FUNCTIONS OF MINOR CONSTITUENTS IN COMMERCIAL SELENIUM RUBY BATCH

In addition to the chemicals essential to the formation of the colorant, the nature of which is well established, successful commercial selenium ruby batches commonly contain a number of characteristic minor ingredients. These are zinc oxide, cryolite or other fluorine compounds, bone ash, and minute amounts of copper or nickel oxide. Laboratory experiments are described which helped to establish the functions of these minor constituents. Owing to the extreme insolubility of copper and nickel sulfide in silicate melts, these compounds form at high temperatures and provide nuclei for the cadmium sulfoselenide which requires a lower temperature for its formation. Bone ash, especially in combination with fluoride, leads to a very insoluble phase, apatite, which enhances the striking of the selenium ruby. Formation of cadmium sulfoselenide will not take place at high temperatures. Introducing fluorine into a silicate glass facilitates molecular rearrangements because of the weaker forces exerted by this monovalent anion as compared with divalent oxygen ions. Fluorides increase the low-temperature mobility of the glass and speed up the striking process. The chief function of zinc oxide is to retain sulfur and selenium in the melt. Alkali sulfoferrite and selenoferrite produce a red-brown color, and their formation in glasses containing strong reducing agents, such as carbon, accounts for the deep color of some glasses containing only small amounts of cadmium sulfoselenide.