Electrochemical stability and corrosion resistance of Ti-Mo alloys for biomedical applications

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Photo-electrochemical investigation of anodic oxide films on cast Ti-Mo alloys I. Anodic behaviour and effect of alloy composition

The anodic behaviour of cast Ti-Mo alloys, having different Mo contents (6-20 wt.%), was investigated in acidic and neutral aerated aqueous solutions. All sample showed a valve-metal behaviour, owing to formation and thickening of barrier-type anodic oxides displaying interference colours Growth kinetics. of passive films is influenced by both anodizing electrolyte and composition of the starting alloy. This last parameter was found to change also the solid-state properties of the films, explored by photoelectrochemical and impedance spectroscopy experiments. Thicker films (U(f) = 8 V/MSE) grown on alloys richer in Mo showed more resistive character and a photocurrent sign inversion under negative bias, that revealed an insulating character, whereas corresponding films grown on alloys with lower Mo content, as well as thinner films, behaved as n-type semiconductors. Results are discussed in terms of formation of a mixed Ti-Mo oxide phase. (C) 2008 Elsevier Ltd. All rights reserved

Investigação da Interface Metal-Porcelana da Liga Ni-Cr-Mo Soldada a LASER

The interface formed between the metal and the porcelain of a LASER welded Ni-Cr-Mo alloy was studied. The characterization was carried out through optical microscopy, scanning electron microscopy, X-ray dispersive spectroscopy-EDS and mechanical testing by three-point flexion test-TPE in the region LASER welded with and without the porcelain. The porcelain adhesion with the alloy alone is possible after the oxidation of the metallic surface and subsequent application of an adhesive called opaco. The applied porcelain, on the base metal and fusion zone presented some distinct behaviors. After the TPF test the base metal presented fractures while that in the fusion zone was completely gone. One noticed that the region submitted to the LASER welding showed less porcelain adhesion than the region of the base metal due to the microestructural refinement of the fusion zone. These results can be evidenced by the EDS of the studied regions. The TPF had demonstrated that the Ni-Cr-Mo alloy submitted to the LASER welding, undergone significant alterations in its mechanical properties after the application of the porcelain.

Simultaneous Determination of Ba, Cr, Mo (Group 1), and Cu, Fe, Ni, and Pb (Group 2) in Commercial Fuel Ethanol by Graphite Furnace AAS

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Evaluation of Lubricating Oil Preparation Procedures for the Determination of Al, Ba, Mo, Si and V by High-Resolution Continuum Source FAAS

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Spectroscopic investigation and thermal behavior of new carbonyl complexes [M(CO)(4)(N-N)(CuX)], (M = W, Mo; N-N=2,2 '-bipyridine, 1,10-phenanthroline; X = Cl, SCN)

M(CO)(4)(N-N)] reacts with CuCl to give new heterobimetallic metal carbonyls of the type [M(CO)(4)(N-N)(CuCl)], M = W, Mo; N-N = 2,2'-bipyridine (bipy), 1,10-phenanthroline (phen). Reactions of [M(CO)(4)(N-N)(CuCl)] with NaSCN produced the series of complexes of general formula [M(CO)(4)(N-N)(CuSCN)]. The i.r. spectral of all the bimetallic carbonyls exhibited the general four m ( CO) band patterns of the precursors. The u.v.-vis. spectral data for precursors and products showed bands associated with pi --> pi* (nitrogen ligands), d-->d (intrametal), as well as MLCT d-->pi* (nitrogen ligands) and MLCT d --> pi*(CO) transitions. The [M(CO)(4)(N-N)(CuX)] (X = Cl, SCN) emission spectra showed only one band associated with the MLCT transition. The t.g. curves revealed a stepwise loss of CO groups. The initial decomposition temperatures of the [M(CO)(4)(N-N)(CuX)] series suggest that the bimetallic compounds are indeed thermally less stable than their precursors, and the X- ray data showed the formation of MO3, CuMO4, Cu2O and CuO as final decomposition products, M = W, Mo. The spectroscopic data suggests that the heterobimetallic compounds are polymeric.

Improvement of the Mo/TiO2-Al2O3 catalyst by the control of the sol-gel synthesis

Traditional hydrotreating catalysts are constituted by molybdenum deposited on Al2O3 promoted by nickel and phosphorous. Several studies have shown that TiO2-Al2O3 mixed oxides are excellent supports for the active phases. Results concerning the preparation, characterization and testing of molybdenum catalyst supported on titania-alumina are presented. The support was prepared by sol-gel route using titanium and aluminum isopropoxides, the titanium one chelated with acetylacetone (acac) to promote similar hydrolysis ratio for both the alcoxides. The effect of nominal molar ratio [Ti]/[Ti+Al] on the microstructural features of nanometric particles was analyzed by X-Ray Diffraction, N-2 Adsorption Isotherms and Transmission Electron Microscopy. The catalytic activity of Mo impregnated supports was evaluated using the thiophene hydrodesulfurization at different temperatures and atmospheric pressure. The pores size distribution curve moves from the micropores to the mesopores by increasing the Ti contents, allowing the fine tuning of average size from 2.5 to 6 nm. Maximal (367 m(2).g(-1)) and minimal (127 m(2).g(-1)) surface area were found for support containing [Ti]/[Ti+Al] ratio equal to 0.1 and 1, respectively. The good mesopore texture of alumina-titania support with [Ti]/[Ti+Al] molar ratio between 0.3 and 0.5 was found particularly valuable for the preparation of well dispersed MoS2 active phase, leading to HDS catalyst with somewhat higher activity than that prepared using a commercial alumina support.

Development of Ti-Mo alloys for biomedical applications: Microstructure and electrochemical characterization

Ti-Mo alloys from 4 to 20 Mo wt.% were arc-melted. Their compositions and surfaces were analyzed by EDX, XRF and SEM. The Mo mapping shows a homogeneous distribution for all alloys. The XRD analysis showed that the crystal structure of the alloys is sensitive to the Mo concentration; a mixture of the hexagonal alpha' and orthorhombic alpha '' phases was observed for the Ti-4Mo alloy, and the alpha '' phase is observed almost exclusively when the concentration of Mo added to the Ti reaches 6%. A significant retention of the beta phase is observed for the alloy containing 10% Mo, while at higher Mo concentrations (15% and 20%), retention of phase beta is only verified. Preliminary electrochemical studies have indicated a valve-metal behavior and good corrosion resistance in aerated Ringer solution for all alloys. (c) 2006 Published by Elsevier B.V.

Estudio de la pasivacion de la aleacion Co-Cr-Mo en suero fisiologico

Results are presented on the mechanism of passivation of Co-Cr-Mo biological implant alloys in physiological serum using open circuit potentiometry, potentiodynamic curves, and electrochemical impedance spectroscopy. The potential dependence of impedance data and the analysis of the parameters obtained indicate a progressive diminution of the initial layer thickness and the simultaneous formation of a second higher resistive layer. In more severe conditions than the existent in human body, the metallographic examination of the alloy surface shows localized corrosion in interdendritric regions. Elemental analysis of the surface reveals the presence of higher chromium content in these regions. The presence of chlorine was not detected, which suggested that during preferential attack, soluble species are also formed.

Influence of brush type as a carrier of adhesive solutions and paper points as an adhesive-excess remover on the resin bond to root dentin

Purpose: To evaluate the influence of the brush type as a earner of priming adhesive solutions and the use of paper points as a remover of the excess of these solutions on the push-out bond strength of resin cement to bovine root dentin. The null hypotheses were that brush type and the use of paper points do not affect the bond strength. Materials and Methods: The canals of 80 single-root bovine roots (16 mm in length) were prepared at 12 mm using the preparation drill (FRC Postec Plus, Ivoclar). Half of each root was embedded in acrylic resin and the specimens were divided into 8 groups, considering the factors brush type (4 levels) and paper point (2 levels) (n = 10): Gr 1: small microbrush (Cavi-Tip, SDI); Gr 2: Microbrush (Dentsply); Gr 3: Endobrush (Bisco); Gr 4: conventional brush (Bisco); Gr 5: Cavi-Tip (SDI) + paper points; Gr 6: Microbrush (Dentsply) + paper points; Gr 7: Endobrush (Bisco) + paper points; Gr 8: conventional brush (Bisco) + paper points. The root dentin was treated with a multistep total-etch adhesive system (All Bond 2). The adhesive system was applied using each microbrush, with and without using paper points. One fiber post was molded with addition silicon and 80 posts were made of resin cement (Duolink), The resin posts were luted (Duolink resin cement), and the specimens were stored for 24 h in water at 37°C. Each specimen was cut into 4 disk-shaped samples (1.8 mm in thickness), which were submitted to the push-out test. Results: The brush type (p < 0.0001) (small microbrush > microbrush = endobrush = conventional brush) and the use of paper points (p = 0.0001) (with > without) influenced the bond strength significantly (two-way ANOVA). The null hypotheses were rejected. Conclusion: The smallest brush (Cavi-Tip) and the use of paper points significantly improved the resin bond to bovine root dentin.

Investigation of the metal/porcelain interface in LASER-welded Ni-Cr-Mo alloy

The interface formed between the metal and the porcelain of laser-welded Ni-Cr-Mo alloy was studied on a metallurgical basis. The characterization was carried out by using optical microscope, electron scan microscopy and X-ray dispersive spectroscopy techniques and mechanical three-point flexion tests, in the laser-welded region, with and without porcelain. The union of the porcelain with the alloy is possible only after the oxidation of the metallic surface and the subsequent application of a bonding agent known as opaque. The porcelain applied to the base metal and weld bead showed different behaviours - after the flexion test, the base metal showed cracks, while that in the weld bead broke away completely. It was noted that the region subjected to laser welding had lower adherence to the porcelain than the base metal region, due to microstructural refinement of the weld bead. These results can be shown by the X-ray dispersive spectroscopy carried out on the regions studied. The flexion tests demonstrated that the Ni-Cr-Mo alloy subject to laser welding had significant alterations in its mechanical properties after application of the porcelain.

Effect of molybdenum on the formation of Ti6Si2B in mechanically alloyed Ti-Mo-Si-B powders

This paper discusses on effect of molybdenum on the Ti6Si2B formation in mechanically alloyed and hot-pressed Ti-xMo-22Si-11B (x= 2, 5, 7 and 10 at%) alloys. High-energy ball milling and hot pressing were utilized to produce homogeneous and dense materials, which were characterized by scanning electron microscopy, X-ray diffraction, electron dispersive spectrometry, and Vickers hardness. The excessive agglomeration during milling was more pronounced in Moricher powders, which was minimized with the formation of brittle phases. Hot pressing of mechanically alloyed Ti-xMo-22Si-11B powders produced dense samples containing lower pore amounts than 1%. Ti6Si2B was formed in microstructure of the hot-pressed Ti-2Mo-22Si-11B alloy only. In Mo-richer quaternary alloys, the Ti3Si and Ti5Si3 phases were preferentially formed during hot pressing. Oppositely to the ternary phase, the Ti3Si phase dissolved a significant Mo amount. Vickers hardness values were reduced in hot-pressed Ti-xMo-22Si-11B alloys containing larger Mo amounts, which were dissolved preferentially in Ti solid solution. © (2012) Trans Tech Publications, Switzerland.