High Interfacial Energy Research Articles

Factors Affecting the Formation of Ba2Ti9O20

The phase development sequence based on a composition equivalent to Ba2Ti9O20 during heating is found to be in the following order: BaTi5O11 > BaTi4O9 > Ba2Ti9O20. The lowest rate of formation of Ba2Ti9O20 is caused by its high surface energy and interface energy, which result in a low nucleation rate. The existence of BaTi5O11 in calcined powder helps to form Ba2Ti9O20 in sintered compacts. The effect of BaTi5O11 on Ba2Ti9O20 formation can be explained by their similar oxygen packing and by reduced volume change during transformation. The amount of BaTi5O11 formed during heating depends greatly on the compositional homogeneity of powders. The addition of SnO2 aids the formation of Ba2Ti9O20 by reduced strain energy at transformation and reduced surface energy.

Microstructures of directionally frozenin situ composites of multicomponent eutectics

Microstructural variations of binary (Sn-Pb, Sn-Cd, Pb-Cd), ternary (Sn-Pb-Cd) and quaternary (Sn-Pb-Cd-Zn) eutectics which were permitted to solidify directionally were investigated in terms of the controlled solidification rates. It was found that, at an appropriate freezing rate, the structure was lamellar and satisfied the Jackson-Hunt relationship, and furthermore, that the order of the layers present in the solidified eutectics was definite, such that in the case of Sn-Pb-Cd ternary eutectic alloy, for instance, the Sn-Cd layers would not be allowed to be in contact. An explanation for this could be the high interfacial energy between the two.

Surface restructuring of polymeric solids and its effect on the stability of the polymer—water interface

Polymeric solids possess the distinct capacity to alter their surface structures between different environments in order to minimize their interfacial free energy with a surrounding medium and thereby minimize the free energy of the system as well. This can sometimes lead to very low values of polymeric solid—environmental fluid interfacial free energies. Under such conditions, the solid—fluid interface is likely to become unstable to mechanical and/or thermal perturbations and this interfacial instability can promote the occurrence of undesirable effects such as the absorption of the fluid into the solid and/or the dissolution of the solid in the fluid. The above considerations were investigated on three types of polymeric surfaces, namely, control Teflon FEP, sputtered Teflon, and chemically etched-sputtered Teflon, which gave rise to high, medium, and low interfacial free energies with water, respectively, as a result of their surface restructuring in the aqueous environment. The dynamics of surface restructuring of the three surfaces under water were followed by measuring the changes in the contact angles of water drops on the solid specimen under octane, as a function of time. The solid—water interfacial free energies of the specimen were estimated by a suitable contact angle procedure which was developed for characterizing the wetting properties of such mobile surfaces in an aqueous environment. Based on the dynamics of solid surface restructuring under water and the contact angle procedure, it was seen that, only in the case of the chemically etched-sputtered solid surface (which reduces its interfacial free energy with water to a very low value as a result of its surface restructuring in the aqueous environment), the polymeric—solid interface becomes unstable and gives rise to the penetration of water into the solid and the possible dissolution of the solid in water. These contact angle results were well supported by the physicochemical characteristics of the different polymer surfaces used in this study.

A new method for the determination of the precipitate-matrix interfacial energy

The experiment described in this paper yields a reasonable value of ..gamma cap alpha../delta' which is also in agreement with values calculated from coarsening data when corrections are made for volume fraction effects. This experimental procedure should be applicable to any system where nucleation is coherent, transformation strains are small and a particle size distribution can be established near grain boundaries while the solute concentration remains constant. It might be possible to extend this to more general situations. For example, when interfacial energies are highly anisotropic, it might be possible to get an approximation of ..gamma.. for the high energy interface by assuming it determines the thermodynamic stability at temperature. Finally, due to the need to image rather small particle sizes accurately in the TEM, the technique would be restricted to precipitates that are ordered, exhibit discrete diffraction spots or are of much larger atomic number than the matrix. Alternatively, lattice imaging techniques could be used rather than conventional CDF images if smaller precipitates have to be detected.

Evaluation of Rubberized Limestone Filler in Asphalt Paving Mixtures

Abstract The method of direct dispersion of small amounts of rubber particles in asphalt binder was associated with difficulties in controlling degradation, mix uniformity, oxidation, and noxious fumes generated by grinding rubber. This study showed that asphalt cements can be modified by adding carboxylated butadiene rubber chemically bound to calcium carbonate to give a wide range of products of different compositions and consistencies. These rubberized fillers can disperse more rapidly in the hot asphalt during the mixing operation and require no adjustments or changes in conventional mixing practices. The conclusions that can be drawn from the experiments conducted include the following: 1. The relatively high stiffening effect of rubberized filler on the F/A binder system is related to its high surface activity or interfacial energy. Limiting values of viscosity increase in F/A binder systems were developed from the effective volume concentration values of rubberized filler to keep resistance to compaction of asphalt paving mixtures within desirable limits. 2. The surface of limestone filler chemically reacted with rubber is rendered more hydrophobic. This results in a pronounced reduction in the stripping of asphalt aggregate surfaces. For uncoated limestone filler, however, the stripping potential increased with the increase of immersion time in water. 3. Temperature susceptibility is decreased by adding rubberized limestone filler to asphalt. 4. Initially, the increase in the RL/L ratio of filler used in the sand-asphalt mixture causes an increase in Marshall stability. After a critical limit (corresponding to the critical effective volume concentration of the fillers in the F/A system), however, the stiffening offers significant resistance to compaction, causing the Marshall stability to decrease. 5. The addition of rubberized filler in RL/L ratios up to 40/60 by weight significantly improved the tensile strength properties of the sand-asphalt mixtures. 6. The values of retained tensile strength after different moisture conditioning methods indicate greater adhesion for mixtures containing rubberized filler up to a RL/L ratio of 40/60 by weight.

Rabbit arterial endothelium and subendothelium. A change in interfacial free energy that may promote initial platelet adhesion.

Endothelial damage and exposure of the subendothelium is accompanied by platelet adhesion and aggregation. Thermodynamically, adhesion will occur if this process decreases the total free energy of the system. In this investigation, we have developed a contact angle technique to measure relative changes in the surface free energy of the arterial wall, before and after the endothelium has been removed. Sections of descending thoracic aorta from seven rabbits were tested with an equilibrium two-phase system of 4% polyethylene glycol (mol wt: 20,000)/4% dextran (mol wt: 2,000,000) in Hepes-buffered physiological saline. The tissue was split longitudinally, immersed in the polyethylene glycol phase, and test droplets of the denser dextran phase were placed on its surface. Advancing contact angles of the drop were measured from photomicrographs taken with polarizing optics. After testing, the endothelium was removed with a saline jet, which we had calibrated previously with scanning electron microscopy, and the tissue was retested. We measured angles of 86.0 +/- 1.1 degree (SEM), n = 64 for the intact endothelium and 20.0 +/- 0.8 degree (SEM), n = 61 on the subendothelial surface. Since the physical behavior of blood is probably similar to our polyethylene glycol bathing medium the subendothelium may also represent a surface of high interfacial free energy in vivo. Assuming that the surface energy of platelets is low, platelet adhesion to the subendothelium could reduce the total free energy of the system, by covering this high interfacial free energy surface.

Reducing the grain size of polycrystalline lead films by the use of barriers to grain growth

The mechanical strength of lead-alloy films used in Josephson junctions is improved by reducing the grain size. One way to achieve this goal is to reduce the rate of grain growth. The activation energy for barrierless growth during vapor deposition was estimated to be about 540 cal/mole for lead films and is assigned to the ordering of atoms. Because of its small value, instead of reducing the rate of grain growths, it seemed best to stop growth by the application of a barrier layer. This is followed by the nucleation of new grains. Five requirements for a barrier-to-grain growth are given out of which the requirement of a high interfacial free energy between barrier and lead is stressed the most. In the experiments Nb, PdSn4, AuIn2, and PdIn3 were used as barriers between lead layers. The grain size of layered films was determined by transmission electron microscopy and was found to be about the same as if the total film thickness were equal to the thickness of one layer. Yet there are small differences between the different barrier layers; their effectiveness increases as their melting points increase. This is because all the requirements for a barrier-to-grain growth suggested in this paper are the better fulfilled the higher the melting point. Some of the layered films were tested for hillock formation due to thermal cycles between room temperature and 4.2 K; on some of them, the superconducting transition temperature was measured and nuclear backscattering spectra taken.

Sand beach energetics: An ecosystem approach towards a high energy interface

General results of a study of energetics on open sandy beaches in South Africa are presented. These sand beaches are considered to interact with adjacent terrestrial environments via the sand dune system and with the sea via the surf zone. A food web is given for the macrofauna showing all known interactions from the supply of food material to the beach, mainly from the sea, to the removal of the macrofauna by birds and fishes. An energy circuit diagram is presented quantifying the main energy flows through this system of filter feeders and scavengers. The interstitial biota of these beaches is considered separate from the macrofauna and consists of bacteria, protozoa and meiofauna feeding on dissolved and particulate organics flushed into the beaches by wave and tide action. Interstitial energy flow and nutrient cycling rates are quantified in an energy circuit diagram. It is suggested that nutrients regenerated by this latter system in the intertidal and surf zone, as well as by the activities of the macrofauna, have sufficient residence times in the surf zone to cause blooms of surf zone phytoplankton which in turn are the main food for the intertidal filter feeders. In this respect the beach and surf zone may represent a more closed system than previously thought. A combined energy circuit diagram is given depicting the beach and surf zone as an ecosystem with the surf zone phytoplankton the producers, the macrofauna the consumers and the interstitial fauna the decomposers. Main imports and exports as well as the consequences of this ecosystem approach are discussed.

Silver Migration in Glass Dams between Silver-Palladium Interconnections

It is shown that two mechanisms are encountered in metal migration in glass-a platelike and treelike growth mechanism. The treelike growth, requiring a much higher interfacial energy contribution, is favored by high voltage application. The interaction of these two mechanisms accounts for the unexpected voltage and gap dependence of the niigration rate. The location of the metallic growth has been established as being in the volume of the glass. Significant differences exist in the electrical characteristics of the substrates of different manufacturers. After the application of glass dams these differences become less pronounced.

Precipitation hardening of aluminum alloys

The author’s charge was to discuss recent trends in research and development on precipitation hardened aluminum alloys and to indicate where research is needed. This will be done for three areas: fatigue, properties of grain boundaries and interfaces, and stability of precipitates at elevated temperatures. Present strong precipitation hardened aluminum alloys do not have high endurance limits. One problem is that the small GP zones are cut by the dislocations giving rise to highly localized deformation which aids fatigue crack initiation. A duplex structure with relatively large uniformly spaced precipitates to give more homogeneous deformation plus small precipitates to give high yield strength is a promising approach. The structures of precipitation hardened aluminum base alloys are essentially controlled by the stabilities of the various precipitates and the interfacial energies. Precipitates with high interfacial energies tend to precipitate preferentially at grain boundaries giving embrittlement. Low interfacial energy means easy nucleation, a uniform precipitate distribution, and resistance to coarsening at elevated temperatures. For elevated temperature use, the precipitate must be stable at elevated temperatures. Precipitation hardened aluminum alloys do not have good elevated temperature properties because the hardening precipitates normally used, GP zones, are not stable at elevated temperatures. Thus a low interfacial energy, ductile precipitate, which is stable at elevated temperatures, is needed for aluminum. Possibilities for achieving such precipitates will be discussed.

Mechanism of alumina buildup in tundish nozzles during continuous casting of aluminum-killed steels

During continuous casting of aluminum-killed steels, the pouring rate through the tundish nozzle often diminishes, posing serious operating problems. This happens because a buildup of microscopic alumina particles at the nozzle orifice effectively decreases the nozzle orifice diameter and causes constriction of the liquid-steel pouring stream. There are two major aspects of the constriction problem: (1) the source of the depositing particles, and (2) the mechanism by which the particles deposit at the nozzle orifice. Detailed microscopic examination of the buildup of alumina particles in nozzles from various casting trials and petrographic examination of the nozzle refractory indicated that the particles depositing at the nozzle orifice were already present in the melt because of deoxidation and reoxidation processes. A model proposed herein explains why and how the alumina particles deposit and stay at the nozzle orifice. The model considers a microscopically thin boundary layer at the nozzle bore where the velocity of the liquid steel approaches zero. Particles passing close to the refractory surface and in the slow-moving boundary layer attach to the wall and to each other. The presence of eddy currents in and close to the turbulent boundary layer increase the particle to particle collision. Such collisions of the particles thrown from outer region of boundary layers with the already attached particles keep on dumping the particles toward the refractory surface. The high interfacial energy of alumina inclusions in steel is a driving force for particles to attach to the refractory wall and to each other, and high-temperature sintering then occurs to form a network of alumina particles.

Melting temperature and enthalpy of isotactic polypropylene

The fusion process, melting temperature and heat of fusion of carefully crystallized fractions of isotactic polypropylene (molecular weights from 5·4 × 10 4 to 2·2 × 10 5) have been investigated. The equilibrium melting temperature, obtained by the extrapolation method in experiments involving very low degrees of crystallinity, corresponds to 208°. The fusion enthalpy was found to be 1·386 cal/mole. This low value and the high depression of Tm o suggest a relatively high interfacial energy; a value of 285 erg/cm 2 is estimated for σ ec .

The Preparation of a Haifnium-Free Magnesium-Zirconium Alloy by Process Separation of Hafnium

Magnesium zirconium alloy for sheathing uranium elements in gas-cooled reactors was successfully prepared from high-purity magnesiumt and zirconium produced by the magnesium reduction of a crude oxide. Hafnium separation, suggested by a higher ratio Hf to Zr in the sludge than in the melt was considered possible owing to its higher density and melting point and its isomorphous behaviour to the strongly electropositive zirconium which readily forms compounds and exhibits a two-phase melt when added in excess of 0.5 per cent. Precipitation of excess zirconium by settling was aided by the development of a flux of high density and low inclusion-flux interfacial energy. Removal of hafnium and other high neutron capture cross-section impurities was achieved.

Resistance to ship's motion: A natural law newly discovered

All-solid-state lithium batteries (ASSLIBs) employing sulfide solid electrolyte hold high promise to replace traditional liquid-electrolyte LIBs due to their high safety and energy density. However, Li dendritic growth in sulfide electrolyte limits the realization of the high energy of ASSLIBs. In this work, we use LiF (or LiI) layer at the interface between Li and sulfide electrolyte and penetrated HFE (or I solution) inside of sulfide electrolyte to suppress the Li dendrite growth. Due to the higher interface energy of LiF/Li than that of LiI/Li, LiF interlayer show much higher capability than LiI in suppressing the Li dendrite. Even if the Li dendrite breaks through LiF (or LiI) interlayer, the Li dendrites will be consumed by coated/penetrated HEF (or I) forming LiF (or LiI) thus preventing Li dendrite growth. A LiNbO3 @LiCoO2/Li7P3S11/Li ASSLIB employing HFE coated/infiltrated Li7P3S11 glass-ceramic as electrolyte, and LiF coated Li metal as anode shows a high reversible discharge capacity of 118.9 mAh g−1 at 0.1 mA cm−2 and retains 96.8 mAh g−1 after 100 cycles. The designed solid electrolyte interphase between Li and solid electrolyte that has a high interface energy to Li provides new opportunity to commercialize the Li metal batteries.