Cadmium (Cd, atomic number 48) is a soft, silvery-white metal. Its classification as a metallic element means it is an electrical conductor. This material is characterized by its malleability and relatively low melting point, sharing chemical similarities with other elements in Group 12 like zinc and mercury.
The Mechanism of Metallic Electrical Conduction
The ability of cadmium to conduct electricity is rooted in the unique bonding structure found in all metallic solids. Metal atoms arrange themselves into a regular, repeating crystalline lattice structure. Unlike non-metals, metal atoms readily give up their valence electrons. These released electrons become delocalized, forming a “sea of electrons” that moves freely throughout the lattice of positively charged metal ions. When an external voltage is applied, it creates an electric field that causes these mobile electrons to drift in a unified direction, constituting an electric current.
Assessing Cadmium’s Conductive Performance
While cadmium is a conductor, its performance differs significantly from metals typically used in electrical wiring. Electrical flow is assessed using resistivity, which measures a material’s opposition to current, or its inverse, conductivity. Copper, the standard for wiring, has a resistivity of approximately \(1.7 \times 10^{-8}\) Ohm-meters. The resistivity of pure cadmium is considerably higher, sitting around \(6.0 \times 10^{-8}\) Ohm-meters. This means cadmium’s electrical conductivity (about \(1.67 \times 10^7\) Siemens per meter) is roughly three and a half times less efficient than copper’s (nearly \(5.88 \times 10^7\) Siemens per meter). Therefore, cadmium is not used for bulk applications like power transmission lines where maximum efficiency is the primary concern, but its conductivity is sufficient for specialized tasks.
Key Industrial Applications of Cadmium’s Properties
Cadmium’s combination of electrical properties, corrosion resistance, and chemical reactivity makes it suitable for niche industrial uses.
Nickel-Cadmium Batteries
The most recognized application is its role in nickel-cadmium (NiCd) batteries. These batteries utilize the reversible chemical reaction of cadmium electrodes to store and release electrical energy. They are known for their long cycle life and dependable performance, even in extreme temperatures.
Protective Plating and Alloys
Cadmium is also used as a protective coating through electroplating, particularly on steel components. Cadmium plating is highly valued in the aerospace and military sectors because it provides superior corrosion resistance in saline environments. It also offers a low coefficient of friction and good lubricity, making it an excellent choice for fasteners, electrical connectors, and switches. Furthermore, the metal is used in specialized alloys, such as cadmium-copper, where a balance of high mechanical strength and good electrical flow is needed, such as in overhead catenary wires for railways.