Minor element additions, influence

V. HIGHER-ORDER SYSTEMS AND THE INFLUENCE OF MINOR ELEMENT ADDITIONS... 

Commercial elemental sulfur is usually of bright-yellow color at 20 °C [36]. Pure orthorhombic a-Ss is, however, of greenish-yellow color at 20 °C but totally colorless at 77 K while commercial sulfur often remains pale-yellow at this temperature [59]. The reasons for this different behavior are twofold. Commercial samples are never pure Ss but besides traces of organic impurities they always contain Sy in concentrations of between 0.1 and 0.5% [59]. Sulfur found as a mineral in Nature sometimes also contains Sy but in addition traces of selenium are quite often present (up to 680 ppm Se, probably as SySe molecules) [60]. These minor components influence the color of the samples at ambient and low temperatures in the sense that a more orange-type of yellow ( egg-yellow ) is recognized. 

Regarding group V and VI elements, minor additions of P, Se and Te are effective to decrease the oxidation rate and the resultant scales are rich in A1203 [33,35], This was explained again by VCR [33, 35], There are optimal amounts for these elements. On the other hand, the influence of V, Nb and Ta belonging to group VA varies very wide-... 

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