Influences of Structure and Composition on the Photoelectrochemical Behaviour of Anodic Films on Zr and Zr-20at.%Ti

photoelectrochemical investigation on anodic films of different thickness grown on sputter-deposited Zr and Zr–20 at.%Ti was carried out. The estimated optical band gap and flat band potential of thick (UF ≥50 V) anodic films were related to their crystalline structure and compared with those obtained for thinner (UF ≤8 V/SCE) anodic oxides having undetermined crystalline structure. The Eg values obtained by photocurrent spectroscopy were also compared with the experimental band gap estimated by other optical ex situ techniques and with the available theoretical estimates of the zirconia electronic structures in an attempt to reconcile the wide range of band gap data reported in the literature. Finally, the optical band gap and flat band potential values obtained for tetragonal Zr0.8Ti0.2O2 mixed oxide were compared with that expected on the basis of a correlation between Eg and the film composition

Photocurrent Spectroscopy Applied to the Characterization of Passive Films on Sputter-Deposited Ti-Zr Alloys

A photoelectrochemical investigation on thin (613 nm) mixed oxides grown on sputter-deposited Ti–Zr alloys of different composition by air exposure and by anodizing (formation voltage, UF = 4 V/SCE) was carried out. The experimental results showed that the optical band gap increases with increasing Zr content in both air formed and anodic films. Such behaviour is in agreement with the theoretical expectation based on the correlation between the band gap values of oxides and the difference of electronegativity of their constituents. The flat band potential of the mixed oxides was found to be almost independent on the Ti/Zr ratio into the film and more anodic with respect to those estimated for oxide grown on pure Zr. The semiconducting or insulating character of the investigated films was strongly influenced by the forming conditions and the alloy composition

Physicochemical characterisation of thermally aged anodic films on magnetron sputtered niobium

The influence of thermal aging, at intermediate temperature (1h at 250°C) and in different environments, on the electronic and solid-state properties of stabilized 160 nm thick amorphous anodic niobia, grown on magnetron sputtered niobium metal, has been studied. A detailed physicochemical characterisation of the a-Nb2O5/0.5M H2SO4 electrolyte junction has been carried out by means of photocurrent and electrochemical impedance spectroscopy as well by differential admittance measurements. A change in the optical band gap (3.45 eV) of niobia film has been observed after aging (3.30 eV) at 250°C in air for 1 hour. A cathodic shift (0.15-0.2 Volt) in the flat band potential of the junction has been observed by the differential admittance (DA) measurements carried out in a large range of electrode potential values (6Volt) and ac frequencies (10 Hz-5 kHz). The frequency dependence of DA data, in absence of an appreciable contribution from surface states distribution, agrees with expectations of the theory of amorphous semiconductor Schottky barrier. The fitting of both components of DA allowed to get information on the distribution of electronic density of states (DOS) as a function of energy and distance from metal oxide interface. The DA measurements evidenced for vacuum treated niobia film an insulating to semiconductor transition with possible metallization of the inner metal/oxide interface. These findings can help to explain the large changes in the measured values of capacitance, after aging, and the larger leakage current observed in niobia electrolytic capacitors

A comparison of electrochemical degradation of phenol on boron doped diamond and lead dioxide anodes

This work compares two electrode materials used to mineralize phenol contained in waste waters. Two disks covered with either boron doped diamond (BDD) or PbO2 were used as anodes in a one compartment flow cell under the same hydrodynamic conditions. Efficiencies of galvanostatic electrolyses are compared on the basis of measurements of Total Organic Carbon (TOC) and Chemical Oxygen Demand (COD). Galvanostatic electrolyses were monitored by analysis of phenol and of its oxidation derivatives to evaluate the operating time needed for complete elimination of toxic aromatics. The experimental current efficiency is close to the theoretical value for the BDD electrode. Other parameters being equal, phenol species disappeared at the same rate using the two electrode materials but the BDD anode showed better efficiency to eliminate TOC and COD. Moreover, during the electrolysis less intermediates are formed with BDD compared to PbO2 whatever the current density. A comparison of energy consumption is given based on the criterion of 99% removal of aromatic compounds

Recent Progress in Corrosion-Resistant New Alloys Prepared by Sputter Deposition

Tailoring corrosion-resistant new alloys has recently been performed mostly by sputter deposition technique. This technique is suitable to form a single phase solid solution even when the boiling point of a component is lower than the melting point of the rest of components and/or when a component is immiscible to another component in the liquid state. Sputter-deposited chromium alloys with valve metals, such as titanium, zirconium, niobium and tantalum are composed of amorphous single phase in wide composition ranges. Molybdenum-valve metal alloys consist mostly of fine-grained bcc single phases. These alloys have very high corrosion resistance in concentrated hydrochloric acids which is higher than that of alloy constituting elements. The corrosion resistance increases with increasing chromium content of chromium-valve metal alloys, while the corrosion resistance decreases with increasing molybdenum content of molybdenum-valve metal alloys. Their corrosion resistance is based on spontaneous passivation. The passive films formed on amorphous chromium-valve metal alloys consist of double oxyhydroxides of chromic ion and valve metal cations. The passive films formed on molybdenum-valve metal alloys are heterogeneous. The exterior of the films is rich in valve metal cations and the interior is rich in tetra valent molybdenum

Energy Balance of Global CO_2 Recycling and Amounts of Reduction of CO_2 Emission

On the basis of tailoring of amorphous alloy electrodes for seawater electrolysis to form H_2 and amorphous alloy catalysts for conversion of CO_2 to CH_4, we are proposing global CO_2 recycling : At deserts; power generation by solar energy, at coasts close to the deserts; production of H_2 by electrolysis of seawater, production of CH_4 by the reaction of H_2 and CO_2 transported, and at energy consuming districts; combustion of CH_4, recovery of CO_2 and transportation of liquefied CO_2 to the coast close to the deserts. Since Egyptian scientists agree with us to do collaboration, the energy balance and the amount of reduction of CO_2 emission in the global CO_2 recycling between Middle East and Japan are estimated for the operation of a 1 GW CH_4-combustion power plant. The energy consumed in a year up to liquefaction of CH_4 including that corresponding to the repayment of solar power plant is almost the same as that spent up to obtaining LNG. The energy necessary for the global CO_2 recycling is only 8.7% higher than the energy necessary for LNG combustion for power generation without control of CO_2 emission. The extra energy is for recovery, liquefaction and transportation of CO_2. The reduction of CO_2 emission by the global CO_2 recycling is 79% of CO_2 emission from an LNG combustion power plant, that is, 2.62 Mtons/year

The Role of Phosphorus in Enhancing Corrosion Resistance of Amorphous Alloys

Phosphorus contained in amorphous metal-metalloid alloys is often beneficial in enhancing the corrosion resistance particularly in strong acids. On the basis of investigations conducted so far, the beneficial role of phosphorus is comprehensively summarized. Immersion of amorphous metal-phosphorus alloys containing passivating elements leads to the formation of elemental phosphorus layer on the topmost surface of the alloy as a result of initial alloy dissolution. The elemental phosphorus layer has high cathodic activity for oxygen and proton reduction and acts as the diffusion barrier against alloy dissolution. These beneficial effects ennoble the open circuit potential, and when the open circuit potential attains the passive region of the alloy spontaneous passivation occurs. An increase in the protectiveness of the passive film by ageing further ennobles the open circuit potential. At the high open circuit potential elemental phosphorus is no longer stable and dissolves into the solution. The passive film thus formed generally consists of passive oxyhydroxide and the phosphorus content in the film is rather low

β-Phase Morphology in Ordered Poly(9,9-dioctylfluorene) Nanopillars by Template Wetting Method

An efficient method based in template wetting is applied for fabrication of ordered Poly(9,9-dioctylfluorene) (PFO) nanopillars with β-phase morphology. In this process, nanoporous alumina obtained by anodization process is used as template. PFO nanostructures are prepared under ambient conditions via infiltration of the polymeric solution into the pores of the alumina with an average pore diameter of 225 nm and a pore depth of 500 nm. The geometric features of the resulting structures are characterized with environmental scanning electron microscopy (ESEM), luminescence fluorimeter (PL) and micro μ-X-ray diffractometer (μ-XRD). The characterization demonstrates the β-phase of the PFO in the nanopillars fabricated. Furthermore, the PFO nanopillars are characterized by Raman spectroscopy to study the polymer conformation. These ordered nanostructures can be used in optoelectronic applications such as polymer light-emitting diodes, sensors and organic solar cells

Oxidation-resistant multilayer coatings using an anodic alumina layer as a diffusion barrier on γ-TiAl substrates

Diffusion barrier layers of anodic alumina, introduced between an oxidation-resistant Al-Nb-Cr alloy and γ-TiAl substrate, have been evaluated using scanning electron microscopy and electron probe microanalysis. Diffusion of titanium to the Al-Nb-Cr coating is obvious when the Al-Nb-Cr alloy coated directly on the TiAl substrate is oxidized at 900°C for 168 h. The anodic alumina layer has been introduced by sputter-depositing aluminum and subsequent anodizing of the aluminum layer at a constant current density in 0.01 mol dm-3 ammonium pentaborate electrolyte at 298 K. Then, the Al-Nb-Cr alloy is further sputter-deposited on the anodized specimens. It is clearly demonstrated that the thin anodic alumina layer, less than 500 nm thick, suppresses effectively the inter-diffusion between the oxidation-resistant alloy coating and the TiAl substrate, particularly when a thin aluminum layer is remained beneath the anodic alumina. Although microcracks are generated and the substrate is oxidized through the cracked regions for the coatings that contain the metallic aluminum layer, the oxidation of the substrate through the cracks is prevented by pre-oxidation treatment at 800°C