GROWTH OF NEAR NET SHAPE SAPPHIRE DOMES USING THE HEAT EXCHANGER METHOD

ON THE BASIS OF PERFORMANCE, SAPPHIRE IS ONE OF THE BEST MATERIALS FOR MISSILE DOME APPLICATIONS. HOWEVER, BOULE UTILIZATION AND HIGH FABRICATION COSTS MAKE IT AN EXPENSIVE CHOICE, AND, THEREFORE, NO U.S. MISSILE PRODUCTION PROGRAMS ARE USING SAPPHIRE DOMES. IT IS DESIRABLE TO GROW NEAR NET-SHAPE SAPPHIRE DOMES FOR MISSILE APPLICATIONS. IT HAS BEEN DEMONSTRATED THAT WHEN MOLYBDENUM SHEETS ARE PLACED IN THE MELT AND SAPPHIRE GROWTH IS CARRIED OUT USING THE HEAT EXCHANGER METHOD, SINGLE CRYSTAL GROWTH IS ACHIEVED IN SPITE OF SUCH PERTURBATION. WHEN DOME-SHAPED MOLYBDENUM PREFORMS WERE NESTED TOGETHER TO PRODUCE SAPPHIRE DOME BLANKS, HIGH OPTICAL QUALITY WAS PRODUCED. HOWEVER, THESE BLANKS WERE CRACKED. THE OBJECTIVE OF THE PHASE I PROGRAM WILL BE TO IDENTIFY THE CAUSE OF CRACKING AND TO DEMONSTRATE THAT CRACK-FREE, DOME-SHAPED SAPPHIRE BLANKS CAN BE PRODUCED DIRECTLY FROM THE MELT.