Zhenhua Dan

Structural Inheritance and Redox Performance of Nanoporous Electrodes from Nanocrystalline Fe85.2B10-14P0-4Cu0.8 Alloys

Nanoporous electrodes have been fabricated by selectively dissolving the less noble α-Fe crystalline phase from nanocrystalline Fe85.2B14–xPxCu0.8 alloys (x= 0, 2, 4 at.%). The preferential dissolution is triggered by the weaker electrochemical stability of α-Fe nanocrystals than amorphous phase. The final nanoporous structure is mainly composed of amorphous residual phase and minor undissolved α-Fe crystals and can be predicted from initial microstructure of nanocrystalline precursor alloys. The structural inheritance is proved by the similarity of the size and outlines between nanopores formed after dealloying in 0.1 M H2SO4 and α-Fe nanocrystals precipitated after annealing of amorphous Fe85.2B14−xPxCu0.8 (x = 0, 2, 4 at.%) alloys. The Redox peak current density of the nanoporous electrodes obtained from nanocrystalline Fe85.2B10P4Cu0.8 alloys is more than one order higher than those of Fe plate electrode and its counterpart nanocrystalline alloys due to the large surface area and nearly-amorphous nature of ligaments.

Ti-Based Bulk Metallic Glasses for Biomedical Applications

Biomedical materials can improve the life quality of a number of people each year. The range of applications includes such as joint and limb replacements, artificial arteries and skin, contact lenses, and dentures. So far the accepted biomaterials include metals, ceramics and polymers. The metallic biomaterials mainly contain stainless steel, Co-Cr alloys, Titanium and Ti-6Al-4V. Recently, bulk metallic glasses as novel materials have been rapidly developed for the past two decades in Mg-, Ln-, Zr-, Fe-, Ti-, Pd-, Cu-, Ni-based alloy systems because of their unique physical, chemical, magnetic and mechanical properties compared with conventional crystalline alloys. Metallic glass formation is achieved by avoiding nucleation and growth of crystalline phases when cooling the alloy from the molten liquid. Therefore, the different atomic configurations induced significantly different characteristic features such as high strength, good corrosion resistance and excellent electromagnetic properties, which are from their crystalline counterparts. Among different bulk metallic glasses, Ti-based bulk metallic glasses are expected to be applied as biomedical materials due to high strength, high elastic limit, low Young’s modulus, excellent corrosion resistance and good bioactivity of Ti element. Many Ti-based metallic glasses have been developed in Ti-Cu-Ni, Ti-Cu-Ni-Co, Ti-Cu-Ni-Zr, Ti-Cu-Ni-Zr-Sn, Ti-CuNi-Sn-B-Si, Ti-Cu-Ni-Sn-Be, Ti-Cu-Ni-Zr-Be, Ti-Cu-Ni-Zr-Hf-Si and Ti-Cu-Ni-Zr-Nb (Ta) alloys, based on the Inoue’s three empirical rules (Inoue, 1995) i.e., 1) multi-component consisting of more than three elements, 2) significant atomic size mismatches above 12% among the main three elements, and 3) negative heats of mixing among the main elements.

Ethanol-Mediated 2D Growth of Cu2O Nanoarchitectures on Nanoporous Cu Templates in Anhydrous Ethanol

Two types of cupric oxide (Cu2O) nanoarchitectures (nanobelts and nanopetal networks) have been achieved via immersion nanoporous copper (NPC) templates in anhydrous ethanol. NPC templates with different defect densities have been prepared by dealloying amorphous Ti60Cu40 ribbons in a mixture solution of hydrofluoric acid and polyvinylpyrrolidone (PVP) with different ratios of HF/PVP. Both a water molecule reactant acting as OH− reservoir and the ethanol molecule serving as stabilizing or capping reagent for inhibiting the random growth of Cu2Oplayed a role of the formation of 2-dimensional Cu2O nanoarchitectures. Cu2O nanobelts are preferred to form in anhydrous ethanol on the NPC templates from Ti60Cu40 ribbons dealloying in the solution with low HF concentration and small addition of PVP; and Cu2O nanopetals are tended to grow in anhydrous ethanol from the NPC templates from Ti60Cu40 ribbons dealloying in the solution with high HF concentration and large addition of PVP. With increasing the immersion time in anhydrous ethanol, Cu2O nanopetals united together to create porous networks about 300 nm in thickness. The defect sites (i.e., twin boundary) on nanoporous Cu ligaments preferentially served as nucleation sites for Cu2O nanocrystals, and the higher defect density leads to the formation of uniform Cu2O layer. Synergistic effect of initial microstructure of NPC templates and stabilizing agent of ethanol molecule results in different Cu2O nanoarchitectures.

Nanoporous Copper Dealloyed from a Nanocrystallized Ticu Alloy

Nanoporous copper (NPC) was fabricated through dealloying nanocrystallized TiSubscript text50Cu50 ribbon alloy under a free immersion condition in HF solutioSubscript textns at 25 °C. Multimodal nanoporous structure was formed due to the presence of Ti3Cu4 phase, which was co-precipitated with Ti2Cu during the heat treatment at T = 400 °C (Italic textTSubscript textg Italic textT Subscript textx). The presence of multiphases in tItalic texthe starting material caused the different behavior in the evolution of nanoporosity. In 0.03 mol/L HF solution, the bimodal nanoporous copper with a pore size of 54 nm and 184 nm was obtained in different regions where the composition differed. The ligament scale lengths in two regions were confirmed to be 54 nm and 203 nm, respectively. In 0.13 mol/L HF solution, the difference in the pore size and phase separation became weak, accompanying with the evolution of larger pores and smaller ligaments. The residue after dealloying was confirmed to be fcc Cu, indicated by the presence of Cu (111), (200), (220) and (311) in XRD patterns and TEM selective area diffraction pattern. The microstructure of the starting materials for dealloying, such as intermetallic phases, played a key role in the formation of the final multimodal nanoporous structure.

Facile Fabrication of Cu2O Nanobelts in Ethanol on Nanoporous Cu and Their Photodegradation of Methyl Orange

Thin cupric oxide (Cu2O) nanobelts with width of few tens of nanometers to few hundreds of nanometers were fabricated in anhydrous ethanol on nanoporous copper templates that was prepared via dealloying amorphous Ti40Cu60 ribbons in hydrofluoric acid solutions at 348 K. The Cu2O octahedral particles preferentially form in the water, and nanobelts readily undergo the growth along the lengthwise and widthwise in the anhydrous ethanol. The ethanol molecules serve as stabilizing or capping reagents, and play a key role of the formation of two-dimensional Cu2O nanobelts. Cu atoms at weak sites (i.e., twin boundary) on the nanoporous Cu ligaments are ionized to form Cu2+ cations, and then react with OH− to form Cu2O and H2O. The two-dimensional growth of Cu2O nanostructure is preferred in anhydrous ethanol due to the suppression of random growth of Cu2O nanoarchitectures by ethanol. Cu2O nanobelts have superior photodegradation performance of methyl orange, three times higher than nanoporous Cu.

Dependence of Soft Magnetic Properties of

Effects of P content in amorphous and nanocrystalline FeSiBPCu soft magnetic alloys were investigated by comparing the corresponding change in the saturation magnetic flux density and coercivity. Ribbons were prepared using a high induction melting and melt spinning method. As-quenched Fe_85.5Si₂B₁₀P_1.5Cu₁ alloy consisted of minor crystalline phase. With an increase of P content, the glass forming ability was enhanced. The decrease in the saturation magnetic flux density associated with increased P content, was mainly ascribed to the decrease in Fe content. Nanocrystalline Fe_87-xSi₂B₁₀P_xCu₁ alloys exhibited higher saturation magnetic flux density and lower coercivity, when x was >2 at%. The best soft magnetic performance was obtained at x = 2 at%, where the saturation magnetic flux density was 1.87 T. The coercivity was decreased with P content, indicating that the size of α-Fe grains became smaller with the increase of P content.

{\rm Fe}_{81-85.5}{\rm Si}_{2}{\rm B}_{10}{\rm P}_{1.5-6}{\rm Cu}_{1}

In this research, the effect of Ta addition on the formation, thermal stability and corrosion behavior of Ti-Zr-Cu-Pd bulk metallic glasses were investigated. The results revealed with minor addition of Ta, higher corrosion resistance and compressive strength as well as large plastic deformation were achieved. Minor addition Ta is effective for the formation of more protectively passive film during the process of anodic polarization. In addition, proper volume fraction nanoparticle with small size is responsible for the large plastic deformation of the as-cast Ti-based bulk metallic glasses with 1% Ta addition.

Alloys on P Content

Ti-based bulk metallic glasses with minor addition of Ag, Au or Pt elements were prepared by copper mold casting. The Microstructure of the as-cast samples was examined by TEM. Nanoparticles identified as cubic Pd3Ti with crystal planes of (111), (200), (220) and (311) are observed in all the alloys modified by the minor addition of Ag, Au or Pt. The results revealed that the glassy/nanoparticle composited alloys exhibited high strength about 2000 MPa and plastic strain between 1.5-10% due to the inhibition of propagation of shear band.

Effect of Minor Addition Ta on the Thermal Stability and Corrosion Resistance of Ti-Zr-Cu-Pd Bulk Metallic Glasses

Nanoporous golf ball-shaped powders with a surface porous layer consisting of fcc Cu and Cu3Au phases have been fabricated by selectively dissolving gas-atomized Ti60Cu39Au1 powders in 0.13 M HF solution. The distribution profiles of the Ti2Cu and TiCu intermetallic phases and powder size play an important role of the propagation of the selective corrosion frontiers. The final nanoporous structure has a bimodal characteristic with a finer nanoporous structure at the ridges, and rougher structure at the shallow pits. The powders with a size of 18–75 m dealloy faster due to their high crystallinity and larger powder size, and these with a powder size of smaller than 18 m tend to deepen uniformly. The formation of the Cu3Au intermetallic phases and the finer nanoporous structure at the ridges proves that minor Au addition inhibits the fast diffusion of Cu adatoms and decreases surface diffusion by more than two orders. The evolution of the surface nanoporous structure with negative tree-like structures is considered to be controlled by a percolation dissolution mechanism.

Effect of Minor Addition of Noble Elements on Microstructure and Mechanical Properties of Ti-Based Bulk Metallic Glasses

Fine nanoporous copper was fabricated from the amorphous Ti-Cu alloys with a minor addition of silver in 10 mM HF solutions. The pore sizes decreased from 100 nm to 12 nm with the increase of the Ag contents in comparison of Ti60Cu40 ribbons free of Ag. With increasing of the dealloying time, the sizes of the nanopores and ligaments increased for the nanostrucutres on Ti60Cu38Ag2 ribbons since the segregation of the Ag phase which triggered the galvanic dissolution of the adjacent Cu matrix in form of micro-couplings to further coarsen the nanoporous Cu. On the contrary, the trace formation of the Ag phase on the Ti60Cu39Ag1 ribbons had a weak ability to motivate the galvanic dissolution, indicating by the constant pore sizes and slight decrease in the ligament sizes with the increase in the dealloying time. The refinement of the nanoporous structures was ascribed to the drastic decrease in the surface diffusivity. The decrease in the surface diffusivity due to the involvement of Ag with a lower surface diffusivity in comparison of Cu was more than one order of magnitude. The involvement of Ag adatoms restricted the diffusion of Cu adatoms in the interface regions in the inward and outward directions.