borides

Borides are binary inorganic compounds formed between boron and another element, typically a metal. They encompass simple stoichiometries such as MB and MB2 and more complex formulations like M2B and M3B2. In many transition-metal borides the boron atoms form rigid networks or layers that contribute to high hardness and thermal stability.

Common classes include transition-metal diborides (MB2), such as TiB2, ZrB2, and HfB2, which often crystallize in a hexagonal AlB2-type structure featuring alternating metal layers and boron sheets. Other borides, such as FeB and Fe2B, are used as diffusion-hardening phases in steel. Some borides exhibit boron-rich frameworks or networks that enhance mechanical properties and stiffness.

Key properties of borides typically include very high melting points, extreme hardness, and good wear and corrosion resistance. Many borides are also chemically inert at elevated temperatures and retain strength under harsh conditions. TiB2, for example, is widely employed as a hard coating and refractory ceramic.

Applications span protective coatings (applied by PVD or CVD), cutting-tool materials, wear parts, and diffusion-barrier components in high-temperature equipment. Synthesis generally involves high-temperature solid-state reactions between boron and the target metal, with coatings often produced by vapor-deposition techniques. Ongoing research explores borides for advanced structural materials, protective coatings, and potential functional properties in extreme environments.