Abstract
Metallurgical carbonylation is a selective chemical refining and materials-production process that exploits the reversible formation of volatile metal and carbon monoxide complexes. First pioneered by Ludwig Mond in the late nineteenth century, the process enables the purification and controlled deposition of metals through cyclic carbonyl formation and thermal decomposition. Among transition metals, nickel, iron, and cobalt exhibit the most industrially relevant carbonyl chemistry, forming Ni(CO)₄, Fe(CO)₅, and Co₂(CO)₈, respectively.
Nickel carbonylation remains the most mature and widely applied system. The Mond process converts reduced nickel into gaseous Ni(CO)₄ at low temperatures and near-atmospheric pressures, followed by decomposition at elevated temperatures to deposit >99.9% pure nickel while recycling CO. Over more than a century, this principle has evolved into atmospheric, medium-pressure, and high-pressure industrial flowsheets, enabling faster kinetics, higher throughput, and diverse product forms including pellets, powders, foams, and coatings. Detailed kinetic studies reveal that Ni(CO)₄ formation is governed by surface-controlled reactions strongly influenced by temperature, CO pressure, crystallographic orientation, and surface activation, with both reaction and mass-transfer limitations relevant under industrial conditions.
Iron carbonylation, although thermodynamically feasible, is kinetically hindered relative to nickel and requires higher temperatures and CO pressures to form Fe(CO)₅. Nevertheless, large-scale production of carbonyl iron powder has been commercialized, particularly for magnetic and powder-metallurgy applications. Cobalt carbonylation is even more kinetically constrained and has received comparatively limited attention, though dicobalt octacarbonyl is formed in mixed-metal systems and plays an important role in organometallic chemistry and catalysis.
Industrial carbonylation processes have enabled the production of exceptionally pure metal powders with tightly controlled particle size and morphology, characteristics unattainable by conventional atomization or reduction methods. Carbonyl-derived nickel and iron powders exhibit high surface area, tunable structures, and excellent magnetic and catalytic properties, supporting applications in batteries, fuel cells, electronics, powder metallurgy, electromagnetic interference shielding, and advanced defense materials. Overall, metallurgical carbonylation remains a unique and powerful technology for metal refining and materials engineering, combining chemical selectivity, process recyclability, and unmatched control over product design, purity and microstructure, as exemplified in the NVD (Nickel Vapor Deposition) products of Weber Manufacturing Technologies Inc.