In order to describe and to study the processes of cold compaction within the discrete element method a three-dimensional model of nanosized powder is developed. The elastic forces of repulsion, the tangential forces of "friction" (Cattaneo-Mindlin), and the dispersion forces of attraction (van der Waals-Hamaker), as well as the formation and destruction of hard bonds between the individual particles are taken into account. The monosized powders with the size of particles in the range 10-40 nm are simulated. The simulation results are compared to the experimental data of the alumina nanopowders compaction. It is shown that the model allows us to reproduce experimental data reliably and, in particular, describes the size effect in the compaction processes. A number of different external loading conditions is used in order to perform the theoretical and experimental researches. The uniaxial compaction (the closed-die compaction), the biaxial (radial) compaction, and the isotropic compaction (the cold isostatic pressing) are studied. The real and computed results are in a good agreement with each other. They reveal a weak sensitivity of the oxide nanopowders to the loading condition (compaction geometry). The application of the continuum theory of the plastically hardening porous body, which is usually used for the description of powders, is discussed.

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Initial investigations on the preparation of highly transparent Fe 2+ :MgAl 2 O 4 ceramics using nanopowders synthesized in a laser plume were carried out. For the first time, dense Fe 2+ :MgAl 2 O 4 ceramics with high transmission in the mid-IR range were fabricated at a temperature as low as 1300°C and with a short sintering time (1 hour). The obtained Fe 2+ :MgAl 2 O 4 ceramics contain a secondary (MgO) 0.91 (FeO) 0.09 phase with a low wt% content, causing a substantial decrease in transmittance in the visible range. The transmittance increases with an increase in wavelength due to a decrease in Rayleigh scattering and reaches 85.6% at λ = 4 μm, which is close to the theoretical value. The absorption cross section of divalent iron ions was estimated to be σ = (1.66 ± 0.14) × 10 −20 cm 2 .