A new variant for measuring the surface tension of liquid metals and alloys by the oscillating drop method

The theoretical background of the oscillating drop technique for measuring surface tension is briefly presented and the different analysis procedures are cited. A new method is described for obtaining oscillation frequencies by fast fourier transformation (FFT) of the pyrometer voltage signals from temperature measurements at the top of the levitated sample. The results on the first experiments on liquid nickel are in a good agreement with the hterature data.Paper presented at the Fourth International Workshop on Subsecond Thermophysics. June 27–29, 1995, Köln, Germany.     

Electrical conductivity measurements in liquid metals by rotational technique

The rotational contactless inductive measurement technique has been developed to measure the electrical conductivity of liquid metals. This method is based on the phenomena when a conductor material rotates in a magnetic field, circulating eddy currents are induced and generate a damping torque proportional to the electrical resistivity of the material. The technique was tested to measure the conductivity of five conductors and one low melting composite (LMA-158).     

Surface tension measurements of refractory liquids using the modified drop weight method

Liquid surface tension measurements using the sessile drop, pendant drop and drop weight methods are discussed. These measurements refer to high temperature materials which melt at temperatures greater than 2000° C. The liquid surface tension of copper was determined to be 1212 dyn/cm at its melting point, and that of Al₂O₃ to be 600 dyn/cm at its melting point. Discussion is presented giving preference to the drop weight method.employed at the Corning Glass Works during the summer of 1966.     

An automatic technique for measuring the surface tension of liquid metals

A methodology for automatic measurement of surface tension of liquid metals is presented. The procedure involves the digitization of a television image of a drop of the liquid metal, image processing to obtain the real coordinates of the drop profile, and a final computation of the drop surface tension by a nonlinear regression technique. The method is faster and more reliable than other classical methods, and yields results that are reproducible and as precise as those obtainable by non-automatic procedures. An important feature of this approach is that it can be used for metallurgical tests to check the quality of an alloy during its production, or to provide surface tension data in non-equilibrium processes.     

A quasi-containerless pendant drop method for surface tension measurements on molten metals and alloys

A quasi-containerles pendant drop method for measuring the surface tension of molten metals and alloys is being developed. The technique involves melting the end of a high-purity metal rod by bombardment with an electron beam to form a pendant drop under ultra-high-vacuum conditions to minimize surface contamination. The magnified image of the drop is captured from a high-resolution CCD camera. The digitized image of the drop is then analyzed to compute the surface tension. A computer program has been developed that reads the pixel intensities from a graphics file containing the digital image. The code searches for the edge of the drop along rows and columns of pixels and stores the edge coordinates in an array. It then computes an optimized theoretical drop shape by solving the Young-Lapface differential equation from which the quantity of surface tension is deduced. This technique has been demonstrated with the surface tension measurement of molten zirconium metal.Paper presented at the Twelfth Symposium on Thermophysical Properties. June 19–24, 1994, Boulder, Colorado, U.S.A.     

Factors limiting the accuracy of measurements of surface tension by the sessile drop method

Different sources of error in determining surface tension by the sessile drop technique are discussed. The influence of uncertainties in measuring drop co-ordinates are quantitatively evaluated, and the results tested on Ag and Pb drops at different temperatures. Shifts in surface tension values, due to errors in determining the exact scale factor and to errors in reading temperature or density, are calculated, and a nomographic chart, to find the optimum drop weight, is also presented.     

Surface tension of liquid inert gases

The surface tension of liquid inert gases, including ³He and ⁴He helium isotopes, has been calculated using a method based on determining the work that must be done to remove an atom from the liquid surface. This approach provides quite satisfactory agreement with the available experimental data. Calculations of the surface tension in liquid helium also take into account the quantum zero-point oscillations of atoms. The role of the dimensional effect in the surface tension for nanodroplets is discussed.     

Surface tension measurements of metallic melts under microgravity

The surface tension of liquid metals and alloys was measured for the first time in microgravity using the oscillating drop technique. Data for pure gold, a congruently melting gold copper alloy, and an eutectic zirconium nickel alloy are presented. We find excellent agreement with available results obtained on Earth by the same technique, but only if the latter are corrected to account for gravity effects. This is not only shows the necessity for the correction of the surface tension data derived from Earth-bound oscillating drop experiments, but also proves its correctness.DeceasedPaper presented at the Fourth International Workshop on Subsecond Thermophysics, June 27–29, 1995, Köln, Germany.     

Surface tension of alloys with additives of alkali metals

The results of studies of surface tension of metal melts with addition of alkali metals, mainly as small additives, are discussed. It is shown that small additives of alkali metals exhibit a high surface activity. The extrema that are observed on the surface tension isotherms of a number of binary systems are built using very few experimental points; hence, their authenticity seems unreliable. The main disadvantages of the methods and the measuring cells used to define the surface tension, etc., which may violate the conditions of thermodynamic equilibrium of the surfaces under study with their saturated vapor, are discussed. In the authors’ opinion, a number of experimental and theoretical problems remain unsolved in the field of the temperature and concentration dependences of the surface tension of alloys with small additions of alkali metals.     

Surface tension of liquid4He. Surface energy of the Bose-Einstein condensate

The surface tension of liquid⁴He was measured by means of surface-wave resonance, and the relative variation showed excellent agreement with that previously obtained by a precise capillary-rise method. The absolute value of the surface tension at absolute zero was measured as 354.4±0.5 mdyne/cm, 6% smaller than the previous value. The surface energy associated with the Bose-Einstein condensate wave function was found to dominate the surface tension in the superfluid phase. The condensate fraction other than in the vicinity of the point was estimated asn ₀(0)-n ₀(T)=A(T/T ), withn ₀(0)=0.125±0.025,A=0.177±0.047, and =5.07±0.17.     

Surface tension of liquid3He at low temperature

The thermal contribution to the surface tension of liquid³He due to the single quasiparticle motion is estimated in the low-T regime using a local approximation for the entropy. The density and temperature dependence of the effective mass is shown to play a crucial role in determining the behavior of (T). The theoretical predictions explain the anomalous behavior of (T) recently observed at low temperature by Suzuki et al.³ Predictions for the temperature dependence of the interfacial tension of liquid³He-⁴He mixtures are also given.     

Ground-based thermophysical property measurements of supercooled and liquid platinum-group metals by electrostatic levitation

In this study, thermophysical properties of several metals of the platinum group (Pd, Rh, Ru, Ir) were found using the unique capabilities (sample stability, imaging) of a vacuum electrostatic levitation furnace developed by the Japan Aerospace Exploration Agency. Over temperature ranges covering the liquid and the supercooled phases, the density was measured and the isobaric heat capacity was estimated. The enthalpy and the entropy of fusion were also calculated.     

Surface tension of liquid3He down to 0.3 K

The surface tension of liquid³He was measured by determining the surface wave velocity in the temperature range from 0.32 to 3.02 K. The decrease of the surface tension from the value at 0 K can be described as 22.3T ² mdyn/cm up to about 0.9 K and is quite different from that of⁴He. The extrapolated value to 0 K is 155.7±0.5 mdyn/cm. The data below 1.6 K were compared with Saam's model, where the surface tension is assumed to be given by the bulk free energy times the surface width and the quasi-two-dimensional free energy. Agreement between the data and the results calculated from the model is much improved if ripplons are taken into account. Data near the gas-liquid critical point, contrary to earlier results, show that the surface tension vanishes with a critical exponent of 1.24±0.05. This is in agreement with Widom's theory.