Yongbai Tang

The magnetocaloric effect and hysteresis properties of melt-spun Gd5Si1.8Ge1.8Sn0.4 alloy

The master Gd5Si1.8Ge1.8Sn0.4 MCE alloy was prepared by the arc-melt method. The alloy was re-melted and melt-spun by single-roller melt spinning at different copper wheel speeds. Temperature-dependent x-ray diffraction (XRD) and magnetic measurement confirm the first-order magnetic–crystallographic transition of as-cast Gd5 Si1.8Ge1.8Sn0.4. From powder XRD results, the melt-spun technique preserves the monoclinic phase of Gd5Si1.8Ge1.8Sn0.4 but broadens the corresponding Bragg reflection which implies the smaller crystalline size of the melt-spun ribbons. For the spun ribbons, the refrigerant capacity (RC) is comparable to that of the as-prepared Gd5Si1.8Ge1.8Sn0.4. The thermal (~9.2 K) and magnetic hysteresis (~62 J kg−1 at 270 K) near TC of the as-cast alloy have been significantly reduced (~4 K and ~5.7 J kg−1 to ~7.5 J kg−1 for ribbons, respectively) with the help of the melt-spun technique. The low hysteresis and large RC values make the spun ribbons suitable for magnetic refrigeration application near room temperature.

Corrosion Inhibition of LaFe11.6Si1.4 Alloy by BTA/Sodium Benzoate

Abstract The corrosion behavior of LaFe 11.6 Si 1.4 alloy was investigated in benzotriazole and sodium benzoate mixed solution. Polarization measurements and electrochemical impendence spectroscopy techniques were used to measure the electrochemical parameters. Experiment results show that the inhibition efficiency is influenced strongly by the concentration of benzotriazole and pH value. The high concentration benzotriazole and high pH value are beneficial to form a compact oxidation layer and thus prevent the dissolution of Fe.

Study on microstructure and mechanical properties of as-cast Mg-Sn-Nd alloys

Abstract Microstructure, tensile properties and compressive creep behaviors of Mg-(1.65–11.52) wt.% Sn-2 wt.% Nd alloys were studied in this paper. The microstructure of the as-cast Mg-Sn-Nd alloys consisted of dendritic α-Mg, Mg 2 Sn and Mg-Sn-Nd ternary phase containing rare earth element. The highest ultimate tensile strength of 140 MPa and percentage elongation after fracture of 9.7%, were achieved with a composition of Mg-8.23 wt.% Sn-2 wt.% Nd. The compressive creep resistance of Mg-8.23 wt.%Sn-2 wt.% Nd alloy was much better than other alloys at 200 °C for applied load of 35 MPa, which was mainly due to the formation of dispersive heat-resistance Mg 2 Sn and Mg-Sn-Nd intermetallic compounds.

Influence of iron on phase and magnetic property of the LaFe11.6Si1.4 compound

The phase relation, microstructure, Curie temperatures, hysteresis, and magnetocaloric effects of LaFex*11.6Si1.4 (x=0.96, 0.98, 1.0, and 1.02) compounds prepared by arc-melting and then annealed at 1423 K (1.5 h)+1523 K (4.5 h) were investigated. The main phase was NaZn13-type phase, the impurity phases included a small amount of a-Fe and LaFeSi phase in four samples. The crystal cell parameters of 1:13 phase increased from 1.1433(5) to 1.1454(4) nm with x increasing from 0.96 to 1.02, respectively. All samples kept the typical first-order magnetic transition. The increase of Fe strengthened IEM behavior, and led to the remarkable enhancement of MCE effect and negative slopes in Arrott plots around TC. The maximum ΔSM (T, H) under a low magnetic field (0-2 T) was 15.3, 16.8, 17.9, and 24.7 J/kg K with increasing of Fe content from x=0.96 to 1.02, respectively.

Microstructure, tensile properties and compressive creep resistance of Mg-(5–8.5)%Sn-2%La alloys

Abstract The microstructure, tensile properties and compressive creep resistance of permanent-mould cast Mg-(5–8.5)%Sn-2%La (mass fraction) alloys were investigated. The results show that Mg-(5–8.5)%Sn-2%La alloys are all composed of α -Mg phase, Mg 2 Sn and Mg-La-Sn compounds. Compared with those of Mg-5%Sn binary alloy, the grain size and the content of Mg 2 Sn compound in Mg-5%Sn-2%La alloy are decreased. With the increase of Sn content in Mg-(5–8.5)%Sn-2%La alloys, the content of Mg 2 Sn compound increases, while that of Mg-Sn-La compound changes little. In addition, the investigation suggests that the thermally stable Mg-Sn-La and Mg 2 Sn compounds can improve the tensile properties and compressive creep resistance of the alloys.

Design of a permanent magnetic circuit with air gap in a magnetic refrigerator

We calculate the magnetic field distribution of a permanent magnetic circuit with an air gap in a magnetic refrigerator by a finite-element method, and compare the field strengths of different structural parameters of the magnetic circuit. We show how the structure of the magnetic circuit can be optimized and present some approaches to improve the structure for a specific magnetic circuit. The main purpose is to provide basic parameters for the design of a practical magnetic refrigerator.

The giant magnetocaloric effect in Gd5Si2Ge2 with low purity gadolinium

The giant magnetocaloric effect Gd5Si2Ge2 alloy was prepared with 99wt% low purity commercial Gd. Powder XRD and magnetic measurements showed that the Gd5Si2Ge2 alloy annealed at 1200°C for 1 h had a significant magneticcrystallographic first order phase transition at about 270 K. The maximal magnetic entropy change is 17.55 J · kg−1 · K−1 under a magnetic field change of 0–5 T. The distinct increase of magnetic entropy change belongs to the first-order phase transition from the orthorhombic Gd5Si4-type to the monoclinic Gd5Si2Ge2-type after high temperature heat-treatment.

Compressive creep behavior of Mg-Sn binary alloy

Mg-Sn based alloy is one of the potential alloys for application at elevated temperature. The compressive creep behavior of ageing-treated Mg-χSn (χ=3%, 5%) alloys was investigated at the temperatures of 423 and 473 K and the stresses from 25MPa to 35MPa. When the tin content varies, the ageing-treated Mg-χSn alloys show quite different creep resistance, which are mainly attributed to the size and distribution of Mg2Sn phases in the ageing-treated Mg-χSn alloys. The calculated value of stress exponent, n=6.3, suggests that the compressive creep behavior of the ageing-treated Mg-5%Sn alloy is controlled by dislocation creep at the temperature of 473 K and the stresses from 25MPa to 35MPa.

Effect of copper ion implantation on corrosion morphology and corrosion behavior of LaFe11.6Si1.4 alloy

The morphology analysis and electrochemical method were used to study the corrosion behavior of LaFe11.6Si1.4 alloy of copper ion implantation. X-ray photoelectron spectroscopy (XPS) and atomic emission spectroscopy (AES) research results showed that a 15 nm-thick oxide film was formed on the surface of sample, and the copper content reached the highest value at 60 nm with a normal distribution. Immersion experiments indicated that the corrosion happened in the copper-poor zone firstly and a galvanic connection was formed among different zones on the surface due to the inhomogeneous distribution of copper. Electrochemical experiment results showed that the corrosion was serious when the ion acceleration voltage increased, and the high acceleration could reduce the thermodynamic performance of corrosion of LaFe11.6Si1.4 alloy.

Comparison between the nearest and the next-nearest neighbor site–spin interactions in the Ising model

A comparison between the nearest and the next-nearest neighbor site-spin interactions in the Ising model of various dimensions is presented. First, by the aid of the Greens function method the exact algebraic equations of the site-spin for the 1d Ising chain, the 2d square and the 3d simple cubic Ising lattices, are established, respectively. Then, according to the recursion principle with respect to these equations of the site-spins the expressions of the nearest and the next-nearest neighbor site-spin interactions of variously dimensional Ising models are obtained. The comparison between the nearest and the next-nearest neighbor site-spin interactions displays that on nearing the transition temperature K, the distinction between these two kinds of interactions is obviously increasing. It shows that the short range ordering plays an important role in the critical behavior of the Ising system. In addition, the abnormal and non-monotonic dependencies of these two near-neighbor correlative interactions upon the magnetization are revealed in the 3d situation