Showing papers in "Materials and Corrosion-werkstoffe Und Korrosion in 2003"

Non destructive determination of the free chloride content in cement based materials

Abstract: A non-destructive chloride sensitive sensor element for use in cement based porous materials is presented. The sensor element determines the activity of the free chloride ions in solutions and in porous cement based materials such as cement paste, mortar or concrete. The calibration in synthetic pore solution showed a response according to Nernst law over three decades of chloride concentration. The sensor element has shown excellent reproducibility and long term stability. The sensor element has been used to monitor the chloride uptake into mortar specimens. The results show a good agreement between the free chloride content determined by the sensor and by pore water expression. Applications in monitoring of reinforced concrete structures and their limitations are discussed. Zerstorungsfreie Erfassung der Konzentration der freien Chloridionen in Zementstein und Mortel In der vorliegenden Arbeit wird ein Chloridsensor zur zerstorungsfreien Erfassung des Chloridgehalts in zementosen Materialien beschrieben. Der Sensor bestimmt die Aktivitat der freien Chloridionen in Losungen und in Zementstein, Mortel oder Beton. Die Kalibrierungskurve in synthetischer Betonporenlosung zeigt das erwartete Nernst'sche Verhalten uber mehr als drei Konzentrationsdekaden. Der Sensor weist eine sehr hohe Reproduzierbarkeit und Langzeitstabilitat auf. Der Chloridsensor wurde eingesetzt, um das Eindringen der Chloridionen in Mortelprufkorpern zu untersuchen. Ein Vergleich der Chloridkonzentration bestimmt durch Auspressen der Porenlosung am Ende der Versuche mit den von Sensoren bestimmten Chloridkonzentration zeigt eine sehr gute Ubereinstimmung. Praktische Anwendungen und die Einsatzgrenzen des Sensors werden diskutiert.

Corrosion process of silver in environments containing 0.1 ppm H2S and 1.2 ppm NO2

Abstract: The effects of sub-ppm levels of nitrogen dioxide and hydrogen sulfide, and the adsorbed water on the corrosion of silver were studied in order to get a better understanding of the atmospheric corrosion process. An in situ mass balance was taken to monitor the kinetic behavior and the surface and the corrosion film were analyzed by X-ray photoelectron spectroscopy (XPS). In H2S environments, the tarnish film consisted of silver sulfide, and the corrosion rate depended upon oxygen as well as relative humidity. Silver was oxidized by only oxygen and the corrosion behavior conformed to a type of a parabolic law. In NO2 environments, the corrosion film consisted of nitrate and oxide, and the corrosion rate depended upon oxygen as well as relative humidity. Compared to hydrogen sulfide, the formation of silver nitrate being strong hydroscopic reduced the effect of humidity on corrosion rate. In H2S + NO2 environment, the corrosion process was independent of both oxygen and humidity, and the kinetic behavior conformed to a linear law. The difference of corrosion process between H2S or NO2 environments and H2S + NO2 environments is thought to be due to the role of nitrogen dioxide as an ionic conductor and the presence of strong oxidizing species such as elemental sulfur which can be produced from the following reaction: H2S + 2NO2 S + 2HNO2. In addition, the role of adsorbed water affecting atmospheric corrosion process was mentioned based on the amount of adsorbed water from the three types of exposure environments. Korrosionsprozess von Silber in Umgebungen mit 0,1 ppm H2S und 1,2 ppm NO2 Um ein besseres Verstandnis der atmospharischen Korrosionsprozesse von Silber zu bekommen, wurden der Einfluss von ppm-Gehalten an Stickstoffdioxid und Schwefelwasserstoff sowie von adsorbiertem Wasser auf die Korrosion von Silber untersucht. Eine in-situ Massenwaage wurde eingesetzt, um das kinetische Verhalten zu kontrollieren. Die Oberflache und der Korrosionsfilm wurden mittels Rontgenphotoelektronenspektroskopie (XPS) analysiert. In H2S-Umgebungen bestand der Anlauffilm aus Silbersulfid und die Korrosionsgeschwindigkeit hing sowohl vom Sauerstoff als auch von der relativen Feuchtigkeit ab. Silber wurde nur durch Sauerstoff oxidiert und das Korrosionsverhalten stimmte mit einem parabolischen Zeitgesetz uberein. In NO2-Umgebungen bestand der Korrosionsfilm aus Nitrat und Oxid und die Korrosionsgeschwindigkeit hing sowohl vom Sauerstoff als auch von der relativen Feuchtigkeit ab. Verglichen mit Schwefelwasserstoff fuhrte die Bildung von stark hydroskopischem Silbernitrat zu einer Verringerung des Einflusses der Feuchtigkeit auf die Korrosionsgeschwindigkeit. In H2S + NO2-Umgebung war der Korrosionsprozess unabhangig von Sauerstoff und Feuchtigkeit und das kinetische Verhalten entsprach einem linearen Zeitgesetz. Es wird angenommen, dass die Unterschiede im Korrosionsprozess zwischen H2S-, NO2- und H2S + NO2-Umgebungen durch die Rolle des Stickstoffdioxids als ionischer Leiter und durch die Anwesenheit von stark oxidierenden Spezies wie elementarer Schwefel, der durch die folgende Reaktion erzeugt werden kann: H2S + 2NO2 S + 2HNO2, verursacht werden. Zusatzlich wird basierend auf der Menge an adsorbiertem Wasser bei den drei Typen der Auslagerungsumgebungen die Rolle des adsorbierten Wassers, das den Korrosionsprozess beeinflusst, erwahnt.

The role of alloying elements in commercial alloys for corrosion resistance in oxidizing-chloridizing atmospheres. Part I: Literature evaluation and thermodynamic calculations on phase stabilities

Abstract: In several high temperature processing environments the presence of chlorine may significantly reduce the life-time of the components. Although metallic materials have been widely used under such conditions there is still a need for data on the role of the different alloying elements in commercial alloys. In the present work this role was investigated in detail at temperatures between 650 and 1000°C in synthetic air containing up to 2 vol.% Cl2. Before starting the experimental investigation a detailed literature evaluation on chlorine high temperature corrosion was performed followed by a thermodynamic assessment of the stability and the partial pressures of the phases formed by the reaction between alloy and environment. The results of this “theoretical approach” are presented in the following first part of the publication while the experimental work will be reported in the second part appearing in a later issue of this journal. Already the results of the “theoretical approach” yield a clear picture of which alloying elements play a detrimental role and which elements are beneficial. These results can be used as a tool for a general assessment of metallic alloys with regard to their performance in oxidizing/chloridizing high temperature environments. In the second part of this work the results from this “theoretical approach” will be compared with the behavior of 14 commercial materials, where the content of the major alloying elements was varied in a systematic manner. Die Rolle der Legierungselemente in kommerziellen Werkstoffen fur die Korrosionsbestandigkeit in oxidierend-chlorierend wirkenden Atmospharen. Teil I: Literaturauswertung und thermodynamische Berechnungen zur Stabilitat der Phasen In einer Reihe von Hochtemperatur-Prozesumgebungen fuhrt die Anwesenheit von chlorhaltigen Verbindungen zu einer deutlichen Verkurzung der Lebensdauer der Anlagenbauteile. Obwohl in diesen Anlagen metallische Legierungen bereits in grosem Umfang eingesetzt werden, besteht immer noch ein ausgepragter Bedarf an Daten zur Rolle des Verhaltens der verschiedenen Legierungselemente unter diesen Bedingungen. In der vorliegenden Arbeit wurde diese Rolle im Detail bei Temperaturen von 650 bis 1000°C in Luft mit Chlorgehalten bis zu 2% vol. untersucht. Vor der Durchfuhrung des experimentellen Teils der Untersuchungen wurde eine umfangreiche Literaturauswertung vorgenommen, gefolgt von thermodynamischen Rechnungen zur Stabilitat und zum Partialdruck der Phasen, die durch die Reaktion der Legierungen mit der Prozesumgebung gebildet werden konnen. Die Ergebnisse dieses “theoretischen Ansatzes” werden im ersten Teil einer zweiteiligen Veroffentlichung vorgestellt, wahrend uber die Ergebnisse der experimentellen Untersuchungen im zweiten Teil berichtet wird, der in einer spateren Ausgabe dieser Zeitschrift erscheint. Bereits die Ergebnisse des “theoretischen Ansatzes” erlauben eine klare Einschatzung, welche Legierungselemente eine positive und welche eine negative Rolle bezuglich der Korrosionsbestandigkeit von metallischen Legierungen in diesen Umgebungen spielen. Diese Ergebnisse konnen als Werkzeug fur die Bewertung des Verhaltens kommerzieller Werkstoffe in oxidierend/chlorierend wirkenden Atmospharen eingesetzt werden. Im zweiten Teil dieser Arbeit werden die Ergebnisse des “theoretischen Ansatzes” mit dem Korrosionsverhalten von 14 kommerziellen Werkstoffen verglichen, bei denen der Gehalt der wichtigsten Legierungselemente in systematischer Weise variiert wurde.

Mechanisms and driving forces of metal dusting

Abstract: The mechanisms of metal dusting as it appears on different ferritic stainless steels and pure iron have been described in detail. A mechanism for metal dusting (MD) of chromia-forming as well as al ...

The influence of NaCl and CO2 on the atmospheric corrosion of magnesium alloy AZ91

Abstract: The influence of NaCI and CO 2 on the atmospheric corrosion of magnesium alloy AZ91 is studied in the laboratory. Samples were exposed under carefully controlled air and flow conditions; the relative humidity was 95%, the temperature was 22.0 °C and the concentration of CO 2 was < 1 ppm or 350 ppm. Different amounts of sodium chloride (0-70 μg/cm 2 ) were added before exposure. The corrosion products were analyzed by gravimetry, ion chromatography, X-ray diffraction and scanning electron microscopy. Mass gain and metal loss results are reported. The combination of high humidity and NaCI is very corrosive towards AZ91. However, the NaCl-induced corrosion is inhibited by ambient concentrations of CO 2 . Exposure in the absence of CO 2 gives rise to heavy pitting, with brucite, Mg(OH) 2 , being the dominant corrosion product. In the presence of CO 2 a layer of hydrated magnesium hydroxy carbonate, Mg 5 (CO 3 ) 4 (OH) 2 . 5 H 2 O forms. A tentative corrosion mechanism is presented that explains the behavior in the two environments.

Protective behaviour of newly developed coatings against metal dusting

Abstract: Publisher Summary This chapter presents that whether a material is resistant to Metal Dusting (MD) depends on the ability of the material to develop a protective oxide scale. Most of the conventional low-cost steels widely used in plant technology do not possess a sufficient potential for protective oxide scale formation. However, to prevent corrosion of the materials, protective coatings rich in Al, Cr, Ti, and Si can be applied, which can form protective oxide scales and thus protect the underlying substrate from corrosive attack. In the chapter, Al, Cr, Si, and Ti have been chosen to produce diffusion and overlay coatings for reasons of their ability to form very stable protective oxide layers. The chapter presents several newly developed coatings and discusses the influence of temperature on oxide formation and behavior of the different coatings. The first type of coatings was applied by the pack cementation method leading to a diffusion coating on the base material. These coatings are based on stable oxide formers, such as Al, Ti, Si, and Cr.

Corrosion behaviour of magnesium sacrificial anodes in tap water

Abstract: The effects of applied current, testing time and microstructure on the electrochemical properties of magnesium-based sacrificial anodes in potable water were evaluated. Galvanostatic tests, potentiodynamic polarisation and scanning electron microscopy (SEM) analyses were used to determine anode efficiency, corrosion rate and microstructures of the Mg-anodes under study. The contribution of processes as mechanical material loss and hydrogen evolution on the current wastage was investigated. The effect of the different microstructures like those obtained by heat treatments to reduce the intermetallic phase was also tested. Die Einflusse des angewendeten Stromes, der Versuchszeit und des Gefuges auf die elektrochemischen Eigenschaften von galvanischen Anoden auf Magnesiumbasis wurden in Trinkwasser untersucht. Galvanostatische Versuche, potentiodynamische Polarisation und Rasterelektronenmikroskopieanalysen kamen zum Einsatz, um die Anodenwirksamkeit, die Korrosionsgeschwindigkeit und das Gefuge der verwendeten Mg-Anoden zu bestimmen. Der Anteil des mechanischen Materialverlustes und der Wasserstoffentwicklung auf den Stromverlust wurden untersucht. Der Einfluss unterschiedlicher Gefuge, wie sie durch Warmebehandlung zur Reduzierung intermetallischer Phasen erzeugt werden, wurde ebenfalls bewertet.

Filamentous carbon formation caused by catalytic metal particles from iron oxide

Abstract: The thermodynamic equilibrium between metallic iron, iron oxides, iron carbides and an hydrocarbon/hydrogen mixture was calculated at 600 °C. On the basis of the metastable Fe-C-O phase diagram, both metallic iron and iron oxides can be directly convertcd into carbides in reducing and carburizing atmosphere. Thermogravimetric (ATG) measurements have been performed in iC 4 H 10 -H 2 -Ar atmosphere at 600 °C on reduced and pre-oxidised iron samples. The kinetic of coke formation was studied on both surface states by sequential exposure experiments. The initial stages of the transformation were characterised by scanning electron microscopy (SEM) observations and X-ray diffraction (XRD) analysis. On a reduced surface, the results are consistent with the mechanism currently proposed to explain catalytic coke formation. Cementite (Fe 3 C) is formed on the iron surface after carbon supersaturation (a c > 1). The graphite deposition on its surface (a c = 1) induces its decomposition. Iron atoms from cementite diffuse through the graphite and agglomerate to small particles that act as catalysts for further carbon deposition. A new mechanism of catalytic particle formation is proposed when an oxide scale initially covers the iron surface. In the carburizing and reducing atmosphere, magnetite (Fe 3 O 4 ) can be directly converted into cementite (Fe 3 C). XPS analysis confirm that, in this process, metallic iron is not an intermediary specie of the oxide/carbide reaction. At the same time, graphite deposition occurs at the metal/oxide interface through the cracks present in the oxide scale. Iron carbide in contact with graphite is partially decomposed and acts as catalyst for graphitic filaments growth.

The role of alloying elements in commercial alloys for corrosion resistance in oxidizing‐chloridizing atmospheres. Part II: Experimental investigations

Abstract: In an extensive study the role of the alloying elements in commercial alloys for corrosion resistance was studied in air without and with 0.1 and 2 vol.% Cl2, respectively. In the first part of this paper [1] the thermodynamic fundamentals were discussed on the basis of the new concept of the quasi-stability diagrams. The second part which is presented here reports the results from investigations at 650, 800 and 1000°C and testing times up to 1000 hrs where 14 commercial alloys were tested with regard to their corrosion behavior. The materials were selected so that the role of the alloying elements Mo, C, Si, Al, N, Fe, Ni and Cr would be evident from the results. The exposure tests were followed by extensive microstructural analyses of the corrosion scales and the metal subsurface zones so that type, mechanism and extent of corrosion could be characterized in great detail. At the end a ranking was possible of the different materials and with regard to the detrimental or beneficial role of the different alloying elements. The present results thus provide a much deeper insight into materials resistance in oxidizing-chloridizing environments at high temperatures. Die Rolle der Legierungselemente in kommerziellen Werkstoffen fur die Korrosionsbestandigkeit in oxidierend-chlorierend wirkenden Atmospharen. Teil II: Experimentelle Untersuchungen In einer umfangreichen Forschungsarbeit wurde die Rolle von Legierungselementen in kommerziellen Legierungen bezuglich deren Hochtemperaturkorrosionsbestandigkeit in Luft ohne und mit 0,1 bzw. 2 vol.% Chlor untersucht. Im ersten Teil des Berichts [1] werden die thermodynamischen Grundlagen auf der Basis des neuen Konzepts des “Quasi-Stabilitatsdiagramms” diskutiert. Der vorliegende zweite Teil berichtet uber die Ergebnisse aus den Korrosionsversuchen bei 650, 800 und 1000°C, in denen 14 kommerzielle Legierungen untersucht wurden und die bis zu 1000 h liefen. Die Werkstoffe waren nach einem System zusammengestellt worden, bei dem die Rolle der Legierungselemente Mo, C, Si, Al, N, Fe, Ni und Cr deutlich werden sollte. An die Korrosionsversuche schlossen sich umfangreiche mikroanalytische Untersuchungen an, in denen sehr detailliert Erscheinungsform, Mechanismen und Ausmas der Korrosion charakterisiert wurden. Am Ende konnte eine Einordnung der verschiedenen Werkstoffe bezuglich ihrer Korrosionsbestandigkeit und der Legierungselemente bezuglich ihrer positiven oder negativen Wirkung vorgenommen werden. Die Ergebnisse konnen einen wesentlichen Beitrag zum besseren Verstandnis der Korrosionseigenschaften technischer Legierungen in oxidierend-chlorierend wirkenden Umgebungen bei hohen Temperaturen liefern.

Corrosion of carbon steel in filling material in an urban environment

Abstract: The corrosion process of carbon steel in soil has been investigated, in particular the influence of the soil of an urban environment. A field test was carried out with test panels buried in trenches. Localized and uniform corrosion rates were evaluated after 1 and 3 years. Soil samples from points adjacent to the panels were analyzed with respect to a number of physical and chemical parameters believed to influence the corrosion process. Corrosion products were analyzed and identified. The study shows that the localized corrosion rate of soil buried constructions may be remarkably high in a filling material in comparison to other soils. The heterogeneity of the soil seems to have a greater influence on the localized corrosion rate than the chemical composition of the soil. However, the uniform corrosion rate was comparatively low in the heterogeneous filling material. Both the high alkalinity in the soil water and the groundwater, and the high total hardness of the soil water in the filling material seem to reduce the uniform corrosion rate. Corrosion rate determinations with commercial probes is also discussed. The linear polarization resistance (LPR), the electric resistance (ER) and the corrosion potential measurement techniques are compared. All probes showed a seasonal variation in corrosion rate. The measurements with commercial probes were associated with some problems, mostly a result of poor contact between the probes and the soil. Korrosion von Baustahl im Fullmaterial in einer stadtischen Umgebung Der Korrosionsprozess von Baustahl in Erde ist untersucht worden, insbesondere der Einfluss von Fullmaterial in der Erde einer stadtischen Umgebung. Eine Feldprufung wurde mit Prufblechen ausgefuhrt, die in Graben eingegraben wurden. Lokalisierte und gleichmasige Korrosionsraten wurden nach 1 und 3 Jahren gemessen. Proben des Erdreiches von Punkten benachbart zu den Prufstucken wurden in Bezug auf eine Anzahl physikalischer und chemischer Parameter analysiert, die den Korrosionsprozess beeinflussen. Korrosionsprodukte wurden analysiert und identifiziert. Das Studium zeigt, dass die lokalisierte Korrosionsrate von in stadtischer Erde eingegrabenem Stahl im Vergleich zu anderen Erden bemerkenswert hoch sein kann. Die Heterogenitat der Erde scheint einen groseren Einfluss auf die lokalisierte Korrosionsrate zu haben als die chemische Zusammensetzung der Erde. Die gleichmasige Korrosionsrate war jedoch im heterogenen Fullmaterial verhaltnismasig niedrig. Die hohe Alkalinitat im Grundwasser und die hohe totale Harte des Grundwassers im Fullmaterial scheint die gleichmasige Korrosionsrate zu reduzieren. Korrosionsmessungen mit kommerziellen Sonden werden auch in diesem Artikel diskutiert. Der lineare Polarisationswiderstand (LPR), der elektrische Widerstand (ER) und die Korrosionspotentialmessungen werden verglichen. Alle Sonden zeigten eine saisonbedingte Variation in den Korrosionsmessungen. Die Messungen mit den kommerziellen Sonden waren mit einigen Problemen verbunden, die meistens durch schlechte Kontakte zwischen den Sonden und der Erde hervorgerufen wurden.

Evolution of reinforcement corrosion due to climatic variations

Abstract: Concrete moisture is the most significant parameter with respect to its durability, however the data on moisture content in real-size structures are scarce in contrast to the numerous literature published on laboratory experiments. The majority of laboratory tests have been performed in chambers with controlled hydrothermal regime, in general to enable the concrete to reach equilibrium and steady-state conditions. However, real weather induces permanent non-steady state situations due to the evolution of temperature and climatic events as snowing or raining. Present paper discusses the effect of climatic events on the hydrothermal performance of concrete and their influence on reinforcement corrosion process. Concerning the moisture level, the degree of saturation, SW, and not the internal relative humidity has been identified to be the controlling parameter of the corrosion process. The psychometric chart and the SW-RH plots are very suitable to study the hydrothermal behaviour. With respect to the corrosion parameters, corrosion potential, resistivity and corrosion rates, they are very influenced by temperature in a complex manner. The temperature is the main factor influencing the degree of saturation in sheltered conditions while rain and snow are so, in unsheltered ones. In opposition, however, what can be expected, climates with higher temperatures are less aggressive than colder ones, except when rain periods are produced during the hotter periods. Entwicklung der Bewehrungsstahlkorrosion durch klimatische Schwankungen Die Betonfeuchtigkeit ist der wichtigste Parameter bezuglich der Dauerhaftigkeit des Stahlbetons. Im Gegensatz zu einer Vielzahl von veroffentlichten Daten aus Laborversuchen gibt es jedoch nur wenige Angaben uber den Feuchtigkeitsgehalt in realen Bauwerken. Die Mehrzahl der Laborversuche wurde in Prufkammern mit kontrollierten hydrothermischen Zustanden durchgefuhrt; in der Regel um Gleichgewichtsbedingungen im Beton zu erreichen. Bei realem Wetter liegen durch Temperaturschwankungen und durch klimatische Ereignisse wie Regen oder Schnee jedoch dauernd Nichtgleichgewichtszustande vor. Die vorliegende Arbeit diskutiert den Einfluss klimatischer Ereignisse auf das hydrothermische Verhalten von Beton und deren Einfluss auf den Bewehrungsstahlkorrosionsprozess. Bezuglich des Feuchtigkeitslevels wurde der Sattigungsgrad, SW, und nicht die interne relative Feuchtigkeit als der bestimmende Parameter des Korrosionsprozesses identifiziert. Die Feuchtigkeitsdarstellung und die SW-RH-Diagramme sind sehr gut geeignet, das hydrothermische Verhalten zu untersuchen. Die Korrosionsparameter (Korrosionspotential, Widerstand und Korrosionsgeschwindigkeit) werden sehr komplex von der Temperatur beeinflusst. Die Temperatur ist der wesentliche Faktor, der den Sattigungsgrad unter geschutzten Bedingungen beeinflusst, wahrend unter ungeschutzten Bedingungen Regen und Schnee entscheidend sind. Im Gegensatz zu dem, was erwartet werden kann, ist jedoch ein Klima mit hoheren Temperaturen weniger aggressiv als eines mit kalteren Temperaturen; auser wenn Regenperioden wahrend heiserer Zeiten vorliegen.

Typical failures in pyrolysis coils for ethylene cracking

Abstract: Publisher Summary This chapter mentions that pyrolysis coils in ethylene cracking furnaces are exposed to very severe conditions, for instance, high temperatures up to 1150 °C, severe start/stop and de-coke cycles, oxidizing and nitriding flue gases at the outside, and carburizing atmospheres at the tube inside surface. Therefore, high-alloyed centrifugal cast Ni–Cr–Fe alloys with adequate high-temperature corrosion resistance, good high-temperature strength, and good machinability and weldability (even after years of service) are required. The chapter highlights the principal alloys for ethylene cracking furnaces. It focuses on the typical failures in pyrolysis coils for ethylene cracking. The dominant failure mechanisms for radiant tubes are: (a) the combined action of carburization and creep ductility exhaustion, and (b) brittle fracture during furnace trips. The first mechanism results in bulging, bending, and ovalization of the tubes. The second mechanism results in large, longitudinal cracks.

Occurrence of Metal Dusting - Referring to Failure Cases

Abstract: Twelve years of research on metal dusting at the Max-Planck-Institut for Iron Research have led to comprehensive knowledge on the mechanisms and kinetics of metal dusting and on ways and means for prevention of this corrosion phenomenon, - this knowledge is shortly summarized in this paper. Inspite of this state of understanding, the present opinion in industry is that metal dusting is mysterious and not predictable and cannot be controlled. This paper is intended to show that the occurrence of metal dusting and its reasons can be well understood, by describing and explaining five failure cases.

Anodic behaviour of WC-Co type hardmetal

Abstract: An understanding of the anodic behaviour of WC-Co type hard-metals is vital for the functional behaviour of this class of materials. The anodic oxidation of WC-13Co grade hardmetal in 0.1 M H 2 SO 4 was investigated. This study is based on electrochemical (linear sweep voltammetry, cyclic voltammetry, impedance spectroscopy), compositional (energy dispersive spectroscopy), structural (X-ray diffraction) and morphological (scanning electron microscopy) investigations. The potential range in which the oxidation of the Co-alloy takes place with respect to the nobler carbide phase was defined. Within this potential interval a passivating behaviour for the binder alloy was shown. The potential threshold for WC oxidation was identified by monitoring the inception of the electrochromic loop. The anodic attack gives rise to the formation of hydrous WO 3 . The attack morphology is characterised by the alteration of the grain shape with formation of jelly-like microscopic and flaky macroscopic structures.

The use of electrochemical techniques for the investigation and monitoring of microbiologically influenced corrosion and its inhibition – a review

Abstract: The background of several electrochemical techniques - recording of the corrosion potential E corr' electrochemical impedance spectroscopy (EIS), electrochemical noise analysis (ENA) and recording of potentiodynamic polarization curves - has been discussed and examples of the use of these techniques in studies of microbiologically influenced corrosion (MIC) and MIC inhibition have been presented. These examples range from the use of the polarization resistance R p and the noise resistance R n in corrosion monitoring in a sewer environment and a gas production field, respectively, to the application of EIS and ENA in the evaluation of the interaction of bacteria with protective coatings on steel exposed to natural seawater (NS). A more detailed analysis based on EIS and ENA of Corrosion protection of Al 2024, mild steel and brass in artificial seawater (AS) by bacteria such as B. subtilis, B. licheniformis, E. coli and Shewanella has been presented. Determination of the changes of R p and R n as well as E corr allows to propose appropriate mechanisms of MIC inhibition. These mechanisms have been confirmed in the case of S. algae by recording of anodic and cathodic potentiodynamic polarization curves after exposure to AS containing the bacteria for extended time periods.

Effect of H2S on metal dusting of iron

Abstract: A review is given on the effect of H 2 S on metal dusting of iron which has been studied by gas carburisation in CO-H 2 -H 2 O-H 2 S and CH 4 -H 2 -H 2 S mixtures at 500 and 700 °C. The presence of H 2 S in carburising gas atmospheres leads to sulphur adsorption on the iron surface, which retards carbon transfer. Segregation experiments and surface analyses have shown that sulphur segregates (and thus adsorbs) on cementite surfaces as well as on iron surfaces. The adsorbed sulphur also suppresses graphite nucleation and thus can stop the reaction sequence of metal dusting. Experiments by thermogravimetric analysis (TGA) have shown that the extent of retardation of metal dusting depends on temperature, carbon activity and H 2 S content. The higher the carbon activity, the higher is the H 2 S content required for suppression of metal dusting. At carbon activities a C > a C (Fe/Fe 3 C) the metastable iron carbide, cementite (Fe 3 C), occurs as an intermediate phase during metal dusting. Carburisation experiments in CO-H 2 -H 2 O-H 2 S mixtures at 500 C and X-ray diffraction analysis (XRD) of carburised samples have revealed that at very high carbon activities a second iron carbide. Hagg carbide (Fe 5 C 2 ). forms on the cementite surface. Microstructural investigations have shown that both metastable carbides decompose during metal dusting. Metal dusting experiments on iron at 700 C have been performed in CH 4 -H 2 -H 2 S gas mixtures. By adding 15 ppm H 2 S to the CH 4 -H 2 atmosphere the onset of metal dusting can be retarded for more than 350 hours. By means of Auger electron spectroscopy (AES), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX) it was shown that coke contains graphite, cementite and iron particles with adsorbed sulphur.

Biofouling control in industrial water systems: What we know and what we need to know

Abstract: Biofouling contributes substantially to economic losses in industry Although much progress has been made in understanding biofouling and its implications in industrial water systems, many questions remain unanswered The cost of biofouling has not been enumerated A prerequisite for this is research to elucidate the contribution that microbiologically influenced corrosion makes, to the overall corrosion process Surface characteristics play a major role in the initial stages of microbial attachment Ways of preventing preferential attachment to certain areas, ie grain boundaries and welds need further investigation Biocides are routinely used to control biofouling Due to the problem of resistance and potential environmental impact, alternative strategies for biofouling control need to be investigated and put to practice These should focus on an integrated approach with the minimum impact on the environment A number of biofouling monitoring devices have been developed The advantages of biofouling monitoring needs to be demonstrated and monitors should become commercially available

Behavior of Ni‐base alloy 625 in methanol‐supercritical water systems

Abstract: Methanol reacts with water under supercritical conditions to form a hydrogen rich gas. This reforming reaction can be performed without the addition of a catalyst. Typical reaction conditions are 25 MPa pressure and 600°C temperature and short residence times. The tubular flow reactor used was made of the nickel base alloy 625. The reactor was operated continuously for more than 1000 hours without problems. The feed concentration was 5 weight-% methanol. The major component of the product gas was hydrogen (up to more than 70 vol-%). Methanol conversion was higher than 99% and the liquid effluent was clear and free of soot. After exposure, the reactor has been sectioned and each section has been analyzed. No major corrosion phenomena were observed. Severe ductility loss of the material could be measured in the higher temperature section of the reactor. Verhalten der Nickelbasislegierung 625 in Methanol-uberkritischen Wassersystemen Methanol zersetzt sich in uberkritischem Wasser unter Bildung eines wasserstoffreichen Gasgemisches. Diese Reformierungsreaktion konnte ohne Zusatz eines Katalysators durchgefuhrt werden. Bei 25 MPa Druck und einer Temperatur von 600°C sind nur kurze Verweilzeiten erforderlich. Das Material des Rohrreaktors besteht aus der Legierung 625 (Werkstoff Nummer 2.4856). Der Reaktor konnte langer als 1000 Betriebsstunden problemlos im Durchflussbetrieb gefahren werden. Eingesetzt wurde ein Wasser/Methanol-Gemisch mit einer Konzentration von 5 Gew.% Methanol. Die Hauptkomponente im Produktgas war Wasserstoff (> 70 Vol.%); es konnte eine Methanol-Konversionsrate von mehr als 99% erreicht werden. Der wassrige Effluent war farblos und rusfrei. Nach Betriebsende wurde das Reaktionsrohr abschnittsweise aufgetrennt und Querschschliffe zur Analyse angefertigt. Es wurden keine schwerwiegenden Korrosionsangriffe festgestellt, allerdings ein starker Duktilitatsverlust im Bereich hoher Rohrtemperaturen.

Copper corrosion inhibition by fast green, fuchsin acid and basic compounds in citric acid solution

Abstract: Fast green (FG), fuchsin basic (FB) and fuchsin acid (FA) were studied as copper corrosion inhibitors in citric acid solution. Five citric acid concentrations were tested from 0.001 to 1.0 M. Twelve FG, FB and FA concentrations were studied from 1 × 10−5 to 1 × 10−1 M, at four temperatures from 298 to 328 K. The gravimetric method was employed to study the protective effect of FG, FB and FA. The order of inhibition efficiency was FB > FA > FG. Conventional adsorption isotherms were tested to fit the experimental data. The best fit was obtained using the Frumkin isotherm model. A thermodynamic/kinetic model of adsorption was also fitted. The projected molecular area of the inhibitors was calculated to elucidate inhibitor orientation in the adsorption process. Korrosion und Korrosionsinhibition von Kupfer mittels der Verbindungen Fast Green, saurem und basischem Fuchsin in Zitronensaure In dieser Studie sind die Verbindungen Fast Green (FG), basisches Fuchsin (FB) und saures Fuchsin (FA), als korrosionshemmende Verbindungen von Kupfer in Zitronensaurelosung untersucht worden. Es sind funf verschiedene Konzentrationen von Zitronensaure untersucht worden, von 0,001 bis 1,0 M, zwolf Konzentrationen von FG, FB und FA von 1 × 10−5 bis 1 × 10−1 M und bei vier verschiedenen Temperaturen, von 298 bis 328 K. Die gravimetrische Methode wurde angewandt, um die Hemmungswirkung der Verbindungen FG, FB und FA zu studieren. Die Reihenfolge der Inhibitoren bezuglich ihrer Effizienz hat sich als FB > FA > FG herausgestellt. Anhand der Anwendung von ublichen Isothermen ist die beste Anpassung der Untersuchugswerte mit der Gleichung nach Frumkin erreicht worden. Weiterhin ist ein thermodynamisches/kinetisches Modell zur Anpassung der Ergebnisse benutzt worden. Mit dem Ziel, die Ausrichtung des Inhibitors innerhalb des Adsorptionsprozesses festzustellen, sind molekulare Modelle zur Bestimmung des Bereiches der organischen Verbindungen angewandt worden.

Influence of reinforcement grade and matrix composition on corrosion resistance of cast aluminium matrix composites (A3xx.x/SiCp) in a humid environment

Abstract: A study of the influence of the silicon carbide (SiCp) proportion and the matrix concentration of four aluminium metal matrix composites (A360/SiC/10p, A360/SiC/20p, A380/SiC/10p, A380/SiC/20p) exposed to high relative humid environment was carried out under simulation in a climatic chamber. The matrix of A360/SiC/xxp composites was virtually free of copper while the A380/SiC/xxp matrix contained 3.13-3.45wt% Cu and 1.39-1.44wt% Ni. The kinetics of the corrosion process was studied on the basis of gravimetric tests. The nature of corrosion products was analysed by Scanning Electron Microscopy (SEM) and Low Angle X-Ray Diffraction (XRD) before and after accelerated testing to determine the influence of microstructural changes on corrosion behaviour during exposure to the corrosive environment. The corrosion damage to Al/SiCp composites was low at 80% Relative Humidity (RH) and increased with temperature, SiCp proportion, relative humidity and Cu matrix concentration. The main attack nucleation sites were the interface region between the matrix and the reinforcement particles. The corrosion process was influenced more by the concentration of alloy elements in the matrix than by the proportion of SiCp reinforcement. Einfluss der Verstarkungsgute und der Zusammensetzung des Grundwerkstoffs auf den Korrosionswiderstand von Aluminiummatrixverbundgusswerkstoffen (A3xx.x/SiCp) in einer feuchten Umgebung Eine Studie zum Einfluss des Siliziumkarbidanteils (SiCp) und der Zusammensetzung des Grundwerkstoffs von vier Aluminiummatrixverbundwerkstoffen (A360/SiC/10p, A360/SiC/20p, A380/SiC/10p, A380/SiC/20p), die in Umgebungen mit relativ hoher Feuchtigkeit ausgelagert waren, wurde unter simulierten Bedingungen in einer Klimakammer durchgefuhrt. Die Matrix des A360/SiC/xxp-Verbundwerkstoffs war praktisch Kupfer-frei wahrend die A380/SiC/xxp Matrix 3,13–3,45 Gew.-% Cu und 1,39–1,44 Gew.-% Ni enthielt. Die Kinetik des Korrosionsprozesses wurde auf der Basis von gravimetrischen Messungen studiert. Die Beschaffenheit der Korrosionsprodukte wurde mittelt REM-Untersuchungen und Kleinwinkelrontgendiffraktometrie (XRD) vor und nach der beschleunigten Prufung analysiert, um den Einfluss der Gefugeveranderungen auf das Korrosionsverhalten wahrend der Auslagerung in der korrosiven Umgebung zu bestimmen. Der Korrosionsschaden an den Al/SiCp-Verbundwerkstoffen war niedrig bei 80% relativer Feuchte und nahm mit der Temperatur, dem SiCp-Anteil, der relativen Feuchte und der Kupferkonzentration der Matrix zu. Die Hauptkeimbildungsbereiche fur den Angriff befanden sich an der Grenzflache zwischen der Matrix und den Verstarkungspartikeln. Der Korrosionsprozess wurde mehr durch die Konzentration der Legierungselemente in der Matrix als durch den Anteil der SiCp-Verstarkung beeinflusst.

In vitro assessment and monitoring of the implant titanium materials – physiological environment interactions

Abstract: Long-term monitoring (for 8000 exposure hours) of titanium and its implant alloys (Ti-5Al-4V, Ti-6Al-4Fe) interactions with Ringer's solutions of different pH-values (2.5, 4.35, 6.98), simulating various conditions that can appear at the contact between implant and tissues was carried out in this paper. All data were statistics treated using Medcalc program. In vitro electrochemical behaviour of titanium and its alloys reveals their self-passivation in Ringer's solutions. Monitoring of the open circuit potentials with time and pH have shown that the passive films on the implant materials studied were very stable for all tested periods. Interactions due to the non-uniformity of the physiological electrolyte pH can not produce any form of local corrosion. The tested materials present low corrosion rates which attest their very good stability for 8000 exposure hours in simulated biological environment. Surface topography characterisation using atomic force microscopy (AFM) data, correlated with the electrochemical parameters, were arguments for the stability of the samples in studied bioliquids. In vitro Beurteilung und Kontrolle von Titanimplantatwerkstoffen – Wechselwirkungen mit der physiologischen Umgebung In der vorliegenden Arbeit wurden Langzeitversuche (fur 8000 Stunden Auslagerung) zur Wechselwirkung von Titan und seinen Implantatlegierungen (Ti5Al-4V9, Ti-6Al-4Fe) mit Ringerlosungen unterschiedlicher pH-Werte (2,5, 4,35, 6,98), die verschiedene Bedingungen beim Kontakt zwischen Implantat und Gewebe simulieren, durchgefuhrt. Alle Daten wurden statistisch mit dem Medcalc-Programm behandelt. Das elektrochemische Verhalten von Titan und seinen Legierungen in vitro zeigte eine Selbstpassivierung in den Ringerlosungen. Die Kontrolle des Potentials bei offenem Stromkreis in Abhangigkeit von der Zeit und dem pH-Wert ergab, dass die Passivfilme an den untersuchten Werkstoffen wahrend der gesamten Versuchszeit sehr stabil waren. Wechselwirkungen infolge Ungleichmasigkeiten des pH-Wertes des physiologischen Elektrolyten konnten keine Form von lokaler Korrosion hervorrufen. Die untersuchten Werkstoffe wiesen geringe Korrosionsgeschwindigkeiten auf, was ihre sehr gute Stabilitat uber 8000 Stunden in der simulierten biologischen Umgebung belegt. Die oberflachentopographische Charakterisierung mittels Atomkraftmikroskopie, korreliert mit den elektrochemischen Parametern, bestatigte die Stabilitat der Proben in den untersuchten Bioflussigkeiten.

Microbiologically influenced corrosion of stainless steels – What is required for pitting?

Abstract: Pitting of stainless steels in environments normally regarded as completely harmless is often attributed to microbial activity. In this paper, attention is drawn on one hand to the basic requirements for pitting of stainless steels to be possible, and on the other hand to various ways how microbial activity could contribute to a fulfilment of these requirements. For pit growth to be possible, three basic requirements must be fulfilled: 1) the environment must contain anions that can form an aggressive solution into the pit, 2) there must be a potential difference between the interior of the pit and the open surface outside the pit, 3) the temperature must exceed a critical value. The main factors that normally influence the possibility of pitting are the chloride content and the oxidising power of the environment, presence of anions other than chloride, temperature, possible presence of deposits on the steel surface, and the composition of the steel. Anions other than chloride in the bulk solution, including sulphate, usually have an inhibiting effect. Thiosulphate, however, is known to promote pitting under certain conditions. The possible ways of microbial activity to enhance pitting could include deposit formation leading to crevice type of attack, local modification of the composition of the environment to a more concentrated one, raising the electrode potential of the steel surface (“ennoblement”), or formation of reaction products that permit active dissolution inside a pit at lower potentials. Special attention is drawn to the possible action of thiosulphate by enhancing the anodic reaction at low potentials of the dissolving surface inside the pits.

Electrochemical behaviour of an archaeological bronze alloy in various aqueous media: New method for understanding artifacts preservation

Abstract: The aim of this work is to investigate the electrochemical behaviour of an archaeological bronze in several aqueous electrolytes (Na2SO4, NaCl, KOH, NaHCO3 and Na3PO4) at 0.01 M. The anodic polarization revealed the dissolution of the material independently from the corrosive medium, but the damaging action is stronger for sulfate and chloride where the pH was below 7. Electrochemical impedance spectroscopy permitted to establish a damage ranking based on the pH of the electrolytes: SO42– > Cl3– ≫ OH– > HCO3– > PO43–. Phosphate was tested successfully as inhibitor for archaeological bronzes against the corrosive action of sulfate and chloride. Elektrochemisches Verhalten eines archaologischen Bronzelegierung in verschiedenen wassrigen Medien: Eine Methode zum Verstandnis der Erhaltung von Kunstwerken Das Ziel dieser Arbeit ist die Untersuchung des elektrochemischen Verhaltens einer archaologischen Bronze in verschiedenen wassrigen Elektrolyten (Na2SO4, NaCl, KOH, NaHCO3 und Na3PO4) bei 0,01 M. Die anodische Polarisation zeigte, dass die Auflosung des Materials unabhangig vom korrosiven Medium ist, dass aber die schadigende Wirkung fur Sulfat und Chlorid, wo der pH-Wert unterhalb 7 lag, starker ist. Die elektrochemische Impedanzspektroskopie erlaubt es eine Reihenfolge hinsichtlich der Starke der Schadigung zu erstellen, die auf dem pH-Wert der Elektrolyten basiert: SO42–> Cl3– ≫ OH– > HCO3– > PO43–. Phosphat wurde erfolgreich als Inhibitor fur archaologische Bronzen gegenuber der korrosiven Wirkung von Sulfat und Chlorid getestet.

Reinforced concrete structures – shall concrete remain the dominating means of corrosion prevention?

Abstract: The acknowledged serious deterioration of reinforced concrete structures due to chloride induced corrosion has been the main fuel for research and development of very dense and impermeable concrete, so-called high performance concrete (HPC). This development has dominated concrete research up through the 80'ies and 90'ies. The results have technically been successful. However, the practical use of such concretes on site have often posed serious difficulties, resulting in at times very low performance concrete structures although HPC was specified. The discrepancy between concrete quality reached in the laboratory, what is being specified in the design and what can realistically be achieved on site is seldom in balance. Alternative means of more or less reliable means of corrosion prevention, often based on organic materials, have during recent years been developed to protect our inorganic concrete and reinforcement. However, a highly reliable means of corrosion prevention has been the introduction of stainless steel reinforcement, which is available with dimensions and strengths directly interchangeable with ordinary carbon steel reinforcement. It has been proven that stainless steel and carbon steel can be in metallic contact when cast into concrete, without causing galvanic corrosion. This seems, for the present, to be like an unexpectedly simple and highly reliable solution to the corrosion problems. As exemplified, this technology is rapidly gaining momentum in highly corrosive environments – and concretes being much more robust to execution can now take over from HPC. Stahlbetonbauwerke – Soll der Beton das dominierende Mittel des Korrosionsschutzes bleiben? Die nur allzu bekannte, tragische Schadigung von Stahlbetonbauteilen aufgrund chloridinduzierter Bewehrungskorrosion war der Hauptbrennstoff, der zur Erforschung und Entwicklung von sehr dichtem und undurchlassigem Beton fuhrte – dem sogenannten Hochfesten Beton. Dieser Beton hat wahrend der 80iger und 90iger Jahre die Betonforschung eindeutig dominiert. Die Ergebnisse sind technisch gesehen ein klarer Erfolg. Der praktische Einsatz solcher Betone war jedoch sehr oft auf der Baustelle mit grosen Schwierigkeiten verbunden. Dies endete nicht selten in minderwertigen Betonbauten, obwohl ein hochfester Beton ausgeschrieben war. Diese Diskrepanz zwischen der Qualitat, die im Betonlabor erreicht wird, und der, die ausgeschrieben wird und der auf der Baustelle letzten Endes vorhandenen, ist nur sehr selten ausgeglichen. Deshalb sind mehr oder weniger zuverlassige Alternativen, die eine Bewehrungskorrosion ausschliesen sollen, wahrend der letzten Jahre entwickelt worden, die oft auf organischen Materialien aufbauen, um den anorganischen Beton und die Bewehrung zu schutzen. Daruber hinaus stellt die Anwendung von nichtrostendem Stahl eine zuverlassige Korrosionsschutzmasnahme dar. Nichtrostender Stahl ist in den gleichen Abmessungen und Festigkeiten lieferbar wie normaler Betonstahl und kann diesen somit unmittelbar ersetzen. Es hat sich gezeigt, dass nichtrostender Stahl und normaler Betonstahl metallisch miteinander in Kontakt stehen konnen, ohne dadurch eine galvanische Korrosion auszulosen, sofern beide Bewehrungen im Beton eingebettet sind. Vorlaufig scheint dies eine unerwartete, verbluffend einfache und zudem sehr zuverlassige Losung des Korrosionsproblems zu sein. Wie die folgenden Beispiele zeigen, gewinnt diese Technologie zunehmend an Bedeutung. Dies gilt insbesondere im Falle aggressiver Umweltbedingungen – und damit konnen Normalbetone, die sehr viel robuster gegenuber der Verarbeitung auf der Baustelle ist, hochfesten Beton ersetzen.

Repassivation of steel in carbonated concrete induced by cathodic protection

Abstract: The paper discusses the peculiarities of cathodic protection applied to steel in carbonated concrete, which are strictly connected to the production of alkalinity at the steel surface. Results of a research on the application of cathodic protection to specimens with steel bars in carbonated concrete are discussed. A thin layer of concrete was realkalized within a period of 4-5 months by applying a current density of 10 mA/m 2 and steel could repassivate even in the presence of small contents of chlorides. A lower current density of 5 mA/m 2 could only maintain steel passive when the concrete in the vicinity of the steel had been previously realkalized through the application of a start-up current density of 70 mA/m 2 for one month. Protection mechanisms are investigated and design of cathodic protection of steel in carbonated concrete is outlined. The possibility of obtaining protection on deeper rebars is also considered.

Metal dusting of ferritic Fe–Al–M–C (M=Ti, V, Nb, Ta) alloys in CO–H2–H2O gas mixtures at 650 °C

Abstract: Iron aluminides are known for their resistance to high temperature oxidation and sulphidation. Only little information is available about carburisation and metal dusting of Fe-Al alloys. Metal dusting experiments with Fe-15Al and Fe-15Al-2M-1C alloys (in at.%) with M = Ti, V, Nb, or Ta were conducted at 650 C in CO-H 2 -H 2 O gas mixtures with the carbon activity a c = 28. The kinetics of the carbon transfer was measured using thermogravimetric analysis (TGA). It is shown that the mass gain kinetics decreases by adding the alloying elements Nb, Ta, V, or Ti with C. Alloying with titanium and carbon leads to the most significant decreasing effect. The metallographic cross section observation showed a general metal wastage for Fe-15Al, but local pitting for the Fe-15Al-2Nb-1C and Fe-15Al-2Ta-1C alloys. For the Fe-15Al-2V-1C and Fe-15Al-2Ti-1C alloys no significant attack was observed. Needle-or plate-like Fe 3 AlC x precipitates were detected in the carburised samples. The existence of this ternary carbide with perovskite structure was predicted by thermodynamic calculations using the software Thermo-Calc. The morphology of graphite on the surface was analysed by scanning electron microscopy (SEM). Mainly fine filaments with iron containing particles were detected. Cementite was detected in the coke layer by X-ray diffraction analysis (XRD).

Combination of thermal activation and addition of H2O2 to improve cerium‐based immersion treatment of alloy AA5083

Abstract: Intensive research has been undertaken in recent years aimed at finding non-contaminating alternatives to surface treatment processes based on the use of chromates. One of the alternatives proposed involves the use of lanthanide salts, and a variety of methods of protection have been described. In this study, the results of the treatment of samples of alloy AA5083 in a solution of Ce(III) at 323 K and incorporating small quantities of oxygenated water are presented. These results indicate that the application of this type of treatment gives a considerable reduction in the time required for this process and high levels of protection. This time reduction is associated with a combined effect caused, in part by the presence of oxygenated water, which facilitates the formation of islands of cerium, and in part by thermal activation, which facilitates a more rapid development of the alumina film over the metal matrix. Lastly, the results obtained indicate that these treatments provide increased resistance of the alloy against pitting corrosion. Kombination von thermischer Aktivierung und Zugabe von H2O2 zur Verbesserung der auf Cer-basierten Tauchbehandlung der Legierung AA5083 In den letzten Jahren wurde intensive Forschung durchgefuhrt, um geeignete Alternativen fur Oberflachenbehandlungsprozesse, die auf dem Einsatz auf Chromat basieren, zu finden. Eine der vorgeschlagenen Alternativen beinhaltet den Einsatz von Lanthanidsalzen. Hierzu sind eine Reihe von Schutzmethoden beschrieben worden. In der vorliegenden Arbeit werden die Ergebnisse der Behandlung von Proben der Legierung AA5083 in einer Ce(III)-Losung und Zugabe geringer Mengen an H2O2 bei 323 K beschrieben. Die Ergebnisse zeigen, dass die Anwendung dieser Art der Behandlung zu einer betrachtlichen Reduzierung der erforderlichen Zeit fur diesen Prozess fuhrt und hohe Schutzeffekte liefert. Diese Zeitreduzierung ist verbunden mit einem kombinierten Effekt, der zum Teil durch die Anwesenheit des H2O2 verursacht ist, was die Bildung von Cerinseln erleichtert, um zum Teil durch thermische Aktivierung, was eine schnellere Entwicklung des Aluminiumoxidfilms uber der Metallmatrix erleichtert. Auserdem zeigen die erzielten Ergebnisse, dass diese Behandlungen einen erhohten Widerstand der Legierung gegenuber Lochkorrosion liefern.

Microprocesses of metal dusting on iron–nickel alloys and their dependence on the alloy composition

Abstract: Metal dusting of iron proceeds via the formation and disintegration of the metastable carbide Fe 3 C, and the resulting fine Fe particles in the coke further catalyse carbon deposition. By contrast, nickel disintegrates directly, and larger grains are released. As revealed by TEM and AEM techniques, in both cases the disintegration proceeds by inward growth of thin graphite filaments, the atomic basal planes of which being oriented perpendicular to the surface thus effecting a high reactivity at the growth front. Consequently, successive alloying of iron with nickel should lead to a change over from one disintegration mechanism to the other, and, in fact, we could evidence that the carbide formation takes place only up to a nickel content of about 5.wt.%. Already at a Ni concentration of 10 wt. % a direct disintegration of the metal proceeds, as it is typical for pure nickel. Furthermore, in all investigated Ni-Fe alloys a surface-near enrichment of Ni was observed which indicates a selective corrosion of Fe, decreasing with increasing Ni content of the basic alloy.

Biofouling on austenitic stainless steels in spent nuclear fuel pools

Abstract: The objective of this study was to investigate the biofilm formation on three different types of austenitic stainless steel (UNS S30400, S30466 and S31600) submerged in a spent nuclear fuel pool. The presence of microorganisms in coupons was characterised using standard culture microbiological methods, microscopic techniques (epifluorescence microscopy and scanning electron microscopy), and molecular biology techniques (denaturing gradient gel electrophoresis and sequencing fragments of 16S rDNA). The microscopy techniques showed signs of colonisation of stainless steels in spite of these extreme conditions. Based on sequencing of cultured microorganisms, different bacteria belonging to a, β, γ-Proteobacteria, Bacilli, and Actinobacteria classes have been identified. The biofilm radioactivity was measured using gamma-ray spectrometry and, according to the data gathered, the radionuclides present in the water pool were entrapped in the biofilm increasing the amount of radiation at the surface of the different materials.