S. Maffi

Photoelectrochemical visualization in real-time of hydrogen distribution in plastic regions of low-carbon steel

The in-situ scanning photoelectrochemical microscopy is a new technique giving images of hydrogen diffusion in the metals in real time with a good resolution. This paper presents some photoelectrochemical images of hydrogen distribution in a low-carbon steel ahead of a crack tip and in the regions submitted to a high deformation such as in the case of the metal bending.

Analytical characterization of electrode surface by X-ray photoelectron spectroscopy. β-PbO2-based cathode in voltage-compatible lithium cells

Lead dioxide cathodes, discharged in a lithium cell at significant points of the discharge curve, have been analysed by XPS and information obtained on the surface chemical composition has been used to elucidate the cell discharge mechanism.General and particular problems and complications arising in XPS investigations when ‘real’ samples are involved are critically outlined with obvious reference to the intrinsic difficulty in the surface analytical characterization of a mixture of lead compounds. An approach is suggested which stresses how even semiquantitative determinations could play a key role in the speciation analysis.

The scanning photoelectrochemical microscopy of diffusing hydrogen into metals

Abstract A new photoelectrochemical (PEC) technique is reported to image in real time the hydrogen diffusion into a metal in situ and continuously by means of a scanning laser spot. When a metal such as iron, stainless steel or nickel covered by a passive film is loaded with hydrogen and illuminated, the photoresponse of the passive film (the electrode is anodically polarized in an alkaline solution) is improved owing to the hydrogen photooxidation. This photoresponse is proportional to the hydrogen concentration in the metal. Scanning the metal surface by a laser spot in real time a well-detailed image is obtained of the diffusing hydrogen into the metal at a microscopic level. The present report describes the scanning photoelectrochemical microscopy (SPEM) of hydrogen diffution into an AISI 304 stainless steel foil.

Study of CdTe electrodeposition from a nonaqueous bath

A detailed investigation has been carried out on the processes occurring during the electrodeposition of cadmium telluride on a nickel electrode from a special bath containing CdCl2, TeCl4 and KI in ethylene glycol at 160 °C. KI was added to the bath both to improve the deposit adhesion on the substrate and to hinder ion complexation. Steady-state current-potential and cyclic voltammetry experiments were performed along with electrolyte ohmic resistance measurements. The experimental results evidenced the fairly good electrochemical behaviour of this organic electrolyte bath and its negligible ohmic resistance. Cyclic voltammetry showed that the reduction of Te(IV) ions occurs via a four-electron process as well as a six-electron process followed by a chemical reaction. Moreover, during slow-scan cyclic voltammetry and steady-state current-potential studies, the underpotential deposition of Cd(II) ions was observed. This behaviour has been attributed to the negative Gibbs free energy change involved in the CdTe-forming reaction.

Lead oxides as cathode materials for voltage-compatible lithium cells

Abstract Yellow β-PbO (massicot) and β-PbO 2 (plattnerite) have been investigated as cathode materials in organic electrolyte lithium cells. The main cha

Photoelectrochemical imaging of non-planar surfaces: the influence of geometrical and optical factors on image formation

In situ scanning photoelectrochemical (PEC) microscopy is a technique for mapping the photocurrent stimulated by a focused light at an electrode-electrolyte interface. This technique gives position-sensitive information on the nature of passivating films (composition, type and degree of crystallization, thickness, etc) that cover metal electrodes. In the analysis of PEC images, further aspects related to the surface shape and/or surface irregularities (roughness, slope errors, surface waviness, etc) have to be taken into account. In this paper we present the effects of non-planar surfaces by measuring the photoresponse of passivating oxide films on cylindrical iron rods with different diameters. The variation of the angle of incidence of the light, as the laser beam scans the surface of the rod, implies either a change in the spot size and different optical response of the oxide-metal system, such as the transmittivity of the oxide, the reflectivity of the metal and the light path inside the film. For evaluating the behaviour of the photocurrent, we have simulated these geometrical and optical effects by using a simple model in geometrical optics approximation. Images have been also acquired at various distances from the beam focus for highlighting the degradation of the spatial resolution induced by the focusing misalignment of the curved samples.

Polyphenylene Sulfide Sulphonic Acid: Processing, Solid State Conductivity and Electrolyte Transport Properties

Abstract Polyphenylene sulfide sulphonic acid is an amorphous, non melting solid which dissolves only in SOCl2, dehydrates at 40–180°C and degrades with heavy weight loss starting from 270°C. The polymer has been tested as solid state component of electrochemical devices in the 20–160°C range with the following results: conductivity (ohm−1 cm−1) = 10−1 in 30% KOH aq., 10−2 in 5 atm steam pressure and 10−5 in air; transport number in KCl (t +) ∼ 1. Possible applications are discussed in relation to the performance of other established material.

Evaluation of the Hydrogen Embrittlement Behaviour by Means of the Permeation Current Measure in Slow Strain Rate Conditions of a Micro-Alloyed Steel

The measure of the hydrogen permeation current through a metal membrane is a well-consolidated electrochemical technique to evaluate the effect of the environment, the polarisation and the type of steel related to hydrogen diffusion. Permeation tests allow to evaluate the stationary flow of hydrogen and the degree of surface coverage. In this work, permeation tests were carried out in a 35g/L NaCl solution at -1.05 V and -2 V vs. SCE on a pipeline micro-alloyed steel. The permeation current was measured on samples without load, with a constant load applied and in slow strain rate conditions. Afterwards, hydrogen permeation parameters were correlated to the results of Slow Strain Rate Tests (SSRT) in order to improve the knowledge on the hydrogen embrittlement mechanism of this type of steels.

Effect of the Heat-Affected Zones on Hydrogen Permeation and Embrittlement of Low-Carbon Steels

Steels with yield strengths below about 900 MPa are essentially immune to hydrogen embrittlement, and almost all pipeline steels have a yield strength below that value. However, same catastrophic failures of pipelines have been reported. Under mechanical stress these failures are due to the local formation of high-hardness martensite (hard spot) during cooling and from the presence of absorbed hydrogen developed under cathodic over-protection. This paper describes a photoelectrochemical, micrographic and fractographic study of the effect of an heat-affected zone (hard spot) on hydrogen permeation and the embrittlement of an API 5L STD X60 steel.

Aromatic polymers for advanced alkaline water electrolysis. II: Polyphenylene sulfonic acid

Abstract Thin (0.055 cm) asbestos cardboards reinforced with sulphonated polyphenylene withstand the action of boiling 30% w/w KOH better than the plain specimen. These materials are manufactured by soaking asbestos with a solution-suspension of the sulphonated polymer in SOCI 2 . With this procedure the concentration ( C % w/w) of the sulphonated polymer into the asbestos host matrix and, thus, the properties of the reinforced cardboard can be modified at will. On raising C from 13 to 31% the tensile strength, water regain and electrical resistance (in 100°C 30% w/w KOH) vary from 57 to 97 kg cm −2 , 35 to 26% w/w and 0.2 to 0.56 Ω·cm 2 for the freshly made cardboards and from 18 to 70 kg cm −2 , 34 to 64% w/w and 0.08 to 0.40 Ω·cm 2 for specimens aged 20 days in boiling 30% KOH. These changes in properties are rationalized on the basis of the weight loss of the cardboard and of the changes in the MgO/SiO 2 mole ratio, IR spectra and SEM micrographs. The data suggest that, in the manufacture of the cardboard, the transfer of the organic polymer from the soaking bath into the asbestos phase depends on the physical form in which the polymer (soluble and suspended gel) is present in the bath and yields a higher concentration of polyphenylene on the surface rather than the inner layers of the cardboard. Improvements are expected from the development of more soluble sulfonated polymers.