金刚石Diamond

金刚石为面心立方结构（空间群 Fd3̄m），晶胞边长 356.7 pm，含 8 个碳原子，C–C 键长 154 pm。没有自由电子，是电绝缘体（禁带 5.5 eV），但晶格振动传热极快，室温导热系数约 2200 W/(m·K)，为铜的 5 倍。折射率高（2.42）、色散大，使钻石“火彩”闪耀。常压下金刚石在热力学上不如石墨稳定，但转化速率极慢，可视为“亚稳态”。在空气中约 700 °C 以上开始燃烧。

Diamond is face-centred cubic (space group Fd3̄m) with a 356.7 pm cell holding eight carbons and C–C bonds of 154 pm. With no free electrons it is an electrical insulator (band gap 5.5 eV), yet lattice vibrations carry heat extremely fast, giving a room-temperature thermal conductivity of about 2200 W/(m·K), five times that of copper. Its high refractive index (2.42) and dispersion create a diamond's 'fire'. At ordinary pressure diamond is less stable than graphite, but the conversion is immeasurably slow, so it is metastable. It begins to burn in air above about 700 °C.

印度是最早的金刚石产地。1772 年拉瓦锡用透镜聚焦阳光燃烧金刚石，只生成 CO₂；1797 年坦南特证明金刚石完全由碳组成。1954 年美国通用电气公司的霍尔用高温高压法（约 5 GPa、1500 °C，金属触媒）首次可重复地合成金刚石。1980 年代起化学气相沉积（CVD）法可在低压下由甲烷-氢气等离子体生长金刚石膜和宝石级单晶。

India was the first source of diamonds. In 1772 Lavoisier burnt diamond with sunlight focused by a lens and obtained only CO₂, and in 1797 Tennant proved diamond is pure carbon. In 1954 Tracy Hall at General Electric achieved the first reproducible synthesis by the high-pressure, high-temperature method (about 5 GPa and 1500 °C with a metal catalyst). From the 1980s chemical vapour deposition grew diamond films and gem-quality crystals at low pressure from methane–hydrogen plasmas.

工业金刚石（多为人造）用于切割、钻探、磨削和抛光工具，金刚石对顶砧可产生数百万大气压用于高压研究；高导热用于大功率电子器件散热片；宽禁带使其成为极端环境半导体候选材料；氮-空位色心金刚石用于量子传感和量子信息。中国河南是全球最大的人造金刚石产地。

Industrial diamond, mostly synthetic, is used in cutting, drilling, grinding and polishing tools; diamond anvil cells reach millions of atmospheres for high-pressure research; its thermal conductivity serves in heat spreaders for high-power electronics; its wide band gap makes it a candidate semiconductor for extreme environments; and diamonds with nitrogen–vacancy centres are used in quantum sensing and quantum information. Henan Province in China is the world's largest producer of synthetic diamond.