High temperature rotating vacuum kiln and method for heat treating solid particulate material under a vacuum

A rotating vacuum kiln comprising:

• a rotating refractory metal cylindrical vessel having inner and outer walls, a cool inlet zone, a hot intermediate zone and a cool exit zone;
• means for charging solid particulate material for heating into said cool inlet zone while under a vacuum;
• a supply of additive or dopant and means for adding said supply of additive or dopant to solid particulate material in said rotating refractory metal cylindrical vessel;
• means for discharging said solid material after heating from said cool exit zone while under a vacuum;
• a first series of inner radiation shields attached to the inner wall of the cylindrical vessel, at said hot intermediate zone, adjacent to said cool inlet zone;
• a second series of inner radiation shields positioned in the cylindrical vessel at said hot intermediate zone, adjacent to said cool exit zone;
• series of screw flights attached to the inner wall of the cylindrical vessel adapted to move solid particulate material in a direction from the charging means to said discharging means;
• a gaseous exhaust conduit extending into said cool exit zone and at least partially into said hot intermediate zone for removing gases and vaporized material therefrom;
• electrical resistance heaters spaced from and about the outer wall of said cylindrical vessel along the hot intermediate zone;
• and
• a plurality of outer radiation shields which are spaced from each other and spaced from, surround and radially enclose said electrical resistance heaters.

A method of heating a solid particulate material to a temperature of 1000° to 1700° C. under a vacuum comprising:

• producing a rotating refractory metal cylindrical vessel having inner and outer walls, a cool inlet zone, a hot intermediate zone, and a cool exit zone, a first series of inner radiation shields at said hot intermediate zone adjacent said cool inlet zone and a second series of inner radiation shields at said hot intermediate zone adjacent said cool exit zone,
• moving solid particulate material through said rotating refractory metal cylindrical vessel while under a vacuum;
• adding a supply of additive or dopant to said solid particulate material;
• heating said solid particulate material to a temperature of 1000° to 1700° C. in said hot intermediate zone;
• and discharging said heated solid particulate material from said cool exit zone.