Characterisation of passive films formed on mild steels in bicarbonate solution by EIS

Passive films formed anodically on carbon steel, chromium steel and high speed steel (HSS) in 0.5 M NaHCO3 and in 0.5 M NaHCO3+0.01 M KCl have been characterised by electrochemical impedance spectroscopy (EIS). Carbon steel presents a wide passive anodic region (0.0-0.9 V vs. saturated calomel electrode (SCE)), while those of chromium steel and HSS, either as-received or heat-treated, are narrower because of transpassive anodic dissolution of Cr above ~0.4 V. This is clearly seen through changes in the impedance spectra. An equivalent circuit is proposed to fit the experimental data, leading to determination of oxide film capacitance and film resistance. The semiconductor properties of the passive films were investigated by Mott-Schottky plots. All steel samples behave like n-type semiconductors, showing that the passive film properties are dominated by iron. However, same differences are found concerning the concentration of donors, i.e. oxygen vacancies, and thickness of the space charge region, which are correlated with the different pitting corrosion resistances of the passivated steels.http://www.sciencedirect.com/science/article/B6TG0-459J02W-3/1/d0da09bd524a79ca783a6a19d9b4974

Tackling perception and deception in STEM: a critical thinking skill for early-career development

The Universitat Politècnica de Catalunya (UPC), the Instituto Superior Técnico (ISTUniversidade de Lisboa) and the Czech Technical University (CTU) have recently launched the Engine4STEMers project, a joint initiative whose objective, among others, is to guide young graduates in their transition to the job market and motivate them to adopt management and leadership skills early in their careers. In this context, this short paper describes the objectives and contents of a Critical Thinking seminar, currently underway at UPC, which is aimed at motivating young STEM graduates to develop the principles of a skeptical attitude towards the information and stimuli that we perceive in order to face uncertainty, biased information and hidden agendas. Engine4STEMers needs analysis has revealed the importance of a good understanding of the concepts of perception and deception to develop effective interpersonal skills and, more importantly, to ease decision-making processes in a VUCA (volatile, uncertain, complex and ambiguous) environment

Metal Oxide and Hydroxide–Based Aqueous Supercapacitors: From Charge Storage Mechanisms and Functional Electrode Engineering to Need‐Tailored Devices

Abstract Energy storage devices that efficiently use energy, in particular renewable energy, are being actively pursued. Aqueous redox supercapacitors, which operate in high ionic conductivity and environmentally friendly aqueous electrolytes, storing and releasing high amounts of charge with rapid response rate and long cycling life, are emerging as a solution for energy storage applications. At the core of these devices, electrode materials and their assembling into rational configurations are the main factors governing the charge storage properties of supercapacitors. Redox‐active metal compounds, particularly oxides and hydroxides that store charge via reversible valence change redox reactions with electrolyte ions, are prospective candidates to optimize the electrochemical performance of supercapacitors. To address this target, collaborative investigations, addressing different streams, from fundamental charge storage mechanisms and electrode materials engineering to need‐tailored device assemblies, are the key. Over the last few years, significant achievements in metal oxide and hydroxide–based aqueous supercapacitors have been reported. This work discusses the most recent achievements and trends in this field and brings into the spotlight the authors' viewpoints

Alpha-Co(OH)(2)/carbon nanofoam composite as electrochemical capacitor electrode operating at 2 V in aqueous medium

In this work, alpha-Co(OH)(2) is electrodeposited onto carbon nanofoam forming a composite electrode operating in a potential window of 2 V in aqueous medium. Prior to electrodeposition, the carbon nanofoam substrate is subjected to a functionalization process, which leads to an increase of about 40% in its specific capacitance value. Formation of cobalt hydroxide clusters onto the functionalized carbon nanofoam by pulse electrodeposition further enhances the specific capacitance of the electrode. The combination of these factors with an enlarged working potential window, results in a material with specific capacitance close to 300 F g(-1) at current density of 1 A g(-1), considering the total mass loading of the composite. This suggests the potential application of the prepared composites in high energy density electrochemical supercapacitors. (c) 2015 Elsevier B.V. All rights reserved

Copper-cobalt foams as active and stable catalysts for hydrogen release by hydrolysis of sodium borohydride

The progress of hydrogen generation by sodium borohydride hydrolysis depends highly on the development of efficient catalysts based on non-noble metals such as cobalt. However, such catalysts undergo extensive deactivation which has a detrimental effect on their stability. Herein, highly porous copper and cobalt-based bimetallic foams, CuxCo100-x (x = 0-100 at%), produced by electrodeposition using the dynamic hydrogen bubble template are reported. The chemical composition of the foams was optimized in order to enhance specific surface area and improve their catalytic activity and stability as heterogeneous catalysts for sodium borohydride hydrolysis. Among the tested catalysts, copper-rich samples like Cu85Co15 are slightly more active than Co-100 and above all, they are less sensitive to deactivation by borates adsorption. Porous copper-rich foams were found to be an alternative to cobalt as low-cost, active and stable heterogeneous catalysts for hydrogen generation by hydrolysis of sodium borohydride. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved

Simulating In Vitro the Bone Healing Potential of a Degradable and Tailored Multifunctional Mg-Based Alloy Platform

This work intended to elucidate, in an in vitro approach, the cellular and molecular mechanisms occurring during the bone healing process, upon implantation of a tailored degradable multifunctional Mg-based alloy. This was prepared by a conjoining anodization of the bare alloy (AZ31) followed by the deposition of a polymeric coating functionalized with hydroxyapatite. Human endothelial cells and osteoblastic and osteoclastic differentiating cells were exposed to the extracts from the multifunctional platform (having a low degradation rate), as well as the underlying anodized and original AZ31 alloy (with higher degradation rates). Extracts from the multifunctional coated alloy did not affect cellular behavior, although a small inductive effect was observed in the proliferation and gene expression of endothelial and osteoblastic cells. Extracts from the higher degradable anodized and original alloys induced the expression of some endothelial genes and, also, ALP and TRAP activities, further increasing the expression of some early differentiation osteoblastic and osteoclastic genes. The integration of these results in a translational approach suggests that, following the implantation of a tailored degradable Mg-based material, the absence of initial deleterious effects would favor the early stages of bone repair and, subsequently, the on-going degradation of the coating and the subjacent alloy would increase bone metabolism dynamics favoring a faster bone formation and remodeling process and enhancing bone healing

Nickel-cobalt oxide modified with reduced graphene oxide: Performance and degradation for energy storage applications

Nickel-cobalt oxide is synthesized in combination with electrochemically reduced graphene oxide (Er-GO) by one-step electrodeposition on stainless steel followed by thermal treatment. The presence of reduced graphene oxide leads to enhanced electrochemical response, with a capacity increase from 113 mA h g−1 to 180 mA h g−1, and to increased faradaic efficiency and rate capability. Compared to Ni-Co oxide, the addition of reduced graphene oxide increases capacity retention from 58% to 83% after 5000 cycles. The material fade during cycling is studied by means of electrochemical impedance spectroscopy, electron diffraction spectroscopy and scanning electron microscopy. As a result, different degradation mechanisms are identified as source of the capacity decay, such as microstructural cracking, phase transformation and parasitic reactions

Saving Raw Materials for Cement Manufacture and Reusing an Untreated Waste from the Petrochemical Industry

This research addresses the replacement of cement by an untreated waste from the petrochemical industry. The effects of partial replacement of cement by spent fluid cracking catalyst (SFCC) on properties of mortar were determined. In this study, a series of mortar mixes was prepared with replacement ratios of 0%, 3%, 6%, and 12%. Furthermore, performance enhancing factors such as SFCC treatment or use of plasticizers were avoided. Workability, compressive strength, and durability related properties were assessed. An improvement regarding resistance to chloride penetration was observed, as well as that, when curing in salt water, the use of SFCC may be advantageous regarding compressive strength

TEOS Nanocomposites for the Consolidation of Carbonate Stone: The Effect of Nano-HAp and Nano-SiO₂ Modifiers

This study aimed at evaluating the effect of hydroxyapatite (HAp) nanosized structures and nanoparticles of hydrophilic silica as modifiers of both acid- and alkaline-catalysed tetraethoxysilane (TEOS)-based products for the consolidation of carbonate stones. Their initial effectiveness and some compatibility aspects were assessed in a porous limestone (sound and artificially aged Ançã stone samples) and two types of treatment (capillary absorption and brushing). The studied products were examined by scanning electron microscopy (SEM) and micro-Raman spectroscopy. Their depth of penetration and strengthening effect were evaluated through drilling resistance. Their action on the substrate was also further assessed by non-destructive methods based on colour variation and Shore-D hardness. Treated stone samples were dissimilarly affected by the tested treatments and exhibited a significant increase in strength with a low risk of over-strengthening. Adequate in-depth penetration patterns, as well as colour compatibility with the substrate were obtained with some of the prepared formulations through two types of treatment, both in sound and aged stone samples. The potential most effective treatments with the lowest colour change were obtained with the acid-catalysed TEOS-based products modified with HAp nanosized structures