Magnesium alloys have good biocompatibility, but their mechanical properties and corrosion resistance may not be satisfied for using as degradable materials within bone due to its high corrosion rate in the physiological environment. Nano β-TCP particles were added into Mg-Zn-Zr alloy to improve its microstructure and the properties. As-extruded Mg-3Zn-0.8Zr alloy and Mg-3Zn-0.8Zr/xβ-TCP （x=0.5%, 1.0% and 1.5%） composites were respectively fabricated. The grains of Mg-Zn-Zr/β-TCP composites were significantly refined. The results of the tensile tests indicate that the ultimate tensile strength and the elongation of composites were improved with the addition of β-TCP. The electrochemical test result in simulation body fluid shows that the corrosion resistance of the composites was strongly enhanced comparing with that of the alloy. The corrosion potential of Mg-3Zn0.8-Zr/1.0β-TCP composite is 1.547 V and its corrosion current density is 1.20×10 6 A/cm 2 .
We report the temperature-and frequency-dependent dielectric spectrum of magnetite ceramic single phase samples at 77.4–300 K and 200 Hz–1 MHz.In temperature-dependent dc resistivity,the sharp transition expected in single crystals is much suppressed.At higher temperatures,the grain boundaries contribute to the relaxation process.Below 120 K,the temperature-dependent dielectric constant reveals a weak broadened peak as cooling,from our analysis this behavior may be intrinsically correlated with the charge ordering of Fe^(3+) and Fe^(2+).Under a relatively low dc bias at 77.4 K,the polarization of the magnetite ceramic decreases,while under a much stronger electrical field,the dielectric spectrum in the lower frequency region is suppressed remarkably for the excitation of carriers bounded by grain boundaries.
