The use and characteristics of cadmium

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Submitted by admin on Mon, 10/22/2018 - 08:49

 

Cadmium is a silvery white shiny metal with a melting point of 320.9 ° C, a boiling point of 765 ° C and a density of 8650 kg / m 3 ; Resilience and ductility. Cadmium slowly oxidizes in humid air and loses its metallic luster. When heated, the surface forms a brown oxide layer. If heated above the boiling point, cadmium oxide fumes will be produced. At high temperatures, cadmium reacts strongly with halogen to form cadmium halide. It can also be directly combined with sulfur to form cadmium sulfide. Cadmium is soluble in acid but insoluble in alkali. The oxidation state of cadmium is +1, +2. Cadmium oxide and cadmium hydroxide have very low solubility, they are soluble in acid, but insoluble in alkali. Cadmium can form a variety of complex ions, such as Cd (NH3), Cd (CN), CdCl and the like.

Here are some common uses and characteristics of cadmium in life:

1. Used in the manufacture of alloys: cadmium as an alloy group can be formulated into many alloys, such as a hard copper alloy containing 0.5% to 1.0% cadmium, which has high tensile strength and wear resistance. Cadmium (98.65%) nickel (1.35%) alloy is the bearing material for aircraft engines. Many low melting point alloys contain cadmium, and the famous Wood fusible alloy contains 12.5% ​​cadmium.

2. Cadmium has a large thermal neutron capture cross section. Therefore, an alloy containing silver (80%) indium (15%) cadmium (5%) can be used as a (neutron absorption) control rod for the atomic reactor.

3. Cadmium compounds have been widely used in the manufacture of (yellow) pigments, plastic stabilizers, (television tube) phosphors, insecticides, fungicides, paints, and the like.

4. For electroplating, etc. Cadmium has a high oxidation potential, so it can be used as a protective film for iron, steel and copper. It is widely used for electroplating and anticorrosion. However, due to its high toxicity, this application has a tendency to shrink.

5. Used for rechargeable batteries: nickel-cadmium and silver-cadmium, lithium-cadmium batteries have the advantages of small size and large capacity.

6. Cadmium is also used in the manufacture of electrical alloys. For example, the electrical contacts in electrical switches mostly use silver cadmium oxide materials, which have the advantages of good electrical conductivity, small arcing, good anti-welding performance, etc. widely used in households. Electrical switches, automotive relays, etc. but because cadmium is toxic and subject to the European Union's Waste Electrical and Electronic Equipment Directive (WEEE) and the "Directive on the Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment" (RoHS) The influence  the silver cadmium oxide material in the electrical switch is gradually replaced by environmentally friendly materials such as silver tin oxide, silver nickel material.

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