Tungsten carbide

Hard, dense and stiff chemical compound

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"Borium" redirects here. Not to be confused with bohrium or barium

Chemical compound

Tungsten carbide (chemical formula: WC) is a chemical compound (specifically, a carbide) made up of equal parts of tungsten and carbon atoms. In its most basic form, tungsten carbide is a fine gray powder. However, it can be pressed and sintered into shapes for use in industrial machinery, cutting tools, chisels, abrasives, armor-piercing shells, and even jewelry.

Tungsten carbide is roughly twice as stiff as steel, with a Young's modulus between 530–700 GPa, and is about twice as dense as steel. It ranks similar to corundum (α-Al₂O₃) in hardness and can be polished and finished using abrasives of superior hardness, such as cubic boron nitride and diamond powder.

Naming

In industrial circles, such as machining, tungsten carbide is often referred to simply as carbide.

Synthesis

Tungsten carbide is synthesized by reacting tungsten metal with carbon at temperatures ranging from 1,400 to 2,000°C. Other methods include a lower temperature fluid bed process that reacts tungsten metal or blue WO₃ with a CO/CO₂ mixture and H₂ at temperatures between 900 and 1,200°C.

WC can also be produced by heating WO₃ with graphite: either directly at 900°C or in hydrogen at 670°C followed by carburization in argon at 1,000°C. Methods of chemical vapor deposition include reacting tungsten hexachloride with hydrogen and methane at 670°C and reacting tungsten hexafluoride with hydrogen and methanol at 350°C:

• WCl₆ + H₂ + CH₄ → WC + 6 HCl
• WF₆ + 2 H₂ + CH₃OH → WC + 6 HF + H₂O

Chemical Properties

Tungsten carbide has two main compounds: WC and tungsten semicarbide (W₂C). Both can appear in coatings, with their proportions varying by coating method.

Another meta-stable compound can be created by heating WC to high temperatures using plasma, followed by quenching in inert gas. This produces macrocrystalline WC particles in a meta-stable form at room temperature, with high hardness (2800-3500 HV) and good toughness.

At high temperatures, WC decomposes into tungsten and carbon. Oxidation starts at 500–600°C. It is resistant to most acids except hydrofluoric/nitric acid mixtures above room temperature.

Physical Properties

Tungsten carbide has a high melting point of 2,870°C, and a boiling point of 6,000°C under standard atmospheric pressure. Its thermal conductivity is 110 W·m^-1·K^-1, with a thermal expansion coefficient of 5.5 μm·m^-1·K^-1.

WC is extremely hard, with a Mohs scale ranking of 9 to 9.5 and a Vickers number around 2600. It has a Young's modulus between 530–700 GPa, a bulk modulus ranging 379-381 GPa, and a shear modulus of 274 GPa. The ultimate tensile strength is approximately 344 MPa, and the compression strength is about 2.7 GPa.

Furthermore, tungsten carbide has a relatively low electrical resistivity of about 0.2 μΩ·m, which is similar to some metals like vanadium.

WC is easily wettable by molten nickel and cobalt, forming a pseudo-binary eutectic with cobalt in the W-C-Co system. It is critical to control carbon content in WC-Co sintered carbides to avoid brittle phases.

Structure

There are two forms of WC: hexagonal (α-WC, space group P6m2) and a high-temperature cubic form (β-WC) with a rock-salt structure. The hexagonal form consists of a simple hexagonal lattice with tungsten atoms in direct layers and carbon atoms in half the interstitial positions. The bond lengths in α-WC reveal tungsten atoms spaced at 291 pm within a layer, 284 pm between layers, and the W-C bond lengths at 220 pm.

Applications

Cemented carbide tools are widely utilized for machining tough materials. They offer higher temperature resistance and superior edge retention over traditional steel tools. This makes them ideal for high-precision and high-quantity production environments. Cemented carbide, also known as tungsten-carbide cobalt, is a matrix composite where tungsten carbide particles are bonded with metallic cobalt. These properties can be further enhanced by coatings such as titanium aluminum nitride to increase thermal stability and tool life.

Ammunition

Tungsten carbide is used in armor-piercing ammunition, particularly where depleted uranium is not an option. It has been used since World War II by the German Luftwaffe. Today, it is common in SLAP (Saboted Light Armor Penetrator) rounds, which feature a plastic sabot and high-density core, ensuring effective penetration due to its hardness.

Mining and Foundation Drilling

Tungsten carbide is extensively employed in the mining industry, where it is used in tools such as top hammer rock drill bits, downhole hammers, roller-cutters, and tunnel boring machines. It offers excellent wear and corrosion resistance, crucial for harsh environments. Bits usually include tungsten carbide buttons set in a steel matrix to extend tool life and improve efficiency.

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Nuclear

Tungsten carbide is an effective neutron reflector and as such was utilized in early nuclear chain reaction experiments. An infamous criticality accident at Los Alamos in 1945 involved tungsten carbide bricks causing severe radiation exposure.

Sports Usage

Trekking pole tips, rollerski tips, and snowmobile studs all make use of tungsten carbide for their superior traction on hard surfaces and ice. Additionally, car, motorcycle, and bicycle tires with tungsten carbide studs offer better performance and durability.

Surgical Instruments and Medical Applications

Surgical instruments, both for open and laparoscopic surgery, are often made from tungsten carbide for improved performance and longevity compared to stainless steel.

Jewelry

Tungsten carbide is popular in the bridal jewelry industry for its extreme hardness and scratch resistance. Although highly resistant, the material can shatter under severe impact, which some consider an advantage as it can be quickly removed in emergencies without bending.

Other Applications

Tungsten carbide is used in ballpoint pen tips, custom guitar slides, brake disc coatings, and as a potential catalyst in various chemical reactions. Its properties ensure superior performance and durability in all these applications.

Toxicity

Exposure to tungsten carbide dust can lead to pulmonary fibrosis similar to silicosis. Additionally, cobalt-cemented tungsten carbide is considered a potential human carcinogen by the American National Toxicology Program.

Features and Applications of Tungsten Carbide Buttons

What is Tungsten Carbide?
Tungsten carbide is an alloy made using powder metallurgy from a hard compound of refractory metal and a bonding metal. This material is known for its high hardness, wear resistance, corrosion resistance, and low thermal expansion coefficient. It is ideal for medium and high-pressure DTH drills.

Advantages of Cemented Carbide Buttons
Tungsten carbide button teeth boast superior wear resistance and impact toughness, leading to higher drilling speeds compared to similar products. The extended passivation period results in a longer lifespan, reducing labor and improving project efficiency.

Applications of Tungsten Carbide Buttons
Tungsten carbide buttons are widely used in oil drilling, snow shoveling, and plowing machines. Depending on the drilling machinery, such as roller cone bits or DTH bits, these buttons are categorized into various styles (P, Z, X types). They are also suitable for cutting tools, mining, road maintenance, and coal drilling. In mining, they are used in quarrying and tunnel construction, either as standalone tools or accessories in rock drills.

tungsten carbide buttons are primarily used in roller cone drills and other drilling tools to penetrate soft to medium-hard rock layers and can serve as alloy sheets for diverse drilling applications.

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1. Unique working performance
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4. Suitable for crushing hard materials like granite and limestone

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