Fine-grained transparent MgAl2O4 spinel obtained by spark plasma sintering of commercially available nanopowders

High transmittance/small grain size pure spinel ceramics were obtained from commercially available nanopowders without sintering aids by spark plasma sintering (SPS). Using a low heating rate up to 10 C/min and a sintering temperature up to 1300 C, transparent polycrystalline MgAl2O4 spinel was fabricated by SPS with an in-line transmission of 74% and 84% for 550 nm (visible) and 2000 nm (NIR) wavelengths respectively. A small average grain size of about 250 nm was obtained and the pores located at the multiple grain junctions had a mean size of about 20 nm. The high in-line transmission was linked not only to the low residual porosity but to the very small pores.