Method for Producing Metal Titanium

Abstract

A method for producing metal titanium by carrying out electrolysis using an anode and a cathode in a molten salt bath, the method using an anode containing metal titanium as the anode, the method comprising a titanium deposition step of depositing metal titanium on the cathode, wherein, in the titanium deposition step, a temperature of the molten salt bath is from 250° C. or more and 600° C. or less, and an average current density of the cathode in a period from the start to 30 minutes later of the titanium deposition step is maintained in a range of 0.01 A/cm.sup.2 to 0.09 A/cm.sup.2.

Claims

1. A method for producing metal titanium by carrying out electrolysis using an anode and a cathode in a molten salt bath, the method using an anode containing metal titanium as the anode, the method comprising: a titanium deposition step of depositing metal titanium on the cathode, wherein, in the titanium deposition step, a temperature of the molten salt bath is from 250° C. or more and 600° C. or less, and an average current density of the cathode in a period from the start to 30 minutes later of the titanium deposition step is maintained in a range of from 0.01 A/cm.sup.2 to 0.09 A/cm.sup.2.

2. The method according to claim 1, wherein in the titanium deposition step, a surface area of a cathode immersed portion that is immersed in the molten salt bath is 3000 mm.sup.2 or more.

3. The method according to claim 1, wherein a surface of the cathode on which metal titanium is deposited in the titanium deposition step has a curved surface shape.

4. The method according to claim 3, wherein the cathode has a cylindrical shape.

5. The method according to claim 1, wherein the molten salt bath contains at least two selected from the group consisting of MgCl.sub.2, NaCl, KCl, CaCl.sub.2, LiCl, alkali metal iodides, and alkali metal bromides.

6. The method according to claim 1, wherein the cathode contains 70% by mass or more of Ti, Mo, or Fe.

7. The method according to claim 1, further comprising an anode dissolving step of dissolving the anode by electrolysis in the molten salt bath prior to the titanium deposition step.

8. The method according to claim 1, further comprising a titanium separation step of separating the metal titanium deposited on the cathode from the cathode after the titanium deposition step.

9. The method according to claim 1, wherein the metal titanium is produced in the form of a sheet having a thickness of from 20 μm to 1000 μm.

Description

EXAMPLES

[0062] Next, the method for producing metal titanium according to present invention was experimentally conducted and its effects were confirmed as described below. However, the description herein is merely for the purpose of illustration and is not intended to be limited thereto.

(Before Electric Conduction)

[0063] In a cylindrical Ni crucible having an inner diameter of 106 mm and a height of 350 mm were placed 725 g of NaCl (special grade manufactured by Kanto Chemical Co., Inc., which was vacuum-dried at 200° C. for one day in advance), 616 g of KCl (special grade manufactured by Kanto Chemical Co., Inc., which was vacuum-dried at 200° C. for one day in advance), and 1967 g of MgCl.sub.2 (anhydrous MgCl.sub.2 which was by-product in the reduction step of the Kroll process). These materials were melted by increasing the temperature to 700° C. with an external heater, and used as a molten salt bath.

[0064] The temperature of the molten salt bath was then decreased to 520° C. except for Comparative Example 3, and this temperature was maintained during the subsequent electric conduction. Before electric conduction, a mixture of titanium sponge with TiCl.sub.4 was mixed with the molten salt bath, thereby feeding 6 mol % of Ti to the molten salt bath. All of these operations were carried out in an Ar atmosphere.

(After Electric Conduction)

[0065] Used as the anode was a metal titanium plate formed into a cylindrical shape having an inner diameter of 89 mm and a height of 100 mm. Also used as the cathode was a rod-shaped cathode having a circular cross-section made of metal molybdenum, metal titanium, or carbon steel. The surface of the cathode has a curved surface shape, more particularly, the cathode has a cylindrical shape.

[0066] For the arrangement of the anode and cathode in the electrolytic bath, the cylindrical anode was arranged such that the central axis thereof is substantially parallel to the depth direction of the molten salt bath, and the rod-shaped cathode was arranged at the center on the inner side of the cylindrical anode.

[0067] A pulsed current that repeated the electric conduction and the stop at predetermined intervals was passed through the anode and the cathode, thereby performing electrolysis to dissolve the anode and deposit metal titanium in the form of a foil on the cathode. Table 1 shows various conditions of Examples 1 to 7 and Comparative Examples 1 to 3.

[0068] Here, in each of Examples 1 to 7 and Comparative Example 3, as shown in Table 1, the pulse current was applied such that the average current density of the cathode was maintained at 0.01 A/cm.sup.2 0.09 A/cm.sup.2, throughout the entire electric conduction period including the period from the start to 30 minutes later of the electric conduction. That is, the average current densities from the start to 30 minutes of the titanium deposition step and after 30 minutes are the same. On the other hand, in each of Comparative Examples 1 and 2, the average current density of the cathode was higher than 0.09 A/cm.sup.2 throughout the entire electric conduction period including the period from the start to 30 minutes later of the electric conduction.

(Recovery of Metal Titanium)

[0069] At the end of electrolysis, the cathode was lifted up from the molten salt bath and washed with water to remove the molten salt adhering to the surface. In each of Examples 1 to 7 and Comparative Examples 1 to 3, metal titanium having a size equivalent to the surface area of the cathode immersed portion was deposited on the cathode. Further, in each of Examples 1 to 7 and Comparative Examples 1 to 3, metal titanium in the form of a foil was deposited on the cathode, and no hole was observed in the appearance of the metal titanium in the form of a foil.

[0070] A notch was then made in the dried metal titanium with a cutter, the notched portion of the metal titanium was grasped with tweezers and a hand, and an attempt was made to peel it off from the cathode by the force of the hand. A case where titanium could be peeled off by the hand was evaluated as higher separability, and a case where titanium could not be peeled off was evaluated as lower separability, which are shown in Table 1. The metal titanium in Examples evaluated as lower separability was recovered by dissolving the cathode with a mixed solution of nitric acid and sulfuric acid.

TABLE-US-00001 TABLE 1 Example Example Example Example Example Example Example Comparative Comparative Comparative 1 2 3 4 5 6 7 Example 1 Example 2 Example 3 Cathode mm 48 20 25 20 20 20 20 48 25 20 Diameter Cathode mm 109 82 51 82 82 75 82 48 113 82 Height Cathode Mo Mo Mo Carbon Ti Mo Mo Mo Mo Mo Material Steel Cathode mm2 16,400 5,150 4,040 5,150 5,150 4,710 5,150 7,210 8,940 5,150 Immersed Suface Area Distance mm 21 35 32 35 35 35 35 21 32 35 between Electrodes Temperature ° C. 520 520 520 520 520 520 520 520 520 700 of Molten Salt Current Pulse Pulse Pulse Pulse Pulse Pulse Pulse Pulse Pulse Pulse Condition Current 0.108 0.150 0.115 0.150 0.150 0.150 0.050 0.226 0.201 0.150 Density at ON ON Time 1.5 s 1.5 s 1.5 s 1.5 s 1.5 s 1.5 s 1.5 s 1.5 s 1.5s 1.5 s Current 0 0 0 0 0 0 0 0 0 0 Density at OFF OFF Time 1.5 s 1.5 s 1.5 s 1.5 s 1.5 s 1.5 s 1.5 s 1.5 s 1.5 s 1.5 s Average A/cm2 0.054 0.075 0.058 0.075 0.075 0.075 0.025 0.113 0.101 0.075 Current Density Form of Foil Foil Foil Foil Foil Foil Foil Foil Foil Foil Titanium Average μm 102 100 40 100 100 235 105 69 114 100 Thickness of Titanium Titanium Higher Higher Higher Higher Higher Higher Higher Lower Lower Lower Separability

[0071] As can be seen from Table 1, on one hand, Examples 1 to 7 where the average current density of the cathode was maintained in the range of from 0.01 A/cm.sup.2 to 0.09 A/cm.sup.2 resulted in higher separability that could be peeled off by the hand, and on the other hand, Comparative Examples 1 and 2 where the average current density of the cathode was higher resulted in lower separability that could not be peeled off by the hand. Further, Comparative Example 3 where the temperature of the molten salt was higher also resulted in lower separability that could not be peeled off by the hand.

(Analysis of Metal Titanium)

[0072] For Example 1, oxygen in metal titanium was analyzed by infrared absorption method using dissolution of an inert gas. Further, for Example 1, iron in metal titanium was analyzed for the dissolved metal titanium by fluorescent X-ray analysis.

[0073] As a result, the oxygen concentration of the metal titanium obtained in Example 1 was 175 ppm by mass, and the iron concentration was 6 ppm by mass. Since the oxygen concentration of the anode made of metal titanium as a raw material was 700 ppm and the iron concentration was 600 ppm, it was confirmed that the metal titanium obtained in Example 1 had higher purity.

Example 8

[0074] Metal titanium was deposited on the cathode under the same conditions as those of Example 1, with the exception that after 30 minutes from the start of applying current (the start of the titanium deposition step), the average current density was 0.11 A/cm.sup.2, which was more than 0.09 A/cm.sup.2. As a result, as in Example 1, no hole was observed in the appearance of the metal titanium in the form of a foil even if it had a larger area, and the metal titanium exhibited higher separability.

Comparative Example 4

[0075] Metal titanium was deposited on the cathode under the same conditions as those of Example 1, with the exception that after 27 minutes from the start of applying current (the start of the titanium deposition step), the average current density was 0.11 A/cm.sup.2, which was more than 0.09 A/cm.sup.2. As a result, although no hole was observed in the appearance of the obtained metal titanium in the form of a foil, the metal titanium showed lower separability that could not be peeled off by the hand.