Coating of Titanium Substrates with ZrO2 and ZrO2-SiO2 Composites by Sol-Gel Synthesis for Biomedical Applications: Structural Characterization, Mechanical and Corrosive Behavior

The use of metallic materials as implants presents some major drawbacks, such as their harmful effects on the living organism, especially those induced by corrosion. To overcome this problem, the implant surface of titanium implants can be improved using a coating of bioactive and biocompatible materials. The aim of this work is the synthesis of SiO2/ZrO2 composites with different percentages of zirconia matrix (20, 33 and 50 wt.%), by the sol-gel method to coat commercial Grade 4 titanium disks using a dip coater. Attenuated total reflectance Fourier transform infrared (ATR/FTIR) spectroscopy was used to evaluate the interactions between the inorganic matrices. Furthermore, the mechanical properties and corrosive behavior of the SiO2/ZrO2 coatings were evaluated as a function of the ZrO2 content. The bioactive properties of the substrate coated with different composites were evaluated using simulated body fluid (SBF). The antibacterial activity was tested against gram-negative and gram-positive Escherichia coli and Enterococcus faecalis, respectively, to assess the release of toxic products from the different composites and to evaluate the possibility of using them in the biomedical field

Pulsed current hard anodizing of heat treated aluminum alloys: Frequency and current amplitude influence

Pulsed current hard anodizing procedures have been applied to the widely used heat treated aluminum alloys AA2024-T3, AA6082-T6 and AA7075-T6. The influence of frequency and of current amplitude on anodic oxide thickness, hardness, defectiveness, volumetric expansion ratio and on process faradic efficiency has been studied. Higher frequencies generate a decrease in coating electric resistance and in general they are less effective in order to overcome typical critical issues arising in alloys difficult to be anodized. In AA2024-T3 and AA6082-T6 higher frequencies led to slight increase in thickness, decrease in compactness and faradic efficiency while hardness remained almost constant or a bit higher. With higher frequencies in AA2024-T3 defective state significantly got worse, in AA6082-T6 it improved. In AA7075-T6 an almost frequency independent behavior occurred. The highest wave amplitude with a slightly cathodic “off” current (reverse pulse) allowed to obtain greater thickness, hardness and compactness while other current amplitudes did not show significant influence on properties analyzed; a very low, but still anodic, “off” current however induced slight hardness decreases

Pulsed current effect on hard anodizing process of 2024-T3 aluminium alloy

This work focused on studying the effects of different electrical parameters on the hard anodizing process (in sulphuric acid bath) of AA 2024-T3, an important heat treated aluminium alloy which has several engineering applications in aerospace, motorsport and automotive fields due to its significant combination of high mechanical properties and low density. Hard anodizing treatment is here crucial for increasing both corrosion and abrasion resistance, but the presence of typical intermetallic precipitates makes the obtainment of a performing non-defective oxide difficult. Different anodizing procedures in direct current (DC), multistep direct current (MSDC), pulsed current (PC) (slow square pulse mode) and their appropriate combination (DC&PC) were studied aiming at obtaining the optimal mechanical properties/thickness/defectiveness compromise. DC and MSDC results showed good hardness values while their optical microscopy characterization indicated a poor defectiveness state; PC modality induced a moderate loss in mechanical performances in all the different duty cycles experimented, while an extremely low defected oxide was obtained with a duty cycle of 50%. Proper merge of a soft and long initial DC current step followed by a suitable balanced final stage in PC allowed to obtain an interesting combination of significant hardness (> 340 HV) in parallel with a good oxide defectiveness state

Hard anodizing of AA2099-T8 aluminum\u2011lithium\u2011copper alloy: Influence of electric cycle, electrolytic bath composition and temperature

AA2099-T8 samples have been hard anodized in a traditional sulphuric bath with the aim of studying the influence of i) electrolyte temperature, ii) Al3+ concentration and iii) different electric cycles in direct current, multi-step direct current and pulsed current (both completely anodic cycles and with cathodic "off" pulses). Anodic oxide thickness, volumetric expansion ratio (Vox/VAl), mean hardness (HV0.05), faradic efficiency and defective state have been analyzed. As temperature decreases, the oxide hardness increases but defectiveness steeply worsens; similarly a middle compromise of Al3+ concentration ensures the best performances. Regimes of high current, from one side, and of low current and current transient, from the other side, strongly affect oxide defective state introducing different types of flaws; an appropriate balance is crucial for a performing non-defected oxide. High current induces the occurrence of parasitic reactions which produce rough and defected Al/ox interface. Low current and current transient induce diffused cracking and detachments of coating fragments which decrease corrosion resistance as shown by potentiodynamic polarization tests. Li-based intermetallics play a crucial role in the last mentioned flaw-creation phenomena since they produce inhomogeneities in electric field distribution and contribute to create unstable oxide structures

Fast and Efficient Dynamic WDM Semiconductor Optical Amplifier Model

A novel state-variable model for semiconductor optical amplifiers (SOAs) that is amenable to block diagram implementation of wavelength division multiplexed (WDM) signals and fast execution times is presented. The novel model is called the reservoir model, in analogy with similar blockoriented models for Raman and erbium-doped fiber amplifiers (EDFAs). A procedure is proposed to extract the needed reservoir model parameters from the parameters of a detailed and accurate space-resolved SOA model due to Connelly, which was extended to cope with the time-resolved gain transient analysis. Several variations of the reservoir model are considered with increasing complexity, which allow the accurate inclusion of scattering losses and gain saturation induced by amplified spontaneous emission. It is shown that at comparable accuracy, the reservoir model can be 20 times faster than the Connelly model in single-channel operation; much more significant time savings are expected for WDM operation. The model neglects intraband SOA phenomena and is thus limited to modulation rates per channel not exceeding 10 Gb/s. The SOA reservoir model provides a unique tool with reasonably short computation times for a reliable analysis of gain transients in WDM optical networks with complex topologies

New gain parameterization for fast semiconductor optical amplifier model

Numerical simulations of semiconductor optical amplifiers (SOA) often are time consuming. Making simplifying assumptions, we obtain a fast model based on the reservoir , representing the total number of useful carriers. In this paper, we explain how this model is developed and how the gain is parameterized. We demonstrate that the scattering losses, dropped in the derivation of the reservoir model, can be re-introduced by applying a simple transformation to the gain coefficient. In this way, the accuracy of the model is greatly increased, but its level of complexity remains low

Corrosion resistance of commonly used plumbing materials for water distribution systems exposed to disinfection treatments

In this study, the corrosion resistance of commonly used plumbing materials was evaluated when three disinfection treatments were applied in hot water distribution systems. In particular copper, brass, stainless steel and galvanised steel were tested in environments containing monochloramine, chlorine dioxide and hydrogen peroxide disinfectants under real field conditions for a long period of time (1 year), in order to evaluate the effect of free corrosion on the metal specimens; chlorinated polyvinylchloride (CPVC) was tested in the same environments in order to evaluate the degradation of the mechanical properties of plastic specimens. The results obtained enabled us to rank the metallic materials corrosion resistance against disinfectants in decreasing order, as follows: stainless steel, copper and copper-based alloys, galvanised steel. CPVC samples proved to be extremely stable in all of the disinfectants investigated, maintaining the same compression behaviour of the pipes aged with untreated water after 12 months of exposur

Dimensional changes in automotive Pouch Li-Ion Cells: A Combined Thermo-Mechanical/electrochemical study

In this work it is proposed an integrated measurement system able to measure simultaneously mechanical properties, dimensional variations and Young modulus, of a pouch lithium-ion battery under operative conditions. At the same time, the designed integrated system allows also the measurement of both electrochemical main quantities (current and potentials) and temperature distribution. The complex testing capabilities system was implemented in an owner-lab-made apparatus. Experimental data collected both under normal operational conditions, as well as on abused batteries, allow to establish safer operational limits and to determine proper operation conditions to prevent the battery malfunctioning