N. N. Oleinikov

Application of non-linear heating regime for the determination of activation energy and kinetic parameters of solid-state reactions

Abstract In the present research, we suggested non-linear heating regime for the thermogravimetric (TG) determination of kinetic parameters of solid-state reactions. The method is based on the application of a hyperbolic heating mode. The method allows the reaction activation energy and kinetic function to be obtained from a series of non-isothermal experiments. Kinetics of the model solid-state reaction Fe 2 O 3 +Li 2 CO 3 =2LiFeO 2 +CO 2 was investigated by the suggested method. The kinetic parameters obtained are in a good agreement with the reference data.

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.

XPS study of water vapour effect on high-TC superconductor surface

Abstract XPS study of the YBaCuO and BiSrCaCuO high-T C superconductor (HTSC) surface layer degradation under water vapour effect has been carried out. Detailed quantitative analysis with the use of the argon ion sputtering has been performed and the degradation products separation within the surface layer has been observed. The similarities and differences between Y- and Bi-based HTSC surface layer changes are discussed.

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.

Interaction of X-ray Amorphous Aluminum Oxide with Lithium Carbonate: Effect of the Chemical History of Aluminum Oxide

The high-temperature (950–1050°C) crystallization behavior of x-ray amorphous Al2O3 and its reaction with lithium carbonate in the range 500–700°C were studied using Al2O3 samples prepared by five different procedures: thermal decomposition of Al(NO3)3 · 9H2O, Al2(C2O4)3 · nH2O, aluminum hydroxides synthesized via Al3+ precipitation from aluminum nitrate and aluminum chloride solutions by a 20% excess of a concentrated NH4OH solution, and sol–gel-prepared aluminum hydroxide. The results demonstrate that the preparation procedure has a significant effect on the crystallization behavior and solid-state reactivity of x-ray amorphous aluminum oxide.

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.

Physicochemical Properties of R1 – xBaxMnO3 ± δ(R = Rare Earth) Solid Solutions

Nd1 – xBaxMnO3 ± δ(0.1 ≤ x≤ 0.5) and R0.7Ba0.3MnO3 ± δ(R = La, Pr, Sm, Eu) solid solutions were prepared from nitrate mixtures by solid-state reactions in air and were characterized by x-ray diffraction and thermogravimetry. The oxygen content of the solid solutions was determined by iodometric titration. The materials were found to have a nearly perfect oxygen stoichiometry (δ ≃ 0). As shown by pH measurements, the solid solutions have a high water resistance (extent of water degradation no larger than 0.1%). The dissociation of the Nd1 – xBaxMnO3 ± δ(0.2 ≤ x≤ 0.4) solid solutions was studied as a function of temperature and oxygen partial pressure (–10 ≤ log(Po2 /Pa) ≤ 1.4) by a special TG technique.

Disaggregation of iron powders at low temperatures

ConclusionsA study was made of the dis aggregation of metallic iron powders at the boiling point of liquid nitrogen. Cryogenic comminution is shown to have advantages over mechanical comminution under ordinary conditions.