Melting point 2870°C, boiling point 6000°C, relative density 15.63 (18°C). Tungsten carbide is insoluble in water, hydrochloric acid, and sulfuric acid, but readily soluble in a mixture of nitric acid and hydrofluoric acid. Pure tungsten carbide is brittle, but small amounts of metals such as titanium and cobalt can reduce its brittleness. Tungsten carbide used as steel cutting tools often incorporates titanium carbide, tantalum carbide, or a mixture thereof to improve its anti-knock properties. Tungsten carbide is chemically stable. In tungsten carbide, carbon atoms embed themselves within the gaps between the tungsten metal lattice without disrupting the original metal lattice, forming an interstitial solid solution, also known as an interstitial (or intercalation) compound. Tungsten carbide can be produced by heating a mixture of tungsten and carbon at high temperatures. The presence of hydrogen or hydrocarbons can accelerate the reaction. If tungsten carbide is produced using tungsten oxygen compounds, the product must be vacuum-treated at 1500°C to remove the carbon and oxygen compounds. Tungsten carbide is suitable for machining at high temperatures and can be used in cutting tools, kiln structural materials, jet engines, gas turbines, nozzles, and more. Another compound of tungsten and carbon is ditungsten carbide, with the chemical formula W2C. It has a melting point of 2860°C, a boiling point of 6000°C, and a relative density of 17.15. Its properties, preparation methods, and uses are similar to those of tungsten carbide. Tungsten steel, also known as cemented carbide, is second only to diamond in hardness. It is chemically stable and, even when heated, resists hydrochloric acid and sulfuric acid, and even remains insoluble in aqua regia. Tungsten is extremely heat-resistant, known as the most insoluble metal in nature, with a melting point of 3410°C. Its hardness is also among the highest among metals, and pressure processing is only possible when heated to very high temperatures. Tungsten steel balls are widely used in water meters, flow meters, and pen manufacturing.
