Search

The aim of the present work was to study the corrosion resistance in Hanks' solution and the in vitro biocompatibility of a TiCN-coated AISI 316 L stainless steel. The electrochemical behavior was assessed using potentiodynamic polarization and electrochemical impedance spectroscopy. Cytotoxicity and genotoxicity tests were performed to evaluate the potential biocompatibility of the specimens. TiCN morphology was investigated using scanning electron microscopy (SEM). Bare 316 L specimens were also evaluated for comparison. The results showed that the film morphology strongly influences the electrochemical behavior of the coated underlying metal. TiCN-coated specimens presented neither cytotoxicity nor genotoxicity.

This study evaluates the possibility of replacing the hexavalent chromium passivation treatment used as a sealer after phosphating of carbon steel (SAE 1010) by a treatment with niobium ammonium oxalate (Ox). Samples of carbon steel (SAE 1010) after being phosphated in a zinc phosphate bath (PZn + Ni) were immersed in solution of niobium ammonium oxalate (250 mg L −1 of Nb) either at pH 3.0 or pH 8.0. A passivation treatment with a solution with CrO 3 (200 mg L −1 of Cr 6+ ) was also used for reference. The corrosion resistance of the phosphated samples after passivation treatments was analyzed in a NaCl 0.5 mol L −1 solution using electrochemical impedance spectroscopy (EIS) and anodic polarization curves. Salt spray tests were also performed to evaluate their corrosion resistance. The results showed that the highest corrosion resistance was obtained by passivation in a solution with (250 mg L −1 of Nb) at pH 8.0.

Whether it contains hexavalent chromium, chromium (VI), or simply Cr(VI), chromating has been largely used for surface preparation of aluminum aimed at corrosion protection due to its effectiveness and easy application. The most used among these processes are those that contain toxic and carcinogenic substances, which generate environmental backlash concerning the disposal of used baths with toxic elements. The high costs involved in the treatment of the disposal solutions prior to being discarded, besides the increasing restrictions concerning the environment, have encouraged research in the search for alternatives with lower toxicities than chromating processes but with high effectiveness for corrosion protection. Surface treatments with alkane diphosphonate molecules (ADM) have been investigated as potential substitutes for chromating. However, their effectiveness in the corrosion protection of aluminum alloys still needs further investigation. In the present study, the corrosion resistance of 1050 aluminum with various surface treatments was investigated by electrochemical techniques and salt spray testing. The corrosion performance of 1050 aluminum samples with a surface treatment that consisted of immersion in ADM was compared with that of the same alloy chromated by immersion in baths of Cr(III) or Cr(VI). The results showed that surface treatment with ADM was effective on samples that had been exposed to boiling water for oxide growth prior to treatment with ADM. The results also showed the superior corrosion performance for samples with the oxide-hydroxide + ADM surface treatment compared to those with both chromating treatments, either with Cr(III) or with Cr(VI). Cr(III) chromating treatment also provided better corrosion performance than chromating with Cr(VI), suggesting that both surface treatments (oxide-hydroxide + ADM and Cr(III)) are potential candidates for substitution for Cr(VI)-containing processes. However, for effective corrosion protection, the ADM treatment has to be carried out on surfaces previously exposed to treatments that favor oxide growth.

The intermetallic phases present in galvanneal coatings are of great importance to their final performance. In the present study the phases in a galvanneal coating on carbon steel for use in the automotive industry were electrochemically and morphologically characterized. The electrochemical techniques employed were potentiodynamic polarization, potentiostatic polarization and coulometric stripping. This last technique has been widely used for characterization of galvanneal coatings. Additionally, X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX) were carried out for chemical and morphological characterization of the phases in the coating. The results indicated that for the zinc richer phases the corrosion mechanism was similar, consisting of Zn selective dissolution and leading to enlargement of cracks and pores initially present in the coating. Two main morphologies were associated with the major phases in the galvannealing coating, namely an elongated rod-like phase and a flat and more compact type. Their chemical composition indicated that they were related to the zeta and delta phases, respectively. Three current density peaks were obtained in the anodic polarization curves and they were related to the zeta, delta and gamma-1 phases in the galvanneal coating. The cracks present in the coating previous to immersion in the stripping solution increasingly enlarged with exposure time to the stripping solution favoring the exposure of the various phases to the electrolyte and led to their concurrent corrosive attack. The corrosion product deposited on the galvanneal coating was mainly composed of a zinc rich product with a platelet-like morphology.

Phosphating and corrosion inhibitors are commonly used for corrosion prevention of metallic materials, mainly carbon steels. In this study, the effect of benzotriazole (BTAH) added to a Zinc phosphating (PZn) bath on the corrosion resistance of a carbon steel (1010) was investigated. Anodic polarization curves and electrochemical impedance spectroscopy (EIS) were used to evaluate the corrosion resistance of the phosphated steel with or without BTAH, in two solutions, 0.1 mol L− 1 H2SO4 and 0.5 mol L− 1 NaCl. The results showed better corrosion resistance for the steel phosphated with BTAH comparatively to that without BTAH.

This paper investigates the corrosion behavior of a NdFeB magnet with cerium-based conversion coatings obtained under different deposition conditions, on phosphated or non-phosphated magnet. The best performance was obtained with a cerium conversion coating, obtained in a two-step process, here named Ce 1 coating. In the first step the magnets were submitted to a phosphating treatment by immersing in a 10 g L − 1 NaH 2 PO 4 solution, acidified with H 3 PO 4 to pH 3.8. After phosphating, the specimens were immersed in a 3 g L − 1 Ce(NO) 3 ; 0.3 g L − 1 H 2 O 2 ; 0.02 g L − 1 H 3 BO 3 at pH 4.0 and 25–30 °C during 120 min, rinsed thoroughly with deionized water and dried. After conversion coating, the magnets were tested for corrosion. The corrosion tests were carried out in aerated sulphate solution, using electrochemical impedance spectroscopy (EIS), cyclic voltammetry and surface analysis methods (SEM and EDS). It was demonstrated that the corrosion resistance was strongly dependent on the previous treatment and the conversion coating conditions.

In this investigation the effect of surface treatments on the corrosion resistance of a commercial NdFeB sintered magnet has been investigated. A solution of 10 g L −1 NaH2PO4, acidified to pH 3.8 has been used for phosphating this magnet. The corrosion resistance of the phosphated magnet was investigated in a 0.10 mol L −1 Na2SO4 solution by electrochemical impedance spectroscopy and cyclic voltammetry with rotating disc electrode. The obtained results reveal that the resistance decreases with exposure time due to the development of pores and/or defects in the conversion coating exposing the substrate to corrosive attack. The effect of tungstate incorporation into the phosphate conversion coating resulting from a phosphating treatment prior to immersion in the tungstate solution was evaluated. The proposed treatment consists of re-immersing the phosphated samples in a 0.1 mol L −1 Na2WO4 solution during 72 h at the open circuit potential (OCP). Under these conditions, the corrosion resistance of the magnet was improved and this was attributed to the formation of a protective layer due to the adsorption of tungstate anions at the metallic substrate exposed in the coating, decreasing metal dissolution. © 2005 Published by Elsevier B.V.

This study reports the results of work carried out to improve the corrosion resistance of NdFeB magnets by a direct phosphate treatment of the NdFeB magnet surface. The growth of a phosphate film on a NdFeB based magnet in a solution of 0.15M NaH 2 PO 4 acidified to pH 3.8, was followed by electrochemical impedance spectroscopy (EIS) and open circuit potential variation as a function of time. After removal from the phosphating solution, the magnet surface was analysed by Auger electron spectroscopy (AES) and energy dispersive X-ray analysis (EDX). Phosphate formation on the surface was confirmed and a significant variation in the Fe/Nd ratio in the phosphate between the Fe and Nd rich phases of the magnet was found. The corrosion resistance of the phosphated magnets was evaluated in a normal enclosed atmospheric environment and in Na 2 SO 4 solution and synthetic saliva by EIS measurements. The corrosion resistance was found to be substantially improved by the presence of a phosphate layer.