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Corrosion Rate (corrosion + rate)
Selected AbstractsCorrosion rates of stainless-steel files in different irrigating solutionsINTERNATIONAL ENDODONTIC JOURNAL, Issue 8 2002M. Dartar Öztan No abstract is available for this article. [source] Mechanical and corrosion behaviour of a Ti-Al-Nb alloy after deformation at elevated temperaturesMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 12 2008M. V. Popa Abstract The mechanical properties of Ti6Al7Nb alloy deformed and heat treated at elevated temperatures were correlated with its microstructure and corrosion behaviour in Ringer (of different pH values: 2.49, 6.9 and 8.9) and Ringer,Brown solutions. Microstructural analysis revealed a Widmanstatten structure for the alloys deformed at 1100,°C (, field) and structure with , grains at 930,°C (,,+,, field). The thermo-mechanical processing improved the electrochemical behaviour of Ti6Al7Nb alloys, especially their passive state. Open circuit potential variations in time reflected more compact, stable, resistant passive films on the surface of the treated alloys. Open circuit potential gradients simulating the non-uniformities of pH along the implant surface have very low values that cannot generate galvanic corrosion. Corrosion rates and ion release are very much reduced. Impedance spectra were fitted with a two time-constants equivalent circuit for some alloys and with three time-constants equivalent circuit for other alloys. [source] Uniform corrosion of titanium in alkaline hydrogen peroxide conditions: influence of transition metals and inhibitors calcium and silicateMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 12 2002J. Rämö Uniform corrosion of titanium was studied in alkaline hydrogen peroxide environments simulating pulp bleaching conditions. Corrosion rates of unalloyed Grade 2 and alloyed Grade 5 were determined as a function of hydrogen peroxide anion (HOO,) concentration. Influences of calcium and silicate inhibitors and iron and manganese were investigated. Without inhibition titanium corroded at HOO, content of 200 mg/l: Grade 2 0.4 mm/y and Grade 5 1.4 mm/y. Addition of calcium (Ca2+) and silicate (SiO32,) diminished the corrosion of Grade 2 to critical anion level 400 mg/l, but could not protect Grade 5 even at the HOO, concentration of 300 mg/l. Presence of iron and manganese raised the critical levels of the both grades. High HOO, anion level was observed as a notable potential difference between titanium and platinum. Gleichmäßige Flächenkorrosion von Titan unter alkalischen Wasserstoffperoxidbedingungen: Einfluss der Übergangsmetalle und der Inhibitoren Kalzium und Silikat Gleichmäßige Flächenkorrosion von Titan wurde in alkalischen Wasserstoffperoxidbedingungen, die Papierbleichbedingungen simulieren, untersucht. Die Korrosionsgeschwindigkeiten von unlegierter Güteklasse 2 und legierter Güteklasse 5 wurden als Funktion der Wasserstoffperoxidanionen(HOO,)konzentration bestimmt. Einflüsse von Kalzium- und Silikatinhibitoren sowie von Eisen und Mangan wurden untersucht. Ohne Inhibierung betrug die Korrosion von Titan bei einem HOO, -Gehalt von 200 mg/l bei der Güteklasse 2 0,4 mm/Jahr und bei der Güteklasse 5 1,4 mm Jahr. Die Zugabe von Kalzium (Ca2+) und Silikat (SiO32,) verminderte die Korrosion der Güteklasse 2 auf ein kritisches Anionenniveau von 400 mg/l; konnte aber Güteklasse 5 selbst bei einer HOO, -Konzentration von 300 mg/l nicht schützen. Die Anwesenheit von Eisen und Mangan erhöhte die kritischen Niveaus für beide Güteklassen. Hohe HOO, -Anionengehalte wurden als beträchtliche Potentialdifferenz zwischen Titan und Platin beobachtet. [source] Surface Modification by Compositionally Modulated Multilayered Zn-Fe Alloy CoatingsCHINESE JOURNAL OF CHEMISTRY, Issue 12 2008V. THANGARAJ Abstract Compositionally modulated multilayered alloy (CMMA) coatings of Zn-Fe were developed from acid chloride baths by single bath technique. The production and properties of CMMA Zn-Fe coatings were tailored as a function of switching cathode current densities (SCCD's) and thickness of individual layers. Corrosion rates (CR) were measured by electrochemical methods. Corrosion resistances were found to vary with SCCD's and the number of sub layers in the deposit. SCCD's were optimized for production of Zn-Fe CMMA electroplates showing peak performance against corrosion. The formation of discrete Zn-Fe alloy layers having different compositions in the deposits were demonstrated by scanning electron microscopy (SEM). Improvements in the corrosion resistance of multilayered alloys are due to the inherent barrier properties of CMMA coatings as evidenced by electrochemical impedance spectroscopy (EIS). Corrosion resistance afforded by Zn-Fe CMMA coatings are explained in terms of the n-type semiconductor films at the interface, supported by Mott-Schottky's plot. It was observed that the alloy with high w(Fe) on the top showed better corrosion resistance compared to that with the less w(Fe) on top. At optimum SCCD's of 3.0,5.5 A·dm,2, a Zn-Fe CMMA coatings with 600 sub layers showed ca. 45 times better corrosion resistance than conventional Zn-Fe alloy of the same thickness. The deposit showed no red rust even up to 1130 h in salt spray test. [source] Corrosion behaviour of high copper dental amalgamsJOURNAL OF ORAL REHABILITATION, Issue 6 2004A. U. J. Yap summary, This study evaluated the corrosion behaviour of two high copper dental amalgam alloys [Dispersalloy (Dentsply-Caulk) and Tytin (Kerr)] in different electrolytes. Amalgam specimens were prepared, coupled to a copper wire, cemented into glass tubes and polished to a 600-grit finish. A corrosion cell was prepared using a carbon counter-electrode, a standard calomel electrode as the reference and amalgam as the working electrode. The alloys were tested in the following mediums at 37 °C: (i) artificial saliva based on Fusayama's solution (FS), (ii) artificial saliva with citric acid adjusted to pH 4·0 (FC) and (iii) 1% sodium chloride solution (SC). Corrosion potentials (Ecorr) and corrosion rates (Icorr) were determined using potentiostatic and impedance spectroscopy methods. Data was subjected to anova/Scheffe's post hoc test at 0·05 significance level. For both alloys, the corrosion potential in FS was significantly greater than in SC. Corrosion potential of Tytin in FS and SC was also significantly greater than in FC. The corrosion rate of Dispersalloy in FC was significantly greater than in FS and SC. For Tytin, corrosion rate in SC was significantly greater than in FS and FC. Although no significant difference in corrosion potential/rate was observed between the alloys when tested in FS, significant differences were observed when electrochemical testing was carried out in FC and SC. The corrosion behaviour of high copper amalgam alloys are both material and environment dependent. Certain food substances may increase the corrosion of high copper amalgams. [source] Boundary element simulation of DC stray currents in oil industry due to cathodic protection interferenceEUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 5 2007I. A. Metwally Abstract This paper presents a 3D theoretical simulation and analysis of DC stray current corrosion (SCC) in oil fields that could contribute to oil leak and finally oil deferment of electric submersible pump (ESP) systems. Application of the boundary element analysis system (BEASY) allowed cathodic protection (CP) interference to be assessed in terms of the normal current density, which is directly proportional to the corrosion rate, rather than using the qualitative approach of measuring the potential shift of the soil. Different real structures consisting of pipelines and/or well casings with different arrangements and interference conditions are simulated. The results reveal that the application of impressed current cathodic protection (ICCP) systems creates DC SCC on other nearby unprotected structures. This is an inherent potential problem with the application of such systems which dominates with decreasing soil conductivity, and/or increasing the anode current density and its proximity to the protected structures. On the contrary, SCC can be reduced by using multi-groundbed anodes. Copyright © 2006 John Wiley & Sons, Ltd. [source] Synergistic effect of halide ions and polyethylene glycol on the corrosion inhibition of aluminium in alkaline mediumJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2009S.A. Umoren Abstract The corrosion inhibition of aluminium in alkaline medium was studied at 30 and 40°C in the presence of polyethylene glycol (PEG) using gravimetric (weight loss) and thermometric techniques. The effect of halides (KCl, KBr, and KI) on the inhibitory action of PEG was also studied. It was found that PEG acted as inhibitor for aluminium corrosion in the alkaline medium. Inhibition efficiency increased with increasing inhibitor concentration. An increase in temperature led to increase in both the corrosion rate and inhibition efficiency in the absence and presence of inhibitor and halides. Phenomenon of chemical adsorption mechanism is proposed from the values of Ea, Qads, and ,G obtained. The adsorption of PEG on the surface of aluminium was found to obey Flory,Huggins and Temkin adsorption isotherms. The synergism parameter, S1 evaluated was found to be greater than unity indicating that the enhanced inhibition efficiency caused by the addition of halides is synergistic in nature. The inhibition efficiency, surface coverage and synergism parameter increased in the order; I,> Br,> Cl, showing that a joint adsorption of PEG and halide ions on aluminium plays a significant role in the adsorption process. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Polyethylene glycol and polyvinyl alcohol as corrosion inhibitors for aluminium in acidic mediumJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2007S. A. Umoren Abstract The corrosion inhibition of aluminum in H2SO4 in the presence of polyethylene glycol (PEG) and polyvinyl alcohol (PVA) as inhibitors at 30,60 °C was studied using gravimetric, gasometric, and thermometric techniques. The inhibition efficiency (%I) increased with increase in concentration of the inhibitors. Increase in temperature increased the corrosion rate in the absence and presence of inhibitors but decreased the inhibition efficiency. Both PEG and PVA were found to obey Temkin adsorption isotherm at all concentrations and temperatures studied. Phenomenon of physical adsorption is proposed from the activation parameters obtained. Thermodynamic parameters reveal that the adsorption process is spontaneous. PEG was found to be a better inhibitor than PVA. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 [source] Controlling the biodegradation rate of magnesium using biomimetic apatite coatingJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 2 2009Yajing Zhang Abstract Magnesium is light, biocompatible and has similar mechanical properties to natural bone, so it has the potential to be used as a biodegradable material for orthopedic applications. However, pure magnesium severely corrodes in a physiological environment, which may result in fracture prior to substantial tissue healing. Hydroxyapatite (HA) is the main composition of natural bone. It has excellent bioactivity and osteoconductivity. In this study, HA coating with two different thicknesses was applied onto the surface of pure magnesium substrates using a biomimetic technique. The corrosion rate of the surface-treated substrates was tested. It was found that both types of coatings substantially slowed down the corrosion of the substrate, and the dual coating was more effective than the single coating in hindering the degradation of the substrate. Thus, the corrosion rate of magnesium implants can be closely tailored by adjusting apatite coating thickness and thereby monitoring the release of magnesium ions into the body. © 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2009 [source] Ion release in patients with metal-on-metal hip bearings in total joint replacement: A comparison with metal-on-polyethylene bearingsJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 5 2002L. Savarino Abstract Polyethylene (PE) wear has been shown to be a problem in long-term joint replacement using metal-on-PE bearing. The use of metallic heads articulating with metallic cups could solve this problem: success will be enhanced if wear and corrosion of the articulating surfaces are maintained at a low level. New models with metal-on-metal bearing have been proposed, to be used mainly for young subjects: such coupling seems to have a reduced release, but it is unclear yet if the medium-term corrosion rate is really negligible or, on the contrary, it is significantly higher than in the metal-on-PE bearing. Aim of our study was the comparison of ion release in the serum of two groups of patients who had the same type of stable cementless prosthesis, but different bearing: twenty-six patients with metal-on-metal (Group A) and fifteen patients with metal-on-PE bearing (Group B) were examined. The follow-up was 14-38 months for group A and 18-34 months for group B. The serum concentration of chromium (Cr), cobalt (Co) and molybdenum (Mo) was measured. Twenty-two patients before surgery were used for comparison (Group C). The reference values were obtained from a population of twenty-two healthy subjects (Group D). Our findings indicate that metal-on-metal bearings produce a significantly higher systemic release of cobalt and chromium (ng/ml) when compared with levels found in metal-on-PE, pre-surgery and reference groups. Such a high release should induce to improve the bearing materials or, at least, to study the biologic fate of metal ions and consequently their long-term effects. In such a way a risk-to-benefit ratio for the patient could be established. © 2002 Wiley Periodicals, Inc. J Biomed Mater Res (Appl Biomater) 63: 467,474, 2002 [source] Corrosion behaviour of high copper dental amalgamsJOURNAL OF ORAL REHABILITATION, Issue 6 2004A. U. J. Yap summary, This study evaluated the corrosion behaviour of two high copper dental amalgam alloys [Dispersalloy (Dentsply-Caulk) and Tytin (Kerr)] in different electrolytes. Amalgam specimens were prepared, coupled to a copper wire, cemented into glass tubes and polished to a 600-grit finish. A corrosion cell was prepared using a carbon counter-electrode, a standard calomel electrode as the reference and amalgam as the working electrode. The alloys were tested in the following mediums at 37 °C: (i) artificial saliva based on Fusayama's solution (FS), (ii) artificial saliva with citric acid adjusted to pH 4·0 (FC) and (iii) 1% sodium chloride solution (SC). Corrosion potentials (Ecorr) and corrosion rates (Icorr) were determined using potentiostatic and impedance spectroscopy methods. Data was subjected to anova/Scheffe's post hoc test at 0·05 significance level. For both alloys, the corrosion potential in FS was significantly greater than in SC. Corrosion potential of Tytin in FS and SC was also significantly greater than in FC. The corrosion rate of Dispersalloy in FC was significantly greater than in FS and SC. For Tytin, corrosion rate in SC was significantly greater than in FS and FC. Although no significant difference in corrosion potential/rate was observed between the alloys when tested in FS, significant differences were observed when electrochemical testing was carried out in FC and SC. The corrosion behaviour of high copper amalgam alloys are both material and environment dependent. Certain food substances may increase the corrosion of high copper amalgams. [source] In vitro evaluation of the effect of a current bleaching agent on the electrochemical corrosion of dental alloysJOURNAL OF ORAL REHABILITATION, Issue 10 2002enay Canay summary, The nightguard bleaching of discoloured teeth is currently performed by using % 10 carbamide peroxide. While the material is effective on the bleaching of natural teeth, it may deteriorate crowns, bridges and amalgam restorations placed in the mouth. The purpose of the present study was to investigate the effect of 10% carbamide peroxide on the electrochemical corrosion of various dental casting alloys used for fixed partial dentures and dental amalgam. Tafel extrapolation curves were obtained by the corrosion cell that facilitated simulation of the oral enviroment and comparison of the corrosion rates of alloys and amalgam was accomplished. The results revealed that unpolished amalgam and nickel-chromium alloy samples had the most and noble alloys had the least corrosion rate. [source] Crack Growth in Soda,Lime,Silicate Glass near the Static Fatigue LimitJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2002Sheldon M. Wiederhorn The atomic force microscope (AFM) was used to explore the nature of features formed on the surfaces of cracks in soda,lime,silicate glass that were held at stress intensity factors below the crack growth threshold. All studies were conducted in water. Cracks were first propagated at a stress intensity factor above the crack growth threshold and then arrested for 16 h at a stress intensity factor below the threshold. The stress intensity factor was then raised to reinitiate crack growth. The cycle was repeated multiple times, varying the hold stress intensity factor, the hold time, and the propagation stress intensity factor. Examination of the fracture surface by optical microscopy showed surface features that marked the points of crack arrest during the hold time. These features were identical to those reported earlier by Michalske in a similar study of crack arrest. A study with the AFM showed these features to be a consequence of a bifurcation of the crack surface. During the hold period, waviness developed along the crack front so that parts of the front propagated out of the original fracture plane, while other parts propagated into the plane. Crack growth changed from the original flat plane to a bifurcated surface with directions of as much as 3° to 5° to the original plane. This modification of crack growth behavior cannot be explained by a variation in the far-field stresses applied to the crack. Nor can the crack growth features be explained by chemical fluctuations within the glass. We speculate that changes in crack growth direction are a consequence of an enhancement in the corrosion rate on the flank of the crack at stresses below the apparent crack growth threshold in a manner described recently by Chuang and Fuller. [source] Pitting corrosion on 316L pipes in terephthalic acid (TA) dryerMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 11 2009Y. Gong Abstract Grade 316L is a type of austenitic stainless steel with ultra-low carbon content and it exhibits superior corrosion resistance. However, pitting is always observed in 316L steel when it is exposed to media containing halide ions. In the present study, we found that in the presence of acetate acid (HAc) containing chloride or bromide ions, pitting occurred on the surface of the rotary steam pipes with the matrix material of 316L steel in terephthalic acid (TA) dryer. In order to identify the causes of the failure, metallographic structures and chemical compositions of the matrix material were inspected by an optical microscope (OM) and a photoelectric direct reading spectrometer. Beside these, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) as well as ion chromatography (IC) were used to analyze the micromorphologies of the corrosion pits and the chemical compositions of the corrosion deposits within them. Analysis of the results revealed the sources of halide ions and the factors accelerating the corrosion rate. Beside these, detailed mechanisms of pitting were discussed and six out of all the seven theoretical morphologies of pitting features were obtained in practice. [source] Molecular characterization and corrosion behavior of thermophilic (55,°C) SRB Desulfotomaculum kuznetsovii isolated from cooling tower in petroleum refineryMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 9 2009B. Anandkumar Abstract Desulfotomaculum kuznetsovii (D. kuznetsovii), a thermophilic sulfate-reducing bacterium (SRB), was identified in a cooling tower of a petroleum refinery by 16S rRNA gene sequencing and its functional gene encoding dissimilatory sulfite reductase (dsrAB). The thermophilic sulfate-reducing bacterial species have been reported for the first time in the cooling towers of an Indian petroleum refinery. The protein coded by dsrAB gene was cloned, expressed, and identified using recombinant DNA technology. Weight loss method, electrochemical and surface analysis showed the corrosion behavior of the isolate. In the presence of D. kuznetsovii, the corrosion rate was higher when compared to control at 55,°C. It suppresses the anodic reaction and enhances the cathodic reaction by the production of organic complex and iron sulfide, respectively. Numerous pitting were noticed on mild steel which is due to the presence of D. kuznetsovii and its role in the corrosion process has been discussed. [source] Scaling characteristics and growth of corrosion product films in turbulent flow solution containing saturated CO2MATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 1 2009Z. F. Yin Abstract In the present study, the surface and cross-section microstructures of the corrosion films were investigated by SEM and the corrosion rate was measured by mass loss at the various conditions associated with the main influencing factors such as temperature, CO2 partial pressure, and flow velocity. The results indicated that the three factors have obvious characteristics and the enhanced interactions among the main influencing factors intensively influence the formation and growth of corrosion film. In addition, there were two corrosion mechanisms connected with the forming film and damaging film. A new lattice model was proposed to describe the general aspects concerning the formation of the corrosion film at the metal surface/solution interfaces. [source] Simulation of galvanic corrosion of magnesium coupled to a steel fastener in NaCl solutionMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 7 2005J. X. Jia Abstract The galvanic corrosion of magnesium alloy AZ91D coupled to a steel fastener was studied using a boundary element method (BEM) model and experimental measurements. The BEM model used the measured polarization curves as boundary conditions. The experimental program involved measuring the total corrosion rate as a function of distance from the interface of the magnesium in the form of a sheet containing a mild steel circular insert (5 to 30 mm in diameter). The measured total corrosion rate was interpreted as due to galvanic corrosion plus self corrosion. For a typical case, the self corrosion was estimated typically to be , 230 mm/y for an area surrounding the interface and to a distance of about 1 cm from the interface. Scanning Kelvin Probe Force Microscopy (SKPFM) revealed microgalvanic cells with potential differences of approximately 100 mV across the AZ91D surface. These microgalvanic cells may influence the relative contributions of galvanic and self corrosion to the total corrosion of AZ91D. [source] Monitoring the corrosion and remediation of reinforced concrete on-site: An alternative approachMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 4 2005N. Birbilis Abstract Difficulties associated with the interpretation of site data collected over long periods of time from commonly used electrochemical corrosion monitoring techniques often make it difficult to assess the corrosion of reinforcing steel. An alternative approach for the interpretation of data is proposed, based on a model of the quality of passive film upon the steel surface. This model leads to a representation of the corrosion state by means of the relationship, over a long period of time, of the corrosion potential and the logarithm of the Linear Polarization Resistance, since both are functions inter alia of corrosion rate. It is shown that for the reinforced concrete panels tested, data points representing this relationship closely fitted a family of results; allowing the development of a "monitoring control diagram", MCD. The MCD reveals that for a fixed geometry and experimental conditions, a relationship between the corrosion potential and polarization resistance of steel exists, facilitating a useful monitoring tool for assessment of both the corrosion and remediation of reinforced concrete structures. Particular emphasis is placed on the latter in this work. [source] Investigations of an ethanolamine-based corrosion inhibitor system for surface treatment of reinforced concreteMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 7 2004V. T. Ngala Abstract Laboratory investigations were performed to assess the efficacy of a proprietary ethanolamine-based corrosion inhibitor system when applied to the surface of reinforced concrete specimens that were chloride-contaminated to varying extents in the presence or absence of carbonation. The corrosion responses of embedded steel bars at various depths of cover were monitored electrochemically during a controlled programme of cyclic wetting and drying undertaken for several months prior to the inhibitor treatment and for approximately eighteen months thereafter. Gravimetric measurements of the quantities and distribution of corrosion on the steel were also made on completion of the exposure tests. Analysis of aqueous extracts from treated concrete revealed that the ethanolamine component of the inhibitor system penetrated to depths of more than 15 mm within the concrete. It was found that, for inhibitor-treated specimens, there was some reduction in the corrosion rate of pre-corroding steel at low cover depths in non-carbonated concrete with modest levels of chloride contamination. At higher levels of chloride contamination and in carbonated specimens, however, the ethanolamine-based inhibitor was apparently ineffective under the conditions investigated. [source] Influence of testing parameters on the corrosion rate of magnesium alloysMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 6 2004M. Kühlein Abstract In sodium chloride solutions alloy composition, phases, microstructure and grain size influence the corrosion behaviour of magnesium alloys. Concentration and distribution of the critical impurities iron, nickel and copper affect the corrosion performance strongly. Salt spray tests according to ASTM B 117 or DIN 50021 are used to control quality of magnesium alloys. Results of these tests often estimate alloy subcontractors and are therefore very important to placing. Standards specify test solution, test temperature and position of specimens during test in the salt spray chamber. Standards not prescribe preparation of test specimens, exposure period, handling of the specimens after salt spray test nor the interpretation of the results. Results of salt spray tests can be only compared, provided that test conditions are exactly given. Whether the standards fulfil the above described criteria, will be shown by extensive investigations. Therefore the influence of exposure period, surface condition and microstructure was investigated. [source] Exfoliation corrosion of aluminum alloy AA7075 examined by electrochemical impedance spectroscopyMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 1 2004F.-H. Cao Abstract A typical aluminum alloy, AA7075, was immersed in the EXCO solution, and its corrosion properties during different immersion time were measured repetitively using electrochemical impedance spectroscopy technique (EIS). The EIS data a were simulated using equivalent circuit with ZView program. The results show that once the exfoliation occurs, the low frequency inductive loop in the Nyquist plot associated with the relaxation phenomenon of reaction intermediates disappears, and the Nyquist plane is mainly composed of two capacitive arcs in the high frequency range and low frequency range respectively. The former originates from the original corroded surface, while the latter from the newly formed interface by exfoliation corrosion (EXCO). With the increased immersion time, the high frequency capacitance arc decreases gradually, while the low frequency capacitance arc increases gradually. From the beginning of immersion up to 9 hours, charge transfer resistance gradually decreases, illustrating the acceleration of the corrosion rate, whereas the proton concentration decreases steeply, indicating the cathodic process is pre-dominant. Then the corrosion rate decreases gradually corresponding to the exhausting of proton ions. The results also show that the exfoliation corrosion is developed from pitting corrosion through intergranular corrosion to general corrosion at the end. [source] The influences of macrosegregation, intermetallic particles, and dendritic spacing on the electrochemical behavior of hypoeutectic Al-Cu alloysMICROSCOPY RESEARCH AND TECHNIQUE, Issue 11 2007Wislei R. Osório Abstract The purpose of this research is (1) to investigate the influence of Al2Cu intermetallic particles associated with the dendritic arm spacing on the corrosion resistance of different hypoeutectic Al-Cu alloys and (2) to evaluate the electrochemical behavior of a hypoeutectic Al-Cu alloy directionally solidified under unsteady-state heat flow. The as-cast samples were produced using vacuum arc remelting and vertical upward water-cooled solidification. Microscopic examinations were carried out with optical microscopy and scanning electron microscopy + energy dispersiveX-ray analyses. To evaluate the surface corrosion behavior of such alloys, all corrosion tests were performed in a 0.5-M NaCl solution at 25°C using an electrochemical impedance spectroscopy technique and potentiodynamic polarization curve analysis. Based on the tests, corrosion rate and impedance parameters were obtained. The present research has underlined the use of appropriate techniques of characterization for determining Al2Cu distribution, morphology, and fraction within the typical microstructures of Al-Cu alloys. The experimental results have established correlations between the Al-rich phase dendritic arm size, the intermetallic particles distribution in the eutectic mixture, the macrosegregation profile, and the resulting corrosion resistance. Microsc. Res. Tech., 2007. © 2007 Wiley-Liss, Inc. [source] Structure and Corrosion of Magnetron Sputtered Pure Mg Films on Silicon SubstratesPLASMA PROCESSES AND POLYMERS, Issue S1 2007Michael Störmer Abstract Physical vapor deposition (PVD) was used to prepare pure magnesium coatings on silicon substrates at various argon pressures and deposition angles. The film morphology was observed to depend on the deposition conditions. The approximately 3 µm thick Mg films exhibited columnar growth with voided boundaries and a fiber texture of the basal planes parallel to the substrate surface, which is typical of low temperature deposition. At low pressure and angle, the films were more compact, the surface roughness was lower, the texture was stronger, and the corrosion performance was improved. A free corrosion potential of ,1,735 mV and a corrosion rate of 335 µm per year were determined. [source] Corrosion inhibition of carbon steel under two-phase flow (water-petroleum) simulated by turbulently agitated systemTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2008Qasim J. M. Slaiman Abstract The corrosion of carbon steel in single-phase (water with 0.1N NaCl) and two immiscible phases (kerosene-water) using turbulently agitated system was investigated. The experiments were carried out for Reynolds number (Re) range of 38 000 to 95 000 using circular disc turbine agitator at 40°C. In two-phase system, test runs were carried out in aqueous phase (water) concentrations of 1% vol, 5% vol, 8% vol, and 16.4% vol mixed with kerosene at various Re. The effect of Re, percent of dispersed phase, dispersed droplet diameter, and number of droplets per unit volume on the corrosion rate were investigated and discussed. Test runs were carried out using two types of inhibitors: sodium nitrite of concentrations 20, 40, and 60 ppm and sodium hexapolyphosphate of concentrations 485, 970, and 1940 ppm in a solution containing 8% vol aqueous phase (water) mixed with kerosene (continuous phase) at 40°C for the whole range of Re. It was found that increasing Re increased the corrosion rate and the presence of water enhanced the corrosion rate by increasing the solution electrical conductivity. For two-phase solution containing 8% vol and 16% vol of water, the corrosion rate was higher than single phase (100% vol water). The main parameters that play the major role in determining the corrosion rate in two phases were concentration of oxygen, solution electrical conductivity, and the interfacial area between the two phases (dispersed and continuous). Sodium nitrite and sodium hexapolyphosphate were found to be efficient inhibitors in two-phase solution for the investigated range of Re. On a étudié la corrosion de l'acier au carbone dans des conditions monophasiques (eau avec 0,1N de NaCl) et diphasiques immiscibles (kérosène-eau) à l'aide d'un système agité turbulent. Les expériences ont été menées pour une gamme de nombre de Reynolds (Re) de 38000 à 95000, avec un agitateur de type Rushton à 40°C. Des tests pour le système diphasique ont été effectuées dans des concentrations de phase aqueuse (eau) de 1%, 5%, 8% et 16,4% en volume, mélangée à du kérosène pour différentes valeurs de Re. L'effet du nombre de Reynolds (Re), le pourcentage de la phase dispersée, le diamètre des gouttelettes dispersées et le nombre de gouttelettes par unité de volume sur le taux de corrosion a été étudié et analysé. Les essais ont été réalisés avec deux types d'inhibiteurs: du nitrite de sodium à des concentrations de 20, 40 et 60 ppm et de l'hexapolyphosphate de sodium à des concentrations de 485, 970 et 1940 ppm dans une solution contenant 8% en volume de phase aqueuse (eau) mélangée à du kérosène (phase aqueuse) à 40°C pour la gamme complète de Re. On a trouvé que l'augmentation du Re augmentait le taux de corrosion et que la présence d'eau améliorait le taux de corrosion en augmentant la conductivité électrique des solutions. Pour la solution diphasique contenant 8% et 16% en volume d'eau, le taux de corrosion est plus grand qu'en monophasique (100% en volume d'eau). Les principaux paramètres qui jouent un rôle majeur dans la détermination du taux de corrosion dans la solution diphasique sont la concentration d'oxygène, la conductivité électrique de la solution et l'aire interfaciale entre les deux phases (dispersée et continue). On a trouvé que le nitrite de sodium et l'hexapolyphosphate étaient des inhibiteurs efficaces dans la solution diphasique pour la gamme de Re étudié. [source] hytic Acid Conversion Coatings of MagnesiumCHINESE JOURNAL OF CHEMISTRY, Issue 4 2010Jianrui Liu Abstract A chrome-free conversion coating treatment for magnesium by phytic acid solution was developed. The immersion experiments were used for evaluating the effects of the processing parameters (such as conversion temperature and time, concentration and pH value of phytic acid solution) on the corrosion resistance of the phytic acid conversion coating. The morphologies and compositions of the coatings were determined by SEM and EDS respectively. The experimental results indicated that the corrosion resistance of the conversion coating formed in the solution containing 0.5% phytic acid at 25°C and pH=4 for 30 min was higher than that of natural oxide, and the conversion coating formed on the surface of magnesium was of multilayer mainly consisting of Mg, C, O and P. The thicknesses of the conversion coatings were approximately 1.0,15 µm and the conversion coatings presented obvious network-like cracks. The electrochemical potentiodynamic polarization experiment indicated that the free corrosion potential of the magnesium with phytic acid conversion coating was increased, and its corrosion current and corrosion rate declined in 3.5% NaCl solution. Phytic acid conversion coating could improve the electrochemical property of magnesium and provide effective protection, which can improve the corrosion resistance of magnesium. [source] Corrosion Behavior of PM Processed Ti,Ca,P Bioceramic Composites in Hank's Balanced Salt Solution Using Potentiodynamic StudiesINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 2 2010Malobika Karanjai Ti,Ca,P bioceramic composites for load bearing implants developed by a new powder metallurgy processing technique were studied for their electrochemical corrosion properties. For determining corrosion behavior of such composites having in situ formed bioactive Ca,P phases, potentiodynamic and studies were conducted in simulated body fluid namely Hank's balanced salt solution. Potentiodynamic polarization tests showed no evidence of pitting corrosion. Corrosion potentials (,0.27 to ,0.53 V) and corrosion rates (0.17,4.46 mills per year) of Ti,Ca,P bioceramic composite samples were superior to earlier reported results for coated Ti implants due to the formation of passive layer of bone-like calcium phosphate on the sample surface. [source] Corrosion behaviour of high copper dental amalgamsJOURNAL OF ORAL REHABILITATION, Issue 6 2004A. U. J. Yap summary, This study evaluated the corrosion behaviour of two high copper dental amalgam alloys [Dispersalloy (Dentsply-Caulk) and Tytin (Kerr)] in different electrolytes. Amalgam specimens were prepared, coupled to a copper wire, cemented into glass tubes and polished to a 600-grit finish. A corrosion cell was prepared using a carbon counter-electrode, a standard calomel electrode as the reference and amalgam as the working electrode. The alloys were tested in the following mediums at 37 °C: (i) artificial saliva based on Fusayama's solution (FS), (ii) artificial saliva with citric acid adjusted to pH 4·0 (FC) and (iii) 1% sodium chloride solution (SC). Corrosion potentials (Ecorr) and corrosion rates (Icorr) were determined using potentiostatic and impedance spectroscopy methods. Data was subjected to anova/Scheffe's post hoc test at 0·05 significance level. For both alloys, the corrosion potential in FS was significantly greater than in SC. Corrosion potential of Tytin in FS and SC was also significantly greater than in FC. The corrosion rate of Dispersalloy in FC was significantly greater than in FS and SC. For Tytin, corrosion rate in SC was significantly greater than in FS and FC. Although no significant difference in corrosion potential/rate was observed between the alloys when tested in FS, significant differences were observed when electrochemical testing was carried out in FC and SC. The corrosion behaviour of high copper amalgam alloys are both material and environment dependent. Certain food substances may increase the corrosion of high copper amalgams. [source] In vitro evaluation of the effect of a current bleaching agent on the electrochemical corrosion of dental alloysJOURNAL OF ORAL REHABILITATION, Issue 10 2002enay Canay summary, The nightguard bleaching of discoloured teeth is currently performed by using % 10 carbamide peroxide. While the material is effective on the bleaching of natural teeth, it may deteriorate crowns, bridges and amalgam restorations placed in the mouth. The purpose of the present study was to investigate the effect of 10% carbamide peroxide on the electrochemical corrosion of various dental casting alloys used for fixed partial dentures and dental amalgam. Tafel extrapolation curves were obtained by the corrosion cell that facilitated simulation of the oral enviroment and comparison of the corrosion rates of alloys and amalgam was accomplished. The results revealed that unpolished amalgam and nickel-chromium alloy samples had the most and noble alloys had the least corrosion rate. [source] Potential high temperature corrosion problems due to co-firing of biomass and fossil fuelsMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 10 2008M. Montgomery Abstract Over the past few years, considerable high temperature corrosion problems have been encountered when firing biomass in power plants due to the high content of potassium chloride in the deposits. Therefore, to combat chloride corrosion problems co-firing of biomass with a fossil fuel has been undertaken. This results in potassium chloride being converted to potassium sulphate in the combustion chamber and it is sulphate rich deposits that are deposited on the vulnerable metallic surfaces such as high temperature superheaters. Although this removes the problem of chloride corrosion, other corrosion mechanisms appear such as sulphidation and hot corrosion due to sulphate deposits. At Studstrup power plant Unit 4, based on trials with exposure times of 3000 h using 0,20% straw co-firing with coal, the plant now runs with a fuel mix of 10% straw,+,coal. Based on results from a 3 years exposure in this environment, the internal sulphidation is much more significant than that revealed in the demonstration project. Avedøre 2 main boiler is fuelled with wood pellets,+,heavy fuel oil,+,gas. Some reaction products resulting from the presence of vanadium compounds in the heavy oil were detected, i.e. iron vanadates. However, the most significant corrosion attack was sulphidation attack at the grain boundaries of 18-8 steel after 3 years exposure. The corrosion mechanisms and corrosion rates are compared with biomass firing and coal firing. Potential corrosion problems due to co-firing biomass and fossil fuels are discussed. [source] Corrosion characteristics of the wrought Ni-Cr-Mo alloysMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 9 2005P. Crook Abstract This paper concerns the wrought, nickel-chromium-molybdenum (Ni-Cr-Mo) alloys, a family of materials with a long history of use in the chemical process industries. Their attributes include resistance to the halogen acids and resistance to pitting, crevice attack, and stress corrosion cracking in hot, halide salt solutions. The purpose of this paper is to characterize the performance of the Ni-Cr-Mo alloys in several key chemicals, using iso-corrosion diagrams. These indicate the expected corrosion rates over wide ranges of concentration and temperature. Furthermore, the differences between individual Ni-Cr-Mo alloys, and their behavior relative to the stainless steels are defined. The data indicate benefits of both a high chromium content and a copper addition, as used in Hastelloy® C-2000® alloy. [source] | ||||||||||||||||||||||||||||