Apparatus and method for processing ceramics

#The invention relates to an apparatus and method for processing ceramic materials. In particular, this invention relates to an apparatus and method for processing ceramic materials involving a combination of microwave and conventional heating, and more particularly to an apparatus and method for controlling the field density of the microwave power through slotted waveguides to uniformly distribute the power throughout the ceramic material, maximizing power absorption by the ware and minimizing power absorption by its surroundings.

#Conventional heating used in the manufacturing of ceramic materials typically utilizes radiative gas flame, electric resistance heating, and the like. Utilization of conventional heating typically results in a thermal differential within the ceramic material. This differential is due, in part, to the fact that radiant heating is applied only to the surface of the material and it relies on the thermal conductivity of the material, typically poor, to transmit the thermal energy beneath the surface and into the interior of the piece. In other words, conventional heating involves heat transfer that is predominantly achieved by radiation or convection to the surface followed by conduction from the surface into the interior of the ceramic body. If a core-surface thermal differential develops that is too great, internal cracking and distortion of the ceramic material can occur. Fast firing further exacerbates this problem of poor heat transfer, and ultimately cracking.

#Additionally, the presence of a core-surface thermal gradient can also result in uneven sintering, specifically surface sintering prior to, and at a faster rate than, interior sintering. As a result, the ceramic material may exhibit non-uniform properties.

#FIG. 1 is a side plan view of an apparatus according to the present invention.

#FIG. 2 is a side elevation view of a detail of an apparatus according to the present invention.

#FIG. 3 is a top plan view of a waveguide configuration of the prior art showing 8 standard feed ports.

#The present invention relates to a method for processing a ceramic material including placing the ceramic material in a microwave heating apparatus having a microwave cavity; subjecting the ceramic material to a combination of microwave radiation and conventional heat; and controlling the uniformity of the processing of the ceramic material so as to avoid deformations and cracking by applying the microwave radiation to the ceramic material through at least one slotted waveguide, which substantially uniformly distributes the microwave radiation throughout the microwave cavity such that the power into the ceramic material is above about 15×10−3 mW/m2 and the maximum deviation between the microwave power supplied to the ceramic material in a first defined area and that supplied to the ceramic material in a second defined area within the cavity is no greater than about 25%, as measured in a static system.

#Preferably, according to the method the power into the ceramic material is above about 17×10−3 mW/m2 and the maximum deviation between the microwave power supplied to the ceramic material in a first defined area and that supplied to the ceramic material in a second defined area within the cavity is no greater than about 22%.

#More preferably, according to the method the power into the ceramic material is above about 17.5×10−3 mW/m2 and the maximum deviation between the microwave power supplied to the ceramic material in a first defined area and that supplied to the ceramic material in a second defined area within the cavity is at or below about 17%.