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Search Results: 1 - 10 of 249230 matches for " Antonio C. Guastaldi "
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Study of Corrosion Resistance of Laser Welded Au-Pd-Ag-In Alloy Using Electrochemical Techniques  [PDF]
Márcio L. Dos Santos, Heloísa A. Acciari, Carla S. Riccardi, Antonio C. Guastaldi
Materials Sciences and Applications (MSA) , 2011, DOI: 10.4236/msa.2011.27098
Abstract: The aim of this work was to evaluate the corrosion resistance of AuPdAgIn alloy, submitted to laser beam welding, in 0.9% NaCl solution, using electrochemical techniques. Measures of the open circuit potential (OCP) versus time were applied to electrochemical experiments, as well as potentiodynamic direct scanning (PDS) and electrochemical impedance spectroscopy (EIS) on AuPdAgIn alloy, submitted to laser beam welding in 0.9% NaCl solution. Some differences observed in the microstructure can explain the results obtained for corrosion potential, Ecorr, and corrosion resistance, Rp. EIS spectra have been characterized by distorted capacitive components, presenting linear impedance at low frequencies, including a non-uniform diffusion. The area of the laser weld presented corrosion potential slightly superior when compared to the one of the base metal. The impedance results suggest the best resistant corrosion behavior for laser weld than base metal region. This welding process is a promising alternative to dental prostheses casting.
Desenvolvimento e caracteriza??o de suportes porosos de polietileno de ultra alto peso molecular (PEUAPM) para utiliza??o como biomaterial para reposi??o e regenera??o óssea
Aparecida, Anahi H.;Guastaldi, Antonio C.;Fook, Marcus V. L.;
Polímeros , 2008, DOI: 10.1590/S0104-14282008000400004
Abstract: the use of polymer as biomaterials has increased in recent years, mainly as polymeric supports in the three-dimensional regeneration and substitution of tissues. although the ultra high molecular weight polyethylene (uhmwpe) shows advantages in its use as biomaterial, particularly as orthopedic implants, its low chemical reactivity constitutes a limiting factor for interaction with the osseous tissue. the morphological modification of this polymer, leading to a porous material, and its association with a bioactive material can provide tailored biomaterials for the regeneration and replacement of osseous tissue. in this work, polymeric porous supports have been prepared by combining the techniques of salt leaching and compression molding with the application of distinct compression pressures. the polymeric supports showed interconnected porosity with size of pores between 34 and 49 mm and porosity between 39 and 53%, which can then be considered as suitable porous biomaterial.
Estudo do biomaterial Ti-6Al-4V empregando-se técnicas eletroquímicas e XPS
Ramires, Ivan;Guastaldi, Antonio Carlos;
Química Nova , 2002, DOI: 10.1590/S0100-40422002000100003
Abstract: the ti-6al-4v alloy used as biomaterial has been used over the last years. the literature shows controversies concerning the kind and the chemical composition of the film naturally and elctrochemically formed on the surface of the titanium alloy. the presente work studies the film composition before and after the electrochemical polarization tests using the x ray photoelectron spectroscopy (xps) technique. the results showed that the film naturally formed on the metallic surface is constituted of a variety of oxides which do not cover the whole surface of the metallic alloy and therefore, metallic ti, al and v can be found on the uncovered areas. the tests of xps made after the polarization up to 4v (sce) showed that the electrochemically formed film is constituted only of tio2 and that the peak current observed around 1,5 v (sce) is due to the oxidation of any kind of titanium oxide or the growth of the film.
Estudo do biomaterial Ti-6Al-4V empregando-se técnicas eletroquímicas e XPS
Ramires Ivan,Guastaldi Antonio Carlos
Química Nova , 2002,
Abstract: The Ti-6Al-4V alloy used as biomaterial has been used over the last years. The literature shows controversies concerning the kind and the chemical composition of the film naturally and elctrochemically formed on the surface of the titanium alloy. The presente work studies the film composition before and after the electrochemical polarization tests using the x Ray photoelectron spectroscopy (XPS) technique. The results showed that the film naturally formed on the metallic surface is constituted of a variety of oxides which do not cover the whole surface of the metallic alloy and therefore, metallic Ti, Al and V can be found on the uncovered areas. The tests of XPS made after the polarization up to 4V (SCE) showed that the electrochemically formed film is constituted only of TiO2 and that the peak current observed around 1,5 V (SCE) is due to the oxidation of any kind of titanium oxide or the growth of the film.
Analyse titanium surface irradiated with laser, with and without deposited of durapatite
Sisti, Karin Ellen;Garcia JR., Idelmo Rangel;Guastaldi, Antonio Carlos;Antoniolli, Andréia C. M. B.;Rossi, Rafael De;Brochado Neto, álvaro de L.;
Acta Cirurgica Brasileira , 2006, DOI: 10.1590/S0102-86502006001000013
Abstract: purpose: the aim of this study was to analyse the surface of titanium implants using disc irradiated with lasers. methods: titanium discs were irradiated with laser high insensitive (nd-yag), deposited durapatite and used thermal treatment. sample received qualitative morphological analyse trough micrographics with many size in sem (scanning electron microscopy). results: surface laser irradiation shows roughness and isomorphic characteristic. the durapatite amplified the titanium surface area by method biomimetic. conclusion: the surface treatment presented more deposition of durapatite, roughness on the surface, better isomorphic characteristic and increase quantitative in titanium surface area, samples shows rugous, roughness and homogeneity there is not found in the implants available at the market.
Geostatistical Modeling of Uncertainty for the Risk Analysis of a Contaminated Site  [PDF]
Enrico Guastaldi
Journal of Water Resource and Protection (JWARP) , 2011, DOI: 10.4236/jwarp.2011.38066
Abstract: This work is a study of multivariate simulations of pollutants to assess the sampling uncertainty for the risk analysis of a contaminated site. The study started from data collected for a remediation project of a steel- works in northern Italy. The soil samples were taken from boreholes excavated a few years ago and analyzed by a chemical laboratory. The data set comprises concentrations of several pollutants, from which a subset of ten organic and inorganic compounds were selected. The first part of study is a univariate and bivariate sta- tistical analysis of the data. All data were spatially analyzed and transformed to the Gaussian space so as to reduce the effects of extreme high values due to contaminant hot spots and the requirements of Gaussian simulation procedures. The variography analysis quantified spatial correlation and cross-correlations, which led to a hypothesized linear model of coregionalization for all variables. Geostatistical simulation methods were applied to assess the uncertainty. Two types of simulations were performed: correlation correction of univariate sequential Gaussian simulations (SGS), and sequential Gaussian co-simulations (SGCOS). The outputs from the correlation correction simulations and SGCOS were analyzed and grade-tonnage curves were produced to assess basic environmental risk.
Fosfatos de cálcio de interesse biológico: importancia como biomateriais, propriedades e métodos de obten??o de recobrimentos
Guastaldi, Antonio Carlos;Aparecida, Anahi Herrera;
Química Nova , 2010, DOI: 10.1590/S0100-40422010000600025
Abstract: for decades the hydroxyapatite (ha) was only bioceramic of calcium phosphate system used for bone replacement and regeneration, due to its similarity to the mineral phase of bones and teeth. because its slow degradation, other calcium phosphate classified as biodegradable started to awaken interest, such as: amorphous calcium phosphate (acp), octacalcium phosphate (ocp) and tricalcium phosphate (tcp). this work presents the evolution of the use of other calcium phosphates due to their better solubility than the ha, comparing their main physical-chemical and biological properties. are also presented the main methods used to obtain bioceramic coatings on metal and polymer surfaces.
Estudos eletroquímicos de ligas Ti-Mo de interesse para biomateriais
Oliveira,Nilson T. C.; Guastaldi,António C.;
Corros?o e Protec??o de Materiais , 2007,
Abstract: ti alloys are being developed to be used in orthopedic implants due their mechanical properties, biocompatibility and corrosion resistance. at this paper are reported electrochemical studies on the as-cast ti-mo alloys with 6, 10 and 20 mo (wt.%), in 0.15 mol/l na2so4 solution and ringer physiological solution. analyses of the rest-potential indicated that all alloys present the same tendency to a spontaneous passivation, while cyclic voltammograms showed not transpassivation up to potentials of 8,0 v (vs ecs), indicating high corrosion resistance. the comparison among open-circuit profiles of the anodic oxides growth in ringer and na2so4 solutions, are showing that the presence of chloride ions during the anodization is not influencing the oxides chemical stability.
Resistência à corros?o das fases presentes em amálgamas dentários
ACCIARI, Heloísa Andréa;GUASTALDI, Antonio Carlos;BRETT, Christopher M. A.;
Eclética Química , 2001, DOI: 10.1590/S0100-46702001000100010
Abstract: in this work, the corrosion resistance behavior of three of their phases presents in dental amalgam has been investigated: g1-ag2hg3 (the matrix phase in the microstructure), g2-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 g2-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.
Caracteriza??o e estudo da corros?o do amálgama dentário Dispersalloy por meio das técnicas de polariza??o potenciodinamica e espectroscopia de impedancia
ACCIARI, Heloísa Andréa;GUASTALDI, Antonio Carlos;TREMILIOSI FILHO, Germano;
Eclética Química , 1997, DOI: 10.1590/S0100-46701997000100010
Abstract: the corrosion of dental amalgam in aqueous media was interpreted by means of a.c. impedance techniques and anodic polarization. the nyquist and bode diagrams are influenced by the porous structure of the amalgams, the surface film formation and the adsorption of intermediates. in general, the impedance spectra are rather complex and very difficult to interpret. the dispersalloy amalgam (high copper, dispersion type alloy) was characterized by scanning electron microscopy and energy dispersive x ray analysis. the chemistry analysis was determined by atomic absorption spectrophotometry. although high copper amalgams as a group show superior physical properties and clinical performance to low copper amalgams, a high copper content does, not necessarily mean improved clinical performance. neverthelless, they too, corrode in the mouth.
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