The aim of this study is to modify the surface of Nitinol (Nickel Titanium Naval Ordnance Laboratory) alloy by covering with diamond-like carbon to improve the corrosion resistance and biocompatibility, and to prevent the toxic nickel ion release inside the human body. This alloy has unique properties, including shape memory effect and super elasticity, which make it an attractive candidate for biomedical applications. Diamond-like carbon (DLC) films were deposited by d.c. magnetron sputtering using a graphite target and argon as the discharge gas. The electrochemical characteristics of the DLC coatings were investigated by electrochemical techniques (potentiodynamic polarization test and electrochemical impedance spectroscopy) at 37• C in Fetal Bovine Serum (FBS). Surface analysis of the DLC coatings was conducted by means of X-Ray Diffraction (XRD), SEM and Vickers microhardness, and the thickness of DLC layer was measured using interferometry technique. The metallic ions release in bulk solution was studied by inductive coupling plasma-mass spectrometry (ICP-MS). In the case of uncoated samples, the release of metallic ions in bulk solution was much higher than in the case of DLC coated samples. Also, the corrosion resistance and Vickers microhardness of DLC-coated samples were improved in comparison with the uncoated samples.
This paper presents an analysis of the possibility of using recycled pork fat-based biodiesel as fuel for aviation turbo-engines. The analysis consists of the assessment of four blends of Jet A kerosene with 10%, 30%, 50%, and 100% biodiesel and pure Jet A that was used as reference in the study. The first part of the paper presents the physical-chemical properties of the blends: density, viscosity, flash point, freezing point, and calorific power. Through Fourier transform infrared spectroscopy (FTIR) analysis, a benchmark was performed on the mixtures of Jet A with 10%, 20%, 30%, 50%, and 100% biodiesel compared with Jet A. The second part of the paper presents the test results of these blends used for fuelling a Jet Cat P80 turbo engine at the Turbo Engines Laboratory of the Aerospace Engineering Faculty of Polyethnic University of Bucharest. These functional tests were performed using different operating regimes as follows: idle, cruise, intermediate, and maximum. For each regime, a testing period of around 1 min was selected and the engine parameters were monitored during the test execution. The burning efficiency was calculated for the maximum regime for all mixtures. To evaluate the functioning stability of the turbo engine using biodiesel, two accelerometers were mounted on the engine support that recorded the radial and axial vibrations. Moreover, to assess the burning stability and to identify other acoustic spectral components when biodiesel is used, two microphones were placed near the jet region. A comparative analysis between blends was made by taking the Jet A fuel as reference.
In this study, a CoCrMo-based metallic alloy was manufactured using a 3D-printing method with metallic powder and a laser-based 3D printer. The obtained material was immersed in a simulated body fluid (SBF) similar to blood plasma and kept 2 months at 37 °C and in relative motion against the SBF in order to mimic the real motion of body fluids against an implant. At determined time intervals (24, 72, 168, 336, and 1344 h), both the metallic sample and SBF were characterized from a physical-chemical point of view in order to assess the alloy’s behaviour in the SBF. Firstly, the CoCrMo based metallic sample was characterized by scanning electron microscopy (SEM) for assessing surface corrosion and X-ray diffraction (XRD) for determining if and/or what kind of spontaneous protective layer was formed on the surface; secondly, the SBF was characterized by pH, electrical conductivity (EC), and inductively coupled plasma mass spectroscopy (ICP-MS) for assessing the metal ion release. We determined that a 3D-printed CoCrMo alloy does not represent a potential biological hazard in terms of the concentration of metal ion releases, since it forms, in a relatively short period of time, a protective CoCr layer on its exposed surface.
The paper presents theoretical considerations on gas bubbles behavior -analytic calculation of bubble time formation, extra pressure needed for the bubble formation and detachment, bubble size and correlation between the extra pressure and the liquid superficial tension.In order to evaluate the theoretical relation for extra pressure calculation, the results of the tests performed on different metallic perforated plates Ø 60, with a specific number of orifices of different diameters, were used. The extra pressure needed for bubble formation varies from approximately 171 Pa for the MPP with 0.9 mm orifices to 245 Pa for the MPP with 0.2 mm orifices.Index Terms-Bubble size, bubble detachment, extra pressure, orifice.
This paper presents the characterization of carbonic functional phase based on carbon mesophase/carbon nanotubes nanocomposites used as functional filler in a polymeric matrix by optical microscopy, X-ray diffraction and functional by electrical resistivity measurements. The nanocomposites were prepared by adding of single walled carbon nanotubes (SWNT) or multi walled carbon nanotubes (MWNT) in a petroleum pitch. It was reported that SWNT behaves as either a metal or a semiconductor depending on the wrapping angle of the graphene sheet and its diameter, while MWNTs are always conductive. Carbonic functional phase was obtained by heat treatment of pitch/nanotubes mixtures at 450oC and 900oC temperatures. Polymeric composites were obtained by adding carbonic functional phase in an epoxy resin matrix. The polymeric composites were functional characterized from electrical point of view, establishing their behaviour. The electrical behaviour of the (SWNT/MWNT)/PP systems heat treated at 450�C is not largely influenced by the CNTs, because they are not creating any conducting connections. The composite systems, heat treated at 450�C, show a high resistivity of 105 ohm�cm, while the systems heat treated at 900�C show a lower electrical resistivity of 10-1 ohm�cm.
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