Magnesium corrosion in different solutions

The corrosion mechanism of Mg alloys in Hank's solution was elucidated by comparing the corrosion of typical Mg alloys (AZ91, ZE41 and Mg2Zn0.2Mn) and high purity Mg in Hank's solution at room temperature and in 3% NaCl saturated with Mg(OH)(2). Corrosion was characterised by the evolved hydrogen and the surfaces after the immersion tests. Corrosion in Hank's solution was weakly influenced by microstructure in contrast to corrosion in the 3% NaCl solution, where second phases cause strong micro-galvanic acceleration. This is attributed to the formation of a more protective surface film in Hank's solution, causing extra resistance between the alpha-Mg matrix and the second phase. The incubation period in Hank's solution was alloy dependent

Corrosion of high purity Mg, AZ91, ZE41 and Mg2Zn0.2Mn in Hank’s solution at room temperature

This work compared the corrosion of typical Mg alloys (AZ91, ZE41 and Mg2Zn0.2Mn) and high purity (HP) Mg in Hank's solution at room temperature and in 3% NaCl saturated with Mg(OH)(2). Corrosion was characterised by the evolved hydrogen and the surfaces after immersion. Corrosion in Hank's solution was weakly influenced by microstructure in contrast to corrosion in the 3% NaCl solution. This is attributed to the formation of a more protective surface film in Hank's solution, causing extra resistance between the alpha-Mg matrix and the second phase. The alloys with substantial Zn contents had a shorter incubation period in Hank's solution. (C) 2010 Elsevier Ltd. All rights reserved

Corrosion mechanism applicable to biodegradable magnesium implants

Much of our understanding of the Mg corrosion mechanism is based on research using aggressive chloride based solutions like 3% NaCl, which are appropriate for understand the corrosion for applications such as auto construction. The chloride ions tend to cause break down of the partly protective surface film on the Mg alloy surface. The corrosion rate increases with exposure time until steady state is reached, which may take several weeks. An overview is provided of the aspects which determine the corrosion of Mg alloys: (i) measurement details; (ii) impurity elements Fe, Ni, Cu and Co; (iii) second phases; (iv) surface films and surface condition and (v) stress corrosion cracking (SCC). This understanding is used to help understand Mg corrosion for Mg as a biodegradable implant for medical applications. Solutions that elucidate these applications tend to form surface films and the corrosion rate tends to decrease with immersion time

Structural, chemical, and electrical properties of ZrO2/Ge system formed via oxidation/nitridation in N2O gas ambient

The effects of oxidation/nitridation for 15 min at different temperatures (300–800 °C) on metal–oxide–semiconductor characteristics of sputtered Zr thin film based on Ge substrate in N2O ambient have been systematically investigated. The crystallinity of the film were evaluated by X-ray diffraction analysis, Raman analysis, and X-ray photoelectron spectrometer. The crystallite size and microstrain of film were estimated by Williamson–Hall plot analysis. Optical microscope was used to examine samples surface condition and high-resolution transmission electron microscopy was carried out to investigate the cross-sectional morphology. GeO2 was detected in samples with oxidation/nitridation temperature above 700 °C. A possible mechanism of Ge atomic diffusion and its rearrangement in ZrO2 has been proposed and explicated

Corrosion behaviour of a nominally high purity Mg ingot produced by permanent mould direct chill casting

The corrosion behaviour was characterized using hydrogen evolution, weight loss, electrochemical impedance spectroscopy (EIS) and cathodic polarization curves, in 3.5% NaCl saturated with Mg(OH) , with tests lasting up to 14days, and compared with the corrosion behaviour of the HP Mg used in our prior research at UQ. The corrosion behaviour was consistent with the uni-positive Mg ion Mg corrosion mechanism, particularly the fact that the corrosion rate measured using electrochemical techniques was consistently lower than that measured independently by weight loss or hydrogen evolution, as predicted by the uni-positive Mg ion Mg corrosion mechanism

Effect of the poly l-lactic acid coating on the corrosion of Magnesium in Hank’s solution

To control the corrosion rate, the Magnesium (Mg) was coated with poly (l-lactic acid) (PLLA) using electrospinning technique. The effectiveness of the PLLA coating on the high purity Magnesium (HP Mg) and alloy AZ91 were tested in Hank’s solution immersion test. The corrosion behaviour of Mg coated PLLA was studied through hydrogen evolution, weight loss and scanning electron microscope (SEM) before, during and after samples were immersed. The solution was maintained at pH 7 by bubbling CO2 gas. The results showed that surface treatment on Mg by coating with PLLA had reduced the rate of corrosion during the immersion test. The PLLA coating was also characterized and the coating adhesion was evaluated

The in vivo and in vitro corrosion of high-purity magnesium and magnesium alloys WZ21 and AZ91

Corrosion was studied in vitro in Nor's solution (CO2 - bicarbonate buffered Hank's solution) at 37 degrees C, and in vivo implanted in the lower back muscle of rats. Nor's solution is a good model for HP Mg and WZ21, because (i) the pH is maintained by the same buffer as in blood and (ii) concentrations of corrosive chloride ions, and other inorganic constituents, are similar to those in blood. The higher in vitro corrosion rate of AZ91 was caused by micro-galvanic from second phases. The lower in vivo corrosion rate of AZ91 was tentatively attributed to suppression of micro-galvanic corrosion by tissue encapsulation. (C) 2013 Elsevier Ltd. All rights reserved

A facile, bio-based, novel approach for synthesis of covalently functionalized graphene nanoplatelet nano-coolants toward improved thermo-physical and heat transfer properties

In this study, we synthesized covalently functionalized graphene nanoplatelet (GNP) aqueous suspensions that are highly stable and environmentally friendly for use as coolants in heat transfer systems. We evaluated the heat transfer and hydrodynamic properties of these nano-coolants flowing through a horizontal stainless steel tube subjected to a uniform heat flux at its outer surface. The GNPs functionalized with clove buds using the one-pot technique. We characterized the clove-treated GNPs (CGNPs) using X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). We then dispersed the CGNPs in distilled water at three particle concentrations (0.025, 0.075 and 0.1 wt%) in order to prepare the CGNP-water nanofluids (nano-coolants). We used ultraviolet–visible (UV–vis) spectroscopy to examine the stability and solubility of the CGNPs in the distilled water. There is significant enhancement in thermo-physical properties of CGNPs nanofluids relative those for distilled water. We validated our experimental set-up by comparing the friction factor and Nusselt number for distilled water obtained from experiments with those determined from empirical correlations, indeed, our experimental set-up is reliable and produces results with reasonable accuracy. We conducted heat transfer experiments for the CGNP-water nano-coolants flowing through the horizontal heated tube in fully developed turbulent condition. Our results are indeed promising since there is a significant enhancement in the Nusselt number and convective heat transfer coefficient for the CGNP-water nanofluids, with only a negligible increase in the friction factor and pumping power. More importantly, we found that there is a significant increase in the performance index, which is a positive indicator that our nanofluids have potential to substitute conventional coolants in heat transfer systems because of their overall thermal performance and energy savings benefits

Influence of sodium on the properties of sol-gel derived hydroxyapatite powder and porous scaffolds

This study investigates the properties of sol-gel derived sodium (Na)-doped hydroxyapatite (HA) powder. Different amounts of Na (1, 5, 10 and 15 mol%) were prepared and the sintered bodies were characterized to determine the current phases, microstructural evolution and mechanical properties. X-ray diffraction analysis reveals that a phase pure HA of crystallite sizes, which varied from 35 nm to 65 nm, was obtained in the synthesized powder after calcining from 500 °C to 1000 °C. Scanning electron microscopy examination shows evidence of larger particle sizes, particularly in samples that contain higher amounts of Na concentration. The resultant powders were subsequently used to prepare porous NA-doped HA bodies through a polymeric sponge method. The addition of 5% Na resulted in a porous body with 27% porosity and was beneficial in enhancing the compressive strength of HA 17-fold compared with undoped HA. The prepared scaffold also shows suitable pore interconnectivity with pore sizes that vary between 100 and 300 μm which is suitable for use as porous bone substitutes