Microwave furnace and a method of sintering

1. A microwave furnace comprising:

a furnace chamber formed between a chamber housing and a sintering platform for an object to be sintered;

a microwave source arranged for emitting microwaves into the furnace chamber;

a susceptor comprising a material which over a temperature range of the material of at least 23° C. to 700° C. couples into microwaves,

wherein the susceptor and the furnace chamber are movable relative to each other between a first position, in which the susceptor is positioned relative to the furnace chamber, and a second position in which the susceptor is positioned further retracted from the furnace chamber relative to the first position.

2. The microwave furnace of claim 1 , wherein the furnace chamber can be opened and closed, and wherein the susceptor and the sintering platform are movable relative to each other during the furnace chamber is closed.

3. The microwave furnace of claim 1 , wherein the susceptor extends in the furnace chamber in the first position, and wherein the susceptor is positioned outside the furnace chamber in the second position.

4. The microwave furnace of claim 1 , being configured for halting the susceptor in determined intermediate positions of the first and second position.

5. The microwave furnace of claim 1 , wherein the susceptor is arranged in a gap between the platform and the housing.

6. The microwave furnace of claim 1 , wherein the susceptor in the first position surrounds a space in which the platform faces.

7. The microwave furnace of claim 6 , wherein the susceptor extends generally straight along a longitudinal axis at a ring-shaped cross-section.

8. The microwave furnace of claim 1 , wherein the susceptor comprises silicon carbide (SiC).

9. The microwave furnace of claim 1 , having a control system for controlling the operation of the microwave furnace, wherein the microwave furnace is configured for moving the susceptor by control of the control system.

10. The microwave furnace of claim 9 , having a temperature sensor, wherein the control system is configured to move the susceptor based on a temperature measured by the temperature sensor.

11. The microwave furnace of claim 1 , wherein the microwave source is based on a magnetron for generating electromagnetic waves of a frequency of between 300 MHz and 300 GHz.

12. The microwave furnace of any of claim 1 , wherein the microwave source is the only energy source of the microwave furnace for sintering.

13. A method of sintering zirconia comprising:

providing an object made of zirconia on a sintering platform in a furnace chamber of a microwave furnace;

positioning a susceptor to a first position in which at least part of the susceptor is arranged within the furnace chamber;

emitting microwaves into the furnace chamber; and

positioning the susceptor to a second position in which the part of the susceptor is arranged outside the furnace chamber.

14. The method of claim 13 , wherein the positioning from the first to the second position is performed simultaneously to emitting microwaves into the furnace chamber.

15. The method of claim 13 , wherein the object is a dental or orthodontic workpiece comprising zirconia, for example a dental restoration, an orthodontic bracket or precursors thereof.

16. The method of claim 13 , wherein prior to the step of emitting microwaves into the furnace chamber the method comprises sintering the object through heating by thermal radiation.