The corrosion behaviour of Mg-Mn and Mg-Mn-Zn magnesium alloy in a phosphate buffered simulated body fluid (SBF) has been investigated by electrochemical testing and weight loss experiment for bone implant application. Long passivation stage and noble breakdown potential in the polarization curves indicated that a passive layer could be rapidly formed on the surface of magnesium alloy in the phosphate buffered SBF, which in turn can protect magnesium from fast corrosion. Surfaces of the immersed magnesium alloy were characterized by SEM, EDS, SAXS and XPS. Results have shown that Mg-Mn and Mg-Mn-Zn alloy were covered completely by an amorphous Mg-containing phosphate reaction layer after 24 h immersion. The corrosion behaviour of magnesium alloys can be described by the dissolving of magnesium through the reaction between magnesium and solution and the precipitating of Mg-containing phosphate on the magnesium surface. Weight loss rate and weight gain rate results have indicated that magnesium alloys were corroded seriously at the first 48 h while Mg-containing phosphate precipitated fast on the surface of magnesium alloy. After 48-96 h immersion, the corrosion reaction and the precipitation reaction reach a stable stage, displaying that the phosphate layer on magnesium surface, especially Zn-containing phosphate layer could provide effective protection for magnesium alloy.

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We have performed systematic first-principles calculations on di-carbide, -nitride, -oxide andboride of platinum and osmium with the fluorite structure. It is found that only PtN2, OsN2 and OsO2 are mechanically stable. In particular OsN2 has the highest bulk modulus of 360.7 GPa. Both the band structure and density of states show that the new phase of OsN2 is metallic. The high bulk modulus is owing to the strong covalent bonding between Os 5d and N 2p states and the dense packed fluorite structure.

Low compressible noble metal carbides with rock-salt structure: ab initio total energy calculations of the elastic stability Yu-Gui YaoInstitute of Physics, Chinese Academy of Sciences, Beijing 100080, ChinaWe have systematically studied the mechanical stability of all noble metal carbides with the rocksalt structure by calculating their elastic constants within the density function theory scheme. It was found that only four carbides (RuC, PdC, AgC and PtC) are mechanically stable. In particular, we have shown that RuC, PdC, and PtC have very high bulk modulus, which has been remarkably observed by the most recent experiment for the case of PtC. From the calculated density of states, we can conclude that these compounds are metallic, like the conventional group IV and group V transition metal carbides.

Open-cell porous Ti with a porosity ranging from 35 to 84% was successfully manufactured by sintering titanium fibres. The microstructure of the porous titanium was observed by SEM and the compressive mechanical properties were tested. By adjusting the spiral structure of the porous titanium, the pore size can be controlled in a range of 150-600 microm. With the increasing of the porosity, compressive yield strength and modulus decrease as predicated. However, high mechanical properties were still obtained at a medium porosity, e.g. the compressive yield strength and the modulus are as high as 100-200 MPa and 3.5-4.2 GPa, respectively, when the porosity is in the range of 50-70%. It was suggested that the porous titanium be strong enough to resist handing during implantation and in vivo loading. It is expected to be used as biocompatible implant, because their interconnected porous structures permit bone tissues ingrowth and the body fluids transportation.