S. N. Paranin

Densification of Nano-Sized Alumina Powders under Radial Magnetic Pulsed Compaction

An influence of aggregation degree of alumina nanopowder and of radial magnetic pulsed compaction conditions on the powder densification and on the density distribution inside compacts has been investigated experimentally. The usage of radial magnetic pulsed compaction allows to compact alumina nanopowders up to high densities at low degree of aggregation. The compacts homogeneity is attained by appropriate compaction pulse duration and by the usage of powder packing prior to compaction until the condition with high local sound speed is achieved.

End Closure Joining of Ferritic-Martensitic and Oxide-Dispersion Strengthened Steel Cladding Tubes by Magnetic Pulse Welding

The magnetic pulse welding (MPW) technique was employed for the end closure joining of fuel pin cladding tubes made of ferritic-martensitic (FM) steel and oxide-dispersion strengthened (ODS) steel. The technique is a solid-state impact joining process based on the electromagnetic force, similar to explosive welding. For a given set of optimal process parameters, e.g., the end-plug geometry, the rigid metallurgical bonding between the tube and end plug was obtained by high-velocity impact collision accompanied with surface jetting. The joint region showed a typical wavy morphology with a narrow grain boundary-like bonding interface. There was no evidence of even local melting, and only the limited grain refinement was observed in the vicinity of the bonding interface without destructing the original reinforcement microstructure of the FM-ODS steel, i.e., a fine grain structure with oxide dispersion. No leaks were detected during helium leakage test, and moreover, the rupture occurred in the cladding tube section without leaving any joint damage during internal pressure burst test. All of the results proved the integrity and durability of the MPWed joints and signified the great potential of this method of end closure joining for advanced fast reactor fuel pin fabrication.

Electrochemical cell with solid oxide electrolyte and oxygen pump thereof

The paper presents the scientific basis and technical implementation of a method for obtaining oxygen by extraction from air using an electrochemical cell based on a solid oxide cell (SOC) with anion-conducting solid electrolyte. A nanopowder of a weak aggregate of the YSZ solid electrolyte and LSM fine powder was used to manufacture SOC. The electrolyte-electrode SOC structure was formed as a tube by joint pressing of functional layers and the further co-sintering at the temperature of 1200°C. The characteristics of an electrochemical cell of the oxygen pump based on a thin-wall tube of the YSZ supporting electrolyte (150 μm) with symmetrical electrodes based on LSM (∼20 μm) are studied. A prototype of a compact oxygen generator (oxygen pump) is developed and manufactured with an electrochemical part based on three serially connected SOCs. The connection is implemented in the form of metallic couplings of the Crofer 22 APU steel. The method of reaction magnetron sputtering was used to protect current leads from corrosion by applying a coating based on a MnxCo3 − xO4 spinel. The efficiency of a demonstration prototype at 800°C was 9 l/h at the power consumption of 50 W. The current density through SOC was 1.1 A/cm2. The prototype was designed to contain no noble metal components. It is shown that the engineering approach applied allows manufacturing effective nanostructural SOCs and devices on their basis.

Intrinsic luminescence centers in scandia, yttria, and their solid solutions

Pulsed cathodoluminescence (PCL) of Y2O3 and Sc2O3 powders, as well as of ceramic samples of binary (11 mol % Sc2O3–ZrO2 and 10 mol % Y2O3–ZrO2) and ternary (xSc2O3–(10–x)Y2O3–ZrO2) (x = 5, 6, 7, 8 mol %) solid solutions are studied in the range of 300–850 nm at room temperature. In Y2O3 and Sc2O3, series of strong narrow luminescence bands emitted by surface bound radicals ...0...0>-Y=O and ...0...0>-Sc=O are found. The PCL spectra of xSc2O3–(10–x)Y2O3–ZrO2 ceramic samples showed the same series of narrow bands at 543, 551, 555, 572, 583, 594, 614, and 639 nm as the yttrium oxide spectra. The existence of these luminescence bands, which correspond to the emission of the ...0...0>-Y=O radical, and the absence of the emission lines of the ...0...0>-Sc=O radical indicate that yttrium ions, due to their larger radius, are the first that are displaced to the surface of crystallites in these systems, which is accompanied by the formation of the second phase in subsurface layers.

Nozzles from Alumina Ceramics with Submicron Structure Fabricated by Radial Pulsed Compaction

By means of magnetic pulsed compaction and sintering of weakly aggregated alumina based nanopowders the jet forming nozzle samples for hydroabrasive cutting were fabricated. The ceramics were obtained from pure alumina, as well as from alumina, doped by TiO2, MgO and AlMg. The ceramic properties of the channel surface and the nozzle volume were investigated. It was shown that the samples sintered from AlMg doped Al2O3 powder had the best desired mechanical properties and structural characteristics: relative density ~0.97, channel microhardness – 18-20 GPa, channel surface roughness ~0.7 /m, average crystallite size ~1 /m.

Fabrication of Microtubular Solid Oxide Fuel Cells by Film Compaction and Co-Sintering

The microtubular design of solid oxide fuel cells (SOFCs), which are promising electrochemical power sources, has a number of significant advantages over traditional planar and tubular designs: increased resistance to the cell (stack) heating rate and packing density of cells in a stack. The paper presents results on the development of a microtubular SOFC (MT-SOFC) fabrication method based on compaction and co-sintering a set of films. The formation of an anode-supported MT-SOFC having a Ni-cermet collector (support) and functional layers of about 300 and 50 μm thick, respectively; a Zr0.84Y0.16O2–δ solid electrolyte layer (40 μm); and a cathode based on La0.7Sr0.3MnO3–δ has been developed. The outer diameter and length of the MT-SOFC were 3.9 and 12 mm, respectively. The maximum specific power generated by the MT-SOFC at 850°C was 0.21 W/cm2.

Pore-Forming Agents for the Supporting Ni-Based SOFC Anode

The effect of the type (semolina, starch, and ashless filter paper) and amount (5 and 10 wt %) of pore-forming agents on the structure of supporting Ni-cermet anodes and characteristics of solid-oxide fuel cells on their basis has been studied. It has been found that the use of paper fibers as the pore-forming agent doubles the open porosity of the anode as compared with equal amounts of semolina or starch. It has been shown that the long cylindrical pores formed by fibers allow fast transport of gases through the anode bulk, which has a positive effect on the fuel cell characteristics.

Behavior of ceramics based on Al2O3 and ZrO2 nanopowders under gamma-ray irradiation

Hardness, fracture strength, wear resistance, and ultimate bending strength of ceramics based on aluminum oxide irradiated with gamma rays (0.8 MeV) up to 2000 Mrad are studied. It is found that mechanical properties of ceramics in which corundum prevails deteriorate under irradiation. Most resistant to gamma irradiation is a ceramic consisting of equal volume fractions of Al2O3 and 2.5 mol % of Y2O3 in ZrO2 (2.5YSZ) solid solution. A different trend of change in the unit cell parameter of the corundum crystal lattice under increasing irradiation dose is detected: as the irradiation dose increases, the unit cell parameter of the corundum crystal lattice increases in ceramics including zirconium oxide (α-Al2O3 + 10% ZrO2) (ZTA10) and α-Al2O3 + 55% YSZ (ATZ50)), and vice versa, it decreases if there is no zirconium oxide in the composition (Al2O3, α-Al2O3 + 4% MgAl2O4 (AM1)).

Solid Oxide Electrolyte Based Oxygen Pump

The method of electrochemical extraction of oxygen from air employing a solid oxide electrolyte (SOE) is presented. The prototype of electrochemical oxygen generator (pump) for medical applications has been developed and fabricated. It is based on thin-walled tubular segments of YSZ electrolyte (170 μm) with LSM based electrodes (~20 μm). Different technologies: nanopowder production by laser ablation, casting of polymer-ceramic tapes, formation of electrodes-electrolyte green structures by radial magnetic pulsed compaction followed by cosintering at 1200°C, were used for segments fabrication. The magnetron sputtering method was applied to protect metallic interconnects (Crofer 22 APU) with (Mn-Co)3O4 layer. Presented oxygen generator prototype produced 9 liters of pure oxygen per hour under applied power of 50 W at 800°C. No noble metals were used in construction.

Fabrication of Components for Solid Oxide Fuel Cells by Tape Casting and Magnetic Pulsed Compaction

Fabrication of dense YSZ electrolytes and porous LSM cathodes in the shape of tubes using a radial magnetic pulsed compaction of multilayered tubular blanks of powder tapes has been investigated. The tapes were prepared with butyral resin binder. The multilayered blanks were compacted magnetically. Magnetic pressures of 0.2-0.3 GPa in amplitude, sintering temperatures as low as 1100-1300 °C (in air) with holding time of 20-540 min have been used. Cathode tubes of 0.2-1.0 mm thick exhibited the reproducible open porosity up to 45 %. YSZ electrolyte tubes with the wall of 100-450 microns thick had near full relative density, 0.97-0.99, and were characterized with grains of 200-500 nm in size on the average depending on the sintering temperature. The electrochemical cells built up of as-prepared tubular electrolytes and traditional research electrodes were tested under the air-hydrogen fuel cell conditions. The specific output power, 0.6 W cm-2, was realized at temperature of 885 °C.