Titanium tubes are generally quite corrosion resistant in organic compounds. Its actual corrosion resistance is related to the reducing and oxidizing properties of the organic acid solution. Of the currently known organic acids, only a few will corrode titanium. For example, hot formic acid, hot oxalic acid, concentrated trichloroacetic acid, etc. in different air; once the air is vented, the corrosion rate of titanium will decrease. Both the water content of the organic compound medium and the air help the titanium to maintain its inertness. Under high temperature and anhydrous conditions, organic compounds can liberate hydrogen, which may lead to the danger of hydrogen absorption and hydrogen embrittlement of titanium. Although the corrosion of titanium in organic compound media is not serious, full attention must be paid to the sensitivity of hydrogen embrittlement and stress corrosion.
Titanium tubes are resistant to a wide range of temperatures and concentrations of acetic acid, and have been used in 204 ° C and 67% terephthalic acid and adipic acid. It has good corrosion resistance in citric acid, tartaric acid, tannic acid, lactic acid and other organic acids.
Titanium tube has strong corrosion resistance in alkali and alkaline media. Whether it is sodium hydroxide, potassium hydroxide or ammonia, calcium hydroxide, magnesium hydroxide are very resistant to corrosion. The corrosion rate of titanium in boiling saturated calcium hydroxide, magnesium hydroxide and ammonia is almost 0. In high temperature and high concentration sodium hydroxide solution, such as 188 ℃ 50% -73% solution, the corrosion rate is possible More than 1.09mm / a. Nevertheless, the hydrogen embrittlement sensitivity of titanium in high-temperature alkaline solutions cannot be ignored. When the temperature exceeds 77 ° C and the pH of the alkaline solution is greater than 12, the possibility of hydrogen absorption and hydrogen embrittlement of titanium in the alkaline solution should be paid special attention to.
Among various metal materials, titanium tubes have good performance in wet chlorine gas, chloride solution (except high temperature and high concentration of ZnCL2, ALCL3 and CaCL2), and solutions containing chlorine compounds (such as chlorohydrochloric acid, etc.). Corrosion resistance has been successfully applied in bleach plants, electrolytic chlorine plants and wastewater treatment plants. However, crevice corrosion occurs in titanium materials in high-temperature and high-concentration chloride solutions, especially when it comes into contact with organic compound materials such as polytetrafluoroethylene.
Titanium causes severe corrosion in dry chlorine gas, and even causes fire and nature. The reaction between Ti and CL to form TiCL4 is an exothermic reaction. Only the water content in the medium is very low, and the heat released can promote the combustion of titanium, knowing that dry chlorine and titanium are depleted. If the chlorine gas contains water, the titanium tetraoxide will undergo a hydrolysis reaction to produce white titanium hydroxide. Titanium hydroxide is a stable solid compound and is not a highly volatile liquid like tetroxide (titanium has a boiling point of 136 ° C). The boundaries between "dry" and "wet" are related to factors such as ambient temperature and alloy composition. According to reports, the minimum moisture content of industrial pure titanium in the passivated chlorine gas at about 200 ° C is about 1.5%; at room temperature, the minimum water content will not catch fire as long as it is maintained at 0.3%-0.4% or more. Titanium-palladium alloys and titanium-nickel-molybdenum alloys can maintain the passivity of metals at lower water contents.
The corrosion resistance of titanium tubes to bromine and iodine is similar to that of chlorine. As long as a certain amount of water is maintained, titanium will not be corroded. However, titanium is corroded in fluorine, hydrofluoric acid or acid fluoride solution even at a very low concentration, and almost no corrosion inhibitor can be used. Therefore, titanium is not recommended for use in environments exposed to fluorine atmosphere. The acid fluoride solution rapidly corrodes titanium due to the presence of hydrofluoric acid. However, some fluorides complexed with metal ions, or extremely stable fluorides (such as fluorocarbons), generally do not corrode titanium.
Titanium pipes have excellent corrosion resistance in both river water and seawater. Especially in seawater, the corrosion performance of titanium is 100 times that of stainless steel. Titanium is the most resistant metal in all natural waters. Titanium may discolor or lose light in high temperature water and water vapor (such as 300 ° C), and even slightly increase weight, but it will not cause corrosion. Titanium is very resistant to corrosion in seawater at temperatures up to 260 ° C. Titanium tube condensers have been used in polluted seawater for more than 20 years, and only a slight discoloration has been found without signs of corrosion.
Industrial pure titanium has better resistance to crevice corrosion, pitting corrosion, and impact corrosion in seawater, and the sensitivity to stress corrosion and corrosion fatigue is not serious. In high-speed flowing seawater (for example, 36.6m / s), erosion speed is somewhat increased. When seawater contains abrasive particles such as sand, it has some impact on the erosion resistance of titanium, but it is not as severe as copper alloys and aluminum alloys. In seawater, titanium is the most ideal material for cavitation corrosion resistance. But because titanium is neither corrosive nor toxic in seawater, it is a good place for marine organisms to attach.
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Titanium tubes are resistant to a wide range of temperatures and concentrations of acetic acid, and have been used in 204 ° C and 67% terephthalic acid and adipic acid. It has good corrosion resistance in citric acid, tartaric acid, tannic acid, lactic acid and other organic acids.
Titanium tube has strong corrosion resistance in alkali and alkaline media. Whether it is sodium hydroxide, potassium hydroxide or ammonia, calcium hydroxide, magnesium hydroxide are very resistant to corrosion. The corrosion rate of titanium in boiling saturated calcium hydroxide, magnesium hydroxide and ammonia is almost 0. In high temperature and high concentration sodium hydroxide solution, such as 188 ℃ 50% -73% solution, the corrosion rate is possible More than 1.09mm / a. Nevertheless, the hydrogen embrittlement sensitivity of titanium in high-temperature alkaline solutions cannot be ignored. When the temperature exceeds 77 ° C and the pH of the alkaline solution is greater than 12, the possibility of hydrogen absorption and hydrogen embrittlement of titanium in the alkaline solution should be paid special attention to.
Among various metal materials, titanium tubes have good performance in wet chlorine gas, chloride solution (except high temperature and high concentration of ZnCL2, ALCL3 and CaCL2), and solutions containing chlorine compounds (such as chlorohydrochloric acid, etc.). Corrosion resistance has been successfully applied in bleach plants, electrolytic chlorine plants and wastewater treatment plants. However, crevice corrosion occurs in titanium materials in high-temperature and high-concentration chloride solutions, especially when it comes into contact with organic compound materials such as polytetrafluoroethylene.
Titanium causes severe corrosion in dry chlorine gas, and even causes fire and nature. The reaction between Ti and CL to form TiCL4 is an exothermic reaction. Only the water content in the medium is very low, and the heat released can promote the combustion of titanium, knowing that dry chlorine and titanium are depleted. If the chlorine gas contains water, the titanium tetraoxide will undergo a hydrolysis reaction to produce white titanium hydroxide. Titanium hydroxide is a stable solid compound and is not a highly volatile liquid like tetroxide (titanium has a boiling point of 136 ° C). The boundaries between "dry" and "wet" are related to factors such as ambient temperature and alloy composition. According to reports, the minimum moisture content of industrial pure titanium in the passivated chlorine gas at about 200 ° C is about 1.5%; at room temperature, the minimum water content will not catch fire as long as it is maintained at 0.3%-0.4% or more. Titanium-palladium alloys and titanium-nickel-molybdenum alloys can maintain the passivity of metals at lower water contents.
The corrosion resistance of titanium tubes to bromine and iodine is similar to that of chlorine. As long as a certain amount of water is maintained, titanium will not be corroded. However, titanium is corroded in fluorine, hydrofluoric acid or acid fluoride solution even at a very low concentration, and almost no corrosion inhibitor can be used. Therefore, titanium is not recommended for use in environments exposed to fluorine atmosphere. The acid fluoride solution rapidly corrodes titanium due to the presence of hydrofluoric acid. However, some fluorides complexed with metal ions, or extremely stable fluorides (such as fluorocarbons), generally do not corrode titanium.
Titanium pipes have excellent corrosion resistance in both river water and seawater. Especially in seawater, the corrosion performance of titanium is 100 times that of stainless steel. Titanium is the most resistant metal in all natural waters. Titanium may discolor or lose light in high temperature water and water vapor (such as 300 ° C), and even slightly increase weight, but it will not cause corrosion. Titanium is very resistant to corrosion in seawater at temperatures up to 260 ° C. Titanium tube condensers have been used in polluted seawater for more than 20 years, and only a slight discoloration has been found without signs of corrosion.
Industrial pure titanium has better resistance to crevice corrosion, pitting corrosion, and impact corrosion in seawater, and the sensitivity to stress corrosion and corrosion fatigue is not serious. In high-speed flowing seawater (for example, 36.6m / s), erosion speed is somewhat increased. When seawater contains abrasive particles such as sand, it has some impact on the erosion resistance of titanium, but it is not as severe as copper alloys and aluminum alloys. In seawater, titanium is the most ideal material for cavitation corrosion resistance. But because titanium is neither corrosive nor toxic in seawater, it is a good place for marine organisms to attach.
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