M.A. Domínguez-Crespo

Fabrication of Sputtered Ce/La, La/Ce Oxide Bilayers on AA6061 and AA7075 Aluminum Alloys for the Development of Corrosion Protective Coatings

This work provides a comparative study on the corrosion protection efficiency of Ce, La films as well as Ce/La and La/Ce oxide bilayered coatings deposited onto AA7075 and AA6061 substrates by the radio frequency (RF) magnetron sputtering technique. The coating thickness ranged approximately from 12 to 835 nm, which changed with the deposition parameters and substrate composition. The relationship between microstructure, roughness and electrochemical performance is examined. The reactivity and crystallinity of rare earth (RE) films can be tailored by adjusting the sputtering parameters. Sputtered La films with thickness ca. 390 nm and average roughness of 66 nm showed the best corrosion protection properties in chloride medium as determined by potentiodynamic curves and electrochemical impedance spectroscopy (EIS). The method to obtain RE bilayered coatings, i.e., La/Ce or Ce/La as well as the substrate composition and applied power conditioned their inhibition properties. The RE bilayered coatings displayed better barrier properties than Ce films, which were poorer than those featured by La films.

Synthesis and Characterization of BiOCl Powders with Soft Templates

Bismuth oxychloride (BiOCl) powders were synthesized via a hydro/solvothermal method from BiCl3. Synthesis were performed in the presence of different capping agents namely polyvinylpyrrolidone (PVP), ethylenediamine (C2H4(NH2)2) or dextrose (C6H12O6). The reaction media, nature of capping agent, weight or molar ratio Bi:capping agent and temperature play an important role in the formation of well-defined morphology of BiOCl powders, which varies from melt crystals to plate-like structures. The as-obtained BiOCl/capping agent systems were characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy and IR spectroscopy. Among the selected capping agents, the C2H4(NH2)2 promote a defined morphology of the BiOCl crystals being a potential soft template. BiOCl/C2H4(NH2)2 system synthesized in aqueous medium clearly illustrate the effect of the Bi:C2H4(NH2)2 ratio on the morphology of BiOCl powders. The photocatalytic activity of BiOCl/C2H4(NH2)2 (1:0.5 molar ratio or 0.5 equiv.) and TiO2:BiOCl composites were evaluated on the degradation of methylene blue (MB) under UV–Vis light irradiation and compared with commercial TiO2 (Degussa, P25). It was pointed out that BiOCl powders with well-defined rectangular plate-like morphology have a higher photocatalytic activity during MB photodegradation in comparison to TiO2:BiOCl composites and similar to commercial TiO2.

Intensification of Electrochemical Performance of AA7075 Aluminum Alloys Using Rare Earth Functionalized Water-Based Polymer Coatings

This work reports the effect of different amounts of ceria nanoparticles on UV resistance and barrier properties of water-based polyurethane (WPU) on glass and AA7075 aluminum alloy substrates. Hybrid coatings were synthesized from an aliphatic WPU–HDI (1,6-hexamethylene di-isocyanate) and cerium oxide nanoparticles (CeO2) with an average particle size distribution of about 25 nm. Different nanoceria amounts (1, 3 and 5 wt %), mixing times (30, 60 and 120 min) and methods to disperse the nanostructures into the polymer matrix (magnetic stirring and sonication) were evaluated. Initially, the dispersion of CeO2 nanoparticles embedded in the polymer matrix and displacement in the corrosion potential (Ecorr) were analyzed by confocal scanning laser microscopy (CLSM) and open circuit potential (Eocp) measurements. According to this behavior, the dispersion and water ratio required during the polymerization process were established. Coated samples obtained after the second stage were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and optical light microscopy. In addition, optical measurements on glass substrates were evaluated with UV-vis spectroscopy. The effect of the synthesis parameters on the corrosion behavior of WPU–CeO2/AA7075 systems was investigated with Eocp and electrochemical impedance spectroscopy (EIS) in a 3 wt % NaCl solution. In addition, the films were subjected to 180 h of accelerated weathering. The results show that the combination of specific nanoceria addition with the optimal synthesis parameters enhances optical transparence of WPU as well as barrier properties. From these, the coated specimens prepared with 3 wt % of ceria content and sonicated for 30 min showed a highly dispersed system, which results in a high charge transfer resistance. The observed properties in clear coats deposited on metallic substrates suggested an improvement in the appearance and less deterioration in UV exposure in comparison with pure WPU, enhancing the protective properties of the AA7075 aluminum alloy when exposed to a corrosive medium.

Stabilized landfill leachate treatment using Guadua amplexifolia bamboo as a source of activated carbon: kinetics study

ABSTRACT In the present study, the characteristics of leachate generated from dumpsite called ‘Zapote’ located in southern region of Tamaulipas, Mexico were evaluated. The adsorption of non-biodegradable organic matter measured as chemical oxygen demand (COD), color and heavy metals from leachate on activated carbon (AC) prepared in acid media from Guadua amplexifolia bamboo has been studied. In addition, the computation of kinetic parameters during the adsorption process as well as the most probable mechanisms was determined. The ACs were analyzed by using scanning electron microscopy and Fourier transform infrared spectroscopy. The experimental data showed that the ACs removed up to 81.4% of color and reduced COD up to 91.6% after 9 h of reaction at 60°C. For heavy metals, the maximum adsorption uptake was achieved at pH = 8.0 within 20 min with removal percentages of 87.0% (Pb(II)), 43.0% (Cu(II)) and 30.5% (Ni(II)). A pseudo-second-order model explained the adsorption kinetics most effectively for Pb, Ni and Cu, while a pseudo-first order was found for Zn. The AC synthesized from the G. amplexifolia species could be potentially used as an effective adsorbent in the reduction of COD, and removal of color and heavy metals.

Morphological and Mechanical Properties Dependence of PLA Amount in PET Matrix Processed by Single-Screw Extrusion

ABSTRACT In this study, the dependence on the morphology and mechanical properties was analyzed when different amounts of polylactic acid are added to the polyethylene terephthalate polymer matrix using single-screw extrusion. Thermograms of the polymer blends obtained by differential scanning calorimetry couple to thermal gravimetric analysis show a displacement in the glass transition temperature with the amount of polylactic acid (1, 2.5, 5, and 7.5 wt%) added to the polymer matrix. Scanning electron microscopy and atomic force microscopy images showed two different kinds of morphology, both characteristics of miscible and partially miscible polymer blends. Fourier transform infrared spectroscopy measurements confirmed a physical interaction by hydrogen bond in the polymer blends. The impact resistance and tensile strength are reduced with the polylactic acid addition and are influenced by the fraction of segments of hydrogen bonded in the polyethylene terephthalate/polylactic acid blends as well as their miscibility. GRAPHICAL ABSTRACT

Role of Preparation Method on the Microstructure and Mechanical Properties of PPy/Ni Organic–Inorganic Hybrid Bilayer Coatings on Carbon Steel

The efficacy of the conducting polymers as coating on a metallic substrate is strongly dependent on the manner how they are applied. Polypyrrole (PPy)/Ni organic–inorganic hybrid coatings were electropolymerized on commercial carbon steel (AISI 1018) by combining potentiostatic and potentiodynamic techniques. In first instance, it was analyzed the electrodeposition of PPy using a constant potential regime and cyclic voltammetry techniques evaluating different synthesis parameters such as deposition time, applied potential, and potential cycles, respectively. Thereafter, it was used a potentiostatic method to obtain PPy/Ni bilayer films. The morphological, mechanical, and adhesion properties of these films depend on the synthesis parameters. The results revealed that polypyrrole films formed by both methods provide a globular-type structure, although coatings produced by cyclic voltammetry are denser and slightly thicker than those produced potentiostatically. Ni (oxide/hydroxide) particles are capable of sealing the pores of globular PPy coatings, thus increasing the hardness of the carbon steel (CS)/PPy/Ni system. As a result of the study, we have seen that PPy/Ni bilayer films are more uniform, compact and enhanced the hardness when the PPy is obtained by cyclic voltammetry than that observed for potentiostatic approach. Specifically, when four potential cycles are used to electropolymerized pyrrole, the more convenience properties in the CS/PPy/Ni arrangement are obtained.