NICKEL

Name: Nickel

Symbol: Ni

Group: 10

Period: 4

Block: d

Category: Transition Metals

Atomic Number: 28

Atomic Mass: 58.693 u

Electrons per Shell: 2, 8, 16, 2

Electronegativity: 1.91

Density: 8.908 g/cc

Melting Point: 1455ºC

Boiling Point: 2913ºC

Thermal Conductivity: 91 W (m·K)

Electrical Conductivity: 1.4 × 10^7 S/m

Magnetic Order: Ferromagnetic

Ordinary State: Solid

Oxidation States: -2, -1, 1, 2, 3, 4

Mohs Hardness: 4

Vickers hardness: 638 MPa

Brinell hardness: 700 MPa

Most stable isotopes: Ni-58 (68.077%), Ni-60 (26.223%), Ni-61 (1.140%), Ni-62 (3.635%), Ni-64 (0.926%)

Discoverer: Axel Friedrik Cronstredt, Swedish (1751)

Nickel is a particularly interesting transition metal, unique in that it combines properties of both iron and copper, yet is not identical to either. Its cosmic origin dates back to the nucleosynthetic processes of supernovae, where it is formed in abundance and ejected at extreme speeds, amalgamating with iron and giving rise to metallic mixtures that, over time, can be found in ferrous meteorites and terrestrial minerals that have undergone multiple geological transformations. In the Earth's crust, nickel frequently occurs alongside cobalt and copper, and most notably in minerals that also host platinum group elements (Pt, Pd, Rh, Ir, Os, Ru), considered precious metals. Although it is often perceived as less common than copper, its abundance in the crust is greater, and geophysical estimates suggest that its concentration increases dramatically towards the Earth's mantle and core. However, its economic exploitation depends on specific, high-concentration deposits that are relatively rare and geopolitically relevant.

In modern metallurgy, nickel is recognized as the alloying element par excellence: a true "brother" to iron that, however, exhibits a balance of properties intermediate between iron and copper. Its high ductility and malleability contrast with the toughness of iron, which, despite offering advantages in formability and corrosion resistance, limits its use as a pure structural material in components subjected to high mechanical stresses. Even so, its ability to form alloys with excellent mechanical properties, thermal stability, and chemical resistance places it at the top of the most valuable non-precious base metals. Alloys such as austenitic stainless steels, nickel-based superalloys (Inconel, Hastelloy, Monel), and low-alloy nickel steels owe their properties of strength, ductility, and durability primarily to this element.

The formal discovery of nickel took place in 1751, when Axel Fredrik Cronstedt, a student of the Swedish Georg Brandt—discoverer of cobalt—managed to isolate it from nickel-bearing copper minerals. Despite its abundance, the recognition of nickel as a distinct element was delayed compared to cobalt due to the difficulty in purifying it and confusion with other metals. This explains why, although civilizations such as the Chinese may have already handled high-ppurity nickel in the form of "white copper," it was not unequivocally identified until the 18th century.

Its appearance resembles that of copper, though it is lighter, with a silver sheen and greater hardness. It is easily rolled and drawn, which, along with its oxidation resistance, explains its historical use in protective and ornamental coatings. From a biological standpoint, nickel is an atypical case in the first series of transition metals: situated between chromium (Z = 24) and zinc (Z = 30), it does not play known essential functions in living organisms, and although the metal itself is not particularly toxic, certain salts and compounds can cause allergic skin reactions in susceptible individuals. Isolated and often misinterpreted studies in non-specialized media have exaggerated this risk, presenting nickel as a severe danger when, in reality, its health impact depends on the chemical form and prolonged exposure.

From a nuclear perspective, nickel occupies a privileged position. With an atomic number Z = 28, it is a "magic number" element—a particularly stable configuration of protons—which contributes to the high binding energy per nucleon of its isotope Ni⁶², the most stable known in nature. Nickel-58 and nickel-60 are the most abundant isotopes on Earth, formed in alpha-capture processes in late stages of stellar evolution. In supernovae, the primordial isotope Ni⁵⁶ is generated in large quantities, but it is unstable and decays first into Co⁵⁶ and then into Fe⁵⁶, the most common stable nucleus in the Universe. These processes explain why nickel, along with iron and cobalt, is relatively abundant on a cosmic scale.

The origin of its name has Central European folkloric roots. German miners in the 18th century called a reddish mineral that looked like copper but did not yield metallic copper when smelted, "kupfernickel" ("goblin Nick's copper"), producing instead a useless substance according to their knowledge at the time. This "Nick" or "Old Nick" was depicted as a gnome or mischievous spirit who tricked miners, depriving them of their "good metal." Over time, the name was shortened to "nickel" and became universal in scientific language. Interestingly, cobalt shares a similar etymological anecdote, derived from "kobold," another subterranean spirit who substituted iron ore with an unknown metal to torment mine workers.

Thus, amidst mining myths, enlightened discoveries, and nuclear processes occurring at billions of degrees inside stars, nickel has become a silent pillar of contemporary metallurgy, supporting everything from chemical reactors to aircraft turbines, and from medical prostheses to circulating coins.

Nickel, an opaque white metal with a subtle, barely perceptible golden tint, shares visual similarities with iridium but is distinguished by its soft, silky feel, typical of soft metals. Easy to polish, it combines a hardness comparable to that of pure iron (4 on the Mohs scale) with remarkable toughness, ductility, and malleability superior to its chemical "brother." This malleability, although it might seem like a disadvantage, is a key strength, as it allows nickel to be hardened through alloys, unlike brittle metals that hardly acquire toughness. Its ability to deform easily makes it ideal for forming processes, while its excellent impact resistance positions it as a robust material.

Although its melting point is lower than iron's, nickel surpasses iron and common steels in resistance to extreme temperatures, both high and low, and to sudden temperature changes. Unlike iron and most steels, which become brittle below 0 °C, nickel maintains its toughness even near absolute zero (-273 °K). Its alloys, known as superalloys, outperform the best grades of steel, especially in demanding applications like aeronautics and submarine construction. This versatility elevates its value, with a price higher than aluminum and competitive with copper, skyrocketing in wartime to three or four times the latter due to its strategic importance.

Nickel frequently appears associated with platinum group metals (PGM), such as palladium and platinum, with which it shares group 10 of the periodic table. Although it is not considered a PGM due to its higher reactivity, it shares certain chemical and physical similarities with these metals, as well as with iron and copper. Unlike platinum group metals, nickel does not form stable carbides at any temperature and is not used as a catalyst, a characteristic function of PGMs. Its combination of physical properties, thermal resistance, and ability to form alloys makes it an indispensable material in critical industries, from metallurgy to advanced technology.

Nickel (Ni) extraction is simpler than iron and cobalt, but more complex than copper. This ease of extraction is related to its position on the periodic table, since as elements move closer to the right side, they become less reactive and, therefore, easier to isolate and more resistant to corrosion.

Unlike iron and copper, there isn't a single dominant ore for obtaining nickel; instead, it is extracted from a variety of compounds. Native nickel is extremely rare and is usually found in meteorites along with iron. Nickel's high corrosion resistance places it closer to the category of metals that could form nuggets in the Earth's crust, a phenomenon more common in chemically nobler metals like copper.

The main nickel ore is niccolite (NiAs), a nickel arsenide. However, nickel more often appears in minerals of complex composition or in combination with iron and copper. Frequently, nickel is a byproduct of iron and copper deposit exploitation. Nickel has a strong affinity for sulfur, which explains why its ores are predominantly sulfides rather than oxides. Nickel oxides are thermodynamically unstable, unlike those of iron and other elements preceding it in the periodic table, such as hematite (Fe₂O₃), eskolaite (Cr₂O₃), and rutile (TiO₂). Although in the Goldschmidt classification nickel is siderophile, its strong association with sulfur also gives it chalcophile characteristics.

Nickel is extracted from its ores through a roasting process in reverberatory furnaces. It is easily reducible with coke and does not require limestone to prevent carbide formation, as it does not form binary compounds with carbon. The Mond process allows for obtaining high-purity nickel (99.99% or more) in the form of small solid spheres.

The main global nickel reserves are found in Australia, Brazil, Russia, New Caledonia, and Cuba. However, the largest current producers are the Philippines, Russia, and Canada. Like all metals, nickel is a non-renewable resource, making it a strategic commodity for nations with large reserves.

Nickel stands out for its remarkable corrosion resistance under a wide variety of conditions, with its ability to withstand alkalis, even in a molten state, being its greatest strength. This resistance exceeds that of other base metals and even some noble and precious metals, making it an exceptional material for extreme chemical environments. Regarding strong acids, nickel shows moderate tolerance to hydrochloric and sulfuric acids, although nitric acid rapidly attacks it. A distinctive feature is its interaction with hydrofluoric acid, in response to which it forms a passivating layer that prevents subsequent corrosion, a characteristic shared by few metals. In freshwater, nickel exhibits optimal resistance for extended periods, and although less effective in seawater, its combination with copper generates alloys that are extraordinarily resistant to saline environments, widely used in desalination towers. In this respect, nickel more closely resembles copper than iron in terms of chemical behavior. In its pure form, nickel develops a passivating oxide layer that protects its surface, although its characteristic metallic luster with a slight golden tinge dulls over time. This unique hue is recognizable even in alloys such as stainless steel, where nickel provides a distinctive hue, less lustrous than that of chromium or chromium-molybdenum steels.

Nickel is not flammable under normal conditions, but it can burn as a fine powder or thin wires in the presence of pure oxygen, unlike what happens with ambient oxygen, as erroneously stated in other sources. When it corrodes, it forms a green patina similar to that of copper, visible in small spots. Its resistance to sweat, salts, organic acids, and other corrosive agents is sufficient for use in its pure state, although alloys with copper are preferred for their superior mechanical properties, lower cost, non-magnetic nature, and greater corrosion resistance. However, nickel is vulnerable in highly oxidizing media, such as pure halogens (except fluorine) and concentrated nitric acid, which vigorously attack it even in its massive form. 

Nickel (Ni) is a versatile metal of great importance in metallurgy due to its unique properties. Its applications focus on the production of alloys, where its ability to improve corrosion resistance, hardness, toughness, and high-temperature strength makes it indispensable. The majority of nickel produced worldwide is used in the manufacture of stainless steel, one of the most widely used alloys in modern industry. Nickel acts as a key alloying element that stabilizes the austenitic crystal structure of steel, which not only improves its corrosion resistance but also gives it ductility and the ability to be cold worked. Austenitic stainless steels, such as the popular Type 304, which contains approximately 8% nickel, are the basis of countless products, from kitchenware and medical equipment to architectural components and storage tanks for the chemical industry. Their resistance to rust and staining makes them the ideal choice for environments where hygiene and durability are crucial.

Nickel is also a fundamental component in the production of superalloys, which are alloys designed to operate under extreme conditions of high temperature and mechanical stress. These alloys are primarily used in the aerospace industry and in power generation. Pure metals, when heated, tend to soften and lose their strength. However, nickel-based superalloys, such as the Inconel series and Waspaloy, maintain their structural integrity even at temperatures exceeding 1000 °C. This makes them essential for manufacturing critical components in jet engines, gas turbines, and nuclear reactors, where safety and performance depend on the ability of materials to withstand hostile environments. The presence of nickel in these alloys contributes to the formation of a hardened matrix structure that resists creep deformation and thermal fatigue, ensuring reliable and prolonged operation.

In addition to stainless steels and superalloys, nickel is used in a wide variety of other alloys. It is a main component in copper-nickel alloys, such as cupronickel, which are used in coin minting (for example, in 1 and 2 euro coins), in the naval industry to manufacture pipes and fittings that resist seawater corrosion, and in the manufacture of musical instruments. Nickel-copper alloys also have excellent resistance to thermal shock and fatigue, making them useful in heat exchangers and condensers. On the other hand, nickel-chromium alloy is known for its high electrical resistance and its ability to withstand high temperatures, making it the preferred material for heating elements in toasters, ovens, and electric heaters. This alloy may contain a small addition of iron (Fe), but the percentage of nickel remains dominant. Nickel is also used in electroplating, an electrolytic coating process that deposits a thin layer of metal onto another object. Nickel plating is applied to protect the surface of an underlying material from corrosion and wear, as well as to provide a bright aesthetic finish. This process is common in the automotive industry and in the manufacture of hardware items. Nickel coating offers superior protection to that of other less noble metals and can be polished to a high luster, making it highly valued for both its functionality and its appearance. In summary, nickel is a pillar of modern metallurgy, whose versatility and unique properties make it fundamental for the development of advanced materials that drive key sectors of global industry.

Nickel, often shrouded in prejudice and misperception, is a transition metal whose reputation has oscillated between industrial recognition and popular rejection. It is true that it can cause allergies in some people, similar to what happens with precious metals such as silver or gold, although less frequently with the latter. It is also true that, in excessive doses and under specific chemical forms, it can be carcinogenic; however, this risk is limited to ingestion or direct exposure to dangerous nickel compounds, not to everyday contact with the pure metal. In its metallic state, it is not classified as toxic, much less as poisonous. Examples of true toxicity, such as nickel tetracarbonyl, respond to the properties of the compound itself and not the metallic element. Paradoxically, nickel is one of the elements most resistant to radiation, both by fusion and fission, making it valuable in environments with high radiation exposure.

One of the factors that has most contributed to its bad reputation is low-cost costume jewelry made with deficient alloys, especially those used in earrings and other pieces that remain in prolonged contact with the skin. In these pieces, nickel content can be released easily due to the absence of effective passivating layers, such as those formed by chromium or chromium-molybdenum. Thus, allergic reactions are more likely to be triggered. However, this circumstance does not occur in high-quality alloys, such as AISI 316 or 316L austenitic stainless steel, tungsten carbide, or modern "cobalt rings," where the high proportion of chromium blocks the release of nickel. In contrast, copper-zinc-nickel alloys, also known as alpaca or "German silver," lack this passive protection and can release the metal, causing irritation in sensitive individuals.

Even in white gold jewelry, controversy has arisen. Higher quality white gold alloys have historically contained nickel for its mechanical properties and its ability to lighten the gold's tone, but have been replaced in many cases by palladium, a more expensive noble metal that, ironically, belongs to the same chemical family as nickel. The change, partly justified by allergies in sensitive individuals, has also been driven by commercial strategies.

In the industrial sector, concern about nickel focuses not only on health but also on economics. Although it is one of the most common base metals—even more abundant than copper—its price is high due to its high demand and strategic nature. It does not reach the critical level of military resources like tungsten or tantalum, but it remains fundamental for metallurgical, chemical, and energy industries. Emerging countries and established powers, such as China, Saudi Arabia, or Malaysia, acquire it in large quantities to support their production of special steels, resistant alloys, and high-tech components.

Nickel is irreplaceable in many aspects, but alternatives have been explored. Manganese is its most direct substitute in austenitic steels, given that it also promotes the gamma phase (austenite) of iron. However, its gamma-forming capacity is inferior, requiring much larger proportions to achieve the same effect, which increases cost and complicates processing. Furthermore, the combination of manganese with high chromium and molybdenum content makes the final alloy more expensive. In Japan, nitrogen-bearing steels, completely free of nickel, have been developed to maintain the austenitic structure, although their manufacturing is complex and costly due to the difficulty of dissolving nitrogen in the metal matrix. In Colombia, thanks to the local availability of manganese, an alternative steel called Fermanganal, composed mainly of iron, manganese, and aluminum, was produced, representing a notable example of technological substitution.

In health terms, the risk of nickel allergy is due to the formation of surface sulfates and carbonates under specific conditions, rather than the pure metal. In quality stainless steels, the passive layer of chromium trioxide acts as an effective barrier, preventing contact between nickel and the skin. In fact, a person allergic to nickel can wear a 316L steel ring without problems, provided it is not damaged or corroded. However, for internal implants, cobalt-chromium alloys or titanium are preferred, which offer superior biocompatibility. The key lies in the integrity and stability of the passivating layer: if it remains intact, nickel remains inert to the human organism.

In summary, nickel is not the villain that many popular beliefs portray. Its dangerousness depends on the context, the chemical form, and the quality of the alloy in which it is found. While in jewelry and personal uses, the possibility of allergy in predisposed individuals must be monitored, in industrial and metallurgical applications, it remains an irreplaceable resource due to its unique ability to stabilize austenite, resist corrosion, and withstand extreme conditions, both thermal and radioactive.