Corrosion resistance of titanium in organic matter
In dilute hydrochloric acid, sulfuric acid and phosphoric acid, titanium dissolves much more slowly than iron. With increasing concentration, especially at elevated temperatures, the rate of titanium dissolution was significantly accelerated, with titanium dissolving rapidly in mixtures of hydrofluoric and nitric acids.
Nitric acid is a kind of oxidizing acid. The surface of titanium in nitric acid can maintain a dense oxide film. With the increase of nitric acid concentration, the surface film is slightly yellow, light yellow, yellowish yellow, brown yellow to blue Various interference colors. The integrity of the oxide film is necessary to maintain the corrosion resistance of titanium. Therefore, titanium in nitric acid has very good corrosion resistance, corrosion rate of titanium with the nitric acid solution temperature increases, the temperature at 190 ~ 230. C, the concentration of 20% to 70%, the corrosion rate up to nearly 10mm / a.
However, adding a small amount of nitric acid solution containing silicon compounds can inhibit the high temperature nitric acid corrosion of titanium. For example, the corrosion rate can be reduced to almost zero when polysiloxane oil is added to 40% high temperature nitric acid solution. Information is also available at 500. Below C, titanium is highly corrosion resistant in 40% to 80% nitric acid solutions and vapors. In contrast, the addition of phosphide to nitric acid leads to accelerated corrosion of titanium, which can be used to prepare its pickling solution using this property of titanium. In fuming nitric acid, when it contains more than 2% of carbon dioxide, it causes volatilization due to a strong exothermic reaction due to insufficient water content. The possibility of volatilization between titanium and nitric acid is related to the content of nitric oxide and water in nitric acid.
However, titanium does not volatilize in nitric acid at a concentration of 80% or less, and a test in 170q2, (20% -80%) HN0 has confirmed this conclusion. Titanium in more than 80% of the high temperature nitric acid application possibilities, from the safety considerations, still need further study at temperatures below 500 ℃, titanium nitrate in the molten mixture (50% KN03 + 50% NaN02 and 40% NaN03 + 7% KN03 + 53% NaN02) does not tend to burn in the reaction.
Sulfuric acid is a strong reductive acid. Titanium has some corrosion resistance to sulfuric acid solution with low concentration and low temperature. At 0 ℃, it can resist sulfuric acid with a concentration of 20%. With the increase of acid concentration and temperature, the corrosion rate increase. Therefore, the stability of titanium in sulfuric acid is poor, even at room temperature dissolved oxygen, titanium can only be resistant to 5% sulfuric acid corrosion at 100 ℃, titanium can only be resistant to 0.2% sulfuric acid corrosion, chlorine corrosion of titanium in sulfuric acid have Inhibition. However, at 90 ℃, sulfuric acid concentration of 50%, but lead to accelerated corrosion of titanium, and even cause a fire. The corrosion resistance of titanium in sulfuric acid can be improved by introducing air, nitrogen, or adding an oxidizing agent to the solution at high levels of heavy metal ions. The main additives that can act as a buffer are iron, copper, Ti4 +, beryllium silver, manganese dioxide, nitric acid, chlorine and organic nitric acid compounds, quinone and anthraquinone derivatives, Combined corrosion inhibitor. In general, titanium in sulfuric acid is not much practical value.
Hydrochloric acid is a reducing acid, titanium in hydrochloric acid, its stability is poor even at room temperature. The corrosion rate gradually increases with the increase of acid solution concentration and temperature. Therefore, the titanium material generally adapted to work at room temperature 3% and 100 ℃, 0.5% hydrochloric acid solution, titanium although not resistant to hydrochloric acid solution corrosion, but also by alloying, anodic passivation and adding inhibitors To improve the titanium corrosion resistance. The most effective corrosion inhibitors belonging to the class of strong oxidized inorganic compounds are nitric acid, potassium dichromate, sodium hypochlorite, chlorine gas, oxygen and high-valent heavy metal ions (mainly Fe ¨, Cu ¢ 2 +, a small amount of precious metal) Oxidation of organic compounds, even chlorine compounds, quinone and anthraquinone derivatives, heterocyclic compounds, complex type corrosion inhibitor, so in the production practice, there is still value.
Acids also belong to reducing acids. The corrosion rate of titanium in phosphoric acid is lower than that of hydrochloric acid or sulfuric acid but higher than that of nitric acid. Titanium is generally suitable for 20. C, 30% or 35 ° C, 20% aerated or not aerated phosphate. The corrosion resistance of titanium in phosphoric acid increases with the increase of acid concentration and temperature, which is similar to that in titanium hydrochloric acid.
Titanium phosphoric acid in the following corrosion reaction, namely 2Ti + 2H, P04 = 2TiP04 + 2H :.
Similar to the case of titanium in sulfuric acid and hydrochloric acid, the addition of an oxidizing agent or other corrosion inhibitor to phosphoric acid is favorable for improving the corrosion resistance of titanium in phosphoric acid. Silver, mercury are also beneficial to improve the corrosion resistance of titanium in phosphoric acid, nitric acid is also an effective oxidant.
Hydrofluoric acid and fluorosilicic acid are the strongest corrosive media, and titanium is subject to severe corrosion even in hydrofluoric acid, which is extremely dilute at room temperature. Therefore, titanium can not be used in hydrofluoric acid at all. Titanium is not only rapidly corroded in hydrofluoric acid but also strongly corroded in fluoric acidic media such as fluorosilicic acid and fluoboric acid. Corrosion of titanium and hydrofluoric acid reaction Ti + 6HF = TiF, +3 H ,. TiF, which is a porous corrosion product with no protective effect, causes rapid evolution of corrosion and titanium is more soluble in mixed acids with hydrofluoric acid and hydrochloric acid or sulfuric acid. Except for the interaction between concentrated acid and metal to titanium corrosion, F-Ti4 + complexation accelerated the dissolution of titanium, the reaction was
Ti + 6HF = TiF64 + 2H + + 2H2 In other acids, such as hydrobromic acid, perchloric acid, formic acid, acetic acid by adding a small amount of soluble fluoride titanium corrosion rate increased by several times. Acid fluoride solutions, such as NaF, KHF: can also cause severe corrosion of titanium. In hydrochloric acid has not found the ideal corrosion inhibitor.
However, the organic acid in addition to formic acid, oxalic acid and a considerable concentration of citric acid, the titanium will not be corroded. For example, in the presence of organic acids such as oxalic acid, butyric acid, lactic acid, maleic acid, succinic acid (hydroxybenzoic acid), tannic acid and tartaric acid, the corrosion resistance of titanium is strong.
Titanium corrosion resistance in alkali Titanium is stable in dilute alkaline solutions (concentrations below 20%); it acts slowly to release and generate titanates in thicker alkaline solutions, especially when heated.
Titanium has good corrosion resistance in most alkaline solutions. The corrosion rate increases with the concentration and temperature of the solution. In the presence of oxygen, ammonia or carbon dioxide in the alkaline solution, titanium accelerates the corrosion of the titanium, In alkaline solution of hydrogen, the corrosion of titanium is poor. However, sodium hydroxide solution also has strong corrosion resistance. For example, the corrosion rate of titanium in 73% sodium hydroxide solution at 130 ℃ is only 0.18mm / a. Titanium is different from other metals in that it does not cause stress corrosion cracking in sodium hydroxide solution, but long-term exposure may Hydrogen embrittlement occurs. Therefore, the use of titanium in caustic and other concentrations of alkali solution temperature should be ≤ 93.33 ℃.
In dilute hydrochloric acid, sulfuric acid and phosphoric acid, titanium dissolves much more slowly than iron. With increasing concentration, especially at elevated temperatures, the rate of titanium dissolution was significantly accelerated, with titanium dissolving rapidly in mixtures of hydrofluoric and nitric acids.
Nitric acid is a kind of oxidizing acid. The surface of titanium in nitric acid can maintain a dense oxide film. With the increase of nitric acid concentration, the surface film is slightly yellow, light yellow, yellowish yellow, brown yellow to blue Various interference colors. The integrity of the oxide film is necessary to maintain the corrosion resistance of titanium. Therefore, titanium in nitric acid has very good corrosion resistance, corrosion rate of titanium with the nitric acid solution temperature increases, the temperature at 190 ~ 230. C, the concentration of 20% to 70%, the corrosion rate up to nearly 10mm / a.
However, adding a small amount of nitric acid solution containing silicon compounds can inhibit the high temperature nitric acid corrosion of titanium. For example, the corrosion rate can be reduced to almost zero when polysiloxane oil is added to 40% high temperature nitric acid solution. Information is also available at 500. Below C, titanium is highly corrosion resistant in 40% to 80% nitric acid solutions and vapors. In contrast, the addition of phosphide to nitric acid leads to accelerated corrosion of titanium, which can be used to prepare its pickling solution using this property of titanium. In fuming nitric acid, when it contains more than 2% of carbon dioxide, it causes volatilization due to a strong exothermic reaction due to insufficient water content. The possibility of volatilization between titanium and nitric acid is related to the content of nitric oxide and water in nitric acid.
However, titanium does not volatilize in nitric acid at a concentration of 80% or less, and a test in 170q2, (20% -80%) HN0 has confirmed this conclusion. Titanium in more than 80% of the high temperature nitric acid application possibilities, from the safety considerations, still need further study at temperatures below 500 ℃, titanium nitrate in the molten mixture (50% KN03 + 50% NaN02 and 40% NaN03 + 7% KN03 + 53% NaN02) does not tend to burn in the reaction.
Sulfuric acid is a strong reductive acid. Titanium has some corrosion resistance to sulfuric acid solution with low concentration and low temperature. At 0 ℃, it can resist sulfuric acid with a concentration of 20%. With the increase of acid concentration and temperature, the corrosion rate increase. Therefore, the stability of titanium in sulfuric acid is poor, even at room temperature dissolved oxygen, titanium can only be resistant to 5% sulfuric acid corrosion at 100 ℃, titanium can only be resistant to 0.2% sulfuric acid corrosion, chlorine corrosion of titanium in sulfuric acid have Inhibition. However, at 90 ℃, sulfuric acid concentration of 50%, but lead to accelerated corrosion of titanium, and even cause a fire. The corrosion resistance of titanium in sulfuric acid can be improved by introducing air, nitrogen, or adding an oxidizing agent to the solution at high levels of heavy metal ions. The main additives that can act as a buffer are iron, copper, Ti4 +, beryllium silver, manganese dioxide, nitric acid, chlorine and organic nitric acid compounds, quinone and anthraquinone derivatives, Combined corrosion inhibitor. In general, titanium in sulfuric acid is not much practical value.
Hydrochloric acid is a reducing acid, titanium in hydrochloric acid, its stability is poor even at room temperature. The corrosion rate gradually increases with the increase of acid solution concentration and temperature. Therefore, the titanium material generally adapted to work at room temperature 3% and 100 ℃, 0.5% hydrochloric acid solution, titanium although not resistant to hydrochloric acid solution corrosion, but also by alloying, anodic passivation and adding inhibitors To improve the titanium corrosion resistance. The most effective corrosion inhibitors belonging to the class of strong oxidized inorganic compounds are nitric acid, potassium dichromate, sodium hypochlorite, chlorine gas, oxygen and high-valent heavy metal ions (mainly Fe ¨, Cu ¢ 2 +, a small amount of precious metal) Oxidation of organic compounds, even chlorine compounds, quinone and anthraquinone derivatives, heterocyclic compounds, complex type corrosion inhibitor, so in the production practice, there is still value.
Acids also belong to reducing acids. The corrosion rate of titanium in phosphoric acid is lower than that of hydrochloric acid or sulfuric acid but higher than that of nitric acid. Titanium is generally suitable for 20. C, 30% or 35 ° C, 20% aerated or not aerated phosphate. The corrosion resistance of titanium in phosphoric acid increases with the increase of acid concentration and temperature, which is similar to that in titanium hydrochloric acid.
Titanium phosphoric acid in the following corrosion reaction, namely 2Ti + 2H, P04 = 2TiP04 + 2H :.
Similar to the case of titanium in sulfuric acid and hydrochloric acid, the addition of an oxidizing agent or other corrosion inhibitor to phosphoric acid is favorable for improving the corrosion resistance of titanium in phosphoric acid. Silver, mercury are also beneficial to improve the corrosion resistance of titanium in phosphoric acid, nitric acid is also an effective oxidant.
Hydrofluoric acid and fluorosilicic acid are the strongest corrosive media, and titanium is subject to severe corrosion even in hydrofluoric acid, which is extremely dilute at room temperature. Therefore, titanium can not be used in hydrofluoric acid at all. Titanium is not only rapidly corroded in hydrofluoric acid but also strongly corroded in fluoric acidic media such as fluorosilicic acid and fluoboric acid. Corrosion of titanium and hydrofluoric acid reaction Ti + 6HF = TiF, +3 H ,. TiF, which is a porous corrosion product with no protective effect, causes rapid evolution of corrosion and titanium is more soluble in mixed acids with hydrofluoric acid and hydrochloric acid or sulfuric acid. Except for the interaction between concentrated acid and metal to titanium corrosion, F-Ti4 + complexation accelerated the dissolution of titanium, the reaction was
Ti + 6HF = TiF64 + 2H + + 2H2 In other acids, such as hydrobromic acid, perchloric acid, formic acid, acetic acid by adding a small amount of soluble fluoride titanium corrosion rate increased by several times. Acid fluoride solutions, such as NaF, KHF: can also cause severe corrosion of titanium. In hydrochloric acid has not found the ideal corrosion inhibitor.
However, the organic acid in addition to formic acid, oxalic acid and a considerable concentration of citric acid, the titanium will not be corroded. For example, in the presence of organic acids such as oxalic acid, butyric acid, lactic acid, maleic acid, succinic acid (hydroxybenzoic acid), tannic acid and tartaric acid, the corrosion resistance of titanium is strong.
Titanium corrosion resistance in alkali Titanium is stable in dilute alkaline solutions (concentrations below 20%); it acts slowly to release and generate titanates in thicker alkaline solutions, especially when heated.
Titanium has good corrosion resistance in most alkaline solutions. The corrosion rate increases with the concentration and temperature of the solution. In the presence of oxygen, ammonia or carbon dioxide in the alkaline solution, titanium accelerates the corrosion of the titanium, In alkaline solution of hydrogen, the corrosion of titanium is poor. However, sodium hydroxide solution also has strong corrosion resistance. For example, the corrosion rate of titanium in 73% sodium hydroxide solution at 130 ℃ is only 0.18mm / a. Titanium is different from other metals in that it does not cause stress corrosion cracking in sodium hydroxide solution, but long-term exposure may Hydrogen embrittlement occurs. Therefore, the use of titanium in caustic and other concentrations of alkali solution temperature should be ≤ 93.33 ℃.
It is not difficult to see from the above, titanium is the chemical industry's most corrosion-resistant, the most promising corrosion-resistant materials, in particular, is that it is completely static and dynamic sea water and marine atmosphere corrosion, and even exceeded some of the resistance Erosion materials.
