JP2005506457A - Electrolytic method and composition for stripping electroless nickel - Google Patents

Abstract

Novel electrolytic stripping solution formulated with oxoacids and / or oxoacid salts and hydrogen peroxide quickly removes electroless nickel from steel, aluminum, and titanium alloys, and other selected conductive substrates can do. These formulations improve the resistance of the substrate to etching and can be formulated without chelates, chromates, nitrates, or concentrated acids, thereby increasing worker safety, The cost for discarding the used stripping solution can be reduced.

Description

FIELD OF THE INVENTION
[0001]
The present invention relates to an electrical stripping method and composition for stripping electroless nickel from a substrate. The electrical stripping method can be described as the reverse of electroplating. Electroplating provides a metal coating on the substrate, while an electrorelease agent removes the coating from the substrate. The coating dissolves upon electrolysis by binding to negative chemical ions in the bath (negative chemical ions are attracted to the surface of the coating by their positive potential). The purpose of the stripper is to remove the coating without damaging the underlying substrate, but most anodic reactions cannot distinguish between the coating and the substrate and etch the substrate. cause.
[0002]
Electroless nickel is a coating with very high chemical resistance and is not easily attacked. One example of the chemical resistance is a “nitric acid drop test”. A drop of concentrated nitric acid is applied to the surface of the electroless nickel coating. If etching occurs within the set time, this test fails. The discovery of relatively mild chemical formulations and procedures that rapidly peel off this very chemical resistant coating has great economic value. It is particularly advantageous if the stripping process can be performed in an environmentally favorable manner and can be used safely for the regeneration of defective plated parts.
[Description of related technology]
[0003]
Since the invention of autocatalytic chemical nickel deposition (currently commercially referred to as electroless nickel plating), the excellent chemical resistance of the deposit has been extensively applied to the protection of various products. This chemical resistance has been improved over the years by innovative formulations to improve the structure of the deposit and further increase the resistance to chemical attack. For this reason, it is not surprising that the operation of peeling the electroless nickel while protecting the base material becomes more and more difficult.
[0004]
Various methods for stripping electroless nickel have been used, but the results vary. One of the first tried methods is electrolytic stripper commonly used for stripping electrolytic nickel. This release agent is manufactured from concentrated sulfuric acid and utilizes a reverse current. Typically, the part to be stripped is immersed in a stripping bath and connected to the positive (anode) lead of a DC power source. Current flows across the bath and flows to the negative electrode (cathode), usually made of lead or graphite. This method makes use of the principle of passivation, ie if the nickel deposit is dissolved by the action of sulfate ions, unlike nickel, the steel substrate in the presence of highly concentrated sulfuric acid. Due to the chemical nature of the material, the steel will be passive to attack and oxygen will be released. This method cannot strip most electroless nickel deposits because electroless nickel becomes passivated just like steel.
[0005]
U.S. Pat. No. 4,356,069 (Cunningham) discloses an electrical nickel stripper composed of concentrated sulfuric acid, chromic acid, and hydrogen peroxide. This formulation claims to strip chromium and nickel from the iron substrate. This patent does not claim that this formulation exfoliates electroless nickel deposits, but is expensive to dispose of large amounts of harmful chromium and sulfuric acid, and oxides before replating The disadvantage is the need to add a step for removing the layer from the substrate.
[0006]
Another chromic acid based electronickel stripper is described in US Pat. No. 4,647,352 (Cook). This patent discloses that a combination of chromic acid, phosphoric acid, and sodium bisulfite can be used to electrically strip electroless nickel. This formulation has the disadvantage that sulfate ions are introduced into the bath, the substrate is prone to corrosion and a barium carbonate treatment is required. Due to the high chromic acid content, it is very expensive to dispose of the used bath.
[0007]
U.S. Pat. No. 4,664,763 (McMullen et al.) Uses a defect-plated part as the anode and / or cathode of an electrolytic stripping cell and applies an alternating current between the electrodes to form a nickel coating. An aqueous stripping solution comprising chromic acid for stripping is disclosed. By this method, the electrolytic and electrolysis nickel coating is supposed to be peeled off. This stripping method describes some optionally used etch inhibitors, such as potassium iodide, to prevent etching of the substrate. This method suffers from high etching costs and high disposal costs due to high chromic acid content.
[0008]
Another electrolytic stripping method uses nitrate, usually ammonium nitrate or sodium, at a concentration of about 3 pounds per gallon. These methods use reverse direct current to remove electroplated nickel and certain low phosphorus electroless nickel deposits from iron and steel. As the nickel dissolves, the pH of the stripping bath changes rapidly, causing severe sludge formation problems. As the exposed base metal becomes passivated under the influence of current, a large area of unpeeled nickel is sporadically passivated, resulting in incompletely delaminated parts. This problem is more pronounced when attempting to exfoliate electroless nickel deposits where phosphorus is greater than about 7%.
[0009]
An immersion nickel stripper (no current required) is disclosed that uses a soluble nitrobenzene compound in solution with a cyanide for stripping nickel deposits. These strippers are used in small amounts for electroless nickel with low phosphorus content, i.e. 1-7%, but electroless nickel deposits with higher phosphorus content do not strip or are practical. It peels only at such a low speed that it does not become. With the advent of pollution regulations, the use of cyanide is becoming more and more expensive as the disposal obligation increases.
[0010]
Nickel stripping baths using water-soluble nitrobenzene compounds, ammonia and ammonium salts or ethylenediamine and / or its homologs are widely accepted. These baths are effective for electrolytic nickel deposits, and some low phosphorus electroless nickel achieves stripping rates of about 0.001 inch / hour, while high phosphorus content electroless nickel Removal is slow with an average of 0.0003 inches / hour. Proper disposal of this type of stripping bath is very expensive due to their toxicity and high chelating ability. These baths operate at about 160-190 ° F. to strip the electroless nickel coating and are very susceptible to damage and thermal chemical degradation due to the loss of volatile chemical components by heat.
[0011]
U.S. Pat. No. 4,554,049 (Bastenbeck) discloses an immersion nickel stripper using sulfamic acid, hydrogen peroxide, nitrate, and chloride. Although this patent claims the exfoliation of low phosphorus electroless nickel (less than 7%), it cannot efficiently exfoliate deposits with high phosphorus content.
[0012]
U.S. Pat. No. 4,720,332 (Coffey) describes soluble nitrobenzene compounds, zwitterions (as chelating agents), sulfide-forming compounds, nickel stripping baths using carbonates, and electroless nickel deposits. Disclose the use of reverse current for rapid removal. This method strips electroless nickel quickly (up to 0.002 inch / hour) and works effectively, but microscopically corrodes in high current density areas and cloudes highly polished surfaces There is.
[0013]
Accordingly, it is an object of the present invention to improve electroless nickel stripping technology by providing a formulation that easily and efficiently strips both low and high phosphorus content electroless nickel deposits with equally high efficiency. There is to do.
[0014]
It is also an object of the present invention to provide a formulation with improved corrosion resistance to a substrate for electrolytically stripping electroless nickel.
[0015]
Another object of the invention is to eliminate chelates, nitrates, chromates, cyanides, and highly concentrated acidic solutions that are safer for use in the workplace and more favorable for the environment. It is to provide a release formulation.
[0016]
Yet another object of the present invention is that from electrolytically deposited bright nickel, electrolytically deposited sulfamate nickel, and high nickel content alloys, with little or no damage to the substrate, It is to provide a formulation and method for stripping electroless nickel.
SUMMARY OF THE INVENTION
[0017]
The electrolytic stripping bath of the present invention is made from oxoacids and / or oxoacid salts and hydrogen peroxide. It has been found that electroless nickel deposits can dissolve at the anode of an electrolytic bath containing oxoacids and / or oxoacid salts and hydrogen peroxide. Iron, cast iron, steel alloy, stainless steel, and titanium substrates have a preferred minimum molar ratio of about 3.75 for a strong oxoacid with a hydrogen peroxide / acid molar ratio of one ionizable hydrogen, Strong oxoacids containing two or more ionizable hydrogens are protected from attack during electrolysis if maintained at a higher hydrogen peroxide / oxoacid molar ratio of about 7.5. When combining a weak oxoacid and a weak oxoacid salt to form a stripping bath, a low peroxide / oxoacid ratio of up to 1.5 can be used. To prevent attack on the aluminum substrate, only sulfuric acid and sulfamic acid and / or their salts may be selected from strong oxoacids, but weak oxoacids and / or salts compatible with hydrogen peroxide may be used. Either can be used. Use only a combination of weak oxoacids and / or oxoacid salts when peeling from electroplated nickel, cast nickel, kovar (iron, nickel, cobalt alloys), and sulfamate nickel substrates Should.
[0018]
For purposes of the present invention, the acid dissociation constant (K₁) Is about 2 × 10^-1If it exceeds, the acid is considered a strong acid. Examples of strong oxo acids are sulfuric acid, nitric acid, sulfamic acid, alkyl sulfonic acid, aryl sulfonic acid, and monoalkyl esters of sulfuric acid.
[0019]
Examples of weak oxo acids include phosphoric acid, pyrophosphoric acid, alkyl phosphoric acid, glucophosphonic acid, oxalic acid, formic acid, propanoic acid, bismethanolpropanoic acid, acetic acid, butanoic acid, benzoic acid, phthalic acid, citric acid, tartaric acid , Malic acid, malonic acid, maleic acid, butyric acid, succinic acid, glycolic acid, glutaric acid, gluconic acid, adipic acid, boric acid, ethylenediaminetetraacetic acid and homologues, nitrilotriacetic acid, aminoacetic acid, and polyvinylsulfonic acid.
[0020]
The concentration of hydrogen peroxide for application of the present invention may be from about 1% to about 99%, but a concentration of about 8% is preferred. While maintaining the disclosed minimum peroxide / oxoacid molar ratio, the oxoacid and / or oxoacid salt can vary from 0.01 mole / liter to saturation.
[0021]
The pH range for practicing the present invention is 0-8, with the preferred pH range being about 1-7, the most preferred range being about 1.5-4.5.
[0022]
Oxygen-free halogen acids (hydrofluoric acid and hydrochloric acid) may be used when the acid and / or salt thereof is used in a stripping bath in an amount greater than about 0.1 mol / liter. Since there appears to be no hydrogen peroxide / acid molar ratio to prevent attack on the surface, it is excluded from the present invention. Iodic acid, bromic acid, and chromic acid, and / or salts are excluded because they are incompatible with hydrogen peroxide when mixed with peroxide or during the stripping process.
DETAILED DESCRIPTION OF THE INVENTION
[0023]
The present invention relates to electroless nickel deposits, iron, cast iron, steel alloys, stainless steel, aluminum, and titanium using a stripping bath made from selected oxoacids and / or oxoacid salts and hydrogen peroxide. That it can be electrolytically stripped from the substrate. Surprisingly, if the stripping bath is made from weak oxoacids and / or oxoacid salts, electroless nickel deposits from electrolytically deposited nickel, cast nickel, kovar, and high nickel alloy substrates can be obtained. Can be peeled off without serious attack. Only when the strong oxoacid and / or strong oxoacid salt is selected from sulfuric acid and its salts and / or sulfamic acid and its salts, the electroless nickel can be stripped from the aluminum substrate without significant attack. Any weak oxoacid and / or oxoacid salt that is compatible with hydrogen peroxide can be used to strip electroless nickel from aluminum. The hydrogen peroxide / oxoacid molar ratio is a minimum of about 3.75 for strong oxoacids containing one ionizable hydrogen and about 7.5 for strong oxoacids containing two or more ionizable hydrogens. Maintaining the higher hydrogen peroxide / oxoacid molar ratio of the base metal protects it from attack during electrolysis. When weak oxoacids and / or weak oxoacid salts are combined to form a stripping bath, a low peroxide / oxoacid ratio of up to 1.5 can be used.
[0024]
Oxygen-free halogen acids (hydrofluoric acid and hydrochloric acid) attack on iron, steel alloys, and aluminum substrates when these acids are present in the stripping bath at concentrations greater than about 0.1 mol / liter Since there is no clear hydrogen peroxide concentration to prevent this, it is excluded from the present invention. If a relatively large amount of oxoacid ions coexist in the solution, a very small amount of halogen ions will not attack the substrate. For example, the amount of chloride ions derived from chlorination of drinking water is not expected to affect the substrate, but when the chloride ion concentration exceeds about 0.1 mol / liter, the substrate is attacked to some extent. Sometimes.
[0025]
Due to practical importance such as bath conductivity and worker safety, the preferred working range is about 5-20% by volume of hydrogen peroxide (10-40% by volume using 50% hydrogen peroxide) The most preferred working range is about 7-10% by volume of hydrogen peroxide (14-20% by volume using 50% hydrogen peroxide). By using an appropriate hydrogen peroxide / acid molar ratio for this hydrogen peroxide concentration range, delamination can be achieved at current densities up to about 100 amps / square foot. There is no maximum concentration limit for hydrogen peroxide other than practical importance, such as worker safety and precautions for disposal.
[0026]
The concentration of oxoacid and / or oxoacid salt can be varied within wide limits provided that the minimum peroxide / acid molar ratio is maintained. The acid and / or salt can vary from 0.01 mol / liter to saturation. However, the electrical resistance of the stripping bath is preferably low because it determines the amount of nickel stripped within a certain time through the current flowing in the bath. Therefore, selecting the amount and type of oxoacids and / or oxoacid salts that increase the conductivity of the solution is very important to remove electroless nickel coatings quickly and economically.
[0027]
The preferred temperature range for operating the stripping bath of the present invention is about 60-115 ° F, most preferably about 80-100 ° F. Of course, lower or higher temperatures can be used, but at lower temperatures the conductivity and solubility will be lower and at higher temperatures hydrogen peroxide decomposition will be accelerated.
【Example】
[0028]
The following examples are included to illustrate the use of the present invention, but do not limit the scope of the invention.
[0029]
Example 1
The baths described below did not chelate, which makes the disposal of the spent stripping bath of this formulation simple and low cost. This bath contains only about 3 times the acetic acid of regular vinegar and is very safe to use. The peroxide content is high enough to bleach hair, but not so high as to pose a serious risk to workers.
Medicine                                  amount
Monosodium phosphate 20g
Acetic acid (68%) 20ml
Hydrogen peroxide (50% by volume) 25ml
Add water (water) to make the total volume 140ml
Peroxide / acid molar ratio 1.82
[0030]
The above chemicals were dissolved to make the total volume of the solution 140 ml. The temperature of the solution was adjusted to 90 ° F. Two 1 inch wide stainless steel cathodes were placed in the solution, placed on either side of the beaker containing the solution, and connected to the negative side of the variable voltage DC power supply. A 1 inch wide mild steel panel pre-plated 0.001 inch with electroless nickel containing about 12% phosphorus was suspended in the center of the beaker between two stainless steel cathodes. The plated panel was connected to the positive side of the power supply. A TEFLON® (polytetrafluoroethylene) coated stir bar was placed in a beaker and the solution was gently stirred to prevent bath layering. Current was applied and the voltage drop across the stripping bath was adjusted to 4. After bubbles were instantaneously formed on the plated part, the nickel began to dissolve in the stripping bath and foaming at the anode was completely stopped. The initial current was 0.75 amperes. After about 30 minutes, the steel base metal began to be exposed at an angle of 90 degrees at the bottom of the plated portion. Unlike the nitrate-based electrolytic stripper, the exposed steel substrate did not release gas. The electroless nickel coating continued to melt and exhibited a parabolic shape as it melted and contracted from the entire surface of the panel. Only when about 30% of the panel area exposed to the solution was covered by the remaining electroless nickel-coated area, gas began to be gradually released from the base metal. After about 45 minutes, no electroless nickel was found on the panel. An additional 15 minutes were allowed to evaporate completely and to see if etching occurred on the steel panel. The inspection confirmed no etching. The mild steel panel was as shiny and smooth as when first dipped into the electroless nickel plating solution.
[0031]
The aluminum test panel was also peeled off with this solution, and good results were obtained as well.
The following examples are carried out as in Example 1 and illustrate various oxoacids and / or oxoacid salts that can be used in the present invention.
[0032]
Example 2
Medicine                                  amount
Sodium bisulfate 12g
15 grams of sodium sulfate
Hydrogen peroxide (50%) 35ml
Add water to bring the total volume of the solution to 140 ml
Peroxide / acid molar ratio 6.1
[0033]
This bath had a lower resistance to current flow than Example 1, an initial voltage drop across the bath of 4 volts, and a starting current of 1.02 amps. A panel equivalent to that used in Example 1 was peeled off in about 30 minutes, and an equivalent good result was obtained.
[0034]
Example 3
Medicine                                  amount
Sulfuric acid (66 ° Baume) 2.35ml
Hydrogen peroxide (50%) 35ml
Add water to bring the total volume of the solution to 140 milliliters
Peroxide / acid molar ratio 15.0
[0035]
This bath was formed as in Example 1. This bath had very good conductivity. The bath peeled from the steel, aluminum, and titanium substrates without visible attack. 2.35 grams of nickel was introduced into the bath and calculations showed that 97.9% of the acid was used for reaction with nickel. With further use of this bath, the pH increased rapidly from the pH of 4.8 measured when the nickel content reached 2.35 grams. By continuing stripping, nickel hydroxide precipitated when the pH reached about 6-7, and hydrogen peroxide decomposed rapidly. During the test no further hydrogen peroxide had to be added.
[0036]
Example 4
Medicine                                  amount
10 grams of citric acid
10 grams of trisodium citrate
Hydrogen peroxide (50%) 20ml
Add water to bring the total volume of the solution to 140 milliliters
Peroxide / acid molar ratio 6.79
[0037]
Good results have been obtained for steel, aluminum, titanium and cast iron substrates.
[0038]
Example 5
Medicine                                  amount
14 grams of ammonium sulfate
Hydrogen peroxide (50%) 20ml
Add water to bring the total volume of the solution to 140 ml
[0039]
This bath sufficiently stripped the electroless nickel without an obvious attack on the steel, but the bath became cloudy with nickel hydroxide as the pH rose to 6-7. The peroxide became more unstable when the pH exceeded 5.5.
[0040]
Example 6
Medicine                                  amount
Magnesium sulfate 15g
Hydrogen peroxide (50%) 25ml
Add water to bring the total volume of the solution to 140 ml
[0041]
This bath stripped the electroless nickel without attacking the steel, but during the test the peroxide was abruptly decomposed due to the high pH of 6-8.
[0042]
Example 7
Medicine                                  amount
10 grams of trisodium citrate
10 grams of citric acid
Hydrogen peroxide (50%) to make the bath 140ml
Peroxide / acid molar ratio 44.4
[0043]
This bath was used to test the upper limit of hydrogen peroxide concentration. This bath worked well and was not significantly different from the results obtained in Example 4.
[0044]
Example 8
Medicine                                  amount
Monosodium phosphate 15g
10 grams of citric acid
Hydrogen peroxide (50%) 20ml
Add water to bring the total volume of the solution to 140 ml
Peroxide / acid molar ratio 7.4
[0045]
The bath exfoliated well to 60 amps / square foot. Some exotherm of the solution was observed due to the electrical resistance of the bath. This bath stripped 3.25 mils of electroless nickel in 1 hour and 10 minutes. No attack on the steel substrate was observed. Little attack on the steel or aluminum substrate was observed.
[0046]
Example 9
Medicine                                  amount
10 grams of sulfamic acid
10 grams of trisodium phosphate
Hydrogen peroxide (50%) 20ml
Add water to bring the total volume of the solution to 140 ml
Peroxide / acid molar ratio 3.4
[0047]
This bath was tested up to 60 amps per square foot. No attack on steel, aluminum or titanium base metal was observed.
[0048]
Example 10
Medicine                                  amount
Formic acid 10ml
10 grams of sodium formate
Hydrogen peroxide (50%) 25ml
Add water to bring the total volume of the solution to 140 ml
Peroxide / acid molar ratio 2.1
[0049]
This bath gave good results for stripping nickel from steel, aluminum and cast iron substrates.
[0050]
Example 11
Medicine                                  amount
Acetic acid (68% by volume) 10ml
10 grams of sodium acetate
Hydrogen peroxide (50%) 20ml
Add water to bring the total volume of the solution to 140 ml
Peroxide / acid molar ratio = 3.1
[0051]
This bath was about one tenth of the bath in Example 1 at a speed of 4 volts due to the low conductivity of the bath. This bath did not attack the steel substrate.
[0052]
Example 12
Medicine                                  amount
10 grams of sodium sulfate
10 grams of glutaric acid
Hydrogen peroxide (50%) 22ml
Add water to bring the total volume of the solution to 140 ml
Peroxide / acid molar ratio = 5.1
[0053]
This bath dissolved 2.51 grams of electroless nickel by the end of the test at pH 4.4. No attack on the steel substrate was observed.
[0054]
Example 13
Medicine                                  amount
5 grams of sodium chloride
Acetic acid (68%) 10ml
Hydrogen peroxide (50%) 20ml
Add water to bring the total volume of the solution to 140 ml
Peroxide / acid molar ratio = 3.1
[0055]
In this bath, the base metal was etched due to the high chloride content.
[0056]
Example 14
Medicine                                  amount
Sodium chlorate 8g
Acetic acid (68%) 20ml
Hydrogen peroxide (50%) 20ml
Add water to bring the total volume of the solution to 140 ml
Peroxide / acid molar ratio = 1.5
[0057]
In contrast to the results of Example 13, this bath exfoliated very well and did not corrode the steel.
[0058]
Example 15
Medicine                                  amount
Citric acid (MW = 210) 10g
10 grams of sodium sulfate
Hydrogen peroxide (50%) 30ml
Add water to bring the total volume of the solution to 140 ml
Peroxide / acid molar ratio = 11.1
[0059]
This bath stripped 4.2 grams of nickel, which is the stoichiometric equivalent of citric acid in the bath. The bath pH began to increase rapidly and the test was terminated. No attack on steel, aluminum, cast iron, or titanium was observed.
[0060]
Example 16
Medicine                                  amount
10 grams of maleic acid
Hydrogen peroxide (50%) 22ml
Add water to bring the total volume of the solution to 140 ml
Peroxide / acid molar ratio = 4.5
[0061]
Good performance and low conductivity were observed with this bath.
[0062]
Example 17
Medicine                                  amount
Sulfuric acid (66 ° Baume) 3ml
12 grams of borax
Hydrogen peroxide (50%) 22ml
Add water to bring the total volume of the solution to 140 ml
Peroxide / acid molar ratio = 7.4
[0063]
This bath effectively peeled off. No attack on the steel or aluminum substrate was observed. A high conductivity of the bath was observed. This bath is 100 amps / ft²With no visible attack on the steel or aluminum substrate.
[0064]
Example 18
Medicine                                  amount
Glycolic acid (commercially available) 10ml
10 grams of sodium sulfate
Hydrogen peroxide (50%) 22ml
Add water to bring the total volume of the solution to 140 ml
Peroxide / acid molar ratio = 2.9
[0065]
The bath exfoliated effectively and no attack on the steel or aluminum base metal was observed.
[0066]
Example 19
Medicine                                  amount
Phosphoric acid (85% by volume) 15ml
Hydrogen peroxide (50%) 25ml
Add water to bring the total volume of the solution to 140 ml
Peroxide / acid molar ratio = 2.9
[0067]
The bath exfoliated effectively and no attack on the steel or aluminum base metal was observed.
[0068]
Example 20
Medicine                                  amount
5 grams of boric acid
10 grams of sodium sulfate
Hydrogen peroxide (50%) 20ml
Add water to bring the total volume of the solution to 140 ml
Peroxide / acid molar ratio = 4.4
[0069]
The initial 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. Nickel hydroxide was precipitated, but peeling continued without attacking the steel or aluminum substrate.
[0070]
Example 21
Medicine                                  amount
Sodium bisulfate 10g
Sodium pyrophosphate 10g
Hydrogen peroxide (50%) 25ml
Add water to bring the total volume of the solution to 140 ml
Peroxide / acid molar ratio = 5.3
[0071]
This bath effectively stripped the electroless nickel and no attack on the steel or aluminum plated substrate was observed.
[0072]
Example 22
Medicine                                  amount
15 grams of citric acid
10 grams of sodium tripolyphosphate
Hydrogen peroxide (50%) 25ml
Add water to bring the total volume of the solution to 140 ml
Peroxide / acid molar ratio = 6.2
[0073]
This bath gave good results when exfoliated from electroplated nickel, cast nickel, and Kovar alloy.
[0074]
Example 23
Medicine                                  amount
Acetic acid (68%) 20ml
15 grams of sodium nitrate
Hydrogen peroxide (50%) 25ml
Add water to bring the total volume of the solution to 140 ml
Peroxide / acid molar ratio = 1.5
[0075]
This bath stripped electroless nickel deposits with an efficiency approaching 100%. No visible attack on the steel substrate was observed. Electrolytically deposited bright nickel dissolved gradually in this bath (oxygen was released from the nickel surface) due to the nitrate content. The aluminum substrate was attacked gradually.
[0076]
Example 24
Medicine                                  amount
15 grams of citric acid
50 grams of ammonium nitrate
Hydrogen peroxide (50%) 25ml
Add water to bring the total volume of the solution to 140 ml
Peroxide / acid molar ratio = 6.1
[0077]
This bath did not exfoliate the electroplated bright nickel very effectively, ie some gas was released as the electroplated nickel dissolved. However, 12% high phosphorus electroless nickel deposits were stripped with nearly 100% efficiency. This formulation can be used with acid to prevent the pH from rising to a point that causes sludge formation in the bath due to nickel hydroxide precipitation, a disadvantage inherent in prior art nitrate electro strippers. This is an improvement over the prior art. This formulation can also strip nitrate-based formulations of high phosphorus electroless nickel and electroplated bright nickel in a single stripping bath without attacking the steel or cast iron substrate. The aluminum substrate is attacked.
[0078]
Example 25
Medicine                                  amount
Nitric acid (68% by volume) 6ml
Hydrogen peroxide (50%) 20ml
Add water to bring the total volume of the solution to 140 ml
Peroxide / acid molar ratio = 3.7
[0079]
The bath stripped the electroplated bright nickel with oxygen outgassing. Due to the high conductivity of this bath, the electroless nickel was stripped very quickly. In this bath, the aluminum substrate was attacked, but the steel or titanium substrate was not attacked.
[0080]
Example 26
In the example below, the volume is 1 liter. This bath illustrates a very low peroxide / oxoacid concentration of 0.3 / 0.04 moles.
Medicine                                  amount
Sulfuric acid (66 ° Baume) 2.3ml
Hydrogen peroxide (50%) 17ml
Add water to bring the total volume of the solution to 1 liter
Peroxide / acid molar ratio = 7.5
[0081]
This bath had low electrical conductivity, but peeled off the electroless nickel with 12% phosphorus content and showed no attack on the steel or aluminum test panel.
[0082]
Example 27
Medicine                                  amount
Methanesulfonic acid 9ml
Hydrogen peroxide (50%) 20ml
Add water to bring the total volume of the solution to 140 ml
Peroxide / acid molar ratio = 3.75
[0083]
This bath had a high conductivity. This bath peeled electroless nickel from steel, cast iron, titanium, and cast nickel without noticeable attack. The aluminum substrate was attacked gradually.
[0084]
Example 28
Medicine                                  amount
14.8 grams of benzenesulfonic acid
Hydrogen peroxide (50%) 20ml
Add water to bring the total volume of the solution to 140 ml
Peroxide / acid molar ratio = 3.75
[0085]
The result obtained was equivalent to the result obtained in Example 27.
[0086]
The following example illustrates the attack on the substrate that occurs due to the low peroxide / oxo acid ratio.
[0087]
Example 29
Medicine                                  amount
Sulfuric acid (66 ° Baume) 5.4ml
Hydrogen peroxide (50%) 20ml
Add water to bring the total volume of the solution to 140 ml
Peroxide / acid molar ratio = 3.75
[0088]
A 1 inch wide unplated steel test panel was immersed in this solution, and the test panel was immediately attacked prior to electrical connection. This panel was replaced with another steel panel plated to 0.001 inch with electroless nickel. This panel was connected to the positive lead of the power supply as in Example 1 and the voltage was adjusted to 4 volts. Due to the high current density, the electroless nickel dissolved rapidly. After stripping the electroless nickel from the panel and removing the panel from the stripping bath, the panel was explosively attacked by the stripping solution remaining on its surface.
[0089]
Example 30
Medicine                                  amount
Acetic acid (68%) 20ml
10 grams of sodium sulfate
Hydrogen peroxide (50%) 10ml
Add water to bring the total volume of the solution to 140 ml
Peroxide / acid molar ratio = 0.77
[0090]
An unplated panel similar to Example 29 was immersed in a stripping solution without electrical connection. The test panel was attacked very slowly by this solution. Similar to Example 29, this panel was replaced with a plated panel and peeled off. When the panel was removed, the steel base metal was attacked, but the attack speed was not explosive. When 15 milliliters of hydrogen peroxide (50%) was added to the above bath, the etching was completely stopped, and the same result as that obtained in Example 1 was obtained.
[0091]
Although the present invention has been described in terms of the embodiments that are presently considered to be most practical and preferred, it is to be understood that the invention is not limited to the disclosed embodiments, and conversely, the spirit and scope of the appended claims Includes various modifications and equivalents.
[0092]
Accordingly, modifications may be made to the invention without departing from the novel aspects defined by the claims. All patents mentioned herein are hereby incorporated by reference in their entirety.

Claims (21)

Electroless nickel deposits from a substrate selected from the group consisting of iron, cast iron, steel alloys, stainless steel, aluminum, electroplated nickel, cast nickel, iron / nickel / cobalt alloys, sulfamate nickel and titanium A method of peeling,
a) in an electrolytic bath,
i) a compound selected from the group consisting of oxoacids, oxoacid salts, and combinations thereof;
ii) immersing the substrate containing electroless nickel in a composition comprising hydrogen peroxide, and b) electrolytically stripping the electroless nickel deposit from the substrate. ,
A strong oxoacid having one ionizable hydrogen and a dissociation constant of at least 2 × 10 ⁻¹ maintains a hydrogen peroxide / acid molar ratio of at least 3.75;
A strong oxoacid with at least two ionizable hydrogens maintains a hydrogen peroxide / acid molar ratio of at least 7.5;
A weak oxoacid with a dissociation constant of less than 2 × 10 ⁻¹ maintains a hydrogen peroxide / acid molar ratio of at least 1.5, provided that
When aluminum is the substrate and a strong oxoacid is used in the composition, the strong oxoacid is selected from the group consisting of sulfuric acid, sulfamic acid, salts thereof, and combinations thereof;
Where the substrate is selected from electroplated nickel, cast nickel, iron / nickel / cobalt alloy, and sulfamate nickel substrates, the composition comprises a weak oxoacid, an oxoacid salt, and combinations thereof The method to use during. The method of claim 1, wherein the strong oxoacid is selected from the group consisting of sulfuric acid, nitric acid, sulfamic acid, alkyl sulfonic acid, aryl sulfonic acid, and monoalkyl esters of sulfuric acid. The weak oxo acid is phosphoric acid, pyrophosphoric acid, alkyl phosphoric acid, glucophosphonic acid, oxalic acid, formic acid, propanoic acid, bismethanolpropanoic acid, acetic acid, butanoic acid, benzoic acid, phthalic acid, citric acid, tartaric acid, apple Selected from the group consisting of acids, malonic acid, maleic acid, butyric acid, succinic acid, glycolic acid, glutaric acid, gluconic acid, adipic acid, boric acid, ethylenediaminetetraacetic acid and congeners, nitrilotriacetic acid, aminoacetic acid, and polyvinylsulfonic acid The method of claim 1, wherein: The method of claim 1, wherein the hydrogen peroxide is present in the composition at a concentration of 1 to 99% by volume. The method of claim 4, wherein the hydrogen peroxide is present at a concentration of about 8% by volume. The method of claim 1, wherein the compound selected from the group consisting of oxoacids, oxoacid salts and combinations thereof is present in the composition at a concentration between 0.01 mol / liter and saturation. The method of claim 1, wherein the pH of the composition is maintained at 0-8. The method of claim 7, wherein the pH of the composition is maintained between 1.5 and 4.5. The method of claim 1, wherein the composition is maintained at a temperature of 60-115 ° F. The method of claim 9, wherein the composition is maintained at a temperature of 80-100 ° F. For electrolytically stripping electroless nickel deposits from a substrate,
a) a compound selected from the group consisting of oxoacids, oxoacid salts, and combinations thereof;
b) a composition comprising hydrogen peroxide having at least 3.75 hydrogen peroxide with a strong oxo acid having one ionizable hydrogen and a dissociation constant of at least 2 × 10 ⁻¹ The acid / acid molar ratio is maintained,
A strong oxoacid with at least two ionizable hydrogens maintains a hydrogen peroxide / acid molar ratio of at least 7.5;
A composition wherein a weak oxoacid having a dissociation constant of less than 2 × 10 ⁻¹ maintains a hydrogen peroxide / acid molar ratio of at least 1.5. 12. The composition of claim 11, wherein the strong oxo acid is selected from the group consisting of sulfuric acid, nitric acid, sulfamic acid, alkyl sulfonic acid, aryl sulfonic acid, and monoalkyl ester of sulfuric acid. The weak oxo acid is phosphoric acid, pyrophosphoric acid, alkyl phosphoric acid, glucophosphonic acid, oxalic acid, formic acid, propanoic acid, bismethanolpropanoic acid, acetic acid, butanoic acid, benzoic acid, phthalic acid, citric acid, tartaric acid, apple Selected from the group consisting of acids, malonic acid, maleic acid, butyric acid, succinic acid, glycolic acid, glutaric acid, gluconic acid, adipic acid, boric acid, ethylenediaminetetraacetic acid and congeners, nitrilotriacetic acid, aminoacetic acid, and polyvinylsulfonic acid The composition of claim 11. 12. The composition of claim 11, wherein the hydrogen peroxide is present in the composition at a concentration of 1 to 99% by volume. 15. The composition of claim 14, wherein the hydrogen peroxide is present at a concentration of about 8% by volume. 12. The composition of claim 11, wherein the compound selected from the group consisting of oxoacids, oxoacid salts and combinations thereof is present in the composition at a concentration between 0.01 mol / liter and saturation. . The composition according to claim 11, wherein the pH of the composition is 0-8. The composition according to claim 17, wherein the pH of the composition is 1.5 to 4.5. Electroless nickel deposits from a substrate selected from the group consisting of iron, cast iron, steel alloys, stainless steel, aluminum, electroplated nickel, cast nickel, iron / nickel / cobalt alloys, sulfamate nickel and titanium A method of peeling,
a) in an electrolytic bath,
i) a compound selected from the group consisting of oxoacids, oxoacid salts, and combinations thereof;
ii) immersing the substrate comprising electroless nickel in a composition consisting essentially of hydrogen peroxide, and b) electrolytically stripping the electroless nickel deposit from the substrate. Become
A strong oxoacid having one ionizable hydrogen and a dissociation constant of at least 2 × 10 ⁻¹ maintains a hydrogen peroxide / acid molar ratio of at least 3.75;
A strong oxoacid with at least two ionizable hydrogens maintains a hydrogen peroxide / acid molar ratio of at least 7.5;
A weak oxoacid with a dissociation constant of less than 2 × 10 ⁻¹ maintains a hydrogen peroxide / acid molar ratio of at least 1.5, provided that
When aluminum is the substrate and a strong oxo acid is used, the strong oxo acid is selected from the group consisting of sulfuric acid, sulfamic acid, their salts, and combinations thereof;
Where the substrate is selected from electroplated nickel, cast nickel, iron / nickel / cobalt alloy, and sulfamate nickel substrates, the composition comprises a weak oxoacid, an oxoacid salt, and combinations thereof The method to use during. 12. A composition according to claim 11, wherein the composition is free of chelates, chromates or cyanides. For electrolytically stripping electroless nickel deposits from a substrate,
a) a compound selected from the group consisting of oxoacids, oxoacid salts, and combinations thereof;
b) a composition consisting essentially of hydrogen peroxide, having one ionizable hydrogen and having a dissociation constant of at least 2.times.10.sup.- ¹ with a strong oxo acid of at least 3.75 peroxidation. Maintaining the hydrogen / acid molar ratio;
A strong oxoacid with at least two ionizable hydrogens maintains a hydrogen peroxide / acid molar ratio of at least 7.5;
A composition that maintains a hydrogen peroxide / acid molar ratio of at least 1.5 for weak oxoacids having a dissociation constant of less than 2 × 10 ⁻¹ .