Recent advances in CO2 laser catalysts

摘要

Abstract: Some decomposition of CO$-2$/ to CO and O$-2$/ occurs with each pulse in electrically excited, pulsed CO$-2$/ lasers. Both the loss of CO$-2$/ and the buildup of O$-2$/ are detrimental to long-life, closed-cycle laser operation. The NASA Laser Atmospheric Wind Sounder (LAWS) will use such a laser requiring three years continuous operation for the performance of global wind measurements while in orbit. For such long-term operation, this application requires a closed-cycle, pulsed C$+18$/O$-2$/ laser and a C$+18$/O-oxidation catalyst which will operate under ambient temperature laser gas conditions without isotropic scrambling. Such CO-oxidation catalysts with high activity at ambient laser temperatures and low oxygen concentrations were nonexistent until fairly recently. The first such catalyst, a noble-metal-reducible-oxide (NMRO) catalyst, based on platinized tin-oxide (Pt/SnO$-2$/), has been significantly improved by research at NASA LaRC. Unfortunately Pt/SnO$-2$/- based catalysts exhibit significant decay in activity with time. These catalysts lose about half of their initial activity within the first few days and then exhibit a further decay half-life of several months. Results of mechanistic studies led to techniques which minimize the activity decay of Pt/SnO$-2$/-based catalysts with somewhat limited success. Subsequently, a new NMRO catalyst consisting of gold on manganese oxide (Au/MnO$-2$/) has recently been developed by joint NASA LaRC/University of Florida research efforts. Initial tests indicate that this new CO-oxidation catalyst is superior to Pt/SnO$-2$/ in activity and decay characteristics. Tests performed to date include both long-term tests of up to six months continuous operation and short-term tests of one week or more which include isotropic integrity testing. These recent advances and results in CO$-2$/ laser catalyst development and testing will be reported and discussed herein. Additional tests of both types of NMRO catalysts are in progress.!