Tungsten carbide

Crystal structure
__ W 4+      __ C 4−
General
Surname	Tungsten carbide
other names	Tungsten monocarbide
Ratio formula	WC
Brief description	gray, shiny metallic, very hard, odorless crystals
External identifiers / databases
CAS number 12070-12-1 EC number 235-123-0 ECHA InfoCard 100,031,918 PubChem 2724274 ChemSpider 2006424 Wikidata Q423265
properties
Molar mass	195.86 g · mol -1
Physical state	firmly
density	15.63 g cm −3 (20 ° C)
Melting point	2785 ° C
boiling point	6000 ° C
solubility	practically insoluble in water (0.1 mg l −1 at 20 ° C) soluble in nitric acid and hydrogen fluoride
safety instructions
GHS labeling of hazardous substances no GHS pictograms H and P phrases H: no H-phrases P: no P-phrases
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Mono-tungsten carbide (usually short tungsten carbide ) is a non-oxidic ceramic or an intermediate crystal phase and a carbide . Due to its hardness, tungsten carbide is the main component of many hard metals that are used as low-wear materials for tools .

As a natural formation, tungsten carbide has been known since 1986 and has been recognized as an independent mineral under the name Qusongit since 2007 .

Extraction and presentation

Tungsten carbide powder is made by direct carburization of tungsten with carbon . For this purpose, mixtures of the metal and carbon black or graphite are heated at a temperature of 1400 to 2000 ° C in a vacuum or under hydrogen.

${\displaystyle \mathrm {W+C\longrightarrow WC} }$

When heating a tungsten-carbon mixture in a carbon tube or high-frequency furnace to approx. 2800 ° C, tungsten carbide blocks are obtained.

Production typically begins with tungsten ore, tungsten scrap, scheelite , tungstic acid or ammonium paratungstate . There are several processes for the production of technical tungsten carbide powders. For example, tungstic acid powder is reduced to tungsten by hydrogen at 750 ° C. The metal particles are carburized at 1400 ° C. This method is used for fine powders with an average grain size of 1 µm.

${\displaystyle \mathrm {H_{2}WO_{4}+3\ H_{2}\longrightarrow W+4\ H_{2}O} }$

${\displaystyle \mathrm {W+C\longrightarrow WC} }$

Tungsten oxides, tungstic acid, ammonium paratungstate and scheelite can also be carburized directly:

${\displaystyle \mathrm {WO_{3}+4\ C\longrightarrow WC+3\ CO} }$

${\displaystyle \mathrm {H_{2}WO_{4}+4\ C\longrightarrow WC+3\ CO+H_{2}O} }$

${\displaystyle \mathrm {(NH_{4})_{10}W_{12}O_{41}\cdot 5\ H_{2}O+48\ C\longrightarrow 12\ WC+10\ NH_{3}+10\ H_{2}O+36\ CO} }$

${\displaystyle \mathrm {CaWO_{4}+4\ C\longrightarrow WC+CaO+3\ CO} }$

Tungsten or tungsten oxide can also be carburized by gases such as carbon monoxide or methane .

${\displaystyle \mathrm {WO_{2}+CH_{4}\longrightarrow WC+2\ H_{2}O} }$

Very fine tungsten carbide can also be obtained by reacting tungsten ore or tungsten scrap with chlorine and subsequent gas phase reduction with hydrogen and carburization:

${\displaystyle \mathrm {W+3\ Cl_{2}\longrightarrow WCl_{6}} }$

${\displaystyle \mathrm {WCl_{6}+3\ H_{2}\longrightarrow W+6\ HCl} }$

${\displaystyle \mathrm {W+C\longrightarrow WC} }$

Tungsten carbide is an interstitial solid solution . Carbon atoms are deposited between the lattice sites of the tungsten as a result of carburization . The reaction proceeds via W ₂ C to the di-tungsten carbide to form WC. Tungsten carbide is also produced by reduction of tungsten oxides with carbon. For this reason, hydrogen is used as a reducing agent in the production of tungsten .

Production and trade

Portions of this article appear since 2010 is out of date to be .
Please help to research and insert the missing information .

The following table shows the production figures for 2004 in tons per year:

region	Western Europe	Eastern Europe	United States	Japan	China	Other
production	13000	1600	5800	4500	13000	1170

Between 2007 and 2010, Germany imported the following quantities of tungsten carbide (in tons):

year	2007	2008	2009	2010
import	2997	3215	1374	2544

The consumption of tungsten for carbide production in tons:

year	China	United States	Europe	Japan	Other
2005	12500	6500	6000	4500	3000
2007	13900	4600	9800	4500	700
2010	18800	6100	6300	4900	2800

properties

Tungsten carbide is a gray, odorless crystalline solid that is practically insoluble in water.

Diwtungsten Carbide W ₂ C is very hard and has a melting temperature of 2750 ° C. Tungsten carbide WC is also very hard and melts at 2785 ° C. A eutectic mixture of the two melts at 2525 ° C.

Other features of toilet:

• Tensile strength > 3500 MPa
• Compressive strength up to 6000 MPa
• Mohs hardness = 9.5

Applications

→ Main article : Carbide

Small solid tungsten carbide drills and cutters

Tungsten carbide is the main component of many types of carbide used for cutting tools and as a material for highly stressed components such as printing blocks or forming tools. Starting in 1914, Hugo Lohmann discovered the various possibilities that resulted from the setting of tungsten carbide with metals of the iron group using powder metallurgical working methods. The tungsten carbide is characterized by its special hardness , which is almost as high as that of diamond . Hence the brand name Widia ( Wi e Dia mant ) for hard metal tools from Krupp . In 1929, Pobedit was developed in the USSR by the company of the same name. Spikes on winter tires for bicycles or automobiles are often made of hard metal. Ballpoint pens are another common use. The balls are made of hard metal in order to guarantee the least possible wear.

In addition, it can be used as a neutron reflector in nuclear weapons to reduce the critical mass .

Since the Second World War, tungsten carbide has been used as a core material in armor-piercing projectiles ( balancing projectiles ), where it displaced hardened steel, because of its hardness and twice the density of steel. From the 1960s onwards, the USA in particular used significantly softer depleted uranium for this purpose , but its use is controversial (toxicity, residual radiation). As a result, tungsten carbide continues to be widely used in armor piercing ammunition.

A ring made from tungsten carbide

For some years now, tungsten carbide has also been processed into jewelry. This is referred to by the misleading name of tungsten jewelry . Tungsten carbide has been used in watchmaking by the Swiss wristwatch manufacturer Rado since 1962 , for the first time in the case of the DiaStar model.

Machining and processing

For use as a WC hard metal , approx. 6 percent by mass of cobalt is added as a binding phase. The grain size of WC hard metals with 6 to 10% cobalt as a binder is approximately 0.5 to 1.2  micrometers . WC hard metal is processed by mixing, grinding, green sintering , burning or hot isostatic pressing (HIPen) at 1600 bar and 1600 ° C. WC hard metals can be processed by grinding as well as wire or spark erosion . In special cases, balls made of carbide are pierced with a laser (hole diameter smaller than 0.25 mm).

As molten tungsten carbide (WSC) in a matrix metal as a rod or in an iron tube, it can be applied to drilling tools for mining, for example, by flame fusion ("autogenous").

Health risks

The handling of hard metal requires special occupational safety measures, because respirable tungsten carbide- cobalt dust can cause pulmonary fibrosis and there are signs of a carcinogenic effect. This is due to the cobalt it contains. The acute toxicity of tungsten carbide is very low.

Engagement ring made from tungsten carbide

Since jewelry rings made of tungsten carbide can hardly be separated due to their hardness, swelling of a finger, e.g. B. by a bee sting or an injury, serious damage can occur because the blood flow is obstructed or completely interrupted. However, in an emergency and with common material thicknesses, it is possible to burst the ring using locking pliers - without significantly crushing the finger.

literature

• Gopal S. Upadhyaya: Cemented Tungsten Carbides: Production, Properties and Testing , Noyes Publications, 1998, ISBN 978-0-8155-1417-6 .
• Alexey S. Kurlov, Aleksandr I. Gusev: Tungsten Carbides: Structure, Properties and Application in Hardmetals , Springer Verlag, 2013, ISBN 978-3-319-00523-2 .

Web links

• Tungsten Carbide-Cobalt - Material Info

Individual evidence

1. ↑ Entry on tungsten carbides. In: Römpp Online . Georg Thieme Verlag, accessed on November 10, 2014.
2. ↑ ^{a b c d e f g h} Entry on tungsten carbide in the GESTIS substance database of the IFA , accessed on May 31, 2015(JavaScript required) .
3. ↑ Werner Baumann, Bettina Herberg-Liedtke: Chemicals in metal processing Data and facts on environmental protection . Springer-Verlag, 2013, ISBN 978-3-642-61004-2 , p. 1556 ( limited preview in Google Book search).
4. ↑ John L. Jambor, David A. Vanko: New Mineral Names . In: American Mineralogist . tape 74 , no. 7-8 , 1989, pp. 946–951 (English, minsocam.org [PDF; 747 kB ; accessed on February 8, 2019] WC from page 948).
5. ↑ Qingsong Fang, Wenji Bai, Jingsui Yang, Xiangzhen Xu, Guowu Li, Nicheng Shi, Ming Xiong, He Rong: Qusongite (WC): A new mineral . In: American Mineralogist . tape 94 , no. 2–3 , 2009, pp. 387–390 (English, rruff.info [PDF; 757 kB ; accessed on February 8, 2019]).
6. ^ RJ Meyer: Wolfram . Springer-Verlag, 2013, ISBN 978-3-662-13401-6 , pp. 188 ( limited preview in Google Book search).
7. ↑ ^{a b c d e f} OECD : Screening Information Dataset (SIDS) Initial Assessment Report (SIAR) for Tungsten carbide (WC) , accessed on December 30, 2017.
8. ↑ ^{a b c d} Martin Bertau, Armin Müller, Peter Fröhlich, Michael Katzberg: Industrielle Inorganische Chemie , ISBN 978-3-527-33019-5 , p. 614.
9. ^ Edward M. Trent, Paul K. Wright: Metal Cutting , Elsevier, 2000, 4th edition, ISBN 978-0-7506-7069-2 , p. 175.
10. ^ Karl Winnacker, Leopold Küchler: Metallurgy . C. Hanser, 1970, ISBN 3-446-10356-2 , pp. 498 ( limited preview in Google Book search).
11. ↑ Norbert Welsch, Jürgen Schwab, Claus Liebmann: Materie earth, water, air and fire . Springer-Verlag, 2013, ISBN 978-3-8274-2265-1 , pp. 275 ( limited preview in Google Book Search).
12. ↑ Patent DE69808514 : Improved ballpoint pen. Filed December 22, 1998 , published January 30, 2003 , applicant: SANDVIK AB (PUBL), Sandviken, inventor: Jerome Cheynet, Sylvie O'Donnell, Björn Uhrenius. ‌
13. ↑ James Smyth Wallace: Chemical Analysis of Firearms, Ammunition, and Gunshot Residue . CRC Press, 2008, ISBN 978-1-4200-6971-6 , pp. 72 ( limited preview in Google Book search).
14. ↑ Peter OK Krehl: History of Shock Waves, Explosions and Impact A Chronological and Biographical Reference . Springer Science & Business Media, 2008, ISBN 978-3-540-30421-0 , pp. 44 ( limited preview in Google Book search).
15. ↑ Elizabeth Doerr: Wristwatch Annual 2004: The Catalog of Producers, Models, and Specifications . ABBEVILLE Press, 2003, ISBN 0-7892-0803-2 ( limited preview in Google Book Search).
16. ↑ Hermann Sicius: Chromium group: elements of the sixth subgroup A journey through the periodic table . Springer-Verlag, 2016, ISBN 978-3-658-13543-0 , pp. 37 ( limited preview in Google Book search).
17. ^ Tungsten carbide based alloys. SVAT - Dr. Welk GmbH, accessed September 8, 2015.
18. ↑ Günter G. Mollowitz: The Accident Assessment of the consequences of work accidents, private accidents and occupational diseases . Springer-Verlag, 2013, ISBN 978-3-662-06549-5 , pp. 549 ( limited preview in Google Book search).
19. ↑ Toxicology of Substances: Toxicology Volume 2 - Toxicology of Substances . John Wiley & Sons, 2012, ISBN 3-527-63555-6 , pp. 16 ( limited preview in Google Book search).
20. ↑ Onmeda.de - tungsten carbide rings
21. ↑ Carolyn L. Gardiner et al .: A comparison of two techniques for tungsten carbide ring removal (PDF Download Available). Retrieved January 27, 2017 (English).