Names | |
---|---|
IUPAC name Tungsten carbide | |
Other names Tungsten(IV) carbide Tungsten tetracarbide | |
Identifiers | |
3D model (JSmol) |
|
ChemSpider | |
ECHA InfoCard | 100.031.918 |
EC Number |
|
PubChem CID |
|
RTECS number |
|
UNII | |
UN number | 3178 |
CompTox Dashboard (EPA) | |
| |
| |
Properties | |
WC | |
Molar mass | 195.85 g·mol−1 |
Appearance | Grey-black lustrous solid |
Density | 15.6 g/cm3 [1] |
Melting point | 2,785–2,830 °C (5,045–5,126 °F; 3,058–3,103 K) [2] [3] |
Boiling point | 6,000 °C (10,830 °F; 6,270 K) at 760 mmHg [3] |
Insoluble | |
Solubility | Soluble in HNO 3 , HF [2] |
1·10−5 cm3/mol [2] | |
Thermal conductivity | 110 W/(m·K) [4] |
Structure | |
Hexagonal, hP2 [5] | |
P6m2, No. 187 [5] | |
6m2 [5] | |
α = 90°, β = 90°, γ = 120° | |
Trigonal prismatic (center at C) [6] | |
Thermochemistry | |
Heat capacity (C) | 39.8 J/(mol·K) [4] |
Std molar entropy (S⦵298) | 32.1 J/mol·K |
Related compounds | |
Other anions | Tungsten boride Tungsten nitride |
Other cations | Molybdenum carbide Titanium carbide Silicon carbide |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). |
Tungsten carbide (chemical formula: WC) is a chemical compound (specifically, a carbide) containing equal parts of tungsten and carbon atoms. In its most basic form, tungsten carbide is a fine gray powder, but it can be pressed and formed into shapes through sintering for use in industrial machinery, cutting tools, chisels, abrasives, armor-piercing shells and jewelry.
Tungsten carbide is approximately twice as stiff as steel, with a Young's modulus of approximately 530–700 GPa, [4] [7] [8] [9] and is twice as dense as steel. It is comparable with corundum (α- Al
2O
3 ) in hardness and can be polished and finished only with abrasives of superior hardness such as cubic boron nitride and diamond powder, wheels and compounds.
Colloquially among workers in various industries (such as machining), tungsten carbide is often simply called carbide.
Tungsten carbide is prepared by reaction of tungsten metal and carbon at 1,400–2,000 °C. [10] Other methods include a lower temperature fluid bed process that reacts either tungsten metal or blue WO
3 with CO/CO2 mixture and H
2 between 900 and 1,200 °C. [11]
WC can also be produced by heating WO3 with graphite: directly at 900 °C or in hydrogen at 670 °C following by carburization in argon at 1,000 °C. [12] Chemical vapor deposition methods that have been investigated include: [10]
There are two well-characterized compounds of tungsten and carbon, WC and tungsten semicarbide, W
2C. Both compounds may be present in coatings and the proportions can depend on the coating method. [13]
Another meta-stable compound of tungsten and carbon can be created by heating the WC phase to high temperatures using plasma, then quenching in inert gas (plasma spheroidization). [14] This process causes macrocrystalline WC particles to spheroidize and results in the non-stoichiometric high temperature phase WC
1-x existing in a meta-stable form at room temperature. The fine microstructure of this phase provides high hardness (2800-3500 HV) combined with good toughness when compared with other tungsten carbide compounds. The meta-stable nature of this compound results in reduced high temperature stability.
At high temperatures WC decomposes to tungsten and carbon and this can occur during high-temperature thermal spray, e.g., in high velocity oxygen fuel (HVOF) and high energy plasma (HEP) methods. [15]
Oxidation of WC starts at 500–600 °C (773–873 K). [10] It is resistant to acids and is only attacked by hydrofluoric acid/nitric acid (HF/HNO
3) mixtures above room temperature. [10] It reacts with fluorine gas at room temperature and chlorine above 400 °C (673 K) and is unreactive to dry H
2 up to its melting point. [10] Finely powdered WC oxidizes readily in hydrogen peroxide aqueous solutions. [16] At high temperatures and pressures it reacts with aqueous sodium carbonate forming sodium tungstate, a procedure used for recovery of scrap cemented carbide due to its selectivity.
Tungsten carbide has a high melting point at 2,870 °C (3,140 K), a boiling point of 6,000 °C (6,270 K) when under a pressure equivalent to 1 standard atmosphere (101.325 kilopascals), [3] a thermal conductivity of 110 W·m−1·K−1, [4] and a coefficient of thermal expansion of 5.5 µm·m−1·K−1. [7]
Tungsten carbide is extremely hard, ranking about 9 to 9.5 on the Mohs scale, and with a Vickers number of around 2600. [8] It has a Young's modulus of approximately 530–700 GPa, [4] [7] [8] [9] a bulk modulus of 379-381 GPa, [17] and a shear modulus of 274 GPa. [18] It has an ultimate tensile strength of 344 MPa, [9] an ultimate compression strength of about 2.7 GPa and a Poisson's ratio of 0.31. [18]
The speed of a longitudinal wave (the speed of sound) through a thin rod of tungsten carbide is 6220 m/s. [19]
Tungsten carbide's low electrical resistivity of about 0.2 µΩ·m is comparable with that of some metals (e.g. vanadium 0.2 µΩ·m). [10] [20]
WC is readily wetted by both molten nickel and cobalt. [21] Investigation of the phase diagram of the W-C-Co system shows that WC and Co form a pseudo binary eutectic. The phase diagram also shows that there are so-called η-carbides with composition (W,Co)
6C that can be formed and the brittleness of these phases makes control of the carbon content in WC-Co cemented carbides important. [21] In the presence of a molten phase such as cobalt, abnormal grain growth is known to occur in the sintering of tungsten carbide, with this having significant effects on the performance of the product material.
There are two forms of WC, a hexagonal form, α-WC (hP2, space group P6m2, No. 187), [5] [6] and a cubic high-temperature form, β-WC, which has the rock salt structure. [22] The hexagonal form can be visualized as made up of a simple hexagonal lattice of metal atoms of layers lying directly over one another (i.e. not close packed), with carbon atoms filling half the interstices giving both tungsten and carbon a regular trigonal prismatic, 6 coordination. [6] From the unit cell dimensions [23] the following bond lengths can be determined: the distance between the tungsten atoms in a hexagonally packed layer is 291 pm, the shortest distance between tungsten atoms in adjoining layers is 284 pm, and the tungsten carbon bond length is 220 pm. The tungsten-carbon bond length is therefore comparable to the single bond in W(CH
3)
6 (218 pm) in which there is strongly distorted trigonal prismatic coordination of tungsten. [24]
Molecular WC has been investigated and this gas phase species has a bond length of 171 pm for 184
W12
C. [25]
Sintered tungsten carbide–cobalt cutting tools are very abrasion resistant and can also withstand higher temperatures than standard high-speed steel (HSS) tools. Carbide cutting surfaces are often used for machining tough materials such as carbon steel or stainless steel, and in applications where steel tools would wear quickly, such as high-quantity and high-precision production. Because carbide tools maintain a sharp cutting edge better than steel tools, they generally produce a better finish on parts, and their temperature resistance allows faster machining. The material is usually called cemented carbide, solid carbide, hardmetal or tungsten-carbide cobalt. It is a metal matrix composite, where tungsten carbide particles are the aggregate, and metallic cobalt serves as the matrix. [26] [27] It has been found wear and oxidation properties of cemented carbide can be improved by replacing cobalt with iron aluminide. [28] [29] [30] Tungsten carbide cutting tools can be further enhanced with coatings such as titanium aluminium nitride or titanium chromium nitride to increase their thermal stability, and prolong tool life.
Tungsten carbide, in its monolithic sintered form, or much more often in cemented tungsten carbide cobalt composite (see above), is often used in armor-piercing ammunition, especially where depleted uranium is not available or is politically unacceptable. W
2C projectiles were first used by German Luftwaffe tank-hunter squadrons in World War II. However, owing to the limited German reserves of tungsten, W
2C material was reserved for making machine tools and small numbers of projectiles. It is an effective penetrator due to its combination of great hardness and very high density. [31] [32]
Tungsten carbide ammunition is now generally of the sabot type. SLAP, or saboted light armour penetrator, where a plastic sabot discards at the barrel muzzle, is one of the primary types of saboted small arms ammunition. Non-discarding jackets, regardless of the jacket material, are not perceived as sabots but as bullets. Both of the designs are, however, common in designated light armor-piercing small arms ammunition. Discarding sabots such as are used with M1A1 Abrams main gun are more commonplace in precision high-velocity gun ammunition. [33] [34]
Tungsten carbide is used extensively in mining in top hammer rock drill bits, downhole hammers, roller-cutters, long wall plough chisels, long wall shearer picks, raiseboring reamers, and tunnel boring machines. In these applications it is also used for wear and corrosion resistant components in inlet control for well screens, sub-assemblies, seal rings and bushings common in oil and gas drilling. [35] It is generally utilised as a button insert, mounted in a surrounding matrix of steel that forms the substance of the bit. As the tungsten carbide button is worn away the softer steel matrix containing it is also worn away, exposing yet more button insert.
Tungsten carbide is also an effective neutron reflector and as such was used during early investigations into nuclear chain reactions, particularly for weapons. A criticality accident occurred at Los Alamos National Laboratory on 21 August 1945 when Harry Daghlian accidentally dropped a tungsten carbide brick onto a plutonium sphere, known as the demon core, causing the subcritical mass to go supercritical with the reflected neutrons. He fell into a coma and died 25 days after the accident. [36] [37] [38]
Trekking poles, used by many hikers for balance and to reduce pressure on leg joints, generally use carbide tips in order to gain traction when placed on hard surfaces (like rock); carbide tips last much longer than other types of tip. [39]
While ski pole tips are generally not made of carbide, since they do not need to be especially hard even to break through layers of ice, rollerski tips usually are. Roller skiing emulates cross country skiing and is used by many skiers to train during warm weather months.
Sharpened carbide tipped spikes (known as studs) can be inserted into the drive tracks of snowmobiles. These studs enhance traction on icy surfaces. Longer v-shaped segments fit into grooved rods called wear rods under each snowmobile ski. The relatively sharp carbide edges enhance steering on harder icy surfaces. The carbide tips and segments reduce wear encountered when the snowmobile must cross roads and other abrasive surfaces. [40]
Car, motorcycle and bicycle tires with tungsten carbide studs provide better traction on ice. They are generally preferred to steel studs because of their superior resistance to wear. [41]
Tungsten carbide may be used in farriery, the shoeing of horses, to improve traction on slippery surfaces such as roads or ice. Carbide-tipped hoof nails may be used to attach the shoes; [42] in the United States, borium – chips of tungsten carbide in a matrix of softer metal such as bronze or mild steel – may be welded to small areas of the underside of the shoe before fitting. [43] : 73
Tungsten carbide is also used for making surgical instruments meant for open surgery (scissors, forceps, hemostats, blade-handles, etc.) and laparoscopic surgery (graspers, scissors/cutter, needle holder, cautery, etc.). They are much costlier than their stainless-steel counterparts and require delicate handling, but give better performance. [44]
Tungsten carbide, typically in the form of a cemented carbide (carbide particles brazed together by metal), has become a popular material in the bridal jewelry industry due to its extreme hardness and high resistance to scratching. [45] [46] Even with high-impact resistance, this extreme hardness also means that it can occasionally be shattered under certain circumstances. [47] Some consider this useful, since an impact would shatter a tungsten ring, quickly removing it, where precious metals would bend flat and require cutting. Tungsten carbide is roughly 10 times harder than 18k gold. In addition to its design and high polish, part of its attraction to consumers is its technical nature. [45] Special tools, such as locking pliers, may be required if such a ring must be removed quickly (e.g. due to medical emergency following a hand injury accompanied by swelling). [48]
Tungsten carbide is widely used to make the rotating ball in the tips of ballpoint pens that disperse ink during writing. [49]
English guitarist Martin Simpson uses a custom-made tungsten carbide guitar slide. [50] The hardness, weight, and density of the slide give it superior sustain and volume compared to standard glass, steel, ceramic, or brass slides.
Tungsten carbide has been investigated for its potential use as a catalyst and it has been found to resemble platinum in its catalysis of the production of water from hydrogen and oxygen at room temperature, the reduction of tungsten trioxide by hydrogen in the presence of water, and the isomerisation of 2,2-dimethylpropane to 2-methylbutane. [51] It has been proposed as a replacement for the iridium catalyst in hydrazine-powered satellite thrusters. [52]
A tungsten carbide coating has been utilized on brake discs in high performance automotive applications to improve performance, increase service intervals and reduce brake dust. [53]
The primary health risks associated with tungsten carbide relate to inhalation of dust, leading to silicosis-like pulmonary fibrosis. [54] Cobalt-cemented tungsten carbide is also anticipated to be a human carcinogen by the American National Toxicology Program. [55]
Tungsten is a chemical element; it has symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isolated as a metal in 1783. Its important ores include scheelite and wolframite, the latter lending the element its alternative name.
Drill bits are cutting tools used in a drill to remove material to create holes, almost always of circular cross-section. Drill bits come in many sizes and shapes and can create different kinds of holes in many different materials. In order to create holes drill bits are usually attached to a drill, which powers them to cut through the workpiece, typically by rotation. The drill will grasp the upper end of a bit called the shank in the chuck.
Tool steel is any of various carbon steels and alloy steels that are particularly well-suited to be made into tools and tooling, including cutting tools, dies, hand tools, knives, and others. Their suitability comes from their distinctive hardness, resistance to abrasion and deformation, and their ability to hold a cutting edge at elevated temperatures. As a result, tool steels are suited for use in the shaping of other materials, as for example in cutting, machining, stamping, or forging.
High-speed steel is a subset of tool steels, commonly used as cutting tool material.
A superhard material is a material with a hardness value exceeding 40 gigapascals (GPa) when measured by the Vickers hardness test. They are virtually incompressible solids with high electron density and high bond covalency. As a result of their unique properties, these materials are of great interest in many industrial areas including, but not limited to, abrasives, polishing and cutting tools, disc brakes, and wear-resistant and protective coatings.
Titanium carbide, TiC, is an extremely hard refractory ceramic material, similar to tungsten carbide. It has the appearance of black powder with the sodium chloride crystal structure.
In machining, a tool bit is a non-rotary cutting tool used in metal lathes, shapers, and planers. Such cutters are also often referred to by the set-phrase name of single-point cutting tool, as distinguished from other cutting tools such as a saw or water jet cutter. The cutting edge is ground to suit a particular machining operation and may be resharpened or reshaped as needed. The ground tool bit is held rigidly by a tool holder while it is cutting.
Diamond-like carbon (DLC) is a class of amorphous carbon material that displays some of the typical properties of diamond. DLC is usually applied as coatings to other materials that could benefit from such properties.
Titanium nitride is an extremely hard ceramic material, often used as a physical vapor deposition (PVD) coating on titanium alloys, steel, carbide, and aluminium components to improve the substrate's surface properties.
Chromium(II) carbide is a ceramic compound that exists in several chemical compositions: Cr3C2, Cr7C3, and Cr23C6. At standard conditions it exists as a gray solid. It is extremely hard and corrosion resistant. It is also a refractory compound, which means that it retains its strength at high temperatures as well. These properties make it useful as an additive to metal alloys. When chromium carbide crystals are integrated into the surface of a metal it improves the wear resistance and corrosion resistance of the metal, and maintains these properties at elevated temperatures. The hardest and most commonly used composition for this purpose is Cr3C2.
Zirconium carbide (ZrC) is an extremely hard refractory ceramic material, commercially used in tool bits for cutting tools. It is usually processed by sintering.
Silicon nitride is a chemical compound of the elements silicon and nitrogen. Si
3N
4 is the most thermodynamically stable and commercially important of the silicon nitrides, and the term ″Silicon nitride″ commonly refers to this specific composition. It is a white, high-melting-point solid that is relatively chemically inert, being attacked by dilute HF and hot H
3PO
4. It is very hard. It has a high thermal stability with strong optical nonlinearities for all-optical applications.
Alloy steel is steel that is alloyed with a variety of elements in total amounts between 1.0% and 50% by weight to improve its mechanical properties.
A cold saw is a circular saw designed to cut metal which uses a toothed blade to transfer the heat generated by cutting to the chips created by the saw blade, allowing both the blade and material being cut to remain cool. This is in contrast to an abrasive saw, which abrades the metal and generates a great deal of heat absorbed by the material being cut and saw blade.
Aluminium magnesium boride or Al3Mg3B56, colloquially known as BAM, is a chemical compound of aluminium, magnesium and boron. Whereas its nominal formula is AlMgB14, the chemical composition is closer to Al0.75Mg0.75B14. It is a ceramic alloy that is highly resistive to wear and has an extremely low coefficient of sliding friction, reaching a record value of 0.04 in unlubricated and 0.02 in lubricated AlMgB14−TiB2 composites. First reported in 1970, BAM has an orthorhombic structure with four icosahedral B12 units per unit cell. This ultrahard material has a coefficient of thermal expansion comparable to that of other widely used materials such as steel and concrete.
Cemented carbides are a class of hard materials used extensively for cutting tools, as well as in other industrial applications. It consists of fine particles of carbide cemented into a composite by a binder metal. Cemented carbides commonly use tungsten carbide (WC), titanium carbide (TiC), or tantalum carbide (TaC) as the aggregate. Mentions of "carbide" or "tungsten carbide" in industrial contexts usually refer to these cemented composites.
Precision glass moulding is a replicative process that allows the production of high precision optical components from glass without grinding and polishing. The process is also known as ultra-precision glass pressing. It is used to manufacture precision glass lenses for consumer products such as digital cameras, and high-end products like medical systems. The main advantage over mechanical lens production is that complex lens geometries such as aspheres can be produced cost-efficiently.
Cutting tool materials are materials that are used to make cutting tools which are used in machining but not other cutting tools like knives or punches.
Iron aluminides are intermetallic compounds of iron and aluminium - they typically contain ~18% Al or more.
{{cite book}}
: CS1 maint: multiple names: authors list (link){{cite web}}
: CS1 maint: unfit URL (link)