Liquid Migration Research Articles

Kinetics of the formation of metal binder gradient in WC–Co by carbon diffusion induced liquid migration

Cemented tungsten carbide (WC–Co) with a cobalt content gradient from the surface to the bulk of a sintered piece is an example of a functionally graded material, the mechanical properties of which are optimized by the unique gradient microstructure, giving rise to superior combinations of wear resistance vs. fracture toughness. A process for creating such cobalt gradients in WC–Co was developed recently based on heat treatments of fully sintered WC–Co materials in carburizing atmospheres. A study of the kinetics of the process is necessary to fully understand the mechanisms of the process in order to achieve desired or designed gradients. In this paper, a series of carburizing experiments were conducted to examine the effects of key process parameters including temperature, composition of the atmosphere, and time on the overall kinetics of the process. A kinetic model was established to predict the thickness of the gradient as a function of these process variables, enabling the design of functionally graded WC–Co through controlling atmosphere and time.

Swelling of Rubber under Nonuniform Stresses and Internal Migration of Swelling Liquid When the Stresses Are Removed

As shown by Treloar, the degree of swelling of a rubber sample is strongly affected by applied stress. His work suggests that the degree of swelling will vary from point to point in a sample, in accordance with the local stress field. Thus, when rubber sheets are bent, they are expected to swell more on the tension side and less on the compression side, and when the bending constraint is removed, recovery toward the initial flat state is expected to be only partial at first and then followed by a slow further recovery. These effects are explored here for natural rubber sheets swollen by dodecane. The measured “set” following release from bending is found to be in accord with simple swelling theory. The time dependence of later recovery is shown to be in agreement with the rate of diffusion of the swelling liquid. It is concluded that internal migration of compatible liquids will cause temporary delays in deformation kinetics and make a significant contribution to energy losses. Also, the bending experiment itself appears to provide a simple and generally applicable method for determining the internal diffusion coefficients of absorbed liquids.

Influence of Liquid Phase Migration on Intermittent Extrusion of Aqueous Al<sub>2</sub>O<sub>3</sub> Paste

Extrusion Freeform Fabrication Process (EFF) is an environmentally friendly solid freeform fabrication method that uses aqueous pastes to fabricate ceramic-based components. The Liquid Phase Migration (LPM) causes variation in liquid content and consequently problems in the paste extrusion. To get uniform ceramics parts with desired composition, the LPM should be avoided in extrusion process. This paper investigated the influence of LPM on extrusion process for aqueous alumina paste in EFF process. It shows that the liquid phase migration occurs in Freeform Extrusion Fabrication process and has a strong impact on extrusion pressure. The LPM can be characterized by the extrusion pressure-ram displacement profiles. The liquid phase migration becomes more serious in intermittent extrusion at low ram velocity.

Inhomogeneous deformation of elastomer gels in equilibrium under saturated and unsaturated conditions

A variational method is employed to obtain governing equations and boundary conditions describing finite strain equilibrium configurations of elastomeric gels. Three situations are considered: a liquid saturated gel, an unsaturated gel, and a gel in equilibrium with a vapor of its own liquid. Surface tractions can lead to equilibrium transitions between these cases. The liquid saturated gel is regarded as immersed in a liquid bath. If this bath becomes depleted, then the gel is unsaturated. The degree of unsaturation – a measure of the amount of liquid that would restore a state of saturation – affects the subsequent mechanical behavior. If the unsaturated system is further allowed to condense or evaporate its liquid component at the gel surface, then a new state of equilibrium is achieved. The transition between the unsaturated case and the case of being in equilibrium with the vapor phase corresponds to the chemical potential variable of the gel changing its value from one that is determined by a volume constraint to the value of the chemical potential in the vapor phase. A finite element method is created on the basis of the variational method and demonstrated in the context of eversion, a deformation that imposes very large finite strains. Liquid migration within the gel is not modeled as our focus is on equilibrium states that occur after all such non-equilibrium processes come to rest.

Extrusion–spheronisation of highly loaded 5-ASA multiparticulate dosage forms

The aim of the current work was to develop an extrusion–spheronisation (E–S) route to manufacture pellets with a high loading (≥90 wt%) of 5-aminosalicylic acid (5-ASA). Ram extrusion studies, supported by centrifuge testing, were employed to investigate the effect of the chemical (acidity) and physical (particle size and shape) characteristics of 5-ASA on the ability of microcrystalline cellulose (MCC)-based pastes to retain water when subjected to pressure. Liquid phase migration (LPM) within the paste during the extrusion, and hence variation in water content of extrudates and reproducibility of the final E–S product, was generally observed. The extent of LPM was found to be related to both the drug loading and its physical properties, most notably the particle shape (needle-like). A reduction in particle size, combined with a change in the shape of the 5-ASA particles, allowed LPM to be reduced considerably or eliminated. The performance of colloidal grades of MCC (Avicel RC591 and CL611) as alternative extrusion aids to the standard Avicel PH101 was also investigated: these proved to be superior aids for the highly loaded 5-ASA pastes as their greater water retention capacity mitigated LPM. Combining these results yielded a route for manufacturing pellets with 5-ASA loading ≥90 wt%.

Microstructural evolution in the partial transient liquid phase diffusion bonding of Zircaloy-4 to stainless steel 321 using active titanium filler metal

Microstructural evolution of the partial transient liquid phase diffusion bonded Zircaloy-4 and stainless steel 321 using an active Ti-base interlayer were studied at different temperatures. Additionally, simple analytical models were developed to predict the evolution of the interlayer and intermetallics during the bonding operation. Bonds were characterized by scanning electron microscopy and energy dispersive X-ray spectrometry. Precision measurement of the interlayer width was made as a function of the bonding temperature. The liquid film migration occurred as a result of chemical solubility differences between the stable and metastable phases. The formation and growth model of the intermetallic compounds at the interfaces of Zircaloy-4/Ti-base interlayer and stainless steel 321/Ti-base interlayer for controlling the bonding process was studied considering the diffusion kinetics and the thermodynamics. The evolution of the interlayer thickness indicated a good agreement between the calculation and experimental measurement. It was also demonstrated that the low isothermal solidification kinetic was not only due to the enrichment of the liquid phase with the base alloying elements such as Ti and Zr, but also the reduction of solid solubility limit of Cu in the base alloys contributed to the reduction of isothermal solidification kinetic.

Molecular-dynamics study of solid–liquid interface migration in fcc metals

In order to establish a link between various structural and kinetic properties of metals and the crystal–melt interfacial mobility, free-solidification molecular-dynamics simulations have been performed for a total of nine embedded atom method interatomic potentials describing pure Al, Cu and Ni. To fully explore the space of materials properties three new potentials have been developed. The new potentials are based on a previous description of Al, but in each case the liquid structure, the melting point and/or the latent heat are varied considerably. The kinetic coefficient, μ, for all systems has been compared with several theoretical predictions. It is found that at temperatures close to the melting point the magnitude of μ correlates well with the value of the diffusion coefficient in the liquid.

Numerical simulation of surfactant-enhanced remediation of heterogeneous aquifer contaminated with nonaqueous phase liquids

A three-dimensional, multiphase, multicomponent compositional simulator was employed to simulate nonaqueous phase liquid (NAPL) migration during surfactant-enhanced aquifer remediation (SEAR) in spatially correlated heterogeneous fields. Aquifer heterogeneity was accounted for by considering the permeability to be a spatially random variable, and a geostatistical method was used to generate random distributions of the permeability. Spatial distributions of saturations in the NAPL and temporal changes of organic recovery, effluent concentrations of organics and surfactant, and pressure drop at the injection well for heterogeneous aquifers were compared with those in a homogeneous aquifer to examine the effects of different levels of heterogeneity. Variations in permeability fields have a pronounced effect on the organic recovery efficiency due to the long-term persistence of nonaqueous phase liquid and additional dispersion. Permeability heterogeneity also leads to the tailing off of effluent organic concentrations and significant loss in injectivity over the remediation period. For a small slug of surfactant, surfactant-enhanced remediation resulted in a relatively small improvement in the recovery of NAPL, especially in highly heterogeneous aquifers. Migration of high-concentration organic plumes to other layers by crossflow was also found to have a significant influence on SEAR behavior.

Influence of Clay Lens on Migration of Light Nonaqueous Phase Liquid in Unsaturated Zone

This study concerns the control of movement of light nonaqueous phase liquid (LNAPL) in unsaturated zone in the presence of relatively low permeability clay lens. A two-dimensional, finite-difference numerical model for the simultaneous movement of LNAPL and water through the unsaturated zone of the soil has been developed. The system is a three fluid phase system (water, LNAPL, and air) but in the derivation of the model, air was treated as an immobile phase at constant atmospheric pressure. The flow equations for LNAPL and water were cast in terms of the wetting and non-wetting fluid pressure heads, respectively. The finite-difference equations were solved implicitly with explicitly scheme using Newton-Raphson iteration with Taylor series expansion to treat nonlinearity. A physical model to represent the infiltration of kerosene above the clay lens was constructed. The numerical results were compared with those observed experimentally. The results of all tests showed that the presence of clay lens controls the vertical movement of LNAPL in heterogeneous porous medium.

The effect of fabric structure and yarn-to-yarn liquid migration on liquid transport in fabrics

Wicking experiments were carried out on a range of cotton and polyester fabrics, which exhibited differences in terms of yarn size, thread spacing, and yarn type. Wicking coefficients in the warp and weft direction as well as for the constituent warp and weft yarns were determined using image analysis technique in which height of liquid front was measured as a function time. Results showed that the wicking in fabrics is determined by the wicking behavior of the yarns, the thread spacing, and, more importantly, the rate at which liquid migrates from longitudinal to transverse threads and again from transverse threads back to longitudinal threads. This yarn migration phenomenon, which has not received significant attention in the past, was studied by measuring the gain in wicking coefficient and the equilibrium wicking height and by actual visualization of the wicking process. Fabric wicking rates were found to be directly associated with yarn wicking behavior. Inter-yarn spaces were found to exert a major influence on fabric wicking behavior.

Modeling of the hygrothermal absorption and desorption for underground building envelopes

The hygrothermal storage characteristics of an underground building envelope have discernible effects on the heat and humidity of the indoor environment. To predict the hygrothermal storage capacity, it is necessary to accurately calculate the transient heat and moisture flux through the envelope. This paper describes the development of a new hygrothermal model described with relative humidity and temperature based on the results of existing researches. The moisture model fully states actual moisture transfer process involving both vapor diffusion and liquid water migration in porous building envelopes. Verified using the results calculated by the mathematical model of Mendes et al., the new hygrothermal model can accurately predict the heat and moisture transfer of building envelopes. Hygrothermal absorption and desorption of three types of common underground building envelopes in Chengdu region in China are analyzed by using the new model. The results show that the hygrothermal absorption and desorption of underground building envelopes must be considered when the heat and moisture environment is controlled by HVAC. Taking account of these factors can reduce air-conditioning equipment capacity and save running energy. Copyright © 2010 Elsevier B.V. All rights reserved.

Control of the Composition Profile of Tungsten-Copper Functionally Graded Materials for Fusion Technology Application

This work aims to process W-Cu FGM for fusion material applications, in particular plasma facing components (PFC). Currently, PFCs are made by multi-material assembly and rely on tungsten armour tile (high heat flux side) which needs to be cooled by the attachment to a heat sink (Cu-alloys). The interfaces in multi-material assembly are unfavourable for the application (high working temperature, thermal fatigue). The use of FGM can be a new promising way. The aim of this study is to analyze the effect of a composition/grain size variation on the liquid phase migration during liquid phase sintering of FGM, in order to control the final composition profile. Bi-layer materials are processed by powder metallurgy route. W-Cu compositions with 10 and 20wt%Cu and with different W-particle sizes are processed starting with attritor-milled W-CuO powder mixtures which are reduced at 350°C. Analysis of copper liquid phase migration for different composition/grain size associations indicates that the phenomenon is driven by differential sinterability in the gradient. The copper liquid migration depends on the differences in sinterability, on the available liquid and open porosity in the structure beyond the melting point of copper. From these analyses, a way to control the gradient profile of W-Cu structure can be proposed.

Effect of starch on extrusion behaviour of ceramic pastes

Starch was used as extrusion aid in the form of solid in different silicon nitride paste formulations. The effect of starch addition on extrusion behaviour of ceramic pastes such as liquid phase migration and extrusion force was investigated. The extrusion behaviours were evaluated by the curves of extrusion force versus extrusion time in a piston-type extruder. The results showed that paste with an appropriate amount of starch can effectively avoid liquid phase migration while surprisingly lowering the extrusion force to a certain extent. The reasons can be attributed to the strong hydrophilic character and lubrication role of starch particles. The mechanism for plasticity improvement of ceramic paste by starch inclusion in the form of solid is put forward for the first time.

Analysis of Casing-Shift Problems in Compacting Reservoirs

Summary In the past, casing-shift problems were thought to be one of the causes of production decline. This motivated field engineers to investigate whether or not casing shift occurred by shooting radioactive bullets in productive layers and measuring the relative movement of casing and formation (Allen 1984). However, the results were ambiguous because of the uncertainty of wireline-logging depth measurements during a long reservoir-compaction period. In this paper, the following will be investigated: How the bonding of casing and formation breaks under confining stresses How a casing slides after the bonding breaks The magnitude of shear force required to induce casing shift The magnitudes of casing shift for typical reservoir conditions To achieve the above objectives, the following laboratory measurements were performed: Construct test samples simulating casings bonded to formation with cement and mudcake. Conduct experiments measuring shear force required to induce casing shift under confining stress. Simulate the correlation of depth and shear and normal stresses around a cased hole using a finite-element model for compacting reservoirs. Compare the results of experiments with simulations to judge the magnitude of casing shift. The laboratory experiments showed that a casing does not simply slip when a shear load is applied. It accompanies shear failure of cement sheath. Hence, when casing shift occurs, shear fractures are also induced in the cement, which may cause gas or liquid migration through the fracture network. Calculations are performed to estimate the shear stress induced at casing/cement and formation/cement interfaces during reservoir compaction using a finite-element-simulation model. Comparing the laboratory-measured sliding shear stress with the calculated shear stress, it is concluded that a small casing slippage may occur at casing/cement and formation/cement interfaces. The amount and distribution of slippage along casing/cement and formation/cement are also evaluated for typical reservoir conditions. The small slippage may be serious enough to reduce production. Hence, reperforation at the expected shift intervals would recover productivity. In addition, the small slippage creates a shear fracture network that may cause gas or liquid migration. Several standard cement tests are described in Nelson and Guillout (2007). This work complements two previous works (Evans and Carter 1963; Ladva et al. 2004) for casing/cement and formation/cement bond strengths using similar cement. Previous work determines cement shear and hydraulic-bond strengths for those with small reservoir compaction, while this work focuses on cement-bond strength for more-severe compactions where casing slippage or failure are initiated. Unlike the standard hydraulic and shear cement bond tests, the current test method closely simulates the in-situ conditions, clarifying the phenomena occurring during casing slippage. In addition, a rule of thumb and a practical method to evaluate the magnitude of casing shift are proposed.

Saturation evolution induced by inner pore structural effects in a porous material during wetting

A series of experiments was conducted to observe the transport phenomena in wood during wetting using a micro CT (scanning analysis technology). Both saturation evolution and corresponding liquid transfer are nondestructively investigated for both pendular and funicular mode at pore structure level in porous media. A method was proposed to obtain the important real inner structure information of porous media, as well as saturation profile and evolution, and corresponding liquid migration. From experimental observations, the pendular and funicular mode could be identified distinctly, and their transport behavior induced by inner structural effects was explored based on local pore structural information. And particularly, the dynamical saturation evolution and corresponding existence of distinct accumulation states were further discussed for the pendular mode.

Development of lateral flow membranes for immunoassay separation

The lateral flow nitrocellulose membrane is one of the commonly used separation media for bacteria detection in drinking water treatment facilities. In order to enhance its performance, control of the membrane surface and cross-section morphology is primarily important. The challenge of this study is to combine various formulations and casting variables to obtain lateral flow nitrocellulose membranes with the desired morphologies. Through the dry-phase inversion method, the drying temperature was found to be an important parameter in synthesizing membranes as it affects pore structures. A high drying temperature causes agglomeration of the polymer matrix, and thus smaller pores were observed on the membrane surface. This further decreases the membrane lateral liquid migration rate, besides reducing the membrane binding ability for bacteria detection. Results show that by decreasing polymer concentration, membrane surface pores became apparently larger, thus creating a faster lateral migration speed of the water solution. A larger pore size increases the chance for the bacteria detecting agent to bind onto the pore layers, which ultimately enhances the bacteria detection ability of the device.

LIQUID PHASE MIGRATION IN EXTRUSION OF AQUEOUS ALUMINA PASTE FOR FREEZE-FORM EXTRUSION FABRICATION

Freeze-form Extrusion Fabrication (FEF) is an additive manufacturing technique that extrudes highly ceramic loaded aqueous paste along 3D contours for complex ceramic part fabrication. The phenomenon of liquid phase migration (LPM) in paste extrusion process will result in variation of liquid content in paste and consequently problems in processing and non-uniform properties of ceramic parts. It is necessary to understand the LPM phenomenon in FEF process. In this paper, the effect of liquid phase migration on extrusion of aqueous alumina paste was investigated for FEF process. The water content and extrusion force data were collected for a series of ram velocities. According to the extrusion force profiles, the extrusion process can be divided into four stages: compaction stage, transient stage, steady stage and dead zone stage. The results show that ram velocity is the key parameter for occurrence of liquid phase migration phenomenon and there is a velocity threshold above which the liquid phase migration will not happen.

Investigation of NAPL transport through a model sand cap during ebullition

AbstractNonaqueous‐phase liquid (NAPL) migration from sediments to the surface of water bodies has been reported frequently at sites with sediments contaminated with NAPLs, such as coal tar and creosote. Commonly, transport of NAPL from sediment is facilitated by gas ebullition caused by anaerobic biodegradation of organic matter in the sediment. A remedy often specified for these sites is a sand cap, and sand caps amended with sorbent materials (such as organoclays) are being pilot‐tested. This article discusses a laboratory study to assess the effectiveness of a sand layer for controlling NAPL migration. The study used a test column composed of a Plexiglas tube containing a tar source that was buried beneath a 30‐cm‐thick layer of fine sand. Water was added to the column until 5 cm of standing water covered the sand layer. To simulate ebullition, air was injected into the base of the sand column at approximately 200 mL/min. It was observed that the gas and NAPL migrated primarily through channels and fractures in the sand, and was not filtered through a network of stable pores. Tar migrated through the sand layer in 12 hours and accumulated on the water surface for several hours before losing its buoyancy and settling back down to the sand surface. After ending the tar migration experiment, the test column was frozen to preserve structures in the sand. The study showed that the tar migrated through the simulated sand cap in small (2‐mm) channels only a few sand grains thick. The results of this laboratory work call into question the effectiveness of sand caps for controlling NAPL migration from sediment in the presence of ebullition. © 2009 Wiley Periodicals, Inc.

Stress-induced destabilization of solidification and melting fronts

The morphological evolution of the initially planar solidification and melting fronts of a thin liquid film in a stressed binary alloy has been investigated when diffusion only proceeds in the liquid phase. A linear stability analysis has been performed and the diffusion-controlled evolution of the shape of both fronts has been characterized. The destabilizing effect of stress on the profiles of the interfaces has been identified for a liquid film at rest when the solid is submitted to constant stress and when it is migrating, due to stress gradient, in the hypothesis where concentration field of solute satisfy Laplace’s equation. The possibility of roughness formation in the early beginning of the development of the solid–liquid interfaces has been finally discussed for alloys in the context of a liquid film migration mechanism.

Effect of nonlinear flow on DNAPL migration in a rough‐walled fracture

Experiments were carried out to investigate the influence of the groundwater flow regime on dense nonaqueous phase liquid (DNAPL) migration in a rough‐walled fracture. Hydraulic and DNAPL migration experiments were performed at Reynolds numbers ranging from 0 to 60.8. Nonlinear groundwater flow occurred in the fracture from Reynolds number of approximately 10. Different migration paths taken by DNAPL were observed between linear and nonlinear flow regimes. Experiments were quantitatively analyzed using the modified invasion percolation (MIP) model, which was found to be attributed to the inertial force of flowing groundwater. The MIP model was reformulated to incorporate the effect of inertia to predict the DNAPL migration path in a rough‐walled fracture. The model data provided a good match to the experimentally determined DNAPL migration. The studies indicated that DNAPL migration depended on the groundwater flow regime, which needs to be considered in order to better understand DNAPL migration in rock fractures.