JP2015098626A - Method for producing refined metal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing refined metal which enables the production of high-purity refined metal.SOLUTION: A method of producing refined metal comprises the steps of: preparing molten salt bath comprising fluoride ions; preparing electrolyte for electrodeposition by introducing metal chloride gas into the molten salt bath; and precipitating metal on a cathode in the electrolyte for electrodeposition by electrolyzing the electrolyte for electrodeposition.

Description

  The present invention relates to a method for producing a purified metal.

  A silicon film used as a solar cell is produced by producing a silicon ingot by the Siemens method, slicing the silicon ingot to a thickness of about 1 mm, producing a silicon wafer, and forming a pn junction on the silicon wafer. (Non-Patent Document 1). At that time, the content of metal impurities in the silicon film must be suppressed to 0.1 mass ppm or less, and the boron content must be suppressed to 0.3 mass ppm or less.

  Further, a high melting point metal film such as tungsten, molybdenum and titanium having high hardness and wear resistance is formed by a thermal spraying method (Patent Document 1) or a chemical vapor deposition (CVD) method (Patent Document 2). . However, when a refractory metal film is formed by a thermal spraying method, there is a drawback that the substrate on which the refractory metal film is deposited is subjected to great thermal damage. In addition, when a refractory metal film is formed by a CVD method, there is a drawback that the film forming speed of the refractory metal film is slow. Note that the silicide film can also be formed by the CVD method (Patent Document 3), but has the same drawback as the case of forming the refractory metal film by the CVD method.

  Therefore, conventionally, an electrolyte for electrodeposition is prepared by adding a metal to be deposited in a molten salt, and a film is formed on the substrate by electrodeposition of the electrolyte for electrodeposition. A method for directly forming a silicon film, a refractory metal film and a silicide film on a substrate has been studied.

For example, in Patent Document 4, TiCl ₄ is introduced into a molten NaCl-KCl (molar ratio = 45: 55) bath containing a crude Ti sponge, and electrolysis is performed using the crude Ti sponge as an anode and a Ti rod as a cathode. Thus, a method of electrodepositing high purity Ti is disclosed.

  Patent Document 5 discloses that titanium tetrachloride is dissolved in an electrolytic bath made of a mixture of two or three of sodium chloride, potassium chloride, and lithium chloride, and between a deposition cathode and an anode for depositing titanium metal. A method for depositing metal titanium on a deposition cathode is disclosed.

  Patent Document 6 discloses that zinc is reduced in a cathode made of liquid zinc by supplying current and titanium tetrachloride to an electrolytic solution that is a melt of lithium chloride and potassium chloride to perform electrolysis. A method for forming a titanium alloy is disclosed.

  Patent Document 7 discloses electrolysis of a molten salt bath in which a titanium halide made of titanium chloride or titanium bromide and an N-alkylpyridinium halide made of butylpyridinium chloride, ethylpyridinium chloride or butylpyridinium bromide are mixed. A method of purifying titanium by performing is disclosed.

  Furthermore, Patent Document 8 discloses a method for producing a polycrystalline silicon thin film by performing electrolysis of a halogen-containing silicon compound in an electrolytic cell composed of a normal electrolyte, a working electrode, and a counter electrode. . Patent Document 8 discloses enormous numbers of examples of the halogen-containing silicon compound and the electrolyte, respectively, but the actual experiment has been carried out as a LiCl—KCl molten salt (LiCl / LiCl) having a eutectic composition as the electrolyte. KCl molar ratio = 59/41) and a combination of silicon tetrachloride as a halogen-containing silicon compound or a mixed gas of silicon tetrachloride / phosphorous trichloride (paragraph [0016], etc. of Patent Document 8).

JP 2006-249578 A JP 2001-011628 A JP 2008-187190 A JP-A-6-173065 JP-A-60-187893 JP-A-62-86188 JP-A-1-290787 JP-A-7-277721

Semiconductor Fundamental Technology Study Group, Silicon Science, Realization Science and Technology Center, 1992

  As described above, various metal deposition methods using the electrodeposition method have been proposed in the present situation, but there is a demand for further purification of the metal obtained.

  In view of the above circumstances, an object of the present invention is to provide a method capable of producing a high-purity purified metal.

According to one aspect of the present invention, a step of producing a molten salt bath containing fluoride ions (F ⁻ ), a step of producing an electrodeposition electrolyte by introducing a metal chloride gas into the molten salt bath, There can be provided a method for producing a purified metal, comprising a step of immersing a cathode in the electrodepositing electrolyte and a step of depositing a metal on the cathode by electrolyzing the electrodepositing electrolyte.

  According to said aspect, the method which can manufacture a highly purified refined metal can be provided.

3 is a flowchart of a method for producing a purified metal according to Embodiment 1. FIG. 3 is a schematic cross-sectional view illustrating an example of a process for producing a molten salt bath in the method for producing a purified metal according to Embodiment 1. It is typical sectional drawing illustrating an example of the process of immersing the electrode in the manufacturing method of the refined metal of Embodiment 1. FIG. FIG. 3 is a schematic cross-sectional view illustrating an example of a process for producing an electrodeposition electrolyte in the method for producing a purified metal according to the first embodiment. FIG. 3 is a schematic cross-sectional view illustrating an example of a process for producing an electrodeposition electrolyte in the method for producing a purified metal according to the first embodiment. It is typical sectional drawing illustrating an example of the process of depositing the metal in the manufacturing method of the refined metal of Embodiment 1. FIG. 5 is a flowchart of a method for producing a purified metal according to Embodiment 2. 2 is a cyclic voltammogram of the electrodepositing electrolyte of Example 1. FIG. 2 is an X-ray diffraction pattern of Si deposited in Experimental Example 1. FIG. 4 is a cyclic voltammogram of the electrodepositing electrolyte of Experimental Example 2.

[Description of Embodiment of Present Invention]
(1) According to one aspect of the present invention, a step of preparing a molten salt bath containing F ⁻ , a step of preparing an electrolyte for electrodeposition by introducing a metal chloride gas into the molten salt bath, There can be provided a method for producing a purified metal comprising the step of depositing a metal on the cathode in the electrodepositing electrolyte by electrolyzing the electrodepositing electrolyte. By setting it as such a structure, a highly purified refined metal can be manufactured. In this specification, “metal” includes metals such as silicon, refractory metals, silicides, and alloys.

(2) According to one aspect of the present invention, in the step of depositing the metal, a step of producing the metal chloride gas using a chlorine (Cl ₂ ) gas generated at an anode in the electrodeposition electrolyte; Preferably, the method further includes a step of introducing the metal chloride gas produced using _two gases into the molten salt bath or the electrodeposition electrolyte. With such a configuration, the Cl ₂ gas generated at the anode is taken out, and the Cl ₂ gas can be reused by producing a metal chloride gas using the Cl ₂ gas.

(3) In one aspect of the present invention, it is preferable that the anode contains carbon. With such a configuration, in the process of depositing metal, Cl ₂ gas can be generated more efficiently at the anode, so that metal chloride gas can be more efficiently produced using the Cl ₂ gas. And reuse of Cl ₂ gas can be further promoted.

  (4) In one aspect of the present invention, the metal includes at least one selected from the group consisting of silicon (Si), titanium (Ti), tungsten (W), zirconium (Zr), and molybdenum (Mo). It is preferable that In the step of depositing metal, when Si is deposited on the cathode, Si can be used for solar cells, for example. Further, when a metal containing at least one selected from the group consisting of Ti, W, Zr and Mo is deposited on the cathode, the metal is used as a protective film having a function of high hardness and wear resistance. Can be used. Further, when at least one type of silicide selected from the group consisting of W, Mo and Ti is deposited on the cathode, it can be used as a low-resistance electrode to the semiconductor substrate, and the semiconductor device operates at a low voltage. Is possible.

  (5) In one aspect of the present invention, the metal chloride gas contains at least one selected from the group consisting of silicon chloride gas, titanium chloride gas, tungsten chloride gas, zirconium chloride gas, and molybdenum chloride gas. It is preferable. In this case, in the step of depositing the metal, a metal containing at least one selected from the group consisting of Si, Ti, W, Zr and Mo can be deposited.

(6) In one aspect of the present invention, the molten salt bath may further contain potassium ions (K ⁺ ) as cations other than metal ions to be electrodeposited. In this case, a high-purity metal film having a smooth surface can be formed by electrodeposition at a relatively low temperature, and the electrodeposition electrolyte can be easily removed by water washing after the metal film is formed. it can.

  (7) In one aspect of the present invention, in the step of preparing the electrodeposition electrolyte, the metal chloride gas may be introduced into the molten salt bath using a metal chloride gas introduction pipe. In this case, an electrolyte for electrodeposition containing at least the metal component of the metal chloride gas in the molten salt bath can be produced by blowing the metal chloride gas into the molten salt bath from the metal chloride gas introduction pipe. .

  (8) In one aspect of the present invention, in the step of producing the electrodeposition electrolyte, the temperature of the molten salt bath when the metal chloride gas is introduced is preferably 573 K or higher. In this case, when the temperature is high, the dissolution rate of the metal chloride gas into the electrodeposition electrolyte is increased, and the dissolution efficiency of the metal chloride gas tends to be improved.

[Details of the embodiment of the present invention]
Hereinafter, an embodiment which is an example of the present invention will be described. Note that in the drawings used to describe the embodiments, the same reference numerals represent the same or corresponding parts.

<Embodiment 1>
FIG. 1 shows a flowchart of a method for producing a purified metal according to Embodiment 1, which is an example of the present invention. The method for producing a purified metal according to the first embodiment includes a step of producing a molten salt bath (S10), a step of immersing an electrode (S20), a step of producing an electrolyte for electrodeposition (S30), and depositing a metal. Step (S40). In addition, it cannot be overemphasized that the process other than S10, S20, S30, and S40 may be included in the manufacturing method of the refined metal of Embodiment 1, and the order of a process is not specifically limited, either.

≪Process for making molten salt bath≫
The step of producing a molten salt bath (S10) is performed by producing a molten salt bath containing fluoride ions. In the step (S10) for preparing the molten salt bath, for example, as shown in the schematic cross-sectional view of FIG. 2, a mixture of powdered potassium fluoride (KF) and powdered potassium chloride (KCl) ( Hereinafter, after containing “KF-KCl mixture”), a mixture of powdered KF and powdered KCl is heated and melted, whereby F ⁻ , potassium ion (K ⁺ ), and chloride. This can be carried out by preparing a molten salt bath 2 containing product ions (Cl ⁻ ).

Regarding the presence of K ⁺ , F ⁻ and Cl ^{− in} the molten salt bath 2, for example, the molten salt bath 2 is dissolved in a mixed solution of nitric acid and hydrofluoric acid and then ICP emission spectrometry (Inductively Coupled Plasma Spectrometry) is used. ). As the ICP emission spectroscopic analyzer, for example, iCAP6200 manufactured by Thermo Fisher Scientific Co., Ltd. can be used. The presence of K ⁺ , F ⁻ and Cl ^{− in} the molten salt bath 2 can also be confirmed, for example, by ion chromatography after the molten salt bath 2 is dissolved in a large amount of water. As the ion chromatography device, for example, HIC-SP manufactured by Shimadzu Corporation can be used.

The molar ratio of KCl to KF ((KCl substance amount n _KCl ) / (KF substance amount n _KF )) in the KF-KCl mixture is preferably 0.2 or more and 5 or less, and 0.5 or more and 2 or less. It is more preferable that When the molar ratio is 1.2, the molten salt bath 2 obtained by melting the KF-KCl mixture has the lowest melting point of 871 K, but the above molar ratio in the KF-KCl mixture is the lowest. When the ratio is 0.2 or more and 5 or less, particularly when the ratio is 0.5 or more and 2 or less, the melting point of the molten salt bath 2 can be made sufficiently lower than the melting point of KF single salt (1133K) it can. For this reason, in this case, there is a tendency that electrolysis of an electrodeposition electrolyte described later produced using the molten salt bath 2 can be performed at a relatively low temperature.

Although the structure of the molten salt bath 2 produced in the step (S10) for producing the molten salt bath is not limited to the above, the molten salt bath 2 is K as a cation other than the metal ions to be electrodeposited as described above. It is preferable to include ⁺ . When the molten salt bath 2 contains only K ⁺ , a high-purity metal having a smooth surface can be deposited by electrodeposition at a relatively low temperature, and adheres to the metal surface after the metal deposition. The electrolyte for electrodeposition can be easily removed by washing with water.

≪Step of immersing electrodes≫
The step of immersing the electrode (S20) can be performed by immersing at least a part of the electrode in the molten salt bath 2 produced in the step (S10) of producing the molten salt bath. The step of immersing the electrode (S20) can be performed by immersing the anode 6 and the cathode 7 in the molten salt bath 2, for example, as shown in the schematic cross-sectional view of FIG.

Here, as the anode 6, it is preferable to use a material containing carbon such as graphite on the surface of the anode 6. When a material containing C is used for the surface of the anode 5 as the anode 6, Cl ₂ gas can be generated in the anode 6 in the step of depositing a metal described later (S 40). _Two gases can be taken out and reused for the production of a metal chloride gas to be described later as a raw material.

  Moreover, as the cathode 7, the surface of the cathode 7 contains at least one selected from the group consisting of iron (Fe), silver (Ag), carbon (C), copper (Cu), and molybdenum (Mo). Is preferably used. When the surface of the cathode 7 contains at least one of Ag and C, the adhesion between silicon (Si) deposited on the surface of the cathode 7 and the cathode 7 can be improved. Moreover, when the surface of the cathode 7 contains at least one of Cu and Mo, the adhesion between tungsten (W) deposited on the surface of the cathode 7 and the cathode 7 can be improved.

  The shape of the cathode 7 is not particularly limited, but is preferably columnar or pipe-shaped. When the shape of the cathode 7 is columnar or pipe-shaped, when a concentrating solar cell is fabricated using Si deposited on the surface of the cathode 7, light incidence from all directions is applied to the surface of the cathode 7. On the other hand, since the light can be used by being incident perpendicularly, the light use efficiency per unit area can be improved.

  In the present specification, the “columnar shape” means a shape extending in an arbitrary direction, and examples thereof include a shape of a cylinder or a prism.

  Further, in this specification, the “pipe shape” is provided inside the outer shell portion so as to extend in the same direction as the outer shell portion extending in an arbitrary direction and the extending direction of the outer shell portion. For example, a shape having a hollow portion extending in the same direction as the extending direction of the prism may be included inside the prism.

≪Process for producing electrolyte for electrodeposition≫
The step (S30) for producing the electrodeposition electrolyte is performed by introducing a metal chloride gas into the molten salt bath 2 produced in the step (S10) for producing the molten salt bath. The step (S30) of producing the electrolyte for electrodeposition can be performed, for example, as follows. First, as shown in the schematic cross-sectional view of FIG. 4, the tip of the metal chloride gas introduction pipe 4 is immersed in the molten salt bath 2. Next, for example, as shown in the schematic cross-sectional view of FIG. 5, the metal chloride gas 5 is blown into the molten salt bath 2 from the metal chloride gas introduction pipe 4, and at least the metal chloride gas 5 is introduced into the molten salt bath 2. By including a metal component, the electrodepositing electrolyte 3 can be produced.

  As the metal chloride gas 5, a metal chloride gas to be deposited on the cathode in the step of depositing a metal to be described later (S <b> 40) can be introduced into the molten salt bath 2. As the metal chloride gas 5, for example, a metal chloride gas containing at least one selected from the group consisting of silicon chloride gas, titanium chloride gas, tungsten chloride gas, zirconium chloride gas and molybdenum chloride gas may be introduced. preferable.

When silicon chloride gas is introduced as the metal chloride gas 5, Si can be deposited on the cathode 7 in the step of depositing a metal (S40) described later. Si deposited on the cathode 7 can be used for a solar cell, for example. As the silicon chloride gas, for example, silicon tetrachloride (SiCl ₄ ) gas can be used.

When a gas containing at least one selected from the group consisting of titanium chloride gas, tungsten chloride gas, zirconium chloride gas and molybdenum chloride gas is introduced as the metal chloride gas 5, it consists of Ti, W, Zr and Mo. A metal containing one selected from the group or an alloy of two or more thereof can be deposited on the cathode 7. A metal made of any one of Ti, W, Zr, and Mo deposited on the cathode 7 or an alloy containing two or more of these is used as a protective film having a function of high hardness and wear resistance, for example. be able to. As the titanium chloride gas, for example, titanium tetrachloride (TiCl ₄ ) gas can be used. As the tungsten chloride gas, for example, at least one selected from the group consisting of tungsten tetrachloride (WCl ₄ ) gas, tungsten pentachloride (WCl ₅ ) gas, and tungsten hexachloride (WCl ₆ ) gas is used. it can. As the zirconium chloride gas, for example, zirconium tetrachloride (ZrCl ₄ ) gas can be used. The molybdenum chloride gas is selected from the group consisting of, for example, molybdenum hexafluoride (MoF ₆ ) gas, molybdenum tetrachloride (MoCl ₄ ) gas, molybdenum pentachloride (MoCl ₅ ) gas, and molybdenum hexachloride (MoCl ₆ ) gas. At least one kind can be used.

  When a mixed gas of at least one gas selected from the group consisting of tungsten chloride gas, molybdenum chloride gas and titanium chloride gas and silicon chloride gas is introduced as the metal chloride gas 5, W, Mo and A metal containing at least one type of silicide selected from the group consisting of Ti (a compound of Si and at least one type selected from the group consisting of W, Mo, and Ti) can be deposited on the cathode 7. The metal deposited on the cathode 7 can be used, for example, as a low-resistance electrode on the semiconductor substrate, enabling the semiconductor device to operate at a low voltage.

  Needless to say, a carrier gas such as argon (Ar) gas may be introduced into the molten salt bath 2 together with the metal chloride gas 5.

  The temperature of the molten salt bath 2 when the metal chloride gas 5 is introduced is preferably 573 K or higher, and more preferably 623 K or higher. When the temperature of the molten salt bath 2 when the metal chloride gas 5 is introduced is 573 K or higher, particularly when it is 623 K or higher, the metal chloride gas 5 is heated to an electrolyte for electrodeposition. The dissolution rate increases and the dissolution efficiency of the metal chloride gas tends to improve.

  Further, the metal chloride gas introduction pipe 4 used in the step (S30) for producing the electrodeposition electrolyte is not particularly limited as long as the metal chloride gas 5 can be introduced into the molten salt bath 2. For example, a stainless steel (SUS) pipe or the like can be used.

≪Metal deposition process≫
In the step of depositing the metal (S40), the metal is deposited on the cathode 7 in the electrodepositing electrolyte 3 by electrolyzing the electrodepositing electrolyte 3 produced in the step of producing the electrodepositing electrolyte (S30). This can be done by precipitating.

  Thereby, as shown in the schematic cross-sectional view of FIG. 6, the metal M is deposited on the surface of the cathode 7 according to the following formula (I), and the purified metal 8 is formed on the surface of the cathode 7.

M ^{n +} + ne ⁻ → M (I)

Here, the anode 6 and the absolute value is preferable to perform the electrolysis of 1 mA / cm ² or more 500mA / cm ² or less as a conductive析用electrolyte 3 a current density of a current flowing between the cathode 7, 1 mA / cm ² or more More preferably, the electrodeposition electrolyte 3 is electrolyzed at 300 mA / cm ² or less. When electrolysis of the electrodepositing electrolyte 3 is performed with the absolute value of the current density of the current flowing between the anode 6 and the cathode 7 being 1 mA / cm ² or more, the formation of the purified metal 8 on the surface of the cathode 7 is performed. This can be done in a shorter time. Further, when electrolysis of the electrodepositing electrolyte 3 is performed with the absolute value of the current density of the current flowing between the anode 6 and the cathode 7 being 500 mA / cm ² or less, particularly 300 mA / cm ² or less, the purity is higher. The purified metal 8 can be formed. Then, the purified metal 8 can be obtained by removing the electrodepositing electrolyte 3 adhering to the surface of the purified metal 8 by washing or the like.

  FIG. 6 shows the case where the electrolysis of the electrodeposition electrolyte 3 is performed while introducing the metal chloride gas 5 from the metal chloride gas introduction pipe 4 into the electrodeposition electrolyte 3. The electrodeposition electrolyte 3 may be electrolyzed in a state where the introduction of the metal chloride gas 5 from the gas introduction pipe 4 to the electrodeposition electrolyte 3 is stopped.

≪Purified metal≫
The purity of the refined metal 8 produced by the refined metal production method of Embodiment 1 is preferably 99.9% by mass or more. When the purity of the purified metal 8 is 99.9% by mass or more, a silicon film is deposited as the purified metal 8 and the conversion efficiency of the solar cell tends to be improved when this is used as a solar cell. Further, when the refined metal 8 containing any one of W, Mo, Zr or Ti or the refined metal 8 containing an alloy of two or more of these is formed as the refined metal 8, the refined metal 8 has a high hardness and When used as a protective film having a wear-resistant function, the function of the film can be improved. Furthermore, when the alloy film in which the metal deposited on the cathode 7 and the metal contained in the cathode 7 are alloyed by the method for producing a refined metal according to Embodiment 1, the alloy film is, for example, wear resistant. It can be used for a protective film or a hydrogen storage alloy film.

  The purity of the purified metal 8 is the ratio of the mass obtained by subtracting the total mass of impurities from the total mass of the purified metal 8 to the total mass of the purified metal 8, and can be calculated by the following formula (II).

  Purity [% by mass] of purified metal 8 = 100 × (mass obtained by subtracting the total mass of impurities from the total mass of purified metal 8) / (total mass of purified metal 8) (II)

  In the present specification, the “impurity” of the purified metal 8 means a component other than the metal to be electrodeposited in, for example, boron, phosphorus, iron, aluminum, lithium, potassium, magnesium and calcium.

  The purity of the purified metal 8 can be measured by glow discharge mass spectrometry (GD-MS). As a measuring device, for example, VG9000 manufactured by Thermo Electron Co., Ltd. can be used. The purity of the purified metal 8 by glow discharge mass spectrometry is, for example, that the purified metal 8 is sputtered from the surface of the purified metal 8 to a thickness of 1 μm or more and 5 μm or less. This can be done by measuring the content of the impurity component.

<Effect>
The present inventors have studied intensively, F from a huge number of molten salt bath which has been proposed up to now ^- with selecting a molten salt bath containing enormous number of metals have been proposed to date source select metal chloride gas from the the metal chloride gas F ^- in the case of manufacturing the析用electrolyte conductivity by introducing a molten salt bath containing performs electrolysis of the conductive析用electrolyte As a result, the inventors have found that the purity of the metal deposited on the cathode can be increased as compared with the case where a molten salt bath is produced using a conventional metal chloride, and the present invention has been completed.

Incidentally, F ^- additive high purity material of a high purity of the metal can be precipitated, such as mixed fluoride when electrolyzing the molten salt bath and metal chloride gas and析用electrolyte conductive prepared by combining comprising This is considered to be because impurities are likely to be mixed because it is difficult to produce, and metal chloride gas can be added as a high-purity substance by distillation purification in the gas state.

<Embodiment 2>
FIG. 7 shows a flowchart of a method for producing a purified metal according to Embodiment 2, which is another example of the present invention. The method for producing a refined metal according to the second embodiment includes a step of producing a molten salt bath (S10), a step of immersing an electrode (S20), a step of producing an electrolyte for electrodeposition (S30), and depositing a metal. A step (S40) of producing a metal chloride gas and a step (S50) of producing a metal chloride gas, wherein the metal chloride gas produced in the step of producing metal chloride gas (S50) is reused. It is said. In addition, it cannot be overemphasized that processes other than S10, S20, S30, S40, and S50 may be included in the manufacturing method of the refined metal of Embodiment 2, and the order of processes is not specifically limited, either. .

Since description of S10 to S40 is the same as that of the first embodiment, a process (S50) for producing a metal chloride gas will be described below. The step of producing the metal chloride gas (S50) is performed by producing the metal chloride gas 5 using the Cl ₂ gas generated at the anode 6 in the electrodeposition electrolyte 3 in the step of depositing metal (S40). Done. The method for producing the metal chloride gas 5 using the Cl ₂ gas generated at the anode 6 is not particularly limited, and for example, a conventionally known method can be used.

In particular, the surface of the anode 6 is preferably made of a material containing carbon such as graphite. In this case, Cl ₂ gas can be more efficiently generated at the anode 6 in the step of depositing metal (S40). Accordingly, it is possible to more efficiently produce a metal chloride gas 5 with the Cl ₂ gas, it is possible to promote the reuse of the Cl ₂ gas.

  Then, the metal chloride gas 5 produced in the step of producing metal chloride gas (S50) is introduced into the molten salt bath 2 produced in the step of producing molten salt bath (S10) or metal chloride. The product gas 5 is introduced into the electrodeposition electrolyte 3 produced by introducing it into the molten salt bath 2.

As a preferred form of the method for producing a refined metal according to the second embodiment, for example, precipitation of Si as the refined metal 8 on the cathode 7 made of Ag is a molten salt bath produced by melting KF and KCl. The electrodepositing electrolyte 3 can be produced by blowing SiCl ₄ gas as the metal chloride gas 5 into the electrode 2, and the electrodepositing electrolyte 3 can be electrolyzed.

In this case, an ion exchange reaction represented by the following formula (III) can be caused by blowing SiCl ₄ gas as the metal chloride gas 5 into the molten salt bath 2 of KF and KCl.

SiCl ₄ + 6F ⁻ → SiF ₆ ²⁻ + 4Cl ⁻ (III)

When the electrodepositing electrolyte 3 is electrolyzed by passing a current between the anode 6 and the cathode 7 immersed in the electrodepositing electrolyte 3 containing SiF ₆ ²⁻ , The reaction represented by the formula (IV) of the following occurs, and the reaction represented by the following formula (V) occurs at the cathode 7.

(Anode) 4Cl ⁻ → 2Cl ₂ + 4e ⁻ (IV)

(Cathode) SiF ₆ ²⁻ + 4e ⁻ → Si + 6F ⁻ (V)

  Therefore, when the reaction formulas (III) to (V) are summarized, a reaction formula represented by the following formula (VI) is obtained.

SiCl ₄ → Si + 2Cl ₂ (VI)
Thus, in the preferred embodiment of the method for producing a purified metal according to the second embodiment, Si as a main product can be deposited on the cathode 7 and Cl ₂ gas as a by-product is generated at the anode. Therefore, the Cl ₂ gas can be reused to produce SiCl ₄ gas as the metal chloride gas 5 that is blown into the molten salt bath of KF and KCl.

  In the preferred embodiment of the method for producing a purified metal according to the second embodiment, the electrodepositing electrolyte 3 can be electrolyzed without changing the composition of the electrodepositing electrolyte 3. Si as the metal 8 can be continuously and efficiently deposited.

From the above viewpoint, the electrodepositing electrolyte 3 is produced by blowing SiCl ₄ gas as the metal chloride gas 5 into the molten salt bath 2 produced by melting KF and KCl, and the electrodepositing electrolyte. It is preferable to deposit Si as the purified metal 8 on the cathode 7 by electrolyzing 3.

<Experimental example 1>
First, powdered KF (manufactured by Wako Pure Chemical Industries, Ltd.) and powdered KCl (manufactured by Wako Pure Chemical Industries, Ltd.) are mixed at a ratio of KF: KCl = 45 mol: 55 mol to obtain a KF-KCl mixture. Was made. Next, after the KF-KCl mixture is accommodated in the container 1 shown in FIG. 2, the KF-KCl mixture in the container 1 is heated to a temperature of 923 K, and the KF-KCl mixture is melted, whereby 200 g of KF- A KCl molten salt bath 2 was prepared. When the composition of the KF-KCl molten salt bath 2 was confirmed, the presence of K ⁺ , F ⁻ and Cl ^{− in} the KF-KCl molten salt bath 2 was confirmed. The composition of the KF-KCl molten salt bath 2 was obtained by collecting 0.2 g of the KF-KCl molten salt bath 2 and dissolving it in 200 g of distilled water. This was confirmed by analysis by graphy.

  Next, as shown in FIG. 3, the anode 6 (counter electrode) made of graphite is immersed in the KF-KCl molten salt bath 2 accommodated in the container 1, and the cathode 7 (working electrode) made of Ag is immersed. I let you. Further, a Pt wire was immersed as a pseudo reference electrode (not shown).

Next, as shown in FIG. 4, after immersing the metal chloride gas introduction pipe 4 made of a stainless steel pipe having a circular opening having a diameter of 0.25 inch in the KF-KCl molten salt bath 2, As shown in FIG. 5, a mixed gas of Ar gas as the carrier gas and SiCl ₄ gas as the metal chloride gas 5 (SiCl ₄ gas partial pressure of 26.4 kPa) is supplied from the metal chloride gas introduction pipe 4 to the KF− By introducing into the KCl molten salt bath 2 at a flow rate of 50 mL / min, bubbling into the KF-KCl molten salt bath 2 with SiCl ₄ gas was performed. Thereby, 1.9 mol equivalent (10.21 g) of SiCl ₄ gas was introduced with respect to 100 mol of the mixture of KF and KCl, and the electrodepositing electrolyte 3 of Experimental Example 1 was produced.

In addition, bubbling to the KF-KCl molten salt bath 2 with SiCl ₄ gas is directly performed on the KF-KCl molten salt bath 2 for 30 minutes, and the tip of the metal chloride gas introduction pipe 4 is moved to KF for 90 minutes thereafter. -KCl molten salt bath 2 was fixed to a portion 2 cm upward from the surface, and a mixed gas of Ar gas and SiCl ₄ gas was allowed to flow.

  Next, by changing the voltage applied between the working electrode and the counter electrode at a scanning speed of 500 mV / s, a cyclic voltammogram of the electrodepositing electrolyte 3 of Experimental Example 1 was produced. FIG. 8 shows a cyclic voltammogram of the electrodepositing electrolyte 3 of Experimental Example 1. In addition, HZ-3000 made by Hokuto Denko Co., Ltd. was used for preparation of the cyclic voltammogram of the electrolyte 3 for electrodeposition of Experimental Example 1.

As shown in FIG. 8, in the cyclic voltammogram of the electrodeposition electrolyte 3 of Experimental Example 1, the potential of the working electrode is 0.5 Vvs. A peak of current density of 25 mA / cm ² was confirmed when K ⁺ / K. Predicting from the peak of the current density, it is considered that 0.02 mol% of K ₂ SiF ₆ is dissolved in the electrodeposition electrolyte 3 of Experimental Example 1.

Further, the potential of the cathode 7 between the anode 6 and the cathode 7 of the electrodepositing electrolyte 3 of Experimental Example 1 is 0.03 Vvs. Electrolysis of the electrodeposition electrolyte 3 of Experimental Example 1 was performed by applying a voltage for 60 minutes so that K ⁺ / K. As a result, as shown in FIG. 6, a Si film was deposited as the purified metal 8 on the cathode 7. The cathode after deposition of the Si film is taken out from the electrodeposition electrolyte 3 of Experimental Example 1 and immersed in water at room temperature for 24 hours, so that the electrodepositing electrolyte 3 attached to the surface of the Si film is washed with water. Removed and dried. And the X-ray-diffraction pattern of Si film after drying was measured using the X-ray-diffraction apparatus (Ultima IV made from Rigaku Corporation; CuK alpha ray, (lambda) = 0.15418nm, 40kV, 40mA). FIG. 9 shows an X-ray diffraction pattern of the Si film obtained in Experimental Example 1.

  In the X-ray diffraction pattern of the Si film obtained in Experimental Example 1 shown in FIG. 9, since an X-ray diffraction peak corresponding to Si is seen, the presence of Si was confirmed.

  Further, the purity of the Si film obtained in Experimental Example 1 was measured by GD-MS. The results are shown in Table 1. Note that VG9000 manufactured by Thermo Electron Co., Ltd. was used as an apparatus for measuring the purity of the Si film obtained in Experimental Example 1. As shown in Table 1, the purity of the Si film obtained in Experimental Example 1 was 99.97%.

<Experimental example 2>
For comparison, instead of introducing the KF-KCl molten salt bath 2 by bubbling with a mixed gas of Ar gas and SiCl ₄ gas, 2 mol equivalent of K ₂ SiF ₆ is mixed with 100 mol of the mixture of KF and KCl. A cyclic voltammogram of the electrodeposition electrolyte of Experiment Example 2 was prepared in the same manner as in Experiment Example 1 except that the electrodeposition electrolyte was prepared. FIG. 10 shows a cyclic voltammogram of the electrodepositing electrolyte 3 of Experimental Example 2.

As shown in FIG. 10, in the cyclic voltammogram of the electrodeposition electrolyte 3 of Experimental Example 2, the potential of the working electrode is 0.5 Vvs. A peak of current density of 2000 mA / cm ² was observed when K ⁺ / K.

  Further, the electrodepositing electrolyte 3 of Experimental Example 2 was electrolyzed in the same manner as in Experimental Example 1, and a Si film was deposited as the purified metal 8 on the cathode 7. Then, the cathode after deposition of the Si film is taken out from the electrodeposition electrolyte 3 of Experimental Example 2, and immersed in water at room temperature for 24 hours, so that the electrodepositing electrolyte 3 adhered to the surface of the Si film is washed with water. Removed and dried. The X-ray diffraction pattern of the Si film obtained in Experimental Example 2 was measured using the same method and the same conditions as in Experimental Example 1. As a result, an X-ray diffraction peak corresponding to the Si film was also confirmed in the X-ray diffraction pattern of the Si film obtained in Experimental Example 2.

  Further, the purity of the Si film obtained in Experimental Example 2 was measured by the same method and the same conditions as in Experimental Example 1. The results are shown in Table 1. As shown in Table 1, the purity of the Si film obtained in Experimental Example 2 was 99.32%.

  Experimental example 1 is an example, and experimental example 2 is a comparative example.

  As shown in Table 1, in Experimental Example 1 in which an electrolyte for electrodeposition was prepared by using a molten salt containing fluoride ions as a molten salt and using a metal chloride gas as a metal source, high purity was obtained. It is confirmed that the metal of this is obtained.

  Although the embodiments and experimental examples of the present invention have been described above, it is also planned from the beginning to appropriately combine the configurations of the above-described embodiments and experimental examples.

  The embodiments and experimental examples disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The aspect of the present invention can be used in a method for producing a refined metal, and can be suitably used particularly for a silicon solar cell production process, an abrasion-resistant surface processing process, and a semiconductor production process.

DESCRIPTION OF SYMBOLS 1 Container 2 Molten salt 3 Electrode for electrodeposition 4 Metal chloride gas introduction pipe 5 Metal chloride gas 6 Anode 7 Cathode 8 Refined metal

Claims (8)

Producing a molten salt bath containing fluoride ions;
Producing an electrolyte for electrodeposition by introducing a metal chloride gas into the molten salt bath;
A method of depositing a metal on a cathode in the electrodepositing electrolyte by electrolyzing the electrodepositing electrolyte. Producing the metal chloride gas using chlorine gas generated at the anode in the electrodeposition electrolyte in the step of depositing the metal;
The method for producing a purified metal according to claim 1, further comprising a step of introducing the metal chloride gas produced using the chlorine gas into the molten salt bath or the electrodeposition electrolyte.   The method for producing a purified metal according to claim 2, wherein the anode contains carbon.   The said metal is a manufacturing method of the refined metal of any one of Claims 1-3 containing at least 1 sort (s) selected from the group which consists of silicon, titanium, tungsten, zirconium, and molybdenum.   5. The metal chloride gas according to claim 1, wherein the metal chloride gas includes at least one selected from the group consisting of silicon chloride gas, titanium chloride gas, tungsten chloride gas, zirconium chloride gas, and molybdenum chloride gas. The manufacturing method of the refinement | purification metal as described in a term.   The manufacturing method of the refined metal of any one of Claims 1-5 containing a potassium ion as cations other than the metal ion which the said molten salt bath deposits.   7. The method according to claim 1, wherein in the step of preparing the electrolyte for electrodeposition, the metal chloride gas is introduced into the molten salt bath using a metal chloride gas introduction pipe. A method for producing purified metal.   The purification according to any one of claims 1 to 7, wherein in the step of preparing the electrodeposition electrolyte, the temperature of the molten salt bath when the metal chloride gas is introduced is 573K or more. Metal manufacturing method.

Images