Functional chromium alloy plating based on trivalent chromium electrolyte

Abstract

To provide an electrolyte solution for electrodeposition of a chromium-iron alloy and an electrodeposition method of the chromium-iron alloy, using trivalent chromium instead of hexavalent chromium which is environmentally undesirable and high in waste cost and achieving a thicker or highly functional coating.SOLUTION: An electrolyte solution for electroplating is formed by dissolving a trivalent chromium salt, an oxalate compound, an iron salt, an aluminum sulfate, an alkali metal sulfate and an alkali metal halide in water or an aqueous solution. A method for chromium plating a substrate using the electrolyte solution comprises introducing a cathode and an anode into the electrolyte solution, and passing current through the electrolyte between the anode and the cathode to deposit a chromium layer on the substrate.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure provides an electrolyte solution for electrodeposition of a chromium alloy, a method for forming the electrolyte solution, and a method for electrodepositing a chromium alloy.

Background Art

[0002] Chromium plating is an electrodeposition process that provides a chromium coating on a substrate. Hard chromium plating typically provides a chromium coating having a thickness of about 10 microns or more, thereby providing the coated substrate with machinability and wear resistance. Other types of chromium plating are decorative chromium plating that typically provides a chromium coating having a thickness ranging from about 0.1 to about 0.5 microns. Chromium plating is often carried out using a bath containing chromium acid and a catalyst based on fluoride, sulfate or organic acid. Chromium acid has chromium(VI), which is an environmentally unfriendly and highly costly hexavalent form of chromium for disposal.

[0003] Trivalent chromium, which has beneficial properties and lower waste treatment costs, is an alternative to hexavalent chromium. Implementing trivalent chromium for thin decorative plating has been somewhat successful, but it remains difficult to achieve thicker or more functional coatings. In addition, trivalent chromium-based baths used for decorative plating typically contain boric acid as a buffer.

[0004] Therefore, there is a need to improve chromium plating methods and the formulation of solutions used for chromium plating.

Summary of the Invention

[0005] The present disclosure provides an electrolyte solution for electrodeposition of a chromium alloy, a method for forming the electrolyte solution, and a method for electrodepositing a chromium alloy.

[0006] 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.

[0007] At least one electrolyte solution for electroplating contains trivalent chromium salt in an amount ranging from about 0.3 mol per liter of the electrolyte solution to about 0.9 mol per liter of the electrolyte solution. The electrolyte solution further contains an oxalate compound in an amount ranging from about 0.2 mol per liter of the electrolyte solution to about 1.2 mol per liter of the electrolyte solution. The electrolyte solution further contains an iron salt in an amount ranging from about 0.005 mol per liter of the electrolyte solution to about 0.2 mol per liter of the electrolyte solution. The electrolyte solution further contains aluminum sulfate in an amount ranging from about 0.05 mol per liter of the electrolyte solution to about 0.5 mol per liter of the electrolyte solution. The electrolyte solution further contains an alkali metal sulfate in an amount ranging from about 0.1 mol per liter of the electrolyte solution to about 2.0 mol per liter of the electrolyte solution. The electrolyte solution further contains an alkali metal halide in an amount ranging from about 0.1 mol per liter of the electrolyte solution to about 0.5 mol per liter of the electrolyte solution.

[0008] At least one method for chromium plating on a substrate using the electrolyte solution is provided. This method includes dissolving trivalent chromium salt in an amount ranging from about 0.3 mol per liter of the electrolyte solution to about 0.9 mol per liter of the electrolyte solution in an aqueous medium. The method further includes dissolving an oxalate compound in an amount ranging from about 0.2 mol per liter of the electrolyte solution to about 1.2 mol per liter of the electrolyte solution. The method further includes dissolving an iron salt in an amount ranging from about 0.005 mol per liter of the electrolyte solution to about 0.2 mol per liter of the electrolyte solution. The method further includes dissolving aluminum sulfate in an amount ranging from about 0.05 mol per liter of the electrolyte solution to about 0.5 mol per liter of the electrolyte solution. The method further includes dissolving an alkali metal sulfate in an amount ranging from about 0.1 mol per liter of the electrolyte solution to about 2.0 mol per liter of the electrolyte solution. The method further includes dissolving an alkali metal halide in an amount ranging from about 0.1 mol per liter of the electrolyte solution to about 0.5 mol per liter of the electrolyte solution. The method further includes passing an electric current through the electrolyte solution between a cathode and an anode to deposit a chromium-iron alloy on the substrate.

[0009] At least one method is provided for chromium plating on a substrate using an electrolyte solution. The method includes introducing a cathode and an anode into an electrolyte solution containing a trivalent chromium salt, an oxalate compound, an iron salt, aluminum sulfate, an alkali metal sulfate, and an alkali metal halide. The method further includes passing an electric current through the electrolyte solution between the anode and the cathode to deposit a chromium-iron alloy layer on the substrate.

[0010] At least one substrate is provided that includes a chromium-iron alloy coating. The chromium-iron alloy coating has a chromium content in the range of about 40 wt% to about 90 wt%, an iron content in the range of about 8 wt% to about 18 wt%, and a carbon content in the range of about 5 wt% to about 50 wt%.

[0011] The above-described features, functions, and advantages can be realized alone in various aspects or can be combined in still other aspects. These details can be seen with reference to the following description and the accompanying drawings.

[0012] To enable a more detailed understanding of the above-described features of the present disclosure, a more detailed description of the present disclosure than that summarized above can be made by referring to aspects illustrated in part in the accompanying drawings. However, it should be noted that since the present disclosure can also admit other equally effective aspects, the accompanying drawings show only typical aspects of this disclosure and should not be regarded as limiting the scope of the present invention.

Brief Description of the Drawings

[0013]

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DETAILED DESCRIPTION OF THE INVENTION

[0014] For ease of understanding, the same reference numbers are used wherever possible to indicate identical elements common to the figures. Additionally, elements of one aspect can be advantageously adapted for use in other aspects described herein.

[0015] DETAILED DESCRIPTION According to aspects of the present disclosure, various methods and formulations for chromium plating a substrate are provided that can obtain a chromium layer (e.g., a chromium coating) formed on a structurally robust, reliable, and cost - effective substrate while using a direct current and a trivalent chromium solution that does not contain boric acid. Thus, the methods and formulations described herein can be advantageously used for hard chromium plating to form a hard chromium layer (e.g., a robust functional chromium layer greater than 10 microns). However, the present disclosure is not limited to hard chromium plating, and the methods and formulations described herein can also be advantageously used to effectively and efficiently perform decorative chromium plating to form a decorative chromium layer (e.g., a chromium layer ranging from 0.25 microns to 1.0 microns).

[0016] The present disclosure further provides an electrolyte solution for electrodeposition of a chromium - iron alloy and a method for forming a chromium - iron alloy. In at least one aspect, the electrolyte solution of the present disclosure is aqueous. In at least one aspect, the electrolyte solution contains an iron salt such as ferrous sulfate or ferric chloride. It has been discovered that one or more of these iron salts present in the electrolyte solution provide a deposit of a thick chromium - iron alloy layer on a substrate such as a steel substrate without the use of hexavalent chromium and pulse plating. The electrolyte solution of the present disclosure further contains at least one complexing agent such as an oxalate compound, e.g., sodium oxalate, that forms a complex with trivalent chromium ions as well as ferrous ions.

[0017] The electrolyte solution of the present disclosure provides a controllable deposit of a chromium - iron alloy on a 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 solution of the present disclosure provides a sufficiently hard chromium-iron alloy deposit that is considered comparable to a typical hexavalent chromium-based coating when used at a pH in the range of about 2 to about 4 and a temperature in the range of about 30°C to about 60°C. In at least one aspect, the iron content of the chromium-iron alloy of the present disclosure is from about 1 wt% iron to about 20 wt% iron based on the total weight of chromium and iron in the alloy.

[0018] The chromium-iron alloy coating of the present disclosure provides similar machinability and wear resistance to a typical hard chromium-plated substrate on substrates such as steel substrates. The chromium-iron alloy of the present disclosure can be disposed in aircraft, spacecraft, ships, engine and flap components, waste cleaning structures, hot structure components for high-performance supersonic, hypersonic, and reentry vehicle structures, automotive parts, buildings such as steel bridges, and propulsion structures such as power generation turbines, vehicle engines, alternative energy applications, and related technologies. As a specific example, the alloy of the present disclosure can be disposed on steel-based landing gears and / or the bottom surface of an aircraft.

[0019] In at least one aspect, the chromium-iron coating of the present disclosure is formed using a single bath technique. The deposition vessel is a laboratory-scale glass beaker or a commercial-scale large polypropylene tank for plating. In at least one aspect, the deposition vessel is an electrolyte solution prepared by simultaneously mixing all the components of the electrolyte solution, or by starting from a chromium salt and a complexing agent and subsequently mixing the iron salt stepwise. An anode (e.g., graphite) is introduced into the beaker containing the electrolyte solution as described below. The deposition process is controlled by applying a direct current, whereby a chromium-iron alloy coating is produced. The thickness of the chromium-iron alloy coating can be controlled by the period during which the direct current is applied to the electrolyte solution electrodes. In at least one aspect, the overall thickness of the chromium-iron alloy 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.

[0020] Changing the thickness and composition of the chromium-iron alloy coating can be controlled by the current density and time scale of the deposition process of the present disclosure.

[0021] The electrolyte solution of the present disclosure contains metal salts. The metal salts used herein can include the anhydrous and / or hydrated forms of the metal salts. In at least one aspect, the metal salts include one or more of trivalent chromium salts and iron salts. The electrolyte solution of the present disclosure further contains at least one complexing agent such as an alkali metal oxalate compound, for example, sodium oxalate or potassium oxalate. A complexing agent such as an alkali metal oxalate compound coordinates with iron ions in the electrolyte solution and promotes controllable deposition of iron onto the substrate when a current density is applied to the electrolyte solution.

[0022] The electrolyte solution of the present disclosure further includes at least one buffering agent such as an aluminum salt, for example, aluminum sulfate or aluminum halide. The buffering agent of the present disclosure maintains the desired pH of the electrolyte solution and does not substantially interfere with the deposition of chromium and iron on the substrate, as detailed below.

[0023] The electrolyte solution of the present disclosure further includes at least one ion conductivity controller such as an alkali metal salt, for example, sodium sulfate or potassium sulfate. The ion conductivity controller of the present disclosure maintains the desired conductivity of the electrolyte solution and does not substantially interfere with the deposition of chromium and iron on the substrate.

[0024] The electrolyte solution of the present disclosure further includes at least one alkali metal halide, for example, sodium fluoride or potassium fluoride. The alkali metal halide of the present disclosure provides an electrolyte solution having wettability and etching properties and can assist in chromium adhesion during chromium plating.

[0025] Optionally, the electrolyte solution of the present disclosure further includes at least one surfactant, for example, sodium lauryl sulfate, sodium lauryl ether sulfate, or potassium lauryl sulfate. The surfactant of the present disclosure reduces pitting corrosion and gas generation during chromium plating.

[0026] In at least one aspect, the pH of the electrolyte solution of the present disclosure is between about 1 and about 6, for example, between about 1.5 and about 4, and for example, the pH is 2 or 4. In at least one aspect, the pH of the electrolyte solution of the present disclosure is controlled by the addition of one or more bases such as sodium hydroxide (NaOH) solution to increase the pH of the solution, or by the addition of one or more acids such as sulfuric acid (H 2 SO 4 ) solution to decrease the pH of the solution. Chromium salts, iron salts, complexing agents, buffering agents, acids, and bases can be obtained from any suitable commercial source such as MERCK-India or Sigma-Aldrich Co. LLC (St. Louis, Missouri).

[0027] Figure 1 is a flow diagram showing a method 100 for forming an electrolyte solution according to one or more aspects of the present disclosure. As shown in Figure 1, in step 110, method 100 includes dissolving a trivalent chromium salt in a medium such as water or an aqueous solution to form a first electrolyte solution. The trivalent chromium salt is a trivalent chromium source. In at least one aspect, the trivalent chromium salt includes chromium(III) halide, chromium(III) sulfate (e.g., Cr 2 (SO 4 ) 3 , Cr 2 (SO 4 ) 3 ·12H 2 O, and / or other chromium(III) sulfates), and / or other chromium(III) salts. Chromium(III) halide includes, for example, chromium(III) chloride (e.g., CrCl 3 , CrCl 3 5H 2 O, CrCl 3 ·6H 2 O, and / or other chromium(III) chlorides).

[0028] In at least one aspect, the concentration of the trivalent chromium salt in the electrolyte of the present disclosure ranges from about 0.1 mole per liter (mol / L) to about 1 mol / L per liter of the electrolyte solution, for example, in the range of about 0.3 mol / L to about 0.9 mol / L, for example, in the range of about 0.2 mol / L to about 0.7 mol / L, for example, in the range of about 0.4 mol / L to about 0.7 mol / L, etc., by way of example, in the range of about 0.5 mol / L to about 0.6 mol / L. In at least one aspect, the amount of the trivalent chromium salt to be dissolved is, as needed, about 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, or 1 mol / L of the electrolyte solution (any of the values can form an upper or lower endpoint). At concentrations above 1 mol / L, it becomes difficult to dissolve the trivalent chromium salt in the electrolyte, and solubility problems may occur.

[0029] In at least one aspect, the trivalent chromium salt is dissolved by stirring at ambient temperature, at room temperature, at about 25 °C, or at a temperature ranging from about 10 °C to about 40 °C, such as from about 20 °C to about 30 °C. In at least one aspect, the temperature at which step 110 is carried out can be, as needed, about 10 °C, 15 °C, 20 °C, 25 °C, 30 °C, 35 °C, or 40 °C (any of the values can form the upper or lower endpoint). In at least one embodiment, the stirring can be carried out for about 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, or 30 minutes, as needed or until all of the trivalent chromium salt is dissolved (any of the values can form the upper or lower endpoint).

[0030] In step 120, method 100 further includes, for example, dissolving an oxalate compound in water or an aqueous solution (such as the first solution) to form an electrolyte solution such as a second electrolyte solution. The oxalate compound includes oxalate that can function as a complexing agent. In at least one aspect, the oxalate compound includes an alkali metal oxalate (such as sodium oxalate (Na 2 C 2 O 4 ), potassium oxalate (K 2 C 2 O 4 ), and / or other alkali metal oxalates) and / or an acid of oxalate (such as oxalic acid (H 2 C 2 O 4 ) and / or other acids of oxalate).

[0031] In at least one aspect, the concentration of the oxalate compound in the electrolyte of the present disclosure ranges from about 0.1 mol / L to about 2.0 mol / L of the electrolyte solution, such as from about 0.2 mol / L to about 1.2 mol / L, such as from about 0.1 mol / L to about 0.9 mol / L, such as from about 0.2 mol / L to about 0.7 mol / L, such as from about 0.4 mol / L to about 0.7 mol / L, and by way of example, within the range of about 0.5 mol / L to about 0.6 mol / L. In at least one aspect, the amount of oxalate compound to be dissolved is, as required, about 0.1 mol / L, 0.2 mol / L, 0.4 mol / L, 0.6 mol / L, 0.8 mol / L, 1.0 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L, or 2.0 mol / L of the electrolyte solution (any of the values can form an upper or lower endpoint).

[0032] In at least one embodiment, to dissolve the oxalate compound to form a complex of oxalate and trivalent chromium, the oxalate compound is placed in a solution (e.g., a solution obtained from another step performed before step 110 or step 120). This solution can be heated to a higher temperature ranging from about 70 °C to about 80 °C and can be stirred for about 1 hour to about 3 hours. In at least one embodiment, the solution is cooled (e.g., to ambient temperature, room temperature, about 25 °C, or a temperature ranging from about 20 °C to about 30 °C). Alternatively, the oxalate compound can be dissolved without heating, in which case the complex of oxalate and trivalent chromium is formed in 3 to 4 days. Advantageously, by heating the solution in step 120 to a temperature ranging from about 70 °C to about 80 °C, the electrolyte solution can be prepared even faster. In at least one embodiment, stirring is performed for about 1 hour, 1 hour 15 minutes, 1 hour 30 minutes, 1 hour 45 minutes, 2 hours, 2 hours 15 minutes, 2 hours 30 minutes, 2 hours 45 minutes, or 3 hours as needed (any of these values can form an endpoint). Further, in at least one embodiment, the temperature at which step 120 is performed is about 50 °C, 55 °C, 60 °C, 65 °C, 70 °C, 75 °C, or 80 °C as needed (any of these values can form an endpoint).

[0033] In step 130, method 100 further includes, for example, dissolving an iron salt in water or an aqueous solution (e.g., a second electrolyte solution) to form an electrolyte solution (e.g., a third electrolyte solution). In at least one embodiment, the iron salt is a divalent iron salt, a trivalent iron salt, or a combination thereof. In at least one embodiment, the iron salt is ferrous sulfate heptahydrate, ferric chloride, or a combination thereof. In at least one embodiment, the iron salt is a divalent iron salt. In at least one embodiment, the divalent iron salt includes iron(II) sulfate, iron(II) chloride, iron(II) acetate, and / or other divalent iron salts. Each of these divalent iron salts can include its corresponding hydrated form. For example, iron(II) sulfate has the formula FeSO 4 ·xH 2having O, wherein x is an integer (e.g., 0, 1, 2, 4, 5, 6, or 7). Thus, in at least one embodiment, 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 having another hydrated state. In at least one embodiment, the iron salt is a trivalent iron salt. In at least one embodiment, the trivalent iron salt includes iron(III) sulfate, iron(III) chloride, iron(III) acetate, and / or other trivalent iron salts. Each of these trivalent iron salts can include its corresponding hydrated form. For example, iron(III) sulfate has the formula Fe 2 (SO 4 ) 3 ·xH 2 O, wherein x is an integer (e.g., 0, 1, 2, 4, 5, 6, or 7). Thus, in at least one embodiment, 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 having another hydrated state. In a further example, iron(III) chloride has the formula FeCl 3 ·xH 2 O, wherein x is an integer (e.g., 0, 1, 2, 4, 5, 6, or 7). Thus, in at least one embodiment, 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 having another hydrated state.

[0034] In at least one aspect, the concentration of the iron salt in the electrolyte of the present disclosure ranges from about 0.005 mol / L to about 0.2 mol / L of the electrolyte solution, for example, in the range from about 0.01 mol / L to about 0.2 mol / L, in the range from about 0.02 mol / L to about 0.2 mol / L, etc. By way of example, it is in the range from about 0.1 mol / L to about 0.2 mol / L. In at least one aspect, the amount of iron salt to be dissolved is, as needed, about 0.005 mol / L, 0.01 mol / L, 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, 0.08 mol / L, 0.09 mol / L, 0.1 mol / L, or 0.2 mol / L of the electrolyte solution (any of the values can form the upper or lower endpoint). The inventors have discovered that at concentrations above 0.2 mol / L, the deposited chromium-iron alloy coating can become soft and more prone to corrosion.

[0035] In at least one aspect, the iron salt is dissolved by stirring at ambient temperature, room temperature, about 25 °C, or a temperature ranging from about 20 °C to about 30 °C. In at least one aspect, the stirring is carried out, as needed, or until all of the iron salt is dissolved, for about 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, or 30 minutes (any of the values can form the upper or lower endpoint). In at least one aspect, the temperature at which step 130 is carried out is, as needed, about 10 °C, 15 °C, 20 °C, 25 °C, 30 °C, 35 °C, or 40 °C (any of the values can form the upper or lower endpoint).

[0036] In step 140, method 100 further includes dissolving a metal salt, for example, in water or an aqueous solution (such as a third electrolyte solution) to form an electrolyte solution (such as a fourth electrolyte solution). The metal salt is a metal ion source that dissolves to provide metal ions such as aluminum ions, and the metal ions can function as a buffer and the higher-valent metal ions in the solution (e.g., Al 3+) can provide an ionic strength. In at least one aspect, the metal salt is a Group 13 metal salt, such as an aluminum salt (e.g., aluminum sulfate (Al 2 (SO 4 ), aluminum chloride (AlCl 3 ), and / or other aluminum salts), such as aluminum halides and / or other metal salts. 3 )

[0037] In at least one aspect, the concentration of the metal salt in the electrolyte of the present disclosure ranges from about 0.01 mol / L to about 1.0 mol / L of the electrolyte solution, such as in the range from about 0.05 mol / L to about 0.8 mol / L, such as in the range from about 0.1 mol / L to about 0.7 mol / L, such as in the range from about 0.2 mol / L to about 0.5 mol / L, for example, in the range from about 0.2 mol / L to about 0.3 mol / L. In at least one aspect, the amount of metal salt to be dissolved is, as needed, about 0.01 mol / L, 0.05 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.8 mol / L, or 1.0 mol / L of the electrolyte solution (any of the values can form an endpoint or a lower endpoint). At concentrations above 1.0 mol / L, it becomes difficult to dissolve the metal salt in the electrolyte, and solubility problems may occur.

[0038] In at least one aspect, the metal salt is dissolved by stirring at ambient temperature, room temperature, about 25 °C, or a temperature ranging from about 20 °C to about 30 °C. 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, as needed or until all the metal salt is dissolved (any of the values can form an endpoint or a lower endpoint). In at least one aspect, the temperature at which step 140 is carried out is, as needed, about 10 °C, 15 °C, 20 °C, 25 °C, 30 °C, 35 °C, or 40 °C (any of the values can form an endpoint or a lower endpoint).

[0039] In Process 150, Method 100 further includes dissolving an alkali metal salt in, for example, water or an aqueous solution (such as a fourth electrolyte solution) to form an electrolyte solution (such as a fifth electrolyte solution). The alkali metal salt can increase the conductivity of the electrolyte solution. In at least one aspect, the alkali metal salt is an alkali metal sulfate (e.g., sodium sulfate (Na 2 SO 4 ), potassium sulfate (K 2 SO 4 ), and / or other alkali metal sulfates).

[0040] In at least one aspect, the concentration of the alkali metal salt in the electrolyte of the present disclosure ranges from about 0.1 mol / L to about 2.0 mol / L, such as from about 0.5 mol / L to about 2.0 mol / L, such as from about 1.0 mol / L to about 1.5 mol / L, etc., for example from about 1.3 mol / L to about 1.4 mol / L. In at least one aspect, the amount of oxalate compound to be dissolved is, as needed, about 0.1 mol / L, 0.2 mol / L, 0.4 mol / L, 0.6 mol / L, 0.8 mol / L, 1.0 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L, or 2.0 mol / L of the electrolyte solution (any value can form an upper or lower endpoint). At concentrations above 2.0 mol / L, it becomes difficult to dissolve the alkali metal salt in the electrolyte, and solubility problems may occur.

[0041] In at least one aspect, the alkali metal salt is dissolved by stirring at ambient temperature, at room temperature, at about 25 °C, or at a temperature ranging from about 10 °C to about 40 °C, for example, from about 20 °C to about 30 °C. In at least one aspect, the temperature at which step 150 is carried out can be, as necessary, about 10 °C, 15 °C, 20 °C, 25 °C, 30 °C, 35 °C, or 40 °C (any of these values can form an upper or lower endpoint). In at least one aspect, the stirring can be carried out, as necessary, or until all of the alkali metal salt is dissolved, for about 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, or 30 minutes (any of these values can form an upper or lower endpoint). In at least one aspect, the alkali metal salt is dissolved by stirring at ambient temperature, room temperature, at about 25 °C for 15 minutes.

[0042] In step 160, method 100 further includes dissolving an alkali metal halide, for example, in water or an aqueous solution (such as a fifth electrolyte solution) to form an electrolyte solution (such as a sixth electrolyte solution). The alkali metal halide can provide an electrolyte solution having wettability and etching properties and can assist in chromium adhesion during chromium plating. In at least one aspect, the alkali metal halide includes an alkali metal fluoride (such as sodium fluoride (NaF), potassium fluoride (KF), and / or other alkali metal fluorides) and / or other alkali metal halides.

[0043] In at least one aspect, the concentration of the alkali metal halide in the electrolyte of the present disclosure ranges from about 0.1 mol / L to about 2.0 mol / L, such as in the range from about 0.1 mol / L to about 0.5 mol / L, such as in the range from about 0.2 mol / L to about 0.5 mol / L, etc., and by way of example, in the range from about 0.3 mol / L to about 0.4 mol / L. In at least one aspect, the amount of the oxalate compound to be dissolved is, as needed, about 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.8 mol / L, or 1.0 mol / L of the electrolyte solution (any of the values can form an upper or lower endpoint). At concentrations above 1.0 mol / L, it becomes difficult to dissolve the alkali metal halide in the electrolyte, and solubility problems may occur.

[0044] In at least one aspect, the alkali metal halide is dissolved by stirring at ambient temperature, at room temperature, at about 25 °C, or at a temperature ranging from about 10 °C to about 40 °C, such as, for example, from about 20 °C to about 30 °C. In at least one aspect, the temperature at which step 160 is carried out is, as needed, about 10 °C, 15 °C, 20 °C, 25 °C, 30 °C, 35 °C, or 40 °C (any of the values can form an upper or lower endpoint). In at least one aspect, the stirring is carried out, as needed, or until all of the alkali metal halide is dissolved, for about 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, or 30 minutes (any of the values can form an upper or lower endpoint). In at least one aspect, the alkali metal halide is dissolved by stirring at ambient temperature, room temperature, about 25 °C for 15 minutes.

[0045] Optionally, in step 170, method 100 further includes dissolving a surfactant, for example, in water or an aqueous solution (such as the sixth electrolyte solution) to form an electrolyte solution (such as the seventh electrolyte solution). The surfactant can prevent or reduce pitting corrosion and reduce gas generation (such as chlorine gas, hydrogen gas, etc.) during chromium plating. In at least one aspect, the surfactant is sodium lauryl sulfate (NaC12 H 25 SO 4 )), sodium lauryl ether sulfate (CH 3 (CH 2 ) 11 (OCH 2 CH 2 ) n OSO 3 Na), potassium lauryl sulfate (KC 12 H 25 SO 4 )) and / or other surfactants.

[0046] In at least one embodiment, the concentration of surfactant in the electrolyte of the present disclosure ranges from about 0.0001 mol / L to about 0.01 mol / L. In at least one embodiment, the amount of surfactant to be dissolved can be about 0.0001 mol / L, 0.0002 mol / L, 0.0004 mol / L, 0.0006 mol / L, 0.0008 mol / L, 0.0010 mol / L, 0.0020 mol / L, 0.0040 mol / L, 0.0060 mol / L, 0.0080 mol / L, or 0.0100 mol / L of the electrolyte solution (any value can form an upper or lower endpoint as needed). For example, in at least one embodiment, the amount of sodium lauryl sulfate, sodium lauryl ether sulfate, or potassium lauryl sulfate ranges from about 0.1 g to about 1 g per liter of the electrolyte solution. At concentrations above 0.01 mol / L, the surfactant can cause excessive foaming and non-uniform deposition in the tank.

[0047] Optionally, in step 180, method 100 includes potassium hydroxide (KOH), sodium hydroxide (NaOH), and / or sulfuric acid (H 2 SO 4Further comprising adjusting the pH of the electrolyte solution using one or more acidic aqueous solutions or basic aqueous solutions such as the like. The volume of the acidic aqueous solution or basic aqueous solution added to the electrolyte solution is small enough so that the concentrations of other components (complexing agents, buffers, etc.) of the electrolyte solution are not substantially affected. Alternatively, solid potassium hydroxide and / or solid sodium hydroxide are added directly to the electrolyte solution, and / or concentrated sulfuric acid is added directly to the electrolyte solution. In at least one embodiment, the pH of the electrolyte solution is adjusted to a target pH of from about 1 to about 7, such as from about 1 to about 5, such as from about 1.5 to about 4, etc., by way of example 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, or 5. In at least one embodiment, the pH of the electrolyte solution of the present disclosure is adjusted before passing an electric current through the electrolyte solution (detailed below). In at least one embodiment, the pH of the electrolyte solution of the present disclosure is maintained within the target pH target pH range while passing an electric current through the electrolyte solution.

[0048] Optionally, in step 190, time is provided to reach an equilibrium state. In at least one embodiment, the solution is left for a time period ranging from 1 hour to 2 days to reach an equilibrium state. The time provided to reach an equilibrium state can 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 value can form an upper endpoint or a lower endpoint as needed).

[0049] In at least one aspect, method 100 is performed in the presented order. Alternatively, method 100 is performed in a different order. In at least one aspect, some steps are performed in sequence and other steps are performed in a different order. For example, steps 110 and 120 are performed in sequence, and steps 130, 140, 150, 160, 170, 180, and 190 are performed in a different order after steps 110 and 120. In another example, steps 110 and 120 are performed in a different order, and steps 130, 140, 150, 160, 170, 180, and 190 are performed in sequence. In another example, steps 110, 120, 130, 140, 150, and 160 are performed in sequence, and steps 170, 180, and 190 are performed in a different order. A set of steps can be performed before another set of steps. For example, steps 110 and 120 can be performed in any order, and after steps 110 and 120 are performed, steps 130, 140, 150, and 160 are performed in any order. As will be understood by those skilled in the art, other orders are also contemplated. Further, one or more of steps 170, 180, and 190 are omitted in some aspects.

[0050] FIG. 2 is a flow diagram showing a method 200 for forming a chromium alloy coating on a substrate by electroplating according to one or more aspects of the present disclosure. In step 210, an electrolyte solution is prepared, such as by the method 100 of FIG. 1. In step 220, method 200 further includes adjusting and / or maintaining the pH of the electrolyte solution to a target pH or target pH range. In at least one aspect, the target pH is a pH ranging from about 1 to about 4. This pH can be maintained at about 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 value can form the upper or lower endpoint as appropriate).

[0051] In process 230, method 200 further includes adjusting and / or maintaining the temperature of the electrolyte solution (e.g., the electrolyte solution formed by process 210). In at least one aspect, the temperature is adjusted / maintained to a target temperature of from about 20°C to about 70°C, such as from about 20°C to about 40°C, such as from about 20°C to about 35°C, by way of example 20°C, 25°C, or 30°C, using any suitable heating or cooling device. In at least one aspect, the temperature of the electrolyte solution is adjusted prior to passing a current through the electrolyte solution. In at least one aspect, the temperature of the electrolyte solution is maintained while passing a current through the electrolyte solution to maintain the appearance of the deposited layer. By maintaining the temperature within the desired range, reproducible results with respect to appearance and alloy composition are more readily obtained.

[0052] The method further includes, in process 240, introducing a cathode including a substrate and an anode into the electrolyte solution, and, in process 250, passing a current through the electrolyte solution between the cathode and the anode to deposit a chromium alloy on the cathode substrate. In at least one aspect, the cathode substrate is, for example, a steel substrate, an iron-based alloy substrate, a copper substrate, a brass substrate, a nickel substrate, a copper-coated substrate (e.g., copper-coated steel or copper-coated iron-based alloy), or a nickel-coated substrate (e.g., nickel-coated steel or nickel-coated iron-based alloy).

[0053] In at least one aspect, the anode includes a carbonaceous electrode material. For example, the carbonaceous anode can be a graphite anode or other anode containing carbon. In at least one aspect, the graphite anode is for a chlorine-based electrolyte solution (e.g., an electrolyte solution containing one or more compounds having chlorides such as chromium(III) chloride), a sulfate-based electrolyte solution (e.g., an electrolyte solution containing one or more compounds having sulfates such as chromium(III) sulfate), or a chloride and sulfate-based electrolyte solution (e.g., an electrolyte solution containing one or more compounds having chlorides and one or more other compounds having sulfates). Advantageously, the graphite anode or other carbonaceous anode minimizes gas evolution and the formation of undesirable by-products and promotes a desirable deposition rate (e.g., ranging from about 1 micron to about 2 microns per minute). Alternatively, a platinum anode or a platinum-plated titanium anode can be used for a sulfate-based electrolyte solution (e.g., an electrolyte solution containing one or more compounds having sulfates such as chromium(III) sulfate). For example, the platinum anode or platinum-plated titanium anode can be used when the electrolyte solution does not contain a compound having chloride so that chlorine gas is not generated, or when the electrolyte solution has less chloride so that the generation of chlorine gas is reduced (e.g., when it is not necessary to reduce the generation of chlorine gas using a carbonaceous anode).

[0054] In at least one aspect, passing an electric current between the cathode and the anode is carried out using a direct current. In at least one aspect, from about 50 mA / cm 2 to about 600 mA / cm 2 , for example from about 100 mA / cm 2 to about 500 mA / cm 2 , for example from about 100 mA / cm 2 to about 400 mA / cm 2 , for example from about 200 mA / cm 2 to about 400 mA / cm 2 , as an example 200 mA / cm 2 , 250 mA / cm 2or 300 mA / cm 2 A direct current having a current density of is used. The value of the current density can be adjusted according to the separation distance between the cathode and the anode. In at least one embodiment, the current density depends on the separation distance between the cathode and the anode and, if necessary, is about 50 mA / cm 2 , 100 mA / cm 2 , 150 mA / cm 2 , 200 mA / cm 2 , 250 mA / cm 2 , 300 mA / cm 2 , 350 mA / cm 2 , 400 mA / cm 2 , 450 mA / cm 2 , or 500 mA / cm 2 (any value can form an upper or lower endpoint if necessary). For example, a current density ranging from about 200 mA / cm 2 to about 400 mA / cm 2 can be applied when the cathode and the anode are separated by about 3 cm. The inventors have discovered that a current density within the above range minimizes the formation of undesirable hexavalent chromium by-products while achieving a reasonable rate, for example, deposition of 0.5 to 1 micron / min.

[0055] Upon passing an electric current between a cathode and an anode, chromium and iron are deposited on the cathode substrate. Step 250 is carried out until a chromium alloy coating layer having a desired thickness is formed on the substrate. In at least one aspect, the chromium alloy coating layer is a chromium-iron alloy having 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 chromium-iron alloy can have about 1 wt%, 2 wt%, 10 wt%, 11 wt%, or 12 wt% iron. Further, the chromium-iron alloy has from about 80 wt% chromium to about 99 wt% chromium, such as from about 85 wt% chromium to about 95 wt% chromium, by way of 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.

[0056] In response to carrying out step 250, chromium is deposited on the substrate. In at least one aspect, chromium and carbon are co-deposited on the substrate. In at least one aspect, step 250 results in 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) being formed on the substrate. In at least one aspect, a chromium layer having a thickness greater than about 5 microns can have a hardness greater than about 800 HV.

[0057] Aspect An electrolyte solution for electroplating, comprising a trivalent chromium salt; an oxalate compound; an iron salt; aluminum sulfate; an alkali metal sulfate; and an alkali metal halide.

[0058] Clause 2. The trivalent chromium salt is present in an amount ranging from about 0.3 mol per liter of the electrolyte solution to about 0.9 mol per liter of the electrolyte solution; the oxalate compound is present in an amount ranging from about 0.2 mol per liter of the electrolyte solution to about 1.2 mol per liter of the electrolyte solution; the iron salt is present in an amount ranging from about 0.005 mol per liter of the electrolyte solution to about 0.2 mol per liter of the electrolyte solution; the aluminum sulfate is present in an amount ranging from about 0.05 mol per liter of the electrolyte solution to about 0.5 mol per liter of the electrolyte solution; the alkali metal sulfate is present in an amount ranging from about 0.1 mol per liter of the electrolyte solution to about 2.0 mol per liter of the electrolyte solution; the alkali metal halide is present in an amount ranging from about 0.1 mol per liter of the electrolyte solution to about 0.5 mol per liter of the electrolyte solution, the electrolyte solution of Clause 1.

[0059] Clause 3. The iron salt is a divalent iron salt containing one or more of iron(II) sulfate, iron(II) chloride, iron(II) acetate, and hydrates thereof, the electrolyte solution of Clause 1 or 2.

[0060] Clause 4. The iron salt is a trivalent iron salt containing one or more of iron(III) sulfate, iron(III) chloride, iron(III) acetate, and hydrates thereof, the electrolyte solution of any one of Clauses 1 to 3.

[0061] Clause 5. The trivalent chromium salt is selected from chromium(III) halide, chromium(III) sulfate, or a combination thereof, the electrolyte solution of any one of Clauses 1 to 4.

[0062] Clause 6. The oxalate compound is selected from sodium oxalate, potassium oxalate, oxalic acid, or a combination thereof, the electrolyte solution of any one of Clauses 1 to 5.

[0063] Clause 7. The alkali metal sulfate is selected from sodium sulfate, potassium sulfate, or a combination thereof, the electrolyte solution of any one of Clauses 1 to 6.

[0064] Item 8. An electrolyte solution according to any one of Items 1 to 7, wherein the alkali metal halide is selected from sodium fluoride, potassium fluoride, or a combination thereof.

[0065] Item 9. An electrolyte solution according to any one of Items 1 to 8, wherein the pH of the electrolyte solution ranges from about 1 to about 4.

[0066] Item 10. An electrolyte solution according to any one of Items 1 to 9, further comprising sodium lauryl sulfate, sodium lauryl ether sulfate, or a combination thereof.

[0067] Item 11. An electrolyte solution for electroplating, comprising an amount of trivalent chromium salt ranging from about 0.3 mol per liter of the electrolyte solution to about 0.9 mol per liter; an amount of oxalate compound ranging from about 0.2 mol per liter of the electrolyte solution to about 1.2 mol per liter; an amount of iron salt ranging from about 0.005 mol per liter of the electrolyte solution to about 0.2 mol per liter; an amount of aluminum sulfate ranging from about 0.05 mol per liter of the electrolyte solution to about 0.5 mol per liter; an amount of alkali metal sulfate ranging from about 0.1 mol per liter of the electrolyte solution to about 2.0 mol per liter; and an amount of alkali metal halide ranging from about 0.1 mol per liter of the electrolyte solution to about 0.5 mol per liter.

[0068] Item 12. The electrolyte solution according to Item 11, wherein the iron salt is a divalent iron salt containing one or more of iron(II) sulfate, iron(II) chloride, iron(II) acetate, and hydrates thereof.

[0069] Item 13. The electrolyte solution according to Item 11 or 12, wherein the iron salt is a trivalent iron salt containing one or more of iron(III) sulfate, iron(III) chloride, iron(III) acetate, and hydrates thereof.

[0070] Item 14. The electrolyte solution according to any one of Items 11 to 13, wherein the trivalent chromium salt is selected from chromium(III) halide, chromium(III) sulfate, or a combination thereof.

[0071] Item 15. An electrolyte solution according to any one of Items 11 to 14, wherein the oxalate compound is selected from sodium oxalate, potassium oxalate, an acid of oxalate, or a combination thereof.

[0072] Item 16. An electrolyte solution according to any one of Items 11 to 15, wherein the alkali metal sulfate is selected from sodium sulfate, potassium sulfate, or a combination thereof.

[0073] Item 17. An electrolyte solution according to any one of Items 11 to 16, wherein the alkali metal halide is selected from sodium fluoride, potassium fluoride, or a combination thereof.

[0074] Item 18. An electrolyte solution according to any one of Items 11 to 17, wherein the pH of the electrolyte solution ranges from about 1 to about 4.

[0075] Item 19. An electrolyte solution according to any one of Items 11 to 18, further comprising sodium lauryl sulfate, sodium lauryl ether sulfate, or a combination thereof.

[0076] Clause 20. A method for chromium plating on a substrate using an electrolyte solution, comprising dissolving in an aqueous medium an amount of trivalent chromium salt ranging from about 0.3 mol per liter of electrolyte solution to about 0.9 mol per liter of electrolyte solution; dissolving an amount of oxalate compound ranging from about 0.2 mol per liter of electrolyte solution to about 1.2 mol per liter of electrolyte solution; dissolving an amount of iron salt ranging from about 0.005 mol per liter of electrolyte solution to about 0.2 mol per liter of electrolyte solution; dissolving an amount of aluminum sulfate ranging from about 0.05 mol per liter of electrolyte solution to about 0.5 mol per liter of electrolyte solution; dissolving an amount of alkali metal sulfate ranging from about 0.1 mol per liter of electrolyte solution to about 2.0 mol per liter of electrolyte solution; dissolving an amount of alkali metal halide ranging from about 0.1 mol per liter of electrolyte solution to about 0.5 mol per liter of electrolyte solution; and passing an electric current through the electrolyte solution between a cathode and an anode to deposit chromium on the substrate.

[0077] 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.

[0078] Clause 22. The method of Clause 20 or 21, wherein the anode is a platinum material, a platinum-plated titanium material, or a carbonaceous electrode material.

[0079] Clause 23. The method of any one of Clauses 20 to 22, wherein the current has a current density in the range of about 150 to about 600 mA / cm 2 by passing a direct current between the anode and the cathode.

[0080] Clause 24. The method of any one of Clauses 20 to 23, wherein the current density has a current density in the range of about 200 to about 400 mA / cm 2

[0081] Clause 25. The method of any one of Clauses 20 to 24, wherein the electrolyte solution is maintained at a temperature in the range of about 20°C to about 60°C.

[0082] The method according to any one of clauses 20 to 25, further comprising adjusting the pH of the electrolyte solution to a pH in the range of from about 1.5 to about 4.

[0083] The method according to any one of clauses 20 to 26, wherein the iron salt is a divalent iron salt comprising one or more of iron(II) sulfate, iron(II) chloride, iron(II) acetate, and hydrates thereof.

[0084] The method according to any one of clauses 20 to 27, wherein the iron salt is a trivalent iron salt comprising one or more of iron(III) sulfate, iron(III) chloride, iron(III) acetate, and hydrates thereof.

[0085] The method according to any one of clauses 20 to 28, wherein the trivalent chromium salt is selected from chromium(III) halide, chromium(III) sulfate, or a combination thereof.

[0086] The method according to any one of clauses 20 to 29, wherein the oxalate compound is selected from sodium oxalate, potassium oxalate, oxalic acid, or a combination thereof.

[0087] The method according to any one of clauses 20 to 30, wherein the alkali metal sulfate is selected from sodium sulfate, potassium sulfate, or a combination thereof.

[0088] The method according to any one of clauses 20 to 31, wherein the alkali metal halide is selected from sodium fluoride, potassium fluoride, or a combination thereof.

[0089] The method according to any one of clauses 20 to 32, further comprising dissolving an amount of sodium lauryl sulfate, sodium lauryl ether sulfate, or a combination thereof ranging from about 0.1 gram per liter of the electrolyte solution to about 1 gram per liter of the electrolyte solution.

[0090] Clause 34. A method of chromium plating on a substrate using an electrolyte solution, comprising introducing a cathode and an anode into an electrolyte solution containing 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 through the electrolyte between the anode and the cathode to deposit a chromium layer on the substrate.

[0091] 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.

[0092] Clause 36. The method of clause 34 or 35, wherein the anode is a platinum material, a platinum-plated titanium material, or a carbonaceous electrode material.

[0093] Clause 37. The method of any one of clauses 34 to 36, wherein the electric current has a current density in the range of about 100 to about 600 mA / cm 2 by passing a direct current between the anode and the cathode.

[0094] Clause 38. The method of any one of clauses 34 to 37, wherein the current density has a current density in the range of about 200 to about 400 mA / cm 2

[0095] Clause 39. The method of any one of clauses 34 to 38, wherein the electrolyte solution is maintained at a temperature in the range of about 20°C to about 60°C.

[0096] Clause 40. The method of any one of clauses 34 to 39, further comprising adjusting the pH of the electrolyte solution to a pH in the range of about 1.5 to about 4.

[0097] Clause 41. The method of any one of clauses 34 to 40, wherein the iron salt is a divalent iron salt including one or more of iron(II) sulfate, iron(II) chloride, iron(II) acetate, and hydrates thereof.

[0098] ​Method according to any of clauses 34 to 41, wherein the iron salt is a trivalent iron salt comprising one or more of iron(III) sulfate, iron(III) chloride, iron(III) acetate, and hydrates thereof.

[0099] Method according to any of clauses 34 to 42, wherein the trivalent chromium salt is selected from chromium(III) halides, chromium(III) sulfate, or combinations thereof.

[0100] Method according to any of clauses 34 to 43, wherein the oxalate compound is selected from sodium oxalate, potassium oxalate, oxalic acid, or combinations thereof.

[0101] Method according to any of clauses 34 to 44, wherein the alkali metal sulfate is selected from sodium sulfate, potassium sulfate, or combinations thereof.

[0102] Method according to any of clauses 34 to 45, wherein the alkali metal halide is selected from sodium fluoride, potassium fluoride, or combinations thereof.

[0103] Method according to any of clauses 34 to 46, further comprising dissolving an amount of sodium lauryl sulfate, sodium lauryl ether sulfate, or combinations thereof ranging from about 0.1 grams per liter of the electrolyte solution to about 1 gram per liter of the electrolyte solution.

[0104] A substrate comprising a chromium-iron alloy coating having a chromium content in the range of about 40 wt% to about 90 wt%, an iron content in the range of about 8 wt% to about 18 wt%, and a carbon content in the range of about 5 wt% to about 50 wt%.

[0105] The substrate according to clause 48, wherein the substrate comprises one or more of steel, copper, brass, or nickel.

[0106] The substrate according to clause 48 or 49, wherein the coating has a thickness in the range of about 1 micron to about 100 microns.

Example

[0107] To further illustrate the embodiments described herein, the following non-limiting examples are provided. However, these examples are not intended to be comprehensive nor are they intended to limit the scope of the embodiments described herein.

[0108] Example 1 The components of Example 1 were first mixed stepwise with chromium chloride hexahydrate and sodium oxalate, and then with the metal salt. The pH of Example 1 was ~2.2.

[0109] TIFF0007689818000001.tif97170

[0110] Example 2 The components of Example 2 were first mixed stepwise with chromium chloride hexahydrate and sodium oxalate, and then with the metal salt. The components of Example 2 were the same as those of Example 1, except that the amount of ferrous sulfate heptahydrate was increased tenfold compared to the components of Example 1. The pH of Example 1 was ~2.2.

[0111] TIFF0007689818000002.tif97170

[0112] Example 3 The components of Example 3 were first mixed stepwise with chromium chloride hexahydrate and sodium oxalate, and then with the metal salt. The components of Example 3 were the same as those of Example 1, except that in Example 3, ferrous sulfate heptahydrate was replaced with ferric chloride. The pH of Example 1 was approximately 2.2.

[0113] TIFF0007689818000003.tif87170

[0114] Figure 3 is an image 300 of chromium-iron alloy plated substrates 310, 320, 330, and 340 formed by the process of Figure 2, where each substrate was plated at a different current density using the electrolyte solution of Example 1. For each chromium-iron alloy plated substrate 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 °C and a pH of about 2.2. The chromium-iron alloy plated substrate 310 was plated at a current density of 100 mA / cm 2 resulting in a chromium-iron alloy layer having a thickness of 12 μm. The chromium-iron alloy plated substrate 320 was plated at a current density of 200 mA / cm 2 resulting in a chromium-iron alloy layer having a thickness of 15 μm. The chromium-iron alloy plated substrate 330 was plated at a current density of 250 mA / cm 2 resulting in a chromium-iron alloy layer having a thickness of 28 μm. The chromium-iron alloy plated substrate 340 was plated at a current density of 300 mA / cm 2 resulting in a chromium-iron layer having a thickness of 32 μm. X-ray fluorescence was performed on a portion of each coating, and the chromium content and iron content were determined in weight %. It should be noted that since X-ray fluorescence does not detect carbon, in at least one aspect, the chromium-iron alloys described herein also contain carbon, but the carbon is not shown in the X-ray fluorescence results. The results are shown in Table I.

[0115] As shown in Table I, any current density ranging from 100 mA / cm 2 to about 300 mA / cm 2 deposits a chromium-iron alloy layer. Current densities ranging from about 200 mA / cm 2 to about 280 mA / cm 2 provide thick chromium-iron alloy layers with low iron content. Further, a current density of 100 mA / cm 2 provides the thinnest chromium-iron alloy with high iron content relative to current densities ranging from about 200 mA / cm 2 to about 300 mA / cm 2

[0116] TIFF0007689818000004.tif66170

[0117] Figure 4 is an image 400 of chromium-iron alloy plated substrates 410, 420, 430, 440, and 450 formed by the process of FIG. 2, each substrate being plated at a different pH using the electrolyte solution of Example 1. For each of the chromium-iron alloy plated substrates 410, 420, 430, 440, and 450, the plating parameters were a direct current at a current density of 250 mA / cm 2 while maintaining the electrolyte solution at a temperature of 30°C for a plating time of about 1 hour. The chromium-iron alloy plated substrate 410 was plated at a pH of 1.0, resulting in a non-uniform chromium-iron alloy deposit that was considered to be less than 10 μm although not measured. The chromium-iron alloy plated substrate 420 was plated at a pH of 2.0, resulting in a non-uniform chromium-iron alloy deposit that was considered to be less than 10 μm although not measured. The chromium-iron alloy plated substrate 430 was plated at a pH of 2.5, resulting in a chromium-iron alloy layer having a thickness of 20 μm. The chromium-iron alloy plated substrate 440 was plated at a pH of 3.0, resulting in a chromium-iron alloy layer having a thickness of 28 μm. The chromium-iron alloy plated substrate 450 was plated at a pH of 3.5, resulting in a chromium-iron alloy layer having a thickness of 45 μm. X-ray fluorescence was performed on a portion of each coating to determine the chromium content and iron content in weight percent. The results are shown in Table II.

[0118] As shown in Table II, any pH from 2.5 to 3.5 deposits a chromium-iron alloy layer. The pH range from 2.5 to 3.0 advantageously provides a thick chromium-iron alloy layer having the desired iron content. A pH of 3.5 provides a thicker chromium-iron alloy layer with a lower iron content compared to the pH range from 2.5 to 3.0.

[0119] TIFF0007689818000005.tif76170

[0120] Figure 5 is an image 500 of chromium-iron alloy plating substrates 510, 520, 530, and 540 formed by the process of Figure 2, each plated at a different current density using the electrolyte solution of Example 2. For each chromium-iron alloy plating substrate 510, 520, 530, and 540, the plating parameters were a plating time of about 1 hour while maintaining the electrolyte solution at a temperature of 30 °C and a pH of about 2.2. The chromium-iron alloy plating substrate 510 was plated at a current density of 100 mA / cm 2 resulting in a chromium-iron alloy layer having a thickness of 30 μm. The chromium-iron alloy plating substrate 520 was plated at a current density of 200 mA / cm 2 resulting in a chromium-iron alloy layer having a thickness of 40 μm. The chromium-iron alloy plating substrate 530 was plated at a current density of 250 mA / cm 2 resulting in a chromium-iron alloy layer having a thickness of 70 μm. The chromium-iron alloy plating substrate 540 was plated at a current density of 300 mA / cm 2 resulting in a chromium-iron layer having a thickness of 50 μm. X-ray fluorescence was performed on a portion of each coating, and the chromium content and iron content were determined in weight percent. The results are shown in Table III.

[0121] As shown in Table III, any current density ranging from 100 mA / cm 2 to about 300 mA / cm 2 deposits a chromium-iron alloy. Current densities ranging from about 100 mA / cm 2 to about 250 mA / cm 2 provide a thick chromium-iron alloy layer. Further, at a current density of 300 mA / cm 2 , the thickness of the chromium-iron alloy is reduced compared to the thickness of the chromium-iron alloy deposited at a current density of 250 mA / cm 2 .

[0122] TIFF0007689818000006.tif66170

[0123] FIG. 6 is an image 600 of chromium-iron alloy plated substrates 610, 620, 630, 640, 650, and 660 formed by the process of FIG. 2, each plated at a different pH using the electrolyte solution of Example 2. For each of the chromium-iron alloy plated substrates 610, 620, 640, 650, and 660, the plating parameters were a direct current at a current density of 250 mA / cm 2 with a plating time of about 1 hour while maintaining the electrolyte solution at a temperature of 30°C. The chromium-iron alloy plated substrate 610 was plated at a pH of 1.5, resulting in a non-uniform chromium-iron alloy deposit. The chromium-iron alloy plated substrate 620 was plated at a pH of 2.0, resulting in a non-uniform chromium-iron alloy deposit. The chromium-iron alloy plated substrate 630 was plated at a pH of 2.5, resulting in a chromium-iron alloy layer having a thickness of 50 μm. The chromium-iron alloy plated substrate 640 was plated at a pH of 3.0, resulting in a chromium-iron alloy layer having a thickness of 70 μm. The chromium-iron alloy plated substrate 650 was plated at a pH of 3.5, resulting in a chromium-iron alloy layer having a thickness of 50 μm. The chromium-iron alloy plated substrate 660 was plated at a pH of 4.0. X-ray fluorescence was performed on a portion of each coating, and the chromium content and iron content were determined in weight %. The results are shown in Table IV.

[0124] As shown in Table IV, any pH from 1.5 to 4.0 deposits a chromium-iron alloy layer. The pH range from 2.0 to 4.0 advantageously provides a thick chromium-iron alloy layer having a desired high chromium content. A pH of 3.0 provides a thicker chromium-iron alloy layer with a good-quality deposit. At a pH of 4, the deposit exhibited burning at the edges, and at a pH of 2 or less, the deposit was non-uniform.

[0125] TIFF0007689818000007.tif87170

[0126] Figure 7 is an image 700 of chromium-iron alloy plating substrates 710, 720, 730, 740, 750, and 760 formed by the process of FIG. 2, each plated at a different current density using the electrolyte solution of Example 3. For each chromium-iron alloy plating substrate 710, 720, 720, 730, 740, and 760, the plating parameters were a plating time of about 1 hour while maintaining the electrolyte solution at a temperature of 30° C. and a pH of about 2.2. The chromium-iron alloy plating substrate 710 was plated at a current density of 100 mA / cm 2 , resulting in a non-uniform chromium-iron alloy deposit having a thickness of less than 10 μm. The chromium-iron alloy plating substrate 720 was plated at a current density of 150 mA / cm 2 , resulting in a non-uniform chromium-iron alloy deposit having a thickness of less than 10 μm. The chromium-iron alloy plating substrate 730 was plated at a current density of 200 mA / cm 2 , resulting in a chromium-iron alloy layer having a thickness of 10 μm. The chromium-iron alloy plating substrate 740 was plated at a current density of 300 mA / cm 2 , resulting in a chromium layer having a thickness of 30 μm. The chromium-iron alloy plating substrate 750 was plated at a current density of 400 mA / cm 2 , resulting in a chromium layer having a thickness of 50 μm. The chromium-iron alloy plating substrate 760 was plated at a current density of 500 mA / cm 2 , resulting in a deposit exhibiting burning at the edges.

[0127] As shown in Table V, any current density ranging from 200 mA / cm 2 to about 400 mA / cm 2 deposits chromium-iron alloy. Current densities ranging from about 300 mA / cm 2 to about 400 mA / cm 2 provide a thick chromium-iron alloy layer. Further, at a current density of 500 mA / cm 2 , the thickness of the chromium-iron alloy increased compared to the thickness of the chromium-iron alloy deposited at a current density of 400 mA / cm 2 , but the edge deposits burned (black powder).

[0128] TIFF0007689818000008.tif87170

[0129] Figure 8 is an image 800 of chromium-iron alloy plating substrates 810, 820, 830, 840, 850, 860, and 870 formed by the process of FIG. 2, each plated at a different pH using the electrolyte solution of Example 3. For each of the chromium-iron alloy plating substrates 810, 810, 820, 850, 860, and 870, the plating parameters were a direct current at a current density of 250 mA / cm while maintaining the electrolyte solution at a temperature of about 30° C. for a plating time of about 1 hour. 2 The chromium-iron alloy plating substrate 810 was plated at a pH of 1.0, resulting in a chromium-iron alloy deposit having a thickness of 20 μm. The chromium-iron alloy plating substrate 820 was plated at a pH of 1.5, resulting in a chromium-iron alloy layer having a thickness of 24 μm. The chromium-iron alloy plating substrate 830 was plated at a pH of 2.0, resulting in a chromium-iron alloy layer having a thickness of 20 μm. The chromium-iron alloy plating substrate 840 was plated at a pH of 3.0, resulting in a chromium-iron alloy layer having a thickness of 16 μm. The chromium-iron alloy plating substrate 860 was plated at a pH of 3.5, resulting in a chromium-iron alloy layer having a thickness of 16 μm. The chromium-iron alloy plating substrate 870 was plated at a pH of 4.0, resulting in a chromium-iron alloy deposit with uneven thickness. X-ray fluorescence was performed on a portion of the coatings deposited at pH 2 and pH 2.5, and the chromium content and iron content were determined in weight %. The results are shown in Table VI.

[0130] As shown in Table VI, any pH from 1.0 to 4.0 deposits a chromium-iron alloy. The pH from 1.0 to 2.5 advantageously provides a thicker chromium-iron alloy layer than higher pH values. Further, the pH from 1.5 to 2.0 provides the thickest chromium-iron alloy layer.

[0131] TIFF0007689818000009.tif97170

[0132] FIG. 9 is an image 900 of chromium-iron alloy plated substrates 910, 920, 930, and 940 formed by the process of FIG. 2, each substrate being plated at a different temperature using the electrolyte solution of Example 3. For each of the chromium-iron alloy plated substrates 910, 920, 930, and 940, the plating parameters were a direct current at a current density of 250 mA / cm 2 with a plating time of about 1 hour while maintaining the electrolyte solution at a pH of about 2.1. The chromium-iron alloy plated substrate 910 was plated at a temperature of 30° C., resulting in a chromium-iron alloy layer having a thickness of 40 μm. The chromium-iron alloy plated substrate 920 was plated at a temperature of 40° C., resulting in a chromium-iron alloy layer having a thickness of 30 μm. The chromium-iron alloy plated substrate 930 was plated at a temperature of 50° C., resulting in a chromium-iron alloy layer having a thickness of 30 μm. The chromium-iron alloy plated substrate 940 was plated at a temperature of 60° C., resulting in a chromium-iron alloy layer having a small thickness. The results are shown in Table VII.

[0133] As shown in Table VII, any temperature ranging from about 30° C. to about 50° C. deposits a chromium-iron alloy layer. The operating temperature of 30° C. provided the thickest chromium-iron alloy layer, although the deposit at 40° C. was aesthetically superior.

[0134] TIFF0007689818000010.tif66170

[0135] Using the electrolyte solution of Example 3, a chromium-iron-alloy coating was deposited at 300 mA / cm while maintaining the electrolyte solution at a temperature of about 40° C. and a pH of about 2.5. 2The coating was deposited onto a Taber Wear panel over a plating time of approximately 2 hours with a direct current of the current density of

[0136] Using the electrolyte solution of Example 1, while maintaining the electrolyte solution at a temperature of approximately 35 °C and a pH of approximately 2.5, a chromium-iron-alloy coating was deposited thereon with a direct current of a current density of 250 mA / cm 2 over a plating time of approximately 2 hours. The alloy composition of the coating measured by SEM-EDS was chromium ~80 wt%, iron ~12 wt%, and carbon ~8 wt%. The hardness values were measured on a coupon "as plated" and also after firing the coupon at approximately 190 °C for 23 hours. The average of five hardness measurements of the "as plated" chromium-iron alloy layer was 1147 HV. The average of five hardness measurements of the "fired" chromium-iron alloy layer was 1249 HV.

[0137] Overall, the present disclosure improves an electrolyte solution for electrodeposition of chromium-iron alloys, a method for forming chromium-iron alloys, and a method for electrodeposition of chromium-iron alloys.

[0138] The descriptions of the various aspects of the present disclosure are presented for purposes of illustration and are not intended to be exhaustive or to limit the disclosed aspects. Numerous 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 terms used herein are chosen in order to best explain the principles of an aspect, the practical application to technologies found in the marketplace, or the technological improvement thereof, or to enable other ones of ordinary skill in the art to understand the aspects disclosed herein. While the foregoing is directed to aspects of the present disclosure, other and further aspects of the present disclosure can be devised without departing from the basic scope thereof.

Claims

1. Trivalent chromium salt; Oxalate compound; Iron salt; Aluminum sulfate; Alkali metal sulfate; and Alkali metal halide comprising, The trivalent chromium salt is present in an amount ranging from 0.3 mol per liter of the electrolyte solution to 0.9 mol per liter; The oxalate compound is present in an amount ranging from 0.2 mol per liter of the electrolyte solution to 1.2 mol per liter; The iron salt is present in an amount ranging from 0.005 mol per liter of the electrolyte solution to 0.2 mol per liter; Aluminum sulfate is present in an amount ranging from 0.05 mol per liter to 0.5 mol per liter; The alkali metal sulfate is present in an amount ranging from 0.1 mol per liter of the electrolyte solution to 2.0 mol per liter; The alkali metal halide is present in an amount ranging from 0.1 mol per liter of the electrolyte solution to 0.5 mol per liter, an electrolyte solution for electroplating.

2. The electrolyte solution according to claim 1, wherein the iron salt is a divalent iron salt containing one or more of iron (II) sulfate, iron (II) chloride, iron (II) acetate, and hydrates thereof.

3. The electrolyte solution according to claim 1 or 2, wherein the iron salt is a trivalent iron salt containing one or more of iron (III) sulfate, iron (III) chloride, iron (III) acetate, and hydrates thereof.

4. The electrolyte solution according to any one of claims 1 to 3, wherein the trivalent chromium salt is selected from chromium (III) halide, chromium (III) sulfate, or a combination thereof.

5. The electrolyte solution according to any one of claims 1 to 4, wherein the oxalate compound is selected from sodium oxalate, potassium oxalate, oxalic acid, or a combination thereof.

6. The electrolyte solution according to any one of claims 1 to 5, wherein the alkali metal sulfate is selected from sodium sulfate, potassium sulfate, or a combination thereof.

7. The electrolyte solution according to any one of claims 1 to 6, wherein the alkali metal halide is selected from sodium fluoride, potassium fluoride, or a combination thereof.

8. The electrolyte solution according to any one of claims 1 to 7, wherein the pH of the electrolyte solution is in the range of 1 to 4.

9. The electrolyte solution according to any one of claims 1 to 8, further comprising sodium lauryl sulfate, sodium lauryl ether sulfate, or a combination thereof.

10. A method (200) for chromium plating a substrate using an electrolyte solution, comprising: introducing a cathode and an anode into an electrolyte solution containing a trivalent chromium salt, an oxalate compound, an iron salt, aluminum sulfate, an alkali metal sulfate, and an alkali metal halide (240); and passing an electric current through the electrolyte between the anode and the cathode to deposit a chromium layer on the substrate (250). comprising: the trivalent chromium salt is present in an amount ranging from 0.3 mol per liter of the electrolyte solution to 0.9 mol per liter of the electrolyte solution; the oxalate compound is present in an amount ranging from 0.2 mol per liter of the electrolyte solution to 1.2 mol per liter of the electrolyte solution; the iron salt is present in an amount ranging from 0.005 mol per liter of the electrolyte solution to 0.2 mol per liter of the electrolyte solution; aluminum sulfate is present in an amount ranging from 0.05 mol per liter of the electrolyte solution to 0.5 mol per liter of the electrolyte solution; the alkali metal sulfate is present in an amount ranging from 0.1 mol per liter of the electrolyte solution to 2.0 mol per liter of the electrolyte solution; the alkali metal halide is present in an amount ranging from 0.1 mol per liter of the electrolyte solution to 0.5 mol per liter of the electrolyte solution.

11. The method (200) according to claim 10, 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.

12. The method (200) according to claim 10 or 11, wherein the anode is a platinum material, a platinum-plated titanium material, or a carbonaceous electrode material.

13. The current has a current density in the range of 10 to 60 mA / cm by passing a direct current between the anode and the cathode. ２ The method (200) according to any one of claims 10 to 12.

14. A current density ranging from 20 to 40 mA / cm ２ The method (200) according to claim 13, having a current density in the range of

15. The method (200) according to claim 13 or 14, wherein the electrolyte solution is maintained at a temperature in the range of 20°C to 60°C.

16. The method (200) according to any one of claims 10 to 15, further comprising adjusting the pH of the electrolyte solution to a pH in the range of 1.5 to 4.

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