Yu. A. Kotov

Synthesis and dynamic compaction of ceramic nano powders by techniques based on electric pulsed power

Abstract Studies on the production of nanometer-sized powders by the exploding wire method were conducted. The aim of the work was to attain a particle distribution with a high yield of particles below 20 nm in size. Powders of alumina and titania were generated during the experiments by maintaining a definite partial pressure of oxygen inside the explosion chamber. The particles are spherical in shape with specific surfaces up to 100 m2/g. The output capacity is on the order of 1 kg/h with an energy consumption of 2 kWh/kg. Alumina powders crystallize in the gamma and delta structures, titania powders consist of anatase and rutile. The second part of the studies deals with the compaction of nano-sized powders by application of pulsed electro-magnetic power. For the compaction of nano-sized Al2O3 powder pressure pulses in the range from 1 GPa to 5 GPa, lasting 3 – 300 μs, were applied. The simply shaped bulk samples maintained a nano-crystalline structure and reached 62 to 83 % of the theoretical density.

A NOVEL NANOSECOND SEMICONDUCTOR OPENING SWITCH FOR MEGAVOLT REPETITIVE PULSED POWER TECHNOLOGY: EXP

A novel nanosecond semiconductor opening switch (SOS) has been developed which has a pulsed power of the GW range and voltage levels of up to a few 100s of kV. The SOS is based on high-voltage solid state rectifiers and is designed for pulsed power generators with inductive energy storage. A 30 115 opening phase duration. a 45 k A interrupted current. and a 450 kV opened SOS voltage have been attained with the use of a three-stage, 2 kJ. 150 kV open circuit Marx generator as the SOS driver. On the basis of the experimental results obtained, we have developed and tested repetitive high-current generators and accelerators with a 0.5 MV output voltage and a 15 to 100 ns pulse width. The ideology is presented of constructing high-power megavolt pulsed generators with an all-solid-state switching system. A description is provided of the setups developed on this principle. We discuss features peculiar to the setups developed and prospects of developing these further .

Novel nanosecond semiconductor opening switch for megavolt repetitive pulsed power technology: experiment and applications

A novel nanosecond semiconductor opening switch (SOS) has been developed which has a pulsed power of the GW range and voltage levels of up to a few 100s of kV. The SOS is based on high-voltage solid state rectifiers and is designed for pulsed power generators with inductive energy storage. A 30 ns opening phase duration, a 45 kA interrupted current, and a 450 kV opened SOS voltage have been attained with the use of a three-stage, 2 kJ, 150 kV open circuit Marx generator as the SOS driver. On the basis of the experimental results obtained, we have developed and tested repetitive high-current generators and accelerators with a 0.5 MV output voltage and a 15 to 100 ns pulse width. The ideology is presented of constructing high-power megavolt pulsed generators with an all-solid- state switching system. A description is provided of the setups developed on this principle. We discuss features peculiar to the setups developed and prospects of developing these further.

The electrical explosion of wire: A method for the synthesis of weakly aggregated nanopowders

This overview covers investigations and designs that demonstrate the opportunity to use the phenomenon of the electrical explosion of wire to produce weakly aggregated nanopowders of metals, alloys, mixtures, and oxides. Some general regularities that facilitate the choice of the circuit parameters and dimensions of the exploding wire necessary for producing particles of the required size are described. The limitations to synthesizing the nanopowders of some metals and oxides are indicated. The method is environmentally clean, offers sufficiently high output capacity, and is energy efficient.

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 of nanometer-sized ain powders by the exploding wire method

Abstract We have performed experiments to explore the possibility of making pure nanometer-sized AIN powders by electrical explosion of aluminum wire in an atmosphere of nitrogen-containing gases. It is shown that raising the density of the energy injected into the metal, applying increased pressures, and a high working-gas flow rate help assure the production of AIN powders with a specific surface up to 53 m 2 /g, d BET =35 nm. Particle shape ranges from nearly spherical to rigorous-cut particles. The yield of such powder accounts for 50 % of the total mass of powder. The powder thus produced contains no more than 1 wt. % of impurities, including oxygen.

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.

High-current electron beam generation by a metal–ceramic cathode

We present results of the investigation of a metal–ceramic cathode suitable for technological applications. The cathode was tested in electron diodes powered by two different high-voltage generators (500 kV, 50 ns, 300 Ω, ⩽200 Hz and 300 kV, 250 ns, 84 Ω, ⩽5 Hz). The metal–ceramic cathode which was made in a form of a disk was composed of TiO2 ceramics with stainless steel spherical particles uniformly inserted inside. It was shown that already at relatively low accelerating fields (E⩽5 kV/cm) fast cathode plasma formation occurs as a result of surface flashover. This surface flashover is initiated in triple points located in micropores which were formed during the process of cathode preparation due to the different thermal expansion coefficients of the ceramic and the metal. Experimental data concerning the uniformity of the light emission from the cathode surface and inside the anode–cathode gap and divergence of the generated electron beams are presented. Also, it is shown that the uniformity of the ge...

Formation of thin YSZ electrolyte films by electrophoretic deposition on porous cathodes

The structure, dispersity, stability, and electrophoretic deposition (EPD) of suspensions of spherical ZrO2 stabilized Y2O3 (YSZ) nanoparticles with a mean size of 10.9 nm onto the porous surface of La0.6Sr0.4MnO3 (LSM) with a pore size of 3–20 μm were studied by electron microscopy, photon correlation spectroscopy, and electroacoustical analysis. The optimum conditions of deposition were attained by using a mixed isopropanol-acetylacetone dispersion medium, which provided the aggregative stability of the suspension with 95% individual particles. The maximum pore size on the covered surface should be up to 0.5 μm if nanoparticles with a mean diameter of 10–20 nm are used. When the pores are larger, the EPD of YSZ will be effective if an additional intermediate LSM layer is formed by EPD to provide the required pore size.