Cerium Implantation Research Articles

Structural modifications of GaN after cerium implantation

Among the family of rare earth (RE) dopants, the doping of first member Ce into GaN is the least studied system. This article reports structure properties of Ce-doped GaN realized by technique of ion implantation. Ce ions were implanted into metal organic chemical vapor deposition grown n- and p-GaN/sapphire thin films at doses 3 × 1014 and 2 × 1015 cm−2. X-ray diffraction scans and Raman scattering measurements exhibited expansion of lattice in the implanted portion of the samples. First order Raman scattering spectra show appearance of several disorder-activated Raman scattering modes in addition to typical GaN features. A dose-dependent decrease in intensity of E2 mode was observed in Raman the spectra of the implanted samples. Ultraviolet Raman spectra of implanted samples show complete quenching of photoluminescence emission and appearance of multiple A1(LO) phonon scattering modes up to fifth order. Moreover, a decrease in intensity and an increase in line width of LO modes as a function of wavenumber were observed for implanted samples. Copyright © 2012 John Wiley & Sons, Ltd.

ChemInform Abstract: The Improvement of the Localized Corrosion Resistance of Stainless Steel by Cerium.

Abstract Rotating disc assemblies are employed to study the cathodic electrode process and its inhibition by cerium implantation into UNS S31603 stainless steel in a solution of 0.6 M NaCl + 0.1 M Na 2 SO 4 . The reduction of oxygen and protons on both gold and untreated steel are shown to be controlled by the mass transport processes in solution. Cerium implantation effectively inhibits the cathodic reduction, reducing the cathodic current by more than two orders of magnitude. The cathodic reduction of oxygen and protons on ion-implanted stainless steel is thus controlled primarily by charge transfer at the electrode. Thermodynamic data suggests that the highly stable cerium oxide may be responsible for blocking the active sites for both cathodic and anodic reactions.

The effects of cerium implantation on the oxidation behavior of AZ31 magnesium alloys

Implantation of cerium ions into the surface of AZ31 magnesium alloys was performed with fluences of 5 × 10 16, 1 × 10 17 and 5 × 10 17 ions/cm 2, respectively. Auger electron spectrometry (AES), X-ray photoelectron spectroscopy (XPS) and glancing angle X-ray diffraction (GAXRD) were used to characterize the implanted surface. The results showed that after treatment a pre-oxidation layer with a duplex structure was formed. The outer layer was mainly composed of MgO, while the inner layer consisted of MgO, Ce 2O 3 and CeO 2. The influence of cerium implantation on the oxidation behavior of AZ31 magnesium alloys was investigated at 773 K in pure O 2 for 90 min. The results indicated that the oxidation resistance of the implanted sample was improved with optimal fluence. The corresponding mechanism of the oxidation behavior was also discussed.

Cyclic oxidation behaviour of cerium implanted AZ31 magnesium alloys

AZ31 samples were implanted with 90 keV cerium ions with a dose of 1 × 10 17 ions/cm 2. Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS) and Glancing angle X-ray diffraction (GAXRD) were used in order to investigate the characterization of elements in the implanted surface. The results indicate that after cerium implantation a pre-oxidation layer with double structure was formed. The influence of cerium implantation on the cyclic oxidation behaviour of AZ31 samples was studied at 773 K in air for 96 h, and the morphologies of the oxide scales were examined by scanning electron microscopy (SEM). It was found that the oxidation resistance of the implanted sample has been improved. The mechanisms to explain the experimental results were also proposed.

Influence of chromium and cerium implantation in the electrochemical development of passive layers on AISI 304L

In this work X-ray photoelectron spectroscopy studies and electrochemical techniques are combined to elucidate the effect of Ce and Cr implantation in the formation and evolution of passive layers generated by potentiodyinamic cycling on AISI 304L steel in alkaline medium. Cerium implantation promotes the formation of a thinner and more protective film on the steel. This fact, noticed in X-ray photoelectron spectroscopy (XPS) analysis, is reflected in the voltammograms by an important decrease of the magnetite formation and Cr3+/Cr6+ oxidation peak and, in the electrochemical impedance spectroscopy (EIS) diagrams, as the disappearance of one time constant. Chromium implantation contributes also to the generation of a thinner film, but more defective than in the case of cerium implantation. These differences are demonstrated in both electrochemical and surface analytical techniques. In the voltammetric curves, the diminution of the iron oxides signal is less notorious and an important increasing in the Cr3+/Cr6+ oxidation peak is registered. The EIS results show the persistence of the same number of time constants detected in the unimplanted steel.

The oxidation behavior of Ce-implanted ZrN coating

The aim of the study was to investigate the influence of cerium ion implantation on the oxidation behavior of ZrN coating. Samples was deposited by cathodic arc deposition and subsequently implanted with different doses of cerium using a MEVVA ion implanter. The ions were extracted with a voltage of 40kV, and the dose ranged from 5×1016 to 2×1017ions/cm2. The air oxidation behaviors at 500°C of as-deposited and Ce-implanted ZrN coatings were characterized by weight gain measurement. The oxidation resistance of ZrN coating reduced after implantation with cerium at low dose but rebounded at higher dose. The oxidation rate of ZrN coatings were 2.18×10−7, 5.21×10−8, 4.18×10−7 and 1.56×10−7mg2cm−4s−1 with dose of 0, 5×1016, 1×1017 and 2×1017ions/cm2. X-ray photoelectron spectroscopy and glancing angle X-ray diffraction were employed to analyze the valence states of the oxide scale and the phase composition of the oxidation layers, respectively. Cerium implantation could improve the oxidation resistance of ZrN coating with higher dose. Finally, the mechanism of the oxidation behavior is discussed.

Influence of chromium and cerium implantation in the electrochemical development of passive layers on AISI 304L

In this work X-ray photoelectron spectroscopy studies and electrochemical techniques are combined to elucidate the effect of Ce and Cr implantation in the formation and evolution of passive layers generated by potentiodyinamic cycling on AISI 304L steel in alkaline medium. Cerium implantation promotes the formation of a thinner and more protective film on the steel. This fact, noticed in X-ray photoelectron spectroscopy (XPS) analysis, is reflected in the voltammograms by an important decrease of the magnetite formation and Cr 3+/Cr 6+ oxidation peak and, in the electrochemical impedance spectroscopy (EIS) diagrams, as the disappearance of one time constant. Chromium implantation contributes also to the generation of a thinner film, but more defective than in the case of cerium implantation. These differences are demonstrated in both electrochemical and surface analytical techniques. In the voltammetric curves, the diminution of the iron oxides signal is less notorious and an important increasing in the Cr 3+/Cr 6+ oxidation peak is registered. The EIS results show the persistence of the same number of time constants detected in the unimplanted steel.

Comportamiento electroquímico de un acero inoxidable AISI 430 implantado con cerio

Chemical treatment in solutions containing cerium compounds has been widely used for prevention of localized corrosion in aluminium alloys (pitting corrosion) as well as in stainless steels (crevice corrosion). Ionic implantation presents several advantages for stainless steels. The present paper is devoted to study the effect of cerium implantation on the properties of passive films formed on an AISI 430 stainless steel in alkaline medium. The electrochemical study is performed by cyclic voltammetry and EIS. The chemical characterisation of the oxides film developed is performed by XPS, and the morphological study corresponds to SEM examination. The results show that cerium implantation hinders magnetite formation as well as chromium oxidation processes.

Modifications of the stainless steels passive film induced by cerium implantation

In this work X-ray photoelectron spectroscopy studies and cyclic voltammetry are combined to elucidate the effect of Ce implantation on the formation and evolution of passive layers generated on AISI 430 and AISI 304L steels in alkaline medium. The passive films develop in implanted steels result thinner and less defective than in unimplanted. This result is interpreted in terms of a cerium-induced inhibition of the passive film re-oxidation (formation of iron and chromium oxides). The main difference between the behaviour of the two types of steel (ferritic and austenitic) seems to be related to the enrichment in nickel promoted by cerium in the outermost layer of AISI 304L.

Characterisation of the electrochemical behaviour of cerium implanted stainless steels

Passive layers formed on a Ce implanted stainless steel in alkaline media are studied to clarify its beneficial effect on stainless steel corrosion resistance. An important decrease in iron and chromium activity peaks is detected by electrochemical techniques. X-ray photoelectron spectroscopy (XPS) analysis shows passive film thickness decreasing together with changes in chemical composition. Cerium implantation modifies the conductivity properties of the passive film, as it is inferred from EIS measurements.

The tribological behaviour of GCr15 bearing steel implanted with cerium

The tribological behaviour of unimplanted and cerium ion implanted GCr15 bearing steel with three kinds of dosages was investigated with an SRV wear tester and dynamic-static friction precision measurement apparatus under dry friction conditions. The tribological behaviour of the samples was also evaluated under liquid paraffin lubrication. The test results showed that the wear resistance of the implanted specimens increased considerably with increasing implantation dose of cerium. Implanted ion cerium increased the wear resistance by 0.1–4.2 times under dry friction. The coefficient of friction decreased with increasing dose of cerium implantation. X-ray photoelectron spectroscopy analytical results showed that cerium is present in Ce 4+ state on the rubbing surface of implanted specimen, and there is no cerium transfer from implanted specimen to friction counterpart. Therefore, it is supposed that the increasing wear resistance was due to the increasing cohesive strength of the oxide film.

The improvement of the localized corrosion resistance of stainless steel by cerium

Rotating disc assemblies are employed to study the cathodic electrode process and its inhibition by cerium implantation into UNS S31603 stainless steel in a solution of 0.6 M NaCl + 0.1 M Na 2SO 4. The reduction of oxygen and protons on both gold and untreated steel are shown to be controlled by the mass transport processes in solution. Cerium implantation effectively inhibits the cathodic reduction, reducing the cathodic current by more than two orders of magnitude. The cathodic reduction of oxygen and protons on ion-implanted stainless steel is thus controlled primarily by charge transfer at the electrode. Thermodynamic data suggests that the highly stable cerium oxide may be responsible for blocking the active sites for both cathodic and anodic reactions.

Influence of cerium implantation on the nucleation and growth of corrosion products on alloy 800H in a mixed sulphidizing/oxidizing environment

The influence of implantation of cerium on the corrosion behavior of an 32Ni-20Cr austenitic steel, Alloy 800H, in a simulated coal-gasification atmosphere has been examined at 700°C. The composition and microstructure of the corrosion products formed after exposure periods between 1 min and 200 h were examined with a range of surface-analytical techniques. The corrosion mechanism of Alloy 800H was characterized as a mixture of oxidation and sulphidation, primarily of Cr and Fe. The oxides provided protection against catastrophic sulphidation. Cerium implantation reduced the corrosive attack, providing the dose was sufficient. The corrosion was more uniform and the products had a higher Cr/Fe ratio compared to those on the unimplanted alloy. It is proposed that these changes resulted from the formation of a more protective and more stable oxide layer, due to the rapid formation of ceria particles, specifically hindering the formation of the less-stable oxides and sulphides.

Effect of cerium implantation on the corrosion of alloy 800H in an S-O-C environment

The corrosion behaviour of a wrought austenitic Fe20Cr32Ni steel, Alloy 800H, was studied in a simulated coal gasification atmosphere at 700°C. Exposures ranged from as short as a few minutes to periods of up to 1000 h. The influence of cerium on the corrosion resistance was established by carrying out identical tests after ion implantation of the specimen surfaces. It was shown that the corrosive attack in the H 2S-containing gas mixture can be reduced for the cerium-implanted material if the implantation dose is sufficiently high. In the case of both implanted and unimplanted material, sulphides and oxides were formed but the corrosion products of the implanted material showed a higher Cr:Fe ratio relative to those of the unimplanted material. It is proposed that this feature is responsible for the observed improvement.

The influence of surface ion implantation upon the oxidation behaviour of a 20% Cr-25% Ni, niobium stabilized austenitic stainless steel, in carbon dioxide, at 825°C

A study has been made of the influence of the surface ion implantation of platinum, silicon, aluminium with and without yttrium and cerium upon the oxidation behaviour of a 20% Cr-25% Ni-Nb stabilized stainless steel. The oxidation tests were in carbon dioxide (1 atm pressure), at 825°C, for periods up to 5900 h. Platinum, silicon and aluminium implantation had no significant influence upon either the extent of kinetics of oxidation or of spallation. An additional implantation of yttrium into a surface layer containing implanted aluminium improved the oxidation resistance slightly but had no effect on oxide adherence. Cerium implantation exerted the greatest influence on the oxidation behaviour of the steel. It reduced by at least a factor of two the attack of the steel throughout the exposure period and also improved oxide adherence. It was combined, probably with chromium, as a mixed oxide. The improvement in oxidation resistance with the incorporation of cerium in the protective barrier film derived from a more effective restriction to cation movement than with the film formed on the steel alone. The mechanical properties of the outer layer were also improved by the incorporation of cerium to account for the improved oxide adherence.