Zhengwang Zhu

Post-melting anomaly of Pb-Bi alloys observed by internal friction technique

With the help of an improved internal friction method, it was found that a peak could appear, as the temperature increased, above the liquidus in each of the internal friction curves of Pb-Bi alloys. The features of this kind of peak are similar to those found during the solid-liquid transition in the same experiments, and in accordance with the characteristics from solid-solid transitions verified by previous investigators. The results suggest that structural changes take place to some extent in the molten alloys as a function of temperature, which have been confirmed by the corresponding calorific peak in a differential scanning calorimeter. This phenomenon might help in understanding the nature of molten alloys and their melting mechanism as well. In addition, the internal friction technique proved to be quite sensitive to liquid structures and effective for studying liquid materials.

Rapid decolorization of acid orange II aqueous solution by amorphous zero-valent iron.

Some problems including low treatment capacity, agglomeration and clogging phenomena, and short working life, limit the application of pre-treatment methods involving zero-valent iron (ZVI). In this article, ZVI was frozen in an amorphous state through a melt-spinning technique, and the decolorization effect of amorphous ZVI on Acid Orange II solution was investigated under varied conditions of experimental variables such as reaction temperature, ribbon dosage, and initial pH. Batch experiments suggested that the decolorization rate was enhanced with the increase of reaction temperature and ribbon dosage, but decreased with increasing initial solution pH. Kinetic analyses indicated that the decolorization process followed a first order exponential kinetic model, and the surface-normalized decolorization rate could reach 2.09 L/(m2 x min) at room temperature, which was about ten times larger than any previously reported under similar conditions. Recycling experiments also proved that the ribbons could be reused at least four times without obvious decay of decolorization rate and efficiency. This study suggests a tremendous application potential for amorphous ZVI in remediation of groundwater or wastewater contaminated with azo dyes.

Characterization of flow units in metallic glass through structural relaxations

We characterize the evolution of flow units associated with the flow “defects” in metallic glass by monitoring the fictive temperature change of a typical metallic glass upon isothermal annealing below its glass transition temperature. The correlations between the fictive temperature Tf, enthalpy change, and the concentration of flow units have been obtained. Such correlations help in understanding the evolution process of flow units, structural feature, and structural relaxation behaviors in metallic glasses, and can rationalize effects of the cooling rate, aging, and annealing on properties and structure of metallic glasses.

Compositional origin of unusual β-relaxation properties in La-Ni-Al metallic glasses

The β-relaxation of metallic glasses (MGs) bears nontrivial connections to their microscopic and macroscopic properties. In an effort to elucidate the mechanism of the β-relaxation, we studied by dynamical mechanical measurements the change of its properties on varying the composition of La60Ni15Al25 in various ways. The properties of the β-relaxation turn out to be very sensitive to the composition. It is found that the isochronal loss peak temperature of β-relaxation, Tβ,peak, is effectively determined by the total (La + Ni) content. When Cu is added into the alloy to replace either La, Ni, or Al, the Tβ,peak increases with decrease of the (La + Ni) content. The trend is in accordance with data of binary and ternary MGs formed from La, Ni, Al, and Cu. Binary La-Ni MGs have pronounced β-relaxation loss peaks, well separated from the α-relaxation. In contrast, the β-relaxation is not resolved in La-Al and La-Cu MGs, showing up as an excess wing. For the ternary La-Ni-Al MGs, increase of La or Ni content is crucial to lower the Tβ,peak. Keeping the Al content fixed, increase of La content lowers the Tβ,peak further, indicating the more important role La plays in lowering Tβ,peak than Ni. The observed effects on changing the composition of La60Ni15Al25 lead to the conclusion that the properties of the β-relaxation are mainly determined by the interaction between the largest solvent element, La, and the smallest element, Ni. From our data, it is further deduced that La and Ni have high mobility in the MGs, and this explains why the β-relaxation in this La-based MGs is prominent and well resolved from the α-relaxation as opposed to Pd- and Zr-based MGs where the solvent and largest atoms, Pd and Zr, are the least mobile.

Characterization of flow units in metallic glass through density variation

The evolution of flow units associated with the flow “defects” in metallic glass is characterized by monitoring the metallic glassy density change upon isothermal annealing far below their glass transition temperature. A meaningful function for the density variation with the concentration of flow units is obtained for the metallic glasses. We show that the correlation between the density variation and the flow unit have implications for understanding the fragility, structural heterogeneous, and structural relaxation behaviors in metallic glasses.

Correlation between local elastic heterogeneities and overall elastic properties in metallic glasses

Abstract The common notion suggests that metallic glasses (MGs) are a homogeneous solid at the macroscopic scale; however, recent experiments and simulations indicate that MGs contain nano-scale elastic heterogeneities. Despite the fundamental importance of these findings, a quantitative understanding is still lacking for the local elastic heterogeneities intrinsic to MGs. On the basis of Eshelbys theory, here we develop a micromechanical model that correlates the properties of the local elastic heterogeneities, being very difficult to measure experimentally, to the measurable overall elastic properties of MGs, such as shear/bulk modulus and Poissons ratio. Our theoretical modeling is verified by the experimental data obtained from various MGs annealed to different degrees. Particularly, we revealed that upon annealing, the Poissons ratio decreases if shear softening dominates the behavior of local soft regions or increase if pressure softening becomes dominant in MGs. Our results provide quantitative insights into the structural mechanism of the Poissons ratio criterion on the ductility long established for MGs. Finally, The correlation between the Poissons ratio of a glass and the fragility of its corresponding liquid is also discussed.

Structure and characterization of magnetoresistance of La0.7Pb0.3MnO3−δ in bulk and films deposited on LaAlO3 (100), (110) and (111) substrates

Abstract The structure and properties of La0.7Pb0.3MnO3−δ (LPMO) bulk and films, which are deposited onto (001), (110) and (111) LaAlO3 (LAO) substrates using the direct current magnetron sputtering technique, are obtained. For bulk of LPMO, Tp is almost equal to Tc (252 K) and its R(T) curve has a bump in low temperature region. For films, the colossal magnetoresistance (CMR) of 28% at 155 K and in 0.5 T was observed on (001) oriented substrate under 9 Pa sputtering gas pressure and substrate temperature of 790 °C. The transport properties of the deposited films are slightly lower than that of the bulk.

Determination of size distribution of precipitates in the cast martensitic steel G-X12CrMoWVNbN 10-1-1 by direct and indirect method

The size distributions of different precipitates have been determined for the quantification of precipitates present in the cast martensitic steel G-X12CrMoWVNbN 10-1-1. Direct and indirect methods have been used to discriminate the different precipitates. The former was carried out by images of precipitates from STEM connecting with EDX analysis, and the latter from TEM. The study was performed on the replicas with precipitates which were extracted from the buck steel. Results gained from direct determination are compared with results from indirect determination. It is shown that the total size distributions are in good agreement for both direct and indirect determination in this type of steel. The discrimination and quantification of different precipitates seem to be difficult for indirect method because of uncertainty concerning the quantitative determination of precipitate parameters.

Origin of Shear Stability and Compressive Ductility Enhancement of Metallic Glasses by Metal Coating.

Metallic glasses (MGs) are notorious for the poor macroscopic ductility and to overcome the weakness various intrinsic and extrinsic strategies have been proposed in past decades. Among them, the metal coating is regarded as a flexible and facile approach, yet the physical origin is poorly understood due to the complex nature of shear banding process. Here, we studied the origin of ductile enhancement in the Cu-coating both experimentally and theoretically. By examining serrated shear events and their stability of MGs, we revealed that the thin coating layer plays a key role in stopping the final catastrophic failure of MGs by slowing down shear band dynamics and thus retarding its attainment to a critical instable state. The mechanical analysis on interplay between the coating layer and shear banding process showed the enhanced shear stability mainly comes from the lateral tension of coating layer induced by the surface shear step and the bonding between the coating layer and MGs rather than the layer thickness is found to play a key role in contributing to the shear stability.

A novel Si/Sn composite with entangled ribbon structure as anode materials for lithium ion battery.

A novel Si/Sn composite anode material with unique ribbon structure was synthesized by Mechanical Milling (MM) and the structural transformation was studied in the present work. The microstructure characterization shows that Si/Sn composite with idealized entangled ribbon structured can be obtained by milling the mixture of the starting materials, Si and Sn for 20 h. According to the calculated results based on the XRD data, the as-milled 20 h sample has the smallest avergae crystalline size. It is supposed that the flexible ribbon structure allows for accommodation of intrinsic damage, which significantly improves the fracture toughness of the composite. The charge and discharge tests of the as-milled 20 h sample have been performed with reference to Li+/Li at a current density of 400 mA g−1 in the voltage from 1.5 to 0.03 V (vs Li/Li+) and the result shows that the initial capacity is ∼1400 mA h g−1, with a retention of ∼1100 mA h g−1 reversible capacity after 50 cycles, which is possible serving as the promising anode material for the lithium ion battery application.