Objective: To develop a low-thermal-mass porcelain firing furnace capable of the high heating and cooling rates required by experimental firing schedules designed to stabilize leucite volume fraction during firing. Previous studies on optimizing firing schedules (Twiggs et al., J Den Res 2002;81:A-484) have been constrained by the limitations of conventional porcelain firing furnaces: limited heating rates and uncontrolled cooling rates. Other studies in this laboratory have utilized infrared furnaces to achieve high heating and cooling rates, but porcelain specimens required coating with an infrared absorber for efficient heating. The goal of this furnace design was to incorporate an infrared susceptor that would enable efficient heating of the porcelain without the need for a special coating.

Method: This furnace design uses a quad-elliptical infrared furnace under computer control. The furnace chamber consists of a coated, nickel-film susceptor inside a fused silica envelope. The susceptor provides a black-body environment with low thermal mass. The porcelain restoration to be fired is positioned inside the nickel-film susceptor. The fused silica envelope allows firing under vacuum.

Results: Heating and cooling rates up to 1000° C/min were obtained over the critical temperature range (600-1000° C), where rate of change in leucite volume fraction has been shown to be significant (Mackert et al., J Dent Res 1999;78:127).

Conclusion: This furnace design allows the high heating and cooling rates—and the control of these rates—necessary for carrying out the firing schedules designed to minimize porcelain thermal instability.

The support of NIH/NIDCR Grant No. DE07806 is gratefully acknowledged.

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