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A hexagonal oxynitride (Li _(0.880.12))Nb _(3.0)(O _(0.13)N _(0.87)) _4 was synthesized through ammonia nitridation of LiNb _3O _8. The structural analysis revealed that this oxynitride consists of alternate stacking of octahedral...
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A hexagonal oxynitride (Li _(0.880.12))Nb _(3.0)(O _(0.13)N _(0.87)) _4 was synthesized through ammonia nitridation of LiNb _3O _8. The structural analysis revealed that this oxynitride consists of alternate stacking of octahedral and prismatic layers with different Li/Nb ratios: significant amounts of Li and Nb atoms (Li/Nb = 43/57) coexist in the octahedral layer, while the prismatic site is preferentially occupied by Nb (Li/Nb = 3/97). A metallic behavior was accompanied by an abrupt drop of electrical resistivity at about 3 K. Furthermore, large diamagnetism and specific-heat anomaly were observed below this temperature, suggesting the appearance of superconductivity in the Li-Nb oxynitride.
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We analyzed the spatial distribution of Ca dopants in ɑ-SiAlON by using a statistical approach that analyzed a high-angle annular dark- field (HAADF) scanning transmission electron microscopy (STEM) image. By evaluating the image...
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We analyzed the spatial distribution of Ca dopants in ɑ-SiAlON by using a statistical approach that analyzed a high-angle annular dark- field (HAADF) scanning transmission electron microscopy (STEM) image. By evaluating the image intensity of each atomic column, we found that the intensity deviation of columns with Ca atoms was twice that of other atomic columns. The results of HAADF-STEM image simulation suggested that there was a long-range repulsive interaction along the [0001] direction between pairs of Ca atoms in the same Ca column. Moreover, correlation of image intensities in neighboring Ca columns suggested the existence of a short-range repulsive force between first-nearest-neighbor Ca atoms. The origin of such anisotropic interactions between pairs of Ca atoms will be discussed.
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Thermal fluids can transport heat to the large surface of a thermoelectric (TE) panel from hot and/or cold sources. The TE power thus obtainable was precisely evaluated using numerical calculations based on fluid dynamics and heat...
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Thermal fluids can transport heat to the large surface of a thermoelectric (TE) panel from hot and/or cold sources. The TE power thus obtainable was precisely evaluated using numerical calculations based on fluid dynamics and heat transfer. The commercial software FLUENT was coupled with a TE model for this purpose. The fluid velocity distribution and the temperature profiles in the fluids and TE modules were calculated in two-dimensional space. The electromotive force was then evaluated for counter-flow and split-flow models to show the effect of a stagnation point. Friction along the fluid surface along a long, flat path was larger than that along a short path split into two parts. The power required to circulate the fluids along the flow path is not negligible and should be considered in TE generation system design.
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Various defects and amorphous transitions are the primary mechanism behind the accumulation of swelling in silicon carbide (SiC). In this study, selected-area He~+ ion irradiation was carried out on single-crystal 4H-SiC using flu...
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Various defects and amorphous transitions are the primary mechanism behind the accumulation of swelling in silicon carbide (SiC). In this study, selected-area He~+ ion irradiation was carried out on single-crystal 4H-SiC using fluences of 1 × 10~(15), 5 × 10~(16), and 1 × 10~(17)cm~(-2) at room temperature. The defect distribution in the samples with varying irradiation fluences was analyzed using transmission electron microscopy (TEM), while the local swelling of regions under varying damage conditions was estimated using electron energy-loss spectroscopy. The results provide the range of swelling in SiC possessing different primary defect types, such as point defects or tiny clusters, black spot defects, and amorphous SiC. A saturation swelling with a value of 2%-3% in the near-surface region, induced by point defects or tiny clusters (invisible in TEM), was observed at room temperature over the fluence range of 1 × 10~(15) to 1 × 10~(17) cm~(-2). This saturation has already reached at a great low dose of about 0.02 dpa. The swelling of the region containing black spot defects ranges from about 3% to 7%. Helium bubbles increase the volume swelling of SiC, while the He~+ ion irradiation may also perform a decreasing effect on the volume swelling below a certain irradiation fluence.
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The performance of a three-dimensional helical thermoelectric generation (TEG) system is examined by exposing it to a temperature difference with hot and cold sources. The helical paths for the two thermal fluids give the TEG devi...
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The performance of a three-dimensional helical thermoelectric generation (TEG) system is examined by exposing it to a temperature difference with hot and cold sources. The helical paths for the two thermal fluids give the TEG device the potential to efficiently convert thermal energy. The characteristic performance of the helical system is numerically analyzed by using the finite-volume method in a compact system. The helical system is compared with a straight system in which all the thermoelectric (TE) elements present equivalent geometry. The difference in the TE performance between the two systems is not significant when the TE surfaces are maintained at constant temperatures. Both the electromotive force and the current in the TEG system increase linearly with the temperature difference ΔT applied at the two module surfaces. The current preferentially flows through a main path determined by the geometry of the TE element. The merits of the helical design are its compactness, space saving, and smooth fluid flow due to gravity, compared with the straight system.
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The formation behaviors of the anodic oxide film that forms on various commercially available aluminum plates were investigated by galvanostatic anodizing in etidronic acid, and their corrosion resistances were examined in a 3.5 w...
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The formation behaviors of the anodic oxide film that forms on various commercially available aluminum plates were investigated by galvanostatic anodizing in etidronic acid, and their corrosion resistances were examined in a 3.5 wt% NaCl solution. High purity aluminum and A1050, A5052, and A7075 aluminum alloys were galvanostatically anodized in an etidronic acid solution. An amorphous porous oxide film formed on the pure aluminum, the A1050 alloy, and the A5052 alloy, whereas a plasma electrolytic oxidation (PEO) film formed on the A7075 alloy. The nanopores formed in the porous oxide film could be sealed with hydroxides by immersion in boiling water. Corrosion-resistant pure aluminum with a measured corrosion current density of icorr = 10~(-9) Am-2 could be formed by anodizing and subsequent pore-sealing. Although the corrosion current increased due to the presence of alloying elements in the matrix, the fabrication of the corrosion-resistant A1050 and A5052 alloys with icorr = 10-6 Am-2 could also be achieved by anodizing. Alternately, the corrosion resistance of the A7075 alloy covered with the PEO film was measured to be icorr = 10~(-4) Am-2 , which is not as small as the icorr of the A1050 and A5052 alloys due to its open microporous structure.
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In order to produce metals directly from the oxides, molten CaocaCl2 mixture offers a strong reducing environment. CaO in CaCl2 melt electrochemically decomposes into metallic Ca and O～(2-) by applying a certain voltage larger th...
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In order to produce metals directly from the oxides, molten CaocaCl2 mixture offers a strong reducing environment. CaO in CaCl2 melt electrochemically decomposes into metallic Ca and O～(2-) by applying a certain voltage larger than the theoretical decomposition voltage of CaO. Ca, deposited on cathode and dissolved in the melt, can work as strong reductant. Various metals such as Ti can be produced directly from their stable oxides. Although this calciothermic reduction forms CaO as by-product close to the cathode, CaO dissolves in CaCl2 melt and decomposes again by electrolysis. This OS process could be applied to solid, liquid and gaseous oxides. By applying the sulfides, good quality of metal is realized because they do not form solid solution of sulfur.
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Thermoelectric (TE) generation performance can be enhanced by stacking several TE modules (so-called cascade-type modules). This work presents a design method to optimize the cascade structure for maximum power output. A one-dimen...
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Thermoelectric (TE) generation performance can be enhanced by stacking several TE modules (so-called cascade-type modules). This work presents a design method to optimize the cascade structure for maximum power output. A one-dimensional model was first analyzed to optimize the TE element dimensions by considering the heat balance including conductive heat transfer, Peltier heat, and Joule heat, assuming constant temperatures at all TE junctions. The number of p-n pairs was successively optimized to obtain maximum power. The power output increased by 1.24 times, from 12.7 W in a conventional model to 15.7 W in the optimized model. Secondly, a two-dimensional numerical calculation based on the finite-volume method was used to evaluate the temperature and electric potential distributions. Voltage-current characteristics were calculated, the maximum power output was evaluated, and the efficiencies of two possible models were compared to select the optimal design. The one-dimensional analytical approach is effective for a rough design, and multidimensional numerical calculation is effective for evaluating the dimensions and performance of cascade-type TE modules in detail.
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Anodizing Al in chromic acid is a very useful surface finishing process for corrosion protection and nanoscale porous structure fabrication, whereas the self-ordering of porous anodic alumina (PAA) in chromic acid has never been f...
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Anodizing Al in chromic acid is a very useful surface finishing process for corrosion protection and nanoscale porous structure fabrication, whereas the self-ordering of porous anodic alumina (PAA) in chromic acid has never been found to date. Herein, we provide a self-ordered PAA film possessing numerous sub100-nm-scale characteristic bumps through anodizing in chromic acid at high temperature. Anodizing of high purity Al plates in a 0.3 M chromic acid solution at conventional low temperatures, such as 293 K, leads to the formation of a disordered PAA film, whereas anodizing at a high temperature of 348 K causes the self-ordering behavior of the pore structure. The PAA film grown in the initial stage possessed the highest regularity, and it decreased with anodizing time due to pore branching during anodizing. A highly ordered PAA film measuring approximately 340 nm in interpore distance can be fabricated by short-term, two-step anodizing in chromic acid at 348 K and 120 V. The ordered PAA film possesses a characteristic nanostructure consisting of hexagonally arranged 100-nm-scale pores and sub100-nm-scale disordered bumps on their pore walls without any electrolyte chromate anion.
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Layered double hydroxides (LDHs) intercalated with CO3 ~(2-) show high hydroxide ion conductivity of the order of 10~(?3) S cm~(?1) under 80% relative humidity. In the present study, (Ni, Mn)-Al LDHs and (Ni, Mn)-Fe LDHs intercala...
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Layered double hydroxides (LDHs) intercalated with CO3 ~(2-) show high hydroxide ion conductivity of the order of 10~(?3) S cm~(?1) under 80% relative humidity. In the present study, (Ni, Mn)-Al LDHs and (Ni, Mn)-Fe LDHs intercalated with CO3 ~(2-) were prepared. The conductivity of (Ni, Mn)-Al LDH and (Ni, Mn)-Fe LDH was higher than that of Ni-Al LDH or Ni-Fe LDH. These LDHs were applied to the catalyst layer in an alkaline fuel cell for the improvement of the oxygen reduction reaction (ORR) at the triple phase boundary (TPB) in the catalyst layer. The addition of LDHs to the catalyst layer increased the current for ORR, indicating that hydroxide ion conducting LDHs introduced OH~? conducting paths and increased TPB region within the catalyst layer. Above all, the addition of (Ni, Mn)-Fe LDH to the catalyst layer more effectively increased the reduction current for ORR than the addition of (Ni, Mn)-Al LDHs or Ni-Fe LDH. H2-O2 fuel cells with Ni-Al or Mg- Al LDHs as an electrolyte and MnO2 as the cathode catalyst were fabricated. The H2-O2 fuel cells were confirmed to be operated.
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