Article

Recent studies on thermophysical properties of metallic alloys with PROSPECT: Excess properties to construct a solution model

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Abstract

We have developed the system PROSPECT for measuring thermophysical properties at high temperature. Precise thermophysical measurements provide accurate excess functions, which represent non-ideality of solutions. We use excess functions to discuss solution models on the basis of electronic structure and thermodynamics. Pd-Fe systems show positive excess volume VE with negative excess Gibbs energy GE. The phase diagrams of these systems have common features with those of other Pd-X and Pt-X systems (where X is Fe, Ni, Co, or Cu), which means they all have order-disorder transitions. The correlation between VE and GE is discussed in terms of the electronic structure of the alloys, and an energy diagram is proposed to understand this correlation. The excess heat capacity Cp E of Fe-Ni melts is positive over a whole composition range and a wide temperature range. We estimate the temperature dependences of the excess enthalpy HE and excess entropy SE of Fe-Ni melts from Cp E. The Lupis-Elliott rule is satisfied for HE and SE with positive Cp E.

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... To address these problems, the application of levitation techniques such as electrostatic levitation [13,14] and electromagnetic levitation (EML) is proposed. Our research group has developed a high-temperature thermophysical property measurement system for liquid metals, which is termed PROSPECT [15][16][17][18]. PROSPECT consists of EML and a superconducting magnet. ...
... The experimental apparatus and detailed procedures were previously reported [15][16][17][18], therefore, only a brief explanation is presented here. Fig. 1 shows a schematic illustration of the experimental equipment (PROSPECT). ...
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This study aimed to provide thermophysical property data of Co–Cr–Mo (CCM) alloys that are used as biomedical materials to understand and improve additive manufacturing processes. The density, surface tension, normal spectral emissivity, specific heat capacity and thermal conductivity of two CCM alloys that contained a low (0.053 mass%) and a high (0.251 mass%) carbon content were measured in a liquid state using an electromagnetic levitation technique. The liquidus temperatures of the CCM alloys were measured by differential scanning calorimetry. A static magnetic field was applied to the levitated CCM droplets to suppress the surface oscillation and translational motion of the droplets, and convection flow inside the droplet for each property measurement as needed. Uncertainty analysis was conducted for all thermophysical property data. No major difference was found in the thermophysical properties for the low- and high-carbon CCM melts within experimental uncertainty. An ideal solution model reproduced the CCM melt density within experimental uncertainty, however, we obtained large positive excess heat capacities of the CCM melts.
... Image-based density measurements using levitation have been reported since the 1960s [24], and have been further refined using modern machine vision algorithms and applying Legendre polynomial fitting to the results of edge detection routines for volume calculation [23,[25][26][27][28]. Modulated laser calorimetry on electromagnetically levitated melts was developed by Fukuyama et al. in 2007 [29]. Data on excess volume from image processing combined with data on excess heat capacities of mixing [30] provide a thermodynamic foundation for constructing realistic solution models for metallic alloys. ...
... The measurements of change in density with melt composition can be used to obtain the excess volume of mixing in the liquid state for multicomponent systems and derive realistic thermodynamic mixing models, as demonstrated by Fukuyama et al. [30] for metal alloy systems. Such measurements for key refractory oxide systems will be the subject of future studies. ...
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Densities of liquid oxide melts with melting temperatures above 2000 °C are required to establish mixing models in the liquid state for thermodynamic modeling and advanced additive manufacturing and laser welding of ceramics. Accurate measurements of molten rare earth oxide density were recently reported from experiments with an electrostatic levitator on board the International Space Station. In this work, we present an approach to terrestrial measurements of density and thermal expansion of liquid oxides from high-speed videography using an aero-acoustic levitator with laser heating and machine vision algorithms. The following density values for liquid oxides at melting temperature were obtained: Y2O3 4.6 ± 0.15; Yb2O3 8.4 ± 0.2; Zr0.9Y0.1O1.95 4.7 ± 0.2; Zr0.95Y0.05O1.975 4.9 ± 0.2; HfO2 8.2 ± 0.3 g/cm3. The accuracy of density and thermal expansion measurements can be improved by employing backlight illumination, spectropyrometry and a multi-emitter acoustic levitator.
... Data were acquired using an electromagnetic levitation (EML) technique with a superconducting magnet. The necessary instrumentation (referred to as the PROSPECT system) was developed at our facilities and has been used to obtain many thermophysical properties of high-temperature liquids [10][11][12][22][23][24][25][26][27][28]. In the PROSPECT apparatus, a static magnetic field is applied to a droplet undergoing EML, which significantly reduces the motion of the center of gravity and the surface oscillations of the droplet, allowing for highly accurate density measurements. ...
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Our group has previously investigated the correlations between the excess volumes, thermodynamic functions and phase diagrams of binary alloy melts, and the present study focused on binary Au-X (X = Cu, Pd and Ni) alloy melts. The Au-Cu and Au-Pd systems have intermetallic compounds with order-disorder transitions. The densities of these alloy melts were determined with small uncertainties using a combination of an electromagnetic levitation technique and a static magnetic field. The densities of these melts varied linearly with temperature, including those temperatures within the supercooled range. These results are discussed herein within a thermodynamic framework based on the correlation between excess volume (VE) and excess Gibbs energy (GE). The data obtained in this work confirmed that binary alloy systems having an order-disorder transition, such as the Au-Cu and Au-Pd systems, belonged to the group defined by VE ≥ 0 and GE < 0. The effect of composition on VE was examined with regard to cluster formation in the liquids. The Au-Ni system was shown to possess a miscibility gap in the solid solution and the corresponding melts had positive VE and positive GE values.
... In our previous research, we found that the Pd-X (X: Fe, Ni, and Cu) systems undergo an order-disorder transition in a solid solution range and have positive excess volume and negative excess Gibbs energy in the liquid state [1][2][3]. The excess volume decreases and the excess Gibbs energy increases as the number of electrons increases in the 3d orbital of X of the Pd-X melts. ...
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This study is a fundamental investigation aimed at developing a new noncontact modulated laser calorimetry method incorporating a static magnetic field to achieve measurement of the true thermal conductivity of a metallic melt. For establishing the experimental principle, a solid platinum sphere was used in this study. The sphere positioned in the centre of a radio frequency coil was heated sinusoidally by a laser; its temperature response was monitored. Analyses of the temperature amplitude and phase difference between the laser input and temperature response yielded the heat capacity, thermal conductivity and hemispherical total emissivity of platinum for temperatures of 1400–1700 K. The obtained data agree with the reference data within experimental uncertainty, which verifies the experimental method.
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Thermal conductivity of liquid silicon is necessary for numerical process modeling. It is also of scientific interest. However, measuring thermal conductivity is a difficult task because of convections in the liquid and contamination from contact materials. To overcome these experimental difficulties, we have developed noncontact modulated laser calorimetry in a dc magnetic field to measure heat capacity, thermal conductivity and emissivity of high-temperature liquid metals. In this study, through improvement in temperature measurements, we considerably reduced the experimental uncertainty of measurements. Furthermore, the thermal conductivity and heat capacity of supercooled liquid silicon were measured. Thermal conductivity of liquid silicon agrees with the values calculated assuming the Wiedemann–Franz law near the melting point. This result suggests that free electrons play a dominant role in the thermal transport process in liquid silicon.
Article
Enthalpy, resistivity and density as a function of temperature of binary Fe-Ni alloys have been measured by a fast resistive pulse heating technique. Six different concentrations, including Invar-type alloy, have been investigated to cover the entire range of the phase diagram. The temperature range was from room temperature to 2400 K.
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The thermodynamic activities and heats of mixing of liquid and solid solutions in the systems Fe-Ni and Fe-Co have been measured by Knudsen-Cell mass spectrometry using a newly designed molecular beam apparatus. The data obtained for the system Fe-Ni agree very closely with previous results and confirm negative deviations over the whole concentration range. Results for Fe - Co indicate negative deviations from ideality for all composition between XCo = 0.05 – 1.00 and positive deviations below XCo = 0.05. This supports calorimetric measurements and is in conflict with a previous mass-spectrometric investigation reporting positive deviations from ideality.
Article
A photoemission investigation of Fe-Pd and Fe-Pt transition-metal alloys, using ∼50–150-eV synchrotron radiation, is presented. We consider in particular the spectral distribution of Fe states when approaching the dilute limit. By means of the Cooper minimum in the 4d and 5d photoionization cross section, we identify structures that have mainly Fe minority- or Fe majority-spin character. The relative position of these peaks is discussed in terms of the covalent interaction between Fe 3d and Pd or Pt d states. Also, the strong resemblance between the distribution of Fe states in the Pd-based and in the Pt-based alloys is demonstrated. We find a consistent behavior of interacting d states towards the dilute limit. It is concluded that the Fe states that are observed in the photoemission spectra of the dilute alloys have mainly majority-spin character and are, because of the covalent interaction with host states, widely distributed over the energy range of the host d band. The Fe minority-spin band, which is centered near the Fermi level, gradually empties with increasing Fe dilution.
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