JPS6056096A - Anodic oxidation of titanium or titanium alloy - Google Patents

Abstract

PURPOSE:To form a white oxide film of high quality by carrying out anodic oxidation in two steps using the 1st electrolytic soln. prepd. by adjusting an aqueous ammonium borofluoride soln. to a specified pH with an alkali and the 2nd electrolytic soln. prepd. by adjusting an aqueous alkali acetate soln. to a specified pH with an acid contg. halogen ion. CONSTITUTION:Ti or a Ti alloy is anodically oxidized in the 1st electrolytic soln. prepd. by adjusting an aqueous ammonium borofluoride soln. to 6-8pH with an alkali to form a film having a color up to grayish green. The anodically oxidized metal is anodically oxidized in the 2nd electrolytic soln. prepd. by adjusting an aqueous alkali acetate soln. to 6-8pH with an acid contg. halogen ion to destory the film formed in the pretreatment stage and to form a white oxide film.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for anodizing titanium or a titanium alloy, and particularly to an anodizing method for forming a stable white oxide film.

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Anodic oxide films of titanium or titanium alloys have excellent corrosion resistance and high dielectric constant, so attempts have been made to use them in chemical equipment, aircraft materials, and electrolytic capacitors.

When titanium is anodized with an aqueous solution of sulfuric acid or phosphoric acid, over time it becomes a unit of A (approximately 5θθ) such as gold-red-purple, blue-purple, red-green, purple, blue-green, pale gray, gray-green, and gray. An interference color film of
It is extremely difficult to form such a stable Th0z rutile film.

Also, as a method of forming an anodic oxide film, a method is known in which a non-aqueous electrolyte such as ethylene glycol or alcohol or a molten salt such as sulfate or nitrate M salt is used as a T-scrap wire, but the former has low conductivity. In addition, the latter has high temperatures, so both have operational difficulties.

In order to eliminate such drawbacks, the present invention attempts to form an extremely high quality white oxide film by an anodic oxide film forming method using a two-step electrolytic method. The present inventor used a solution obtained by neutralizing an aqueous ammonium borofluoride solution with an alkali as the seventh electrolyte, and a solution obtained by neutralizing an aqueous alkaline tartrate solution with an acid containing halodane ions as a mud a electrolyte. Then, in the first electrolysis step, an insulating oxide film is formed on the titanium surface, and then in the first electrolysis step,
By once destroying the above insulation film and forming a new oxide film on it, we succeeded in forming a thick oxide film. -A7.g9!r publication)).

In order to form such a high-quality white oxide film, the present inventor conducted various studies and used the above-mentioned specific electrolyte, and adjusted the pH of the electrolyte using the specific solution and created a two-stage anode. Although we succeeded in forming a stable white nO2 rutile type film through oxidation, further research revealed that a similarly high-quality oxide film could be produced by using alkali acetate as the electrolyte instead of the alkaline tartrate electrolyte. This is what I discovered.

In the previous invention, the pu adjustment VC of the alkaline tartrate electrolyte used for the secondary electrolysis is halodane (excluding fluorine).
One of the characteristics of this invention is the use of acids containing ions, such as hydrochloric acid, hypochlorous acid, and hydrobromic acid, but in the present invention, a weakly acidic ammonium borofluoride aqueous solution is used as a caustic agent for Pl&. Neutralize with alkali to pH 6. θ～g
, the first electrolyte was adjusted to θ and the formation voltage was 90~
/, forming a gray-green film at about 20V, and then neutralizing the alkali acetate with an acid containing halogen (excluding fluorine) ions such as chlorine ions.
In electrolysis g, the film of gray-green color produced in the first electrolysis step is once destroyed, its insulation is destroyed, and a thick white oxide film is formed on the new fc in the second electrolysis step. It is.

Next, examples of the present invention will be shown.

Titanium or titanium alloys are subjected to the following preliminary treatments according to the standard procedure: (1) Surface polishing (using abrasive paper 6θθ); (2) Water washing; (3) Alcohol washing; O4) Alkaline degreasing (caustic nodizer) or sodium phosphate/θ-chi aqueous solution, 6
(0 to 70°C, 70 minutes); (5) Water washing'; (61 Chemical polishing (nitric acid/θVol, hydrofluoric acid/OVol, water g 0Vol%, 20 to 30°C, 20 to 30 seconds); (7) Washing with water; (8) Activation (10 HCt, 70
(9) Washing with water - The titanium or titanium alloy pretreated above is anodized as follows: First electrolyte: ammonium borofluoride 6θf/l, pH adjusted with KOH,
The temperature is adjusted to S to S, and electrolysis is carried out as described below using titanium or carbon as a cathode at 6θC or less.

/ 0. ,l　,2゜ 2 Left 0 Red Green 36theta purple Riza θ blue-green 39θ g ioo entry line 7//.

1 //Ota //7 /θ I/, 2θ th, 2 [solution; Potassium acetate A Of/l, HC1VCtepHt-t,
g ~7,. The titanium or titanium alloy obtained by crushing 2 and adding 4tIIL11 θ, /N hydrochloric acid A tttl to borax as a buffer solution and washing with water after the first electrolysis was treated in the same manner as in the seventh electrolysis. , follow the electrolysis below.

/ Haθ 100. 2 μ Gray edge 17g 1Jt7g Gray 3 7.2 67/ 7 7/ g 7/ 97/ 10 7/ Gray white/S l 7 25 70 White 30 7/ l10 71 50 7/ Otsu θ 7/ As above In the first electrolysis, Elypl+ is adjusted to HCl, but if this is neutralized with an organic acid such as acetic acid or a halogen-free acid such as sulfuric acid, a white skin ah may be obtained, but the reproducibility is low. was discovered.

The oxide film thus obtained has a thickness of /S-2θμ, and is sealed in accordance with a conventional method (boiling water, 5 minutes).

When the following crevice corrosion test M was performed on the oxide film produced in the above example, no crevice corrosion phenomenon was observed in the film having a thickness of about θμ as shown in the table below.

Note that the crevice corrosion test results in this example are centered on the 3-day g
A test piece with 3 holes drilled in it (, 2
×30 Chin) and both Ii! The sterol-acrylic base agent containing the crystal Bcz dispersed in the sterol-acrylic material was superimposed, and a titanium lut nut was inserted into the hole of both and the sample material was tightened and immersed in an aqueous solution of NaCA. death,
After a certain period of time, the overlapping surface 4f: opened, and the presence or absence of crevice corrosion was determined with the naked eye and with a 700x microscope.

Claims (1)

[Claims] When anodizing titanium or titanium alloy, an aqueous ammonium borofluoride solution prepared with an alkali to have a pH of 0 to 0 is prepared in the 1'11. Use the aqueous alkaline acetate solution as a filtrate and add it to pHA, θ~g, with an acid containing halogen ions.
A method for anodizing titanium or a titanium alloy, characterized by carrying out anodization by co-step electrolysis using a solution prepared at , θ as a co-electrolyte.