Avaliação das propriedades físico-químicas de ligas à base de cobre com potencial atividade microbicida
Data
2024-05-29
Autores
Guerini, Guilherme Gonçalves 
Orientadores
Silva, Ricardo Alexandre Galdino da
Tipo
Dissertação de mestrado
Título da Revista
ISSN da Revista
Título de Volume
Resumo
O cobre (Cu) e suas ligas têm atraído a atenção de pesquisadores nos últimos anos devido à sua capacidade microbicida contra diversos microrganismos, possuindo várias aplicações na medicina e como forma de prevenir a propagação de doenças em ambientes de alta circulação humana (hospitais e transporte público). Porém, a utilização do cobre puro é inviável devido aos processos de oxidação e corrosão em diferentes meios que afetam a estética e a vida útil do material. Assim, no intuito de melhorar o comportamento de corrosão sem prejudicar a atividade microbicida, neste estudo foram avaliadas inicialmente seis ligas de CuZnNi e o latão 70/30 para entender suas características físico-químicas em diferentes eletrólitos e sua atividade microbiológica contra bactérias e leveduras de interesse clínico. Para isto, foram realizados testes físico-químicos e eletroquímicos para caracterização das amostras em solução de NaCl 0,5 ϻ e de suor artificial para mimetizar condições desafiadoras e aquelas encontradas no cotidiano. Já para os testes microbiológicos foram realizados ensaios com bactérias e leveduras para avaliar sua capacidade microbicida e de evitar a formação de biofilmes. Tais ensaios conduziram o trabalho à seleção de uma liga que apresentasse a melhor capacidade de resistência à corrosão para a mesma atividade microbicida observada nas demais ligas. Os dados obtidos por difratometria de raios X confirmaram a presença de duas fases ricas em cobre, ambas provenientes do processo de solidificação do material. Além disso, os resultados mostraram que a adição de níquel promoveu um refinamento da microestrutura das ligas. As medidas de potencial de circuito aberto mostraram que o aumento do teor de Ni nas ligas tornam os valores de potenciais mais positivos, sugerindo que os materiais tornam se mais nobres. Os resultados indicaram também que a liga Cu68,85Zn26,36Ni4,69, denominada A5, apresentou o melhor comportamento em relação a resistência à corrosão para um mesmo comportamento microbicida frente as outras ligas estudadas. Assim, a liga Cu68,85Zn26,36Ni4,69 foi selecionada para dar continuidade aos testes com solução de NaCl 0,5 ϻ e suor artificial, em comparação com o cobre puro. Quanto à voltametria cíclica, em suor artificial, observou-se uma inversão na intensidade dos picos de oxidação referentes à formação dos íons Cu+ e Cu2+. A liga apresentou menor potencial de corrosão e maior taxa de corrosão em suor artificial. A espectroscopia por impedância eletroquímica demonstrou uma maior resistência do cobre em ambos os meios e a liga A5 mostrou uma menor resistência à transferência de carga (Rct) para o suor artificial. A espectrometria de emissão óptica com plasma indutivamente acoplado mostrou que em suor artificial a liga A5 apresentou maior liberação de íons nos primeiros minutos de imersão. Por fim, pode-se sugerir que as espécies Cu2O, Cu(OH)2, CuCl2, ZnCl2 e Zn(OH)2 são os produtos de corrosão majoritários para os meios analisados. Quanto a atividade microbiológica, a liga A5 foi capaz de inativar os microrganismos testados em menos de 30 min de contato. Além disso, ela apresentou uma capacidade pronunciada de morte celular com uma melhor dispersão de biofilme quando comparada com o aço inoxidável 304 (superfície inerte). Assim, o presente estudo indica que a liga Cu68,85Zn26,36Ni4,69 reuniu as melhores características para se tornar uma alternativa para futuras aplicações nos setores médicos e sanitários.
Copper (Cu) and its alloys have attracted the attention of researchers in recent years due to their microbicidal capacity against various microorganisms, having several applications in medicine and as a way of preventing the spread of diseases in environments with high human circulation (hospitals and public transport). However, the use of pure copper is unfeasible due to oxidation and corrosion processes in different media that affect the aesthetics and useful life of the material. Thus, to improving corrosion behavior without harming microbicidal activity, this study initially evaluated six CuZnNi alloys and 70/30 brass to understand their physicochemical characteristics in different electrolytes and their microbiological activity against bacteria and yeast of clinical interest. To this end, physical-chemical and electrochemical tests were carried out to characterize the samples in NaCl 0.5 ϻ solution and artificial sweat to mimic challenging conditions and those found in daily life. Microbiological tests were carried out with bacteria and yeast to evaluate their microbicidal capacity and to prevent the formation of biofilms. Such tests led the work to select the alloy that contained the best ability to resist corrosion for the same microbicidal activity observed. Data obtained by X-ray diffractometry confirmed the presence of two copper-rich phases, both originating from the material's solidification process. From this, a screening of the alloys was carried out in a NaCl 0.5 ϻ solution, in which the results showed that the addition of nickel promoted a refinement of the microstructure of the alloys. Open circuit potential measurements showed that the increase in Ni content in the alloys shifts the open circuit potentials of the alloys to more positive values, suggesting that they become more noble in the face of corrosion. The results indicated that the alloy Cu68.85Zn26.36Ni4.69, called A5, presented the best behavior in relation to corrosion resistance for the same microbicidal behavior compared to the other alloys studied. Therefore, the Cu68.85Zn26.36Ni4.69 alloy was selected to continue the tests with 0.5 ϻ NaCl solution and artificial sweat in comparison with pure copper. As for cyclic voltammetry in artificial sweat, an inversion in the intensity of the oxidation peaks related to the formation of Cu+ and Cu2+ ions was observed. The alloy showed lower corrosion potential and higher corrosion rate in artificial sweat. The electrochemical impedance results demonstrated greater copper resistance in both media and the A5 alloy showed greater electrical conductivity (lower Rct) for artificial sweat. Optical emission spectrometry with inductively coupled plasma showed that in artificial sweat the A5 alloy suffered greater release of ions into the solution. Finally, it can be suggested that the species Cu2O, Cu(OH)2, CuCl2, ZnCl2 and Zn(OH)2 are the major corrosion products for the analyzed media. As for microbiological activity, the A5 alloy was able to inactivate the tested microorganisms in less than 30 min under contact. Furthermore, it showed a pronounced cell killing capacity with better biofilm dispersion when compared to 304 stainless steel (inert surface). Thus, the present study indicates that the Cu68.85Zn26.36Ni4.69 alloy has the best characteristics to become an alternative for future applications in the medical, food and health sectors.
Copper (Cu) and its alloys have attracted the attention of researchers in recent years due to their microbicidal capacity against various microorganisms, having several applications in medicine and as a way of preventing the spread of diseases in environments with high human circulation (hospitals and public transport). However, the use of pure copper is unfeasible due to oxidation and corrosion processes in different media that affect the aesthetics and useful life of the material. Thus, to improving corrosion behavior without harming microbicidal activity, this study initially evaluated six CuZnNi alloys and 70/30 brass to understand their physicochemical characteristics in different electrolytes and their microbiological activity against bacteria and yeast of clinical interest. To this end, physical-chemical and electrochemical tests were carried out to characterize the samples in NaCl 0.5 ϻ solution and artificial sweat to mimic challenging conditions and those found in daily life. Microbiological tests were carried out with bacteria and yeast to evaluate their microbicidal capacity and to prevent the formation of biofilms. Such tests led the work to select the alloy that contained the best ability to resist corrosion for the same microbicidal activity observed. Data obtained by X-ray diffractometry confirmed the presence of two copper-rich phases, both originating from the material's solidification process. From this, a screening of the alloys was carried out in a NaCl 0.5 ϻ solution, in which the results showed that the addition of nickel promoted a refinement of the microstructure of the alloys. Open circuit potential measurements showed that the increase in Ni content in the alloys shifts the open circuit potentials of the alloys to more positive values, suggesting that they become more noble in the face of corrosion. The results indicated that the alloy Cu68.85Zn26.36Ni4.69, called A5, presented the best behavior in relation to corrosion resistance for the same microbicidal behavior compared to the other alloys studied. Therefore, the Cu68.85Zn26.36Ni4.69 alloy was selected to continue the tests with 0.5 ϻ NaCl solution and artificial sweat in comparison with pure copper. As for cyclic voltammetry in artificial sweat, an inversion in the intensity of the oxidation peaks related to the formation of Cu+ and Cu2+ ions was observed. The alloy showed lower corrosion potential and higher corrosion rate in artificial sweat. The electrochemical impedance results demonstrated greater copper resistance in both media and the A5 alloy showed greater electrical conductivity (lower Rct) for artificial sweat. Optical emission spectrometry with inductively coupled plasma showed that in artificial sweat the A5 alloy suffered greater release of ions into the solution. Finally, it can be suggested that the species Cu2O, Cu(OH)2, CuCl2, ZnCl2 and Zn(OH)2 are the major corrosion products for the analyzed media. As for microbiological activity, the A5 alloy was able to inactivate the tested microorganisms in less than 30 min under contact. Furthermore, it showed a pronounced cell killing capacity with better biofilm dispersion when compared to 304 stainless steel (inert surface). Thus, the present study indicates that the Cu68.85Zn26.36Ni4.69 alloy has the best characteristics to become an alternative for future applications in the medical, food and health sectors.
Descrição
Citação
GUERINI, Guilherme Gonçalves. Avaliação das propriedades físico-químicas de ligas a base de cobre com potencial atividade microbicida. 2024. 126 f. Dissertação (Mestrado em Química - Ciênica e Tecnologia da Sustentabilidade) - Instituto de Ciências Ambientais, Químicas e Farmacêuticas, Universidade Federal de São Paulo, Diadema, 2024.