JPH07216600A - Method for electrolytically pickling stainless steel sheet and electrode used therefor - Google Patents

Abstract

PURPOSE:To remarkably improve the service life of an anode by forming a plural-layer coating film of iridium oxide, tantalum oxide and manganese dioxide on a titanium substrate as the anode to be used in pickling, using an electrode provided with catalytic activity and insolubility and controlling the anode current density and pickling soln. composition. CONSTITUTION:A coating film consisting of a mixture of 50-80mol% iridium oxide and 15-50mol% tantalum oxide and with the weight controlled to >=20g/m<2>, expressed in terms of metallic iridium, is formed on a substrate of titanium or titanium alloy. A surface layer consisting of >=20g/m<2> electrodeposited manganese dioxide is provided on the coating film as an intermediate layer to constitute an electrode. When pickling is conducted, the anode current density is controlled to <=30A/dm<2>, and an electrolytic pickling soln. contg. manganese ion is used. Since this constitution consists of the substrate, the intermediate layer excellent in adhesion and the dense surface layer, the substrate is not passivated, and the service life is prolonged because the intermediate and surface layers have electrode catalytic activity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for electrolytic pickling of a stainless steel plate and an electrode used therefor.

[0002]

2. Description of the Related Art Conventionally, a silicon iron alloy electrode has been used as an anode used when electrolytically pickling a stainless steel sheet in a nitric acid aqueous solution or a neutral sodium sulfate aqueous solution. Therefore, the appearance of an insoluble electrode, which is highly electrolyzed, has been desired. Therefore, there is an example in which the titanium electrode coated with iridium oxide is used, but the consumption of iridium oxide is still large and the life is not yet sufficient.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an electrolysis method using an insoluble electrode which has catalytic activity and is durable against a pickling solution when electrolytically pickling a stainless steel sheet. It is in.

[0004]

According to the present invention, when electrolytically pickling a stainless steel sheet in a nitric acid aqueous solution or a neutral sodium sulfate aqueous solution, an iridium oxide of 50 to 50 is formed on a conductive metal substrate made of titanium or its alloy. An electrode provided with an intermediate layer made of a mixed oxide of 85 mol% and tantalum oxide 15 to 50 mol% and having a weight of 20 g / m ² or more in terms of metal iridium, and a surface layer made of electrodeposited manganese dioxide. It is an electrolytic pickling method for a stainless steel plate, which is used as an anode, and is an electrode for electrolytic pickling used in this method.

Electrodes in which manganese dioxide is electrodeposited on a titanium substrate via an intermediate layer are known. Japanese Patent Publication 45-364
No. 83 discloses platinum, palladium, and titanium on the surface of titanium, zirconium, tantalum, or an alloy containing them as a matrix.
An insoluble electrode for electrolysis is described in which a thin layer of rhodium or an alloy containing them as a matrix is provided and manganese dioxide is electrodeposited thereon. However, platinum, palladium, and rhodium, which form the intermediate layer, have poorer resistance to the acidic electrolyte than iridium oxide. According to the description in the specification, a thin layer having a thickness of about 0.02 to 0.1 μm is used. When this electrode is used for electrolysis in a sulfuric acid acidic solution, oxygen permeates the titanium substrate surface, By forming an insulative oxide film on the surface of the substrate, the voltage rises and the performance of manganese dioxide on the surface cannot be fully exhibited.

Further, in JP-A-53-97771, an intermediate layer of platinum group metal oxide and MnOx (x is 1.5 or more and less than 2.0) is formed on a conductive metal substrate such as titanium. Described insoluble anodes having a surface layer of manganese oxide containing a non-stoichiometric compound. However, also in this electrode, the intermediate layer is a thin layer of about 0.002 to 0.02 μm, and although there is a description of the iridium oxide layer as the material thereof, it is possible to obtain iridium and tantalum which have good adhesion to the substrate and the surface layer. There is no description about mixed oxides. In addition, the surface layer needs to have a certain thickness or more to increase resistance to electrolytic pickling solution, but manganese oxide containing a non-stoichiometric compound is formed by thermal decomposition of a manganese compound solution. Must be laminated while firing a large number of times, which requires processing time.

The substrate of the electrode used in the present invention is titanium or a titanium alloy, and examples of the titanium alloy include titanium-tantalum, titanium-niobium and titanium-palladium alloys. The electrode may have various shapes such as a plate shape, a rod shape, an expanded shape, and a punching shape.

The substrate surface is subjected to grit blasting, shot blasting, or sand blasting. Alumina, silicon carbide, sand or the like is used as the blast material, and the particle diameter thereof is preferably about 200 to 1000 μm.

The intermediate layer is composed of a mixture of iridium oxide and tantalum oxide, with iridium oxide in the range of 50 to 85 mol% and tantalum oxide in the range of 15 to 50 mol%. If the amount of iridium oxide is less than 50 mol%, the catalytic ability of oxygen generation is poor and the durability of the intermediate layer itself is poor. When it exceeds 85 mol%, the adhesion of the coating film is poor, and the adhesion of manganese dioxide when manganese dioxide is electrodeposited on the surface is poor.

The intermediate layer is formed by adding a metal salt such as iridium chloride, iridium chloride or tantalum chloride to ethyl alcohol,
It is formed by dissolving it in a solvent such as butyl alcohol or propyl alcohol to prepare a mixed solution having a predetermined composition and subjecting it to thermal decomposition treatment. 1 to evaporate the solvent after coating
It is dried at 00 to 150 ° C. for about 10 to 20 minutes, and then pyrolyzed at 400 to 550 ° C. for 10 to 30 minutes in an electric furnace in an air or oxygen atmosphere. If the heat treatment temperature is lower than the above range, the thermal decomposition is insufficient, and if it is higher than the above range, the titanium substrate is oxidized and damaged.

If the amount of the intermediate layer coated on the surface of the substrate is less than 20 g / m ^{2 in} terms of metal iridium, the permeation of oxygen cannot be sufficiently suppressed. If it exceeds 100 g / m ² , the adhesion strength between the intermediate layer and the titanium substrate decreases, and the amount of expensive iridium used increases, which is not preferable. A suitable thickness is about 4 to 10 μm.

The electrodeposition of manganese dioxide forming the surface layer is
0.1-1.0 mol / LH₂SO _Four-0.5 to 1.5
mol / LMnSO_FourIn solution, temperature 30-90 ℃, current
Density 0.1-1.0 A / dm²It is good to electrodeposit on. Electric
Flow density is 1.0 A / dm²Larger and electrodeposited dioxide man
The gun becomes brittle and a dense film cannot be obtained. 0.1 A /
dm²If it is less than 1, the deposition rate will be slow and the deposition will take a long time.
It is not economical because it does. This surface layer is manganese dioxide
As 20 g / m²If it is above, both the electrode catalytic activity and the life are
Will be good. A suitable thickness is 5 to 15 μm.
It

In order to carry out electrolytic pickling of a stainless steel sheet according to the present invention, a current density of 30 A / dm ² or less is suitable, and under this condition, the dissolved amount of manganese dioxide can be kept small. When manganese ions are dissolved in the electrolytic solution, the electrodeposition reaction of manganese dioxide on the anode also proceeds at the same time, and the apparent dissolved amount of manganese dioxide can be further reduced, so that the anode has a longer life. be able to. Such manganese ions may be added, but when a trace amount of manganese is contained as an impurity in the stainless steel plate (for example, SUS304, SUS3
16 etc.), a part of the steel sheet surface is dissolved in the pickling solution, and by utilizing this, the electrolytic reaction can be advantageously promoted.

[0014]

The tantalum oxide in the intermediate layer of the electrode used in the present invention forms a mixture with iridium oxide to enhance the adhesion between the substrate and the surface layer. Further, the electrodeposited manganese dioxide forming the surface layer is denser in quality than the manganese dioxide produced by the chemical method, and there is an advantage that a considerable thickness can be electrodeposited in one step. In particular, electrolytic pickling of stainless steel sheets has a lower current density (30 A /
dm ² or less), the durability as a surface layer is sufficient. Further, the intermediate layer itself also has a catalytic ability to generate oxygen, and it is convenient because even if the manganese dioxide in the surface layer is cracked or dropped, the intermediate layer acts as an electrode catalyst.

The step of electrolytic pickling of the stainless steel sheet is carried out while continuously flowing the stainless steel sheet in the lengthwise direction in an electrolytic bath. At that time, the stainless steel sheet becomes a cathode at a position where a metal anode is provided as a counter electrode, and others. The position becomes an anode, and such pole conversion is alternately performed. Manganese contained in the stainless steel plate is eluted into the electrolytic bath when the stainless steel plate becomes the anode, and is deposited as manganese dioxide on the surface layer of the metal anode that is the counter electrode when the stainless steel plate becomes the cathode, that is, the anode according to the present invention. It seems to do.

[0016]

The present invention will be described in detail below with reference to examples and comparative examples. The composition% is a unit by weight unless otherwise specified.

Example 1, Comparative Examples 1 to 3 Commercially available titanium plates (1 × 10 × 0.1 cm) were removed with acetone.
After greasing, using alumina grit (# 30), pressure 4
kg / cm²It was blasted in. The surface below
A solution of the composition was applied. Tantalum pentachloride 0.32 g Iridium chloride 1.00 g Hydrochloric acid 0.5 mL Butyl alcohol 10 mL After application, dry at 120 ° C. for 20 minutes, then at 450 ° C.
By heat treatment in an electric furnace for 20 minutes, Ta₂O_Five
(30 mol%)-IrO₂(70 mol%) mixed oxide
A coating consisting of Repeat this operation to iridium
25g / m in conversion ²The containing intermediate layer was obtained.

Next, the above plate was placed at 0.5 mol / LH ₂ SO ₄
It was placed in a +1 mol / LMnSO ₄ solution, and this was used as an anode, and a zirconium plate of the same size was used as a cathode for electrolysis. The electrolysis conditions are a temperature of 55 ° C. and a current density of 0.2 A / dm.
^2. Electrolysis was carried out for 90 minutes at a distance between the electrodes of 25 mm, and 60 g / m ² of MnO ₂ was electrodeposited on the intermediate layer.

This electrode was applied to a 10% Na ₂ SO ₄ solution (pH
3.0) In a solution, a current density of 30 A / dm ² was used as an anode, and a SUS304 stainless steel plate of the same size was used as a cathode, and the time until MnO ₂ was completely dissolved was measured and found to be 6300 hours. there were. When the time until the electrolysis voltage increased by 5 V was measured as the life of the electrode, it was 8500 hours. For comparison, the mixed oxide of the intermediate layer was converted into iridium in an amount of 5 g / m ² or 10 g / m ² .
The electrodes produced in the same manner except that they were coated with m ² and 15 g / m ² had a life of 1400 hours, 2200 hours, and 28 hours, respectively.
It was 00 hours, and MnO ₂ remained on the surface of the electrode thereafter.

Example 2, Comparative Examples 4 and 5 The electrodes prepared in the same manner as in Example 1 were subjected to 15% HNO at 50 ° C.
_{Using 3} as an anode at a current density of 15 A / dm ² in a solution and using SUS304 stainless steel plate as a cathode, the time until the MnO ₂ was completely dissolved was measured and found to be 7550 hours. When the time until the electrolysis voltage increased by 5 V was measured as the life of the electrode, 110
It was 50 hours.

On the other hand, for comparison, only iridium oxide in the intermediate layer was converted into metal iridium at 25 g / m ² and 5 respectively.
When the same test as in Example 2 was conducted using the electrodes prepared in the same manner as above except that the electrodes were coated with 0 g / m ² , the electrode life was 1200 hours and 1800 hours, respectively.
It can be seen that the intermediate layer coating has weak mechanical strength and a short life.

Example 3 An example was applied to the discharge surface of a titanium plate (25 × 50 × 0.5 cm).
Ta in the same way as 1 ₂O_Five(20 mol%)-IrO₂
The mixed oxide layer of (80 mol%) is 50 in terms of iridium.
g / m²Of MnO on top of this₂80 g / m²
It was electrodeposited. By combining four of these electrodes, an electrode made of titanium
One electrode was prepared by bolting to the electrode substrate. This is S
US304 stainless steel plate electrolytic pickling line as anode
Used. At the position where the stainless steel plate is the anode,
SUS304 stainless steel was used as the cathode. electrolytic
Liquid is 10% Na at 50 ℃₂SO_Four(PH 3.0)
The average current density during the test was 15 A / dm²Met.
This electrode can be used for 2 years and is industrially usable.
It was.

[0023]

The electrode used in the present invention has an intermediate layer composed of a mixed oxide of iridium and tantalum, which has excellent adhesion to a substrate, and a surface layer composed of dense electrodeposited manganese dioxide. Since the passivation of the titanium substrate is prevented and both layers have the electrocatalytic activity, the life of the stainless steel plate as the electrolytic pickling anode can be remarkably extended. When manganese is contained in the stainless steel sheet, a part of it is eluted as manganese ion in the electrolytic solution,
Since this is electrodeposited as manganese dioxide on the anode,
The apparent wear of the surface layer is reduced, and the life is further extended.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor, Hisao Kojima, 3rd light, Oshima, Kashima-machi, Kashima-gun, Ibaraki Kashima Plant, Sumitomo Metal Industries, Ltd. (72) Kenji Kanai, 3rd light, Oshima, Kashima-machi, Kashima-gun, Ibaraki Prefecture Sumitomo Metal Industries Kashima Factory

Claims (5)

[Claims] 1. When electrolytically pickling a stainless steel sheet in a nitric acid aqueous solution or a neutral sodium sulfate aqueous solution, 50 to 85 mol% of iridium oxide and 15 to 50 mol% of tantalum oxide are formed on a conductive metal substrate made of titanium or its alloy. Mol%
A stainless steel sheet, characterized in that an electrode provided with an intermediate layer made of a mixed oxide of and having a weight of 20 g / m ² or more in terms of metal iridium and a surface layer made of electrodeposited manganese dioxide is used as an anode. Electrolytic pickling method. 2. The method of electrolytic pickling of a stainless steel sheet according to claim 1, wherein the anode current density is 30 A / dm ² or less. 3. The electrolytic pickling method for a stainless steel sheet according to claim 1, wherein an electrolytic pickling solution containing manganese ions is used. 4. A conductive metal substrate made of titanium or an alloy thereof, comprising a mixed oxide of 50 to 85 mol% of iridium oxide and 15 to 50 mol% of tantalum oxide and having a weight of 20 g / m in terms of metal iridium. An electrode for electrolytic pickling of a stainless steel plate, comprising an intermediate layer of ² or more and a surface layer of electrodeposited manganese dioxide. 5. The electrode for electrolytic pickling of a stainless steel sheet according to claim 4, wherein the surface layer has a weight of 20 g / m ² or more.