JP2945136B2 - Pickling method for metal products containing at least one titanium or a chemically similar element to titanium using a pickling bath - Google Patents

Abstract

The process for pickling in an acid bath containing an oxidant is distinguished in that, to increase the action of the pickling process, at least one peroxygenated compound of titanium or at least one element of the titanium family included in the product to be pickled is formed, with the metal ionised to a higher valency, the formation of the peroxygenated compound is monitored by measuring the redox potential and the quantity of oxidising agent is limited to conserve an oxy-reduction potential above the passivation potential of the metal product.

Description

The present invention relates to a method of pickling a metal product containing at least one of titanium and / or an element chemically similar to titanium in an acid bath.

It is known in the metallurgy field that metal or alloy products that have been forged or heat treated during the manufacturing process are covered with rust skin (alamine). In order to improve the surface quality of the final product, it is necessary to remove all rust layers by pickling.

In a known pickling treatment, a pickling bath composed of nitric acid HNO ₃ and hydrofluoric acid HF (a pickling bath having a ratio of 6 to 16% of nitric acid and 1 to 5% of hydrofluoric acid per one) is used. Pickle the final product. The working temperature of the pickling bath in this case is 40 ° C to 60 ° C.

One of the most commonly used pickling baths for pickling titanium is
Based on nitric acid, which is extremely toxic
Generating a vapor of NO _2, the liquid waste contains a nitrogen compound (nitrite and nitrate) are. Although the maximum nitrate content allowed by law is relatively high, nitrites make the harmful substance nitrosamine, so their maximum content is much lower.

It is also known to pickle titanium-based metallurgical products using a bath composed of a mixture of halogen acids containing hydrochloric acid HCl and hydrofluoric acid HF as the main components.

The disadvantage of this method is that upon dissolution, the titanium is reduced to valence III to form volatile compounds.

For example, it is converted to TiCl ₃ when dissolved titanium in hydrochloric acid, the TiCl ₃ sublimes at 80 ° C. or less. This TiCl ₃ is decomposed to TiCl ₄ + TiCl ₂ before sublimation according to the following reaction equation: 2TiCl ₃ → TiCl ₄ + TiCl ₂ (I) TiCl ₄ is particularly volatile, and its vapor pressure is 42 mm / at 50 ° C.
Hg.

It is an object of the present invention to pickle a metallurgical product containing titanium or at least one chemically similar element of titanium in an acid medium by introducing an oxydant into the pickling bath which does not have the disadvantages of the above pickling process. It is an object of the present invention to provide a method for increasing the kinetics of pickling by using (1) titanium or at least one of titanium contained in the pickled product.
By forming at least one composeperoxygene of an element chemically similar to the two titaniums to make the metal a higher valent ion, and (2) measuring the redox potential (3) Limiting the amount of the oxidizing agent so that the oxidation-reduction potential is equal to or lower than the passivation potential of the metal product.

The underlying fact of this method is that the oxygenate of a metal becomes more aggressive when it becomes a higher valent ion than the metal itself and its lower valent oxide. is there. Higher valent ions mean in particular such ions as titanate, vanadate, zirconate, niobate, tantalate, uranate.

The above pickling bath is preferably a bath containing an acid selected from the group consisting of hydrofluoric acid, sulfuric acid, hydrochloric acid, phosphoric acid and formic acid. the mixture can also be used in the mineral acid such as the acid or HF-H ₂ sO _4.

In order to start the pickling reaction, an oxidizing agent having a strong oxidizing ability to form a peracid compound of at least one metal is introduced into the pickling bath.

It should be noted that titanium or an element chemically similar to titanium forms a peracid compound with the oxidizing agent. Depending on the degree of oxidation achieved, the following compounds are obtained: (Where M is Ti or a chemical analog of Ti) This compound is a particularly powerful oxidant, the persalt (pers).
el).

The oxidizing agent is preferably selected from hydrogen peroxide, urea peroxide or a gas such as ozone or oxygen.

Hydrogen peroxide is introduced directly into the pickling bath in an amount of less than 0.5% by weight. In addition, they can be introduced in the form of persalts or peracids which decompose in an acidic medium to give hydrogen peroxide. Urea peroxide can be used in amounts up to 1.2% by weight.

 The present invention will be more readily understood from the following description.

The present invention relates to a method for pickling a metal or alloy product comprising titanium or at least one chemically similar element of titanium, in particular vanadium, zirconium, niobium, tantalum and uranium, in a pickling bath.

The mechanism of the pickling reaction is almost the same for each of the above metals and their alloys. Therefore, the pickling method for titanium will be described in detail as an example.

The underlying pickling bath is preferably a bath of hydrofluoric acid with a hydrofluoric acid concentration in the range of 0.2 to 10% by weight, but is chemically similar to titanium contained in the pickling product. Other acids, such as sulfuric acid, can be used as long as they contain the acid in the form of a peracid compound.

In the example of pickling titanium, laboratory tests have shown that titanium oxide is attacked by hydrofluoric acid by the following reaction: 2Ti + 6HF → 2TiF ₃ + 3H ₂ ↑ (II) Excess HF If present, titanium trifluoride will be Ti tetrafluoride
It is converted to F _4.

In the method of the present invention, at least one metal oxide is formed into higher valent ions in order to increase the rate of the pickling reaction. In the case of pickling titanium, it forms pertitanate, a peracid compound of titanium which is particularly aggressive for titanium and its oxides.

This pertitanate can be made by reacting hydrogen fluoride on titanium fluoride, for example, by the following reaction: Ti ⁴⁺ + H ₂ O ₂ + 2H ₂ O → TiO ₄ ^2- + 6H ⁺ (III) 2TiO ₄ ^{2 -} + Ti + 16H ⁺ → 3Ti ⁴⁺ + 8H ₂ O (IV) In the reaction (IV), excess H ² disappears and H ₂ O is formed, whereby H ⁺ is contained in the crystal lattice network of the pickled metal or alloy. There is less entry and consequently less brittleness of the pickled product.

Pertitanate can also be obtained by the action of urea peroxide, which produces hydrogen peroxide by decomposition. Urea peroxide is a solid and therefore easier to transport.

In addition, pertitanate can be formed by injecting ozone into the bath. The reaction of forming pertitanate in this case is as follows: Ti ⁴⁺ + O ₃ + H ₂ O → Ti ₄ ^2- + H ₂ ⁺ (V) 2TiO ₄ ² + Ti + 16H ⁺ → 3Ti ⁴⁺ + 8H ₂ O (VI) Oxygen can be used instead of ozone.

It is known that the introduction of a persalt into an acidic medium decomposes to produce hydrogen peroxide. Examples of persalts that can be used include permanganate, persulfate, pertitanate, pervanadate, perborate and the like.

Further, a peracid compound which is decomposed into H ₂ O ₂ in an acidic medium can also be used. Examples of the peracid compound include perboric acid, titanium peroxide, peracetic acid, and persulfuric acid, which are used in other industrial fields.

The formation of TiO ₄ ^2- depends on the oxidation-reduction potential of the pickling bath (potentiel de
oxydoreduction). This oxidation-reduction potential (REDOX potential) is a potential difference between a non-corrosive electrode (for example, a platinum electrode) immersed in a pickling bath to be measured and a reference electrode (for example, an Ag / AgCl or saturated calomel electrode). is there.

This measurement characterizes the oxidizing power of the pickling bath.
The pickling bath can be readjusted to maintain the pickling bath at a predetermined oxidizing ability by introducing the compound based on the measured value. In order to pickle titanium or a titanium compound, the redox potential must be within the following range: (+150, -350) mV / Ag / AgCl In the method of the present invention, the main oxidizing agent is titanium or titanium. Pickling efficiency of titanium and its alloys, titanium and chemically similar elements and alloys using a standard bath containing preferably only a single acid Is to improve.

In one embodiment of the method of pickling titanium using the method of the present invention,
The weight loss of flat products is 40 to 80 g / m ² . The surface condition obtained is comparable to that obtained using the nitric acid / hydrogen fluoride method and there is no excessive pickling bath action. When hydrogen peroxide is used, the treated surface becomes white and has an aesthetically pleasing appearance.

An important aspect of the method of the present invention is that the oxidizing agent is made "in situ" without adding harmful or contaminants.

Since the pickling reaction is caused by titanium peroxide or a peroxide of an element chemically similar to titanium, the consumption of hydrofluoric acid is reduced.

The method of the present invention does not cause air pollution and the wastewater can be treated and recycled, so that the service life of the pickling bath can be extended.

For the formation of peracid compounds (pertitanate, perzirconate, pertantalate, perniobate, peruranate, pervanadate), it is only necessary to add H ₂ O ₂ which has no ecological problem. This H ₂ O ₂ is the preferred H ₂ for living organisms
It is decomposed into O and O _2.

Therefore, the method of the present invention can reduce the emission of harmful substances to the atmosphere and the outflow to wastewater, and further can eliminate these altogether.

The wastewater and the used pickling bath can be treated according to the regulations of industrial countries. For example, treatment with lime latex can precipitate metal hydroxides and prevent harmful anions from flowing out. On the contrary,
All of these are dissolved in water when nitrates are used. The method of the present invention is an economic method.

In the method of the present invention, since the oxidizing agent bath can be used without generating excessive hydrogen, the diffusion of hydrogen into the metallographic network of the pickled product, which tends to occur in the reducing agent bath, is reduced, and the product after pickling is reduced. Is less brittle.

Continued on the front page (72) Inventor Prost, Laurent 73400 Eugene Lou-Leon Ecofe 151 (58) Field surveyed (Int. Cl. ⁶ , DB name) C23G 1/10

Claims (12)

(57) [Claims] 1. A method of introducing a metal product or an alloy product containing at least one titanium or a chemically similar element of titanium into an acid bath containing an oxidizing agent and pickling in an acid bath, wherein a reaction rate of the pickling (1) Titanium or at least one titanium contained in the pickled product
Forming at least one kind of peracid compound of an element chemically similar to the two titanium atoms, turning the metal into an ion having a higher valence, and (2) measuring the oxidation-reduction potential to form the peracid compound. And (3) limiting the amount of the oxidizing agent so that the oxidation-reduction potential is equal to or lower than the passivation potential of the metal product. 2. The method according to claim 1, wherein the acid bath is a bath containing one acid selected from the group consisting of hydrofluoric acid, sulfuric acid, hydrochloric acid, phosphoric acid and formic acid. 3. The method according to claim 1, wherein the oxidizing agent is oxygen gas or ozone gas. 4. The method according to claim 1, wherein the oxidizing agent is hydrogen peroxide or urea peroxide. 5. The method according to claim 1, wherein the redox potential at the time of pickling titanium or a titanium compound is in the range of (+150, -350) mV / Ag / AgCl. 6. The amount of hydrogen peroxide introduced into the acid bath is 0.5
5. The method according to claim 4, which is less than or equal to% by weight. 7. The method according to claim 4, wherein the amount of urea peroxide introduced into the acid bath is not more than 1.2% by weight. 8. The method according to claim 1, wherein the oxidizing agent is a peroxide salt.
The method described in. 9. The method according to claim 8, wherein the peroxide salt is a highly oxidizable peroxide salt of titanium or at least one element chemically similar to titanium contained in the pickled product. 10. The method according to claim 1, wherein the oxidizing agent is a peracid compound. 11. The method according to claim 10, wherein the peracid compound is titanium or a peracid compound of at least one element chemically similar to titanium contained in the pickled product. 12. The method according to claim 1, wherein the element chemically similar to titanium is vanadium, zirconium, niobium, tantalum or uranium.