The electrochemiluminescent behavior of luminol on an electrically heating controlled microelectrode at cathodic potential

A new ECL detection system equipped with an electrically heating controlled microelectrode as the working electrode was established in this paper. The electrically heated microelectrode was made of a platinum wire (25 μm in diameter, 6 mm in long). Linear scan voltammetry has been applied to investigate the ECL behavior of luminol on the heated microelectrode during cathotic scanning. Good sensitivity and reproducibility for measurement of the ECL of luminol could be obtained at the heated microelectrode.     

Solvothermal oxidation of gallium metal

Solvothermal oxidation of gallium metal in various organic solvents at 300 °C under the autogenous vapor pressure of the solvents was examined. The reaction of gallium metal in 1-butanol or 2-methoxy-ethanol at 300 °C did not proceed and unreacted gallium metal was recovered even with prolonged reaction time. On the other hand, gallium metal reacted in aminoalcohols such as 2-aminoethanol, 2-methylaminoethanol, 2,2′-iminodiethanol and 2,2′,2″-nitrilotriethanol yielding γ-Ga₂O₃. The product obtained by this reaction has a relatively large crystallite size as compared with γ-Ga₂O₃ prepared by the conventional method.     

Full transition from metal to ceramic by direct oxidation of metallic cobalt powder

The study deals with the direct oxidation kinetics of micronic cobalt metal particles and its simulation for the complete transition from metal to ceramic. The simulation was also experimentally verified. All the three possible interfaces, Co/CoO, CoO/Co₃O₄ and Co₃O₄/O₂ (air), have been taken into consideration for the simulation. The complete oxidation kinetics has been investigated from the thermogravimetric studies under isothermal conditions in the temperatures 973–1173 K. A quantitative interpretation based on the diffusion of Co or oxygen ions through the grown oxide layer has been proposed. The activation energy for the oxidation kinetics calculated from the Arrhenius law was 161 ± 20 kJ mol⁻¹.     

Dry etching of diamond nanowires using self-organized metal droplet masks

In a top-down approach diamond nanowires (DNW) were fabricated by anisotropic oxygen plasma etching of undoped or boron doped polycrystalline diamond layers. Dewetting an evaporated metal film, resulting in randomly distributed metal droplets of 5-50 nm in diameter, created the etching mask. This study focused on the investigation of the effect of the metal layer type, i.e., Al, Ti, Co, Ni, Cu, Pd, Pt and Au, and thickness on surface density, shape and size of the resulting droplets. Two dry etching techniques were studied: (1) Capacitively Coupled Plasma Reactive Ion Etching (CCP-RIE) and (2) Inductively Coupled Plasma Reactive Ion Etching (ICP-RIE). Using CCP-RIE diamond etch rates were between 10 nm/min and 50 nm/min; however, diamond/Ni selectivity was not high enough to fabricate nanowires > longer than 250 nm. ICP-RIE etching created tapered, high aspect diamond nanostructures at 1000 W plasma power, 10 W platen power for ion acceleration and long etching times (> 40 min) while preserving the mask. Anisotropy can be improved by the addition of Ar in the plasma and the reduction of the pressure. So far, vertically aligned diamond nanowires of 800 nm in length were obtained by ICP-RIE etching in appropriate conditions.     

Adsorption of heavy metal cations using coal fly ash modified by hydrothermal method

In this study, the adsorption properties of synthetic zeolite produced from Brazilian coal fly ash were investigated for some heavy metal cations (Zn, Cu, Mn and Pb). The batch method has been employed, using metal concentrations in solution ranging from 100 to 3000 mg/l. Preliminary statistical analysis has indicated that temperature and time of synthesis of zeolites were the most important variables that affect the their adsorption capacity. Results lead to the conclusion that a hydrothermal treatment can increase from 2 to 25 times the adsorption capacity (CA) of the coal ash comparing to its original capacity. The ion-exchange characteristic of the zeolites was determined using Langmuir, Freundlich and Dubinin-Kaganer-Radushkevich isotherms. The adsorption increases as cation concentrations in aqueous solution increases. The preference order observed for adsorption is Pb > Cu > Zn > Mn.     

Catalytic clean-up of gasification gas with precious metal catalysts - A novel catalytic reformer development

Several precious metal catalysts were prepared on modified zirconia and tested for the selective catalytic clean-up of the gasification gas. The activity of the precious metal catalysts were compared to that of the modified zirconia supported nickel catalyst and to the support. The activities of the catalysts were tested in a monolithic form in a quartz laboratory reactor at temperatures of 600-900 °C under atmospheric pressure using synthetic sulfur containing gas mixture. In addition, the stability of the Ni and Rh catalysts was examined by measuring the activities at 800 °C for 10 h using sulfur containing gas. The simulated gas contained CO, CO₂, CH₄, C₂H₄, H₂, N₂, H₂O, H₂S, NH₃ and a tar model compound, i.e. a mixture of naphthalene and toluene. The addition of metal on the support promoted the activity in tar model compound decomposition only at the temperature range of 850-900 °C. The order of activity was Rh ≈ Ni > Pd > Ir > Ru > Pt. Almost complete tar model compound conversion was achieved with Rh, as well as with Ni, at 900 °C. At lower temperatures, the support showed higher activity in tar model compound decomposition compared to the metal/support catalysts tested. Only Ni and Ru showed moderate activity in ammonia decomposition. In regard to sulfur tolerance at 800 °C, Rh was activated during the 10 h experiment while the activity of Ni decreased. The performance of both was restored after the overnight N₂ flush and the conversion of the tar model compound was higher for Rh (64%) than for Ni (46%).     

Electrochemistry of ytterbium (III) in molten alkali metal chlorides

This work presents the electrochemical study of Yb(III) ions in molten alkali metal chlorides in the temperature range 723-1073 K. Transient electrochemical techniques such as linear sweep, cyclic and square wave voltammetry, and potentiometry at zero current have been used to investigate the reduction mechanism, transport parameters and thermodynamic properties of the reaction YbCl₂ + 1/2Cl₂ = YbCl₃ The results obtained show that the reduction reaction Yb(III) + e⁻ ⇔ Yb(II) is reversible being controlled by the rate of the mass transfer. The diffusion coefficient of [YbCl₆]³⁻ complex ions has been determined at different temperatures in the fused eutectic LiCl-KCl, the equimolar NaCl-KCl and the CsCl media. The apparent standard potential of the soluble-soluble redox system Yb(III)/Yb(II) has been obtained by cyclic voltammetry. The influence of the nature of the solvent on the electrochemical and thermodynamic properties of ytterbium compounds is discussed.     

Enhancement of oxygen reduction activity of nanoshell carbons by introducing nitrogen atoms from metal phthalocyanines

Nanoshell carbon is a type of catalytically grown nanocarbon with a hollow, round, shell-like structure, with a diameter in the range of approximately 20-50 nm. It has been shown to possess the electrocatalytic activity for oxygen reduction reaction (ORR) and is also expected to be a non-Pt catalyst for polymer electrolyte fuel cells. This paper reports the synergetic enhancement of the ORR activity of nanoshell carbons caused by the coexistence of nitrogen atoms. The nanoshell carbons were prepared by the carbonization of furan resin in the presence of acetylacetonates (AAs) and of phthalocyanines (Pcs), which contained Fe, Co, and Ni. The Pc-derived nanoshells (MP-T series; M = Co or Fe, T = carbonization temperature) showed higher ORR activities than the AA-derived nanoshells (MA-T series; M = Co or Fe, T = carbonization temperature) when the same metal elements were employed. An XPS study revealed that nitrogen species were introduced to the surface of the nanoshells when Pcs were used as the nanoshell-forming catalysts, and that no metal species remained on the nanoshells. Principally, the ORR activity of the carbons was governed by the presence of the nanoshells and further enhancement could be achieved by the introduction of nitrogen atoms. 0.78 V of OCV and 0.21 W cm⁻² of the maximum power density were observed for a fuel cell whose MEA consisted of 3CoP1000 cathode and a commercial Pt/C anode, when it was operated at 80 °C under a pressurized condition of 0.35 MPa.     

Diameter control of carbon nanotubes by changing the concentration of catalytic metal ion solutions

We have developed a simple new method to control the diameter of carbon nanotubes (CNTs) using catalytic nanoparticle arrays fabricated by filling the pores of well-ordered porous anodic aluminum oxide (AAO) templates with a metal ion solution. Fe ion solution was used to fill the pores in which Co had been deposited electrochemically, and then the template was dried naturally on a magnet. After this process, the pores were widened in NaOH solution. Well-graphitized multi-walled CNTs were grown from almost all the pores and were very long in length and homogeneous in diameter. We were able to control the diameter of CNTs, simply, by changing the concentration of iron ion solution. For example, the average outer diameters of the CNTs are 7 ± 1.5, 13 ± 1, and 17 ± 1 nm when the concentrations of Fe ion in their mother solutions were 1.0 × 10⁻³, 3.0 × 10⁻³, and 6.0 × 10⁻³ M, respectively. The inner diameters of these CNTs corresponded to the calculated diameters of Fe nanoparticles by assuming that all Fe ions contained in each pore are reduced to a single nanoparticle. This means that homogeneous nanoparticles are made in each pore. Our new method could be used to fabricate homogeneous nanoparticles from most metal ion solutions.     

Catalytic etching of {100}-oriented diamond coating with Fe, Co, Ni, and Pt nanoparticles under hydrogen

Etching of a highly {100}-oriented diamond coating, {100}HODC, with hydrogen gas using Fe, Co, Ni, and Pt nanoparticles as a catalyst was examined at high temperatures over 700 °C by high-resolution scanning electron microscopy and Raman spectroscopy. The metal atoms vacuum-evaporated onto the {100}HODC formed nanoparticles themselves when heated at high temperatures; e.g. 700 °C, in a flowing gas mixture of H₂ (10%) + N₂ (90%). At 800 °C, short nano-channels and etch pits holding metal nanoparticles were formed by Fe, Co, and Ni. The shapes of the Co and Ni nanoparticles in the etch pits were affected by the shape of the etch pits; reversed pyramidal shape. On the other hand, the top view of the Fe nanoparticles embedded in the etch pits showed a distorted round shape, probably due to the formation of something such as iron carbide, while the carbon content was unknown. Apparently, etching of the {100}HODC by Pt nanoparticles was observed after the treatment at 1000 °C. The difference in the catalytic etching behavior among these metal particles, the potential etching mechanism of diamonds with hydrogen by metal nanoparticles, probably as melted metal nanoparticles, and the formation mechanism of vacant etch pits were discussed.     

Influence of pulse plating parameters on the electrocodeposition of matrix metal nanocomposites

Electrocodeposition of alumina particles with copper and nickel from acidic electrolytes has been investigated using different deposition techniques. Compared to direct current (DC) deposition, both pulse plating (PP) and pulse-reverse plating (PRP) facilitated higher amounts of particle incorporation. With conventional DC plating the maximum alumina incorporation is ∼1.5 wt% in a nickel and ∼3.5 wt% in a copper matrix. However, the implementation of rectangular current pulses can give considerably higher particle contents in the metal layer. A maximum incorporation of 5.6 wt% Al₂O₃ in a copper matrix was obtained by PP at a peak current of 10 A dm⁻², a duty cycle of 10% and a pulse frequency of 8 Hz. In general, low duty cycles and high pulse frequencies lead to an enhanced particle codeposition. The microstructure and the hardness of both pure metal films and nanocomposite coatings showed only a weak dependence on the PP and PRP conditions.     

Electrochemical and corrosion behavior of Ti-xAl-yFe alloys prepared by direct metal deposition method

The electrochemical and corrosion behavior of Ti-based alloys was investigated. The direct metal deposition technique was used to fabricate 21 alloys with different ratio of metals (0 ≤ Al ≤ 27 wt.%, 0 ≤ Fe ≤ 25 wt.%). Corrosion resistance of each alloy was evaluated both qualitatively and quantitatively by voltammetric measurements in the simulated human body fluid conditions (Hank's solution). The corrosion rates of the materials were compared in Hank's solution using Tafel extrapolation method. Among the Ti-xAl-yFe alloys the Ti-7Al-4Fe alloy exhibited the slowest corrosion rate of 7.7 × 10⁻⁴ mm/year and the least value of passive current density (6.3 × 10⁻³ A/m²). The alloy is resistant to pitting corrosion as well.     

Catalytic effect of metal oxides on pyrolysis of sewage sludge

The effect of metal oxides (Al₂O₃, CaO, Fe₂O₃, TiO₂, and ZnO) on the pyrolysis of sewage sludge was investigated. The experiments were performed in a thermogravimetric analyzer (TGA) to check the pyrolysis behavior of raw sludge, demineralized sludge and demineralized sludge with metal oxides added, respectively. The results showed that the presence of Fe₂O₃ and ZnO probably inhibited the decomposition of organic matters in demineralized sludge samples to generate more solid residues, while Al₂O₃, CaO, and TiO₂ promoted the degradation of organic matters throughout the whole pyrolysis temperature ranges. All the metal oxides studied accelerated the initial decomposition of sludge samples. Al₂O₃ and TiO₂ might decrease the total pyrolysis time, while CaO, Fe₂O₃, and ZnO prolong pyrolysis time. The structure of demineralized sludge samples might be changed due to the addition of CaO, TiO₂, and ZnO. Between 550 K and 750 K, the conversion of organic matters (mainly cellulose and lignin) in sludge samples was enhanced by Al₂O₃ and TiO₂, but inhibited by CaO, Fe₂O₃, and ZnO. The effects of metal oxides on the weight loss rate of cellulose in demineralized sludge samples presented the following decreasing order of DE-ZnO > DE-TiO₂ > DE-SS > DE-Al₂O₃ > DE-Fe₂O₃ > DE-CaO.     

Effect of Fe2O3 addition on consolidation and properties of 8 mol% yttria-stabilized zirconia by high-frequency induction heated sintering (HFIHS)

Dense nanophase 8 mol% yttria-stabilized zirconia was sintered by high-frequency induction heated sintering (HFIHS) within 6 min from 8YSZ nanopowder prepared by co-precipitation method. Sintering was accomplished under the combined effects of an induced current and mechanical pressure. Highly dense 8YSZ with relative density of up to 96% was produced under simultaneous application of a 60-MPa pressure and the induced current. The effects of Fe₂O₃ additions on the sintering behavior, mechanical properties and ionic conductivities of the 8YSZ were investigated.     

Corrosion of similar and dissimilar metal crevices in the engineered barrier system of a potential nuclear waste repository

Crevice corrosion is considered possible if the corrosion potential (E_corr) exceeds the repassivation potential for crevice corrosion (E_rcrev). In this study, potentiodynamic polarization and potentiostatic hold were used to determine the E_rcrev of similar and dissimilar metal crevices in the engineered barrier system of the potential Yucca Mountain repository in 0.5 M NaCl, 4 M NaCl, and 4 M MgCl₂ solutions at 95 °C. The results were compared with data previously obtained using crevices formed between Alloy 22 and polytetrafluoroethylene. It was observed that, except for Type 316L stainless steel, all other metal-to-metal crevices were less susceptible to crevice corrosion than the corresponding metal-to-polytetrafluoroethylene crevices. Measurements of galvanic coupling were used to evaluate the crevice corrosion propagation behavior in 5 M NaCl solution at 95 °C. The crevice specimens were coupled to either an Alloy 22 or a Titanium Grade 7 plate using metal or polytetrafluoroethylene crevice washers. Crevice corrosion of Type 316L stainless steel propagated without repassivation. For all the tests using a polytetrafluoroethylene crevice washer, crevice corrosion of Alloy 22 was initiated at open circuit potential by the addition of CuCl₂ as an oxidant, whereas no crevice corrosion of Alloy 22 was initiated for all the tests using Alloy 22 or Titanium Grade 7 metals as crevice washer. However, crevice corrosion propagation was found to be very limited under such test conditions.     

Pressure infiltration of boron nitride preforms with molten aluminum

The infiltration of compacted cubic BN (cBN) with molten aluminum has been investigated as a potential route for a cheap and easy method of manufacturing cBN/metal composites. CBN compacts have been infiltrated with molten Al at a temperature between 670 and 800 °C and pressure of 15 MPa in vacuum. At these temperatures no pronounced interactions between hexagonal and cubic BN with Al was observed, allowing the complete infiltration of cBN with 12 μm mean grain size. After infiltration at 800 °C, the temperature was increased without pressure to convert aluminum into borides and AlN. The hardness of the resulting materials depends on the content of hexagonal, cubic BN and the rate of conversion of Al into borides and AlN. The infiltration height of less than 1 mm obtained from infiltrating the 3 μm cBN powder green compacts gave a hardness of 22.0 ± 0.6 GPa after heat treatment.     

Comparison between the design of experiments and simulation in the three-phase distillation in a sieve tray column for glycerine dehydration

Design of experiments (DOE) is a value scientific approach used to understand the processes in a better way and to determine how the inputs affect the response(s). In this work, this method has been applied to study the behavior of the three-phase distillation in a sieve tray column, through the effects of the process and geometrical variables. The experimental values were compared with predicted values obtained by simulation using the equilibrium and nonequilibrium models. Three-phase distillation has been used for glycerine dehydration using toluene as entrainer, in order to avoid the glycerol degradation by distillation at atmospheric pressure. The best conditions found were: vapor flow rate of toluene = 23.5 kg/h, feed flow rate = 2.2 kg/h and feed concentration = 50 wt% glycerol, using the layout L₄ with fractional hole area = 0.04 and weir height = 70 mm. The nonequilibrium model based on Eckert and Vanek's approach (2001) and Chen–Chuang's correlation (1993) have been used to estimate the binary coefficients of mass transport. The predicted values obtained by the experimental model and by the nonequilibrium model have represented the behavior of the dehydration in the sieve tray column studied. Both models underpinned the experimental results obtained for this column.     

Rheological properties of ethylene ionomer neutralized with binary metal cation

The roles of ionic bonding in molten ethylene ionomers without ionic aggregates were rheologically characterized in linear regions under shear. We have measured melt viscosities of ethylene-methacrylic acid (EMAA) ionomers by means of dynamic shear experiment. The samples used in this study were binary mixtures selected from Na, Mg and Zn salts of EMAA (MAA=5.4 mol%). The dynamic shear properties revealed that the time-material superposition is applicable to these ionomer blends in a temperature range from 140 to 200 °C. It was also found that these binary mixtures unexpectedly give decreases of zero shear viscosities obtained from a time-material superposition, if the cations were selected from different metal groups such as alkali, alkaline earth and transition metals. This behavior can be explained by the acid-cation exchange mechanism.     

Li-intercalation behaviour of vanadium oxide thin film prepared by thermal oxidation of vanadium metal

In order to produce thin films of crystalline V₂O₅, vanadium metal was thermally oxidised at 500 °C under oxygen pressures between 250 and 1000 mbar for 1-5 min. The oxide films were characterised by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), X-ray diffraction (XRD) and Rutherford backscattering spectrometry (RBS). The lithium intercalation performance of the oxide films was investigated by cyclic voltammetry (CV), chronopotentiometry and electrochemical impedance spectroscopy (EIS). It was shown that the composition, the crystallinity and the related lithium intercalation properties of the thin oxide films were critically dependent on the oxidation conditions. The formation of crystalline V₂O₅ films was stimulated by higher oxygen pressure and longer oxidation time. Exposure for 5 min at 750 mbar O₂ at 500 °C resulted in a surface oxide film composed of V₂O_5, and consisting of crystallites up to 200 nm in lateral size. The thickness of the layer was about 100 nm. This V₂O₅ oxide film was found to have good cycling performance in a potential window between 3.8 and 2.8 V, with a stable capacity of 117 ± 10 mAh/g at an applied current density of 3.4 μA/cm². The diffusion coefficients corresponding to the two plateaus at 3.4 and 3.2 V were determined from the impedance measurements to (5.2 and 3.0) × 10⁻¹³ cm² s⁻¹, respectively. Beneath the V₂O₅ layer, lower oxides (mainly VO₂) were found close to the metal. At lower oxygen pressure and shorter exposure times, the oxide films were less crystalline and the amount of V⁴⁺ increased in the surface oxide film, as revealed by XPS. At intermediate oxygen pressures and exposure times a mixture of crystalline V₂O₅ and V₆O₁₃ was found in the oxide film.     

Study of vapor liquid two-phase frictional pressure drop in a vertical heated spirally internally ribbed tube

Experiments of vapor liquid two-phase frictional pressure drop of upward flow boiling in a smooth tube and in a spirally internally ribbed tube were conducted, respectively. The spirally internally ribbed tube has an outside diameter of 22 mm and an inside diameter of 11 mm (an equivalent inside diameter of 11.6 mm) and the smooth tube has an outside diameter of 19 mm and an inside diameter of 15 mm. The test tubes were vertically installed and uniformly heated by electricity to achieve flow boiling test conditions. The available heated length of both test tubes is 2500 mm. The working fluids are water and kerosene, respectively. The experimental pressure is 6 bar for flow boiling of water and 3 bar for flow boiling of kerosene. The exit vapor quality of the test sections is about 0.3. The two-phase Reynolds number ranges from 8000 to 28,000. The experimental two-phase frictional pressure drops in the smooth tube are compared with the predicted results by the two-phase flow homogeneous model and the Friedel formula (Friedel, 1979. Improved friction pressure drop correlation for horizontal and vertical two-phase pipe flow. European Two-phase Flow Group Meeting, Ispra, Italy), respectively. It shows that the experimental results agree with the Friedel formula better than the two-phase flow homogenous model. By comparison, the two-phase frictional pressure drops in the spirally internally ribbed tube are 1.6-2.7 times greater than that in the smooth tube. A physical explanation of the increase of the two-phase frictional pressure drop in the spirally internally ribbed tube is given. According to the two-phase flow homogeneous model, a correlation of two-phase friction factor is proposed for the spirally internally ribbed tube and it is applicable to pressures up to 6 bar.