p.1 

OAR Box 1313 

Prepped by LaTeia Shed 

Document Number: 

75) ll-B-49 

Docket Number: 

A-88-02 

Printed 6/12/2008 9:03:30 AM Sheet 75 of 99 
MRI$ 

P.2 

A-88-02 

MIDWEST RESEARCH INSTITUTE 

TX- CH-ffi Suite 35( 

•101 Harrison Oaks Boulevarc 

Cary. N.C. 275U 

\u-*\ 

Date: May 20, 1988 

(Finalized November 3, 1988) 

Subject: Site Visit—Engelhard Corporation 

Chromium Electroplating NESHAP \88, —•*—s\~ ..-\ \\ 

EPA Contract 68-02-3817; ESD Project 85/(M\Kf'v* V \^J^ 

MRI Project 7717-K \0>->-"** 

From: Robin Barker 

To: Andrew Smith 

ESD/ISB/SSS (MD-13) 

U. S. Environmental Protection Agency 

Research Triangle Park, N.C. 27711 

I. Purpose 

The purpose of the visit was to obtain infonnation on the 

manufacture and use of the trivalent chromium process sold by Engelhard 

Corporation (formally Harshaw/Filtrol Partnership) as a substitute for the 

hexavalent chromium process used for decorative chromium electroplating 

applications. 

II. Place and Date 

Engelhard Corporation 

23800 Mercantile Road 

Beachwood, Ohio 44122 

(216) 464-5710 

December 2, 1987 

III. Attendees 

Engelhard Corporation (Engelhard) 

0. Kent Dickie, Product Manager - Metal Finishing 

H. Richard Garner, Vice President and General Manager Metal 

Finishing and Industrial Products 

Dennis R. Masarik, Technical Director Metal Finishing and Industrial 

Products 

U. S. Environmental Protection Aqency (EPA) 

Andrew M. Smith, ISB 
P.3 

2 

Midwest Research Institute (MRI) 

Robin Barker 

IV. Discussion 

A meeting was held with personnel from Engelhard to discuss the 

trivalent chromium process. The discussion focused on the trivalent 

chromium process requirements and limitations, basic differences between 

the double-cell (Canning) process and the single-cell (Allbright-Wilson) 

process, as well as Engelhard's ability to supply the trivalent chromium 

process if market demand increases. This discussion was followed by a 

tour of the production facility in Cleveland, Ohio. 

A. Engelhard's Trivalent Chromium Process Requirements and 

Limitations 

Engelhard has successfully operated their trivalent chromium 

processes since 1975. Engelhard has recently developed a trivalent 

chromium bath, Tri-Chrome® Plus, that operates at higher bath temperatures 

and faster plating rates than the baths that were marketed 1n the late 

1970's and early 1980's. Attachment 1 1s the product information brochure 

supplied by Harshaw on the Tri-Chrome® Plus plating process. 

The trivalent chromium process can be used only for decorative 

chromium plating applications. Decorative chromium applications require 

chromium plate thicknesses ranging from 0.0001 to 1.0 thousandth of an 

inch (mils). The trivalent chromium process is capable of plating the 

full range of thicknesses required for decorative applications; however, 

the process is unable to achieve the plate thicknesses required for hard 

chromium plating applications (>1.0 to 30 mils). 

The Tri-Chrome® Plus process requires good control of metal 

contamination. Metals enter the bath due to dragout from previous plating 

baths or dissolution of the part. Metal contaminants can be removed by 

"dummying" the solution or adding in a purifier solution to the bath. 

"Dummying" the bath is performed by placing a nonproduct part in the bath 

and setting the current density so that the contaminant metal will be the 

metal that plates out of the solution onto the part and the trivalent 

chromium will remain in the solution. The addition of a purifier solution 

to the bath results in precipitation of metal contaminants which are then 

removed from the bath solution by filtration. 

To reduce dragin of metals from other plating baths and to prevent 

solution contamination, the trivalent chromium process requires sufficient 

rinsing between the nickel plating bath and the trivalent chromium bath. 

Following the trivalent chromium plating bath, adequate rinsing also is 

required to remove the chlorides which can cause corrosion. Engelhard 

recommends three counterflow rinses before and after the trivalent 

chromium plating bath. 

* * . 
P.4 

All trivalent chromium processes require a base layer of nickel 

plate of at least two to three-tenths of a mil. This layer of nickel is 

required because a nickel plate is microporous and a thinner layer of 

nickel would expose small portions of the base metal. In hexavalent 

chromium plating, the microporous nickel plate is "chromated" from the 

chromate compounds available in the bath, which covers the exposed 

portions of the base metal and provides corrosion resistance. However, in 

trivalent chromium plating, hexavalent chromium is a bath contaminant and 

a thicker layer of nickel and chromium (0.25 mils) is required to'give the 

part corrosion resistance that is comparable to a hexavalent chromium 

plated part. Also, rust inhibiting post dips are recommended for use with 

trivalent chromium baths to aid in corrosion resistance. 

Brass, zinc, and tubular (hollow) steel parts require special 

provisions when a trivalent chromium process is used. The metals found 1n 

these parts (copper, zinc, and lead) can contaminate the trivalent 

chromium solution if the parts fall off the racks and the metals dissolve 

in the solution or if the coverage in the nickel bath is poor so that the 

base metals are exposed and dissolve in the solution. These problems can 

be overcome by checking for and removing all parts that may have fallen 

from the racks into the solution and by ensuring that the coverage in the 

nickel bath is sufficient to cover the part so that portions of the base 

metal are not exposed. Tubular (hollow) brass or steel parts present 

unique problems because the nickel plating process does not have the 

throwing power to cover the internal surfaces of tubular parts. The inner 

surfaces of the tubular parts that are not covered with nickel can result 

1n lead or copper contamination of the trivalent chromium solution. 

B. The Double-Cell Process Versus the Single-Cell Process 

Both single-cell and double-cell processes are used in trivalent 

chromium plating. The double-cell process was the first process developed 

that used trivalent chromium. The double-cell process was developed in 

1854, but did not become commercially viable until the mid-1980's. The 

single-cell process was developed in the mid-1970's. Double-cell 

processes are manufactured and sold by Frederick Gumrn Chemical Company and 

MacDermid, Inc. The single-cell processes are manufactured and sold by 

Engelhard and OMF/Udylite International Corporation. The major 

differences between the two processes are discussed below. 

The double-cell process solution contains minimal to no chlorides, 

whereas, the single-cell process contains a high concentration of 

chlorides. Due to the high chloride concentration in the single-cell 

process, thorough rinsing is required after the trivalent chromium bath to 

remove any chlorides left on the part that can start corrosion. Three or 

four counterflow rinses are deemed sufficient for removal of the 

chlorides. 

The double-cell process utilizes lead anodes that are placed in 

anode boxes that contain a dilute sulfuric acid solution and are lined 

with a permeable membrance. The single-cell process utilizes carbon or 

graphite anodes that are placed in direct contact with the plating 
P.5 

solution. The anode solution in the double-cell process must be treated 

and disposed approximately every 2 months, and the solution remade to 

enable the process to plate efficiently. Also, the anode boxes lined with 

the permeable membranes are susceptible to breakage by parts hitting the 

boxes as they enter and exit the plating tank. When the anode boxes or 

membranes are broken, the compartment must be replaced and the bath 

adjusted to its normal operating range before plating can be restarted. 

In the single-cell process, if the anodes are broken they need only be 

replaced to maintain the correct anode to cathode ratio. 

The plating rate of the double-cell and single-cell processes are 

comparable to the hexavalent chromium process at 4 mi month s of an Inch 

per minute. However, there is a new high-efficiency single-cell process 

that has a plating rate of 10 millionths of an inch per minute. 

For more detailed information on both processes, refer to 

Attachment 2 which is an article written by Dr. Donald L. Snyder of 

Engelhard that will be published in the spring of 1988 in "Plating and 

Surface Finishing." This article compares the double-cell and single-cell 

trivalent chromium processes to the hexavalent chromium process now used 

in the majority of decorative plating facilities. 

C. Production Capacity and Staffing 

Engelhard personnel were asked what problems might occur in 

supplying trivalent chromium processes if market demand increased 

significantly. Harshaw believes that there would be no problems in the 

chemical supply, production capacity, or equipment supply needed to meet 

an increase in demand. The majority of chemicals used in the manufacture 

of the plating bath, except for the trivalent chromium compound, are 

common compounds that can be purchased from a variety of suppliers. The 

trivalent chromium compound is bought in a foreign market; however, 

Engelhard contacted the supplier to determine if the demand for the 

compound could be met, and the supplier did not anticipate any problems. 

The trivalent chromium bath is made up of four component mixtures: 

(1) TC-stabilizer, (2) TC-regulator, (3) TC-addit1ve, and (4) TC-adjuster. 

The current production for the trivalent chromium bath components is well 

below the production capacity for the plant. Bath components are produced 

by mixing individual chemical components in a large tank prior to 

packaging. The limiting component mixture, TC-stab1lizer, is the only 

chemical component mixture that involves a mild chemical reaction, and, 

therefore, requires a longer holding time than the other chemical 

component mixtures to allow the reaction to go to completion. The holding 

time for the TC-stabilizer is 8 hours, which requires the component 

mixture to be packaged during the second shift. With the existing mixing 

tanks at the facility, the production could be increased to 35,960 i 

(9,500 gal) per month for the TC-stabilizer. The total production 

capacity for the facility is 227,130 to 302,840 % (60,000 to 80,000 gal) 

of the trivalent chromium bath components per month. At present, the 

plant is operating one 8-hour shift and a partial second and third 

shift. Within 3 to 4 months, the plant could add new mixing tanks and a 

# 
P.6 

new packaging line to increase total production if market demand were to 

increase significantly. 

Engelhard personnel indicated that'the technical staff required to 

meet a significant demand for trivalent chromium could be met by training 

existing distributors, hiring new employees, and redistributing the 

current technical support staff. Meeting the demand for technical support 

due to a dramatic increase in the trivalent chromium market would.require 

some shifting of resources and additional training. A 6-mont"h time frame 

would allow Engelhard to meet the demand. 

2 Attachments 

vi~ 
^ipptUS; ChrottilutH Plallng 

Trivalent: 

The Second Decade 

By DR. DONALD L. SNYDER 

Research Director 

Harshaw/Filtrol 

Beachwood, Ohio 

56 PRODUCTS FINISHING 

T

hree major historical events occurred in the development of 

present-day trivalent chromium 

electroplating processes.1 Over 100 

years passed between the first major 

historical event, when trivalent chromium electroplating was originally 

observed in the laboratory by Professor Robert Bunson' in 1854, and the 

second, the introduction of the first 

MARCH, I98B 

tUnrr**-atafflr 

:

-W li'. 

\*w |-vt»*>& 

Electroplating from trivalent chromium solutions was 

commercialized ftioro than ten years ago; In this second 

decade the number ul solutions available ahd the 

numbei- of reasons to consider trivalent have proliferated * 

commercially successful trivalent 

chromium process, in 1975.' 

Professor Bunson's trivalent chromium electrowinning process required the use of a double-cell plating tank, with the anode isolated 

from the catholyte by a membrane. 

This double-cell configuration was a 

major factor that retarded the development "of trivalent chromium. 

MARCH. 1988 

COLOR of deposits (above) from today's 

trivalent chromium plating solutions is 

very close to the blue-white of the 

deposits from traditional hexavalent 

chromium plating solutions. 

It wasn't until the single-cell process was developed in 1975 that trivalent chromium became a commercial 

suqeess. The new trivalent chromium 

process was similar to other processes 

PRODUCTS FINISHING 57 
1 

Chromium Plating 

* > ' 

Trivalent processes are used today 

on a wide variety of parts... 

iff 

platers were used to, such as nickel, 

copper, and hexavalent chromium 

electroplating. 

About ten years after the introduction of the first commercially successful decorative trivalent chromium 

processes, the third major event occurred: the introduction of several 

other trivalent chromium plating 

processes. These processes can be 

categorized into two general groups: 

those that require the anode to be 

separated from the chromium electrolyte by a membrane and those that 

do not. 

It wasn't until approximately two 

years after the original discovery of 

trivalent chromium plating that 

Geuther4 published information on 

the first reported process for electroplating chromium from a hexavalent chromium electrolyte. Because 

his process did not require the separation of the anode from the cathode 

by a membrane, and was easy to operate, much of the chromium electroplating research in the early 1900's 

was based upon the hexavalent chromium ion. Also, sulfate, one of the 

catalysts necessary for decorative 

electroplating of chromium from a 

hexavalent chromium electrolyte, was 

a naturally occurring impurity in 

58 PRODUCTS FINISHING. 

chromic acid, permitting chromium 

to be plated easily from these early 

solutions. 

Because the hexavalent-chromiumion processes were easier to use than 

trivalent-chromium processes, hexavalent chromium electroplating was 

essentially the only commercial decorative-chromium electroplating process in use until the introduction of 

the trivalent chromium process in approximately 1975. 

By the mid-1980's, platers in the 

United States "had verified the commercial viability of trivalent chromium processes by operating over 

100 trivalent chromium tanks, representing well over 50,000 gallons of 

installed operating solution. Trivalent 

processes are used today on a wide 

variety of parts and assemblies, ranging from carpenter tools to surgical 

tools, as well as on furniture, bumpers, and wire racks. 

Even though the trivalent chromium introduced in 1975 has advantages, there are also limitations for 

some platers, in terms of plating rate, 

thickness of electrodeposit and the 

color of the deposit. 

Some of the trivalent chromium 

processes introduced during the mid1980's have overcome several of these 

limitations.' One single-cell process 

has a plating rate at least two times 

that of the older trivalent process and 

can deposit chromium almost one mil 

thick. This single-cell process and all 

the double-cell processes produce 

deposits similar in color to those 

from that of hexavalent chromium. 

MARCH. 1988 

gftUgMj^^ttHU 

TABLE I 

Chrnrtlliitt. PlnllHt) Pollution fcniiHnl Cos! 

[Equipment Cos! t -8 •••, 8;s; ^^^gfM^^^^M^^'5 5-5 

>. Hexavalent Chromium 

> • Reaction tank 

';!.• Mixer ..__ _ . „. 

i»Pumps ' ••.• • ! i; 8 7 i&f3&M?{»M-J« Controls and DumosrMi' drver.*">v :J 

* • i 

m Reduction ^'#ltl^#if ( Chromium Hydroxide Precipitation j 

'.Y 8'- ! ; r^l'*TfM"PrtM?iK»Pfi' * Neutralizing \3t\\.Y:iti\'Y' Filter press j 

:

'': ' ! \l I'^^-^MH' '

 SeI,lin9 tank'*>***^. Sludge H 

1

 Control panel and controls -; * 

'Estimated Cost:. $15,000 . 

[.Operation Cost 

!•... Estimated Annual Cost (1 gpt* 

'• Hexavalent Chromium 

t 

• j ?j Hexavalent cnromlum (gg^i Tri 

Reduction I W$,t).Am^\0^0ff^ 

'reciDitation ;- ir-8-;. 255.W8> "'."'•'::J&S»iM;.~ 

Trivalent Chromium 

~ • 5&5Ui •• 

$ 38 i."1 : •Chromium Hydroxide Precipitation i\:)55 :=8 :.-. 

:

 255.ji?^ 

|;Sludge Disposal ; !^8 . ;•.-,,.;;,.; 8jj|j; 3.805 (14,200 lbs.)p&|&8' 538 (2,000 lbs.) ^yi 

! Total Cost 77l!r$5.540iiLJjM^i8B;. ^ 

Process Comparisons 

Because all the trivalent chromium 

processes on the market today fall 

into two general classes, based on 

their general chemistry, the processes 

will be divided into these two groups 

for this comparison. 

The first classification includes the 

original process introduced in 1975, 

several other newer but very similar 

processes, and the new light-colored, 

high-speed version introduced in 

1987. They are all similar in chemistry in that they are single-cell 

processes. 

The second type, a double-cell process, requires the separation of the 

anode from the chromium electrolyte 

and cathode. 

Even though suppliers indicate that 

MARCH, 1988 

there are several types of hexavalent 

chromium electroplating processes, 

the great majority of those now used 

commercially Tdr decorative plating 

are similar enough to be grouped together for purposes of this 

comparison. 

Safer. An increasingly important 

consideration when comparing trivalent chromium with hexavalent chromium processes is the safety, health, 

and environmental concern. Because 

the trivalent chromium ion is utilized, 

chromic acid is not present in the 

plating process. The trivalent chromium ion is much less toxic, yielding 

lower health and environmental control costs and concerns than those of 

hexavalent chromium. 

The total chromium content of 

PRODUCTS FINISHING 59 
Chromium Plating? 

T5T T.'7'.rY" "~VP'\ i-"s *vi *,!•-*:-" r*f "*"•'"" ? 

•'•'•' ''''.' I rY..r \L5\iiti'\55.\ 

PH __ _ 

Temperature • ' '••'•* 5.'•' 

Current Density (Cathode) 

Agitation ''•''•<';* Y •• 5•:./.•'<••'. 

Anodes 

Single-Cell 

Double-Cell 

Chromium 

Single-Cell 

Double-Cell 

Filtration 

Single-Cell 

Double-Cell 

Rectilier 

Trivalent '• 

Chromium 

2.3-4.0 

" 80-120*F 

40-100 ASF 

; Mild Air 7 '"' 

Special Graphite 

Lead In Anode Box 

15-20 g/liter. 

! 5-10 g/Nter .

; 

Only lor Solids 

Continuous With Carbon 

6-12 V ' ' 

Hexavalent Y 

Chromium 

Less than 1 

110-115*F 

175-200 ASF 

None ' 

Lead /Lead Alloy 

150-300 g/liler 

Uncommon 

6-12 V 

trivalent chromium solutions is approximately one-fifth that of hexavalent chromium solutions. This is one 

reason why trivalent chromium processes are environmentally easier to 

operate. 

The trivalent chromium ion is 

presently not listed as a potentially 

carcinogenic agent, as is the hexavalii" lent chromium ion. Trivalent chromium processes are also much easier 

to handle environmentally. 

As a result of the chemistry of 

trivalent chromium's electrolyte, 

misting does not occur during plating, as it does during hexavalent 

chromium plating. Thus less ventilation than would be required with hexavalent solutions is satisfactory. 

Use of trivalent chromium also reduces waste-disposal problems and 

60 PRODUCTS FINISHING 

costs. Waste treatment of hexavalent 

chromium requires a two-stage treatment. The hexavalent chromium ion 

is first reduced to the trivalent chromium ion; then it can be precipitated 

as chromium hydroxide. Trivalent 

chromium plating solutions, which 

are already in the reduced trivalent 

state, require only the chromiumhydroxide-precipitation step. 

Table 1 compares the equipment 

and operating cost for waste treating 

a typical 12 oz/gal hexavalent chromium plating bath with that for a 2.7 

oz/gal trivalent chromium plating 

bath. The treatment procedure and 

associated costs greatly favor the use 

of trivalent. 

Operating advantages. Safety and 

waste-disposal considerations in 

chromium plating are very important 

MARCH. 1988 

TABLE III 

Hexavalent fcluottilurU troubleshooting Guide 

",. 1 i. • ; <;; '!' r'-fr- r'I|!f Typical Probloms ?p^tP^^^|Pf? ' 

.;••,-. 8 ;v^8^i:;-vV^. Low . Curren ,.^. f c 

7W7"".""'-* •-•"•* 

! Causes 

Poor

 : i :

 !t • •••'.'••*'•""••"""•'.'";«• Low-uurreni''.*;.;: ;;• Gray \ 

Coverage "Burnin g " Whitewash' Density Stain ~ '• Deposits * 

Ratio 

j Temperature 

High/Low 

Catalyst 

; Part 

! Configuration 

Rack Overload 

..Metallic 

I Impurities 

Nickel Deposit 

j High Current 

i Density . . 

Bl-Polarity 

,' Chloride 

; Contamination 

High Trivalent 

Chromium 

, 

... 

.... 

• Intermittent 

t Electical Contact 

X 

xr'l' 

X 

X 7 1:, 

X 

•'..;;}- • 

ii.*. ! jS. 

-:•-•' t; 

\s.5iMm 

7

r

.FV?iW 

X 

lii,x. ill' 

Migm. 

T* '-vrp-rr 

.*rr.:Z.y,T*""~ 

Y5mw 

•StfW-iH* 

x 

•W553-

*

;SV'f|v'v

 kf.tiX 

*rt*?---f .*.—-i-r-.* 

^'S.rr.rrp; 

x 

-,rrr--r"*"!V."-*H"';T! 

'triv'.X' 0;'!.*,j 

WY,ki:$aiYYt\ 

^.:>..Y^5) 

ft*:.*.***?;- *•) 

¥.*:.•;. 

and greatly favor trivalent chromium 

processes. But this fact becomes less 

significant if the operating conditions 

do not also favor trivalent chromium 

electroplating. 

Table II lists the typical operating 

conditions for trivalent and hexavalent chromium electroplating processes. Trivalent chromium processes 

are operated in the pH range of 2.1 

to 4.0. Hexavalent chromium has a 

much lower pH, due to the presence 

of chromic acid. 

Hexavalent chromium plating processes are operated over a relatively 

MARCH. 1988 

narrow temperature range, near 

110F. The processes with formulations similar to that of the original 

trivalent chromium process operate 

near ambient temperatures, while tlie 

newer trivalent chromium processes 

generally operate at about 100F. 

Lead anodes are used in both the 

hexavalent chromium and the doublecell trivalent chromium processes. 

Graphite anodes are used in the 

•single-cell trivalent chromium 

processes. 

One distinction between different 

trivalent chromium processes is that 

PRODUCTS FINISHING 61 
Chromium Plating??-": 

-TABLE* IV; 

tuvnletil bht-oitilumltttHiblcshootlng Guide 

Causes 

Typical Problem 

Dark Smudges Poor Coverage White Patches 

Metallic Impurities 

Chemical Imbalance 

Zinc Contamination 

Cause Solution 

Metallic Impurities Purlly or Dummy 

Chemical Imbalance Check pH, Specific Gravity, and Ampere Hours 

Zinc Contamination Purlly or Dummy 

some of the solutions used in the 

single-cell processes do not have to be 

filtered except to remove solids from 

the bath, such as after chemical purification, while others require more 

frequent filtration. 

Recommendations call for doublecell trivalent chromium processes and 

a few single-cell processes to be continuously filtered with carbon. Hexavalent chromium processes are almost never filtered. 

Both hexavalent and trivalent 

chromium deposition have the same 

current requirements. For maximum 

coverage and throw, a 15-voIt rectifier can be used on some of the singlecell trivalent chromium processes 

when extremely deep recesses need to 

be plated. In general, though, a sixto 12-volt rectifier is all that is necessary to plate chromium from trivalent 

solutions. Every area of the part that 

has been nickel plated will be covered 

with chromium. In most cases, hexavalent chromium processes do not 

62 PRODUCTS FINISHING 

have the covering or throwing power 

of trivalent processes and can not 

plate into the recesses as well as 

nickel. 

Troubleshooting. Table III is a 

troubleshooting.guide for hexavalent 

chromium electroplating, while Table 

IV is a troubleshooting guide for 

trivalent chromium electroplating. 

The troubleshooting guide for trivalent chromium is simplified because 

trivalent chromium processes, as 

compared with hexavalent chromium 

processes, have improved covering 

power, will not burn, can tolerate any 

levels of current interruptions and 

ripple, will tolerate sulfate and chloride drag-in, can be used to plate 

around holes, and will not produce 

hexavalent-chromium staining. 

Productivity. Productivity is increased when trivalent chromium 

processes are used because less stripping and replating of parts is required. Chromium color buffing is 

also eliminated when using most 

MARCH, 1988 

^ 

trivalent chromium prpcesses. Production can be increased because 

more parts can be placed on a rack 

and more racks can be placed on a 

workbar. This is so because there is 

less likelihood of burning, and covering power is better. 

Because trivalent chromium plates 

in lower-current-density areas, plating racks can be constructed of lighter 

material. 

In most plating operations, the 

hexavalent chromium plating step is 

the limiting process within the plating line. With the high covering and 

throwing properties of trivalent chromium electroplating solutions, however, typically the nickel tank becomes the limiting tank. 

Costs. Based upon over ten years 

of operating experience, most platers 

have found that the cost of single-cell 

trivalent chromium plating is less 

than that of hexavalent chromium 

plating, even though the cost of solution for trivalent chromium is 

higher than that for hexavalent. 

Operating costs for trivalent chromium are also lower because maintenance costs are lower and the inert 

anodes have indefinite life. The lead 

anode used in hexavalent chromium 

processes must be cleaned, conditioned, and replaced at times. 

The single-cell trivalent chromium 

process uses graphite anodes that are 

relatively inexpensive, require little 

maintenance, and are only replaced 

when mechanically damaged. 

Anodes for the double-cell trivalent chromium processes also have a 

MARCH. 1988 

.. .trivalent chromium plates in 

lower-current-density areas... 

199 

long life, but the anode comparU 

ments are very expensive to replace 

when mechanically damaged. An extra operating expense is that the solution inside the anode compartment 

must be changed frequently. The anode boxes also take up more room in 

the tank, which might increase the 

chance of mechanical damage and reduce the usable plating volume. 

Operating costs for both hexavalent and trivalent chromium can bc 

reduced by returning drag-out solution to the plating tank. Since the 

original trivalent chromium processes 

operate at ambient temperatures, little evaporation.takes place, making 

it difficult to return dragged out plating solution to the plating tank. The 

new, high-efficiency single-cell trivalent chromium process and the doublecell trivalent chromium processes 

both operate at above ambient temperatures, however, increasing evaporation and the opportunity to reuse 

dragged-out plating solution. Atmospheric evaporators are routinely 

used on the dragged-out solutions 

from the single-cell trivalent chromium processes. 

Contamination. Both the singleand double-cell trivalent chromium 

processes are more sensitive to metalPRODUCTS FINISHING 63 
{.Chromium Plating" 

66 

Carbon and hydrogen peroxide can 

be used to remove many organic 

impurities. 

199 

lie impurities than are hexavalent 

chromium processes. But once present in the solution, impurities can be 

removed easily. Chemical purifying 

solutions are available to precipitate 

metallic impurities. Some of these purifiers can even be added during plating. By dummying the plating solution and using purifiers one can 

maintain a trivalent chromium plating bath indefinitely if it is being contaminated only by metallic impurities. Carbon and hydrogen peroxide 

can be used to remove many organic 

impurities. 

Throwing Power. Trivalent chromium electroplating processes have 

better throwing power than hexavalent chromium processes. 

Plating Rate. The high-efficiency 

single-cell trivalent chromium process 

has a reported plating rate of around 

10 millionths of an inch per minute 

while the double-cell processes reportedly plate at less than four millionths of an inch per minute. The 

other single-cell processes plate at 

about four millionths per minute. 

Micro-discontinuous Chromium. 

All trivalent chromium processes produce micro-discontinuous chromium 

64 PRODUCTS FINISHING 

deposits from the bath. Deposits 

from hexavalent chromium processes 

must undergo various post-plating 

or pre-plating steps to induce 

microdiscontinuity. 

For highly corrosive environments, 

microdiscontinuous chromium improves corrosion resistance of nickelchromium electroplates. Under typical 

conditions, the corrosion characteristics of trivalent chromium electrodeposits plated over at least 0.3 mil 

of nickel compare favorably or are 

better than chromium deposits produced from hexavalent chromium plating solutions.' In most cases, at least 

10 millionths of an inch of chromium 

is specified for corrosion protection. 

Color. Historically, the color of 

trivalent chromium electrodeposits is 

different than that produced from 

hexavalent chromium electrolytes. 

Hexavalent chromium electrolytes 

produce deposits that are slightly blue 

in color, making them appear white 

to the human eye. Deposits from the 

original trivalent chromium processes 

do not contain this blue coloration, 

making them appear darker in color. 

In contrast, the new double-cell trivalent chromium processes and the highefficiency single-cell trivalent chromium process produce chromium deposits that are very similar in color 

to that of hexavalent chromium. 

Many platers and most consumers 

cannot distinguish between the color 

of the deposits from these new trivalent processes and that from hexavalent processes. 

The "pewter" or "stainless steel" 

MARCH. 1988 

fc 

look of deposits from the original 

trivalent chromium process is, to 

many people, very appealing. It has 

been specified for some applications 

because of its rich appearance. 

Deposit Thickness. A major distinction between hexavalent chromium and trivalent chromium is that 

chromium can be plated to almost 

any thickness from a hexavalent 

chromium plating bath, while deposit 

thickness from trivalent solutions is 

limited. The original single-cell trivalent chromium process allows plating 

a maximum chromium thickness of 

approximately 50 millionths of an 

inch. The double-cell trivalent chromium process, in field experience, 

plates a maximum thickness of less 

than 10 millionths of an inch. The 

high-efficiency single-cell trivalent 

chromium process allows plating up 

to approximately one mil. For this 

reason, hexavalent chromium plating 

processes are favored for true hard 

chrome applications. 

Wear. In most cases, the wear 

resistance of trivalent chromium deposits is the same as that of chromium deposits from hexavalent solutions. Most studies also report that 

the hardness of the deposits is also essentially identical. 

The Second Decade 

The original, and very successful, 

single-cell trivalent chromium process 

has now been used commercially for 

more than ten years. Within the second decade of trivalent chromium 

electroplating, an improvement in the 

original commercial process was 

MARCH. 1988 

made, which has increased its plating 

efficiency and made the color of its 

deposit similar to that of hexavalent 

chromium deposits. The commercialization of a. number of single-cell 

trivalent chromium processes and the 

introduction of the double-cell trivalent chromium process came about 

during the second decade. The doublecell processes also produce deposits 

similar in color to that obtained from 

hexavalent chromium plating 

processes. 

With the increase in plating efficiency, higher deposit thickness, and 

color similar to hexavalent chromium 

deposits, trivalent chromium deposits 

can now be introduced to new markets. Also, with the stricter safety, 

health, and environmental regulations, trivalent chromium processes 

become even more desirable than 

hexavalent chromium processes. 

Trivalent processes present fewer air, 

water and health/safety problems. 

Both the first- arid second-decade 

trivalent chromium processes are 

ready for the challenges of the future 

of chromium plating. PF 

For more data circle 292 on Postpaid Card 

REFERENCES 

I.D. L. Snyder, AESF Chromium Colloquium, Feb. 1987. Also, an article on ihc history of Irivalent chromium electroplating is to 

be published in Plating and Surface Finishing 

in Ihe spring of 1988. 

2. R.JV. Bunson, Pogg, Ann 1854, 91, 619-25. 

3. USP: 3.954,574; 4,038,160; 4,053,374; 

4,093,521; and 4,184.929. 

4. A. Ceuther, Liebig. Ann 1856, 99,314. 

5. D.L. Snyder, Plating and Surface Finishing. 

1979, 66, 60-65. 

PRODUCTS FINISHING 65 
P.12 

TCRLC-0387R 

HARSHAW PLATING PRODUCTS 

OPERATING INSTRUCTIONS 

HARSHAW TRI-CHROME® LC 

TRIVALENT CHROMIUM 

PLATING PROCESS 

INTRODUCTION 

® Harshaw TRI-CHROME LC is a new technology chromium 

plating process using no chromic acid and offering the 

following advantages: 

1. Reduced effluent problems - no need- to reduce 

toxic hexavalent chromium. Reduced sludge 

volume. 

2. No toxic hexchromium - no mist suppressants 

needed. 

3. Improved covering power. 

4. Complete absence of "burning at high current 

density. 

Note: Due to the high plating speed of 

LC at lower pH's some microcracked deposits 

can be detected. These deposits can give 

the appearance of burning. 

5. One formulation for both decorative and hazefree microdiscontinuous deposits. 

6. Improved metal distribution: more uniform 

thickness across current densities. Simplifies 

rack design. 

7. Tolerates current interruption, sulfate and 

chloride drag-in. 

8. Better evaporation - reducing cost. 

9. Anodes will last indefinitely. 

Harshaw Tri-Chrome can replace conventional or proprietary 

chromic acid based electrolytes without change of processing sequences. Timing sequences on present equipment 

need little, if any, alteration. 

Harshaw Tri-Chrome LC will help provide a lighter color 

deposit than first generation trivalent chromiums. 

KLCEIVEP '"'" ^ HARSHAW/FILTROL ^ 3 587 

HARSHAW/FILTROL PARTNERSHIP • 30100 CHAGRIN BOULEVARD • CLEVELAND. OHIO 44124 • (216) 292-9200 

u 
- 2 -

HARSHAW TRI-CHROME® LC PLATING PROCESS 

SOLUTION COMPOSITION 

Material 

TC Additive 

TC Stabilizer 

TC Regulator 

Chromium (Cr+3) 

Boric Acid (H3BO3) 

OPERATING CONDITIONS 

360-420 g/L 

55-75 g/L 

2.0-5.0 ml/L 

20-23 g/L 

60-65 g/L 

PH 2.3-2.9 

Temperature 

Cathode Current Density 

Agitation 

Anodes 

Anode Current Density 

Specific Gravity 1.2.0-1.24 

Range 

(48-56 oz/gal) 400 g/L 

(5.5-7.5 %/vol) 6 5 ml/L 

(2-5 gal/1000 gal) 3.0 ml/L 

(2.7-3.0 oz/gal) 22 g/L 

63 g/L 

Optimum 

2.5-2.7 

(80-110°F) 85-90°F 

860-1080 A/m2 (80-100 ASF) 

Mild Air Agitation 

Harshaw Special Graphite 

Maximum 54 0 A/m2 (50 ASF) 

1.22 

(53.3 oz/gal) 

(6.5 %/vol) 

(3 gal/1000) 

(2.9 oz/gal) 

fc 
P.M 

- 3 -

PROCESS CONTROL 

General 

All constituents should be maintained within the ranges 

specified under "Solution Composition". Additions of 

all constituents sho.uld be made no less often than every 

5 amp-hours/litre (20 A/h gal.) or each eight hours 

of accumulated operation. Extension of the foregoing 

current-time relationships will result in imbalance 

of the solution and the necessity to make large additions 

which will require additional electrolyzing to restore 

the bath to operating condition. Addition schedules 

should be established for each installation to adjust 

for varying amounts of drag-out. All additions should 

be made during or just preceding electrolysis. 

TC Additive 

TRI-CHROME TC Additive is used for makeup and replenishment. It provides conductivity to the bath and 

also replaces chromium lost through drag-out. TC Additive 

may dissolve with difficulty unless special precautions 

are used. Fast addition rates may result in the formation 

of wet- lumps of additive which may not dissolve. The 

TC Additive is preferably distributed slowly and evenly 

over the surface of the solution, giving most of the 

material time to dissolve before further additions are 

made. Small frequent additions are therefore preferred. 

The concentration of TC Additive should be maintained 

by keeping the specific gravity of the solution at a 

minimum value of 1.18. An addition of 22.5 g/L (3 oz/gal) 

of TC Additive will raise the specific gravity approximately 0.01 units. It is preferred to make this addition 

subsequent to additions of TC Chrome Adjuster (see 

Specific Gravity). 

High concentrations of TC Additive may result in the 

formation of some crystals, especially if the solution 

temperature is low. The presence of crystals may result 

in plugged air agitation lines or coated anodes. The 

latter may result in reduced current. If the crystals 

pose a problem, the affected equipment and anodes should 

be removed and cleaned (scrubbed). Low concentrations 

of TC Additive will reduce conductivity of the bath 

resulting in reduced current or the need for increased 

voltage to maintain cathode current density. 

TRI-CHROME TC Additive is a light green powder and will 

tend to dust easily. Proper safety procedures should 

be used which are suitable for the handling of powdered 

material that can produce dusting. 
•- 4 -

TC Chrome Adjuster 

TRI-CHROME TC Chrome Adjuster is used to replenish the 

chromium plated from the solution and is added on the 

basis of ampere-hours. TC Chxbme Adjuster must be distributed slowly and evenly over the surface of the solution in the same manner as TC Additive discussed above. 

TC Chrome Adjuster will have a consumption rate of 22,5-340 

g/10.00 amp-hours (8-12 oz/1000 A-h) and should "be added 

at least after each eight hours of accumulated actual 

plating time. 

TRI-CHROME TC Chrome Adjuster is a dark green powder 

and will tend to dust easily. Proper safety procedures 

should be used which are suitable for the handling of 

powdered material that can produce dusting. 

TC Stabilizer 

TRI-CHROME TC Stabilizer forms a stable compound with 

the chromium allowing it to plate out from the trivalent 

state. High concentration of TC Stabilizer may result 

in some precipitation of chromium salts especially if 

the solution is unbalanced in other respects, such as 

high pH, and high temperature. Low stabilizer reduces 

plating rate. It is therefore important that TC 

Stabilizer be maintained within the range specified. 

TC Stabilizer is consumed by drag-out and electrolysis. 

A consumption rate of 1000 mL/1000 amp-hours (35 fl. 

oz/1000 A-h) may be used until a specific consumption 

rate for the individual installation can be established 

based on analysis. 

TC Regulator 

TRI-CHROME TC Regulator functions to clear the deposit 

of dark smudges and provide satisfactory metal distribution. Low TC Regulator may result in dark smudges in 

the deposit and decrease chromium thickness in mid-current 

density areas. High concentrations are not especially 

harmful, however, amounts greater than 10 mL/L (10 

gal/1000 gal) may result in reduced cover and/or hazy 

white patches in the deposits. 

TC Regulator is consumed mainly by electrolysis and 

should be added based on an average consumption of 2 5-50 

mL (1-2 fl oz) per 1000 amp hours. 

TC Corrector 

TC Corrector is used at the time of make-up, 3 mL/L 

(3 gal/1000 gal). Further additions may be required 

in some installations but should be added only on the 

advice of a Harshaw Representative. Harshaw TC Corrector helps improves throw. 

/J* 
P.16 

- 5 -

£H 

Optimum operating pH is in the range of 2.5-2.7 pH values 

between 2.3-2.9 can be used, however, at high pH (2.9) 

coverage is improved at the expense of plating speed. 

pH should be measured with a pH meter fitted with a 

sleeve type calomel electrode (see Analytical Methods 

for measure of pH). Due to the dark color of the 

solution, most pH papers will produce unsatisfactory 

results and their use is not recommended. pH adjustments 

should be made on the basis of 2 mL/L (2 gal/1000 gal) 

concentrated hydrochloric acid to lower the pH 0.1 units 

or 2 mL/L (2 gal/1000 gal) of concentrated ammonium 

hydroxide (Sp. Gr. 0.89) to raise the pH 0.1 units. 

Additions of hydrochloric acid or ammonia will initially 

produce large temporary changes in pH which will then 

reach equilibrium over a period of time. Because of 

this, pH cannot be accurately measured for about 8-12 

hours following an addition of acid or ammonia. 

pH adjustments should be limited to 0.2 pH units at 

one time. pH adjustments greater than 0.2 pH units 

are preferably made in steps over a period of several 

hours, e.g., a desired adjustment of 0.4 pH uhit should 

be made by addition of enough hydrochloric acid (or 

ammonia) to change 0.2 pH unit, waiting several hours, 

and then adding the additional requirement. 

Temperature 

Optimum temperature range is 80°-110°F. At lower temperatures there is some danger of crystallization while 

higher temperatures will reduce covering power. Cooling 

may be required when operating continuously at more 

than 0.5 amp/litre (2 amp/gal) (see Equipment-Cooling). 

Consultation with Harshaw for appropriate cooling recommendations is suggested. Operating at temperatures 

below 80°F may cause precipitation. Heating above 110°F 

will redissolve precipitate. 

Cathode Current Density/Plating Rate 

It is suggested that an average cathode current density 

of 860-1080 A/m2 (80-100 ASF) be used to provide a balance 

between consumption of additives, deposition rate, rectifier requirements and cooling capacity. Increasing 

current density will result in decreasing cathode 

efficiency resulting in increased covering power but 

at the same time decreasing deposition rate (especially 

in' high current density areas), increasing consumption 

of additives and possibly over-heating (requiring additional cooling). In extreme cases where the utmost 
- 6 -

in coverage is required as well as uniformity of metal 

thickness, it may be advantageous to strike at higher 

current density, e.g., 1600-2100 A/m2 (150-200 ASF) 

for thirty seconds. ... f 

Under optimum conditions, (6-10 y in.) of chromium will 

be deposited per minute at 1080 A/m2 (100 ASF). Increasing current density will not significantly increase 

the plating rate due to a decrease in cathode efficiency. 

Air Agitation 

The role of air agitation is to insure uniformity of 

metal distribution rather than to stop high current 

density burning. The agitation should be mild and. as 

uniform as possible. (See Equipment) Too much agitation 

results in • a slight loss of coverage and too little 

results in uneven metal distribution. 

Air Agitation should be turned off during idle periods. 

Specific Gravity 

Specific Gravity should be measured with a suitable 

hydrometer (see Analysis Bulletin). The specific gravity 

of the solution should be maintained at a minimum of 

1.18. Operation of the bath at specific gravity of 

1.22 will produce best results with greater tolerance 

to the effects of metallic impurities. Operation of 

the bath at specific gravity greater than 1.24 may result 

in some crystallization especially if the solution is 

allowed to cool below 27°C (80°F). Warming the solution 

to operating temperature, 27-43°C (80-110°F), will usually 

redissolve the crystals. (see Equipment-Anodes) Specific 

gravity is maintained by addition of TC Additive following 

adjustment .of the bath (if necessary) with TC Chrome 

Adjuster. 

The following table provides conversion information 

from specific gravity to Baume in the event this type 

of hydrometer is available: 

Specific Gravity °Baume 

1.190 23.2 

1.200 24.2 

1.210 25.2 

1.220 26.2 

1.230 27.1 

1.240 28.1 

M 
P.18 

- 7 -

SOLUTION MAINTENANCE 

The Tri-Chrome solution is maintained by addition of 

TC Additive, TC Chrome Adjuster, TC Stabilizer, TC 

Regulator and control of pH as described under "Process 

Control". The information given should allow for near 

optimum performance for most installations. Occasionally, 

the solution should be analyzed and adjustments made 

to optimize the solution. 

Large additions of TC Additive, 22.5 g/L (3 oz/gal) 

or greater, TC Chrome Adjuster, 7.5 g/L (1 oz/gal) or 

greater, or smaller quantities if both are added, may 

unbalance the chromium complex requiring re-electrolysis 

(30-60 minutes) to avoid plate defects. To avoid reelectrolysis, additions should be broken up and spread 

out over 24 operating hours, along with the regular 

maintenance additions. 

SOLUTION PREPARATION 

The sequence outlined below should be followed as closely 

as possible. Suitable precautions should be taken where 

noted to insure proper make-up and aging of the solution. 

1) Read "Equipment" section to insure that the tank 

has been cleaned out properly and the proper equipment is in place. 

2) Fill the properly prepared plating tank one-half 

full with clean city water. Turn on the air agitation and heat the solution to 60-65°C (140-150°F). 

Disconnect heat after reaching this temperature. 

3) Add (1.3 oz/gal) 10 g/L Boric Acid. Let mix until 

dissolved. 

4) Using air agitation, slowly add the Tri-Chrome 

TC Additive (400 g/L or 3.33 lbs/gal) making sure 

that the material is dissolving as fast as it is 

being added. (See Process Control-TC Additive) 

Undissolved material on the bottom of the tank 

may dissolve with difficulty and seriously affect 

proper break-in of the solution. The temperature 

of the solution will fall during the addition due 

to the solution of the TC Additive. It will be 

helpful to reheat the solution to 35°C (95°F) to 

facilitate dissolving the TC Additive. 

5) Install anodes at this time (see Equipment-Anodes). 

6) Fill the tank to. about 85% of its final volume 

with cold water. At this time the solution temperature should be "about 25-30°C (77-86°F). Continue 
P.19 

- 8 -

to agitate the solution (use mechanical agitation 

if necessary) to insure /complete solution of the 

TC Additive. It is preferred to agitate the solution for 16-24 hours to insure complete solution. 

7) With good agitation, add 6.5 %/vol (65 mL/L or 

6.5 gal/1000 gal) TC Stabilizer. Add TC Stabilizer 

only as fast as thorough mixing of previous additions of TC Stabilizer will allow to avoid localized high concentrations. 

8) Mix for a few minutes and add 3.0 Ml/L (3.0 gal/1000 

gal) TC Regulator. Adjust temperature to 29°C 

(85°F). 

9) Add 8 gal/1000 gal. Hydrochloric Acid and check 

pH after 8-10 hours. 

10) Add 3 mL/L (3 gal./1000 gal.) TC Corrector. 

11) Insert previously nickel plated corrugated steel 

dummy cathodes. A total area of about 25-100m2/ 

1000 litres (1-4 ft2/100 gal) should be used. 

Add water to the working level at this time and 

begin electrolyzing. 

12) The solution must be electrolyzed at this point 

to complex bath constituents properly. Electrolysis 

should be performed at 1080 A/m2 (100 ASF) using 

0.25-1.0 amp/litre (1-4 amp/gal) for one hour at 

operating temperature. 

13) After the one hour electrolysis period, the solution 

can be put into operation. Defects in the deposit, 

especially at high current density areas, can be 

eliminated by further electrolysis. 

METALLIC CONTAMINATION 

Due to the very mild acidity of the solution (pH 2.3-2.9) 

and the continuous removal of trace metallic contamination 

by plating, there should be no excessive buildup of 

impurities unless parts are frequently lost from racks 

or if post-nickel rinsing is inadequate. In some cases, 

electrolytic purification may be recommended to insure 

that trace elements are kept within the tolerable levels, 

and this is best achieved by plating periodically for 

a few hours at 108-324 A/m2 (15-45 ASF) using nickel 

plated corrugated steel cathodes. 

The information below gives a guide to maximum levels 

of trace elements when present alone and shows that 

copper and zinc must be maintained at a low level. 

JJ 
P.20 

- 9 -

In practice, contaminants are found together, and under 

these conditions may reinforce one another.- For example, 

0.05 g/L zinc, 0.10 g/L iron and 0.01 g/L copper may 

well be more harmful than 0.20. g/L nickel alone, even 

though all elements are present/' within their tolerance 

limits. 

Occasional difficulties have arisen in practice due 

to siphoning of nickel solution along compressed -air 

lines. To avoid this, air lines should be fitted with 

anti-siphon devices (e.g., the drilling of a small hole 

at the highest point). 

In cases of gross contamination, methods are available 

for removal of metallic impurities by precipitation 

with TC Purifier, (see Harshaw Plating Processes Bulletin, 

"Purification of Tri-Chrome Trivalent Chromium Plating 

Solutions".) 

Important Note: 

Imbalance in solution composition may lead to brown/black 

marks which can be confused with nickel or iron contamination. Poorly maintained solutions, especially those 

deficient in TC Stabilizer and/or TC Chrome Adjuster, 

or too high in pH or temperature, will also be more 

susceptible to the effects of metallic contamination. 

If an analysis is available, the solution should always 

be optimized before attributing the defect to metallic 

contamination. In many cases readjustment of the solution will cure the problem without use of TC Purifier. 

1. Copper - maximum 0.02 g/L 

This is rarely found in practice unless solution 

is allowed to come into contact with exposed copper 

structures (e.g., bus bars) or brass/copper parts 

are allowed to dissolve in the bath. 

Symptoms 

First shown by a graying at high current density, 

extending to lower current densities as the concentration increases. At very high concentrations, 

mid-current density areas can appear black and 

exposed nickel is stained brown (by immersion plate 

of copper). 

Removal 

If copper is the only contaminant it is best to 

plate out on nickel plated corrugated metal cathodes 

at low current density of 108-324 A/m2, (15-45 

ASF). If other contaminants need to be removed, 

TC Purifier will remove copper at the same time 

as other metallic contaminants. 
P.21 

- 10 -

Zinc - maximum 0.0 5 g/L 

Zinc contamination can * occur in plants plating 

zinc die castings especially when parts are so 

shaped that they cannot be fully copper/nickel 

plated. 

Symptoms 

Low levels of zinc contamination result in a reduction in coverage and a characteristic sharp 

white edge at the chromium cut-off. (Normal TriChrome deposits have a diffuse blue/brown cut-off 

in low current density areas.) High levels of 

zinc contamination show a white iridescent stain 

at low current density areas and this can spread 

into mid-current density regions in the presence 

of other contaminants. 

Removal 

If zinc is the only contaminant and is present 

at a low level it can best be removed by plating 

out as for copper. High levels of contamination 

usually require treatment with TC Purifier. 

Nickel - maximum 0.20 g/L 

Some nickel contamination is found in all baths, 

due to drag-in and dissolution from nickel plated 

parts lost from racks. The level of nickel contamination is found when post-nickel rinsing is poor 

or parts retaining nickel solution are processed. 

The presence of nickel tends to reduce the tolerance 

to other contaminants such as copper and iron. 

Symptoms 

Contamination is indicated by dark brown or black 

marks at mid-current densities. These tend to 

be streaky and sharp-edged, unlike those resulting 

from iron contamination. Nickel contamination 

can also be recognized by the reduction in staining 

below the cut-off although coverage is not reduced 

as with zinc. In combination with iron the region 

below the cut-off becomes golden (see Iron) and 

the marks black. 

Removal 

Nickel plates out very slowly and is not normally 

removed while plating out zinc or copper. The 

recommended method of removal is to use TC Purifier. 

/ * 
P.22 

- 11 " 

Iron - maximum 0 . 5 g/L •, 

Iron contamination can arise in two ways, by dissolution of parts lost from racks or by bipolarity 

effects when using plain unplated steel dummy sheets. 

Tri-Chrome is tolerant to iron, which when present 

alone can be detected by the golden yellow stain 

present below the chromium cut-off. 

Symptoms 

Iron alone can cause brown fluffy marks at medium 

current density, together with obvious iron deposition (see above) in very low current density 

areas. A small amount of iron (0.05-0.10 g/L) 

is beneficial in extending cover and minimizing 

the effects of slight zinc contamination. 

Removal 

Iron plates out slowly at 108-324 A/m2 (15-45 ASF) 

on nickel plated corrugated steel cathodes but 

care should be taken not to introduce iron by the 

use of unplated cathodes. For larger concentrations 

of iron the use of TC Purifier is recommended. 

Lead - maximum 0.0 2 g/L 

Lead contamination may arise as a consequence pf 

inadequate cleaning of tanks which have been used 

for hexavalent chromium solutions. Removal of 

lead is not always complete even with hydrochloric 

acid leaching and lead contamination manifests 

itself usually after the first overnight standing 

period. 

Symptoms 

White patches in low current density areas, spreading 

around the back of parts as a white haze. Some 

high current density adhesion failure may also 

be noted when high levels of lead are present. 

Removal 

Lead plates out readily at low current densities 

of 108-216 A/2 (10-20 ASF) and is best removed 

by this means. 
P.23 

- 12 -

TROUBLESHOOTING SUMMARY 

I. Poor Coverage 

air agitation too high 

TC Additive or specific gravity too low 

needs plating, if additions have just 

been made 

zinc contamination 

lead contamination 

temperature too high 

current density too low 

nitrate contamination 

oxidation of excess TC Purifier (dark 

band may also be present at chromium 

cut-off) 

II. Deposition Rate Too Low 

pH too high 

TC Regulator too low 

TC Stabilizer too low 

TC Additive or specific gravity too low 

inadequate air agitation over vertical 

surfaces 

III. Non-Uniform Metal Distribution 

air agitation too low or badly positioned 

air coil 

TC Regulator low 

poor rack design 

poor anode positioning 

IV. Poor Conductivity 

poor electrical connections 

TC Additive too low 

low temperature 

low anode area 

anodes covered with crystals 

V. Crystallization 

solution too cold (crystallized salts 

may be slow to redissolve) 

excessive evaporation during idle periods 

TC Additive too high 

VI. Microcracks Fail to Form 

insufficient chromium thickness 

cracks difficult to see unless the parts 

are copper plated (Dubpurnell Test) 

(7 
P.24 

- 13 -

VII. Dark Smudges on Work Pieces 

metallic contamination 

low TC Regulator | 

low TC Stabilizer"made worse if TC Additive 

and TC Chrome Adjuster are also low, 

e.g., by excessive dilution 

VIII. White Patches on Work 

zinc contamination 

drying-on of nickel solution due to excessively hot nickel solution or prolonged 

drying 

incorrect precleaning prior to nickel 

lead contamination 

high non-pitter in nickel solution 

high TC Regulator 

microcracked in HCD area due to excessive 

current 

IX. Adhesion Loss 

post nickel rinse contaminated with chromic 

acid 

lead contamination 

bipolarity during exit from nickel tank 

bipolarity during entrance to chromium 

tank 

inadequate nickel activation (re-chroming) 

current density too high 

TC Additive low (i.e., low specific gravity) 

X. White Film on Work 

This is usually due to the- presence of a precipitate formed by adding TC Purifier. . The precipitate can best be removed by filtration, preferably through a filter precoated with filter 

aid. 

The precipitated film can be wiped off easily 

and is normally found only on excessively 

contaminated solutions requiring constant 

TC Purifier additions. 

EQUIPMENT 

Tanks 

The tank lining must be of plastic (PVC, ABS, polyethylene, or rubber. Lead-lined tanks must not be used. 

Existing lead-lined tanks can be converted by lining 

with V rigid plastic sheet, insuring that the final 
- 14 -

assembly is leak-proof. A less preferred alternative 

is to fit a flexible plastic liner, but this is not 

recommended due to the likelihood of mechanical damage. 

If a flexible liner must be used, it is suggested that 

a sheet of rigid PVC be placed on the tank bottom, above 

the flexible liner, to minimize possible damage to the 

liner. 

Existing plastic or rubber tanks must be thoroughly 

cleaned to remove all traces of lead chromate which 

may be adhering to the tank walls. Both lead and 

chromates. are undesirable contaminants. Scrapping and 

leaching with sodium metabisulphite solution are required 

to insure complete cleanliness. After cleaning, the 

lining should be leached with 5% hydrochloric acid before 

use. Any film left after this operation should be scrubbed off and the tank again leached with 1% hydrochloric 

acid. 

Anodes 

Existing lead anodes must be replaced by special graphite 

anodes, fitted with titanium anode hangers specially 

designed to insure sound electrical and mechanical 

contact. Anodes and hangers are available from Harshaw.. 

Consultation with Harshaw is recommended for proper 

installation of anodes and hangers. As a general guide, 

the total immersed anode area should be twice the cathode 

area and should be sufficient to allow for a maximum 

anode current density of 540 A/m2 (50 ASF). A nominal 

24" x 2" (610 mm x 50 mm) diameter anode has a maximum 

effective area of 1 ft2 (0.1m2). The top of the anode 

should be at least 2.5 cm (one inch) below solution 

level. 

Copper anode rails or bus bars should be heavily 

nickel-chromium plated to avoid possible copper contamination and exposed bus bar should be shielded from 

solution by a plastic shield or by wrapping with plastic 

waterproof tape, etc. 

Anodes should not be removed until at least 30 minutes 

after plating stops as they may be saturated with electrolytically produced noxious compounds. 

Continuous use of extremely high anode current densities 

will significantly shorten anode life. Anodes should 

be inspected for a coating or crystals if bath crystallization is noted. Operation of the bath with coated 

anodes will in effect produce high anode current 

densities. (see Specific Gravity) 

/f 
P.26 

- 15 -

Air Agitation 

Perforated plastic air lines must be installed to give 

uniform mild agitation below the.fcathode area. Oil-free 

air from a blower should be used. 

It should be kept in mind that the air agitation is 

used to provide solution movement over the surface .. of 

the cathode and is not used to improve limiting current 

density as, for example, in nickel plating. Too much 

air agitation may result in a reduction of chromium 

coverage whereas too little may result in non-uniform 

thickness. 

Air lines should be designed as for nickel plating 

(Harshaw Technical Bulletin-Installation of Air agitation 

Systems for Electroplating Solutions), however, the 

air pipes should be spaced 100-150mm (4-6 in.) apart, 

not over 150mm (6 in.). The number of pipes used should 

be sufficient to cover the anticipated cathode area 

above the pipes plus 75mm (3 in.) in each direction. 

Due to the low pressure required for proper agitation, 

all perforated air lines must be installed level and 

in the same plane or uneven agitation will result. 

Valves for each air pipe should be provided to adjust 

the air volume at the tank. To prevent the possibility 

of siphoning solution out of the tank, a siphon-break 

hole should be drilled at the highest point of the air 

line(s) above the solution level. 

Cooling/Heating 

Because the process operates at temperatures of 27-43°C 

(80-110°F) some heating is necessary. The use of titanium 

coils with boiler heating (controlled by thermostat) 

is appropriate. In high production units with high 

square footages some cooling may be necessary. 

If external cooling is to be used, the circulating plating 

solution should not be "over-cooled" (below 7 5°F) due 

to crystallization of the plating solution. 

Ampere-Hour Meter 

An ampere-hour meter is necessary for optimum control 

of solution composition as maintenance additions are 

best made on an ampere-hour basis. In most automatic 

operations, the chromium ampere-hours can be related 

to the nickel ampere-hour meter by suitable corrections 

for time and current. 
P.27 

- 16 -

Rectifiers 

Existing 6-9 volt rectifiers are suitable for some installations, depending on anode area, cathode area, 

anode-to-cathode spacing, voltage losses in bus bars, 

etc., but for parts consistently requiring very good 

coverage, 9 to 12 volt rectifiers give more flexibility. 

Ventilation 

Although there is no toxic chromic acid spray emitted 

by the Tri-Chrome solution, the gassing at the cathode 

may, under certain conditions, produce an overspray 

that may be objectionable. For this reason, exhaust 

ventilation is recommended. Existing ventilation for 

hexavalent chromium baths is satisfactory. 

Filtration 

Tri-Chrome plating solutions requiring TC Purifier 

additions may create enough insoluble material in the 

solution to produce a white film on the work. Filtration 

of the solution, especially during the period immediately 

following TC Purifier addition, may therefore be desirable. Filters -constructed of materials suitable for 

use with high chloride nickel solutions are satisfactory 

for use with the Tri-Chrome solution. 

The use of an approved type of filter aid is recommended 

to assist in removing the insoluble material. Consultation with Harshaw for satisfactory types of filter aids 

is suggested. 

The residue filtered from the Tri-Chrome solution should 

not be subjected to the action of strong mineral acids; 

noxious fumes may result if this practice is followed. 

See separate bulletin on the "Filtration of Tri-Chrome 

Plating Solutions" for information on filter size and 

filtration techniques. 

These data are believed io be accurate but are not guaranteed to be so. 

Nothing herein shall be construed as suggesting the use of our product 

in violation ot any laws, regulations or rights ot third parties. Buyer should 

evaluate suitability and safety of product tor buyer's use. We cannot 

assume liability for results that buyer obtains with our products since 

conditions are not under our control. 

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