Science, Tech, Math › Science Learn About Refractory Metals Get the Definition and Find out Which Elements the Term Refers To Share Flipboard Email Print Alchemist-hp/Wikimedia Commons/CC by Attribution-NonCommercial-NonDerivative 3.0 Science Chemistry Chemistry In Everyday Life Basics Chemical Laws Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Terence Bell University of British Columbia Carleton University Terence Bell wrote about commodities investing for The Balance, and has over 10 years experience in the rare earth and minor metal industries. our editorial process Twitter Twitter LinkedIn LinkedIn Terence Bell Updated December 10, 2018 The term 'refractory metal' is used to describe a group of metal elements that have exceptionally high melting points and are resistant to wear, corrosion, and deformation. Industrial uses of the term refractory metal most often refer to five commonly used elements: Molybdenum (Mo)Niobium (Nb)Rhenium (Re)Tantalum (Ta)Tungsten (W) However, broader definitions have also included the less commonly used metals: Chromium (Cr)Hafnium (Hf)Iridium (Ir)Osmium (Os)Rhodium (Rh)Ruthenium (Ru)Titanium (Ti)Vanadium (V)Zirconium (Zr) The Characteristics The identifying feature of refractory metals is their resistance to heat. The five industrial refractory metals all have melting points in excess of 3632°F (2000°C). The strength of refractory metals at high temperatures, in combination with their hardness, makes them ideal for cutting and drilling tools. Refractory metals are also very resistant to thermal shock, meaning that repeated heating and cooling will not easily cause expansion, stress, and cracking. The metals all have high densities (they're heavy) as well as good electrical and heat conducting properties. Another important property is their resistance to creep, the tendency of metals to slowly deform under the influence of stress. Owing to their ability to form a protective layer, the refractory metals are also resistant to corrosion, although they do readily oxidize at high temperatures. Refractory Metals & Powder Metallurgy Due to their high melting points and hardness, the refractory metals are most often processed in powder form and never fabricated by casting. Metal powders are manufactured to specific sizes and forms, then blended to create the right mixture of properties, before being compacted and sintered. Sintering involves heating the metal powder (within a mold) for a long period of time. Under heat, the powder particles begin to bond, forming a solid piece. Sintering can bond metals at temperatures lower than their melting point, a significant advantage when working with the refractory metals. Carbide Powders One of the earliest uses for many refractory metals arose in the early 20th century with the development of cemented carbides. Widia, the first commercially available tungsten carbide, was developed by Osram Company (Germany) and marketed in 1926. This led to further testing with similarly hard and wear resistant metals, ultimately leading to the development of modern sintered carbides. The products of carbide materials often benefit from mixtures of different powders. This process of blending allows for the introduction of beneficial properties from different metals, thereby, producing materials superior to what could be created by an individual metal. For example, the original Widia powder was comprised of 5-15% cobalt. Note: See more on refractory metal properties in the table at the bottom of the page Applications Refractory metal-based alloys and carbides are used in virtually all major industries, including electronics, aerospace, automotive, chemicals, mining, nuclear technology, metal processing, and prosthetics. The following list of end-uses for refractory metals was compiled by the Refractory Metals Association: Tungsten Metal Incandescent, fluorescent, and automotive lamp filamentsAnodes and targets for x-ray tubesSemiconductor supportsElectrodes for inert gas arc weldingHigh capacity cathodesElectrodes for xenon are lampsAutomotive ignition systemsRocket nozzlesElectronic tube emittersUranium processing cruciblesHeating elements and radiation shieldsAlloying elements in steels and superalloysReinforcement in metal-matrix compositesCatalysts in chemical and petrochemical processesLubricants Molybdenum Alloying additions in irons, steels, stainless steels, tool steels and nickel-base superalloysHigh-precision grinding wheel spindlesSpray metallizingDie-casting diesMissile and rocket engine componentsElectrodes and stirring rods in glass manufactureElectric furnace heating elements, boats, heat shields, and muffler linerZinc refining pumps, launders, valves, stirrers and thermocouple wellsNuclear reactor control rod productionSwitch electrodesSupports and backing for transistors & rectifiersFilaments & support wires for automobile headlightVacuum tube gettersRocket skirts, cones, and heat shieldsMissile ComponentsSuperconductorsChemical process equipmentHeat shields in high-temperature vacuum furnacesAlloying additives in ferrous alloys & superconductors Cemented Tungsten Carbide Cemented Tungsten CarbideCutting tools for metal machiningNuclear engineering equipmentMining and oil drilling toolsForming diesMetal forming rollsThread guides Tungsten Heavy Metal BushingsValve seatsBlades for cutting hard and abrasive materialsBall point pen pointsMasonry saws and drillsHeavy MetalRadiation shieldsAircraft counterweightsSelf-winding watch counterweightsAerial camera balancing mechanismsHelicopter rotor blade balance weightsGold club weight insertsDart bodiesArmament fusesVibration dampingMilitary OrdnanceShotgun pellets Tantalum Electrolytic capacitorsHeat exchangersBayonet heatersThermometer wellsVacuum tube filamentsChemical process equipmentHigh-temperature furnaces componentsCrucibles for handling molten metal and alloysCutting toolsAerospace engine componentsSurgical implantsAlloy additive in superalloys Physical Properties of Refractory Metals Type Unit Mo Ta Nb W Rh Zr Typical Commercial Purity 99.95% 99.9% 99.9% 99.95% 99.0% 99.0% Density cm/cc 10.22 16.6 8.57 19.3 21.03 6.53 lbs/in2 0.369 0.60 0.310 0.697 0.760 0.236 Melting Point Celcius 2623 3017 2477 3422 3180 1852 °F 4753.4 5463 5463 6191.6 5756 3370 Boiling Point Celcius 4612 5425 4744 5644 5627 4377 °F 8355 9797 8571 10,211 10,160.6 7911 Typical Hardness DPH (vickers) 230 200 130 310 -- 150 Thermal Conductivity (@ 20 °C) cal/cm2/cm°C/sec -- 0.13 0.126 0.397 0.17 -- Coefficient of Thermal Expansion °C x 10 -6 4.9 6.5 7.1 4.3 6.6 -- Electrical Resistivity Micro-ohm-cm 5.7 13.5 14.1 5.5 19.1 40 Electrical Conductivity %IACS 34 13.9 13.2 31 9.3 -- Tensile Strength (KSI) Ambient 120-200 35-70 30-50 100-500 200 -- 500°C 35-85 25-45 20-40 100-300 134 -- 1000°C 20-30 13-17 5-15 50-75 68 -- Minimum Elongation (1 inch gauge) Ambient 45 27 15 59 67 -- Modulus of Elasticity 500°C 41 25 13 55 55 1000°C 39 22 11.5 50 -- -- Source: http://www.edfagan.com What Is Iridium? 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