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A new branched morphology of metallic niobium powder particles was produced by calciothermic reduction of niobium oxides in molten CaCl 2 . The influence of some reaction parameters on the powder particle morphology was studied, and the formation mechanism was investigated. It was found that the formation of intermediate complex niobium oxides (Ca x Nb 2 O y ) was crucial in the formation of niobium powder particles with the branched morphology. Based on this finding, the formation mechanism of the branched morphology in four stages was proposed. These Nb powder particles with microscopic branches can prevent particle sintering during the fabrication process of electric capacitors, allowing the latter to exhibit a higher capacitance. [ABSTRACT FROM AUTHOR]

Ozone gas in an ambient pressure was blown to Cr2O3 powder. The higher oxides, CrO3, Cr2O5, Cr5O12, and Cr3O8, could be synthesized above 373 K. Both CrO3 and Cr2O5 were found by in situ X-ray diffraction measurements. It was known that they could be produced only at high pressure of oxygen and at high temperatures. The CrO3 formed was melted at 470 K in an ozone atmosphere and decomposed above 500 K. Because of thermal decomposition of ozone and the higher oxides, no higher oxides were formed above 660 K. The phase formation was discussed using the kinetic stability diagram. [ABSTRACT FROM AUTHOR]

Abstract: Metallic tantalum powder with broccoli-like morphology, consisting of spherical fine particles and of long rods or thin plates, was prepared in a hundred gram scale by calcium reduction of Ta2O5 in molten CaCl2. The properties as electrolytic capacitor were evaluated in comparison with commercial powder obtained by Na reduction and with powder consisting of only fine particles obtained by Ca reduction. The capacitance was larger than that of conventional powder with the same surface area, because the broccoli-like powder showed a strong resistance against shrinkage during high temperature annealing due to the framework of branches. The powder with new broccoli-like morphology can circumvent the conventional treatments for grain size control and gas removal. [Copyright &y& Elsevier]

Abstract: “Broccoli”-like morphology of Ta powder was found when Ca reduces Ta2O5 in the molten CaCl2. It consisted of fine particles and branches, and it was different from the conventional spherical particles. The formation of this morphology depended on the stacking methods of the starting materials. Eight types of filling methods proved that the branch was formed when the CaO-enriched region was locally produced near the oxide. [Copyright &y& Elsevier]

Abstract: A new cell concept for calciothermic reduction is presented where TiO2 is used as the raw material for reduction. The reduction system consists of a single cell, where both the reduction reaction and the electrolytic reaction for recovery of reducing agent coexist in the same molten CaCl2 bath. TiO2 powder reacts with a few mol%Ca dissolved in the melt. Sufficiently deoxidized titanium metal was obtained at the bottom of the cell. Because the molten CaCl2 has a large solubility for CaO, both mechanisms of the halide flux deoxidation and the electrochemical deoxidation work efficiently once the metallic Ti was precipitated. The reducing agent is in situ recovered by electrolysis of CaO as, Some experimental results are presented for confirmation of this proposal and mechanism. [Copyright &y& Elsevier]

A new process is studied to synthesize the hydrogen storage alloy directly from its oxides. This method combines the calcium co-reduction and the in situ dissolution of the by-product CaO into the molten salt. The binary alloy of 30 mol% Ti–70 mol% V was chosen as an example. When V2O5 and TiO2 were used as the starting materials, the reduction and alloying occurred separately in part, because V2O5 was melted below the reaction temperature and the preferentially reduced metallic V droplets deposited on TiO2 powder, which hindered the reduction of TiO2. The well-homogenized alloy could be obtained from the mechanical mixture of refractive V2O3 and TiO2. The molten CaCl2 was needed to dissolve CaO for complete reaction. The obtained alloy powder showed capability of hydrogen storage after activation. [Copyright &y& Elsevier]

The Fe2VAl Heusler alloy was reported to have good thermoelectric properties. Because the natural resource of vanadium is insufficient, Fe2TiAl based alloys were studied. Ni, Co, or Cr was substituted to stabilize the Heusler structure and to control the valence electrons. The Seebeck coefficients decreased in the Heusler single-phase region when these fourth elements were added, probably because the Fermi level was lying above the minimum in the density of state. The maximum and minimum Seebeck coefficients were +50 μV/K in Fe2(Ti0.6Cr0.4)Al and -34 μV/K in (Fe0.2Co0.8)2TiAl, respectively. Their electric conductivities were metallic judged by their temperature dependency. The characteristic semiconducting behavior of the Fe2VAl Heusler alloy due to a pseudo gap in the density of state was not observed in the substituted Fe2TiAl alloys. [Copyright &y& Elsevier]

Analytical expression of electric power was deduced in case of the large-scale thermoelectric device that consists of the cylindrical double tubes like roll cake and is exposed to the two thermal fluids. The output powers of 16 systems were mathematically described by the simultaneous equations based on heat exchange. The temperature profiles in the device depend on the flow directions of hot and cold fluids, but the flow directions did not change the output power. Resultantly, eight sets of solutions for the output power were deduced. The maximum output power was the largest in the two systems (V2CC-I and V2CC-II system), where two fluids flow in counter directions and one of the fluids goes into the system from the inside of the inner cylinder. These chosen systems can generate the thermoelectric power equivalent with the single cylinder system (V1C system) using only 36% material of V1C. [Copyright &y& Elsevier]

Analytical expression of electric power was deduced in case of the large-scale thermoelectric device that consists of the multiple cylindrical tubes like roll cake exposed to two thermal fluids. The output powers of the four arrangements were mathematically solved from heat transfer theory. The maximum output power of roll-cake module was practically the largest for the system of the counter flow with a single thermoelectric tube (V1C system), but 1/4 of the ideal output power (V1II system). The multiplication of thermoelectric tubes can shorten significantly the device length, although the output power decreases only a little. For example, the double vortical tubes (V2CC system) can generate 95.7% output power by 38.5% diameter, compared with the single tube (V1C system). [Copyright &y& Elsevier]

Analytical expression of electric power was deduced in case of the large-scale cylindrical thermoelectric tubes exposed to two thermal fluids. The output powers of the proposed six geometrical arrangements were mathematically solved from heat transfer theory, and compared with the flat panel systems. The maximum output was the largest in the ideally cooled systems. In the other realistic systems, it was the largest for the system of the counter flow with a single thermoelectric tube. The multiplication of thermoelectric panels can shorten significantly the device length, although the output from the multi-tubes decreases only a little. For example, the double helical tubes (T2CH system) can generate 96% output by 35% length, compared with the single tube in the counter flow (T1C system). [Copyright &y& Elsevier]

Electric power was estimated in case of the large-scale flat thermoelectric panels exposed to two thermal fluids. The output powers of the proposed 15 systems were analytically deduced from heat transfer theory, and written by non-dimensional functions to reflect the characteristics of system design. The maximum output was the largest in the ideal isothermal systems. In the other realistic systems, it was the largest for the system of the counter flow with one panel. The multiplication of thermoelectric panels can shorten significantly the device area, although the output from the multi-panels decreases a few percent. The worse heat conductivity, λ of thermoelectric materials and the better heat transfer at the surfaces are desired for these fluid systems, in addition to the better figure of merit, Z. [Copyright &y& Elsevier]

Thermoelectric power generation has the potential to recover a large amount of energy loss at the vapor condensers in the steam-based power plants. A suitable arrangement of thermoelectric modules was designed from the heat transfer theory in the cylindrical heat exchanger. Even under the practical operation limits, 150 kW can be generated by the thermoelectric conversion. [ABSTRACT FROM AUTHOR]

For obtaining better oxidation resistance of niobium in air, a niobium silicide was non-electrolytically deposited onto niobium from the molten salt, where a disproportional reaction occurs between Na2SiF6, SiO2, and Si. A single phase of NbSi2 was formed with a homogeneous thickness of about 10 μm above 1073 K. The oxidation resistance of pure niobium with this coating layer was improved. During the oxidation at the high temperatures, Nb5Si3 was formed at the interface between the Nb substrate and the NbSi2 layer. Due to this intermediate layer formation, the oxidation resistance became better than for pure NbSi2. [Copyright &y& Elsevier]

High-aspect ratio ordered nanomaterial arrays exhibit several unique physicochemical and optical properties. Porous anodic aluminum oxide (AAO) is one of the most typical ordered porous structures and can be easily fabricated by applying an electrochemical anodizing process to Al. However, the dimensional and structural controllability of conventional porous AAOs is limited to a narrow range because there are only a few electrolytes that work in this process. Here, we provide a novel anodizing method using an alkaline electrolyte, sodium tetraborate (Na2B4O7), for the fabrication of a high-aspect ratio, self-ordered nanospike porous AAO structure. This self-ordered porous AAO structure possesses a wide range of the interpore distance under a new anodizing regime, and highly ordered porous AAO structures can be fabricated using pre-nanotexturing of Al. The vertical pore walls of porous AAOs have unique nanospikes measuring several tens of nanometers in periodicity, and we demonstrate that AAO can be used as a template for the fabrication of nanomaterials with a large surface area. We also reveal that stable anodizing without the occurrence of oxide burning and the subsequent formation of uniform self-ordered AAO structures can be achieved on complicated three-dimensional substrates. [ABSTRACT FROM AUTHOR]

Highlight • An analytical solution of the solidification equations of steel was obtained. Abstract An approximate analytical model has been developed to obtain simultaneous solutions for nonlinear solute- and heat-transfer equations for multi-component alloy steels; in this model, a linear relation between the solid fraction and the temperature in the mushy zone was assumed. This model predicts important parameters, such as the solidus temperature for the multi-component steel materials that have not been well confirmed by the reliable measurement in a real process. The predicted temperature, solidification constants, and effective partition ratios of solutes were in good agreement with both the reported measurements and generally accepted values. The predicted solidus temperatures were also in reasonable agreement with the reported zero ductile temperature of Fe–C–Mn steel and the thermo-analytically measured solidus temperatures of steels of various grades. The solutions were also in good agreement with those separately performed numerical thermal analysis. The model involves the solution for Fe-C binary alloy which is consistent with the Neumann's solution in the low carbon range. Thus, this model provides approximate analytical solutions that can reduce the computational load, saving time and cost. [ABSTRACT FROM AUTHOR]

Metallic niobium powder was produced for applications in electric capacitors via calciothermic reduction of niobium hydroxide in molten CaCl 2 . Sub-micrometer spherical metallic particles with coral-like morphologies reflected the particle size of the starting oxide powder. A fine powder was obtained from the mixtures of niobium hydroxide and CaO or Ca(OH) 2 , respectively. Sintered pellets of the metallic powder showed a higher capacitance (CV) than those of the simply reduced powder without pre-treatment, because the shrinkage during sintering was smaller. The CV was as large as that of commercially sintered pellets for tantalum capacitors. Therefore, this niobium powder would act as a higher-voltage capacitor by applying chemical anodic treatment at higher voltages, and lower oxygen content in the reduced power could realize a lower leak current. [ABSTRACT FROM AUTHOR]

Highlights: [•] Growth behavior of anodic porous alumina formed in malic acid solutions was investigated. [•] Porous alumina was formed at grain boundaries during the initial stage of anodizing. [•] Growth region extended to the entire aluminum surface as the anodizing time increased. [•] Anodic porous alumina with cell diameters of approximately 300–800nm is formed. [ABSTRACT FROM AUTHOR]

Abstract: A Nb–Ti–Ni hydrogen permeable alloy was synthesized as a powder using the OS process, which involves the simultaneous reduction of a mixture of Nb, Ti, and Ni oxides by Ca that is generated from molten CaCl2 via electrolysis. The mechanism confirmed that a BCC-(Nb, Ti) phase easily formed at an early stage of the reaction followed by the generation of a B2-TiNi phase from the lower oxides such as NbO and Ti2O. The oxygen content of the synthesized alloy decreased significantly to 0.27mass% with increased electric charge. The three elements were uniformly distributed at the macroscopic level. [Copyright &y& Elsevier]

Abstract: Calciothermic reductions of Ta2O5 and Nb2O5 are proposed aiming at the fine powder preparation for the larger capacitance of condensers. Because the molten CaCl2 can coexist stably with metallic Ca, and because it can dissolve a few mol%Ca and about 20mol%CaO, the reductant Ca can be supplied to the oxide via molten CaCl2, and the reaction by-product CaO can be in situ eliminated from the reaction interface. The metallic powder was obtained after an hour at 1173K. In the prolonged time the particles sintered together, but oxygen was gradually removed to the level of a few thousands ppm. [Copyright &y& Elsevier]

• High-speed galvanostatic anodizing was achieved using a nanodimpled aluminum. • The peak voltage considerably decreased, whereas the plateau was unchanged. • The possible applied current density increased with the size of the nanodimples. • The speed of the anodizing process without oxide burning increased by five times. • This method is useful in various acidic electrolyte solutions at high voltages. Rapid formation of a porous alumina film without oxide burning was achieved by anodizing in etidronic acid at large current densities using a nanodimpled aluminum surface. After the electropolished aluminum specimens were galvanostatically anodized in a 0.3 M etidronic acid solution at 293 K, a uniform porous alumina film without oxide burning was formed at relatively low current densities of up to 20 Am−2. After the first anodizing process, an array of dimples was fabricated on the aluminum surface by oxide film removal in a chromic acid/phosphoric acid solution. After the nanostructured aluminum specimen was galvanostatically anodized once again under the same conditions, the possible applied current density without burning increased with the size of the nanodimples, and the current density during the high-speed anodizing process of the dimpled aluminum specimen increased by five times. Many pores grew on the whole surface of the aluminum dimples from the initial anodizing stage; then, pores that grew from the bottom of the dimples survived the anodizing process, and a clear porous alumina film was formed as the voltage reached the maximum value. [ABSTRACT FROM AUTHOR]

• Aluminum was galvanostatically anodized in ammonium carbonate solutions. • A micro- and nanoporous multi-layer structure grew by continuous visible sparking. • The multi-layer consisted of an outer crystalline oxide and inner amorphous oxide. • The nanopores of the inner oxide can be sealed by immersion in boiling water. A plasma electrolytic oxidation (PEO)/anodic aluminum oxide (AAO) multi-layer film was fabricated via one-step galvanostatic anodizing of high-purity aluminum in 0.3–2.0 M ammonium carbonate ((NH 4) 2 CO 3) solutions at 283–333 K and 25–400 Am−2. Anodizing at higher concentrations and higher temperatures caused the formation of relatively uniform anodic oxide film on the aluminum substrate. Characteristic voltage-time curves with two high-plateau voltages at approximately 250 V and 375 V were obtained during galvanostatic anodizing. A multi-layer structure of an outer PEO layer with a crystalline γ-Al 2 O 3 structure and an inner amorphous AAO layer with nano-cylinerical pores was formed by continuous visible sparking occurring after passing the first voltage plateau region. The whole aluminum surface was covered with the multi-layer structure after reaching the second voltage region. The thickness of the multi-layer increased with time via the further anodizing process at the second plateau voltage. Pore sealing of the inner nanoporous film was achieved by immersion post-treatment in boiling water. [ABSTRACT FROM AUTHOR]

Electrochemical and morphological characterization of the porous alumina formed by galvanostatic anodizing in etidronic acid under various operating conditions was performed. High-purity aluminum plates were anodized in 0.03–3 M etidronic acid solutions at 273–333 K and 0.25–500 Am−2 for up to 24 h. Galvanostatic anodizing in etidronic acid operated over a wide range voltage measuring from a few V to 246 V. The time required for the steady growth of porous alumina not only depends on the current density but also the temperature and the concentration of the electrolyte solution during galvanostatic anodizing. The average, maximum, and minimum cell sizes of the porous alumina were directly proportional to the anodizing voltage with a proportionality constant of 2.5, 3.5 and 0.7, respectively, and were independent of other parameters. The number density of the cell was also a function of the anodizing voltage and agreed with the theoretical value obtained for ordered porous alumina with an ideal honeycomb distribution. The maximum voltage measured during galvanostatic anodizing was linearly proportional to the plateau voltage with a proportionality constant of 1.4. Image 1 • Galvanostatic anodizing in etidronic acid operated at a maximum voltage of 246 V. • The time required for steady growth decreased with increasing current density. • The average cell size was directly proportional to the anodizing voltage. • The minimum and maximum cell sizes were also directly proportional to the voltage. • The number density of the cell was only a function of the anodizing voltage. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A thin layer of gold was coated on an aluminum dimple array and then heated. • The gold layer was transformed into numerous gold particles by the thermal treatment. • The transformation rate increases with the temperature of the thermal treatment. • Multiply-twinned particles were distributed on the surface. • The gold particle array exhibited excellent adhesion properties. Abstract Gold nanoparticles were fabricated on an ordered aluminum dimple array via aluminum anodizing, sputter coating, and thermal treatment, and the transformation behavior and nanostructural characterization were investigated in detail. Electropolished aluminum specimens were anodized in an oxalic acid solution under self-ordering conditions at 40 V, and then the porous alumina was selectively dissolved to expose an ordered aluminum dimple array with each dimple measuring 100 nm. A thin layer of gold was coated onto the dimple array, and a thermal treatment was subsequently performed. The gold layer was transformed into numerous particles by the thermal treatment due to dewetting. When the values of gold layer thickness, thermal treatment temperature, and thermal treatment duration were optimized, the gold particles were located at the bottom of each aluminum dimple. Consequently, multiply-twinned particles with polygonal and elliptical shapes were regularly distributed on the aluminum dimple array treated at 473 K. Although the rate of the transformation induced by dewetting increased with the temperature of the thermal treatment, non-uniform gold nanostructures were formed by extended thermal treatment at 873 K. The gold particles formed on the aluminum surface exhibited excellent adhesion upon ultrasonication. [ABSTRACT FROM AUTHOR]

We demonstrate mirror-finished superhydrophobic aluminum surfaces fabricated via the formation of anodic alumina nanofibers and subsequent modification with self-assembled monolayers (SAMs). High-density anodic alumina nanofibers were formed on the aluminum surface via anodizing in a pyrophosphoric acid solution. The alumina nanofibers became tangled and bundled by further anodizing at low temperature because of their own weight, and the aluminum surface was completely covered by the long falling nanofibers. The nanofiber-covered aluminum surface exhibited superhydrophilic behavior, with a contact angle measuring less than 10°. As the nanofiber-covered aluminum surface was modified with n-alkylphosphonic acid SAMs, the water contact angle drastically shifted to superhydrophobicity, measuring more than 150°. The contact angle increased with the applied voltage during pyrophosphoric acid anodizing, the anodizing time, and the number of carbon atoms contained in the SAM molecules modified on the alumina nanofibers. By optimizing the anodizing and SAM-modification conditions, superhydrophobic behavior could be achieved with only a brief pyrophosphoric acid anodizing period of 3 min and subsequent simple immersion in SAM solutions. The superhydrophobic aluminum surface exhibited a high reflectance, measuring approximately 99% across most of the visible spectrum, similar to that of an electropolished aluminum surface. Therefore, our mirror-finished superhydrophobic aluminum surface based on anodic alumina nanofibers and SAMs can be used as a reflective mirror in various optical applications such as concentrated solar power systems. [ABSTRACT FROM AUTHOR]

A fully-Lagrangian numerical model was applied for understanding packed bed structures containing non-spherical solids, such as coke, and the high-temperature melt trickle flow characteristics of such beds. Smoothed-particle hydrodynamics (SPH) simulations can track the motion of liquids without discriminating between continuous and dispersed phases, and the extended discrete element method (DEM) is employed as a highly accurate method for simulation of non-spherical solid-particle motion. Based on this model, we carried out large-scale trickle flow simulations using more than 10 million particles, investigated case studies of statistical processing, and evaluated the effects of packed bed formed from various non-spherical coke samples. We found that the pathway that the passing rivulet takes down depends on the structure of the void and the neck size between two voids. If the connecting neck is larger than the capillary length λ = σ / ρ g , the slag will drain. The shape of pathway was related that the solids shape factor which is considered by the projected area in the direction of gravity. Even if cokes with similar size were obtained by sieving, low sphericity cokes block slag flow through channeling voids, i.e., as the projected area of the non-spherical solid shape increased, the liquid hold up showed a tendency to increase. [ABSTRACT FROM AUTHOR]

The fabrication of submicrometer-scale ordered convex lens array was demonstrated through nanoimprint lithography using an aluminum dimple array mold fabricated by etidronic acid anodizing and selective oxide dissolution. Highly-pure aluminum plates were anodized in a 0.2 M etidronic acid solution at 260 V for the formation of ordered porous alumina. The anodized specimens were immersed in a 0.2 M CrO 3 /0.51 M H 3 PO 4 solution to dissolve the porous alumina, and an ordered dimple array measuring approximately 670 nm in dimple diameter was obtained on the aluminum surface. Phosphonic acid-based self-assembled monolayers (SAMs) were coated on the aluminum dimple array as a release agent for nanoimprint lithography. The shape of the aluminum dimple array mold was transferred to a UV curable photopolymer by nanoimprint lithography. An ordered convex lens array, which corresponded to the negative shape of the dimple array, was successfully obtained by the removal of curable polymer. However, the polymer surface was contaminated with phosphonate molecules due to the multilayered phosphonate films being formed on the aluminum mold. This contamination can be avoided by ultrasonication of the aluminum mold before nanoimprint lithography. [ABSTRACT FROM AUTHOR]

The fabrication of superhydrophilic and superhydrophobic aluminum alloys was achieved by pyrophosphoric acid anodizing and SAM (self-assembled monolayer) modification. The anodizing of three kinds of aluminum alloys, including 3004, 1N30, and 8021, in a concentrated pyrophosphoric acid solution resulted in the formation of numerous anodic alumina nanofibers. In addition, insoluble intermetallic compounds contained in the alloy matrix were exposed to the surface with increasing anodizing time, and nanofiber-tangled intermetallic particles also formed on the surface during anodizing. These anodized aluminum alloys exhibited a superhydrophilic behavior measuring less than 4° in the contact angle, and this superhydrophilicity was maintained via the long-term anodizing process. The nanofiber-covered aluminum alloys were immersed in fluorinated phosphonic acid SAM/ethanol solutions, thereby modifying SAMs on the anodic alumina nanofibers. The contact angle of the SAM-modified aluminum alloys increased with the immersion time and temperature of the SAM solution, and the surface was drastically shifted to superhydrophobicity, measuring more than 150°, from superhydrophilicity. However, exceeding 10 min in the anodizing process caused the contact angle to decrease and the gradual disappearance of hydrophobicity due to the formation of many hydrophilic intermetallic particles on the surface. The short-term pyrophosphoric acid anodizing and subsequent SAM modification are useful for the formation of various superhydrophilic and superhydrophobic aluminum alloys. [ABSTRACT FROM AUTHOR]

Fabrication of a nanoporous tungsten oxide film via anodizing of tungsten in an ammonium nitrate (NH 4 NO 3 )/ethylene glycol (EG)/water (H 2 O) mixture is reported for use as a visible light-driven photocatalyst. Anodizing of tungsten in a 1.0 M NH 4 NO 3 /EG solution containing less than 0.1 vol% H 2 O resulted in active dissolution of the tungsten substrate. As the H 2 O concentration increased to more than 25 vol%, a thin barrier oxide film was formed on the tungsten substrate. A thick porous tungsten oxide with numerous nanopores measuring several tens of nanometer in diameter was fabricated via anodizing at a moderate H 2 O concentration of 1.0 vol%. The porous oxide consisted of a double-layered structure with an outer porous layer and an inner dense layer, and the outer porous layer became thinner as the NH 4 NO 3 concentration decreased. A uniform porous oxide film from the top surface to the bottom interface was fabricated via anodizing at 20 V in a 0.02 M NH 4 NO 3 /EG solution containing 1.0 vol% H 2 O at 313 K. The porous tungsten oxide exhibited visible light-driven photocatalytic activity for the photocatalytic decomposition of methylene blue. [ABSTRACT FROM AUTHOR]

Advanced hard anodic alumina coatings measuring Hv = 610–769 on the Vickers hardness scale were obtained on an aluminum surface via aluminum anodizing using a new electrolyte, etidronic acid. The ordered porous alumina was fabricated by two-step etidronic acid anodizing at 260 V under self-ordering conditions, and pore-widening was carried out to control the porosity of the porous alumina. The Vickers hardness of the ordered porous alumina increased with decreasing diameter of the pores and porosity. Aluminum specimens were also anodized by the constant-current method under various concentrations, temperatures, and current densities. The Vickers hardness increased with decreasing concentration and temperature because chemical dissolution of the anodic oxide during anodizing was suppressed. A hard porous alumina measuring Hv = 610 was obtained by anodizing in a 0.05 M etidronic acid solution at 278 K and 5 Am − 2 . Subsequent thermal treatment caused the dehydration and corresponding hardening of the porous alumina, and a higher porous alumina hardness of Hv = 769 was successfully achieved by thermal treatment at 873 K for 12 h. [ABSTRACT FROM AUTHOR]

Counter-flowing thermal fluids are conducive to generate a homogeneous temperature difference on thermoelectric (TE) generator. This study allowed the hot and cold fluids of having constant inlet temperature to flow in the opposite, and examined TE performance of module at different flow rates. The results show that TE performance gradually increases with flow rate in the initial stage of fluid flow, and reaches a transient peak value after the module surfaces are completely covered by thermal fluids, and then tends to be stable. High flow rate leads to larger performance and reduces the time of achieving them. Effect of flow rate on stable performance is slightly more than that of inlet temperature of thermal fluids, which makes regulating the flow rate to be a feasible way to harvest more heat for TE conversion. Module features present a specific trend and provide the supports for the benefit of counter-flowing thermal fluids. [ABSTRACT FROM AUTHOR]

We report the growth of electrochemically deposited liquid lithium droplet in LiCl–KCl–Li 2 O melt at 673–723 K. To understand the transient behavior of liquid lithium in the electrolyte, the interface between the electrodeposited molten metal phase and the molten salt system was observed in situ using a high-speed digital microscope. We found that the droplets on the electrode are slightly flattened, when the colloidal Li content decreases due to an increasing Li 2 O content. This mechanism indicates that the heterogeneous distribution of the colloid Li may be due to the local Li solubility in the electrolyte. [ABSTRACT FROM AUTHOR]

Anodizing of aluminum in an arsenic acid solution is reported for the fabrication of anodic porous alumina. The highest potential difference (voltage) without oxide burning increased as the temperature and the concentration of the arsenic acid solution decreased, and a high anodizing potential difference of 340 V was achieved. An ordered porous alumina with several tens of cells was formed in 0.1–0.5 M arsenic acid solutions at 310–340 V for 20 h. However, the regularity of the porous alumina was not improved via anodizing for 72 h. No pore sealing behavior of the porous alumina was observed upon immersion in boiling distilled water, and it may be due to the formation of an insoluble complex on the oxide surface. The porous alumina consisted of two different layers: a hexagonal alumina layer that contained arsenic from the electrolyte and a pure alumina honeycomb skeleton. The porous alumina exhibited a white photoluminescence emission at approximately 515 nm under UV irradiation at 254 nm. [ABSTRACT FROM AUTHOR]

A superhydrophilic aluminum surface covered by numerous alumina nanofibers was fabricated via pyrophosphoric acid anodizing. High-density anodic alumina nanofibers grow on the bottom of a honeycomb oxide via anodizing in concentrated pyrophosphoric acid. The water contact angle on the nanofiber-covered aluminum surface decreased with time after a 4 μL droplet was placed on the surface, and a superhydrophilic behavior with a contact angle measuring 2.2° was observed within 2 s; this contact angle is considerably lower than those observed for electropolished and porous alumina-covered aluminum surfaces. There was no dependence of the superhydrophilicity on the density of alumina nanofibers fabricated via different constant voltage anodizing conditions. The superhydrophilic property of the surface covered by anodic alumina nanofibers was maintained during an exposure test for 359 h. The quick-drying and snow-sliding behaviors of the superhydrophilic aluminum covered with anodic alumina nanofibers were demonstrated. [ABSTRACT FROM AUTHOR]

Self-ordered porous alumina was fabricated via anodizing in an acid salt electrolyte solution, sodium hydrogen sulfate (NaHSO 4 ). High-purity aluminum specimens were anodized in a NaHSO 4 solution under various operating conditions with adjusted concentrations, temperatures, applied voltages, and times. Self-ordering was achieved via NaHSO 4 anodizing at appropriate applied voltages ranging from 20 to 28 V, and ordered cell arrangements with the cell size of 55–77 nm were successfully fabricated. Sulfur atoms originating from the electrolyte anions were incorporated into the ordered porous alumina. A honeycomb distribution consisting of a thick outer layer with a high concentration of sulfur and a very thin inner skeleton with a relatively low concentration sulfur was formed via NaHSO 4 anodizing. Our results suggested that there are now many electrolyte options for the fabrication of self-ordered porous alumina with a wide range of nanosizes. [ABSTRACT FROM AUTHOR]

Ordered porous alumina (OPA) with large-scale circular and hexagonal pores was fabricated via etidronic acid anodizing. High-purity aluminum plates were anodized in 0.2–4.2 M etidronic acid solution at 145–310 V and 288–323 K. Self-ordering of porous alumina was observed at 165 V and 313 K in 4.2 M, at 205 V and 303 K in 1.0 M, and at 260 V and 298 K in 0.2 M, and the cell diameter was measured to be 400–640 nm. The ordering potential difference decreased with the electrolyte concentration increasing. OPA without an intercrossing nanostructure could be fabricated on a nanostructured aluminum surface via two-step anodizing. Subsequent pore-widening in etidronic acid solution caused the circular dissolution of anodic oxide and the expansion of pore diameters to 470 nm. The shape of the pores was subsequently changed to a hexagon from a circle via long-term pore-widening, and a honeycomb structure with narrow alumina walls and hexagonal pores measuring 590 nm in its long-axis was formed in the porous alumina. Transition of the nanostructure configuration during pore-widening corresponded to differences in the incorporated phosphorus distribution originating from the etidronic acid anions. [ABSTRACT FROM AUTHOR]

The transient behavior of the immiscible two liquids interface, which is initiated by the rising gas bubble was investigated using Smoothed Particle Hydrodynamics (SPH) model. This developed numerical method is using fully Lagrangian particle-based model, which can track the movement of both the gas and the liquid phase directly. Numerical simulations have been performed for different conditions corresponding to different values of surface tension, viscosity and density, and the predicted topological changes as well as the theoretical pressure and interfacial shape of bubbles are validated. In the case of immiscible two liquids, the column of a lower liquid phase penetrating into the upper liquid phase influences interface area, whose shape strongly depends on the wake flow pattern of a bubble. Thus, the dynamic balance between the buoyancy and the liquid–liquid interfacial tension determines an interface area. Under higher surface tension condition, such as molten metal–slag system, the liquid–liquid interface shape is greatly influenced by the fluctuation of a bubble. Then, nonlinearly changed interface shape can be observed, indicating that this shape becomes easily unstable by slight change of the curvature. [ABSTRACT FROM AUTHOR]

Self-ordered periodic porous alumina with an undiscovered cell diameter was fabricated via electrochemical anodizing in a new electrolyte, phosphonic acid (H 3 PO 3 ). High-purity aluminum plates were anodized in phosphonic acid solution under various operating conditions of voltage, temperature, concentration, and anodizing time. Phosphonic acid anodizing at 150–180 V caused the self-ordering behavior of porous alumina, and an ideal honeycomb nanostructure measuring 370–440 nm in cell diameter was successfully fabricated on the aluminum substrate. Conversely, disordered porous alumina grew at below 140 V, and anodizing at above 190 V caused local thickening due to oxide burning. Two-step phosphonic acid anodizing allows the fabrication of high aspect ratio ordered porous alumina. HPO 3 2− anions originated from the electrolyte were incorporated into the porous oxide during anodizing. Consequently, a double-layered porous alumina consisting of a thick outer layer containing incorporated HPO 3 2− anions, and a thin inner layer without anions was constructed via phosphonic acid anodizing. [ABSTRACT FROM AUTHOR]

Ironmaking technology is currently focused on the introduction of the decreased reducing agent operation of a blast furnace in order to decrease CO 2 emissions. Because the coke ratio is reduced in this operation, causing a huge pressure drop, it has become increasingly important to understand the in-furnace phenomena using the non-empirical method. In this study, the DEM–CFD simulation was carried out to analyze the heat and mass transfer between the gaseous phase and the particles in a packed bed. In particular, the effect of recently proposed helical structure of coke and ore layers was compared with the traditional layer-by-layer structure. This comparison shows that the helical structure is effective for the smooth gas flow in the packed bed. It was found that the increase of the gas flow rate in a large grain size coke layer, would not affect the total permeability of the packed bed. Since the helical structure decreases the amount of inflow of the gaseous phase to the ore bed, the reduction rate of this ore tends to decrease the thickness of the layered structure, but this effect is relatively small. The helical structure becomes more permeable, if a thicker layer is maintained even under the decreased coke ratio condition. [ABSTRACT FROM AUTHOR]

The formation behavior of anodic alumina nanofibers via anodizing in a concentrated pyrophosphoric acid under various conditions was investigated using electrochemical measurements and SEM/TEM observations. Pyrophosphoric acid anodizing at 293 K resulted in the formation of numerous anodic alumina nanofibers on an aluminum substrate through a thin barrier oxide and honeycomb oxide with narrow walls. However, long-term anodizing led to the chemical dissolution of the alumina nanofibers. The density of the anodic alumina nanofibers decreased as the applied voltage increased in the 10–75 V range. However, active electrochemical dissolution of the aluminum substrate occurred at a higher voltage of 90 V. Low temperature anodizing at 273 K resulted in the formation of long alumina nanofibers measuring several micrometers in length, even though a long processing time was required due to the low current density during the low temperature anodizing. In contrast, high temperature anodizing easily resulted in the formation and chemical dissolution of alumina nanofibers. The structural nanofeatures of the anodic alumina nanofibers were controlled by choosing of the appropriate electrochemical conditions, and numerous high-aspect-ratio alumina nanofibers (>100) can be successfully fabricated. The anodic alumina nanofibers consisted of a pure amorphous aluminum oxide without anions from the employed electrolyte. [ABSTRACT FROM AUTHOR]

Polymer nanoimprinting of submicrometer-scale dimple arrays with structural coloration was demonstrated. Highly ordered aluminum dimple arrays measuring 530–670 nm in diameter were formed on an aluminum substrate via etidronic acid anodizing at 210–270 V and subsequent anodic oxide dissolution. The nanostructured aluminum surface led to bright structural coloration with a rainbow spectrum, and the reflected wavelength strongly depends on the angle of the specimen and the period of the dimple array. The reflection peak shifts gradually with the dimple diameter toward longer wavelength, reaching 800 nm in wavelength at 670 nm in diameter. The shape of the aluminum dimple arrays were successfully transferred to a mercapto-ester ultra-violet curable polymer via self-assembled monolayer coating and polymer replications using a nanoimprinting technique. The nanostructured polymer surfaces with positively and negatively shaped dimple arrays also exhibited structural coloration based on the periodic nanostructure, and reflected light mostly in the visible region, 400–800 nm. This nanostructuring with structural coloration can be easily realized by simple techniques such as anodizing, SAM coating, and nanoimprinting. [ABSTRACT FROM AUTHOR]

Carbonate ions in LiCl–Li 2 O salt are a source of carbon contamination in the electrolytic refining of metal oxides, and their concentration is also an essential information for understanding the CO 2 decomposition process. In this study, the solubility of gaseous CO 2 in molten LiCl–Li 2 O was studied with the goal of developing processes to decompose the oxides effectively. Ar–CO 2 gas mixtures were dissolved in molten salts containing various amounts of Li 2 O, and the solubility of the CO 2 gas was calculated by measuring the mass difference between the molten salts before and after the CO 2 dissolution. The molar amount of dissolved CO 2 gas was almost as large as the molar quantity of Li 2 O when the partial pressure of CO 2 was 1.0 or 0.5 atm for Li 2 O concentrations in the range of 0–60 mol%. This confirms that a large quantity of the oxide ions reacted with the CO 2 gas, resulting in the generation of carbonate ions. [ABSTRACT FROM AUTHOR]

Anodic oxide fabricated by anodizing has been widely used for nanostructural engineering, but the nanomorphology is limited to only two oxides: anodic barrier and porous oxides. Therefore, the discovery of an additional anodic oxide with a unique nanofeature would expand the applicability of anodizing. Here we demonstrate the fabrication of a third-generation anodic oxide, specifically, anodic alumina nanofibers, by anodizing in a new electrolyte, pyrophosphoric acid. Ultra-high density single nanometer-scale anodic alumina nanofibers (1010 nanofibers/cm2) consisting of an amorphous, pure aluminum oxide were successfully fabricated via pyrophosphoric acid anodizing. The nanomorphologies of the anodic nanofibers can be controlled by the electrochemical conditions. Anodic tungsten oxide nanofibers can also be fabricated by pyrophosphoric acid anodizing. The aluminum surface covered by the anodic alumina nanofibers exhibited ultra-fast superhydrophilic behavior, with a contact angle of less than 1°, within 1 second. Such ultra-narrow nanofibers can be used for various nanoapplications including catalysts, wettability control, and electronic devices. [ABSTRACT FROM AUTHOR]

Abstract: Micro-, submicron-, and nano-scale titanium dioxide particles were reduced by reduction with a metallic calcium reductant in calcium chloride molten salt at 1173K, and the reduction mechanism of the oxides by the calcium reductant was explored. These oxide particles, metallic calcium as a reducing agent, and calcium chloride as a molten salt were placed in a titanium crucible and heated under an argon atmosphere. Titanium dioxide was reduced to metallic titanium through a calcium titanate and lower titanium oxide, and the materials were sintered together to form a micro-porous titanium structure in molten salt at high temperature. The reduction rate of titanium dioxide was observed to increase with decreasing particle size; accordingly, the residual oxygen content in the reduced titanium decreases. The obtained micro-porous titanium appeared dark gray in color because of its low surface reflection. Micro-porous metallic titanium with a low oxygen content (0.42wt%) and a large surface area (1.794m2 g−1) can be successfully obtained by reduction under optimal conditions. [Copyright &y& Elsevier]

The self-ordering behavior of anodic porous alumina that was formed by anodizing in selenic acid electrolyte (H2SeO4) at various concentrations and voltages was investigated with SEM and AFM imaging. A high purity aluminum foil was anodized in 0.1-3.0M selenic acid solutions at 273K and at constant cell voltages in the range of 37 to 51V. The regularity of the cell arrangement increased with increasing anodizing voltage and selenic acid concentration under conditions of steady oxide growth without burning. Anodizing at 42-46V in 3.0M selenic acid produced highly ordered porous alumina. By selective dissolution of the anodic porous alumina, highly ordered convex nanostructures of aluminum with diameters of 20nm and heights of 40nm were exposed at the apexes of each hexagonal dimple array. Highly ordered anodic porous alumina with a cell size of 102nm from top to bottom can be fabricated by a two-step selenic acid anodizing process, that includes the first anodizing step, the selective oxide dissolution, and the second anodizing step. [ABSTRACT FROM AUTHOR]

Abstract: In a metallurgical process, gas–liquid flow plays an important role in increasing the efficiency by stirring liquid mechanically or by injecting a gas. Owing to the difficulty of direct observation in a high-temperature system or real furnace experiment, numerical analysis is useful and widely studied. However, flexible treatment of complicated free surface behavior such as fragmentation and coalescence of liquids is still a difficult problem. This paper presents a new particle-based simulation scheme for gas–liquid flow. We improved the numerical stability, which is generally a problem with the particle method, and verified the model’s accuracy for fundamental gas–liquid flow analysis. Because all the phases were discretized as particles in Moving Particle Semi-implicit (MPS) method, the proposed model can track the movement of both the gas and liquid phases directly. A large difference in the real density between the gas and liquid phases makes the gas–liquid interface behavior unstable. This study proposed an optimization of the weakly compressible Poisson equation, an initial particle arrangement, and a smoothed interface density in order to stabilize the multi-density flow analysis. This model guarantees conservation of the fluid volume even for a high-density-ratio flow like that at a gas–liquid interface. Therefore, a gas–liquid interface has been represented with high accuracy. We believe that this scheme is also applicable to phenomena in an actual process that includes many dispersal phases. [Copyright &y& Elsevier]

Abstract: The growth behavior of anodic porous alumina formed via anodizing in a new electrolyte, squaric acid (3,4-dihydroxy-3-cyclobutene-1,2-dione), is reported for the first time. A high-purity aluminum foil was anodized in a 0.1M squaric acid solution at 293K and a constant applied potential of 100-150V. Anodic oxides grew on the aluminum foil at applied potentials of 100-120V, but a burned oxide film was formed at higher voltage. Anodic porous alumina with a cell size of approximately 200–400nm and sub-100-nm-scale pore diameter was successfully fabricated by anodizing in squaric acid. The cell size of the anodic oxide increased with anodizing time because of the uneven growth of the porous layer. The anodic porous alumina obtained by squaric acid anodizing consists of amorphous Al2O3 containing 5-6 at% carbon from the electrolyte. [Copyright &y& Elsevier]

Highlights: [•] A metallic Ti–Zr alloy was obtained by electroless reduction for capacitor applications. [•] The reduction mechanisms were studied by SEM, XRD, EPMA, and an oxygen analyzer. [•] The alloy was obtained by electroless reduction in the presence of excess calcium reductant. [•] A micro-porous Ti–Zr alloy was successfully obtained. [•] The alloy has a low oxygen content and a large surface area. [ABSTRACT FROM AUTHOR]

Highlights: [•] A new aluminum bulk micromachining through an anodic oxide mask was developed. [•] Laser irradiation of anodized aluminum results in the formation of a locally exposed aluminum pattern. [•] The anodic oxide acted as a resist mask during electrochemical etching. [•] A hemicylindrical microgroove with a flat surface was fabricated by electrochemical etching. [•] Free-standing oxides formed by an undercutting were easily removed by ultrasonication. [Copyright &y& Elsevier]

Abstract: Fine Nb2O5 powder was filled into a basket-type cathode and immersed in molten CaCl2–0.5mol% CaO at 1173K. Nb2O5 immediately reacted with CaO in the molten CaCl2 and formed calcium niobites that exhibited rod- or plate-like morphology. After the electrolysis of CaO with a graphite consumable anode, spherical particles of metallic niobium powder containing a residual oxygen concentration of 0.673mass% O were obtained. [Copyright &y& Elsevier]