Li Xingguo

Synthesis and Cyclic Hydrogenation Properties of Magnesium Ultrafine Nanoparticles Prepared by Acetylene Plasma

Ultrafine Mg nanoparticles of around 40 nm in size were prepared by an acetylene plasma metal reaction, which is a revised approach of the traditional hydrogen plasma metal reaction. The morphology and the cyclic hydrogenation properties were investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), specific surface area (BET) tests, and the kinetics of hydrogenation and dehydrogenation. Because of the short diffusion distance and the large specific surface area, the kinetics of hydrogenation and dehydrogenation of the small Mg nanoparticles improved. The nanostructured carbon cover on the Mg nanoparticles decreased the amount of Mg nanoparticle oxidation and also prevented the growth of Mg nanoparticles during the hydrogenation and dehydrogenation process. Therefore, the Mg ultrafine nanoparticles exhibited excellent cycling stability. Cycling tests showed little loss in hydrogen storage capacity after 30 cycles.

Resistivity?temperature characteristics of sol gel YBa2Cu3Oy samples synthesized in flowing oxygen atmosphere

The relationship of resistivity versus synthesizing temperature of sol gel YBa2Cu3Oy samples was studied when prepared under flowing oxygen conditions. A set of high-temperature ρ–T curves was obtained for the whole process. After the sample finished the test measuring, its resistivity was ρ300=9.83 ×10−3Ω.cm at room temperature. The ρ–T curve also showed that the orthorhombic–tetragonal phase transformation of sol-gel YBa2Cu3Oy sample occurred at 581 degrees C for the sample in the rising temperature process, but at 613 degrees C in the cooling process, lower than that of the samples made by using the conventional powder metallurgy methods.

A New Process of Manufacturing “Oxygen-free” Gd

Abstract “Oxygen-free” Gd was fabricated by hydrogen plasma arc melting (HPAM). The HPAM is more different than the traditional Ar plasma arc melting (PAM) in Oxygen removal. It is attributable to the hydrogen atoms dissociated and activated in high temperature HPAM. In addition an increased diffusion of oxygen in Gd-O solid solution to the surface also plays an important role in removal of oxygen. The substances are confirmed by optical emission spectroscopy (OES), which are involved in the plasma like Ar I, Ar II and H I and some possible reactions. The effect of H with thermodynamic estimation was discussed in detail.

High-density MgB2 superconducting bulk samples prepared at ambient pressure

High-density MgB2 (HD-MgB2) superconducting samples (D ⩾ 2.2 g/cm3), using different sources of magnesium powder as raw material, were synthesized in ambient pressure in a rich Mg environment. The magnesium powders used in the fabrication process include nanometer-sized magnesium particles, powders from Alfa Aesar, ordinary off-the-shelf powder, and magnesium chip. The fabrication procedure involved a double-sintering process in a rich-Mg environment. A transition temperature Tc of 39 K was observed. Samples with the equally high density and matching superconducting properties were obtained as well by a triple sintering process of the MgB2 powder directly from Alfa Aesar.