Zeolite-based photocatalysts immobilized on aluminum support by plasma electrolytic oxidation

The preparation and properties of zeolite-containing oxide coatings obtained by plasma electrolytic oxidation are investigated and discussed. Pure and Ce-exchanged natural (clinoptilolite) and synthetic (13X) zeolites are immobilized on aluminum support from silicate-based electrolyte. Obtained coatings are characterized with respect to their morphology, phase and chemical composition, photocatalytic activity and anti-corrosion properties. It is observed that all mentioned properties of obtained coatings are dependent on processing time and type of immobilized zeolite. Coatings with Ce-exchanged zeolite show higher photocatalytic activity and more effective corrosion protection than those with pure zeolite. The highest photocatalytic activity is observed for coatings processed in pulsed a DC regime for 30 minutes containing Ce-exchanged 13X zeolite, followed by those containing Ce-exchanged clinoptilolite. Pronounced anti-corrosion properties feature almost all samples containing Ce-exchanged 13X zeolite

PEO Coatings with Active Protection Based on In-Situ Formed LDH-Nanocontainers

In the present work, for the first time Zn-Al layered double hydroxide (LDH) nanocontainers were grown in-situ on the surface and in the pores of plasma electrolytic oxidation (PEO) layer and then loaded with a corrosion inhibitor to provide an active protection. The developed LDH-based conversion process ensures partial sealing of the pores and provides an effective corrosion inhibition on demand leading to increased fault-tolerance and self-healing properties. The structure, morphology and composition of the LDH-sealed PEO coatings on 2024 aluminum alloy were investigated using SEM, TEM/FIB, XRD and GDOES. Electrochemical impedance spectroscopy and scanning vibrating electrode techniques show a remarkable increase in the corrosion resistance and fault tolerance when PEO coating is sealed with a LDH-inhibitor treatment

Novel electrochemical method of fast and reproducible fabrication of metallic nanoelectrodes

A novel electrochemical wire etching method of fabrication of ultrasharp nanoelectrodes is reported. Tungsten wires can be sharpened to less than 10 nm tip radius in a reproducible manner in less than 1 min by using controllable hydrodynamic electrolyte flow combined with optimized electrochemical etching parameters. The method relies on the variations of the electric field at the surface of a metal wire, while the electrolyte solution is in motion, rather than on the ionic gradient generated in a static solution. (C) 2014 AIP Publishing LLC

The Role of Cu-Based Intermetallic on the Direct Growth of a ZnAl LDH Film on AA2024

The direct ZnAl layered double hydroxide growth on AA2024 is a fast-occurring reaction, yet is characterized by an inhomogeneous film thickness. It has been shown that at the periphery of Cu-rich intermetallic, the flakes tend to be larger and denser. A combination of in situ and ex situ measurements were used to monitor the changes in the layered double hydroxide film grown on the regions of intermetallics. Immediately after immersion, an activation of the intermetallic phases is observed due to the dealloying process with an almost immediate film growth. Dealloying is followed by trenching of the adjacent Al matrix leading to an excessive production of large and dense layered double hydroxide flakes at the periphery of the intermetallic. However, the scanning electron microscopy cross-section images revealed that the trenching process leads to defects in the area surrounding the intermetallic. This could weaken the corrosion resistance performance of the layered double hydroxide conversion coating and lead to adhesion failure of consecutive polymer coatings. Nevertheless, this work highlights a few advantages and drawbacks of the layered double hydroxide conversion coatings and pathways to its potential optimization and improvement

Properties of ZnO/ZnAl2_2O4_4 composite PEO coatings on zinc

Recently the successful formation of PEO coatings on zinc in a phosphate aluminate electrolyte was shown. The produced composite coatings contain various mixtures of ZnO and ZnAl$_2$O$_4$. In frame of the current study, the properties of the formed coatings including adhesion/cohesion, wear, corrosion and photocatalytic activity were analysed to identify possible applications. However, the coatings show internal porosity and a sponge-like structure. Thus the cohesion within the coating is quite low. Pull-off tests have demonstrated clear rupture within the PEO layer at strength values as low as 1 MPa. The photocatalytic activity is limited, in spite of the formation of a higher amount of ZnO at shorter treatment times. Interestingly, the composite coatings of ZnO and higher amounts of ZnAl$_2$O$_4$ spinel showed a higher activity, but not sufficient for fast and effective catalytic cleaning applications

Silica-Based Nanocoating Doped by Layered Double Hydroxides to Enchance the Paperboard Barrier Properties

Paperboard is an environment -friendly multi -layer material widely used for packaging applic a- tions. However, for food packaging paperboard lacks essential barrier properties towards oxygen and water vapor. Conventional solutions to enhance these barrier properties (e.g. paperboard film coating with synthetic polymers) require special manufacturing facilities and difficult the end -of - life disposal and recycling of the paperboard. Paperboard coating with silica -based formulations is an eco -friendly alternative hereby disclosed. Silica -nanocoating s were prepared by sol -gel synth e- sis, with or without the addition of Zn(2) -Al -NO 3 layered double hydroxides (LDHs), and applied on the surface (ca 2 g/m 2 ) of industrial paperboard samples by a roll -to -roll technique. The ph y- sicochemical features of silica -nanocoatings were studied by FTIR -ATR, SEM/EDS, XRD analysis and surface energy measurements. The barrier properties of uncoated and silica -coated pape r- board were accessed by water vapor transmission rate (WVTR) and oxygen permeability ( J O 2 ) measurements. The best barrier results were obtained for paperboard coated with a mixture of tetraethoxysilane (TEOS) and 3 -aminopropyltriethoxysilane (APTES), with and without the in- corporation of LDHs

Iron oxidation at low temperature (260–500 C) in air and the effect of water vapor

The oxidation of iron has been studied at low temperatures (between 260 and 500 C) in dry air or air with 2 vol% H2O, in the framework of research on dry corrosion of nuclear waste containers during long-term interim storage. Pure iron is regarded as a model material for low-alloyed steel. Oxidation tests were performed in a thermobalance (up to 250 h) or in a laboratory furnace (up to 1000 h). The oxide scales formed were characterized using SEM-EDX, TEM, XRD, SIMS and EBSD techniques. The parabolic rate constants deduced from microbalance experiments were found to be in good agreement with the few existing values of the literature. The presence of water vapor in air was found to strongly influence the transitory stages of the kinetics. The entire structure of the oxide scale was composed of an internal duplex magnetite scale made of columnar grains and an external hematite scale made of equiaxed grains. 18O tracer experiments performed at 400 C allowed to propose a growth mechanism of the scale

Polar and antipolar polymorphs of metastable perovskite BiFe0.5Sc0.5O3

A metastable perovskite BiFe0.5Sc0.5O3 synthesized under high-pressure (6 GPa) and high-temperature (1500 K) conditions was obtained in two different polymorphs, antipolar Pnma and polar Ima2, through an irreversible behavior under a heating/cooling thermal cycling. The Ima2 phase represents an original type of a canted ferroelectric structure where Bi3+ cations exhibit both polar and antipolar displacements along the orthogonal [110](p) and [1 (1) over bar0](p) pseudocubic directions, respectively, and are combined with antiphase octahedral tilting about the polar axis. Both the Pnma and the Ima2 structural modifications exhibit a long-range antiferromagnetic ordering with a weak ferromagnetic component below T-N similar to 220 K. Analysis of the coupling between the dipole, magnetic, and elastic order parameters based on a general phenomenological approach revealed that the weak ferromagnetism in both phases is mainly caused by the presence of the antiphase octahedral tilting whose axial nature directly represents the relevant part of Dzyaloshinskii vector. The magnetoelectric contribution to the spontaneous magnetization allowed in the polar Ima2 phase is described by a fifth-degree free-energy invariant and is expected to be small

Preliminary Investigation of the Corrosion Behavior of Proprietary Micro-alloyed Steels in Aerated and Deaerated Brine Solutions

The corrosion performance of fairly new generation of micro-alloyed steels was compared in different concentrations of aerated and deaerated brines. Electrochemical polarization, weight loss and surface analyses techniques were employed. The results showed a threshold of corrosion rate at 3.5 wt.% NaCl in both aerated and deaerated solutions. The average corrosion current density for steel B, for example, increased from 1.3 µA cm¯² in 1 wt.% NaCl to 1.5 µA cm¯² in 3.5 wt.% NaCl, but decreased to 1.4 µA cm¯² in 10 wt.% deaerated NaCl solutions. The aerated solutions exhibited an average of over 80% increase in corrosion current density in the respective concentrations when compared with the deaerated solution. These results can be attributed to the effects of dissolved oxygen (DO) which has a maximum solubility in 3.5 wt.% NaCl. DO as a depolarizer and electron acceptor in cathodic reactions accelerates anodic metal dissolution. The difference in carbon content and microstructures occasioned by thermo-mechanical treatment contributed to the witnessed variation in corrosion performance of the steels. Specifically, the results of the various corrosion techniques corroborated each other and showed that the corrosion rate of the micro-alloyed steels can be ranked as CR[Steel A] < CRₓ₆₅ < CR[Steel B] < CR[Steel C]