The element nickel occurs naturally as a metal in many different compounds. It has a wide range of properties and is used in a variety of industrial applications. Nickel also has a wide range of oxidation states.

In compounds, nickel typically exists in the +2 oxidation state. Nickel oxide, NiO, is the ionic compound of nickel and oxygen. Nickel oxide adopts a NaCl structure with octahedral Ni2+ and O2- sites. This simple structure is commonly referred to as the rock salt structure. Like most binary metal oxides, it is often non-stoichiometric, meaning the Ni:O ratio deviates from 1:1. The stoichiometrically correct NiO is green, while the non-stoichiometric form is black.

ACUTE EXPOSURE: Nickel oxide can cause respiratory irritation. Chronic exposure may lead to nickel dermatitis, a type of skin irritation. It can also irritate the eyes and upper respiratory tract. Nickel oxide fumes are flammable and toxic when inhaled. Fires involving nickel oxide should be extinguished with dry chemical, carbon dioxide or Halon extinguishers.

CHRONIC EXPOSURE: This substance has been shown to be a human carcinogen. It can also induce skin sensitization. It can induce asthma and bronchoconstriction (narrowing of the airways in the lungs). Nickel oxide has been reported to cause nickel toxicity in laboratory animals.

DATA SOURCES: 1. National Toxicology Program Chemical Repository, Research Triangle Park, NC. 2. NTP Technical Report No. 506, 1993.

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