Academic literature on the topic 'Mott-Schottky'

The semiconductor properties of passive films formed on AISI 316 stainless steel in sulfuric acid solution were studied by employing Mott-Schottky analysis in conjunction with the point defect model. The donor density of the passive films, which can be estimated by the Mott-Schottky plots, changes depending on the film formation potentials. Based on the Mott-Schottky analysis, an exponential relationship between donor density and the film formation potentials of the passive films was developed. The results showed that the donor densities evaluated from Mott-Schottky plots are in the range 2-3 × 1021 cm−3and decreased with the film formation potential. By assuming that the donors are oxygen ion vacancies and/or cation interstitials, the diffusion coefficient of the donors, (), is calculated to be approximately 3.12 × 10−16 cm2/s.

Mott-Schottky analysis has been carried out to study the semiconducting behavior of Ag2S-AgI material, which is used as membrane material in iodide ion sensors. Polycrystalline Ag2S-AgI materials with mixing ratios 1:1wasprepared by co-precipitation method and Mott-Schottky analysis was carried out. The impedance was recorded using a Solartron 1280 Schlumberger frequency response analyzer at 5 KHz and 10 mV perturbing signal. A straight line with a positive slope is observed between + 0.2 V to -0.2 V (SSE) indicating n-type semiconductor behavior of polycrystalline Ag2S-AgI membrane. The donor concentration ND was calculated from the slope using dielectric constant of Ag2S-AgI. The values obtained are ~ 6 orders of magnitude lower than in metals. This is an important implication for the charge and potential distribution at the semiconductor/electrolyte interface. The Mott Schottky analysis hasshown that the present materials are n-type semiconductors with donor defect concentration of 7.4x1017/cm3. DOI: http://dx.doi.org/10.3126/jncs.v28i0.8113 Journal of Nepal Chemical Society Vol. 28, 2011 Page: 89-93 Uploaded Date: May 24, 2013

A new method was introduced to research the corrosion resistance of enamel coatings which were sintered at different temperatures in this paper. 1 – 4 Scanning electrochemical microscopy (SECM) conjunction with capacitance-potential test and Mott–Schottky analysis technique were used to study the coating failure process and semiconductor conduction behavior of enamel coating in 3.5[Formula: see text]wt.% NaCl solution. The high strength steel (SAPH440) was selected as the metal substrate. The coatings which were sintered at different temperatures on the high strength steel were analyzed and their corrosion behaviors and microstructures were also measured by potentiodynamic polarization curves, Mott–Schottky analysis technique and scanning electrochemical microscopy. 5 – 10 In this paper, five kinds of enamel coatings were prepared on high strength steel. The SECM results show that the Faraday current of the microprobe tip gradually decreases with the soaking time increasing, which indicates that the coatings become failure slowly with the invasion of water and aggressive ions. At the same time, the tip current was homogeneous during the immersion process, which reflected that the surface of the sample remained stable, no obvious bulges appeared. Capacitance–potential test and Mott–Schottky analysis 7 , 8 show that the external ions and water molecules gradually penetrate into the coating; coating showed characteristics of [Formula: see text]-type semiconductor as time increases, the capacitance increases gradually, the space charge layer thickness decreases, slope of Mott–Schottky curve decreased gradually which indicates that the failure of coating in the process of soaking slowly with the charge carrier density increases.

Metal complexes of Schiff bases are considered as promising materialsfor energy storage and photovoltaic devices. In this work, thesemiconducting properties of a polymer film of a nickel salen-type complex(poly-Ni(CH3O-Salen)) were studied by spectrophotometric and electrochemicalimpedance spectroscopy methods. The Mott-Schottky analysis showed that the polymerfilm is a semiconducting material with a fairly narrow band gap, high chargecarrier density and p-type conductivity. Using the method of electrochemicalimpedance spectroscopy, the limiting stage of the oxygenphotoelectroreduction reaction, the process of charge transfer from the filmto molecular oxygen, has been established. Keywords: Schiff bases, Mott-Schottky analysis, photovoltaic devices, semiconductor properties.\

The effect of chloride ions on the passivity of titanium in sulfuric acids was investigated by potentiodynamic and potentiostatic anodizing, Mott-Schottky analysis and the point defect model (PDM). The anodizing results indicated that chloride ions facilitate the anodic passivity of titanium in sulfuric acids. Based on the Mott-Schottky analysis in conjunction with the PDM, it was shown that the donor density decreases exponentially with increasing film formation potential. Also, the results indicated that with the increasing concentration of chloride ions, the donor density decreases, while the diffusivity of the donors increases at the same film formation potential.

The development of efficient non-precious metal electrocatalysts through more economical and safe methods is consistent with the goals of sustainable development and accelerating the achievement of “carbon neutrality” in the 21st century but remains potentially challenging. Mott–Schottky heterojunction interfaces generated from metal/semiconductor have been a hot topic of recent research because of the unique built-in electric field effect which allows the preparation of more superior catalysts for water electrolysis. Herein, a glutinous rice potpourri-like Mott–Schottky two-dimensional (2D) nanosheet (abbreviated as Ni/CeO2 HJ-NSs) electrocatalyst composed of metal nickel (Ni) and cerium oxide (CeO2) hetero-nanoparticles was synthesized by a simple and scalable self-assembly and thermal reduction strategy. The experimental results and mechanistic analysis show that the Mott–Schottky heterojunction interface composed of metallic Ni and n-type semiconductor CeO2 with built-in electric field induces the electron redistribution at the interface to accelerate the dissociation of water and the binding of reaction intermediates, thus achieving lower water dissociation energy and more thermoneutral ΔGH* value to expedite the kinetics of the hydrogen evolution reaction (HER). Thus, the prepared Ni/CeO2 HJ-NSs exhibit excellent HER catalytic performance in 1 M KOH electrolyte with an overpotential of only 72 mV at 10 mA cm−2, as well as a moderate Tafel slope of 65 mV dec−1 and an extraordinary long-term stability over 50 h, laying a solid foundation for further in-depth investigation. The synthesis of splendid electrocatalysts by exploiting the metal/semiconductor interface effect provides an innovative way for the future generation of Mott–Schottky-based heterostructures with three or more heterocompositions with two or more heterojunction interfaces.

A highly active Mott–Schottky nanocatalyst for the efficient dehydrogenation of ammonia-borane was constructed by rationally tuning the Schottky barrier of Co/P_xCN (P-doped g-C₃N₄) via simply varying the doping amount of P atoms.

In this study, the SnO2 nanoparticle powders were compacted into a disk shape form of under a ultrahigh pressure up to 49.6 GPa. Complex impedance analysis of nano-SnO2 thick film/electrode system was studied as a function of applied potential. A calculated Mott– Schottky plot for the film is presented. Both flat-band potential and donor concentration were estimated from the space charge capacitance at a definite frequency. The film can be described as an n-type semiconductor with a high concentration of donors. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/34827

A nickel alloy with high chrome and molybdenum content was found to form a highly resistive and passive oxide layer. The donor density and mobility of ions in the oxide layer has been determined as a function of the electrical potential when alkaline water layers are on the alloy surface in order to account for the relative inertness of the nickel alloy in corrosive environments.

La nature intermittente de l'énergie solaire est souvent résolue par un couplage entre le PV et une batterie. Notre approche plus fondamentale vise à développer des matériaux capables de combiner ces deux fonctions à l'échelle moléculaire. Des nanocristaux de TiO2 de 5 nm ont été synthétisés dans notre groupe, ce qui a permis une réaction quantitative de photorecharge sous illumination standard. Nous présentons ici une étude originale portant sur l'évolution des propriétés optoélectroniques et de la dynamique du transfert de charge dans une électrode de TiO2 à l'aide d'expériences spectroscopiques in operando effectuées pendant le fonctionnement de la batterie. L'augmentation de la valeur de la bande interdite et de l'absorbance a été observée lors de l'insertion du lithium dans TiO2. Un décalage négatif en énergie de la bande de conduction indique un potentiel plus oxydant des trous photogénérés dans le Li0.6TiO2 par rapport au TiO2 initial. En analysant les processus de recombinaison dans Li0.6TiO2, nous avons établi une compétition entre les processus ultra-rapides (gamme ps) de recombinaison directe et de transfert de charge vers Ti3+ dans Li0.6TiO2, ce qui limite potentiellement le rendement de la réaction de photorécharge. Cette étude a été étendue à d'autres matériaux d'insertion généralement utilisés dans les batteries lithium-ion (Li4Ti5O12, LiCoO2, LiFePO4, MoO3, etc.). Les positions de bord de bande, la bande interdite, le type de porteurs de charge et leur concentration ont été mesurées et rassemblées dans une base de données. Basé sur ces résultats, la possibilité de photorécharge induite par la lumière a été évaluée et les premiers résultats discutés
The problem of intermittent nature of solar energy is often addressed by the traditional coupling of the PV and battery units. Our more fundamental approach targets the development of materials able to combine solar energy conversion and storage at the molecular level. The 5 nm anatase TiO2 nanocrystals were synthesized in our group affording a quantitative photorecharge reaction by a sole contribution of illumination. Here, we present a study of the evolution of the optoelectronic properties and dynamics of charge transfer in TiO2 electrode using in situ / in operando experiments performed during the battery functioning (UV-visible, Mott-Schottky, fluorescence spectroscopy). The increase of the bandgap value and the rise of absorbance are observed upon lithium insertion into TiO2. A negative shift of the conduction band indicates a more oxidizing potential of the photogenerated holes in Li0.6TiO2 compared to TiO2. By analysis of the recombination processes in TiO2 upon lithium insertion, we established a competition of the ultra-fast (ps range) processes of direct recombination and charge transfer towards Ti3+ in Li0.6TiO2, potentially limiting the yield of the photorecharge reaction. This study was extended to other insertion materials typically used in lithium-ion batteries (Li4Ti5O12, LiCoO2, LiFePO4, MoO3, etc.). The measured band edge positions, band gap, charge carrier type and concentration were gathered into a database, based on which the fundamental evaluation of the possibility of the light-induced photorecharge was conducted. The first results of the photoelectrochemical study of chosen materials are also discussed

Les couches d’oxyde de titane (TiO2) sont largement utilisées pour la préparation de matériaux auto nettoyants. En effet, ce semi-conducteur présente deux propriétés photo induites : la catalyse et la super hydrophilie. Cette dernière propriété est définie comme la diminution sous exposition UV de l’angle de contact d’une goutte d’eau déposée à la surface du TiO2. Ce travail a fait le lien entre l’apparition de la super hydrophilie photo induite et les propriétés semi conductrices des couches de TiO2. La caractérisation par impédancemétrie de deux couches ayant des propriétés physico chimiques identiques mais l’une étant super hydrophile sous exposition UV et l’autre non, a mis en en évidence la présence d’états de surface (c’est à dire des états d’énergie situés dans le gap) spécifiques aux couches super hydrophiles. Ceux ci sont responsables de l’ancrage du niveau de Fermi suite à l’exposition UV. Une différence de potentiel apparaît alors dans la double couche, et la diminution d’angle de contact observée sous exposition UV peut être modélisée par la théorie de l’électro mouillage. Une contribution de nature électro statique est apportée à l’énergie de surface du fait de l’ancrage du niveau de Fermi dans les états de surface. La nature de ces états de surface n’a pu être déterminée d’un point de vue chimique, mais elle est cohérente avec le mécanisme de la super hydrophilie photo induite impliquant des lacunes d’oxygène photo générés.

The presented diploma thesis deals with the preparation of perovskite single crystals by inverse thermal crystallization and subsequent study of the basic properties of these hybrid organic-inorganic materials that can be used in various optoelectronic (photodetectors, transistors, lasers, LEDs) or photovoltaic applications. Their behavior in the electric field was studied by impedance spectroscopy. Impedance and capacitance-voltage (C-V) characteristics (frequency dependences) were measured in the dark and in the light. From the impedance dependences for measurements at 0 V voltage in the dark, the equivalent circuit was modeled and its parameters and dielectric constant were determined. From the C-V dependence, Mott-Schottky analysis determined the parameters – "flat-band" potential U_"fb" and charge carrier density N_"C-V" , the parameter – the so-called Warburg coefficient was found, which together with the parameter N_"C-V" was used to calculate the diffusion coefficient D.

Ce travail porte sur l'étude du comportement protecteur vis-à-vis de la corrosion de revêtements amorphes base Si élaborés par dépôt chimique en phase vapeur.
Le caractère protecteur de revêtements de type SiOx et SiOxNy a été analysé sur différents types de substrats. La tenue à la corrosion résulte de la faible porosité et de la nature très isolante de ces couches.
La protection fournie par des dépôts SiCx et SiCxNy utilisés comme couche d'accrochage au DLC (“Diamond Like Carbon”) a ensuite été étudiée. L'influence du taux d'incorporation d'azote de films SiCxNy a révélé une corrélation entre la structure chimique, déterminée par XPS, et le caractère semi-conducteur de la couche, établi par Mott-Schottky. La tenue à la corrosion a été directement associée à la densité de porteurs de charge.
L'étude a été complétée par une caractérisation électrochimique et une approche tribocorrosion du caractère protecteur fourni par des revêtements duplex SiCxNy / DLC.

El objetivo de esta tesis es la síntesis de películas delgadas de SnS utilizando técnicas de bajo coste con el fin de fabricar células solares. Nuestra contribución radica en estudiar nuevos materiales susceptibles de ser utilizados para aplicaciones fotovoltaicas, y que puedan ser preparados con técnicas de bajo coste como la técnica de Pyrolysis de Spray Químico (CSP) y caracterizar algunos materiales elegidos para este fin como el Sulfuro de Estaño (SnS). Se han fabricado células solares a partir de la disposición de capas: Mo / SnS / Tampón / i-ZnO / ZnO: Al / Al / Metal. Las capas de buffer serían: In2S3 o CdS. En la primera etapa hemos procedido a la optimización de los parámetros de deposición de películas delgadas de SnS usando la técnica de la CSP, -Variación de la relación [S] / [Sn]. -Variación de la temperatura del substrato. -Variación de la naturaleza del sustrato utilizando sustrato como vidrio, óxido de estaño de indio (ITO) y vidrio recubierto de molibdeno. Las fuentes de productos químicos y disolventes utilizados son: - Cloruro de dihidrato dihidratado para Tin (Sn), Thiourea, Agua destilada como disolvente de la solución, Ethanol (10% de 50mL) con el fin de reducir la tensión superficial del agua que es 72 Nm-1, para permitir la dispersión de la solución depositada sobre el sustrato fácilmente. En una segunda etapa se han dopado pel¿culas delgadas de SnS con algún elemento en la tabla de Mendeleiev para modificar las propiedades f¿sicas y qu¿micas de las pel¿culas. Los elementos químicos utilizados fueron: Plata, Aluminio y Hierro. Se han utilizado varias técnicas de caracterización: - Difracción de rayos X (XRD) para la estructura cristalina de las películas - Espectroscopía Raman para la calidad de las películas - Microscopía electrónica de barrido (SEM) para morfología superficial - Microscopía de Fuerza Atómica (AFM) para topografía de superficie - Análisis dispersivo de energía de rayos X (EDAX) adjunto a SEM para la composición de la película - Espectrofotometría óptica para la transmisión y la determinación del gap - Método de 4 puntas para medición de resistividad del SnS dopado -Mott-Schottky para determinar el tipo de semiconductor y la concentración de portadores Los principales resultados obtenidos en esta tesis pueden resumirse como sigue: -Las películas delgadas mono-sulfuro (SnS) deben depositarse sobre un sustrato de vidrio con [S] / [Sn] igual a una (1) y la temperatura del sustrato igual a 350 ° C para obtener películas densas, bien cubiertas y homogéneas sin agujeros Y grietas. Distancia entre la boquilla al sustrato 25 cm, volumen pulverizado 5 ml, presión de aire 0,7 bar y velocidad de pulverización de 1,5 ml / min. - Para películas dopadas por Plata y Aluminio, todas las películas son estructura ortorrómbica con (111) como pico principal. La intensidad del pico principal aumenta cuando el porcentaje de elemento dopante aumenta en la solución inicial sin ninguna fase secundaria para el dopaje con Al y con Ag8SnS6 y Ag para el dopaje Ag. - El análisis de SEM y AFM demuestra que el elemento dopante Ag no tiene efecto en la morfología y ni en la topografía mientras que el dopaje Al actúa sobre la morfología superficial produciendo una morfología que presenta muchos agujeros para muestras dopadas de 3% a 7%. - EDAX destaca un aumento de Ag en películas cuando la cantidad de Ag aumenta en la solución con S/ Sn¿0,98 cerca de 1 al 5% de porcentaje de dopado de Ag donde como para el dopaje EDAX destaca la mejora de la estequiometría con un aumento del porcentaje de Al Atómica en películas cuando la concentración de Al aumenta en la solución inicial con S / Sn = 0, 99 al 10%. - La resistividad de las muestras dopadas con Ag y Al aumenta con la concentración de dopado y se observa un aumento del gap óptico de 1.66eV a 1.70eV para SnS dopado por Ag y SnS dopado por Al, respectivamente.
ß-In2S3 thin films deposited by Chemical Spray Pyrolysis technique at different substrate temperatures (250 °C-300 °C-350 °C) showed well crystallized thin films with (0 0 12) as preferred direction perpendicular to the plane containing the surface of glass substrate. SEM images showed dense, uniform, well-covered layers that adhere well to substrates and no crack and void space were noted for all substrate temperatures. Microanalysis X confirms the presence of In and S elements with good stoichiometry after vacuum annealing for 30 minutes. Raman spectroscopy analysis confirms ß-In2S3 phase with more prominent modes after vacuum annealing. We also noted a reduction in the gap energies after annealing for films prepared at 250 °C and 350 °C substrate temperatures while for those prepared at 300 °C, the energy of the gap remains stable. Tin mono-sulfide (SnS) thin films must be deposited onto glass substrate with [S]/[Sn] ratio equal to one (1) and substrate temperature equal to 350 °C to obtained dense, well-covered, and homogeneous films without pinholes and cracks. Distance between nozzle to substrate is kept to 25cm, sprayed volume 5mL, air pressure 0.7bar and spray rate 1.5 mL/min. Films doped with Silver (Ag) and Aluminum (Al) were all orthorhombic structure with (111) as main peak. The intensity of main peak increased when the percentage of dopant element increased in the initial solution without any secondary phase for Al-doping films and with Ag8SnS6 and Ag for Ag-doping ones. SEM and AFM analysis showed that Ag-doping element had no effect in the morphology and the topography while Al-doping affected the surface morphology with "fishing net" like morphology with lots of holes for samples doped from 3% to 7%. EDS highlighted an increase of Ag in films when its amount increased in the solution with S/Sn¿0.98 near to 1 at 5% of Ag-doping percentage where as for Al-doping EDS highlighted improvement of stoichiometry with an increase of Al percentage atomic in films when Al concentration increased in the initial solution with S/Sn¿0.99 at 10%. Electrical and energy band gap measurement showed a decrease of resistivity when Ag and Al percentages increased in the solution to reach relatively low resistivity of 108¿.cm and 170¿.cm at 10% for both, and an increased of energy band gap when the Ag and Al-doping elements increased in the solution with 1.66eV and 1.70eV for SnS doped with Ag and SnS doped with Al, respectively. Spray pyrolyzed SnS thin films doped with indium were studied using various optical and electrical techniques. Structural analysis shows that all films crystallize in orthorhombic structure with (111) as a preferential direction without secondary phases. Doping of SnS layers with indium results in better morphology with increased grain size. Absorption measurements indicate dominant direct transition with energy decreasing from around 1.7 eV to 1.5 eV with increased indium supply. Apart from direct transition, an indirect one, of energy of around 1.05 eV, independent on indium doping was identified. The photoluminescence study revealed two donors to acceptor transitions between two deep defect levels and one shallower with energy of around 90 meV. The observed transitions did not depend significantly on In concentration. The conductivity measurements reveal thermal activation of conductivity with energy decreasing from around 165 meV to 145 meV with increased In content. Finally, we were investigated the J-V characteristics of FTO/CdS/SnS,FTO/ZnO/CdS/SnS, FTO/ZnO:Al/CdS/SnS, FTO/ZnO:Al/SnS and FTO/In2S3/SnS solar cells and we found that efficiencies are very low due probably to the recombination at the junction, grain boundaries, etc.
L'objectiu d'aquesta tesi és la síntesi de pel·lícules primes de SnS utilitzant tècniques de baix cost per tal de fabricar cèl·lules solars amb alta eficiència. La nostra contribució rau en estudiar nous materials susceptibles de ser utilitzats per a aplicacions fotovoltaiques, i que puguin ser preparats amb tècniques de baix cost com la tècnica de Spray Piròlisis Químic (CSP) i caracteritzar alguns materials triats per a aquest fi, com ara el Sulfur de estany (SnS). S'han fabricat cèl·lules solars a partir de la disposició de capes: Mo/SnS /Tampó/i-ZnO/ZnO: Al/ Metall. Les capes de per al bufer intermèdi has sigut de In2S3 i CdS. En la primera etapa hem procedit a l'optimització dels paràmetres de deposició de pel·lícules primes de SnS usant la tècnica CSP. -Variació de la relació [S] / [Sn]. -Variació de la temperatura Ts del substrat. -Variació de la naturalesa del substrat utilitzant substrat com: vidre simple, òxid d'estany d'indi (ITO) i vidre recobert de molibdè. Les fonts de productes químics i dissolvents utilitzats han sigut; Clorur d'estany per a l'estany (Sn), thiourea per sofre (S). Aigua destil·lada com a dissolvent de la solució. Ethanol (10% de 50ml) per tal de reduir la tensió superficial de l'aigua que és 72 Nm-1, per a permetre la dispersió de la solució dipositada fàcilment sobre el substrat. En una segona etapa s'han dopat pel.lícules primes de SnS amb algun element en la taula de Mendeleiev per modificar les propietats físiques i químiques de les pel.l¿cules. Els elements químics utilitzats són: Plata (Ag+), alumini (Al3+), Ferro (Fe2+), Coure (Cu2+) i Antimoni (SB3+) com a font de nitrat de plata (AgNO3), Clorur d'alumini (AlCl3) (FeCl2·4H2O ), Clorur de Coure (CuCl2 i Clorur de Antimoni (SbCl3). S'han utilitzat diverses tècniques de caracterització: - Difracció de raigs X (XRD) per a l'estructura de les pel·lícules i cristal - Raman Spectroscopy per a la qualitat de les pel·lícules - Microscòpia electrònica de rastreig (SEM) per morfologia superficial - Microscòpia de Força Atòmica (AFM) per topografia de superfície - Anàlisi dispersiu d'energia de raigs X (EDAX) adjunt a SEM per a la composició de la pel·lícula -Espectrofotometría per a la transmissió i el mesurament de la banda d'energia utilitzant la trama de Tauc - Tècnica de punta-sonda per a mesurament de resistivitat amb dopat SnS -Mott-Schottky per determinar el tipus de semiconductor i la concentració de portadors Els principals resultats obtinguts en aquesta tesi poden resumir així: -Les pel·lícules primes mico-sulfur (SnS) han de dipositar-sobre un substrat de vidre amb [S]/[Sn] igual a una (1) i la temperatura del substrat igual a 350 °C per obtenir pel·lícules denses, ben cobertes i homogènies sense forats I esquerdes. Distància entre el filtre al substrat 25 cm, volum polvoritzat 5 ml, pressió d'aire 0,7 bar i velocitat de polvorització de 1,5 ml / min. Per pel·lícules dopades per Plata i alumini, totes les pel·lícules són estructura ortorrómbica amb (111) com pic principal. La intensitat del pic principal augmenta quan el percentatge d'element dopant augmenta en la solució inicial sense cap fase secundària per al dopatge amb Al i amb Ag8SnS6 i Ag per al dopatge Ag. L'anàlisi de SEM i AFM demostra que l'element dopant Ag no té efecte en la morfologia i la topografia mentre que el dopatge en actua sobre la morfologia superficial produint una morfologia que presenta molts forats per a mostres dopades de 3% a 7%. EDAX destaca un augment de Ag en pel·lícules quan la quantitat d'Ag augmenta en la solució amb S / Sn¿0,98 prop d'1 a 5% de percentatge de dopatge d'Ag on com per al dopatge EDAX destaca la millora de l'estequiometria amb un augment del percentatge d'al Atòmica en pel·lícules quan la concentració d'al augmenta en la solució inicial amb S / Sn = 0,99 al 10%.
Sall, T. (2017). Preparation and Characterization of SnS thin films by Chemical Spray Pyrolysis for fabrication of solar cells [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/95412
TESIS

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Universidade Federal de Sao Carlos
In this work, the corrosion behavior of three Fe-Mn-Si-Cr-Ni (Co) shape memory stainless steels (SMSS) in aggressive environments was characterized. The electrochemical corrosion behavior in 0.5 M H2SO4 solution was obtained by potentiodynamic polarization, linear polarization, potential decay curves, electrochemical impedance spectroscopy (EIS), and Mott-Schottky analyses. Localized corrosion resistance was evaluated by potentiodynamic polarization measurements in 3.5% NaCl solution. The corrosion performance in highly oxidizing environments was evaluated based on immersion tests in boiling HNO3 solution. The passive film composition was analyzed by X-ray photoelectron spectroscopy (XPS). The test results were compared with that of a type 304 (SS 304) austenitic stainless steel. The three SMSSs exhibited a passive behavior in 0.5 M H2SO4 solution; however, their anodic behavior in the active dissolution region was markedly different. The passive current densities of the SMSSs were similar to that of SS 304, although the critical anodic current required for passivation was higher. The corrosion rate of the SMSSs in 0.5 M H2SO4 solution was much higher than that of SS 304. It was observed that the amount of Cr and Mn plays an important role in the corrosion behavior of SMSS. The XPS analyses indicated substantial Si content (in the chemical form of a silicate) in the anodic passive films formed on SMSS. Mott-Schottky analyses suggested that the Si acts as a dopant in the films, making them less defective and thicker than the films formed on SS 304. Due to their high manganese content, SMSSs are highly prone to pitting corrosion in chloride environments. SMSSs exhibit better corrosion resistance than SS 304 in highly oxidizing environments.
Neste trabalho, a resistência à corrosão de três ligas inoxidáveis Fe-Mn-Si-Cr-Ni-(Co) com efeito de memória de forma (EMF) foi caracterizada em ambientes corrosivos. O comportamento eletroquímico em solução de ácido sulfúrico (H2SO4) 0,5 M foi obtido por polarização potenciodinâmica, polarização linear, curvas de decaimento de potencial, impedância eletroquímica e gráficos de Mott-Schottky. A resistência à corrosão localizada foi avaliada por testes potenciodinâmicos em solução de cloreto de sódio (NaCl) 3,5%. A resistência à corrosão em ambiente fortemente oxidante foi avaliada por ensaios de imersão em solução de ácido nítrico (HNO3) em ebulição. A composição do filme passivo foi analisada por espectroscopia de fotoelétrons excitados por raios X (XPS). Os resultados foram comparados com o de um aço inoxidável AISI 304. As três ligas com EMF apresentaram passividade em solução de H2SO4 0,5 M, no entanto, o comportamento anódico das ligas na região de dissolução ativa foi notavelmente diferente. Os valores de densidade de corrente passiva das ligas foram próximos ao do aço inoxidável AISI 304, no entanto a densidade de corrente crítica necessária para o início da passivação foi maior. A taxa de corrosão da ligas com EMF foi muito maior do que a do aço inoxidável AISI 304 em solução de H2SO4 0,5 M. Os teores de Cr e Mn têm grande influência na resistência à corrosão dessas ligas. As análises por XPS revelaram um filme passivo rico em Si4+ (na forma química de silicato). Os gráficos de Mott-Schottky sugerem que a alta proteção dos filmes passivos formados anodicamente em solução de H2SO4 0,5M está associada à incorporação de Si4+. O Si4+ age como um dopante nos filmes, tornando-os menos defeituosos e mais espessos do que os filmes formados no aço inoxidável AISI 304. Devido ao elevado teor de Mn (8-14 % em peso), as ligas inoxidáveis com EMF são muito propensas à corrosão por pites em ambientes com cloretos. As ligas inoxidáveis com EMF exibem melhor resistência à corrosão do que o aço inoxidável AISI 304 em ambientes fortemente oxidantes.

Le développement de la plaque bipolaire - PB -métallique nécessite une amélioration des propriétés du matériau qui la constitue. L'utilisation de l'acier implique une meilleure compréhension du film passif - FP. En effet, le cahier des charges de la PB demande une bonne conduction électronique ainsi qu'une longue durée de vie. L'amélioration de ces paramètres passe par une meilleure corrélation et compréhension entre les propriétés semi-conductrices et la résistance à la corrosion. La difficulté liée à l'étude de la passivation réside dans les nombreux phénomènes modifiant le comportement du film passif. De nombreux modèles présentés dans la littérature peuvent être utilisés pour caractériser la passivation. L'un des principaux, le Modèle de Défauts Ponctuels de D. D. Macdonald (Point Defect Model - PDM), décrit le FP à partir d'une série de réactions électrochimiques se déroulant à l'interface métal/oxyde et à l'interface oxyde/électrolyte. La réactivité est limitée par le transport de matière à travers l'oxyde. Après une étude bibliographique, ce phénomène semble être un paramètre discriminant dans le choix des modèles. Une méthode de sélection permettant une utilisation de chacun de ces modèles en fonction de leurs spécificités est proposée. Ainsi, cette méthode est basée sur la corrélation entre la mesure du transport de matière à partir des équations du PDM et l'analyse des Spectres d'Impédance Electrochimique (SIE). Le PDM caractérisant le transport de matière indépendamment de la SIE, il devient possible de déterminer le bien-fondé de la prise en compte de celui-ci dans les mesures de spectroscopie d'impédance électrochimique. L'évolution de la densité du porteur de charge majoritaire avec le potentiel de formation de l'oxyde permet d'accéder au coefficient de transport à partir des équations du PDM. Connaissant l'épaisseur de l'oxyde par des mesures XPS, la constante de temps et la fréquence caractéristique peuvent être déterminées. Sur la base de ces deux valeurs, un modèle descriptif d'analyse des spectres est sélectionné en évitant le sur-paramétrage. Cette méthode est appliquée d’abord à un matériau modèle, le chrome pur exposé à un milieu acide (pH 2), à différentes températures (30°C et 80°C). Elle valide la nécessité de la prise en compte du transport de matière à 80°C ainsi que la présence d'une surface composée d'une couche d'oxyde interne et d'une couche d'hydroxyde externe. Dans un second temps, cette méthode est utilisée sur un matériau industriel, un acier de type AISI 316L, à différents pH (1,2 et 3) et à différentes températures (30°C et 80°C). Elle a permis de décrire l'oxyde en surface comme une jonction p-n prenant en compte une couche riche en chrome interne avec un gradient de concentration de fer. Cette méthode a permis de caractériser de manière approfondie l'acier de type AISI 316L. Bien que ne concernant que le substrat, cette étape est déterminante dans l'amélioration des performances des PB métalliques
Developments in metallic bipolar plate, to apply more widely fuel cells, require an improved of the constitutive material. The use of stainless steel calls for a good understanding of the passive film. The required specifications are for good electrical conductivity and a long life-time. Those two parameters correspond to a correlation between the semiconductive properties and the good corrosion behavior. Nevertheless, the main problems of the passivity lie on the multiplicity of the phenomena that alter the passive film behavior. Numerous models described in the literature can be used to characterize the passivation. The Point Defect Model (PDM) describes the passivation through electrochemical reactions at the metal / oxide and at the oxide / electrolyte interfaces. The reactivity is limited by mass transport through the oxide. From the literature, those phenomena seems to be a discriminating parameter in the choice of a model. The selective method proposed allows us to use each model taking into account their specifics. This methodology is based on the correlation between the mass transport characterization, thanks to the PDM, and the analysis of the Electrochemical Impedance Spectroscopy (EIS). The PDM determines the transport coefficient apart from EIS measurements, so to validate the consideration of the mass transport during the analysis of the electrochemical impedance spectra. The evolution of the main charge carrier density as a function of the oxide formation potential allows us to calculate the transport coefficient from PDM equations. Thanks to the thickness of the oxide (determined by X-ray Photoelectron Spectroscopy), the time constant of the mass transport is determined. Based on this value, a descriptive model is used to analyze the EIS data, avoiding overparametrization. This method is applied first on a model material, pure chromium exposed to acidic solution (pH 2) at several temperatures (30°C and 80°C). It shows that the mass transport has to be taken into account at 80°C and the EIS model considers an inner chromium oxide layer and an outer chromium hydroxide. Secondly, the method is used to characterize an industrial material, AISI 316L stainless steel, at several pH (1, 2 and 3) and at several temperatures (30°C and 80°C). In this case, the oxide is describe as a p-n semiconductor junction with an chromium rich inner layer and an outer iron rich layer. The present methodology permits to deeply characterize the AISI 316L stainless steel. Even if this study concerns the substrate, this step is decisive to improve the performances of the metallic bipolar plates

Graphenes in the form of flexible thin films treated with different types of plasma were investigated by Mott-Schottky analysis. The possibility of variation of electrical conductivity in graphene prepared by plasma treatment was shown. Obtained materials are promising for electric energy storage devices.

The influence of bicarbonate ion (HCO3−) concentration and related environmental parameters such as pH and temperature on the passivation of API-X100 pipeline steel is the focus of this investigation. NS4 solution simulating groundwater trapped under disbonded coatings at regions where near-neutral stress corrosion cracking (SCC) occurs was used as a reference. Bicarbonate content in the solutions was increased steadily and the critical HCO3− concentration at which passivation becomes evident is found using potentiodynamic polarization sweeps. Multi-step dissolution is observed especially in higher pH solutions, owing to the involvement of hydroxide ions (OH−) in the adsorption of hydrous Fe(OH)2. Dynamic electrochemical impedance spectroscopy (DEIS) is used to study and compare interfacial processes in active, pre-passive, passive, and trans-passive regions. The results of the potentiodynamic and DEIS tests achieve good agreement. The protective properties of the passive film formed at three different HCO3− concentrations (critical passivation and two higher concentrations) and temperatures (25, 50, and 75 °C) are studied. The combined effect of HCO3− and temperature resulted in a pH range from ∼6.7 to 9.3 for the nine conditions in the corresponding test matrix. Passive films were formed at a suitable anodic potential and then studied with electrochemical impedance spectroscopy (EIS), Mott-Schottky, and cyclic voltammetry (CV) tests. Evidence of adsorption and diffusion, in addition to significant resistance from the passive film, is observed and accounted for in the equivalent circuit, which achieved good correspondence when fitted with the experimental data. The protective properties of the overall passive film are enhanced with increased bicarbonate and decreased temperature. Positive slopes in the Mott-Schottky plots reveal the n-type semi-conductive behavior of the passive films in all conditions and the CV results highlight the proposed reaction sequences occurring in different potential scan regions. CV measurements also confirm the enhanced protective properties of passive films with increased bicarbonate and lower temperatures observed in the EIS analysis.