Effect of pre-load pressure on transparency of alumina by the spark plasma sintering

Fine-grained transparent alumina ceramics were successfully prepared by the spark plasma sintering technique at 1 350 °C for 5 min dwelling time without any sintering aids. Effects of pre-load pressure on microstructure and transparency were investigated systematically. For a low pre-load pressure, 10 MPa, with normal characteristic fast heating rate (100 °C/min), high in-line transmission of 56% at 640 nm and 84% at 2 000 nm can be reached, further increase of pre-load pressure leads to decrease in transmittance.