Fly ash (FA) was used successfully as a carrier for the corrosion inhibitor molybdate and applied as an extender pigment in an epoxy coating. To enhance interaction, molybdate was attached to FA through intercalation in layered double hydroxide (LDH), facilitated by surface modification of FA. Molybdate was incorporated into LDH either via direct synthesis or ion exchange. Directly synthesized LDH significantly increased molybdate storage in FA. The FA-inhibitor combination was tested in three ways: molybdate release kinetics, corrosion of an ultra-low carbono (ULC) steel in chloride solution, protection of ULC steel conferred by particles embedded in an epoxy coating. Short-term molybdate release was favored by ion exchange, long-term release by deglomeration of LDH. ULC steel corrosion inhibition in 0.1 M NaCl reached 89%. Incorporating the material into epoxy coatings mitigated steel corrosion, validated by electrochemical impedance spectroscopy. This study underscores the efficacy of FA-LDH-molybdate systems in corrosion protection. (FA coating interaction LDH, , (LDH) exchange FAinhibitor ways kinetics ultralow ultra low (ULC solution Shortterm Short term longterm long 01 0 1 0. 89 89% spectroscopy FALDHmolybdate (LDH 8

Abstract Mild steel (MS) corrosion inhibition by Terminalia mantaly (TM), in 1.0 M HCl, was studied using weight loss and linear polarization methods, at different reaction conditions. Gas chromatography-mass spectrometry (GC-MS) was used to determine the possible extract components. Fourier transformed infrared spectroscopy (FTIR) and optical microscopy were used to investigate the interaction of the plant extract phytochemicals with the MS surface. The obtained results revealed that the inhibition efficiency percentage (IE%) increased with a decrease in the TM concentration, and decreased with a rise in temperature (T). The IE% also decreased as the hydrochloric acid (HCl) concentration increased. Inhibition occurred through the TM phyto-molecules adsorption onto the MS surface. The corrosion inhibition kinetics followed a zero order reaction, and it was uni-molecular. The linear polarization showed that TM is a mixed-type inhibitor. Gibb’s free energies values confirmed a spontaneous process, while TM adsorption onto the MS surface was found to obey physisorption, aligning with the Langmuir’s and El-Awady’s adsorption isotherm models.

ABSTRACT Processing crudes with high naphthenic acid content causes corrosion problems on the crude oil distillation units. The total acid number (TAN) is commonly used to evaluate the corrosivity of crude oils; thus for decision-making related to corrosion mitigation and control in refineries. However, the TAN only represents the number of carboxylic groups present in the crude oil and does not consider the structural characteristics of the naphthenic acids, nor their reactivity, which are highly relevant to corrosion. On the other hand, the study of naphthenic acids as fractions with specific structural characteristics should enable the identification of differences in the corrosivity of crude oil with the same naphthenic acid concentration. In this research work, the fractioning of a commercial mixture of naphthenic acids was performed using the ionic strength of their respective salts. The structural characterization of the obtained fractions was conducted using Fourier-transform infrared and mass spectroscopy, gel permeation chromatography, and nuclear magnetic resonance. Furthermore, the corrosion rate of AISI SAE 1005 steel exposed to each fraction of naphthenic acids in the temperature range between 270 and 350 °C was determined. Based on these results, a kinetic model of parallel reactions for predicting the concentration of dissolved iron in crude oil containing a mixture of naphthenic acids is proposed and validated.

RESUMEN El procesamiento de crudos con alto contenido de ácidos nafténicos causa problemas de corrosión en las unidades de detilación. El Número Total Ácido (TAN) es comunmente usado para evaluar la corrosividad de crudos, y por lo tanto es un parametro usado para la toma de decisiones relacionadas con el control de la corrosión de la refinerías. Sin embargo, el TAN solo representa el número de grupos carboxílicos presentes en el crudo y no considera las características estructurales de los ácidos nafténicos ni su reactividad en las reacciones de corrosión. En este trabajo se desarrolló el fraccionamiento de una mezcla comercial de ácidos nafténicos a partir de la solubilidad de sus respectivas sales. Se determinaron parámetros estructurales característicos de los ácidos nafténicos de cada fracción usando Espectroscopia de Infrarrojo, Cromatografía De Permeación en Gel, Resonancia Magnética Nuclear, Espectroscopia de Masas y Análisis Elemental. Se realizó el estudio cinético de la reacción de corrosión de un acero AISI 1005 expuesto a cada fracción de ácidos nafténicos en el rango de temperatura entre 270 y 350°C. Finalmente, se propuso un modelo de reacciones paralelas para la predicción de la concentración de hierro disuelto debido a la reacción de corrosión, a partir de la concentración molar de cada una de las fracciones que conforman la mezcla de ácidos nafténicos.

Austenitic stainless steels processed by rolling are widespread in technological applications, since they have excellent mechanical and corrosion properties. This study investigated the effect of the cooling rate, microstructure and properties of 316L austenitic stainless steel under cold rolled conditions and by rapid solidification. The microstructure of the cold rolling processing steel was composed of austenite and a low percentage of delta ferrite. For the rapid solidification condition, the microstructure evolved from columnar and acicular dendrites to equiaxed dendrites with decreasing cooling rates, without the presence of delta ferrite due to the high cooling rate. Furthermore, thermal analyses in both routes revealed that oxidation kinetics was slower after rapid solidification in synthetic air. The microhardness in the cold rolling condition was lower than in the rapid solidification condition since the microstructure under the solidification condition is more refined. The sample in the rapid solidification condition region RS1 presented the highest corrosion resistance considering the pit potential. The passivation current density in the cold rolled condition was 5.72x10-5A/cm2, while under the rapid solidification condition, regions RS1 and RS2 were 2.24x10-5 A/cm2 and 3.72x10-6 A/cm2, respectively, and region RS3, did not present a passivation region in a broad range of potentials.

Abstract Integrating knowledge is the fundamental task of chemistry education and it is in this context that research in steel corrosion inhibition gives us the opportunity to put it into practice. This allows the integration of knowledge of electrochemical kinetics with organic chemistry and instrumental analytical chemistry via the use of a low-cost open source potentiostat and its use in the study of the anticorrosive properties of 1-phenyl-H-tetrazole-5-thiol. This experience will allow the student to determine the corrosion rate of SAE 1020 carbon steel in aerated simulated seawater, this is a NaCl solution at 3.0% by weight saturated with oxygen O2 in the presence and absence of 1-phenyl-H- Tetrazole-5-thiol in two concentrations in a standard 3-electrode electrochemical cell in a range of -0.2 to -0.7 V vs. ENH.

Resumen Integrar conocimientos es la tarea fundamental de la educación química y es en este contexto en el cual la investigación en inhibición de corrosión de acero nos brinda la oportunidad de llevarlo a la práctica. Esto permite integrar conocimientos de cinética electroquímica con química orgánica y química analítica instrumental vía el uso de un potenciostato de fuente abierta de bajo costo y su utilización en el estudio de las propiedades anticorrosivas del 1-fenil-H-tetrazol-5-tiol. Esta experiencia le permitirá al estudiante determinar la velocidad de corrosión de acero al carbono SAE 1020 en agua de mar simulada aireada, esto es una solución de NaCl al 3,0 % en peso saturada de oxígeno O2 en presencia y ausencia de 1-fenil-H-tetrazol-5-tiol en dos concentraciones en una celda electroquímica estándar de 3 electrodos en un rango entre -0,2 a -0,7 V vs. ENH.

The electro-oxidation of 4-amino-3-methyl-1,2,4-triazole-5-thione (MTSNH) on a bronze substrate in an alkaline methanol solution produces a homogeneous polymer film. The formation kinetics of the film was investigated using cyclic voltammetry, chronoamperommetry and electrochemical impedance spectroscopy. Cyclic voltammograms indicated that the polymer film (pMTSNH) was formed anodically between -350 and 350 mV/SCE. During the second cycle, the oxidation peak of the monomer disappeared, indicating the formation of the insulating film. We have also shown that the monomer oxidation reaction is essentially irreversible and controlled by a diffusion process. The inhibition efficiency of this polymer was determined by potentiodynamic polarization and electrochemical impedance spectroscopy in a 3.5% NaCl solution.

In the present work, the microstructure, electrochemical behavior and localized corrosion of the AA2198-T851 Al-Cu-Li alloy were studied. The microstructure was correlated with corrosion results obtained by immersion, gel visualization and scanning electrochemical microscopy (SECM) tests. Immersion and gel visualization tests showed high kinetics of corrosion attack during the first hours of immersion. SECM analyzes by means of surface generation/tip collection (SG/TC) mode detected hydrogen evolution generated during spontaneous corrosion from severe localized corrosion (SLC) sites on the metal surface. SECM results revealed sites of intense hydrogen evolution after 2 h of immersion and increased amounts of corrosion products after 4 h of immersion. Hydrogen evolution sites detected by SECM were associated with severe localized corrosion (SLC).

ABSTRACT This work studies the high temperature corrosion behavior of new heat-resistant steel with salt coating method of 75%Na2SO4+25%NaCl coating on the steel surface at 700ºC. The chemical composition of corrosion products and surface morphology of the corrosion layer were analyzed using X-ray diffractometer (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and investigate the effect of Cu content on high temperature corrosion behavior of heat resistant steel. The results show that the thermal corrosion kinetics curve of tested steel follows the parabolic law and the surface is composed of Fe2O3 and FeCr2O4. The corrosion layer were divided into two layers, the outer layer was loose and porous while the inner layer was dense and continuous. The structure of the oxide film consists of various protective oxide films; with increasing of Cu content, the high-temperature corrosion resistance of heat-resistant steel was improved and the thickness of the corrosion layer was decreased which led to improving the bonding strength between the inner layer and the matrix. The results of EDS analysis shows that Cu elements can promote the outward diffusion of Cr elements to oxidation of the steel to form a Cr2O3 protective oxide film for preventing the diffusion of chlorine elements, oxygen elements into the interior toward the steel with slow down the process of "activation oxidation", reduce the sensitivity of intergranular corrosion and achieve the function of protecting materials.

The precursor sols of Al2O3 and mixed NbxOy/Al2O3 oxides were synthesized by the sol-gel process using acetylacetone to control the reaction kinetics of the organometallic oxides in the mixture. The layers of the precursor sols of Al2O3 and NbxOy/Al2O3 were deposited on AISI steel 1020 by manual immersion (dip coating). The lyophilized sols were characterized by X-ray diffraction, thermal analysis and scanning electron microscopy with EDXS before the recoating process. The influence of the ceramic coating of corrosive processes of AISI steel 1020 were investigated by electrochemical measurements. The only identified phase was poorly crystallized boehmite with homogeneous mixture of Al, Nb, O and C ions in mixed NbxOy/Al2O3 oxides. The ceramic layers deposited appeared to have physical and chemical homogeneity and the steel samples with these deposits had lower corrosion potential. However, the precursor sol Al2O3 showed better steel corrosion protection with lower current density, and more corrosive potential.

In this series of papers, AC induced corrosion of steel pipe under cathodic protection was investigated. In this Part III, the most realistic model was devised, i.e., the cathodic current was composed of the reductions of dissolved oxygen partly controlled by diffusion and of the water following the Tafel law. The cathodic protection potential necessary to mitigate the corrosion for various AC amplitudes were evaluated. In this modeling approach, no change of soil properties due to AC corrosion is considered. Mean DC values of corrosion potential shift and the corrosion current density in presence of AC signal were calculated in reduced scale making possible field applications by introducing an appropriate set of corrosion kinetics parameter collected without AC signal. In a highly corrosive soil, the reduction of dissolved oxygen is slow compared with that of the water reduction, and then the corrosion behavior becomes similar to the case examined in Part II.

This work ultimately pays careful consideration to a method that respects the environment, and that can be developed across the accumulation of research to reduce the corrosion of metals in sea water. Extracts of Ziziphus lotus (wild jujube) were tested as a corrosion inhibitor of copper in sea water, using polarization methods and weight loss measurements. We also present by SEM the morphology of copper surface analyzed after immersion in inhibited and uninhibited electrolytes. The inhibition efficiency of Ziziphus lotus extracts was calculated and compared. We note good agreement between these methods. The obtained results revealed that the tested inhibitor significantly reduced the kinetics of the corrosion process of copper. Its efficiency increases with the concentration, and attained 93% at 5 g/L. The effect of temperature on the corrosion behavior of copper in natural sea water was also studied in the range of 293 K and 323 K, to determine thermodynamic data of activation.

The superduplex stainless steels (SDSS) are widely used in chemical, oil and gas industries, to pipelines and storage material facilities. In welding process or working in temperature elevated, secondary phases may appear in the form of precipitates, as the sigma phase (σ) which is an intermetallic compound. This compound is harmful to the properties of steel, deteriorating its mechanical properties, such as decreasing corrosion resistance and toughness. In this paper it is analyzed the formation, kinetics and microstructural evolution of sigma phase in SDSS UNS S32750 after isothermal aging at 700ºC, 750ºC and 800ºC. In this work sigma phase kinetics is studied by JMAK theory and by two microstructural path descriptors, SV, interfacial area per unit of volume between sigma phase and austenite, and <λ>, mean chord length of sigma, both in function of the VV, volumetric fraction of sigma, known in the literature as microstructural partial path (MP). The MP formulation is common in recrystallization studies, but so far has not been used in the sigma phase precipitation studies, being applied here for the first time. The results indicated that the sigma phase nucleates by site saturation with anisotropic linear impingement. This means that sigma phase nucleates on edges.

One of the most studied deleterious phases in stainless steels is the sigma phase, due to its high potential to decrease the toughness and corrosion resistance of these steels. Eight samples of as-received cold rolled UNS S32205 duplex stainless steel were submitted to isothermal heat treatments at 850 oC during 10, 15, 30, 60, 120, 180, 240, and 300 minutes in order to study the precipitation kinetics of the sigma and chi deleterious phases. Several complementary microstructural analysis techniques were used to determine the volume fraction of the intermetallic phases, including optical microscopy and scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS). Evaluation was made of the kinetics of isothermal formation of sigma and chi phases in commercial duplex stainless steels (UNS S32205). The results indicated two different mechanisms for sigma phase precipitation: sigma phase formed from the chi phase for shorter isothermal heat treatment times, and sigma phase precipitated at the ferrite-austenite interface for longer isothermal heat treatment times, using a temperature of 850 oC. The phase transformation kinetics determined using the JMA equation indicated that chi phase precipitation caused faster sigma phase formation.

Cefixime was investigated as a corrosion inhibitor for mild steel in an hydrochloric acid solution. The results revealed that the order of reaction is 0.427, with activation energy found to be 41.7 kJ/mol. Cefixime was effective in increasing the inhibition efficiency for all inhibition concentrations. The corrosion rate profile was found to be second- order kinetics with respect to corrosion activity.

This work investigates the influence of deleterious phases precipitation on the corrosion resistance of two wrought superduplex stainless steels UNS S32750 with similar composition, but different grain sizes. Isothermal treatments were carried out to introduce different amounts of deleterious phases, such as chi (χ), sigma (σ) and secondary austenite (γ2). The specimens were tested by double loop electrochemical potentiodynamic reactivation test (DL-EPR). The kinetics of precipitation in the two steels was different due to the difference of the grain sizes. The results show a correlation between the sensitization degrees, measured by DL-EPR, with the amount of deleterious phases precipitated.