Microwave heating apparatus for laboratory analyses

Abstract

A microwave oven particularly suitable for laboratory analytical use is described. The oven is designed for chemical digestion and the drying of materials to very low moisture levels. The oven utilizes a rotating platform to move the material being subjected to microwave radiation through the oven chamber to ensure uniform contact of the microwaves with the material. Radiation mixers and radiation isolators are also used to disperse radiation in the oven and absorb excess radiation.

What is claimed is: 
     
       1. An analytical microwave apparatus that is especially suitable for laboratory heatings to digest or dry small analytical samples, which comprises a chamber, which retains microwave radiation therein except for that which exits back out through an opening in the chamber which is an entrance for such radiation, which chamber is devoid of any microwave absorbent material except for any analytical samples being heated, a magnetron located outside of such chamber, a wave guide located between the chamber and the magnetron and communicating them through the chamber opening, an isolator, comprising a magnetic shape in the wave guide, and a dummy load and a heat sink, in combination, external to such wave guide, which dummy load absorbs any microwave radiation that exits from the chamber through the wave guide, a first fan or blower for directing air past the heat sink to cool it, so that the air can cool the heat sink continuously over long time periods when the magnetron is operating at full power and there are no analytical samples in the chamber, mechanical radiation mixing means for dispersing throughout the chamber microwave radiation entering the chamber from the wave guide, a second fan or blower, of variable speed capability, for cooling the chamber by drawing air through it, and for removing from the chamber any volatiles that may be generated by the analytical samples during heating thereof, a turntable for moving analytical samples in the chamber while they are being subjected to microwave radiation therein, and programmable means for controlling power input to the magnetron and the duration of such power input, so that the analytical samples may be safely and effectively heated to digest or dry them without damaging the magnetron and without allowing escaping of microwave radiation from the analytical microwave apparatus. 
     
     
       2. An analytical microwave apparatus according to claim 1 wherein the turntable is of synthetic organic polymeric plastic material which is transparent to microwave radiation. 
     
     
       3. An apparatus according to claim 2 wherein the turntable is of polypropylene, polycarbonate, polyester or polytetrafluoroethylene. 
     
     
       4. An apparatus according to claim 2 wherein the turntable is of variable speed capability. 
     
     
       5. An apparatus according to claim 4 wherein the speed of rotation of the turntable is adjustable within the range of 1/2 to 20 revolutions per minute. 
     
     
       6. An apparatus according to claim 1 wherein the chamber includes interior walls of microwave transparent and chemically resistant material and a door interior wall of such material. 
     
     
       7. An apparatus according to claim 1 wherein the programmable means for controlling power input to the magnetron and for controlling the duration of such power input includes a microprocessor. 
     
     
       8. An apparatus according to claim 7 which comprises a digital panel readout which provides visible information about the program in operation in the apparatus. .Iadd. 
     
     
       9.  An analytical microwave apparatus that is suitable for laboratory heatings to digest or dry analytical samples, which comprises a chamber, which retains microwave radiation therein except for that which exits back out through an opening in the chamber, which is an entrance for such radiation, which chamber is devoid of any microwave absorbent material except for any analytical samples being heated, a magnetron located outside of such chamber, a wave guide located between the chamber and the magnetron and communicating them through the chamber opening, an isolator, comprising a magnetic shape in the wave guide, and a dummy load and a heat sink, in combination, external to such wave guide, which dummy load absorbs any microwave radiation that exits from the chamber through the wave guide, means for directing air past the heat sink to cool it, so that the air can cool the heat sink continuously over long time periods when the magnetron is operating at full power and there is no analytical sample in the chamber, mechanical radiation mixing means for dispersing throughout the chamber microwave radiation entering the chamber from the wave guide, a turntable for moving an analytical sample in the chamber while it is being subjected to microwave radiation therein, and programmable means for controlling power input to the magnetron and the duration of such power input, so that analytical samples may be safely and effectively heated to digest or dry them without damaging the magnetron and without allowing escaping of microwave radiation from the analytical microwave apparatus. .Iaddend. .Iadd. 
     
     
       10.  An analytical microwave apparatus according to claim 9 wherein the means for directing air past the heat sink to cool it is a blower. .Iaddend. .Iadd.11. An analytical microwave apparatus according to claim 9 wherein the means for directing air past the heat sink to cool it is a fan. .Iaddend.