G. P. Murav'eva

Stability of Tetragonal ZrO2 toward External Influences

The response of the nonequilibrium phase T-ZrO2 to various physicochemical influences was studied by x-ray diffraction analysis. The results indicate a significant sensitivity of the T-ZrO2 → M-ZrO2 phase transition to some of the influences: pressing at elevated temperatures (100–250°C) accelerates the formation of the equilibrium phase, whereas Al2O3 additions notably slow down the process (stabilize the metastable phaseT-ZrO2). Mechanochemical treatment and freezing at 77 K have no effect on the character of the phase transition.

Microwave Synthesis of γ-Fe2O3

Fine-particle Fe2O3 is prepared via microwave processing of Fe(NO3)3 · nH2O, followed by low-temperature annealing. The particle size of the resulting γ-Fe2O3 is 5–6 nm after microwave processing and 80–110 nm after subsequent low-temperature heat treatment.

Topochemical Memory Effect in the Formation of Barium Hexaferrite

The topochemical memory effect in Ba(NO3)2 : Fe2O3 = 1 : 6 reaction mixtures containing α-Fe2O3 with different particle sizes was studied at low (540–630°C; the main reaction product BaFe2O4) and high (900–930°C; the main product, BaFe12O19) reaction temperatures. The results indicate that the particle size of Fe2O3 has a significant effect on the BaFe2O4 yield in the low-temperature solid-state reaction (<585°C), in contrast to the liquid-assisted reaction (>585°C). In the subsequent high-temperature solid-state reaction (900–930°C), the BaFe12O19 yield depends on the particle size of Fe2O3 , regardless of the initial reaction temperature. It is shown that, to achieve a high BaFe12O19 yield, the process conditions should be optimized in both the low- and high-temperature stages.