Microwave sinter forging of alumina powder

Microwave sintering under load is expected to be a promising technique to process ceramics with fine microstructure. This paper presents a new setup allowing sinter forging ceramic compacts in a 2.45 GHz single-mode microwave cavity. This setup has the following features: maximum temperature of 1600 °C, heating rate between 1 and 250 °C min−1, maximum stress of 50 MPa applied upon an 8 mm diameter sample. A specific protocol has been defined to calibrate the pyrometer used to measure the sample temperature. Alpha-alumina compacts have been microwave sinter forged under various stresses in the range 0–30 MPa. The results are compared to those obtained in a conventional furnace under 0, 4 and 8 MPa. Final axial and radial shrinkages are identical with the two techniques. The final relative density of the material is not affected by load and is equal to 0.94 and 0.96 in microwave sinter forging and conventional sinter forging, respectively. Two assumptions are proposed to explain this difference: a microwave effect and a temperature discrepancy. Finally the load does not significantly affect grain growth.