Radiation synthesis of ceramics based on double spinels, technology development and investigation of structure-dependent functional properties

Abstract

Radiation-thermal synthesis of high-density ceramics with double spinel structure is considered as an energy-efficient alternative to prolonged furnace firing limited by diffusion at grain boundaries and achievement of theoretical density. An approach to controlling defectiveness at the nano level through generation of non equilibrium vacancies and interstitials under irradiation is described, which intensifies mass transfer and promotes formation of homogeneous solid solutions critical for microhardness, fracture toughness, and radiation resistance. Oxide systems Mg(1−x)ZnxAl2O4 and MgAl(2−x)CrxO4 obtained from fine-dispersed oxides after prolonged planetary mixing, pressing at 200 MPa, and subsequent processing on a linear electron accelerator (1.4 MeV) at controlled heating 800-1400 °C and absorbed doses 50-500 kGy were investigated; phase composition was confirmed by X-ray diffraction, microstructure by electron microscopy, density by hydrostatic method. Nonlinear densification with a threshold change of mechanisms around 300 kGy is shown: for MgAl2O4 average density increases from 2.453 to 3.518 g/cm³, relative density from 68.52 to 98.27%, open porosity decreases from 28.43 to 0.84%, linear shrinkage reaches 16.89%. Doping improves mechanical properties while maintaining brittle fracture character: HV increases from 13.42 GPa (MgAl2O4) to 16.12 GPa (MgAl1.6Cr0.4O4), K1c from 1.87 to 2.93 MPa·m^0.5, elastic modulus up to 291.5 GPa. Thermal conductivity shows a trend close to 1/T (18.45→7.65 Wt/(m·K) at 298→1073 K), coefficient of thermal expansion increases to 8.56·10^−6 K^−1. Radiation-shielding properties correlate with density and composition: attenuation coefficient for γ-radiation at 0.662 MeV reaches 0.312 cm^−1 for Mg0.5Zn0.5Al2O4 and exceeds heavy concrete, providing reduction in thickness of shielding screens; statistical processing and multifactor models support optimization of regimes and confirm reproducibility of the technology for special-purpose structures.