JPS58161780A - Method for preventing corrosion of ti in nitric acid solution - Google Patents

Abstract

PURPOSE:To effectively prevent the corrosion of Ti due to a nitric acid soln., by adding an oxidizing agent which oxidizes Ti to quatervalent oxide to the nitric acid soln. which is in contact with the Ti. CONSTITUTION:The corrosion of Ti due to a nitric acid soln. is effectively prevented by adding an oxidizing agent which oxidizes Ti to quatervalent oxide, that is, TiO2 and forms a TiO2 coating on the Ti surface to the nitric acid soln. contacting with the Ti. A reagent supplying an oxidizing ion selected from Cr<6+>, Fe<3+>, Cu<2+>, Mn<7+>, V<5+>, Ce<4+>, Se<4+>, Bi<3+>, etc. or a reagent supplying oxygen such as peroxide, peroxy acid or oxygen is used as the oxidizing agent, and the oxidizing agent is added to the nitric acid soln. at >=0.0005wt% concn.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides the
This is related to the spirit protection method of i.

Ri has superior nitric acid resistance compared to other corrosion-resistant metal materials, such as stainless steel and nickel alloys, and is widely used as the main material in various types of equipment that handle nitric acid. However, under high-temperature conditions, there is a tendency for the nitric acid resistance to deteriorate, and the corrosion rate at high temperatures is said to be particularly low in the case of the ordinary nitric acid concentration ring 11 of about 2 to B regulation. Therefore, research has been conducted to improve nitric acid resistance, and various T
i alloys (such as T I-67a) have been proposed.

Although these alloys achieve their intended purpose,
Since both are expensive, it is difficult to expand their application to general-purpose equipment, and there is a need for a method to improve the corrosion resistance of inexpensive pure Ti from an environmental perspective.

In view of this unfortunate situation, the present invention has researched the corrosion mechanism and anti-corrosion mechanism of ri, and as a result, we have discovered that carbon dioxide is added to the nitric acid solution brought into contact with Ti.
It was discovered that the corrosion rate of 7i was significantly reduced by adding r and the like, and as a result of further investigation, the present invention was completed. In other words, the means for improving Ti corrosion resistance in the present invention means that Ti is added to T1 to 4 f/R (DI# compounded oxidation oxidizer) at a stage after Ti is assembled as a raw material or as a chemical device or equipment. The key point is that it is treated with a nitric acid solution.There are no particular restrictions on the pre-treatment of the tomb, the presence or extent of post-treatment, the use of other reagents, etc., but the results of the experiment are described below. At the same time, the characteristics and effects of the present invention will be clarified, and the advantageous conditions of the present invention will be explained.

Since Ti is originally a metal with good corrosion resistance, there have not been many reports on research into improving the corrosion resistance of Ti. Therefore, although theoretical elucidation is extremely insufficient, under such circumstances, KCr6+ in non-oxidizing solutions such as hydrochloric acid and sulfuric acid.

It is known that the corrosion resistance of Tl is improved by adding ``pe'', Cu2+, etc.The reason for this is as follows.
On the other hand, when it comes into contact with hydrochloric acid or sulfuric acid, no oxide WI is formed on the surface of 11, and the metal Ti itself is actively dissolved and the corrosion rate increases considerably.

(It is speculated that this is because T1 is divided into high-potential particles by the oxidizing agent at r6 + fathom, and an immobile O skin II (titanium oxide) is formed on the surface. However, originally
Unlike bottles or sulfuric acid solutions, there is no need to add oxidation, and a passive film is formed on the surface just by contacting the nitric acid. This is the dissolution phenomenon of Ti in fIm liquids such as sulfuric acid.
Compared to its own active dissolution, gold (can be said to be a different phenomenon.

Therefore, in order to improve the corrosion resistance of Ti in nitric acid solution, it is necessary to prevent the already formed passive film from dissolving. It was impossible to divert or divert the corrosion resistance in the 11tays solution.

Therefore, we thought that it was necessary to clarify the chemical properties of the Ti film and conducted various studies.

First, the passive skin @0 state formed when T1 is immersed in a nitrate solution is measured using photoelectron spectroscopy (EgCA method).
Therefore, the ratio of the photoelectron intensity of the 1B orbital electron in the oxygen atom KsP to the photoelectron intensity of the 2P orbital electron in the Ti atom (/Ti2.)d
There is lJ"t", and 1m of the book of Fuyuancho film is Ti2O3:c
I found out something. On the other hand, as a TI oxide, T10
．． There are Ti2O3, 7101, etc., but thermodynamically T
It is said that I O2 is the most stable.
i 203Teu Ni**flD#IKkI"I"Clk does not exist stably during the Clk period, and I thought that [J9 or Fi] may dissolve after a chemical change occurs. As a result, based on the inference that it would be desirable to replace Tig03 as a simple film, we considered that it was necessary to form a Ti0g film directly on the surface of T1 or to change the aforementioned T12o3 into TlogK chemical hair, As a result of further investigation, we added Cr' to the nitric acid solution and added T to the solution.
When I was applied, the ESC of the passive film formed
The results of analysis A revealed that the photoelectron intensity ratio (01(ke1.2p) is 2.0) was 7102. Then, the Ti test piece on which the Ti0Q film was formed was treated with the above treatment #
It has been found that corrosion progresses extremely slowly not only in liquids but also in f# liquids containing nitric acid alone. Regarding the chemical changes on the surface of 1!4 nitric acid with and without the addition of kCr', the results of separate research have revealed the following differences.

(1) When there is no Cr'+ 7i -1→Tj" +2el- Tゑm+, i3+ shi.-2T1"+8
H20--→TiJ203+6H11! lCr'+
If there is ri −1→Ti″” +2e−
Ti"+Cr'+ --BT'i"-1-Cr5+)T
:"+2H20→TiO2+4H" In other words, it was found that in the coexistence of Cr'+, ri3+ can be oxidized to TI. Next, we searched for an oxidizing agent that could oxidize Ti3+- to T14+, added it to the nitric fjI solution instead of Cr6+, and treated the Ti test piece in the same way. Show the effect. Therefore, the oxidizing agent used in the present invention is
7i can be freely selected and used as long as it can be oxidized to 4@li oxide (Ti02), and there are no particular restrictions. That is, it does not matter whether it is metal salts, oxygen acids, silane, oxygen, oxides, peracids, persalts, peroxides, etc., but particularly effective are oxidizing ions (such as Cr''',
y@3 + , Cu2 +.

Mn ' `` e v ''' + c e ' + e
s e ''', s i ''' *), or oxygen supply reagents (peroxides, peracids, oxygen acids) sieves.The amount of these acids (vinyl agents) For example, oxidizing ions and oxygen supply reagents have shown significant effects under coexistence of 0.0005 tS or more.

Next, we will show a test example of a cold-rolled industrially pure titanium plate (vacuum annealed, plate thickness: 1
m) was cut into a size of 20 x 40 sw, and the surface was polished with wet emery paper. This was placed in a flask with a capacity of 11, 760 volumes of the test solution was poured into the flask, and a reflux cooling type condenser was installed at the top of the flask. The solution was heated from the outside with a heater to maintain the boiling point for 48 hours. The interview test N1 is "CR".

F15", Cu2", Mn", V", C@", 820g
Contains an appropriate amount of each of 2 and 4. This is a nitric acid solution of AN.

After the test was completed, the test piece was taken out and the weight change was determined, and the flat corrosion rate was also determined and the relationship between the oxidizing agent addition aplL and the nitric acid concentration was plotted, and the results shown in Figures 1 to 6 were obtained. Ta. As is clear from these figures, the corrosion resistance to titanium O nitric acid solution improves in proportion to the amount of oxidizing agent added.

[Brief explanation of the drawing]

Figures 1 to 6 are graphs showing the improvement in corrosion resistance achieved by each oxidizing agent. Applicant Kobe Steel, Ltd. Power Reactor and Nuclear Fuel Development Corporation Continued from page 1 - 27-306 0 Inventor Fumio Kamikubo 8-2105 Tsuchiyama-cho, Nada-ku, Kobe City 0 Applicant Power Reactor and Nuclear Fuel Development Business 1-9-13 Akasaka, Minato-ku, Tokyo

Claims (1)

[Claims] Nitric acid f characterized in that an oxidizing agent that oxidizes Ti to a tetravalent oxide is added to a nitric acid solution that contacts fllTi.
Method for preventing corrosion of Ti in 8gl. (2. In claim 1, Cr". 3+ 7+ 5+, 4+F・, Cu2", Mn, V,
Co, Ss. A method for preventing corrosion of Ti by adding an oxidizing ion supplying reagent selected from Bi3+, etc., or an oxygen supplying reagent such as peroxide, peracid, oxygen, etc. as an oxidizing agent. 13) The method for preventing corrosion of Ti according to claim 2, which prevents corrosion by increasing the concentration of oxidizing ions or the concentration of the Fi oxygen supplying reagent to 6 parts by weight or more.