L. Peraldo Bicelli

Photo-electrochemical imaging of hydrogen-induced damage in stainless steel

Blisters and their surrounding crack-tip areas in AISI 304 stainless steel have been imaged by Scanning Photo-Electrochemical Microscopy (SPEM), a technique providing photo-electrochemical images of hydrogen trapping and detrapping into blisters in real time, in situ and in continuous under hydrogen charging. The increased hydrogen concentration has also been imaged in the plastic enclave at the crack tip around a blister during its growth. The images acquired in time sequence can be examined as a single frame or assembled in a 2D or 3D movie, both in grey scale or false colour.

Influence of the nature of metals on the formation of the deposit's polycrystalline structure during electrocrystallization

Abstract The influence of the nature of metals on the formation of the deposits polycrystalline structure during electrochemical crystal growth has been investigated. Cd, Cu and Ni were selected for the theoretical simulation, they being typically representative of each of the three classes into which metals are traditionally divided according to their increasingly slower kinetics. The theoretical results confirm previous classification and substantially agree with the experimental ones on Cd, Cu and Ni electrodeposition.

The photoelectrochemical behaviour of polycrystalline AgIn5Se8

Abstract Polycrystalline samples of n-type AgIn5Se8 were prepared from the constituent element and employed as electrodes in photoelectrochemical cells. These semiconductor electrodes were characterized by spectral response, Mott—Schottky plots, current—voltage measurements and complex impedance analyses. The polycrystalline n-AgIn5Se8 electrodes show a very encouraging photoelectrochemical behaviour, since capable of offering solar to electrical conversion efficiencies of the order of 3%. However, stability tests run both under illumination and in the dark, revealed that this interesting photoelectrochemical performance worsened upon time of illumination. This was interpreted in terms of photocorrosion which leads to the formation of a selenium film on the surface of the semiconductor electrode.

Scanning photoelectrochemical analysis of hydrogen permeation on ASTM A516 grade60 steel welded joints in a H2S containing solution

Hydrogen permeation through a welded joint of an ASTM A516 grade60 steel immersed in a H2S solution was investigated using the scanning photoelectrochemical microscopy, an in situ technique providing images of the spatial distribution of hydrogen diffusion in real time and with good resolution. The paper presents images of hydrogen spatial distribution in the material including the base metal and heat-affected zone. Electrochemical impedance measurements were also performed in order to complement the information obtained.

Effects of visible light on hydrogen permeation in metals

Abstract The influence of light on hydrogen electropermeation through a thin membrane of iron, stainless steel and palladium, respectively, has been investigated. Hydrogen is cathodically evolved at one side of the membrane and anodically monitored at the other side. Illumination of the inlet side produces a decrease of the permeation current due to combined heating and “photo” effects which seem to reduce the degree of surface coverage with hydrogen. On the other hand, three different processes are observed when illuminating the anodically polarized outlet side: hydrogen electro-oxidation, hydrogen photo-oxidation (both to produce protons) and water photo-oxidation. As the photocurrent is proportional to the hydrogen flux at the metal surface, it is possible to monitor with an optical probe the local distribution of the diffusing hydrogen atoms at the metal surface. This technique allows in situ and continuous non-destructive control of all those metal which are susceptible to hydrogen damage.

Surface investigation of NiNb2O6 electrodes for water photoelectrolysis

Abstract The columbite-type modification of NiNb 2 O 6 has been characterized particularly in view of its application as a photoanode in solar cells for water photoelectrolysis. Both single-crystal and pellet electrodes have been considered, more especially examining their surface properties and photoelectrochemical behaviour after thermal reduction in a hydrogen atmosphere. In fact, following this treatment, we obtained an n-type material presenting a typical anodic photoresponse which by a point by point topological investigation was shown to be not uniform on the different regions of the electrode surface. A specific research was, therefore, performed in order to find out the surface treatments (mechanical polishing, chemical etching and photoetching) able to improve the oxide performance. The results are discussed taking the NiNb 2 O 6 band structure into account.

Structure formation during electrocrystallization of metal films

Publisher Summary Metal deposits are largely employed in microelectronics, for optical devices, in cosmic and atomic technology, in galvanotechnique, and in other fields. Their numerous practical applications are based on the possibility of depositing metal films with a favorable combination of their functional properties. In addition, there is also the possibility to prepare metal deposits with particular physical and mechanical properties, which substantially differ from those of the same metals in their usual massive state. These possibilities offer the opportunity for improving the physical and technical parameters of materials and devices and for promoting new technical branches. To reproduce the overall mechanism of formation of the structure of the deposits, it is necessary to examine all the consecutive steps of their growth. In the case of the heterogeneous crystallization on a foreign substrate, two main growth steps of the deposits may be considered in connection with the formation of the different structural defects. They are the initial nucleation step and the subsequent deposit growth step “in thickness.” The initial crystallization step includes the formation of the nuclei on the substrate—their lateral growth until a thin compact deposit layer is produced.

Computer simulation of CdTe electrodeposition

Abstract Following the simple kinetic model, based on the Butler-Volmer equation, developed by Engelken and Van Doren, a computer simulation has been performed of CdTe electrodeposition at 160 °C from a special ethylene glycol-based bath containing CdCl2 (1 M), TeCl4 (0.01 M) and KI (0.3 M). From the fitting of the experimental data, the values of the thermodynamic, kinetic and mass transport parameters of the electrodeposition process were obtained. Other simulations in which the influence of Cd and Te concentrations in the electrolyte has been analysed proved that the given bath composition has been optimized to obtain electronic-grade CdTe over a wide range of deposition potentials (more than 50 mV around the point of perfect stoichiometry). They also showed that, as a consequence of the high ratio between the Cd and Te concentrations in solution, the potential of perfect stoichiometry is less negative than the Cd Nernst potential, so that Cd underpotential deposition is possible. The results have been discussed within the framework of those obtained by Engelken and Van Doren in aqueous solution.

Electrochemical formation of thin films of binary III-V compounds

Publisher Summary This chapter discusses the progress chart of science for the formation by electrochemical deposition of III–V compound thin films. Currently, the electronic and optoelectronic industries provide some of the largest markets and challenges for thin-film semiconductors. The techniques for the growth of these materials include physical methods—namely, molecular beam epitaxy (MBE), liquid-phase epitaxy (LPE), liquid encapsulated Czochralski (LEC), and sputtering—and chemical methods—namely, chemical vapor deposition (CVD), metalorganic chemical vapor deposition (MOCVD), metalorganic vapor phase epitaxy (MOVPE), and electrodeposition. Physical methods are expensive, but they give relatively more reliable and reproducible results. Electrochemical synthesis is one of the oldest methods for the formation of thin films and may offer a simple and viable alternative to the complicated and expensive high-temperature and/or high-vacuum processes. The electrochemical deposition technique is particularly suited to the preparation of polycrystalline and amorphous thin-film semiconductors for applications in which the use of high-performance materials is not necessary and cost effectiveness is the most important aspect.