Method for producing high-purity polyvalent metals by electrolysis of bromide-based molten salts

Abstract

The application provides a method for preparing high-purity multi-valence metal by bromide-based molten salt electrolysis, comprising the following steps: 1) adding dry bromide-based molten salt into an electrolysis device, then heating to above the melting temperature and keeping the temperature to make the bromide-based molten salt in a molten state, wherein the bromide-based molten salt comprises 40-100 wt.% of bromide salt and 0-60 wt.% of chloride salt; 2) adding multi-valence metal and multi-valence metal stabilizing salt into the molten salt obtained in step 1), and obtaining low-valence multi-valence metal salt after soaking; 3) inserting the crude multi-valence metal as an anode and a metal plate as a cathode into the molten salt, and obtaining high-purity metal by constant current electrolysis after power-on. The multi-valence metal obtained by the method has a purity of 99.99% or above and a crystal grain size of 1000 microns or above.

Description

Technical Field

[0001] This invention belongs to the technical field of preparing high-purity metals by electrolysis of multivalent metals, specifically relating to a method for preparing high-purity multivalent metals by electrolysis of bromide-based molten salt. Background Technology

[0002] High-purity metals generally refer to metals with a purity of 99.9% or higher (even 99.995% or higher). They are characterized by extremely low impurity content, resulting in superior performance and widespread use in integrated circuit manufacturing, energy, biomedicine, and chemical industries. Further deep purification of crude metals is generally required to achieve high-purity standards, primarily through methods such as molten salt electrolysis and electron beam melting. Electron beam melting utilizes electron beam bombardment under high vacuum for zone or bulk melting, removing volatile impurities, but it requires sophisticated equipment and is expensive. Molten salt electrolysis is an effective method for preparing high-purity metals. However, current molten salt electrolysis processes mainly employ alkali metal fluoride and alkali metal chloride systems. These systems have weak polarization between cations and anions, leading to tight complexation between high-valence metal cations and anions, making them difficult to reduce to low-valence metal salts. This results in metal ions coexisting in multiple valence states in the molten salt, causing current cycling and wasted energy during electrolysis, significantly reducing electrolysis efficiency. Summary of the Invention

[0003] To address the problems existing in the prior art, this invention provides a method for preparing high-purity multivalent metals by electrolysis of bromide-based molten salt. The method aims to utilize the weak polarization characteristics of bromide-based molten salt to stabilize multivalent metal ions in a low valence state, thereby greatly improving current efficiency and reducing process energy consumption. At the same time, it optimizes cathode deposition kinetics, thereby improving the grain size and purity of the metal products.

[0004] According to one aspect of the present invention, a method for preparing high-purity multivalent metals by bromide-based molten salt electrolysis is provided, comprising the following steps:

[0005] 1) Add the dry bromide-based molten salt to the electrolysis equipment, then heat it to above its melting temperature and keep it at the temperature to make it molten, thereby obtaining molten salt. The bromide-based molten salt includes 40~100 wt.% bromide salt and 0~60 wt.% chloride salt.

[0006] 2) Add a multivalent metal and a multivalent metal stabilizer to the molten salt obtained in step 1), and soak to obtain a low-valence multivalent metal salt. The amount of metal and metal stabilizer added must ensure that the concentration of the low-valence multivalent metal ions obtained by reduction is higher than 1 wt.%.

[0007] 3) Using a crude multi-valence metal as the anode and a metal plate as the cathode, the plates are inserted into the molten salt. After applying an electric current, constant current electrolysis is used to obtain high-purity metal. The cathode current density is 0.05~0.8 A / cm². 2 The anode current density is 0.02~0.5 A / cm². 2 The electrolysis time is 0.5~20 h.

[0008] As a preferred embodiment of the method for preparing high-purity multivalent metals by electrolysis of bromide-based molten salt according to the present invention, in step 1), the bromide salt includes one or more of lithium bromide, potassium bromide, sodium bromide, cesium bromide, calcium bromide, magnesium bromide, and cesium bromide, and the chloride salt includes one or more of lithium chloride, sodium chloride, calcium chloride, potassium chloride, cesium chloride, and magnesium chloride.

[0009] As a preferred embodiment of the method for preparing high-purity multivalent metals by molten salt electrolysis according to the present invention, in step 1), the electrolysis equipment includes a muffle furnace with a heating temperature of 400~900 ℃.

[0010] As a preferred embodiment of the method for preparing high-purity multivalent metals by bromide-based molten salt electrolysis according to the present invention, in step 2), the multivalent metals include Ti, V, Cr, Zr, Hf, Ta or Nb; furthermore, the purity of the multivalent metals is 99~99.9%.

[0011] As a preferred embodiment of the method for preparing high-purity multivalent metals by electrolysis of bromide-based molten salt according to the present invention, in step 2), the multivalent metal stable salt includes TiCl3, VCl3, CrCl3, ZrCl4, HfCl3, TaCl5 or NbCl5.

[0012] As a preferred embodiment of the method for preparing high-purity multivalent metals by electrolysis of bromide-based molten salt according to the present invention, in step 2), the low-valence multivalent metal salt includes TiCl2, VCl2, CrCl2, ZrCl2, HfCl2, TaCl3 or NbCl3.

[0013] As a preferred embodiment of the method for preparing high-purity multivalent metals by bromide-based molten salt electrolysis according to the present invention, in step 2), the soaking time is 10~50 h.

[0014] As a preferred embodiment of the method for preparing high-purity multivalent metals by bromide-based molten salt electrolysis according to the present invention, in step 3), the crude multivalent metal is a multivalent metal with a purity not higher than 99%.

[0015] As a preferred embodiment of the method for preparing high-purity multivalent metals by bromide-based molten salt electrolysis according to the present invention, in step 3), the metal plate includes nickel, tungsten, molybdenum, iron, copper, stainless steel or multivalent metals.

[0016] According to another aspect of the present invention, a high-purity variable valence metal prepared by any of the preceding methods is provided, wherein the purity of the metal is 99.99% or higher and the grain size is 1000 μm or higher.

[0017] In this invention, the purpose of using bromide-based molten salt as the electrolyte is as follows: 1) This molten salt has the characteristic of weak polarization, and bromine can stably coordinate with the low-valence state ions of variable-valence metals, thereby stabilizing the variable-valence metal ions in the low-valence state and inhibiting the occurrence of disproportionation reactions. Under these conditions, the current efficiency can be significantly improved; 2) Compared with halogen elements such as fluorine and chlorine, the coordination between bromine and low-valence variable-valence metals is weakened, making it easier to detach during cathode deposition. This lowers the energy barrier for metal ion desolvation, reduces the cell voltage, optimizes cathode kinetics, accelerates metal ion deposition, and weakens the deposition of impurity metals, resulting in higher purity of the metal deposited on the cathode; 3) Because the cell voltage is lower during the electrolysis of the bromide-based system, the overpotential of cathode deposition is lower, and the driving force for metal deposition is weaker, which is insufficient for nucleation growth. Instead, crystal growth occurs via helical dislocations, resulting in larger grains in the cathode product. Furthermore, adding an appropriate amount of chloride to the bromide not only lowers the melting point of the system but also intensifies the competition between chlorine and bromine for coordination with low-valence, multi-valence metal ions, thereby further weakening the coordination between the target metal ion and the anion. In addition, multi-valence metal stable salts generally exist in chloride form, which can be directly added to the system and dissolved, while bromides of multi-valence metal stable salts are extremely expensive and not easily dissolved in molten salt systems.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. This invention employs bromide-based molten salt as the electrolyte, utilizing the coordination stability of bromine with low-valence, multi-valence metal ions to suppress disproportionation reactions, thereby inhibiting current cycling waste of multi-valence metal ions and achieving improved current efficiency. The current efficiency generated by the scheme based on this invention is no less than 90%.

[0020] 2. By weakening the coordination between anions and multivalent metal ions, this invention reduces the energy barrier for metal ion desolvation, thereby effectively reducing the electrolytic cell voltage, improving cathode efficiency, and lowering process costs.

[0021] 3. This invention accelerates metal deposition kinetics, increasing the deposition rate of the target metal and reducing the deposition rate of impurity metals. Furthermore, under relatively small overpotential conditions, metal growth occurs via helical dislocations, effectively improving product purity and grain size. The metal purity obtained using this invention can reach the 4N level (i.e., purity above 99.99%), with an average grain size exceeding 1000 μm. Attached Figure Description

[0022] Figure 1 Physical image of the high-purity titanium product obtained by electrolysis in Example 1 of this invention;

[0023] Figure 2 A photograph of the high-purity titanium product obtained by electrolysis in Example 2 of this invention. Detailed Implementation

[0024] The technical solutions described below in conjunction with the embodiments will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] This invention provides a method for preparing high-purity multivalent metals by electrolysis of bromide-based molten salts, comprising the following steps:

[0026] 1) Add the dry bromide-based molten salt to the electrolysis equipment, then heat it to above its melting temperature and keep it at the temperature to make it molten, thereby obtaining molten salt. The bromide-based molten salt includes 40~100 wt.% bromide salt and 0~60 wt.% chloride salt.

[0027] 2) Add a polyvalent metal (e.g., Ti, with a purity between 99% and 99.9%) and its corresponding polyvalent metal stabilizing salt (e.g., TiCl3) to the molten salt obtained in step 1). After soaking, a low-valence polyvalent metal salt (e.g., TiCl2) is obtained. The amount of metal and metal stabilizing salt added must ensure that the concentration of the low-valence polyvalent metal ions obtained from the reduction is higher than 1 wt.%.

[0028] 3) Using a crude multivalent metal (e.g., Ti with a purity below 99%) corresponding to the multivalent metal described in step 2), as the anode and a metal plate (e.g., nickel) as the cathode, insert the metal into the molten salt. After applying current, electrolysis is performed using a constant current to obtain a high-purity metal. The cathode current density is 0.05-0.8 A / cm². 2 The anode current density is 0.02-0.5 A / cm². 2 The electrolysis time is 0.5-20 h.

[0029] Preferably, in step 1), the drying specifically involves heating to above 300 °C and holding at that temperature for at least 12 hours under an inert atmosphere.

[0030] Preferably, in step 1), the bromide salt includes one or more of lithium bromide, potassium bromide, sodium bromide, cesium bromide, calcium bromide, magnesium bromide, and cesium bromide, and the chloride salt includes one or more of lithium chloride, sodium chloride, calcium chloride, potassium chloride, cesium chloride, and magnesium chloride.

[0031] Preferably, in step 1), the electrolysis equipment includes a muffle furnace with a heating temperature of 400~900 ℃.

[0032] Preferably, in step 2), the multivalent metal can also be V, Cr, Zr, Hf, Ta or Nb.

[0033] Preferably, in step 2), the multivalent metal stable salt can also be VCl3, CrCl3, ZrCl4, HfCl3, TaCl5 or NbCl5.

[0034] Preferably, in step 2), the low-valence polyvalent metal salt can also be VCl2, CrCl2, ZrCl2, HfCl2, TaCl3 or NbCl3, and the low-valence polyvalent metal salt corresponds to the metal of the polyvalent metal salt.

[0035] Preferably, in step 2), the soaking time is 10-50 h.

[0036] Preferably, in step 3), the crude multivalent metal is a multivalent metal with a purity not higher than 99%.

[0037] Preferably, in step 3), the metal plate can also be tungsten, molybdenum, iron, copper, stainless steel or a multivalent metal. When a multivalent metal is selected as the cathode, the multivalent metal is the same metal as the aforementioned multivalent metal.

[0038] The high-purity metals prepared by any of the aforementioned methods have a purity of over 99.99% and a particle size of over 1000 μm.

[0039] Example 1

[0040] A method for preparing high-purity multivalent metals by electrolysis of bromide-based molten salts includes the following steps:

[0041] 1) Weigh 200 g of LiCl-LiBr according to the eutectic ratio (LiCl:LiBr=20:80 wt.%), stir evenly, pour into an alumina crucible, place in an electrolytic furnace under an inert atmosphere, heat to 300 ℃ for 12 h of vacuum drying, and then heat to 600 ℃ (above the melting temperature) to make it molten, thus obtaining molten salt;

[0042] 2) Add 7.5g TiCl3 to the molten salt obtained in step 1) to prepare a titanium salt with a titanium ion concentration, and add 10g pure titanium sheet (purity 99.5%). After soaking for 12 h, Ti is obtained. 2+ ;

[0043] 3) A 6 mm diameter coarse Ti rod (99% Ti content) is used as the anode, and a 3 mm diameter Ni rod is used as the cathode. The oxide layer on the surface is cleaned off, and the rods are inserted parallel to the molten salt from the top of the electrolytic furnace. After energizing, constant current electrolysis is used to obtain high-purity metal. The cathode current density is 0.2 A / cm². 2 The anode current density is 0.1 A / cm². 2 The electrolysis time is 2 hours. Crude titanium dissolves at the anode and titanium is deposited at the cathode, thus achieving electrolytic refining and extraction of titanium.

[0044] The cathode titanium was found to have a purity of 99.995%, an average grain size of over 2000 μm, and a current efficiency of 97%.

[0045] Example 2

[0046] A method for preparing high-purity multivalent metals by electrolysis of bromide-based molten salts includes the following steps:

[0047] 1) Weigh 200 g of NaCl-NaBr according to the eutectic ratio (NaCl:NaBr=16:84 wt.%), stir evenly, pour into an alumina crucible, place in an electrolytic furnace under an inert atmosphere, heat to 300 ℃ for 12 h of vacuum drying, and then heat to 800 ℃ (above the melting temperature) to make it molten, thus obtaining molten salt;

[0048] 2) Add 7.5g TiCl3 to the molten salt obtained in step 1) to prepare a titanium salt with a titanium ion concentration, and add 10g pure titanium sheet (purity 99.5%). After soaking for 12 h, Ti is obtained. 2+ ;

[0049] 3) A 6 mm diameter coarse Ti rod (99% Ti content) is used as the anode, and a 3 mm diameter Ni rod is used as the cathode. The oxide layer on the surface is cleaned off, and the rods are inserted parallel to the molten salt from the top of the electrolytic furnace. After applying current, constant current electrolysis is used to obtain high-purity metal. The cathode current density is 0.4 A / cm². 2 The anode current density is 0.15 A / cm². 2 The electrolysis time is 2 hours. Crude titanium dissolves at the anode and titanium is deposited at the cathode, thus achieving electrolytic refining and extraction of titanium.

[0050] The cathode titanium was found to have a purity of 99.991%, an average grain size of over 1200 μm, and a current efficiency of 95%.

[0051] Example 3

[0052] A method for preparing high-purity multivalent metals by electrolysis of bromide-based molten salts includes the following steps:

[0053] 1) Weigh 200 g of LiCl-LiBr according to the eutectic ratio (LiCl:LiBr=20:80 wt.%), stir evenly, pour into an alumina crucible, place in an electrolytic furnace under an inert atmosphere, heat to 300 ℃ for 12 h of vacuum drying, and then heat to 600 ℃ (above the melting temperature) to make it molten, thus obtaining molten salt;

[0054] 2) Add 7.5g ZrCl4 to the molten salt obtained in step 1) to prepare a titanium salt with a titanium ion concentration, and add 10g of pure zirconium sheet (purity 99.3%). After soaking for 12 h, Zr is obtained. 2+ ;

[0055] 3) A 6 mm diameter coarse Zr rod (Zr content 99%) is used as the anode, and a 3 mm diameter Ni rod is used as the cathode. The oxide layer on the surface is polished clean, and the rods are inserted parallel to the molten salt from the top of the electrolytic furnace. After energizing, constant current electrolysis is used to obtain high-purity metal. The cathode current density is 0.2 A / cm². 2 The anode current density is 0.1 A / cm². 2 The electrolysis time is 2 hours. The crude zirconium at the anode dissolves and the zirconium at the cathode is deposited, thus realizing the electrolytic refining and extraction of zirconium.

[0056] The cathode zirconium was found to have a purity of 99.99%, a grain size of over 1000 μm, and a current efficiency of 95%.

[0057] Comparative Example 1

[0058] A method for preparing multivalent metals by electrolysis of fluoride-based molten salt includes the following steps:

[0059] 1) Weigh 200 g of LiF-NaF-KF according to the eutectic ratio (LiF:NaF:KF=29.3:11.7:59 wt.%), stir evenly, pour into an alumina crucible, place in an electrolytic furnace under an inert atmosphere, heat to 300 ℃ for 12 h of vacuum drying, and then heat to 600 ℃ (above the melting temperature) to make it molten, thus obtaining molten salt;

[0060] 2) Add 10g of K2TiF6 to the molten salt obtained in step 1) to prepare a titanium salt with a titanium ion concentration, and add 10g of pure titanium sheet. After soaking for 12 h, Ti is obtained. 3+ ;

[0061] 3) A 6mm diameter Ti rod (99% Ti content) is used as the anode, and a 3mm diameter Ni rod is used as the cathode. The oxide layer on the surface is cleaned off, and the rods are inserted parallel to the molten salt from the top of the electrolytic furnace. After energizing, constant current electrolysis is used to obtain high-purity metal. The cathode current density is 0.2 A / cm². 2 The anode current density is 0.3 A / cm². 2 The electrolysis time is 2 hours. Crude titanium dissolves at the anode and titanium is deposited at the cathode, thus achieving electrolytic refining and extraction of titanium.

[0062] Measurements showed that the cathode titanium had a purity of 99.9%, a grain size of approximately 50 μm, and a current efficiency of 80%. Because fluoride ions readily adsorb onto the surface of the deposited titanium on the cathode, they hindered the growth of the titanium grains, indirectly leading to an increase in oxygen content. Furthermore, the resulting cathode titanium powder, due to its fine grain size, easily detached from the cathode, resulting in a decrease in current efficiency.

[0063] Comparative Example 2

[0064] A method for preparing multivalent metals by chloride-based molten salt electrolysis includes the following steps:

[0065] 1) Weigh 200 g of LiCl-KCl according to the eutectic ratio (LiCl:KCl=45:55 wt.%), stir evenly, pour into an alumina crucible, place in an electrolytic furnace under an inert atmosphere, heat to 300 ℃ for 12 h of vacuum drying, and then heat to 600 ℃ (above the melting temperature) to make it molten, thus obtaining molten salt;

[0066] 2) Add 7.5g TiCl3 to the molten salt obtained in step 1) to prepare a titanium salt with a titanium ion concentration, and add 10g pure titanium sheet. After soaking for 12 h, Ti is obtained. 2+ ;

[0067] 3) A 6 mm diameter coarse Ti rod (99% Ti content) is used as the anode, and a 3 mm diameter Ni rod is used as the cathode. The oxide layer on the surface is cleaned off, and the rods are inserted parallel to the molten salt from the top of the electrolytic furnace. After energizing, constant current electrolysis is used to obtain high-purity metal. The cathode current density is 0.2 A / cm². 2 The anode current density is 0.1 A / cm². 2 The electrolysis time is 2 hours. Crude titanium dissolves at the anode and titanium is deposited at the cathode, thus achieving electrolytic refining and extraction of titanium.

[0068] Measurements showed that the titanium cathode had a purity of 99.97%, a grain size of approximately 200 μm, and a current efficiency of 82%. In typical chloride systems, multiple valence ions coexist (e.g., Ti). 3+ and Ti 2+ This can easily lead to current cycling waste and a decrease in current efficiency. In addition, the grain growth mode in this system is instantaneous nucleation, and the grains gradually grow as the electrolysis time increases. However, due to its slow kinetic rate, its growth rate and grain size are between those of the bromide and fluoride salt systems.

[0069] Comparative Example 3

[0070] A method for preparing multivalent metals by electrolysis of a chlorobromide-based molten salt includes the following steps:

[0071] 1) Weigh 200 g of LiCl-LiBr (LiCl:LiBr=90:10 wt.%) according to the ratio, stir evenly and pour into an alumina crucible. Place it in an electrolytic furnace under an inert atmosphere, heat to 300 ℃ and vacuum dry for 12 h. Then heat to 600 ℃ (above the melting temperature) to make it molten, and obtain molten salt.

[0072] 2) Add 7.5g TiCl3 to the molten salt obtained in step 1) to prepare a titanium salt with a titanium ion concentration, and add 10g pure titanium sheet. After soaking for 12 h, Ti is obtained. 2+ ;

[0073] 3) A 6 mm diameter coarse Ti rod (99% Ti content) is used as the anode, and a 3 mm diameter Ni rod is used as the cathode. The oxide layer on the surface is cleaned off, and the rods are inserted parallel to the molten salt from the top of the electrolytic furnace. After energizing, constant current electrolysis is used to obtain high-purity metal. The cathode current density is 0.2 A / cm². 2 The anode current density is 0.1 A / cm². 2 The electrolysis time is 2 hours. Crude titanium dissolves at the anode and titanium is deposited at the cathode, thus achieving electrolytic refining and extraction of titanium.

[0074] The cathode titanium was found to have a purity of 99.98%, a grain size of about 400 μm, and a current efficiency of 90%.

[0075] It should be noted that, based on the above embodiments of the present invention, those skilled in the art can fully realize the scope of the independent claims and dependent claims of the present invention, and the implementation process and methods are the same as those in the above embodiments; and the parts of the present invention not described in detail belong to the well-known technology in the art. However, the protection scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing high-purity multivalent metals by electrolysis of bromide-based molten salt, characterized in that, Includes the following steps: 1) Add the dry bromide-based molten salt to the electrolysis equipment, then heat it to above its melting temperature and keep it at the temperature to make it molten, thereby obtaining molten salt. The bromide-based molten salt includes 40~100 wt.% bromide salt and 0~60 wt.% chloride salt. 2) Add a multivalent metal and a multivalent metal stabilizer to the molten salt obtained in step 1), and soak to obtain a low-valence multivalent metal salt. The amount of metal and metal stabilizer added satisfies the requirement that the concentration of the low-valence multivalent metal ions obtained from the reduction is higher than 1 wt.%. 3) Using a crude multi-valence metal as the anode and a metal plate as the cathode, the plates are inserted into the molten salt. After applying an electric current, constant current electrolysis is used to obtain high-purity metal. The cathode current density is 0.05~0.8 A / cm². 2 The anode current density is 0.02~0.5 A / cm². 2 The electrolysis time is 0.5~20 h.

2. A method for preparing high-purity multivalent metals by electrolysis of bromide-based molten salt as described in claim 1, characterized in that, In step 1), the bromide salt includes one or more of lithium bromide, potassium bromide, sodium bromide, cesium bromide, calcium bromide, magnesium bromide, and cesium bromide, and the chloride salt includes one or more of lithium chloride, sodium chloride, calcium chloride, potassium chloride, cesium chloride, and magnesium chloride.

3. A method for preparing high-purity multivalent metals by electrolysis of bromide-based molten salt as described in claim 1, characterized in that, In step 1), the electrolysis equipment includes a muffle furnace with a heating temperature of 400~900 ℃.

4. A method for preparing high-purity multivalent metals by electrolysis of bromide-based molten salt as described in any one of claims 1 to 3, characterized in that, In step 2), the multivalent metal includes Ti, V, Cr, Zr, Hf, Ta, or Nb.

5. A method for preparing high-purity multivalent metals by electrolysis of bromide-based molten salt as described in any one of claims 4, characterized in that, In step 2), the multivalent metal stable salt includes TiCl3, VCl3, CrCl3, ZrCl4, HfCl3, TaCl5, or NbCl5.

6. A method for preparing high-purity multivalent metals by electrolysis of bromide-based molten salt as described in any one of claims 5, characterized in that, In step 2), the low-valence multivalent metal salt includes TiCl2, VCl2, CrCl2, ZrCl2, HfCl2, TaCl3 or NbCl3.

7. A method for preparing high-purity multivalent metals by electrolysis of bromide-based molten salts as described in claim 5 or 6, characterized in that, In step 2), the soaking time is 10-50 h.

8. A method for preparing high-purity multivalent metals by electrolysis of bromide-based molten salts as described in any one of claims 1 to 3, 5, and 6, characterized in that, In step 3), the crude multivalent metal is a multivalent metal with a purity of no more than 99%.

9. A method for preparing high-purity multivalent metals by electrolysis of bromide-based molten salts as described in any one of claims 1 to 3, 5, and 6, characterized in that, In step 3), the metal plate includes nickel, tungsten, molybdenum, iron, copper, stainless steel, or a multivalent metal.

10. A high-purity, multi-valence metal, wherein the metal is prepared by the method according to any one of claims 1 to 9, and the purity of the metal is 99.99% or higher and the grain size is 1000 μm or higher.

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