Nickel Metal Hydride

Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow to react with air under standard conditions because a passivation layer of nickel oxide forms on the surface that prevents further corrosion. Even so, pure native nickel is found in Earth's crust only in tiny amounts, usually in ultramafic rocks, and in the interiors of larger nickel–iron meteorites that were not exposed to oxygen when outside Earth's atmosphere.

Meteoric nickel is found in combination with iron, a reflection of the origin of those elements as major end products of supernova nucleosynthesis. An iron–nickel mixture is thought to compose Earth's outer and inner cores.

Use of nickel (as natural meteoric nickel–iron alloy) has been traced as far back as 3500 BCE. Nickel was first isolated and classified as an element in 1751 by Axel Fredrik Cronstedt, who initially mistook the ore for a copper mineral, in the cobalt mines of Los, Hälsingland, Sweden. The element's name comes from a mischievous sprite of German miner mythology, Nickel (similar to Old Nick), who personified the fact that copper-nickel ores resisted refinement into copper. An economically important source of nickel is the iron ore limonite, which is often 1–2% nickel. Other important nickel ore minerals include pentlandite and a mix of Ni-rich natural silicates known as garnierite. Major production sites include the Sudbury region, Canada (which is thought to be of meteoric origin), New Caledonia in the Pacific, and Norilsk, Russia.

Nickel is one of four elements (the others are iron, cobalt, and gadolinium) that are ferromagnetic at about room temperature. Alnico permanent magnets based partly on nickel are of intermediate strength between iron-based permanent magnets and rare-earth magnets. The metal is used chiefly in alloys and corrosion-resistant plating. About 68% of world production is used in stainless steel. A further 10% is used for nickel-based and copper-based alloys, 9% for plating, 7% for alloy steels, 3% in foundries, and 4% in other applications such as in rechargeable batteries, including those in electric vehicles (EVs). Nickel is widely used in coins, though nickel-plated objects sometimes provoke nickel allergy. As a compound, nickel has a number of niche chemical manufacturing uses, such as a catalyst for hydrogenation, cathodes for rechargeable batteries, pigments and metal surface treatments. Nickel is an essential nutrient for some microorganisms and plants that have enzymes with nickel as an active site.

Properties

Atomic and physical properties

Nickel is a silvery-white metal with a slight golden tinge that takes a high polish. It is one of only four elements that are ferromagnetic at or near room temperature; the others are iron, cobalt and gadolinium. Its Curie temperature is , meaning that bulk nickel is non-magnetic above this temperature. The unit cell of nickel is a face-centered cube with the lattice parameter of 0.352 nm, giving an atomic radius of 0.124 nm. This crystal structure is stable to pressures of at least 70 GPa. Nickel is hard, malleable and ductile, and has a relatively high electrical and thermal conductivity for transition metals. The high compressive strength of 34 GPa, predicted for ideal crystals, is never obtained in the real bulk material due to formation and movement of dislocations. However, it has been reached in Ni nanoparticles.

Electron configuration dispute

Nickel has two atomic electron configurations, r3d 4s and r3d 4s, which are very close in energy; rdenotes the complete argon core structure. There is some disagreement on which configuration has the lower energy. Chemistry textbooks quote nickel's electron configuration as r4s 3d, also written r3d 4s. This configuration agrees with the Madelung energy ordering rule, which predicts that 4s is filled before 3d. It is supported by the experimental fact that the lowest energy state of the nickel atom is a 3d 4s energy level, specifically the 3d(F) 4s F, ''J'' = 4 level.NIST Atomic Spectrum Database
To read the nickel atom levels, type "Ni I" in the Spectrum box and click on Retrieve data.

However, each of these two configurations splits into several energy levels due to fine structure, and the two sets of energy levels overlap. The average energy of states with r3d 4s is actually lower than the average energy of states with r3d 4s. Therefore, the research literature on atomic calculations quotes the ground state configuration as r3d 4s.

Isotopes

The isotopes of nickel range in atomic weight from 48  u () to 78 u ().

Natural nickel is composed of five stable isotopes, , , , and , of which is the most abundant (68.077% natural abundance).

Nickel-62 has the highest binding energy per nucleon of any nuclide: 8.7946 MeV/nucleon. Its binding energy is greater than both and , more abundant nuclides often incorrectly cited as having the highest binding energy. Though this would seem to predict nickel as the most abundant heavy element in the universe, the high rate of photodisintegration of nickel in stellar interiors causes iron to be by far the most abundant.

Nickel-60 is the daughter product of the extinct radionuclide (half-life 2.6 million years). Due to the long half-life of , its persistence in materials in the Solar System may generate observable variations in the isotopic composition of . Therefore, the abundance of in extraterrestrial material may give insight into the origin of the Solar System and its early history.

At least 26 nickel radioisotopes have been characterized; the most stable are with half-life 76,000 years, (100 years), and (6 days). All other radioisotopes have half-lives less than 60 hours and most these have half-lives less than 30 seconds. This element also has one meta state.

Radioactive nickel-56 is produced by the silicon burning process and later set free in large amounts in type Ia supernovae. The shape of the light curve of these supernovae at intermediate to late-times corresponds to the decay via electron capture of to cobalt-56 and ultimately to iron-56. Nickel-59 is a long-lived cosmogenic radionuclide; half-life 76,000 years. has found many applications in isotope geology. has been used to date the terrestrial age of meteorites and to determine abundances of extraterrestrial dust in ice and sediment. The half-life of nickel-78 was recently measured at 110 milliseconds, and is believed an important isotope in supernova nucleosynthesis of elements heavier than iron. Ni, discovered in 1999, is the most proton-rich heavy element isotope known. With 28 protons and 20 neutrons, Ni is "doubly magic", as is Ni with 28 protons and 50 neutrons. Both are therefore unusually stable for nuclei with so large a proton–neutron imbalance.

Nickel-63 is a contaminant found in the support structure of nuclear reactors. It is produced through neutron capture by nickel-62. Small amounts have also been found near nuclear weapon test sites in the South Pacific.

Occurrence

On Earth, nickel occurs most often in combination with sulfur and iron in pentlandite, with sulfur in millerite, with arsenic in the mineral nickeline, and with arsenic and sulfur in nickel galena. Nickel is commonly found in iron meteorites as the alloys kamacite and taenite. Nickel in meteorites was first detected in 1799 by Joseph-Louis Proust, a French chemist who then worked in Spain. Proust analyzed samples of the meteorite from Campo del Cielo (Argentina), which had been obtained in 1783 by Miguel Rubín de Celis, discovering the presence in them of nickel (about 10%) along with iron.

The bulk of nickel is mined from two types of ore deposits. The first is laterite, where the principal ore mineral mixtures are nickeliferous limonite, (Fe,Ni)O(OH), and garnierite (a mixture of various hydrous nickel and nickel-rich silicates). The second is magmatic sulfide deposits, where the principal ore mineral is pentlandite: .

Indonesia and Australia have the biggest estimated reserves, at 43.6% of world total.

Identified land-based resources throughout the world averaging 1% nickel or greater comprise at least 130 million tons of nickel (about the double of known reserves). About 60% is in laterites and 40% in sulfide deposits.

On geophysical evidence, most of the nickel on Earth is believed to be in Earth's outer