United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-83-002 July 1983
SER& Project Summary
Reduced-Pollution Corrosion-
Protection Systems
Christian J. Staebler, Jr. and Bonnie F. Simpers
This study evaluated newer less
polluting metal plating materials and
processes as potential alternatives to
currently used plating systems. Viable
replacements were established for
cyanide cadmium, cyanide copper, and
hexavalent chromium electroplating.
Available alternatives to solvent-borne
paints and phenolic-type paint strippers
have slightly lower performance
characteristics than their higher
polluting counterparts. Through
comprehensive testing performance
characteristics were established for
replacement systems of each type. The
performance, economic, and
environmental aspects of the new
coating systems were compared to
those for a control system currently in
use.
Alternative coating systems
evaluated for cyanide cadmium electro-
plating included non-cyanide cadmium
electroplating, mechanical plating of
cadmium and tin-cadmium, spray-and-
bake aluminum-filled resin coatings,
and ion-vapor-deposition (IVD) of
aluminum. Each of these alternatives
eliminated the cyanide waste treatment
problem and the last two also
eliminated the use of cadmium, another
toxic material. Although none of the
systems evaluated can be considered a
better alternative to cyanide cadmium
electroplating, each exhibited certain
advantages while offering the same
basic performance as cyanide cadmium
plating. Non-cyanide copper electro-
plating (the alternative evaluated for
cyanide copper electroplating) and tri-
valent chromium electroplating (the
alternative to hexavalent chromium
electroplating) were shown to provide
performances comparable to their
higher polluting, higher waste
treatment requirement control systems.
Water-borne paints and power
coatings, both of which eliminate the
need for solvent collection systems in
coating applications were evaluated as
potential alternatives for solvent-borne
paints. Although the performance
characteristics of these water-borne
paints and powder coatings were
shown to be comparable to those for
the solvent-borne control system, no
single system provided equivalent
performance for all characteristics.
Evaluation of non-phenolic paint
strippers against phenolic strippers
demonstrated the effectiveness of the
non-phenolic strippers in eliminating
the phenolic waste disposal problem.
Both acid and non-acid immersion and
brush-on type strippers were evaluated.
This Project Summary was developed
by EPA's Industrial Environmental
Research Laboratory, Cincinnati. OH.
to announce key findings of the
research project that is fully
documented in a separate report of the
same title (see Project Report ordering
information at back).
Introduction
Mounting concern over environmental
pollution, in light of more stringent EPA
and OSHA regulations, has prompted the
metal finishing industry to expand use of
newer, less-polluting corrosion
protection systems in place of currently
used organic solvent systems and
cyanide or cadmium plating solutions.
The aerospace and metal finishing
industries have available many new
coating systems that can be considered
as non-polluting or as having reduced-
pollution characteristics compared to the
currently used systems. Corrosion resist-
ance data for these systems are limited,
however, especially with respect to long-
term exposure. As a result, customer
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confidence in these systems is not high
and this has inhibited their widespread
utilization. Understandably, the metal
finishing industry is reluctant to the
introduction of new systems for which
supporting test data are limited and
manufacturing costs are not clearly
defined. The approach taken in this
project was to evaluate and demonstrate
the durability of these new systems by
conducting extensive tests to meet the
acceptance criteria of the aerospace and
metal finishing industries.
Conclusions
Replacement Coatings for
Cyanide-Cadmium
Electroplating
Several replacement systems are avail-
able for cyanide-cadmium electroplating,
including non-cyanide cadmium electro-
plating, mechanical plating, spray-and-
bake aluminum coating, and ion-vapor-
deposited (IVD) aluminum. These
systems, each of which has advantages
and disadvantages compared to
conventional cadmium electroplating,
can provide protection equivalent to that
given by cyanide cadmium electroplating
for various applications and cause fewer
harmful environmental effects than
cyanide cadmium electroplating. Kadizid*,
a non-cyanide cadmium electroplating
system, provides excellent adhesion and
corrosion resistance with no sign of
hydrogen embrittlement while
eliminating the need for cyanide waste
treatment. Transiflo*, a mechanically
plated cadmium coating, provides good
adhesion and excellent corrosion resist-
ance with no sign of hydrogen
embrittlement. No waste treatment is
required for the Transiflo plating system.
Alumazite Z*, a spray-and-bake aluminum
coating, provides excellent adhesion and
corrosion resistance with no sign of
hydrogen embrittlement.Since no
cyanides or cadmium is required with use
of Alumazite Z, waste treatment
problems are eliminated. Ivadize*, an ion-
vapor-deposited (IVD) aluminum coating,
provides excellent adhesion and
corrosion resistance with no potential for
hydrogen embrittlement. Again, no
cyanide or cadmium is used in the
process and, as before, waste treatment
problems are eliminated.
'Mention of trade names or commercial products
does not constitute endorsement or recommenda-
tion for use by the U.S Environmental Protection
Agency.
Replacement Coatings for
Organic Solvent-Borne Paints
Now available are water-borne paints
and powder coatings that conform to the
requirements of MIL-C-81773 (polyure-
thane topcoat). The hazards associated
with the use of solvent-borne paints, as
well as the need for solvent collection
facilities, are eliminated with the use of
either of these replacement coatings.
Three of the water-borne paints
evaluated, including one air-drying
system and two bake-curing systems,
have coating properties close to those for
the control system. These include film
properties (appearance, adhesion,
impact, and flexibility), fluid resistance,
and weatherability. Five of the powder
coatings evaluated also have coating
properties similar to those of the control
system. These include film properties
(appearance, adhesion, impact, and
flexibility), fluid resistance, and
weatherability.
Replacement Coatings for
Cyanide Copper Electroplating
A non-cyanide copper electroplating
system is available which is capable of
performance equivalent to that of
currently used cyanide-type copper
electroplating systems per MIL-C-14550.
Enthobrite Cu-942 provides excellent
adhesion, solderability, and decarb
protection with no sign of hydrogen
embrittlement while eliminating the need
for cyanide waste treatment.
Replacement Coatings for
Hexavalent Chromium Plating
A trivalent chromium plating system,
evaluated as a replacement for decorative
hexavalent chromium electroplating,
provided performance equivalent to that
for the hexavalent system while
eliminating the toxicity and waste
treatment problems associated with
hexavalent chromium. Trichrome
showed good appearance, adhesion, and
corrosion resistance, with no sign of
hydrogen embrittlement.
Replacement Coatings for
Phenolic Paint Strippers
Several acid and non-acid, brush-on
and immersion-type, non-phenolic paint
strippers show promise as potential
replacements for phenolic paint strip-
pers. The performance of these systems
approximates that of the standard
phenolic paint stripper (MIL-R-81294) in
appearance, removal power, rinsability,
coating and remover residue, and,
refinishability.
This technology development program
established the availability of many new
less-polluting corrosion protection
systems as viable alternatives to present
high-pollution systems. This effort has
encouraged manufacturers to develop or
improve less-polluting metal finishing
systems. If the development efforts are
continued, aerospace and metal finishing
firms should be able to implement the
following new systems with a high
degree of confidence:
• Water-borne, chemical milling
maskant systems evaluated under
the present project. These systems
show promise as replacements for
high-polluting systems. Additional
pilot-plant (50-gallon) testing on
both typical flat and curved panels
are needed to demonstrate the
viability of these systems for future
and most current commercial and
military aircraft. This testing would
provide the data needed to
implement the less-polluting,
water-borne maskants within the
critical timeframe on such new
aircraft as the 757 and 767 com-
mercial airliners and ATF, FSW,
V/STOL, AV-8B, and F-18 military
aircraft.
• Improved water-borne paints, paint
strippers, and spray-and-bake
corrosion protection coatings are
under development by several
manufacturers. Development of
these new products is seen to be a
direct result of thefavorablepublic-
ity that this program has received.
Evaluation of Results
Replacement Coatings for
Cyanide-Cadmium
Electroplating
Cadmium is normally plated from
cyanide-type electroplating baths. The
high level of toxicity of these baths
necessitates the costly waste treatment
procedures using either chlorine or
hypochlorites be used to destroy the
cyanide before disposing of these
solutions. Several cyanide-free cadmium
electroplating baths are now available;
preliminary investigations indicate that
these baths have potential as
replacement systems. Mechanical
plating of powdered cadmium also
provides a potential alternative for
cyanide-type cadmium electroplating.
\
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Several aluminum coatings are also
available as potential replacements for
cadmium plating, lon-vapor-deposited
(IVD) aluminum and aluminum-filled
resin spray-and-bake coatings are of
particular interest because they would
eliminate toxicity problems related to the
use of cadmium.
Four types of potential replacement
coatings (Table 1) for cyanide cadmium
plating (non-cyanide cadmium,
mechanical plating, spray-and-bake
aluminum, and IVD aluminum) were
tested to determine the best system
available in each category and to aid in
evaluating the relative merits of the four
types. Three non-cyanide cadmium
plating systems were evaluated as
potential replacements for cadmium
cyanide electroplating. These systems,
Lea-Ronal's Kadizid, Lea-Ronal's Cad-AI,
and Enthone's Enthobright CAD-935,
were evaluated in Hull cell tests to
determine throwing power and
brightness. Cadmium and tin-cadmium
applied by mechanical plating were also
considered as potential replacement
systems for cadmium cyanide electro-
plating. The 3M Company's Transiflo
process was used to apply these coati ngs.
Two spray-and-bake aluminum coatings
were evaluated as potential replace-
ments for cyanide cadmium plating.
Alumazite Z from Tiodize and HiKote 3
from Hi Shear were applied to 4130 steel
panels with and without MIL-P-23377
epoxy primer. The coatings were tested to
determine their adhesion, corrosion, and
fluid resistance. Panels of 4130 steel
were coated with aluminum by McDonnell
Douglas using their ion-vapor-deposition
(IVD) process. A chromate conversion
coating was applied to the coated panels.
The relative corrosion resistance of
each coating system was determined
using the 5%-salt spray corrosion test.
Two to four panels of each system were
subjected to 5%-salt spray until failure.
Cyanide cadmium-plated panels were
also run as controls. The corrosion
resistance of a coating system, measured
as time to failure, varies with the sub-
strate to which it is applied.
Sustained load testing was conducted
on selected coating systems to evaluate
the potential for embrittlement failure
resulting from hydrogen absorption.
Notched tensile specimens made from
both 300M and 4340 high-strength
steels were coated with the various
coating systems and subjected to a static
load at 75% of the ultimate notched
tensile strength for 200 hr or until failure.
The ultimate notched tensile strength
Table 1. Cyanide Cadmium Replacement Coatings
Cyanide
Cadmium
• Readily
available
Non-Cyanide
Cadmium
• Reduces
waste treat-
Mechanical
Plating
Advantages
• Eliminates
cyanides
Spray-and-Bake
Aluminum
• Eliminates •
cyanides
IVD
Aluminum
Eliminates
cyanides
ment req.
Techniques • Eliminates
well-established cyanides
Proven system • Conversion
costs low
Eliminates • Eliminates • Eliminates
hydrogen cadmium cadmium
embrittlement
• Reduces waste • Eliminates
treatment req. waste treat-
ment req.
• Eliminates •
hydrogen
embrittlement
• Uses conven- •
tional spray
equipment
• Can be formu-
lated for max
performance
Eliminates
hydrogen
embrittlement
Use to 5fO°C
(950°F) (CD
limited to 232°C
(450°F)
Uses toxic
chemicals
• Higher
makeup cost
Disadvantages
Requires new
equipment
Organic solvent*
collection
system req.
Requires new
equipment
Requires costly
waste treatment
• Part size
limited
was determined by continuously loading
uncoated specimens until failure.
The performance characteristics of
each of the systems selected as replace-
ments for cyanide cadmium plating
approximated those of the cyanide
cadmium control coating. Adhesion,
corrosion resistance, and hydrogen
embrittlement were evaluated for each of
the selected coatings (Table 2). The
adhesion of non-cyanide cadmium plate,
spray-and-bake aluminum, and IVD
aluminum was excellent. Satisfactory
adhesion was obtained with the
mechanical plating and cyanide cadmium
control coatings. When considered
against the minimum requirements of the
QQ-P-416 and MIL-C-81562 specifica-
tions, corrosion resistance of the selected
coatings is excellent. IVD aluminum
showed excellent corrosion resistance on
4130 steel with minimal variation in
results for the IVD aluminum. The
Alumazite Z coating also showed slightly
improved corrosion resistance over the
cyanide cadmium plate for 4130 steel. No
hydrogen embrittlement occurred as a
result of coating application for any of the
selected coatings.
Replacement Coatings for
Organic Solvent-Borne Paints
Paints are used in many decorative and
corrosion protection applications for
home appliances, automobiles,
aluminum siding, garden furniture,
aircraft skins, and many other
applications. Maskants are used to
protect parts from being etched during
the chemical milling process. Currently
used paint and maskant systems employ
organic solvents as volatile components.
Toxicity of these organic solvents
requires that stringent pollution-control
procedures be followed in the use of
these systems to meet established
standards for maximum discharge levels.
Besides increasing costs, additional
problems associated with using organic
solvent paints include flammability,
rising prices, and decreasing availability
of the solvents. The use of water as the
solvent component virtually eliminates
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Table 2. Cyanide Cadmium Replacement Coatings: Performance Summary
Corrosion resistance,
hr to failure**
System
Cyanide cadmium
electroplate*
Non-cyanide cadmium
electroplate* (Kadizid)
Mechanical cadmium
plating* (Transit lo)
Spray-and-bake aluminum
f Alumazite Z)
IVD aluminum* (Ivadize)
Adhesion
(bend test)
Good
Excellent
Good
Excellent
Excellent
4130 4340
576 2514
— 2°76t
2574
700
7752
Hydrogen
D6AC embrittlement
2172 Pass
Pass
3522 Pass
Pass
*Chromate conversion coating applied to plated panel.
**Average of four panels.
t/4 verage of two panels.
these problems. Several of the water-
borne paints currently available have
been designed to withstand the
applications mentioned above. Powder
coatings, applied by fluidized bed or
electrostatic powder spray, also eliminate
the problems associated with organic
solvents. Many different resins have
been used for these 100%-solids resin
systems, each with a different set of
properties. Formulations of the same
basic resin can be varied to adjust some of
these properties. Several water-borne
maskants have been developed to replace
the organic solvent-type systems
currently used for chemical milling
applications.
Twelve water-borne paint systems,
obtained from eight companies, were
evaluated. Seven of these systems cure
at room temperature; five require a
higher temperature cure. Each of the
systems, as well as the solvent-based
control, were applied to aluminum panels
that had been pretreated and alodined.
Each topcoat was applied to the primer
supplied for the system; in addition,
several of the topcoats were applied to
the solvent-based epoxy primer. The
panels were then subjected to
preliminary screening tests. These tests
were performed in accordance with the
requirements of MIL-P-23377 and MIL-
C-81773. Of the properties tested,
adhesion, impact, and flexibility were
considered most important. Test results
were analyzed to select the best coatings
for further testing. Three of the coatings,
Aquathane II and epoxy primer (air dry),
Aqualure 634-W-804 with Aqualure
primer (bake cure) and LP-3724 with LP-
3779 primer (bake cure) provided the best
combination of properties based on these
criteria.
Eight powder coatings (acrylic, epoxy,
polyamide, polyester [three types], nylon
and vinyl) were evaluated. Each of these
resins was applied by electrostatic
powder spray to steel and aluminum
panels. Nylon was also applied to
aluminum and steel panels by a fluidized
bed. A primer was used for the nylon and
polyamide coatings. Coated panels were
subjected to preliminary screening tests
according to MIL-C-81773 procedures.
As was the case with the water-borne
paints, adhesion, impact, and flexibility
were considered the most important of
the properties tested. Some of the resins
were applied at two coating thicknesses
to evaluate the effect of thickness on
coating properties.
Candidate water-borne maskants were
subjected to preliminary screening tests
to evaluate appearance, peelability,
etchant resistance, line definition and
scribability. Each of the maskants had a
uniform appearance with nopin-holingor
bubbling. The thickness of the Adcoat and
Dee Aircraft maskants was 12 mils
(0.0005 in.) while that of the Turco
material was 8 mils (0.0003 in.).
Final characterization tests of the
selected water-borne paints and powder
coatings included additional fluid
resistance tests, higher impact levels,
and hydrolytic stability evaluation. The
performance of the water-borne paints is
comparable to that of the organic solvent
paint control with respect to most
properties; the bake-cure systems were
slightly better than the air-dry systems.
The selected powder coatings performed
as well as or better than the organic-
solvent paint control in most cases. The
nylon powder coatings provided the best
overall performance.
The selected water-borne paints and
powder coatings applied to aluminum
test panels were also subjected to 12
months of outdoor (southerly) expos ure at
Grumman's Test Site located in the U.S.
Coast Guard Station at Fire Island, N.Y.
The epoxy/polyurethane control system,
as well as the Aquathane II and Aqualure
634-W-804 paint systems and the acrylic
powder coating, resisted the 12-month
weathering period rather well. The
coated panels experienced no significant
loss in properties. The epoxy powder
coating on aluminum test panels also
showed no significant loss in properties
despite chalking and a severe loss of
gloss; however, this coating on steel test
panels had severe corrosion after 6
months' exposure. Although the oven-
cured, water-borne paint system (LP
3778 primer and LP 3724 topcoat)
showed no corrosion after 12 months'
exposure, its adhesion, flexibility, and
impact resistance decreased after 3
months' exposure. Polyester 156 coating
applied to aluminum test panels experi-
enced a slight decrease in impact resist-
ance. When applied to steel test panels,
however, the Polyester 156 coating
showed evidence of corrosion around the
panel edges after 3 months' exposure,
with a slight decrease in flexibility and
impact resistance. Both the nylon powder
spray and fluidized-bed coating exhibited
a sharp loss in gloss and a decrease in
flexibility and impact resistance, even
though no loss of adhesion occurred. The
substrate used did not appear to affect the
wearability of these coatings. The acrylic
and polyamide powder spray coatings
showed evidence of corrosion after 3
months' exposure and severe corrosion
after 6 months' exposure, and were
unable to undergo testing after 12
months' exposure (corrosion was too
severe).
Replacement Coatings for
Cyanide Copper Electroplating
Copper is normally plated from
cyanide-type electroplating baths. The
high level of toxicity of these baths
necessitates the use of expensive waste
treatment procedures involving either
chlorine or hypochlorites to destroy the
cyanides before disposing of these
solutions. Several cyanide-free copper
electroplating baths are available and
have potential to become replacement
systems. Five cyanide-free systems were
evaluated and compared to the standard
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Table 3. Non-Cyanide Copper Plating: Screening Tests
Hull cell tests
2.5 liter (0.66-gal) solution tests
System
Mac Dermid Rocheltex
(cyanide type control)
Lea-Ronal Cu-Pure
Enthone Cu-942
Bright
range,
A/m2
(A/ft2)
11-387
(1-36)
11-324
(1-30)
11-1290
Throwing
power
Good
Good
Excellent
Current
density,
A/m2
(A/ ft2)*
270
(25)
390
(36)
780
Surface
condition
Smooth
Smooth
Smooth
Edges
Slight
burning
Some
burning
No
Comments
Excessive
gassing
Some
foaming
No gassing
Plating rate,
/jm/min
(mil/min)
0.495
(0.020)
0.406
(0.0161
0.813
RMS
value
55-100
60-125
45-55
Heat treat
evaluation
Some
decarb
Minute
decarb
No
Harstan Fluoborate
M&TAC-94
M&T Pyrophosphate
(1-120)
11-774
(1-72)
11-324
(1-30)
11-234
(1-22)
(72)
and bright burning or foaming (0.032)
decarb
Poor
Good
Poor
^Optimum current density as determined by Hull cell tests.
Mac Dermids' Rocheltex cyanide copper
plating system. These include Cu-Pure
and Unichrome Pyrophosphate (alkaline
types), Enthobrite Cu-942 and AC-94
Bright Acid Copper (acid sulfate types),
and Copper Fluoborate (acid fluoborate
type). The five non-cyanide, copper
plating systems were screened in Hull
cell tests to determine bright range and
throwing power (Table 3). Cu-Pure and
Enthobrite Cu 942 were selected for final
screening because they had the best
combination of cost, maintenance
requirements, and bright range/throwing
power of the systems evaluated. Because
the Enthobrite Cu-924 system did not gas
or foam, gave a smooth bright plate with no
edge burning, had a 60-100 percent higher
plating rate, and provided better protection
against steel decarburization, it was
selected for further testing. Sustained-
load tests were conducted to determine
the extent of hydrogen absorption in acid
copper-plated material and to evaluate
the potential for embrittlement failure. All
specimens exceeded the minimum test
requirements without failure.
The characterization of Enthobrite Cu-
942 showed that this non-cyanide copper
plating system exceeded the require-
ments established for copper plating in
MIL-C-14450 (Table 4). The adhesion and
solderability of the copper plate were
excellent. No hydrogen embrittlement
was evident in notched tensile tests of the
Cu-942-plated specimens. The Cu-942
plating adequately protected the steel
from decarburization during heat
treatment.
Table 4. Enthobrite Cu-942 Non-Cyanide Copper Plating Characterization Tests
Property Procedure Results
Thickness
Adhesion
Decarburization
protection
Solderability
Hydrogen
embrittlement
Permascope
Sheet bend
Metallographic
examination
Solder 232°C (450°F)-
sheet bend
75% UNTS/200 hr
28-33 ^m @ 0.813 fjm/min
(1.1-1.3 mils @ 0.032 mils/min)
Excellent*
No decarburization
Excellent*
Pass
*Copper plate immediately following nickel strike.
Replacement Coatings for
Hexavalent Chromium Plating
Chromium is normally plated from
hexavalent chromic acid electroplating
baths for decorative application such as
home appliances, marine hardware,
automobile hardware, zinc die casting,
brass forgings, and steel stampings. The
toxicity and waste treatment require-
ments of hexavalent chromium compared
to those of trivalent chromium make a
trivalent chromium plating system
desirable. Substrates to which chromium
plating are commonly applied include
1010-1020 steel and 4340 high-strength
steel. The pretreatment procedure
includes vapor degreasing, alkaline
cleaning, and reverse-etching of the
metal surface to be plated. A nickel
underplate is required for decorative
chromium plating to provide good plate
adhesion and maximum corrosion
protection. The performance of trivalent
chromium plating on buffed and unbuffed
1010 steel panels was screened with
respect to appearance, corrosion-resist-
ance and adhesion (Table 5). These tests
showed that the appearance of both the
trivalent and hexavalent chromium plate
was excellent. Both types were smooth
and bright, with the trivalent plate being
somewhat brighter than the hexavalent
plate. By comparison, the unbuffed panel
plated with trivalent chromium was
bright but not smooth, magnifying the
orange-peel effect of the unbuffed panels.
Plate adhesion was evaluated by bending
the panels to break and examining the
break at 4X magnification for lifting or
peeling. No separation was evident at the
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Table S. Trivalent Chromium Plating: Evaluation of Properties
Property
Appearance
Trichrome*
lunbuffed
1010 steel)
Bright
Trichrome*
(buffed
1010 steel)
Smooth and very bright
Hexavalent
Chromium'' (buffed
1010 steel)
Smooth and bright
Adhesion (bend test) Poor
Corrosion (salt spray) 96 hr**
Good
282 hr**
Good
96 hr**
* 25.4 nm (1.0 mil) semi-bright nickel
10.2 urn (0.4 mil) bright nickel
0.25 um (0.01 mil) chrome (trivalent or hexava/ent).
** Each of 4 panels failed at 96 hr.
*»* A verage of 4 panels: 2 failed at 48 hr, 1 failed at 288 hr, 1 failed at 744 hr.
chromium-nickel interface, the nickel-
nickel interface, or the nickel-base metal
interface on either the trivalent or
hexavalent chromium plates on the
buffed panels. The adhesion of the plate
to the unbuffed panel, on the other hand,
was poor (the underplate lifted from the
substrate and the chromium separated
from the underplate). This loss of
adhesion was apparently due to the
roughness of the substrate. Corrosion
resistance was determined by exposure
of four plated panels to 5%-salt spray
solution until failure. Two trivalent
chromium, Jsuffed panels failed at 48 hr,
one at 288 hr and one at 744 hr (an
average of 282 hr). This average is
considerably higher than that obtained
with the hexavalent chromium panels, all
four of which failed at 96 hr. Although the
variation in the trivalent chromium
results indicates that this bath may need
further work to provide consistently
higher corrosion protection, the results
do show that trivalent chromium has
excellent potential for providing improved
corrosion protection over the hexavalent
chromium while maintaining the
performance in other properties.
In addition to the above tests hydrogen
embrittlement tests were performed to
provide final characterization of the
chromium plating systems. Six notched
tensile specimens of 4340 steel were
heat treated to 1790-1930 MPa (260-
280 ksi) and plated with duplex nickel and
chromium. Three specimens were plated
with trivalent chromium and three
specimens were plated with hexavalent
chromium. All specimens were baked for
3 hr at 191 °C (375°F) following plating to
provide embrittlement relief. Three bare
control specimens were installed in a
universal testing machine and
continuously loaded until failure
occurred to determine the ultimate
notched tensile strength (UNTS). The
average UNTS was found to be 56.5 MPa
(389.3 ksi). The plated specimens were
then subjected to a sustained load of 75%
of the ultimate notched tensile strength
for 200 hr. The trivalent chromium-plated
specimens exceeded the 200-hr
exposure with no failure. The hexavalent
chromium-plated specimens all failed in
less than 7 hr; however, since chromium
plating on high-strength steel is normally
baked for 23 hr to provide complete
hydrogen embrittlement relief,
hexavalent chromium-plated specimens
should pass the notched tensile test.
Differences in the nickel baths used for
the trivalent and hexavalent chromium
specimens may have contributed to these
test failures.
Replacement Systems for
Phenolic Paint Strippers
Paint strippers are widely used through-
out the metal-finishing industry to
remove paint from parts to permit repair,
inspection, or refinishing. Most paint
strippers contain chromates, methylene
chloride, phenols, or strong acids. The
normal procedure involves application of
the paint stripper, allowing it to remain on
the part for a specified time period and
then washing it off with water. In many
cases, the wash water containing the
paint stripper and removed paint is fed
into drains that go to leaching ponds or
sewers. This can result in serious water
pollution, especially when highly toxic
chromates or phenols are involved.
Several paint strippers containing no
phenols have been developed as potential
replacements for phenolic paint
strippers.
The coating used for all paint stripper
tests (MIL-P-23377 epoxy primer/MIL-C-
81773 polyurethane topcoat systems)
was applied to 2024-T3 aluminum alloy i
panels according to conventional proce- '
dures and air-dried for 7 days prior to use.
The paint surface to be stripped was
completely covered with remover, either
by immersion or by brush. After the
required contact time, the area was
rinsed with water and the loosened paint
removed by brushing.
Testing of potential replacement
systems for phenolic paint strippers was
performed to determine the best system
available of each of the four types: acid
brush-on, non-acid brush-on, acid
immersion, and non-acid immersion.
Strippers in each category were
subjected to various screening tests
applicable to that category and compared
to the phenolic non-acid brush-on type
stripper used as a control. Preliminary
screening tests were conducted to
determine the stripper's remover power,
rinsability, coating and remover residue,
and general properties.
Preliminary screening tests were
conducted with the brush-on application
strippers. The performance of the six
candidate non-acid brush-on strippers
varied widely; the removal power, or time
required for completion of lifting, ranged
from 20 to more than 80 min. This time
was determined to be that required for
completion of all lifting and wrinkling
action, using a remover volume sufficient
to completely cover the test area. A more
quantitative removal power test, which
determined the total area lifted in a
specific time using a specific volume of
remover, showed that two of the
removers lifted the paint film in 30 min or
less using a specific remover volume
(Table 6). These removers, Sprazee (BASF
Wyandotte Corp.) and T-5873 stripper
(Turco Co.), also showed good rinsability,
coating residue, and remover residue.
Each of the three candidate acid brush-on
strippers (Oakite Visstrip, Turco T-2822,
and Turco T-6017) showed excellent
removal power in both the time and area-
lifted removal tests. These strippers also
showed excellent rinsability, coating
residue, and remover residue properties.
The removers were then subjected to
further evaluation. Sprazee and T-5873
strippers were selected from the non-acid
brush-on strippers for further evaluation.
The refinishing properties of the
selected brush-on strippers were
determined by applying the paint system
(epoxy primer per MIL-C-81773) to
panels which had been stripped with
each candidate system, and then testing
to determine the adhesion, appearance,
and gloss of the applied paint film. The
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Table 6. Brush-On Paint Strippers: Characterization Tests
Manufacturer
Phenolic control
• Turco
Trade
name
T-5469
Appearance
Homogeneous
Consistency
& How
Smooth, even coat
nemover
power,
(time to lift,
min:sec)
5:17
Contact
time
(min:sec)
5:30
Remover
10 ml
(% lifted)
100%
Volume
25ml
(% lifted)
100%
Non-phenolic non-acid
• BASF Sprazee
• Turco T-5873
Non-phenolic, acid
• Oakite Visstrip
• Turco 7-2822
• Turco T-6017
Homogeneous Fairly even coat 56:50 30:00
Homogeneous Smooth, even coat 20:05 6:45
Separated Smooth, even coat 8:28 5:20
Homogeneous Smooth, even coat 8:18 6:20
Slight separation Fairly even coat 3:20 3:10
82%
42%
92%
99%
87%
97%
100%
97%
99%
98%
* Gloss on original paint Him: 94.
**Maximum allowable weight change: aluminum ±0.016%; steel ±0.010%.
*»•» /y rj — NQ( determined.
Rinsability
Coating
residue
(% removed)
Ftefinishing Corrosion compatibility
properties weight change, %**
Remover
residue Gloss* Adhesion Aluminum
Steel
Excellent
>99%
Much residue
91
Good
0.011%
+0.007%
Good
Excellent
96%
>99%
Easily rinsed
Much residue
N.D.
90
N.D.**
Good
N.D.***
+0.007%
N.D.***
+0.031%
Excellent
Excellent
Excellent
95%
>99%
>99%
Easily rinsed
Easily rinsed
Easily rinsed
90 Good Heavy
corrosion
91 Good 1.36%
92 Some lifting 7.5%
-0.055%
-0.95O%
+0.258%
appearance of each of the refinished
films was good, with a reduction in gloss
from the original paint film of only 2 to 4
units. The adhesion of refinished films
was determined by the wet tape test. Good
adhesion was evident on all but one of the
refinished films; in that one, which used
the Turco T-6017 stripper, the topcoat
lifted from the primer on one of the two
panels; the other panel showed good
adhesion. The corrosion compatibility of
the selected paint strippers was also
determined for aluminum and steel
substrates. As expected, the acid paint
strippers are not compatible with either
aluminum or steel substrates. These
substrates corroded to varying degrees
after one week of exposure to the paint
stripper at 38°C (100°F). The Turco T-
5873 non-acid stripper also showed
corrosion of the steel substrate.
The performance of the candidate
immersion-type paint strippers was
evaluated in tests similar to those used
for the brush-on type removers; the major
difference being the paint removal tech-
nique. Results are summarized in Table 7.
One of the two non-acid immersion-type
strippers evaluated (Magnus 766)
showed good removal power and good
rinsability, with 90% paint lifted after a
22-min contact time. Two acid-
immersion paint strippers were
evaluated; one of these (Oakite Stripper
SA) showed good removal power with
excellent rinsability and a coating residue
of only 2% after an 11-min contact time.
This stripper left a residue after contact
with the bare substrate for 15-min at
38°C (100°F) and thorough rinsing. The
refinishing properties and metal
compatibility of the selected immersion
paint strippers were also evaluated. The
refinishing properties of both strippers
were good, with a 5-unit loss of gloss
compared to the original paint film and
only slight lifting of the paint system and
small blisters in the wet tape test of the
Stripper SA-stripped panels. The corro-
sion tests show that the acid stripper was
not compatible with either aluminum or
steel, while the non-acid stripper
(Magnus 766) was compatible only with
the aluminum substrate.
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Table 7. Immersion Paint Strippers: Preliminary Evaluation and Characterization
Manufacturer
Non-phenolic,
non-acid
• BASF
• Magnus
Trade
name
Rapoff
766
Appearance
Separated
Slight separation
Removal power
(time to lift,
min: sec)
>80.00
22:08
Rinsabilitv
Good
Good
Coating
residue
(% removed)
<1%
90%
Remover
residue
Much residue
Some residue
Refinishing
properties
Gloss" Adhesion
89 Good
Corrosion
compatibility
weight change, %**
Aluminum Steel
-0.003% -0.112
Non-phenolic, acid
Oakite
Oakite
Stripper EZ
Stripper SA
Separated
Homogeneous
>80:00
11:08
Fair
Excellent
10%
98%
Slight residue
Much residue
89 SI lifting -5.88% -0.912
"Gloss on original paint film: 94,
"Maximum allowable weight change, aluminum - ±0.016%; steel - ±0.010%.
Christian J. Staebler, Jr., and Bonnie F. Simpers are with Grumman Aerospace
Corporation. Bethpage, NY 11714.
Hugh B. Durham is the EPA Project Officer (see below).
The complete report, entitled "Reduced-Pollution Corrosion-Protection Systems,"
(Order No. PB 83-153 056; Cost: $13.00, subject to change) will be available
only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
CO
CO
C-J
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Postage and
Fees Paid
Environmental
Protection
Agency
EPA 335
Official Business
Penalty for Private Use $300
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DIVISION
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