Showing papers on "Sessile drop technique published in 1986"

Wettability of some metals against zirconia ceramics

Abstract: The wetting of ceramics by liquid metals and alloys is a major factor controlling the effectiveness of brazing which is used extensively in the joining of ceramics [1, 2]. The wettability of the molten metals against the ceramics can be investigated by measuring the contact angle, 0, between the peripheral surface of a small sessile drop of molten metal and the horizontal surface of the ceramics substrate as shown in Fig. 1. The angle, 0, is related to the solid and liquid surface energies, ?st and 7LG, and the solid-liquid interfacial energy, 7SL by the Young's equation

Comparison of surface tension measurements using the levitated droplet method

Abstract: Measurements of the surface tension of some metals by the levitating drop technique have been carried out by two independent laboratories in order to establish the levels of agreement. Results obtained for pure iron, cobalt, and copper showed reasonable agreement, but in the case of stainless steel, significant differences were apparent, which were shown to be a consequence of the different hydrogen concentrations in the respective environmental gases. Surface tension values for pure gold obtained by this method showed good agreement with the data obtained by established methods and show that the levitating drop technique is capable of yielding reliable results.

Wetting of TiC-Wc system carbides with molten Ni3Al

Abstract: In this work an investigation was made of the wettability of titanium and tungsten carbides and also of (Ti, W)C solid solutions by the molten intermetallic compound Ni/sub 3/Al, which has been used for some time as a binder for sintered carbides. The wetting process was investigated using the stationary variation of the sessile drop method in vacuum on a special induction unit with an Alundum tube enveloping a graphite fabric one, which serves as the heating body. The carbide-intermetallide contact zone was investigated by optical microscopy and micro-x-ray spectral analysis. The investigations conducted showed the possibility in principle of creation of compact TiC-WC pseudobinary system carbide-Ni/sub 3/Al intermetallide composites produced by liquid-phase sintering. Diagrams and table are included.

Physicochemical principles of the formation of composite materials based on titanium diboride

Abstract: Adhesion of iron-based alloys (Fe-Ni, Fe-Cr within the concentration range of 2 to 30 wt.% Ni or Cr) to titanium diboride has been studied using the sessile drop technique. The energy parameters of wetting, work of adhesion and interfacial surface tension have been calculated. The structure and phase compositions of the contact area of interaction have been investigated by metallographic methods and energy dispersive X-ray microanalysis. The given iron-based alloys have been found to be promising as binding metals for composite materials based on titanium diboride.

Interfacial tension and flotation characteristics of liquid metal-sodium flux systems

Abstract: Interfacial tensions between two liquid phases are discussed based on Dupre’s and Good’s equations. Thermodynamically, it is argued that the interfacial tension will always be less than the sum of the surface tensions of the two pure phases. The interfacial tensions between different metals and sodium fluxes were measured using the sessile drop technique combined with X-ray radiography. The metal-flux systems studied were Ag, Bi, Cu, Pb, and Sn with NaF, NaCl, Na2CO3, Na3AlF6, and Na2OSiO2. The interfacial tension decreased with temperature for all the systems studied. For a given flux, the highest value of the interfacial tension was obtained for the system with the largest value of the surface tension of the metal. The average value of Good’s interaction parameter was 0.31 for metals and sodium fluxes. The lowest value of the interaction parameter was obtained when using cryolite as flux.

Electrocapillarity in the aluminum reduction cell

Abstract: The effect of the current density on the interfacial tension between aluminum and cryolite containing melts was measured based on the sessile drop method and an X-ray radiographic technique. The experiments were carried out under constant current densities in graphite crucibles with BN lining. When the aluminum drop was the cathode, the interfacial tension was almost independent of the current density. During electrolysis, the interfacial tension increased with decreasing NaF/AlF3 ratio in a similar manner to that observed when no electrolysis was performed. The interfacial tension between aluminum and an electrolyte containing between 5 to 10 wt pct A1F3, 5 wt pct CaF2, and 5 wt pct A12O3 is 690 ± 60 mN/m for cathodic current densities between 0.1 and 0.6 A/cm2. Interruption of electrolysis caused an instantaneous decrease in the interfacial tension followed by a slow increase with time. This sudden drop together with a decrease in interfacial tension with reversal of cell polarity indicate that the metallic side of the interface has an excess positive charge. The interface was enriched with NaF during electrolysis as indicated by the slow recovery of the interfacial tension after current interruption.

Contact angle and surface tension measurements of a five-ring polyphenyl ether

Abstract: Contact angle measurements were performed for a five-ring polyphenyl ether isomeric mixture on M-50 steel in a dry nitrogen atmosphere. Two different techniques were used: (1) a tilting plate apparatus, and (2) a sessile drop apparatus. Measurements were made for the temperature range 25 to 190 C. Surface tension was measured by a differential maximum bubble pressure technique over the range 23 to 220C in room air. The critical surface energy of spreading (gamma (sub c)) was determined for the polyphenyl ether by plotting the cosine of the contact angle (theta) versus the surface tension (gamma (sub LV)). The straight line intercept at cosine theta = 1 is defined as gamma (sub c). Gamma (sub c) was found to be 30.1 dyn/cm for the tilting plate technique and 31.3 dyn/cm for the sessile drop technique. These results indicate that the polyphenyl ether is inherently autophobic (i.e., it will not spread on its own surface film until its surface tension is less than gamma (sub c). This phenomenon is discussed in light of the wettability and wear problems encountered with this fluid.

Determination of mechanical properties of the egg by the sessile drop method.

Abstract: Publisher Summary This chapter discusses the mechanical properties of the egg by the sessile drop method. The stiffness expressed by the different parameters depends on various mechanical properties of the cell components, for example, the surface force, rigidity of the cortex, intracellular pressure, or rigidity of endoplasmic structures. The surface force is determined from the degree of deformation of the egg under a gravitational or centrifugal force, the density difference between the egg protoplasm and the surrounding medium, the size of the egg, and the magnitude of the gravitational or centrifugal acceleration, using relationships obtained from the form of a theoretical sessile drop. A simple and accurate method to determine the density of the egg protoplasm is by the “isopycnotic method”. The chapter discusses possible errors and limitations of the sessile drop method in determining the surface force of the sea urchin eggs. It stated that neglecting the rigidity of the endoplasm may not introduce serious errors in surface force determination in unfertilized sea urchin eggs. In fertilized eggs, however, the errors may be larger because structures having considerable rigidity such as the sperm aster or mitotic apparatus are formed in the endoplasm. It is supposed that the density of the protoplasm is practically uniform in echinoderm eggs because eggs do not display any orientations in gravitational fields.

Surface Energy as an Indicator of Interfacial Mechanical Response

Abstract: Contact angles between silicon and a variety of silicon carbide-based fibers have been measured and correlated to the mechanical behavior of the fiber-matrix interface. Infiltration by the molten silicon into the fibers and/or reaction with excess carbon to form silicon carbide gives rise to low contact angles and high toughness interfaces. It is suggested that the high toughness of the interface is morphology-controlled.