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The role of iron-reducing bacteria (IRB) in biocorrosion is under discussion. According to some reports, IRB are able to induce protection of carbon steel while others suggest an important enhancement of corrosion through the reduction and removal of passive films of ferric compounds on the metal surface. In this work, we review recent knowledge concerning microbial respiration, the ecology of IRB containing biofilms and the corrosive or protective effect of such biofilms on metal surfaces.

Several methods for material characterization and surface analysis such as scanning electron microscopy (SEM), energy dispersion X-ray analysis (EDX), environmental scanning electron microscopy (ESEM), petrographic analyses, Mossbauer spectroscopy (MS), conventional X-ray diffraction (XRD), grazing incidence diffraction (GID), Raman spectroscopy (RS), other spectroscopic techniques like X-ray photoelectron spectroscopy (XPS), reflection electron energy-loss spectroscopy (REELS) and advanced combined applications of synchrotron based μ-X-ray diffraction/μ-X-ray fluorescence (SR-μXRD/μXRF) can be used for assessing weathering and biodeterioration effects on materials (such as stone buildings, metallic artefacts, pigments, mixtures, and processes) of cultural property. Molecular biology techniques to identify the microbial components of biofilms are also described. Different examples of the use of these methods in the field of cultural property preservation are presented.

Microorganisms are able to drastically change the electrochemical conditions at the metal/solution interface by biofilm formation. These changes can range from the induction or acceleration of corrosion to corrosion inhibition. Any inhibitory action developed by bacteria may be accomplished within the varied and complex biofilm/corrosion products interactions occurring on a biofouled metal surface. Biocorrosion and its counter process, microbial inhibition of corrosion, are rarely linked to a single mechanism or to a single species of microorganisms. Microorganisms can induce corrosion inhibition according to two general mechanisms or their combination: i) neutralizing the action of corrosive substances present in the environment; ii) forming protective films or stabilizing pre-existing protective films on a metal. Different practical cases illustrating these mechanisms are presented in this overview. It must be stressed that some times the inhibitory action of bacteria can be reversed to a corrosive action in bacterial consortia located within biofilm thickness.

Several methods for material characterization and surface analysis — such as scanning electron microscopy (SEM), environmental scanning electron microscopy (ESEM), atomic force microscopy (AFM), confocal laser microscopy (CLM), energy dispersion X-ray (EDX) analysis, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), petrographic analyses, Mossbauer spectroscopy (MS), and synchrotron X-ray diffraction (SR-XRD) — can be used for assessing weathering and biodeterioration effects on stone monuments and buildings of the cultural heritage. Novel DNA-based molecular biology techniques to identify the microbial components of damaging biofilms are also described. This article presents the pros and cons of these methods illustrated in some cases with studies made on the Ibero American cultural heritage.

Comparative assessment of atmospheric and microbiological deterioration of constructional material of a church, which is part of the Colombian cultural heritage was made using different microbiological and surface analytical techniques complemented by electron microscopy. The main constructional material of the church of Veracruz in the urban area of the city of Medellin is peridotite, an ultramafic igneous rock containing >90% of iron and magnesium minerals such as olivine and pyroxene. Assessment showed that the atmospheric characteristics in the city of Medellin are only slightly aggressive, suggesting that weathering would not be the main cause of decay of the structural material. The main microorganisms isolated from the facade of the church were heterotrophic bacteria and fungi, and phototrophic microalgae and cyanobacteria. Lichens and mosses were also found colonizing the rock. Experimental evidence suggests that deterioration of the peridotite is mainly due to acidifying bacteria and other microbial contaminants and that atmospheric factors would only play a secondary role in the decay.

The three important factors influencing the deterioration of monuments and buildings belonging to the cultural heritage are: (a) biodeterioration processes, (b) atmospheric deterioration or weathering of the materials exposed to open air, and (c) natural and anthropogenic pollution. Thus, the environment plays a decisive role in the type and extent of deterioration processes experienced by the cultural property. In the literature on atmospheric corrosion or weathering of structural materials of cultural heritage there is a lack of understanding of the relevance of biodeterioration processes. Moreover, the close relationship between the environment and the microbial communities colonizing monuments and buildings is generally ignored. With the aim of clarifying this relationship a brief overview of several cases of biodeterioration in four sites of Latin American cultural heritage is presented here. An analysis of the structural material composition and its physicochemical characteristics was made in each case by using surface analysis techniques complemented by electron microscopy. Microbiological techniques for the isolation and culture of microbial contaminants were also used, and the information was correlated with experimental data on the concentration of atmospheric pollutants in each particular case. A synergistic relationship between biological and atmospheric effects on the deterioration of structural materials was observed, although in marine and in industrial/urban atmospheres the weathering effects were predominant.

Biocorrosion and biofouling processes are mediated by microorganisms adhered to the metal surfaces or embedded in a gelatinous matrix called biofilm. Biofilms affect the interaction between metals and the environment not only in deleterious processes like corrosion but also in several biological processes applied to materials recovery and handling. The growth of the microorganisms capable to induce biocorrosion is conditioned by favorable environmental conditions. However, the chemical agents generally used to prevent or protect metallic structures from biocorrosion are highly toxic and after use can have a negative impact on the environment. Four different approaches developed in our laboratory to prevent and control biocorrosion but minimizing the environmental impact, are successively presented in this paper: a) the use of ozone as an environmentally friend biocide for cooling water systems; b) the assay of the effectiveness of natural biocides on planktonic and sessile bacteria; c) the potential use of film forming corrosion inhibitors; d) the use of innovative preventing substances., Los procesos de biocorrosión y biofouling están mediados por microorganismos que adhieren a las superficies metálicas embebidos en una matriz gelatinosa llamada biofilm. Los biofilms afectan a la interacción entre metales y el medio ambiente, no solo a través de procesos deletéreos tales como la corrosión sino, también, en el manipuleo de diversos materiales. El crecimiento de los microorganismos capaces de inducir biocorrosión esta condicionado por un medio ambiente favorable. Sin embargo, generalmente, los agentes químicos usados para prevenir o proteger las estructuras metálicas de la biocorrosión son altamente tóxicos y su uso puede tener un impacto negativo para el ambiente. En este trabajo se presentan cuatro vías diferentes, desarrolladas en nuestro laboratorio, para prevenir y controlar la biocorrosión minimizando el impacto ambiental: a) uso del ozono en sistemas de enfriamiento de agua; b) ensayos de efectividad de biocidas naturales sobre bacterias sésiles y planctónicas; c) uso de inhibidores de corrosión formadores de film; d) uso de nuevas sustancias preventivas., Facultad de Ciencias Exactas

Microbial colonization of metals and alloys of industrial usage takes place through the formation of biofilms made of bacteria, extracellular polymeric substances (EPS) and mainly water. These biological deposits can drastically modify the corrosion behavior of structural metals and alloys enhancing localized alterations in the type and concentrations of ions, pH, and oxygen levels. However, biofilms also facilitate the formation of diffusional barriers to the exchange of chemical species from and towards the metal/solution interface. Problems due to biocorrosion and biofouling of industrial systems range from heavy microbiological contamination with consequent energy and efficiency losses to structural failures owing to corrosion. The use of appropriate monitoring strategies complemented with field and laboratory microbiological techniques is necessary to reach a proper understanding of the effects derived from microbiological activity and the role of biofilms in the corrosion reaction to later implement effective control and preventive countermeasures. It must be emphasized that this assessment should be made for each industrial system, considering its previous history, present operational conditions, physicochemical composition of the intake water and the number and identity of microbial contaminants. Cleaning procedures, most relevant biocides and other methods for prevention and control of biocorrosion like coatings, and cathodic protection are successively described. Updated information about monitoring strategies is also included in the final part of the paper.

The effect of dissolved ozone on the electrochemical behaviour of heat exchanger structural materials (carbon steel, stainless steel, copper, 70:30 copper–nickel, aluminium brass and titanium grade 1) was studied to evaluate the possibility of using ozone as sole biocide in cooling water treatment. With this purpose, voltammetric and open circuit potential (OCP) against time measurements at different ozone concentrations between 0.1 and 1.2 ppm were made. Results show different electrochemical responses according to the metal characteristics and the solution composition. First, the passivity of titanium and stainless steel was not affected by ozone. A linear OCP against log time relationship was found for titanium, suggesting the growth of a barrier film in both O2 and O2/O3 solutions. Mild steel does not passivate in synthetic cooling water either with O2 or O2/O3 in the solution. In the presence of ozone the breakdown of passivity is facilitated and makes the repassivation difficult. Ozone enhances the dissolution of Cu2O and the formation of Cu(II) species leading to less protective films. Both processes are strongly influenced by the pH. Finally, the dissolution of aluminium brass is higher than that of copper or copper–nickel.

Many of the monuments of the Mayan civilization are suffering deterioration caused by environmental factors (high temperatures and relative humidities), increasing contamination from natural and anthropogenic sources, and by the action of micro- and macro-biological communities. Archaeological sites and historical monuments in the Mayan area were constructed with different limestones which offer different resistances to degradation by the various types of contamination. Two different sampling sites were chosen at the archaeological site of Uxmal in the Yucatan Peninsula, Mexico. Heterotrophic bacteria, cyanobacteria and different fungi were isolated and classified taxonomically. The other archaeological site chosen for this study was the fortress of Tulum, located at the side of the Caribbean Sea and exposed to chloride of marine spray and sand erosion. In this case, heterotrophic aerobic and anaerobic bacteria, cyanobacteria and fungi were isolated from the four sampling areas selected. In both archaeological sites crust deposits were observed by using light microscopy, SEM and ESEM. Surface analyses were made by means of EDAX and electron microprobe. Possible mechanisms of stone decay, based on the type of microorganisms isolated, the physico-chemical characteristics of the constructional materials and environmental factors are discussed.

Cooling water treatment requires effective, environmentally-safe biocides compatible with system operation. The unique combination of high biocidal activity during use with no toxic discharge, could render dissolved ozone a safe biocide for cooling water treatment. Planktonic and sessile cells of Pseudomonas fluorescens (a frequent microbial contaminant of industrial systems) were used in this work to assess the biocidal effectiveness of ozone. Dissolved ozone showed to be effective at concentrations between 0.1 and 0.3 ppm, to eliminate completely the levels of planktonic cells used in this paper (10 7 –10 8 cell/ml) within a range of contact times between 10 and 30 min. However, ozone at 0.15 ppm was only able to diminish sessile cell population by two or three orders of magnitude. This minor biocidal effectiveness of ozone against bacterial biofilms is discussed in this paper, taking into account recent concepts on structure and dynamics of biofilms. Different metallic substrata were assayed to verify if there was any effect of metal nature on the biocidal action. Open circuit potentials vs. time experiments and potentiodynamic polarization curves were made for assessing the effect of dissolved ozone on the corrosion behavior of the metals tested.

The efficacy of ozone biocidal action against planktonic and sessile Pseudomonas fluorescens was studied using different contact times and biocide concentrations. Bacterial biofilms were formed on different metallic substrata frequently used as structural materials in industrial installations. The results showed that the biocidal action of ozone against planktonic cells can be represented by a dose‐response relationship in which the contact time factor was more significant than the concentration. The efficacy of ozone against sessile bacteria was lower than that found for planktonic cells. Turbulent flow significantly improved the inactivation rate, suggesting that a diffusional impediment was involved in the mass transfer process. However, diffusional resistance alone cannot explain the observed decrease in biocidal efficacy. Ozone penetration into the biofilm appeared to be a function of simultaneous diffusion and a reaction of the biocide in the biofilm matrix; the latter may be the result of microscal...

An immunonoglobulin solution containing IgA, IgG and IgM was used to prevent theformation of Pseudomonas fluorescens ( P. fluorescens ) biofilms on carbonsteel and two different types of stainless steel (SS) of industrial grade. A marked inhibition ofbacterial adhesion was found when an immunoglobulin film was formed on the metal surface priorto the immersion of the sample in bacterial cultures. Microscopic techniques like scanning electronmicroscopy (SEM) and environmental scanning electron microscopy (ESEM) were used forassessing adhesion inhibition. The electrochemical behavior of the steels was evaluated by meansof potentiodynamic runs, corrosion potential vs. time evolution and linear polarization resistancetechniques applied in the presence and the absence of the immunoglobulins.

The influence of mixed anaerobic bacterial biofilms comprising Desulfovibrio vulgaris and Desulfovibrio desulfuricans and pure Vibrio alginolytics aerobic biofilms on cathodically protected AISI 304L stainless steel (SS) coupons was studied by means of epifluorescence microscopy, scanning electron microscopy (SEM) and electrochemical measurements. SS samples were protected by applying —0.7 and —0.9 V vs saturated calomel electrode (SCE) potential levels during different exposure periods between 3 h and 14 d. Bacterial settlement and growth were reduced by cathodic protection in the initial stages of biofilm formation. The number of attached bacteria did not decrease when cathodic protection was applied on SS coupons after a stationary biofilm was formed. Localized attack by pitting was observed under both conditions (with and without protection) in the presence of the anaerobic bacteria. This could not be avoided by applying cathodic protection. Bacterial biofilms modified the morphology of calcareous dep...

Biofouling and biocorrosion lead to an important modification of the metal/ solution interface inducing changes in the type and concentration of ions, pH values, oxygen levels, flow velocity, etc. Metal dissolution in seawater is mainly conditioned by two different processes: (a) biofouling settlement and (b) corrosion products formation. Corrosion-resistant alloys such as stainless steel present an ideal substratum for microbial colonization, rather similar to inert non-metallic surfaces, due to the lack of corrosion products. Stainless steels are sensitive to pitting and other types of localized corrosion in chloride-containing media such as seawater. Biofilms and bacterial metabolism may accelerate the initiation of crevice attack by depletion of oxygen in the crevice solution due to microbial respiration. Bacterial colonization occurs within a period of 24–72 h on stainless steel samples exposed to natural seawater and, depending on environmental conditions, a copious and patchy biofilm is generally formed. Different interpretations of biofilms' effects on corrosion are critically discussed. A practical case, involving polluted harbour seawater, is reported to illustrate biofilm and corrosion interactions on stainless steel samples.

This communication provides an overview of the literature on the biocorrosion of steel in marine media, influenced by the presence of sulphate-reducing bacteria (SRB). Electrochemical aspects, microbial interactions within biofilms, the significance of medium composition and the role of iron sulphides, and hydrogen effects are discussed. A brief description of recent experiments involving the use of electrochemical techniques for corrosion assessment, surface studies employing energy dispersive X-ray analysis (EDAX), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and electron microprobe complemented with electron microscopy observations, as well as the application of novel techniques, such as micro sensors and atomic force microscopy, is given. The growth of SRB in marine environments causes significant modifications of many physicochemical parameters at the steel/seawater interface, including local changes in pH and redox potential values, variations in anion and cation concentrations and alteration of the composition and structure of corrosion products. Complex chemical and biological reactions and equilibria are also markedly altered during bacterial proliferation. These effects, which are absent in abiotic media, often lead to significant changes in the corrosion behaviour of steel. The complicated nature of the local environment at the steel/seawater interface is enhanced in the presence of microorganisms and their extracellular polymeric substances (EPS). As a consequence of biofilm heterogeneity, areas with different ion concentrations are formed and the development of corrosion product layers of dissimilar protective characteristics occurs.

Biofouling and corrosion products on 70/30 cupronickel exposed to polluted seawater were studied by SEM with EDAX analysis. Layers of corrosion products containing dissimilar levels of sulphide, iron, copper and nickel were detected. An outer porous layer covered by a biofilm was present in all samples. Only a few genera of diatoms and protozoa could be found in the biofilm. Biofilm establishment on cupronickel was delayed compared with other more inert materials previously assayed. Electrochemical measurements showed that sulphide ions affect cupronickel passivity, interfering in the formation of the outer passive layers.

The electronic properties of passive films on Fe-Cr alloys were determined by the photoelectrochemical technique. Measurement of the flat band potential for the passive films on the different alloys indicated that the film is doped in- creasingly n-type as the Cr concentration in the base alloy is increased. This doping is due to a Cr oxide with Cr in the 4+ or 6+ valence state. The concentration of this doping species increases as the concentration of Cr in the Fe-Cr alloy is increased. The n-type doping has the effect of de- creasing the number of oxygen vacancies in the Fe-Cr passive film. Since oxygen vacancies are the mobile point defect species in the Fe-Cr passive film, decreasing this species decreases the oxygen vacancy flux and ultimately the passive film growth kinetics. The contribution of film dis- solution and cation transmission through the passive film was also analyzed. Film dissolution was shown to be the major contribution to the passive current density.

Biofouling and microbially influenced corrosion (MIC) are mediated by micro-organisms attached to the metal surface and/or embedded in a gelatinous organic matrix (the biofilm). Microbial adhesion processes lead to an important modification of the metal/solution interface, inducing changes in the type and concentrations of ions, pH, oxygen levels, flow velocity and buffering capacity of the liqud microenvironment or the interface. This feature drastically changes the classical concept of electrochemical interface used in corrosion studies. Metal dissolution at a biofouled surface will be conditioned by two different processes occurring at the metal/solution interface: passivity, directed from the metal to the solution, and biofouling settlement, oriented towards the metal substratum. Electrochemical concepts, adapted to the characteristics of the biologically conditioned interface to interpret the corrosion process, and process analysis to interpret biofouling, are used in a unified approach for understanding biofilms, MIC and their interactions.

SAE 1020 carbon steel samples were tested in laboratory experiments using two different microbial strains isolated from cutting-oil emulsions: Pseudomonas fluorescens and Desulfovibrio vul...

Electrochemical techniques such as: corrosion and critical pitting potential measurements, direct current potentiostatic and potentiodynamic polarization, linear polarization resistance, split-cell current measurements, electrochemical impedance, electrochemical noise, and electrical resistance probes are evaluated for use in investigating microbiologically influenced corrosion. Examples are given to illustrate the capabilities and limitations of each technique.

Type 304 (UNS S30400) stainless steel (SS) specimens with different microstructural characteristics are used to study the influence of heat treatment on microbiologically induced corrosion. The effects of chloride and inorganic and biogenic sulfide are analyzed. Sensitized metal probes were affected by the presence of aggressive anions and pitting potential values were more cathodic than those in the as-received state. Corrosion is enhanced by the synergistic action of biogenic sulfides and chloride anions.

An industrial plant contains several environments where corrosion and fouling processes are potentially troublesome, such as cooling water systems, storage tanks, water and wastewater treatment facilities and piping (Characklis, 1986). Corrosion is one of the undesirable results of fouling, in addition to energy losses owing to increased heat transfer and frictional resistances. A recirculating cooling water system provides a good example of an industrial environment where corrosion and fouling hazard is particularly critical and needs to be kept under strict control.

Stainless steels (SS) are frequently used in a variety of industrial applications, where good corrosion resistance is needed. SS are usually in contact with waters of very dissimilar nature that generally, are favorable environments for microbial growth. Thus, they are susceptible to microbiologically influenced corrosion MIC (Pope et al., 1989).

In previous studies it was observed that endodontic silver cones placed in fine canals became dislodged as a result of corrosion. To investigate the corrosion of high purity silver, potentiostatic and potentiodynamic electrochemical techniques were used. Triangular potential sweeps made in physiological solutions and human plasma showed similar potential-current relationships. However, in human plasma, peak currents were lower and peak potentials were more anodic than those observed in the physiological solutions. The electron microprobe analysis and the EDAX of the film formed in the biological fluids revealed the presence of silver and chloride and a certain amount of carbon. The addition of small quantities of Na 2 S to the physiological solutions favoured metal dissolution and promoted the formation of a mixed film of AgCI and Ag 2 S. According to these results chloride and sulphide anions seem to be particularly aggressive towards the metal surface in implanted silver cones. Precautions to avoid direct contact of the cones with saliva and tissue fluids must be taken. Fractures and discontinuities present in the cement considerably increase the corrosion risks.

The corrision of mild steel in media with and without bacterial cultures was assessed using potentiostatic and potentiodynamic techniques and the production of biofilm on the metal surface was studied by scanning electron microscopy. Metal in a solution consisting of the inorganic components of Postgate's medium C was not passivated, but a passive surface was indiced by the addition of lactate, citrate, or phosphate. The breakdown potential ( E b of the passivated metal was most anodic for phosphate. No significant change in the electrochemical behaviour of the steel was seen when the formulation of Postgate's medium C was completed by the addition of yeast extract, but chloride, added to allow the growth of Vibrio alginolyticus , caused a reduction in the E b value. Vibrio alginolyticus reduced the E b value in Postgate's medium C from −0·37 to −0·43V, indicating its corrosive capacity. This value was reduced still further, to −0·60V, when sulphate-reducing bacteria were also present. Scanning electron microscopy showed the presence of colonies of V. alginolyticus on the metal surface. When cleaned, it was apparent that intense pitting had occurred beneath these colonies. It is suggested that V. alginolyticus may promote chemical or SRB-induced corrosion by removing a passive film from the metal, allowing aggressive species such as sulphides to affect the surface.

Pitting potential was used recently to asses the aggressiveness of the biological species in the microbial corrosion of aluminum alloys in fuel-water systems. This parameter is analyzed he...

The localized corrosion of mild steel in neutral buffered solutions containing sodium sulphide is studied using potentiostatic and potentiodynamic techniques complemented by scanning electron microscopy and energy dispersive X-ray analysis. The breakdown potential depends linearly with the logarithm of the sodium sulphide concentration. At potentials close to − 0.70 V (SCE), the nucleation and growth of a ferrous sulphide layer replacing the initial ferrous hydroxide film occurs prior to pit growth. In the − 0.70 to − 0.60 V range the logarithm of the induction time for pit initiation decreases linearly with the reciprocal of the applied potential. At potentials more positive than − 0.60 V the oxide formation hinders pit growth leading to a partial passivation. The results suggest that two-dimensional salt islands are formed before pitting as it has been postulated for iron in halide-containing solutions.

The electrochemical behaviour of bright polycrystalline gold electrodes was studied under both voltammetric and open-circuit conditions, in the potential range of the thermodynamic stability of bulk water, using x M H3PO4 − M Na3PO4 (0.05 < x < 0.1; 0 < y < 0.05) and x′ M H2SO4 + y′ M K2SO4 (0 < x′ < 0.13; 0 < y′ < 0.13) solutions. The electrooxidation of glucose on gold occurs mainly in the electrical double-layer potential region, but additional anodic contributions are found in the potential range corresponding to the formation of oxygen-gold species. Anodic products, intermediates resulting from the electrooxidation of glucose and anions present in solution influence the electroformation and electroreduction of the oxide layer, causing a redistribution of AuO bond energies. This open-circuit potential decay, measured immediately after the voltammetric electrooxidation, shows that the kinetics of oxide-layer electroreduction changes with the electrolyte composition.

The localized corrosion of mild steel in neutral buffered solutions containing NaF is studied using potentiostatic and potentiodynamic techniques, complemented by scanning electron microscopy. The results obtained are similar to those reported for the pitting of mild steel in the presence of other aggressive anions. The breakdown potential depends linearly on the logarithm of the NaF concentration. The logarithm of the induction time for pit initiation decreases linearly with the reciprocal of the applied potential. At potential values more positive than the breakdown potential, a competitive surface mechanism involving the formation of the passive film and the nucleation and growth of a ferrous salt layer is postulated to explain pitting corrosion. The proposed reaction model reproduces reasonably well the corresponding experimental current transients.

The redox potential, generally employed in microbiological studies, is used here as a practical parameter to assess, according to the redox characteristics of a system, whether corrosion conditions can be reached or not.In fuel/water systems, where the associaiion of different species of bacteria and fungi is usual, the use of this parameter is of special interest to determine the importance of each specie in the corrosion process. The use of the redox potential together with electrochemical parameters such as pitting potential or corrosion potential is also discussed.