96 research outputs found
The effect of surface preparation on the protective properties of Al2O3 and HfO2 thin films deposited on cp-titanium by atomic layer deposition
Atomic layer deposition (ALD), a method that allows the formation of thin and conformal films on substrates of interest, was employed to prepare thin films of alumina (Al2O3) and hafnia (HfO2), with the aim of protecting the surface of the commercially pure titanium (cp-Ti) used in biomedical applications. Prior to deposition, cp-Ti specimens have been prepared in two ways \u2013 grinding and grinding followed by polishing. Such surfaces have been denoted as rough and smooth, respectively. The thickness, composition, morphology and topography of alumina and hafnia films have been determined using ellipsometry, focused ion beam microscopy with energy dispersive X-ray spectroscopy, time-of-flight secondary ion mass spectrometry and 3D profilometry. A homogeneous stoichiometric composition of alumina and hafnia was obtained with a layer thickness of ca. 150 nm. The anti-corrosive properties of ALD thin films were measured in simulated body fluid solution, using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curves. The roughness of the cp-Ti surface plays an important role in the protective properties of these films, especially those of hafnia. In general, when deposited on a smooth surface, ALD films with better anti-corrosive properties were obtained, as evidenced by EIS long-term, 40-day tests. ALD films showed very low porosity, calculated from electrochemical parameters, and significantly lower corrosion current densities, compared with those from bare cp-Ti specimens. Lower porosity and slightly better protective properties were provided by films of hafnia. On the other hand, according to EIS long-term tests, alumina retained slightly greater impedance values than hafnia. Since both alumina and hafnia are biocompatible materials, this study confirms the possibility of their use to reduce the risk of failure of medical implants made of cp-Ti, in the human body environment
Effects of metal-on-metal wear on the host immune system and infection in hip arthroplasty
Methods We reviewed the available literature on the influence of degradation products of MOM bearings in total hip arthroplasties on infection risk. Results Wear products were found to influence the risk of infection by hampering the immune system, by inhibiting or accelerating bacterial growth, and by a possible antibiotic resistance and heavy metal co-selection mechanism. Interpretation Whether or not the combined effects of MOM wear products make MOM bearings less or more prone to infection requires investigation in the near future
The effect of copolymerisation on the performance of acrylate-based hybrid sol-gel coating for corrosion protection of AA2024-T3
The study was focused on the optimisation of the copolymerisation process of acrylate-based hybrid sol-gel coating to obtain long-lasting corrosion protection of AA2024-T3. The coating was synthesised using the radical copolymerisation process of methyl methacrylate (MMA) and 3-methacryloxypropyl trimethoxysilane (MAPTMS) performed under air and nitrogen (oxygen-free) atmospheres, followed by acidic hydrolysis and polycondensation in the presence of silica prepared from tetraethyl orthosilicate (TEOS). The sol synthesis was evaluated at various stages using real-time infrared spectroscopy, multinuclear liquid- and solid-state magnetic resonance spectroscopy and gel permeation chromatography. After deposition on AA2024-T3 substrate and curing, the coating properties were further evaluated by contact profilometer and focused ion beam/scanning electron microscopy coupled with energy-dispersive X-ray spectrometry. The corrosion performance was evaluated in 0.1 M NaCl solution using electrochemical impedance spectroscopy and salt spray chamber testing. The results indicated that the reaction performed in the nitrogen atmosphere increases the degree of the copolymerisation of acrylates groups, resulting in a larger molecular weight of the formed copolymer. After curing, both sol-gels formed continuous, smooth, 3c4 \u3bcm thick coatings that provided excellent barrier properties. However, when coating synthesised under nitrogen atmosphere, the coating provided better long-term corrosion resistance reaching almost 1 G\u3a9 cm2 after 6 months immersion in 0.1 M NaCl solution. Superior corrosion resistance was also confirmed in the salt spray chamber where the coating prepared under N2 atmosphere remained unchanged more than 500 hours
The synergistic effect of cerium acetate and sodium sulphate on corrosion inhibition of AA2024-T3 at various temperatures
The present work examines the corrosion inhibition of aluminium alloy 2024-T3 immersed in NaCl+Ce(OAc)3 and NaCl+Ce(OAc)3+Na2SO4 solutions to evaluate the synergetic effect between cerium and sulphate ions at various temperatures (5 \ub0C, 25 \ub0C and 50 \ub0C). The electrochemical properties were studied using short-term potentiodynamic measurements and long-term electrochemical impedance measurements. The surface topography, morphology and composition of cerium deposits formed on the alloy surface after two days of immersion were evaluated using scanning electron microscopy combined with energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. The results revealed an efficient long-term (up to 8 weeks) corrosion inhibition in NaCl+Ce(OAc)3 that was superior in the NaCl+Ce(OAc)3+Na2SO4 solution, especially at lower temperatures (5 \ub0C > 25 \ub0C > 50 \ub0C). The composition of the Ce-based film varied with the temperature and the presence of Na2SO4, resulting in different mixtures of Ce(III) and Ce(IV) species. The synergistic effect of cerium and sulphate ions on corrosion inhibition was reflected by a higher degree of cerium oxidation from Ce3+ to Ce4+ at a low temperature and the incorporation of sulphates into the formed film, which protected the surface from the corrosion medium more efficiently
Al2O3and HfO2Atomic Layers Deposited in Single and Multilayer Configurations on Titanium and on Stainless Steel for Biomedical Applications
Thin films of alumina and hafnia were prepared by atomic layer deposition, with the aim of investigating the use of such films in biomedical applications. Films were deposited on commercially pure titanium and on medical stainless steel. Two configurations were prepared: single alumina films, 20 nm and 60 nm thick, and a multilayer film, 60 nm thick, consisting of alumina/hafnia/alumina layers, each 20 nm thick. The morphology, structure and composition of the coated alloys were characterized using scanning electron microscopy with energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. In addition, ellipsometry and atomic force microscopy coupled with scanning Kelvin probe force microscopy, were used to study the thickness and the topography with surface potential properties. An improvised method, involving the Vickers hardness test, was applied to assess the delamination of the deposited films. Coated specimens, as well as bare substrates, were tested at 37 C in simulated body fluid, using potentiodynamic polarization and electrochemical impedance spectroscopy as techniques for assessing corrosion susceptibility. In general, single and multilayer thin films possess excellent barrier properties and are worth investigating further for biomedical applications. The degree of protection is dependent mainly on film thickness and on the type of substrate, and less on configuration
Corrosion protection of aluminium pretreated by vinyltriethoxysilane in sodium chloride solution
The corrosion protection of vinyltriethoxysilane (VTES) films on aluminium during exposure to 3% NaCl was investigated using electrochemical impedance spectroscopy (EIS), potential-time measurements and optical microscopy coupled with image analysis. Composition and thickness of films were analyzed using Auger electron spectroscopy (AES) combined with depth profiling. It was shown that films deposited from 5% solution were significantly thicker and exhibited lower porosity and better corrosion stability, as compared to films deposited from 2 vol.% solution. VTES films deposited from 5 vol.% solutions and cured for 30 min exhibited better protection properties than other investigated films
Corrosion protection of aluminium pretreated by vinyltriethoxysilane in sodium chloride solution
The corrosion protection of vinyltriethoxysilane (VTES) films on aluminium during exposure to 3% NaCl was investigated using electrochemical impedance spectroscopy (EIS), potential-time measurements and optical microscopy coupled with image analysis. Composition and thickness of films were analyzed using Auger electron spectroscopy (AES) combined with depth profiling. It was shown that films deposited from 5% solution were significantly thicker and exhibited lower porosity and better corrosion stability, as compared to films deposited from 2 vol.% solution. VTES films deposited from 5 vol.% solutions and cured for 30 min exhibited better protection properties than other investigated films
Corrosion protection of carbon steel by silica-based hybrid coatings containing cerium salts: Effect of silica nanoparticle content
One strategy for minimising corrosive attack on carbon steel involves the application of hybrid coatings rich in rare earths, on the basis of their low toxicity and environmental sustainability. Tetraethoxysilane (TEOS) and 3-glycidoxypropyl-trimethoxysilane (GPTMS) were each used here as precursors, together with various quantities of colloidal silica suspension, to improve barrier properties of the coatings. Ce(NO3)(3)center dot 6H(2)O was added as a source of Ce(III) for further inhibition of corrosion. The corrosion resistance of each kind of sample was evaluated using potentiodynamic polarisation measurements and electrochemical impedance spectroscopy (EIS) in 0.35 wt.% NaCI solution. The electrochemical behaviour at various immersion times was modelled by equivalent circuits to demonstrate the effect of silica nanoparticle loading on corrosion. Additional testing was performed under harsh conditions of salt spray chamber. The microstructure and composition of sol-gel coatings were characterised by scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM/EDS), focused-ion beam SEM/EDS analysis, X-ray photoelectron spectroscopy and confocal microscopy. (C) 2015 Elsevier B.V. All rights reserved
Isolated Sphenoid Sinus Aspergillosis with Intracranial Extension: Report on Three Cases
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