Cobalt-Containing Iron Oxide Pigments

The iron oxide pigments described in Section 5.1.1 are either doped or coated with cobalt  

Body-doped pigments contain 2-5 wt.% cobalt that is uniformly distributed throughout the bulk of the pigment particles. It is either incorporated during production of the FeOOH precursor or precipitated as the hydroxide onto one of the intermediate products [5.13] using cobalt(II) salts as the cobalt source. 

Cobalt-coated pigment particles (1.6-4 wt.% Co) consist of a core of Y-F6203 or non-stoichiometric iron oxide phase, and a 1-2 nm coating of cobalt ferrite with a 

Pigments with a higher coercive field strength (ca. 70 kA m ) and smaller particle size (particle length ca. 0.15-0.2 pm) are used for super VHS cassettes. 

Pigments treated with only small amounts of cobalt (0.5-1 wt.% Co, coercive field strength ca. 31 kA m ) are used as an alternative to cobalt-free Y f 203 pigments 

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The incidence of false positive results was not reported in the Dewberry Davis study. However, several elements sometimes found in paint films can be expected to contribute to false positive results if present in sufficient concentrations and suitable chemical form these include copper, cobalt, mercury, manganese, and iron. Vind et al. (1976) reported that positive responses were not obtained under typical testing conditions for iron oxide pigments. In contrast, they found that neat biocides (containing mercury or copper) and driers (containing cobalt or manganese) did turn black in the presence of sulfide ions. However, they concluded that given the usually low concentrations of these materials in paints, interference due to these elements would be minimal. 

Cobalt-containing pigments are mainly produced by the magnetic iron oxide producers listed in Section 5.1.1. World production for 1995 was 40000 t, of which the highest proportion (ca. 85 %) was used for video tapes. 

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