63 research outputs found
Report on the characterisation of collected materials on historical aircraft - Deliverable D2.2
No full textThe present deliverable reports on the study of reference wrecks and their constituent materials carried out in Tasks 2.1 and 2.2 of WP2. It aims at characterizing materials collected on selected aircraft/wrecks including the study of the metallic Al alloys, their original protective coatings and their alteration (mainly corrosion)
Etude de bioactivité, résistance à la corrosion et comportement en fatigue de l'alliage Ti-12Mo-6Zr-2Fe après différents traitements de surface
No full textDemand for new implants with improved bioactivity, corrosion resistance, and optimal mechanical properties has been increasing considerably. In this sense, different surface treatments are applied in titanium alloys to improve their osteointegration process. Nevertheless, the developments of new bioactive surfaces could cause a considerable reduction in fatigue and corrosion strength leading to catastrophic failures in clinical use. For these reasons, this work studied the biocompatibility, corrosion and fatigue performance of Ti-12Mo-6Zr-2Fe alloy treated with three different surface modifications, namely, chemical surface treatment (CST), nanotubes (Nt) and nanopores (NP). Samples were immersed in simulated body fluid (SBF) solution during different periods, 0, 1, 7, and 14 days. After 14 days immersed in SBF, samples with CST showed high hydroxyapatite (HAp) formation; Likewise, samples with Nt and NP exhibited lower and moderated HAP formation, respectively. In samples without surface treatment was not observed HAp formation. The electrochemical behavior was studied through polarization curves and electrochemical impedance spectroscopy (EIS). Samples with Nt and NP displayed higher corrosion resistance and lower passivation current (Ipass) compared with untreated samples, after 14 days of immersion in SBF; samples with CST showed the worst corrosion performance for all the surface conditions studied. Furthermore, within the framework of electrochemical investigations, EIS results of Nt and NP samples showed a characteristic behavior that could not be modeled by traditional equivalent circuits. Thus, it was proposed a two-channel transmission line model for analyzing this impedance results, leading to a successful fitting of the EIS data. Finally, was observed a reduction of the fatigue resistance in the samples treated with NP and CST, associated with hydrogen embrittlement processes, due to the pick-up of hydrogen during the respective surface treatments.La demande de nouveaux implants avec une meilleure bioactivité, résistance à la corrosion et des propriétés mécaniques optimisées a augmenté considérablement. Différents traitements de surface sont appliqués sur des alliages de titane pour améliorer leur processus d’ostéo-intégration. Néanmoins, le développement de nouvelles surfaces bioactives pourrait causer une réduction considérable de la résistance à la fatigue et à la corrosion, ce qui peut entraîner des défaillances catastrophiques dans leurs utilisations cliniques. Ainsi, dans ce travail, la performance en biocompatibilité, en fatigue et en corrosion de l’alliage de Ti-12Mo-6Zr-2Fe (TMZF) a été étudié. Cet alliage a été soumis à trois modifications de surface différentes, à savoir le traitement chimique de surface (CST, en anglais, pour Chemical Surface Treatment), les nanotubes (Nt) et les nanopores (NP). Les échantillons ont été immergés dans une solution physiologique appelée SBF (en anglais, pour Simulated Body Fluid) avec des durées d’immersion différentes : 0, 1, 7, et 14 jours. Après 14 jours d’immersion dans SBF, les échantillons qui ont subi un traitement chimique de surface ont montré une formation importante d’hydroxyapatite (HAp), nécessaire pour assurer une bonne osseo-intégration de l’implant. De même, les échantillons avec des nanotubes et nanopores montrent une formation, respectivement, faible et modérée de HAp. Dans les échantillons sans traitement de surface, la formation de HAp n’a pas été observée. Le comportement électrochimique a été étudié par des courbes de polarisation et par spectroscopie d’impédance électrochimique (SIE, ou EIS en anglais, pour Electrochemical Impedance Spectroscopy). Les échantillons avec NT et NP manifestent une meilleure résistance à la corrosion et un domaine de passivité (Ipass) plus faible, en comparaison avec les échantillons non traités après 14 jours d’immersion dans SBF. Les échantillons qui ont subi un traitement chimique de surface (CST) ont démontré une résistance à la corrosion faible par rapport aux autres surfaces étudiées. Par ailleurs, dans le contexte des investigations électrochimiques, les résultats de SIE d’échantillons NT et NP ont montré un comportement caractéristique qui ne pouvait pas être modélisé par les circuits équivalents traditionnels. Ainsi, un modèle de ligne de transmission de deux canaux a été proposé pour analyser ces résultats d’impédance, permettant un ajustement réussi des données de SIE. Finalement, une réduction de la résistance à la fatigue a été observée dans les échantillons traités avec NP et CST, via une fragilisation par l'hydrogène, en raison du captage d’hydrogène pendant les traitements de surface
Fatigue behavior of Ti-6Al-4v alloy with surface modified by chemical treatment
No full textChemical surface treatments (CST) in cementless and endosseous
implants are used to increase the implant-bone contact area, reducing the period
of osseointegration and favouring bonding ability between implants and bone.
However, surface modifications can affect the fatigue strength of these materials,
especially the fatigue crack nucleation. For these reasons, this work evaluated the
influence of the surface modification using acid etching, combined with alkaline
treatment on the fatigue strength of Ti-6Al-4V ELI alloy. The topography
developed by chemical surface treatments was examined by scanning electron
microscopy (SEM) and confocal laser scanning microscopy (CLSM). Increased
roughness and the effective surface area were investigated and compared with the
Ti-6Al-4V samples without modification. Surface composition was analyzed by
energy dispersive X-ray spectroscopy (EDS). Axial fatigue resistances of polished
and modified surfaces were determined by stepwise load increase tests and
staircase test method. Finally, SEM was employed to examine the fracture surface
of the tested specimens. According to the results, it was observed a similar fatigue
behavior of the chemically treated Ti-6Al-4V alloy compared to the samples without treatment.Não recebi financiamentoTratamentos químicos sobre a superfície dos implantes intra-ósseos são
usados para aumentar a área de contato do par implante-osso, diminuindo o
período de osseointegração e favorecendo a capacidade de ligação entre o
implante e o osso. No entanto, modificações de superfície podem afetar a
resistência à fadiga destes materiais, especialmente quanto a nucleação de trinca
por fadiga. Por estas razões, este trabalho avaliou e analisou a influência na
resistência à fadiga das ligas de Ti-6Al-4V ELI com modificações na superfície,
geradas por tratamentos ácidos e um posterior tratamento alcalino. A mudança na
topografia promovida pelos tratamentos químicos foi examinada com microscopia
eletrônica de varredura (MEV) e microscopia confocal de varredura a LASER
(CLSM). O aumento da rugosidade e da área efetiva de contato foram estudadas e
comparadas com as amostras de Ti-6Al-4V sem modificação. A composição
química da superfície foi analisada por espectroscopia com energia dispersiva de
raios-X (EDS). A resistência axial à fadiga dos corpos-de-prova polidos e
modificados foi determinada pelo método escalonado de tensões e o método
“staircase”. Finalmente, Imagens por MEV foram usadas para examinar a
superfície de fratura dos espécimenes fraturados após serem testados à fadiga.
De acordo com os resultados obtidos, observou-se um comportamento
semelhante no desempenho à fadiga do material com a superfície tratada
quimicamente com H3PO4 ou HCl e posteriormente com NaOH, em comparação
com o sem tratamento
Study of bioactivity, corrosion resistance and fatigue behavior of Ti-12Mo-6Zr-2Fe alloy after different surface treatments
No full textLa demande de nouveaux implants avec une meilleure bioactivité, résistance à la corrosion et des propriétés mécaniques optimisées a augmenté considérablement. Différents traitements de surface sont appliqués sur des alliages de titane pour améliorer leur processus d’ostéo-intégration. Néanmoins, le développement de nouvelles surfaces bioactives pourrait causer une réduction considérable de la résistance à la fatigue et à la corrosion, ce qui peut entraîner des défaillances catastrophiques dans leurs utilisations cliniques. Ainsi, dans ce travail, la performance en biocompatibilité, en fatigue et en corrosion de l’alliage de Ti-12Mo-6Zr-2Fe (TMZF) a été étudié. Cet alliage a été soumis à trois modifications de surface différentes, à savoir le traitement chimique de surface (CST, en anglais, pour Chemical Surface Treatment), les nanotubes (Nt) et les nanopores (NP). Les échantillons ont été immergés dans une solution physiologique appelée SBF (en anglais, pour Simulated Body Fluid) avec des durées d’immersion différentes : 0, 1, 7, et 14 jours. Après 14 jours d’immersion dans SBF, les échantillons qui ont subi un traitement chimique de surface ont montré une formation importante d’hydroxyapatite (HAp), nécessaire pour assurer une bonne osseo-intégration de l’implant. De même, les échantillons avec des nanotubes et nanopores montrent une formation, respectivement, faible et modérée de HAp. Dans les échantillons sans traitement de surface, la formation de HAp n’a pas été observée. Le comportement électrochimique a été étudié par des courbes de polarisation et par spectroscopie d’impédance électrochimique (SIE, ou EIS en anglais, pour Electrochemical Impedance Spectroscopy). Les échantillons avec NT et NP manifestent une meilleure résistance à la corrosion et un domaine de passivité (Ipass) plus faible, en comparaison avec les échantillons non traités après 14 jours d’immersion dans SBF. Les échantillons qui ont subi un traitement chimique de surface (CST) ont démontré une résistance à la corrosion faible par rapport aux autres surfaces étudiées. Par ailleurs, dans le contexte des investigations électrochimiques, les résultats de SIE d’échantillons NT et NP ont montré un comportement caractéristique qui ne pouvait pas être modélisé par les circuits équivalents traditionnels. Ainsi, un modèle de ligne de transmission de deux canaux a été proposé pour analyser ces résultats d’impédance, permettant un ajustement réussi des données de SIE. Finalement, une réduction de la résistance à la fatigue a été observée dans les échantillons traités avec NP et CST, via une fragilisation par l'hydrogène, en raison du captage d’hydrogène pendant les traitements de surface.Demand for new implants with improved bioactivity, corrosion resistance, and optimal mechanical properties has been increasing considerably. In this sense, different surface treatments are applied in titanium alloys to improve their osteointegration process. Nevertheless, the developments of new bioactive surfaces could cause a considerable reduction in fatigue and corrosion strength leading to catastrophic failures in clinical use. For these reasons, this work studied the biocompatibility, corrosion and fatigue performance of Ti-12Mo-6Zr-2Fe alloy treated with three different surface modifications, namely, chemical surface treatment (CST), nanotubes (Nt) and nanopores (NP). Samples were immersed in simulated body fluid (SBF) solution during different periods, 0, 1, 7, and 14 days. After 14 days immersed in SBF, samples with CST showed high hydroxyapatite (HAp) formation; Likewise, samples with Nt and NP exhibited lower and moderated HAP formation, respectively. In samples without surface treatment was not observed HAp formation. The electrochemical behavior was studied through polarization curves and electrochemical impedance spectroscopy (EIS). Samples with Nt and NP displayed higher corrosion resistance and lower passivation current (Ipass) compared with untreated samples, after 14 days of immersion in SBF; samples with CST showed the worst corrosion performance for all the surface conditions studied. Furthermore, within the framework of electrochemical investigations, EIS results of Nt and NP samples showed a characteristic behavior that could not be modeled by traditional equivalent circuits. Thus, it was proposed a two-channel transmission line model for analyzing this impedance results, leading to a successful fitting of the EIS data. Finally, was observed a reduction of the fatigue resistance in the samples treated with NP and CST, associated with hydrogen embrittlement processes, due to the pick-up of hydrogen during the respective surface treatments
Study and develop stabilization treatment for multi-materials and galvanic corrosion assessment - Deliverable D3.2
No full textThe purpose of this deliverable is to report on the work carried out in Task 3.2 of WP3 (Curative conservation treatments), concerning the study and development of treatments for multi-materials (Al alloys associated with steel)
Protective treatments for the protection and preservation of aircraft artefacts from world war II
No full textThis study explores the effectiveness of different coatings in preserving aluminum alloy aircraft wrecks. In cultural heritage conservation, coatings must not only protect artefacts under corrosive exhibition conditions but also maintain their visual integrity and be reversible for future treatments. Three coatings were selected and tested: ParaloidTM, commonly used in conservation; DinitrolTM, an industrial product for aluminum protection; and Cutin, a novel coating derived from recycled tomato peels. Each coating was assessed based on its protective ability, aesthetic impact, and reversibility.ParaloidTM, while aesthetically pleasing and easily reversible, offers limited protection, especially outdoors.DinitrolTM demonstrated superior protective qualities, with high impedance values indicating strong corrosion resistance. However, its reversibility properties are limited. Cutin showed promise as a protective coating. It is
also reversible with ethanol. However, its current formulation affects the surface appearance due to residual tomato pigments
Social Structure and Process of a Banana Plantation on the Pacific Coast of Costa Rica
No full textThe University of Kansas has long historical connections with Central America and the many Central
Americans who have earned graduate degrees at KU. This work is part of the Central American Theses
and Dissertations collection in KU ScholarWorks and is being made freely available with permission of the
author through the efforts of Professor Emeritus Charles Stansifer of the History department and the staff of
the Scholarly Communications program at the University of Kansas Libraries’ Center for Digital Scholarship.
http://kuscholarworks.ku.ed
Sendo Escritor
No full textTese (doutorado) - Universidade Federal de Santa Catarina, Centro de Comunição e Expressão, Programa de Pós-Graduação em Literatura, Florianópolis, 2011A tese levanta questões sobre a experiência da escrita para além do caráter institucionalizado da autoria conforme definida pela função autor. Através da análise de "falas de si" de escritores e de aspirantes a escritor, busca debater a constituição do sujeito escritor: aquele sujeito que se constitui a partir de sua própria escrita, assumindo (ou não) diferentes posições em relação às instituições de escrita. Esta possível constituição do sujeito escritor é analisada através de passagens efetuadas por escritores no decorrer de suas experiências com a escrita: o escritor iniciante (passando de não-escritor a escritor), o escritor em consagração (passando de escritor a autor) e o escritor ao final de sua escrita, que desiste de escrever (passando de escritor/autor a não-escritor). Através de depoimentos autobiográficos, o escritor vai além de suas ficções narradas, e testemunha seu aparecimento enquanto sujeito escritor, sempre em constante mudança, transformação e criação de si mesmo. Num movimento de subjetivação de si, como formula Marguerite Duras, escreve para saber o que escreveria se escrevesse. Com isso, torna-se outro a partir daquilo que escreve, pela crença num sujeito escritor que transforma sua própria vida em existência estética, em um modo de vida.This dissertation brings up questions about the experience of writing, beyond the institutional character of authorship provided by the Author Function. By analyzing #speeches of the self# by writers and aspiring writers, it proposes a debate on the constitution of the writing subject: a subject that constitutes itself from its own writing, taking on (or not) different positions regarding writing institutions. The study of this possible constitution of the writing subject focuses on three changes made by writers during their writing experiences, corresponding to: (1) the beginner (changing from non-writer to writer), (2) the writer to be acclaimed (changing from writer to author), and (3) the writer at the end of his/her writing activity, the one who gives up writing (changing from writer/author to non-writer). Through autobiographical texts, a writer goes beyond his/her narrated fictions, and testifies his/her appearance as a writing subject, in permanent change, always transforming and creating him/herself. In a movement of subjectivation of the self, he/she writes in order to know what he/she would write if he/she wrote (as Marguerite Duras would say). Thus, the writer becomes another one by writing what he/she writes, by the faith in a writing subject the transforms his/her own life in an aesthetic existence, in a way of life
El emprendimiento y los procesos de enseñanza - aprendizaje formativos en niños de cuarto grado en educación básica de la unidad educativa Cesar Rohon Sandoval, del cantón Salinas, parroquia Anconcito en la provincia de Santa Elena. En el periodo lectivo 2021-2022
No full textEsta investigación hace referente al emprendimiento y los procesos de enseñanza – aprendizaje en los estudiantes cabe realzar que el emprendimiento permite el desarrollo de habilidades como creatividad, trabajo en equipo y visión ganadora dentro del campo educativo, pero además de eso, cabe recalcar que se trata de analizar qué factores impiden que los estudiantes aprendan a emprender para tener una mejor visión de la investigación, se utiliza un método mixto cuantitativo y cualitativo que permitirá producir resultados más claros y conclusiones más precisas. Finalmente, este estudio es exploratorio, no experimental, descriptivo, documental y de campo, en el cual se utilizó una variedad de métodos y herramientas de recolección de datos tales como; Las encuestas y entrevistas que nos permiten profundizar en la búsqueda de información. Consecutivamente aplicado los instrumentos se conoce los siguientes resultados que los educandos conocen que es emprender, como realizarlo y los beneficios que se obtiene al crear un emprendimiento, de la misma manera los docentes conocen las estrategias, las habilidades y destrezas que los estudiantes desarrollan con el emprendimiento pero que les hace falta implementarlo dentro del salón de clases para mejorar continuamente el proceso de enseñanza aprendizaje, finalmente este trabajo va a permitir encontrar las ventajas y desventajas que tiene la institución educativa al implementar el emprendimiento dentro del proceso
educativo o aula clase en diferentes materias que ayuden a desarrollar con amplitud las destrezas y habilidades de los educandos preparándolos así para el desenvolvimiento dentro de la sociedad y un futuro mejor con éxito
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