E. V. Kalinkina

Solid-state synthesis of nanocrystalline strontium zirconate assisted by mechanical activation

Nanocrystalline SrZrO3 has been synthesized by a solid-state procedure using mechanical preactivation of a strontium carbonate–zirconia mixture in an AGO-2 centrifugal planetary mill. The effect of mechanical activation of the reactant mixture on the processes occurring during its subsequent heating has been studied by thermal analysis. The resulting strontium zirconate has been characterized by X-ray diffraction and by scanning and transmission electron microscopy.

Influence of mechanical activation on the kinetic features of SrZrO3 formation

Strontium zirconate SrZrO3 has been synthesized via heating of equimolar mixture of SrCO3 and ZrO2 at 900–1050°C with and without preliminary mechanical activation of the reactants. Data on the degree of SrZrO3 formation have been analyzed using the basic equations of the kinetics of solid-state reactions. The best agreement of the theoretical prediction with the experimental results has been obtained in the case of the Zhuravlev-Lesokhin-Tempelman equation. Mechanical activation of the SrCO3-ZrO2 mixture for 2–10-min causes marked acceleration of SrZrO3 formation in the course of subsequent sintering.

Effect of the mechanical activation of nepheline concentrate on its binding properties in mixed cements

Binding properties of a Portland cement-nepheline-water formulation were studied in relation to its nepheline content by using a preliminary mechanical activation. A thermal analysis was used to estimate the hydration rate of cement phases in the system under study. The accelerating role of nepheline in hardening of mechanically activated Portland cement-nepheline formulations was revealed and found to be more pronounced in early stages. The gain in the strength of the cement stone was analyzed in relation to the formulation composition and hardening duration.

Solid-state synthesis of nanocrystalline BaZrO3 using mechanical activation

Nanocrystalline BaZrO3 has been prepared by solid-state reaction, using preliminary mechanical activation of a stoichiometric mixture of BaCO3 and ZrO2. The mechanical activation was performed in an AGO-2 centrifugal planetary mill for 10 min at a centrifugal factor of 40g. The effect of mechanical activation of the reactant mixture on the processes that take place during subsequent heating of the mixture has been studied using a combination of thermoanalytical techniques. The synthesized barium zirconate, with an average crystallite size from 50 to 100 nm, has been characterized by X-ray diffraction and scanning and transmission electron microscopy.

Interaction of magnesia-ferriferous slag with sodium hydroxide solutions: Experimental and physicochemical modeling

The effect of carbon dioxide as milling medium on the ability of magnesia-ferriferous slag to dissolve in alkali solutions was examined. The degree of extraction of silicon and aluminum from the slag into a sodium hydroxide solution was studied in relation to the milling time in a ball mill, milling atmosphere, and NaOH concentration. The surface of slag particles mechanochemically carbonated upon grinding in a carbon dioxide atmosphere exhibits enhanced reactivity, which is consistent with an increase in the compression strength of geopolymer samples prepared on the basis of this slag. The experimental results are in good agreement with the results of thermodynamic modeling of the interaction of slags with alkali using Selektor program complex.

Effect of mechanical activation on kinetic features of BaZrO3 formation

Barium zirconate BaZrO3 has been prepared via heating of equimolar mixture of BaCO3 with ZrO2 at 900–1050°C with and without preliminary mechanical activation of the reactants. Degree of BaZrO3 formation has been analyzed using basic equations of kinetics of solid-phase reactions in comparison with analogous synthesis of strontium and calcium zirconates. The relative efficiency of mechanical activation in the zirconates synthesis follows the Ca > Sr ≈ Ba series.

Binding properties of ferromagnesian slags after mechanical activation with alkaline-earth carbonates

We have studied the feasibility of improving the reactivity of ferromagnesian slag through the mechanical activation of the slag with small additions of carbonate minerals in a centrifugal planetary mill. The results demonstrate that, like in the case of the mechanical activation of the slag in a carbon dioxide atmosphere, the process leads to a similar carbonization product, which is considerably more capable of hydraulic hardening than is the slag mechanically activated in air. The highest strength is offered by slag-carbonate materials containing 0.25–1 wt % carbonate (in terms of CO2).

Synthesis of geopolymer materials based on slags of nonferrous metallurgy with the use of mechanoactivation

The production of geopolymer material (alkali-activated cement) is investigated as a result of the interaction of the mechanoactivated granular magnesite-ferriferrous slag, which is the processing waste of copper-nickel ores and alkali silicate. The preliminary mechanoactivation of the slag in carbon dioxide is demonstrated to result in an increase in the strength of geopolymer samples in comparison to similar processes in air. The mechanism of the effect of CO2 as a medium for slag mechanoactivation on the physical-mechanical properties of geopolymer is proposed.

Nanostructure of CaMgSi 2 O 6 (Diopside) and CaTiO 3 (Perovskite) mechanically activated in carbon dioxide

The micro- and nanostructure of materials resulting from mechanochemical interactions of natural diopside (CaMgSi2O6) and synthetic perovskite (CaTiO3) with CO2 have been studied by transmission electron microscopy (TEM) and high-resolution TEM. The results indicate that CO2 absorption is accompanied by CO2 “dissolution” in the form of CO32− ions in the structurally disordered silicate or titanate matrix. The diopside activation product is a quasi-homogeneous amorphous carbonate-silicate phase. The mechanically activated perovskite is a nanocomposite consisting of CaTiO3 nanocrystals embedded in a carbonated amorphous titanate matrix.

Solid-phase synthesis of nanocrystalline lanthanum zirconate using mechanical activation

Nanocrystalline lanthanum zirconate La2Zr2O7 was synthesized by the solid-phase method using preliminary mechanical activation of a La2O3 and ZrO2 mixture. Processes occurring during heating the mixture of mechanoactivated lanthanum and zirconium oxides were studied using the X-ray phase analysis, IR spectroscopy, and complex thermal analysis. Synthesized lanthanum zirconate was characterized by the X-ray phase analysis and transmission electron microscopy methods.