Patent ID: 8431878

Claim:
A microwave furnace comprising: a furnacing chamber within a retaining cavity, said chamber being at least partly surrounded by microwave transparent insulation; at least one susceptor at least partly between the insulation and the chamber, said susceptor comprising coarse grain polycrystalline β alumina wherein said susceptors are of at least two types, a first of said types being a primary susceptor acting as a susceptor at room temperature and a second of said types being a secondary susceptor of a material that acts as a susceptor at a temperature higher than room temperature and having a softening or decomposition temperature higher than the lowest of a softening or decomposition temperature of said first susceptor type, a source for electromagnetic radiation to be supplied in to said susceptors in an area so that said first susceptor type is heated by said radiation which in turn heats said second susceptor type to a temperature at which said second susceptor type becomes directly heated by said radiation and apparatus for removing the first susceptor type from said area thus permitting said second susceptor type to reach a temperature above the lowest of the softening or decomposition temperature of the first susceptor type without causing softening or decomposition of the first susceptor type and apparatus for moving material to be heated in the furnace through the furnacing chamber in the form of a tunnel chamber.