MICROWAVE AUTOGENOUS FIRING OF STRUCTURAL CERAMICS

摘要

Thermal analyses and dielectric property measurements of the heavy clay bodies provide data for body compositions best suited for hybrid microwave/gas firing systems. Brick clay bodies, being impure ceramic systems, contain compounds with good dielectric properties and are therefore well suited to hybrid gas/microwave firing. The presence of carbon, hematite, carbonates and other mineral compounds increases the complex permittivity and results in a marked improvement in the efficiency of microwave coupling. Hybrid firing of these lossy brick bodies can therefore harness the mechanism known as Microwave Autogenous Firing (MWAF). This mechanism can be used to minimize the microwave proportion in the total energy balance to the lowest practical level. Less cost is therefore incurred on expensive microwave energy, while deriving the maximum benefit from the more efficient microwave volumetric heating. The ultimate goal in developing the MWAF process is the reduction of overall energy consumption and the achievement of faster firing cycle times. The precise control of the MWAF process is achieved by the use of controlled levels of microwave power, applied during the appropriate reaction stages in the firing cycle. The part of the preheat stage of the cycle, referred to as the "microwave window", is the critical stage where the most efficient combination of microwave energy and natural gas firing is utilized. The paper reports on some important aspects of recent pilot plant scale development work carried out, using an intermittent gas fired hybrid kiln, equipped with a 75kW, 915MHz microwave energy supply. The paper proposes some typical design features of a full scale continuously firing MWAF system envisaged in the future structural ceramics industry.