Spark plasma sintering of transparent thick magnesium aluminate spinel ceramics

Magnesium aluminate spinel is a promising material for optical application. It can be used as transparent armor, spacecraft windows, scanners, optical elements in night vision systems, as well as a base (matrix) for scintillation and laser materials. The wide range of practical applications of MgAl2O4 ceramics is due to the complex of its unique properties. The research is aimed to creating transparent ceramic materials with an increased shape factor, relevant and of high practical importance. In the presented work, a comprehensive characterization of the commercial nanopowder of magnesium aluminate spinel is completed. Its main structural features are defined. Rheological properties of nanopowder in the process of its compression and thermal consolidation are investigated on the basis of the provisions of the mechanistic pressing model by approximating experimental data of compaction during spark plasma sintering with a dimensionless logarithmic equation, the graphical representation of which allows us to evaluate the possibility of achieving a non-porous state of the consolidated material and optimize the modes of spark plasma sintering. Shown, that the structure of the sealing surface and the search for the optimal way to increase pressure and temperature during spark pulse plasma sintering on this surface can be used to optimize the consolidation modes of transparent ceramics. Verified discrete element modeling of the processes of packing and consolidation of particles of magnesium aluminate spinel nanopowder has been performed. Model and field experiments have shown that the revealed combination of temperature (1300 °C) and static pressure (100 MPa) is sufficient to obtain a porous ceramic structure and does not lead to excessive recrystallization. It is shown that transparent ceramics based on magnesium aluminate spinel with an increased shape factor can be produced by spark plasma sintering at temperature of 1300 °C and static pressure of 100 MPa. The optical and mechanical properties of the manufactured transparent ceramics are comparable to their analogues. The light transmission of samples reaches 41% of the visible spectrum and 64% in the infrared spectrum, the Vickers microhardness value is 15.6±0.5 GPa, crack resistance is 4.4±0.4 MPa·m1/2, compressive strength is 1.37±0.23 GPa, Poisson's ratio is 0.26±0.01, Young's modulus - 278±6 GPa, shear modulus - 110±2 GPa.