Refractory metals are a class of metals that are extraordinarily resistant to heat and wear and have extremely high melting points. Reactive metals have a strong affinity for oxygen and nitrogen at elevated temperatures and are highly resistant to corrosion at low temperatures.
There are four distinct refractory metals. They are tungsten, molybdenum, tantalum, and columbium.
- Tungsten is a steel-gray metal that with impurities is brittle and not very workable but in pure form is very ductile and easy to work with. Of all metals in pure form, tungsten has the highest melting point, lowest thermal expansion coefficient, and highest tensile strength.
- Molybdenum is a silvery white metal with a very high melting point and a low thermal expansion coefficient. They are used to fabricate evaporation crucibles, electrodes, rocket technology, furnace components, glass and zinc processing tools, and electrical contacts.
- Tantalum is a dark blue-grey, dense, ductile, very hard, brittle, and highly conductive metal. It is renowned for its corrosion resistance and has a very high boiling point (3017°C). It is mainly used in tantalum capacitors in equipment such as cell phones, DVD players, game systems, and computers. It is also used for laboratory equipment and as a substitute for platinum.
- Niobium or columbium is a rare, soft, grey, ductile metal with very similar properties to tantalum. It becomes a superconductor at cryogenic temperatures. It has a low density compared to other refractory metals and is corrosion resistant. It is used in superalloys, superconductors, steel production, and electroceramics among other areas.
Types of Reactive Metals
There are three distinct reactive metals. They are zirconium, titanium, and beryllium.
- Zirconium is a lustrous, grayish-white, soft, ductile, and malleable metal. At low purities it becomes hard and brittle and must be separated from halfnium to be used most effectively. It is highly resistant to multiple types of corrosion. Most zirconium is utilized for high temperature applications in its ore form zircon. A few specialized applications for zirconium metal also exist including use in the nuclear, space, and aeronautic industries.
- Titanium is a silver colored metal that has a low density and is strong, lustrous, and corrosion-resistant. Pure titanium has been used for orthopedic and dental implants, however it is mostly applied as an alloy with iron, aluminum, vanadium, and/or molybdenum among others in applications that require light weight, high strength-to-weight ratio, corrosion resistant, and/or nonmagnetic properties. They are used most notably in the aerospace and automotive industries as lightweight parts, the medical industry as implants, and the chemical and petroleum industries as equipment alternatives to higher cost or shorter lifespan metals.
- Beryllium is a steel-grey, strong, lightweight, and brittle metal and is one of the only low-density metals known to be toxic. Beryllium is primarily used as a hardening agent in alloys, notably beryllium copper. It also is used in structural, aerospace, and heat transport applications because of its favorable density and thermal conductivity. Because of its toxicity, it is relatively used in commercial applications.
Selecting metals and metal alloys requires an analysis of the desired dimensions and specifications. Dimensions to consider include outer diameter (OD), inner diameter (ID), overall length, and overall thickness. Other specifications of importance (based on application) include product shape, tensile strength, yield strength, melting point, conductivity, corrosion resistance, ductility, and malleability. These properties differ based on the forming method and alloy composition.
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