Wolfram carbide. Physical properties, toxicity, application

Tungsten carbide (also known as tungsten monocarbide) is a chemical compound of tungsten, carbon, and ceramics. This substance is one of the strongest of all known ceramics, hardness comparable to diamond: HRC is about 90 units, according to Mohs mineralogical scale it is the 9th place. Another positive feature of tungsten carbide is good wear resistance, high melting point and excellent resistance to oxidation. This substance is currently actively used to create a cutting tool and cores of armor-piercing shells.

Physical properties of tungsten carbide

1. Under normal conditions, tungsten carbide granular is a powder of gray color with a metallic reflection.

2. Soluble in water.

3. Rockwell hardness is from 87 to 92 units.

4. The melting point of tungsten carbide is 2870 degrees.

5. The density is 15.8 g / cm3.

6. The modulus of elasticity is 450 ÷ 650 GPa

7. The thermal effect is 8.4 +/- 0.2 kcal / mole

8. The entropy of the standard is 8.5 +/- 1.5 calories / (mole per hail).

9. The heat capacity at a temperature equal to 293 degrees is 8.53 calories / (mole per hail).

10. Thermal conductivity at an ambient temperature of 25 degrees is 0.07 cal / (centimeter / s / degree).

11. The thermal expansion coefficient is 3.84 (3.9) × 106 deg-1.

12. The electrical resistance at a temperature of 200 degrees is 19.2 +/- 0.3 microohm / centimeter.

13. The electrical conductivity is 52200 Ohm-1 * centimeter-1.

Structure of tungsten carbide

At present two WC forms are known - β-WC high-temperature cubic and α-WC hexagonal.

Application of tungsten carbide

- in the technique for making tools that must have high hardness and good corrosion resistance;

- for wear-resistant surfacing of various parts that will be used in conditions of intensive wear with medium impact loads;

- wide application in manufacturing of various cutters, drills, abrasive disks, bits for drilling, milling cutters and other cutting tools;

- The cost of tungsten makes it possible to use its alloys in various areas (it is in the composition of hard alloys known under the names "Wins" and "Relit," about 90%);

- used in surfacing and gas-thermal spraying in the form of a powder material for the manufacture of wear-resistant coatings;

- this is one of the materials used to replace the chromium plating process using a gas-flame high-speed spraying;

- At present, tungsten carbide is the dominant one in the manufacture of shells and cores of armor-piercing bullets (however, there is a tendency for gradual displacement of tungsten carbide with depleted uranium) ;

- in the production of heavy-duty balls with a size of 1 mm for ball-point pens (polishing is carried out in a special apparatus for several days using a small amount of diamond paste);

- in the production of bracelets for elite Swiss watches, jewelry - rings, bracelets and coulombs, which due to the wear resistance of tungsten carbide are guaranteed eternal shine;

- used as a substrate for a catalyst made of platinum;

- Tungsten carbide is used to create mechanical seal shafts of certain mechanisms in those cases where the environment has a high viscosity and / or abrasiveness.

Toxicity of tungsten carbide

This substance is chemically inert. For this reason, under normal conditions, it does not present any danger to humans. The lethal dose is not determined for either humans or animals. Studies that were carried out at the Dresden Technical University and the University of Leipzig showed that the dust of tungsten carbide can penetrate into living organisms. At the same time, fine particles are non-toxic, but when combined with certain substances they pose a danger to the well-being of cells. With long exposure to cobalt dust and the substance we are considering, fibrosis can develop in the body.