Chemical Composition Of Oxide Layer Research Articles

Positive Effect of Mischmetal Ce/La (Cerium and Lanthanum) on High Temperature Oxidation of Ni80Cr20 Alloys

The effect of Mischmetal Ce/La on the high temperature oxidation of the heat resistant Ni80Cr20 alloys is studied in order to increase the alloys life time at high temperature. The oxidation kinetic follows the parabolic behavior for both alloys Ni80Cr20‐0 without reactive element and Ni80Cr20‐Ce/La with reactive elements Ce/La. The presence of Ce/La elements strongly decreases the oxidation kinetic. Oxide layer is found to be very adhesive on the alloy containing the reactive elements by scratch test adhesive energy measurement. These results are discussed and correlated with the oxide microstructure, mechanical properties of oxide such stress, and chemical composition of oxide layer.

Impact of oxidation of copper and its alloys in laboratory-simulated conditions on their antimicrobial efficiency

Copper and its alloys are known for their antimicrobial activity, which makes them appealing materials for various touch surfaces in public facilities. These materials are also known for being prone to tarnishing, especially in contact with human palm sweat. The paper describes investigations on tarnishing of copper and various copper alloys by oxidation at elevated temperatures. After evaluation of thickness and chemical composition of oxide layers, microbiological tests were carried out in order to determine the impact of oxidation on antimicrobial efficiency of copper alloys.

The Influence of Selective Laser Melting (SLM) Process Parameters on In-Vitro Cell Response.

The use of laser 3D printers is very perspective in the fabrication of solid and porous implants made of various polymers, metals, and its alloys. The Selective Laser Melting (SLM) process, in which consolidated powders are fully melted on each layer, gives the possibility of fabrication personalized implants based on the Computer Aid Design (CAD) model. During SLM fabrication on a 3D printer, depending on the system applied, there is a possibility for setting the amount of energy density (J/mm3) transferred to the consolidated powders, thus controlling its porosity, contact angle and roughness. In this study, we have controlled energy density in a range 8–45 J/mm3 delivered to titanium powder by setting various levels of laser power (25–45 W), exposure time (20–80 µs) and distance between exposure points (20–60 µm). The growing energy density within studied range increased from 63 to 90% and decreased from 31 to 13 µm samples density and Ra parameter, respectively. The surface energy 55–466 mN/m was achieved with contact angles in range 72–128° and 53–105° for water and formamide, respectively. The human mesenchymal stem cells (hMSCs) adhesion after 4 h decreased with increasing energy density delivered during processing within each parameter group. The differences in cells proliferation were clearly seen after a 7-day incubation. We have observed that proliferation was decreasing with increasing density of energy delivered to the samples. This phenomenon was explained by chemical composition of oxide layers affecting surface energy and internal stresses. We have noticed that TiO2, which is the main oxide of raw titanium powder, disintegrated during selective laser melting process and oxygen was transferred into metallic titanium. The typical for 3D printed parts post-processing methods such as chemical polishing in hydrofluoric (HF) or hydrofluoric/nitric (HF/HNO3) acid solutions and thermal treatments were used to restore surface chemistry of raw powders and improve surface.

Influence of extracellular polymeric substances (EPS) from Pseudomonas NCIMB 2021 on the corrosion behaviour of 70Cu–30Ni alloy in seawater

Copper alloys, often used in cooling circuits of industrial plants using seawater as coolant, can be affected by biocorrosion induced by biofilm formation. Extracellular polymeric substances (EPS) produced by bacteria play a fundamental role in the different stages of biofilm formation, maturation and maintenance. The influence of loosely bound (LB) and tightly bound (TB) EPS, extracted from marine Pseudomonas NCIMB 2021, on the electrochemical behaviour of 70Cu–30Ni (wt.%) alloy in static artificial seawater (ASW) and on the chemical composition of oxide layers was studied by combined electrochemical measurements (polarization curves, EIS) and surface analysis (XPS, ToF-SIMS). Results were compared with those obtained in the presence of bovine serum albumin (BSA), a model protein. Compared to 70Cu–30Ni alloy in static ASW without biomolecules, for which a thick duplex oxide layer (outer redeposited Cu2O layer and inner oxidized nickel layer) is shown, the presence of BSA, TB EPS and LB EPS leads to a mixed oxide layer (oxidized copper and nickel) with a lower thickness. In the biomolecules-containing solutions, this oxide layer is covered by an adsorbed organic layer, mainly composed of proteins. A model is proposed to analyse impedance data obtained at the corrosion potential. The fitting procedure of impedance diagrams allows extracting the anodic charge transfer resistance, from which the corrosion current density can be calculated. The results show a slow-down of the anodic reaction in the presence of biomolecules (BSA, TB EPS and LB EPS), and a corrosion inhibition effect by LB EPS and to a lesser extent by BSA. No detrimental effect is evidenced with TB EPS.

Effect of protein adsorption on the corrosion behavior of 70Cu–30Ni alloy in artificial seawater

Copper alloys often used in cooling circuits of industrial plants can be affected by biocorrosion induced by biofilm formation. The objective of this work was to study the influence of protein adsorption, which is the first step in biofilm formation, on the electrochemical behavior of 70Cu–30Ni (wt.%) alloy in static artificial seawater and on the chemical composition of oxide layers. For that purpose, electrochemical measurements performed after 1h of immersion were combined to surface analyses. A model is proposed to analyze impedance data. In the presence of bovine serum albumin (BSA, model protein), the anodic charge transfer resistance deduced from EIS data at Ecorr is slightly higher, corresponding to lower corrosion current. Without BSA, two oxidized layers are shown by XPS and ToF-SIMS: an outer layer mainly composed of copper oxide (Cu2O redeposited layer) and an inner layer mainly composed of oxidized nickel, with a global thickness of ~30nm. The presence of BSA leads to a mixed oxide layer (CuO, Cu2O, Ni(OH)2) with a lower thickness (~10nm). Thus, the protein induces a decrease of the dissolution rate at Ecorr and hence a decrease of the amount of redeposited Cu2O and of the oxide layer thickness.

Role of chemical composition of oxide layer on stainless steel for ZrO2 coating by hydrothermal process

Thin films of ZrO2 have been developed by hydrothermal process on pre-oxidized stainless steel (SS) surfaces composed of different oxides like spinels or α-Fe2O3. Variations in thicknesses and uniformity of ZrO2 films have been observed on different pre-oxidized SS surfaces. Raman scattering spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy and X-ray diffraction techniques have been used to explain mechanisms of formation of ZrO2 films on various pre-oxidized SS surfaces. A pre-oxidized layer of α-Fe2O3 seems to be an ideal oxide on the SS surface for uniform coating of ZrO2. This may be attributed to close match of lattice parameters of ZrO2 with that of α-Fe2O3.

Influence of BSA adsorption on the oxide layers developed on 70Cu-30Ni alloy in static artificial seawater

Copper alloys usually used in cooling circuits of industrial plants can be affected by biocorrosion induced by biofilm formation. The global objective is to study the influence of biomolecules adsorption, which is the first step in biofilm formation, on the electrochemical behaviour of 70Cu-30Ni (wt. %) alloy and the chemical composition of oxide layers. In this work, the chosen biomolecule was the bovine serum albumin (BSA, model protein) and electrochemical measurements performed after 1 h of immersion in static artificial seawater were combined to surface analyses. In the presence of BSA, the charge transfer resistance deduced from EIS data at E corr is higher, corresponding to lower corrosion current. Without BSA, two oxidized layers are shown by XPS and ToF-SIMS: an outer layer mainly composed of copper oxide (Cu2 O redeposited layer) and an inner layer mainly composed of oxidized nickel, with a global thickness of ~30 nm. The presence of BSA leads to a mixed oxide layer (CuO, Cu2 O, Ni(OH)2 ) with a lower thickness (~10 nm). Thus, the protein induces a decrease of the dissolution rate at E corr and hence a decrease of the amount of redeposited Cu2 O and of the oxide layer thickness.

Comprehensive investigation of the corrosion state of the heat exchanger tubes of steam generators. Part I. General corrosion state and morphology

The present work, constituting the first part of a series of two, deals with a systematic investigation of the general corrosion state of 22 heat exchanger tubes originating from different steam generators of the Paks NPP (Hungary). While the passivity of the inner surface of the stainless steel tube specimens was studied by voltammetry, the morphology and chemical composition of the oxide layer formed on the surfaces were analyzed by SEM–EDX method. Based on the measured corrosion characteristics (corrosion rate, thickness and chemical composition of the protective oxide layer) a strong dependence of these parameters on the decontamination history of the steam generators was revealed. It is well documented that the chemical decontamination carried out by a non-regenerative version of the AP-CITROX procedure does exert, on the long run, a detrimental effect on the corrosion resistance of steel surfaces. Therefore, process restrictions and modifications to minimize corrosion damages have be defined.