Comportamento anticorrosivo de tintas de base aquosa aplicadas em substratos ferrosos : Estudo por espectroscopia de impedância electroquímica

Dissertação de Mestrado em Química apresentada à Faculdade de Ciências da Universidade do PortoEstuda-se o comportamento anticorrosivo de tintas de base aquosa aplicadas em substratos ferrosos por espectroscopia de impedância electroquímica e por corrosão acelerada em cabina de nevoeiro salino. Avalia-se o desempenho anticorrosivo de resinas de composição diferente (uma dispersão acrílica, uma dispersão de estireno-acrilato, uma emulsão alquídica e uma emulsão de éster de epóxido) verificando-se uma melhor protecção por parte das emulsões. Em alguns casos tintas fabricadas com essas resinas revelam pior protecção anticorrosiva relativamente aos das próprias resinas. Este comportamento pode ser explicado pela presença de aditivos na tinta que provocam uma maior sensibilidade à água por parte da película.Apresenta-se o estudo de factores que influenciam as características anticorrosivas de uma tinta baseada numa dispersão acrílica: concentração volúmica de pigmentos (CVP), pigmentos inertes (óxido de ferro, talco e barite) e pigmentos anticorrosivos (fosfato de zinco, fosfossilicato de cálcio, estrôncio e zinco e sílica permutadora de catiões). Verifica-se que o aumento da concentração volúmica de pigmentos facilita a permeabilidade da água, com a consequente menor resistência da tinta, mas há uma zona intermédia de CVP onde as características anticorrosivas são superiores. A avaliação dos pigmentos inertes mostra a vantagem no uso de pigmentos lamelares e o estudo com pigmentos anticorrosivos permite estabelecer uma ordem para a sua eficácia: fosfato de zinco > fosfossilicato de cálcio, estrôncio e zinco > sílica permutadora de catiões cálcio. Comparados com primários de base solvente, os primários aquosos apresentam um desempenho inferior, mas a protecção que conferem é melhorada quando são integrados num sistema de pintura constituído por uma camada de primário e uma camada de tinta de acabamento. Há evidências experimentais para a recuperação das características protectoras da película após períodos de secagem o que sugere que os primários aquosos estu ..

Corrosion resistance and tribological behavior of ZK30 magnesium alloy coated by plasma electrolytic oxidation

The rapid bio-corrosion of magnesium-based alloys, the formation of hydrogen gas and, consequently, the premature loss of biomechanical functions hinder their applications as biodegradable implant materials. The corrosion becomes even accelerated, when fretting wear occurs at implant junctions, as a result of repeated disruptions of the magnesium (hydr)oxide layer formed on implant surfaces. To improve the overall performance of these materials in a bio-relevant environment, especially corrosion resistance and wear resistance, in this research, plasma electrolytic oxidation (PEO) was applied to create a coating on a magnesium alloy, ZK30. The resulting gains in corrosion resistance and wear resistance were evaluated. In vitro immersion tests in Hank’s solution at 37 ◦C showed a reduction in hydrogen release from the PEO-treated alloy. The results obtained from applying the scanning vibrating electrode technique (SVET) indicated a decreased susceptibility of the PEO- treated alloy to localized corrosion, accounting for the improved corrosion resistance. In addition, PEO was found to change the surface topography and roughness, in addition to surface chemistry, which contributed to an increased but stable coefficient of friction and a decreased material removal rate, as revealed by the tribological tests with a ball-on-plate configuration. The results indicate an enlarged opportunity of magnesium-based ma-terials for orthopedic applications, where friction and wear are involved, by applying PEO

Electrochemical and mechanical behavior of UV curing paint on hybrid films modified with polyethyleneglycol plasticizer applied on tinplate

The objective of this work is to coat tinplate with a hybrid film obtained from a sol-gel process constituted by the alkoxide precursor tetraethoxysilane (TEOS) and 3-trimethoxysilylpropyl methacrylate (TMSM), with the addition of cerium nitrate (0.01 M) and polyethyleneglycol plasticizer (20 g.L-1) to the sol formulation. The films were obtained by dip-coating, applying one and two layers and curing them at different temperatures (60°C and 90°C) for 20 minutes, and adhering UV curing paint to each film respectively. The results showed that the double layered hybrid film obtained at 60°C had a higher layer of thickness and the best performance in the electrochemical assays, in other words, higher resistance to corrosion. Furthermore, in studies following the application of UV coating, the hybrid-film monolayer cured at 60°C wich had an organic coating of cured UV applied to it, achieved a performance similar to that of the pretreated alkyd greenhouse currently used in the metal packaging industry

Corrosion resistance and tribological behavior of ZK30 magnesium alloy coated by plasma electrolytic oxidation

The rapid bio-corrosion of magnesium-based alloys, the formation of hydrogen gas and, consequently, the premature loss of biomechanical functions hinder their applications as biodegradable implant materials. The corrosion becomes even accelerated, when fretting wear occurs at implant junctions, as a result of repeated disruptions of the magnesium (hydr)oxide layer formed on implant surfaces. To improve the overall performance of these materials in a bio-relevant environment, especially corrosion resistance and wear resistance, in this research, plasma electrolytic oxidation (PEO) was applied to create a coating on a magnesium alloy, ZK30. The resulting gains in corrosion resistance and wear resistance were evaluated. In vitro immersion tests in Hank's solution at 37 °C showed a reduction in hydrogen release from the PEO-treated alloy. The results obtained from applying the scanning vibrating electrode technique (SVET) indicated a decreased susceptibility of the PEO-treated alloy to localized corrosion, accounting for the improved corrosion resistance. In addition, PEO was found to change the surface topography and roughness, in addition to surface chemistry, which contributed to an increased but stable coefficient of friction and a decreased material removal rate, as revealed by the tribological tests with a ball-on-plate configuration. The results indicate an enlarged opportunity of magnesium-based materials for orthopedic applications, where friction and wear are involved, by applying PEO.</p

Corrosion resistance and tribological behavior of ZK30 magnesium alloy coated by plasma electrolytic oxidation

The rapid bio-corrosion of magnesium-based alloys, the formation of hydrogen gas and, consequently, the premature loss of biomechanical functions hinder their applications as biodegradable implant materials. The corrosion becomes even accelerated, when fretting wear occurs at implant junctions, as a result of repeated disruptions of the magnesium (hydr)oxide layer formed on implant surfaces. To improve the overall performance of these materials in a bio-relevant environment, especially corrosion resistance and wear resistance, in this research, plasma electrolytic oxidation (PEO) was applied to create a coating on a magnesium alloy, ZK30. The resulting gains in corrosion resistance and wear resistance were evaluated. In vitro immersion tests in Hank's solution at 37 °C showed a reduction in hydrogen release from the PEO-treated alloy. The results obtained from applying the scanning vibrating electrode technique (SVET) indicated a decreased susceptibility of the PEO-treated alloy to localized corrosion, accounting for the improved corrosion resistance. In addition, PEO was found to change the surface topography and roughness, in addition to surface chemistry, which contributed to an increased but stable coefficient of friction and a decreased material removal rate, as revealed by the tribological tests with a ball-on-plate configuration. The results indicate an enlarged opportunity of magnesium-based materials for orthopedic applications, where friction and wear are involved, by applying PEO.Accepted Author ManuscriptBiomaterials & Tissue Biomechanic

Characterisation of microbial attack on archaeological bone

As part of an EU funded project to investigate the factors influencing bone preservation in the archaeological record, more than 250 bones from 41 archaeological sites in five countries spanning four climatic regions were studied for diagenetic alteration. Sites were selected to cover a range of environmental conditions and archaeological contexts. Microscopic and physical (mercury intrusion porosimetry) analyses of these bones revealed that the majority (68%) had suffered microbial attack. Furthermore, significant differences were found between animal and human bone in both the state of preservation and the type of microbial attack present. These differences in preservation might result from differences in early taphonomy of the bones. © 2003 Elsevier Science Ltd. All rights reserved