Composition Of Surface Oxide Layer Research Articles

A new insight into the mechanism of Ce enhancing high temperature oxidation resistance of hot-formed steel

In this paper, the effect of Ce addition on high temperature oxidation behavior of hot-formed steel was studied by high temperature oxidation experiment. The structure and phase composition of surface oxide layer of specimens with different Ce content were systematically analyzed by SEM, EDS, XPS. The results showed that the addition of Ce promoted the formation of a dense oxide layer during the initial oxidation stage, and effectively weaken the oxidation degree of the steel surface. Meanwhile, the Ce2O3 particles segregation in Si–Cr rich phase reduced the concentration of vacancy defects in oxide layer and enhanced the adhesion between oxide layer and substrate. After Ce addition, the surface oxidation resistance of hot-formed steel is significantly improved.

Interactions between Metallic Interconnects and Ceramic Electrodes in SOFC Operating Environments: Air Side

Ferritic stainless steel (FSS) bipolar plates are widely used to interconnect individual cells in planar Solid Oxide Fuel Cell (SOFC) stacks. In this study, thin films of ceramic and cermet electrode materials, La0.8Sr0.2MnO3 (LSM) for the cathode and Ni-Y2O3/ZrO2 (Ni-YSZ) for the anode, were screen printed on Sanvik's Sanergy HT, a specialty FSS alloy (with and without Co or Co/Ce surface coatings). Samples were then placed in a test rig which allows simultaneous exposures to humidified (3% H2O) single (air/air) and dual atmospheres (air/H2) at 800°C for 100 hours. This research is focused on the FSS surface oxide layers and the phenomena governing materials interactions during realistic SOFC exposures that drive degradation. The surface oxide layer composition and morphology are heavily influenced by the dual atmosphere exposures and contact with electrode materials. For example, air-side surface oxide layers are generally thicker and contain more Fe than those formed in single-atmospheres, and surface oxide layer thickness and composition is altered in the presence of contacting electrodes in comparison with gas-only exposures. These and other recent data suggest that corrosion studies performed without relevant SOFC stack environments (e.g., air-only and without contacting electrodes) may not reveal all of the pertinent high-temperature behaviors.

Surface characterization of passive film and elemental release analysis of a Ni–Cr alloy during bleaching, part I: effects of different bleaching agents

The aim of this study was to evaluate the elemental release from a Ni-Cr dental casting alloy subjected to 10% hydrogen peroxide (HP) or 10% carbamide peroxide (CP) solutions and to determine the composition of surface oxide layer formed on alloy samples. Cylinder-shaped 15 specimens were cast from a Ni-Cr alloy and divided into three groups (n = 5). Samples were exposed either to phosphate-buffer solution, HP, or CP for 30days, and total mass and individual elements (Ni, Cr, Mo) released into solutions were measured by means of atomic absorption spectrometry. Before and after elemental release measurements, a scanning electron microscope (SEM) accompanied by energy dispersive spectroscopy (EDS) (SEM/EDS) was used to analyze the surface morphology, and surface characterization of passive film formed on alloy samples was also performed by using X-ray photoelectron spectroscopy (XPS). The presence of bleaching agents induced the mass released compared to control group (4.9μg/cm(2)); this effect was recorded in both HP (171.2μg/cm(2)) and CP (59.7μg/cm(2)). XPS data showed that Cr and Ni levels in oxide layers formed on HP group were higher, Mo level was lower than those of CP group.

Corrosion resistance studies on grain-boundary etched drug-eluting stents

In this paper we compare the influence of different microstructures on the corrosion resistance of new drug-eluting stainless steel stents, which have been produced by grain-boundary-selective electrochemical etching processes. The morphology of the stent surfaces was analysed by scanning electron microscopy (SEM), and the surface composition was investigated with Auger electron spectroscopy (AES) as well as with energy dispersive X-ray analysis (EDX). The passivity of the different microstructured stents was studied by cyclovoltammetry in Ringer solution. Release of nickel and chromium was assessed after potentiostatic experiments in Ringer solution by analysing the collected electrolyte with AAS. For stents produced by different two-step etching procedures bringing about ideal morphologies regarding the mechanical and biological properties of the surface, no significant differences in the passivation behaviour could be observed. A two-step process using first nitric acid and oxalic acid in a second step produces stent surfaces with very good corrosion properties: electrochemical analysis shows that the range of stable passivity is the same as for conventional stent surfaces, and low rates of nickel and chromium release are observed. The etching procedures do not seem to change the surface oxide layer composition.

Effects of AP-CITROX Decontamination Procedure on the Surface Oxide Layer Composition of Stainless Steel Originating from the Primary Circuit of a VVER-Type Nuclear Reactor

A real specimen originating from the primary circuit of a VVER-440 type pressurized water cooled nuclear reactor has been studied by Conversion Electron Mossbauer Spectroscopy (CEMS) in order to find out how the AP-CITROX decontamination procedure modifies the structure and composition of the surface oxide layer of stainless steel which is used in the steam generator. Other methods like voltammetry, gravimetry, and SEM-EDAX were also applied to characterize the samples and to help the interpretation of CEMS results. It was found that, in contradiction with expectations, the presence of the surface magnetite layer could not be convincingly identified even on the non-decontaminated sample. This finding together with the relatively weak Mossbauer signals indicated that the surface oxide layer is strongly Fe-depleted. It was also concluded that the upper layer of the bulk steel (under the oxide layer) has an altered composition probably due to irradiation-enhanced diffusion of the metallic constituents. It was established that the AP-CITROX decontamination procedure does not exert detrimental effects on the thickness and composition of the surface oxide layer.

High-Efficiency GaAs MOS Solar Cells by Anodization in Active Region

Anodization of GaAs in various modes is investigated for possible application to MOS solar cells. It is found that anodization in active region using AGW electrolyte is very effective for increasing the open-circuit cell voltage, giving reproducibly 0.7–0.8 V. On the other hand, anodization in the passive region leads to an anomalous cell characteristic with much reduced photocurrents. The mechanism causing the difference is explained in terms of electrochemical control of the composition of surface oxide layer on the basis of detailed electrical and AES analyses.