Method and device for microwave sintering large ceramic articles

Claim 1

A high power microwave sintering system for sintering ceramic articles comprising: an adjustable power microwave source for generating microwaves at an output thereof at a frequency of at least 28 gigahertz; an untuned microwave cavity formed of an electrically conductive housing having at least one inside dimension which is at least 100 times greater than the free space wavelength of said microwaves produced by said microwave source; an overmoded waveguide means connected between the output of said source and said housing for transmitting microwave energy between said source and said housing and feeding microwave energy into said cavity in a plurality of available propagating modes within said cavity; a microwave mode stirring means disposed within said cavity and formed to couple with available standing wave propagating mode patterns within said cavity so that said stirring means works in conjunction with said overmoded waveguide means feed to provide a substantially uniform microwave energy field throughout said cavity; a high temperature support means removably disposed within said cavity for supporting an article to be sintered in a central location within said cavity; an insulating means including an insulating material disposed about and in contact with said article for thermally insulating said articles, said insulating material being transparent to microwaves so that as said article is heated by applying microwave energy to said cavity microwave energy is freely transmitted uniformly into said article through said insulating material while surface heat loss from said article is minimized; and means for measuring the temperature of said article.

Claim 9

A method for uniformly microwave sintering a green ceramic article, comprising the steps of: introducing said article into an untuned microwave cavity having at least one dimension at least 100 times greater than the free space wavelength of the applied microwave fed by a variable power microwave energy source operating at a frequency of at least 28 GHz; feeding microwave energy from said source into said cavity so as to establish a uniform microwave field within said cavity at a power level sufficient to raise the temperature of said article at a rate of up to about 200° C./min. until a desired peak sintering temperature is obtained; maintaining said article at the selected sintering temperature by regulating the power applied to said cavity for a period sufficient to increase the density of said article to a desired value; and reducing the microwave power to the cavity at a rate sufficient to lower the temperature of the article at a preselected rate to prevent stress cracking during cool down of the article.

Claim 10

A method for uniformly microwave sintering a green ceramic article, comprising the steps of: introducing said article into an untuned microwave cavity having at least one dimension at least 100 times greater than the free space wavelength of the applied microwave fed by a variable power microwave energy source operating at a frequency of at least 28 GHz; feeding microwave energy from said source into said cavity so as to establish a uniform microwave field within said cavity at a power level sufficient to raise the temperature of said article at a rate of up to about 200° C./min. until a desired peak sintering temperature is obtained; maintaining said article at the selected sintering temperature by regulating the power applied to said cavity for a period sufficient to increase the density of said article to a desired value; and reducing the microwave power to the cavity at a rate sufficient to lower the temperature of the article at a preselected rate to prevent stress cracking during cool down of the article.