JPH0147560B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to the creation of a method for forming heat-resistant and corrosion-resistant coatings on titanium-based members, and includes titanium or titanium alloy materials that exhibit excellent heat and corrosion resistance in steam cooling circulation pipes of nuclear power generators and other high-temperature and corrosive environments. The purpose is to provide a method that can appropriately manufacture system members. In nuclear reactors, water, water,
It is generally known that it is necessary to circulate heavy water or other coolant between the outside of the reactor body and the outside of the reactor body, and pipe materials are used to circulate such coolant. However, the pipe material does not have favorable durability under high temperature and corrosive conditions.
That is, although stainless steel pipe materials have traditionally been used for this purpose, they are subject to significant corrosion and therefore require frequent inspection and replacement.
Moreover, the corrosion causes a coolant leakage accident. Therefore, it is possible to use titanium or a titanium alloy material. Namely, this titanium or titanium alloy member is generally recognized as a metal with excellent hardness, strength, and corrosion resistance, but the present inventors' study According to the findings, the corrosion resistance is not necessarily satisfactory. With a lid, the present inventor used a pure titanium molding material (H: 0.015% or less as an impurity,
According to the results of examining the corrosion status of O: 0.20% or less, N: 0.05% or less, Fe: 0.2% or less) by immersing them in 98% sulfuric acid at room temperature for 20 days, the corrosion loss was measured at 15%. It has been confirmed that the corrosion resistance is as high as ~25%, and it is not possible to obtain sufficient corrosion resistance in the high-temperature and corrosive environment of a nuclear reactor as described above. In view of these circumstances, the present invention proposes the formation of an oxide film on the surface of titanium or titanium alloy materials as described above. We succeeded in efficiently forming a stable state that does not change even under corrosive conditions. That is, the present invention proposes that a titanium-based member such as titanium or a titanium alloy member is used as an anode and anodized in an electrolytic solution using oxalic acid, acetamide, and boric acid or ammonium borate. In this case, a titanium electrode plate is used as the cathode in the anodizing treatment, and the area of the cathode plate is larger than the area of the anode titanium-based member to be oxidized, and electricity is applied, and high voltage and low current are used. and then anodized. Further, it is preferable that the anodized product is immersed in vegetable oil or other oil and subjected to a diffusion treatment at a temperature of 100° C. or higher. That is, the basic feature of the present invention is that oxalic acid (H ₂ C ₂ O ₄ .2H ₂ O) is used as the electrolytic solution, which is stronger than the strong acid conventionally used in this type of anodizing treatment. It also has little effect on the formed oxide film and forms a dense film. In addition, the acetamide added in this case is a weak alkaline substance that improves the conductivity of the electrolytic bath, increases processing efficiency, and improves the bond between molecules caused by the difference in purity in the titanium or titanium alloy plate. For these, boric acid (H ₃ BO ₃ ) or ammonium borate [(NH ₄ ) ₂ O ₅ B ₂ O ₅・8H ₂ O] can supplement the pH to a certain extent for the weak acid treatment baths mentioned above. Moreover, the pH of the bath is adjusted to create an electrolytic bath that generally has a pH of about 6 to 6.5. Regarding the composition relationship, it is 5 to 5 for water.
Add 8wt of oxalic acid and add 1~1 to acetamide.
4wt%, boric acid or ammonium borate 1.5~
It is preferable to adjust the amount by adding and mixing to about 4wt%, and for the above acetamide, 2% of the above amount is added.
Adjustments can be made by substituting butylene diol for up to about one-fold. However, when carrying out such anodic oxidation treatment, it is necessary to use a titanium plate as the cathode for the anode of the titanium or titanium alloy plate as described above, especially pure titanium with a purity of 99% or more that does not contain the above-mentioned impurities. Preferably, a plate is used. In other words, when using the treatment bath of the present invention in which acetamide is added to improve conductivity, as described above, the lead or anti-alloy plate used as a cathode will suffer from significant melting loss, as described above. If a pure titanium plate is used, such melting loss can be effectively avoided. It is also preferable that the plate surface of such a cathode plate is considerably larger than the surface of the anode member to be oxidized, and generally has a surface area that is twice or more, preferably three times or more, than the surface of the anode member. By using a cathode plate, it is possible to achieve an appropriate distribution of anode current density and form a dense anodic oxidation coating. The current used is around 15V, which is generally used for this type of processing.
It is more appropriate to use a high-voltage, low-current type than something like 500A, and to explain the circumstances in between, according to the results of detailed research conducted by the present inventor, the current flow for anodizing In order to promote the formation of a film, a high volt value (high voltage) is advantageous, while a low amperage value (low current) is preferred in order to make the formed film uniform. It is preferable. The current actually used by the present inventor was a 100V.30A current using a high-voltage, low-current rectifier, and a method was adopted in which the voltage was gradually lowered after the first few seconds of application.
Finally, process with a current like 20V.20~40A,
In both cases, favorable results were obtained. In general, good anodic oxidation results can be obtained using a DC power supply, but even when using an AC power supply, proper stirring and control of the bath composition concentration must be carried out to ensure uniformity of the bath composition. Specifically, the electrolytic treatment bath is stirred using electromagnetic stirring or other means, and the additives mentioned above are added so as to gradually increase the concentration of the bath composition as the oxide film formation process progresses. It is possible to obtain the same good processing results as when using . Immediately after the treatment of the present invention as described above, the material obtained is immersed in vegetable oil or other oils and subjected to a diffusion treatment at a temperature of 100° C. or higher. The wear resistance, corrosion resistance, toughness, and elasticity of the oxide film formed by such diffusion treatment can be further improved. It is generally appropriate to carry out this treatment within 24 hours after the oxide film forming treatment. The details of specific embodiments according to the present invention are as follows. Example 1 60 parts of oxalic acid and 10 parts of acetamide to 1000 parts of water
An anode made of a titanium alloy material with a surface area of 500 cm ² and a cathode made of a pure titanium material with a surface area of 2000 cm ² are placed opposite each other in a treatment bath containing 20 parts of boric acid.
Anodizing was carried out under conditions where the bath temperature was 30°C and a high voltage and low current of 100V.30A was first applied, and then the current was increased to 20V.30A for 2 to 3 seconds. The surface area of the cathode member is 4 compared to the surface area of the anode member.
The surface of the anode member to be treated was properly activated at the beginning of the application of current, and then the formation of an oxide film proceeded, and the amount of the film formed was 20%. It is about 3μ in minutes, but
In 60 minutes, the amount formed rapidly increased to around 10μ, and 180
The oxide film was formed to a thickness of 60μ or more in minutes, and the formed oxide film was dense and stable, and was uniformly formed over the entire surface of the anode plate. The obtained oxide film-forming material was then immersed in vegetable oil (eg, sesame oil, rapeseed oil), and the vegetable oil was heated to perform a diffusion treatment at 130 to 150° C. for 1 hour. That is, the results of a heat and corrosion resistance test of the material obtained by such treatment confirmed that it had extremely good properties. The test method involved placing the above-mentioned member in an oxidizing atmosphere furnace, heating it to 1000°C for about 4 hours, holding it at that temperature for 1.5 hours, then lowering the temperature to 850°C for 1.5 hours, and then releasing it. Although it was cold,
All of the samples in which the oxide film was formed to a thickness of about 10 μm or more as described above were stable, and no change was observed in the surface of the oxide film or metal layer. Separately, a corrosion test was conducted in which the material was immersed in 50% sulfuric acid water and heated to 95°C or higher for 3 hours, but as mentioned above, no oxide film of 10μ or more was formed. It was confirmed that there was no change and it had excellent heat and corrosion resistance. On the other hand, as comparative examples, pure titanium and titanium alloy plates were not subjected to the treatment of the present invention, and plates were treated to form an anodic oxide film for about 4 hours in a treatment bath containing 250 parts of sulfuric acid to 1000 parts of water. A titanium alloy plate with an anodized film of about 15μ on average and a pure titanium plate with an anodized film of about 20μ were obtained, and separately, the above pure titanium plate and titanium alloy plate were subjected to the above-mentioned process. Titanium alloy plates that were oxidized for 8 hours under the same conditions as above had a slightly porous oxide film with an average thickness of 20μ, and pure titanium plates had a similarly porous anodic oxide film of about 32μ. I got what I had. However, these comparative materials were subjected to the same high-temperature oxidation treatment at 1000°C for 1.5 hours as described above and a corrosion test at 95°C in a 25% sulfuric acid solution, and the results are summarized in the following table.

[Table] In other words, even if pure titanium exhibits relatively favorable heat and corrosion resistance, as shown in the table above, corrosion occurs to some extent, and corrosion occurs considerably in titanium alloy plates. On the other hand, in the case of the present invention, as mentioned above, there was no oxidation corrosion in any of the tests, and it was confirmed that it had excellent heat and corrosion resistance. Although the above-described embodiments of the present invention relate to titanium alloy plates, it is obvious that the present invention can be applied to pure titanium members as well.
Furthermore, it can be easily understood with reference to the test results for the above-mentioned comparative example that when the present invention is applied to this pure titanium member, it exhibits even better heat and corrosion resistance than that of the above-mentioned example. According to the present invention as described above, it is possible to accurately obtain titanium-based members that are extremely excellent in heat and corrosion resistance, and thereby to be used in high-temperature applications such as reactor coolant circulation pipes, heat exchangers, and boilers. In addition, the present invention is industrially highly effective because it can appropriately provide various members that exhibit excellent durability when used in corrosive environments.

Claims (1)

[Scope of Claims] 1. A titanium-based member, such as titanium or a titanium alloy member, which is anodized in an electrolytic solution containing oxalic acid, acetamide, boric acid, or ammonium borate, using a titanium-based member as an anode. Heat-resistant and corrosion-resistant coating formation method. 2. A method for forming a heat-resistant and corrosion-resistant coating on a titanium-based member according to claim 1, using a titanium electrode plate as a cathode. 3. The method for forming a heat-resistant and corrosion-resistant coating on a titanium-based member according to claim 1, wherein the area of the cathode plate is made larger than the area of the anode titanium-based member to be oxidized and subjected to energization. 4. A method for forming a heat-resistant and corrosion-resistant coating on a titanium-based member according to claim 1, which comprises anodizing using high voltage and low current. 5 A titanium-based member such as titanium or a titanium alloy member is used as an anode, anodized in an electrolytic solution using oxalic acid, acetamide, and boric acid or ammonium borate, and the anodized material is injected into vegetable oil or other oils. A method for forming heat-resistant and corrosion-resistant coatings on titanium-based members, which is characterized by immersing them in water and performing a diffusion treatment under temperature conditions of 100°C or higher.