Showing papers on "Sessile drop technique published in 1999"

Wettability at high temperatures

Abstract: Chapter headings and selected sub-headings: Series Preface. Preface. Fundamental Equations of Wetting. Surface and interfacial energies in solid / liquid / vapour systems. Dynamics of Wetting by Metals and Glasses. Non-reactive wetting. Reactive wetting. Methods of Measuring Wettability Parameters. Sessile drop experiments. Surface Energies. Data for metals and alloys. Data for non-metallic compounds. Wetting Properties of Metal / Metal Systems. Effects of alloying elements. Systems that form intermetallic compounds. Wetting Properties of Metal / Oxide Systems. Non-reactive pure metal / ionocovalent oxide systems. Effect of electronic structure of the oxide. Wetting of fluorides. Wetting Properties of Metal / Non-Oxide Ceramic Systems. Metals on predominantly covalent ceramics. Wetting Properties of Metal / Carbon Systems. Non-reactive systems. Reactive systems. Wetting by Glasses and Salts. The glassy state. Wetting behaviour. Wetting When Joining. Flow into capillary gaps. Effects on mechanical properties. Appendices. List of symbols. Index

The Leidenfrost point : Experimental study and assessment of existing models

Abstract: Recent demands for superior material properties and more efficient use of materials and production time are forcing manufacturers to develop intelligent processing techniques for enhanced process control in order to better dictate the end product. In the heat treatment and processing of metallic alloys, the desire to obtain parts of enhanced and uniform mechanical properties is requiring increased control over heat removal rates and enhanced temperature control. In particular, spray quenching has been shown to be an effective means to control and enhance the cooling rates of heat treatable aluminum alloys. This study presents a detailed and thorough parametric study of the Leidenfrost point (LFP), which serves as the temperature boundary between the transition and film boiling regimes. Sessile drop evaporation experiments were conducted with acetone, benzene, FC-72, and water on heated aluminum surfaces with either polished, particle blasted, or rough sanded finishes to observe the influential effects of fluid properties, surface roughness, and surface contamination on the LFP. A weak relationship between surface energies and the LFP was observed by performing droplet evaporation experiments with water on polished copper, nickel, and silver surfaces. Additional parameters which were investigated and found to have negligible influence on the LFP included liquidmore » subcooling, liquid degassing, surface roughness on the polished level, and the presence of polishing paste residues. The accumulated LFP data of this study were used to assess several existing models which attempt to identify the mechanisms which govern the LFP. The disagreement between the experimental LFP values and those predicted by the various models suggests that an accurate and robust theoretical model which effectively captures the LFP mechanisms is currently unavailable.« less

Melt corrosion of oxide and oxide–carbon refractories

Abstract: Penetration and dissolution mechanisms are reviewed for predominantly single phase oxide, two phase oxide, and oxide–carbon composite refractories by liquid silicates. Theoretical models of these processes, as well as static (sessile drop, dipping, and crucible) and dynamic (rotating finger and rotary slag) experimental tests, along with their practical limitations are considered. Direct (congruent or homogeneous) attack involves dissolution of a solid into a liquid with no intermediate solid phase leading to active corrosion. Indirect (incongruent or heterogeneous) attack leads to formation of one or more new solid phases at the original solid/liquid interface. This may lead to passive corrosion. Examples of direct and indirect attack in a range of refractory–liquid systems are described highlighting the critical influence of the composition and hence viscosity of the local liquid adjacent to the solid. Penetration and corrosion can be controlled either through the local liquid composition via th...

The surface tension of molten aluminum and Al-Si-Mg alloy under vacuum and hydrogen atmospheres

Abstract: The surface tensions of pure molten aluminum, A356 alloy (Al-7 pct Si-0.3 pct Mg), and strontium-modified A356 alloy have been measured under vacuum and hydrogen atmospheres using the sessile drop technique. The values obtained for pure aluminum at 680 °C and for A356 alloy and modified A356 alloy at 630 °C are 1.007, 0.889, and 0.844 N/m, respectively, when measured under vacuum. The addition of hydrogen gas to the atmosphere of the liquid droplet has no significant effect on the surface tension of the unmodified A356 alloy, while it lowers the surface tension of the modified alloy to 0.801 N/m. This effect is possibly due to the formation of SrH2.

Axisymmetric drop shape analysis as penetration Langmuir balance

Abstract: A new Langmuir-type pendant-drop penetration film balance has been developed combining a Langmuir-type pendant-drop film balance with a new rapid-subphase-exchange technique. In addition to the determination of surface pressure—molecular area isotherms of insoluble monolayers deposited on the surface of a pendant drop, it allows the study of reactions with some surfactant added to the subphase. The monolayer is spread on the surface of a drop suspended from a capillary, which is the outer one of an arrangement of two coaxial capillaries connected to the different branches of a microinjector. Once the film is brought to the desired state of compression by varying the drop volume with the microinjector, the subphase liquid in the drop can be exchanged quantitatively by means of the coaxial capillaries. This exchange is complete for a through-flow of at least three times the drop volume, and the monolayers endure it at all tested film pressures. The determination of surface tension as a function of surface area is performed using axisymmetric drop shape analysis (ADSA). The complete set-up, i.e., the image capturing and microinjector system is fully computer controlled by a user-friendly and fully Windows integrated program, including the ADSA surface tension calculus algorithm. As a penetration film balance, pendant-drop methodologies offer a wide range of advantages such as a more stringent control of the environmental conditions and therefore, more uniform temperature, pressure and concentration along the interface, small amounts of material needed, and a 20 times greater interface/volume ratio than in conventional Langmuir toughs.

Influence of Surface Roughness on Wetting Dynamics

Abstract: Using the molecular-kinetic theory of wetting, we analyze the dynamic contact angle of a sessile drop of squalane spreading spontaneously on Langmuir−Blodgett multilayer substrates (behenic acid on...

Simultaneous Determination of Surface Tension and Density of Polymer Melts Using Axisymmetric Drop Shape Analysis

Abstract: By employing a new strategy, we show that axisymmetric drop shape analysis (ADSA) can be used to determine simultaneously the surface tension and the density of polymer melts from sessile drops at elevated temperatures. To achieve this, two developments were necessary. First, the ADSA algorithm had to be modified to replace the density by the mass of the drop as an input parameter. Since ADSA also yields the volume, the density became output rather than input. Second, a closed high-temperature chamber whose temperature could be precisely controlled and a sample holder that allowed the formation of highly axisymmetric sessile drops at elevated temperatures had to be developed. For a typical polymeric material (polystyrene), it is demonstrated that measurements with sessile drops yield essentially the same surface tension values and temperature coefficients as measurements with pendant drops. The densities determined with ADSA are comparable to independent PVT results.

Microsphere tensiometry to measure advancing and receding contact angles on individual particles

Abstract: In this paper, a method to measure the advancing and receding contact angles on individual colloidal spheres is described. For this purpose, the microspheres were attached to atomic force microscope cantilevers. Then the distance to which the microsphere jumps into its equilibrium position at the air-liquid interface of a drop or an air bubble was measured. From these distances the contact angles were calculated. To test the method, experiments were done with silanized silica spheres (4.1 μm in diameter). From the experiments with drops, an advancing contact angle of 101 ± 4° was determined. A receding contact angle of 101 ± 2° was calculated from the jump-in distance into a bubble. Both experimental techniques gave the same contact angle. In contrast, on similarly prepared planar silica surfaces, a clear hysteresis was measured with the sessile drop method; contact angles of 104.5 ± 1° and 93.8 ± 1° were determined for the advancing and receding contact angles, respectively.

Comparison of the surface energetics data of eucalypt fibers and some polymers obtained by contact angle and inverse gas chromatography methods

Abstract: This study compares two approaches to determine the surface energy of solids, and its acid-base components in particular: inverse gas chromatography (IGC) and analysis of contact angle data using the Good-van Oss theory. The comparison is made in the context of wood fibers from Eucalyptus globulus and Eucalyptus regnans pulped by the kraft and neutral sulfite semi-chemical (NSSC) processes, and of selected polymers. Contact angles on wood fibers were measured using the Wilhelmy method and on polymer samples using the sessile drop technique. For the dispersive component of the surface energy, the level of agreement between the two approaches was reasonable, using alkanes for the IGC measurements and diiodomethane for the Wilhelmy and sessile drop techniques. However, agreement was poor for the acid and base characteristics when monopolar probes were used for IGC and water, formamide, and diiodomethane for contact angle measurements. The Good-van Oss approach suggested that all fibers and polymers are monop...

Spin coating and air-jet blowing of thin viscous drops

Abstract: Using the lubrication approximation we investigate the spreading of a finite-sized thin drop of incompressible Newtonian fluid on a planar substrate subjected to a jet of air blowing normally to the substrate. Three specific problems are studied in detail: a jet of air acting normally to the substrate when gravity effects are negligible, a jet of air directed vertically downward onto a sessile drop on a horizontal substrate, and a jet of air directed vertically upward onto a pendent drop on a horizontal substrate. The dynamics of the moving contact line are modeled by means of a generalized “Tanner Law” relating the contact angle to the speed of the contact line. Both symmetric two-dimensional and axisymmetric three-dimensional geometries are considered; the latter case is equivalent to that of an axisymmetric drop spreading on a substrate rotating with constant angular velocity (the simplest model for spin coating). Quasistatic solutions for the drop profile are obtained in the limit of small capillary number and the stability of equilibrium solutions to small perturbations is determined. The analysis is then extended to include drops with a dry patch at their center which are found to be unconditionally unstable in all the cases investigated.

The effects of high-power diode laser radiation on the wettability, adhesion and bonding characteristics of an alumina/silica-based oxide and vitreous enamel

Abstract: An amalgamated alumina/silica-based oxide compound (AOC) was surface treated using a 60 W high power diode laser (HPDL). The effects of HPDL radiation on the wettability and adhesion characteristics of the AOC and a vitreous enamel have been determined. The basic process phenomena are investigated and the effects of laser irradiation in terms of composition and microstructure are presented. Without laser treatment of the AOC surface it was not possible to fire the enamel onto the AOC. However, wetting experiments using a number of control liquids, by the sessile drop technique, revealed that laser treatment of the AOC surface resulted in the polar component of the surface energy increasing after laser treatment from 2.00 mJm-2 to 16.15 mJm-2. Additionally, surface roughness measurements revealed that after laser treatment, the surface roughness had decreased from an Ra value of 25.85μm to 6.27μm, whilst an energy disperse X-ray analysis (EDX) revealed that the relative surface oxygen content of the AOC had increased by 36.29% after laser treatment. Thus, laser treatment was identified as effecting a decrease in the enamel contact angle from 1180 to 330; consequently allowing the vitreous enamel to wet the surface. The bonding mechanisms were identified as being principally due to van der Waals forces, however, some evidence of chemical bonding was observed. The work has shown clearly that laser radiation can be used to alter the wetting characteristics of the AOC.

Colloidal Protein Solutions as a New Standard Sensor for Adhesive Wettability Measurements.

Abstract: Wetting experiments are carried out for the investigation of the interfacial interactions that take place when various solid materials are in contact with protein colloidal solutions. These materials are chosen because they are widely used in the field of orthopedic surgery. Contact angles (sessile drop) and surface tension (du Nouy's ring method) are measured in standardized conditions which take into account the various parameters disturbing wetting phenomena. An original cumulative deposits method (CDM) described here permits observation of the evolution of the wettability and allows estimation of the protein adhesion rate. Two families of materials emerge according to their behavior when they are in contact with the protein solution. One set (a chromium cobalt alloy and two polyethylenes) presents no detectable adhesion. The other set (stainless steel, zirconia, alumina, virgin and nitrogen implanted titanium alloy) shows a cumulative adhesion of proteins. We propose to adopt a BSA buffered solution as a referential sensor to characterize solid surfaces. From the CDM, the practical parameter P *, called the adhesive wettability power, can be used in order to analyze and classify biomaterials.

Effect of gas evolution at solid-liquid interface on contact angle between liquid Si and SiO2

Abstract: The contact angle between liquid Si and SiO2 was measured with the sessile drop method at 1723 K. The contact angle changed very unusually due to the evolution of SiO gas at the solid/liquid interface. It was found that the real contact angle between liquid Si and SiO2 is about 80° or less at 1723 K though the apparent contact angle of 95° was observed for a long time during the experiment. The difference in the contact angle can be explained with a model of a composite material. Although the real contact angle is more important in a physical point of view, the apparent contact angle should be adopted in some cases such as simulation works.

The Modified Young's Equation for the Contact Angle of a Small Sessile Drop from AN Interface Displacement Model

Abstract: We derive the modified Young's equation for the contact angle of a fluid droplet on a rigid substrate using an interface displacement model and identify the line tension with the excess free energy per unit length calculated previously for a straight three-phase contact line

Effect of metal particles oxidation during the APS on the wettability.

Abstract: Investigations have been carried out to study the in flight oxidation of iron particles during Atmospheric Plasma Spray (APS) process The molten particles are quenched by an inert gas (argon) and collected in a experimental set-up especially developed for this purpose With this set-up, more than 90 wt% of the particles are collected Investigation methods such as XRD, Mossbauer spectroscopy and SEM-EDX are used to determine the amount and the distribution of oxide formed The results indicate that wustite (FeO) is present at the surface and also in the core of the particles This oxide phase represents about 12 wt% of the collected particles and is stable over time Sessile drop studies of molten iron on alumina and zirconia substrates are carried out to simulate the wetting of oxidized iron particles during coating formation It is found that the oxidation state of iron particles during APS has a significant effect on the observed contact angles A decrease of the contact angle is observed in the case of oxidized iron particles

Development and characterisation of Ag-Cu-Ti brazes prepared with planar flow casting

Abstract: Using the technique of rapid quenching from the melt, it becomes possible to prepare active brazes of Ag–Cu–Ti composition with varying silver content for joining alumina ceramics, involving a single technological operation in the form of ribbons up to 40 mm wide and 50–100 μm thick. The melting temperature of the alloys increased with decreasing silver content, in agreement with the phase diagram. The wetting of the alumina by the brazes, determined by the sessile drop method, has been satisfactory for all alloys. The ceramic/ceramic joints attain high joint strengths above 150 MPa. Microchemical and structural investigations of the reaction interlayer (alumina/Ag–Cu–Ti/alumina joint) have been performed using x-ray spectroscopy, EDX analysis and scanning electron microscopy. By transmission electron microscopy and electron diffraction the structures formed in the reaction zone of the joint have been determined. It has been found that the reaction zone near alumina consists of TiO while the zone further from alumina, rich in Ag–Cu, contains mainly the mixture of Ti 2 O 3 and Cu 2 O.

Nucleation at surfaces: the importance of interfacial energy.

Abstract: The nucleation and growth of stone-forming minerals on the surfaces of other crystalline phases, cellular material, and immobilized macromolecules must be important in the formation of stones in the urinary tract. The nucleation and growth of calcium oxalate monohydrate (COM) crystals were studied using the constant composition kinetics technique, in solution supersaturated with respect to COM (sigmaCOM = 1.44). The solid phases during the reaction were examined by x-ray diffraction, scanning electron microscopy, and diffuse reflectance Fourier transform infrared spectroscopy. Human serum albumin was found to nucleate COM crystals when immobilized on hydroxyapatite (HAP) surfaces. The induction period for nucleation of COM on HAP surfaces preadsorbed with albumin significantly decreased to about 65 min from about 230 min for pure HAP particles. The initial growth rate of COM on pure HAP particles, Rm approximately/= 0.56 X 10(-7) mol/min per m2, was slower than that for HAP surfaces preadsorbed with albumin, 2.14 x 10(-7) mol/min per m2. The surface properties were characterized using contact angle measurements by sessile drop and thin layer wicking. The thermodynamic results suggested that surfaces with high Lewis base parameter values (gamma-) and low interfacial tension with water (gammaSL) are more effective in the nucleation and growth of crystal phases.

The effect of surface preoxidation of sintered silicon carbide on its wettability by silver–copper based brazing alloys in vacuo

Abstract: The sessile drop method has been used to determine time dependence of contact angle at 850°C in vacuo for Ag–28wt.%Cu, Ag–35wt.%Cu–1.5wt.%Ti and Ag–22wt.%Cu–12wt.%In–2wt.%Ti on pressureless sintered SiC in the as-polished and high temperature preoxidized conditions. Contact angle was independent of time for the Ti-free alloy and was increased from 137 to 161 or 162° by preoxidising the SiC. Contact angle decreased with time when Ti was present typically from 80 to 110° initially to 5 to 20° after 90 min at 850°C, again values being higher for the preoxidised condition. These behaviours are attributed to the effects of preoxidation in replacing the thin amorphous silica film on the polished surface by a thicker crystalline film which retards the action of Ti in promoting the wettability desired for brazing purposes.