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Two quaternary magnesium alloys based on ternary Mg-5wt.%Zn-4wt.%Ca containing either Co(2wt.%) or Zr(0.5wt.%) were rapidly solidified using melt spinning. The nano-scale second phase distribution and thermal stability were studied using TEM, STEM and EDS system. Microhardness measurements conducted in the aged condition have identified that the Mg-Ca-Zn-Co alloy presented a peak value at 150 o C followed by a hardness decrease. The Mg-Ca-Zn-Co alloy showed refined quaternary precipitates distributed along the cell boundary and a refined grain structure, yielding higher hardness values than the Mg-Ca-Zn-Zr alloy at all aging temperatures.

In this paper, polyethylene glycol (PEG) molecules have been grafted onto the surface of nanometer silica in toluene by using 1,4-phenylene diisocyanate (PPDI) as a coupling agent, and dibutyltion dilaurate (DBTDL) as a catalyst. This process was executed by using a one-step procedure involving a first reaction of PPDI with silica and a subsequent reaction of isocyanate-bound silica with PEG. The PEG-grafted silica has been characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and SEM analyses. The effects of reaction time, temperature and molar ratio of reactant on the effectiveness of the surface grafting were also investigated. Optimum grafting conditions of PEG were obtained at the temperature of 80• C for 8 h. Maximum grafting of PEG molecules ratio was 22.6%, and maximum overall grafting ratio was 35%, as determined by TGA.

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