Note: Descriptions are shown in the official language in which they were submitted.
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ELECTROLYTIC METHOD OF AND COMPOSITIONS FOR
STRIPPING ELECTROLESS NICKEL
FIELD OF THE INVENTION
The present invention relates to an electrical stripping process and
compositions for
stripping electroless nickel from a substrate. An electrical stripping process
can be described
as the reverse of electroplating. While electroplating applies a coating of
metal to a substrate,
an electrical stripper removes a coating from the substrate. The coating is
dissolved during
electrolysis by combining with negative chemical ions in a bath, which are
attracted to its
surface by its positive potential. While the object of a stripper is to remove
a coating without
damage to the underlying substrate, most anodic reactions cannot differentiate
between the
coating and the substrate resulting in etching of that substrate.
Electroless nickel is a very chemical resistant coating and is difficult to
attack. An
illustration of its chemical resistant is the "nitric acid drop test". A drop
of concentrated nitric
acid is applied to the electroless nickel coating's surface. If any etching
occurs within a set
time period, the test fails. The discovery of relatively mild chemical
formulations and
procedures that will rapidly strip these very chemical resistant coatings is
of great economic
value. This is especially true when the stripping process can be made
environmentally friendly
and safe to use in the recovery of defectively plated parts.
2. DESCRIPTION OF THE RELATED ART
Since the invention of autocatalytic chemical nickel deposition (now commonly
called
electroless nickel plating), the excellent chemical resistance of the deposit
has found wide use
in protecting a variety of manufactured articles. This chemical resistance has
been improved
over the years through innovative formulations that modify the structure of
the deposit to make
it even more resistant to chemical attack. Not surprisingly, the task of
stripping electroless
nickel while saving the substrate has become increasingly difficult.
Various methods have been used to attempt to strip electroless nickel with
varying
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degrees of success. One of the earliest methods tried was an electrolytic
stripper which was in
common use for stripping electrolytic nickel. The stripper was made from
concentrated sulfuric
acid, utilizing reverse current. Typically, a part to be stripped was immersed
in a stripping bath
and connected to the positive (anodic) lead of a direct current source.
Current traversed the
bath to the negative electrode (cathode) which was usually made of lead or
graphite. The
method utilized the principal of passivity, a. e., when the nickel deposit had
been dissolved by
the action of the sulfate ion, unlike the nickel, the chemical characteristics
of the steel substrate
in the presence of the very concentrated sulfuric acid would make the steel
passive to attack and
oxygen would be evolved. This method failed when trying to strip most
electroless nickel
deposits because, just as steel, the electroless nickel became passive.
U. S. Patent 4,356,069 (Cunningham) describes an electrical nickel stripper
composed
of concentrated sulfuric acid, chromic acid, and hydrogen peroxide. This
formulation claimed
to strip chromium as well as nickel from ferrous substrates. While the patent
does not claim
that the formulation will strip electroless nickel deposits, it suffers from
the disadvantages of
high disposal costs of its large hazardous chromium and sulfuric acid content,
and the added
step of having to remove an oxide layer from the substrate before replating
can be attempted.
Another chromic acid based electrical nickel stripper is described in U. S.
Patent
4,647,352 (Cook). This patent states that the combination of chromic acid,
phosphoric acid,
and sodium bisulfate can be used to electrically strip electroless nickel. The
formulation
suffers from its sensitivity to the introduction of sulfate ions to the bath
which caused it to etch
the substrate mandating the use of barium carbonate treatment. Disposal of
spent stripping
baths is very expensive due to the high chromic acid content.
U. S. Patent 4,664,763 (McMullen et al.) discloses an aqueous stripping
solution
comprising chromic acid utilizing defectively plated parts as either or both
the anode and
cathode of an electrolytic stripping cell and applying an alternating current
across the
electrodes to strip the nickel coatings. Electrolytic and electrolysis nickel
coatings are said to
be stripped by tlus method. This stripping method cites several optional etch
inhibitors, such
as potassium iodide, to help prevent etching of the substrate. This method
suffers from the
possibility of etching and the high disposal cost of the high chromic acid
content.
Other electrolytic stripping processes utilize nitrates, normally ammonium or
sodium
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nitrate, at a concentration of about three pounds per gallon. These processes
use reverse direct
current to remove electroplated nickel and some low phosphorous electroless
nickel deposits
from iron and steel. As nickel dissolves, the stripping bath undergoes rapid
pH changes that
produce heavy sludging problems. Sporadic passivity of large areas of
unstripped nickel occur
as the exposed base metal becomes passive under the influence of the electric
current causing
an incompletely stripped part. The problem is more pronounced when trying to
strip
electroless nickel deposits above about seven percent phosphorous.
Immersion nickel strippers (no electrical current needed) were introduced that
utilized
soluble nitrobenzene compounds in solution with cyanide compounds to strip
nickel deposits.
These strippers found limited use for stripping electroless nickel with a low
phosphorous
content, i.e., 1%-7 %, however, the higher phosphorous content electroless
nickel deposits
either did not strip or stripped at such low rates that the process proved to
be impractical.
With the advent of pollution controls, the use of cyanide became more and more
expensive as
the liability of disposal increased. a
Nickel stripping baths that utilize water soluble nitrobenzene compounds,
either
ammonia and ammonium salts or ethylene diamine and/or its homologs, have
gained wide
acceptance. These baths work well on deposits of electrolytic nickel and some
low
phosphorous electroless nickels have achieved stripping rates of about 0.001
inch/hour,
however, the high phosphorous content electroless deposits slowed the removal
to, on average,
less than 0.0003 inch an hour. Proper disposal of these types of stripping
baths is very
expensive because of their toxicity and high chelating power. These baths
operate at about
160 - 190 ° Fahrenheit to strip electroless nickel coatings and are
very vulnerable to damage by
heat through loss of volatile chemicals components as well as thermal chemical
decomposition.
U. S Patent 4,554,049 (Bastenbeck) discloses an immersion nickel stripper
which uses
sulfamic acid, hydrogen peroxide, nitrates, and chlorides. The patent claims
to strip low
phosphorous electroless nickel (less than 7%) but cannot effectively strip
deposits of greater
phosphorous content.
U. S. Patent 4,720,332 (Coffey) describes a uckel stripping bath that utilizes
soluble
nitrobenzene compounds, Zwitterions (as chelating agents), sulfide producing
compounds,
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carbonates, and the use of reverse current for the fast removal of electroless
nickel deposits.
While this method strips electroless nickel fast (up to 0.002 inchlhour) and
works well, it
sometimes microscopically etches in high current density areas dulling highly
polished
surfaces.
Thus, it is the objective of this invention to improve the art of stripping
electroless
nickel by providing formulations to electrolytically strip electroless nickel
deposits of both low
and high phosphorous content with equal high efficiency and ease.
It is also an objective of this invention to provide formulations to
electrolytically strip
electroless nickel with improved resistance to etching the substrate.
It is a further objective to provide a choice of alternative stripping
formulations that are
safer to use in the workplace and more environmentally friendly by eliminating
chelates,
nitrates, chromates, cyanide, and highly concentrated acidic solutions.
It is yet an obj ective to provide formulations and processes to strip
electroless nickel
from electrolytically deposited bright nickel, electrolytically deposited
sulfamate nickel, and
high nickel content alloys with little or no damage to the substrate.
SUMMARY OF THE INVENTION
The electrolytic stripping baths of the present invention are made from
oxoacids,
and/or oxoacid salts, and hydrogen peroxide. It has been discovered that
electroless nickel
deposits can be dissolved at the anode of electrolytic baths containing
oxoacids, and/or
oxoacid salts, and hydrogen peroxide. The substrates of iron, cast iron, steel
alloy, stainless
steel, and titanium are protected from attack during electrolysis if the
hydrogen peroxide/acid
mole ratio is maintained above a minimum preferred mole ratio of about 3.75
for strong
oxoacids with one ionizable hydrogen and about 7.5 hydrogen peroxide/oxoacid
mole ratio for
strong oxoacids with two or more ionizable hydrogens. Peroxide/oxoacid ratios
as low as 1.5
may be used when combining weak oxoacids with weak oxoacid salts to construct
a stripping
bath. To prevent attack on aluminum substrates only sulfuric and sulfamic
acids and/or their
salts may be selected from the strong oxoacids while any of the hydrogen
peroxide compatible
weak oxoacids and/or salts may be used. Only combinations of weak oxoacids
and/or oxoacid
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salts should be used when stripping from the substrates of electroplated
nickel, cast nickel,
kovar (iron, nickel, cobalt alloy), and sulfamate nickel.
For purposes of this invention an acid is considered strong if it has a
dissociation
constant (K1) greater than about 2 X 10-1 . Examples of strong oxoacids
include sulfuric,
nitric, sulfamic, alkyl sulfonic, aryl sulfonic, and monoalkyl esters of
sulfuric acid.
Examples of weak oxoacids include phosphoric, pyrophosphoric, alkyl
phosphoric,
glucophosphonic, oxalic, formic, propanoic, bis methanol propanoic, acetic,
butanoic, benzoic,
phthalic, citric, tartaric, malic, malonic, malefic, butyric, succinic,
glycolic, glutaric, gluconic,
adipic, boric, ethylenediaminetetraacetic and homologs, nitrilotriacetic,
amino acetic, and
polyvinyl sulfonic acid.
The concentration of hydrogen peroxide for the application of this invention
can range
from about one percent to about 99 percent, but a concentration of about eight
percent is
preferred. While maintaining the disclosed minimum peroxide/oxoacid mole
ratios the
oxoacid and/or oxoacid salts may vary from 0.01 mole/liter to saturation.
The pH range for implementation of the invention is about 0-8, while the
preferred pH
range is about 1-7; and the most preferred range is about 1.5-4.5.
The oxygen free halogen acids (hydrofluoric and hydrochloric) are excluded
from the
invention because there seems to be no hydrogen peroxide/acid ratio that will
prevent attack
on iron or steel substrates when these acids and/or their salts are used in
the stripping bath in
amounts above about 0.1 mole/liter. Iodic, bromic, and chromic acids and/or
salts are
excluded because of their incomparability with hydrogen peroxide either upon
mixing with
peroxide or during the stripping process.
DETAILED DESCRIPTION OF THE INVENTION
The present invention discloses that electroless nickel deposits can be
electrolytically
stripped from substrates of iron, cast iron, steel alloy, stainless steel,
aluminum, and titanium
utilizing stripping baths made from selected oxoacids and/or oxoacid salts and
hydrogen
peroxide. Surprisingly, electrolytically deposited nickel, cast nickel, kovar,
and high nickel
alloy.substrates can be stripped of electroless nickel deposits without
significant substrate
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attack provided the stripping bath is made from weak oxoacids and/or oxoacid
salts.
Electroless nickel can be stripped from aluminum substrates without
significant attack only if
the strong oxoacids and /or strong oxoacids salts are selected from sulfuric
acid and its salts
and/or sulfamic acid and its salts. Any of the hydrogen peroxide compatible
weak oxoacids
and/or oxoacid salts may be used to strip electroless nickel from aluminum.
The base metals
are protected from attack during electrolysis if the hydrogen peroxide/oxoacid
mole ratio is
maintained above a minimum of about 3.75 for strong oxoacids with one
ionizable hydrogen
and about 7.5 hydrogen peroxide/oxoacid mole ratio for strong oxoacids with
two or more
ionizable hydrogens. Peroxide/oxoacid ratios as low as 1.5 may be used when
combining
weak oxoacids and/or weak oxoacid salts to construct a stripping bath.
The oxygen free halogen acids (hydrofluoric and hydrochloric) are excluded
from this
invention because there is no apparent concentration of hydrogen peroxide that
will prevent
attack of iron, steel alloy, and aluminum substrates when these acids are
present in the
stripping bath at a concentration greater than about 0.1 mole/liter. Very
small amounts of
halogen ions do not seem to attack the substrate if accompanied in solution by
relatively large
amounts of oxoacid ions. For example, the amount of chloride ion resulting
from chlorination
of drinking water does not seem to affect the substrate, however, if the
concentration of
chloride ion rises above about 0.1 mole per liter, some attack of the
substrate may result.
Practical considerations such as bath conductivity and operator safety have
lead to a
preferred working range of about 5 - 20 % by volume hydrogen peroxide (10 - 40
% by
volume using 50 % hydrogen peroxide) and a most preferred working range of 7-
10 % by
volume hydrogen peroxide (14-20 % by volume using 50 % hydrogen peroxide).
Using the
proper hydrogen peroxide/acid mole ratio for this range of hydrogen peroxide
concentration
allows stripping at current densities up to about 100 amps/sq.ft. There is no
maximum
concentration limitation for the hydrogen peroxide except for the practical
considerations of
operator safety, disposal considerations, etc.
The concentration of oxoacid and/or oxoacid salts may vary over wide limits as
long as
the minimum peroxide/acid mole ratios are maintained. The acid and/or salts
may vary from
0.01 mole/liter to saturation. However, since the current that flows through
the bath
determines the amount of nickel stripped during a time period, it is preferred
that the stripping
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bath have a low electrical resistance. Therefore, selection of the amount and
type of oxoacids
and/or oxoacid salts that increase the conductivity of the solution is of
great importance for the
rapid and economic removal of the electroless nickel coating.
The preferred temperature range for operating the stripping baths of this
invention is
about 60-115 ° F, and the most preferred is about 80-100 ° F. Of
course,. lower or higher
temperatures may be used, however, lower conductivity and solubility will be
experienced at
lower temperatures, and accelerated peroxide decomposition may occur at higher
temperatures.
EXAMPLES
The following examples are given to demonstrate the application of the
invention but
not limit in any way the scope of the invention:
Example 1
The following bath was not chelated which makes waste treatment of spent
stripping
baths of this formulation simple and low in cost. It contained only about
three times the acetic
acid content of ordinary vinegar which makes it very safe to use. While the
peroxide content
was high enough to bleach hair, it is not a high enough concentration to be a
serious hazard to
workers.
CHEMICAL AMOUNT
Monosodium Phosphate 20 grams
Acetic Acid (68%) 20 milliliters
Hydrogen Peroxide (50%,25 milliliters
v)
Water (Tap) to make e of 140 milliliters
a total volum
Peroxide/Acid Mole Ratio:
1.82
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The above chemicals were dissolved to make a total solution volume of 140
milliliters.
The temperature of the solution was adjusted to 90 ° Fahrenheit. Two
one inch wide stainless
steel cathodes were placed into the solution on either side of the beaker that
contained the
solution and connected to the negative side of a variable voltage direct
current power supply.
A one-inch wide mild steel panel that had been previously plated with 0.001
inch electroless
nickel containing about 12% phosphorous was suspended in the middle of the
beaker between
the two stainless steel cathodes. The plated panel was connected to the
positive side of the
power supply. A TEFLON~ (polytetrafluoroethylene) coated stirnng rod was
placed in the
beaker and was used to slowly stir the solution to prevent stratification of
the bath. The
current was applied and the voltage drop across the stripping bath was
adjusted to four. After
a momentary formation of bubbles on the plated part, the nickel began to
dissolve into the
stripping bath and all bubbling at the anode stopped. The starting current was
0.75 amps.
After about thirty minutes, the steel base metal began to be exposed at the 90-
degree angles on
the bottom of the plated part. Unlike nitrate based electrolytic strippers,
the exposed steel
substrate did not gas. The electroless nickel coating continued to dissolve,
and as it receded, it
assumed a parabolic shape as it shrank from all sides of the panel. Only when
the remaining
electroless nickel coated area covered about 30% of the area of the panel
exposed to the
solution did gassing slowly began to occur from the base metal. After about
forty-five
minutes, no electroless nickel could be seen on the panel. An additional
fifteen minutes of
time was allowed to insure complete stripping and to see if any etching would
occur on the
steel panel. Examination revealed no etching. The mild steel panel was bright
and polished
just as it was when first immersed into the electroless nickel plating
solution.
Aluminum test panels were also stripped in this solution with equally good
results.
The following examples were constructed as in Example 1 and illustrate the
varied
oxoacids and/or oxoacid salts that may be used in this invention:
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Example 2
CHEMICAL AMOUNT
Sodium Hydrogen Sulfate 12 grams
Sodium Sulfate 15 grams
Hydrogen Peroxide (50%) 35 milliliters
Water to made a total solution volume of 140 milliliters
Peroxide/Acid Mole Ratio: 6.1
This bath had less resistance to the flow of current than Example 1 and the
starting
current was 1.02 amperes at a starting voltage drop across the bath of four
volts. An identical
panel to the one used in Example 1 was stripped in about thirty minutes with
identical good
results.
Example 3
CHEMICAL AMOUNT
Sulfuric Acid (66° Baume) 2.35 milliliters
Hydrogen Peroxide (50%) 35 milliliters
Water to made a total solution volume of 140 milliliters
Peroxide/Acid Mole Ratio: 15.0
This bath was constructed as in Example 1. This bath had very good
conductivity. It
stripped from the substrates of steel, aluminum, and titanium with no visible
attack. 2.35
grams of nickel were introduced into the bath and calculations showed that
97.9 % of the acid
had been used to react with nickel. Additional use of this bath caused the pH
to rise rapidly
from the 4.8 pH that was measured when the nickel content reached 2.35 grams.
Continued
stripping caused precipitation of nickel hydroxide and rapid decomposition of
the hydrogen
peroxide as the pH reached about 6-7. No additions of hydrogen peroxide were
necessary
during the test.
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Example 4
CHEMICAL AMOUNT
Citric Acid 10 grams
Trisodium Citrate 10 grams
Hydrogen Peroxide (50%) 20 milliliters
Water to made a total solution volume of 140 milliliters
Peroxide/Acid Mole Ratio: 6.79
Good results on substrates of steel, aluminum, titanium, and cast iron were
obtained.
Example 5
CHEMICAL AMOUNT
Ammonium sulfate 14 grams
Hydrogen Peroxide (50%) 20 milliliters
Water to made a total solution volume of 140 milliliters
This bath stripped electroless nickel well with no apparent attack on steel,
however, the
bath became turbid with nickel hydroxide as the pH climbed to 6-7. Peroxide
became more
unstable as the pH climbed above 5.5.
Example 6
CHEMICAL AMOUNT
Magnesium Sulfate 15 grams
Hydrogen Peroxide (50%) 25 milliliters
Water to made a total solution volume of 140 milliliters
to
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This bath stripped electroless nickel without attack on steel, however,
peroxide
decomposition was rapid due to the high pH of 6-8 during the test.
Example 7
CHEMICAL AMOUNT
Trisodium Citrate 10 grams
Citric Acid 10 grams
Hydrogen Peroxide (50%) to make 140 milliliters of bath
Peroxide/Acid Mole Ratio: 44.4
This bath was used to test the upper limit of hydrogen peroxide concentration.
The
bath worked well with no discernable difference from those obtained in Example
4.
Example 8
CHEMICAL AMOUNT
Monosodium Phosphate 15 grams
Citric Acid 10 grams
Hydrogen Peroxide (50%) 20 milliliters
Water to make a total solution volume of 140 milliliters
Peroxide/Acid Mole Ratio: 7.4
This bath stripped well to 60 amps./sq.ft. Some heating of the solution was
noted due
to the bath's electrical resistance. The bath stripped 3.25 mills of
electroless nickel in one
hour and ten minutes. No attack on steel substrate was noted. No discernable
attack on steel
or aluminum substrates was observed.
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Example 9
CHEMICAL AMOUNT
Sulfamic Acid 10 grams
Trisodium Phosphate 10 grams
Hydrogen Peroxide (50%) 20 milliliters
Water to make a total solution volume of 140 milliliters
Peroxide/Acid Mole Ratio: 3.4
This bath was tested to 60 amps./sq. ft. No attack on steel, aluminum, or
titanium base
metals was observed.
Example 10
CHEMICAL AMOUNT
Formic Acid 10 milliliters
Sodium Formate 10 grams
Hydrogen Peroxide (50%) 25 milliliters
Water to make a total solution volume of 140 milliliters
Peroxide/Acid Mole Ratio: 2.1
This bath gave good results stripping nickel from steel, aluminum, and cast
iron
substrates.
Example 11
CHEMICAL AMOUNT
Acetic Acid (68%, 10 milliliters
v.)
Sodium Acetate 10 grams
Hydrogen Peroxide 20 milliliters
(50%)
12
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Water to make a total solution volume of 140 milliliters
Peroxide/Acid Mole Ratio = 3.1
This bath stripped about 10 times slower at four volts than the bath in
Example 1
because of poor bath conductivity. The bath does not attack steel substrate.
Example 12
CHEMICAL AMOUNT
Sodium Sulfate 10 grams
Glutaric Acid 10 grams
Hydrogen Peroxide (50%) 22 milliliters
Water to make a total solution volume of 140 milliliters
Peroxide/Acid Mole Ratio = 5.1
This bath dissolved 2.51 grams of electroless nickel before the test was
terminated at
pH 4.4. No attack on steel substrate was observed.
Example 13
CHEMICAL AMOUNT
Sodium Chloride 5 grams
Acetic Acid (68%) 10 milliliters
Hydrogen Peroxide 20 milliliters
(50%)
Water to make a total
solution volume
of 140 milliliters
Peroxide/Acid Mole 3.1
Ratio =
With this bath, steel base metal etched because of the high chloride content.
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Example 14
CHEMICAL AMOUNT
Sodium Chlorate 8 grams
Acetic Acid (68%) 20 milliliters
Hydrogen Peroxide 20 milliliters
(50%)
Water to make a
total solution
volume of 140 milliliters
Peroxide/Acid Mole 1.5
Ratio =
This bath stripped very well and did not etch steel, contrary to the results
in Example
13.
Example 15
CHEMICAL AMOUNT
Citric Acid (MW=210)10 grams
Sodium Sulfate 10 grams
Hydrogen Peroxide 30 milliliters
(50%)
Water to make a
total solution
volume of 140 milliliters
Peroxide/Acid Mole 11.1
Ratio =
The bath stripped 4.2 grams nickel which is the stoichiometric equivalent of
the citric
acid in the bath. The pH of the bath began to rise rapidly and the test was
terminated. No
attack on steel, aluminum, cast iron, or titanium substrates was noted.
Example 16
CHEMICAL AMOUNT
Malefic Acid 10 grams
Hydrogen Peroxide (50%) 22 milliliters
14
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Water to make a total solution volume of 140 milliliters
Peroxide/Acid Mole Ratio = 4.5
With this bath, good performance and reduced conductivity were observed.
Example 17
CHEMICAL AMOUNT
Sulfuric Acid (66° Baume) 3 milliliters
Borax 12 grams
Hydrogen Peroxide (50%) 22 milliliters
Water to make a total solution volume of 140 milliliters
Peroxide/Acid Mole Ratio = 7.4
This bath stripped well. No attack on steel or aluminum substrates was
observed.
High bath conductivity was noted. The bath stripped at 100 amp./ft.a with no
visual attack on
steel or aluminum substrates.
Example 1 ~
CHEMICAL AMOUNT
Glycolic Acid (cormnercial) 10 milliliters
Sodium Sulfate 10 grams
Hydrogen Peroxide (50%) 22 milliliters
Water to make a total solution volume of 140 milliliters
Peroxide/Acid Mole Ratio = 2.9
This bath stripped well. No attack on steel or aluminum base metals was
observed.
is
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Example 19
CHEMICAL AMOUNT
Phosphoric Acid (85%, v.) 15 milliliters
Hydrogen Peroxide (50%) 25 milliliters
Water to make a total solution volume of 140 milliliters
Peroxide/Acid Mole Ratio = 2.9
This bath stripped well. No attack on steel or aluminum base metals was
observed.
Example 20
CHEMICAL AMOUNT
Boric Acid 5 grams
Sodium Sulfate 10 grams
Hydrogen Peroxide (50%) 20 milliliters
Water to make a total solution volume of 140 milliliters
Peroxide/Acid Mole Ratio = 4.4
The beginning pH of this batch was 5.32. When the pH reached 5.84, a
precipitate
began to form in the bath. The nickel content of the bath was 0.6 grams.
Although nickel
hydroxide was precipitating, stripping continued with no attack on steel or
aluminum
substrates.
Example 21
CHEMICAL AMOUNT
Sodium Hydrogen Sulfate 10 grams
Sodium Pyrophosphate 10 grams
Hydrogen Peroxide (50%) 25 milliliters
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Water to make a total solution volume of 140 milliliters
Peroxide/Acid Mole Ratio = 5.3
This bath stripped electroless nickel well. No attack on steel or aluminum
plated
substrates was observed
Example 22
CHEMICAL ~ AMOUNT
Citric Acid 15 grams
Sodium Tripolyphosphate 10 grams
Hydrogen Peroxide (50%) 25 milliliters
Water to make a total solution volume of 140 milliliters
Peroxide/Acid Mole Ratio = 6.2
This bath gave good results when stripping from electroplated nickel, cast
nickel, and
Kovar alloy.
Example 23
CHEMICAL AMOUNT
Acetic Acid (68%) ' 20 milliliters
Sodium Nitrate 15 grams
Hydrogen Peroxide (50%) 20 milliliters
Water to make a total solution volume of 140 milliliters
Peroxide/Acid Mole Ratio =1.5
This bath stripped electroless nickel deposits at near 100% efficiency. No
visible
attack on steel substrates was observed. Bright electrolytically deposited
nickel was slowly
(oxygen liberated at nickel's surface) dissolved in this bath because of the
nitrate content.
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Aluminum substrates were slowly attacked.
Example 24
CHEMICAL AMOUNT
Citric Acid 15 grams
Ammonium Nitrate 50 grams
Hydrogen Peroxide (50%) 25 milliliters
Water to make a total solution volume of 140 milliliters
Peroxide/Acid Mole Ratio = 6.1
This bath stripped bright electroplated nickel with less efficiency, i.e.,
some gassing
occurs as the electroplated nickel was dissolved. However, 12 % high
phosphorous electroless
nickel deposits were stripped at near 100 % efficiency. This formulation is an
improvement
over prior art because it allows the use of an acid to keep the pH from rising
to a point where
nickel hydroxide precipitation causes sludging of the bath which is an
inherent deficiency of
prior art nitrate electrolytic strippers. It also allows the nitrate based
formulation to strip high
phosphorous electroless nickel and bright electroplated nickel in one
stripping bath with no
attack on steel or cast iron substrates. Aluminum substrates are attacked.
Example 25
CHEMICAL AMOUNT -
Nitric Acid (68%, v.) 6 milliliters
Hydrogen Peroxide (50%) 20 milliliters
Water to make a total solution volume of 140 milliliters
Peroxide/Acid Mole Ratio = 3.7
This bath stripped bright electroplated nickel with gassing of oxygen. It
stripped
electroless nickel very rapidly because of high conductivity. With this bath,
aluminum
is
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substrates, but not steel or titanium substrates, were attacked.
Example 26
The following example has a volume of one liter. This bath illustrates a very
low
peroxide/oxoacid concentration of 0.3/0.04 moles.
CHEMICAL AMOUNT
Sulfuric Acid (66° Baume) 2.3 milliliters
Hydrogen Peroxide (50%) 17 milliliters
Water to make a total solution volume of one liter
Peroxide/Acid Mole Ratio = 7.5
Although its conductivity was reduced, this bath stripped electroless nickel
of 12
phosphorous content with no discernable attack on steel or aluminum test
panels.
Example 27
CHEMICAL AMOUNT
Methane Sulfonic Acid 9 milliliters
Hydrogen Peroxide (50%) 20 milliliters
Water to make a total solution volume of 140 milliliters
Peroxide/Acid Mole Ratio = 3.75
This bath had high conductivity. It stripped electroless nickel from steel,
cast iron,
titanium, and cast nickel without discernable attack. Aluminum substrates were
slowly
attacked.
19
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Example 2g
CHEMICAL AMOUNT
Benzene Sulfonic Acid 14.g grams
Hydrogen Peroxide (50%) 20 milliliters
Water to make a total solution volume of 140 milliliters
Peroxide/Acid Mole Ratio = 3.75
The results obtained were identical to those obtained in Example 27.
The following examples illustrate attack on the substrate because of low
peroxide/oxoacid ratios:
Example 29
CHEMICAL ~~~T
Sulfuric Acid (66° Baume) 5.4 milliliters
Hydrogen Peroxide (50%) 20 milliliters
Water to made a total solution volume of 140 milliliters
Peroxide/Acid Mole Ratio = 3.75
A one-inch wide tinplated steel test panel was immersed into the solution and
was
immediately attacked before electrical connection was made to the test panel.
This panel was
replaced with another steel panel that was plated with 0.001 inch electroless
nickel. The panel
was connected to the positive lead of the power supply as in Example 1 and
voltage was
adjusted to four volts. The electroless nickel was rapidly dissolved because
of the high current
density. After the panel was stripped of electroless nickel and the part was
being removed
from the stripping bath, it was explosively attacked by the stripping solution
remaining on its
surface.
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Example 30
CHEMICAL AMOUNT
Acetic Acid (68%) 20 milliliters
Sodium Sulfate 10 grams
Hydrogen Peroxide 10 milliliters
(50%)
Water to make a
total solution
volume of 140 milliliters
PeroxidelAcid Mole 0.77
Ratio =
An unplated test panel identical to that of Example 29 was immersed into the
stripping
solution without electrical contact. The test panel was very slowly attacked
by the solution.
As in Example 29, the panel was replaced by a plated one and stripped. When
the panel was
removed, the steel base metal was attacked but was not explosive in its rate
of attack.
Addition of 15 milliliters of hydrogen peroxide (50%) to the above bath
stopped all the etching
and produced results identical to those obtained in Example 1.
While the invention has been described in connection with what is presently
considered
to be the most practical and preferred embodiments, it is to be understood
that the invention is
not limited to the disclosed embodiments, but on the contrary is intended to
cover various
modifications and equivalent arrangements included within the spirit and scope
of the
appended claims.
Thus, it is to be understood that variations in the present invention can be
made
without departing from the novel aspects of this invention as defined in the
claims. All patents
cited herein are hereby incorporated by reference in their entirety and relied
upon.
21
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