Determinación de la adhesión de hidroxiapatita sobre Ti cp utilizando impedancia electroquímica

La espectroscopia de impedancia electroquímica es una de las técnicas más modernas utilizadas para caracterizar las propiedades eléctricas de una película cerámica y su adhesión a la superficie metálica. Este trabajo representa parte de un proyecto en ejecución en el que se propone evaluar la solubilidad de una película de hidroxiapatita (HA) depositada sobre la superficie pulida de Ti cp por el método biomimético, después de varios períodos de inmersión en un medio fisiológico con la composición siguiente (g/L): NaCl 8,74; NaHCO3 0,35; Na2HPO4 0,06; NaH2PO4 0,06. A través de la técnica de impedancia es posible determinar la cantidad de disolución que penetra en la película y, a partir de esto, estimar la solubilidad y el límite de saturación que conduce a la pérdida de adhesión mediante un gráfico que describe el perfil de las variaciones de la capacidad eléctrica en función del tiempo. Las mediciones de impedancia fueron realizadas a potenciales de circuito abierto después de varios períodos de inmersión, en el intervalo de 100 KHz a 10 mHz . Los diagramas de Bode muestran claramente que el recubrimiento provee una protección cada vez menos eficaz con el aumento del tiempo de exposición en disolución fisiológica. La máxima impedancia |z| obtenida, correspondiente a un período de 24 h en el que la protección fue más efectiva, permaneció alrededor de 106Ω · cm2 a 0,01 Hz

Corrosión de juntas soldadas empleando láser y brazing de una aleación odontológica AuPdAgIn

La soldadura ha sido utilizada en la Odontología para resolver problemas de adaptación de las prótesis, permitiendo trabajar con sus segmentos, mejorando la distribución uniforme de fuerzas, haciendo mínimos los traumas o fallas en el hueso, en el implante o en la prótesis. En esta investigación, fue estudiada la corrosión de la aleación AuPdAgIn, utilizada en prótesis sobre implantes en un medio de NaCl 0,9 %, aireado, que simulaba las condiciones del ambiente bucal, después de haber sido sometida a dos procesos de soldadura: láser y brazing. El desarrollo de nuevos equipos de soldadura a láser, de menor costo, tamaño y simplicidad técnica, permitió una mayor utilización de este proceso en la confección de prótesis comparada con la brazing, pues utiliza como fuente de calor un haz de luz concentrado de elevada energía que no causa distorsión en la pieza prostética. Estos dos procesos generan diferencias en las microestructuras; para la soldadura a láser, dentrítica refinada debido a la gran velocidad de enfriamiento (5,96 · 103 ºC/s) y en la brazing (80 ºC/s), granular. La región de soldadura a láser tuvo un desempeño mejor, por presentar un potencial de corrosión más positivo a circuito abierto. Las mediciones de impedancia fueron realizadas a potenciales de circuito abierto después de 24 h de inmersión, se aplicó una perturbación de 10 mV y se obtuvieron cinco puntos por década de frecuencia en el intervalo de 100 kHz a 10 mHz

A STUDY ABOUT CELL ACTIVITY ON ANODIZED Ti-6Al-4V BY MEANS OF PULSED CURRENT

Titanium and some of its alloys exhibit excellent anti-corrosive and biocompatibility properties due to rapid formation of a passive film on their surfaces when exposed to the atmosphere. However, such materials presentpoor osteoindutive properties. Surfaces modified via anodization are being proposed in this study to promote a chemical interaction between implants and bone cells. For this purpose, samples in Ti-6Al-4V alloy discs were anodized in a phosphoric acid solution using pulsed current for being applied in orthopaedic implants. The pulsed current is based on duty cycle (DC), which was supplied by a square wave pulse rectifier at 100 Hz and maximum tension of 30 V. A scanning electron microscope was used to obtain images of the anodized surfaces, thus revealing the presence of uniformly distributed pores over the entire surface, measuring approximately 2 m in diameter. Osteogenic cells grown on the surface of the control and anodized samples were assayed for cytotoxicity and mineralized matrix formation. The anodized surfaces presented a higher rate of viable cells after 10 days, as well as a higher amount of nodules (p = 0.05). In conclusion, these results suggest that the nanotopography promoted by anodization using pulsed current induces beneficial modulatory effects on osteoblastic cells

Corrosion resistance of the phases presents in dental amalgams

Neste trabalho avaliou-se a resistência à corrosão em solução salina das fases presentes na microestrutura de amálgamas dentários comerciais: gama1-Ag2Hg3, o eutético Ag-Cu e gama2-Sn7-8Hg, empregando-se técnicas eletroquímicas de potencial a circuito aberto com o tempo, de polarização potenciodinâmica e de espectroscopia de impedância eletroquímica. As ligas metálicas em estudo já foram caracterizadas em um trabalho prévio, por meio de microscopia eletrônica de varredura e difratometria de raios X. A resistência à corrosão se origina da formação de filmes passivos na superfície metálica e parece estar determinada pela natureza rugosa e porosa das superfícies.In this work, the corrosion resistance behavior of three of their phases presents in dental amalgam has been investigated: gamma1-Ag2Hg3 (the matrix phase in the microstructure), gamma2-Sn7-8Hg (the phase most susceptible to corrosion in the oral cavity, according to the literature) and Ag-Cu eutectic (the component of the more modern powder alloys, the objective being to reduce the quantity of gamma2-Sn7-8Hg formed during the amalgamation and in this way increase its corrosion resistance). Electrochemical measurements were carried out in 0,9% aqueous sodium chloride in order to simulate the aggressivity of the oral cavity, using open circuit potential measurements, polarization curves and electrochemical impedance. The corrosion resistance exhibited by alloys can be associated with formation of a corrosion layer and seems to be dominated by the presence of a porous layer in the surface

Effect of Pulsed Current Frequency and Anodisation Time on Surface Properties of Electropolished and Nonelectropolished Titanium Substrates

Surface characteristics of anodic films formed on electropolished and nonelectropolished titanium substrates have been evaluated using different sets of anodisation parameters at room temperature. Surfaces were analysed by light microscopy, Raman spectroscopy, scanning electron microscopy, and X-ray diffraction. The formation of TiO2 anatase phase was only detected on nonelectropolished substrates and there seems to be a larger amount of anatase as samples are anodised; consequently, the smallest crystals were obtained at the highest frequency of pulsed current. EIS results showed that there is no difference in the degree of compactness along the layer thickness

Corrosão do aço-carbono: uma abordagem do cotidiano no ensino de química

In this paper, two simple ways of evaluating carbon steel sheet corrosion in a hydrochloric acid solution were presented as an experimental proposal for corrosion teaching. The first method is based on direct measurements of mass before and after corrosion tests. The second approach follows the principle of visual colorimetry by which soluble corrosion products are transformed into red complexes allowing monitoring of the products'concentration according to increases in solution color intensity. Both methods proved able to determine the corrosion rate

EFFECT OF PHOSPHORIC ACID CONCENTRATION AND ANODIZING TIME ON THE PROPERTIES OF ANODIC FILMS ON TITANIUM

In this study, it was investigated the influence of electrolyte concentration and anodizing time on the electrochemical behaviour and morphology of anodic films formed on commercially pure Ti. Electrochemical methods and surface analyses were used to characterize the films. It was found that the electrolyte concentration and anodizing time affect the growth and protective characteristics of films in a physiologic medium. It was possible to observe their non-uniformity on Ti substrates under the tested conditions. In potentiodynamic profiles, it was observed that passivation current values are affected by an anodizing time increase. Variations in impedance spectra were associated with an increase of defects within the film