JP7575445B2 - Titanium plating electrolyte and method for manufacturing titanium-plated member using the titanium plating electrolyte - Google Patents

Description

The present disclosure relates to a titanium plating electrolyte and a method for producing a titanium-plated member using the titanium plating electrolyte. This application claims priority to Japanese Patent Application No. 2020-036786, filed on March 4, 2020. All contents of said Japanese patent application are incorporated herein by reference.

Titanium (Ti) is a metal with excellent corrosion resistance, heat resistance, and specific strength. However, titanium is expensive to produce and difficult to smelt and process. This has prevented titanium from being widely used. Currently, as one method of utilizing the high corrosion resistance and high strength of titanium and titanium compounds, a dry film formation method using CVD (Chemical Vapor Deposition) or PVD (Physical Vapor Deposition) has been industrialized in part. However, the dry film formation method tends to be difficult to form a film on a substrate with a complex shape. As an alternative to the dry film formation method, a method of electrolytically depositing titanium in a molten salt has been proposed (for example, International Publication No. 2018/216320 (Patent Application No. 2017-100757) (Patent Document 1), International Publication No. 2017/159324 (Patent Document 2)).

International Publication No. 2018/216320 International Publication No. 2017/159324

The titanium plating electrolyte according to one embodiment of the present disclosure comprises:
at least one alkali metal ion selected from the group consisting of lithium ions, sodium ions, and potassium ions;
at least one halide ion selected from the group consisting of fluoride ions and chloride ions;
Titanium ions,
and an oxide ion,
The content of the oxide ions is 0.1 mol % or more and 1 mol % or less based on the total amount of anions and cations contained in the titanium plating electrolyte.

A method for producing a titanium-plated member according to one embodiment of the present disclosure includes the steps of:
Providing a substrate having an electrically conductive surface;
immersing the substrate in the titanium plating electrolyte, the titanium plating electrolyte being molten;
and applying a voltage between the substrate and an anode corresponding to the substrate to form a titanium plating film on the conductive surface of the substrate.

FIG. 1 is a flow chart showing a procedure for manufacturing a titanium-plated member. FIG. 2 is a schematic cross-sectional view showing an example of a state in which a substrate is immersed in a molten titanium plating solution composition. FIG. 3 is an SEM image of the surface of a titanium plated member.

[Problem that this disclosure aims to solve]
The method of electrodepositing titanium in a molten salt is capable of forming a titanium plating film with a smoother surface than the above-mentioned dry film formation method, but there is still room for improvement, such as the formation of a titanium plating film suitable for the application of the titanium-plated member (hereinafter sometimes referred to as a "titanium-plated member").

The present disclosure has been made in consideration of the above circumstances, and aims to provide a titanium plating electrolyte and a method for manufacturing a titanium-plated member using the titanium plating electrolyte. In particular, the present disclosure aims to provide a titanium plating electrolyte suitable for manufacturing electrodes for electrolysis, and a method for manufacturing a titanium-plated member using the titanium plating electrolyte.

[Effects of this disclosure]
According to the present disclosure, it is possible to provide a titanium plating electrolyte and a method for producing a titanium-plated member using the titanium plating electrolyte. In particular, according to the present disclosure, it is possible to provide a titanium plating electrolyte suitable for producing an electrode for electrolysis and a method for producing a titanium-plated member using the titanium plating electrolyte.

[Description of the embodiments of the present disclosure]
First, the embodiments of the present disclosure will be listed and described.
[1] A titanium plating electrolyte according to one embodiment of the present disclosure comprises:
at least one alkali metal ion selected from the group consisting of lithium ions, sodium ions, and potassium ions;
at least one halide ion selected from the group consisting of fluoride ions and chloride ions;
Titanium ions,
and an oxide ion,
The content of the oxide ions is 0.1 mol % or more and 1 mol % or less based on the total amount of anions and cations contained in the titanium plating electrolyte.
The titanium plating electrolyte according to one embodiment of the present disclosure has the above-mentioned configuration, and is therefore particularly suitable for the manufacture of electrodes for electrolysis. In other words, by using the molten salt of the titanium plating electrolyte as a plating bath in titanium plating, titanium plating suitable for the manufacture of electrodes for electrolysis can be performed.

[2] The halide ion includes the chloride ion,
The content of the chloride ions is preferably 0.1 mol % or more and 99.9 mol % or less based on the total amount of anions contained in the titanium plating electrolyte, which makes it possible to adjust the melting point of the titanium plating electrolyte to a desired temperature.

[3] The halide ion includes the fluoride ion,
The content of the fluoride ions is preferably 0.1 mol % or more and 99.9 mol % or less based on the total amount of anions contained in the titanium plating electrolyte, which makes it possible to adjust the melting point of the titanium plating electrolyte to a desired temperature.

[4] The content of the titanium ions is preferably 0.1 mol% or more and 20 mol% or less relative to the total amount of cations contained in the titanium plating electrolyte. By specifying it in this way, it becomes possible to perform titanium plating with appropriate plating efficiency.

[5] A method for producing a titanium-plated member according to one embodiment of the present disclosure includes the steps of:
Providing a substrate having an electrically conductive surface;
a step of immersing the substrate in the titanium plating electrolyte according to any one of the above items [1] to [4], the titanium plating electrolyte being molten; and
and applying a voltage between the substrate and an anode corresponding to the substrate to form a titanium plating film on the conductive surface of the substrate.
The method for producing a titanium-plated member according to one embodiment of the present disclosure has the above-described configuration, and thus can perform plating suitable for producing electrodes for electrolysis.

[6] The conductive surface of the substrate preferably contains at least one selected from the group consisting of nickel, iron, copper, molybdenum, tungsten, carbon, and stainless steel. By specifying in this way, a titanium-plated member containing titanium plating with high strength can be manufactured.

[Details of the embodiment of the present disclosure]
Hereinafter, one embodiment of the present disclosure (hereinafter, referred to as "the present embodiment") will be described. However, the present embodiment is not limited thereto. In this specification, the notation in the form of "A to Z" means the upper and lower limits of a range (i.e., A or more and Z or less). When no unit is stated for A and a unit is stated only for Z, the unit of A and the unit of Z are the same.

<Electrolyte for titanium plating>
The titanium plating electrolyte according to this embodiment is
at least one alkali metal ion selected from the group consisting of lithium ions, sodium ions, and potassium ions;
at least one halide ion selected from the group consisting of fluoride ions and chloride ions;
Titanium ions,
and an oxide ion,
The content of the oxide ions is 0.1 mol % or more and 1 mol % or less based on the total amount of anions and cations contained in the titanium plating electrolyte.

In this embodiment, the term "electrolyte for titanium plating" refers to an electrolyte used as a plating bath (molten salt bath) when performing titanium plating. The electrolyte for titanium plating may be in a solid state or in a liquid state (i.e., in a molten salt state) when not used as a plating bath, such as during storage. In this embodiment, the term "electrolyte" refers to a concept including a substance that ionizes into cations and anions when dissolved in a solvent (so-called electrolyte in the narrow sense) and the solvent. The electrolyte for titanium plating includes at least one alkali metal ion, at least one halide ion, the titanium ion, and the oxide ion. Here, the alkali metal ion and the halide ion can be understood as being contained in the electrolyte for titanium plating as a solvent. The titanium ion can also be understood as corresponding to a cation when the electrolyte in the narrow sense is ionized into cations and anions.

<Alkali metal ion>
In this embodiment, the alkali metal ion contained in the titanium plating electrolyte is at least one selected from the group consisting of lithium ions, sodium ions, and potassium ions. The alkali metal ions may be used alone or in combination. In one aspect of this embodiment, the alkali metal ions may include lithium ions, or may include lithium ions and potassium ions.

The lithium ion supply source is not particularly limited, but examples thereof include lithium fluoride, lithium chloride, lithium bromide, and lithium iodide. In this embodiment, the content of lithium ions is preferably 0.1 mol% or more and 99.9 mol% or less, and more preferably 1 mol% or more and 99 mol% or less, based on the total amount of cations contained in the titanium plating electrolyte. The content of lithium ions in the titanium plating electrolyte can be measured, for example, by inductively coupled plasma (ICP) analysis.

The sodium ion source is not particularly limited, but examples thereof include sodium fluoride, sodium chloride, sodium bromide, and sodium iodide. In this embodiment, the content of sodium ions is preferably 0.1 mol% or more and 99.9 mol% or less, and more preferably 1 mol% or more and 99 mol% or less, based on the total amount of cations contained in the titanium plating electrolyte. The content of sodium ions in the titanium plating electrolyte can be measured, for example, by inductively coupled plasma (ICP) analysis.

The source of potassium ions is not particularly limited, but examples thereof include potassium fluoride, potassium chloride, potassium bromide, and potassium iodide. In this embodiment, the content of potassium ions is preferably 0.1 mol% or more and 99.9 mol% or less, and more preferably 1 mol% or more and 99 mol% or less, based on the total amount of cations contained in the titanium plating electrolyte. The content of potassium ions in the titanium plating electrolyte can be measured, for example, by inductively coupled plasma (ICP) analysis.

In this embodiment, the content of alkali metal ions is preferably 80 mol% or more and 99.9 mol% or less, and more preferably 88 mol% or more and 99.5 mol% or less, based on the total amount of cations contained in the titanium plating electrolyte. Here, when multiple types of alkali metal ions are contained in the titanium plating electrolyte, the content of the alkali metal ions means the sum of the content of each element. The content of alkali metal ions in the titanium plating electrolyte can be measured, for example, by inductively coupled plasma (ICP) analysis.

<Titanium ion>
Examples of titanium ions include titanium (II) ions and titanium (III) ions. In the present embodiment, the titanium ions preferably include titanium (III) ions. Here, when a Roman numeral in parentheses is shown together with an element symbol or an element name, the Roman numeral indicates the valence of the element immediately before it. For example, titanium (II) ions mean "Ti ²⁺ ". Titanium (III) ions mean "Ti ³⁺ ". Titanium (IV) ions mean "Ti ⁴⁺ ".

The source of titanium (III) ions is not particularly limited, but examples thereof include titanium (III) trichloride (TiCl ₃ ), lithium hexafluorotitanate (III) (Li ₃ TiF ₆ ), potassium hexafluorotitanate (III) (K ₃ TiF ₆ ), and the like.

Titanium (III) ions may also be obtained by reducing titanium (IV) ions in a molten salt of a titanium plating electrolyte precursor through a comproportionation reaction represented by the following formula (1):
3Ti ⁴⁺ +Ti metal → 4Ti ³⁺ formula (1)

The source of the titanium (IV) ions is not particularly limited, and examples thereof include hexafluorotitanate (IV) (H ₂ TiF ₆ ), potassium hexafluorotitanate (IV) (K ₂ TiF ₆ ), ammonium hexafluorotitanate (IV) ((NH ₄ ) ₂ TiF ₆ ), sodium hexafluorotitanate (IV) (Na ₂ TiF ₆ ), potassium titanium oxalate dihydrate (K ₂ TiO(C ₂ O ₄ ) _{2.2H 2} O), titanium tetrachloride (IV) (TiCl ₄ ), and the like.

The shape of the titanium metal used in the above-mentioned comparator reaction is not particularly limited, but examples include sponge-like, powder-like, etc.

The content of titanium ions in the titanium plating electrolyte is not particularly limited and can be set appropriately depending on the plating conditions. The content of titanium ions may be, for example, 0.1 mol% to 20 mol%, or 0.5 mol% to 12 mol%, based on the total amount of cations contained in the titanium plating electrolyte.

In one aspect of this embodiment, when the titanium ions include titanium (III) ions, the content of titanium (III) ions may be, for example, 0.1 mol% to 20 mol% or 0.5 mol% to 12 mol% relative to the total amount of cations contained in the titanium plating electrolyte. The content of titanium (III) ions in the titanium plating electrolyte can be measured, for example, by inductively coupled plasma (ICP) analysis.

<Other cations>
The titanium plating electrolyte may contain cations other than lithium ions, sodium ions, potassium ions, and titanium ions, as long as the effects of the present embodiment are achieved. Examples of cations other than lithium ions, sodium ions, potassium ions, and titanium ions include silicon ions and magnesium ions.

<Halide ions>
In this embodiment, the halide ion contained in the titanium plating electrolyte is at least one selected from the group consisting of fluoride ions and chloride ions. The halide ions may be used alone or in combination. In one aspect of this embodiment, the halide ions may include chloride ions, or may include chloride ions and fluoride ions.

The source of fluoride ions is not particularly limited, but examples thereof include lithium fluoride, sodium fluoride, potassium fluoride, magnesium fluoride, etc. In this embodiment, the content of fluoride ions is preferably 0.1 mol% or more and 99.9 mol% or less, more preferably 10 mol% or more and 50 mol% or less, and even more preferably 30 mol% or more and 45 mol% or less, based on the total amount % of anions contained in the titanium plating electrolyte. The content of fluoride ions in the titanium plating electrolyte can be measured, for example, by inductively coupled plasma (ICP) analysis.

The chloride ion source is not particularly limited, but examples thereof include lithium chloride, sodium chloride, potassium chloride, magnesium chloride, etc. In this embodiment, the content of chloride ions is preferably 0.1 mol% or more and 99.9 mol% or less, more preferably 50 mol% or more and 99.9 mol% or less, and even more preferably 55 mol% or more and 70 mol% or less, based on the total amount of anions contained in the titanium plating electrolyte. The content of chloride ions in the titanium plating electrolyte can be measured, for example, by inductively coupled plasma (ICP) analysis.

In one aspect of this embodiment, when the halide ions include fluoride ions and chloride ions, the total content of the fluoride ions and chloride ions is preferably 90 mol% or more and 99.9 mol% or less, more preferably 90 mol% or more and 99 mol% or less, and even more preferably 95 mol% or more and 97 mol% or less, based on the total amount of anions contained in the titanium plating electrolyte. The total content of the fluoride ions and chloride ions can be measured, for example, by ICP analysis.

The molar ratio of the fluoride ions to the chloride ions, F ⁻ :Cl ⁻ , is preferably 30:70 to 50:50, and more preferably 30:70 to 45:55. The molar ratio F ⁻ :Cl ⁻ can be measured, for example, by ion chromatography (IC) or ICP analysis.

<Oxide ion>
Examples of oxide ions include O ²⁻ , O ³⁻ , etc. In this embodiment, the oxide ions preferably include O ²⁻ .

The source of oxide ions is not particularly limited, but examples thereof include lithium oxide (Li ₂ O), sodium oxide (Na ₂ O), potassium oxide (K ₂ O), titanium oxide (TiO ₂ ), and the like.

The content of oxide ions is 0.1 mol% or more and 1 mol% or less, preferably 0.15 mol% or more and 0.8 mol% or less, and more preferably 0.2 mol% or more and 0.5 mol% or less, based on the total amount of anions and cations contained in the titanium plating electrolyte. The content of oxide ions in the titanium plating electrolyte can be measured, for example, by inductively coupled plasma (ICP) analysis.

The inventors believe that by including oxide ions in the titanium plating electrolyte at the above-mentioned content ratio, when titanium plating is performed using the molten salt of the titanium plating electrolyte as a plating bath, the titanium ions contained in the plating bath will combine with the oxide ions to generate titanium oxide fine particles. The generated titanium oxide fine particles are taken into the titanium plating during film formation, and it is believed that unevenness is imparted to the surface of the titanium plating film. As a result, it is believed that the surface area of the titanium plating film will be larger than that of a smooth titanium plating film. When such a titanium plating film is applied to an electrode for electrolysis (electrolysis), the surface area of the electrode will increase, lowering the voltage in electrolysis and improving the efficiency of electrolysis. In other words, the titanium plating electrolyte is suitable for manufacturing electrodes for electrolysis.

<Other anions>
The titanium plating electrolyte may contain anions other than fluoride ions, chloride ions, and oxide ions, as long as the effects of the present embodiment are achieved. Examples of anions other than fluoride ions, chloride ions, and oxide ions include bromide ions and iodide ions.

In one aspect of this embodiment, when lithium fluoride and lithium chloride are used as the source of lithium ions, fluoride ions, and chloride ions, the total content of the lithium fluoride and lithium chloride is preferably 90 mol% or more and 99 mol% or less, and more preferably 95 mol% or more and 97 mol% or less, based on the total amount of the titanium plating electrolyte. The total content of the lithium fluoride and lithium chloride can be measured, for example, by ICP analysis.

The molar ratio LiF:LiCl of the lithium fluoride and the lithium chloride is preferably 30:70 to 50:50, and more preferably 30:70 to 45:55. The molar ratio LiF:LiCl can be measured, for example, by ion chromatography (IC) or ICP analysis.

<Manufacturing method of titanium-plated member (1)>
A method for producing a titanium-plated member according to one aspect of this embodiment includes the steps of:
A step (S10) of preparing a substrate having a conductive surface;
A step (S20) of immersing the substrate in the titanium plating electrolyte, the titanium plating electrolyte being molten;
and applying a voltage between the substrate and an anode corresponding to the substrate to form a titanium plating film on the conductive surface of the substrate (S30) (see FIG. 1).

<Step of preparing a substrate having a conductive surface (S10)>
In this step, a substrate having a conductive surface is prepared. The term "substrate having a conductive surface" refers to a substrate having a surface on which charged particles (electrons, ions, etc.) can drift and conduct electricity due to the action of an electric field. The conductive surface according to this embodiment may contain a substance having a melting point higher than the temperature of the titanium plating electrolyte, which is a molten salt. The conductive surface may be made of a substance having a melting point higher than the temperature of the titanium plating electrolyte, which is a molten salt. If a substance having a melting point lower than the temperature of the titanium plating electrolyte, which is a molten salt, is used as the conductive surface, it will dissolve in the titanium plating electrolyte, which is a molten salt, in the "step of forming a titanium plating film on the conductive surface of the substrate" described later, and the function of the substrate as a cathode tends to decrease.

The substrate having a conductive surface may be, for example, a substrate made entirely of a conductive material, or a substrate in which a conductive material is coated on the surface of a substrate precursor made of an insulator. In one aspect of this embodiment, the substrate may include a material having a melting point higher than the temperature of the titanium plating electrolyte, which is a molten salt. The substrate may be made of a material having a melting point higher than the temperature of the titanium plating electrolyte, which is a molten salt.

The conductive surface of the substrate preferably contains at least one selected from the group consisting of nickel (Ni), iron (Fe), copper (Cu), molybdenum (Mo), tungsten (W), carbon, and stainless steel, and more preferably is at least one selected from the group consisting of Ni, Fe, Cu, Mo, W, carbon, and stainless steel. Examples of carbon include glassy carbon and graphite. Examples of stainless steel include SUS304, SUS310S, and SUS430.

The shape of the substrate is not particularly limited. For example, substrates having various shapes such as plate-like, columnar, pipe-like, two-dimensional mesh-like, and three-dimensional mesh-like shapes can be used.

<Step of immersing substrate in titanium plating electrolyte (S20)>
In this step, the prepared substrate 1 is immersed in the titanium plating electrolyte 20. In one aspect of this embodiment, in this step, the prepared substrate 10 and the anode 30 corresponding to the substrate 10 may be immersed in the titanium plating electrolyte 20 (see FIG. 2). The titanium plating electrolyte 20 is molten. That is, in this step, the titanium plating electrolyte 20 is a molten salt. In one aspect of this embodiment, the titanium plating electrolyte 20 may be contained in a container 40 (see FIG. 2).

The temperature of the titanium plating electrolyte, which is a molten salt, is preferably equal to or higher than the melting point of the titanium plating electrolyte and equal to or lower than the melting point of the material that constitutes the conductive surface. More specifically, the temperature of the titanium plating electrolyte, which is a molten salt, is more preferably equal to or higher than 500°C and equal to or lower than 850°C, and even more preferably equal to or higher than 500°C and equal to or lower than 750°C.

The anode may contain a substance having a melting point higher than the temperature of the titanium plating electrolyte, which is a molten salt. The anode may be made of a substance having a melting point higher than the temperature of the titanium plating electrolyte, which is a molten salt. Specific examples of the anode include anodes containing metallic titanium, glassy carbon, platinum, etc.

<Step of forming titanium plating film on conductive surface of substrate (S30)>
In this step, a voltage is applied between the substrate and an anode corresponding to the substrate to form a titanium plating film on the conductive surface of the substrate. In addition, in the step of forming the titanium plating film (this step), it is preferable to apply a voltage between the substrate and the anode so that the cathode potential of the substrate is 0.85 V to 1.2 V based on the oxidation-reduction potential of Li ⁺ /Li.

Specifically, it is preferable to electrolyze the titanium plating electrolyte by applying a voltage between the substrate and the anode while the substrate and the anode are immersed in the titanium plating electrolyte, which is a molten salt, so that the cathode potential at the substrate is 0.85 V to 1.2 V based on the oxidation-reduction potential of Li ⁺ /Li, thereby causing the titanium (III) ions, which are titanium ions, to be reduced to metallic titanium on the conductive surface of the substrate, which is the cathode, and the surface is covered with metallic titanium, thereby forming a titanium plating film.

The setting range of the cathode potential is more preferably 1 V to 1.2 V, and even more preferably 1 V to 1.1 V, based on the oxidation-reduction potential of Li ⁺ /Li. The cathode potential can be monitored, for example, using an electrochemical measurement device (manufactured by Hokuto Denko Corporation, product name: HZ-7000).

<Other processes>
The method for producing a titanium-plated member according to this embodiment may further include other steps in addition to the steps described above, such as a step of performing preliminary electrolysis for the purpose of removing impurities contained in the titanium plating electrolyte, which is a molten salt, a step of cleaning the titanium-plated substrate, and a step of drying the titanium-plated substrate after cleaning.

<Manufacturing method of titanium plated member (2)>
A method for producing a titanium-plated member according to another aspect of this embodiment includes the steps of:
preparing a substrate having a metal element on a surface thereof;
and (b) immersing the substrate in the titanium plating electrolyte to perform electroless plating, the titanium plating electrolyte being molten.

<Step of Preparing Substrate>
In this step, a substrate is prepared. The substrate contains a metal element on its surface. "Containing a metal element on its surface" means that the substrate has a substance containing a metal element as a constituent element on its surface. Examples of the substance containing a metal element include simple metals, alloys, ceramics, etc. The substance containing a metal element according to this embodiment may have a melting point higher than the temperature of the titanium plating electrolyte. If a substance having a melting point lower than the temperature of the titanium plating electrolyte is used on the substrate surface, the substrate surface tends to dissolve in the titanium plating electrolyte in the step of immersing the substrate in the titanium plating electrolyte and performing electroless plating, which will be described later.

<Step of immersing the substrate in a titanium plating electrolyte and performing electroless plating>
In this step, the prepared substrate is immersed in a molten titanium plating electrolyte to perform electroless plating.

The temperature of the titanium plating electrolyte is preferably equal to or higher than the melting point of the titanium plating electrolyte and equal to or lower than the melting point of the substance containing the metal element contained on the surface of the substrate. More specifically, the temperature of the titanium plating electrolyte is preferably equal to or higher than 500°C and equal to or lower than 850°C, and more preferably equal to or higher than 500°C and equal to or lower than 750°C.

Although the detailed mechanism has not been made clear, the inventors believe that in the method for producing a titanium-plated member according to this embodiment, titanium metal is deposited on the surface of a substrate to form electroless plating through the reaction represented by the following formula (2) or (3): In other words, in the method for producing a titanium-plated member according to this embodiment, it is possible to deposit titanium metal on the surface of a substrate without passing a current through the substrate.
2Ti ²⁺ → Ti ⁴⁺ +Ti metal Formula (2)
4Ti ³⁺ → 3Ti ⁴⁺ +Ti metal Formula (3)

When the substrate is immersed in the titanium plating electrolyte, the entire substrate may be immersed in the titanium plating electrolyte. Alternatively, only a portion of the substrate may be immersed in the titanium plating electrolyte.

The time for which the substrate is immersed in the titanium plating electrolyte (hereinafter sometimes referred to as the "immersion time") is not particularly limited, but may be, for example, 10 minutes or more and 120 minutes or less, 40 minutes or more and 100 minutes or less, or 60 minutes or more and 90 minutes or less. In this case, if the immersion time is long, an alloy containing the above-mentioned Ti and a metal element derived from the substrate tends to be easily generated.

<Other processes>
The method for producing a titanium-plated member according to this embodiment may further include other steps in addition to the steps described above, such as a step of cleaning the titanium-plated member and a step of drying the titanium-plated member after cleaning.

The titanium-plated parts produced in this way have high hardness, a large surface area, and a protective film (titanium plating film) that is highly resistant to corrosion and wear. Therefore, they can be used in a variety of fields, including electrolysis and electricity storage.

The above description includes the following additional features.
(Appendix 1)
at least one alkali metal ion selected from the group consisting of lithium ions, sodium ions, and potassium ions;
at least one halide ion selected from the group consisting of fluoride ions and chloride ions;
Titanium ions,
and an oxide ion,
a content ratio of the oxide ions is 0.1 mol % or more and 1 mol % or less based on the total amount of anions and cations contained in the titanium plating electrolyte.
(Appendix 2)
the alkali metal ions include the lithium ions,
2. The titanium plating electrolyte according to claim 1, wherein the content of the lithium ions is greater than 0 mol % and not more than 99.9 mol % based on the total amount of cations contained in the titanium plating electrolyte.
(Appendix 3)
The alkali metal ions include the sodium ions,
3. The titanium plating electrolyte according to claim 1, wherein the content of the sodium ions is greater than 0 mol % and not more than 99.9 mol % based on the total amount of cations contained in the titanium plating electrolyte.
(Appendix 4)
the alkali metal ions include the potassium ions,
4. The titanium plating electrolyte according to claim 1, wherein the content of potassium ions is greater than 0 mol % and not more than 99.9 mol % based on the total amount of cations contained in the titanium plating electrolyte.

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these.

<Preparation of electrolyte for titanium plating>
The following operations were all carried out in an air atmosphere. First, the salts constituting the main bath shown in Table 1, Li ₂ O and K ₂ TiF ₆ , were mixed so that the concentration of K ₂ TiF ₆ was 2 mol% and the concentration of Li ₂ O was the concentration shown in Table 1. At this time, the total content ratio of the salts constituting the main bath was 97.0 to 98 mol%. The resulting mixture was then heated to 550°C to prepare a precursor of a titanium plating electrolyte of molten salt. To the obtained precursor, a sponge titanium (16 mg per 1 g of precursor) was added in an amount twice the amount required to generate titanium (III) ions (titanium ions), and was dissolved sufficiently. It was confirmed that the sponge titanium that was not completely dissolved in the molten salt was precipitated. In this way, a titanium plating electrolyte (samples No. 1 to 10) of a molten salt was prepared.

<Manufacturing of titanium plated parts>
Next, the obtained molten salt of the titanium plating electrolyte of Samples No. 1 to 10 was used as a plating bath to manufacture titanium plated members in the following procedure. The following steps were performed in an atmosphere of Ar gas (98.3% to 100%). The plating bath used was thoroughly dried in a furnace. First, a substrate (30 mm long x 50 mm wide x 0.5 mm thick) made of Ni plate manufactured by Nilaco Corporation was prepared as a cathode (a step of preparing a substrate having a conductive surface). Then, the substrate and a Ti plate serving as an anode were immersed in the titanium plating electrolyte, which is the above-mentioned molten salt (a step of immersing a substrate in a titanium plating electrolyte). Finally, a voltage was applied between the substrate serving as a cathode and the anode under the following conditions to form a titanium plating film on the surface of the substrate (a step of forming a titanium plating film on the conductive surface of a substrate). The voltage applied between the substrate serving as a cathode and the anode was measured using an HZ-7000 device manufactured by Hokuto Denko Corporation. In this manner, Sample No. Each of the titanium plating electrolytes No. 1 to No. 10 was used as a plating bath to prepare titanium-plated members of the corresponding samples No. 1 to No. 10.

(Measurement conditions)
Measuring device: HZ-7000 (manufactured by Hokuto Denko Corporation)
Cathode: Ni plate (manufactured by Nilaco Corporation)
Anode: Ti plate (manufactured by Nilaco Corporation)
Reference electrode: Platinum pseudo reference electrode (manufactured by Nilaco Corporation)
Temperature: 550°C
Current density: 100mA/ ^cm2
Atmosphere: Ar gas (98.3% to 100%) (the balance is air)

<Surface observation of titanium plated parts>
The surfaces of the titanium-plated members of Samples No. 1 to 10 were observed with a scanning electron microscope (SEM) (see, for example, FIG. 3). The surfaces of the titanium-plated members were also analyzed using an EDX attached to the SEM, and elemental analysis of the surfaces of the titanium-plated members was performed. As a result, the presence of titanium element and oxygen element was confirmed on the surfaces of the titanium-plated members. Furthermore, the size of the particles containing titanium element on the surfaces of the titanium-plated members was about 100 to 200 nm (see, for example, FIG. 3). Based on the above results, it was suggested that particles consisting of titanium oxide were contained in the titanium plating film on the surface of the titanium-plated members.

Electrolysis Test
An electrolysis test (electrolysis test) of salt water was carried out using each of the titanium-plated members of Samples No. 1 to 10 as an anode in the following procedure. First, the titanium-plated members as the anodes and a Ni plate (manufactured by Nilaco Corporation) as the cathode were mounted in a square tank with an ion exchange membrane in the center. Then, salt water was electrolyzed under the following electrolysis conditions. The electrolysis area of the ion exchange membrane electrolytic tank was 1 ^dm2 , and a cation exchange membrane for salt electrolysis was used as the diaphragm.

<Electrolysis conditions>
The anolyte was 250±10 g/L NaCl, and the catholyte was 30±0.1 mass% NaOH aqueous solution. The electrolysis temperature was 80 to 90° C., and the current density was 5 kA/ ^m2 .

<Evaluation>
The cell voltage was measured when salt water was electrolyzed using each electrolytic cell, and the value (voltage difference) obtained by subtracting the value of sample No. 1 from the measured value for each of samples No. 1 to 10 was used for evaluation. A negative voltage difference (V) was deemed to be acceptable. The results are shown in Table 1. Here, samples No. 1 and 6 correspond to comparative examples, while samples No. 2 to 5 and samples No. 7 to 10 correspond to examples.

From the results of Table 1, when titanium plating is performed using a titanium plating electrolyte having an oxide ion (O ^2- ) content of 0.1 mol% or more and 1 mol% or less as a plating bath of molten salt, when an electrolysis test is performed using a titanium-plated member obtained by this plating method as an anode, the electrolysis voltage difference shows a negative value, and it is found that the electrolysis efficiency is improved. That is, it is found that when titanium plating is performed using a titanium plating electrolyte having an oxide ion content of 0.1 mol% or more and 1 mol% or less as a plating bath of molten salt, plating suitable for manufacturing an electrode for electrolysis can be performed. The inventors believe that when titanium plating is performed using the molten salt of the titanium plating electrolyte as a plating bath, titanium ions contained in the plating bath and the oxide ions are combined to generate fine particles of titanium oxide. It is considered that the generated fine particles of titanium oxide are taken into the titanium plating during film formation, and unevenness is given to the surface of the titanium plating film. As a result, the surface area of the titanium plating film in this embodiment is larger than that of a smooth titanium plating film, and it is considered that the electrolysis efficiency is improved as described above.

Although the embodiments and examples of the present invention have been described above, it has been planned from the outset that the configurations of the above-mentioned embodiments and examples may be appropriately combined.

The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is indicated by the claims, not by the embodiments and examples described above, and is intended to include the meaning equivalent to the claims and all modifications within the scope.

10 Substrate, 20 Titanium plating electrolyte, 30 Anode, 40 Container

Claims (6)

at least one alkali metal ion selected from the group consisting of lithium ions, sodium ions, and potassium ions;
at least one halide ion selected from the group consisting of fluoride ions and chloride ions;
Titanium ions,
and an oxide ion,
a content ratio of the oxide ions is 0.1 mol % or more and 1 mol % or less based on the total amount of anions and cations contained in the titanium plating electrolyte,
Zinc-free electrolyte for titanium plating. the halide ions include the chloride ions,
2. The titanium plating electrolyte according to claim 1, wherein the content of the chloride ions is 0.1 mol % or more and 99.9 mol % or less based on the total amount of anions contained in the titanium plating electrolyte. the halide ions include the fluoride ions,
3. The titanium plating electrolyte according to claim 1, wherein a content of said fluoride ions is from 0.1 mol % to 99.9 mol % based on a total amount of anions contained in said titanium plating electrolyte. The titanium plating electrolyte according to any one of claims 1 to 3, wherein the content of the titanium ions is 0.1 mol% or more and 20 mol% or less with respect to the total amount of cations contained in the titanium plating electrolyte. Providing a substrate having an electrically conductive surface;
immersing the substrate in the titanium plating electrolyte according to any one of claims 1 to 4, the titanium plating electrolyte being molten;
applying a voltage between the substrate and an anode corresponding to the substrate to form a titanium plating film on the conductive surface of the substrate;
A method for producing a titanium-plated member comprising the steps of: The method for producing a titanium-plated member according to claim 5, wherein the conductive surface of the substrate contains at least one selected from the group consisting of nickel, iron, copper, molybdenum, tungsten, carbon and stainless steel.