High potential cathodic polarization of oxidized aluminium electrodes in neutral and acid media

The cathodic polarization of an oxidized 99.9995% aluminium electrode at potentials from −2 to −2.5 V(SCE) in several electrolytes of neutral and acid pH values has been studied. Potentiodynamic oxidation of cathodically polarized aluminium electrodes following the technique of Rozenfel'd et al. have been performed and analyzed. In solutions of pH 1–2.1, the oxide film present on the aluminium surface is partially removed by means of a continuous cathodic polarization at those potentials; there is evidence of a small amount of oxide formation following oxide removal and metal etching. The cathodic behaviour in acid and neutral media is interpreted on the basis of a local alkalization resulting from the H₂ evolution. A possible mechanism for the oxide removal is discussed.     

Characterization of poly(isothianaphthene) derivatives and analogs by using solid-state 13C NMR

The combination of several options of a multipurpose ¹³C CP/MAS solid-state pulse sequence allows the characterization of insoluble poly(isothianaphthene) (PITN) derivatives and analogs. In order to improve solubility and processability of low bandgap polymers, poly (5-tert.butylisothianaphthene) and poly(5,6-dihexoxyisothianaphthene) have been synthesized and analyzed. The same chemistry also allows for the synthesis of poly(2,3-dihydro-1H-indene) and poly (isoindole). Based on model compounds, a proper ¹³C NMR assignment enables one to predict the geometric structure (aromatic versus quinoid) of these conducting polymers.     

Nanoscale friction of partially oxidized silicon nitride thin films

The nanoscale friction of partially oxidized silicon nitride thin films deposited by reactive magnetron sputtering was investigated. Post deposition thermal annealing in O₂, trying to simulate the oxidation by atmospheric oxygen in working conditions, formed a partially oxidized layer at the surface with maximum thickness around 10 nm. Unidirectional sliding tests showed a decrease of the low-load friction coefficients of the sliding pair for the samples annealed in oxygen as compared to the non-annealed ones. The results are discussed on the lights of our extension of the crystal chemistry model, which establishes a relationship between ionic potential and friction coefficient.     

Chemical modification of electrochemically oxidized and partially rereduced carbon fibre electrodes

Carbon fibre electrodes (residual graphite oxide fibres) electrochemically oxidized and partially rereduced in concentrated H₂SO₄ have excellent cation-exchanging properties. Chemically modified carbon fibre electrodes have been prepared by Na⁺-exchange of residual graphite oxide fibres and subsequent action of chlorocompounds in methanolic solutions (the Williamson reaction).The attachment of the various reagents on to the carbon fibres is reflected through the corresponding cyclic voltammograms obtained in aqueous buffer solutions. When modified with iron phthalocyanine, carbon fibre electrodes show a significant catalytic effect on the electrochemical reduction of oxygen in aqueous and methanolic solutions.     

13C CPMAS NMR,XRD, d.c. and a.c. electrical conductivity of aromatic acids doped polyaniline

Aromatic acids, para-toluene sulfonic acid (PTSA) and sulfosalicylic acid (SSA), doped polyanilines at different dopant levels and prepared by chemical and electrochemical methods are characterized by the high-resolution solid-state ¹³C CPMAS NMR technique. X-ray diffraction (XRD) patterns of highly protonated samples show a peak around 24 °. There is increase in crystallinity as the dopant concentration is increased. Temperature dependence of d.c. electrical conductivity measurements suggests that conduction takes place in an inhomogeneous medium consisting of ‘metallic’ polymer particles embedded in an insulating matrix. A.c. electrical conductivity measured on some of these samples shows that σ_ac ∝ ω^s in the frequency range 10 Hz to 100 kHz, and s is found to decrease as the dopant concentration and the temperature are increased. For higher dopant concentration samples, σ_ac is found to be temperature independent in the frequency range 10 Hz–100 kHz. The real part of the dielectric constant showed a steep increase at low frequencies. The results of a.c. transport are discussed in terms of hopping of charges among defect states.     

Structural analysis of deprotonated polyaniline by solid-state 13C N.M.R.

The chemical structure of a deprotonated polymer prepared by the oxidation of aniline with ammonium persulfate was analysed with solid-state ¹³C n.m.r. by using N,N′-diphenyl-p-phenylenediamine, N,N′-diphenyl-p-quinonediimine and N,N-dimethylindoaniline as model compounds. The polymer was found to consist of both amine and benzenoid-quinoid repeating units.     

Electrochemical behaviour of microcrystalline aluminium in neutral fluoride containing solutions

The electrochemical behaviour of microcrystalline pure aluminium coating (mc-Al), fabricated by a magnetron sputtering technique, has been investigated in NaF as well as NaF + NaCl aqueous solutions. Results indicate that the anodic polarization characteristic changes with NaF concentration. F⁻ anions promote the formation of a passive film, whose semiconducting properties were investigated. When the F⁻ concentration is high ([F⁻] ? 0.03 mol/L) the passive film is mainly composed of aluminium fluoride, which is an n-type semiconductor on mc-Al and a p-type semiconductor on polycrystalline Al (pc-Al). In NaF + NaCl aqueous solutions, Cl⁻ and F⁻ ions compete in affecting the type of semiconducting passive films formed on mc-Al.     

Analysis of electrochemical noise obtained from pure aluminium in neutral chloride and alkaline solutions

The present work involves the analysis of electrochemical noise obtained from pure aluminium during breakdown of the oxide film in aqueous neutral chloride solution and hydrogen evolution in alkaline solution. Since the noise data involve information on such stochastic processes as uniform corrosion, breakdown of the oxide film and hydrogen evolution, they were analysed based upon a stochastic theory: the plot of the cumulative probability numerically calculated was first transformed from the domain of the frequency of events to the mean free time domain and then, the Weibull probability plot was constructed by fitting Weibull distribution function to the calculated cumulative probability. Finally, the conditional event generation rate was numerically determined as a function of time. From two linear regions in one Weibull probability plot, it was concluded that breakdown of the oxide film and hydrogen evolution, respectively, were clearly distinguished from uniform corrosion in the Weibull probability plot. In addition, the roles of anion additives in breakdown of the oxide film and hydrogen evolution were also discussed in terms of the distribution of the mean free time and the conditional event generation rate.     

A scanning electron microscope study of the surface morphology of TD-NiCr oxidized at 800°C to 1200°C

Scanning electron microscopy was used to study the surface morphology of oxides formed on TD-NiCr at 800, 1000, and 1200° C for times up to 64 hr. Surfaces abraded with 120 grit oxidized to form Cr ₂O₃ which gradually developed large crystals of Cr₂O₃ (R~5 m). The shape of the crystals suggested vapor growth. Surfaces polished through 0.5 m diamond paste and oxidized had NiO on the surface except over grain boundaries and scratches which had Cr₂O₃ covering them. The NiO was faceted but showed little evidence of vapor growth. Wire samples of TD-NiCr 0.005 in. diam were oxidized at 1200°Cfor up to 50 hr at pressures from 10^–5 to 700 Torr. The only oxide formed was Cr₂O₃. Extensive large surface crystals ofCr₂O₂ resulting from vaporization and condensation were observed at pressures of 10Torr and above, but not at lower pressures. Humid air oxidation altered the oxide morphology markedly.     

A.C. anodizing of aluminium alloys

Three age-hardening aluminium alloys were compared with aluminium of commercial purity in terms of their susceptibility to anodization in an alternating current in 10% sulphuric acid at 35 V. Modifying additions of nitric acid and sodium sulphate were used to increase the rate of film growth. The former was relatively ineffective and the latter was very effective but vielded soft highly porous films. Neither is considered to be ideal in the context of functional engineering anodized surfaces.     

A comparative study of magnetron co-sputtered nanocrystalline titanium aluminium and chromium aluminium nitride coatings

A comparative study of magnetron co-sputtered (Ti,Al)N and (Cr,Al)N coatings was made. It was found that while both coatings followed similar development pattern with increasing nitrogen pressure, the (Cr,Al)N coatings achieved much higher deposition rate and hardness, suggesting the coatings had a great potential for many industrial applications.     

The influence of deformation conditions in solid-state aluminium welding processes on the resulting weld strength

Solid bonding of aluminium is an important joining technology with applications in fabrication, forming and new low-carbon recycling routes. The influence of deformation conditions on the strength of the resulting weld has yet to be fully assessed, preventing optimization of current processes and development of new ones.     

High resolution imaging of martensitic all-weld metal

Martensitic steel welds show promising results regarding their strength while they may tend to be brittle. As martensite is a quite complex microstructure, high resolution techniques like electron backscatter diffraction (EBSD) and atom probe tomography (APT) are valuable tools for an in-depth characterisation. In this study, the average block size and misorientation distribution of martensitic all-weld samples were evaluated with EBSD. A lower carbon content led to a smaller block size and consequently a higher toughness of the all-weld sample. Furthermore, APT revealed a concentration fluctuation of the main alloying elements and particles with a high carbon content. It is discussed how these methods can be used in the future to design the microstructure to achieve optimum properties.     

电解铝厂整流系统中性点不接地感应电压的危害及消除

通过对电解铝厂整流系统中性点不接地感应电压的产生及危害原因的分析，探讨了消除感应电压的途径及方法。     

Resistance welding of aluminium and aluminium alloys

Special features of the process of resistance welding of aluminium and its alloys and also equipment manufactured by the CEA and supplied by Weber Comechanics are described.     

A solid-state EMF study of the Fe-S-O and Co-S-O ternary systems

The equilibrium oxygen potentials of the two-phase equilibria Fe₃O₄/Fe_1–xS, Co_1–xS/Co₃S₄, Co₃S₄/CoS₂, Co_1–xS/CoO, and CoO/CoSO₄ were measured as a function of temperature. A solid-state emf technique using calcia-stabilized zirconia (CSZ) solid electrolyte was used. These equilibria were studied atP _SO21 atm; the equilibrium Co_1–xS/CoO was also studied atP _SO20.1 atm. Two emf cell designs were used for the measurements atP _SO21 atm andP _SO21 and 0.1 atm, respectively. The homogeneity range of FeS in equilibrium with Fe₃O₄ and that of Co_1–xS in equilibrium with CoO at 1073 K andP _SO21 atm were measured by electron microprobe analysis.     

Kinetics for pitting corrosion of a 13 Cr steel in neutral chloride solutions

The kinetics of pitting corrosion is pre-dominantly a function of the induction time and of the pitting potentials, so that it is indispensable to find all those two parameters. In order to find the potential one may use potentiostatic methods, the criterion of pitting corrosion being the current increase and the pit formation made visible in the stereomicroscope. The induction time increase as the applied potential decreases. The differences in the shape of the pits(spherical, semispherical, conical) have not been clearly interpreted so far; basically, in most cases, the cross section of the pits is semispherical at first, the radius increasing double the radius of the opening of the pit. From this moment on there is only pit growth to the depth, the pit becoming of conical shape. The overall mechanism is diffusion controlled, and the reduction of oxygen may play a certain role, too.     

Stress corrosion cracking of B13, a new high strength aluminium lithium alloy

The present paper focuses on the study of SCC behaviour of a new Al–Cu–Li alloy. For this purpose, two conventional media – NaCl and NaCl + H₂O₂ – were used for comparison with commercial alloys 7075 and 8090. This new alloy shows lower susceptibility to SCC than conventional alloys as it does not undergo environmentally-induced embrittlement in NaCl solutions and in 1 M NaCl + 0.3% H₂O₂ in which the 7075 and 8090 alloys, respectively, undergo environmentally-induced fracture.Solution composition was modified in order to determine the environmental conditions and strain rates under which this new alloy will crack due to a stress corrosion cracking phenomenon. The addition of 0.6 M sulphates to 1 M NaCl + 0.3% H₂O₂ solution allows the definition of a range of strain rate (between 10⁻⁷ and 10⁻⁶ s⁻¹) in which this new alloy undergoes stress corrosion cracking.