High temperature industry raw materials

Metals with a melting point higher than 1650 ℃ and certain reserves, as well as metals with a melting point higher than zirconium (1852 ℃), are generally referred to as refractory metals.

Tungsten and molybdenum are both high-temperature resistant metals with good thermal conductivity, conductivity, low coefficient of thermal expansion, high temperature strength, low vapor pressure, and wear resistance. They are important materials for electronic and power equipment manufacturing, metal material processing, glass manufacturing, high-temperature furnace structural component manufacturing, aerospace, and defense industry applications.

In addition to tungsten and molybdenum, other refractory metals include tantalum, niobium, zirconium, titanium, and hafnium. High temperature resistant metals play a significant role in industrial development

tungsten

Tungsten is the refractory metal with the highest melting point. As a refractory metal, the most important advantage of tungsten is its excellent high-temperature strength and corrosion resistance to molten alkali metals and vapors. Tungsten only exhibits oxide volatilization and liquid-phase oxides above 1000 ℃. However, it also has the disadvantage of high plastic brittle transition temperature and difficulty in plastic processing at room temperature. Refractory metals represented by tungsten have been widely used in metallurgy, chemical industry, electronics, light sources, mechanical industry, and other sectors.

molybdenum

Molybdenum has relatively stable chemical properties. Molybdenum is stable in air or water at room temperature or not too high. Molybdenum is heated in the air, and its color begins to change from white to dark gray; When the temperature rises to 520 ℃, molybdenum begins to slowly oxidize, generating yellow molybdenum trioxide (MoO3, which turns white when the temperature drops to room temperature); When the temperature rises above 600 ℃, molybdenum is quickly oxidized to MoO3. Molybdenum begins to generate MoO2 when heated to 700-800 ℃ in water vapor. It is further heated, and molybdenum dioxide is further oxidized to molybdenum trioxide. Molybdenum can self ignite in pure oxygen, producing molybdenum trioxide.

tantalum

Tantalum has excellent chemical properties and extremely high corrosion resistance. It does not react with hydrochloric acid, concentrated nitric acid, and aqua regia under both cold and hot conditions. However, tantalum can be corroded in hot concentrated sulfuric acid. At temperatures below 150 ℃, tantalum will not be corroded by concentrated sulfuric acid. Only at temperatures above this temperature will it react. In concentrated sulfuric acid at 175 ℃ for 1 year, the corroded thickness is 0.0004 millimeters. Soaking tantalum in sulfuric acid at 200 ℃ for one year only damages the surface by 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 accelerates, with a surface corrosion of 1.368 millimeters after soaking for one year. The corrosion rate in sulfuric acid (containing 15% SO ₂) is more severe than in concentrated sulfuric acid. After soaking in this solution at 130 degrees for 1 year, the surface is corroded to a thickness of 15.6 millimeters. Tantalum can also be corroded by phosphoric acid at high temperatures, but this reaction usually occurs above 150 degrees. After soaking in 85% phosphoric acid at 250 degrees for 1 year, the surface is corroded by 20 millimeters. In addition, tantalum can quickly dissolve in a mixture of hydrofluoric acid and nitric acid, and can also be dissolved in hydrofluoric acid. However, tantalum is more afraid of strong alkalis. In a 40% concentration caustic soda solution at 110 degrees, tantalum will be rapidly dissolved. In a potassium hydroxide solution of the same concentration, it will be rapidly dissolved at only 100 degrees. Except for the situations mentioned above, general inorganic salts cannot corrode tantalum below 150 degrees Celsius. Experiments have shown that tantalum does not react with alkaline solutions, chlorine gas, bromine water, dilute sulfuric acid, and many other agents at room temperature, only reacting with hydrofluoric acid and hot concentrated sulfuric acid. This situation is relatively rare in metals.

But at high temperatures, the oxide film on the surface of tantalum is destroyed, so it can react with various substances. At room temperature, tantalum can react with fluorine. At 150 ℃, tantalum is inert to chlorine, bromine, and iodine. At 250 ℃, tantalum still has corrosion resistance to dry chlorine gas. When heated to 400 ℃ in chlorine gas containing water vapor, it can still maintain brightness. At 500 ℃, it begins to corrode. At temperatures above 300 ℃, tantalum reacts with bromine, while it remains inert to iodine vapor until the temperature reaches red heat. Hydrogen chloride reacts with tantalum at 410 ℃ to produce pentachloride, while hydrogen bromide reacts with tantalum at 375 ℃. When heated to 200 ℃ or lower, S can interact with Ta, while carbon and hydrocarbons can interact with tantalum at 800-1100 ℃.

niobium

Niobium is a gray white metal with a melting point of 2468 ℃, a boiling point of 4742 ℃, and a density of 8.57 grams per cubic centimeter. Niobium is a glossy gray metal with paramagnetism, and it exhibits superconductive properties at low temperatures. At standard atmospheric pressure, its critical temperature is 9.2K, which is the highest among all elemental superconductors. Its magnetic penetration depth is also the highest among all elements. Niobium is one of the three elemental type II superconductors, with the other two being vanadium and technetium. The purity of niobium metal greatly affects its superconducting properties.

Niobium has a low capture cross-section for thermal neutrons, making it quite useful in the nuclear industry. At room temperature, niobium is stable in air and does not completely oxidize when red hot in oxygen. At high temperatures, it directly combines with sulfur, nitrogen, and carbon and can form alloys with titanium, zirconium, hafnium, and tungsten. It does not react with inorganic acids or bases and is insoluble in aqua regia, but is soluble in hydrofluoric acid. The oxidation states of niobium are -1,+2,+3,+4, and+5, with+5 valence compounds being the most stable.

Niobium metal is extremely stable in air at room temperature and does not interact with air. Although it has a higher melting point in its elemental state (2468 ° C), its density is lower than other refractory metals. Niobium can also resist various types of erosion and form a dielectric oxide layer.

The electropositivity of niobium is lower than that of the zirconium element located to its left. Its atomic size is almost the same as the tantalum atom located below it, which is caused by the lanthanide contraction effect. This makes the chemical properties of niobium very similar to those of tantalum. Although its corrosion resistance is not as high as tantalum, it is cheaper and more common, so it is often used as a substitute for tantalum in situations with lower requirements, such as as as as a coating material for chemical tanks in chemical factories.

zirconium

Zirconium, atomic number 40, atomic weight 91.224, is a silver gray metal with a shiny appearance resembling steel. It has a melting point of 1852 ° C, a boiling point of 4377 ° C, and a density of 6.49 grams per cubic centimeter. Zirconium easily absorbs hydrogen, nitrogen, and oxygen; Zirconium has a strong affinity for oxygen, and oxygen dissolved in zirconium at 1000 ° C can significantly increase its volume. The surface of zirconium is prone to forming a layer of oxide film, which has a glossy appearance similar to steel. It has corrosion resistance, but is soluble in hydrofluoric acid and aqua regia. At high temperatures, it can react with non-metallic elements and many metallic elements to form solid solutions. Zirconium has good plasticity and is easy to process into plates, wires, etc. Zirconium can absorb a large amount of gases such as oxygen, hydrogen, and nitrogen during heating, and can be used as a hydrogen storage material. Zirconium has better corrosion resistance than titanium, approaching niobium and tantalum. Zirconium and hafnium are two metals with similar chemical properties and coexisting together, and contain radioactive substances.

hafnium

Hafnium has chemical properties very similar to zirconium, with good corrosion resistance and is not easily corroded by general acidic or alkaline aqueous solutions; Easily soluble in hydrofluoric acid to form fluorinated complexes. At high temperatures, hafnium can also directly combine with gases such as oxygen and nitrogen to form oxides and nitrides.

Hafnium often has a+4 valence in compounds. The main compound is hafnium oxide HfO2. There are three different variants of hafnium oxide: hafnium oxide obtained by continuous calcination of hafnium sulfate and chloride oxide is a monoclinic variant; The hafnium oxide obtained by heating the hydroxide of hafnium at around 400 ℃ is a tetragonal variant; If calcined above 1000 ℃, cubic variants can be obtained. Another compound is hafnium tetrachloride, which is a raw material for preparing metal hafnium and can be obtained by reacting chlorine gas on a mixture of hafnium oxide and carbon. Hafnium tetrachloride comes into contact with water and immediately hydrolyzes into highly stable HfO (4H2O) 2+ions. HfO2+ions exist in many compounds of hafnium, and can crystallize needle shaped hydrated hafnium oxychloride HfOCl2 • 8H2O crystals in hydrochloric acid acidified hafnium tetrachloride solution.

titanium

Titanium has a metallic luster and ductility. The density is 4.5 grams per cubic centimeter. Melting point 1660 ± 10 ℃. Boiling point 3287 ℃. The valences are+2,+3, and+4. The ionization energy is 6.82 electron volts. The main characteristics of titanium are low density, high mechanical strength, and easy processing. The plasticity of titanium mainly depends on its purity. The purer titanium, the greater its plasticity. Has good corrosion resistance and is not affected by atmospheric and seawater. At room temperature, it will not be corroded by hydrochloric acid below 7%, sulfuric acid below 5%, nitric acid, aqua regia, or dilute alkaline solutions; Only hydrofluoric acid, concentrated hydrochloric acid, concentrated sulfuric acid, etc. can act on it.