Showing papers on "Sessile drop technique published in 2002"

Wetting and bonding strength in Al/Al2O3 system

Abstract: Experimental results are presented on the investigation of the correlation between wetting and bonding properties in Al/Al 2 O 3 couples. Applying the sessile drop method the wettability of alumina substrates by molten Al was investigated at temperatures from 953–1373 K under a dynamic vacuum of 0.2 mPa. A special procedure to study shear strength of metal–ceramic joints using the sessile drop samples has been elaborated. The results clearly indicate that the shear strength of Al/Al 2 O 3 joints strongly depends on wetting properties in Al/Al 2 O 3 system, i.e. the lower the contact angle Θ , the higher the value of interfacial shear strength.

Surface Tension and Its Temperature Coefficient of Molten Tin Determined with the Sessile Drop Method at Different Oxygen Partial Pressures

Abstract: The surface tension of molten tin has been determined by the sessile drop method at The surface tension of molten tin has been determined by the sessile drop method at temperatures ranging from 523 to 1033 K and in the oxygen partial pressure (P-O2) range from 2.85 x 10(-19) to 8.56 x 10(-6) MPa, and its dependence on temperature and oxygen partial pressure has been analyzed. At P-O2 = 2.85 x 10(-19) and 1.06 x 10(-15) MPa, the surface tension decreases linearly with the increase of temperature and its temperature coefficients are -0.151 and -0.094 mNm(-1) K-1, respectively. However, at high P-O2 (3.17 x 10(-10), 8.56 x 10(-6) MPa), the surface tension increases with the temperature near the melting point (505 K) and decreases above 723 K. The surface tension decrease with increasing P-O2 is much larger near the melting point than at temperatures above 823 K. The contact angle between the molten tin and the alumina substrate is 158-173degrees, and the wettability is poor.

Influence of drop volume on surface tension evaluated using the pendant drop method

Abstract: The pendant drop technique is one of the most accurate methods to measure surface tension of liquids Recently, it has been found that the value of the surface/interfacial tension found using the pendant drop method might be drop-volume dependent In this work, the surface tension of glycerol at a 25 °C and the surface tension of polypropylene at 240 °C were measured using the pendant drop method for different drop volumes It was shown that the values of the surface tension depend on the drop size if no calibration to take into account the anisotropy in the optical enlargement is performed However, when a calibration procedure for optical anisotropy correction is performed, the values of the surface tension obtained do not depend on the volume drop size and they corroborate the values in the literature

Surface tension, wettability and reactivity of molten titanium in Ti/yttria-stabilized zirconia system

Abstract: The wettability and the interaction between pure liquid titanium and yttria-stabilized zirconia were investigated by the sessile drop method in argon atmosphere at 1973 K. The micrographic observations made on cross sections perpendicular to the interface using EPMA show that interfacial reactions occurred at high temperature. However, the contact angles are relative stable and larger than 90° within experimental duration. The density and surface tension of molten titanium found equal to 4.12±0.01 g cm−3 and 1.46±0.05 N m−1, respectively. The contact angle increases with increasing the substrate porosity. The influence of porosity on the wettability can be explained by analogy with the influence of surface roughness.

Preparation of Plastic and Biopolymer Multilayer Films by Plasma Source Ion Implantation

Abstract: The plasma source ion implantation (PSII) technique was used to improve the adhesion between linear low-density polyethylene (LLDPE) and biopolymer. LLDPE was treated with the PSII using O2 or CF4 gas to modify its surface. After modification, chitosan or corn zein was used for coating on LLDPE. Wettability of the LLDPE surface was evaluated with a contact angle meter by the sessile drop method. X-ray photoelectron spectroscopy (XPS) was used to analyze the LLDPE surface. Before and after treatment, in the case of LLDPE treated with O2 PSII, oxygen-containing functional groups were formed on the implanted surface. In the CF4 PSII treated LLDPE, it was observed that the fluorine concentration on the surface of LLDPE remarkably increased and hydrophobic groups were formed by chemical reaction. Bilayer films coated with chitosan or corn zein showed 10 times lower oxygen permeability. Tensile strength of multilayer films was decreased a little compared with that of LLDPE. The plastic and biopolymer multilayer...

Evaluation of Surface Tension and Adsorption for Liquid Fe-S Alloys

Abstract: Surface tension of liquid iron is strongly influenced by the adsorption of sulfur. In this study, surface tensions of liquid Fe-S alloys at 1823 K were measured by the sessile drop technique in a purified argon atmosphere. Experimental results were compared with the model based on Butler's equations considering the effect of size and interactions of the adsorbed elements assuming that the system was composed of Fe-"FeS" binary. The model could evaluate the surface tension and the adsorption of sulfur more reasonably rather than a simple ideal adsorption model. In the calculations, excess free energy expanded by Margules' series over the entire composition range of Fe-FeS system was used.

Wettability of TiC by commercial aluminum alloys

Abstract: The effect of alloying elements on the wettability of TiC by commercial aluminum alloys (1010, 2024, 6061 and 7075) was investigated at 900°C using a sessile drop technique. Wetting increased in the order 6061 < 7075 < 2024 < 1010 for both, static argon or vacuum atmospheres. Alloys 1010 and 2024 wet TiC under both atmospheres, leading to contact angles in the order of 60° and less, while 7075 only wets under vacuum, with the poorest wettability being exhibited by 6061. Evaporation of Zn and Mg under vacuum conditions contributed to the rupture of the oxide film covering the aluminum drop and thereby improving wetting and spreading. Continuous and isolate Al4C3 was detected in all the cases. CuAl2 precipitation at the interface slightly decreased Al4C3 formation and increased the adhesion of 2024 to TiC.

Simultaneous determination of toluene diffusion coefficient in air from thin tube evaporation and sessile drop evaporation on a solid surface

Abstract: In this work, we simultaneously determined the diffusion coefficient of toluene vapor in air by following the toluene evaporation in two different geometries: in a thin glass tube and a sessile drop on poly(tetrafluoroethylene) (Teflon) substrate in the same cell by inducing a quasi-steady liquid−vapor phase transition. A glass cell whose walls were lined with activated carbon was used in both experiments. Photography was applied to monitor the sessile drop evaporation, which occurred with constant contact angle mode (approximately 43°). When the restriction of evaporation space by the presence of the substrate surface [f(θ) factor] was considered in the sessile drop evaporation, the toluene vapor diffusion coefficient in air was found to be close in both methods. The diffusion coefficient was found to vary linearly with the temperature for both methods, and there is a 3.17 power dependence when the absolute temperatures are used. However, this figure is higher than the 1.75−2.00 power dependence, which ...

Interfacial Tension between Isotropic and Anisotropic Phases of a Suspension of Rodlike Particles

Abstract: The interfacial tension, γ, between the coexisting isotropic and chiral nematic phases of aqueous suspensions of cellulose crystallites was determined at very low ionic strengths by the sessile drop method as a function of the concentration of cellulose crystallites. Values for γ were measured in the range 10-3 to 10-4 mN/m, increasing with crystallite concentration. The measured values are in the range predicted by theories based on Onsager's second virial approximation when the equivalent hard-core dimensions of the rods are estimated from the phase separation data. However, the values for γ strongly depend on the concentration of particles, in contrast to theoretical predictions. The polydispersity in particle dimensions may contribute to this discrepancy.

The production of Al-Mg alloy/SiC metal matrix composites by pressureless infiltration

Abstract: Metal matrix composites have been produced by pressureless infiltration of Al-Mg alloys into SiC preforms at 900°C under N2 for different infiltration times. The wettability of the ceramic reinforcement by the Al-Mg alloy is crucial in determining whether an MMC can be produced by pressureless infiltration. Sessile drop results show that Al alloys with Mg contents greater than 8 wt% had a contact angle lower than 90°C after 5 minutes contact time. This was in agreement with the pressureless infiltration results as MMCs have been produced after 30 minutes with these alloys. Sessile drop experiments also show that SiC is similarly wetted by Al-Mg alloys under both N2 and Ar. It is concluded that the infiltration process does not involve the intermediate nitride phase suggested by other authors.

Surface Tension and Its Temperature Coefficient of Molten Silicon at Different Oxygen Potentials

Abstract: Previous investigations on the effects of temperature and impurities on the, surface tension of molten silicon, and relevant measurement methods have been reviewed, and the influence of oxygen partial pressure (P-O2) in the atmosphere has been analyzed emphatically, on the basis of the results obtained by the sessile drop method and calculations. In the case of P-O2 less than or equal to P-O2.(sat) (the saturated oxygen partial pressure in the Si(l)-O-2(g)-SiO2(S) system), the surface tension First remains almost constant and then decreases remarkably with the increase of P-O2, the temperature coefficient of surface tension (partial derivativesigma/partial derivativeT) is negative and increases with the oxygen partial pressure, and the molten silicon drop is very sensitive to outside vibrations, However. in the case of P-O2 > P-O2.(sat) the surface tension increases slightly with the oxygen partial pressure, partial derivativesigma/partial derivativeT is higher and also increases with P-O2 the molten silicon drop is not influenced by environmental disturbances and remains stable, and EPMA (electron probe microanalyzer) analysis indicates the formation of a thin SiO2(S) film on the surface of the molten silicon drop which might account fur the surface tension increase.

Surface chemistry of Eucalyptus wood pulp fibres: Effects of chemical pulping

Abstract: The surface chemistry of Eucalyptus grandis wood pulp fibres was investigated using the sessile drop apparent contact angle, XPS and TOF-SIMS techniques. Pulp fibres were studied using different chemical pulping conditions. The pulping affected the surface coverage of lignin and extractives, as indicated by XPS, and the work of adhesion with water, as estimated from contact angle determinations.The amount of surface lignin decreased while surface extractives and work of adhesion with water increased in relation to the amount of active alkali used in the pulping. Desorption and analysis of surface extractives by TOF-SIMS showed sterols, fatty acid calcium and sodium salts. After acetone extraction the spectra obtained by TOF-SIMS showed changes. However, calcium and sodium salts of fatty acids were still detected, indicating their resistance to solvent extraction. This resistance to extraction can affect the lignin and extractive surface coverage estimations using XPS due to the contribution of the carbon content after extraction. The extent of interference was, however, uncertain.

Wettability and phase formation in TiC/Al-alloys assemblies

Abstract: The effect of alloying elements on the wetting behavior of TiC substrates by commercial aluminum alloys (1010, 2024, 6061, 7075) and its relation to phase formation at the metal–ceramic interface was investigated at 900 °C using a sessile drop technique. It was found that wetting behavior in Al-alloys/TiC is typical of reactive systems, furthermore, wettability of TiC by pure Al-1010 was better than the alloys. Interface examination revealed the formation of Al 4 C 3 in all the cases; the thickness of the reaction layer varied within the samples and was discontinuous in nature, particularly for the 7075/TiC and 6061/TiC systems, which exhibited poor wetting. The formation of alloyed phases in the ceramic surface decreased the amount of the undesirable Al 4 C 3 at the metal/ceramic interface.

Surface Tension and Wettability of Liquid Fe-16 mass%Cr-O Alloy with Alumina

Abstract: The surface tension and wettability of liquid Fe-16 mass%Cr-S alloy with alumina substrate at 1823 K and the temperature dependence of surface tension of liquid Fe-16 mass% Cr-S alloy in the temperature range of 1808-1883 K were measured using the sessile drop technique. The surface tension and contact angle of liquid Fe-16 mass%Cr-S alloys with alumina substrate decreased markedly with increasing sulphur concentration in the alloys. The variation of surface tension of liquid Fe-16 mass% Cr-S alloys with sulphur activity can be described by the following equation: σ 1g = 1640 - 182 ln(1 + 157a s ) (mass% O=0.0037-0.0075, mass% S ≤ 0.195) (mN/m). The interfacial tension between liquid Fe-16 mass% Cr-S alloys and alumina substrate, calculated using Young's equation, can be expressed by the following equation: σs l = 2170 - 220 ln(1 + 237a S ) (mass% O=0.0037-0.0075, mass% S ≤ 0.195) (mN/m). The work of adhesion between liquid Fe-16 mass% Cr-S alloys and alumina had a tendency to increase with increasing sulphur concentration. The temperature coefficient of surface tension, dσ/dT, for Fe-16 mass% Cr-S system in the temperature range of 1808-1883 K increased with increasing sulphur concentration, and changed from negative to positive value when the sulphur concentration exceeded 20 mass ppm.

Molecular Scale Aspects of Liquid Contact on a Solid Surface

Abstract: Molecular dynamics simulations related to the contact structure of liquid droplet on a solid surface are compared for a simple Lennard-Jones fluid system and a practical water-on-platinum system. The contact angle for the Lennard-Jones system seems to be simply scaled with the potential energy parameter between liquid and solid, even though the layered liquid structure near the surface gives some complexity. On the other hand, a water droplet in contact with a platinum surface shows quite intrigue results. The water droplet gives a finite contact angle on the absorbed monolayer water film. The contact angle is determined by the surface energy between this monolayer water film and bulk liquid water. The dependence of contact angle on the platinum crystal lattice structure is explained by the structure of this monolayer water film.

Investigation of specific volume of glass-forming Pd-Cu-Ni-P alloy in the liquid, vitreous and crystalline state

Abstract: The thermal expansion of the glass-forming alloy Pd 43 Cu 27 Ni 10 P 20 in the liquid and the vitreous state, as well as in the crystalline state, was measured continuously by means of sessile drop technique. From the data obtained on density and thermal expansion, the specific volume could be deduced as a function of temperature in the complete temperature range from the stable liquid to the vitreous state for this alloy. Comparing these experimental results with the enthalpy function obtained from former calorimetric investigation, a similarity between the temperature dependence of both thermodynamic quantities is observed in the regime of the entire liquid state as well as at the glass transition. Accordingly, the correlation between these thermodynamic functions is discussed on the basis of the free-volume model. The temperature dependence can be attributed to structural relaxation processes and the change in the fractional free volume.