1. Industrial Application Common nickel industries include mining, smelting, electroplating, chemicals, petroleum refining, dyes, and coin manufacturing. Pure nickel (99.4%) is used for electroplating. Nickel alloys are used to make instruments and machine parts. Nickel powder is used as a catalyst. Nickel is also used to make alkaline batteries, porcelain enamels, etc. Nickel compounds commonly encountered in industry include nickel monoxide (NiO), nickel oxide (Ni2O3), nickel hydroxide [Ni(OH)2], nickel sulfate (NiSO4·7H2O), nickel chloride (NiCl2) and nickel nitrate [Ni(NO3)2·6H2O], etc. The gaseous nickel is carbonyl nickel [Ni(CO)4]. 2. Physical and chemical properties Nickel is a silvery white hard metal, mainly derived from sulfide ores and arsenic nickel ores. Among the inorganic compounds of nickel, oxides and hydroxides are insoluble or slightly soluble in water, while its salts are easily soluble in water.