Alloys and Cemented Carbides

Cobalt powder is an important component in cemented carbides (hard metals). The product and its use of cobalt are described in Chapter 26 Tungsten. 

Above a certain temperature, the Curie temperature, the ferromagnetic properties are lost Cobalt is a ferromagnetic metal with a remarkably high Curie temperature as can be seen from Table 30.3. 

The element cobalt is inclined to form complexes and to bind different ligands to these complexes. This makes the metal suitable as a catalyst An important industrial process using cobalt as a catalyst is the removal of sulfur from oil by hydrodesulfurization. In this case the catalyst is composed of an inert carrier material, alumina, and a mixture of cobalt and molybdenum oxides. The organically bound sulfur is removed as hydrogen sulfide, which is neutralized. The oil can then be delivered with very low sulfur content. This has been of great importance for the environment in our populahon centers. 

Since cobalt can change between the oxidation states +2 and -r3 the element is an effective catalyst for oxidation reactions. The element is in fact an additive to nearly all catalysts for oxidahon reactions in organic chemistry, for instance in the oxidation of toluene to benzoic acid. COjO and LaCoOj are also used as components in catalysts for the oxidation of CO in automobile exhaust gases. 

Cobalt can also be used for decolorizing glass. Iron oxide in the glass gives a yellow color. Addition of a balanced amount of cobalt gives a blue color. The complementary effects - yellow and blue - create an impression of colorless glass. 

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Overall, this is the most significant use of cobalt, as shown in Table I (48% total use). Metallic cobalt is an important alloying element in numerous applications, such as super alloys (cobalt, nickel, iron based), magnetic alloys (soft, AlNiCo, SmCo), wear-resistant alloys, high speed steels, prosthetic alloys, and cemented carbide. 

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