Design and Initial Operation of a 6 kW 2.45 GHz Single-Mode Microwave CavityFurnace

摘要

A single-mode cavity microwave furnace, operating in the TE(103) mode at 2.43GHz, has been set up at the Naval Research Laboratory (NRL) and is currently being used to investigate sintering of nanocrystalline ceramics. This memorandum will discuss the apparatus used and the results obtained to date. The high purity A12O3 and TiO2 nanocrystaline powders were first uniaxially pressed to 14 MPa, cold isostatically pressed (CIP'ed) to various pressures > or = 420 MPa and finally sectioned into wafers. The density of the green compacts was 30 to 38% theoretical density (TD). The compacts were placed in insulating fiberboard caskets which were lossy enough at room temperature to provide hybrid heating. At temperatures above 600 deg C, the compacts were heated primarily by the microwave radiation. The wafers were heated in the microwave furnace for up to three hours at temperatures < or = 1720 deg C. The temperature of the workpiece was monitored using an optical pyrometer. Final densities up to 80% TD have been obtained to date for Al2O3 and up to 52% TD for TiO2. The sintered compacts were characterized by x ray diffraction and by scanning electron microscopy to determine the phase and grain size.