High temperature chemistry of molten glass ion emitters

Thermodynamic calculations have been performed to predict the chemical behavior of ten elements in molten borosilicate glass to gain new insights into the ion formation mechanisms for this class of ion emitters. General trends identified during the computational studies include: (1) all of the analyte elements studied are reduced, at least in part, to the elemental state (which is predicted to be soluble in the molten glass); (2) a finite percentage of each of the analytes volatizes in the elemental state, with a possibility that an electron will be stripped to form a positive ion; (3) dilution of the element in the molten glass matrix tends to reduce the evaporation rate of the analyte element for a given temperature (as compared to the pure material), allowing vaporization to occur evenly and at higher temperatures; and (4) rhenium, dissolved from the supporting filament, is predicted to be present in the molten glass. This Re is probably present as an oxide, which is believed to enhance ion emission probabilities by increasing the work function of the surface. The results of this study support the hypothesis that the ion formation mechanism for the elements investigated involves the volatilization of the element as both neutral and ionic atomic species, possibly as a Saha-Langmuir type process. Other ion emission processes are probably active for those analytes that are not easily reduced to the elemental state in the molten glass matrix.