Electrochemical and structural characterization of heat-treated Cr3C2-NiCr coatings

The influence of heat-treatments on the electrochemical behavior of thermal spray Cr3C2-NiCr coatings prepared by high velocity oxygen fuel (HVOF) was studied in NaCl solution, at 25 degrees C, using open-circuit potential (E-OC) and electrochemical impedance spectroscopy (EIS) measurements. Coating characterization were performed before and after the heat-treatments and electrochemical tests by scanning electron microscopy, X-ray diffraction, and Auger electron spectroscopy. In addition to the changes in the original powder composition occurring during HVOF process, heat-treatment performed at 450 degrees C caused no significant changes in electrochemical response compared with untreated sample, and at 760 degrees C the main difference was the formation of a thin and defective layer of Cr2O3 at the coating surface, which increased the total impedance at the first day of immersion. Higher influence on the electrochemical was noted for samples treated at 880 degrees C, which also showed higher E-OC and total impedance, and lower corrosion current. This behavior was interpreted considering the formation of a chromium oxide layer on the coating surface, dissolution and decomposition of smaller carbide particles and their surface enrichment with Cr due to C diffusion and dissolution into the matrix, and possible Ni, Cr, and Fe diffusion to coating/substrate interface. (c) 2006 the Electrochemical Society.

Influence of cerium (IV) ions on the mechanism of organosilane polymerization and on the improvement of its barrier properties

In this work, the effect of cerium (IV) ammonium nitrate (CAN) addition on the polymerization of bis-[triethoxysilyl]ethane (BTSE) film applied on carbon steel was studied. The electrochemical characterization of the films was carried out in 0.1 mol L(-1) NaCl solution by open-circuit potential measurements, anodic and cathodic polarization curves and electrochemical impedance spectroscopy (EIS). Morphological and chemical characterization were performed by atomic force microscopy (AFM), contact angle measurements, infrared-spectroscopy, nuclear magnetic resonance and thermogravimetric analysis. The results have clearly shown the improvement on the protective properties of the Ce(4+) modified film as a consequence of the formation of a more uniform and densely reticulated silane film. A mechanism is proposed to explain the accelerating role of Ce(4+) ions on the cross-linking of the silane layer. (C) 2008 Elsevier Ltd. All rights reserved.

Repeatability of corrosion parameters for titanium-molybdenum alloys in 0.9% NaCl solution

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Electrochemical study of TEOS, TEOS/MPTS, MPTS/MMA and TEOS/MPTS/MMA films on tin coated steel in 3.5% NaCl solution

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Highly corrosion resistant siloxane-polymethyl methacrylate hybrid coatings

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

A study of histological responses from Ti-6Al-7Nb alloy dental implants with and without plasma-sprayed hydroxyapatite coating in dogs

Titanium alloys are hoped to be used much more for applications as implant materials in the medical and dental fields because of their basic properties, such as biocompatibility, corrosion resistance and specific strength compared with other metallic implant materials. Thus, the Ti-6Al-7Nb alloy that has recently been developed for biomedical use, that is, primarily developed for orthopaedic use, is to be studied in this paper, for application in dental implants. The biocompatibility test in vivo was carried out in dogs and the osseointegration was verified through histological analysis of the samples of the Ti-6Al-7Nb alloy with and without hydroxyapatite coating that were inserted in the alveoli. Within the controlled conditions the samples did not show any toxic effects on the cells. (C) 2001 Kluwer Academic Publishers.

Inhibiting effect of citric acid on the pitting corrosion of tin

Potentiostatic and potentiodynamic studies were carried out to establish the inhibiting effects of citric acid on the pitting corrosion of tin. The critical potential (E-crit), which leads to pitting or general corrosion, was determined in sodium perchlorate solution in the pH range 1.0 to 4.0. Pit nucleation and growth, at pH 4.0, can be described by instantaneous nucleation followed by progressive nucleation. The results show that the minimum acid concentration needed to inhibit pitting of tin is 10(-2) M. Pitting occurrence by direct interaction between metal and perchlorate anions was observed.

XPS study of the corrosion protection of fluorozirconate glasses dip-coated with SnO2 transparent thin films

Tin oxide nanoparticles prepared by an aqueous sol-gel method were deposited by dip-coating on fluorozirconate glass, ZBLAN (53%ZrF4-20%BaF2-4%LaF3-3%AlF3-20%NaF) to improve its resistance against wet corrosion. The aqueous leaching of uncoated and SnO2-coated fluorozirconate glass was studied by X-ray photoemission spectroscopy (XPS) and it was shown that even an ultra thin tin dioxide film provides good protection of the glass surface against the bulk propagation of the hydrolytic attack.

Study on the initial stages of water corrosion of fluorozirconate glasses

The surface corrosion process associated with the hydrolysis of fluorozirconate glass, ZBLAN (53ZrF(4), 20BaF(2), 20NaF, 4LaF(2), 3AlF(3)) was investigated using X-ray photoelectron spectroscopy (XPS), grazing-incidence small angle X-ray scattering (GISAXS), X-ray reflectivity (XRR) and scanning electron microscopy (SEM). After a short exposure period (25 min) of the glass surface to deionized water the XPS data indicate an increase of the oxygen content accompanied by a decrease of fluorine concentration. The analysis of the chemical bonding structure identified the predominant surface reaction products as zirconium hydroxyfluoride and oxyfluoride species. The second most abundant glass component, bariumfluoride, remains almost unaffected by oxygen, while sodium fluoride is completely removed from the attacked surface region. The detected structural and compositional changes are related to the selective dissolution of the glass components leading to the formation of a new surface phase. This process is accompanied by a visible surface roughening caused by reprecipitated species, observed by SEM. The modification of the glass surface is responsible for an increase of the GISAXS intensity. The scattering was attributed to nanovoids formed at the surface region of the glass with an average size of 2.4 +/- 0.05 nm. (C) 2004 Elsevier B.V. All rights reserved.

Effect of commercial mouthwashes on the corrosion resistance of Ti-10Mo experimental alloy

The purpose of this work was to evaluate the effect of three commercial mouthwashes on the corrosion resistance of Ti-10Mo experimental alloy. Experiments were made at 37.0 +/- 0.5 degrees C in a conventional three-compartment double wall glass cell containing commercial mouthwashes. Three mouthwashes with different active ingredients were tested: ( I) 0.05% sodium fluoride + 0.03% triclosan; (II) 0.5 g/l cetylpyridinium chloride + 0.05% sodium fluoride; (III) 0.12% chlorohexidine digluconate. The assessment of the individual effect of active ingredients was studied by using 0.05% sodium fluoride. Commercially pure titanium (CP Ti) was used as control. Microstructures from Ti-10Mo experimental alloy and CP Ti were also evaluated using optical microscopy. Ti-10Mo as-cast alloy shows the typical rapidly cooled dendrites microstructure (beta phase) while CP Ti has exhibited a metastable martensitic microstructure. Electrochemical behavior of dental materials here studied was more affected by mouthwash type than by Ti alloy composition or microstructure. In both alloys passivation phenomenon was observed. This process may be mainly related to Ti oxides or other Ti species present in spontaneously formed film. Small differences in passive current densities values may be connected with changes in film porosity and thickness. Protective characteristics of this passive film are lower in 0.05% sodium fluoride + 0.03% triclosan mouthwash than in the other two mouthwashes tested.

Gross anatomy of the portal vein and its tributaries in the opossum (Didelphis albiventris)

The gross anatomy of the portal vein (V. portae) and its tributaries was studied through anatomical methods, i.e. dissection, corrosion and diaphanization, in 45 opossums (Didelphis albiventris). In all animals the portal vein was formed by the junction of the cranial mesenteric, caudal mesenteric and lienal veins (V. mesenterica cranialis, V. mesenterica caudalis and V. lienalis, respectively). Many collateral tributaries were observed running into the portal venous trunk.

A comparative study of the corrosion of high copper dental amalgams

Metallographic studies carried out for Tytin-Plus and Dispersalloy amalgams show a porous multiphase material, whose surface phases are: gamma-(Ag3Sn), gamma(1)-(Ag2Hg3), eta'-(Cu6Sn5) and epsilon-(Cu3Sn). Additionally, Dispersalloy is present in the Ag-Cu eutectic. The application of surface analysis by SEM reveal a heterogeneous distribution of the above mentioned phases. Microstructures consisting of colonies or clusters were not observed. The corrosion testing of these materials was done in 0.9% NaCl aerated solution at 25 degrees C using potentiodynamic polarization curves and ac impedance measurements. The corrosion process in these multiphase systems can be interpreted as the sum of more than one electrodissolution process and the posterior formation of corrosion films. on each electrode, the corrosion film is formed by different mechanisms. (C) 1998 Elsevier B.V. B.V. All rights reserved.

Development of Ti-Mo alloys for biomedical applications: Microstructure and electrochemical characterization

Ti-Mo alloys from 4 to 20 Mo wt.% were arc-melted. Their compositions and surfaces were analyzed by EDX, XRF and SEM. The Mo mapping shows a homogeneous distribution for all alloys. The XRD analysis showed that the crystal structure of the alloys is sensitive to the Mo concentration; a mixture of the hexagonal alpha' and orthorhombic alpha '' phases was observed for the Ti-4Mo alloy, and the alpha '' phase is observed almost exclusively when the concentration of Mo added to the Ti reaches 6%. A significant retention of the beta phase is observed for the alloy containing 10% Mo, while at higher Mo concentrations (15% and 20%), retention of phase beta is only verified. Preliminary electrochemical studies have indicated a valve-metal behavior and good corrosion resistance in aerated Ringer solution for all alloys. (c) 2006 Published by Elsevier B.V.

Preparation and properties of colloidal particles. Silica on yttrium iron garnet

Various properties of particles can be altered by coating them with a layer of different chemical composition. Yttrium iron garnet (YIG) particles has been coated with silica for control of their sintering, corrosion resistance, and stabilization of magnetic properties. This silica cover was obtained by hydrolysis of tetraethylorthosilicate (TEOS) in 2-propanol. This material was characterized by transmission (TEM) electron microscopy, (XEDS) X-ray energy-dispersive spectrometry, (XPS) X-ray photoemission spectroscopy and (VSM) vibrating sample magnetometry. YIG was heterocoagulated by silica as indicated by TEM micrographies. XPS measurements indicated that only binding energy for silicon and oxygen was found on the silica shell, which confirms that the YIG was covered. The values of the saturation magnetization differ from the heterocoagulated system to well-crystallized YIG.

Film formation and surface growth on tin electrodes in bicarbonate solutions: an impedance spectroscopy study

The electrochemical behaviour of potentiodynamically formed thin anodic films of polycrystalline tin in aqueous sodium bicarbonate solutions (pH approximate to 8.3) were studied using cyclic voltammetry and electrochemical impedance spectroscopy. Different equivalent circuits corresponding to various potential regions were employed to account for the electrochemical processes taking place under each condition. (C) 2004 Elsevier Ltd. All rights reserved.