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- ItemEffects of melting conditions on platinum-inclusion content in phosphate laser glasses(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1995) Campbell, John H.; Wallerstein, Edward P.; Hayden, Joseph S.; Sapak, David L.; Warrington, David E.; Marker III, Alex J.Results from small-scale glass melting experiments aimed at reducing the density of platinum particles in phosphate laser glasses are discussed. The platinum particles originate from the crucibles used to melt the laser glass and can cause optical damage in glasses used in high-peak-power lasers. The melting experiments examine the effects of a) temperature and temperature gradients; b) processing time; and c) O₂ atmosphere on the formation and dissolution of platinum inclusions in LG-750 phosphate laser glass. Results show that most platinum inclusions originate early in the melt cycle, with thermal gradients within the melter being one of the major causes. By using oxidizing conditions (O₂), the platinum inclusions can be dissolved into the glass during the course of the melt cycle. Results from the laboratory-scale melting experiments have been incorporated into a proprietary laser-glass melting process. The laser glass prepared under these conditions has an average of less than 0.1 platinum inclusions/1, which represents a 1000-fold reduction over the previously available phosphate laser glasses.
- ItemEffects of process gas environment on platinum-inclusion density and dissolution rate in phosphate laser glasses(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1995) Campbell, John H.; Wallerstein, Edward P.; Toratani, Hisayoshi; Meissner, Helmuth E.; Nakajima, Sadahiro; Izumitani, Tetsuro S.The effects of process gas environment on reducing the density of platinum inclusions in phosphate laser glasses are examined. The platinum inclusions originate from the crucibles used to melt the laser glass and can lead to optical damage in glasses used in highpeak- power lasers. The melting experiments examine the effects of N₂, O₂ and CI₂ gases on inclusion density and platinum dissolution rates. The more oxidizing the process gas conditions, the greater the dissolution rate (O₂ + CI₂ > O₂ » N₂). A thin-film mass transport model is used to analyze dissolution rate data for small plates of platinum over a range of temperatures from 1000 to 1200°C and oxygen fugacity of 10³ to 1 bar. At 1200°C the platinum dissolution rate is approximately 3.0- 10⁻⁸ (Pₒ₂)⁰⁷ (in g/(cm² * s)) where Pₒ₂ is the oxygen fugacity of the process gas in bar. Using CI₂ rather than O₂ causes a measurable increase in the optical absorption of the glass that may be due to either a red-shift and/or a greater absorption coefficient for the platinumchlorine complex.
- ItemModeling platinum-inclusion dissolution in phosphate laser glasses(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1995) Campbell, John H.An analytic model is developed describing the dissolution of platinum inclusions in LHG-8 and LG-750 metaphosphate laser glasses. The model assumes a spherical geometry and a diffusion-limited rate process in a quiescent fluid. The time for complete dissolution of a platinum inclusion is proportional to the square of the inclusion radius and is computed to be about 10 h at 1100°C for inclusions 10 µm in diameter in these glasses. This agrees with experimental results. When melting in a platinum vessel, the dissolution of the crucible walls limits the size of the platinum inclusion that can be dissolved because of the background contribution to the ionic platinum content. This effect is included in the model and is related to the exposed surface-area-to-volume ratio of the platinum vessel.