Wettability of SiC and alumina particles by liquid Bi under liquid Al

In this paper a new experimental method to measure contact angle of liquid metals on solid particles under an immiscible second liquid metal is described. This includes efficient mixing of the three-phase system (two immiscible liquid metals with solid dispersed particles) with subsequent solidification. The micrographs of the cross sections of samples are analyzed for the distribution of the particles between the bulk of the two metals and the interface between them. As an alternative, exact positions of the particles can be measured at the interface between the two solidified metals. These two measurements are used to estimate the contact angle of one liquid metal on the solid particles under another, immiscible liquid metal. As an example, contact angle of a liquid Bi-rich alloy on SiC and alumina particles is measured under liquid Al-rich alloy. The liquid Bi-rich alloy was found to wet perfectly (with zero contact angle) alumina particles under liquid Al-rich alloy, while the contact angle on SiC is found to be around 88°. These contact angle data are shown to be relevant to control the stability of liquid metallic emulsions formed between the two immiscible liquid metals stabilized by the solid particles.     

Drop detachment and motion on fuel cell electrode materials

Liquid water is pushed through flow channels of fuel cells, where one surface is a porous carbon electrode made up of carbon fibers. Water drops grow on the fibrous carbon surface in the gas flow channel. The drops adhere to the superficial fiber surfaces but exhibit little penetration into the voids between the fibers. The fibrous surfaces are hydrophobic, but there is a substantial threshold force necessary to initiate water drop motion. Once the water drops begin to move, however, the adhesive force decreases and drops move with minimal friction, similar to motion on superhydrophobic materials. We report here studies of water wetting and water drop motion on typical porous carbon materials (carbon paper and carbon cloth) employed in fuel cells. The static coefficient of friction on these textured surfaces is comparable to that for smooth Teflon. But the dynamic coefficient of friction is several orders of magnitude smaller on the textured surfaces than on smooth Teflon. Carbon cloth displays a much smaller static contact angle hysteresis than carbon paper due to its two-scale roughness. The dynamic contact angle hysteresis for carbon paper is greatly reduced compared to the static contact angle hysteresis. Enhanced dynamic hydrophobicity is suggested to result from the extent to which a dynamic contact line can track topological heterogeneities of the liquid/solid interface.     

Love type waves in a porous layer with irregular interface

The dispersion equation is derived relating to the frequency and the phase velocity of propagation of Love waves in a nondissipative liquid filled porous solid underlain by an isotropic and homogeneous half space. The rectangular irregularity in the interface between the upper porous layer and the lower semi-infinite medium with a source in it is studied herein. The modified dispersion equation of Mal and the standard dispersion equation of Love waves are deduced as particular cases. In the present study, the frequency equation is obtained by applying the method of perturbation and the phase velocity curves have been drawn for different irregularities by using the numerical parameteric values as suggested by Biot.     

Non-isothermal injection molding with resin cure and preform deformability

In this paper, a non-isothermal model to simulate some injection molding processes used to fabricate composite materials is deduced. The model allows the solid constituent in both the dry and the wet region to deform during infiltration. The dry porous material is assumed to behave elastically, while the mixture of resin and preform is assumed to behave as a standard linear solid. The model also takes into account the fact that the liquid undergoes an exothermic cross-linking reaction during infiltration and eventually gels stopping the infiltration process. Focusing then on one-dimensional problems it is shown that the integration of the mechanical problem in the uninfiltrated region can be reduced to the integration of an ordinary differential equation defining either the space-independent volume ratio or the location of the infiltration front, depending on whether the flow is driven by a given infiltration velocity or by a given inlet pressure. The remaining system of partial differential equations in the two interfaced and time-dependent domains is then posed with the proper interface and boundary conditions. After writing the problem in a Lagrangian formulation fixed on the solid constituent, domain decomposition techniques are used for the simulation.     

Control of the degree of pore-opening for porous metals

A mechanism-based analytical model for calculating the Degree of Pore-Opening (DPO) of porous metals processed via negative pressure infiltration method is developed. The emphasis is placed on predicting the dependence of DPO on the infiltration pressure difference, particle size, surface tension, and wetting angle between liquid metal and particles. Experimental measurements are subsequently performed to check the accuracy of model predictions, and it is shown that the proposed model can be used to quantitatively control the microstructure of porous metals during infiltration processing.     

Direct measurement of drainage curves in infiltration of SiC particle preforms: influence of interfacial reactivity

We present dynamic measurement of drainage curves in two systems having relevance to metal matrix composite processing, namely SiC/Al and SiC/Al-12.2at%Si. Data show that liquid/solid chemical reactions that cause a lowering of the contact angle do indeed drive spontaneous ingress of metal into the preforms at fixed applied pressure; however, these also hinder infiltration under continuous infiltration, lower pressurization rates causing a reduced level of penetration by the metal at given pressure. Metal/reinforcement chemical interactions that can drive wetting by lowering the contact angle are, therefore, not necessarily beneficial in the pressure infiltration processing of particle reinforced metals.     

Wetting and capillarity in the Sn/graphite system

Aiming to investigate the role of wettability in the infiltration of tin into graphite particle compacts, sessile drop and infiltration experiments have been carried out at temperatures in the range of 300–700 °C. The surface tension of liquid tin and the contact angle at the tin/graphite interface have been measured in an argon atmosphere by means of the sessile drop technique, while pressure infiltration of Sn into compacts of graphite particles (27.2 μm of average diameter) has been carried out in air. The results indicate that the threshold pressure for infiltration is proportional to the work of immersion, as predicted by the capillary law. The particle geometric factor derived from the slope of the straight line is similar to that obtained previously from infiltration of aluminum. Although these results may indicate that the oxide layer that covers the tin surface plays a minor role in the infiltration process, a definitive conclusion may require a more detailed analysis of this interesting system.     

乳化炸药结构模型的计算

乳化炸药的结构是影响乳化炸药性能的主要参数，许多结构参数如渗透压，单位体积界面积等的计算对乳化炸药结构的理解很有意义。该文采用伽辽金方法求解Ｌａｐｌａｃｅ－Ｙｏｕｎｇ方程，对简化后的单分散体系进行计算。获得了平均曲率，接触角，体积分数，接触面积分数，单位体积界面积等参数之间的关系，并提出了接触角不为零时的渗透压表达式。     

Wetting behaviour of lead-free Sn-based alloys on Cu and Ni substrates

The present work was carried out in the framework of the study of new lead-free solder alloys for technical applications in electronic devices. In the focus of this characterisation the wetting behaviour of several Sn-rich alloys belonging to the In–Sn, Au–Sn and Cu–Sn systems has been studied by measuring the contact angle variations on Cu and Ni substrates as a function of time and temperature. The interface between the alloy and the substrate has been analysed by the use of optical microscopy and scanning electron microscopy combined with energy-dispersive X-ray spectrometry in order to study the reaction between the alloy and the solid substrate and the possible formation of different compounds at the interface. A remarkable effect of the two different substrates on the behaviour of the contact angle as a function of temperature and on the morphology of the interface between the liquid solder and the solid substrate was observed for the In–Sn and Cu–Sn, while the Au–Sn system shows a very similar wetting behaviour on Cu and Ni.     

Wetting ability of biological liquids in presence of metallic nanoparticles

The wetting ability of water and of some biological liquids was measured on different biocompatible surfaces with and without different colloidal metals. Insoluble nanoparticles disperse in biological tissues enhance some properties, such as the interface adhesion between two surfaces, the X-ray contrast of medical images and the absorbed dose during radiotherapy treatments. The introduction of nanoparticles in the liquids generally improves the wetting ability and changes other properties of the solution, due to the different distribution of the adhesion forces, to the nature, morphology and concentration of the added nanoparticles. An investigation on the contact angle of the liquid drops, physiological liquids, including the human blood, placed on different substrates (polymers, ceramics and metals) with and without the use of metallic nanoparticles is presented, evaluated and discussed.     

多孔金属通孔度的控制

依据多孔金属的渗流制备原理,建立了控制通孔度的理论计算模型,研究了压差△Ｐ,球状填料半径Ｒ、金属液的表面张力σ以及金属液／颗粒间澜有θ对通孔度Ｉ的影响规律,实验证实该模型与实验结果良好吻合,可用于渗流法制备多孔金属时通孔度的定量控制。     

Evolution equation for nonlinear Scholte waves

The evolution equations for nonlinear Scholte waves (finite amplitude elastic waves propagating along liquid/solid interface), which account for the second order nonlinearity of a liquid, are derived for the first time. For mathematical simplicity the nonlinearity of the solid, which influence is expected to be weak in the case of weak localization of the Scholte wave, is not taken into consideration. The analysis of these equations demonstrates that the nonlinear processes contributing to the evolution of the Scholte wave can be divided into two groups. The first group includes nonlinear processes leading to wave spectrum broadening which are common to bulk pressure waves in liquids and gases. The second group includes the nonlinear processes which are active only in the frequency down-conversion (leading to wave spectrum conservation or narrowing), which are specific to the confined nature of the interface wave. It is demonstrated that the nonlinear parameters, which characterize the efficiency of various nonlinear processes in the interface wave, strongly depend on the relative properties of the contacting liquid and solid (or, in other words, on the deviation of the Scholte wave velocity from the velocities of sound in liquid and in solid). In particular, the sign of the nonlinear parameter responsible for the second harmonic generation can differ from the sign of the nonlinear acoustic parameter of the liquid. It is also verified that there are particular liquid/solid combinations where the nonlinear processes, which are inactive in the frequency up-conversion, dominate in the evolution of the Scholte wave. In this case distortionless propagation of the finite amplitude harmonic interface wave is possible. The proposed theory should find applications in nonlinear acoustics, geophysics, and nondestructive testing.     

Effect of Melt Superheating Treatment on Directional Solidification Interface Morphology of Multi-component Alloy

The influence of melt superheating treatment on the solid/liquid (S/L) interface morphology of directionally solidified Ni-based superalloy DZ125 is investigated to elucidate the relationship between melt characteristic and S/L interface stability. The results indicate that the interface morphology is not only related to the withdrawal velocity (R) but also to the melt superheating temperature (Ts) when the thermal gradient of solidification interface remains constant for different Ts with appropriate superheating treatment regulation. The interface morphology changes from cell to plane at R of 1.1 μm/s when Ts increases from 1500°C to 1650°C, and maintains plane with further elevated Ts of 1750°C. However, the interface morphology changes from coarse dendrite to cell and then to cellular dendrite at R of 2.25 μm/s when Ts increases from 1500°C to 1650°C and then to 1750°C. It is proved that the solidification onset temperature and the solidification interval undergo the nonlinear variation when Ts increases from 1500°C to 1680°C, and the turning point is 1650°C at which the solidification onset temperature and the solidification interval are all minimum. This indicates that the melt superheating treatment enhances the solidification interface stability and has important effect on the solidification characteristics.     

Generalized Rayleigh-Lamb equation

The dynamics of the vapor-liquid interface when a solid particle heated to a high temperature comes into contact with a cold liquid is analyzed. The generalized Rayleigh-Lamb equation taking into account temperature changes in the liquid and the vapor, the saturation vapor pressure change associated with it, and the emergence of the mass flux due to liquid evaporation at the interface is deduced. At medium parameters far from the critical point, the generalized Rayleigh-Lamb equation reduces to its well-known form. Around the critical point, the difference between the obtained equation and arising modes of changes of the vapor-liquid interface can be rather considerable. Unlike the well-known Stefan problem, far from the critical liquid temperature, the phase transition temperature and, respectively, the saturation vapor pressure change with the vapor-liquid interface movement, which yields various modes of dynamics of the vapor cavity. In the special case of small variations from the stationary mode, an analytical solution for the problem on a small change in the vapor cavity radius with time was developed.     

Morphologies and Superhydrophobicity of Hybrid Film Surfaces Based on Silica and Fluoropolymer

Fluoropolymer and different kinds of silica particles were used for controlling surface chemistry and morphology, respectively. A superhydrophobic surface originated from strawberry-like or quincunx-shaped composite silica particles was obtained. The dual size particles are obtained by utilizing the graft of different modified silica particles with epoxy functional group and amine functional group, This makes the surface of film form a composite interface to have irregular binary structure which plays an essential role in trapping air between the substrate surface and the liquid droplets to be necessary for high contact angle and low contact angle hysteresis. The maximum contact angle for water on the hybrid film is about 174±2° and the contact angle hysteresis is less than 2°. The surface morphologies, roughness and the wettability on the surface of films containing different structural silica particles were compared. It was shown that the hierarchical irregularly structure with a low roughness factor and high air-trapped ratio is indispensable for superhydrophobic surface. Although this structural surfaces based on composite silica particles play a vital role in governing the surface wettability, it is necessary to combine with a low surface energy to make the surface superhydrophobic.     

Nanobubbles at Water-Solid Interfaces: Calculation of the Contact Angle Based on a Simple Model

Nanobubbles have been found to form at the interface of water and solid surfaces. We examine the conditions for such bubbles to form and estimate the pressure inside the bubble based on thermodynamic considerations. Using a simple model we calculate the contact angle for a wide range of temperatures and hypothetical substrates possessing a continuous range of strengths. We show that as the temperature increases the shape of a bubble changes continuously from a spherical cap with low curvature to a complete sphere. An equivalent effect results from either increasing the strength of the solid or decreasing the surface tension. A model of a substrate formed by layers of materials is proposed to obtain a nanobubble with a particular contact angle.     

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

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.     

Designing of antibacterial plastics: thymol release from photocured thymol-doped acrylic resins

Antibacterial thymol-doped plastics can be prepared by photopolymerisation of solutions of thymol in tripropylenglycoldiacrylic monomer. The antibacterial properties of these doped plastics depend on the thymol release rate and this study reports results about the release of thymol from doped resin discs in different media under different conditions. Thymol-doped resin can release thymol in air, even though at a much slower rate than pure thymol in the form of solid powder. In particular. it has been found that the rate of release of thymol in air is mainly dependent on the temperature and on the thymol content in the resin. On the other hand, when a thymol-doped resin is put in contact with liquids, the rate of diffusion of thymol into surrounding liquids depends mainly on the chemical nature of the liquid, other than on the thymol concentration in the resin. In particular, the release is affected by the capability of the liquids to swell the resin and by the plasticizing effect of thymol. The release of thymol can be quantitatively described by a Weibull-type equation up to complete release of thymol.