The surface tension of the liquid Ti-V system is systematically measured using the oscillating drop technique during electromagnetic levitation. Temperature- and compositional dependence are both investigated. The entire compositional range is covered. A linear decrease with increasing temperature is found for the pure elements as well as for all investigated alloys. The surface tension generally increases with increasing V-content. The obtained data are in good agreement with the Butler model for the ideal solution. Additionally, the Butler model for the regular solution was evaluated in the context of the obtained surface tension data. In contrast to many other Ti-based alloys, the Butler model for the regular solution yields no additional benefit for Ti-V, since there is only a neglectable small deviation between the calculations for the ideal and regular solution. Segregation effects are modeled using the Butler equation for an ideal solution. The findings are discussed considering already existing trends for the mixing behavior of liquid Ti-alloys. The results strongly suggest, that the Ti-V system obeys in general the ideal solution law.

Round-robin measurement of surface tension of high-temperature liquid platinum was conducted free of any contamination from the supporting materials and oxygen adsorption, using an electrostatic levitator (ESL), two electromagnetic levitator (EML), and an aerodynamic levitator (ADL). The measured temperature dependences of the surface tension using ESL and two EMLs were in good agreement and were expressed as σ=1,798±74.3−(0.12±0.0445)×(T−2,041)\sigma =\mathrm{1,798}\pm 74.3-(0.12\pm 0.0445)\times (T-\mathrm{2,041}) [10–3 N·m–1] (1,900–2,600 K). However, the surface tension values measured with ADL were slightly lower than those exceeding the uncertainty of the measurement plots at high temperatures.

Transitions from the liquid to the solid state of matter are omnipresent. They form a crucial step in the industrial solidification of metallic alloy melts and are greatly influenced by the thermophysical properties of the melt. Knowledge of the thermophysical properties of liquid metallic alloys is necessary in order to gain a tight control over the solidification pathway, and over the obtained material structure of the solid. Measurements of thermophysical properties on ground are often difficult, or even impossible, since liquids are strongly influenced by earth's gravity. Another problem is the reactivity of melts with container materials, especially at high temperature. Finally, deep undercooling, necessary to understand nucleus formation and equilibrium as well as non-equilibrium solidification, can only be achieved in a containerless environment. Containerless experiments in microgravity allow precise benchmark measurements of thermophysical properties. The electromagnetic levitator ISS-EML on the International Space Station (ISS) offers perfect conditions for such experiments. This way, data for process simulations is obtained, and a deeper understanding of nucleation, crystal growth, microstructural evolution, and other details of the transformation from liquid to solid can be gained. Here, we address the scientific questions in detail, show highlights of recent achievements, and give an outlook on future work.

Temperature dependent isobaric molar heat capacity cP was measured in a containerless way for liquid Ti and two AlTi binary liquid alloys. The technique of electromagnetic levitation was used in combination with laser modulation calorimetry. In all cases, linear temperature dependencies were found: At the corresponding liquidus temperatures, cP equals 49.75(±2.0) J∙K-1mol-1, 57.43(±2.9) J∙K-1mol-1, and 42.60(±2.2) J∙K-1mol-1, for Ti, Al20Ti80 and Al50Ti50, respectively. The respective temperature coefficients amount to -1.67∙10-2J∙K-2mol-1, -2.73∙10-2J∙K-2mol-1, and +7.83∙10-2J∙K-2mol-1. For liquid Ti, there is a good agreement with existing literature data. The results are discussed in relation to the Neumann-Kopp rule.

During metallurgical processing, gas bubbles nucleate and interact with the microstructure, which can result in severe defects. The research presented in this article focuses on in situ observation of bubble movement in semi-solid aluminum alloys (Al-Ge and Al-Cu) during a melting cycle. X-radiography is used to monitor the migration of H-bubbles in the semi-solid mush. For both alloys, H-bubbles are observed to burrow through the mushy zone towards the colder side of a horizontal gradient furnace leaving behind solute-enriched channels. This stands in contrast to the commonly observed bubble movement towards the hot side of the material caused by Marangoni flow-fields surrounding the gas pocket induced by gradients in the bubble's surface tension. Different dependencies of the surface tension on temperature and concentration for the two alloys are presented as explanation for the observed atypical phenomenon. These results suggest different dominant effects acting on the bubbles, temperature for Al-Ge and concentration for Al-Cu, and explain the cryophile behavior observed.

The present study is an overview of the surface properties of liquid Al-Ni alloys, which are of great importance for the design and development of new Al-Ni and Ni-based industrial alloys, widely used as functional and structural materials. The solidification and thus, the microstructural evolution are directly dependent on the interface/surface properties of metallic melts. Therefore, numerical simulation of microstructure evolution requires reliable property data as input to such models. Taking into account the experimental difficulties related to a high reactivity of liquid Al-Ni alloys and the effects of impurities on their surface properties, the surface tension over the whole concentration range has been determined in the frameworks of three international research projects. Namely, the surface tension measurements have been carried out by both traditional container-based and as an alternative, containerless methods within the ESA-MAP ThermoProp and ESA-MAP Thermolab Projects and also under the EU FP6-IMPRESS Project. The obtained datasets were analysed and subsequently compared with the model predicted values as well as with the literature data. A strong exothermic mixing characterises the Al-Ni system and the presence of a few intermetallic compounds in the solid state leads to the formation of short range ordered elements or complexes in the liquid phase, at least near the melting temperature, which significantly affects the surface properties of alloy melts. Aiming to estimate the effects of short range ordering on these properties, the Compound Formation Model (CFM) and the Quasi Chemical Approximation (QCA) for regular solution were applied.

Excess volume data of 32 liquid alloys were reviewed and plotted versus their excess free energies. It is hereby found that all combinations of the signs of EV and EG are possible. The excess volume data split into two different curves which are monotonous in EG. For one of these curves the signs of EV and EG are equal and they are opposite for the other. We improved our previously developed model and found that there is an unspecified sign which can be chosen either+ or -, depending on the system. This explains why there are two curves corresponding to the experimental finding. The model relates excess volume, excess free energy and isothermal compressibility with each other whereby the concept of internal pressure is used. The model can also predict the excess volume as function of the excess free energy, when the correct sign, either + or -, is known and a reasonable assumption is made for the effective isothermal compressibility. In the present work, the latter has been estimated as an average from the isothermal compressibility values over the involved pure elements. Good qualitative and quantitative agreement with the experimental data is obtained for the systems investigated. The model is valid at least for -3RT < EG< +1RT. (C) 2020 Elsevier B.V. All rights reserved.

In this Erratum, we present corrections of some of the formulas published in our article “Surface tension of liquid Ti with adsorbed oxygen” [J. Mol. Liquids 290 (2019) 111226]. Apart from a few typographic errors, this affects the way the energy barriers are calculated for adsorption and desorption. Fortunately, the impact on the figures is negligibly small, so that results, discussion, and conclusions remain unchanged.

Surface tensions of electromagnetically levitated liquid Ti-samples were measured under the influence of oxygen. The partial pressure of oxygen is controlled by means of yttria-stabilized zirconia tubes as well as Ar/H2/H2O buffer gas mixtures. In addition, TiO samples were prepared by adding different amounts of TiO2 powder to pure Ti. No significant dependence of the surface tension on the applied oxygen partial pressure was found for the samples processed. However, the surface tension was found to strongly depend on the bulk oxygen mole fraction determined by chemical analysis. From some experiments a small time dependence of the surface tension became evident.The observed dependencies of the surface tension on oxygen mole fraction as well as on time could be described by the model developed in the present work. It is based on adsorption/desorption rate equations and the surface tension is calculated from the ideal Butler equation. Non-ideal interactions ΔH≠0 between oxygen and titanium are taken into account.It is generally observed that, due to the strong attractive interaction between Ti and oxygen, the surface tension of Ti is much less sensitive to the presence of oxygen than the surface tension of other metallic systems.

The normal spectral emissivity ε of four compositions in the Al-Ti binary liquid system was measured in dependence of the wavelength and temperature. It was found that all compositions show negligible temperature dependence. At a wavelength of 940 nm, the emissivity amounts to 0.37, 0.40, 0.32, and 0.31 for Ti, Al20Ti80, Al50Ti50, and Al70Ti30, respectively. The dependence of the emissivity on composition is in good agreement with literature data of binary and multi-component Al-Ti-based alloys. Using the classical Drude model, electrical resistivities are predicted for the Al-Ti system from the measured emissivities. Comparison with existing data from literature for Al show reasonable agreement.

Surface tension and viscosity of liquid Cr-Fe-Ni alloys were measured by means of the oscillating drop method using the electromagnetic levitation facility TEMPUS. Experiments were carried out under microgravity achieved during a parabolic flight of an airplane. The obtained surface tensions agree well with those determined under gravity conditions although they are found slightly smaller. The obtained viscosities exhibit very good agreement with corresponding data measured by the oscillating cup method confirming the accuracy of the obtained data through both techniques. Thermodynamic model calculations agree with our experimental findings.

Liquid Ni-Ti alloys were processed in a containerless way using the technique of electromagnetic levitation in order to determine their densities. An improved optical method was utilized where, in addition to recording shadowgraph images from the side, a second camera recorded images of the sample from the top. A correction factor for the density was calculated from the top-view images. This method yields measurements insensitive to droplet rotation and static deformation which removes the need to assume axial symmetry. The measured densities are discussed in terms of the molar volume. A negative molar excess volume was obtained, indicating that Ni-Ti is a highly non-ideal system. These measurements were then used to test a recently proposed relationship between the molar excess volume, the excess free energy, and the isothermal compressibility. For the first time, the excess volume of a binary alloy, i.e. , Ni-Ti, is adequately predicted by a thermodynamic model.

The surface tensions γ of liquid Al–Au binary alloys are measured contactlessly using the oscillation drop technique of electromagnetic levitation. Data are obtained in experiments performed on ground and in micro-gravity during a parabolic flight campaign. For all samples and for all compositions, the surface tension decreases linearly with temperature. At 1400 K, γ monotonously decreases with increasing Al concentration. Features of compound formation, such as a maximum in the isothermal surface tension, are not evident from the experimental data. The results are in good agreement with the Butler and the Chatain model both using the sub-regular solution approximation.

We investigate temperature-and composition-dependent structural and dynamical properties of Al-Au melts. Experiments are performed to obtain accurate density and viscosity data. The system shows a strong negative excess volume, similar to other Al-based binary alloys. We develop a molecular-dynamics (MD) model of the melt based on the embedded-atom method (EAM), gauged against the available experimental liquid-state data. A rescaling of previous EAM potentials for solid-state Au and Al improves the quantitative agreement with experimental data in the melt. In the MD simulation, the admixture of Au to Al can be interpreted as causing a local compression of the less dense Al system, driven by less soft Au-Au interactions. This local compression provides a microscopic mechanism explaining the strong negative excess volume of the melt. We further discuss the concentration dependence of self-and interdiffusion and viscosity in the MD model. Al atoms are more mobile than Au, and their increased mobility is linked to a lower viscosity of the melt.

The energetics of mixing in the Fe–Cr liquid phase has been analysed through the study of the concentration dependence of various thermodynamic, structural, surface (surface tension and surface segregation) and transport properties (diffusivity and viscosity) by the first or the Quasi-Chemical Approximation (QCA) for regular solutions, developed by Bhatia and Singh, in the framework of statistical mechanical theory in conjunction with the Quasi-Lattice Theory (QLT). There is some disagreement regarding the assessments of the Fe–Cr phase diagram available in the literature, but all versions reported indicate the presence of a σ intermediate phase in the solid state. Since the arrangement of molecules in a liquid alloy is in some respects similar to that of a crystal, at least near to its melting temperature, the complex formation phenomenon in Fe–Cr melts has been described in terms of the microscopic functions (concentration fluctuations in the long-wavelength limit and chemical short-range order parameter).

For the study of the interaction of a liquid alloy with differently oriented single crystalline sapphire surfaces precise surface tension data of the liquid are fundamental. We measured the surface tension of liquid Al-Cu contactlessly on electromagnetically levitated samples using the oscillating drop technique. Data were obtained for samples covering the entire range of composition and in a broad temperature range. The surface tensions can be described as linear functions of temperature with negative slopes. Moreover, they decrease monotonically with an increase of aluminium concentration. The observed behaviour with respect to both temperature and concentration is in agreement with a thermodynamic model calculation using the regular solution approximation. Surface tensions were used to calculate interfacial energies from the contact angles of liquid Cu droplets, deposited on the C(0001), A(11-20), R(1-102) surfaces of an α-Al2O3 substrate. The contact angles were measured by means of the sessile drop method at 1380 K. In the Cu/α-Al2O3 system, no anisotropy is evident neither for the contact angles nor for the interfacial energies of different surfaces. The work of adhesion of this system is isotropic, too.

Molar excess volume of Cu-Ti liquid mixture has been investigated to elucidate how the excess volume in binary alloys is related to mixing enthalpy and microscopic interactions. Cu-Ti is used as a key example for systems showing positive excess volume and negative mixing enthalpy. For this purpose, the density of several Cu-Ti binary mixtures has been measured over the whole composition range by the containerless technique of electromagnetic levitation as a function of temperature. A linear temperature dependence of the density has been found for all investigated alloys. In addition, the density decreases with increasing Ti content in the alloys, showing a negative deviation from the ideal solution model. As mentioned, a positive excess volume was found whereas the enthalpy of mixing is negative. This behavior has been discussed in relation with chemical ordering and the role played by attractive and repulsive interactions in the system, according to previous results obtained by means of molecular dynamics simulation on binary dense fluids.

The available experimental data for the density and viscosity of liquid cadmium, cobalt, gallium, indium, mercury, silicon, thallium, and zinc have been critically examined with the intention of establishing both a density and a viscosity standard. All experimental data have been categorized into primary and secondary data according to the quality of measurement, the technique employed and the presentation of the data, as specified by a series of criteria. The proposed standard reference correlations for the density of liquid cadmium, cobalt, gallium, indium, silicon, thallium, and zinc are characterized by percent deviations at the 95% confidence level of 0.6, 2.1, 0.4, 0.5, 2.2, 0.9, and 0.7, respectively. In the case of mercury, since density reference values already exist, no further work was carried out. The standard reference correlations for the viscosity of liquid cadmium, cobalt, gallium, indium, mercury, silicon, thallium, and zinc are characterized by percent deviations at the 95% confidence level of 9.4, 14.0, 13.5, 2.1, 7.3, 15.7, 5.1, and 9.3, respectively.