WOCAFIX tungsten carbide electrospark deposition device

Chemical compound

"Borium" redirects here.
For the synthetic chemical element, see Borium. Wolfram carbide

Wolfram carbide

(chemical formula:
Toilet
) is a chemical compound (specifically carbide) containing equal parts tungsten and carbon atoms. In its basic form, tungsten carbide is a fine gray powder, but it can be pressed and shaped through a process called sintering for use in industrial equipment, cutting tools, abrasives, armor-piercing projectiles, and jewelry.

Tungsten carbide is approximately twice as hard as steel, with a low modulus of approximately 530–700 GPa (77,000 to 102,000 psi),[4][7][8][9] and twice the density of steel—almost in the middle between news and gold. It is comparable to corundum (α-Al 2O 3) in hardness and can only be polished and processed with high-hardness abrasives such as cubic boron nitride diamond powder, wheels and compounds.

Content

• 1 Naming
• 2 Synthesis
• 3 Chemical properties
• 4 Physical properties
• 5 Structure
• 6 Applications 6.1 Cutting tools for machining
• 6.2 Ammunition
• 6.3 Rock and foundation drilling
• 6.4 Nuclear
• 6.5 Use of sports
• 6.6 Surgical instruments
• 6.7 jewelry
• 6.8 Other

Synthesis

Tungsten carbide is produced by the reaction of tungsten metal and carbon at 1400–2000 °C.[11] Other methods include a proprietary lower temperature fluidized bed process that reacts either tungsten metal or blue WO3 with a CO/CO2 mixture and H2 at 900 to 1200 °C.[12]

The toilet can also be produced by heating WO 3 with graphite: directly at 900 °C or in hydrogen at 670 °C followed by carburization in argon at 1000 °C.[13]Chemical vapor deposition methods that have been investigated include:[13] eleven]

• reacting tungsten hexachloride with hydrogen (as the reducing agent) and methane (as the carbon source) at 670 °C (1238 °F)

WCl 6 + HOUR 2 + CH 4 → WC + 6 HCl

• reacting tungsten hexafluoride with hydrogen (as a reducing agent) and methanol (as a carbon source) at 350 °C (662 °F)

WF 6 + 2 HOUR 2 + CH 3rd → WC + 6 HF + HOUR 2O

Receipt[edit | edit code]

Tungsten carbide can be obtained by one of the following methods.
Direct saturation of tungsten with carbon

The process of producing tungsten carbide is based on a direct reaction:

W+C→WC{\displaystyle {\mathsf {W+C\rightarrow WC}}}

The formation of WC occurs with the formation of tungsten monocarbide on the surface of tungsten particles, from which carbon diffuses into the particle and forms an underlying layer of W2C composition.

When producing WC, tungsten powder, reduced from its oxide, and carbon black are used. Powdered substances taken in the required ratio are mixed, briquetted or tamped into graphite containers and placed in an oven. To protect the powder from oxidation, the synthesis process is carried out in a hydrogen environment, which reacts with carbon at temperatures above 1300 °C to form acetylene. The formation of tungsten carbide occurs mainly through the gas phase due to the carbon contained in the gases. The following carbidization reactions occur:

2C+H2→C2H2{\displaystyle {\mathsf {2C+H_{2}\rightarrow C_{2}H_{2}}}} 2W+C2H2→2WC+H2{\displaystyle {\mathsf {2W+C_{2 }H_{2}\rightarrow 2WC+H_{2}}}}

In the presence of carbon monoxide in the medium, the process proceeds according to the reaction

C+CO2→2CO{\displaystyle {\mathsf {C+CO_{2}\rightarrow 2CO}}} 2CO+W→WC+CO2{\displaystyle {\mathsf {2CO+W\rightarrow WC+CO_{2}} }}

Typically, the process of producing tungsten carbide is carried out at a temperature of 1300−1350 °C for fine-grained tungsten powders and 1600 °C for coarse-grained ones, and the holding time is from 1 to 2 hours. The resulting slightly sintered tungsten carbide blocks are crushed and sifted through sieves.

Reduction of tungsten oxide with carbon followed by carbidization This method, in contrast to the above, combines the process of reduction and carbidization of tungsten, while the missing amount of soot is added to the charge to form carbide.
The reduction of tungsten oxide WO3 occurs through the gas phase in an environment of CO and hydrogen. Reduction of tungsten compounds followed by carbidization Another method of producing tungsten carbide is heating a mixture of tungstic acid, tungstic anhydride (WO3) or ammonium paratungstate ((NH4)10 [H2W12O42] x H2O
) in an environment of hydrogen and methane at a temperature of 850−1000 ° C. By vapor deposition The production of tungsten carbide from the gas phase is based on the decomposition of tungsten carbonyl at a temperature of 1000 °C. Electrolysis of Molten Salts Electrolysis of a mixture of molten sodium borate, sodium carbonate, lithium fluoride and tungsten anhydride produces tungsten carbide. Tungsten carbide single crystals WC single crystals can be obtained by melt growth. To do this, a mixture with the composition Co−40%WC is melted in an aluminum oxide crucible at a temperature of 1600 °C and, after homogenization of the melt, the temperature is reduced to 1500 °C at a rate of 1−3 °C/min and maintained at this temperature for 12 hours. After which the sample is cooled and the cobalt matrix is ​​dissolved in boiling hydrochloric acid. The Czochralski method can also be used to grow large single crystals (up to 1 cm).

Chemical properties

There are two well-characterized tungsten-carbon compounds, WC and tungsten semicarbide

, W 2C. Both compounds may be present in coatings, and the proportions may depend on the coating method.[14]

Another metastable tungsten-carbon compound can be created by heating the WC phase to high temperatures using plasma and then quenching in an inert gas (plasma spheroidization).[15].

This process causes spheroidization of the macrocrystalline WC particles and results in a non-stheiometric high-temperature phase. Toilet 1 exists in a metastable form at room temperature. The fine microstructure of this phase provides high hardness (2800-3500 HV) combined with good toughness compared to other tungsten carbide compounds. The meta-stable nature of this compound results in reduced high temperature stability.

At high temperatures, WC decomposes into tungsten and carbon, which can occur at high temperatures. thermal spray, such as in high velocity oxygen fuel (HVOF) and high energy plasma (HEP) techniques.[16]

WC oxidation begins at 500–600 °C (932–1112 °F).[11] Resistant to acid and attacked only by hydrofluoric acid/nitric acid (HF/HNO 3) mixtures above room temperature.[11] It reacts with fluorine gas at room temperature and chlorine above 400 °C (752 °F) and does not react when dried to the melting point.[11] Fine WC is easily oxidized into hydrogen peroxide in aqueous solutions.[17] At high temperatures and pressures, it reacts with aqueous sodium carbonate to form sodium tungstate, a procedure used to recover cemented carbide scrap due to its selectivity.

Physical properties

Tungsten carbide has a high melting point at 2870 °C (5200 °F), boiling point 6000 °C (10830 °F) at a pressure equivalent to 1 standard atmosphere (100 kPa),[2] thermal conductivity 110 W m−1 K −1,[4] and a coefficient of thermal expansion of 5.5 µ

m m−1 K−1.[7]

Tungsten carbide is extremely hard and ranks between 9 and 9.5. Mohs scale, and with Vickers the number is about 2600.[8] It has a minor modulus of approximately 530–700 GPa,[4][7][8][9] and a bulk modulus of 630–655 GPa and a shear modulus of 274 GPa.[18] Tensile strength of 344 MPa,[9] compressive strength of about 2.7 GPa and Poisson's ratio of 0.31.[18]

Longitudinal wave speed (speed of sound) through a thin tungsten carbide rod 6220 m/s.[19]

Low tungsten carbide electrical resistivity about 0.2 µ

ohm m comparable to some metals (e.g. vanadium 0.2
μ
ohm m).[11][20]

The toilet is easily moistened with molten nickel and cobalt.[21] An examination of the phase diagram of the WC-Co system shows that WC and Co form a pseudo-binary system. eutectic. The phase diagram also shows that there are so-called η-carbides of composition (W, Co) 6C that can form, and the brittleness of these phases makes it important to control the carbon content of WC-Co carbides.[21]

Literature

• Mikhailova M., Filippov V., Muslakov V.
  Soft magnetic ferrites for radio-electronic equipment. Directory. - M. Radio and communications, 1983.
• Kunevich A.V.
  Ferrites, catalog M., 1991
• Kunevich A.V., Podolsky A.V. Sidorov I.N.
  “Ferrites: Encyclopedic reference book. Magnets and magnetic systems. Volume 1" Lik publishing house, 2004
• Zhuravlev
  G.I. Chemistry and technology of ferrites - Leningrad: Chemistry. Leningr. department, 1970. - 191 p.
• Smith, Y., Wayne, H.
  Ferrites. - Moscow: Foreign Literature, 1962. - 504 p.

Structure

Structure of α-WC, carbon atoms are gray.[5]
There are two shapes of the toilet: a hexagon shape, α-WC (hP2, space group n6m2, no. 187),[5][6] and a cubic high-temperature shape, β-WC, which has the structure of rock salt.[22] The hexagonal shape can be thought of as consisting of a simple hexagonal lattice of metal atoms layers lying directly on top of each other (i.e. not tightly packed), with carbon atoms filling half the voids, giving both tungsten and carbon a regular trigonal prism. 6 coordination.[6] From the unit cell dimensions[23], the following bond lengths can be determined: the distance between tungsten atoms in a hexagonally packed layer is 291 μm, the shortest distance between tungsten atoms in adjacent layers is 284 μm, and the tungsten carbon bond length is 220 μm. Thus, the tungsten-carbon bond length is comparable to the single bond in W(CH3)6 (218 pm), in which the trigonal-prismatic coordination of tungsten is highly distorted.[24]

Molecular WC has been studied and this gas phase has a bond length of 171 pm for 184W12 C.[25]

Applications

Cutting tools for machining

See also: Cemented carbide

Carbide drills and end mills

Sintered tungsten carbide-cobalt cutting tools are highly abrasion resistant and can withstand higher temperatures than standard high speed steel (HSS) tools. Carbide cutting surfaces are often used for machining through materials such as carbon steel or stainless steel, and in applications where steel tools will wear quickly, such as in high-volume, high-precision manufacturing. Because carbide tools hold a sharp cutting edge better than steel tools, they tend to provide better finishing on parts, and their heat resistance allows for faster machining. The material is usually called cemented carbide, hard carbide, hard metal or cobalt tungsten carbide. It is a metal matrix composite where tungsten carbide particles are the aggregate and cobalt metal serves as the matrix.[26][27]

Ammunition

Tungsten carbide in its monolithic sintered form, or much more commonly in cobalt tungsten carbide composite (in which fine ceramic tungsten carbide particles are embedded in a metal cobalt binder, forming a metal matrix composite or MMC), is often used in armor-piercing ammunition, especially where depleted uranium is not available or is politically unacceptable. W 2C shells were first used by German Luftwaffe tank squadrons in World War II. However, due to limited supplies of tungsten in Germany, W 2C material was reserved for the manufacture of machine tools and a small number of projectiles. It is an effective penetrator due to its combination of high hardness and very high density.[28][29]

Tungsten carbide ammunition is now generally categorized as a sabot type. SLAP, or padded light armor piercer, where a plastic tray is ejected at the muzzle of the barrel, is one of the main types of sabotage ammunition for small arms. Jackets that are not thrown away, regardless of the material of the jacket, are perceived not as clogs, but as bullets. However, both designs are common to designated light armor-piercing small arms ammunition. Elimination of the sabots used with the M1A1 Abrams main gun is more common in precision gun ammunition.[30][31]

Mining and foundation drilling

Tricone roller cone assembly from a boring reamer showing raised tungsten carbide buttons inserted into the rollers
Tungsten carbide is widely used in the mining industry in hammer drill bits, face hammers, roller cutters, long wall plow chisels, long wall miner picks boring reamer and tunnel boring machines. It is typically used as a button insert set in a surrounding matrix of steel that forms the base of the bit. As the tungsten carbide button wears, the softer steel matrix containing it also wears away, exposing even more of the button inserts.

Nuclear

Tungsten carbide is also an effective neutron reflector and as such was used during early research into nuclear chain reactions, especially for weapons. A criticality accident occurred at Los Alamos National Laboratory on August 21, 1945, when Harry Daghlian accidentally dropped a tungsten carbide brick onto a plutonium sphere known as a demon core, causing a subcritical mass to go supercritical with reflected neutrons.

Use of sports

A Nokian bicycle tire with tungsten carbide studs.
The spikes are surrounded by aluminum. Trekking poles, used by many hikers for balance and to reduce pressure on the joints of the legs, usually use carbide tips to achieve traction when placed on hard surfaces (such as rocks); carbide tips last much longer than other types of tips.[32]

While ski pole tips are not usually made of carbide, as they do not need to be particularly hard even to break through layers of ice, as is usually the case with roller ski tips. Roller skating imitates cross-country skiing and is used by many skiers for training during the warmer months.

Sharpened, carbide-tipped studs (known as studs) can be inserted into the drive tracks of snowmobiles. These studs improve traction on icy surfaces. Longer V-shaped segments are inserted into grooved bars, called wear bars, under each snowmobile ski. Relatively sharp carbide edges improve handling on harder, icy surfaces. Carbide tips and segments reduce wear that occurs when the snowmobile travels over roads and other abrasive surfaces.[33]

Car, motorcycle and bicycle tires with tungsten carbide studs provide better traction on ice. They are generally preferred over steel studs due to their superior wear resistance.[34]

Tungsten carbide can be used in cooking, horse shoeing to improve traction on slippery surfaces such as roads or ice. Carbide-tipped hoof nails can be used to secure shoes;[35] in the US, bur—tungsten carbide shavings in a matrix of softer metal such as bronze or mild steel—can be welded to small areas of the underside of shoes before fitting.[36]: 73

Surgical instruments

Tungsten carbide is also used to make surgical instruments intended for open surgery (scissors, forceps, hemostats, blade handles, etc.) and laparoscopic surgery (grippers, scissors/cutter, needle holder, cautery, etc.). They are much more expensive than their stainless steel counterparts and require delicate handling, but provide better performance.[37]

Jewelry

Tungsten Carbide Ring
Tungsten carbide, typically in the form of cemented carbide (carbide particles soldered together with metal), has become a popular material in the wedding jewelry industry due to its extreme hardness and high scratch resistance.[38][39] Even with high impact resistance, this extreme hardness also means that it can sometimes break under certain circumstances.[40] Some find this useful because the impact can destroy the tungsten ring, quickly removing it and causing the precious metals to bend and require cutting. Tungsten carbide is approximately 10 times harder than 18-karat gold. Besides its design and high gloss, part of its appeal to consumers lies in its technical nature.[38] Special tools, such as locking pliers, may be required if such a ring must be quickly removed (for example, due to a medical emergency following a hand injury with swelling).[41]

Another

Spherical tungsten carbide under scanning electron microscope, magnification x950, materials laboratory
Tungsten carbide is widely used to make the rotating ball in the tips of ballpoint pens that disperse ink while writing.[42]

Tungsten carbide is a common material used in the production of gauge blocks, used as a system for producing precision lengths in dimensional metrology.[ citation needed

]

English guitarist Martin Simpson is famous for using tungsten carbide on custom slide guitars.[43] The hardness, weight and density of the slide make it excellent. maintain volume compared to standard guides made of glass, steel, ceramic or brass.

Tungsten carbide has been studied for its potential use as a catalyst and has been found to resemble platinum in its catalysis of the production of water from hydrogen and oxygen at room temperature, reduction of tungsten trioxide by hydrogen in the presence of water, and isomerization from 2,2-dimethylpropane to 2-methylbutane.[44] It has been proposed as a replacement for iridium catalyst in hydrazine-powered satellite engines.[45]

Tungsten carbide coating has been used on brake rotors in high-performance automotive systems to improve performance, extend service intervals, and reduce brake dust.[46]

Application

Due to the above properties, there are several applications for tungsten carbide.

1. It is used to produce parts with high corrosion resistance, wear resistance and hardness: milling cutters, abrasive materials, cutters, drills, chisels, etc.
2. The connection in question is used for surfacing and thermal spraying in order to increase wear resistance by creating a hard surface.
3. Tungsten carbide is used as a material for watch bracelets, bullet and projectile cores, jewelry, etc.

Applications of Tungsten Carbide

The optimal temperature range for items made from it is considered to be 200 - 300°C. The elasticity of this material ensures its use under alternating loads.

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   Carbides. - Metallurgy, 1968. - P. 300.
2. ↑ 1 2 3 Tretyakov V.I.
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3. Toth L.
   Carbides and nitrides of transition metals. - Mir, 1974. - pp. 21-23. — 296 p.
4. Editorial team: Knunyants I. L. (chief editor).
   Chemical encyclopedia: in 5 volumes - Moscow: Soviet Encyclopedia, 1988. - T. 1. - P. 420-421. — 623 p. — 100,000 copies.
5. ↑ 1 2 Samsonov G.V.
   Physical materials science of carbides. - Naukova Dumka, 1974. - P. 79-397. — 454 p.
6. Kieffer R., Benezovsky F.
   Hard alloys. - Metallurgy, 1971. - P. 47. - 392 p.
7. ↑ 1 2 Samsonov G.V., Vinitsky I.M.
   Refractory compounds (handbook). - Metallurgy, 1976. - P. 560.
8. Lidin R. A., Molochko V. A., Andreeva L. L.
   Chemical properties of inorganic substances. - Chemistry, 2000. - P. 330. - 480 p.
9. The letter H (Hartkern) in the designation of German WWII ammunition means “with a solid cermet core.”
10. Thus, a 20-mm DM43 BPS, when fired from a MK 20 RH 202 cannon (initial speed 1100 m/s) at a distance of 1000 m, is capable of penetrating 35 mm of steel armor at an impact angle of 0°, and only 8 mm of armor at an angle of 60°. Jane's Infantry Weapons 1996-97, 456.
11. Dmitry Safin.
    [science.compulenta.ru/570052/ A low-cost method for the electrolytic production of hydrogen is presented (Russian). Compulenta (October 15, 2010). — Prepared from Wiley. Retrieved October 16, 2010.
12. [www.nanorf.ru/events.aspx?cat_id=223&d_no=1389&print=1&back_url=%2fevents.aspx%3fcat_id%3d223%26d_no%3d1389 04/15/2009 Is tungsten carbide nanodust hazardous to health?] Russian electronic nanojournal (nanotechnologies and their application)
13. [www.microelements.ru/W Tungsten. W.]