Nickel oxide is an inorganic substance with chemical formula of NiO and molecular weight of 74.71. It is a green black cubic crystal and insoluble in water. The color turns yellow when heated, which is obtained by the action of nickel and oxygen at more than 400 ºC, or by the pyrolysis of nickel carbonate at 350 ºC. It is used for making alloys, batteries, glasses, enamels, ceramics, electronic components, nickel salts and catalysts.