The simple body is the most common metal and ferromagnetic material in everyday life, most often in the form of various alloys. Pure iron is a ductile transition metal, but the addition of very small quantities of additives considerably modifies its mechanical properties. Allied with carbon and with other additive elements it forms steels, whose sensitivity to thermomechanical treatments makes it possible to diversify

Iron belongs to the group of elements at the origin of transition metals, it shows characteristic analogies with ruthenium, osmium, cobalt and nickel.

Nuclear physico-chemistry, isotopes, frequency
Iron 56 is the heaviest stable nuclide resulting from the fusion of silicon by reactions during stellar nucleosynthesis, which in fact leads to nickel 56, which is unstable and gives 56Fe by two successive + decays; the elements of higher atomic number are synthesized by more energetic reactions intervening rather during the explosion of supernovas.

Nuclear properties
Iron core 56 has the lowest mass per nucleon of all nuclides but not the highest binding energy, due to a slightly higher proportion of protons than nickel 62 which has highest binding energy per nucleon9.

Iron 56 results from the natural decay of nickel 56, an unstable isotope produced in the heart of massive stars by fusion of silicon 28 during alpha cascade reactions which stop at nickel precisely because the latter has the binding energy highest nuclear per nucleon: continuing the fusion, for example to produce zinc 60, would consume energy instead of releasing it.

Main article: Isotopes of iron.
Iron has 28 known isotopes, with a mass number varying from 45 to 72, as well as six nuclear isomers. Among these isotopes, four are stable, 54Fe, 56Fe, 57Fe and 58Fe, 56Fe being by far the most abundant (91.754%), followed by 54Fe (5.845% possibly slightly radioactive with a half-life greater than 3.1 1022 years) , 57Fe (2.119%) and 58Fe (0.282%). The standard atomic mass of iron is 55.845 (2) u.

The most stable of the radioisotopes of iron is 60Fe with a half-life of 1.5 million years, followed by 55Fe (2.7 years), 59Fe (slightly less than 44.5 days) and 52Fe (8, 5 hours).

Occurrence and natural abundance
Iron is thus the most abundant element in the heart of giant red stars; it is also the most abundant metal in meteorites as well as in the nucleus of planets, like that of Earth.

Mineral iron is present in nature in pure form or in nickel-based alloys, most often of meteoritic origin but also in the form of terrestrial iron called "telluric". Too rare and especially disseminated, it is manufactured artificially by Man blacksmith and steelmaker and massively in certain Caucasian civilizations for more than three millennia from its main minerals. The chemical and mineral combinations involving iron are plethoric, but the real relatively pure ores with high iron content are much less common and often very localized in iron mines, most of which are known from high antiquity.

Iron is the 6th most abundant element in the Universe, it is formed as a "final element" of nuclear fusion, by fusion of silicon in massive stars. While it makes up about 5% (by mass) of the Earth's crust, the Earth's core is believed to be largely an iron-nickel alloy, making up 35% of the mass of the Earth as a whole. Iron is perhaps, in fact, the most abundant element on Earth or at least comparable (in just 2nd position) in mass to oxygen, but only the 4th most abundant element in the earth's crust.

Convection currents in the outer layer of the Earth's core (outer core), of the mainly iron-nickel liquid "alloy", are assumed to be the source of the Earth's magnetic field.

Functions in the biosphere
Iron plays a major role as a trace element or micronutrient for many species and as an element regulating the amplitude and dynamics of oceanic primary productivity, which makes it an essential component of marine biogeochemical cycles and marine carbon sinks10 .

Recent data show that the ocean iron cycle initially thought to be linked to the intake of iron-rich dust is actually much more complex, and closely coupled biogeochemically with major nutrients (carbon, nitrogen) 10. It was shown in 2017 that in iron-poor areas of the Antarctic, particulate iron from planing rocks by glaciers is an alternative source of iron that phytoplankton can exploit11. Studies have shown that certain phytoplankton do seem to benefit from a high level of CO2, but to assimilate this CO2 they also need iron; it has been speculated since the end of the 20th century that sowing the ocean with iron could help limit climate change. However, we discover that in most phytoplankton species this iron is assimilable only in the presence of carbonates. Problem: carbonates are destroyed by the acidification induced by the solubilization of CO2 in water12.

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