No abstract

In chromium electrodeposition, as with other metals, it is possible to obtain differences in coloration, whether it is black or white chromium. Both films have been obtained using two very similar baths, except that black chromium has KNO3 in solution. We found that the electrochemical deposits of both kinds of Cr follow a diffusion-controlled nucleation and growth mechanism of 3D centres. In fact, while white chromium exhibited a simple 3D nucleation mechanism, the black chromium was found to be complicated by the concurrent nitrate ions- reduction processes on the surface of recently formed Cr nuclei

This work deals with the kinetic changes originated by nitrate presence on copper nucleation. From analysis of experimental potentiostatic current transients recorded during copper electrodeposition from aqueous solutions, with and without nitrate ions, it is shown that when NO3- are present, the copper nucleation rate increases while the number density of active site almost remains constant for every applied potential considered.

The application of the unified physics is the way to understand the phenomenology and mechanics of super plastic flow (SPF). In this scenery, the main proposed in this work is to establish the effect of grain size and thermomechanical conditions on the activation energy for super plastic flow (Qspf) in Zn-22Al eutectoid alloy by applying the quantum mechanics and relativistic model (QM-RM) proposed by Muñoz-Andrade. Analyses on the experimental results reported before by some authors, it is shown for grain size of 0.35 μm that the calculated Qspf by using QM-RM for grain boundary sliding is 55.669 kJ/mol at 303 K and strain rate of 1 s−1. These results are in closed agreement with the value of Qa = 54 kJ/mol reported previously by using the theoretical and conventional methodology set up by Mohamed and Langdon. However, for grain size of 0.8μm, the calculated Qspf is 67.864 kJ/mol at 473 K and strain rate of 1×10−2 s−1. Furthermore, in order to understand the phenomenology and mechanics of SPF in Zn-22Al eutectoid alloy, the variation of the activation energy with the temperature; stress and strain rate is analyzed in association with coupled mechanisms during SPF, such as grain boundary sliding, cooperative grain boundary sliding and self-accommodation process related to the microstructure.

Losses from corrosion are a damage which is difficult to quantify at world level, and a large variety of service failure problems of materials is due mainly to corrosion-related problems. One of the localized types of corrosion is originated by exposure to stainless steel at work temperatures where the sensitization phenomenon occurs. This phenomenon occurs due to second stage precipitation at grain boundaries, whether by thermal treatment or by welding. In this study, a thermally treated steel AISI 304 was used, and it shows the results of various chemical and electrochemical attacks to reveal the presence of carbides at grain boundaries, chromium carbides are precursors of localized corrosion. Linear polarization was performed in the sensitized samples to estimate the repercussion of this phenomenon on the overall corrosion resistance of the stainless steel. Surface evaluation was carried out using a Scanning Electron Microscope and an EDS X-ray detector, through which it was possible to do an in situ chemical analysis of the particles and the extracted carbides, after having dissolved the steel matrix electrochemically.