JPH07228934A - Titanium material for soda electrolysis anode - Google Patents

Abstract

PURPOSE:To obtain a titanium material for soda electrolysis anode, excellent in alkali corrosion resistance as well as in crevice corrosion resistance in a neutral chloride environment, by specifying the composition of an alloy consisting of Pd, Ru, Fe, O, and Ti. CONSTITUTION:This material is a titanium material for soda electrolysis anode having an alloy composition consisting of, by weight, 0.01-0.10% each of Pd and/or Ru, <=0.20% Fe, <=0.30% O, and the balance Ti with inevitable impurities. This titanium material can be suitably used for a soda electrolysis plant where the material is brought into contact with high temp. salt water of about 80-100 deg.C and the possibility of contamination with alkali, such as NaOH, is present.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a titanium material for an anode of a soda electrolysis plant which is in contact with hot salt water of 80 to 100 ° C. and may contain an alkali such as sodium hydroxide.

[0002]

2. Description of the Related Art Today, soda electrolysis is mostly carried out by the diaphragm method. The diaphragm method uses an anode chamber and a cathode chamber, which are partitioned by a diaphragm that is an ion exchange membrane, and continuously supplies saline to the anode chamber to release chlorine on the anode surface first and then to send it to the cathode chamber. This time, it is a method of generating hydrogen on the cathode surface and recovering sodium hydroxide accumulated in the cathode chamber separated from the anode chamber by the diaphragm. In this anode chamber
Since a 10 to 25% NaCl aqueous solution is placed at 80 to 100 ° C and a voltage is applied from an external power source so that the chlorine gas generation potential (about +1.2 to 1.4 V standard hydrogen electrode reference) is obtained during operation, The environment is a chlorine-corrosive high temperature environment that is neutral.

The surface of this anode pure titanium material is coated with an oxide of a metal such as platinum, rhodium, palladium, iridium or the like to improve the electrolysis efficiency. Titanium, which is the base material for improving the life of the anode, is used. It is necessary to improve the corrosion resistance of the material itself.

Therefore, as the anode which can withstand such a high temperature corrosive environment, pure titanium, which has been known as a material having excellent corrosion resistance against chlorine gas, chlorine ions, etc., has been used as the corrosion resistant material constituting the body. Widely used.

However, although pure titanium shows excellent corrosion resistance with respect to corrosion of exposed surfaces such as the electrode surface, it is fixed as in the case where the electrode surface is appropriately supported / fixed by the gripping means such as the electrode supporting portion. It was found that the deterioration of the corrosion resistance of pure titanium is unavoidable even in a NaCl solution if a very fine gap exists between the member and the electrode surface.

By the way, as a material having good crevice corrosion resistance in a high temperature and neutral chloride environment which is more general than conventional materials,
Titanium alloys may be used and such alloys include Ti-0.15Pd (ASTM, Grade 7), Ti-0.8 Ni-0.
3 Mo alloy (ASTM, Grade 12), Ti- (0.005-0.2%) Ru
-(0.01-2.0%) Ni alloy (see JP-A-61-127844), Ti- (0.03-0.1%) Pd alloy (JP-A-63-118034)
(See Japanese Patent Publication) is being developed. In particular, the above-mentioned JP-A-61-1
The Ti-0.05% Ru-0.5% Ni disclosed in 127844 is:
It has been reported that it exhibits good crevice corrosion resistance even in a 10-25% NaCl solution at 80-100 ° C, which is an environment for soda electrolytic anodes ("Soda and Chlorine" No. 12, 1987, pp. 21). ~ 2
3).

[0007]

Therefore, it is conceivable to use a titanium alloy as an anode material for soda electrolysis in place of pure titanium, but this time, a problem of corrosion in an alkaline environment occurred. Hereinafter, the corrosion resistance in this alkaline environment is referred to as alkali corrosion resistance.

That is, when the soda electrolyzer is operated, the alkaline component often flows from the cathode chamber to the anode chamber due to the deterioration of the ion exchange membrane at the boundary between the cathode chamber and the anode chamber, and such a positive voltage is generated. In an alkaline environment with a buildup, this time, not only pure titanium material,
There is a problem that the Ti-0.05% Ru-0.5% Ni alloy is also corroded.

Therefore, in order to improve the life of the anode electrode material during soda electrolysis, not only the conventional corrosion resistance evaluated by crevice corrosion resistance, but also alkali corrosion resistance is required at the same time. The material it had was unknown.

It is an object of the present invention to provide a titanium material for soda electrolysis which is excellent in crevice corrosion resistance in a neutral chloride environment and also excellent in alkali corrosion resistance.

[0011]

The present inventors have examined the corrosion resistance of titanium materials in a soda electrolysis environment, especially the crevice corrosion resistance, and obtained the following findings to complete the present invention.

Although crevice corrosion resistance is insufficient with pure titanium, Pd and Ni are added alone or Ni and Mo or Ni are added.
The crevice corrosion resistance of titanium was improved by adding it to titanium at the same time as Ru, and sufficient crevice corrosion resistance was obtained in a soda electrolysis environment with an appropriate amount of addition.

On the other hand, as for the alkali corrosion resistance under a positive voltage (corrosion resistance in an alkaline environment), pure Ti is better than the titanium alloy, and when Fe, Ni and Mo are added, Alkali corrosion resistance tends to decrease,
Especially when the Fe and Ni contents were increased, remarkable deterioration was observed.
It has been found that not only has little effect on the alkali corrosion resistance, but it is further improved when a small amount is added.

The commercial material Ti-0.15Pd (ASTM Grade 7) was also good in alkali corrosion resistance under a positive voltage, but if Pd was added too much, the corrosion rate increased slightly. Since it was observed, the Pd addition amount is preferably less than 0.15%, and the corrosion-resistant material added with the Pd addition amount being suppressed as compared to Grade 7 is suitable as an anode material for soda electrolysis.

Further, the material satisfying the above conditions has a small amount of expensive Pd added as compared to Grade 7, and there is an advantage that it is a lower cost material. As a result of examining addition of Ru at the same time as Pd, it was found that although the effect is lower than that of Pd, the effect similar to that of Pd can be obtained by adding Ru.

In the above-mentioned Japanese Patent Laid-Open No. 63-118034, Ti
Although-(0.03-0.1%) Pd alloys are disclosed, their use is only described for crevice corrosion resistance in neutral environments such as power plant condensers. It can be said that such alkali corrosion resistance is unexpected.

Therefore, the gist of the present invention is that, in% by weight, one or two of Pd and Ru are each: 0.01 to
A titanium material for a soda electrolytic anode, which has an alloy composition of 0.10%, Fe: 0.20% or less, oxygen: 0.30% or less, and the balance unavoidable impurities and titanium.

[0018]

The reason why the alloy composition is limited as described above in the present invention will be described. In the present specification, “%” is “% by weight” unless otherwise specified.

Pd and Ru: Pd and Ru all improve the crevice corrosion resistance and alkali corrosion resistance of titanium, but in order to improve the crevice corrosion resistance and alkali corrosion resistance, one or two of them can be used. Respectively, it is necessary to add 0.01% or more.On the other hand, addition of Pd or Ru exceeding 0.10% not only saturates the crevice corrosion resistance but also tends to increase the alkali corrosion amount. In the present invention, each of one or two of them is limited to 0.10% or less. Preferably, each is 0.03 to 0.07%.

Fe: Fe has the effect of improving the mechanical properties by the grain refinement effect of titanium, but if it exceeds 0.20%, both crevice corrosion resistance and alkali corrosion resistance deteriorate.
In the present invention, the upper limit is 0.20%. Preferably, 0.
It is less than 15%.

Oxygen: Oxygen has the effect of increasing the mechanical strength, but does not deteriorate the cold workability. 0.30%
Is the upper limit. It is preferably 0.10% or less.

Normally, titanium and titanium alloys generally contain C and N as impurities, but it is difficult to control the components and the amount (0.005 to 0.015) that is contained in a commercially available sheet material is used.
%), There is no particular problem in the present invention.

Neutral Corrosion Environment and Alkali Corrosion Environment : As described above, conventional pure titanium exhibits sufficient practical corrosion resistance as long as it is used in a neutral corrosion environment for a soda electrolytic anode. Currently, there is a strong demand for manufacturing cost reduction, and there is a demand for improvement in crevice corrosion resistance, and a titanium alloy tends to be used instead of pure titanium. However, as a result of subsequent research and development, when the anode chamber is alkalized due to the inflow of alkaline liquid due to the deterioration of the diaphragm, even titanium alloys that have shown sufficient corrosion resistance up to that point show a marked deterioration in life. The cause has not been fully clarified yet, and it is considered that this is because, for example, the passivation film is destroyed by the intermetallic compound of Ni and Ti. However, in the present invention, even if it is a titanium alloy, as described above, by using a titanium alloy having a specified component composition, it is possible to avoid the problem of deterioration in corrosion resistance, which is seen in crevice corrosion resistance and alkali corrosion resistance. This is unexpected. Next, the operation of the present invention will be described more specifically by way of examples.

[0024]

Example A material having an alloy composition shown in Table 1 was melted. In manufacturing, using a non-consumable electrode type plasma arc melting furnace, a square ingot having a thickness of 20 mm, a width of 75 mm and a length of 95 mm was melted. After that, homogenization heat treatment was performed in vacuum at 1100 ° C. for 24 hours, and hot forging, hot rolling, machining, and vacuum annealing (720 ° C. × 0.5 hr) were performed.

From the test material thus obtained, test pieces having a thickness of 2 mm × a side of 30 mm and a square of a thickness of 2 mm × diameter of 15 mm were prepared, the former for the crevice corrosion test and the latter for the alkali corrosion test, respectively. I served. In each case, the surface of the test piece was polished with emery paper # 320, degreased and washed with acetone, and then dried, and subjected to each test.

In the crevice corrosion test, a Teflon plate of the same size as the test piece is arranged in the order of test piece-Teflon plate-test piece, and one side
A pure Ti bolt was passed through the hole in the center of a 30 mm square, and a test piece with a gap formed by tightening it with a nut made of pure titanium that had been oxidized by atmospheric annealing was placed in a glass container at 90 ° C.
It was dipped in a 25% NaCl solution of No. 2 and subjected to a 720-hour corrosion test, and the corrosion in the gap was visually observed to check the presence or absence of corrosion.

The pure titanium bolts and nuts and the test piece were insulated with a Teflon bush, the tightening force was kept constant at 10 kgf-cm using a torque wrench, and the NaCl solution was used in a non-deaerated state. . Three sets of test pieces were used for each material, and the respective results were obtained.

The alkali corrosion resistance test was carried out by using a potentioset power source at 90 ° C. in a 30% NaOH aqueous solution so that the test piece was anodically polarized, set to +1.3 V (standard hydrogen electrode standard), and after holding for 200 hours. The corrosion rate of the test piece was calculated from the weight change of the test piece. The NaOH solution was tested in a non-degassed state. As conventional materials, JIS Grade 2 pure titanium commercial materials, ASTM Grade 7, 12
A commercially available material was used.

The results of these tests are summarized in Table 1.
Examples No. 1 to 10 are materials of the present invention, Nos. 11 to 12 are conventional materials, No. 13
-21 are comparative materials. No crevice corrosion resistance (○), alkali corrosion resistance 0.10 mm
If it is less than / y, it passes.

The following can be seen from the results shown in Table 1. Conventional material No. 11 is a pure titanium material and its crevice corrosion resistance is insufficient. Similarly, conventional material No. 12 ASTM Grade 7 has excellent crevice corrosion resistance, but its alkali corrosion resistance is somewhat insufficient. Material No. 13, ASTM Grade 12, has insufficient alkali corrosion resistance.

From the results of comparative materials Nos. 14 and 15, if the Pd content is 0.01% or less, the improvement in crevice corrosion resistance is insufficient,
At 0.25%, the alkali corrosion resistance is slightly lower than that of comparative material No. 18, and it can be seen that there is no merit of adding a large amount of Pd.

From the results of comparative materials Nos. 16 and 17, the crevice corrosion resistance was insufficient at 0.01% or less and the crevice corrosion resistance was saturated at 0.24% as in the case of the Pd amount. It can be seen that addition of more than 0.10% has no merit because a decrease in corrosiveness is observed.

Comparative material No. 19 shows the effect of Fe.
If the amount is too large, both crevice corrosion resistance and alkali corrosion resistance deteriorate. Comparative materials No. 20 and 21 show the effect of Ni.As with the conventional material No. 13, although Ni is effective in improving crevice corrosion resistance, it can significantly reduce alkali corrosion resistance. I understand. From now on, it will show excellent effects on both crevice corrosion resistance and alkali corrosion resistance.
The unexpected effect of the present invention is clear.

[0034]

[Table 1]

[0035]

As described above, according to the present invention, expensive Pd
By reducing the amount, it is possible to improve the alkali corrosion resistance, which is a factor that hinders the extension of the electrode life, and is a soda electrolytic anode that has excellent crevice corrosion resistance and alkali corrosion resistance by an inexpensive means. Since a titanium material can be obtained, the practical value of the present invention is great.

Claims (1)

[Claims] 1. One or two each of Pd and Ru in weight%: 0.01 to 0.10%,
Fe: 0.20% or less, Oxygen: 0.30% or less, and a titanium material for a soda electrolytic anode, which has an alloy composition of the balance unavoidable impurities and titanium.