Can tantalum materials come into contact with alkaline media?

This post was last edited by Wang Genrong on 2017-1-7 at 13:44. Element overview: Chemical symbol Ta; a steel-gray metal that belongs to group VB in the periodic table. Its atomic number is 73, and its atomic weight is 180.9479. It has a body-centered cubic crystal structure, with the +5 oxidation state being the most common. Tantalum was discovered in 1802 by the Swedish chemist A.G. Ekeberg, and was named after the Greek mythological figure Tantalus. In 1903, German chemist W. von Bolton first prepared the malleable metal tantalum for use as a filament material. In 1940, high-capacity tantalum capacitors were introduced and widely used in military communications. During World War II, the demand for tantalum surged. After the 1950s, as the use of tantalum in capacitors, superalloys, the chemical industry, and the nuclear industry continued to expand, the demand for it increased year by year, which spurred research into tantalum extraction processes and the development of related production techniques. China established its tantalum metallurgy industry in the early 1960s. Tantalum has a relatively low hardness, which is related to its oxygen content; the Vickers hardness of ordinary pure tantalum in the annealed state is only 140 HV. Its melting point is as high as 2995°C; among elemental substances, it ranks fifth, right after carbon, tungsten, rhenium, and osmium. Tantalum is ductile and can be drawn into thin filaments to form foil. Its coefficient of thermal expansion is very small. It expands by only 0.0066 percent for every increase of one degree Celsius. In addition, it has great toughness, even better than that of copper. Chemical properties: Tantalum also possesses excellent chemical properties, with very high corrosion resistance; it does not react with hydrochloric acid, concentrated nitric acid, or aqua regia, whether under cold or hot conditions. However, tantalum can be corroded by hot concentrated sulfuric acid; below 150°C, it is not corroded by concentrated sulfuric acid, and a reaction occurs only at temperatures higher than this. In concentrated sulfuric acid at 175°C, the thickness of corrosion after one year is 0.0004 millimeters. When tantalum is immersed in sulfuric acid at 200°C for one year, the surface layer is damaged by only 0.006 millimeters. At 250 degrees, the corrosion rate increases, with an annual corrosion thickness of 0.116 millimeters; at 300 degrees, the corrosion rate is even higher, resulting in a surface corrosion depth of 1.368 millimeters after one year of exposure. The corrosion rate in fuming sulfuric acid (containing 15% SO3) is more severe than that in concentrated sulfuric acid; after being immersed in this solution at 130 degrees for 1 year, the thickness of corrosion on the surface reached 15.6 millimeters. Tantalum is also corroded by phosphoric acid at high temperatures, but this reaction generally occurs only above 150 degrees. When immersed in 85% phosphoric acid at 250 degrees for one year, the surface corrodes by 20 millimeters. Additionally, tantalum dissolves rapidly in a mixture of hydrofluoric acid and nitric acid, and it can also be dissolved in hydrofluoric acid. However, tantalum is even more sensitive to strong alkalis; in an alkaline solution at 110 degrees with a concentration of 40%, tantalum dissolves rapidly. In a potassium hydroxide solution of the same concentration, it dissolves quickly at just 100 degrees. Except for the situations mentioned above, ordinary inorganic salts generally cannot corrode tantalum at temperatures below 150 degrees. Experiments have shown that at room temperature, tantalum is inert to alkaline solutions, chlorine gas, bromine water, dilute sulfuric acid, and many other chemicals; it reacts only in the presence of hydrofluoric acid and hot concentrated sulfuric acid. Such a situation is relatively rare in metals. However, at high temperatures, the oxide layer on the surface of tantalum is destroyed, allowing it to react with various substances; at room temperature, tantalum can react with fluorine. At 150 degrees, tantalum is inert to chlorine, bromine, and iodine. At 250 degrees, it retains corrosion resistance even in dry chlorine gas; when heated to 400 degrees in chlorine gas containing water vapor, it still stays shiny. Corrosion begins at 500 degrees. Above 300 degrees, tantalum reacts with bromine, while it remains inert to iodine vapor until the temperature reaches incandescence. Hydrogen chloride reacts with tantalum at 410 degrees to produce pentachloride, while hydrogen bromide reacts with tantalum at 375 degrees. At temperatures of 200 degrees or lower, S can react with Ta, while carbon and hydrocarbons react with tantalum at temperatures between 800 and 1100 degrees. The properties of tantalum enable it to be used in a wide range of applications. In equipment for producing various inorganic acids, tantalum can be used as a substitute for stainless steel, offering a service life that is dozens of times longer than that of stainless steel. Furthermore, in industries such as chemicals, electronics, and electrical engineering, tantalum can replace the role previously played by the precious metal platinum, thereby **reducing** costs. Tantalum is used to manufacture capacitors for military equipment. The United States has an **extremely developed industry and is the world’s largest arms exporter. Half of the world’s production of tantalum is used in the manufacture of tantalum capacitors, while the Logistics Agency of the U.S. Department of Defense is the largest holder of tantalum, having once purchased one-third of the world’s tantalum powder.

First of all, thank you for your reply. What you provided is content from Baidu Baike, and it isn’t very useful in addressing my question

I can only say you’re too rich – using tantalum for waste water? Besides, tantalum isn’t resistant to alkalis!

Rich guy, let’s be friends. We’re reluctant to use tantalum for our key equipment and pipelines; are you really going to use it for wastewater treatment? A liner with PTFE and PO will do the trick.

If the pH value of the solution exceeds 8-9, it will corrode tantalum

I don’t quite understand this; I only know that it’s expensive

Use this for wastewater? ? ? ? ?