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

Structural, morphological and magnetic properties variation of nickel-manganese ferrites with lithium substitution

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.

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

Using non-isothermal thermogravimetry (TG), the oxidation kinetics of oxygen-deficient lithium-titanium ferrospinel, Li0.649Fe1.598Ti0.5Zn0.2Mn0.051O4-d, manufac- tured by ceramic engineering is investigated. The oxidation annealing of powder samples is performed in air. Accord- ing to the X-ray phase analysis, the processes giving rise to variations in oxygen content occur within single-phase spinel structure. The experimental kinetic results are pro- cessed using the Netzsch Thermokinetics software. The oxidation rate constants and the effective coefficients of atmospheric oxygen diffusion into the ferrites are deter- mined. The effective activation energy E of oxygen dif- fusion is found to be 1.95 eV. It is demonstrated that an increase in the oxygen non-stoichiometry parameter d as a result of recovery annealing of ferrite powders in vacuum at T = 1,070 K for 2 h gives rise to a slight decrease in E down to 1.89 eV. The activation energy of oxygen grain- boundary diffusion is identified by the electroconduction method. The resulting value 1.93 eV is fairly consistent with that obtained by TG.

Investigation of oxidation processes in non-stoichiometric lithium–titanium ferrites using TG analysis

Kinetic changes in the phase composition of the Li2CO3–Fe2O3–ZnO system are investigated by the methods of X-ray phase and TG/DTG analysis. The powder mixture components were in the ratio corresponding to Li0.4Fe2.4Zn0.2O4 ferrite. The synthesis was performed by thermal heating of mixture reagents in a furnace and heating of the mixture upon exposure to high-power beam of accelerated electrons with energy of 2.4 MeV. It is demonstrated that the sequence of phase formation is independent of the heating method. The radiative effect of synthesis intensification is most strongly manifested in the initial stage of forming lithium monoferrite phases. The rate of diffusion interaction of intermediate phases also increases upon exposure to the electron beam in the stage of end-product formation.

Dependence of lithium–zinc ferrospinel phase composition on the duration of synthesis in an accelerated electron beam

The influence of mechanical activation of the Li2CO3–Fe2O3 initial reagents on ferrite phase formation in lithium ferrite LiFe5O8 is investigated. Methods of x-ray powder diffraction (XRD) and thermomagnetometry with differential scanning calorimetry (TG(M)/DSC) are used to compare the efficiency of nonisothermal synthesis at identical temperatures and burning times of the initial and mechanically activated reagent mixtures. It is demonstrated that preliminary mechanical activation of the initial Li2CO3–Fe2O3 reagent mixture considerably increases the reactivity of the solid phase system, thereby allowing the temperature of the thermal synthesis of lithium ferrite LiFe5O8 to be decreased significantly.

Influence of mechanical activation of initial reagents on synthesis of lithium ferrite

It is shown that layer-by-layer measurements of the electron-transfer activation energy in polycrystalline ferrites allow the profiles of depth distribution of oxygen introduced from the atmosphere into a ferrite at the stage of sintering or thermal treatment to be studied using a simple experimental technique. The analytical equations proposed here make it possible to determine the volume and grain-boundary diffusion coefficients of oxygen using a minimum number of adjustable parameters.

Grain-boundary diffusion of oxygen in polycrystalline ferrites

In the present paper, the phase composition and morphology of lithium-titanium ferrospinel, synthesized by ceramic technology and subjected to thermal (T) and radiation-thermal (RT) annealing at a temperature of 1373 K, are studied. RT annealing of samples was performed by heating radiation of high-power electron beam pulses with energy 1.8 MeV. Bulk-density powders and powders compacted under a pressure of 1200 kg/cm2 were used as samples. The results obtained indicate the polyphase composition of initial powders. Annealing decreases the relative content of the secondary LiFeO2-based phase and increases the relative content of the master LiFe5O8-based phase. The efficiency of this process depends on the powder compactness and the heating regime. RT annealing significantly increases the rate of dissolution of the LiFeO2-based phase. An impact diffraction analysis has shown that the secondary phases have polycrystalline structures, whereas the LiFe5O8-based phase is formed by monocrystalline particles. Annealing of the compacted powder by an electron beam completely eliminates polycrystalline aggregates with ultradisperse grained structure.

A. M. Pritulov

Papers

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

Dependence of lithium–zinc ferrospinel phase composition on the duration of synthesis in an accelerated electron beam

Influence of mechanical activation of initial reagents on synthesis of lithium ferrite

Grain-boundary diffusion of oxygen in polycrystalline ferrites

Electron-microscopic study of morphology and phase composition of lithium-titanium ferrites