Improved insulation for an induction-heated ZrO/sub 2/ furnace

The induction-heated ZrO/sub 2/ muffle furnace is extensively used for the production of silica fibers used as optical waveguides in the communications industry. The furnace typically operates in air between 2200/sup 0/ and 2300/sup 0/C. Improved materials and design that will increase the life, the operating temperature, as well as the physical size and particulate cleanliness of the furnace atmosphere, are continually being sought. This note describes the general makeup and operating characteristics of the furnace and the improved performance achieved by using skull-melted ZrO/sub 2/ grain (grog) as the insulating material surrounding and supporting the ZrO/sub 2/ heater (muffle). Noteworthy milestones in the development of oxides as a direct heating element have been made.