CHEMICAL VAPOR DEPOSITION PLATINUM COATINGS FOR INCREASED CHEMICAL ROCKET EFFICIENCY

EXTRAORDINARY INCREASES IN ROCKET COMBUSTION CHAMBER OPERATING TEMPERATURE HAVE BEEN ACHIEVED WITH IRIDIUM-COATED RHENIUM ROCKET THRUSTERS. THIS HAS RESULTED IN A GREATER THAN 20-SECOND IMPROVEMENT IN SPECIFIC IMPULSE WITH NO SACRIFICE IN LIFETIME. THREE OF THE PLATINUM GROUP METALS, PLATINUM, RHODIUM, AND IRIDIUM, HAVE THE CAPABILITY TO PROTECT REFRACTORY STRUCTURAL MATERIALS FROM OXIDATION AT TEMPERATURES SUBSTANTIALLY HIGHER THAN ACHIEVABLE WITH STATE-OF-THE-ART (SILICIDE) COATINGS. BESIDES HAVING HIGH MELTING POINTS, THESE METALS ARE HIGHLY OXIDATION-RESISTANT. IRIDIUM HAS BEEN DEPOSITED BY CHEMICAL VAPOR DEPOSITION (CVD) AND HAS DEMONSTRATED ITS USEFULNESS FOR LONG-TERM PROTECTION OF RHENIUM THRUST CHAMBERS UNDER OXIDIZING CONDITIONS AT 2200 DEGREES CELSIUS. IRIDIUM HAS TWO DRAWBACKS HOWEVER: ITS RELATIVE SCARCITY AND HIGHER OXIDATION RATE COMPARED TO THOSE OF PLATINUM AND RHODIUM. THE MELTING POINT OF PLATINUM, 1770 DEGREES CELSIUS, IS LOWER THAN THAT OF IRIDIUM, BUT IS STILL AMPLE FOR NIOBIUM ALLOYS AND IS SUBSTANTIALLY HIGHER THAN THE 1400 DEGREES CELSIUS LIMIT FOR SILICIDE-BASED COATINGS. PLATINUM IS ALMOST 100 TIMES AS ABUNDANT AS IRIDIUM IN RECOVERABLE MINERAL DEPOSITS, AND IS MORE GLOBAL WIDESPREAD. NO SATISFACTORY TECHNIQUE CURRENTLY EXISTS FOR FORMING ADHERENT, NON-POROUS DEPOSITS OF PLATINUM ON COMPLEX SHAPES SUCH AS THRUST CHAMBERS. IN THIS PROGRAM, THE FEASIBILITY OF CVD FOR FORMING THICK, ADHERENT NON-POROUS DEPOSITS OF PLATINUM ON COMPLEX SHAPES SUCHAS THRUST CHAMBERS. IN THIS PROGRAM, THE FEASIBILITY OFCVD FOR FORMING THICK, ADHERENT SYSTEM INTO A USABLE PRODUCT COULD OFFER THE ORDER OF MAGNITUDE ADVANCE IN POWER SOURCE TECHNOLOGY SOUGHT FOR SPACE APPLICATIONS.