S. Q. Chen

Insight into the high reactivity of commercial Fe–Si–B amorphous zero-valent iron in degrading azo dye solutions

Improving intrinsic reactivity is one of the key requirements in applying zero-valent iron in the field. As a new kind of zero-valent iron, iron based amorphous alloys were recently found to be capable of rapidly remediating wastewater. However, the mechanisms for the rapid degradation have not yet been fully understood. In this study, commercial Fe–Si–B amorphous alloy ribbons (Fe–Si–BAR) were used to degrade azo dyes (Direct Blue 6 and Orange II) to study the reaction kinetics, pathway and mechanism behind the high reactivity of these iron based amorphous alloys. The results show that, under the same conditions, the surface normalized reaction rate constants for the decomposition of Orange II and Direct Blue 6 by Fe–Si–BAR could be 1300 and 60 times larger respectively than those obtained by using 300 mesh iron powders. Through UV-vis spectrophotometry and mass spectrometry, it is found that the intermediate products of the azo dyes degraded by Fe–Si–BAR are similar to those produced in degradation by iron powders. However, the controlling step of the degradation reaction by Fe–Si–BAR turns out to be the diffusion process rather than the surface chemical reaction found in the reaction by iron powders. Further analysis indicates that the high degradation efficiency of Fe–Si–BAR results from its amorphous structure and the metalloid additions, which could enhance the catalytic effect and promote the formation of a non-compact and easily detached oxide layer on the surface. The experiments under different environmental conditions show that the factors that influence the degradation efficiency of crystalline iron powders affect that of Fe–Si–BAR in a similar way, but Fe–Si–BAR is capable of efficiently degrading wastewater under broader conditions than the crystalline iron powders. The results indicate that Fe–Si–BAR is a promising environmental catalyst for wastewater treatment.

Unexpected high performance of Fe-based nanocrystallized ribbons for azo dye decomposition

Different from the reported results, multiphase (Fe73.5Si13.5B9Nb3Cu1)91.5Ni8.5 nanocrystalline ribbons (CR-II) show much better degradation capability in Orange II than their metallic glass (MG) counterparts. CR-II ribbons have superior properties, such as high degradation capability, good durability and facile fabrication. In particular, high degradation efficiency could be expected even under an alkaline environment, while most reported zero-valent metals would only be available for acid or neutral environments. Galvanic cells between the α-Fe nanocrystals and intermetallics contribute to the high degradation capability of CR-II by accelerating the α-Fe nanocrystals to lose electrons, leading to the fracture of the azo bond (–NN–). Additionally, 3D nanoporous architectures and 3D flowerlike nanostructure sediments formed during the degradation process are also beneficial to the high degradation capability by promoting mass transport. These findings could provide new clues to design new materials with superior degradation capability and low cost for wastewater treatment.

Serration behaviours in metallic glasses with different plasticity

Abstract We present a statistical study of serration behaviours in Pd77.5Cu6Si16.5, Ti41Zr25Be26Ag8, Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 and Fe50Ni30P13C7 metallic glasses with different plasticity. The four samples show similar serration patterns in the beginning of yielding, and different patterns during later loading. These results indicate that the shear band initiation process in metallic glasses follow some similar dynamics. And the later serration process follows different dynamics and will lead to different plasticity. Here we interpret these serration behaviours from a perspective of inhomogeneity. The different serration patterns and shear band dynamics could be reasonably understood. The serration pattern of the Fe-based sample suggests that the brittleness of metallic glasses might result from a lower degree of inhomogeneity, and a less tendency of forming shear band intersections. This study might provide new experimental evidences for different micro-structures (or inhomogeneity) and dynamic behaviours in metallic glasses with different plasticity.

Serration Behavior of a Zr-Based Metallic Glass Under Different Constrained Loading Conditions

To understand the plastic behavior and shear band dynamics of metallic glasses (MGs) being tuned by the external constraint, uniaxial compression tests were performed on Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 MG samples with aspect ratios of 0.5:1, 1:1, 1.5:1, 2:1, 2.5:1, and 3:1. Better plasticity was observed for the samples with smaller aspect ratio (under higher constraint degree). In the beginning of yielding, increasing serration (jerky stress drop) size on the loading curves was noticed for all samples. Statistical analysis of the serration patterns indicated that the small stress-drop serrations and large stress-drop serrations follow self-organized critical and chaotic dynamics, respectively. Under constrained loading, the large stress-drop serrations are depressed, while the small stress-drop serrations are less affected. When changing the external constraint level by varying the sample aspect ratio, the serration pattern, shear band dynamics, and plastic behavior will change accordingly. This study provides a perspective from tuning shear band dynamics to understand the plastic behavior of MGs under different external constraint.

A study of cooling process in bulk metallic glasses fabrication

To study the temperature distribution and evolution during bulk metallic glasses fabrication, finite element method was taken to simulate the cooling process in glassy alloys fabricated by water quenching and copper mold casting. The temperature distribution and evolution in different-sized samples in the two methods were successfully reproduced. The result showed that the temperature distribution in the alloy was strongly affected by fabricating method. Two relations were then proposed to estimate the cooling rate in different-sized samples prepared by these two methods. By comparing the reported data of critical size and critical cooling rate, we showed that the reported critical size and critical cooling rate of metallic glasses didn’t follow a heat transfer relation. Those critical-sized glassy alloys actually experienced cooling rates much larger than the critical cooling rates estimated by the classical nucleation theory or experiments on milligram-scaled samples. It results from the increasing degr...

Oxide-derived nanostructured metallic-glass electrodes for efficient electrochemical hydrogen generation

Nanostructured materials with large surface areas are continuing to be at the forefront of catalytic applications. But the nanostructure synthesis methods are often lengthy, costly and difficult. Here we report the first successful fabrication of metallic-glass (MG) hierarchical nanostructures by combining thermoplastic forming and electrochemical reduction process. By the simple synthesis technique, the oxide-derived MG nanorod arrays (OD-MG NRAs) electrode with higher specific surface area exhibits an enhanced catalytic activity towards hydrogen evolution reaction than that of untreated flat MG. The OD-MG NRAs electrode demonstrates efficient electrochemical hydrogen generation in an acidic electrolyte (10 mA cm−2 at overpotential of 63 mV; Tafel slope of 42.6 mV dec−1) and possesses impressive self-stabilizing catalytic activity over a long-term operation. These features promise an attractive catalyst for large-scale hydrogen production.