JPH0586432A - Activation treatment for surface amorphous alloy for electrode for solution electrolysis - Google Patents

Abstract

PURPOSE:To provide surface activation treatment method for an amorphous alloy reduced in the concentration of expensive platinum group elements and having superior properties required of an energy saving and highly corrosion resistant electrode, such as capacity for generating large amount of chlorine gas by means of low voltage when used as anode for the electrolysis of aqueous solution of sodium chloride, capacity for minimizing the amount of oxygen as contaminant, and usability as a long-life electrode. CONSTITUTION:An amorphous alloy having a composition consisting of one or >=2 kinds among valve metals, one or >=2 kinds among platinum group metals, and the balance essentially nickel is immersed into hydrofluoric acid, by which the platinum group metals can be concentrated in the surface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for activating an amorphous alloy which is suitable as an electrode material for electrolysis of an aqueous sodium chloride solution having various concentrations, temperatures and pHs.

[0002]

2. Description of the Related Art Conventionally, an electrode in which a corrosion-resistant metal such as titanium is coated with a noble metal or a noble metal oxide has been industrially used for electrolysis of an aqueous sodium chloride solution. Also,
The present inventors have registered Japanese Patent Nos. 1153531 and 1213069 using a platinum group amorphous alloy as materials for the same purpose, and Japanese Patent Application No. 58-1711.
Filed as No. 62.

[0003]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention Electrodes which are currently used industrially and which are coated with a noble metal on a corrosion-resistant metal are liable to peel off when used as an anode in seawater, and have low corrosion resistance and a short life. There is. On the other hand, electrodes with a corrosion-resistant metal coated with a noble metal oxide also have drawbacks such as oxide peeling during use, and a relatively large amount of oxygen generated along with oxidation of chlorine ions, resulting in low energy efficiency. There is. Further, a common problem of the noble metal-coated electrode, the noble metal oxide-coated electrode, and the amorphous platinum group alloy electrode is that an expensive noble metal is used as a main raw material.

[0004]

When the present invention is used, for example, as an anode for electrolysis of various sodium chloride aqueous solutions, a large amount of chlorine gas is generated at a low voltage, the amount of mixed oxygen is low, and the electrode has a long life. It is an object of the present invention to provide a surface activation treatment method for an amorphous alloy which has excellent performance as an energy-saving and highly corrosion-resistant electrode and can be used, and which is expensive and has a low platinum group element concentration.

Normally, alloys are crystallized in the solid state, but a method that does not form long-periodic regularity in the atomic arrangement in the process of solid formation, such as limiting the alloy composition and solidifying from the molten state by rapid quenching, is applied. Then, an amorphous structure that does not have a crystal structure and is similar to a liquid is obtained, and such an alloy is called an amorphous alloy. Amorphous alloys have remarkably high strength as compared with conventional practical metals, and exhibit various properties such as unusually high corrosion resistance depending on the composition.

On the other hand, two of the inventors of the present invention have previously described the patent No. 11
No. 5,353,1 and No. 1213069, the inventors applied for inventing an amorphous alloy electrode material for electrolysis mainly containing a platinum group metal and a semimetal, and when these materials were used as an anode for electrolysis of a high temperature concentrated aqueous solution, chlorine It has extremely high electrocatalytic activity for gas production, but is inactive for the generation of competing interfering reaction, oxygen, which is a highly efficient energy-saving material and has high corrosion resistance. Disclosed by patent.

Furthermore, the inventors of the present invention have disclosed in Japanese Patent Application No. 58-171.
No. 162 has invented and filed a surface activated amorphous alloy for electrodes for solution electrolysis, which is mainly composed of a platinum group metal and a semimetal. This is produced by applying the method for activating the surface of an amorphous metal, which was previously filed by Japanese Patent Application No. 56-84413 by the two inventors of the present invention, to the above-mentioned alloy exhibiting excellent electrocatalytic activity. Is. It has an electrocatalytic activity excellent as an anode for producing sodium hypochlorite, which generates chlorine by electrolysis of a solution that is difficult to generate chlorine, such as dilute NaCl solution that is not heated and has a concentration of seawater. It is a material provided with. Although these inventions each provide an electrode material having excellent properties,
All of them were expensive because their main components were platinum group metals.

Therefore, as a result of further studies, the inventors of the present invention set the platinum group metal to 10 atomic% or less, and the balance consisting of one or more valve metals and Ni, and in some cases a small amount of P. By immersing the contained amorphous alloy in hydrofluoric acid, it was found that a material having a sufficiently high electrocatalytic activity can be obtained even if the expensive platinum group element concentration is low, and the present invention has been accomplished.

[0009]

In order to further enhance the catalytic activity as the electrode for electrolysis, it is necessary to increase the electrochemically effective surface area and collect the platinum group metal acting as the active site of the electrode reaction on the surface. However, Cu-Ti, Cu-Zr, Fe-Zr
Amorphous alloys such as Ti or Zr by hydrofluoric acid
Is selectively dissolved, but Ni-Ta and Ni-Nb are not known to be selectively dissolved.

On the other hand, the present inventors have found that when a platinum group metal is added to a Ni-valve metal alloy, one or more valve metals and one or two platinum group metals are used.
It has been found that nickel and valve metal are selectively dissolved by immersing an amorphous alloy containing at least one kind and substantially consisting of nickel in hydrofluoric acid. The concentration and temperature of the hydrofluoric acid can be appropriately selected according to the composition of the target amorphous alloy, and commercially available concentrated hydrofluoric acid can be used as it is. When an amorphous alloy of Ni-valve metal-platinum group metal is immersed in hydrofluoric acid, some of Ni and Nb, Ta, Ti, and Zr forming the alloy preferentially dissolve uniformly from the alloy surface, Since the alloy surface becomes finer, it becomes black and the platinum group metal that plays a role of electrode activity is concentrated on the surface. Therefore, the surface activation treatment may be terminated when the surface becomes black. Even if the surface activation treatment is applied to a crystalline alloy having the same average composition as the amorphous alloy of the present invention, since the crystalline alloy has a multiphase structure and contains a compound phase, Ni and Nb, Ta, T
The surface activation treatment is not effective because it is difficult to uniformly dissolve i, Zr and the like. On the other hand, in the amorphous alloy of the present invention, since the constituent elements are uniformly distributed, Ni and Nb, Ta, Ti, Zr, etc. are uniformly dissolved in hydrofluoric acid, and the effective surface area is remarkably increased. The platinum group metal responsible for the electrode activity is concentrated on the surface, and the entire alloy surface can be sufficiently activated.

The amorphous alloy used in the activation treatment method of the present invention is prepared by various methods which have been widely used.
That is, various methods of rapidly quenching and solidifying a liquid alloy, various methods of forming an amorphous alloy through a gas phase, methods of destroying the long-period structure of a solid surface by ion implantation and alloying necessary elements, etc. Any method for producing an amorphous alloy may be used.

Example 1 Using homemade nickel phosphide and a commercially available metal as raw materials, the raw metal was mixed so as to have the composition shown in Table 1 and melted by high frequency induction heating in an argon atmosphere to prepare a raw alloy. By remelting these alloys in an argon atmosphere and solidifying rapidly by using the single roll method,
Thickness 0.01-0.05mm, width 1-5mm, length 3-
A 20 m amorphous alloy thin plate was obtained. The formation of amorphous structure was confirmed by X-ray diffraction. The surfaces of these alloy samples were polished in cyclohexane up to silicon carbide paper No. 1000. To confirm that the corrosion resistance of these alloys is sufficiently high, the anodic polarization curves of all these alloys were measured in 0.5M NaCl solution at 30 ° C. Figure 1
The polarization curves of these alloys are
It is common to amorphous alloys and is almost indistinguishable from each other. All of these alloys are self-passivated, and when anodic polarized, 1.0-1.1V
Up to (SCE), it shows a low passive state holding current of 2 × 10 ⁻² Am ⁻² or less. When the potential further rises, it is almost 1.2V (SC
E) From the vicinity, an increase in current due to generation of chlorine and oxygen is observed.

[0013]

[Table 1]

[0014]

These alloys were immersed in 46% hydrofluoric acid at room temperature for a few minutes to a few tens of minutes until the surface turned black, and subjected to a surface activation treatment.
The anodic polarization curve measured twice in NaCl solution is shown in FIG. The polarization curves of the amorphous alloys of the present invention after the activation treatment are the same as those shown in FIG. 2, and it is difficult to distinguish which of the alloys has the polarization curve when superposed on one figure.
0.4-0.8V in the first polarization curve after activation treatment
A current density of about 10 ° A · m ⁻² is observed near (SCE). This corresponds to the dissolution of surface components that were not completely dissolved in hydrofluoric acid during the activation treatment. However, when the potential is returned to a higher potential and then the potential is returned and the polarization curve is measured a second time after the activation treatment, the current density around 0.4 to 0.8 V (SCE) is no longer observed. Therefore, it is shown that once polarized to a high potential for chlorine generation and all the components that are dissolved from the surface are dissolved, the alloy does not dissolve after the second time. 1.0
At a potential higher than the vicinity of V (SCE), there is no difference between the first and second times, and the chlorine generation current is observed. For example 1.2V
Comparing the current densities before and after the activation treatment near (SCE), the activation treatment actually improves the chlorine generation current by four digits or more.

In order to examine the corrosion resistance during electrolysis, 1.25
After carrying out constant current electrolysis with V (SCE) for 12 hours, it was washed with distilled water and acetone and dried in a desiccator for 12 hours. After weighing this sample with a microbalance, 2
Electrolysis was carried out for 4 hours at 1.25 V (SCE), and washing, drying and weighing were carried out in the same manner as described above, and the amount of corrosion loss when carrying out constant electrolysis for 24 hours was quantified. Such measurement was performed on sample No. 3, 13, 1 which has been subjected to an activation treatment typical of the alloy of the present invention.
No changes in sample weight before and after the constant potential electrolysis for 24 hours could not be detected. Therefore, it was revealed that these electrodes were not corroded at all even when used in 0.5N NaCl solution as electrodes for chlorine generation. Using some of the representative alloys of the present invention, constant current electrolysis was carried out at various current densities, and chlorine generated during electrolysis of 1000 coulomb / l was measured by iodometry. The results are shown in Table 2. Pt- which is most active as a practical electrode for electrolysis under these conditions
The amorphous alloy electrodes of the present invention are mostly more active than the Ir / Ti electrodes. Further, both alloys are inexpensive because they have a low platinum group metal content.

[0017]

[Table 2]

Example 2 The amorphous alloy of the present invention prepared in the same manner as in Example 1 and subjected to the surface activation treatment is used for chlorine production in the soda electrolysis industry. Chlorine in a 4M NaCl solution at pH 4 and 80 ° C. The generation characteristics were investigated. FIG. 3 is an example of a polarization curve and shows that an inexpensive material like the present invention has a sufficiently high electrocatalytic activity.

[0019]

Industrial Applicability As described above in detail, even though the amount of expensive platinum group element is extremely low, it has an extremely high electrocatalytic ability as an electrode for electrolysis of an aqueous sodium chloride solution and has a high corrosion resistance under electrolysis conditions. It is a long-life, energy-saving and stable electrode material with high stability that cannot be detected even in balance.

[Brief description of drawings]

1 is a polarization curve of an amorphous alloy as-solidified by quenching measured in a 0.5N NaCl solution at 30 ° C. (Sample No. 1)
6, No. 17),

2 is a polarization curve of a surface-activated amorphous alloy measured in a 0.5 N NaCl solution at 30 ° C. (Sample N
o. 26),

FIG. 3 is a polarization curve (Sample No. 16) of a surface-activated amorphous alloy measured in a 4M NaCl solution at 80 ° C. and pH 4.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Asahi Kawashima 37-17 Hiyoridai, Sendai City, Miyagi Prefecture

Claims (2)

[Claims] 1. A surface amorphous alloy for electrolysis in solution electrolysis, which comprises one or more valve metals and one or more platinum group metals, with the balance substantially nickel, and hydrofluoric acid. A method for activating an amorphous alloy for electrode in solution electrolysis, which comprises concentrating a platinum group metal on the surface by immersing in a solution. [Claim 2] A surface amorphous alloy for electrolysis in solution electrolysis, which comprises one or more valve metals, one or more platinum group metals, and a small amount of phosphorus, the balance being nickel. A method for activating an amorphous alloy for an electrode for solution electrolysis, which comprises concentrating a platinum group metal on the surface by immersing in a hydrofluoric acid.