Nickel

                               
Nickel carbonyl, [Ni(CO)4], is an extremely toxic gas and exposure should not exceed 0.007 mg M-3.

Nickel is found as a constituent in most meteorites and often serves as one of the criteria for distinguishing a meteorite from other minerals. Iron meteorites, or siderites, may contain iron alloyed with from 5 to nearly 20% nickel. The USA 5-cent coin (whose nickname is "nickel") contains just 25% nickel. Nickel is a silvery white metal that takes on a high polish. It is hard, malleable, ductile, somewhat ferromagnetic, and a fair conductor of heat and electricity.

                   Nickel is silvery-white. hard, malleable, and ductile metal. It is of the iron group and it takes on a high polish. It is a fairly good conductor of heat and electricity. In its familiar compounds nickel is bivalent, although it assumes other valences. It also forms a number of complex compounds. Most nickel compounds are blue or green. Nickel dissolves slowly in dilute acids but, like iron, becomes passive when treated with nitric acid. Finely divided nickel adsorbs hydrogen.

Characterstics:
Nickel is a hard, silvery-white metal, which is malleable and ductile. The metal can take on a high polish and it resists tarnishing in air.
Nickel is ferromagnetic and is a fair conductor of heat and electricity.
Most nickel compounds are blue or green.


Physical Properties:
The Physical properties of Nickel are the characteristics that can be observed without changing the substance into another substance. Physical properties are usually those that can be observed using our senses such as color, luster, freezing point, boiling point, melting point, density, hardness and odor. The Physical Properties of Nickel are as follows:

 *Color : Silvery-white metal
 *Phase : Solid
 *Conductivity: Fairly good conductor of heat and electricity
 *Ductility: It can be beaten into extremely thin sheets
 *Malleability: It’s capable of being shaped or bent
 *Luster: Exhibits a shine or glow
 *Hardness: Harder than iron
 *Ferromagnetic: Nickel is easily magnetized

Chemical Properties:
            They are the characteristics that determine how it will react with other substances or change from one substance to another. The better we know the nature of the substance the better we are able to understand it. Chemical properties are only observable during a chemical reaction. Reactions to substances may be brought about by changes brought about by burning, rusting, heating, exploding, tarnishing etc. The Chemical Properties of Nickel are as follows:

 *Corrosion: highly resistant to rusting and corrosion
 *Reactivity with Oxygen: Nickel metal does not react with air under ambient conditions but in the finely            dispersed state nickel it ignites spontaneously in air
 *Alloys: Stainless steel and copper-nickel alloy tubing
 *Compounds: Used for electroplating and to make nickel alloys


Reactions:
Reaction with air:mild, w/ht ⇒ NiO                                           Reaction with 6 M HCl:mild, ⇒ H2, NiCl2
Reaction with 15 M HNO3:passivated                                      Reaction with 6 M NaOH:none


Applications:
                   The major use of nickel is in the preparation of alloys. Nickel alloys are characterized by strength, ductility, and resistance to corrosion and heat. About 65 % of the nickel consumed in the Western World is used to make stainless steel, whose composition can vary but is typically iron with around 18% chromium and 8% nickel. 12 % of all the nickel consumed goes into super alloys. The remaining 23% of consumption is divided between alloy steels, rechargeable batteries, catalysts and other chemicals, coinage, foundry products, and plating.
Nickel is easy to work and can be drawn into wire. It resist corrosion even at high temperatures and for this reason it is used in gas turbines and rocket engines. Monel is an alloy of nickel and copper (e.g. 70% nickel, 30% copper with traces of iron, manganese and silicon), which is not only hard but can resist corrosion by sea water, so that it is ideal for propeller shaft in boats and desalination plants.


Nickel is used in corrosion-resistant alloys, such as stainless steel. (Stainless steel is the application in which most nickel is used.)
Tubing made from a copper-nickel alloy is used in desalination plants. This alloy is naturally resistant to corrosion by seawater and to biofouling.
Many coins contain nickel.
Nickel steel is used for burglar-proof vaults and armour plate.
Nickel is also used in batteries - for example NiCd (nickel-cadmium) rechargeable batteries - and in magnets.


Health Effects of Nickel:
                      Nickel is a compound that occurs in the environment only at very low levels. Humans use nickel for many different applications. The most common application of nickel is the use as an ingredient of steal and other metal products. It can be found in common metal products such as jewelry.

Foodstuffs naturally contain small amounts of nickel. Chocolate and fats are known to contain severely high quantities. Nickel uptake will boost when people eat large quantities of vegetables from polluted soils. Plants are known to accumulate nickel and as a result the nickel uptake from vegetables will be eminent. Smokers have a higher nickel uptake through their lungs. Finally, nickel can be found in detergents.

Humans may be exposed to nickel by breathing air, drinking water, eating food or smoking cigarettes. Skin contact with nickel-contaminated soil or water may also result in nickel exposure. In small quantities nickel is essential, but when the uptake is too high it can be a danger to human health.

An uptake of too large quantities of nickel has the following consequences:
- Higher chances of development of lung cancer, nose cancer, larynx cancer and prostate cancer
- Sickness and dizziness after exposure to nickel gas
- Lung embolism
- Respiratory failure
- Birth defects
- Asthma and chronic bronchitis
- Allergic reactions such as skin rashes, mainly from jewelry
- Heart disorders

Nickel fumes are respiratory irritants and may cause pneumonitis. Exposure to nickel and its compounds may result in the development of a dermatitis known as “nickel itch” in sensitized individuals. The first symptom is usually itching, which occurs up to 7 days before skin eruption occurs. The primary skin eruption is erythematous, or follicular, which may be followed by skin ulceration. Nickel sensitivity, once acquired, appears to persist indefinitely.

Carcinogenicity- Nickel and certain nickel compounds have been listed by the National Toxicology Program (NTP) as being reasonably anticipated to be carcinogens. The International Agency for Research on Cancer (IARC) has listed nickel compounds within group 1 (there is sufficient evidence for carcinogenicity in humans) and nickel within group 2B (agents which are possibly carcinogenic to humans). OSHA does not regulate nickel as a carcinogen. Nickel is on the ACGIH Notice of Intended Changes as a Category A1, confirmed human carcinogen.

                                                   Published by Ravindra.K(Mechanical Engineering)