US3474010A - Method of electroplating corrosion resistant coating - Google Patents

Description

3,474,010 METHOD F ELECTROPLATING @QRROSION RESISTANT C(EATING Warren H. McMullen, East Brunswick, N.J., and Otto Kardos, Hazel Park, Micl1., assignors to MdzT Chemicals Inc., New York, N.Y., a corporation of Delaware No Drawing. Filed Oct. 26, 1966, Ser. No. 589,527

Int. Cl. C233) /50, 5/46, 5/08 11.5. Cl. 204-40 12 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a novel electroplating process. More particularly, it relates to a novel process for electroplating a nickel deposit characterized by its protective action and its ability to be chromium plated to yield a product which is highly resistant to corrosion.

As is well known to those skilled-in-the-art, a chromium plated product may be prepared by depositing on a basis metal a first plate of semi-bright nickel characterized by its ductility and leveling; a second plate of bright nickel; and a final chromium plate. Although this system may permit attainment of a product characterized by improved resistance to corrosion, it has been found not to be satisfactory under extreme conditions. For example, if such a system be subjected to three cycles of the standard CASS Test (ASTM designation B380-61T), it will be found that the surface will show definite evidence of corrosion resulting in loss of surface brilliance and attractiveness. These effects are regarded as indicating unsatisfactory performance over the extended course of the three cycles of the test. For many uses, it is desired to prepare a chromium plated article characterized by its ability to resist atmospheric corrosion after extended periods of time equivalent to three cycles of these tests.

It is an object of this invention to provide a novel nickel plate characterized by its ability to receive a chromium plate having improved resistance to corrosion. It is another object of this invention to provide a novel chromium plate characterized by its high resistance to corrosion, particularly under conditions of extended duration. Other objects will be apparent to those skilledin-the-art from inspection of the following description.

In accordance with certain of its aspects, the novel process of this invention for preparing a nickel surface characterized by its ability to receive a chromium plate possessing a high degree of corrosion resistance comprises electrodepositing onto a basis metal a first sulfur-containing bright nickel plate; immersing said first sulfurcontaining bright nickel plate into an aqueous electroplating bath containing about l-l87 g./l. Ni+ 110- 225 g./l. NiCl -6H O, and 300-900 g./l. Ni(BF and electrodepositing at least 0.6 micron of an outer microcracked nickel plate from said bath.

The basis metal which may be plated in accordance with the process of this invention may be iron including iron alloys such as steel, copper, nickel, brass, bronze, zinc; or alloys of any of these metals, etc. The outstand ing results of this invention may be particularly ap parent when the basis metal is steel. It is a particular feature of the novel process of this invention that it may nited States Patent 0 "too permit attainment of plated products having outstanding and unexpected properties when the material on which the plate may be deposited is a zinc-base die casting.

In accordance with certain of its aspects, the first step of the progress of this invention may include deposition onto the basis metal of a deposit of copper hereinafter referred to as the base copper plate. In the case of zinc-base die-castings, this may be essential; in the case of other basis metals, e.g. steel, it may be omitted. Deposition onto the zinc-base die casting of the desired base copper plate may be effected by depositing copper for example from a cyanide-copper plating bath. Typically, such a bath may have the composition set forth in Table I wherein all values are in grams per liter (g./l.) except where otherwise indicated:

1 Added as copper cyanide CuCN.

Deposition of the base copper plate may be carried out by electroplating for 8-12 minutes, say 10 minutes, at 60 C.70 C., say 65 C., and cathode current density of 3-6 a.s.d., say 4.5 a.s.d. Preferably the bath may be agitated as by air agitation or cathode rocker. During this time copper may be deposited having a thickness of 7.515 microns, typically 12 microns.

The basis metal, typically either (a) a zinc-base diecasting bearing the hereinbefore disclosed base copper plate; or (b) a steel basis metal which may optionally bear a base copper plate, may then be further treated in accordance with the process of this invention. Preferably there may be deposited upon the basis metal, including the zinc-base die casting bearing the base copper plate, a first layer of a sulfur-free, ductile, semi-bright nickel plate. The semi-bright nickel plate may typically be deposited by electrodeposition from a Watts-type bath, a sulfamate bath, a fluoborate-type bath, a chloride-free sulfate bath, a chloride-free sulfamate bath, etc., or by other means including decomposition of nickel carbonyl with resultant deposition of nickel.

A typical Watts bath which may be used in practice of this invention may include the following components in aqueous solution, all values being in grams per liter (g./l.) except for the pH (nickel chloride used may be NiCl -6H O; nickel sulfate may be NiSO -6H O. When nickel chloride or sulfate is referred to in the tables, the

hexahydrate is intended) TAB LE II Minimum Maximum Preferred Component:

Nickel sulfate'fiHzO 200 500 300 Nickel ClllOIlde-fiHzO 30 45 Boric acid 35 55 45 Semi-bright additi 0. 2 3 0.75 pH electrornetric 3 5 4. 0

A typical sulfamate-type bath which may be used in the practice of this invention may include the following components:

3 A typical fluoborate-type bath which may be used in the practice of this invention may include the following components:

TAB LE IV Minimum Maximum Preferred Component:

- Nickel fiuoborate 250 400 300 Nickel chloride-611 10 60 20 Boric acid 15 30 20 Semi-bright additive. 0. 2 3 0. 75 pH electrometric 2 4 3. 0

TAB LE V Minimum Maximum Preferred Component:

Nickel sulfate-611 0 300 500 400 Boric acid 35 55 45 Semi-bright additive--- 0. 2 3 O. 75 pH electrometrlc 3 5 4. 0

A typical chloride-free sulfamate-type bath which may be used in practice of this invention may include the following components:

. TAB LE VI Minimum Maximum Preferred Component:

Nickel sulfamate 300 600 350 Boric acid 35 55 45 Semibright additive 0. 2 3 0. 75 pH electrometric 3 5 4. 0

It will be apparent that the above baths may contain components in amounts falling outside the preferred minima and maxima set forth; but most satisfactory and economical operation may normally be effected when the components are present in the baths in the amounts indicated.

Semi-bright additives which may be employed in practice of this first step of the process of this invention (using the baths of Tables II-VI) may typically include, for example, coumarin, butyne diol, chloral hydrate, formaldehyde, piperonal, diethoxylated butyne diol, bromal hydrate, etc. The preferred semi-bright additive may be coumarin used in concentration of 0.2-3 g./l., typically 0.75 g./l.

Electrodeposition of the first, sulfur-free, ductile semibright nickel plate may be carried out from the semi bright plating baths of Tables lI-VI, by use of a cathode current density of 1-10 a.s.d., say 5 a.s.d., at temperature of 50-60 C., say 55 C. for 20-30 minutes, typical ly 25 minutes. During this time, it may be possible to deposit on the basis metal a deposit of semi-bright nickel typically having a thickness of 5-40 microns, say 25 microns.

The semi-bright nickel plate may be essentially sulfurfree, i.e. contain less than about 0.004% sulfur and typically 0.002%-0.004%, and sometimes as low as 0.0010%' 0.0015% sulfur. The ductility of the semi-bright plate may be such that T/2R may have a value of about 0.5 when measured by the well-known standard Chrysler Micrometer Test.

In accordance with practice of the preferred embodiment of this invention, there may be electrodeposited a layer of bright nickel plate onto the first nickel plate. The results of this invention may be achieved by the use of the second layer of bright nickel plate with or without the first or semi-bright layer. It may be found, however, that outstanding and unexpected results, in terms of extended corrosion life, may be achieved when both the first semi-bright layer and the second layer of bright nickel plate are present.

Electrodeposition of bright nickel may be carried out by plating from baths containing nickel sulfate; a chloride, typically nickel chloride; a buffering agent, typically boric acid; and a wetting agent. Such baths may include the Watts bath and the high chloride bath. Other baths may contain, as the source of the nickel, a combination of nickel fluoborate with nickel sulfate and nickel chloride, or a combination of nickel sulfamate and nickel chloride. Typical Watts-type baths and high chloride baths are noted in Tables VII and VIII.

TABLE VII.WATTS TYPE BATHS Minimum Maximum Preferred Components:

Nickel sulfatefiHgO 200 400 li00 Nickel chloride-GHzO 30 75 i0 Boric acid 30 50 t0 Temperature, C-.. 38 65 0 Agitation 0 pH 2. 5 4. 5 1i. .5

! Mechanical and/0r air or solution pumping, etc.

TABLE VIII.HIGH CHLORIDE BATES Minimum Maximum Preferred Components:

Nickel chloride-611 0 150 300 225 Nickel sulfate-61120 40 150 "45 Boric acid 30 50 i0 38 65 i5 2. 5 4. 5 l3. 5

1 Mechanical and/or air or solution pumping.

There may also be present in the electroplating bath of Tables VII-VIII primary nickel brighteners in amount of 0002-02 g./l., say 0.2 g./l.; secondary brighteners in amount of l-3O g./l., say 5 g./l.; and secondary auxiliary brighteners in amount of 0.53 g./l., say 1 g./l. Typical primary brighteners may include acetylenic compounds such as butyne diol, diethoxylated butyne diol, phenyl propiolamide or pyridinium compounds such as quaternized pyridine derivatives e.g. a,a'-bis(pyridinium iodide)-2,6- lutidine. Typical secondary brighteners may include e.g. sulfo-oxygen compounds typified by saccharin, benzene monosulfonate, etc. Typical secondary auxiliary brighteners may include sodium allyl sulfonate, sodium 3-chloro butene l-sulfonate.

Deposition of the bright nickel plate may be carried out at temperatures of 4060 C., say 50 C. at pH of 2.5-4.5, say 3.5 for 8l4 minutes, say 10 minutes to permit attainment of a bright nickel plate having a thickness of 7-12 microns, say 10 microns.

In practice of the novel process of this invention, there may be deposited onto the first nickel plate (optionally but preferably bearing a layer of a second or bright nickel plate), an outer micro-cracked nickel plate having a thickness of at least about 0.6 micron and typically 0.6-3 Inicrons, preferably about 2 microns.

Deposition of the outer nickel plate may be carried out preferably by immersing the basis metal bearing said plate(s) into an electroplating bath containing (a) 120- 187 g./l. nickel ion Ni++, (b) -225 g./l. nickel chloride NiCl -6H O, c) 300900 g./l. nickel fiuoborate Ni(BF (d) a primary brightener, (e) a secondary brightener, (f) an additive heterocyclic having at least two nitrogen atoms in an otherwise carbocyclic ring structure. Typically such baths may be as noted in Table IX.

1 Mechanical and/or air or solution pumping.

The primary brighteners which may be used in this step of this invention may include those materials (present in very low or relatively low concentrations, typically 0.002-O.4 g./l., say 0.2) which by themselves may or may not produce any visible brightening action.

These primary brighteners may permit attainment of bright nickel deposits when used in compounds of secondary brighteners. Secondary brighteners, which are ordinarily used in combination with primary brighteners but in higher concentrations, typically 0.1 g./l.-1 g./l., may produce some brightening or grain refining effect, but when used alone do not have mirror bright deposits at desired brightening rates. Typical primary brighteners which may be used in this step of the process of this invention may include acetylenic compounds such as butyne diol, diethoxylated butyne diol, phenyl propiolamide, propargyl alcohol, 3-butyne l-ol, 2-methyl-3-butyne-2-ol, or pyridinium compounds such as quaternized pyridine derivatives. Typical secondary brighteners which may be used in this step of the process of this invention may include e.g. sulfo-oxygen compounds such as saccharin, sodium benzene monosulfonate, sodium vinyl sulfonate, sodium metabenzene disulfonate, etc.

The preferred primary brightener may be acetylenic compounds, typically Z-butyne diol-1,4 and the preferred secondary brighteners may be sulfo-oxygen containing compounds, preferably saccharin.

The electroplating baths from which the micro-crack outer nickel plate may be deposited may contain an additive heterocyclic chemical compound having at least two nitrogen atoms in an otherwise carbocyclic ring structure. These heterocyclic compounds may be monocyclic, dicyclic, bicyclic, tricyclic, etc. although commonly they may be monocyclic. They may contain 2,3,4, etc. nitrogen atoms in an otherwise carbocyclic ring structure. Typical ring structures which may be employed may include: pyrazole (i.e. 1,2-diazole), 2-isoimidazole (i.e. 1,3-isodiazole), 1,2,3-tn'azole, 1,2,4-triazole, pyridazine (i.e. 1,2- diazine), pyrimidine (i.e. 1,3-diazine), pyrazine (i.e. 1,4- diazine), piperazine, s-triazine (i.e. 1,3-5-triazine), as-triazine (i.e. 1,2,4-triazine), v-triazine (i.e. 1,2,3-triazine), 1,5-pyrindine (i.e. 4-pyrindine), isoindazole (i.e. benzpyrazole), cinnoline (i.e. 1,2-benzodiazine), quinazoline (i.e. 1,3-benzodiazine), naphthyridine, pyrido[3,4-b]-pyridine, pyrido[3,2-b] pyridine, pyrido[4,3-b] pyridine, purine, hexamethylenetetramine, bis-pyridinium compounds, etc.

Inertly substituent compounds having the above ring structures may be employed; Typical inert substituents which may be borne by any of these rings may include inert hydrocarbon groups, typified by aromatic groups such as naphthyl, xylene, tolyl, or aliphatic groups typified by alkyl groups, methyl, ethyl, propyl, and butyl. The preferred substitutents may include lower alkyl, e.g., those having less than 5-6 carbon atoms; and these lower alkyl groups may be substituted on the carbon atoms present, on the nitrogen atoms present (e.g. 2,6 dimethyl pyrazine) or they may be present as bridging groups forming additional rings (as may be the case with 1:1 ethylene, 2:2'dipyridinium halides such as the dibromide or the dichloride). The additive heterocyclic compounds may have one or more of their nitrogen atoms quaternized as by reaction of the heterocyclic compound with hydrochloric acid, hydrobromic acid, sulfuric acid, etc.; in this latter instance, compounds otherwise of lesser utility because of their low solubility may be rendered substantially more soluble in quaternized form.

Typical illustrative compounds which may be employed in practice of this invention may be the following: s-triazine, u-triazine, v-triazine, pyridazine, pyrimidine, indole, isobenzazole, pyridine, isoindazole, cinnoline, quinazoline, naphthyridine, pyrido[3,4-b]-pyridine, pyrido- [3,2-b]-pyridine, pyrido[4,3-b]-pyridine, hexarnethylene tetramine, piperazine, pyrazine, 2,6-dimethyl pyrazine, etc.

Although it may be found that substantially improved results may be achieved in practice of the instant invention by using additive heterocyclic compounds falling within the above categories, outstandingly superior results may be achieved by use of the following specific illustrative compounds:

(I) hexamethylene tetramine (II) pyrazine (III) 2,6-dimethyl pyrazine These additive heterocyclic compounds may be present in the baths to produce the micro-crack outer nickel plate in eiiective amounts to which may typically be 0.1-0.8 g./l., typically about 0.25 g./l. Preferably the compound employed may be used in the form of its quaternized compound (i.e. at least one of the nitrogen atoms may be quaternized with e.g. hydrochloric acid or a hydrocarbon halide such as methyl chloride.

The preferred additive heterocyclic compound may be 1:1 ethylene 2:2 dipyridinium dichloride, typically available under the trademark Ortho di Quat.

Typical illustrative baths which may be used in this step of the process of this invention may contain the following:

TABLE X Components Minimum Maximum Preferred Ni 120 187 150 Nickel chloride -6H3O 225 150 Nickel fiuoborate 300 900 450 Primary brightener, e.g. butyne (1101 0. 002 0. 4 0. 2 Secondary brightener, e.g. saccharin- 0. 1 1 0. 25 Additive, e.g. lzlethylene 2:2dipyridinium dichloride 0. 1 0. 8 0. 25

TABLE XI Components Minimum Maximum Preferred Ni++ 187 Nickel chloride -6Hz0 110 225 150 Nickel fluoborate 300 900 450 Primary brightener, e.g. butyne diol 0. 002 0. 4 0. 2 Secondary brightener, e.g. sacoharin- 0. 1 1 0. 25 Additive compound, e.g. hexameth- 1 ylene tetramine 0. 1 0. 8 0. 25

TABLE XII Components Minimum Maximum Preferred Ni' 120 187 150 Nickel chloride -6H 110 225 150 Nickel fluoborate. 300 900 450 Primary brightener, e.g. butyne dioL 0. 002 0. 4 0. 2 Secondary brighteuer, e.g. saccharin. O. 1 1 0. 25 Additive compound, e.g. pyrazine 0. 1 0. 8 0. 25

Deposition of the micro-cracked nickel deposit or plate may be carried out at 40 C.-60 C., say 50 C. at pH of 2.5-4.5, say 3.5, for 2.4 minutes, say 2 minutes to permit attainment of a bright nickel plate having a thickness of at least about 0.6 micron, preferably 0.6-3 microns, say 1 micron.

It is a particular feature of the so-deposited nickel plate that it is characterized by its micro-cracked structure. Typically, when deposited in thicknesses of at least about 0.6 micron, and preferably 0.6-3 microns, say 1 micron, it is found that the deposit may contain at least about 10 cracks per cm., preferably about 100-600 cracks per cm., and typically about 250 cracks per cm. This micro-crack pattern at the noted thicknesses permits attainment of a bright to mirror-bright nickel plate which is characterized by its high resistance to corrosion as such.

It is a feature of this outer nickel plate that it may be mirror bright and when deposited in the manner hereinbefore set forth, may permit attainment of a highly leveled mirror bright surface particularly characterized by its ability to receive a chromium plate and which will permit attainment of a chromium plated composite having an unexpected degree of resistance to corrosion.

Chromium may be deposited on the bright nickel plate in accordance with the practice of the process of this invention 'by deposition from the chromium plate bath having the composition set forth in Table XIII.

TABLE XIII Components Minimum Maximum Preferred ClOa 250 400 250 80-4- 2. 5 4. 2.

Sulfate may be provided in the form of sodium sulfate or sulfuric acid. There may also be present in the chromium plating bath other ingredients typified by those which render the bath self-regulating or high speed. Typical of such other components in the bath may be strontium ion (provided in the form of strontium sulfate or strontium chloride) or SiF provided in the form of potassium silicofiuoride.

Chromium plating in accordance with the process of this invention may be carried out at 45 C.-55 0., say 50 C. for 2-4 minutes, say 3 minutes, with a cathode current density of 12-20 a.s.d. say 14 a.s.d. Typically this may permit attainment of a chromium plate having a thickness of 0.1-1.0 micron, say 0.25 micron.

It is a particularly outstanding feature of the novel product of this invention that it is extremely resistant to the effects of corrosive atmosphere over an extended period of time. It may be found, for example, that if a chromium plated product, prepared in accordance with the process of this invention, be subjected to severe corrosive conditions as, for example, in the CASS Test or Corrodkote Test, this novel product may unexpectedly exhibit substantially no visible corrosion at the end of three cycles of the test. Typical bright chromium plated deposits may, even under the most favorable conditions, exhibit a substantially noticeable degree of corrosion after the first cycle of the Corrodkote Test.

Practice of the novel process of the invention may be observed from the following illustrative examples wherein, unless otherwise indicated, all parts are parts by weight.

EXAMPLES In these examples unless otherwise specifically indicated, plating was carried out on a 1010 alloy steel basis metal plate having a thickness of about 1.5 mm. and dimensions of cm. x 15 cm.

In all cases, unless otherwise specified, the steel was given a normal cleaning cycle prior to further treating to remove rust spots, grease, oil, etc. No copper plate was applied to the steel before further treating.

Where a semi-bright nickel plate was deposited onto the clean steel basis metal, it was deposited from a nickel plating bath containing 45 g./l. of nickel chloride 8 6H O, 300 g./l. of nickel sulfate-6H O, 45 g./l. of boric acid, and 0.2 g./l. of 1,4-butyne diol with the electrometric pH maintained at about 3.5. Plating was carried out at cathode current density of 6 a.s.d. at 55 C. for 35 minutes to yield a deposit of semi-bright nickel having a thickness of 30 microns.

Where a bright nickel deposit is referred to in these examples, this was obtained by electrodeposition from a plating bath containing 60 g./l. of nickel chloride- 6H O, 300 g./l. of nickel sulfate-6H O, 40 g./l. of boric acid, and butyne diol as a primary brightener in amount of 0.2 g./l. saccharin as a secondary brightener in amount of 1 g./l., and butyne diol monosulphonate as a secondary auxiliary brightener in amount of 1 g./l. The bath was maintained at electrometric pH of 3.5 during the 10 minutes of electroplating at 55 C. to permit attainment of a bright nickel plate having a thickness of 7.5 microns.

Electrodeposition of the micro-cracked nickel plate in practice of this invention was carried out in these examples from a bath containing g./l. nickel chloride-6H O, 450 g./l. nickel fluoroborate, 0.2 g./l. of butyne diol primary brightener, 0.25 g./l of saccharin secondary brightener together with designated amounts, as hereinafter indicated, of additive heterocyclic compound. The bath was maintained at an electrometric pH of 4 and a temperature of 55 C. during the plating time which varied as hereinafter set forth to produce the thickness of plate.

Where decorative chromium plate is referred to, it was obtained by deposition from a bath containing 250 g./l. chromic acid and 25 g./l. of sulfate provided as sulfuric acid. Deposition for 1.25 minutes at cathode current density of 21.6 a.s.d. permitted attainment of a decorative chromium plate having a thickness of 0.25 micron. Here, as elsewhere, the abbreviation a.s.d. designates amperes per square decimeter.

Example 1 In this control example, the standard steel basis metal. panel was plated with bright nickel plate, and then chromium plated.

Example 2 In this example, which represents practice of a preferred embodiment of the process ofthis invention, the standard steel basis metal panel was plated with bright nickel plate, micro-crack nickel, for 2 minutes in a bath containing 0.25 g./l. hexamethylenetetramine, and then chromium plated.

Example 3 In this control example, the standard steel basis metal panel was plated with a bright nickel plate and then chromium plated.

Example 4 In this example, which represents a control, the standard steel basis metal panel was plated with semibright nickel plate, bright nickel plate, and chromium.

Example 5 In this example, which represents practice of a preferred embodiment of the process of this invention, the standard steel basis metal panel was plated with semibright nickel plate, micro-crack nickel, for 2 minutes in a bath containing 0.25 g./l. of hexamethylenetetramine and then chromium plated.

Example 6 In this example, which represents a control, the standard steel basis metal panel was plated with semi-bright nickel plate and chromium.

Example 7 In this example, which represents practice of a preferred embodiment of the process of this invention, the

.9 standard steel basis metal panel was plated with semibright nickel plate, micro-crack nickel, and chromium. The micro-crack nickel was plated from a bath containing 0.25 g./l. of lzl'ethylene, 2:2'dipyridinium-dichloride for 2 minutes to yield a plate 1.0 micron thick. Each of the steel basis metal panels of these examples was subjected to the standard CASS Test hereinbefore detailed. The test was carried out by maintaining each panel under test conditions as noted in Table XIII and after the test the surface was examined for basis metal corrosion. in Examples 6 and 7, the test used was the Corrodkote Test.

TABLE XIV Inspection of the samples at the end of the three cycles of the test indicated that the control samples of Examples 1, 3, 4 and 6 were heavily corroded, all of the other specimens showed substantially no corrosion. Panels of Examples 2, 5, and 7 indicated a high resistance to corrosion under the test conditions and showed a minimum number of surface imperfections. The panel of Example showed a highly outstanding resistance to corrosion; in fact, at the conclusion of the very severe test, they were substantially identical in brightness to examples before the test.

Comparison of Example 4 (which is typical of prior art chromium plated duplex nickel) with Examples 2, 5, and 7 (which are illustrative of the process of this invention) clearly demonstrates the superiority of the novel process of this invention.

Thus from Table XIII it will be apparent that the novel process of this invention permits attainment of a chromium plate product which is characterized by its unexpectedly high resistance to corrosion. It will be particularly apparent that the panels prepared in accordance with the preferred embodiments of the process of this invention (Example 2) are particularly outstanding.

Although this invention has been disclosed by reference to preferred illustrative examples, it will be apparent to those skilled-in-the-art that various modifications and changes may be made thereto which fall within the scope of this invention.

We claim:

1. The process for preparing a nickel surface characterized by its ability to receive a chromium plate possessing a high degree of corrosion resistance which comprises electrodepositing onto a basis metal a first nickel plate; immersing said first nickel plate into an aqueous bath containing about 120-187 g./l. Ni+ 110-125 g./l.

NiCl -6H O and 300-900 g./l. Ni(BF and electrodepositing at least 0.6 micron of an outer microcracked nickel plate from said bath.

2. The process as claimed in claim 1 for preparing a nickel surface characterized by its ability to receive a chromium plate possessing a high degree of corrosion resistance wherein said outer nickel plate is deposited from said electroplating bath containing, as brightener, an effective amount of an additive heterocyclic compound having at least two nitrogen atoms in an otherwise carbocyclic ring structure.

3. The process as claimed in claim 1 for preparing a nickel surface characterized by its ability to receive a chromium plate possessing a high degree of corrosion resistance wherein said outer nickel plate isdeposited from said electroplating bath containing, as brightener, an eifective amount of an additive heterocyclic compound selected from the group consisting of hexamethylene tetramine, piperazine, pyrazine, 2,6 -dimethyl pyrazine, and lzl'ethylene 2:2 dipyridinium dichloride.-

4. The process as claimed in claim 1 for preparing-a nickel surface characterized byits'ability to receive-a chromium plate possessing a high degree of corrosion resistance wherein said outer nickel plate is deposited from said electroplating bath containing, as brightener, an effective amount of an additive heterocyclic compound 1:l' ethylene 2:2 di-pyridinium dichloride.

5. The process as claimed in claim 1 for preparing a nickel surface characterized by its ability to receive a chromium plate possessing a high degree of corrosion resistance wherein said first nickel plate is a sulfur-free semi-bright nickel plate.

6. The process as claimed in claim 1 for preparing a nickel surface characterized by its ability to receive a chromium plate possessing a high degree of corrosion resistance wherein said first nickel plate is a bright nickel plate.

7. The process as claimed in claim 1 for preparing a nickel surface characterized by its ability to receive a chromium plate possessing a high degree of corrosion resistance wherein said first nickel plate includes a layer of sulfur-free semi-bright nickel plate under a layer of bright nickel plate.

8. The process for preparing a nickel surface characterized by its ability to receive a chromium plate posessing a high degree of corrosion resistance which comprises electrodepositing onto a basis metal a first nickel plate; immersing said first nickel plate as cathode into an aqueous electroplating bath containing 120-187 g./l. Ni++, -225 g./l. NiCl -6H O, 300-900 g./l. Ni(BF.,) primary brightener, secondary brightener, and, as brightener, an effective amount of an additive heterocyclic compound having at least two nitrogen atoms in an otherwise carbocyclic ring structure; maintaining an anode in said bath; passing current between said anode and said cathode and depositing on said cathode an outer microcracked nickel plate having a thickness of at least about 0.6 micron.

9. The process as claimed in claim 8 for preparing a nickel surface characterized by its ability to receive a chromium plate possessing a high degree of corrosion resistance wherein said additive heterocyclic compound is present in amount of 0.1-0.8 g./l.

10. The process as claimed in claim 9 for preparing a nickel surface characterized by its ability to receive a chromium plate possessing a high degree of corrosion resistance wherein said additive heterocyclic compound is selected from the group consisting of hexamethylene tctramine, piperazine, pyrazine, 2,6-dimethyl pyrazine, and 1:1 ethylene 2:2 dipyridinium dichloride.

11. The process as claimed in claim 10 for preparing a nickel surface characterized by its ability to receive a chromium plate possessing a high degree of corrision resistance wherein said heterocyclic compound is 1:1' ethylene 2:2 dipyridi-nium dichloride.

12. The process for preparing a nickel surface characterized by its ability to receive a chromium plate possessing a high degree of corrosion resistance which comprises electrodepositing onto a basis metal a first sulfurcontaining bright nickel plate; and immersing said first nickel plate as cathode into an aqueous electroplating bath containing -187 g./l. Ni++, 110-225 g./l. NiCl -6H 0, 300-900 g./l. Ni(BF primary brightener, secondary brightener, and 0.1-0.8 g./l. of an additive selected from the group consisting of hexamethylene tetramine, piperazine, pyrazine, and 2,6-dimethyl pyrazine; maintaining an anode in said bath; passing current between said anode and cathode and depositing on 3,474,010 11 I ,7 T 12 s'i dw'ithode in-utf microcracked nickel plate "having JOHN H. MACK, Primai'il Examiner i i 9 legs? about 0 G. L. KAPLAN, Assistant Examiner References Cite U'NITED'STATES'PATENTS i .,3*388,Q49,- 6/1968 De Castelet 204-41XR 9- ,,4 3,408,272 10/1968 Such et a1. 204L 11 XR