ABSTRACT Aluminium generally presents good corrosion resistance to the atmosphere. However, unpro... more ABSTRACT Aluminium generally presents good corrosion resistance to the atmosphere. However, unprotected aluminium and aluminium alloys weather outdoors to an ugly grey colour, which deepens to black in industrial atmospheres, and undergo superficial pitting in marine atmospheres, etc. Finishing technologies are applied for their protection and decoration in a wide range of applications. These technologies basically consist of two protection processes: anodizing and painting; the latter going from conventional solvent base paints to modem water-borne, high solids and powder coatings. This paper considers the weathering performance of three paint systems: alkyd, polyurethane and polyester, after more than three years of exposure in a wide spectra of Ibero-American atmospheric conditions. The information reported includes resistance to undercutting corrosion at the scribe, filiform corrosion, fungal attack and change in the physical-chemical properties of the paint surface (loss of gloss, colour changes, chalking, etc.).El aluminio, en general, presenta una buena resistencia a la corrosión en la atmósfera. Sin embargo, el aluminio sin ninguna protección y las aleaciones de aluminio expuestas a la intemperie envejecen mostrando un color gris, negro en el caso de atmósferas industriales, sufren la formación de picaduras en atmósferas marinas, etc. Para su protección, o a efectos decorativos, se le aplican diferentes procesos de acabado en un amplio rango de aplicaciones. Estos procesos de acabado, básicamente consisten en dos métodos de protección: anodizado y pintado; este último abarca desde pinturas convencionales de base disolvente hasta modernos sistemas base agua, de alto contenido en sólidos o pinturas en polvo. Este trabajo considera el comportamiento de tres sistemas de pinturas: alquídico, poliuretano y poliéster, tras más de tres años de exposición en un amplio espectro de condiciones atmosféricas de Iberoamérica. La información presentada incluye la resistencia a la deslaminación en la incisión, corrosión filiforme, ataque por hongos y cambios en las propiedades físico-químicas de la superficie de la pintura (pérdida de brillo, color, entizado, etc.)
ABSTRACT The research work performed on 12 coil coating materials in the frame of the PATINA Netw... more ABSTRACT The research work performed on 12 coil coating materials in the frame of the PATINA Network (Anticorrosive Protection in the Atmosphere) sponsored by CYTED is discussed. It includs the task accomplished by Science and Technology institutions of Ibero-America on formulations supplied by different prcoduction Sector companies from the participating countries, between 1996 and 2000. Coil coating schemes were exposed outdoors, according to ISO 2810 standards, in 9 ambient conditions of the MICAT (Ibero-American Test Stations Network), CYTED. The protective characteristics on the steel base metal was determined as a function of time, following ISO 4628 and ASTM D 3274 standards. Electrochemical impedance spectroscopy (EIS) was applied on various materials after 1, 2, 3 years and 42 months exposure, to evaluate the weathering effect in different atmospheric conditions.Se discute el trabajo realizado sobre 12 diferentes recubrimientos para banda continua en el marco de la Red PATINA (Protección Anticorrosiva en la Atmósfera), patrocinada por el CYTED. Incluye las actividades llevadas a cabo por instituciones de Ciencia y Técnica de Iberoamérica, sobre distintas formulaciones provistas por empresas productoras de los países participantes, entre 1996 y 1999. Se expusieron a la intemperie, en distintas condiciones ambientales de la Red de Estaciones MICAT, CYTED, siguiendo la norma ISO 2810, recubrimientos de diferentes formulaciones. Se evaluaron las características protectoras sobre el acero de base en función de los parámetros medio-ambientales y los tiempos de exposición programados, según la normas ISO 4628, 4623 y ASTM D 3274. Se aplicaron dos esquemas de protección orgánicos sobre las muestras de acero, otros cuatro sobre muestras de acero previamente protegido con Zn y otros seis sobre acero galvanizado (2) y recubierto con galvalume (4), con y sin incisión en cada esquema hasta llegar el acero. Se discuten los resultados obtenidos al cabo de 1, 2, 3 años y 42 meses en función de la agresividad de cada sitio de ensayo. Se aplicó espectroscopia de impedancia electroquímica (EIE) al cabo de diferentes períodos de exposición para evaluar la incidencia del deterioro de cada recubrimiento sobre la respuesta global de los esquemas, en varias de las condiciones de ensayo.
The durability of a paint coating applied on a galvanized steel surface which has been exposed fo... more The durability of a paint coating applied on a galvanized steel surface which has been exposed for a certain time to the atmosphere depends on the aggressiveness of the atmosphere, the preparation of the weathered surface prior to painting, and the type of coating applied. This work presents the results of an atmospheric corrosion study carried out over 11 years in three Spanish atmospheres of highly different degrees of aggressiveness (Madrid, Bilbao, and Tenerife), applying eight paint coatings on galvanized steel weathered in different conditions and using different methods to prepare the aged metallic surface prior to painting.
... Gregorio del Amo 8, E-28040 Madrid, Spain 2 Laboratorio Nacional de Engenharia e Tecnologia I... more ... Gregorio del Amo 8, E-28040 Madrid, Spain 2 Laboratorio Nacional de Engenharia e Tecnologia Industrial, Azinhaga dos Lameiros à Estrada do Paco do Lumiar, P-1699 Lisboa Codex, Portugal Keywords: Rusted Steel, Rust Converter, Tannic Acid, Gallic Acid, Phosphoric Acid ...
The hydrotalcite structure is an ionic lamellar solid with positively charged layers incorporatin... more The hydrotalcite structure is an ionic lamellar solid with positively charged layers incorporating two kinds of metallic cations and hydrated gallery anions. The ability of these compounds to retain aggressive ions and simultaneously release a corrosion inhibitor is the main reason for the development of hydrotalcite compounds to replace hexavalent chromium compounds (chromates) as inhibitive pigments.In this study, alkyd coatings
ABSTRACT In the field of anticorrosive primer paints there is growing interest to find environmen... more ABSTRACT In the field of anticorrosive primer paints there is growing interest to find environmentally friendly anticorrosive pigments to replace Cr(VI) pigments which are highly toxic both to the environment and to human health, with known carcinogenic effects. This has become a major challenge of the last decades for all the sectors involved in metallic protection. One of the alternatives of great scientific interest is the use of ion exchange pigments, which are mostly naturally abundant, easily synthesised, relatively cheap, and above all environmentally friendly. Studies of these pigments have not been conclusive about their anticorrosive efficiency and controversy surrounds their functional mechanisms, exchange capacity and anticorrosive performance.This paper focuses on the anticorrosive protection afforded by one anion-exchange pigment: hydrotalcite/vanadate (HT/V). Alkyd primer coatings formulated with non-toxic HT/V pigment have been applied on carbon steel specimens, and the effect of the pigment on the protective properties of the coatings has been evaluated by means of natural and accelerated corrosion tests (humidity, salt spray and Kesternich, 0.2 L SO2). A traditional zinc chromate (ZC) pigment has also been used for comparative purposes. The exchange and inhibitor capacity of the HT/V has also been evaluated.The inhibiting power of the HT/V pigment in solution is seen to be less than that of the traditional ZC pigment, showing also a low exchange capacity and solubility. On the other hand, the behaviour of the HT/V pigmented primers applied on carbon steel is suitable in moderate environments and deficient in aggressive environments, in both natural atmospheres and accelerated tests, and is much poorer than that of the zinc chromate.
Specimens of AISI 304 and AISI 430 stainless steels (SS) were implanted with nitrogen, argon and ... more Specimens of AISI 304 and AISI 430 stainless steels (SS) were implanted with nitrogen, argon and silicon up to an ion dose of 1 Â10 15 ion/cm 2 at an accelerating potential of 150 keV. AISI 304 and 430 SS specimens were analysed as-received and after ion implantation using X-ray photoelectron spectroscopy (XPS) in conjunction with Ar + -ion sputtering. Surface chromium enrichment was observed with the argon ion-implanted specimens compared with the non-implanted specimens, enhancing their corrosion resistance. Nitrogen implantation does not seem to have a significant effect on the structure and composition of the passive layer. Finally, silicon-implanted SSs show a very different passive layer, in which SiO 2 is the main component of the outer surface. D
ABSTRACT Among the anticorrosive protection technologies for magnesium alloys, the development of... more ABSTRACT Among the anticorrosive protection technologies for magnesium alloys, the development of paint systems is a pressing need especially for the automotive and aeronautical industries. Conventional technologies are based on the use of Cr(VI) based compounds, both in pretreatments and primers, but for health and environmental reasons these technologies are being abandoned. An added problem in the painting of magnesium alloys is the lack of adhesion and the high reactivity of magnesium substrates, which may lead to underfilm corrosion and detachment of the paint system. Therefore, the selection of a suitable pretreatment is crucial. Our research seeks to evaluate the anticorrosive behaviour of Cr(VI)-free surface pretreatments applied on different magnesium alloys, AZ31, AZ91 and AM60 and to analyse whether they could be protective enough to assure the successful protection of the substrate without the application of a topcoat. The considered alternatives are four chemical conversion coatings including two coatings obtained by plasma electrolytic oxidation (PEO). A chromate conversion coating has been also applied as reference. Different corrosion tests have been carried out in both natural (marine and urban atmospheres) and accelerated environments: salt fog, condensing humidity and cyclic test (salt fog/dry/humidity). Electrochemical characterization by electrochemical impedance spectroscopy (EIS) has been also performed. The results show a notably better anticorrosive behaviour of PEO coatings compared to chemical conversion coatings for all the considered magnesium alloys in both, natural and accelerated environments. However, none of the studied coatings seem to successfully protect magnesium alloys in aggressive atmospheres (marine) without the application of a topcoat. On the other hand, although PEO coatings have shown an acceptable good behaviour in very low aggressive environments (urban), it would be also recommended the application of a topcoat.
... For example, a combination of calcium ion exchange silica (Shieldex ® ) with zincphosphate/mo... more ... For example, a combination of calcium ion exchange silica (Shieldex ® ) with zincphosphate/molybdate (Actirox ... of steel at the scribe was found in the paints formulated with zincchromate. ... The evaluation of rusting and blistering of the painted surface was performed according ...
This paper analyses the causes of the early corrosion failure of phosphorus deoxidized copper tub... more This paper analyses the causes of the early corrosion failure of phosphorus deoxidized copper tubes which formed part of an airconditioning unit. The failure of the tubes occurred after 2 ± 3 months service time. X-ray photo-electron spectroscopy (XPS), Auger electron spectroscopy (AES), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) techniques were used. Corrosion tests were also performed at the laboratory using three types of uncorroded copper tubes, 40, 80 and 100% relative humidities, 20 and 40 8C temperature, and two commercial lubricant oils. Organic acids, chloride and sulphur were found as sources of corrosion failure.
Copper is used in numerous applications, e.g., in the chemical and electronics industries, in hea... more Copper is used in numerous applications, e.g., in the chemical and electronics industries, in heat exchanger systems, in construction for roofing, plumbing, and decorative purposes, and in artistic applications such as chalcographic plates and enamels. Extensive studies have been performed on atmospheric copper corrosion at high humidity in contaminated and uncontaminated environments. However, very little is known about the chemical composition of the tarnish layer that develops during atmospheric copper corrosion at low humidities.
ABSTRACT Anomalously large differences between values of the polarization resistance R(p) measure... more ABSTRACT Anomalously large differences between values of the polarization resistance R(p) measured in the time and frequency domains pose a serious problem in determination of the corrosion rate from the Stern-Geary equation. A theoretical model is used to derive expressions for a quantitative interpretation of the effect of a number of parameters on the apparent R(p) values obtained by de and ac measurements. Problems associated with the determination of the true R(p) value are discussed, and some relevant questions concerning the minimum frequency needed for impedance measurements are identified.
ABSTRACT One of the first commercial ion-exchange anticorrosive pigments to be developed was Shie... more ABSTRACT One of the first commercial ion-exchange anticorrosive pigments to be developed was Shieldex® (Si/Ca). Its proposed corrosion protection mechanism, based on the retention of aggressive cations and the subsequent release of calcium cations, has created certain controversy. A number of studies have focused on the anticorrosive behavior of this pigment on carbon steel and galvanized steel to replace chromates (Cr6+) as inhibitor pigment, but none has considered its performance on aluminum or aluminum alloys. In this research, alkyd coatings have been formulated with Si/Ca pigment at different concentrations and applied on aluminum 1050 (Al 99.5%) specimens. These specimens have then been subjected to accelerated tests (condensing humidity, salt spray, and Kesternich) and natural weathering in atmospheres of different aggressivity. Corrosion performance has been also evaluated in the laboratory by electrochemical impedance spectroscopy. The study has also considered an organic coating with zinc chromate anticorrosive pigment for comparative purposes. The results obtained with organic coatings formulated with Si/Ca pigments confirm that they provide corrosion protection of the underlying aluminum substrate, even improving the behavior of the reference zinc chromate in some environmental conditions.
The stability of a rusted steel surface exposed to a 0.1 M sodium sulphate solution has been stud... more The stability of a rusted steel surface exposed to a 0.1 M sodium sulphate solution has been studied. Electrochemical impedance spectroscopy, polarization resistance and atomic absorption analysis techniques were used in conjunction with mild steel specimens rusted in a rural atmosphere and treated with different concentrations of phosphoric acid. Since most of the impedance diagrams obtained differ from the typical semicircle, it is not clear how to obtain kinetic information on the corrosion process. The polarization resistance technique gives more useful data. 157
ABSTRACT Aluminium generally presents good corrosion resistance to the atmosphere. However, unpro... more ABSTRACT Aluminium generally presents good corrosion resistance to the atmosphere. However, unprotected aluminium and aluminium alloys weather outdoors to an ugly grey colour, which deepens to black in industrial atmospheres, and undergo superficial pitting in marine atmospheres, etc. Finishing technologies are applied for their protection and decoration in a wide range of applications. These technologies basically consist of two protection processes: anodizing and painting; the latter going from conventional solvent base paints to modem water-borne, high solids and powder coatings. This paper considers the weathering performance of three paint systems: alkyd, polyurethane and polyester, after more than three years of exposure in a wide spectra of Ibero-American atmospheric conditions. The information reported includes resistance to undercutting corrosion at the scribe, filiform corrosion, fungal attack and change in the physical-chemical properties of the paint surface (loss of gloss, colour changes, chalking, etc.).El aluminio, en general, presenta una buena resistencia a la corrosión en la atmósfera. Sin embargo, el aluminio sin ninguna protección y las aleaciones de aluminio expuestas a la intemperie envejecen mostrando un color gris, negro en el caso de atmósferas industriales, sufren la formación de picaduras en atmósferas marinas, etc. Para su protección, o a efectos decorativos, se le aplican diferentes procesos de acabado en un amplio rango de aplicaciones. Estos procesos de acabado, básicamente consisten en dos métodos de protección: anodizado y pintado; este último abarca desde pinturas convencionales de base disolvente hasta modernos sistemas base agua, de alto contenido en sólidos o pinturas en polvo. Este trabajo considera el comportamiento de tres sistemas de pinturas: alquídico, poliuretano y poliéster, tras más de tres años de exposición en un amplio espectro de condiciones atmosféricas de Iberoamérica. La información presentada incluye la resistencia a la deslaminación en la incisión, corrosión filiforme, ataque por hongos y cambios en las propiedades físico-químicas de la superficie de la pintura (pérdida de brillo, color, entizado, etc.)
ABSTRACT The research work performed on 12 coil coating materials in the frame of the PATINA Netw... more ABSTRACT The research work performed on 12 coil coating materials in the frame of the PATINA Network (Anticorrosive Protection in the Atmosphere) sponsored by CYTED is discussed. It includs the task accomplished by Science and Technology institutions of Ibero-America on formulations supplied by different prcoduction Sector companies from the participating countries, between 1996 and 2000. Coil coating schemes were exposed outdoors, according to ISO 2810 standards, in 9 ambient conditions of the MICAT (Ibero-American Test Stations Network), CYTED. The protective characteristics on the steel base metal was determined as a function of time, following ISO 4628 and ASTM D 3274 standards. Electrochemical impedance spectroscopy (EIS) was applied on various materials after 1, 2, 3 years and 42 months exposure, to evaluate the weathering effect in different atmospheric conditions.Se discute el trabajo realizado sobre 12 diferentes recubrimientos para banda continua en el marco de la Red PATINA (Protección Anticorrosiva en la Atmósfera), patrocinada por el CYTED. Incluye las actividades llevadas a cabo por instituciones de Ciencia y Técnica de Iberoamérica, sobre distintas formulaciones provistas por empresas productoras de los países participantes, entre 1996 y 1999. Se expusieron a la intemperie, en distintas condiciones ambientales de la Red de Estaciones MICAT, CYTED, siguiendo la norma ISO 2810, recubrimientos de diferentes formulaciones. Se evaluaron las características protectoras sobre el acero de base en función de los parámetros medio-ambientales y los tiempos de exposición programados, según la normas ISO 4628, 4623 y ASTM D 3274. Se aplicaron dos esquemas de protección orgánicos sobre las muestras de acero, otros cuatro sobre muestras de acero previamente protegido con Zn y otros seis sobre acero galvanizado (2) y recubierto con galvalume (4), con y sin incisión en cada esquema hasta llegar el acero. Se discuten los resultados obtenidos al cabo de 1, 2, 3 años y 42 meses en función de la agresividad de cada sitio de ensayo. Se aplicó espectroscopia de impedancia electroquímica (EIE) al cabo de diferentes períodos de exposición para evaluar la incidencia del deterioro de cada recubrimiento sobre la respuesta global de los esquemas, en varias de las condiciones de ensayo.
The durability of a paint coating applied on a galvanized steel surface which has been exposed fo... more The durability of a paint coating applied on a galvanized steel surface which has been exposed for a certain time to the atmosphere depends on the aggressiveness of the atmosphere, the preparation of the weathered surface prior to painting, and the type of coating applied. This work presents the results of an atmospheric corrosion study carried out over 11 years in three Spanish atmospheres of highly different degrees of aggressiveness (Madrid, Bilbao, and Tenerife), applying eight paint coatings on galvanized steel weathered in different conditions and using different methods to prepare the aged metallic surface prior to painting.
... Gregorio del Amo 8, E-28040 Madrid, Spain 2 Laboratorio Nacional de Engenharia e Tecnologia I... more ... Gregorio del Amo 8, E-28040 Madrid, Spain 2 Laboratorio Nacional de Engenharia e Tecnologia Industrial, Azinhaga dos Lameiros à Estrada do Paco do Lumiar, P-1699 Lisboa Codex, Portugal Keywords: Rusted Steel, Rust Converter, Tannic Acid, Gallic Acid, Phosphoric Acid ...
The hydrotalcite structure is an ionic lamellar solid with positively charged layers incorporatin... more The hydrotalcite structure is an ionic lamellar solid with positively charged layers incorporating two kinds of metallic cations and hydrated gallery anions. The ability of these compounds to retain aggressive ions and simultaneously release a corrosion inhibitor is the main reason for the development of hydrotalcite compounds to replace hexavalent chromium compounds (chromates) as inhibitive pigments.In this study, alkyd coatings
ABSTRACT In the field of anticorrosive primer paints there is growing interest to find environmen... more ABSTRACT In the field of anticorrosive primer paints there is growing interest to find environmentally friendly anticorrosive pigments to replace Cr(VI) pigments which are highly toxic both to the environment and to human health, with known carcinogenic effects. This has become a major challenge of the last decades for all the sectors involved in metallic protection. One of the alternatives of great scientific interest is the use of ion exchange pigments, which are mostly naturally abundant, easily synthesised, relatively cheap, and above all environmentally friendly. Studies of these pigments have not been conclusive about their anticorrosive efficiency and controversy surrounds their functional mechanisms, exchange capacity and anticorrosive performance.This paper focuses on the anticorrosive protection afforded by one anion-exchange pigment: hydrotalcite/vanadate (HT/V). Alkyd primer coatings formulated with non-toxic HT/V pigment have been applied on carbon steel specimens, and the effect of the pigment on the protective properties of the coatings has been evaluated by means of natural and accelerated corrosion tests (humidity, salt spray and Kesternich, 0.2 L SO2). A traditional zinc chromate (ZC) pigment has also been used for comparative purposes. The exchange and inhibitor capacity of the HT/V has also been evaluated.The inhibiting power of the HT/V pigment in solution is seen to be less than that of the traditional ZC pigment, showing also a low exchange capacity and solubility. On the other hand, the behaviour of the HT/V pigmented primers applied on carbon steel is suitable in moderate environments and deficient in aggressive environments, in both natural atmospheres and accelerated tests, and is much poorer than that of the zinc chromate.
Specimens of AISI 304 and AISI 430 stainless steels (SS) were implanted with nitrogen, argon and ... more Specimens of AISI 304 and AISI 430 stainless steels (SS) were implanted with nitrogen, argon and silicon up to an ion dose of 1 Â10 15 ion/cm 2 at an accelerating potential of 150 keV. AISI 304 and 430 SS specimens were analysed as-received and after ion implantation using X-ray photoelectron spectroscopy (XPS) in conjunction with Ar + -ion sputtering. Surface chromium enrichment was observed with the argon ion-implanted specimens compared with the non-implanted specimens, enhancing their corrosion resistance. Nitrogen implantation does not seem to have a significant effect on the structure and composition of the passive layer. Finally, silicon-implanted SSs show a very different passive layer, in which SiO 2 is the main component of the outer surface. D
ABSTRACT Among the anticorrosive protection technologies for magnesium alloys, the development of... more ABSTRACT Among the anticorrosive protection technologies for magnesium alloys, the development of paint systems is a pressing need especially for the automotive and aeronautical industries. Conventional technologies are based on the use of Cr(VI) based compounds, both in pretreatments and primers, but for health and environmental reasons these technologies are being abandoned. An added problem in the painting of magnesium alloys is the lack of adhesion and the high reactivity of magnesium substrates, which may lead to underfilm corrosion and detachment of the paint system. Therefore, the selection of a suitable pretreatment is crucial. Our research seeks to evaluate the anticorrosive behaviour of Cr(VI)-free surface pretreatments applied on different magnesium alloys, AZ31, AZ91 and AM60 and to analyse whether they could be protective enough to assure the successful protection of the substrate without the application of a topcoat. The considered alternatives are four chemical conversion coatings including two coatings obtained by plasma electrolytic oxidation (PEO). A chromate conversion coating has been also applied as reference. Different corrosion tests have been carried out in both natural (marine and urban atmospheres) and accelerated environments: salt fog, condensing humidity and cyclic test (salt fog/dry/humidity). Electrochemical characterization by electrochemical impedance spectroscopy (EIS) has been also performed. The results show a notably better anticorrosive behaviour of PEO coatings compared to chemical conversion coatings for all the considered magnesium alloys in both, natural and accelerated environments. However, none of the studied coatings seem to successfully protect magnesium alloys in aggressive atmospheres (marine) without the application of a topcoat. On the other hand, although PEO coatings have shown an acceptable good behaviour in very low aggressive environments (urban), it would be also recommended the application of a topcoat.
... For example, a combination of calcium ion exchange silica (Shieldex ® ) with zincphosphate/mo... more ... For example, a combination of calcium ion exchange silica (Shieldex ® ) with zincphosphate/molybdate (Actirox ... of steel at the scribe was found in the paints formulated with zincchromate. ... The evaluation of rusting and blistering of the painted surface was performed according ...
This paper analyses the causes of the early corrosion failure of phosphorus deoxidized copper tub... more This paper analyses the causes of the early corrosion failure of phosphorus deoxidized copper tubes which formed part of an airconditioning unit. The failure of the tubes occurred after 2 ± 3 months service time. X-ray photo-electron spectroscopy (XPS), Auger electron spectroscopy (AES), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) techniques were used. Corrosion tests were also performed at the laboratory using three types of uncorroded copper tubes, 40, 80 and 100% relative humidities, 20 and 40 8C temperature, and two commercial lubricant oils. Organic acids, chloride and sulphur were found as sources of corrosion failure.
Copper is used in numerous applications, e.g., in the chemical and electronics industries, in hea... more Copper is used in numerous applications, e.g., in the chemical and electronics industries, in heat exchanger systems, in construction for roofing, plumbing, and decorative purposes, and in artistic applications such as chalcographic plates and enamels. Extensive studies have been performed on atmospheric copper corrosion at high humidity in contaminated and uncontaminated environments. However, very little is known about the chemical composition of the tarnish layer that develops during atmospheric copper corrosion at low humidities.
ABSTRACT Anomalously large differences between values of the polarization resistance R(p) measure... more ABSTRACT Anomalously large differences between values of the polarization resistance R(p) measured in the time and frequency domains pose a serious problem in determination of the corrosion rate from the Stern-Geary equation. A theoretical model is used to derive expressions for a quantitative interpretation of the effect of a number of parameters on the apparent R(p) values obtained by de and ac measurements. Problems associated with the determination of the true R(p) value are discussed, and some relevant questions concerning the minimum frequency needed for impedance measurements are identified.
ABSTRACT One of the first commercial ion-exchange anticorrosive pigments to be developed was Shie... more ABSTRACT One of the first commercial ion-exchange anticorrosive pigments to be developed was Shieldex® (Si/Ca). Its proposed corrosion protection mechanism, based on the retention of aggressive cations and the subsequent release of calcium cations, has created certain controversy. A number of studies have focused on the anticorrosive behavior of this pigment on carbon steel and galvanized steel to replace chromates (Cr6+) as inhibitor pigment, but none has considered its performance on aluminum or aluminum alloys. In this research, alkyd coatings have been formulated with Si/Ca pigment at different concentrations and applied on aluminum 1050 (Al 99.5%) specimens. These specimens have then been subjected to accelerated tests (condensing humidity, salt spray, and Kesternich) and natural weathering in atmospheres of different aggressivity. Corrosion performance has been also evaluated in the laboratory by electrochemical impedance spectroscopy. The study has also considered an organic coating with zinc chromate anticorrosive pigment for comparative purposes. The results obtained with organic coatings formulated with Si/Ca pigments confirm that they provide corrosion protection of the underlying aluminum substrate, even improving the behavior of the reference zinc chromate in some environmental conditions.
The stability of a rusted steel surface exposed to a 0.1 M sodium sulphate solution has been stud... more The stability of a rusted steel surface exposed to a 0.1 M sodium sulphate solution has been studied. Electrochemical impedance spectroscopy, polarization resistance and atomic absorption analysis techniques were used in conjunction with mild steel specimens rusted in a rural atmosphere and treated with different concentrations of phosphoric acid. Since most of the impedance diagrams obtained differ from the typical semicircle, it is not clear how to obtain kinetic information on the corrosion process. The polarization resistance technique gives more useful data. 157
Uploads
Papers by J. Simancas