What Is Tungsten Carbide?
Tungsten carbide, a compound of tungsten and carbon, is known for its exceptional hardness, high modulus of elasticity (Young’s modulus), and excellent corrosion resistance. It combines the properties of both metals and ceramics, making it extremely rigid and durable.
Discovered in Chusum County, Shannan City, Tibet Autonomous Region, China, natural tungsten carbide was named Qusongite in 2007. Exposure to tungsten carbide dust can cause pulmonary fibrosis, similar to silicosis, and WC-Co alloys are considered potential carcinogens.
Uses of Tungsten Carbide
Primarily, tungsten carbide serves as a crucial material for cemented carbides, particularly in WC-Co alloys, which exhibit outstanding mechanical properties upon mixing and sintering with cobalt (Co). These alloys, alongside WC-Ni alloys containing nickel (Ni), are renowned for their rigidity, hardness, and wear resistance. They find extensive use in cutting tools, wire drawing dies, rolling rolls, and various types of dies.
Enhancements in oxidation and corrosion resistance are achieved by adding titanium carbide (TiC) and tantalum carbide (TaC) to WC-Co alloys.
Properties of Tungsten Carbide
With a melting point of 2,870°C and a boiling point of 6,000°C, tungsten carbide appears as a gray or black solid. Its Young’s modulus is approximately 550 GPa, making it significantly more rigid than steel, and its hardness rivals that of α-aluminum oxide.
Structure of Tungsten Carbide
The chemical formula of tungsten carbide is WC, featuring a molar mass of 195.851 g/mol. It exists in two forms: hexagonal α-tungsten carbide and cubic β-tungsten carbide, with distinct structural properties and a high density of 15.63 g/cm3 for the α form.
Other Information on Tungsten Carbide
1. Synthesis of Tungsten Carbide
Tungsten carbide is synthesized through high-temperature reactions between carbon and tungsten, utilizing various methods such as the fluidized bed technique or direct heating with graphite and tungsten(VI) oxide. Alternative methods include reactions involving tungsten hexachloride or tungsten hexafluoride with suitable carbon sources and reducing agents.
2. Reaction of Tungsten Carbide
This compound exhibits strong resistance to acids and is insoluble in water, hydrochloric acid, and sulfuric acid. It dissolves in nitric hydrofluoric acid and aqua regia. Tungsten carbide begins to oxidize at temperatures between 500-600°C and reacts with fluorine and chlorine under specific conditions. In fine powder form, it oxidizes in aqueous hydrogen peroxide solutions and reacts with sodium carbonate at elevated temperatures and pressures.