Cao Chongde

Direct Measurement of the Metastable Liquid Miscibility Gap in Fe–Co–Cu Ternary Alloy System

The metastable liquid–liquid phase separation in undercooled Fe–Co–Cu ternary alloy melts (XCu = 0.10–0.84; XCo:XFe = 1:3, 1:1 and 3:1) is investigated by differential thermal analysis in combination with glass fluxing technique. In almost every case, the undercooling of the homogeneous alloy melt was sufficient to reach the boundary line of the submerged miscibility gap. The differential-thermal-analysis signals indicate that this separation into a (Fe,Co)-rich liquid phase L1 and a Cu-rich liquid L2 is exothermic and proceeds until the rapid solidification of the L1 phase occurs. At a given Cu concentration and with the increase of Co content, the phase separation temperatures decrease monotonically between the corresponding values of the boundary systems Fe–Cu and Co–Cu. The boundary lines of the miscibility gap, which are determined for the three quasi-binary cross-sections of the (Fe,Co)–Cu alloy system, show remarkably flat domes. The occurrence of the liquid phase separation shows an evident influence on the subsequent γ-Fe(Co,Cu)→α-Fe(Co, Cu) solid phase transformation.

Structures and physical properties of R2TX3 compounds

Rare-earth compounds have been an attractive subject based on the unique electronic structures of the rare-earth elements. Novel ternary intermetallic compounds R2TX3 (R = rare-earth element or U, T = transition-metal element, X = Si, Ge, Ga, In) are a significant branch of this research field due to their complex and intriguing physical properties, such as magnetic order at low temperature, spin-glass behavior, Kondo effect, heavy fermion behavior, and so on. The unique physical properties of R2TX3 compounds are related to distinctive electronic structures, crystal structures, microinteraction, and external environment. Most R2TX3 compounds crystallize in AlB2-type or derived AlB2-type structures and exhibit many similar properties. This paper gives a concise review of the structures and physical properties of these compounds. Spin glass, magnetic susceptibility, resistivity, and specific heat of R2TX3 compounds are discussed.

Thermophysical properties of Ni-5%Sn alloy melt

The surface tension and specific heat of Ni-5%Sn alloy melt were measured by the oscillating drop method and the drop calorimetric method using electromagnetic levitation, respectively. The temperature coefficient of surface tension is 6.43×10−4 N·m−1K−1 within the temperature regime of 1464–1931 K. The enthalpy change was measured in the temperature range from 1461 to 1986 K, and the average specific heat was obtained as 43.03 J·mol−1K−1. Some other thermophysical properties, such as viscosity, solute diffusion coefficient, density, thermal diffusivity and thermal conductivity of this alloy melt, were derived based on the experimentally measured surface tension and specific heat. Using these thermophysical parameters, the relation between solute trapping and undercooling in rapidly solidified α-Ni was calculated, and the theoretical prediction shows a good agreement with experimental data.

Rapid eutectic growth in undercooled Al-Ge alloy under free fall condition

Eutectic growth in Al-51.6%wt Ge alloy has been investigated during free fall in a drop tube. With decreasing undercooling ΔT, the microstructural evolution has shown a transition from lamellar eutectic to anomalous eutectic. A maximum cooling rate of 4.2×104K/s and undercooling of up to 240K (0.35TE) are obtained in the experiment. The eutectic coupled zone is calculated on the basis of current eutectic and dendritic growth theories, which covers a composition range from 48%-59% Ge and leans towards the Ge-rich side. The two critical undercoolings for the eutectic transition are ΔT1*=101K and ΔT2*=178K. When ΔT≤ΔT*1, the microstructure for Al-51.6% Ge eutectic shows lamellar eutectic. If ΔT≥ΔT*2, the microstructure shows anomalous eutectic. In the intermediate range of ΔT*1

Metastable phase separation and rapid solidification of undercooled Co-Cu alloy under different conditions

The metastable liquid phase separation and rapid solidification behaviours of Co61.8Cu38.2 alloy were investigated by using differential thermal analysis (DTA) in combination with glass fluxing, electromagnetic levitation (EML) and drop tube techniques. It is found that the liquid phase separation process and the solidification microstructures intensively depend on the experimental processing parameters, such as undercooling level, cooling rate, gravity level, liquid surface tension and the wetting state of crucible. Large undercooling and surface tension difference of the two liquids tend to facilitate further separation and cause severe macrosegregation. On the other hand, rapid cooling and low gravity effectively suppress the coalescence of the minority phase. Severe macrosegregation patterns are formed in the bulk samples processed by both DTA and EML. In contrast, disperse structures with fine spherical Cu-rich spheres homogeneously distributed in the matrix of Co-rich phase have been obtained in drop tube.

Ternary Eutectic Growth in a Highly Undercooled Liquid Alloy

The crystal nucleation and growth mechanism during the formation of Ag 42.4 Cu 21.6 Sb36 ternary eutectic are investigated under substantial undercooling conditions. The x-ray diffraction analysis shows that the solidified eutectic phases are not involved (Ag) within a wide undercooling range of 6–114 K. This indicates that under high undercooling condition, the phase constitution of Ag–Cu–Sb eutectic is different from that in the equilibrium phase diagram. With the increase of undercooling, the crystalline morphology of Ag 42.4 Cu 21.6 Sb36 alloy transforms from the mixed structure of primary θ(Cu2Sb), two pseudobinary eutectics and (e+θ+Sb) ternary eutectic into a unique (e+θ+Sb) ternary eutectic. The calculated results indicate that θ(Cu2Sb) is the leading nucleating phase among the three eutectic phases. In addition, the growth morphology of primary e(Ag3Sb) compound in Ag60Cu6Sb34 alloy exhibits the characteristics of solid solution and its orthorhombic dendrite grows along the 111 directions.

Bulk Heterojunction Photovoltaic Devices Based on a Poly(2-Methoxy, 5-Octoxy)-1, 4-Phenylenevinylene-Single Walled Carbon Nanotube-ZnSe Quantum Dots Active Layer

A solution-processed bulk heterojunction photovoltaic cell is fabricated based on poly[(2-methoxy, 5-octoxy)-1,4-phenylenevinylene](MOPPV)-single walled carbon nanotube(SWNT)-ZnSe quantum dots. The surface morphology shows the formation of an interpenetrating network between well-dispersed SWNTs and ZnSe in the MOPPV matrix. A blue-shifted absorption band indicates the strong electron interaction between SWNTs, ZnSe and MOPPV. A marked increase in the short-circuit current and power conversion efficiency (PCE) of ITO/PEDOT:PSS/MOPPV-SWNT-ZnSe/LiF/Al devices was achieved and compared with that without SWNTs. Results indicate that the enhanced performance is contributed by a high photocurrent due to efficient exciton dissociation and increased mobility for carrier transport in the SWNT pathway.