Effects of process gas environment on platinum-inclusion density and dissolution rate in phosphate laser glasses

Abstract

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.