A. M. Murzakaev

Properties of oxide nanopowders prepared by target evaporation with a pulse-periodic co2 laser

The design and characteristics of a setup for producing metal oxide nanopowders with an output of up to 20 g/h are discussed. The grain mean size in the powders is 15 nm, and the radiation power consumption is 30—40 (W h)/g. Y2O3-stabilized ZrO2 (YSZ) and Al2O3 + YSZ nanopowders are prepared by target evaporation with a pulse-periodic CO2 laser, followed by vapor condensation in an air stream. The mean power, peak power, and efficiency of the pulse-periodic CO2 laser, excited by a combined discharge, are, respectively, 1 kW, 10 kW, and ≈10%. Data for the powder specific surface, grain shape, and grain size distribution, as well as results of X-ray phase and structure analysis, are reported.

Production and characteristics of composite nanopowders using a fiber ytterbium laser

A fiber ytterbium laser is used to obtain weakly aggregated nanopowders for yttria-stabilized zirconia solid electrolytes, ZnO and ZnS phosphors, and YAG- and Y2O3-based optical ceramics. The characteristics of the nanopowders are reported. The productivity and energy consumptions of the process with the use of fiber and CO2 lasers are compared. The influence of the buffer gas pressure in the evaporation chamber on the specific surface area of the nanopowder and particle size distribution is studied. The elemental composition of nanoparticles is found to change relative to the composition of the target when yttrium aluminum garnet is evaporated. In the pulsed mode of operation, the energy needed for nanopowder production is minimal when the radiation pulse is about 100 μs long.

Properties of powders produced by evaporating CeO2/Gd2O3 targets exposed to pulsed-periodic radiation of a CO2 laser

The characteristics (phase composition, grain shape, grain size distribution, and specific surface area) of Ce0.78Gd0.22O2-δ nanopowders produced by exposing the target to pulsed CO2 laser radiation are reported. Reasons for a threefold increase in the output of the experimental powder-preparation unit (up to 60 g/h) with the characteristic grain size (≈10 nm) remaining unchanged are discussed.

Aggregation of air-dry alumina powder nanoparticles redispersed in an aqueous medium

The aggregation of air-dry Al2O3 nanopowders prepared by electrical wire explosion (EWE) and plasma deposition in a gas atmosphere was studied by dynamic laser light scattering during redispersion in water. The specific surface of nanopowders was from 9 to 38 m2/g. It was shown that aqueous suspensions of nanopowders stabilized by a double electric layer with an electrokinetic ξ-potential magnitude of 30–40 mV contain coexisting individual particles and their primary aggregates (35–50 wt %). The average size of the primary aggregate is approximately three times larger than the average size of an individual particle. The former probably consists of a central particle surrounded by the first coordination sphere. As the medium pH varies from 2.5 to 11.5, the electrokinetic potential of the Al2O3 nanoparticle suspension monotonically decreases from +40 to −40 mV. Near the isoelectric point (IEP), aggregation is significantly enhanced, which results in the formation of larger secondary aggregates of 103–104 individual particles. The use of Na citrate as an electrostatic stabilizer prevents the formation such large aggregates, and only an increase in the fraction of primary aggregates and a decrease in the number of individual particles occur near the IEP.

Properties of nickel oxide nanopowders prepared by electrical explosion of a wire

The properties of NiO nanopowders prepared by electrical explosion of a wire in an oxygen-containing atmosphere are presented. Most of the NiO nanopowders are found to be oxygen-enriched, the excess of oxygen depending mainly on the nickel vapor concentration. The dependences of the powder particle size on the oxygen concentration and overheating of the exploding metal are discussed. The powder nanoparticles are both single-crystal and polycrystalline with a rhombohedral lattice and have different shapes (from cubic to spherical). There typical sizes range from 15 to 50 nm, depending on the explosion conditions.

Iron oxide nanopowders prepared by the electroexplosion of wire

We have studied the effect of process parameters (supplied energy, oxygen concentration in the gas mixture, and others) on the particle size and yield of iron oxide nanopowder obtained by the electroexplosion of wire. Under optimal conditions, up to 25% of the particles in the powder were 15–20 nm in size (specific surface of up to 100 m2/g). Using several independent characterization techniques, we determined the phase composition, elemental composition, and structure of the material in the bulk and on the surface of the particles. The majority phase in the powder (90–98 wt %) is the metastable oxide γ-Fe2O3, which is sufficiently stable under ordinary storage conditions. The powder also contains the stable oxide α-Fe2O3. The effect of annealing in air and helium on the phase composition and carbon content of the powder is examined. The results are interpreted in terms of redox and diffusion processes.

Electrochemical properties of cathodes made of (La,Sr)(Fe,Co)O3 containing admixtures of nanoparticles of cupric oxide and intended for fuel cells with a solid electrolyte based on ceric oxide

The electric and electrochemical characteristics of cathodes made of La0.6Sr0.4Fe0.8Co0.2O3−δ (LSFC) and intended for fuel cells with electrolytes based on ceric oxide are studied. Adding cupric oxide into the LSFC cathode is shown to exert a favorable effect of the properties of the LSFC-CuO/SDC electrode system, where SDC stands for the CeO2-Sm2O3 electrolyte. The effect produced by cupric oxide when added in the form of nanopowder is perceptibly greater than in the case of micropowdered CuO. Adding a mere 0.5 wt % of nanopowdered CuO reduces the LSFC cathode resistance nearly tenfold. The cathode’s adhesion to the electrolyte substantially improves as well, which makes it possible to lower the cathode’s firing temperature by 100°C. The maximum of electrochemical activity is intrinsic to cathodes containing 2 wt % CuO, with the caking temperature of 1000°C. According to a 2011-h life test of the LSFC-SDC composite cathodes containing nanopowdered CuO, temporal stability of their electrochemical characteristics improves with the SDC content. The time dependences of the polarization resistance of cathodes containing 40–50 wt % SDC look like decaying exponential curves. The steady-state polarization resistance, calculated on the basis of this, is equal to 0.1–0.2 ohm cm2. At an overvoltage of less than 100 mV, the cathodes may provide for a current density of 0.5–1.0 A cm−2.

Localization of uranium in radiation-damaged nanoheterogeneous natural zircon

High-uranium natural zircon with signs of hydrothermal (up to 300°C) treatment is studied via transmission electron microscopy, Raman spectroscopy, electron probe microanalysis, and local energy-dispersive analysis performed in situ with a transmission electron microscope. Uranium-based phases are not found in the regions with uranium concentrations of up to 10 wt % that exceed considerably the limit of solubility in synthetic zirconium silicate. Uranium is dissolved in a heterogeneous matrix that is formed as a result of the decomposition of radiation-damaged (a dose of 1017 α-decays/mg) zircon under hydrothermal influence. The matrix incorporates amorphous partially hydrated silicon oxide and nanocrystalline cubic (Zr,Hf)1-yMeyO2 stabilized with metal Me impurities (Y, Ca, Al, Fe; y ≈ 0.04). Cubic zirconium oxide is regarded as the preferred phase for uranium localization, while the total impurity concentration is ~0.13.

Forming a carbide coating on the surface of aluminum nanoparticles and producing nanopowders from Al-Al4C3 using the method of electric explosion of wire

The controlled feeding of butane to inert working gas in the process of producing aluminum nanopowders using the method of electrical explosion of wire (EEW) allows carbide coatings to be formed on the surface of aluminum particles, reducing the agglomeration of the particles and producing Al-Al4C3 nanopowders of various compositions and dispersivity. The dependences that the specific surface area of powder, the content of crystalline aluminum carbide, and the phase composition of powders have on the quantity of the butane fed at different values of energy input into the wire are presented. The morphology of the particles is examined. The powders were analyzed using BET, X-ray diffraction (XRD), thermogravimetry-differential scanning calorimetry-mass spectrometry (TG/DSC/MS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM).

Properties of the translucent ceramics Nd: Y2O3 prepared by pulsed compaction and sintering of weakly aggregated nanopowders

A translucent cubic yttria ceramic material doped by neodymium, namely, 1Nd: Y2O3, with particles of micrometer size (5–17 μm) and clearly defined boundaries is synthesized from nanopowders prepared by laser-induced evaporation with the use of magnetic pulsed compaction and vacuum sintering. Owing to the high activity of nanoparticles, the sintering is performed at temperatures below 1750°C without densifying additives. An increase in the sintering temperature to 900°C leads to an increase in the visual transparency of the ceramic materials and a decrease in the radiation attenuation coefficient. The samples of the translucent ceramics are characterized by rather large values of the microhardness (11.8 GPa) and the fracture toughness as compared to those of single crystals of the same composition. The fracture toughness of the ceramic material increases by a factor of approximately 2.5 with a decrease in the average crystallite size from 5.0 to 0.6 μm.