Yu. A. Kunitskii

Doped ZnS:Mn nanoparticles obtained by sonochemical synthesis.

A study of sonochemically synthesized ZnS:Mn nanoparticles is presented. The particles prepared at low rf power (about 20 W) and room temperature coalesce to form morphologically amorphous large species (30-100 nm in diameter). As the power is increased in the range from 20 to 70 W, and the solution temperature is raised to 60 to 80 degrees C, finer particles are produced with the size ranging from 2 to 20 nm and improved crystallinity. The results indicate the dispersion of the Mn(2+) ions at near-surface sites in the particles. It is shown that the sonochemically fabricated particles approach the quality of the ones obtained by a standard chemical route and show a reasonable luminescence performance.

Structure and properties of gas-thermal coatings of Fe-B-C and Fe-Ti-B-C alloys

This article presents the results of investigations of the structure and certain properties of gas-thermal coatings of Fe/sub 61/B/sub 37/C/sub 2/ and an alloy of similar composition with the addition of titanium which may be described by the formula Fe/sub 67/Ti/sub 7/B/sub 24/C/sub 2/.

Structural characteristics of flame-sprayed Fe-Ni-B alloy coatings

ConclusionsFlame-sprayed Fe40Ni40B20 alloy coatings have a mainly amorphous structure with a small amount of fine, 0.5- to 1-μm.crystalline inclusions. The crystalline phases are (Fe, Ni)3B and Fex Ni23-xB6. The structure of the precipitated crystalline inclusions in the amorphous matrix is not related to that of the eutectic of the starting alloy powder used for spraying. In the direction from the base to the free surface the coating structure varies: The volume concentration of the crystalline phases changes, which is reflected in the emission of secondary ions of the main components of the deposited alloy.

Variational Calculations of Positron Characteristics in Metals

Energies of the formation of monovacancies, as well as the binding energies and work functions of quasi-free and localized positrons and positroniums have been calculated in terms of the gradient version of the density-functional method using the stable-jellium model. The calculations show that for the metals possessing negative positron work function, the presence of vacancies in the subsurface region can lead to the change in the sign of the work function. The same effect of the change in the sign of the work function of a quasi-free positron can be caused by the presence of a dielectric coating on the metal surface. Comparison with the experiment is performed.

Effect of a thermal factor on the concentration-structure ordering in ion-plasma W-Ti-B condensates

Small-angle X-ray scattering is used to study the effect of deposition and annealing conditions on the concentration-structure ordering in ion-plasma W-Ti-B condensates. At a relatively low condensation temperature of a solid solution (up to Tc = 770 K), the formed modulated structure has a uniform volume distribution of its structural elements. A stage-by-stage transition from a volume-modulated to a two-dimensional modulated structure is revealed when the condensation temperature increases from 570 to 1170 K. As the annealing time of the metastable postcondensation state of an ion-plasma condensate increases, the diffusion mobility of metallic atoms (W, Ti) decreases upon the formation of a modulated ordered structure. The action of a radiation factor in a three-electrode ion sputtering scheme enhances the concentration phase separation in a condensate, decreases the transition temperature, and stimulates an increase in concentration ordering wavelength λod.

Structural transformations occurring in flame-sprayed Ni60Nb40 alloy coatings during heating in the presence of oxygen

ConclusionsDuring the heating of flame-sprayed Ni60Nb40 alloy coatings in the presence of oxygen the process of crystallization of their amorphous matrix occurs at T > 750°K through the formation of the niobium oxide Nb2U5 and precipitation of nickel. Decomposition of the amorphous matrix is accompanied by a decrease in length of the coatings. The oxidation of niobium at 750–890°K prevents the formation of the equilibrium phases of the Ni-Nb system during the crystallization of the amorphous structure. During heating in the 890–1110°K range the metastable Ni8Nb phase is present in the coatings.

Structure and some physical properties of plasma-sprayed coatings of the nickel boride Ni3B

ConclusionsDuring plasma-spraying a multiphase structure composed of an amorphous matrix and crystalline Ni, Ni2B, and Ni3B phases forms in an Ni3B alloy. In the range 360–530° K the amorphous matrix experiences structural relaxation, which is responsible for a nonmonotonic character of the temperature dependence of the electrical resistivity and elongation of coatings. The amorphous phase crystallizes in the region of 570°K. The decomposition of the amorphous structure leads to a fall in electrical resistivity and to the appearance of a volume effect. Phase transitions in the range of postcrystallization temperatures for the amorphous structure have a less marked effect on the ρ = f (T) and ΔZ/Z300°K = f(T) relationships.