Surface tension and contact angles of molten cadmium telluride

The surface tension and contact angle of molten cadmium telluride (CdTe) were measured as a function of temperature by the sessile drop technique. A FORTRAN code was developed to calculate the surface tension of sessile drops, with the contact angle ranging from O to 180°. The wetting of cadmium telluride melt was studied on different surfaces. The surface tension of cadmium telluride was about 160 ±5 dynes · cm^–1[1.6 m^–1] at the melting point of 1093°C. The contact angle of CdTe melt was about 65° on a quartz optical flat, 75° on commercial fused quartz, and 125° on boron nitride coated quartz.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Wear behavior of carbide coated Co–Cr–Mo implant alloy

The wear behavior of a new type of metal carbide surface coating on Co–Cr–Mo implant alloy was studied. The coating was created using a microwave plasma-assisted reaction. Codeposition of impurity diamond film, diamond particles, and soot was prevented by controlling process conditions. Wear tests were carried out using a sapphire ball-on-Co–Cr–Mo disc unidirectional sliding configuration with harsh conditions of high contact stress and slow sliding speed in both no-lubrication, and deionized water lubrication environments. In the case of uncoated Co–Cr–Mo discs, the effect of deionized water lubrication was remarkable and reduced the wear factor by one order of magnitude compared to the no-lubrication tests. The wear factor of carbide coated Co–Cr–Mo discs was slightly smaller than that of uncoated Co–Cr–Mo discs with deionized water lubrication (2.7×10^–6 mm³N^–1m^–1 vs. 4.2×10^–6mm³N^–;1m^–1). The addition of deionized water lubrication did not greatly affect the wear factor of carbide coated Co–Cr–Mo discs. The influence of surface geometry resulting from the brain coral-like surface morphology of carbide layers on wear behavior was analyzed considering stress concentrations and effective contact area.     

Measurement of the Surface Tension of Undercooled Liquid Ti90Al6V4 by the Oscillating Drop Technique

The surface tension of liquid Ti₉₀Al₆V₄ was measured. The samples have been processed containerlessly by electromagnetic levitation, which allows the handling of highly reactive materials and measurements in the undercooled temperature region. The use of digital image processing allows the identification of oscillation modes and calculation of the surface tension from the l = 2 and m = 0, m = 2 oscillation modes. A linear least squares fit to the data showed the following temperature dependence: = 1.389 ± 0.09 – 9.017 × 10^–4 ± 5.64 × 10^–5(T – 1660°C) [Nm^–1]     

The stability of sapphire whiskers in nickel at elevated temperatures

Composites of 1 to 20 vol % sapphire whiskers contained in a nickel matrix were produced by roll-bonding and by hot-pressing. The composites were examined using transmission electron microscopy, X-ray and electron diffraction, optical microscopy and mass spectrographic analysis. Composites were annealed in vacuum (1.3×10^–3 N m^–2), in low-pressure air (13.3 N m^–2) and in dried hydrogen (101.3 N m^–2) in the temperature range 1100 to 1400° C for times up to 3800 h. Whiskers in situ and the whisker/matrix interface were observed by transmission electron microscopy; matrix dislocations were associated with whiskers and were stable after annealing at 1400° C. Whiskers extracted from annealed composites showed significant morphological changes. These were attributed to: (i) ovulation from the tips of whiskers by interfacial diffusion, (ii) waisting from surface undulations, (iii) Ostwald ripening and (iv) constant-volume shape changes.     

The surface tension of liquid pure aluminium and aluminium-magnesium alloy

This paper discusses the results of several experiments designed to further illustrate the recent findings of the present authors according to which, if a virtually leak-fee maximum bubble pressure system is used to measure the surface tension of liquid aluminium, a surface tension around 1100 mJ m^–2 is first obtained, decreasing to the oxidized value (around 865 mJ m^–2) as the experiment proceeds and oxygen enters the system mainly through the capillary walls. The peculiarities and difficulties inherent to the maximum bubble pressure method are illustrated. For instance, a study of the time needed for the surface tension to decrease to the oxidized value as a function of temperature reveals the important role played by the vapour pressure in the process. This is further illustrated by considering Al-Mg alloys, as magnesium has a different heat of vaporization and a much larger vapour pressure than aluminium at the measuring temperatures. Results for the changes in density and surface tension for the oxidized and unoxidized cases induced by magnesium (up to 8 wt%) are also presented and compared to previous data.     

A microscopic study of preferred orientation and adhesion of solid copper particles on (0001) sapphire substrates

The microscopic phenomena of solid copper particles equilibrating on (0001) sapphire surfaces have been investigated by scanning electron microscopy. Very sharp and clear silhouettes of the particles are developed. At temperatures between 900 and 1080° C, with the oxygen partial pressure lower than 10^–17 atm, the copper particles tend toward their equilibrium shape as the {111} and {110} preferred faces develop eventually into truncated octahedra or tetrakaidecahedra. Recrystallization of the particles originating at the particle-substrate interface by a heteroepitaxial mechanism is discussed. The {111} plane of the copper particles does not grow parallel to the (0001) sapphire surface as previously reported, but rather with about 20° of tilt, suggesting epitaxial growth of the Cu {112} plane on the (0001) sapphire surface. The surface energy of solid copper decreases with the increase of temperature and/or oxygen partial pressure while the work of adhesion between solid copper and (0001) sapphire can be enhanced by increasing the temperature and/or decreasing the oxygen partial pressure.     

Surface Tension Measurements on CMSX-4 Superalloy by the Drop-Weight and Oscillating-Drop Methods

The surface tension of the CMSX-4^®reg; superalloy has been determined by the drop-weight and oscillating-drop methods which are well adapted to reactive materials. The recommended values are 1.59 J·m^–2 for the surface tension at the liquidus temperature and –0.14× 10^–3 J·m^–2· K^–1 for the temperature coefficient. A conclusion of the present work is that the interpretation of surface tension measurements performed on a complex alloy generally requires additional work to be performed on simpler associated binary or ternary systems, as well as some support from solidification experiments.     

Non-Contact Measurements of Surface Tension and Viscosity of Niobium, Zirconium, and Titanium Using an Electrostatic Levitation Furnace

The surface tension and viscosity of liquid niobium, zirconium, and titanium have been determined by the oscillation drop technique using a vacuum electrostatic levitation furnace. These properties are reported over wide temperature ranges, covering both superheated and undercooled liquid. For niobium, the surface tension can be expressed as (T)=1.937×10³–0.199(T–T _m) (mN·m^–1) with T _m=2742 K and the viscosity as (T)=4.50–5.62×10^–3(T–T _m) (mPa·s), over the 2320 to 2915 K temperature range. Similarly, over the 1800 to 2400 K temperature range, the surface tension of zirconium is represented as (T)=1.500×10³–0.111(T–T _m) (mN·m^–1) and the viscosity as (T)=4.74–4.97 ×10^–3(T–T _m) (mPa·s) where T _m=2128 K. For titanium (T _m=1943 K), these properties can be expressed, respectively, as (T)=1.557×10³–0.156(T–T _m) (mN·m^–1) and (T)=4.42–6.67×10^–3(T–T _m) (mPa·s) over the temperature range of 1750 to 2050 K.     

Erbium Segregation in Silicon Layers Grown by Molecular-Beam Epitaxy

In the course of molecular-beam epitaxy of Er-doped Si on Si(100) substrates at 450–650°C, the dopant tends to segregate in the surface layer at doping levels from 10¹⁷ to above 10¹⁹ cm^–3. The introduction of oxygen into the growing epilayer—either from the gas phase at an oxygen pressure of 6.7 × 10^–6 Pa or from an SiO₂ layer on the substrate surface—suppresses the surface segregation of Er.     

Thermophysical Property Measurements of Liquid and Supercooled Iridium by Containerless Methods

Thermophysical properties of equilibrium and supercooled liquid iridium were measured using noncontact diagnostic techniques in an electrostatic levitator. Over the 2300–3000 K temperature range, the density can be expressed as ρ (T)=19.5×10³ − 0.85(T− T_m) (kg·m⁻³) with T_m=2719 K. The volume expansion coefficient is given by 4.4 × 10⁻⁵ K⁻¹. In addition, the surface tension can be expressed as γ (T)=2.23 × 10³ − 0.17(T−T_m)(10⁻³N·m⁻¹) over the 2373–2833 K span and the viscosity as η(T)=1.85 exp [3.0× 10⁴/(RT)](10⁻³Pa·s) over the same temperature range.     

Containerless Property Measurements of Liquid Palladium

Some thermophysical properties of liquid and supercooled palladium were measured using containerless techniques. Over the 1640–1875 K temperature interval, the density could be expressed as (T)=10.66× 10³ –0.77(T–T_m)(kg·m^–3) and the ratio between the isobaric heat capacity and the hemispherical total emissivity could be rendered as (J·mol^–1·K^–1), where T_m=1828 K. The volume expansion coefficient was also determined as 7.2 × 10^–5 K^–1.     

Heat transfer in liquid oxygen boiling in a large volume

The heat transfer in liquid oxygen boiling in the temperature range -194 to -153°C at pressures of (0.025–1.08) · 10⁶ N/m² was experimentally investigated. The empirical dependence of the heat-transfer coefficient on thermal flux density and pressure is derived.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 21, No. 2, pp. 276–282, August, 1971.     

Bonding mechanism between alumina and niobium

Diffusion couples of Al₂O₃ single-crystal, sapphire, and Nb polycrystal were heat-treated in the temperature range 1873 to 2073 K under pressure in the range 3 to 15.2 MN m^–2 for various times up to 3.6×10³ sec. Tensile testing at various temperatures up to 1873 K in a vacuum of about 10^–3 Pa, Knoop hardness testing at room temperature, optical microscopy, scanning electron microscopy, transmission electron microscopy, and electron-probe X-ray microanalysis studies were carried out on the specimens. From the results, it was concluded that the fairly high bond strength of a Al₂O₃-Nb interface might be attributed to the formation of a thin NbO _x layer, which had grown epitaxially on the Al₂O₃ surface. Lattice matching between Al₂O₃ and NbO _x phases was also considered.     

Dynamic measurement of the surface tension of liquid helium with a two-dimensional electron probe

Electrons deposited above the free surface of liquid helium exhibit coupled electron-ripplon modes whose frequencies are simply related to the surface tension of helium. The hydrodynamic expression for the ripplon dispersion relation for pure⁴He is shown to be valid up to the wavevector range 10⁵ cm^–1<q<2×10⁶ cm^–1 of the coupled modes. For a small amount of³He (X ₃10^–6–10^–8) added to pure⁴He, we measure the variation of the surface tension in the 60–600 mK temperature range. These experiments, which cover the frequency range v10–300 MHz, agree fairly well with previous static (capillary) or low-frequency (surface sound velocity) experiments.     

Non-contact measurements of thermophysical properties of niobium at high temperature

Four thermophysical properties of both solid and liquid niobium have been measured using the vacuum version of the electrostatic levitation furnace developed by the National Space Development Agency of Japan. These properties are the density, the thermal expansion coefficient, the constant pressure heat capacity, and the hemispherical total emissivity. For the first time, we report these thermophysical quantities of niobium in its solid as well as in liquid state over a wide temperature range, including the undercooled state. Over the 2340 K to 2900 K temperature span, the density of the liquid can be expressed as _L (T) = 7.95 × 10³ – 0.23 (T – T _m)(kg · m^–3) with T _m = 2742 K, yielding a volume expansion coefficient _L(T) = 2.89 × 10^–5 (K^–1). Similarly, over the 1500 K to 2740 K temperature range, the density of the solid can be expressed as _s(T) = 8.26 × 10³ – 0.14(T – T _m)(kg · m^–3), giving a volume expansion coefficient _s(T) = 1.69 × 10^–5 (K^–1). The constant pressure heat capacity of the liquid phase could be estimated as C _PL(T) = 40.6 + 1.45 × 10^–3 (T – T _m) (J · mol^–1 · K^–1) if the hemispherical total emissivity of the liquid phase remains constant at 0.25 over the temperature range. Over the 1500 K to 2740 K temperature span, the hemispherical total emissivity of the solid phase could be rendered as _TS(T) = 0.23 + 5.81 × 10^–5 (T – T _m). The enthalpy of fusion has also been calculated as 29.1 kJ · mol^–1.     

XPS study of oxygen plasma activated PET

A study on oxygen plasma functionalization of polyethyleneterephthalate (PET) is presented. Samples were exposed to a weakly ionized, highly dissociated RF oxygen plasma with an electron temperature of 5 eV, a density of positive ions of 8×10¹⁵ m⁻³ and a density of neutral oxygen atoms of 4×10²¹ m⁻³. The oxygen pressure was 75 Pa and the discharge power was 200 W. The wettability of plasma-modified samples was determined by measuring the contact angle of a water drop, while the appearance of the functional groups on the sample surface was determined by using a high-resolution X-ray photoelectron spectrometer (XPS). Already in the order of seconds of the plasma treatment the samples were covered by the surface functional groups. These results were explained by the high flux of oxygen atoms onto the sample surface. The stability of functional groups on the plasma-modified PET surface stored in a dry plastic box was monitored by using XPS as a function of the ageing time. After 1 day of ageing, the concentration of newly formed functional groups decreased by about 15%.     

Diffusion of zinc in commercial Al-Zn alloys under high pressure

The effective interdiffusion coefficients of zinc in commercial Al-Zn alloys are obtained within the temperature range 773 to 883 K under pressures from 0 to 0.41 GPa. From the temperature dependence of the effective interdiffusion coefficients, the activation energies for the 701, 703 and 705 alloys are evaluated to be 125, 124 and 127 kJ/mol respectively, and their pre-exponential factors are 3.0 × 10^–5, 4.0 × 10^–5, and 3.9 × 10^–5 m²/s respectively. The activation volumes, V, for diffusion of zinc in the commercial Al-Zn alloy are 8.30 × 10^–6, and 8.60× 10^–6 m³/mol at 823 and 883 K, respectively. The ratios of the activation volume to the molar volume of aluminum, V/V₀, are 0.83 at 823 K and 0.86 at 883 K. This means that the diffusion of zinc in the commercial Al-Zn alloys occurs predominantly by the monovacancy mechanism at 823 and 883 K.     

Surface free energy of nickel and stainless steel at temperatures above the melting point

The surface tension (liquid-state surface free energy) of pure nickel and type 304 stainless steel was measured in a narrow temperature range above the melting point by the sessile drop method. The temperature coefficients of surface free energy in the liquid state were found to be –1.76 erg cm^–2 C^–1 for nickel and –2.48 erg cm^–2 C^–1 for stainless steel. These values are shown to be a factor of 2 larger than those previously determined for the solid surface free energies of nickel and stainless steel, but have the same sign. The latent heats of fusion of nickel and 304 stainless steel were determined by comparison of variations of solid and liquid-state surface energies with temperature and found to be 292 and 284 erg cm^–2 respectively. Measurement of the contact angle for a nickel sessile drop on thoria and a stainless steel sessile drop on alumina showed a decrease in the angle with an increase in temperature.     

Fatigue endurance of aged glass fibre reinforced cement

The resistance to flexural fatigue of glass fibre reinforced cement (GRC) stored in water for six years, has been studied. Peak stresses of between 6.0 and 18.2 MN m^–2 were used. At stresses of 10.0 and 18.2 MN m^–2 the median times before failure were 1.95×10⁵ and 2.0×10³ cycles, respectively. At a stress of 8.1 MN m^–2, six out of sixteen samples tested survived 4.65×10⁶ cycles. At a stress of 6 MN m^–2, all of the samples survived 1.75×10⁶ cycles. An unreinforced mortar specimen was also studied and its fatigue endurance showed greater scatter than the GRC samples.     

Effects of annealing atmosphere on thermoelectric signals from ZnO films

Zinc oxide epilayer films were grown on vicinal cut sapphire substrates by pulsed laser deposition with in situ annealing oxygen pressures varied from 0 to 10 × 10³ Pa. The best crystalline quality was obtained for ZnO layer with annealing oxygen pressure of 6 × 10³ Pa. Laser induced thermoelectric voltage (LITV) were observed along the tilting angle orientation of the substrate when the pulsed KrF excimer laser of 248 nm were irradiated on the films. The largest LITV signal was measured for the film grown at 6 × 10³ Pa annealing oxygen pressure. According to the measured LITV signals, Seebeck anisotropy was evaluated and was found to range from 3 to 12 μV/K for ZnO films annealed at different oxygen pressures from 2 to 10 × 10³ Pa. It is suggested that oxygen ambient plays an important role in the electronic properties of the ZnO films.