Preparation

Nickel (II) oxide is prepared by heating pure nickel powder with oxygen at a temperature above 400°C. In some commercial processes, green Nickel (II) oxide is made by heating a mixture of nickel powder and water in air at 1,000°C. Adding some Nickel (II) oxide to the above mixture enhances the rate of reaction. An alternative method of preparation of the green oxide involves thermal decomposition of an oxo acid salt of nickel at elevated temperatures. Thus, nickel nitrate, nickel sulfate or, more conveniently, nickel carbonate when heated at 1,000°C, yields the green oxide. The black oxide, on the other hand, is produced at a lower temperature from incomplete calcination of the carbonate or nitrate salt at 600°C. The oxygen content of the black form is slightly greater than its green counterpart.

Reactions

Several nickel salts are obtained by reactions of nickel oxide with mineral acids. Thus, the reaction of black nickel oxide with hot dilute sulfuric acid forms nickel sulfate, NiSO4?6H2O. Similarly, dilute nitric acid, hydrochloric, and hydrobromic acids when heated react with the black form of nickel oxide to yield corresponding nickel salts as hexahydrates. Heating nickel oxide with hydrogen, carbon, or carbon monoxide reduces it to metallic nickel. Nickel oxide combines with sodium or potassium hydroxide at elevated temperatures (>700°C), forming sodium or potassium nickelate; i.e., K2NiO2: NiO + 2NaOH → Na2NiO2 + H2O

Hazard

Confirmed carcinogen.

Flammability and Explosibility

Nonflammable

Safety Profile

Confirmed carcinogen with experimental carcinogenic and tumorigenic data. Poison by intratracheal, intravenous, and subcutaneous routes. Mutation data reported. Can react violently with fluorine, hydrogen peroxide, hydrogen sulfide, iodine, barium oxide + air. See also NICKEL COMPOUNDS.

Physical Properties

Green cubic crystals; transforms to a grayish black octahedral form, known as black oxide, when strongly ignited; black oxide has a metallic luster; density of green oxide is 6.72 g/cm3; Mohs hardness 5.5; melts at 1955°C; insoluble in water; soluble in acids at ordinary temperatures; black form dissolves in hot acids.

General Description

Nickel(II) oxide (NiO) is a metal oxide based nanomaterial with a good semiconducting property. Nanosized nickel oxide can be found in a variety of morphologies which include nanoflowers, spheres, wires, and tubes. It exhibits high performance in applications which require charge transfer and charge transport based processes. It can be prepared by a variety of physical and thermal methods such as sol-gel, hydrothermal and solvothermal techniques.