Enhanced high-temperature dielectric properties and microwave absorption of SiC nanofibers modified Si3N4 ceramics within the gigahertz range

Photocatalytic efficiency of Fe2O3/TiO2 for the degradation of typical dyes in textile industries: Effects of calcination temperature and UV-assisted thermal synthesis.

Reduced Graphene Oxide Functionalized Strontium Ferrite in Poly(3,4‐ethylenedioxythiophene) Conducting Network: A High‐Performance EMI Shielding Material

Synthesis of LiBaZrOx ceramics with a core-shell structure

A hypereutectic Al–15Si alloy (Si 15 wt.%, Al balance) was irradiated by high current pulsed electron beam (HCPEB). The HCPEB treatment causes ultra-rapid heating, melting and cooling at the top surface layer. As a result, the special “halo” microstructure centering on the primary Si phase is formed on the surface due to interdiffusion of Al and Si elements. The composition of the “halo” microstructure is distributed continuously from the center to the edge of the “halo”. Compared to an untreated matrix, the remelted layer underneath the surface presents single contrast because of the compositional homogeneity after HCPEB treatment. The thickness of the remelted layer increases slightly from 4.4 μm (5 pulses) to 5.6 μm (25 pulses). HCPEB treatment broadens and shifts the diffraction peaks of Al and Si. The lattice parameters of Al decreases due to the formation of a supersaturated solid solution of Al in the melted layer. Through analysis of Raman spectra and transmission electron microscopy (TEM), the amorphous Si (a-Si) and nanocrystalline Si are formed in the near-surface region under multiple bombardments of HCPEB. The relative wear resistance of a 15-pulse sample is effectively improved by a factor of 9, which can be attributed to the formation of metastable structures.

Improved wear resistance of Al–15Si alloy with a high current pulsed electron beam treatment

The oxidation kinetics of ultrafine metallic iron powder to hematite (α-Fe2O3) up to temperatures 800 °C were studied in air using non-isothermal and isothermal thermogravimetric (TG) analysis. The powders with average particles size of 90, 200, and 350 nm were made by the electric explosion of wire. It was observed that the reactivity of the iron powder is increased with the decreasing particle size of powder. The experimental TG curves clearly suggest a multi-step process for the oxidation, and therefore a model-fitting kinetic analysis based on multivariate non-linear regressions was conducted. The complex reaction can be best described with a three-step reaction scheme consisting of two concurrent and one parallel reaction step. In one reaction pathway Fe is oxidized to α-Fe2O3. The other pathway is described by the oxidation of Fe to magnetite (Fe3O4). At higher temperatures the formed Fe3O4 is further oxidized in a α-Fe2O3. It is established that the best fitting three-step mechanism employed a branching set of n-order equations for each step.

The oxidation kinetics study of ultrafine iron powders by thermogravimetric analysis

Structural, electromagnetic, and dielectric properties of lithium-zinc ferrite ceramics sintered by pulsed electron beam heating

Using the methods of X-ray phase and DSC analyses, a correlation is established between ordering/disordering of the structure of lithium pentaferrite (LPF—Li0.5Fe2.5O4−δ) and its nonstoichiometry with respect to oxygen. Ferrite specimens with a reduced content of oxygen were prepared by thermal annealing in vacuum (P = 2 × 10−4 mmHg). It is shown that this treatment results in oxygen nonstoichiometry and causes a transition of LPF into a state with random distribution of cations in the crystal lattice. Using nonisothermal thermogravimetry (TG), the kinetic dependences of oxygen absorption by the anion-deficient LPF are investigated within the temperature interval T = (350–640) °C in the course of its oxidation annealing in air. The kinetic experiment data are processed with the Netzsch Thermokinetics software. The oxidation rate constants, the effective coefficients, and the activation energy of oxygen diffusion in the material under study are derived. Their values are in a satisfactory agreement with those earlier obtained for the lithium–titanium ferrite ceramic material of the following composition: Li0.649Fe1.598Ti0.5Zn0.2Mn0.051O4−δ. The effective activation energy of oxygen diffusion in LPF calculated within the temperature interval T = (350–640) °C is found to be E
 d = 1.88 eV. In its value, it is close to the activation energy of oxygen diffusion along grain-boundaries in the lithium–titanium ferrite ceramic material.

Investigation of structural states and oxidation processes in Li0.5Fe2.5O4−δ using TG analysis

In the present work, the possibilities of application of the thermomagnetometry TG(M)/DTG(M) method for estimation of the phase homogeneity of end products of synthesis at different stages of ferritizing annealing are considered on the example of solid-state synthesis of Li0.5(1−x)Fe2.5−0.5xZnxO4 and Li0.5(1 + x)Fe2.5−1.5xTixO4 (x = 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6) lithium-substituted ferrospinels. Results of thermomagnetometric analysis are compared with XRD data. It is shown that the resolution of the TG(M)/DTG(M) method on two orders exceeds capabilities of the traditional XRD method. Considerable influence of both intermediate grinding and mixing of samples and concentration of an inducted impurity on the homogeneity of the synthesized powders is confirmed.

https://link.springer.com/content/pdf/10.1007%2Fs10973-012-2618-6.pdf

Analysis of the phase composition and homogeneity of ferrite lithium-substituted powders by the thermomagnetometry method

In the present work, the conventional method of increasing the efficiency of solid-phase synthesis of lithium–zinc ferrites that involves multiple intermediate grinding of briquetted reaction mixtures annealed at high temperatures is compared with a new radiation-thermal (RT) method using a high-power pulsed beam of accelerated electrons for heating of reaction mixtures. An analysis of the TG(M)/DTG(M) curves recorded in a magnetic field demonstrates that the efficiency of Li0.3Zn0.4Fe2.3O4 synthesis from Li2CO3–Fe2O3–ZnO mechanical mixture at a temperature of 700 °C during 120 min is equivalent to thermal annealing at 800 °C, but with the triple annealing duration.

A. P. Surzhikov

Papers

The oxidation kinetics study of ultrafine iron powders by thermogravimetric analysis

Structural, electromagnetic, and dielectric properties of lithium-zinc ferrite ceramics sintered by pulsed electron beam heating

Investigation of structural states and oxidation processes in Li0.5Fe2.5O4−δ using TG analysis

Analysis of the phase composition and homogeneity of ferrite lithium-substituted powders by the thermomagnetometry method

Thermogravimetric investigation of the effect of annealing conditions on the soft ferrite phase homogeneity