Cobalt, Co

Cobalt is a steel-grey, slightly magnetic metal. It melts at 1490°C. The metal dissolves readily in dilute mineral acids  

The dissolution in nitric acid is accompanied by the formation of nitrogen oxide  

In aqueous solutions cobalt is normally present as the cobalt(II) ion Co sometimes, especially in complexes, the cobalt(III) ion Co is encountered. These two ions are derived from the oxides CoO and C02O3 respectively. The cobalt(II)-cobalt(III) oxide C03O4 is also known. 

In the aqueous solutions of cobalt(II) compounds the red Co ions are present. Anhydrous or undissociated cobalt(II) compounds are blue. If the dissociation of cobalt compounds is suppressed, the colour of the solution turns gradually to blue. 

Cobalt(III) ions Co are unstable, but their complexes are stable both in solution and in dry form. Cobalt(II) complexes ean easily be oxidized to cobalt(III) complexes. 

In the 16th century it was known that certain minerals could turn glass deep blue. Cobalt, first discovered in 1739 was shown to be the element contained within them that caused this - hence the term cobalt blue . The most important ores are cobaltite (CoAsS) and erythrite (Co3(As04)2). 

Natural isotopes of cobalt and their solar abundances 

See 5 Fe (to which5 6 Co decays) for a discussion of the nucleosynthesis of56 Ni (parent of56 Co) by equilibrium and quasiequilibrium processes during supernova nuclear burning. 

The mass-59 isotope is the only stable isotope of natural cobalt. It has 

In massive stars a comparable amount of 59Co is also synthesized as itself in the s process, as it occurs in the thermonuclear shells of pre-core-collapse presupernova stars. The weak s process occurs in helium burning as itestablishes the large (C,0) core of the presupernova star, and also during the C burning in the presupernova structure. 

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Radioactive cobalt, Co, produced by bombarding stable Co with low energy neutrons, has appHcation in radiochemistry, radiography, and food steriliza tion (26-28) (see FoOD PROCESSING RADIOISOTOPES STERILIZATION TECHNIQUES). 

The mechanics of materials approach to the estimation of stiffness of a composite material has been shown to be an upper bound on the actual stiffness. Paul [3-4] compared the upper and lower bound stiffness predictions with experimental data [3-24 and 3-25] for an alloy of tungsten carbide in cobalt. Tungsten carbide (WC) has a Young s modulus of 102 X 10 psi (703 GPa) and a Poisson s ratio of. 22. Cobalt (Co) has a Young s modulus of 30x 10 psi (207 GPa) and a Poisson s ratio of. 3. 

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