Showing papers on "Sessile drop technique published in 1996"

Flow in an open channel capillary

Abstract: The problem of capillary-driven flow in a V-shaped surface groove is addressed. A nonlinear diffusion equation for the liquid shape is derived from mass conservation and Poiseuille flow conditions. A similarity transformation for this nonlinear equation is obtained and the resulting ordinary differential equation is solved numerically for appropriate boundary conditions. It is shown that the position of the wetting front is proportional to (Dt)½ where D is a diffusion coefficient proportional to the ratio of the liquid-vapour surface tension to viscosity and the groove depth, and a function of the contact angle and the groove angle. For flow into the groove from a sessile drop source it is shown that the groove angle must be greater than the contact angle. Certain arbitrarily shaped grooves are also addressed.

Wetting kinetics and bonding of Al and Al alloys on α-SiC

Abstract: The wetting behaviour of aluminium on basal planes of α-SiC single crystals was investigated between 1000 and 1200 K by the sessile drop technique in high vacuum. The experiments were focused on wetting kinetics to determine the mechanisms controlling the rate of spreading and to identify all the characteristic contact angles formed during an isothermal experiment. Pure Al and Al alloys with silicon, copper and tin were studied. In some experiments SiC substrates covered by a silica layer 10–50 nm thick were used.

Reactive Wetting in the Liquid‐Silicon/Solid‐Carbon System

Abstract: The wettability of glassy carbon by liquid silicon has been investigated at 1430°C in argon by using techniques of both in situ formation and capillary formation of sessile drops. Analyses of the results showed that there are three distinct contributions of reaction to wetting: (a) dissolution of solid substrate carbon in liquid silicon; (b) formation of a continuous SiC layer at the solid side of the interface, and (c) a contribution of the free energy released by the reaction localized at the interface between liquid silicon and solid carbon.

Axisymmetric Drop Shape Analysis (ADSA)

Abstract: VIII. Applications and Illustrations 490 A. ADSA-P 490 B. ADSA-D 502References 505I. INTRODUCTION Numerous methodologies have been developed for the measurement of contact angles and surface tensions as outlined in Chapter 8 and Refs. 1-4. Liquid surface tension measurements commonly involve the determination of the height of a meniscus in a capillary, or on a fiber or a plate. Contact angles are most commonly measured by aligning a tangent with the profile of a sessile drop at the point of contact with the solid surface. Other notable methods are the Wilhelmy slide (Chapter 8) and the capillary rise technique (Chapter 9). An overview of such techniques reveals that in most instances a balance must be struck between the simplicity, the accuracy, and the flexibility of the methodology.

Measurement of dynamic/advancing/receding contact angle by video‐enhanced sessile drop tensiometry

Abstract: A sessile drop tensiometer enhanced by video‐image digitization is designed for the experimental measurement of dynamic/advancing/receding contact angle. A collimated light beam passes through the sessile drop of liquid and a silhouette of the drop is created. The equipment video images the silhouette, digitizes the image, and locates the edge coordinates of the drop. A new technique, replacing the classical selected plane method, is developed to obtain the values of capillary constant and the radius of curvature at apex from the edge coordinates of digitized drop profile. Four parameters (location of apex, radius of curvature at apex, and the capillary constant) are calculated from the best fit between the edge coordinates and the theoretical curve obtained from the Laplace equation. The contact angle is then obtained from the location of the air/solid interface and the best‐fitted sessile drop profile. By controlling the humidity of air phase surrounding the drop, this technique can measure the advancing and receding contact angles and monitor the rate of advancing and receding of the three‐phase line simultaneously. This technique works well on contact angle measurement for sessile drops with or without an equator. Preliminary studies on the dynamic contact angle have been made for water drops on paraffin, polymethylmethecrylate, and glass. The technique is capable of giving contact angle of 0.2° precision.

The effect of surface and hydrodynamic forces on the shape of a fluid drop approaching a solid surface

Abstract: This paper describes an experiment designed to measure surface and hydrodynamic forces between a mercury drop and a flat mica surface immersed in an aqueous medium. An optical interference technique allows measurement of the shape of the mercury drop as well as its distance from the mica, for various conditions of applied potential, applied pressure, and solution conditions. This enables a detailed exploration of the surface forces, particularly double-layer forces, between mercury and mica. A theoretical analysis of drop shape under the influence of surface forces shows that deformation of the drop is a sensitive indicator of the forces, as well as being a very important factor in establishing the overall interaction between the solid and the fluid.

Influence of interfacial reaction rates on the wetting driving force in metal/ceramic systems

Abstract: The wetting of copper-silicon alloys of various compositions on vitreous carbon substrates at 1423 K was studied by the sessile drop method. The morphology and chemistry of products of interfacial reactions between silicon and carbon were characterized by scanning electron microscopy (SEM), electron probe microanalysis, and high-resolution optical profilometry. In addition to measurements of contact angles and spreading kinetics in the reactive Cu-Si/Cv system, similar measurements were performed for the nonreactive Cu-Si/SiC system. It was found that the reaction rate has no effect on the final contact angle, which is nearly equal to the thermodynamic contact angle of the alloy on the reaction product. These findings appear to be valid for a wide range of interfacial reaction rates and for different types of interfacial reactions.

Variation of contact angles with temperature and time in the Al-Al2O3 system

Abstract: The contact angles of liquid Al on polycrystalline Al2O3 determined by the conventional sessile drop method were obtuse (∼120 deg) up to 900 °C but decreased rapidly at 1000 °C. When the molten Al was squeezed through a narrow orifice and dropped onto the substrate, the contact angle at 900 °C was 77 deg and decreased linearly with temperature. At 1000 °C and 1100 °C, the contact angles decreased slowly with holding times up to 50 and 6 hours, respectively. At 1200 °C, the contact angle also decreased with holding time up to 40 minutes, after which it oscillated, resulting in a ring pattern on the substrate. The structural change of the Al2O3 substrate surface is suggested to be an important variable that determines the wetting behavior of the Al-Al2O3 system.

Study on contact angles of Au, Ag, Cu, Sn, Al and Al alloys to SiC

Abstract: Contact angles of Au, Ag, Cu, Sn, Al and Al alloys to SiC were measured by use of sessile drops heated by a high frequency induction coil designed to be convex against the SiC plate. Three crystal configurations of α-SiC, polycrystalline plane of sintered SiC, SiC (1 1 1) plane, and SiC (1 0 0 0) plane were used as base plates. Au, Sn, Al and Al alloys showed a large contact angle of about 150 ° at each melting temperature, however those of Ag and Cu were in the range of 105–121°. Every contact angle of Al and its alloys decreased to under 90° when held at 1350 °C. SiC (1 0 0 0) plane gave a lower contact angle than the other two SiC planes for Cu, Al and Al-Si alloys.

Optimization of wettability and adhesion in reactive nickel-based alloys/alumina systems by a thermodynamic approach

Abstract: Optimization of wetting and adhesion in metal/oxide systems can be achieved by using solutes to control the chemistry of the interfaces and the thickness of reaction product layers. This approach is illustrated by results obtained for Ni alloy/Al 2 O 3 systems. Wettability experiments are performed by the sessile drop technique under high vacuum or a static neutral gas atmosphere. Interfacial chemistry and morphology are determined using scanning electron microscopy and electron microprobe analysis. Adhesion is qualitatively characterized by the type of fracture observed during cooling of sessile drop samples.

Wettability of aluminum nitride by molten metals

Abstract: The sessile drop method has been used with a vacuum of 2.10−3 Pa to examine the wettability of aluminum nitride by fourteen molten pure metals as well as the effects of adding chromium, vanadium, niobium, tantalum, and titanium to the liquids on the wetting angle in systems containing aluminum nitride and liquid tin, copper, and germanium. Aluminum nitride is wetted only by molten silicon and aluminum. Out of the elements examined, titanium is the most adhesion-active for this ceramic. The results are examined from the viewpoint of thermodynamic wetting theory.

Influence of phosphorus addition on the surface tension of liquid iron and segregation of phosphorus on the surface of Fe-P alloy

Abstract: This article presents a study of the surface tension and phosphorus surface segregation in Fe-P alloys. The surface tension was measured by the sessile drop technique. The result of the dynamic surface tension for the low phosphorus content alloys shows that the alloy surface vaporization has a clear effect on the surface tension and causes a positive surface tension temperature coefficient. However, from this article, it is evident that phosphorus in liquid iron acts as a surface active element similar to arsenic. The surface segregation was determined using Auger electron spectroscopy. The result on the surface analysis of as-solidified sample indicates that the adsorption of impurity elements, such as oxygen, carbon, and nitrogen, can conceal phosphorus segregation on the free surface. Phosphorus segregation was also examined in the samples as-cleaned by Ar+ and then treated 30 minutes at 650°C. Phosphorus was found to segregate extensively on the surface of the alloys. On the basis of the analysis of the published data, the surface active intensity sequence of some nonmetallic elements was arrayed, and the surface active intensity of fluorine and boron in liquid iron was estimated.

The nature of interfacial phenomena at copper-titanium/alumina and copper-oxygen/alumina interfaces

Abstract: Experiments with liquid copper-titanium alloy and copper-3 w/o oxygen alloys in contact with polycrystalline alumina in both a sessile drop and capillary rise configuration are used to demonstrate that reactive metals such as copper-titanium alloys in contact with ceramic surfaces exhibit a complex wetting behavior. Although both liquids form acute contact angles in the sessile drop configuration, the copper-titanium liquid does not rise to significant heights in a capillary tube. The observed acute angle morphology of liquid copper-titanium alloys in the sessile drop experiment is a consequence of reaction layer formation. with gravity assisting the liquid to spread into an acute angle configuration. In contrast, in addition to forming an acute angle in the sessile drop configuration, the copper-oxygen alloys also instantly infiltrate micro-capillary channels in alumina.

Interfacial tension and contact angle variations of SUS304 melt in contact with solid oxides and CaO-SiO 2 -Al 2 O 3 (CaF 2 ) slags at 1470°C

Abstract: Study on the interfacial properties of SUS304 melt in contact with pedestal oxides and also liquid slags of varying chemistry was carried out by using a combination of the sessile drop method and a X-ray fluoroscopic technique at 1470°C. Interfacial tension and contact angle were obtained directly from a numerical solution of the Young-laplace equation. Surface tension of SUS304 was found to be 1467 mN.m in Ar-atmosphere which was considerably lower than that of pure iron. This may be due to the existence of surface active elements such as (Cr, Ni and Mn etc. in SUS304. Interfacial tensions of SUS304 in contact with CaO-Sio2-Al2O3(CaF2) slags were in the range of 925 to 1 148 mN/m. The contact angle between SUS 304 and various pedestal was about 120° regardless of pedestal oxides. A12O3. TiO2 and SiO2. Contact angles between SUS304 and the pedestal alumina coexisting with liquid CaO-SiO2-Al2O3CaF3) were in the range of 125° to 142°.

Contact Angle and Liquid Surface Tension Measurements: General Procedures and Techniques

Abstract: EVA I. VARGHA-BUTLER College of Pharmacy, Dalhousie University, Halifax, Nova Scotia, CanadaI.II.IntroductionContact Angle Measurement381 A. Flat plate 381 B. Individual fiber 385 C. Powders and granules 385 D. Capillary tube 386 E. Mat and woven fabric 387III. Liquid-Vapor Surface Tension Measurement 387 A. Wilhelmy plate 388 B. Drop shape methods 389IV. Measuring Liquids 390 A. Liquid selection 390 B. Liquid purity 391 C. Handling and storage of high-purity liquids 392V. Solid Surfaces 394 A. Surface techniques-nonbiological 395 preparation materials B. Surface preparation techniques-biological materials 402 C. Cleaning and handling solid surfaces 407References 407I. INTRODUCTION The accurate measurement of contact angles is essential in many areas of applied surface thermodynamics. As was seen in Chapters 3 and 5, the contact angle provides a unique means of determining solid-vapor and solid-liquid surface tensions. The range of applications of this measurement is remarkable, both as a simple tool to assess, for example, the cleanliness of surfaces, and as a highly sensitive scientific measurement aimed at providing information on the solid surface tension and the physical state of the surface. When first encountered, the measurement of contact angles appears to be quite straightforward. This apparent simplicity is, however, very misleading, and experience has shown that the acquisition of thermodynamically significant contact angles requires painstaking effort. This chapter addresses the many practical issues pertaining to the measurement of contact angles and liquid surface tensions, including the preparation of suitable solid surfaces and measuring liquids.

Surface Tension of Calcium Aluminosilicate Glass Using Computerized Drop Shape Analysis

Abstract: Numerical analysis is used in this study to derive surface tension from the shape of a liquid silicate sessile drop. The speed afforded by the drop shape analysis package facilitates analysis of experimentally derived drop profiles. Drop symmetry, contact angles, and local shape variations can be readily determined, thereby permitting the detection of experimental errors. The experimental and analytical technique was first validated by determining the surface tension of high-purity gallium and aluminum under carefully controlled furnace atmospheres. Results for a calcium aluminosilicate melt are compared to pendant drop and maximum-bubble pressure measurements reported in the literature. The use of an internal scaling factor and the effect of substrate interactions are discussed.

The spreading kinetics of Ag–28Cu(L) on nickel(S): Part I. Area of spread tests on nickel foil

Abstract: Dynamic hot-stage microscopy and sessile drop experiments have identified three stages in the spreading of Ag–28 wt. % Cu liquid on the surface of high-purity Ni foil: (I) nonreactive flow, (II) secondary spreading, and (III) breakout flow. The first stage is deGennes-type spreading driven by capillary forces and resisted by viscous drag. A (Cu, Ni) reaction layer forms quickly at temperature along the liquid-solid interface. Stage I ends when the liquid braze attains a quasistatic contact angle on the reacted surface. Stage II spreading involves a complex advance of a thin liquid sheet outward from the triple line as a result of differences in wetting between Ni grain surfaces and grain boundaries. The advancing liquid meniscus is distorted as the liquid moves ahead along the better wetted grain boundary regions and is held back (pinned) on those surfaces that are poorly wet, resulting in a stick-slip motion of the triple line. The change in contact area with time is linear during this stage, and the rate of spreading is independent of temperature in the range of 780–870 °C. Although the diffusion of Cu into Ni grain boundaries likely drives the capillary flow, it is not the controlling process since an activation energy is not observed. The final stage of spreading, breakout flow, involves the flooding of the liquid braze over previously wetted surfaces due to a change in the balance of interfacial energies. Spreading ends during stage II or III either by isothermal solidification which stems from interdiffusion between the braze filler and the substrate or by curtailment of the liquid supply when it pulls back on the (Cu, Ni) reaction layer. Hold time, peak temperature, and heating rate all have an effect on both the terminal area of spread and the spreading kinetics of braze flow on polycrystalline Ni. The heating rate effect has not been emphasized in previously published literature for soldering and brazing and, if overlooked could easily impair one's ability to apply test results to other studies or practical situations. Roughness-enhanced spreading was not observed with the Ni foil surfaces used in this study. There was, however, a localized effect on the shape of the triple line that did not affect spreading kinetics or terminal area of spread in a systematic fashion.

Effect of Wettability of Grains by a Liquid Phase on Grain Growth Behavior of La-Doped SrTiO3 Ceramics

Abstract: The relationship between the grain growth and the wettability of grains by a liquid phase was discussed on the basis of the observation of the microstructure of La-doped SrTiO3 ceramics and the measurement of the contact angle of the liquid phase (Sr1Ti3.206La0.328O7.904) on the SrTiO3 substrate using the sessile drop method. The contact angle of the liquid phase in SrTiO3, which was the composition at 1490°C as determined from the SrO-TiO2 phase diagram, on the SrTiO3 substrate was 22°. The contact angle of the liquid phase containing La2O3 was 22°. The contact angles of the liquid phases in the cases of SrTiO3 containing SiO2 and a mixture of SiO2 and Bi2O3 were 16° and 9°, respectively. The contact angle was decreased by the addition of SiO2 and/or Bi2O3. The liquid phase of La-doped SrTiO3 ceramics was considered to have relatively poor wetting and to localize at the triple grain junctions at high temperatures and then to be exuded from the inner part to the surface of the samples during cooling. The nucleation and grain growth occur at this spot where the liquid phase is present. Thus, exaggerated grain growth occurs. The number of nuclei increases with the increase of the volume of liquid phase upon increasing the Ti/Sr ratio, which leads to the inhibition of grain growth. On the other hand, since the liquid phase of La-doped SrTiO3 containing SiO2, Bi2O3 can uniformly wet the grains, the growth rates of all grains are almost the same and exaggerated grain growth is not observed.

Effect of oxygen on the wettability of sapphire by liquid palladium

Abstract: The surface tension of liquid palladium and the contact angle between liquid palladium and sapphire have been measured at 1833 K as a function of oxygen pressure by the sessile drop method. Oxygen acted as a surface-active element on the surface of liquid palladium and at the interface between liquid palladium and sapphire, resulting in the decrease of the surface tension and the contact angle. The work of adhesion calculated from their values increased with increasing oxygen pressure, and had a constant value above 400 Pa. The maximum excess concentration of oxygen was estimated to be 7.3×10−6 mol m−2 for the surface and 6.9×10−6 mol m−2 for the interface.