zin c contaminatio n lea d contaminatio n temperatur e to o hig h curren t densit yto o lo w nitrat e contaminatio n oxidatio n o f exces s T C Purifie r (dar k ban d ma yals o b e presen t a t chromiu m cut-off ) II . Depositio n Rat e To o Lo w

p H to o hig h T C Regulato r to o lo w T C Stabilize r to o lo w T C Additiv e o r specifi c gravit yto o lo w inadequat e ai r agitatio n ove r vertica l surface s III . Non-Unifor m

Meta l Distributio n ai r agitatio n to o lo wo r badl ypositione d ai r coi l T C Regulato r lo w poo r rac k desig n poo r anod e positionin g IV . Poo r Conductivit y

poo r electrica l connection s T C Additiv e to o lo w lo wtemperatur e lo wanod e are a anode s covere d wit h crystal s V . Crystallizatio n

solutio n to o col d (crystallize d salt s ma yb e slo wt o redissolve ) excessiv e evaporatio n durin g idl e period s T C Additiv e to o hig h VI . Microcrack s Fai l t o For m

insufficien t chromiu mthicknes s crack s difficul t t o se e unles s th e part s ar e coppe r plate d (Dubpurnel l Test ) 

# (7P.2 4

- 1 3 -
VII . Dar k Smudge s o n Wor k Piece s

metalli c contaminatio n lo wT C Regulato r | lo wT C Stabilizer"mad e wors e i f T C Additiv e an d T C Chrom e Adjuste r ar e als o low , e.g. , byexcessiv e dilutio n VIII . Whit e Patche s o n Wor k

zin c contaminatio n drying-o n o f nicke l solutio n du e t o excess ivel yho t nicke l solutio n o r prolonge d dryin g incorrec t precleanin g prio r t o nicke l lea d contaminatio n hig h non-pitte r i n nicke l solutio n hig h T C Regulato r microcracke d i n HC D are a du e t o excessiv e curren t IX . Adhesio n Los s

pos t nicke l rins e contaminate d wit h chromi c aci d lea d contaminatio n bipolarit ydurin g exi t fro mnicke l tan k bipolarit ydurin g entranc e t o chromiu m tan k inadequat e nicke l activatio n (re-chroming ) curren t densit yto o hig h T C Additiv e lo w(i.e. , lo wspecifi c gravity ) X . Whit e Fil mo n Wor k

Thi s i s usuall ydu e t o the

- presenc e o f a precip

itat e forme d byaddin g T C Purifier . . Th e precip

itat e ca n bes t b e remove d b yfiltration , prefer

abl ythroug h a filte r precoate d wit h filte r aid . Th e precipitate d fil mca n b e wipe d of f easil y an d i s normall yfoun d onl yo n excessivel y contaminate d solution s requirin g constan t T C Purifie r additions . EQUIPMEN T Tank s Th e tan k linin g mus t b e o f plasti c (PVC , ABS , polyethyl

ene , o r rubber . Lead-line d tank s mus t no t b e used . Existin g lead-line d tank s ca n b e converte d bylinin g wit h V

rigi d plasti c sheet , insurin g tha t th e fina l- 1 4 -

assembl yi s leak-proof . Ales s preferre d alternativ e i s t o fi t a flexibl e plasti c liner , bu t thi s i s no t recommende d du e t o th e likelihoo d o f mechanica l damage . I f a flexibl e line r mus t b e used , i t i s suggeste d tha t a shee t o f rigi d PV C b e place d o n th e tan k bottom , abov e th e flexibl e liner , t o minimiz e possibl e damag e t o th e liner . Existin g plasti c o r rubbe r tank s mus t b e thoroughl y cleane d t o remov e al l trace s o f lea d chromat e whic h ma yb e adherin g t o th e tan k walls . Bot h lea d an d chromates . ar e undesirabl e contaminants . Scrappin g an d leachin g wit h sodiu mmetabisulphit e solutio n ar e require d t o insur e complet e cleanliness . Afte r cleaning , th e linin g shoul d b e leache d wit h 5 % hydrochlori c aci d befor e use . An yfil mlef t afte r thi s operatio n shoul d b e scrub

be d of f an d th e tan k agai n leache d wit h 1 % hydrochlori c acid . Anode s Existin g lea d anode s mus t b e replace d b yspecia l graphit e anodes , fitte d wit h titaniu manod e hanger s speciall y designe d t o insur e soun d electrica l an d mechanica l contact . Anode s an d hanger s ar e availabl e fro mHarshaw. . Consultatio n wit h Harsha wi s recommende d fo r prope r installatio n o f anode s an d hangers . A s a genera l guide , th e tota l immerse d anod e are a shoul d b e twic e th e cathod e are a an d shoul d b e sufficien t t o allo wfo r a maximu m anod e curren t densit yo f 54 0 A/m 2 (5 0 ASF) . Anomina l 24 " x 2 " (61 0 mmx 5 0 mm ) diamete r anod e ha s a maximu m effectiv e are a o f 1 ft 2 (0.1m 2 ) . Th e to p o f th e anod e shoul d b e a t leas t 2. 5 c m(on e inch ) belo wsolutio n level . Coppe r anod e rail s o r bu s bar s shoul d b e heavil y nickel-chromiu mplate d t o avoi d possibl e coppe r contam
inatio n an d expose d bu s ba r shoul d b e shielde d fro m solutio n b ya plasti c shiel d o r b ywrappin g wit h plasti c waterproo f tape , etc . Anode s shoul d no t b e remove d unti l a t leas t 3 0 minute s afte r platin g stop s a s the yma yb e saturate d wit h electro

lyticall yproduce d noxiou s compounds . Continuou s us e o f extremel yhig h anod e curren t densitie s wil l significantl yshorte n anod e life . Anode s shoul d b e inspecte d fo r a coatin g o r crystal s i f bat h crystal

lizatio n i s noted . Operatio n o f th e bat h wit h coate d anode s wil l i n effec t produc e hig h anod e curren t densities . (se e Specifi c Gravity ) 

# /fP.2 6

- 1 5 - Ai r Agitatio n Perforate d plasti c ai r line s mus t b e installe d t o giv e unifor mmil d agitatio n belo wthe. f cathod e area . Oil-fre e ai r fro ma blowe r shoul d b e used . I t shoul d b e kep t i n min d tha t th e ai r agitatio n i s use d t o provid e solutio n movemen t ove r th e surfac e . . o f th e cathod e an d i s no t use d t o improv e limitin g curren t densit yas , fo r example , i n nicke l plating . To o muc h ai r agitatio n ma yresul t i n a reductio n o f chromiu m coverag e wherea s to o littl e ma yresul t i n non-unifor m thickness . Ai r line s shoul d b e designe d a s fo r nicke l platin g (Harsha wTechnica l Bulletin-Installatio n o f Ai r agitatio n System s fo r Electroplatin g Solutions) , however , th e ai r pipe s shoul d b e space d 100-150m m(4- 6 in. ) apart , no t ove r 150m

m ( 6 in.) . Th e numbe r o f pipe s use d shoul d b e sufficien t t o cove r th e anticipate d cathod e are a abov e th e pipe s plu s 75m m( 3 in. ) i n eac h direction . Du e t o th e lo wpressur e require d fo r prope r agitation , al l perforate d ai r line s mus t b e installe d leve l an d i n th e sam e plan e o r uneve n agitatio n wil l result . Valve s fo r eac h ai r pip e shoul d b e provide d t o adjus t th e ai r volum e a t th e tank . T o preven t th e possibilit y o f siphonin g solutio n ou t o f th e tank , a siphon-brea k hol e shoul d b e drille d a t th e highes t poin t o f th e ai r line(s ) abov e th e solutio n level . Cooling/Heatin g Becaus e th e proces s operate s a t temperature s o f 27-43° C (80-110°F ) som e heatin g i s necessary . Th e us e o f titaniu m coil s wit h boile r heatin g (controlle d b ythermostat ) i s appropriate . I n hig h productio n unit s wit h hig h squar e footage s som e coolin g ma yb e necessary . I f externa l coolin g i s t o b e used , th e circulatin g platin g solutio n shoul d no t b e "over-cooled " (belo w7 5°F ) du e t o crystallizatio n o f th e platin g solution . Ampere-Hou r Mete r A n ampere-hou r mete r i s necessar yfo r optimu mcontro l o f solutio n compositio n a s maintenanc e addition s ar e bes t mad e o n a n ampere-hou r basis . I n mos t automati c operations , th e chromiu mampere-hour s ca n b e relate d t o th e nicke l ampere-hou r mete r bysuitabl e correction s fo r tim e an d current .P.2 7

- 1 6 - Rectifier s Existin g 6- 9 vol t rectifier s ar e suitabl e fo r som e in

stallations , dependin g o n anod e area , cathod e area , anode-to-cathod e spacing , voltag e losse s i n bu s bars , etc. , bu t fo r part s consistentl yrequirin g ver ygoo d coverage , 9 t o 1 2 vol t rectifier s giv e mor e flexibility . Ventilatio n Althoug h ther e i s n o toxi c chromi c aci d spra yemitte d byth e Tri-Chrom e solution , th e gassin g a t th e cathod e may , unde r certai n conditions , produc e a n overspra y tha t ma yb e objectionable . Fo r thi s reason , exhaus t ventilatio n i s recommended . Existin g ventilatio n fo r hexavalen t chromiu mbath s i s satisfactory . Filtratio n Tri-Chrom e platin g solution s requirin g T C Purifie r addition s ma ycreat e enoug h insolubl e materia l i n th e solutio n t o produc e a whit e fil mo n th e work . Filtratio n o f th e solution , especiall ydurin g th e perio d immediatel y followin g T C Purifie r addition , ma ytherefor e b e desir

able . Filter s -constructe d o f material s suitabl e fo r us e wit h hig h chlorid e nicke l solution s ar e satisfactor y fo r us e wit h th e Tri-Chrom e solution . Th e us e o f a n approve d typ e o f filte r ai d i s recommende d t o assis t i n removin g th e insolubl e material . Consulta

tio n wit h Harsha wfo r satisfactor ytype s o f filte r aid s i s suggested . Th e residu e filtere d fro mth e Tri-Chrom e solutio n shoul d no t b e subjecte d t o th e actio n o f stron g minera l acids ; noxiou s fume s ma yresul t i f thi s practic e i s followed . Se e separat e bulleti n o n th e "Filtratio n o f Tri-Chrom e Platin g Solutions " fo r informatio n o n filte r siz e an d filtratio n techniques .

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t an y laws , regulation s o r rights ot thir d parties . Buye r shoul d evaluate suitabilit

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y o f product to r buyer' s use . W e canno t assum e liabilit

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