Photoactivity of nanostructured porous Nb2O5 : effect of Pt, Ta, Cu, and Ti impregnation

In the present work, we report the obtaining of nanostructured porous Nb2O5 by anodizing process, with Pt, Ta, Cu, or Ti impregnation, and by magnetron sputtering process. The techniques of scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy were used to evaluate the morphology, and the composition and crystalline structure of nanoporous Nb2O5. The photocatalytic activity was evaluated by electrochemical photocurrent tests under UV light illumination. Nanostructured porous Nb2O5 with Pt, Ta, Cu, and Ti impregnation presented bandgap reduction and 10 times higher photocurrent density in the presence of UV light when compared to the not impregnated nanoporous Nb2O5

Nitretação a plasma de zircônia estabilizada com ítria: um estudo comparativo

Este trabalho apresenta a investigação experimental da nitretação da zircônia parcialmente estabilizada com ítria (3% mol), utilizando dois diferentes métodos de nitretação: i) nitretação a plasma por radiofrequência e ii) nitretação por indução eletromagnética, através de um forno de indução de alta frequência. As características morfológicas e físico-químicas da camada resultante do processo de nitretação a plasma foram analisadas por diferentes técnicas, tais como espectroscopia de retroespalhamento Rutherford e difração de raios X e análise química por espectroscopia Raman e Espectroscopia de fotoelétrons excitados por raios X. A estrutura da camada nitretada a plasma é complexa, sendo composta de zircônia tetragonal e cúbica, bem como de oxinitreto de zircônio. Este artigo descreve uma comparação entre duas técnicas de nitretação para determinar a eficiência de cada método. A técnica de nitretação a plasma por radiofrequência foi mais efetiva que por indução eletromagnética devido a incorporação de nitrogênio na matriz da zircônia. http://dx.doi.org/10.18226/23185279.v5iss1p1

Application of Taguchi method to study morphological evolution of TiO2 nanotubes obtained via anodization process

The growth of titanium dioxide nanotubes (TiO2) via anodization process depends on the controlling parameters such as applied potential, anodization time, and electrolyte composition. In the present work, the Taguchi method was applied to evaluate statistically the influence of the anodization parameters on the morphology of anodized TiO2 films. Mixture of ethylene-glycol and glycerol was used as an electrolyte and the settings of the experimental design were parameterized on the basis of four important anodization factors consisting of chemical pretreatment, amount of fluoride, water content and applied potential. Samples were characterized by XRD and FEG-SEM. Based on 4 variables at 3 different settings, full factorial plan requires 34 = 81 tests. In this work the experiment was designed on the basis of an L9 (34) orthogonal array (4 variables, 3 levels, 9 tests). The optimum conditions were found on the basis of smaller-is-better and larger-is-better analyses. The signal-to-noise ratio was employed to find optimal process parameters levels and to analyze the influence of these parameters on the tubular length, internal and external diameters and formation of nanograss on the film surface. Hence, it is clearly shown that the performance of TiO2 nanotubes can be evaluated by the Taguchi method

Wear resistance of plasma electrolytic oxidation coatings on Ti-6Al-4V ELI alloy processed by additive manufacturing

The additive manufacturing (AM) technique can produce Ti-6Al-4V ELI (extra low interstitial) alloy for personalized biomedical devices. However, the Ti-6Al-4V ELI alloy presents poor tribological behavior. Regarding this, coatings are a feasible approach to improve the wear resistance of this alloy. In the literature, the tribological behavior of TiO2 coatings incorporated with Ca and P formed by one-step plasma electrolytic oxidation (PEO) on Ti-6Al-4V ELI alloy processed by AM has not been investigated. Thus, in the present work, it was studied the influence of Ti-6Al-4V ELI alloy processed by AM on the wear resistance and morphologic of the coating obtained by PEO (plasma electrolytic oxidation). In this way, three different voltages (200, 250, and 300 V) were employed for the PEO process and the voltage effect on the properties of the coatings. The coatings were characterized by contact profilometry, scanning electron microscopy, energy-dispersive spectroscopy, the sessile drop method, grazing-incidence X-ray diffraction, and wear tests, on a ball-on-plate tribometer. The increase in applied voltage promoted an increase in roughness, pore area, and a decrease in the pore population of the coatings. In addition, the coatings, mainly composed of anatase and rutile, showed good adhesion to the metallic substrate, and the presence of bioactive elements Ca and P were detected. The thickness of the coatings obtained by PEO increases drastically for voltages higher than 250 V (from 4.50 ± 0.33 to 23.83 ± 1.5 µm). However, coatings obtained with lower voltages presented thin and dense layers, which promoted a superior wear resistance (increase in wear rate from 1.99 × 10−6 to 2.60 × 10−5 mm3/s). Finally, compared to the uncoated substrate, the PEO coatings increased the wear resistance of the titanium alloy obtained by AM, also showing a superior wear resistance compared to the commercial Ti-6Al-4V alloy previously evaluated, being such a positive and promising behavior for application in the area of metallic implants

Desempeño fotoeletroquímico de nanoestruturas de niobio obtenidas por anodización: efecto de la concentración de glicerol / Desempenho fotoeletroquímico das nanoestruturas de nióbio obtidas por anodização: efeito da concentração de glicerol

Se han realizado muchos estudios sobre el comportamiento de nanotubos de dióxido de titanio (TiO2) para aplicaciones fotocatalíticas. Sin embargo, se han reportado pocos estudios involucrando metales como niobio (Nb). Los óxidos de niobio presentan propiedades catalíticas muy similares a las del TiO2, con la ventaja de que Brasil concentra el 96% de las reservas mundiales de Nb. Procesos que utilizan técnicas electroquímicas como anodización han sido empleados para la obtención de sólidos nanoporosos en metales. En este estudio, las muestras de metales de niobio fueron anodizadas a 90V durante 90 minutos. El electrolito utilizado en la anodización fue una mezcla de glicerol, NH4F y agua. Las muestras anodizadas fueron tratadas térmicamente a 450°C en atmósfera de N2 por 60 minutos. La caracterización estructural fue realizada por difracción de rayos-X y microscopía electrónica de barrido. El desempeño fotoelectroquímico fue evaluado mediante ensayos de fotocorriente en solución de KOH 0,1 M con diferentes concentraciones de glicerol: 0,1 M y 0,2 M. Se constató la presencia de nanotubos de óxido de Nb luego de la anodización, lo que puede haber contribuido a mejorar  el desempeño fotoelectroquímico de los sistemas evaluados. La adición de glicerol a la solución de KOH 0,1 M contribuye al aumento del desempeño fotoelectroquímico.

Overview of sterilization methods for UHMWPE through surface analysis

The sterilization process is essential for the use of biomaterials in the human body in order to avoid contamination. However, the effect of such required pretreatment on the surface must be also evaluated since some modifications may cause a shortened lifespan of this material or changes in properties of interest. Moreover, improvements in sterilization techniques may even enhance properties while the surface is cleaned. The thorough understanding of the effect that the sterilization processes have on the surface of ultra-high molecular weight polyethylene (UHMWPE), widely used biomaterial in orthopedic joint prosthesis, is, therefore, a key study since some modifications during traditional sterilization could be a major problem for patients who have undergone arthroplasty surgery. This work brings a comprehensive study on sterilization techniques already available and extensively used (hydrogen peroxide plasma, ethylene oxide, steam autoclave) and a comparison with results obtained for recently developed cold plasma-based sterilization technique. The effects of the processes have been extensively compiled by data obtained for thermal analysis, nanoscale wear and friction, physicochemical, topographical, wettability, and in vitro cytotoxicity experiments. An overall outlook on the set of samples points out to cold plasma oxidation (CPO) being an adequate and potential candidate for improving wear resistance, while maintaining thermal stability and a restrained adhesion of L929 cells, provoked by its hydrophilicity and larger surface area

Avaliação das propriedades físico-químicas, mecânicas e tribológicas de filmes finos de VC, Si3N4 e TiN/Ti

Neste trabalho foram estudadas correlações entre estrutura e propriedades de certos revestimentos baseados em filmes finos cerâmicos, mais especificamente carbeto de vanádio, nitreto de silício e nitreto de titânio sobre titânio. As condições e parâmetros de deposição dos filmes, tais como composição e fluxo dos gases reativos, temperatura do substrato e outras, foram variados para obter filmes com composições, densidades e espessuras convenientes. As características físico-químicas dos filmes foram determinadas mediante a utilização de um grande número de ferramentas analíticas, descritas no texto. A avaliação do comportamento mecânico, tribológico e de resistência à corrosão dos filmes também foram determinadas por um apreciável número de métodos, os quais são descritos em detalhes no texto. Os resultados indicam algumas correlações importantes entre dureza, resistência ao desgaste e resistência à corrosão por um lado, e composição, densidade real e estrutura cristalina, por outro lado. Da mesma forma, foi possível estabelecer fatos novos sobre a adesão de filmes finos a substratos de aço e o transporte de diferentes espécies químicas envolvidas através de estruturas TiN/Ti/aço nitretado. Perspectivas para a continuidade do trabalho de pesquisa aqui relatado são discutidas no capítulo de Conclusões.We report here on the investigation of correlations between structure and properties of certain coatings based on ceramic thin films, more specifically vanadium carbide, silicon nitride and titanium nitride on titanium. The films deposition conditions and parameters, such as the reactive gases compositions and flux, the substrate temperature during deposition and others, were varied in order to obtain films with convenient composition, density and thickness. The physicochemical characteristics of the films were determined by a large number of analytical techniques, as described in the text. The evaluation of the mechanical, tribologic, and corrosion behavior of the thin film coatings was also determined by a substantial number of techniques, all described in the text. The results indicate some important correlations between hardness, wear and corrosion resistance on one hand, and composition, real density, and crystalline structure on the other hand. In the same lines, it was possible to establish new facts about adhesion of thin film coatings on steel substrates and the transport of the involved chemical species across TiN/Ti/nitrided steel structures. The prospects for continuations of this work are discussed in the Conclusões chapter

Avaliação das propriedades físico-químicas, mecânicas e tribológicas de filmes finos de VC, Si3N4 e TiN/Ti

Neste trabalho foram estudadas correlações entre estrutura e propriedades de certos revestimentos baseados em filmes finos cerâmicos, mais especificamente carbeto de vanádio, nitreto de silício e nitreto de titânio sobre titânio. As condições e parâmetros de deposição dos filmes, tais como composição e fluxo dos gases reativos, temperatura do substrato e outras, foram variados para obter filmes com composições, densidades e espessuras convenientes. As características físico-químicas dos filmes foram determinadas mediante a utilização de um grande número de ferramentas analíticas, descritas no texto. A avaliação do comportamento mecânico, tribológico e de resistência à corrosão dos filmes também foram determinadas por um apreciável número de métodos, os quais são descritos em detalhes no texto. Os resultados indicam algumas correlações importantes entre dureza, resistência ao desgaste e resistência à corrosão por um lado, e composição, densidade real e estrutura cristalina, por outro lado. Da mesma forma, foi possível estabelecer fatos novos sobre a adesão de filmes finos a substratos de aço e o transporte de diferentes espécies químicas envolvidas através de estruturas TiN/Ti/aço nitretado. Perspectivas para a continuidade do trabalho de pesquisa aqui relatado são discutidas no capítulo de Conclusões.We report here on the investigation of correlations between structure and properties of certain coatings based on ceramic thin films, more specifically vanadium carbide, silicon nitride and titanium nitride on titanium. The films deposition conditions and parameters, such as the reactive gases compositions and flux, the substrate temperature during deposition and others, were varied in order to obtain films with convenient composition, density and thickness. The physicochemical characteristics of the films were determined by a large number of analytical techniques, as described in the text. The evaluation of the mechanical, tribologic, and corrosion behavior of the thin film coatings was also determined by a substantial number of techniques, all described in the text. The results indicate some important correlations between hardness, wear and corrosion resistance on one hand, and composition, real density, and crystalline structure on the other hand. In the same lines, it was possible to establish new facts about adhesion of thin film coatings on steel substrates and the transport of the involved chemical species across TiN/Ti/nitrided steel structures. The prospects for continuations of this work are discussed in the Conclusões chapter