Synthesis of highly-infrared transparent Y₂O₃–MgO nanocomposites by colloidal technique and SPS

Infrared (IR) transparent Y₂O₃–MgO nanocomposites with a volume ratio of 50:50 were synthesized by combining colloidal and spark-plasma-sintering (SPS) techniques. In order to attain well-dispersed and homogeneous starting Y₂O₃–MgO nanopowder mixture, the effects of the pH value and the amount of polyetherimide (PEI) dispersant on the suspension stability were studied. Rheological measurement reveals that highly-dispersed and stable suspension was obtained at 7 wt% of PEI dispersant under pH = 10.6. The obtained nanopowders with particle size of 20–30 nm were densified using SPS at several sintering temperatures. The sintered composites show fine grains, narrow grain size distribution and uniform microstructure. The nanocomposite sintered at 1250 °C showed the maximum IR transmittance of 84% at a wavelength range of 2.5–6 μm. The Vickers hardness of the nanocomposite was about 11.9 ± 0.3 GPa, which is significantly higher than those of single phase MgO or Y₂O₃. Successful fabrication of the high-performance Y₂O₃–MgO nanocomposite indicates that i) the colloidal technique is an effect method to obtain highly dispersed and homogeneous nanopowders and ii) the SPS technique is a powerful tool to fabricate fine-grained dense transparent ceramics, which are suitable for fabricating IR transparent Y₂O₃–MgO composite ceramics from commercial starting powders.