High Frequency Melting Research Articles

Phase equilibria and liquidus projection determination of the Ce–Co–Sb ternary system

The Ce-Co-Sb ternary system is experimentally investigated, including the isothermal section at 823 K and the supplementary measurements at 673 K, as well as the liquidus projection of this system. For the isothermal section at 823 K, the phase equilibria in the whole composition range are determined using the equilibrated alloys prepared by the combination of arc melting method and high frequency melting method under the protection of an argon atmosphere, in case of the volatility of Sb and the oxidation of Ce. To confirm the phase relations at 673 K from previous literature report, some phase equilibria are re-determined on the basis of supplementary experiments. Two ternary compounds, (CeCouSb2) and CeCoSb3 are observed and the isothermal sections of the Ce-Co-Sb system at 823 and 673 K are finally constructed. The solidification paths of the Ce-Co-Sb as-cast alloys are analyzed to ascertain the primarily solidified phases from liquid. Both the liquidus projection and the isothermal sections of the Ce-Co-Sb system are determined based on the microstructures, crystal structures and phase compositions determined by scanning electron microscopy, X-ray diffraction and electron probe micro-analyzer, respectively. Some phase transition temperatures of the Ce-Co rich region are determined by means of differential scanning calorimeter.

Thermoelectric high ZT half-Heusler alloys Ti1−x−yZrxHfyNiSn (0 ≤ x ≤ 1; 0 ≤ y ≤ 1)

In order to achieve homogeneous products of n-type Ti1−xZrxNiSn, Ti1−xHfxNiSn, and corresponding Sn/Sb substituted alloys, the synthesis conditions were tuned by an optimized arc melting technique, an intermediate high frequency melting step, long time ball milling and a multi-step hot pressing technique. To counteract on the generally high thermal conductivity in half-Heusler alloys fine-grained precipitates from decomposition reactions may help to enhance phonon scattering and as a result reduce the thermal conductivity. Therefore the binodal and spinodal curves in the isopleths TiNiSn–ZrNiSn and TiNiSn–HfNiSn were calculated in order to optimize heat treatment conditions.Furthermore the thermoelectric behavior of Ti1−xHfxNiSn and respective Sn/Sb substituted compounds in the temperature range from room temperature to 873 K was characterized by measurements of the electrical resistivity, ρ, the Seebeck coefficient, S, the thermal conductivity, λ, from which we calculated the dimensionless figure of merit, ZT, and also the efficiency, η, for thermoelectric power generation. Due to the high market price of Hf, a Ti1−xZrxNiSn series with and without Sn/Sb substitution was successfully synthesized with ZT∼1 for TiNiSn and ZrNiSn and ZT∼1.2 for Ti0.5Zr0.5NiSn0.98Sb0.02. The experimental data are discussed in the context of respective DFT calculations.

Thermoelectric properties of meltspun Ba8Cu5(Si,Ge,Sn)41 clathrates

The type-I clathrates Ba8Cu5(Si,Ge,Sn)41 show promising thermoelectric (TE) properties. We investigated the influence of Sn substitution for Ge on the TE properties of Ba8Cu5Si6(Ge,Sn)35 samples prepared by the fast and economic melt–spinning technique and compared our results with a sample series prepared using the conventional synthesis method of high–frequency melting and hot pressing. All samples crystallize in cubic symmetry with the space group Pm3¯n. Scanning electron microscopy (SEM) together with energy dispersive x-ray spectroscopy (EDX) revealed a maximum solid solubility limit of 0.6 Sn atoms per unit cell. Electrical transport measurements showed metal–like behavior. The negative slope of the Hall resistivity ρH points on the dominance of electrons in this material, confirmed by Seebeck coefficient measurements. With increasing Sn content the Cu concentration decreases and vacancies appear. These secondary effects have a stronger influence on electrical transport than the direct influence of the Sn substitution. The electronic transport is dominated by alloy scattering at high temperatures and neutral–impurity scattering at low temperatures. The phononic thermal conductivity is by a factor of two lower than in the hot pressed samples. The dimensionless figure of merit ZT = 0.43 at 773 K is reached for the sample with the highest Sn content.

Use of a Soluble Anode in Electrodeposition of Thick Bismuth Telluride Layers

Integration of thermoelectric devices within an automotive heat exchanger could enable conversion of lost heat into electrical energy, contributing to improved total output from the engine. For this purpose, synthesis of thick bismuth telluride (Bi2Te3) films is required. Bismuth telluride has been produced by an electrochemical method in nitric acid with a sacrificial bismuth telluride anode as the source of cations. The binary layer grows on the working electrode while the counter-electrode, a Bi2Te3 disk obtained by high frequency melting, is oxidized to BiIII and TeIV. This process leads to auto-regeneration of the solution without modification of its composition. The thickness of films deposited by use of the Bi2Te3 anode was approximately 10 times that without. To demonstrate the utility of a soluble anode in electrochemical deposition, we report characterization of the composition and morphology of the films obtained under different experimental conditions. Perfectly dense and regular Bi2Te3 films (∼400 μm) with low internal stress and uniform composition across the cross-section were prepared. Their thermoelectric properties were assessed.

Effect of Zr, Mo and Y Adding on Microstructure, Mechanical and Electrical Properties of Au-Pd, Pt-Ir and Pd-Ru Systems

Abstract The effect of Zr, Mo and Y adding on mechanical and electrical properties of Au-Pd, Pt-Ir and Pd-Ru systems was investigated. The alloys were prepared in a vacuum high frequency melting furnace. X-ray diffraction and metallographic microscopy were employed to detect the microstructures. Electric bridge and eddy current conductive instrument were used to test the electrical resistivity, and the mechanical properties of the alloys were tested by AG-X100KN type tensile testing machine. The results show that adding of rare metal elements in Au-Pd, Pt-Ir and Pd-Ru systems could refine structures of the alloys effectively, increase their melting points, densities and electrical resistivities, and improve mechanical properties of the alloys, but the elongations of the alloys is decreased.

Effects of Zr, Mo and Y-Doping on Microstructure and Mechanical, Electrical Properties of Au-Pd Binary Alloy

Abstract Au-Pd alloys doped with Zr, Mo and Y, respectively, were prepared in a vacuum high frequency melting furnace. The effects of rare metal doping on Microstructure and mechanical, electrical properties of the binary alloy was investigated. X-ray diffractometer and metallographic microscopy were employed to detect the microstructures. Electric bridge and eddy current conductive instrument were employed to test the electrical resistivity and the mechanical properties of alloys were tested by AG-X100KN type tensile testing machine. The results show that adding rare metal elements into Au-Pd system could refine microstructure effectively, increase the melting point, density and electrical resistivity of the alloy, and improve mechanical properties, but the processing property of the alloy is decreased.

Structural and thermoelectric properties of Ba8Cu5SixGe41−xclathrates

Intermetallic clathrates are known for their high thermoelectric efficiency. However, to realize mass market applications, efficient low-cost representatives have to be found. Here we investigate the candidate material Ba${}_{8}$Cu${}_{5}$Si${}_{x}$Ge${}_{41\ensuremath{-}x}$, $0\ensuremath{\le}x\ensuremath{\le}41$ by x-ray powder diffraction (XPD), energy dispersive x-ray spectroscopy, and electrical and thermal transport property measurements. Polycrystalline samples are prepared by high frequency melting and subsequent ball milling and hot pressing. The type-I clathrate structure is confirmed in all samples by XPD. The structural details are evaluated by the Rietveld method. The results show that when Ge is replaced by Si, linear variations can be observed for the lattice parameter, cages size, atomic displacement parameters of Ba in the large cage, and atomic parameters $x$ of $16i(x,x,x)$ and $z$ of $24k(0,y,z)$. However, the atomic parameters $y$ of $24k(0,y,z)$ and interatomic distance between the atoms at the $24k$ site vary nonlinearly with the Si content ${x}_{\text{Si}}$. Nonlinear behavior also appears for the Si occupation at the $24k$ site. These nonlinear variations result in the electronic band structure changing nonmonotonically with ${x}_{\text{Si}}$, which explains the observed nonmonotonic variations of the transport properties. The lattice thermal conductivity shows ${x}_{\text{Si}}$ independence, which escapes from our anticipation that the larger the tetrakaidecahedra cage, the lower the lattice thermal conductivity in clathrates. The insignificance of resonant scattering for the lattice thermal conductivity might be the reason for the observed independence. The highest dimensionless thermoelectric figure of merit $ZT$ of 0.5 at about $550{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$ is achieved for Ba${}_{8}$Cu${}_{5}$Si${}_{3}$Ge${}_{38}$.

ChemInform Abstract: SrAu4.76In1.24 with YbMo2Al4‐Type Structure.

AbstractSrAu4.76In1.24 is synthesized by high frequency melting of the elements followed by annealing at 1400 K for 5 min and at 900 K for 4 h.

Crystal structure, magnetic behaviour and valence state of ytterbium in the Yb 4Ni 10+ xGa 21− x phase

The ternary phase Yb 4Ni 10+ x Ga 21− x has been synthesised from the elements by high frequency melting in argon atmosphere. The homogeneity region has been established from X-ray powder data and confirmed by EDX analysis for 0.3≤ x≤1. The crystal structure of Yb 4Ni 10+ x Ga 21− x has been estimated from X-ray single crystal data: space group C2/ m (no. 12), Z=2, a=20.6815(9) Å, b=4.0560(4) Å, c=15.3520(7) Å, β=124.800(3)°, R( F)=0.023 for 1701 symmetry independent reflections with F( hkl)>4 σ( F). A special feature of the structure is the local disorder within the gallium/nickel network. Neglecting atomic disorder in the region of the Ga9 and Ga11 positions, the Yb 4Ni 10+ x Ga 21− x structure is an occupation variant of the Ho 4Ni 10Ga 21 type with nickel atoms partially replacing the Ga atoms in the 2 d sites at the centers of distorted icosahedra. From magnetic susceptibility and from L III-XAS spectra, the valence state of ytterbium is near 3+.

The crystal structure and magnetic properties of YbMSb, MCu, Ag, Au

The compounds Yb(Cu,Ag,Au)Sb were synthesized via high frequency melting of the elements in a closed Ta-crucible. The crystal structure of the novel phases was determined from X-ray powder Rietveld refinements. Dependent on the ratio R Yb/ R (Cu,Ag,Au) different structure types were encountered: YbCuSb (ordered Ni 2In-type, R F=0.036), YbAgSb (TiNiSi-type, R F=0.054) and YbAuSb (LiGaGe-type, R F=0.038). The results of the magnetic measurements revealed that the compounds YbCuSb and YbAgSb are temperature independent Pauli-type paramagnets whilst a small magnetic moment (≈1β B) was observed for YbAuSb. In good agreement, X-ray absorption spectroscopy (at 10 and 300 K) confirmed for all three compounds dipositive Yb temperature independent valencies of 2.06 (M = Ag), 2.08 (Cu) and 2.14 (Au); possibly owing to small amounts (less than upo to ≈ 4%) of Yb 3+ grain boundary effects.

Crystal structure and magnetic behaviour of ternary YbTGa 2 compounds (T = Ni, Pd, Pt) and quaternary solid solutions YbPd 1− xAg xGa 2

Compounds YbTGa 2 with TNi, Pd, Pt and alloys YbPd 1− x Ag x Ga 2 have been synthesized by argon high frequency melting from metal ingots in tantalum crucibles followed by homogenization annealing at 600 or 400°C respectively. From X-ray powder diffraction data. Yb{Ni.Pd,Pt}Ga 2 was found to be isotypic with MgCuAl 2-type, with a small solid solubility for Ag in YbPdGa 2 (0 ⩽ x ⩽ 0 2). At 600°C the solid solubility of Pd in βYbAgGa 2 (βYbAgGa 2-type) was 0.7 ⩽ x ⩽ 1.0. The YbTGa 2 (T = Ni, Pd, Pt) compounds are paramagnets, where the ytterbium adopts the 2F 7 2 ground state. The magnetic results of the solid solution YbPd 1− x Ag x Ga 2 are characterized by an intermediate or mixed valence behavior of the ytterbium atom (Yb 2+å Yb 3+), whereas XAS measurements establish a mixed valence system.

YbAgGa 2: Synthesis, crystal structure and magnetic behaviour

A novel intermetallic compound with two crystallographic modifications, α- and β-YbAgGa 2, was prepared by argon high frequency melting from ingots of the elements in tantalum crucibles with homogenization heat treatments at 600 °C (β-YbAgGa 2) and 400 °C (α-YbAgGa 2). The crystal structure of β-YbAgGa 2 has been refined from powder diffraction data obtained using a Ge(111) primary monochromator and a linear position-sensitive detector. The sample was measured in transmission mode with Cu Kα 1 radiation in the range 10° < 2θ < 130°, Δθ = 0.02°: a = 6.9653(3) A ̊ , b = 4.3362(2) A ̊ , c = 10.3386(4) A ̊ , V = 311.85(4) A ̊ 3 . Full profile refinement led to the residual values R(I) = 0.061 and R(P) = 0.081 (for 303 reflections), space group Pnma, oP16; 4 Yb in 4(c) x 1 4 z, x = 0.2241(2), z = 0.82774(9) , 4 Gal = 0.926(6)Ga + 0.074(6)Ag in 4(c), x = 0.2950(3), z = 0.5369(2), 4 Ga2 in 4(c), x = 0.0751(3), z = 0.1497(2), 4 Ag = 0.951(6)Ag + 0.049(6) Ga in 4(c), x = 0.4595(2), z = 0.0983(1). Coordination numbers are 16 for Yb, 10 for Ga and 12 for Ag. Shortest interatomic distances were revealed for the following: YbGa, 3.014 Å; YbAg, 3.183 Å; YbYb, 3.832 Å; GaGa, 2.622 Å; GaAg, 2.720 Å; AgAg, 3.024 Å. The structure of β-YbAgGa 2 is a distorted variant of the ScRhSi 2 type. Magnetic susceptibility measurements (4.8–900 K) revealed a rather low effective paramagnetic moment for β-YbAgGa 2 (0.5 μ B ( Yb atom) −1, Θ p = 6.5 K ) whereas a tripositive ground state is inferred for α-YbAgGa 2 (about 4.5 μ B (Yb atom) −1, Θ p = −71 K ).

New ytterbium compounds with the BaAl 4 type of structure: crystal chemistry and magnetic properties of Yb(Cu,Ag,Au,Pd,Pt) xGa 4 - x

Ternary samples with the composition Yb(Cu,Ag,Au,Pd,Pt) xGa 4 - x have been synthesized from the elements by high frequency melting followed by heat treatment at 600 °C. The crystal structure of all compounds was investigated using X-ray single-crystal or powder techniques and belongs to the BaAl 4 type of structure. The homogeneity regions of the Yb(Cu,Ag,Au,Pd,Pt) xGa 4 - x phases have been established from X-ray powder diffraction analyses and lie in the range x = 0.30 –0.95 for Cu, 0.25 –0.43 for Ag, 0.22 –1.45 for Au, 0.23 –0.65 for Pt and near x = 0.25 for Pd. The unit cell dimensions vs. composition reveal a significant deviation from Vegard's rule for Cu and Au and a slight deviation for Ag and Pt. A partially ordered occupation of the 4 d and 4 e sites in the BaAl 4 structure type has been found depending on the M/Ga ratio in the homogeneity range. The weak temperature-dependent paramagnetism of these compounds is due to the non-magnetic ground state of ytterbium (Yb 2+). However, for YbPt 0.5Ga 3.5 a rather intermediate valence behaviour (Yb 2+ → Yb 3+) is encountered.

市販クラウン・ブリッジ用ニッケルクロム合金の機械的性質に及ぼす鋳造法の影響

We measured Tensile Strength and Vickers Hardness with using testpieces casted Ni-Cr Alloys by melting cast technic (high frequency melting in the argon atmosphere, atmospheric high frequency melting, melting by blowpipe with natural gas and oxygen).And we gained next conclusion after appraising qualitative deterioration of the alloy in quantity by cotributive percentage of casting defect.