Zn and Ca were selected as alloying elements to develop an Mg-Zn-Ca alloy system for biomedical application due to their good biocompatibility. The effects of Ca on the microstructure, mechanical and corrosion properties as well as the biocompatibility of the as-cast Mg-Zn-Ca alloys were studied. Results indicate that the microstructure of Mg-Zn-Ca alloys typically consists of primary α-Mg matrix and Ca₂Mg₆Zn₃/Mg₂Ca intermetallic phase mainly distributed along grain boundary. The yield strength of Mg-Zn-Ca alloy increased slightly with the increase of Ca content, whilst its tensile strength increased at first and then decreased. Corrosion tests in the simulated body fluid revealed that the addition of Ca is detrimental to corrosion resistance due to the micro-galvanic corrosion acceleration. In vitro hemolysis and cytotoxicity assessment disclose that Mg-5Zn-1.0Ca alloy has suitable biocompatibility.
The microstructure and wear resistance of Stellite 6 alloy hardfacing layer at two different temperatures (room temperature and 300°C) were investigated by plasma arc surfacing processes on Q235 Steel. Tribological test was conducted to characterize the wear property. The microstructure of Stellite 6 alloy coating mainly consists of α-Co and (Cr, Fe)7C3 phases. The friction coefficient of Stellite 6 alloys fluctuates slightly under different loads at 300°C. The oxide layer is formed on the coating surface and serves as a special lubricant during the wear test. Abrasive wear is the dominant mechanism at room temperature, and microploughing and plasticity are the key wear mechanisms at 300°C.
Organic
molecular wires that operate stably at ambient temperatures
are a necessary first step toward practical and useful molecular-scale
electronic devices, which have thus far been hampered by many factors,
including the structural and electron configurational instability
of organic molecules. We report here that a single disulfanyl carbon-bridged
oligo(phenylenevinylene) (COPV6) molecule embedded between thermally
stable electroless Au-plated electrodes of a 4 nm nanogap undergoes
coherent resonant tunneling at both 9 and 300 K and functions even
after storage in air at room temperature. Such enormous stability
is ascribed to the unique structural characteristics of COPV6, that
is, rigidity, planarity, thermal stability, resistivity against oxidation
and reduction, and an organic insulating sheath that protects the
π-system. When sandwiched between the gaps without pinning,
this molecule behaves as a Coulomb island with sequential single-electron
tunneling at 9 K that disappears at 300 K while maintaining a stable
electron flow.
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