S. A. Ghyngazov

Investigation of Diffusion of Magnesium in Lithium Fluoride Crystals by the SIMS Method

Using secondary ion mass spectroscopy, diffusion of magnesium impurity in lithium fluoride is investigated. A temperature dependence of the magnesium diffusion coefficients within the temperature interval 870–1073 K is established, which is described by an expression of the following type: D = 2.8·10–3·exp(–1.5/kT). Combining the data on self-diffusion of cations with the results of the ion conductivity measurements, estimation is made of the thermodynamic parameters characterizing the jump of a diffusant. The calculated frequencies of the impurity ion jump to the cation vacancy are reported.

Determination of the oxygen diffusion coeficient in polycrystalline Li-Ti ferrites

Two independent methods, the isotope method based on nuclear microanalysis and the method based on measuring the electronic-conductivity activation energy, are used to determine the grain-boundary diffusion and volume diffusion of an oxygen isotope 18O in a polycrystalline lithium-titanium ferrite at the thermal annealing temperature 1073 K. A comparative analysis is conducted of the potential of the methods in studying oxygen diffusion in the material concerned. It is shown that the technique for obtaining the diffusion parameters from the electronic conductivity measurements allows a comparatively precise determination of both the volume and grain-boundary diffusion coefficients of oxygen in polycrystalline ferrites.

The effect of a low-energy high-current pulsed electron beam on surface layers of porous zirconium ceramics

The effect of a high-current pulsed electron beam of low-energy electrons on surface layers of porous zirconium ceramics has been studied. It is established that electron treatment leads to melting of the surface layer and its subsequent crystallization accompanied by the formation of a microstructure differing from the initial state. It is established that porosity decreases in the treatment region, the size of grains increases, and their shape changes. Grains are found to arrange themselves in the direction to the sample surface. Their linear sizes in the transverse and longitudinal directions are, respectively, 1.4 and 7 μm on average, i.e., differ significantly. It is shown that the surface layer modified by an electron beam is characterized by elevated microhardness as compared with the initial state.

Study of the Influence of Uniaxial Strain and Electron Irradiation on the Deformation of Polytetrafluoroethylene Film

Experimental studies of the dependence of the deformation ε1max on the strain σ and the relative changes in the width and thickness of the unirradiated and irradiated polytetrafluoroethylene film on the relative elongation are carried out. It was found that these quantities depend essentially on the load. The curves obtained are satisfactorily described by a linear model.

Influence of Mechanical Treatment on Consolidation Processes of Ultradisperse Powders of Stabilized Zirconium Oxide

The effect of preliminary machining of ultradisperse powders of stabilized zirconium dioxide and its composite on consolidation in compacts under uniaxial static pressing and subsequent sintering is studied. The investigations were carried out with powders of compositions (in mol %) 97ZrO2–3Y2O3 and 80Al2O3–20(ZrO2–Y), which were obtained by the sol-gel and the plasma-chemical method, respectively. Mechanical processing of powders was carried out in two ways. The first method consisted in preliminary static pressing of powders at elevated pressure of 900 MPa and their subsequent grinding in a ball mill. The second method consisted in grinding the initial powders in an Activator-2SL planetary mill with drums and grinding balls of zirconia. It is established that mechanical treatment significantly affects the density of compacts. In this case, there is no strict correlation between the density of the sintered ceramic and the density of compacts. With increasing density of compacts, their expansion can be observed at the isothermal holding stage, which leads to a decrease in density of the ceramic. It is shown that, in dry grinding to improve the technological properties of ultradisperse powders obtained by the sol-gel and plasma-chemical methods, the most suitable is the method of mechanical treatment, which consists in pre-pressing the powders at elevated pressure and then grinding them in a ball mill.

Diffusion mass transfer in ionic materials under intense electron irradiation

The results of studies on the impact of an electron beam with the energy of 1-2 MeV on diffusion processes in materials with ionic bonds are presented in the paper. Used electron beam intensity is allowed to provide heating of the material to temperatures of 1600 K. Diffusion of Na, Mg, Al ions into single crystals KBr in the temperature range 573-883 K, Al ions in the NiO-AlO system at 1373-1573 K, was studied. Diffusion annealing carried out under thermal and radiation-thermal heating of the samples. Then diffusion coefficients were determined. It was found stimulating action of irradiation on diffusion processes of Mg, Al ions in Kbr and Al ions in the NiO-Al2O3 system, which consists in increasing the diffusion coefficients at radiation-thermal annealing. The observed effect is achieved by increasing the effective rate of diffusion jumps.

Influence of an initial chemical state of cation impurities on their diffusion in ionic crystals

Depth profiles of magnesium, fluorine and oxygen impurities was examined in the surface layers of alkali-halide crystals using method of secondary ion mass spectrometry. Samples of potassium bromide, coated with a surface film of magnesium fluoride were subjected to isothermal diffusion annealing in air at various times. It is shown that the diffusion of O ions occurs from the ambient atmosphere besides the diffusion of Mg and F ions during annealing of KBr crystals. Accurate estimation of the diffusion coefficients of cationic impurity Mg requires taking into account the possible interaction of this impurity and oxygen. The effect of an intensive electron beam on diffusion of magnesium impurity in crystals of fluoride of lithium is studied.

Electron microscopy studies of near-surface layers of ZrO2(Y)-Al2O3 composite ceramic modified by high-current beam of low-energy electrons

The influence of a high-current pulsed beam of low-energy electrons (HCBLE) on the structural state of near-surface layers of ZrO2(Y)-Al2O3 composite ceramic with various levels of porosity is studied using scanning electron microscopy (SEM). It is demonstrated that the electron processing leads to melting and subsequent crystallization of the ceramic near-surface layer with thickness of 30–40 μm. The surface microstructure and cross section of electron-beam-modified layers of ceramic specimens are analyzed using SEM. It is revealed that, in the irradiated near-surface layer of all considered ceramic types, there are actually no pores and grains of the corundum phase. It is found that electron beam irradiation leads to a decrease in grain size and formation of texture in the near-surface layers.

Investigation of the structural–phase state of ultrafine plasmochemical ZrO2 (Y) powders

The methods of X–ray phase analysis, thermogravimetry and differential scanning calorimetry were used to study the structural and phase state of ultrafine powders (UFP) of ZrO2(Y) obtained by plasmochemical synthesis. It is shown that these UFPs are in a highly nonequilibrium state due to the presence of adsorbates and bound water, and the distribution of the stabilizing impurity in the volume of the particles is nonuniform.

The Effect of Atmospheric Ionization on Oxygen Diffusion in Polycrystalline Ferrites under e-Beam Irradiation

It is shown that activation of the process of oxygen diffusion in polycrystalline lithium-titanium ferrites heated by a beam of high-energy electrons in the range of temperatures 873–1173 K occurs due to two factors: gas medium ionization by an e-beam and acceleration of diffusion processes directly in the matrix in the irradiation field.