Thesis (MSc.(Chemistry) - University of Pretoria, 2007. / M. R. Phupheli on cover title differs from the title page where name is written as: Phupheli Milingoni Robert. Confirmed with Student Administration that information correlates with their records. Summary in English.

Thesis (Ph. D.)--State University of New York at Binghamton, Materials Science and Engineering Program, 2009. / Includes bibliographical references.

Les organes de frottement en carbure de silicium répondent à des critères de fonctionnement exigeants grâce aux propriétés offertes par cette céramique. Son faible coefficient de dilatation thermique et sa bonne conductivité thermique la rendent moins sensible aux chocs thermiques que les autres céramiques et particulièrement, en frottement, où la génération locale de chaleur peut s’avérer importante. Ces performances tribologiques sont conditionnées par son environnement mécanique, par la nature de la face de frottement antagoniste et surtout par le comportement des éléments interfaciaux circulant dans le contact. Le frottement du couple homogène SiC/SiC dans une configuration anneau/anneau a tout d’abord été étudié et son mécanisme d’usure a été établi, montrant un glissement sec difficile et une usure prononcée. Des alternatives ont alors été étudiées : revêtement du carbure par du DLC ou remplacement de la contreface par une bague carbone-graphite. Les imprégnations des bagues carbone-graphites par différents composés, polymères avec la résine phénolique et le PTFE ou métallique avec l’antimoine permettent d’en façonner les propriétés et, par conséquent, la réponse tribologique. Les essais sont réalisés à l’aide d’un tribomètre en glissement rotatif et ont permis de caractériser ces comportements tribologiques en fonction de différentes conditions de pression de contact, de vitesse et de température. Une analyse thermique a également été développée grâce à l’utilisation d’une caméra thermique infrarouge et a permis d’identifier les flux thermiques et le champ de températures durant le frottement. Des analyses physico-chimiques par EDS et spectroscopie Raman ont permis de décrire les transferts de matière mis en jeu et ont mis en évidence des phénomènes locaux d’oxydation de l’interface. La forte participation des imprégnants du carbone-graphite à la formation du troisième corps a été montrée. La spectroscopie Raman a également permis d’étudier le caractère cristallin des surfaces et du troisième corps formé et de mettre en évidence des phénomènes de contraintes en surface à l’origine des mécanismes d’endommagement. Il a ainsi pu être reconstitué un scénario complet des différentes étapes du glissement en termes de bilans de matière et d’énergie dans le contact. / Silicon carbide friction bodies fulfill high operation criteria owing to the properties provided by this ceramic. Its low thermal expansion coefficient and good thermal conductivity make it less sensitive to thermal shocks than other ceramics and particularly in friction, where the local heat generation may be significant. These tribological performances are then conditioned by the mechanical environment, by the nature of the counterface and above all by the interfacial elements circulating inside the contact. The friction of the homogeneous SiC/SiC pair in a ring-on-ring configuration was first studied and its wear mechanism was redefined. A hard silicon carbide counterface showed a difficult dry sliding and a high wear, alternative materials were studied: DLC coating on silicon carbide rings or carbon-graphite rings. Impregnation of the carbon-graphite rings with different compounds, polymers with the phenolic resin and PTFE or metal with antimony, shaped its properties and therefore, the tribological behaviour. Friction tests are carried out using a rotary sliding tribometer. They characterized the tribological behaviour for different operating conditions of contact pressure, sliding velocity and temperature of the environment. In addition, a thermal analysis was also implemented by using an infrared thermal camera in order to identify heat flows in the system and the temperature field for the entire duration of the tests. Physico-chemical analysis using EDS and Raman spectroscopy permitted to describe the transfers of material which take place during the tests and highlighted the local oxidation phenomena of the interface. The strong contribution of the carbone-graphite impregnants to the formation of the third body was also shown. Raman spectroscopy was also used to examine the crystalline state of the surfaces and the third body. Raman spectroscopy highlighted also stresses which are the source of the damage mechanisms. The different stages of the phenomena taking place during sliding inside the contact in terms of material and energy balance were then described.

Made available in DSpace on 2017-07-20T12:40:17Z (GMT). No. of bitstreams: 1 Cleverson Santos.pdf: 2904178 bytes, checksum: 85140c2fc4cb486fe6c03e6a011296a3 (MD5) Previous issue date: 2016-05-06 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This thesis describes the preparation, characterization and application of electrochemical sensors and biosensors, using different modification techniques, based on Au as transducer. The enzymatic biosensor applied on the detection of pesticide carbaryl was built on a gold electrode functionalized with a monolayer of polyamidoamine dendrimer of fourth generation with a cystamine core (PAMAM-G4) on which it was immobilized the acetylcholinesterase enzyme (AChE), with the aid of glutaraldehyde. After evaluate and determine the best conditions for immobilization of the AChE enzyme (glutaraldehyde concentration of 1% (v/v) and the concentration of enzyme units 496 U. mL-1) on the monolayer of PAMAM, the catalytic activity of the enzyme was evaluated by chronoamperometry in presence of enzymatic substrate AChI obtaining = 2.9 . −1 . The biosensor response for carbaryl detection was based on the inhibition of the enzymatic activity caused by the pesticide. It was verified that 5 min in the pesticide solution is sufficient to block the enzyme active sites. After determining the best conditions for the construction of the biosensor, it was applied for carbaryl detection in the concentration range from 1.0 to 9.0 mol. L-1. The detection and quantification limits were found to be 0.0108 mol. L-1 and 0.032 mol. L-1, respectively. In the second chapter, it is reported the development of an immunosensor applied to qualitative detection of antibodies (AB) T. cruzi. The sensor was built on gold electrode modified with the thiol 3-mercaptopropionic acid (MPA) and the antigens (AG) T. cruzi were covalently immobilized on this surface by the reaction with EDC and NHS. The influence of concentration and of immersion time in the AG solution were evaluated using the techniques of cyclic voltammetry and electrochemical impedance spectroscopy in presence of [Fe(CN)6]3-/4- and the results showed that the best conditions were immersion time of 15 minutes and AG concentration of 0.5 g. L-1.The possible sites of non-specific binding were blocked with bovine serum albumin (BSA). The immersion time in the solution (AB) was also evaluated and the results showed that 30 minutes are sufficient for all specific bonds sites were occupied by AB T. cruzi. Selectivity tests in the absence of AB, only in the serum sample, and in the presence of AB Toxoplasma were performed. The results demonstrated that the immunosensor is selective, since it presented charge transfer resistance (Rct) values in the presence of AB T. cruzi 70% higher than the Rct values in presence of possible interferences.Therefore, the immunosensor presents itself as an alternative to qualitative diagnosis of american trypanosomiasis. In the third chapter, it is reported the modification of carbon graphite electrodes (CG) obtained from dry batteries zinc/carbon with Au microparticles obtained by potentiostatic electrodeposition. The variables involved in the electrodeposition process, such as the gold salt concentration, time and deposition potential were evaluated and optimized using cyclic voltammetry technique in the presence of redox couple [Fe(CN)6]3-/4-. The best conditions for the Au deposition were electrodeposition time of 700 s, potential of +0.3 V and concentration of 10.0 mmol. L-1. In these conditions, Au spherical particles were obtained with an average size of 420 nm, which were homogeneously deposited on the surface of GC electrode and promoted the increase of the electroactive area (GC electrode showed an area of 0.12 cm2 and GC/Au electrode presented an area of 0.25 cm2). The GC/Au electrode was applied for the separation and quantification of dopamine and uric acid present in a mixture. The voltammetric results showed that the GC/Au sensor is selective, once the potential peak separation between the DA and UA species was 370 mV. The detection and quantification limits were found to be 1.86 mol. L-1 and 6.09 mol. L-1 for dopamine and uric acid 17.5 mol. L-1 and 58.5 mol. L-1, respectively. In the development of the three electrochemical devices gold electrodes were used. From the results obtained for the three developed electrochemical devices it can be concluded that high electric conductivity, chemical stability, biocompatibility, ability to miniaturization in the form of microstructures and ease of functionalization of Au electrodes make them suitable conductive matrixes for construction of electrochemical sensors and particularly biosensors. / Esta tese descreve a preparação, caracterização e aplicação de sensores e biossensores eletroquímicos, utilizando diferentes técnicas de modificação baseadas no Au como transdutor. O biossensor enzimático aplicado na detecção do pesticida carbaril foi construído sobre um eletrodo de ouro funcionalizado com uma monocamada do dendrímero poliamidoamina de quarta geração com núcleo de cistamina (PAMAMG4),sobre o qual foi imobilizada com o auxílio de glutaraldeído a enzima acetilcolinesterase (AChE).Após avaliar e determinar as melhores condições de imobilização da enzima AChE (concentração de GLUT 1% (v/v) e concentração de unidades enzimáticas 496 U. mL-1) sobre a monocamada de PAMAM,a atividade catalítica da enzima AChE imobilizada foi avaliada por cronoamperometria na presença do substrato enzimático (AChI) obtendo-se o = 2,9 . −1. A resposta do biossensor na detecção de carbaril foi baseada na inibição da atividade enzimática causada pelo pesticida. Foi constatado que 5 min de imersão na solução do pesticida foram suficientes para que os sítios ativos da enzima fossem bloqueados. Após determinar as melhores condições de construção do biossensor, este foi aplicado na detecção de carbaril na faixa de 1,0 a 9,0 mol. L-1. Os limites de detecção e quantificação encontrados foram de 0,0108 mol. L-1 e 0,032 mol. L-1, respectivamente. No segundo capítulo é relatado o desenvolvimento de um imunossensor aplicado na detecção qualitativa de anticorpos (AB) T. cruzi. O sensor foi construído sobre eletrodo de ouro modificado com o tiol ácido 3-mercaptopropiônico (MPA) e sobre esta superfície foram imobilizados covalentemente pela reação com EDC e NHS, os antígenos (AG) T. cruzi. A influência da concentração da solução de AG e do tempo de imersão nesta solução para a construção do imunossensor foram avaliadas utilizando as técnicas de voltametria cíclica e espectroscopia de impedância eletroquímica na presença de [Fe(CN)6]3-/4- e os resultados demonstraram que as melhores condições foram: tempo de 15 min e concentração de 0,5 g. L-1. Os possíveis sítios de ligações não específicas foram bloqueados com albumina de soro bovino (BSA). O tempo de imersão na solução de AB também foi avaliado. Os resultados mostraram que 30 min são suficientes para que todos os sítios de ligações específicos fossem ocupados pelos AB T. cruzi. Testes de seletividade na ausência de AB,apenas em amostra de soro e também na presença de AB de Toxoplasma foram realizados. Os resultados demonstraram que o imunossensor é seletivo, pois este apresentou valores de resistência de transferência de carga (Rct) na detecção de AB T. cruzi 70% maiores do que na detecção dos possíveis interferentes. Portanto, o imunossensor apresenta-se como uma alternativa no diagnóstico qualitativo de tripanossomíase americana. No terceiro capítulo é descrito a modificação de eletrodos de carbono grafite (CG) obtidos de pilhas secas de zinco/carbono com micropartículas de Au obtidas pela eletrodeposição potenciostática. As variáveis envolvidas no processo de eletrodeposição, tais como concentração do sal de ouro, potencial e tempo de deposição foram avaliadas e otimizadas utilizando a técnica de voltametria cíclica na presença do par redox [Fe(CN)6]3-/4-. As melhores condições foram: tempo de 700 s, potencial de +0,3 V e concentração de 10,0 mmol. L-1. Nestas condições, foram obtidas partículas de Au esféricas com tamanho médio de 420 nm, as quais se apresentaram homogeneamente dispersas sobre toda a superfície do eletrodo de CG e promoveram o aumento da área eletroativa, (o eletrodo CG apresentou uma área de 0,12 cm2 e o eletrodo CG/Au uma área 0,25 cm2). O desempenho do eletrodo CG/Au foi avaliado na separação e quantificação de dopamina e ácido úrico presentes em uma mistura. Os resultados voltamétricos demonstraram que o sensor CG/Au é seletivo, pois apresentou separação de potencial pico de 370 mV entre as duas espécies. Os limites de detecção e quantificação encontrados foram de 1,86 mol. L-1 e 6,09 mol. L-1 para dopamina, e 17,5 mol. L-1 e 58,5 mol. L-1 para ácido úrico, respectivamente. A partir dos resultados obtidos para os três dispositivos eletroquímicos desenvolvidos pode-se concluir que a elevada condutividade elétrica, estabilidade química, biocompatibilidade, possibilidade de miniaturização na forma de microestruturas e a facilidade de funcionalização dos eletrodos de Au fazem destes matrizes condutoras apropriadas para construção de sensores e particularmente biossensores eletroquímicos.

De nos jours, les matériaux carbonés macroscopiques font face à un nombre croissant d'applications en catalyse, soit en tant que supports, soit directement en tant que catalyseurs sans métal. Cependant, il reste difficile de développer un support de catalyseur hiérarchisé à base de. carbone ou un catalyseur utilisant un procédé de synthèse beaucoup plus simple. À la recherche de nouveaux matériaux carbonés structurés pour la catalyse hétérogène, nous avons exploré le potentiel du feutre de carbone / graphite du commerce (FC / FG). Le but du travail décrit dans cette thèse a été le développement du monolithe FG et FC en tant que catalyseur sans métal pour les réactions d’oxydation en phase gazeuse et en tant que support de catalyseur, notamment pour le palladium, pour les réactions d’hydrogénation en phase liquide, et leur rôle dans la performance de réaction de ces catalyseurs. En raison de leur surface de chimie inerte avec une mouillabilité inappropriée, une telle étude avait pour condition d'activer celles d'origine. Par conséquent, des FG et des FC modifiés bien arrondis ont été synthétisés avec des propriétés physico-chimiques adaptées par une série de procédés de traitement chimique, tels que l'oxydation, l'amination, la thiolation, le dopage à l'azote et au soufre. L’oxydation partielle du sulfure d’hydrogène en soufre élémentaire et l’hydrogénation sélective du cinnamaldéhyde α, β-insaturé, en tant que réactions sensibles à l’effet des propriétés du catalyseur sur l’activité et la sélectivité, combinées à des techniques de caractérisation, ont été choisis pour étudier l’effet de la matériaux carbonés sur le comportement catalytique. / Nowadays, macroscopic carbon materials are facing an increasing number of applications in catalysis, either as supports or directly as metal-free catalysts on their own. However, it is still challenging to develop hierarchical carbon-based catalyst support or catalyst using a much simple synthesis process. In the quest for novel structured carbon materials for heterogeneous catalysis we explored the potential of commercial carbon/graphite felt (CF/GF). The aim of the work described in this thesis has been the development of GF and CF monolith as metal-free catalyst for gas-phase oxidation reactions and as catalyst support, notably for palladium, for liquid-phase hydrogenation reactions, and their roles in the reaction performance of these catalysts. Due to their inert chemistry surface with inappropriate wettability, a prerequisite for such a study was to activate the origin ones. Therefore, well-rounded modified GFs and CFs were synthesized with tailored physic-chemical properties by a series of chemical treatment processes, such as oxidation, amination, thiolation, nitrogen- and sulfur-doping. The partial oxidation of hydrogen sulfide into elemental sulfur and selective hydrogenation of α, β-unsaturated cinnamaldehyde, as the sensitive test reactions to the influence of the catalyst properties on activity and selectivity, combined with characterization techniques, were chosen to investigate the effect of functionalized carbon materials on the catalytic behavior.

In this thesis, the aim is to study possible tribo-materials for a rotating inlet valve and to find a suitable material combination for the contact. The valve is part of a modern oil-free and high temperature steam engine. Systematic material selection together with tribological tests and wear analyses are performed. The metals Nitronic 60 and Stellite 6B are tested as self-mated metals, and run against graphite. None of these combinations are found suitable. However, the tests show carbon-based materials to be promising. After further study another carbon-based material, antimony impregnated mechanical carbon is selected as valve seat. For the mating part valve distributor, the material ZrO2-MgO is selected. This tribo-pair has shown friction and wear in the same interval as oil-lubrication. The friction and wear are 50% respectively 10% of the second best tribo-pair found in this thesis. The valve seat material is realizable if supported by a valve block of a Ni-resist cast iron with thermal expansion similar to the valve seat. Lastly a redesign of the valve distributor is suggested to comply with ceramic design guidelines. / Målet med denna rapport är att studera möjliga tribo-material för en roterande inloppsventil och att hitta en lämplig materialkombination för kontakten. Ventilen är en del av en modern oljefri och högtempererad ångmotor. Ett systematiskt materialval tillsammans med tribologiska tester och nötningsanalyser utförs. Metallerna Nitronic 60 och Stellite 6B testas dels mot sig själva, och dels mot grafit. Ingen av dessa kombinationer finns lämplig. Testerna visar dock att kolbaserade material är lovande och eftervidare studier är ett annat kolbaserat material, antimonimpregnerat mekaniskt kol, väljs till ventilsätet. Till motytan till ventilsätet, ventilfördelaren, väljs materialet ZrO2-MgO. Detta tribo-par har visat friktion och nötning i samma intervall som oljesmörjning. Friktionen och nötningen är 50 % respektive 10 % av det näst bästa tribo-paret som hittats i denna avhandling. Ventilsätets material är realiserbart om det stöttas i ett ventilblock av ett ”Ni-resist” gjutjärn med en värmeexpansion som liknar ventilsätets. Slutligen föreslås en omkonstruktion av ventilfördelaren för att uppfylla riktlinjerna för keramisk konstruktion.