Property of nickelThe position of nickel in the periodic table determines a series of physical and chemical properties of nickel and its compounds. Many of the physical and chemical properties of nickel are similar to those of cobalt and iron. Because it is adjacent to copper, it is closer to copper in terms of sulfur affinity and oxygen affinity, and will lose its metallic luster and become darker. 1.1 Physical properties of nickel Nickel is a silvery-white metal. Its physical properties are quite consistent with those of metal cobalt and iron. The main manifestations are: A. The specific gravity of nickel: 8.908 at 20°C, and the reliable value is 8.9~ 8.908, the specific gravity of liquid nickel at the melting point is 7.9. B. The specific heat of nickel: varies from 420 to 620 Joules/kg·K in the temperature range of 0 to 1000°C, with a significant peak at the Curie point or its attachment, and the ferromagnetism is lost at this temperature. C. The resistance of nickel: at 20°C, it varies from 6.8 to 9.9 microohm centimeters (10 to 8Ωm) according to its purity of 99.99 to 99.8%. Although nickel-based alloys are widely used in thermoelectric elements, pure nickel has virtually no such use due to oxidation. D. The thermoelectricity of nickel is different from that of iron, copper, silver, gold and other metals. It is more negative than platinum, so the current at the cold end flows from platinum to nickel. Therefore, when nickel is used as a thermoelectric element, a high electromotive force can be generated. E. Nickel is magnetic and is the main component of many magnetic materials (from soft magnetic alloys with high magnetic permeability to permanent magnet alloys with high coercivity), and its content is usually 10 to 20%. 1.2 Chemical properties of nickel Metal nickel is one of the ferromagnetic metals in Group 8 of the periodic table of elements. It has an atomic number of 28, an atomic weight of 58.71, a melting point of 1453±1°C, and a boiling point of 2800°C. Naturally occurring metallic nickel has five stable isotopes: Ni5867.7%, Ni6026.2%, Ni611.25%, Ni623.66%, and Ni641.66%. Its main chemical properties are: A. Dilute sulfuric acid and hydrochloric acid can slowly dissolve nickel, and dilute nitric acid reacts quickly with nickel, but concentrated nitric acid passivates nickel, and nickel and alkali have no effect. Nickel is resistant to all organic compounds. B. Pure nickel has a silvery white luster. When it interacts with water vapor and oxygen in the air, a NiO film is formed on the nickel surface to prevent further oxidation. Sulfur-containing gases severely corrode nickel, especially when the crystallization temperature of nickel and nickel sulfide Ni3S2 is above 643oC. Nickel has no significant effect on chlorine below 500°C. C. The electrode potential of nickel is -0.227 volts at 20°C and -0.231 volts at 25°C. If there are a small amount of impurities in the solution, especially when sulfur is present, nickel will be significantly passivated. D. Since the surface of nickel can form a dense nickel oxide film, it dissolves very slowly in dilute acid and is easily passivated in strong oxidizing media. It also has good corrosion resistance to alkali solutions, salt water and organic matter.