Thick and Dense Anodic Oxide Layers Formed on Aluminum in Sulphuric Acid Bath

Thick and dense oxide layers were obtained on aluminium in sulphuric acid electrolyte. For this purpose, the methodology of experimental design was used. A three-variables Doehlert design (bath temperature, anodic current density, sulphuric acid concentration), was achieved. In order to maximize the growth rate and the density of the anodic oxide layer, optimum path study was conducted. Under the determined optimal anodizing conditions (5.7℃, 3 A·dm -2 , C sul =140 g·L -1 ), the estimated response values we...     

Preparation of nanostructured tin oxide using a sol-gel process based on tin tetrachloride and ethylene glycol

A sol-gel process starting with tin tetrachloride and ethylene glycol as precursors, has been successfully used to prepare nanostructured tin oxide powders. The molecular structure evolution during the process has been identified using infrared spectroscopy and the underlying reaction mechanisms of the sol-gel process are proposed. Results suggest that the -OHCH₂CH₂OH- prevent Cl^– ions from access to tin ions due to steric effect and hence increase the stability of the sol solution. Ethylene glycol functions not only as a complexion agent to form a polymer network but also as a spacer to modulate the distance between metal ions, preventing metal oxide particles from aggregation during earlier stages of organics removal. Further, conversion of xerogel to tin oxide are studied using thermogravimetric analysis, X-ray diffraction, and electron microscopy. It is found that cassiterite begins to form at a temperature as low as 250 °C when organics start to burn off. However, nanocrystalline tin oxide powders are formed only after the chemically bonded hydroxyl groups are completely removed at about 600 °C.     

Characterization of nano-crystalline LiNiVO4 synthesized by hydrothermal process

LiOH·H₂O, Ni(CH₃COO)₂·4H₂O and NH₄VO₃ were used to synthesize nano-crystalline LiNiVO₄ by hydrothermal process in deionized water at 150 °C for 2 h and subsequent calcination at 300-600 °C for 6 h. By using an X-ray diffractometer (XRD), a transmission electron microscope (TEM) and a selected area electron diffraction (SAED) method, nano-crystalline LiNiVO₄ with inverse spinel structure was detected. The stretching vibration of VO₄ tetrahedrons analyzed by a Fourier transform infrared spectrometer (FTIR) was split into three bands at 661, 746 and 835 cm^− 1, and that analyzed by a Raman spectrometer was detected at 823.9 and 787.7 cm^− 1. The thermogravimetric and differential thermal analyses (TGA and DTA) show two discrete weight losses at 25-117 °C and 117-600 °C and four endothermic peaks at 84, 145, 202 and 372 °C, corresponding to the evaporation of water and the decomposition of inorganic and organic compounds.     

Potentiodynamical co-deposited manganese oxide/carbon composite for high capacitance electrochemical capacitors

Manganese oxide/carbon composite materials were prepared by introducing the carbon powders into the potentiodynamical anodic co-deposited manganese oxide in 0.5 mol L^− 1 MnSO₄ and 0.5 mol L^− 1 H₂SO₄ mixed solution at 40 °C. The surface morphology and structure of the composite material were examined by scanning electron microscope and X-ray diffraction. Cyclic voltammetry tests and electrochemical impedance measurements were applied to investigate the performance of the composite electrodes with different ratios of manganese oxide and carbon. These composite materials with rough surface, which consisted of approximately amorphous manganese oxide, were confirmed to possess the ideal capacitive property. The highest specific capacitance of manganese oxide/carbon composite electrode was up to 410 F g^− 1 in 1.0 mol L^− 1 Na₂SO₄ electrolyte at the scan rate 10 mV s^− 1. The synthesized composite materials exhibited ideal capacitive behavior indicating a promising electrode material for electrochemical supercapacitors.     

Hydrothermal precipitation of hydroxyapatite on anodic titanium oxide films containing Ca and P

Highly-crystallized hydroxyapatite (HA) can be precipitated during heat treatment in high-pressure steam at 300 °C on an anodic titanium oxide film containing Ca and P (AOFCP), which has been electrochemically formed on a titanium substrate prior to the hydrothermal treatment. Factors affecting the precipitation, such as a percentage of distilled water in the autoclave and additives in the AOFCP, were evaluated by scanning electron microscopy. Ca²⁺ and PO^3– ₄ ions were leached from the AOFCP into a water layer covering the film surface, and nucleate HA heterogeneously on the porous TiO₂ matrix of the AOFCP which was made by the ion leaching. The morphology of the precipitated crystals was significantly affected by the water volume ratio because the concentrations of the Ca²⁺ and PO₄ ^3– ions varied depending on the thickness of the water layer. The amount of the precipitation decreased on the AOFCP which was formed in the solution containing a small amount of Mg²⁺ ions or formed on Ti-6Al-4V alloy instead of titanium.     

AES and SIMS investigations of the oxide films on Fe-40Cr-Ru alloys

Auger and SIMS depth profiling have been used to investigate the effect of ruthenium addition on the oxidation behaviour of the Fe-40Cr-Ru alloys oxidized in air at 500 °C. Auger results revealed that the oxide films formed on the Fe-40Cr-Ru alloys consisted of a thin iron oxide external layer and a chromium-rich internal layer. Ruthenium was not found in these oxide layers. Secondary ion mass spectrometry measurements also indicated a thin Fe⁺-rich film as an outer layer with a predominantly chromium oxide in the internal layer of the film. Furthermore, ruthenium was incorporated in the entire oxide film and promoted the formation of a thin compact film.     

Transparent nanoporous tin-oxide film electrode fabricated by anodization

A transparent nanoporous tin oxide film electrode was fabricated by anodizing a tin film on a fluorine-doped tin oxide (FTO) film electrode. The resulting anodized nanoporous tin oxide (ANPTO) film has columnar-type pore channels with around 50 nm in diameter and is optically transparent. Electrochemical measurements with Fe(CN)₆³⁻ as a redox probe clearly revealed that the ANPTO film could be used for a working electrode with a large internal surface area. Moreover, it was found that ANPTO film had a wider anodic potential window (> ca. 2.0 V) than conventional metal oxide electrodes, such as FTO and indium tin oxide film electrodes (> ca. 1.3 V). The wide anodic potential window improves applicability of a transparent metal oxide electrode for various electrochemical oxidation reactions, which are often interfered by oxygen evolution in water. These results conclude that the ANPTO film can be used as an advanced transparent nanoporous film electrode.     

Oxidation behavior of AlN substrate at low temperature

The oxidation onset and the kinetics of polycrystalline AlN substrates were studied by measuring the weight percent of oxygen in the surface layer and the surface roughness with energy dispersive X-ray spectroscopy (EDX) and atomic force microscopy (AFM), respectively. The oxidation started in the temperature range 800–900 °C and the entire surface of the AlN substrate was covered with an Al₂O₃ oxide layer below 1100 °C. The oxidation kinetics followed a linear rate law below 1000 °C and a parabolic rate law above 1100 °C. Above 1100 °C, the surface roughness increased abruptly by the irregular shape of overgrown oxide, which might enhance the adhesion of metal to the AlN surface in a metallization process. With an increase of the oxidation temperature above 1200 °C, the oxide layer split during cooling due to the thermal expansion mismatch between the AlN matrix and the Al₂O₃ oxide layer.     

Oxidation behaviour and strength of B4C-30 wt% SiC composite materials

The oxidation behaviour and the effect of oxidation on the room-temperature flexural strength of B₄C-30 wt% SiC composite material were investigated. The weight changes of the samples exposed to air at temperatures between 500 and 1000 °C were continuously monitored with a microbalance. At temperatures below 800 °C, the weight change of the specimen was negligible. As the temperature was increased to 800 °C, parabolic weight gain was observed. The rate of the weight gain increased with exposure temperature. The oxidation product formed on the surface was found to be a crystalline boric oxide (B₂O₃) by X-ray analyses. The oxide layer was severely cracked due to the thermal expansion mismatch between the oxide layer and the substrate. However, the room-temperature flexural strength was increased when the samples were exposed at temperature between 700 and 900 °C, apparently due to the blunting of strength-limiting defects at the surface. When the temperature was higher than 1000 °C, a severe reduction in strength was observed. The reliability of the composite material was also improved significantly by such exposures.     

A Fourier transform interferometric study of phosphate coatings on iron

A Fourier transform interferometric study of phosphate coatings on iron plates using absorption-reflexion techniques indicated the following succession of chemical events on the surface of Armco iron dependent on time of immersion into the standard zinc phosphating solution: (a) activated formation via a redox reaction of an initial layer of hydrated iron oxide/hydroxides and nitrosyl iron complexes containing isolated PO ₄ ^3– (and possibly NO ₂ ^– ) ions in water solution; (b) chemical transformation of the initial layer into a first, adherent and chemically stable layer containing amorphous hydrated iron phosphate and acid iron phosphates; (c) growth of thicker layers progressively enriched of zinc ions, until only hydrated zinc phosphate crystals are deposited in the outer layer. This complex structure of the coating does not undergo significant chemical changes by heating to normal technological temperatures between 150 and 180° C. Only minor changes in water content are shown by the chemical evolution of the infra-red spectra up to such temperatures. Strong changes of the chemical structure of the coating (producing pyro- and metaphosphates) require temperatures higher than 200° C, and coincide with loss of adhesion of the coating to the iron support.     

Manganese dioxide structural effects on its thermal decomposition

In this work, the influence of the structure, composition and morphology on the amount of mass lost from γ-MnO₂ during heat treatment, and the activation energy for this process (from iso-conversional kinetic analysis), was determined using a statistical approach. It was found that the differential thermogravimetric (DTG) data for electrolytic manganese dioxide (EMD) samples typically show two regions of mass loss; water bound to surface sites and structural water at or near the surface removed between ∼120 and 200 °C, and bulk hydroxyl groups lost in the range ∼200-400 °C. The composition and morphology had the greatest effect on the amount of mass lost; namely, BET surface area and percentage Mn(III) for the first process (r² = 0.92) and percentage Mn(IV), percentage Mn(III) and cation vacancy fraction for the second (r² = 0.89). The activation energy for the first processes was most affected by BET surface area, c₀ and crystallite size in the (2 2 1) direction (r² = 0.89). Relatively poor correlations were found between the amount of water lost and the activation energy for the second process and the material properties measured in this work. This likely relates to the slow kinetics of the first mass loss which complicates the relationships existing for the second.     

Thermal evolution of phosphorodiamidic acid as a model for nitrogen stability in phosphate glasses

The thermal evolution at a heating rate of 3°C min^–1 of phosphorodiamidic acid, HPO₂(NH₂)₂, was studied up to 600°C. Thermogravimetric analysis revealed three stages at 120, 320 and 600°C. Nuclear magnetic resonance and Fourier transform-infrared analysis have been used to characterize the thermal products. At 120°C, phosphorodiamidic acid condenses without any weight loss into an ammonium salt of P,P-diamidoimidodiphosphoric acid. It is transformed at 320°C into a more condensed product containing 17.7 wt % nitrogen and showing P-NH-P and P-O-P linkages. At 600°C, the product still contains 10 wt% nitrogen. Phosphorus nuclear magnetic resonance shows that it is composed of nitrogen-containing Q³ groups and ultraphosphate Q³ groups. It is concluded that nitrogen cannot be held in the phosphate network if it contains hydroxyl groups, and that incorporation of nitrogen requires both reducing and nitriding conditions.     

Plastic substrate with gas barrier layer and transparent conductive oxide thin film for flexible displays

A novel plastic substrate for flexible displays was developed. The substrate consisted of a polycarbonate (PC) base film coated with a gas barrier layer and a transparent conductive thin film. PC with ultra-low intrinsic birefringence and high temperature dimensional stability was developed for the base film. The retardation of the PC base film was less than 1 nm at a wavelength of 550 nm (film thickness, 120 µm). Even at 180 °C, the elastic modulus was 2 GPa, and thermal shrinkage was less than 0.01%. The surface roughness of the PC base film was less than 0.5 nm. A silicon oxide (SiO_x) gas barrier layer was deposited on the PC base film by a roll-to-roll DC magnetron reactive sputtering method. The water vapor transmission rate of the SiO_x film was less than 0.05 g/m²/day at 40 °C and 100% relative humidity (RH), and the permeation of oxygen was less than 0.5 cc/m² day atm at 40 °C and 90% RH. As the transparent conductive thin film, amorphous indium zinc oxide was deposited on the SiO_x by sputtering. The transmittance was 87% and the resistivity was 3.5 × 10^− 4 ohm cm.     

Corrosion properties of a novel bulk Cu0.5NiAlCoCrFeSi glassy alloy in 288 °C high-purity water

Corrosion properties of a bulk Cu_0.5NiAlCoCrFeSi glassy alloy such as electrochemical corrosion potential (ECP), potentiodynamic polarization, and weight loss measurements were carried out for the first time in 288 °C high-purity (outlet conductivity < 0.07 μS cm^− 1) water. The change of ECP with dissolved oxygen (DO) showed a sigmoid curve. In addition, the Cu_0.5NiAlCoCrFeSi alloy exhibited a wide passive region and the passive current density was ∼ 2 × 10^− 4 A cm^− 2 in deaerated water containing 0.01 N sodium sulfate (Na₂SO₄) at 288 °C. A very low weight loss of ∼ 4.5 μg mm^− 1 was also found for the Cu_0.5NiAlCoCrFeSi alloy after immersion in deaerated 288 °C water for 12 weeks.     

Study on conductivity and redox stability of iron orthovanadate

FeVO₄ was synthesised by conventional solid state technique. Impedance measurements using a silver electrode were unsuccessful due to a solid state reaction between FeVO₄ and Ag, forming α-AgVO₃ and α-Fe₂O₃ at the interface. Impedance measurements, with a platinum electrode, reaffirmed that FeVO₄ exhibits semiconductor behaviour in air. In a reducing atmosphere, 5% H₂/Ar, high electronic conductivity, from 1 S cm⁻¹ at 300 °C to 2 S cm⁻¹ at 700 °C, was observed with an activation energy of 0.13(1) eV. X-ray diffraction, thermogravimetric analysis and differential scanning calorimetry data determined that the change in electronic conductivity was due to the degradation of the material into FeV₂O₄ and α-Fe₂O₃. It is believed that the conduction was due to electron hopping between vanadium d-orbitals. Neither FeVO₄ nor FeV₂O₄ are deemed suitable as anode materials for solid oxide fuel cells, due to redox instability.     

Metalorganic chemical vapor deposition of SrRuO3 thin film and its characterization

Synthesis of conducting oxide strontium ruthenate is carried out in a hot-wall tubular reactor, using Sr(C₁₁H₁₉O₂)₂/Ru(C₅H₅)₂/O₂ reaction system. Owing to a large difference in depositing efficiency between strontium and ruthenium precursors, the stoichiometric ratio of thin film is controlled in one cycle of two consecutive depositions at different temperatures. Thin films of SrRuO₃ single phase are synthesized in the subsequent 700°C annealing. Thin films of SrRuO₃ with extra ruthenium oxide can also be prepared by adjusting the molar ratio of RuO₂ and SrO layers. The deposition sequence of ruthenium oxide first, strontium oxide later is preferred. If the deposition sequence is reverse, the thin film is plagued with unreacted oxides even when the annealing temperature is raised to 800°C. The relative ease of preparing SrRuO₃ thin films, when RuO₂ is under SrO, is attributed to evaporation of ruthenium oxide in O₂ and diffusion in its open columnar microstructure. The sheet resistivity of thin film decreases with the ruthenium content. The room temperature resistivity of SrRuO₃ film of Ru/(Sr + Ru) = 0.5 is around 910 ohm-cm. The room-temperature resistivity of Ru/(Ru + Sr) = 0.53 decreases to 470 ohm-cm. The root mean square surface roughness of 700°C synthesized SrRuO₃ thin film is 22 nm, in a 2 × 2 m² area of film thickness 280 nm.     

The interaction of oxygen with high loaded Ru/γ-Al2O3 catalyst

The interaction of oxygen with the Ru/γ-Al₂O₃ catalyst comprising metal particle with sizes of 1-16 nm, was examined over a temperature range 20-400 °C. The catalyst loaded with 10.8 wt.% Ru was prepared by incipient wetness from RuCl₃ precursor. The structure of the Cl-containing catalyst and the catalyst after elimination Cl⁻ ions was characterized using H₂ and O₂ chemisorption, O₂ uptake, BET, XRD and TEM. The Cl⁻ ions in the catalyst decreased the H₂ and O₂ chemisorption capacity of Ru and caused large discrepancies between the mean particle size calculated from gas chemisorption and from TEM. Exposure to O₂ at 100-200 °C caused oxidation of small Ru particles, while larger particles were covered with very thin Ru_xO_y skin (undetected by XRD and TEM). The O/Ru ratio increased up to 200 °C implying high affinity of the small Ru particles to oxygen. Oxidation at 250 °C led to the formation of poorly crystalline RuO₂ particles with a mean size of 4 nm, and coverage of large Ru particles with 1.6 nm thick oxide layer. At 300 and 400 °C crystallization of the RuO₂ phase, as well as significant agglomeration of oxide particles was observed. However, even at 400 °C, metallic Ru was detected by XRD, TEM and SAED suggesting that large metal particles were not fully oxidized under the used conditions. Also, the O₂ uptake at 400 °C was lower than expected for oxidation of Ru metal to RuO₂. For the catalyst after elimination Cl ions the O₂ uptake (O/Ru ratio = 1.50) was higher, than for sample with large amount of Cl ions (O/Ru ratio = 1.34), indicating that the presence of Cl inhibits ruthenium oxidation in the Ru/Al₂O₃ catalyst.     

One-step through-mask electrodeposition of a porous structure composed of manganese oxide nanosheets with electrocatalytic activity for oxygen reduction

Potentiostatic electrolysis of a mixed aqueous solution of Bu₄NBr and MnSO₄ at +1.0 V (vs. Ag/AgCl) on Pt electrode led to the oxidation of Br⁻ and Mn²⁺ ions. X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and X-ray diffraction (XRD) revealed that this anodic process was followed by the deposition of insulating crystals of bromide salt of Bu₄N⁺ and the subsequent formation of layered manganese oxide in the interstitial spaces of the bromide grains already grown. Dissolution of the bromide crystals in water left a well-dispersed porous texture composed of manganese oxide nanosheets. The resulting MnO_x-modified electrode exhibited a larger catalytic current for the reduction of oxygen in alkaline solution, compared to the bare Pt electrode.     

Synthesis of Bi2Fe4O9 via PVA sol-gel route

Bi₂Fe₄O₉ powders were synthesized by a sol-gel process using polyvinyl alcohol (PVA) as a complexing agent. Differential scanning calorimetry (DSC), thermogravimetric (TG), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and Field emission scanning electron microscope (FSEM) techniques were used to characterize precursor and derived oxide powders. The effect of the ratios of positively charged valences to hydroxyl groups of PVA (Mⁿ⁺/-OH) on the formation of Bi₂Fe₄O₉ was investigated. XRD analysis showed that single-phase Bi₂Fe₄O₉ was obtained from the Mⁿ⁺/-OH = 2:1 and Mⁿ⁺/-OH = 1:1 precursors at the temperature of 700 °C. For the precursor with Mⁿ⁺/-OH = 4:1, pure Bi₂Fe₄O₉ formed at the temperature of 800 °C. Bi₂Fe₄O₉ powders clacined at 700 °C from Mⁿ⁺/-OH = 2:1 precursor shows weak ferromagnetism.     

Evaluation of lanthanum ferrite coated interconnect for intermediate temperature solid oxide fuel cells

In this paper, an La_0.8Sr_0.2FeO_3−δ (LSF20) protective layer has been prepared on SUS430 alloy substrate using the atmospheric plasma spraying technology combined with nitrate solution impregnation and its effectiveness was evaluated. Thermodynamic and electrochemical performance tests confirmed the effectiveness of the LSF20 protective layer for decreasing the oxidation rate of the alloy and abating the chromium poisoning to the cathode. Upon exposure to air at 800 °C for 100 h, the oxidation rate of LSF20-coated alloy was reduced 56 folds compared to that of the uncoated alloy, and the LSF20-coated alloy produced a low area specific resistance of 1 mΩ cm² after oxidized in air at 800 °C for 1000 h. Half-cell measurement results indicate that the influence of chromium poisoning on the La_0.8Sr_0.2MnO_3−δ cathode was greatly inhibited with the LSF20-coated SUS430 alloy as interconnects.