Title:
COMPOSITE NICKEL IRON ELECTROPLATE AND METHOD OF MAKING SAID ELECTROPLATE
United States Patent 3812566
Abstract:
A composite nickel-iron electroplate comprised of two essential layers, the first layer comprised of an iron-nickel alloy wherein the iron is present in an amount ranging from about 20 percent to about 45 percent by weight iron and having a minimum thickness of about 0.1 mil; and a top layer comprised of a microdiscontinuous chromium electrodeposit.
US Patent References:
Metallic protective coating
Brown - August 1959 - 2900707
Method of depositing a corrosion resistant composite nickel electroplate
Brown et al. - August 1966 - 3268424
Method for covering objects with a decorative bright-nickel/chromium coating, as well as objects covered by applying this method
Odekerkem - January 1967 - 3298802
Article coated with a coelectrodeposit of nickel and plastic particles, an overlayerthereon, and method of making said article
Brown et al. - December 1967 - 3356467
ELECTRODEPOSITION OF CHROMIUM
Such et al. - October 1968 - 3408272
Metallic protective coating
Brown - August 1959 - 2900707
Method of depositing a corrosion resistant composite nickel electroplate
Brown et al. - August 1966 - 3268424
Method for covering objects with a decorative bright-nickel/chromium coating, as well as objects covered by applying this method
Odekerkem - January 1967 - 3298802
Article coated with a coelectrodeposit of nickel and plastic particles, an overlayerthereon, and method of making said article
Brown et al. - December 1967 - 3356467
ELECTRODEPOSITION OF CHROMIUM
Such et al. - October 1968 - 3408272
Application Number:
05/383428
Publication Date:
05/28/1974
Filing Date:
07/27/1973
View Patent Images:
Export Citation:
Assignee:
Oxy Metal Finishing Corporation (Warren, MI)
Primary Class:
Other Classes:
428/675, 205/176, 205/113, 428/935, 428/926, 428/678, 428/667, 428/676, 428/679
International Classes:
C25D5/12; C25D5/10; B23P3/00; C23B5/50
Field of Search:
204/40,41,43T 19/183.5 29/196.6
US Patent References:
| 3461048 | METHOD OF ELECTRODEPOSITING DUPLEX MICROCRACK CHROMIUM | August 1969 | Mahlstedt |
Other References:
C and EN, pp. 80-81, Jan. 21, 1963. .
J. C. Merriam, The Iron Age, pp. 73-76, Sept. 22, 1966..
Primary Examiner:
Kaplan G. L.
Attorney, Agent or Firm:
Claeboe B. F.
Parent Case Data:
CROSS REFERENCE TO RELATED CASES
This application is a continuation of application Ser. No. 268,350, filed July 3, 1972, now abandoned.
Claims:
What is claimed is
1. An electroplated article comprising a base, an electrodeposited iron-nickel alloy layer on said base wherein said alloy has an iron content from about 20 to 45 percent by weight, a nickel content from approximately 80 to 55 percent by weight and the thickness of said alloy layer being at least 0.1 mil, and an essentially pure nickel coating electrodeposited on said alloy layer and having a thickness of at least 0.05 mils so that when a chromium deposit is electroplated upon said nickel coating the chromium layer becomes microdiscontinuous essentially throughout its area and corrosion of said iron-nickel alloy layer is inhibited.
2. An electroplated article as defined in claim 1, wherein the iron-nickel deposit has a thickness of up to about 2.0 mils.
3. An electroplated article as defined in claim 1, wherein the microdiscontinuous chromium coating is a microcracked chromium.
4. An electroplated article as defined in claim 1, wherein the chromium coating is a microporous chromium coating.
5. An electroplated article as defined in claim 1, wherein the base for said iron-nickel alloy layer is selected from the group consisting of copper and brass.
6. A process for producing an electroplated article which comprises electrodepositing an iron-nickel alloy upon a metallic base susceptible to corrosion and in which said alloy has an iron content from about 20 to 45 percent by weight, a nickel content from approximately 80 to 55 percent by weight, and in which during electrodepositing the thickness of said alloy layer is controlled to a thickness of at least 0.1 mil, and electrodepositing upon said alloy layer an essentially pure nickel coating to a thickness of at least 0.05 mils, so that when a chromium deposit is electroplated upon said nickel coating the chromium layer becomes microdiscontinuous essentially throughout its area and corrosion of said iron-nickel alloy layer is inhibited.
7. A process as defined in claim 6, wherein the iron-nickel layer is deposited to a thickness of up to about 2.0 mils.
8. A process as defined in claim 6, wherein the micro-discontinuous chromium coating is a microcracked chromium.
9. A process as defined in claim 6, wherein the chromium coating is a microporous chromium.
10. A process as defined in claim 6, in which the base is selected from the group consisting of copper and brass.
1. An electroplated article comprising a base, an electrodeposited iron-nickel alloy layer on said base wherein said alloy has an iron content from about 20 to 45 percent by weight, a nickel content from approximately 80 to 55 percent by weight and the thickness of said alloy layer being at least 0.1 mil, and an essentially pure nickel coating electrodeposited on said alloy layer and having a thickness of at least 0.05 mils so that when a chromium deposit is electroplated upon said nickel coating the chromium layer becomes microdiscontinuous essentially throughout its area and corrosion of said iron-nickel alloy layer is inhibited.
2. An electroplated article as defined in claim 1, wherein the iron-nickel deposit has a thickness of up to about 2.0 mils.
3. An electroplated article as defined in claim 1, wherein the microdiscontinuous chromium coating is a microcracked chromium.
4. An electroplated article as defined in claim 1, wherein the chromium coating is a microporous chromium coating.
5. An electroplated article as defined in claim 1, wherein the base for said iron-nickel alloy layer is selected from the group consisting of copper and brass.
6. A process for producing an electroplated article which comprises electrodepositing an iron-nickel alloy upon a metallic base susceptible to corrosion and in which said alloy has an iron content from about 20 to 45 percent by weight, a nickel content from approximately 80 to 55 percent by weight, and in which during electrodepositing the thickness of said alloy layer is controlled to a thickness of at least 0.1 mil, and electrodepositing upon said alloy layer an essentially pure nickel coating to a thickness of at least 0.05 mils, so that when a chromium deposit is electroplated upon said nickel coating the chromium layer becomes microdiscontinuous essentially throughout its area and corrosion of said iron-nickel alloy layer is inhibited.
7. A process as defined in claim 6, wherein the iron-nickel layer is deposited to a thickness of up to about 2.0 mils.
8. A process as defined in claim 6, wherein the micro-discontinuous chromium coating is a microcracked chromium.
9. A process as defined in claim 6, wherein the chromium coating is a microporous chromium.
10. A process as defined in claim 6, in which the base is selected from the group consisting of copper and brass.
Description:
BACKGROUND OF THE INVENTION
The present invention relates to an improved process for forming a composite iron-nickel electroplate on a metal base susceptible to corrosion and more particularly it relates to improvements in the forming of a composite electroplate comprising at least two layers of various electroplates which are adjacent or contiguous to each other and to a plating bath useful in the process.
U.S. Pat. No. 3,090,733 describes a composite electroplate on a base metal which is made up of three layers of nickel electroplate. The intermediate nickel layer has a higher sulfur content than the nickel layers that sandwich it. Case No. 2,915, application Ser. No. 268,348 filed on July 3, 1973, now abandoned, entitled "Electrodeposition of Bright Nickel Iron Electrodeposits" relates to a means of obtaining bright nickel iron electrodeposits.
For many years, electrodeposited nickel has been employed as a substrate for the electrodeposition of chromium in order to impart satisfactory corrosion resistant properties to a metallic surface. Efforts have been made to obtain various alloys of nickel in order to decrease the cost of obtaining a satisfactory corrosion resistant film. Iron nickel deposits have been used previously for the electrodeposition of electromagnetic films. These films have extremely thin surfaces and normally are not decorative in character or exposed to corrosive environments.
SUMMARY OF THE INVENTION
It has been found that satisfactory bright iron nickel alloy deposits can be obtained which are comparable to 100 percent nickel deposits in brightness, leveling and ductility with good corrosion resistant properties as a substrate for chromium electrodeposition. In particular, the relatively thin coatings of bright iron-nickel having less than about 2.0 mil thickness with an alloy content of about 20 to 45 percent iron function more effectively than an equivalent bright nickel coating when copper or brass undercoats are employed.
DESCRIPTION OF PREFERRED EMBODIMENTS
The invention is concerned with a composite iron nickel electroplate comprising as essential layers onto a metallic substrate, such as copper or brass; a first layer comprised of an iron-nickel alloy wherein the iron is present in an amount ranging from about 20 percent to about 45 percent by weight iron and the layer has a minimum thickness of about 0.1 mil; and a second layer comprised of a microdiscontinuous chromium coating.
It is preferred that the iron-nickel layer have a maximum thickness of about 2.0 mils. The thickness of the deposit may be varied depending on cost, degree of corrosion protection desired and the like. One can obtain a bright iron-nickel alloy deposit of from about 20 percent to about 45 percent by weight iron. The iron-nickel alloy electrodeposit that may be employed can be obtained by electrolyzing a bath containing one or more salts of nickel, one or more salts of iron and a bath soluble complexing agent. A bath soluble nickel brightener may also be added to the bath to obtain a bright deposit.
In order to introduce iron and nickel ions into the bath, any bath soluble iron or nickel containing compound may be employed providing the corresponding anion is not detrimental to the bath. Preferably inorganic nickel salts may be employed, such as nickel sulfate, nickel chloride and the like, as well as other nickel materials such as nickel sulfamate and the like. When nickel sulfate salts are used they are normally present in amounts ranging from 40 to 300 grams/liter (calculated as nickel sulfate 6H 2 O); nickel chloride may also be used and is present in an amount ranging from about 80 to 250 grams/liter. The chloride or halide ions are employed in order to obtain satisfactory conductivity of the solution and at the same time to obtain satisfactory corrosion properties of the soluble anodes.
Preferably the inorganic salts of iron are employed, such as ferrous salts, such as ferrous sulfate, ferrous chloride and the like. These salts are present in an amount ranging from about 3 to 60 grams/liter. Other bath soluble iron salts that may be employed, such as soluble ferrous fluoborate, or sulfamate and the like.
The iron complexing agent that is employed in the present invention is one that is bath soluble and contains complexing groups independently selected from the group consisting of carboxy and hydroxy provided at least one of the complexing groups is a carboxy group and further provided that there are at least two complexing groups. The complexing agent that may be employed is present in an amount ranging from about 10 to about 100 grams/liter. Suitable complexing agents are hydroxy substituted lower aliphatic carboxylic acids having from two to eight carbon atoms, from one to six hydroxyl groups and from one to three carboxyl groups such as ascorbic acid, isoascorbic acid, citric acid, malic acid, gluteric acid, gluconic acid, muconic, glutamic, gluheptonate, glycollic acid, aspartic acid and the like, as well as amine containing complexing agents such as nitrilotriacetic acid, ethylene diamine tetraacetic acid, as well as the water soluble salts thereof such as ammonium and the alkali metal salts such as potassium, sodium, lithium and the like. It can also be appreciated that the iron may be introduced into the bath as a salt of the complexing agent.
By "carboxy" is meant the group-COOH. However, it is to be appreciated that in solution the proton disassociates from the carboxy group and therefore this group is to be included in the meaning of carboxy.
The purpose of the complexing agent is to keep the metal ions, in particular the ferrous and ferric ions, in solution. It has been found that as the pH of a normal Watts nickel plating bath increases above a pH of 3.0, ferric ions tend to precipitate as ferric hydroxide. The complexing agent will prevent the precipitation from taking place and therefore makes the iron and nickel ions available for electrodeposition from the complexing agent.
Because of the operating parameters employing the complexing agent, the pH of the bath preferably ranges from about 2.5 to about 5.5 and even more preferably about 3 to about 3.5.
The temperature of the bath may range from about 120°F to about 180°F, preferably about 160°F.
The average cathode current density may range from about 10 amps to about 70 amps sq. ft., preferably about 45 amps sq. ft.
It is preferred that the complexing agent concentration should be at least three times the total iron ion concentration in the bath. The complexing agent concentration ratio to total iron ion concentration may range from 3 to 50:1.
The bath may also contain various buffers such as boric acid and sodium acetate and the like ranging in amounts from about 30 to 60 grams/liter, preferably 40 grams/liter. The ratio of nickel ions to iron ions ranges from about 5 to about 50 to 1.
While the bath may be operated without agitation, various means of agitation may be employed such as mechanical agitation, air agitation, cathode rod movement and the like.
It has been found that various nickel brightening additives may be employed to impart brightness, ductility and leveling to the iron nickel deposits. Suitable additives are the sulfo-oxygen compounds as are described as brighteners of the first class described in Modern Electroplating, published by John Wiley and Sons, second edition, page 272.
The amount of sulfo-oxygen compounds employed in the present invention ranges from about 0.5 to about 10 g/l. It has been found that saccharin may be used in amounts ranging from 0.5 to about 5 g/l resulting in a bright ductile deposit. When other sulfo-oxygen compounds are employed, such as naphthlene-trisulfonic, sulfobenzaldehyde, dibenzenesulfonamide, good brightness is obtained but the ductility is not as good as with saccharin. In addition to the above sulfo-oxygen compounds that may be used, others are sodium allyl sulfonate, benzene sulfinates, vinyl sulfonate, Beta-styrene sulfonate, cyano alkane sulfonates (having from one to five carbon atoms).
The bath soluble sulfo-oxygen compounds that may be used in the present invention are those such as the unsaturated aliphatic sulfonic acids, mononuclear and binuclear aromatic sulfonic acids, mononuclear aromatic sulfinic acids, mononuclear aromatic sulfonamides and sulfonimides, and the like.
It has also been found that acetylenic nickel brighteners may also be used in amounts ranging from about 10 to about 500 mg/l. Suitable compounds are the acetylenic sulfo-oxygen compounds mentioned in U.S. Pat. No. 2,800,440. These nickel brighteners are the oxygen containing acetylenic sulfo-oxygen compounds. Other acetylenic nickel brighteners are those described in U.S. Pat. No. 3,366,557 such as the polyethers resulting from the condensation reaction of acetylenic alcohols and diols such as propargyl alcohol, butyndiol, and the like and lower alkylene oxides such as epichlorohydrin, ethylene oxide, propylene oxide and the like.
It has also been found that nitrogen heterocyclic quaternary or betaine nickel brighteners may also be used in amounts ranging from about 1 to about 50 mg/l. Suitable compounds are those nickel brighteners described in U.S. Pat. No. 2,647,866 and the nitrogen heterocyclic sulfonates described in U.S. Pat. No. 3,023,151. Preferred compounds described therein are the pyridine quaternaries or betaines or the pyridine sulfobetaines. Suitable quaternaries that may be employed are quinaldine propane sultone, quinaldine dimethyl sulfate, quinaldine allyl bromide, pyridine allyl bromide, isoquinaldine propane sultone, isoquinaldine dimethyl sulfate, isoquinaldine allyl bromide, and the like.
At times the low current density areas are not fully bright. To extend the current density range of the iron-nickel bath of the present invention other organic sulfide nickel brighteners are employed in amounts ranging from about 0.5 to about 40 mg/l of the electroplating bath composition. These organic sulfides are of the formula: ##SPC1##
where R 1 is hydrogen or a carbon atom of an organic radical, R 2 is nitrogen or a carbon atom of an organic radical and R 3 is a carbon atom of an organic radical. R 1 and R 2 or R 3 may be linked together through a single organic radical.
More specifically, the bath soluble organic sulfide compounds used are 2-amino thiazoles and isothioureas having the formulae: ##SPC2##
wherein R 6 is selected from H, lower alkyl sulfonic acid groups, aryl sulfonic acid groups, lower alkoxy aryl sulfonic acid groups and the salts thereof; R 4 and R 5 are selected from H, halogen, lower alkyl groups and the bivalent radical ##SPC3##
in which the R 10 groups are selected from H, halogen and lower alkyl groups; R 9 is selected from lower alkyl sulfonic acid groups and lower alkyl carboxy acid groups and the salts thereof; and R 7 and R 8 are selected from H, halogen, lower alkyl groups and the bivalent radical ##SPC4##
in which the R 11 groups are selected from H, halogen and lower alkyl groups.
It is to be appreciated that in referring to halogens, it is intended to include chlorine, bromine, fluorine and iodine, although chlorine is generally preferred. Moreover, where reference is made to lower alkyl or alkoxy groups, it is intended to include groups containing from about one to six carbon atoms in a straight or branched chain, with from about one to four carbon atoms being preferred. Additionally, in referring to the sulfonic or carboxy acids and their salts, it is intended to include those sulfonic and carboxy acids which have halogen substituents on their alkyl, alkoxy or aryl groups and wherein the salts are exemplified by the alkali metal salts, sodium, potassium, lithium, cesium and rubidium, particularly sodium. In referring to the bivalent radicals above, a six membered ring is formed when R 4 and R 5 are joined and a five membered ring is formed when R 7 and R 8 are joined.
Suitable compounds are those of the formula: ##SPC5##
Compound (1), 2-aminothiazole and compound (2), 2-amino-benzothiazole can be reacted with bromoethane sulfonate, propane sultone, benzyl chloride, dimethylsulfate, diethyl sulfate, methyl bromide, propargyl bromide, ethylene dibromide, allyl bromide, methyl chloro acetate, sulfophenoxyethylene bromide, the latter, for example, can be reacted with compound (1) to give compound (3), etc., to form compounds that give even improved results over compounds (1) and (2). Also, substituted 2-aminothiazoles and 2-aminobenzothiazoles, such as 2-amino-5-chlorothiazole, 2-amino-4-methylthiazole, etc., can be used instead of compounds (1) and (2). To form compounds such as (5) and (6), thiourea can be reacted with propiolactone, butyrolactone, chloroacetic acid, chloropropionic acid, propane sultone, dimethyl sulfate, etc. Also, phenyl thiourea, methyl thiourea, allyl thiourea and other similar substituted thioureas may be used in the reactions to form compounds similar to types (5) and (6).
It is to be appreciated that the above nickel brighteners must be soluble in the electroplating bath and may be introduced into the bath, when an acid is involved, as the acid itself or as a salt having bath soluble cations, such as ammonium ions or the alkali metal ion such as lithium, potassium, sodium and the like.
The top layer is a microdiscontinuous chromium electro-deposit. By "microdiscontinuous" is meant that the chromium deposit is micro porous or is microcracked. In other words, the top chromium layer has micro apertures to the layer below. The microdiscontinuity can be obtained in a variety of means. One means would be to impart a microdiscontinuity of the chromium deposits as it is being deposited. A second means of obtaining a microdiscontinuous coating is to electrodeposit the layer below the chromium in such a state that the microcracking will occur in the lower layer prior to the electrodeposition of the chromium which thereby results in a microcracked chromium deposit. Such means are described in application Ser. No. 259,525, filed on June 5, 1972, now U.S. Pat. No. 3,761,363. Another way to obtain a microdiscontinuous chromium coating is described in U.S. Pat. No. 3,563,864, wherein the nickel deposit is deposited in such a state that the nickel deposit will microcrack during or after the chromium deposition thereby resulting in a microcracked chromium deposit.
It is to be appreciated that various electrodeposits can also be placed onto the substrate prior to the nickel-iron deposit or subsequent to the nickel-iron deposit. The deposits below the nickel-iron deposit may be copper, brass and the like. The deposits subsequent to the nickel-iron deposit can be nickel, cobalt, nickel-cobalt alloy and the like.
Microdiscontinuity can also be obtained by incorporating various fine bath insoluble particles into an iron-nickel bath used to deposit nickel on top of the nickel-iron deposit and below a chromium deposit. The resulting electrodeposited chromium coating is microporous in structure. Similar procedures are described in U.S. Pat. No. 3,151,971-3.
It can be appreciated that the nickel salts that may be employed in the present invention may be substituted with minor amounts up to 50 percent with cobalt salts in order to achieve different corrosion behavior.
A suitable composition that may be employed in the iron-nickel deposit is described below: Material Concentration Preferred Range Concentration ______________________________________ Nickel sulfate 40 to 300 g/l 50 g/l 6H 2 O Nickel Chloride 80 to 250 g/l 100 g/l . 6H 2 O Ferrous sulfate 5 to 40 g/l 15 g/l 7H 2 O Complexing 10 to 100 g/l 20 g/l agent Boric Acid 30 to 60 g/l 45 g/l Cathode current 25 to 55 ASF density average Anode current 10 to 20 ASF density Temperature 140° F to 160° F pH 2.5 to 5.5 3.0 to 4.2 Agitation air or rod Brightener see above ______________________________________
It is to be appreciated that various other additives may be employed to effect desirable results such as surface active agents to overcome any undesirable problems that may occur in particular situations such as, pitting.
When significant amounts of iron are being introduced into the system, it has been found that soluble iron anodes or nickel-iron alloy anodes should be employed. The ratio of nickel to iron in the anode area should be maintained at approximately four to one. Preferably dual (nickel and iron) anodes are used and the iron anodes should be insulated from a direct contact to the anode rail and connected subsequently to the anode rail through a highly electrically resistant device such as a nickel-chrome wire or controlled by a separate rheostat to maintain a total current to the iron anodes of about 8 percent to about 30 percent preferably about 10 percent to 25 percent of the total anode current. Anode bags, filter bags, hoses, tank linings etc. should be those which are generally employed in other bright nickel processes.
EXAMPLE NO. 1
Preformed steel panels having high and low current density areas were plated with a checkpoint thickness of 0.5 mils sulfur free simi-bright nickel deposit followed by 0.3 mils of bright iron-nickel at the same checkpoint and subsequently over plated with a thin microcracked nickel deposit of 0.07 mils using the procedure described in Case No. 2855, Ser. No. 259,525 filed on June 5, 1972 entitled, Microcracked Nickel Plating Bath. A final chromium deposit was plated on the microcracked nickel.
The bright iron-nickel deposit had an iron content of 20 percent.
These panels were exposed at a marine site. After about 10 months exposure, the panels were found to have extensive staining from corrosion of the nickel-iron deposit, but the substrate steel was completely protected.
EXAMPLE NO. 2
Preformed steel panels, having high and low current density areas, were plated with sulfur free simi-bright nickel deposit to a checkpoint thickness of 0.5 mils followed by a bright iron-nickel deposit of 0.3 mils thickness at the checkpoint. Some of the panels were subsequently overplated by a thin nickel deposit containing very fine SiO 2 particles which induces microporosity in the final chromium deposit. Other panels were chromium plated directly on the bright nickel-iron deposit.
The bright iron deposit had an iron content of 22.8 percent.
At the end of one winter exposure at two sites near Detroit, Mich., the panels were examined. None of the panels showed any failure or penetration to the steel substrate, so the protective value of the composite plate was excellent. Very slight staining from corrosion of the nickel-iron layer was evident at one site.
EXAMPLE NO. 3
Preformed steel panels having high and low current density areas were plated with a checkpoint thickness of 0.5 mils bright acid copper followed by 0.3 mils of bright iron-nickel at the same checkpoint and subsequently overplated with a thin nickel deposit (0.1 mil) containing fine particles which induced microporosity in the final chromium deposit.
The bright iron-nickel deposit had an iron content of 36 percent.
These panels were exposed in the Corrodkote test for 2 cycles of 20 hours each (ASTM B380-65). At the end of the first cycle, no failure of the deposit had occurred. At the end of the second cycle of exposure, some stain was present in the extreme low current density area but no penetration of the deposit to the substrate steel had occurred.
The present invention relates to an improved process for forming a composite iron-nickel electroplate on a metal base susceptible to corrosion and more particularly it relates to improvements in the forming of a composite electroplate comprising at least two layers of various electroplates which are adjacent or contiguous to each other and to a plating bath useful in the process.
U.S. Pat. No. 3,090,733 describes a composite electroplate on a base metal which is made up of three layers of nickel electroplate. The intermediate nickel layer has a higher sulfur content than the nickel layers that sandwich it. Case No. 2,915, application Ser. No. 268,348 filed on July 3, 1973, now abandoned, entitled "Electrodeposition of Bright Nickel Iron Electrodeposits" relates to a means of obtaining bright nickel iron electrodeposits.
For many years, electrodeposited nickel has been employed as a substrate for the electrodeposition of chromium in order to impart satisfactory corrosion resistant properties to a metallic surface. Efforts have been made to obtain various alloys of nickel in order to decrease the cost of obtaining a satisfactory corrosion resistant film. Iron nickel deposits have been used previously for the electrodeposition of electromagnetic films. These films have extremely thin surfaces and normally are not decorative in character or exposed to corrosive environments.
SUMMARY OF THE INVENTION
It has been found that satisfactory bright iron nickel alloy deposits can be obtained which are comparable to 100 percent nickel deposits in brightness, leveling and ductility with good corrosion resistant properties as a substrate for chromium electrodeposition. In particular, the relatively thin coatings of bright iron-nickel having less than about 2.0 mil thickness with an alloy content of about 20 to 45 percent iron function more effectively than an equivalent bright nickel coating when copper or brass undercoats are employed.
DESCRIPTION OF PREFERRED EMBODIMENTS
The invention is concerned with a composite iron nickel electroplate comprising as essential layers onto a metallic substrate, such as copper or brass; a first layer comprised of an iron-nickel alloy wherein the iron is present in an amount ranging from about 20 percent to about 45 percent by weight iron and the layer has a minimum thickness of about 0.1 mil; and a second layer comprised of a microdiscontinuous chromium coating.
It is preferred that the iron-nickel layer have a maximum thickness of about 2.0 mils. The thickness of the deposit may be varied depending on cost, degree of corrosion protection desired and the like. One can obtain a bright iron-nickel alloy deposit of from about 20 percent to about 45 percent by weight iron. The iron-nickel alloy electrodeposit that may be employed can be obtained by electrolyzing a bath containing one or more salts of nickel, one or more salts of iron and a bath soluble complexing agent. A bath soluble nickel brightener may also be added to the bath to obtain a bright deposit.
In order to introduce iron and nickel ions into the bath, any bath soluble iron or nickel containing compound may be employed providing the corresponding anion is not detrimental to the bath. Preferably inorganic nickel salts may be employed, such as nickel sulfate, nickel chloride and the like, as well as other nickel materials such as nickel sulfamate and the like. When nickel sulfate salts are used they are normally present in amounts ranging from 40 to 300 grams/liter (calculated as nickel sulfate 6H 2 O); nickel chloride may also be used and is present in an amount ranging from about 80 to 250 grams/liter. The chloride or halide ions are employed in order to obtain satisfactory conductivity of the solution and at the same time to obtain satisfactory corrosion properties of the soluble anodes.
Preferably the inorganic salts of iron are employed, such as ferrous salts, such as ferrous sulfate, ferrous chloride and the like. These salts are present in an amount ranging from about 3 to 60 grams/liter. Other bath soluble iron salts that may be employed, such as soluble ferrous fluoborate, or sulfamate and the like.
The iron complexing agent that is employed in the present invention is one that is bath soluble and contains complexing groups independently selected from the group consisting of carboxy and hydroxy provided at least one of the complexing groups is a carboxy group and further provided that there are at least two complexing groups. The complexing agent that may be employed is present in an amount ranging from about 10 to about 100 grams/liter. Suitable complexing agents are hydroxy substituted lower aliphatic carboxylic acids having from two to eight carbon atoms, from one to six hydroxyl groups and from one to three carboxyl groups such as ascorbic acid, isoascorbic acid, citric acid, malic acid, gluteric acid, gluconic acid, muconic, glutamic, gluheptonate, glycollic acid, aspartic acid and the like, as well as amine containing complexing agents such as nitrilotriacetic acid, ethylene diamine tetraacetic acid, as well as the water soluble salts thereof such as ammonium and the alkali metal salts such as potassium, sodium, lithium and the like. It can also be appreciated that the iron may be introduced into the bath as a salt of the complexing agent.
By "carboxy" is meant the group-COOH. However, it is to be appreciated that in solution the proton disassociates from the carboxy group and therefore this group is to be included in the meaning of carboxy.
The purpose of the complexing agent is to keep the metal ions, in particular the ferrous and ferric ions, in solution. It has been found that as the pH of a normal Watts nickel plating bath increases above a pH of 3.0, ferric ions tend to precipitate as ferric hydroxide. The complexing agent will prevent the precipitation from taking place and therefore makes the iron and nickel ions available for electrodeposition from the complexing agent.
Because of the operating parameters employing the complexing agent, the pH of the bath preferably ranges from about 2.5 to about 5.5 and even more preferably about 3 to about 3.5.
The temperature of the bath may range from about 120°F to about 180°F, preferably about 160°F.
The average cathode current density may range from about 10 amps to about 70 amps sq. ft., preferably about 45 amps sq. ft.
It is preferred that the complexing agent concentration should be at least three times the total iron ion concentration in the bath. The complexing agent concentration ratio to total iron ion concentration may range from 3 to 50:1.
The bath may also contain various buffers such as boric acid and sodium acetate and the like ranging in amounts from about 30 to 60 grams/liter, preferably 40 grams/liter. The ratio of nickel ions to iron ions ranges from about 5 to about 50 to 1.
While the bath may be operated without agitation, various means of agitation may be employed such as mechanical agitation, air agitation, cathode rod movement and the like.
It has been found that various nickel brightening additives may be employed to impart brightness, ductility and leveling to the iron nickel deposits. Suitable additives are the sulfo-oxygen compounds as are described as brighteners of the first class described in Modern Electroplating, published by John Wiley and Sons, second edition, page 272.
The amount of sulfo-oxygen compounds employed in the present invention ranges from about 0.5 to about 10 g/l. It has been found that saccharin may be used in amounts ranging from 0.5 to about 5 g/l resulting in a bright ductile deposit. When other sulfo-oxygen compounds are employed, such as naphthlene-trisulfonic, sulfobenzaldehyde, dibenzenesulfonamide, good brightness is obtained but the ductility is not as good as with saccharin. In addition to the above sulfo-oxygen compounds that may be used, others are sodium allyl sulfonate, benzene sulfinates, vinyl sulfonate, Beta-styrene sulfonate, cyano alkane sulfonates (having from one to five carbon atoms).
The bath soluble sulfo-oxygen compounds that may be used in the present invention are those such as the unsaturated aliphatic sulfonic acids, mononuclear and binuclear aromatic sulfonic acids, mononuclear aromatic sulfinic acids, mononuclear aromatic sulfonamides and sulfonimides, and the like.
It has also been found that acetylenic nickel brighteners may also be used in amounts ranging from about 10 to about 500 mg/l. Suitable compounds are the acetylenic sulfo-oxygen compounds mentioned in U.S. Pat. No. 2,800,440. These nickel brighteners are the oxygen containing acetylenic sulfo-oxygen compounds. Other acetylenic nickel brighteners are those described in U.S. Pat. No. 3,366,557 such as the polyethers resulting from the condensation reaction of acetylenic alcohols and diols such as propargyl alcohol, butyndiol, and the like and lower alkylene oxides such as epichlorohydrin, ethylene oxide, propylene oxide and the like.
It has also been found that nitrogen heterocyclic quaternary or betaine nickel brighteners may also be used in amounts ranging from about 1 to about 50 mg/l. Suitable compounds are those nickel brighteners described in U.S. Pat. No. 2,647,866 and the nitrogen heterocyclic sulfonates described in U.S. Pat. No. 3,023,151. Preferred compounds described therein are the pyridine quaternaries or betaines or the pyridine sulfobetaines. Suitable quaternaries that may be employed are quinaldine propane sultone, quinaldine dimethyl sulfate, quinaldine allyl bromide, pyridine allyl bromide, isoquinaldine propane sultone, isoquinaldine dimethyl sulfate, isoquinaldine allyl bromide, and the like.
At times the low current density areas are not fully bright. To extend the current density range of the iron-nickel bath of the present invention other organic sulfide nickel brighteners are employed in amounts ranging from about 0.5 to about 40 mg/l of the electroplating bath composition. These organic sulfides are of the formula: ##SPC1##
where R 1 is hydrogen or a carbon atom of an organic radical, R 2 is nitrogen or a carbon atom of an organic radical and R 3 is a carbon atom of an organic radical. R 1 and R 2 or R 3 may be linked together through a single organic radical.
More specifically, the bath soluble organic sulfide compounds used are 2-amino thiazoles and isothioureas having the formulae: ##SPC2##
wherein R 6 is selected from H, lower alkyl sulfonic acid groups, aryl sulfonic acid groups, lower alkoxy aryl sulfonic acid groups and the salts thereof; R 4 and R 5 are selected from H, halogen, lower alkyl groups and the bivalent radical ##SPC3##
in which the R 10 groups are selected from H, halogen and lower alkyl groups; R 9 is selected from lower alkyl sulfonic acid groups and lower alkyl carboxy acid groups and the salts thereof; and R 7 and R 8 are selected from H, halogen, lower alkyl groups and the bivalent radical ##SPC4##
in which the R 11 groups are selected from H, halogen and lower alkyl groups.
It is to be appreciated that in referring to halogens, it is intended to include chlorine, bromine, fluorine and iodine, although chlorine is generally preferred. Moreover, where reference is made to lower alkyl or alkoxy groups, it is intended to include groups containing from about one to six carbon atoms in a straight or branched chain, with from about one to four carbon atoms being preferred. Additionally, in referring to the sulfonic or carboxy acids and their salts, it is intended to include those sulfonic and carboxy acids which have halogen substituents on their alkyl, alkoxy or aryl groups and wherein the salts are exemplified by the alkali metal salts, sodium, potassium, lithium, cesium and rubidium, particularly sodium. In referring to the bivalent radicals above, a six membered ring is formed when R 4 and R 5 are joined and a five membered ring is formed when R 7 and R 8 are joined.
Suitable compounds are those of the formula: ##SPC5##
Compound (1), 2-aminothiazole and compound (2), 2-amino-benzothiazole can be reacted with bromoethane sulfonate, propane sultone, benzyl chloride, dimethylsulfate, diethyl sulfate, methyl bromide, propargyl bromide, ethylene dibromide, allyl bromide, methyl chloro acetate, sulfophenoxyethylene bromide, the latter, for example, can be reacted with compound (1) to give compound (3), etc., to form compounds that give even improved results over compounds (1) and (2). Also, substituted 2-aminothiazoles and 2-aminobenzothiazoles, such as 2-amino-5-chlorothiazole, 2-amino-4-methylthiazole, etc., can be used instead of compounds (1) and (2). To form compounds such as (5) and (6), thiourea can be reacted with propiolactone, butyrolactone, chloroacetic acid, chloropropionic acid, propane sultone, dimethyl sulfate, etc. Also, phenyl thiourea, methyl thiourea, allyl thiourea and other similar substituted thioureas may be used in the reactions to form compounds similar to types (5) and (6).
It is to be appreciated that the above nickel brighteners must be soluble in the electroplating bath and may be introduced into the bath, when an acid is involved, as the acid itself or as a salt having bath soluble cations, such as ammonium ions or the alkali metal ion such as lithium, potassium, sodium and the like.
The top layer is a microdiscontinuous chromium electro-deposit. By "microdiscontinuous" is meant that the chromium deposit is micro porous or is microcracked. In other words, the top chromium layer has micro apertures to the layer below. The microdiscontinuity can be obtained in a variety of means. One means would be to impart a microdiscontinuity of the chromium deposits as it is being deposited. A second means of obtaining a microdiscontinuous coating is to electrodeposit the layer below the chromium in such a state that the microcracking will occur in the lower layer prior to the electrodeposition of the chromium which thereby results in a microcracked chromium deposit. Such means are described in application Ser. No. 259,525, filed on June 5, 1972, now U.S. Pat. No. 3,761,363. Another way to obtain a microdiscontinuous chromium coating is described in U.S. Pat. No. 3,563,864, wherein the nickel deposit is deposited in such a state that the nickel deposit will microcrack during or after the chromium deposition thereby resulting in a microcracked chromium deposit.
It is to be appreciated that various electrodeposits can also be placed onto the substrate prior to the nickel-iron deposit or subsequent to the nickel-iron deposit. The deposits below the nickel-iron deposit may be copper, brass and the like. The deposits subsequent to the nickel-iron deposit can be nickel, cobalt, nickel-cobalt alloy and the like.
Microdiscontinuity can also be obtained by incorporating various fine bath insoluble particles into an iron-nickel bath used to deposit nickel on top of the nickel-iron deposit and below a chromium deposit. The resulting electrodeposited chromium coating is microporous in structure. Similar procedures are described in U.S. Pat. No. 3,151,971-3.
It can be appreciated that the nickel salts that may be employed in the present invention may be substituted with minor amounts up to 50 percent with cobalt salts in order to achieve different corrosion behavior.
A suitable composition that may be employed in the iron-nickel deposit is described below: Material Concentration Preferred Range Concentration ______________________________________ Nickel sulfate 40 to 300 g/l 50 g/l 6H 2 O Nickel Chloride 80 to 250 g/l 100 g/l . 6H 2 O Ferrous sulfate 5 to 40 g/l 15 g/l 7H 2 O Complexing 10 to 100 g/l 20 g/l agent Boric Acid 30 to 60 g/l 45 g/l Cathode current 25 to 55 ASF density average Anode current 10 to 20 ASF density Temperature 140° F to 160° F pH 2.5 to 5.5 3.0 to 4.2 Agitation air or rod Brightener see above ______________________________________
It is to be appreciated that various other additives may be employed to effect desirable results such as surface active agents to overcome any undesirable problems that may occur in particular situations such as, pitting.
When significant amounts of iron are being introduced into the system, it has been found that soluble iron anodes or nickel-iron alloy anodes should be employed. The ratio of nickel to iron in the anode area should be maintained at approximately four to one. Preferably dual (nickel and iron) anodes are used and the iron anodes should be insulated from a direct contact to the anode rail and connected subsequently to the anode rail through a highly electrically resistant device such as a nickel-chrome wire or controlled by a separate rheostat to maintain a total current to the iron anodes of about 8 percent to about 30 percent preferably about 10 percent to 25 percent of the total anode current. Anode bags, filter bags, hoses, tank linings etc. should be those which are generally employed in other bright nickel processes.
EXAMPLE NO. 1
Preformed steel panels having high and low current density areas were plated with a checkpoint thickness of 0.5 mils sulfur free simi-bright nickel deposit followed by 0.3 mils of bright iron-nickel at the same checkpoint and subsequently over plated with a thin microcracked nickel deposit of 0.07 mils using the procedure described in Case No. 2855, Ser. No. 259,525 filed on June 5, 1972 entitled, Microcracked Nickel Plating Bath. A final chromium deposit was plated on the microcracked nickel.
The bright iron-nickel deposit had an iron content of 20 percent.
These panels were exposed at a marine site. After about 10 months exposure, the panels were found to have extensive staining from corrosion of the nickel-iron deposit, but the substrate steel was completely protected.
EXAMPLE NO. 2
Preformed steel panels, having high and low current density areas, were plated with sulfur free simi-bright nickel deposit to a checkpoint thickness of 0.5 mils followed by a bright iron-nickel deposit of 0.3 mils thickness at the checkpoint. Some of the panels were subsequently overplated by a thin nickel deposit containing very fine SiO 2 particles which induces microporosity in the final chromium deposit. Other panels were chromium plated directly on the bright nickel-iron deposit.
The bright iron deposit had an iron content of 22.8 percent.
At the end of one winter exposure at two sites near Detroit, Mich., the panels were examined. None of the panels showed any failure or penetration to the steel substrate, so the protective value of the composite plate was excellent. Very slight staining from corrosion of the nickel-iron layer was evident at one site.
EXAMPLE NO. 3
Preformed steel panels having high and low current density areas were plated with a checkpoint thickness of 0.5 mils bright acid copper followed by 0.3 mils of bright iron-nickel at the same checkpoint and subsequently overplated with a thin nickel deposit (0.1 mil) containing fine particles which induced microporosity in the final chromium deposit.
The bright iron-nickel deposit had an iron content of 36 percent.
These panels were exposed in the Corrodkote test for 2 cycles of 20 hours each (ASTM B380-65). At the end of the first cycle, no failure of the deposit had occurred. At the end of the second cycle of exposure, some stain was present in the extreme low current density area but no penetration of the deposit to the substrate steel had occurred.