Tungsten carbide
From Wikipedia, the free encyclopedia
| Tungsten carbide | |
|---|---|
 | |
| General | |
| Molecular formula | WC |
| Molar mass | 195.86 g·mol−1 |
| Appearance | grey-black solid |
| CAS number | [12070-09-9] |
| Properties | |
| Density and phase | 15.8 g·cm−3, solid |
| Solubility in water | Insoluble |
| Melting point | 2870 °C, 5198 °F (3143K) |
| Boiling point | 6000°C, 10832 °F (6273K) |
| Thermal conductivity | 84.02 W·m−1·K−1 |
| Tensile strength | 0.3448 GPa |
| Mohs hardness | 9 |
| Structure | |
| Coordination geometry | ? |
| Crystal structure | Hexagonal |
| Thermodynamic data | |
| Standard enthalpy of formation ΔfH°solid | ? kJ·mol−1 |
| Standard molar entropy S°solid | ? J·K−1·mol−1 |
| Hazards | |
| EU classification | not listed |
| NFPA 704 | |
| Supplementary data page | |
| Structure and properties | n, εr, etc. |
| Thermodynamic data | Phase behaviour Solid, liquid, gas |
| Spectral data | UV, IR, NMR, MS |
| Related compounds | |
| Other anions | Tungsten boride Tungsten nitride |
| Other cations | Molybdenum carbide Titanium carbide Silicon carbide |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references | |
Tungsten carbide, WC, or W2C, is a chemical compound containing tungsten and carbon, similar to titanium carbide. Its extreme hardness makes it useful in the manufacture of cutting tools, abrasives and bearings, as a cheaper and more heat-resistant alternative to diamond. Tungsten carbide is also used as a scratch-resistant material for jewelry including watch bands and wedding rings.
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[edit] Uses in machine tools
Carbide cutting surfaces are often useful when machining through materials such as carbon steel or stainless steel, as well as in situations where other tools would wear away, such as high-quantity production runs. Sometimes, carbide will leave a better finish on the part, and allow faster machining. Carbide tools can also withstand higher temperatures than standard high speed steel tools.
Machining with carbide can be difficult, as carbide is more brittle than other tool materials, making it susceptible to chipping and breaking. To offset this, many manufacturers sell carbide inserts and matching insert holders. With this setup, the small carbide insert is held in place by a larger tool made of a less brittle material (usually steel). This gives the benefit of using carbide without the high cost of making the entire tool out of carbide. Also, the inserts can be changed without losing much accuracy, allowing the machinist to simply swap out a broken insert without re-zeroing the machine. Most modern face mills use carbide inserts, as well as some lathe tools and endmills.
To increase the life of carbide tools, they are sometimes coated. Two such coatings are TiN (titanium nitride) and TiC (titanium carbide). Most coatings generally increase a tool's hardness and or lubricity. A coating allows the cutting edge of a tool to cleanly pass through the material without having the material gall (stick) to it. The coating also helps to decrease the temperature associated with the cutting process and increase the life of the tool.
[edit] Military use
Tungsten carbide is often used in armor-piercing ammunition, especially where depleted uranium is not available or not politically acceptable. The first use of W2C projectiles occurred in Luftwaffe tank-hunter squadrons, which used 37 mm autocannon equipped Ju-87G Stuka attack planes to destroy Soviet T-34 tanks in WWII. Owing to the limited German reserves of tungsten, W2C material was reserved for making machine tools and small numbers of projectiles for the most elite combat pilots, like Hans Rudel.
Tungsten carbide ammunition can be of the sabot type (a large arrow surrounded by a discarding push cylinder) or a subcaliber ammunition, where copper or other relatively soft material is used to encase the hard penetrating core, the two parts being separated only on impact. The latter is more common in small-caliber arms, while sabots are usually reserved for artillery use.
[edit] In sports
Hard carbides, especially tungsten carbide, are used by athletes, generally on poles which impact hard surfaces. Trekking poles, used by many hikers for balance and to reduce pressure on leg joints, generally used carbide tips in order to gain traction when placed on hard surfaces (like rock); such carbide tips last much longer than other types of tips. Rocks along many popular hiking trails, such as the Appalachian Trail and Pacific Crest Trail, are scratched and pockmarked from hundreds or thousands of impacts from pole tips. [citation needed]
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. Because skiers require traction on bitumen (asphalt) carbide tips are used in the sport. [citation needed]
[edit] In fiction
In the Halo video game series, Magnetic Accelerator Cannon projectiles are coated in a hard outer layer of tungsten carbide.
In Monty Python's Flying Circus, in a sketch involving a dispute between a famous playwright and his son, a coal miner. The son mentions that they have started using some new 'tungsten carbide drills,' to which the father's response is 'Tungsten carbide drills?! What the bloody 'ell's tungsten carbide drills?!'
