Transparent Ceramics Fabricated via Spark Plasma Sintering–Magnesium Aluminate Spinel with Increased Aspect Ratio

Abstract: Magnesium aluminate spinel is a promising transparent ceramic material. It can be used as transparent armor as windows for spacecraft, in scanners and optical elements in night-vision systems, and as a matrix for scintillation and laser materials. The broad range of applications for ceramics based on MgAl2O4 is due to their unique combination of properties. Research aimed at developing transparent ceramic materials with an increased aspect ratio is highly relevant and has significant practical importance. This study gives a comprehensive characterization of a commercial nanopowder of magnesium aluminate spinel. The primary structural properties of the nanopowder are determined. The rheological properties of the nanopowder during its compression and thermal consolidation are investigated based on the principles of a mechanistic pressing model by approximating the experimental densification data using a dimensionless logarithmic equation. The graphical representation of this equation enables the evaluation of the potential for achieving a pore-free state in the consolidated material and the optimization of the parameters for spark plasma sintering. Constructing a densification surface and identifying the optimal path for increasing pressure and temperature during spark plasma sintering on this surface can be used to optimize the consolidation parameters for transparent ceramics. Verified discrete-element modeling of the packing and consolidation processes of magnesium aluminate spinel nanopowder particles is conducted. Both model-based and experimental results show that the identified combination of temperature (1300°C) and static pre-pressing pressure (100 MPa) is sufficient to achieve a pore-free ceramic structure without causing excessive recrystallization. Transparent ceramics based on high-aspect-ratio magnesium aluminate spinel can be fabricated using the spark plasma sintering method at a temperature of 1300°C and a static pre-pressing pressure of 100 MPa. The optical and mechanical properties of the fabricated transparent ceramics are comparable to or exceed those of similar materials. The light transmittance of the samples reaches 41% in the visible region of the spectrum and 64% in the infrared region. The Vickers microhardness value is 15.6 ± 0.5 GPa; the fracture toughness is 4.4 ± 0.4 MPa · m1/2; the compressive strength is 1.37 ± 0.23 GPa; the Poisson ratio is 0.26 ± 0.01; the Young modulus is 278 ± 6 GPa; and the shear modulus is 110 ± 2 GPa. © Pleiades Publishing, Ltd. 2024.