CN112239876A

CN112239876A - Functional chromium alloy plating from trivalent chromium electrolytes

Info

Publication number: CN112239876A
Application number: CN202010685421.8A
Authority: CN
Inventors: V·伊杰里; S·P·盖多斯; S·莫汗
Original assignee: Boeing Co
Current assignee: Boeing Co
Priority date: 2019-07-18
Filing date: 2020-07-16
Publication date: 2021-01-19
Also published as: US20210017659A1; JP2021036073A; CA3084881A1; AU2020205312A1; EP3767012A1

Abstract

The present invention relates to functional chromium alloy plating from trivalent chromium electrolytes. In particular, the invention provides electrolyte solutions for electrodepositing ferrochromium and methods of electrodepositing ferrochromium. The electrolyte solution for electroplating may contain trivalent chromium salts, oxalate compounds, iron salts, aluminum sulfate, alkali metal sulfates, and alkali metal halides. The electrolyte solution may be formed by dissolving a trivalent chromium salt, an oxalate compound, an iron salt, aluminum sulfate, an alkali metal sulfate, and an alkali metal halide in water or an aqueous solution. Electrodepositing a ferrochrome alloy on a substrate may include introducing a cathode and an anode into an electrolyte solution comprising a trivalent chromium salt, an oxalate compound, an iron salt, aluminum sulfate, an alkali metal sulfate, and an alkali metal halide. Electrodeposition may also include passing an electric current between the anode and the cathode through the electrolyte solution to deposit chromium and iron on the cathode.

Description

Functional chromium alloy plating from trivalent chromium electrolytes

Technical Field

The invention provides electrolyte solutions for electrodepositing chromium alloys, methods of forming electrolyte solutions, and methods of electrodepositing chromium alloys.

Background

Chrome plating is an electroplating process that provides a chromium coating on a substrate. Hard chrome plating provides a chrome coating layer typically having a thickness of about 10 microns or more, thereby providing hardness and wear resistance to the coated substrate. Another type of chromium plating is decorative chromium plating which provides a chromium coating typically having a thickness of about 0.1 to about 0.5 microns. Chromium plating is generally carried out using a bath (bath) containing chromic acid and a catalyst based on fluorides, sulfates or organic acids. Chromic acid has the hexavalent form of chromium, chromium (VI), which is environmentally less preferred and expensive to dispose of.

Trivalent chromium, which has good properties and lower waste disposal costs, is a replacement for hexavalent chromium. Trivalent chromium has been applied with some success over thin decorative coatings, but thicker or functional coatings are still difficult to achieve. In addition, trivalent chromium-based baths for decorative plating usually contain boric acid as a buffering agent.

Thus, there is a need for improved chromium plating processes and formulations of solutions for chromium plating.

Disclosure of Invention

At least one electrolyte solution for electroplating comprises a trivalent chromium salt, an oxalate compound, an iron salt, aluminum sulfate, an alkali metal sulfate, and an alkali metal halide.

At least one electrolyte solution for electroplating comprises a trivalent chromium salt in an amount from about 0.3mol/L to about 0.9mol/L of the electrolyte solution. The electrolyte solution also includes an oxalate compound in an amount of about 0.2mol/L to about 1.2mol/L of the electrolyte solution. The electrolyte solution further comprises an iron salt in an amount of about 0.005mol/L to about 0.2mol/L of the electrolyte solution. The electrolyte solution also includes aluminum sulfate in an amount of about 0.05mol/L to about 0.5 mol/L. The electrolyte solution further comprises an alkali metal sulfate in an amount of about 0.1mol/L to about 2.0mol/L of the electrolyte solution. The electrolyte solution also includes an alkali metal halide in an amount of about 0.1mol/L to about 0.5mol/L of the electrolyte solution.

The present invention provides at least one method of plating chromium on a substrate using an electrolyte solution. The method includes dissolving a trivalent chromium salt in an amount of from about 0.3mol/L to about 0.9mol/L of the electrolyte solution in an aqueous medium. The method also includes dissolving the oxalate compound in an amount of about 0.2mol/L to about 1.2mol/L of the electrolyte solution. The method also includes dissolving an amount of the iron salt of about 0.005mol/L to about 0.2mol/L of the electrolyte solution. The process further includes dissolving aluminum sulfate in an amount of about 0.05mol/L to about 0.5 mol/L. The method also includes dissolving an amount of alkali metal sulfate from about 0.1mol/L to about 2.0mol/L of the electrolyte solution. The method also includes dissolving the alkali metal halide in an amount of about 0.1mol/L to about 0.5mol/L of the electrolyte solution. The method further includes passing an electric current between the anode and the cathode through the electrolyte solution to deposit the ferrochrome alloy on the substrate.

The present invention provides at least one method of plating chromium on a substrate using an electrolyte solution. The method includes introducing a cathode and an anode into an electrolyte solution comprising a trivalent chromium salt, an oxalate compound, an iron salt, aluminum sulfate, an alkali metal sulfate, and an alkali metal halide. The method further comprises passing an electric current between the anode and the cathode through the electrolyte solution to deposit a ferrochrome layer on the substrate.

The present invention provides at least one substrate comprising a ferrochrome coating. The chromium-iron alloy coating has a chromium content of about 40 wt.% to about 90 wt.%, an iron content of about 8 wt.% to about 18 wt.%, and a carbon content of about 5 wt.% to about 50 wt.%.

The features, functions, and advantages that have been discussed can be achieved independently in various aspects or may be combined in yet other aspects, further details of which can be seen with reference to the following description and drawings.

Drawings

So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to aspects, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical aspects of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective aspects.

FIG. 1 is a flow diagram illustrating a method of forming an electrolyte solution according to one or more aspects of the present disclosure;

FIG. 2 is a flow diagram illustrating a method of forming a chromium alloy coating on a substrate by electrodeposition in accordance with one or more aspects of the present invention;

FIG. 3 is an image of a ferrochrome plated substrate formed by the method of FIG. 2, each substrate being plated at a different current density;

FIG. 4 is an image of a ferrochrome plated substrate formed by the method of FIG. 2, each substrate being plated at a different pH;

FIG. 5 is an image of a ferrochrome plated substrate formed by the method of FIG. 2, each substrate being plated at a different current density;

FIG. 6 is an image of a ferrochrome plated substrate formed by the method of FIG. 2, each substrate being plated at a different pH;

FIG. 7 is an image of a ferrochrome plated substrate formed by the method of FIG. 2, each substrate being plated at a different current density;

FIG. 8 is an image of a ferrochrome plated substrate formed by the method of FIG. 2, each substrate being plated at a different pH;

FIG. 9 is an image of a ferrochrome plated substrate formed by the method of FIG. 2, each substrate being plated at a different temperature.

To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. Additionally, elements of one aspect may be advantageously adapted for utilization in other aspects described herein.

Detailed Description

In accordance with aspects of the present invention, methods and formulations are provided for plating chromium on a substrate using direct current and boric acid-free chromium solutions while still forming a structurally robust, cost-effective chromium layer (e.g., a chromium coating) on the substrate. Thus, the methods and formulations described herein may be advantageously used for hard chrome plating to form a hard chrome layer (e.g., a robust functional chrome layer greater than 10 microns). However, the present invention is not limited to hard chrome plating, and the methods and formulations described herein may also be advantageously used to effectively and efficiently perform decorative chrome plating, forming a decorative chrome layer (e.g., a chrome layer ranging from 0.25 microns to 1.0 microns).

The invention also provides electrolyte solutions for electrodepositing ferrochrome and methods of forming ferrochrome. In at least one aspect, the electrolyte solution of the present invention is aqueous. In at least one aspect, the electrolyte solution comprises an iron salt, such as ferrous sulfate or ferric chloride. It has been found that the presence of one or more of these iron salts in the electrolyte solution provides for the deposition of a thick ferrochrome layer on a substrate (e.g., a steel substrate) without the use of hexavalent chromium and pulse plating. The electrolyte solution of the present invention further contains a complexing agent such as an oxalate compound (e.g., sodium oxalate) that forms a complex with trivalent chromium ions as well as ferrous iron ions.

The electrolyte solution of the present invention provides controlled deposition of ferrochrome on the substrate. In at least one aspect, the substrate is a steel substrate, a copper substrate, a brass substrate, a copper-coated substrate, a nickel-coated substrate, or other metal or metal alloy containing substrate. In at least one aspect, the electrolyte solutions of the present invention provide satisfactory hard ferrochrome deposits, which are considered comparable to conventional hexavalent chromium-based coatings, when used at a pH of about 2 to about 4 at a temperature of about 30 ℃ to about 60 ℃. In at least one aspect, the ferrochrome alloy of the present invention has an iron content of from about 1% by weight iron to about 20% by weight iron, based on the total weight of chromium and iron in the alloy.

The ferrochrome coating of the present invention may provide a substrate, such as a steel substrate, having hardness and wear resistance similar to conventional hexavalent hard chrome plated substrates. The ferrochrome alloy of the present invention may be placed in aircraft, spacecraft, watercraft, engines and flaps, parts of exhaust erosion structures, warm structural parts for high performance supersonic, hypersonic and space re-loader structures, automotive parts, building structures (e.g., steel bridges) and propulsion structures (e.g., power turbines, vehicle engines, energy utility alternatives and related technologies). As a specific example, the alloy of the present invention may be placed on a steel landing gear and/or the underside of an aircraft.

In at least one aspect, the ferrochrome coating of the present invention is formed using a single plating bath technique. The deposition vessel was a laboratory-scale glass beaker or a large polypropylene tank for commercial-scale plating. In at least one aspect, the deposition vessel contains an electrolyte solution prepared by: all the components of the electrolyte solution are mixed simultaneously, or in a stepwise manner, the chromium salt and the complexing agent are first mixed, followed by the iron salt. As described in more detail below, an anode (e.g., graphite) is introduced into a beaker containing an electrolyte solution. The application of direct current regulates the deposition process which forms the ferrochrome coating. The thickness of the ferrochrome coating may be controlled by the duration of the direct current applied to the electrolyte solution electrodes. In at least one aspect, the total thickness of the ferrochrome coating is from about 1 micron to about 100 microns, such as from about 10 microns to about 50 microns, such as from about 20 microns to about 40 microns, such as about 30 microns.

Variations in the thickness and composition of the ferrochrome coating may be controlled by the current density and time range of the deposition process of the present invention.

The electrolyte solution of the present invention contains a metal salt. As used herein, a metal salt may include anhydrous and/or hydrate forms of the metal salt. In at least one aspect, the metal salt comprises one or more of a trivalent chromium salt and an iron salt. The electrolyte solution of the present invention also includes at least one complexing agent, such as an alkali metal oxalate compound, e.g., sodium oxalate or potassium oxalate. Complexing agents, such as alkali metal oxalate compounds, coordinate iron ions in the electrolyte solution and promote controlled iron deposition on the substrate when a current density is applied to the electrolyte solution.

The electrolyte solution of the present invention also includes at least one buffering agent, such as an aluminum salt, e.g., aluminum sulfate or aluminum halide. As described in more detail below, the buffers of the present invention maintain the desired pH of the electrolyte solution and do not substantially interfere with chromium and iron deposition on the substrate.

The electrolyte solution of the present invention further comprises at least one ionic conductivity control agent, such as an alkali metal salt, for example sodium sulfate or potassium sulfate. The ionic conductivity control agents of the present invention maintain the desired conductivity of the electrolyte solution and do not substantially interfere with chromium and iron deposition on the substrate.

The electrolyte solution of the present invention further comprises at least one alkali metal halide, such as sodium fluoride or potassium fluoride. The alkali metal halides of the present invention provide wetting and etching properties to the electrolyte solution and may aid in chromium adhesion during chromium plating.

Optionally, the electrolyte solution of the present invention further comprises at least one surfactant, such as sodium lauryl sulfate, sodium lauryl ether sulfate, or potassium lauryl sulfate. The surfactant of the present invention reduces pitting and gas generation during chromium plating.

In at least one aspect, the electrolyte solution of the present invention has a pH of from about 1 to about 6, for example from about 1.5 to about 4, for example a pH of 2 or 4. In at least one aspect, one or more bases (e.g., sodium hydroxide (NaOH) solution) are added to increase the pH of the solution or one or more acids (e.g., sulfuric acid (H) is added₂SO₄) Solution) to reduce the pH of the solution, thereby controlling the pH of the electrolyte solution of the present invention. Chromium salts, iron salts, complexing agents, buffers, acids and bases may be obtained from any suitable commercial source, for example, from MERCK-India or Sigma-Aldrich Co.LLC of St.Louis, Mo.

Fig. 1 is a flow diagram illustrating a method 100 of forming an electrolyte solution in accordance with one or more aspects of the present invention. As shown in fig. 1, at operation 110, the method 100 includes dissolving a trivalent chromium salt in a medium (e.g., water or an aqueous solution) to form a first electrolyte solution. Trivalent chromium salts are a source of trivalent chromium. In at least one aspect, the trivalent chromium salt includes a chromium (III) halide, chromium (III) sulfate (e.g., Cr₂(SO₄)₃、Cr₂(SO₄)₃·12H₂O and/or other chromium (III) sulfates) and/or other chromium (III) salts. For example, the chromium (III) halide can include chromium (III) chloride (e.g., CrCl)₃、CrCl₃·5H₂O、CrCl₃·6H₂O and/or other chromium (III) chloride).

In at least one aspect, the concentration of the trivalent chromium salt in the electrolyte of the present invention is from about 0.1 moles per liter (mol/L) to about 1mol/L of the electrolyte solution, such as from about 0.3mol/L to about 0.9mol/L, such as from about 0.2mol/L to about 0.7mol/L, such as from about 0.4mol/L to about 0.7mol/L of the electrolyte solution, such as from about 0.5mol/L to about 0.6 mol/L. In at least one aspect, the amount of dissolved trivalent chromium salt is about 0.1mol/L, 0.2mol/L, 0.3mol/L, 0.4mol/L, 0.5mol/L, 0.6mol/L, 0.7mol/L, 0.8mol/L, 0.9mol/L, or 1mol/L of the electrolyte solution, where any value can constitute an upper endpoint or a lower endpoint as desired. At concentrations above 1mol/L, it may become difficult to dissolve the trivalent chromium salt in the electrolyte, leading to solubility problems.

In at least one aspect, the trivalent chromium salt is dissolved by stirring at ambient temperature, at room temperature, at about 25 ℃, or at a temperature of about 10 ℃ to about 40 ℃ (e.g., about 20 ℃ to about 30 ℃). In at least one aspect, the temperature at which operation 110 is performed can be about 10 ℃, 15 ℃, 20 ℃, 25 ℃, 30 ℃, 35 ℃, or 40 ℃, any of which can constitute an upper endpoint or a lower endpoint as desired. In at least one aspect, the stirring can be carried out for about 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, or 30 minutes, any of which can be configured as an upper endpoint or a lower endpoint as desired, or until all of the trivalent chromium salt has dissolved.

At operation 120, the method 100 further includes dissolving the oxalate compound in, for example, water or an aqueous solution (e.g., a first solution) to form an electrolyte solution, e.g., a second electrolyte solution. Oxalate compounds include oxalates that can function as complexing agents. In at least one aspect, the oxalate compound includes an alkali metal oxalate (e.g., sodium oxalate (Na)₂C₂O₄) Potassium oxalate (K)₂C₂O₄) And/or other alkali metal oxalates) and/or acids of oxalates (e.g., oxalic acid (H)₂C₂O₄) And/or oxalate salts).

In at least one aspect, the oxalate compound in the electrolyte of the invention is at a concentration of from about 0.1mol/L to about 2.0mol/L of electrolyte solution, such as from about 0.2mol/L to about 1.2mol/L, from about 0.1mol/L to about 0.9mol/L, such as from about 0.2mol/L to about 0.7mol/L, such as from about 0.4mol/L to about 0.7mol/L of electrolyte solution, such as from about 0.5mol/L to about 0.6 mol/L. In at least one aspect, the amount of oxalate compound dissolved is about 0.1mol/L, 0.2mol/L, 0.4mol/L, 0.6mol/L, 0.8mol/L, 1.0mol/L, 1.2mol/L, 1.4mol/L, 1.6mol/L, 1.8mol/L, or 2.0mol/L of the electrolyte solution, where any value can constitute an upper endpoint or a lower endpoint as desired.

In at least one aspect, to dissolve the oxalate compound and form a complex of oxalate and trivalent chromium, the oxalate compound is placed in a solution (e.g., a solution resulting from operation 110 or another operation performed prior to operation 120), the solution may be heated to an elevated temperature of about 70 ℃ to about 80 ℃, and the solution may be stirred for about 1 hour to about 3 hours. In at least one aspect, the solution is cooled (e.g., to ambient temperature, to room temperature, to a temperature of about 25 ℃, or to a temperature of about 20 ℃ to about 30 ℃). Alternatively, the oxalate compound may be dissolved without heating, in which case a complex of oxalate and trivalent chromium is formed in 3 to 4 days. Advantageously, heating the solution to a temperature of about 70 ℃ to about 80 ℃ at operation 120 may allow for faster preparation of the electrolyte solution. In at least one aspect, the stirring is carried out for about 1 hour, 1 hour 15 minutes, 1 hour 30 minutes, 1 hour 45 minutes, 2 hours 15 minutes, 2 hours 30 minutes, 2 hours 45 minutes, or 3 hours, any of which can constitute an upper endpoint or a lower endpoint as desired. Further, in at least one aspect, the temperature at which operation 120 is performed can be about 50 ℃, 55 ℃, 60 ℃, 65 ℃, 70 ℃, 75 ℃, or 80 ℃, any of which can constitute an upper endpoint or a lower endpoint as desired.

At operation 130, the method 100 further includes dissolving the iron salt, such as in water or an aqueous solution (e.g., the second electrolyte solution), to form an electrolyte solution (e.g., the third electrolyte solution). In at least one aspect, the iron salt is a ferrous salt, a ferric salt, or a combination thereof. In at least one aspect, the iron salt is ferrous sulfate heptahydrate, ferric chloride, or a combination thereof. In at least one aspect, the iron salt is a divalent iron salt. In at least one aspect, the ferrous salts Include Iron (II) sulfate, iron (II) chloride, iron (II) acetate, and/or other ferrous salts. Each of these ferrous salts may include its respective hydrated form. For example, iron (II)Having the formula FeSO₄·xH₂O, where x is an integer (e.g., 0, 1, 2, 4, 5, 6, or 7). Thus, in at least one aspect, iron (II) sulfate is anhydrous iron (II) sulfate, iron (II) sulfate monohydrate, iron (II) sulfate dihydrate, iron (II) sulfate tetrahydrate, iron (II) sulfate pentahydrate, iron (II) sulfate hexahydrate, iron (II) sulfate heptahydrate, or iron (II) sulfate with other hydration states. In at least one aspect, the iron salt is a ferric salt. In at least one aspect, the ferric salts include iron (III) sulfate, iron (III) chloride, iron (III) acetate, and/or other ferric salts. Each of these ferric salts may include its respective hydrated form. For example, iron (III) sulfate has the formula Fe₂(SO₄)₃·xH₂O, where x is an integer (e.g., 0, 1, 2, 4, 5, 6, or 7). Thus, in at least one aspect, iron (III) sulfate is anhydrous iron (III) sulfate, iron (III) sulfate monohydrate, iron (III) sulfate dihydrate, iron (III) sulfate tetrahydrate, iron (III) sulfate pentahydrate, iron (III) sulfate hexahydrate, iron (III) sulfate heptahydrate, or iron (III) sulfate with other hydration states. In one other example, iron (III) chloride has the formula FeCl₃·xH₂O, where x is an integer (e.g., 0, 1, 2, 4, 5, 6, or 7). Thus, in at least one aspect, the iron (III) chloride is anhydrous iron (III) chloride, iron (III) chloride monohydrate, iron (III) chloride dihydrate, iron (III) chloride tetrahydrate, iron (III) chloride pentahydrate, iron (III) chloride hexahydrate, iron (III) chloride heptahydrate, or iron (III) chloride with other hydration states.

In at least one aspect, the concentration of the iron salt in the electrolyte of the present invention is from about 0.005mol/L to about 0.2mol/L of the electrolyte solution, such as from about 0.01mol/L to about 0.2mol/L, such as from about 0.02mol/L to about 0.2mol/L of the electrolyte solution, such as from about 0.1mol/L to about 0.2 mol/L. In at least one aspect, the amount of dissolved iron salt is about 0.005mol/L, 0.01mol/L, 0.02mol/L, 0.03mol/L, 0.04mol/L, 0.05mol/L, 0.06mol/L, 0.07mol/L, 0.08mol/L, 0.09mol/L, 0.1mol/L, or 0.2mol/L of the electrolyte solution, wherein any value can constitute an upper endpoint or a lower endpoint as desired. The inventors have found that at concentrations above 0.2mol/L the deposited ferrochrome coating becomes soft and also more susceptible to corrosion.

In at least one aspect, the iron salt is dissolved by stirring at ambient temperature, at room temperature, at a temperature of about 25 ℃, or at a temperature of about 20 ℃ to about 30 ℃. In at least one aspect, the stirring is carried out for about 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, or 30 minutes, any of which can be configured as an upper endpoint or a lower endpoint as desired, or until all of the iron salt has dissolved. In at least one aspect, the temperature at which operation 130 is performed can be about 10 ℃, 15 ℃, 20 ℃, 25 ℃, 30 ℃, 35 ℃, or 40 ℃, any of which can constitute an upper endpoint or a lower endpoint as desired.

At operation 140, the method 100 further includes dissolving the iron salt, such as in water or an aqueous solution (e.g., a third electrolyte solution), to form an electrolyte solution (e.g., a fourth electrolyte solution). Metal salts are metal ion sources that dissolve to provide metal ions, such as aluminum ions, due to the high valence state of the metal ions in solution (e.g., Al)³⁺) Which can act as a buffer and can provide ionic strength. In at least one aspect, the metal salt includes a group 13 metal salt such as an aluminum salt (e.g., aluminum sulfate (Al)₂(SO₄)₃) Aluminum halides such as aluminum chloride (AlCl)₃) And/or other aluminum salts) and/or other metal salts.

In at least one aspect, the concentration of the metal salt in the electrolyte of the present invention is from about 0.01mol/L to about 1.0mol/L of the electrolyte solution, such as from about 0.05mol/L to about 0.8mol/L, such as from about 0.1mol/L to about 0.7mol/L, such as from about 0.2mol/L to about 0.5mol/L of the electrolyte solution, such as from about 0.2mol/L to about 0.3 mol/L. In at least one aspect, the amount of dissolved metal salt is about 0.01mol/L, 0.05mol/L, 0.1mol/L, 0.2mol/L, 0.3mol/L, 0.4mol/L, 0.5mol/L, 0.6mol/L, 0.8mol/L, or 1.0mol/L of the electrolyte solution, where any value can constitute an upper endpoint or a lower endpoint as desired. At concentrations above 1.0mol/L, it may become difficult to dissolve the metal salt in the electrolyte, leading to solubility problems.

In at least one aspect, the iron salt is dissolved by stirring at ambient temperature, at room temperature, at a temperature of about 25 ℃, or at a temperature of about 20 ℃ to about 30 ℃. In at least one aspect, the stirring is carried out for about 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, or 30 minutes, any of which can be configured as upper or lower endpoints as desired, or until all of the metal salt has dissolved. In at least one aspect, the temperature at which operation 140 is performed can be about 10 ℃, 15 ℃, 20 ℃, 25 ℃, 30 ℃, 35 ℃, or 40 ℃, any of which can constitute an upper endpoint or a lower endpoint as desired.

At operation 150, the method 100 further includes dissolving the alkali metal salt, such as in water or an aqueous solution (e.g., a fourth electrolyte solution), to form an electrolyte solution (e.g., a fifth electrolyte solution). The alkali metal salt can improve the conductivity of the electrolyte solution. In at least one aspect, the alkali metal salt comprises an alkali metal sulfate (e.g., sodium sulfate (Na)₂SO₄) Potassium sulfate (K)₂SO₄) And/or other alkali metal sulfates).

In at least one aspect, the concentration of alkali metal salt in the electrolyte of the present invention is from about 0.1mol/L to about 2.0mol/L, such as from about 0.5mol/L to about 2.0mol/L, such as from about 1.0mol/L to about 1.5mol/L, such as from about 1.3mol/L to about 1.4 mol/L. In at least one aspect, the amount of oxalate compound dissolved is about 0.1mol/L, 0.2mol/L, 0.4mol/L, 0.6mol/L, 0.8mol/L, 1.0mol/L, 1.2mol/L, 1.4mol/L, 1.6mol/L, 1.8mol/L, or 2.0mol/L of the electrolyte solution, where any value can constitute an upper endpoint or a lower endpoint as desired. At concentrations above 2.0mol/L, it may become difficult to dissolve the alkali metal salt in the electrolyte, leading to solubility problems.

In at least one aspect, the alkali metal salt is dissolved by stirring at ambient temperature, at room temperature, at about 25 ℃, or at a temperature of about 10 ℃ to about 40 ℃ (e.g., about 20 ℃ to about 30 ℃). In at least one aspect, the temperature at which operation 150 is performed can be about 10 ℃, 15 ℃, 20 ℃, 25 ℃, 30 ℃, 35 ℃, or 40 ℃, any of which can constitute an upper endpoint or a lower endpoint as desired. In at least one aspect, stirring can be carried out for about 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, or 30 minutes, any of which can be configured as upper or lower endpoint as desired, or until all of the alkali metal salt has dissolved. In at least one aspect, the alkali metal salt is stirred at ambient temperature, at room temperature, at about 25 ℃ for 15 minutes.

At operation 160, the method 100 further includes dissolving the alkali metal halide, such as in water or an aqueous solution (e.g., a fifth solution), to form an electrolyte solution (e.g., a sixth electrolyte solution). The alkali metal halide can provide wetting and corrosion properties to the electrolyte solution and can aid in the adhesion of chromium during the chromium plating process. In at least one aspect, the alkali metal halide includes an alkali metal fluoride (e.g., sodium fluoride (NaF), potassium fluoride (KF), and/or other alkali metal fluorides) and/or other alkali metal halides.

In at least one aspect, the concentration of the alkali metal halide in the electrolyte of the present invention is from about 0.1mol/L to about 1.0mol/L, such as from about 0.1mol/L to about 0.5mol/L, such as from about 0.2mol/L to about 0.5mol/L, such as from about 0.3mol/L to about 0.4 mol/L. In at least one aspect, the amount of oxalate compound dissolved is about 0.1mol/L, 0.2mol/L, 0.3mol/L, 0.4mol/L, 0.5mol/L, 0.6mol/L, 0.8mol/L, or 1.0mol/L of the electrolyte solution, where any value can constitute an upper endpoint or a lower endpoint as desired. At concentrations above 1.0mol/L, it may become difficult to dissolve the alkali metal halide in the electrolyte, leading to solubility problems.

In at least one aspect, the alkali metal halide is dissolved by stirring at ambient temperature, at room temperature, at about 25 ℃, or at a temperature of about 10 ℃ to about 40 ℃ (e.g., about 20 ℃ to about 30 ℃). In at least one aspect, the temperature at which operation 160 is performed can be about 10 ℃, 15 ℃, 20 ℃, 25 ℃, 30 ℃, 35 ℃, or 40 ℃, any of which can constitute an upper endpoint or a lower endpoint as desired. In at least one aspect, the stirring can be carried out for about 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, or 30 minutes, any of which can be configured as an upper endpoint or a lower endpoint as desired, or until all of the alkali metal halide has dissolved. In at least one aspect, the alkali metal halide is stirred at ambient temperature at room temperature for 15 minutes at about 25 ℃.

Optionally, at operation 170, the method 100 further includes dissolving a surfactant in the surfactant solutionsSuch as water or an aqueous solution (e.g., a sixth electrolyte solution) to form an electrolyte solution (e.g., a seventh electrolyte solution). The surfactant can prevent or reduce pitting corrosion and reduce gas generation (e.g., chlorine, hydrogen, etc.) during the chromium plating process. In at least one aspect, the surfactant comprises sodium lauryl sulfate (NaC)₁₂H₂₅SO₄) Sodium lauryl ether sulfate (CH)₃(CH₂)₁₁(OCH₂CH₂)_nOSO₃Na), potassium lauryl sulfate (KC)₁₂H₂₅SO₄) And/or other surfactants.

In at least one aspect, the concentration of the surfactant in the electrolyte of the present invention is from about 0.0001mol/L to about 0.01 mol/L. In at least one aspect, the amount of dissolved surfactant can be about 0.0001mol/L, 0.0002mol/L, 0.0004mol/L, 0.0006mol/L, 0.0008mol/L, 0.0010mol/L, 0.0020mol/L, 0.0040mol/L, 0.0060mol/L, 0.0080mol/L, or 0.0100mol/L of the electrolyte solution, where any value can constitute an upper endpoint or a lower endpoint as desired. For example, in at least one aspect, the amount of sodium lauryl sulfate, sodium lauryl ether sulfate, or potassium lauryl sulfate per liter of electrolyte solution is about 0.1g to about 1 g. At concentrations above 0.01mol/L, the surfactant can cause excessive foaming and uneven deposition of the plating solution.

Optionally, at operation 180, the method 100 further includes using one or more of aqueous acid or aqueous base (e.g., potassium hydroxide (KOH), sodium hydroxide (NaOH), and sulfuric acid (H)₂SO₄) Adjusting the pH of the electrolyte solution. The volume of the aqueous acid or aqueous alkaline solution added to the electrolyte solution is sufficiently small that the concentration of other components of the electrolyte solution (complexing agents, buffers, etc.) is not substantially affected. Alternatively, solid potassium hydroxide and/or solid sodium hydroxide is added directly to the electrolyte solution and/or concentrated sulfuric acid is added directly to the electrolyte solution. In at least one aspect, the pH of the electrolyte solution is adjusted to a target pH of about 1 to about 7, such as about 1 to about 5, such as about 1.5 to about 4, such as 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, or 5. In at least one aspect, electricity of the invention is conditioned prior to passing an electric current through an electrolyte solutionThe pH of the electrolyte solution (as described in more detail below). In at least one aspect, the pH of the electrolyte solution of the present invention is maintained at a target pH or target pH range during passing a current through the electrolyte solution.

Optionally, at operation 190, a time to reach an equilibrium state is provided. In at least one aspect, the solution is allowed to stand for a period of 1 hour to 2 days to reach an equilibrium state. The time provided for reaching the equilibrium state may be about 1 hour, 3 hours, 6 hours, 9 hours, 12 hours, 15 hours, 18 hours, 21 hours, 24 hours, 27 hours, 30 hours, 33 hours, 36 hours, 39 hours, 42 hours, 45 hours, or 48 hours, any of which may constitute the upper or lower endpoint as desired.

In at least one aspect, the method 100 proceeds in the order presented. Alternatively, the method 100 is performed in a different order. In at least one aspect, some of the operations are performed in a sequential order, while other operations are performed in a different order. For example,

operations

110 and 120 are performed in a sequential order, while

operations

130, 140, 150, 160, 170, 180, and 190 are performed in a different order after

operations

110 and 120. In another example, operation 110 and operation 120 are performed in a different order, while

operations

130, 140, 150, 160, 170, 180, and 190 are performed in order. In another example,

operations

110, 120, 130, 140, 150, and 160 are performed in a sequential order, while

operations

170, 180, and 190 are performed in a different order. One set of operations may be performed before another set of operations. For example,

operations

110 and 120 may be performed in any order, and after

operations

110 and 120 are performed,

operations

130, 140, 150, and 160 may be performed in any order. Other orders are contemplated, as will be appreciated by those skilled in the art. Further, in some aspects, one or more of

operations

170, 180, and 190 may be omitted.

FIG. 2 is a flow diagram illustrating a method 200 of forming a chromium alloy coating on a substrate by electrodeposition in accordance with one or more aspects of the present invention. At operation 210, an electrolyte solution is prepared, for example, by the method 100 of fig. 1. At operation 220, the method 200 further includes adjusting and/or maintaining the pH of the electrolyte solution at a target pH or target pH range. In at least one aspect, the target pH is a pH in the range of about 1 to about 4. The pH may be maintained at about 1, 1.2, 1.4, 1.5, 1.6, 1.8, 2, 2.2, 2.4, 2.6, 2.8, 3.0, 3.2, 3.4, 3.6, 3.8, or 4.0, any of which may constitute an upper or lower endpoint as desired.

At operation 230, the method 200 includes adjusting and/or maintaining a temperature of an electrolyte solution (e.g., the electrolyte solution formed by operation 210). In at least one aspect, the temperature is adjusted and/or maintained at a target temperature of about 20 ℃ to about 70 ℃, such as about 20 ℃ to about 40 ℃, such as about 20 ℃ to about 35 ℃, such as 20 ℃, 25 ℃, or 30 ℃, using any suitable heating or cooling device. In at least one aspect, the temperature of the electrolyte is adjusted prior to passing an electric current through the electrolyte solution. In at least one aspect, the temperature of the electrolyte is maintained during passing current through the electrolyte solution to maintain the appearance of the deposited layer. Maintaining the temperature within the desired range helps to obtain reproducible results in terms of appearance and alloy composition.

At operation 240, the method further includes introducing a cathode and an anode into the electrolyte solution, the cathode comprising the substrate, and passing an electric current between the cathode and the anode through the electrolyte solution to deposit a chromium alloy layer on the cathode substrate at operation 250. In at least one aspect, the cathode substrate is, for example, a steel substrate, an iron alloy substrate, a copper substrate, a brass substrate, a nickel substrate, a copper-coated substrate (e.g., copper-coated steel or copper-coated iron alloy), or a nickel-coated substrate (e.g., nickel-coated steel or nickel-coated iron alloy).

In at least one aspect, the anode comprises a carbonaceous electrode material. For example, the carbonaceous anode may be a graphite anode or other carbon-containing anode. In at least one aspect, the graphite anode is used in a chloride-based electrolyte solution (e.g., an electrolyte solution comprising one or more compounds having chloride ions, such as chromium (III) chloride), a sulfate-based electrolyte solution (e.g., an electrolyte solution comprising one or more compounds having sulfate groups, such as chromium (III) sulfate), or a chloride and sulfate-based electrolyte solution (e.g., an electrolyte solution comprising one or more compounds having chloride ions and one or more other compounds having sulfate groups). Advantageously, graphite anodes or other carbonaceous anodes minimize gas evolution and the formation of undesirable byproducts and promote desired deposition rates (e.g., about 1 to about 2 microns per minute). Alternatively, a platinum anode or a platinum-plated titanium anode may be used for a sulfate-based electrolyte solution (e.g., an electrolyte solution of one or more compounds having sulfate, such as chromium (III) sulfate). For example, a platinum anode or a platinized titanium anode may be used when the electrolyte solution is chloride free and thus does not produce chlorine gas, or when the electrolyte solution has less chloride and thus produces less chlorine gas (e.g., without the use of a carbonaceous anode to reduce the production of chlorine gas).

In at least one aspect, passing an electric current between the anode and the cathode can be performed using direct current. In at least one aspect, the current density of the direct current used is about 50mA/cm²To about 600mA/cm²E.g. about 100mA/cm²To about 500mA/cm²E.g. about 100mA/cm²To about 400mA/cm²E.g. about 200mA/cm²To about 400mA/cm²E.g. 200mA/cm²、250mA/cm²Or 300mA/cm². The value of the current density may be adjusted according to the distance between the cathode and the anode. In at least one aspect, the current density is about 50mA/cm depending on the distance between the cathode and the anode²、100mA/cm²、150mA/cm²、200mA/cm²、250mA/cm²、300mA/cm²、350mA/cm²、400mA/cm²、450mA/cm²Or 500mA/cm²Any of which may constitute an upper endpoint or a lower endpoint, as desired. For example, about 200mA/cm may be applied when the cathode and anode are separated by about 3cm²To about 400mA/cm²The current density of (1). The inventors have found that a current density in the above range minimizes the formation of undesirable hexavalent chromium byproducts while achieving a reasonable deposition rate, for example 0.5 to 1 micron/minute.

Chromium and iron are deposited on the cathode substrate in response to passing an electric current between the cathode and the anode. Operation 250 is performed until a chromium alloy coating having a desired thickness is formed on the substrate. In at least one aspect, the chromium alloy coating is a ferrochrome alloy, wherein the ferrochrome alloy has from about 1 wt.% iron to about 60 wt.% iron, such as from about 1 wt.% iron to about 20 wt.% iron, such as from about 1 wt.% iron to about 5 wt.% iron, or from about 10 wt.% iron to about 20 wt.% iron, based on the total weight of the alloy. For example, the weight% of iron of the ferrochrome alloy may be 1, 2, 10, 11 or 12 weight%. Further, the ferrochrome alloy has from about 80 wt% chromium to about 99 wt% chromium, for example from about 85 wt% chromium to about 95 wt% chromium, for example about 99 wt% chromium, 98 wt% chromium, 90 wt% chromium, 89 wt% chromium or 88 wt% chromium, based on the total weight of the alloy.

In response to performing operation 250, chromium is deposited on the substrate. In at least one aspect, the chromium and carbon are co-deposited on the substrate. In at least one aspect, operation 250 is performed until a chromium layer (e.g., a chromium coating) or a chromium carbon layer (e.g., a chromium carbide coating) having a desired thickness (e.g., a thickness greater than about 5 microns) is formed on the substrate. In at least one aspect, the chromium layer having a thickness greater than about 5 microns may have a thickness greater than about 800 HV.

Aspects of the invention

Clause 1. an electrolyte solution for electroplating, comprising: a trivalent chromium salt; an oxalate compound; a ferric salt; aluminum sulfate; an alkali metal sulfate; and alkali metal halides.

Clause 2. the electrolyte solution of clause 1, wherein the trivalent chromium salt is present in an amount from about 0.3mol/L to about 0.9mol/L of the electrolyte solution; the oxalate compound is present in an amount of about 0.2mol/L to about 1.2mol/L of the electrolyte solution; the iron salt is present in an amount of about 0.005mol/L to about 0.2mol/L of the electrolyte solution; aluminum sulfate is present in an amount of about 0.05mol/L to about 0.5 mol/L; the alkali metal sulfate is present in an amount of about 0.1mol/L to about 2.0mol/L of the electrolyte solution; and the alkali metal halide is present in an amount of about 0.1mol/L to about 0.5mol/L of the electrolyte solution.

Clause 3. the electrolyte solution of clause 1 or 2, wherein the iron salt is a ferrous salt including one or more of iron (II) sulfate, iron (II) chloride, iron (II) acetate, and hydrates thereof.

Clause 4. the electrolyte solution of any one of clauses 1 to 3, wherein the ferric salt is a ferric salt including one or more of ferric sulfate (III), ferric chloride (III), ferric acetate (III), and hydrates thereof.

Clause 5. the electrolyte solution of any one of clauses 1 to 4, wherein the trivalent chromium salt is selected from chromium (III) halides, chromium (III) sulfate, or a combination thereof.

Clause 6. the electrolyte solution of any one of clauses 1 to 5, wherein the oxalate compound is selected from sodium oxalate, potassium oxalate, an oxalate acid, or a combination thereof.

Clause 7. the electrolyte solution of any one of clauses 1 to 6, wherein the alkali metal sulfate is selected from sodium sulfate, potassium sulfate, or a combination thereof.

Clause 8 the electrolyte solution of any one of clauses 1 to 7, wherein the alkali metal halide is selected from sodium fluoride, potassium fluoride, or a combination thereof.

Clause 9 the electrolyte solution of any one of clauses 1-8, wherein the pH of the electrolyte solution is from about 1 to about 4.

Clause 10. the electrolyte solution of any one of clauses 1 to 9, further comprising sodium lauryl sulfate, sodium lauryl ether sulfate, or a combination thereof.

Clause 11. an electrolyte solution for electroplating comprising a trivalent chromium salt in an amount from about 0.3mol/L to about 0.9mol/L of the electrolyte solution; an oxalate compound in an amount of about 0.2mol/L to about 1.2mol/L of the electrolyte solution; an iron salt in an amount of about 0.005mol/L to about 0.2mol/L of the electrolyte solution; aluminum sulfate in an amount of about 0.05mol/L to about 0.5 mol/L; an alkali metal sulfate in an amount of about 0.1mol/L to about 2.0mol/L of the electrolyte solution; and an alkali metal halide in an amount of about 0.1mol/L to about 0.5mol/L of the electrolyte solution.

Clause 12. the electrolyte solution of clause 11, wherein the iron salt is a ferrous salt including one or more of iron (II) sulfate, iron (II) chloride, iron (II) acetate, and hydrates thereof.

Clause 13. the electrolyte solution of clause 11 or 12, wherein the ferric salt is a ferric salt including one or more of ferric sulfate (III), ferric chloride (III), ferric acetate (III), and hydrates thereof.

Clause 14. the electrolyte solution of any one of clauses 11 to 13, wherein the trivalent chromium salt is selected from chromium (III) halides, chromium (III) sulfate, or a combination thereof.

Clause 15. the electrolyte solution of any one of clauses 11 to 14, wherein the oxalate compound is selected from sodium oxalate, potassium oxalate, an oxalate acid, or a combination thereof.

Clause 16. the electrolyte solution of any one of clauses 11 to 15, wherein the alkali metal sulfate is selected from sodium sulfate, potassium sulfate, or a combination thereof.

Clause 17. the electrolyte solution of any one of clauses 11 to 16, wherein the alkali metal halide is selected from sodium fluoride, potassium fluoride, or a combination thereof.

Clause 18 the electrolyte solution of any one of clauses 11 to 17, wherein the pH of the electrolyte solution is from about 1 to about 4.

Clause 19. the electrolyte solution of any one of clauses 11 to 18, further comprising sodium lauryl sulfate, sodium lauryl ether sulfate, or a combination thereof.

Clause 20. a method of plating chromium on a substrate using an electrolyte solution, the method comprising dissolving a trivalent chromium salt in an amount from about 0.3mol/L to about 0.9mol/L of the electrolyte solution in an aqueous medium; an oxalate compound in an amount that dissolves from about 0.2mol/L to about 1.2mol/L of the electrolyte solution; dissolving an amount of iron salt of about 0.005mol/L to about 0.2mol/L of the electrolyte solution; dissolving aluminum sulfate in an amount of about 0.05mol/L to about 0.5 mol/L; an alkali metal sulfate in an amount to dissolve from about 0.1mol/L to about 2.0mol/L of the electrolyte solution; dissolving an alkali metal halide in an amount of about 0.1mol/L to about 0.5mol/L of the electrolyte solution; and passing an electric current between the anode and the cathode through the electrolyte solution to deposit chromium on the substrate.

Clause 21. the method of clause 20, wherein the cathode is a steel substrate, a copper substrate, a brass substrate, a nickel substrate, a copper-coated substrate, or a nickel-coated substrate.

Clause 22 the method of clause 20 or 21, wherein the anode is a platinum material, a platinized titanium material, or a carbonaceous electrode material.

Clause 23. the method of any one of clauses 20 to 22, wherein the current density of the current is from about 150 to about 600mA/cm by passing a direct current between the anode and the cathode²。

Clause 24. the method of any one of clauses 20 to 23, wherein the current densityHaving a current density of about 200 to about 400mA/cm²The current density of (1).

Clause 25. the method of any one of clauses 20 to 24, wherein the electrolyte solution is maintained at a temperature of about 20 ℃ to about 60 ℃.

Clause 26. the method of any one of clauses 20 to 25, further comprising adjusting the pH of the electrolyte solution to a pH of about 1.5 to about 4.

Clause 27. the method of any one of clauses 20 to 26, wherein the iron salt is a ferrous salt including one or more of iron (II) sulfate, iron (II) chloride, iron (II) acetate, and hydrates thereof.

Clause 28. the method of any one of clauses 20 to 27, wherein the ferric salt is a ferric salt including one or more of ferric sulfate (III), ferric chloride (III), ferric acetate (III), and hydrates thereof.

Clause 29. the method of any one of clauses 20 to 28, wherein the trivalent chromium salt is selected from chromium (III) halides, chromium (III) sulfate, or a combination thereof.

Clause 30 the method of any one of clauses 20 to 29, wherein the oxalate compound is selected from sodium oxalate, potassium oxalate, an oxalate acid, or a combination thereof.

Clause 31. the method of any one of clauses 20 to 30, wherein the alkali metal sulfate is selected from sodium sulfate, potassium sulfate, or a combination thereof.

Clause 32. the method of any one of clauses 20 to 31, wherein the alkali metal halide is selected from sodium fluoride, potassium fluoride, or a combination thereof.

Clause 33. the method of any one of clauses 20 to 32, further comprising dissolving sodium lauryl sulfate, sodium lauryl ether sulfate, or a combination thereof in an amount of about 0.1g/L to about 1g/L of the electrolyte solution.

Clause 34. a method of plating chromium on a substrate using an electrolyte solution, the method comprising: introducing a cathode and an anode into an electrolyte solution comprising a trivalent chromium salt, an oxalate compound, an iron salt, aluminum sulfate, an alkali metal sulfate, and an alkali metal halide; and passing an electric current between the anode and the cathode through the electrolyte to deposit a chromium layer on the substrate.

Clause 35. the method of clause 34, wherein the cathode is a steel substrate, a copper substrate, a brass substrate, a nickel substrate, a copper-coated substrate, or a nickel-coated substrate.

Clause 36. the method of clause 34 or 35, wherein the anode is a platinum material, a platinized titanium material, or a carbonaceous electrode material.

Clause 37. the method of any one of clauses 34 to 36, wherein the current density of the current is from about 100 to about 600mA/cm by passing a direct current between the anode and the cathode²Or about 10 to about 60mA/cm²。

Clause 38. the method of any one of clauses 34 to 37, wherein the current density has from about 200 to about 400mA/cm²Or from about 20 to about 40mA/cm²The current density of (1).

Clause 39. the method of any one of clauses 34 to 38, wherein the electrolyte solution is maintained at a temperature of about 20 ℃ to about 60 ℃.

Clause 40 the method of any one of clauses 34 to 39, further comprising adjusting the pH of the electrolyte solution to a pH of about 1.5 to about 4.

Clause 41. the method of any one of clauses 34 to 40, wherein the iron salt is a ferrous salt including one or more of iron (II) sulfate, iron (II) chloride, iron (II) acetate, and hydrates thereof.

Clause 42. the method of any one of clauses 34 to 41, wherein the ferric salt is a ferric salt including one or more of ferric sulfate (III), ferric chloride (III), ferric acetate (III), and hydrates thereof.

Clause 43 the method of any one of clauses 34 to 42, wherein the trivalent chromium salt is selected from chromium (III) halides, chromium (III) sulfate, or a combination thereof.

Clause 44. the method of any one of clauses 34 to 43, wherein the oxalate compound is selected from sodium oxalate, potassium oxalate, an oxalate acid, or a combination thereof.

Clause 45 the method of any one of clauses 34 to 44, wherein the alkali metal sulfate is selected from sodium sulfate, potassium sulfate, or a combination thereof.

Clause 46. the method of any one of clauses 34 to 45, wherein the alkali metal halide is selected from sodium fluoride, potassium fluoride, or a combination thereof.

Clause 47. the method of any one of clauses 34 to 46, further comprising dissolving sodium lauryl sulfate, sodium lauryl ether sulfate, or a combination thereof in an amount of about 0.1g/L to about 1g/L of the electrolyte solution.

Clause 48. a substrate comprising: a ferrochrome coating having a chromium content of about 40% to about 90% by weight, an iron content of about 8% to about 18% by weight, and a carbon content of about 5% to about 50% by weight.

Clause 49 the substrate of clause 48, wherein the substrate comprises one or more of steel, copper, brass, or nickel.

Clause 50 the substrate of clause 48 or 49, wherein the coating has a thickness of from about 1 micron to about 100 microns.

Examples

The following non-limiting examples are provided to further illustrate the various aspects described herein. These embodiments, however, are not intended to be all inclusive and are not intended to limit the scope of the aspects described herein.

Example 1

The components of example 1 were mixed in a stepwise manner, wherein the chromium chloride hexahydrate and the sodium oxalate were first mixed, followed by the metal salt. The pH of example 1 was about 2.2.

Example 2

The components of example 2 were mixed in a stepwise manner, wherein the chromium chloride hexahydrate and the sodium oxalate were first mixed, followed by the metal salt. The composition of example 2 is similar to the composition of example 1 except that the amount of ferrous sulfate heptahydrate is increased by a factor of 10 compared to the composition of example 1. The pH of example 1 was about 2.2.

Example 3

The components of example 3 were mixed in a stepwise manner, wherein the chromium chloride hexahydrate and the sodium oxalate were mixed first, followed by the metal salt. The composition of example 3 is similar to that of example 1 except that iron chloride is substituted for ferrous sulfate heptahydrate in example 3. The pH of example 1 was about 2.2.

FIG. 3 is an image 300 of ferrochrome plated

substrates

310, 320, 330 and 340 formed by the method of FIG. 2, each plated at a different current density using the electrolyte solution of example 1. For each of the ferrochrome plated

substrates

310, 320, 330, and 340, the plating parameters were: a plating time of about 1 hour while maintaining the electrolyte solution at a temperature of 30 ℃ and a pH of about 2.2. The ferrochrome plated substrate 310 was plated at 100mA/cm²The current density plating of (2) was carried out to obtain a ferrochrome layer having a thickness of 12 μm. The ferrochrome plated substrate 320 was 200mA/cm²The current density plating of (2) was carried out to obtain a ferrochrome layer having a thickness of 15 μm. The ferrochrome plated substrate 330 was plated at 250mA/cm²The current density plating of (2) to obtain a ferrochrome layer having a thickness of 28 μm. The ferrochrome plated substrate 340 was plated at 300mA/cm²The resulting chromium-iron layer was plated at a current density of 32 μm. A portion of each coating was subjected to X-ray fluorescence analysis to determine the chromium content and iron content (in wt%). Note that the X-ray fluorescence analysis does not detect carbon, and thus in at least one aspect, the ferrochrome alloys described herein also contain carbon, although no carbon is shown in the X-ray fluorescence analysis results. The results are shown in table I.

As shown in Table I, 100mA/cm²To about 300mA/cm²Any current density within the range provides for deposition of the ferrochrome layer. About 200mA/cm²To about 280mA/cm²The current density in the range provides a thick ferrochromium layer with low iron content. Furthermore, relative to about 200mA/cm²To about 300mA/cm²Current density in the range of 100mA/cm²The current density of (a) provides the thinnest ferrochrome alloy with high iron content.

FIG. 4 is an image 400 of ferrochrome plated

substrates

410, 420, 430, 440, and 450 formed by the method of FIG. 2, each plated at a different pH using the electrolyte solution of example 1. For each of the ferrochrome plated

substrates

410, 420, 430, 440, and 450, the plating parameters were: the current density is 250mA/cm²The plating time was about 1 hour while the electrolyte solution was maintained at a temperature of 30 c. The ferrochrome coated substrate 410 was coated at a pH of 1.0 to yield a sporadic ferrochrome deposit, which was not measured but is believed to be less than 10 μm. The ferrochrome-plated substrate 420 was plated at a pH of 2.0 to yield a sporadic ferrochrome deposit, which was not measured but is believed to be less than 10 μm. The ferrochrome plated substrate 430 was plated at a pH of 2.5 to yield a ferrochrome layer thickness of 20 μm. The ferrochrome plated substrate 440 was plated at a pH of 3.0 to yield a ferrochrome layer thickness of 28 μm. The ferrochrome plated substrate 450 was plated at a pH of 3.5 to yield a ferrochrome layer thickness of 45 μm. A portion of each coating was subjected to X-ray fluorescence analysis to determine the chromium content and iron content (in wt%). The results are shown in table II.

As shown in Table II, any pH in the range of 2.5 to 3.5 provides for deposition of the ferrochrome layer. A pH range of 2.5 to 3.0 advantageously provides a thick ferrochromium layer with the desired iron content. A pH of 3.5 provides a thicker ferrochrome layer with a lower iron content relative to a pH range of 2.5 to 3.0.

FIG. 5 is an image 500 of ferrochrome plated

substrates

510, 520, 530, and 540 formed by the method of FIG. 2, each plated at a different current density using the electrolyte solution of example 2. For each of the ferrochrome plated

substrates

510, 520, 530, and 540, the plating parameters were: plating time of about 1 hour while maintaining the electrolyte solutionMaintained at a temperature of 30 ℃ and a pH of about 2.2. The ferrochrome plated substrate 510 was plated at 100mA/cm²The current density plating of (2) was carried out to obtain a ferrochrome layer having a thickness of 30 μm. The ferrochrome plated substrate 520 was 200mA/cm²The current density plating of (2) to obtain a ferrochrome layer having a thickness of 40 μm. The ferrochrome plated substrate 530 was plated at 250mA/cm²The current density plating of (2) was carried out to obtain a ferrochrome layer having a thickness of 70 μm. The ferrochrome plated substrate 540 was plated at 300mA/cm²The current density plating of (2) was carried out to obtain a ferrochrome layer having a thickness of 50 μm. A portion of each coating was subjected to X-ray fluorescence analysis to determine the chromium content and iron content (in wt%). The results are shown in table III.

As shown in Table III, 100mA/cm²To about 300mA/cm²Any current density within the range provides for deposition of ferrochrome. About 100mA/cm²To about 250mA/cm²A current density in the range provides a thick ferrochrome layer. Furthermore, relative to at 250mA/cm²The thickness of the deposited ferrochrome alloy is 300mA/cm²The thickness of the ferrochrome alloy at the current density of (a) is reduced.

FIG. 6 is an image 600 of ferrochrome plated

substrates

610, 620, 630, 640, 650 and 660 formed by the method of FIG. 2, each plated at a different pH using the electrolyte solution of example 2. For each of the ferrochrome plated

substrates

610, 620, 630, 640, 650, and 660, the plating parameters were: the current density is 250mA/cm²The plating time was about 1 hour while the electrolyte solution was maintained at a temperature of 30 c. The ferrochrome plated substrate 610 is plated at a pH of 1.5 to produce a scattered ferrochrome deposit. The ferrochrome plated substrate 620 is plated at a pH of 2.0 to produce a scattered ferrochrome deposit. The ferrochrome plated substrate 630 was plated at a pH of 2.5 to yield a ferrochrome layer thickness of 50 μm. The ferrochrome plated substrate 640 was plated at a pH of 3.0 to a thickness of 70 μmA ferrochrome layer. The ferrochrome plated substrate 650 was plated at a pH of 3.5 to obtain a ferrochrome layer thickness of 50 μm. The ferrochrome plated substrate 660 was plated at a pH of 4.0. A portion of each coating was subjected to X-ray fluorescence analysis to determine the chromium content and iron content (in wt%). The results are shown in table IV.

As shown in Table IV, any pH in the range of 1.5 to 4.0 provides for deposition of the ferrochrome layer. The pH range of 2.0 to 4.0 advantageously provides a thick ferrochromium layer with the desired high iron content. A pH of 3.0 provides a thicker ferrochrome layer with good deposit quality. At a pH of 4, the deposit burns at the edges, whereas at a pH below 2, the deposit scatters.

FIG. 7 is an image 700 of ferrochrome plated

substrates

710, 720, 730, 740, 750, and 760 formed by the method of FIG. 2, each plated at a different current density using the electrolyte solution of example 3. For each of the ferrochrome plated

substrates

710, 720, 730, 740, 750, and 760, the plating parameters were: a plating time of about 1 hour while maintaining the electrolyte solution at a temperature of 30 ℃ and a pH of about 2.2. The ferrochrome plated substrate 710 was plated at 100mA/cm²Current density plating to obtain a scattered ferrochrome deposit believed to be less than 10 μm thick. The ferrochrome plated substrate 720 was plated at 150mA/cm²Current density plating to obtain a scattered ferrochrome deposit believed to be less than 10 μm thick. The ferrochrome plated substrate 730 was at 200mA/cm²The current density plating of (2) to obtain a ferrochrome layer having a thickness of 10 μm. The ferrochrome plated substrate 740 was plated at 300mA/cm²The resulting chromium-iron layer was plated at a current density of 30 μm. The ferrochrome plated substrate 750 was at 400mA/cm²The current density plating of (2) was carried out to obtain a ferrochrome layer having a thickness of 50 μm. The ferrochrome plated substrate 760 was measured at 500mA/cm²Current density plating of (a) to give a deposit that appears burned at the edges.

200mA as shown in Table V/cm²To about 400mA/cm²Any current density within the range provides for deposition of ferrochrome. About 300mA/cm²To about 400mA/cm²A current density in the range provides a thick ferrochrome layer. Furthermore, relative to at 400mA/cm²The thickness of the deposited ferrochrome alloy at a current density of 500mA/cm²The thickness of the ferrochrome alloy at current density of (a) increases, but the deposit at the edges burns (black powder).

FIG. 8 is an image 800 of ferrochrome plated

substrates

810, 820, 830, 840, 850, 860, and 870 formed by the method of FIG. 2, each plated at a different pH using the electrolyte solution of example 3. For each of the ferrochrome plated

substrates

810, 820, 830, 840, 850, 860, and 870, the plating parameters were: the current density is 250mA/cm²The plating time was about 1 hour while the electrolyte solution was maintained at a temperature of 30 c. The ferrochrome plated substrate 810 was plated at a pH of 1.0 to yield a ferrochrome layer thickness of 20 μm. The ferrochrome plated substrate 820 was plated at a pH of 1.5 to yield a ferrochrome layer thickness of 24 μm. The ferrochrome plated substrate 830 was plated at a pH of 2.0 to obtain a ferrochrome layer having a thickness of 20 μm. The ferrochrome plated substrate 840 was plated at a pH of 3.0 to yield a 16 μm thick ferrochrome layer. The ferrochrome plated substrate 860 was plated at a pH of 3.5 to yield a ferrochrome layer thickness of 16 μm. The ferrochrome plated substrate 870 is plated at a pH of 4.0 to produce a thin, scattered ferrochrome deposit. A portion of the coating deposited at pH 2 and pH 2.5 was subjected to X-ray fluorescence analysis to determine chromium content and iron content (in wt%). The results are shown in table VI.

As shown in Table VI, any pH in the range of 1.0 to 4.0 provides for deposition of the ferrochrome alloy layer. A pH in the range of 1.0 to 2.5 advantageously provides a thicker ferrochrome layer relative to a higher pH. Furthermore, a pH in the range of 1.5 to 2.0 provides the thickest ferrochrome alloy layer.

FIG. 9 is an image 900 of ferrochrome plated

substrates

910, 920, 930, and 940 formed by the method of FIG. 2, each plated using the electrolyte solution of example 3 at a different temperature. For each of the ferrochrome plated

substrates

910, 920, 930, and 940, the plating parameters were: the current density is 250mA/cm²The plating time is about 1 hour while maintaining the electrolyte solution at a pH of about 2.1. The ferrochrome plated substrate 910 was plated at a temperature of 30 c to obtain a ferrochrome layer having a thickness of 40 μm. The ferrochrome-plated substrate 920 is plated at a temperature of 40 ℃ to obtain a ferrochrome layer having a thickness of 30 μm. The ferrochrome plated substrate 930 was plated at a temperature of 50 c to obtain a ferrochrome layer having a thickness of 30 μm. The ferrochrome-plated substrate 940 is plated at a temperature of 60 ℃ to obtain a ferrochrome alloy layer with a low thickness. The results are shown in table VII.

As shown in Table VII, any temperature in the range of about 30 ℃ to about 50 ℃ provides for deposition of the ferrochrome layer. The 30 c operating temperature provides the thickest ferrochrome alloy layer, but the 40 c deposit is more aesthetically pleasing.

The electrolyte solution of example 3 was used, and the passing current density was 300mA/cm²The direct current of (a) deposits a ferrochrome coating on the Taber Wear plate for a plating time of about 2 hours while maintaining the electrolyte solution at a temperature of about 40 c and a pH of about 2.5. The alloy composition of the coating was determined by SEM EDS to be about 41 wt% chromium, about 10 wt% iron and about 49 wt% carbon. Hardness values were measured on "as plated" coupons and after baking the coupons at 190 ℃ for 23 hours. The wear resistance of the obtained ferrochrome coating was evaluated. Using Taber abrasion according to ASTM D4060The test carries out the measurement of the abrasion resistance. The grinding wheel used was CS10, loaded 500g per grinding wheel, and operated at 60rpm for 10,000 cycles. The Taber abrasion index is less than 10. The average of the 5 hardness measurements for the "as-plated" ferrochrome layer was 1056 HV. The average of the 5 hardness measurements for the "baked" ferrochrome layer was 1187 HV.

The electrolyte solution of example 1 was used, and the passing current density was 250mA/cm²The direct current of (a) deposits a ferrochrome coating on the steel substrate for a plating time of about 2 hours while maintaining the electrolyte solution at a temperature of about 35 c and a pH of about 2.5. The alloy composition of the coating was determined by SEM EDS to be about 80 wt% chromium, about 12 wt% iron and about 8 wt% carbon. Hardness values were measured on the "as-plated" sample pieces and after baking the sample pieces at 190 ℃ for 23 hours. The average of the 5 hardness measurements for the "as plated" ferrochrome layer was 1147 HV. The average of the 5 hardness measurements for the "baked" ferrochrome layer was 1249 HV.

In summary, the present invention provides an improved electrolyte solution for electrodepositing ferrochrome, a method of forming ferrochrome, and a method of electrodepositing ferrochrome.

The description of the various aspects of the present invention has been presented for purposes of illustration, but is not intended to be exhaustive or limited to the disclosed aspects. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described aspects. The terminology used herein is chosen to best explain the principles of the aspects, the practical application or technical improvements to the technology found in the marketplace, or to enable others of ordinary skill in the art to understand the aspects disclosed herein. While the foregoing is directed to aspects of the present invention, other and further aspects of the invention may be devised without departing from the basic scope thereof.

Claims

1. An electrolyte solution for electroplating, comprising:

a trivalent chromium salt;

an oxalate compound;

a ferric salt;

aluminum sulfate;

an alkali metal sulfate; and

an alkali metal halide.

2. The electrolyte solution of claim 1, wherein:

the trivalent chromium salt is present in an amount from about 0.3mol/L to about 0.9mol/L of the electrolyte solution;

the oxalate compound is present in an amount of about 0.2mol/L to about 1.2mol/L of the electrolyte solution;

the iron salt is present in an amount of about 0.005mol/L to about 0.2mol/L of the electrolyte solution;

said aluminum sulfate is present in an amount of about 0.05mol/L to about 0.5 mol/L;

the alkali metal sulfate is present in an amount of about 0.1mol/L to about 2.0mol/L of the electrolyte solution; and is

The alkali metal halide is present in an amount of about 0.1mol/L to about 0.5mol/L of the electrolyte solution.

3. The electrolyte solution of claim 1, wherein the iron salt is a ferrous salt comprising one or more of iron (II) sulfate, iron (II) chloride, iron (II) acetate, and hydrates thereof.

4. The electrolyte solution of claim 1, wherein the ferric salt is a ferric salt comprising one or more of ferric sulfate (III), ferric chloride (III), ferric acetate (III), and hydrates thereof.

5. The electrolyte solution of claim 1, wherein the trivalent chromium salt is selected from chromium (III) halides, chromium (III) sulfate, or combinations thereof.

6. The electrolyte solution of claim 1, wherein the pH of the electrolyte solution is from about 1 to about 4.

7. The electrolyte solution of claim 1, further comprising sodium lauryl sulfate, sodium lauryl ether sulfate, or a combination thereof.

8. A method (200) of plating chromium on a substrate using an electrolyte solution, the method comprising:

a step (240) of introducing the cathode and the anode into an electrolyte solution comprising a trivalent chromium salt, an oxalate compound, an iron salt, aluminum sulfate, an alkali metal sulfate, and an alkali metal halide; and

a step (250) of passing an electric current between the anode and the cathode through the electrolyte solution to deposit a chromium layer on the substrate.

9. The method (200) of claim 8, further comprising adjusting the pH of the electrolyte solution to a pH of about 1.5 to about 4.

10. A substrate (310), comprising:

a ferrochrome coating having a chromium content of about 40 wt.% to about 90 wt.%, an iron content of about 8 wt.% to about 18 wt.%, and a carbon content of about 5 wt.% to about 50 wt.%.