The effect of size and type of alumina nanopowder phase on the transparency and bending strength of bodies sintered with MgO and La2O3 sintering aid

The present research has investigated two types of phases (alpha and gamma) of alumina with different sizes (200 nm, 50 nm, and 1000 nm) on the microstructure, transparency, and flexural strength of spark plasma sintered (SPSed) samples. XRD results showed that the powders with a particle size of 1000 nm and 200 nm have a hexagonal crystal system (α- phase), and the nanopowder with a particle size of 50 nm exhibited a cubic lattice (γ phase of alumina). The bulk density of the bulk sample sintered with a particle size of 50 nm, 200 nm, and 1000 nm was 98%, 99%, and 97% of the theoretical density, respectively. The light transmission at sample-200 nm in wavelength of 800 nm was the maximum value (20%), and the other sample-50 nm and -1000 nm obtained 2.5% and 15% light transmission, respectively. IR transmission in the 1000 nm, 200 nm, and 50 nm samples was 15%, 65%, and 25% (at a wavelength of 2.5 µm). The result of bending strength in the sample-200 nm was achieved (133.37 MPa), and this sample is fine-grained and has less porosity compared to the two other samples.