Physical and chemical properties of nickel
Physical Properties
Nickel is a ductile and ductile metal that can be rolled into a thin foil. Tensile strength 40-50 kgf/mm2, tensile strength 8 kgf/mm2, yield strength 12 kgf/mm2; relative elongation 40%; modulus of normal elasticity 205 Gn/m2; Brinell hardness 600-800 Mn/m2. From absolute zero to 631°K, ferromagnetic physical properties are retained. Ferromagnetism is due to the structure of the outer electron shells. For the same reason, alloys and a number of nickel derivatives (oxides, and compounds with halogens.) are magnetically ordered with a ferro- and rarely a ferrimagnetic structure. Under normal conditions, the crystal lattice has a β-structure with a face-centered cubic structure (a = 3.5236. But after cathodic sputtering in an H2 atmosphere, the lattice acquires a dense hexagonal structure (a = 2.65 [pic], c = 4.32 [pic]), which converts to a cubic structure above t° 200 °C. Nickel with a cubic lattice has a specific gravity of 8.9 g/cm³, melting point 1453 °C; boiling point 3000 °C; specific heat capacity (t° 20 °C), melting point 20 °C. Heat capacity (t° 20 °C) 0.44 kJ/(kg-K); temperature coefficient of linear expansion 13.3x10-6 (0-100 °C); thermal conductivity at 25 °C 90.1 vml (m-K)[0.215 cal/(cm-sec-oC)].
Chemical properties
In terms of chemical activity, this metal stands between the noble metals and iron. In compounds, Ni is most often divalent. In the form of powder actively absorbs H2, CO, but when saturated with gases, loses its mechanical properties. When heated up to 500°C, it reacts with oxygen. Finely dispersed powder is pyrophoric - it is self-igniting in air. NiO oxide is greenish crystals, insoluble in water (the mineral bunsenite). When burned in sulfuric vapor, it forms sulfide Ni3 S2. Monosulfide NiS is made by heating NiO with sulfur. Nitrogen does not interact with this metal up to 1400 °C. Nitride Ni3 N is formed by heating powder Ni with nitrogen (t ° 445 ° C). In red-hot phosphorus vapor forms phosphide Ni3 P2. With arsenic, the compoundsNi5 As2, Ni3 As (the mineral maucherite) and NiAs. The NiAs lattice has a hexagonal arrangement of arsenic atoms, with Ni atoms squeezed in between. This structure is typical of many metallides. The unstable Ni3 C carbide is formed after long (hundreds of hours) carburizing (carburizing) of powder Ni in a CO atmosphere at 300 °C. The molten nickel easily dissolves carbon, which is released as graphite when cooled. With the loss of graphite, ductility decreases.
Chemical activity
Nickel is chemically less reactive than iron and is more resistant to acids and moisture. It reacts with organic acids only after a long exposure. In hydrochloric and sulfuric acids dissolves slowly, in dilute nitric acid - easily, and concentrated nitric acid passivates nickel, though to a lesser extent than Fe. Acid salts of nickel are bivalent. Almost all of them are highly soluble in water, where they give an acidic reaction. Only the salts of carbonic and phosphoric acids are poorly soluble. NiSO4 sulfate crystallizes as emerald green crystals of nickel vitriol NiSO4 x7H2 O. When calcined to 800 °C, almost all of the nickel salts decompose. This metal is resistant to strong alkalis, but dissolves in ammonia solution in the presence of (NH4)2 CO3 with the formation of intense blue solutions. Selective ammonia formation is used in the hydrometallurgical extraction of nickel from ores.
The chemical properties change with temperature. When heated, nickel reacts with SO2, NH4 and nitrogen oxides and, as a finely ground powder, with CO to form carbonyl Ni (CO)4. Thermal dissociation of the carbonyl produces the purest nickel.
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