Zhanbo Sun

Microstructures of melt-spun Cu100-x-Crx (x=3.4-25) ribbons

Abstract Cu 100− x –Cr x ( x =3.4–25) ribbons were prepared by melt-spinning. Examination revealed that a supersaturated solid solution and a few very fine Cr-rich particles can be obtained for the Cu 96.6 Cr 3.4 ribbon. When x is ≥9, a microstructure with refined Cu- and Cr-rich phases can be obtained by melt spinning. The analyses indicated that the Cr-rich phase in the ribbons may be formed in two ways. One is the direct solidification from the liquid alloys during melt spinning, the diameter range of the Cr-rich particles formed lying between 30 and 200 nm. The other is the solid-phase separation of a Cu-rich supersaturated solid solution, the diameter of Cr-rich particles formed being only several nanometers.

Effects of Ni addition on liquid phase separation of Cu–Co alloys

Abstract This article deals with the effects of Ni addition on liquid phase separation of Cu–Co alloys. The results reveal that Ni addition can partly restrain the liquid phase separation of Cu–Co alloys, resulting in a decrease of the volume fraction for the Co-rich particles from the liquid phase separation and in refined microstructures. The composition analysis indicates that Ni is dissolved in both the Co-rich and the Cu-rich phases, but the Ni content in the Co-rich phase is much higher than that in the Cu matrix. The decreasing amount of Co-rich particles from the liquid phase separation and the refined microstructure are responsible for the GMR improvement of Cu–Co alloys with Ni addition.

Supercooling, isothermal soaking and liquid phase separation of Cu-Co alloys

Abstract In this paper, liquid phase separation of Cu 75 Co 25 and Cu 85 Co 15 alloys has been investigated during isothermal soaking at different supercooling rates. The results reveal that the liquid phase separation occurring during isothermal soaking can develop to a relatively large extent compared with continuous rapid cooling, resulting in larger quantities and larger sizes of Co-rich particles. The primary dendrites formed at small supercoolings tend to re-dissolve into the Cu-rich liquid and shrink locally in size leading to dendrites that break into segments. These dendrites and their small segments can collide with each other under the action of the electromagnetic force during high frequency induction heating and accumulate to form large Co-rich particles. It is found that whether the Co-rich droplets from the liquid separation solidify or not depends on the extent of the liquid phase separation at fixed temperature. Once the composition of Co-rich liquid reaches to the miscibility gap borderline, solidification can immediately take place.

Nanoporous Ag–CeO2 ribbons prepared by chemical dealloying and their electrocatalytic properties

A novel and facile strategy for the preparation of a monolithic Ag–CeO2 composite is reported. Here, nanoporous Ag–CeO2 ribbons are successfully prepared through dealloying melt-spun Al79.5Ag20Ce0.5 alloy in a 5 wt% NaOH aqueous solution, followed by calcining in air. The Ag–CeO2 ribbons with a homogeneous pore/grain structure are thermally stable up to 973 K because of the formation of Ag cores and CeO2 shells. Uniform CeO2 particles with lengths of about 5 nm are dispersedly loaded on the fine Ag grains of the porous structure. The Raman spectra show that a larger number of oxygen vacancies are formed in the CeO2 nanoparticles with an increase of the calcination temperature. The electrochemical tests reveal that the nanoporous Ag–CeO2 catalyst exhibits an enhanced activity toward the direct oxidation of sodium borohydride. The superior catalytic activity is attributed to the enhancement of the interfacial interaction between Ag and CeO2. The present work opens up a novel method to prepare metal–CeO2 nanocomposites with high catalytic performance and low cost.

Baize-like CeO2 and NiO/CeO2 nanorod catalysts prepared by dealloying for CO oxidation

Baize-like monolithic CeO2 and NiO/CeO2 nanorod catalysts were prepared by combined dealloying and calcination and the catalytic activities were evaluated using CO catalytic oxidation. The CeO2 catalysts were composed of nanorods and exhibited a three-dimensional supporting structure with pores. After introduction of NiO, dispersed NiO nanosheets and nanoparticles were supported on the surface of CeO2 nanorods and they were not well-crystallined due to CeO2 inhibiting the NiO crystallization. The Raman and x-ray photoelectron spectroscopy analyses revealed that the introduction of NiO species into CeO2 generated more coordinate unsaturated Ni atoms, oxygen vacancies, defects and active sites for CO catalytic reactions. The reaction activation energy of NiO/CeO2 nanorod catalyst prepared from the Al83Ce10Ni7 precursor alloy was just 31.2 kJ mol-1 and the CO conversion can reach up to 97% at 240 °C, which was superior to that of pure CeO2 and nanoporous NiO. The enhanced catalytic activity of baize-like NiO/CeO2 nanorods can be attributed to the strong synergistic effects between finely dispersed NiO species and surface oxygen vacancies in CeO2 nanorods.

Liquid Phase Separation of Cu-Cr Alloys during Rapid Cooling

The ribbons of Cu-Cr alloys with high Cr content (15%-35%, mass fraction) were prepared by rapid solidification. The microstructures of solidified samples were analyzed by scanning electron microscopy and transmission electron microscopy. The results reveal that a representative liquid phase separation microstructures are observed in Cu75Cr25 ribbons solidified at a cooling rate of about 10^4K/s. The liquid phase separation is not restrained when the cooling rate is enhanced to about 10^7K/s. However, the size of Cr particles solidified from Cr-rich liquid or Cr-rich regions in alloy melts could be refined by increasing the cooling rates. The size of Cr particles increases with increasing Cr contents when the ribbons contain 15% to 35%Cr.

Large magnetocaloric effect at low magnetic field in Ni50―xCoxMn35In15 ribbons

Recently, the magnetocaloric effect (MCE) of Ni-Mn-based Heusler alloys has attracted more attention due to its metamagnetic shape-memory effect. However, most MCE investigations focused on the bulk alloys developed at high magnetic field (>2 T). In this paper, by employing the melt-spinning technique, a large MCE at low magnetic field was found in a ribbon of Ni50−xCoxMn35In15. The magnetic entropy change ΔS reaches the maximum value of 5.35 J/kg K at 1 T field in the Ni49CoMn35In15 ribbon near room temperature, and its corresponding temperature span arrives 24 K. The refrigerant capacity is enhanced with the increase of the Co substitution. Such a large MCE at low magnetic field in the Ni50−x CoxMn35In15 ribbon with a wide temperature range provides a potential candidate for room temperature magnetic refrigeration.

Effects of Ti addition on microstructures of melt-spun CuCr ribbons

Abstract The microstructure and resistivity of melt-spun CuCrTi ribbon were studied. The results reveal that the maximal size of the primary Cr particles in the microstructures is below 100 nm by 0.65%-3.8%Ti (mole fraction) addition and the resistivity of annealed ribbons of 0.65%-1.3%Ti addition can meet the need of the contact materials used by the medium-voltage vacuum interrupters. By contrasting the melt-spun microstructures to the annealed microstructures, the primary Cr particles do not grow up quickly in the annealing process. The X-ray diffraction studies reveal that alloying increases the amount of the solute in Cu and Cr phases and results in the increase of resistivity. By the thermodynamic analysis, adding Ti to CuCr 29 alloys increases the critical supercooling of the liquid/solid transformation, which makes the critical radius of nucleation decrease and the rate of nucleation increase. As a result, the microstructure of CuCr ribbon can be further refined.

Rapid solidification of Cu60Co30Cr10 alloy under different conditions

Abstract Metastable liquid phase separation and rapid solidification in a metastable miscibility gap were investigated on the Cu 60 Co 30 Cr 10 alloy by using the electromagnetic levitation and splat-quenching. It is found that the alloy generally has a microstructure consisting of a (Co,Cr)-rich phase embedded in a Cu-rich matrix, and the morphology and size of the (Co,Cr)-rich phase vary drastically with cooling rate. During the electromagnetic levitation solidification processing the cooling rate is lower, resulting in an obvious coalescence tendency of the (Co,Cr)-rich spheroids. The (Co,Cr)-rich phase shows dendrites and coarse spheroids at lower cooling rates. In the splat quenched samples the (Co,Cr)-rich phase spheres were refined significantly and no dendrites were observed. This is probably due to the higher cooling rate, undercooling and interface tension.

Effects of Cr content on electrochemical properties of melt-spun Al75-xSi25Crx alloy anodes for lithium-ion batteries

Abstract Melt-spun Al 75- x Si 25 Cr x ( x =2, 4, 7, 10, mole fraction, %) alloys were investigated as anode materials for lithium-ion batteries. The as-quenched ribbons consist of nano-grains and metallic glass. The electrochemical measurements reveal that an activation behavior is exhibited in the anodes. The specific capacity of the Al 73 Si 25 Cr 2 anodes can reach a maximum of 1119 mA·h/g and maintain at 586 mA·h/g after 30 cycles. A more stable cycle performance is shown and a capacity loss is only 24% over 30 cycles for Al 71 Si 25 Cr 4 . The intermetallic compounds with Li cannot be detected in the lithiated anodes. After the ribbons were annealed, the specific capacities become much lower due to the formation of inert Al 13 Si 4 Cr 4 , and an AlLi phase can be tested in the lithiated anodes. The Cr dissolved in the non-equilibrium alloys causes low lithiation activity and strong structure stability, which could be the main reason of the activation and a restriction of structure evolution.