Bonded phase Carbon content, determination

Because the solubility coefficients of carbon in the solid and the liquid phase are almost the same, zone melting, which is used to prepare high-purity crystals of many other elements, is not suitable in the case of boron. Technical boron, which is often taken as the ingredient for the preparation of boron compounds, contains up to about 0.5% carbon. However, in several preparative methods for boron compounds the carbon content may be reduced by secondary chemical or physical reactions. The purest P-rhombohedral boron crystals that have become available up to now were produced by Wacker-Chemie, Munich, FRG. Despite the claimed purity of 99.9999% with respect to other elements, even this high-purity boron contains carbon in concentrations of typically 30 to 80 ppm. Therefore, apart from boron carbide containing carbon as a determining bonding partner, in the assessment of the properties of boron and boron compounds attention must be paid to the fact that a certain, usually unknown carbon content could have influenced the properties determined. 

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