The effect of molybdenum on corrosion of low-temperature nitrided stainless steels in sulphate–chloride solution

Resistance of stainless steels to pitting corrosion is strongly enhanced by nitriding at 380–450°C. In this work, anodic behaviour of steels with 0.13, 2.1, 4.5 and 6.1 wt% Mo was studied before and after nitriding at 450°C for 30 h which gave 13.0–15.8 wt% N at the surface. Electrochemical measurements were carried out in 0.1 M Na₂SO₄ + 0.4 M NaCl at pH 3.0. Nitriding of steels with lower Mo contents (0.13 and 2.1 wt% Mo) enhanced the resistance to pitting corrosion; steels with higher Mo contents retained their high resistance to pitting but underwent an activation. Nitrogen increased anodic reactivity in initial stages of polarisation, and it also increased the passivation rate. X-ray photoelectron spectroscopy analysis showed that anodic films on nitrided steels contained oxides at the outer surface and Cr–N species deeper from the surface. The enhanced resistance to pitting corrosion of low-temperature nitrided steels is explained by the increased anodic reactivity which leads to the formation of a salt-type film with Cr/Fe oxides and Cr–N species.In Honour of Professor Kurt Schwabe.     

Formation of hydrated titanium dioxide from seeded titanyl sulphate solution

The paper analyses the influence of various kinds and amounts of titanium dioxide nuclei addition to a solution of titanyl sulphate on the conversion degree of TiOSO₄ to hydrated titanium dioxide and sulphuric acid. An industrial solution of titanyl sulphate used to produce titanium white was used in the present investigations. It was found that the course of hydrolysis clearly depended on the investigated parameters. The anatase nuclei calcined at 373 K and 333 K and rutile nuclei increased the degree of titanyl sulphate hydrolysis as compared to non-nucleation hydrolysis. The final degree of hydrolysis was by 1–2 % higher than that achieved without any nuclei addition. The constant rates of both colloidal intermediate and final crystalline products formation were higher in the hydrolysis process with both anatase nuclei after heat treatment at lower temperature and rutile nuclei in comparison to the same processes conducted in the absence of these nuclei. Presented at the 35th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 26–30 May 2008.     

Corrosion behavior of magnesium and its alloy in NaCl solution

The electrochemical behavior of cast Mg, AZ91, and cast AZ91 in 0.1 M NaCl solution is investigated by measuring open-circuit potential (OCP), steady-state current-potential, and electrochemical impedance spectra (EIS). The similar electrochemical impedance behavior is found of three corrosion electrodes. There are two capacitances in high-and medium-frequency domains and one inductive loop or component in low-frequency domain. From equivalent circuit simulation, cast AZ91 has the worst corrosion resistance. The EIS results are in good agreement with those obtained by OCP and polarization curves. Based on the Cao theory, a simple corrosion mechanism is put forward, supplying a possible explanation for low-frequency inductive behavior for Mg and its alloy in NaCl solution at OCP. Published in Russian in Elektrokhimiya, 2007, Vol. 43, No. 7, pp. 878–885. The text was submitted by the authors in English.     

Corrosion behavior of PEO-treated AZ31 Mg alloy in chloride solution

Corrosion behavior and resistance of plasma electrolyte oxidation (PEO)-treated AZ31 Mg alloy were investigated by immersion and potentiodynamic polarization tests in 0.5 M NaCl solution in view of the PEO film thickness and sealing treatment of the PEO films in boiling water. The PEO films were formed using pulse current for various durations in 1 M NaOH?+?0.5 M NaF solution. Filiform corrosion was observed during the immersion test while pitting corrosion occurred during the potentiodynamic polarization test, irrespective of sealing treatment of the PEO films. Corrosion resistance of AZ31 Mg alloy was improved remarkably by the formation of thicker PEO films and their sealing treatments.     

Characterization of a laser‐nitrided titanium alloy by electron backscattered diffraction and electron probe microanalysis

After a laser gas nitriding treatment of the Ti‐7.5Al (atom %) titanium‐based alloy, we used a combination of electron backscattered diffraction (EBSD) in scanning electron microscope and electron probe microanalysis (EPMA) techniques in order to efficiently characterize the different phases in the resolidified layer. Representative measurements of chemical composition and reliable determination of crystal structure were possible for each phase of the complex microstructure. The reaction zone is formed by a mixture of isostructural TiN phases with dendritic and/or ‘coarse’ needles morphology, fixed into a α′‐Ti matrix (martensite) with a thin needle aspect. The nitrogen solubility was found to remain very low in the α′‐Ti matrix (up to 2–3 atom %), while in the TiN phase, an aluminum solubility as high as 4 atom % was measured, reducing drastically the nitrogen content into a Ti₇₉N₁₇Al₄ chemical composition. Copyright © 2005 John Wiley & Sons, Ltd.     

Hydrolysis of titanium sulphate compounds

The influence of TiOSO₄ and free sulphuric acid concentrations in the starting solution on the degree of titanyl sulphate conversion to hydrated titanium dioxide and post-hydrolytic sulphuric acid was studied. Titanyl sulphate solution, an intermediate product in the commercial preparation of titanium dioxide pigments by sulphate route, was used. It was found that the degree of hydrolysis markedly depends on the studied parameters. The lower was the content of TiOSO₄ in the starting solution, the higher conversion was achieved. The degree of hydrolysis at the final stage varied between 81 % (420 g TiOSO₄ dm⁻³, 216 g H₂SO₄ dm⁻³) and 92 % (300 g TiOSO₄ dm⁻³, 216 g H₂SO₄ dm⁻³). The same relation was obtained when changing the concentration of free H₂SO₄ in the starting solution. The degree of hydrolysis at the final stage varied between 49 % (261 g H₂SO₄ dm⁻³, 340 g TiOSO₄ dm⁻³) and 96 % (136 g H₂SO₄ dm⁻³, 340 g TiOSO₄ dm⁻³). The particle size of the obtained hydrated titanium dioxide (HTD) also depends on the initial solution composition. Presented at the 34th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 21–25 May 2007.     

Corrosion resistance in chloride solution of the AlSi10Mg alloy obtained by means of LPBF

The paper deals with the corrosion resistance in chloride solutions of an AlSi10Mg alloy obtained by laser powder bed fusion (LPBF) process. The potentiodynamic tests were carried out in solutions having different chloride contents. The results emphasize the role of chloride concentration on localized corrosion. The increase of concentration reduces pitting potential. In addition, the influence of the post-processing heat treatment temperature was recognized. Penetrating attacks occurred either on after low temperatures stress relieving or specimens without any treatment, promoted by selective dissolution of the α-Al phase stimulated by galvanic coupling with noble silicon precipitates at the border of the melt pool. Such penetrating morphology was not observed after heat treatments at high temperature.     

Interpretation of sputter depth profiles by mixing simulations

The interpretation of sputter depth profiles can be simplified by use of computer simulations. Distortions caused by mixing effects and distortions caused by the information depth of the analytical method have to be distinguished. Atomic mixing and the information depth distort the depth profile simultaneously. Therefore, it is necessary to take into consideration a superposition of both distortion effects. The sputtering of a GaAs/A1As multilayer has been calculated on a personal computer with the binary collision approximation code T-DYN by Biersack and with an own layer model. A new computer code LAMBDA has been used for the investigation of the influence of the AES information depth in addition to atomic mixing and preferential sputtering. A comparison of the calculated and the measured depth profile explains the observed effects. Therefore conclusions can be drawn about the original elemental distribution in the sample from the measured depth profile.     

Interpretation of sputter depth profiles by mixing simulations

The interpretation of sputter depth profiles can be simplified by use of computer simulations. Distortions caused by mixing effects and distortions caused by the information depth of the analytical method have to be distinguished. Atomic mixing and the information depth distort the depth profile simultaneously. Therefore, it is necessary to take into consideration a superposition of both distortion effects. The sputtering of a GaAs/A1As multilayer has been calculated on a personal computer with the binary collision approximation code T-DYN by Biersack and with an own layer model. A new computer code LAMBDA has been used for the investigation of the influence of the AES information depth in addition to atomic mixing and preferential sputtering. A comparison of the calculated and the measured depth profile explains the observed effects. Therefore conclusions can be drawn about the original elemental distribution in the sample from the measured depth profile.     

The rapid estimation of titanium in alloy steel

Titanium in alloy steels has been rapidly estimated with moderate accuracy by taking the steel into solution with perchloric acid and precipitating the element from an ammoniacal solution containing E.D.T.A., magnesium sulphate being used to accelerate precipitation. The Ti was then determined colorimetrically using the yellow colour developed by hydrogen peroxide in acid solutions.     

Corrosion behavior of a cobaltchromium-molybdenum alloy

Conclusions The combination of electrochemical techniques contributed to the knowledge of the corrosion mechanism of Co-Cr-Mo alloy under in vitro conditions. The X-ray diffraction technique permitted identification of some phases formed on the surface. The corrosion resistance of this alloy in 0.15 M NaCl was higher than the resistance of those presented by the cobalt and chromium under the same experimental conditions. Its corrosion mechanism involves the spontaneous formation of a film with dielectric properties, which protects the metal surface. Dedicated to the ninetieth anniversary of Ya.M. Kolotyrkin’s birth. This article was submitted by the authors in English.     

Comparison of depth profiles in SIMS by a fuzzy method

Automated quantitative comparison of depth-profiles recorded by SIMS based on a fuzzy difference measure has been used to characterize Sb and B implantation profiles in a marker experiment to study the diffusion of As in silicon. The variations of the concentration (intensity) measurements are described by a fuzzy set that is specified by smoothing the data with a polynomial digital filter. For each depth an individual spread as the size of variation is defined. Applications of the method enabled the influence of As-concentration and of annealing conditions on the implantation profiles of Sb and B to be quantified.     

Experimental shift allowance in the deconvolution of SIMS depth profiles

We study the deconvolution of the secondary ion mass spectrometry (SIMS) depth profiles of silicon and gallium arsenide structures with doped thin layers. Special attention is paid to allowance for the instrumental shift of experimental SIMS depth profiles. This effect is taken into account by using Hofmann's mixing‐roughness‐information depth model to determine the depth resolution function. The ill‐posed inverse problem is solved in the Fourier space using the Tikhonov regularization method. The proposed deconvolution algorithm has been tested on various simulated and real structures. It is shown that the algorithm can improve the SIMS depth profiling relevancy and depth resolution. The implemented shift allowance method avoids significant systematic errors of determination of the near‐surface delta‐doped layer position. Copyright © 2013 John Wiley & Sons, Ltd.     

Corrosion inhibition of ammonium molybdate for AA6061 alloy in NaCl solution and its synergistic effect with calcium gluconate

The corrosion inhibition of ammonium heltamolybdate (AH) and calcium gluconate (CG) for AA6061 alloy in 3% NaCl solution was investigated by the electrochemical measurements. It indicates that AH inhibits the corrosion of AA6061 alloy and acts as an anodic inhibitor. Maximum inhibition efficiency reaches 74.3% at the concentration of 1 × 10^?4 mol.l^?1 AH. The results of the electrochemical studies reveal AH is physically adsorbed on the AA6061 alloy surface and the adsorption follows Langmuir isotherm. The combination of AH and CG enhances the inhibition efficiency to 95.9%. The enhanced inhibition is attributed to the promotion of AH adsorption by CG. The mixture of AH and CG is a mixed‐type inhibitor and renders the corrosion potential to more positive values. Copyright © 2011 John Wiley & Sons, Ltd.     

Electropolishing of titanium alloy under hydrodynamic mode

Titanium (Ti) alloys are widely used in aerospace industry due to the low density and high corrosion resistance. However, machining and polishing remain great challenges because of the hardness and chemical stability. With a home-made electrochemical machining workstation, cyclic voltammetry is performed at a wide potential range of [0 V, 20 V] to record the details of passivation and depassivation processes under a hydrodynamic mode. The results show that the thickness of viscous layer formed on the alloy surface plays a crucial effect on the electropolishing quality. The technical parameters, including the mechanical motion rate, polishing time and electrode gap, are optimized to achieve a surface roughness less than 1.9 nm, which shows a prospective application in the electrochemical machining of Ti and it alloys.     

Quantification of antimony depth profiles in Sb-doped tin dioxide thin films

Sb-doped SnO₂ thin films, deposited by atomic layer epitaxy (ALE) for gas sensor applications, have been characterized by secondary ion mass spectrometry (SIMS). Quantification of the depth profile data has been carried out by preparing a series of ion implanted standards. Average concentrations determined by SIMS have been compared with Sb/Sn ratios obtained by X-ray fluorescence (XRF) spectrometry and proton induced X-ray emission (PIXE) spectrometry and have been found to be in good agreement. However, a detection limit of 5×10¹⁸ at cm^-3 could only be obtained because of mass interferences. SIMS data show that the ALE technique can be used to produce a controllable growth and doping of thin films.     

Corrosion of titanium diboride in molten FLiNaK(eut)

Pure and enriched titanium dibromide (TiB₂) samples (prepared by hot isostatic pressing) with different mole ratios of Ni and Ta were investigated in contact with molten eutectic salt (FLiNaK_(eut); LiF/NaF/KF 42.5 mole %: 11.5 mole %: 42.0 mole %) at 600°C. Corrosion resistance of the materials was studied, the mass losses and depths of corrosion were calculated, and sample surfaces were investigated by scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX). Nickel addition decreased the corrosion resistance of TiB₂. Simultaneous additions of both elements, Ni and Ta, as well as the addition of Ta only showed reducing effect on grain formation and they increased the corrosion resistance which is highest in the last case.     

Quantification of antimony depth profiles in Sb-doped tin dioxide thin films

Sb-doped SnO(2) thin films, deposited by atomic layer epitaxy (ALE) for gas sensor applications, have been characterized by secondary ion mass spectrometry (SIMS). Quantification of the depth profile data has been carried out by preparing a series of ion implanted standards. Average concentrations determined by SIMS have been compared with Sb/Sn ratios obtained by X-ray fluorescence (XRF) spectrometry and proton induced X-ray emission (PIXE) spectrometry and have been found to be in good agreement. However, a detection limit of 5x10(18) at cm(-3) could only be obtained because of mass interferences. SIMS data show that the ALE technique can be used to produce a controllable growth and doping of thin films.     

Toward accurate characterization of nitrogen depth profiles in ultrathin oxynitride films

Good accuracy in depth profile analyses of nitrogen in ultrathin oxynitride films is desirable for process development and routine process monitoring. Low energy SIMS is one of the techniques that has found success in the accurate characterization of thin oxynitride films. This work investigated the artifacts in a typical depth profile analysis of nitrogen with the current SIMS technique and the ways to improve the accuracy by selecting optimal analytical conditions. It was demonstrated that surface roughness developed rapidly in a SiO₂/Si stack when it was bombarded with an O₂⁺ beam at 250 eV and angle of incidence from 70 to 79° . The roughness caused distortion in the measured depth profiles of nitrogen and the major component elements. However, the above roughness and the distortion in the depth profiles can be eliminated by using a 250 eV O₂⁺ beam at an angle of incidence above 80° . Depth profile analyses with a 250 eV 83° O₂⁺ beam exhibited minimal surface roughening and insignificant variation in the secondary ion yield of SiN^? from SiO₂ bulk to the SiO₂/Si interface, facilitating an accurate analysis of nitrogen distribution in a SiO₂/Si stack. In addition, depth profiles of the major component elements such as ¹⁸O^? and ²⁸Si^? delivered clear information on the location of the SiO₂/Si interface. Using the new approach, we compared nitrogen distribution in thin SiNO films with the decoupled‐plasma nitridation (DPN) at various powers. Copyright © 2008 John Wiley & Sons, Ltd.