Fabrication of transparent mullite ceramic by spark plasma sintering from powders synthesized via sol-gel process combined with pulse current heating

摘要

Mullite nanopowders were synthesized by combining the advantages of the sol-gel process with the rapid synthesis provided by pulse current heating. The mullite ceramic with an infrared transmittance of 83-88% in the wavelength range from 2.5 to 4 μm with a fine grain size of 200 nm was obtained by spark plasma sintering at 1350 ℃. Due to the high relative density and the small grain size, the hardness and toughness values of the sample reached 17.82 GPa and 3.6 MPa m~(1/2), respectively. In contrast, when the mullite powders synthesized in a muffle furnace, an intermediate phase occurred so that the powder synthesis required high crystallization temperatures and resulted in agglomerated particles. Thus, the mullite ceramics required high temperatures for densification. As a result, the optical and mechanical properties of the ceramics were poor due to the low relative density and the elongated grain growth.