Effect of metal purity and testing procedure on surface tension measurements of liquid tin

The surface tension of liquid tin of three different grades of purity (99.85, 99.96, and 99.999%) was measured by the classical sessile drop method over the temperature range 523–1023 K, in heating and cooling regimes. The results obtained show that the metal purity affects the values of surface tension and its temperature dependence. The highest values of surface tension and smooth linear temperature dependence were obtained in cooling regime for tin of the highest purity. With increasing content of impurities, both surface tension and its temperature coefficient decrease while the scatter of the data increases. The surface tension values measured on heating regime show higher scatter, compared to those obtained in cooling regime, and the temperature dependence of the surface tension is curvilinear rather than linear.     

Measurement of surface tension and specific heat of Ni-18.8 at.% Si alloy melt by containerless processing

The surface tension and specific heat of superheated and undercooled Ni-18.8 at.% Si alloy melt have been measured by the oscillating drop method and the drop calorimetry technique in combination with electromagnetic levitation, respectively. The surface tension follows a linear relationship with temperature within the range of 1370–2100 K. The surface tension at the melting temperature and the temperature coefficient are determined to be 1.796 N/m and −3.858 × 10⁻⁴ N/m/K, respectively. The specific heat is determined to be 40.80 ± 1.435 J/mol/K over the temperature range 1296–2000 K. The maximum undercooling of 178 K is achieved in the experiments. Based on the measured data of surface tension and specific heat, the viscosity, solute diffusion coefficient, density and thermal diffusivity of liquid Ni-18.8 at.% Si alloy are calculated.     

Thermophysical Properties of Ag and Ag–Cu Liquid Alloys at 1098K to 1573K

The surface tension and density of liquid Ag and Ag–Cu alloys were measured with the sessile drop method. The sessile drop tests were carried out at temperatures from 1098K to 1573 K, on cooling (temperature decreasing stepwise) under a protective atmosphere of high purity Ar (6N). The density of liquid Ag and Ag–Cu alloys decreases linearly with increasing temperature, and an increase in concentration of copper results in a lower density. The surface tension dependence on temperature can be described by linear equations, and the surface tension increases with increasing Cu content. The results of the measurements show good agreement with existing literature data and with thermodynamic calculations made using the Butler equation.     

Surface tension of mercury on glass,molybdenum and tungsten substrates

The surface tension of mercury on a glass substrate has been determined by the sessile drop technique. It was found that the uncorrected value of surface tension varied with changes in the drop diameter in the range from 0.60 to 4.10 cm. From the Worthington equation for curvature a corrected surface tension of 456 dyn/cm was obtained for the 4.1 cm diameter drop, a value which is in reasonable agreement with previous investigations. However, application of a curve fitting procedure to the results from the smaller drops gave a corrected surface tension which was approximately independent of diameter but at a smaller average value of 413 dyn/cm. The surface tension of a 1.20 cm diameter drop was also measured on tungsten and molybdenum substrates and, in general, corrected values larger than on glass were derived. It is suggested that the small corrected values obtained for drops ⩽2.06 cm in diameter are due to adsorption of impurity from the glass substrate.     

Surface tension of liquid Cu and anisotropy of its wetting of sapphire

Precise surface tension data of liquid Cu are fundamental for studying its interaction with differently oriented single crystalline sapphire surfaces. For this reason, the surface tension of liquid Cu was measured covering a wide temperature interval of 1058 °C ≤ T ≤ 1413 °C. To avoid contamination of the sample from contact with container walls, the measurement was performed contactlessly in an electromagnetic levitation furnace using the oscillating drop method. A fast digital CMOS-camera (400 fps) recorded top view images of the oscillating sample. From an analysis of the frequency spectrum the surface tension was determined. The measured surface tension of Cu was used to calculate interfacial energies from contact angles of liquid Cu droplets, deposited on the C(0001), A(11-20), R(1-102) and M(10-10) surfaces of sapphire substrates. These were measured by means of the sessile drop method at 1100 °C using a drop dispenser. Within the first minutes of contact with the sapphire substrates, the contact angles of liquid Cu droplets rise to their equilibrium values. From these, in addition to interfacial energies also works of adhesion were determined.     

Drop Calorimetry Studies on 9Cr–1W–0.23V–0.06Ta–0.09C Reduced Activation Steel

The temperature dependence of enthalpy increment (H _T − H ₂₉₈) of 9 mass% Cr–1 mass% W–0.23 mass% V–0.06 mass% Ta–0.09 mass% C reduced activation steel has been measured by inverse drop calorimetry in the temperature range 400 K to 1273 K. A critical comparison of present isothermal enthalpy measurements with the results of our previous dynamic calorimetry studies has been made to reveal clearly the occurrence of various diffusional phase transformations that occur at high temperature. These phase changes are marked by the presence of distinct inflections or cusps in an overall nonlinear variation of enthalpy values with temperature. The principal thermal relaxation step of the martensitic microstructure obtained through quenching from the high-temperature γ-austenite phase is observed around 793 K. The ferromagnetic-to-paramagnetic transition of the α-ferrite phase is found to occur at 1015 K. The equilibrium values of γ-austenite start (Ae ₁) and finish (Ae ₃) temperatures are found to be 1063 K and 1148 K, respectively. A value of 12 J · g⁻¹ has been estimated for Δ°H ^α→γ the latent heat associated with the α → γ transformation. The measured enthalpy increment variation of the α-ferrite phase with temperature has been fitted to a suitable empirical function to estimate the temperature-dependent values of the specific heat. A comparison of the drop calorimetry-based indirect estimate of the specific heat with the direct differential scanning calorimetry-based values revealed that the drop calorimetry estimates are systematically lower than its dynamic calorimetry counterpart. This difference is attributed to the fact that, under finite heating rate conditions that are typical of dynamic calorimetry, measurements are made under nonequilibrium conditions. Notwithstanding this limitation, there is a good overall agreement between the two C _p values and also among the phase transformation temperatures so that a reliable assessment of thermal properties and phase transformation characteristics of reduced activation steel can be determined by a combined analysis of the results of drop and differential scanning calorimetry.     

Direct measurement of drainage curves in infiltration of SiC particle preforms

Drainage curves (plots of the non-wetting fluid saturation versus applied pressure) for infiltration of SiC particle preforms with Al and Al–12.2 at.% Si are measured at 1023 K (750 °C) with a pressure infiltration apparatus adapted for direct tracking of the metal ingress into the porous preform. From these curves the work of immersion is estimated by integration over the whole range of saturation and pressures from 0.1 MPa to 10 MPa, which in turn is used to deduce the metal contact angle on the ceramic. Drainage curves obtained for powder beds based on monomodal SiC particles of mean diameter from 6.5 μm to 40 μm yield values for the work of immersion and contact angles that are consistent among themselves and are in good agreement with data in the literature determined by the sessile drop method.     

Effects of pH and sintering temperature on the synthesis and electrical properties of the bilayered LaSr2Mn2O7 manganite prepared by the sol–gel process

The bilayered LaSr₂Mn₂O₇ manganite was synthesized by the sol–gel process at different pH values (3.5, 7, and 9.5) and different sintering temperatures (1553, 1623, and 1723 K) to investigate the effects of growth conditions upon the structural and electrical properties of the samples under investigation. X-Ray diffraction and FT-IR spectroscopy techniques confirm the phase formation for all samples. However, samples sintered at 1553, 1623, and 1723 K, and formed at pH = 7 are single phased having a tetragonal structure. Study of these single-phased samples indicates that with increase in the sintering temperature from 1553 to 1723 K, the average grain size increases from ~200 to ~1000 nm. To investigate the influence of grain size on the conduction mechanism, resistivity of the samples was measured as a function of temperature. The data obtained was analyzed by the adiabatic small polaron hopping model. These analyses show the influence of grain size on the parameters obtained by fitting the data by the above models.     

Determination of surface tension coefficient of liquid metals and alloys using the phenomenon of capillary wave formation

A possibility of determining the surface tension coefficient of 6H13 liquid steel and of technically pure iron (ArmcoFe) has been presented. In the investigation the phenomenon of ring structure formation (capillary waves) on the surface of a molten metal affected by light pulses of a glass neodymium laser (λ = 1,06 μm, τ_i ≈ 1 ms, E_i ≈ 6J) has been considered. The values obtained for the surface tension coefficient are in good agreement with those determined by other methods (for liquid metals in the temperature range 2000K – 5000K).     

Sidewall roughness characterization and comparison between silicon and SU-8 microcomponents

Surface characterization of microcomponents provides key information to help understand and predict the performance of microdevices. For example, in a microgear transmission, the surface roughness has a strong effect on the friction, running life and power consumption. In a static fluid microdevice, the liquid distribution is influenced by the surface tension and capillary force, which are primarily determined by the surface roughness. In a flowing microchannel case, surface roughness results in unsteady secondary flows. In this paper, a study is presented to characterize the surface roughness of silicon and SU-8 microcomponents. The silicon components studied are fabricated using an ICP plasma etching system manufactured by Surface Technology Systems. The sidewall roughness of the component is measured using atomic force microscopy. Repeated measurements have been conducted at different sidewall depths of the microstructure. The AFM images of the measurements are present. The measurement results show that the sidewall is smoother at the lower level than that at the upper level in a Si microstructure, and the average roughness R_a obtained throughout the depth is 151.11 nm. The UltraThick SU-8 Process (UTSP) provides another way to fabricate microstructures as thick as 1 mm with a very vertical sidewall. The roughness contour of the sidewall shows that the surface topography is similar throughout the depth. The average roughness R_a is 46.46 nm. Other surface parameters, such as R_q, R_p − p, R_pk and R_sk, are also obtained and analysed. The implication of the smooth surface roughness of SU-8 structures to their applications is discussed in terms of transmission efficiency, the changes in friction to flowing liquid in a microchannel and the changes in the surface tension and capillary effect.     

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.     

Analysis of multi-pass evaporators using orthogonal collocation

A thermal analysis of the evaporator of a water chiller system having a single shell and eight tube passes has been performed using the technique of orthogonal collocation. Refrigerant R-22 flows inside the tubes, and water flows in the shell. It is demonstrated here that the proposed approach is suitable for estimating the steady rate of heat exchanged and the overall pressure drop in the tubes, and presents itself as a suitable alternative to conventional numerical integration techniques. The predictions are made using well-known and contemporary two-phase heat transfer and pressure drop correlations. The use of a few collocation points is sufficient to predict results that are in good agreement with the results obtained with conventional integration. For the evaporator, the rated cooling effect is 140.67 kW and the rated overall pressure drop is 13.789 kPa. In comparison, the orthogonal collocation approach predicts values of 142.01 kW and 16.591 kPa, respectively.     

Thermophysical Properties of the Refrigerant Mixtures R417A and R417B from Dynamic Light Scattering (DLS)

Dynamic light scattering (DLS) has been used for the measurement of several thermophysical properties of the refrigerant mixtures R417A (50 % by mass 1,1,1,2-tetrafluoroethane—R134a, 46.6 % pentafluoroethane—R125, 3.4 % n-butane—R600) and R417B (79 % by mass R125, 18.25 % R134a, 2.75 % R600). Both refrigerant mixtures are designed for a replacement of R22 (chlorodifluoromethane) in existing refrigeration systems. Thermal diffusivity and sound speed have been obtained by light scattering from the bulk fluid for the liquid phase under saturation conditions over a temperature range from about 283 K up to the liquid–vapor critical point with estimated uncertainties between 1 % and 3 % and between 0.5 % and 2 %, respectively. By applying the method of DLS to a liquid–vapor interface, also called surface light scattering, the saturated liquid kinematic viscosity and surface tension have been determined simultaneously. These properties have been measured from 253.15 K up to the liquid–vapor critical point with estimated uncertainties between 1 % and 3 % for kinematic viscosity and between 1 % and 2 % for surface tension. The measured thermal diffusivity, sound speed, kinematic viscosity, and surface tension are represented by interpolating expressions with differences between the experimental and calculated values that are comparable with but always smaller than the uncertainties. The results are discussed in detail in comparison with literature data and with various prediction methods.     

Comparative properties of ternary oxides of ZrO2-TiO2-Y2O3 obtained by laser ablation, magnetron sputtering and sol-gel techniques

Thin films of ternary oxides of zirconium (Zr), yttrium (Y) and titanium (Ti) were obtained by the sol-gel, magnetron sputtering and laser ablation techniques. Zirconium propoxide, titanium isopropoxide and yttrium nitrate hexahydrate reagents were used as precursors in the sol-gel process. The Zr/Ti and Zr/Y molar ratios have been controlled by varying the precursors and surfactant concentration. The obtained gels were supported by dip coating on α-alumina supports, dried at 373 K and calcinated at 873 K. The powders obtained after the removal of carbon residuals were subsequently pressed and calcinated for using as targets for the magnetron sputtering and pulsed laser deposition techniques. The chemical composition was determined by Auger Electron Spectroscopy. The surface topography was investigated by Atomic Force Microscopy, while the crystallinity was evaluated from X-ray diffraction. The electrical response of the deposits to nitrogen oxides (NO_x) toxic gas is discussed according to the experimental conditions.     

Spreading of liquid lead droplets on metallic iron covered by silicon oxide particles or films

As well known, the spreading of a liquid metal droplet on a solid metal is very sensitive to the presence of chemical heterogeneities on the solid metal. In this study, wetting experiments with liquid lead on heterogeneous surfaces composed of iron and silicon oxide particles or films were performed using the dispensed drop technique. High purity iron and binary iron–silicon substrates with different silicon contents were studied. Before the wetting experiments, the substrates are annealed at 850 °C in a N₂–H₂ atmosphere in order to reduce iron oxides and to form silicon oxide particles or films on the surface. The liquid lead droplet is then released onto the metallic substrate partly or wholly covered by the oxides. The spreading of the liquid metal droplet strongly depends on the surface area fraction covered by the oxides.     

Determination of the surface tension of liquid stainless steel

The surface tensions (σ) and temperature dependencies (dσ/dT) of several commercial 4-series ferritic stainless steels have been measured using the sessile drop technique on an Al₂O₃ plate over the temperature range 1789 to 1883 K in an atmosphere of high purity (P _{O 2} < 10^?19 MPa) argon gas. Precise densities of liquid stainless steels have also been obtained using the modified sessile drop method in order to calculate accurate values of the surface tension. The surface tensions of liquid stainless steels decreased markedly with increasing sulphur concentration in the steels. The variation of surface tensions of liquid stainless steels can be described by the following equation σ = 1790 ? 182 ln (1 + 260a _S) (mN/m) when only S is considered or σ = 1820 ? 304 ln (1 + 383a _O) ? 182ln (1 + 260a _S) (mN/m) when both S and O are considered. The equations apply to the following compositional ranges: mass%O = 0.0022–0.0064, mass%S = 0.0008–0.05. The temperature coefficient of the surface tension (dσ/dT) of liquid stainless steel was found to change from negative to positive at a sulphur concentration of about 30 mass ppm in the steel. Nitrogen was found to have little effect on the surface tension of liquid stainless steel.     

Liquid oxygen liquid acquisition device bubble point tests with high pressure lox at elevated temperatures

When transferring propellant in space, it is most efficient to transfer single phase liquid from a propellant tank to an engine. In earth’s gravity field or under acceleration, propellant transfer is fairly simple. However, in low gravity, withdrawing single-phase fluid becomes a challenge. A variety of propellant management devices (PMDs) are used to ensure single-phase flow. One type of PMD, a liquid acquisition device (LAD) takes advantage of capillary flow and surface tension to acquire liquid. The present work reports on testing with liquid oxygen (LOX) at elevated pressures (and thus temperatures) (maximum pressure 1724 kPa and maximum temperature 122 K) as part of NASA’s continuing cryogenic LAD development program. These tests evaluate LAD performance for LOX stored in higher pressure vessels that may be used in propellant systems using pressure fed engines. Test data shows a significant drop in LAD bubble point values at higher liquid temperatures, consistent with lower liquid surface tension at those temperatures. Test data also indicates that there are no first order effects of helium solubility in LOX on LAD bubble point prediction. Test results here extend the range of data for LOX fluid conditions, and provide insight into factors affecting predicting LAD bubble point pressures.     

Surface tension of low GWP refrigerants R1243zf,R1234ze(Z), and R1233zd(E)

The surface tension of R1243zf, R1234ze(Z), and R1233zd(E) were measured at temperatures from 270 K to 360 K by an experimental apparatus based on the differential capillary rise method. The deviation between the measured surface tension of R134a and R245fa and the calculated surface tension with REFPROP 9.1 (Lemmon et al., 2013) was ±0.13 mN m⁻¹, which is less than the estimated propagated uncertainty in surface tension of ±0.2 mN m⁻¹. Eleven points, thirteen points, and ten points of surface tension data were provided for R1243zf, R1234ze(Z), and R1233zd(E), respectively, in this paper. The measured data and the estimated surface tension using the methods of Miller, 1963, Miqueu et al., 2000, and Di Nicola et al. (2011) agree within the standard deviation of ±0.43 mN m⁻¹. The empirical correlations that represent the measured data within ±0.14 mN m⁻¹ were proposed for each refrigerant.     

Synthesis and characterization of mesoporous silicon directly from pure silica sodalite single crystal

Mesoporous silicon granules with high surface area were synthesized directly from pure silica sodalite single crystals, with the starting shape retained. The sodalite single crystals were reduced by a magnesiothermal process in vacuum at 630 °C. The X-ray diffraction patterns indicate the presence of crystal silicon. Transmission electron microscopy studies reveal that the obtained silicon granules are composed of a monocrystalline surface with an island-like mesoporous internal structure. The results of N₂ adsorption and desorption analysis indicate that the surface area is around 308 m² g⁻¹ and the single point pore volume is 0.37 cm³ g⁻¹. The photoluminescence emission centered at 2.7 eV may be due to both an oxidized surface and quantum confinement effects. These results reveal that the silicon granules possess a different microstructure from those of etched silicon films. The present synthetic design correlates the microporous zeolite and mesoporous silicon together and gives a new way for enlarging the structural diversity of porous silicon crystal.     

Comparison of models for silicon etching in CF4 + O2 plasma

The plasma chemical etching (PCE) of Si in CF₄ + O₂ plasma is considered. The concentrations of plasma components are calculated using values extrapolated from experimental data. Resulting calculations of plasma components are used for the calculation of Si etching rates. The concentrations of the adsorbed layer and surface components, obtained from analysis of PCE of silicon, are used for the comparison of site-balance and adsorbed-layer models. It is found that adsorbed-layer model predicts higher concentration of SiO₂ molecules on the surface than site-balance model. The difference in SiO₂ concentration is important during ion-beam-assisted etching and reactive ion etching processes as the models predict different etching rates due to different sputtering yields of Si atoms and SiO₂ molecules.