MlCROWA VE PROCESSING OF CERAMICS: Guidelines Used at the Oak Ridge National Laboratory MARK A. JANNEY, HAL D. KIMREY, AND JAMES O. KlGGANS Oak Ridge National Laboratory'" P.O. Box 2008 Oak Ridge, Tennessee 37831-6087 ABSTRACf 173 To make meaningful comparisons between conventional and microwave processing of materials, one must conduct experiments that are as similar as possible in the two environments. Particular attention must be given to thermal conditions, sample parameters, and furnace environment. Under thermal conditions, one must consider temperature measurement (pyrometer or thermocouple, sheath type, and arcing of thenno- couples), thennal history (heating and cooling rates, thermal gradients), and exothennic reactions. Regarding sample parameters, one must consider sample size, and packing powders and insulation systems. With respect to furnaces, one must consider differences in atmosphere, impurities, and uniformity of heating. Examples will be drawn from diffusion, grain growth, sintering, nitridation, and drying experiments conducted at the Oak Ridge National Laboratory (ORNL) over the past six years. INTRODUCTION There is a critical need to compare the results obtained from microwave processing with those from conventional processing when conducting an investigation of the effects of microwave heating on materials. Side-by-side comparisons are required for at least three reasons. First, literature data from similar investigations are not sufficient. For example, in the study of diffusion, the scatterband of data from various investigators using different materials is typically an order of magnitude or greater. Second,· there are lot-to- lot variations in the composition and processing of materials that greatly affect their properties. If the same material is not used in both the conventional and the microwave studies, meaningful comparisons might not be made. Finally) the claims in the microwave processing literature such as lowered sintering temperatures [1,2], accelerated kinetics in ceramic, polymeric, and organic systems [3-6], and reduced activation energies [1,3-5] are suspect to many researchers both inside and outside the microwave processing community. STANDARD ASSUMPTIONS The experimental procedures described in this paper are built upon a few standard assumptions that are common to all of the experiments cited herein. Multimode cavities were used in all of the work reported here. Thus, there are certain details that might not be strictly applicable to work in single-mode cavities. Also, most of the experiments reported here were conducted at 2.45 GHz, the most common microwave processing frequency. However, the general principles involved are the same irrespective of cavity mode structure or frequency. It is further assumed that processing parameters such as heating rate, soak temperature, processing atmosphere and total pressure, and calibration of instruments such as pyrometers and thermocouples are the same for lx>th conventional and microwave processing. *Operated by Martin Marietta Energy Systems, Inc., under contract DE-AC05- 840R21400 for the U.S. Department of Energy. Mal. Res. Soc. Symp. Proc. Vol. 269. ,91992 Materials Research Society