Showing papers on "Sessile drop technique published in 1998"

Wettability of carbon by aluminum and aluminum alloys

Abstract: Wetting (both equilibrium contact angle and spreading kinetics) of aluminum and aluminum alloys with silicon and titanium on carbon substrates is investigated as a function of temperature and carbon microstructure. Experiments are carried out by the sessile drop technique under high vacuum, in the range from 1023 to 1250 K. Three different types of carbon substrates are examined: vitreous carbon, pyrolytic carbon and graphite pseudo single crystals. It is shown that an increase in temperature and a decrease in the preferred orientation of the graphite basal planes with respect to the substrate surface greatly enhance the three-phase line reactivity and the spreading kinetics. From a practical point of view the results obtained in this study show that in processes involving short-time contact (up to a few minutes) between deoxidized molten Al (or Al–Si and Al–Ti alloys) and carbon at T

Wettability of nickel coated graphite by aluminum

Abstract: Graphite is a very attractive candidate for aluminum–metal matrix composites. However, aluminum does not wet graphite, which makes the production of aluminum–graphite composites difficult. Nickel is a material known to be wetted by aluminum. In the presence of a nickel intermediate layer between the aluminum and graphite, wetting of the graphite by aluminum was expected to improve. To determine the wettability of aluminum on nickel coated graphite, the sessile drop technique along with a high temperature X-ray setup was used. Aluminum drops on substrates of graphite, electrolytic nickel, and nickel coated graphite were studied. Contact angles determined for these samples showed that graphite is non-wetting while the nickel coated graphite provided better wetting than electrolytic nickel. The aluminum/substrate interface of the samples was examined microscopically using scanning electron microscopy.

The work of adhesion of polymer/wall interfaces and its association with the onset of wall slip

Abstract: The interfacial characteristics of a variety of polymer/wall interfaces were measured by using the sessile drop method in order to calculate the work of adhesion. Polymers included linear low-density as well high-density polyethylenes, while wall substrates included clean stainless steel and modified stainless steel by applying two different fluoropolymers in order to alter its surface energy. A linear correlation is found between the critical shear stress for the onset of slip and the work of adhesion of the corresponding polymer/wall interface, in agreement with earlier publications of Hill et al. (1991) and Hatzikiriakos et al. (1993). In the present work, the experimental results are interpreted in terms of parameters defined by these two theories. It is suggested that small deviations from the no-slip boundary condition in the case of polymer melt flow are due to a stress-induced chain detachment/desorption of polymer chains from the wall.

Wettability of transition metal oxide surfaces

Abstract: The wettability of transition metal oxide surfaces (TiO 2 , ZrO 2 and HfO 2 ) by water was investigated by measuring the contact angles using the sessile drop method. The oxide surfaces were prepared by thermal oxidation of polished metal foils of Ti, Zr and Hf, which had been polished to different levels of surface roughness. The surfaces were also characterized by optical microscopy, X-ray diffraction (XRD), atomic force microscopy (AFM) and Auger/XPS (AES/ESCA) methods. From the dependence of contact angles on surface roughness for the three investigated oxides, contact angles on flat surfaces were calculated as 70.7°, 59.9° and 74.0° for TiO 2 , ZrO 2 and HfO 2 , respectively. These results suggest that the three oxides do not provide acceptable waterproofing coatings on silica fibers used for space shuttle thermal insulation.

Determination of the nature of metal-oxide interfacial interactions from sessile drop data

Abstract: The nature of the interfacial metal M–oxide A n O m bond in non-reactive systems is discussed by correlating the work of immersion, obtained from sessile drop data, to the energy of formation of bulk M oxides and A–M alloys. The conclusions of this new analysis are fundamentally different from those proposed in the past using similar approaches.

Estimation of the surface energy and acid-base properties of wood by means of wetting method

Abstract: The important surface energy and acid-base properties for pine wood (Pinus silvestris L.) have been estimated by using two contact angle techniques (CAT), e.g., the sessile drop method and the Wilhelmy plate method, respectively. According to the results, the pine wood may be characterized as a low surface energy polymer due to its low surface energy. The surface energy, γ s , for the pine wood was being larger in the direction parallel to the grains as compared with the perpendicular direction. The Lifshitz-van der Waals (LW) energy component, γ s LW is the major energy component for the pine wood as compared with the acid-base energy component, γ s AB . Furthermore, it seems that the LW energy component, γ s LW , of pine wood is independent of the choice of wetting methods and of the chemical composition of the surface. However, the surface acid-base (AB) energy component, γ s AB , for the pine wood seems to be dependent on the wetting methods chosen. Subdivided into its contributions, the surface of pine wood seems to be weaker in the acidic energy parameter, γ s + , and stronger in the basic energy parameter, γ s - . Rough estimation of the contact angle hysteresis (CAH) and surface roughness (SR) has also been measured separately in the parallel direction and the perpendicular directions, respectively.

Axisymmetric Drop Shape Analysis (ADSA) and its Applications

Abstract: Publisher Summary This chapter discusses axisymmetric drop shape analysis (ADSA) and its application. It provides an account of these ADSA methodologies. It contains a description of the numerical algorithms and their implementation. The applicability of ADSA is illustrated extensively for the investigation of surface tension measurements with pendant and sessile drops and contact angle experiments with sessile drops using both axisymmetric drop shape analysis - profile (ADSA-P) and axisymmetric drop shape analysis - diameter (ADSA-D). The advantages of pendant and sessile drop methods are numerous. In comparison with a method such as the Wilhelmy plate technique, only small amounts of the liquid are required. Drop shape methods easily facilitate the study of both liquid-vapor and liquid-liquid interfacial tensions. Also, the methods have been applied to materials ranging from organic liquids to molten metals and from pure solvents to concentrated solutions. There is no limitation to the magnitude of surface or interracial tension that can be measured: The methodology presented in this chapter works as well at 103 mJ/m 2 as at 10 -3 mJ/m 2.

Influence of melt carbon and sulfur on the wetting of solid graphite by Fe-C-S melts

Abstract: The interfacial phenomena between carbonaceous materials such as graphite, coke, coal, and char and Fe-C-S melts are important due to the extensive use of these materials in iron processing furnaces However, the understanding of the interfacial phenomena between these kinds of carbonaceous materials and molten iron alloys is far from complete In this study, graphite was selected as the solid carbonaceous material because its atomic structure has been well established The sessile drop method was adopted in this investigation to measure the contact angle between solid graphite and molten iron and to study the interfacial phenomena The influence of carbon and sulfur content in Fe-C-S melts on the wettability of solid graphite has been investigated at 1600 °C The melt carbon content was in the range of 013 to 224 wt pct, and the melt sulfur content was in the range of 005 to 037 wt pct X-ray energy-dispersive spectrometer (EDS) analysis was conducted on an HITACHI S-4500 scanning electron microscope to detect composition distribution at the interfacial region It was found that contact of solid graphite with Fe-C-S melts will result in a nonequilibrium reactive wetting It involved carbon transfer from the solid to the liquid and iron transfer from the liquid to the solid The Fe-C-S melts exhibited relatively poor wetting when the reactions were absent The mass transfer between solid graphite and Fe-C-S melts was observed to strongly enhance the wetting phenomena It is proposed that the decrease of system free energy corresponding to the mass transfer reactions strongly influences the formation of the interface region and results in the progressive spreading of the wetting line The composition and thickness of the graphite/iron interfacial layer was dependent on the intensity of mass transfer across the interface The resulting change in the interfacial energy γls is a strong function of mass transfer, and it varies in accordance with time of contact The influence of carbon content on the wetting phenomena could only be seen at in the initial stages, whereas the influence of sulfur on the wettability was found when the system approached equilibrium Therefore, the interfacial tension in its equilibrium condition at the graphite/Fe-C-S melt interface was determined only by the extent of sulfur adsorption at this interface

Interfacial tension effects on slag-metal reactions

Abstract: Dynamic Xray imaging of a metal droplet in a slag phase is an elegant way to monitor the rate of the interfacial reactions. In an attempt to follow the kinetics of dephosphorization, the changes in...

Wetting prevention by thermal marangoni effect. Experimental and numerical simulation

Abstract: The behaviour of small liquid drops, hanging from a circular disk and approaching a flat wall at a different temperature is studied experimentally and numerically. If the pendant drop and the solid surface are at the same temperature and if the liquid wets the solid, the drop spreads over the surface forming a liquid bridge in times of the order of milliseconds. If the upper disk is heated and/or the solid surface is cooled, then the drop does not wet the wall, even if pressed against the surface, but it is deformed in a completely reversible way, similarly to an elastic material (e.g. like a rubber balloon). To investigate this unusual and intriguing phenomenon, a systematic experimental programme has been carried out on silicone oils (with different viscosities) and on diesel oils. At the same time the problem was studied numerically under the assumption that a thin air film exists between the drop and the solid surface. This film is formed by the entrainment of the surrounding air caused by the Marangoni flow directed, along the liquid surface, from the upper disk towards the contact zone. If suitable conditions are established, the pressure in the air film balances the pressure necessary to deform the liquid drop, preventing the wetting of the solid surface. The experimental results agree with the proposed numerical model. In particular the computed equilibrium air film thicknesses are compared with the thicknesses measured with a background illumination system and with an interferometric technique; a good agreement is found between numerical and experimental results, for different liquids and different geometrical configurations.

Measurement of Ultralow Interfacial Tension with Application to Surfactant-Enhanced Alkaline Systems

Abstract: This paper discusses the dynamic interfacial tension (IFT) variation in a system containing an acidic oil in contact with an alkaline solution which may contain a preformed surfactant. A modified technique similar, in principle, to the sessile drop technique is used for monitoring the dynamic IFT which is in the ultralow range. The technique is then applied for measuring ultralow IFTs in systems consisting of acidic oils and alkaline solutions containing preformed surfactants. The effect of aqueous phase pH, surfactant concentration, and oil phase acid concentration on the dynamic IFT variation in these systems is determined by using this technique.

Microscopy and electron spectroscopic study of the interfacial chemistry in Al–Ti alloy/graphite systems

Abstract: The chemical and physical interaction of liquid metal surfaces with various substrates is an important, largely unexplored aspect of technology, with implications in composite science and catalysis. In the present case, we have employed X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES), in conjugation with sessile drop wettability tests, to examine the interfacial properties and surface chemistry of the systems formed by adding liquid drops of select Al–Ti alloys to graphite substrates. A variety of different chemical states was revealed in the XPS results, suggesting the formation of separate regions composed of elemental metals, alloys and carbides. Many of the specific features detected appear to depend on the various treatment properties, e.g. the temperature, bulk alloy composition, size and shape of the alloy drop and time of interaction. The surface analyses were also supported by optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD) studies. The combined results suggest the induction of a strong reaction between titanium and carbon, resulting in an improvement in the wettability of the alloy with the graphite substrate and a corresponding structure transformation from the (LAl–Ti+Al3Ti) state to the (LAl–Ti+TiC) semi-liquid state. © 1998 Kluwer Academic Publishers

Strange spreading behavior of tricresyl phosphate

Abstract: The spreading of a sessile drop can be explained by a dynamic energy balance in which released excess capillary energy causes triple-line motion while wetting front speed is moderated by viscous dissipation within the liquid. This energy balance leads to a well-known relationship between dynamic and equilibrium contact angles and spreading speed. Experiments conducted with a silicone oil, poly(dimethylsiloxane), confirmed the validity of this equation. Similar experiments of spreading of tricresyl phosphate (TCP) on the same three substrates, glass, Halar (polyethylene−chlorotrifluoroethylene), and polypropylene, led to anomalous behavior: among other observations, we noted that the (apparent) spreading force needed for a given spreading speed was too high. Here, we suggest a tentative theory involving molecular orientation or conformation of the asymmetrical liquid molecules after they have been “laid down” on the solid substrates during spreading. As TCP molecules orientate near the triple line, the li...

Wettability, surface tension, and reactivity of the molten manganese/zirconia-yttria ceramic system

Abstract: A basic research study for improvement of plasma-sprayed zirconia coatings has been conducted. The contact angle and surface tension of the molten manganese/zirconia-yttria ceramic system were measured at 1573 K by the sessile drop method, suggesting that molten manganese would spontaneously infiltrate open pores in zirconia coatings. Structure and elementary composition development of zirconia ceramics caused by reaction with manganese were examined by using scanning electron microscopy (SEM), an electron probe microanalyzer (EPMA), and an X-ray diffractometer (XRD). Manganese not only stabilized cubic zirconia but also contributed to the growth and volume increase of zirconia particles. In this article, the mechanism of making zirconia coatings dense with manganese is discussed based on the results of experiments.

Wettability of aluminium nitride by tin-aluminium melts

Abstract: The wettability of aluminium nitride by Sn–Al melts was studied by the sessile drop method in a vaccum of 2 × 10−3 Pa at 1100 °C over the whole concentration region. The minimum interval on the contact-angle concentration dependence curve was observed at intermediate composition. For comparison, experiments were also performed on porous AlN. Wetting of porous nitride is worse than the dense nitride. The results have been analysed on the basis of the relation between wettability and the chemical interface reactivity in solid–liquid metal systems.

Surface interactions between fayalite slags and synthetic spinels and solid solutions

Abstract: To obtain a better understanding of the complex corrosion mechanisms occurring at the interface, the surface and interfacial properties between fayalite-type slags and homogeneous, synthetic spinels and solid solutions of these spinels were investigated. These oxides represent the conventional refractory components. The sessile drop technique incorporating high-temperature X-ray radiography was employed for this purpose. The experimental temperature was 1200 °C and the oxygen potential was 10−9 atm controlled by CO/CO2 gas mixture. The contact angles between the solid substrates and molten silica-rich fayalite slag ranged from 0 deg for MgFe2O4 to 23 deg for MgAl2O4. When iron-rich slags were employed, the contact angles ranged from 15 deg for MgCr2O4 to 22 deg for MgAl2O4. The interfacial reactions between the slags and the various spinel materials and the dissolution of the solids into the slags are discussed.

Analysis of an Oxygen Dissolution Process Concerning Czochralski (CZ) Si Crystal Growth using the Sessile Drop Method

Abstract: A new sessile drop method has been developed for measuring the oxygen dissolution rate from silica glass to silicon melt. Compared to the oxygen dissolution rate obtained using a conventional measurement method, a much larger value has been obtained with the sessile drop method. The experimental accuracy of the sessile drop method was analyzed, and it was found that the main error resulted from the weight change of a blank silica plate following heat treatment. A rectification method was suggested.

Analysis of Oxygen Evaporation Rate and Dissolution Rate Concerning Czochralski Si Crystal Growth: Effect of Ar Pressure.

Abstract: A small sessile drop sample and a small crucible sample were used for measuring oxygen evaporation rate and dissolution rate. Dependence of the oxygen evaporation rate (from surface of silicon melt) and dissolution rate (from silica glass to silicon melt) on Ar pressure from 20 to 3800 Torr was investigated at different temperatures. The oxygen evaporation rate and dissolution rate increased monotonically with decreasing Ar pressure, and increased remarkably with increasing temperature. The relationship between the oxygen dissolution rate and the interfacial phase of the brownish rings has also been investigated. The interfacial phase disappeared when the oxygen dissolution rate was sufficiently high.

Influence of reactive solute transport on spreading kinetics of alloy droplets on ceramic surfaces

Abstract: This paper focuses on the question of the processes which can be ratelimiting for reactive spreading in the sessile drop configuration. It will be shown that for a class of systems, spreading kinet...