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As a non-caking salt used for nickel plating, each molecule of the nickel sulfate crystal is usually hydrated with six molecules of water. Known also as nickelous sulfate and sulfuric acid nickel (2+) salt, the mineral is sometimes used in homeopathic remedies for treating seborrheic dermatitis and chronic dandruff.
The prismatic blue or emerald green crystals, nicknamed "blue salt", feature 2 hydrogens, 4 oxygens, 1 sulfur, and 1 nickel atom plus six oxygens and 12 hydrogens for the hexahydrate group. The molecular weight is given as 262.86 with a melting point of 53.3 degrees Celsius and a boiling point of 840 degrees Celsius. The crystals form two phases: the alpha-form, which is a blue tetragonal geometry with a refractive index of 1.511 and the beta-form, which is a green monoclinic crystal at a lower refractive index of 1.487. At 100 degrees Celsius, the nickel salt loses five of its water molecules, at 103 degrees Celsius, all six waters of hydration are removed from the nickel sulfate, and at 280 degrees Celsius, a green-yellow anhydrous salt is formed. In water, nickel sulfate forms an acidic aqueous solution with pH of about 4.5 and it is odorless with a sweet, astringent taste.
Natural crystals of hydrated nickel sulfate, known as retgersite, are found as a secondary mineral in nickel-bearing deposits, and were first discovered in Peru around 1948. The attractive but fragile tetragonal trapezhedral crystals can feature as many as 46 to 54 faces, perfect cleavage, and are highly sought as prized specimens by rock hounds. In the laboratory, crystals of nickel sulfate are grown by supercooling, and large clusters are grown first by supercooling and then by evaporation. Nickel sulfate hexahydrate, a salt created by combining sulfuric acid with nickel, is utilized in metal plating, blackening zinc and brass, and as a fixative or mordant in dyeing and printing textiles.
As part of the modern nickel ore refining process and recovery of spent metal processing solutions, crystal nickel sulfate is created. Mirror-like finishes and corrosion resistance are imparted to steel, aluminum, and plastic substrates using nickel sulfate, most often in combination with electrodeposited chromium. Industrial uses include the manufacturing of organic nickel salts such as nickel ammoninium sulfate, ceramics, coatings, and as a catalyst for nickel and nickel carbonate reactions. In the high tech world, nickel electroplating is used to create stampers or molds that produce compact discs, and the molds and dies used to manufacture modern aircraft wing sections. Nickel foam derived from blue salt is used for battery electrodes, designer jewelry, and microdevices targeted for optical and medical applications. Nickel salts are considered highly toxic when ingested or injected, and are a suspected carcinogen. Some people develop a contact allergy to nickel and nickel sulfate, resulting in dermatitis.
Omar Alvarado, Thomas J. Fellers and Michael W. Davidson - National High Magnetic Field Laboratory, 1800 East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, 32310.
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