Competitive Absorption of Polar and Non-Polar Liquids into Latex Bound Porous Structures of Fine Ground Calcium Carbonate

Fine calcium carbonate is frequently used as coating pigment, e.g. in paints, paper and board. Emulsion polymer latex provides a typical binder incorporated in such coatings. Exposure of the resulting porous structure to liquid, depending on latex concentration level, results in ab- and adsorption as the liquid is drawn into the structure by capillarity and the nature of the relative surface chemistry of the pores. Previous work has shown that typical coating structures act to separate oil components according to their surface energy characteristics and solubility index in respect to pigment surface and intra-latex diffusion. This study considers water and alkane (hexadecane) as model liquids. Absorption rate into compressed tablets of ground calcium carbonate is observed with and without the presence of latex. Polyacrylate dispersant used in manufacture renders the pigment surface both hydrophilic and hygroscopic and, therefore, controls the differential dynamic wetting characteristics of the porous structure for either polar or non-polar liquid. In competition with hexadecane saturating the pore structure of a latex-free sample, polar water is seen to displace the non-polar liquid instantaneously, causing disintegration of the packed porous structure. In the presence of latex binder, however, the structurally destructive pressure this creates is contained, and retardation of the polar water is observed. The required pre-wetting action of water vapour diffusion on the polyacrylate pigment surface is considered to be an integral part of the successful competition between oil and water in the offset printing process, as non-polar oil absorbs steadily into a water pre-saturated structure.     

Relating Liquid Location as a Function of Contact Time Within a Porous Coating Structure to Optical Reflectance

Refractive index differences between a first and a second fluid can be utilised to obtain information about the location and amount of the fluids in a porous medium in the case where the light absorption coefficient of the skeletal material is small and the light scattering coefficient high using optical measurement methods. An example of such a medium is an air-filled paper coating, and the fluid that of a printing ink liquid phase absorbing into the coating during printing. We examined capillary absorption of mineral oil, used in offset printing ink, into model coatings compressed from dispersed mineral pigments with a range of latex binder levels, and established a porosity-normalised relationship for light reflectance change as a function of absorbed mass of the liquid established at a given time after initial contact with the liquid. The results suggest a significant change in reflectance due to the absorption, and progressive absorption behaviour of the liquid in the coatings can be monitored by the change in reflectance following a newly established relationship derived from the observational data. The findings support the concept of a preferred pathway flow for the wetting front, defined by differential pore size and connectivity, and a longer time saturation front flow lagging behind the wetting front, which theoretically at the limit of infinite time coincides with the wetting front, the time constant of the approach being related to the permeability of the porous network.     

Influence of Porosity on Ultra-High Vacuum Gas-Tightness in Cold-Sprayed Aluminum Coatings

Vacuum chambers used in high-energy particle accelerator experiments are conventionally made of bulk beryllium, which shows significant drawbacks due to cost and toxicity. An alternative solution could be to develop chambers made of polymer-based composites. Since these materials exhibit high outgassing not compatible with an ultra-high vacuum environment, a suitable gas-tight coating is required. Cold spray deposition of aluminum can be a solution, provided that the coating behaves as a perfect vacuum barrier. Porosity, especially percolating porous networks, is key to coating gas tightness issues. This work addresses the relationship between porosity and gas-tightness in cold spray coatings. To do so, coatings with different porosity were achieved playing with powder morphology, composition, and process parameters. Their gas tightness was evaluated by helium leak tests. Classical microscopy, being essentially a 2D analysis, is strongly limited when dealing with 3D properties as porosity percolation. For this reason, 3D X-ray microtomography images of coatings were obtained and treated by image analysis methods: pores were compared in terms of size and shape. Overall porosity properties, including percolation and a homogeneity criterion, were also investigated. Percolating porosity was highlighted for several samples which showed poor gas-tightness properties. The permeability of percolating pore structures was then numerically computed by a fast Fourier transform-based method, to quantify the mass flow through the coating. Results of those computations were finally compared to experimental coating leak rate measurements, in an effort to elucidate the link between gas tightness and morphology of the pore space.

     

Flow boiling enhancement of FC-72 from microporous surfaces in minichannels

The microporous coatings can remarkably enhance the liquid boiling heat transfer. Therefore, they are promising to be introduced into minichannels in the design of the cooling system of high-power microchips. However, the flow boiling heat transfer characteristics from microporous surfaces in the minichannels have not been extensively studied, and the pertinent knowledge is rather fragmentary. The present research is an experimental investigation on flow boiling of a dielectric fluid FC-72 from microporous coating surfaces in horizontal, rectangular minichannels of 0.49, 0.93 and 1.26 mm hydraulic diameter. Effects of coating structural parameters, such as the particle diameter and coating thickness, were investigated to identify the optimum microporous coating for heat transfer enhancement. All microporous surfaces in this paper were found to significantly enhance FC-72 flow boiling heat transfer in minichannels. With the optimum coating, the heat transfer coefficients could be 7-10 times those of the uncoated surface, and the boiling wall temperature was reduced by about 10 K. The flow boiling phenomena in the present minichannels were distinctly different from those in conventional-sized channels, due to the wall confinement effect on vapor bubbles. The confinement effect was evaluated by taking the contributions of the liquid mass flux and channel size into consideration. It was found that the very strong confinement effect was unfavorable with respect to flow boiling enhancement of the microporous coatings in the minichannels.     

PREPARATION AND PROPERTIES OF ULTRAFINE COMPOSITE POWDERS OF Fe_3O_4 AND Ni/MICA

This paper presents the preparation of ultrafine powders of Fe3O4 and Ni by a chemical method, followed by mixing the prepared powders with mica and other ultrafine powders for synthesizing microwave absorption coatings. The microwave attenuation rate of the coatings was measured by the Microwave Network Analyzer in the frequency range of 8-12 GHz at room temperature. The results indicate that microwave could be absorbed by the coatings with an effectiveness strongly dependent on the powder sort and content and the coating thickness.     

Achieving Rapid Absorption and Extensive Liquid Uptake Capacity in Porous Structures by Decoupling Capillarity and Permeability: Nanoporous Modified Calcium Carbonate

Porous media with rapid absorption properties are greatly sought after in the fields of super absorbers and catalysts. Natural materials, such as diatomite, or synthetic zeolite feature strongly in industrial reaction processes. Most, or all, of such materials, however, are surface acidic. A novel rapidly absorbing alkaline porous structure, with a high absorption capacity, is presented here. As in the case of diatomite or zeolite, the pigment design incorporates strong capillarity within a highly permeable packed medium. A model is proposed for general use with highly absorbing media that can be proven microscopically to have separate domains of micro- or nano-capillarity embedded within a permeable matrix. The new pigment morphology, based on natural ground calcium carbonate (gcc), exhibits this property using special surface structure modifications. It is contrasted with standard gcc by using consolidated tablet blocks made from a suspension of the pigment and chosen mixtures thereof. The blocks are characterised after drying by mercury porosimetry, and the absorption dynamic of a selected liquid is studied. It is shown that using a self-assembly method of discrete pore structures provides a much faster absorption rate and a liquid capacity for up to 10 times more fluid than a conventional homogeneously distributed pore concept. In such unique discrete network systems, the mercury intrusion curve provides a separable analysis of permeability and capillarity in respect to the inflection point of the cumulative intrusion curve. The discrete decoupled properties each follow the absorption behaviour predicted by previous modelling (Ridgway and Gane, Colloids and Surfaces A: Physicochemical and Engineering Aspects, 206(1–3), 2002). The absorption driving force is shown to be determined by the proportion of fine pores present up to a size equal to a Bosanquet inertially-defined optimum within the timescale of absorption. Combining the wetting force, from the capillarity-controlled fine pore structure, with the experimental flow resistance of the sample, consisting of the assembly of particles, it is possible to predict the trends in absorption dynamic using the pore and throat model Pore-Cor.* Use of this model allows existing materials as well as new synthetic designs to be modelled prior to manufacture. The novel alkaline material is compared with independent absorption data for diatomite and shown to be comparable. *Pore-Cor is a software product name of the Environmental and Fluid Modelling Group, University of Plymouth, Devon PL4 8AA, U.K.     

石英添加量对搪瓷涂层微观结构及摩擦磨损性能的影响

采用一次浸搪法制备石英添加量为0%、4%、8%和12%的搪瓷涂层,通过HSR-2M型高速往复摩擦试验机测试涂层摩擦学性能,SEM和EDS分别表征涂层微观组织和磨损形貌,并分析磨损机理. 结果表明:搪瓷涂层中石英添加质量分数为0%和4%时,涂层气孔率大、气孔密度低,摩擦时形成的微裂纹易沿着气孔间最短距离方向扩展,硬质磨屑转移至摩擦对偶表面而使涂层磨痕底部形成尖锐的凹槽,磨损形式主要为磨粒磨损和脆性断裂. 而石英添加质量分数为8%和12%的涂层气孔率小、气孔密度高,其中8%添加量涂层的孔径分布更加均匀,磨损率及磨痕深度仅为未添加涂层的1/3. 摩擦过程中孔径均匀的小尺寸气孔增大了裂纹扩展时所需的能量势垒而阻碍裂纹扩展,磨屑被气孔拦截后在磨损表面形成密实的堆积层,避免了摩擦对偶与涂层的直接接触而起到减摩作用,磨损形式主要为磨粒磨损.      

An Analysis of Three-Phase Pore Occupancies and Relative Permeabilities in Porous Media with Variable Wettability

In three-phase flow, the macroscopic constitutive relations of capillary pressure and relative permeability as functions of saturation depend in a complex manner on the underlying pore occupancies. These three-phase pore occupancies depend in turn on the interfacial tensions, the pore sizes and the degree of wettability of the pores, as characterised by the cosines of the oil–water contact angles. In this work, a quasi-probabilistic approach is developed to determine three-phase pore occupancies in media where the degree of wettability varies from pore to pore. Given a set of fluid and rock properties, a simple but novel graphical representation is given of the sizes and oil–water contact angles underlying three-phase occupancies for every allowed combination of capillary pressures. The actual phase occupancies are then computed using the contact angle probability density function. Since a completely accessible porous medium is studied, saturations, capillary pressures, and relative permeabilities are uniquely related to the pore occupancies. In empirical models of three-phase relative permeability it is of central importance whether a phase relative permeability depends only on its own saturation and how this relates to the corresponding two-phase relative permeability (if at all). The new graphical representation of pore sizes and wettabilities clearly distinguishes all three-phase pore occupancies with respect to these saturation-dependencies. Different types of saturation-dependencies may occur, which are shown to appear in ternary saturation diagrams of iso-relative permeability curves as well, thus guiding empirical approaches. However, for many saturation combinations three-phase and two-phase relative permeabilities can not be linked. In view of the latter, the present model has been used to demonstrate an approach for three-phase flow modelling on the basis of the underlying pore-scale processes, in which three-phase relative permeabilities are computed only along the actual flow paths. This process-based approach is used to predict an efficient strategy for oil recovery by simultaneous water-alternating-gas (SWAG) injection.     

The Constitute Law of Gas Seepage in Rock Fractures Undergoing Three-dimensional Stress

This paper is based on the research we have done in recent years of the constitute law of gas seepage in rock fractures. Both experiments and theoretical derivations will be discussed. The gases used in our experiments include methane and CO₂, both of which are highly adsorptive. The experiments were conducted mainly in coal fractures. The results reveal that the permeability coefficient of gas in rock fractures varies parabolically with respect to fracture pore pressure. When the pore pressure is below a certain value, the permeability coefficient decreases while the pore pressure increases. It is different from the water seepage law in fractures. Analysis shows that this abnormality is caused by adsorption. It is also concluded that the tangent deformation has the same effects as normal deformation on gas seepage law. The permeability of gas in fractures has a negative exponent relationship with both normal deformation and tangent deformation.     

浸油碳化物衍生碳润滑涂层的承载机制研究

采用高温氯化处理工艺在碳化硅表面制备了具有多孔结构的碳化物衍生碳涂层(CDC),考察了浸油(聚a烯烃,PAO)对CDC涂层承载性能的影响.结果表明:在低载(5 N)下,浸油前后涂层的摩擦磨损性能相当,随着载荷的增加,尤其是在中等载荷(~10 N)下,浸油涂层的摩擦性能变差,表现为较大的摩擦系数与磨损.分析认为CDC涂层的孔洞被PAO填充,其孔壁在摩擦过程中受到载荷应力与液压的双重作用而破碎,是导致浸油CDC涂层磨损加剧,承载能力大大降低的主要原因.     

A Multiscale Network Model for Simulating Moisture Transfer Properties of Porous Media

A multiscale network model is presented to model unsaturated moisture transfer in hygroscopic capillary-porous materials showing a broad pore-size distribution. Both capillary effects and water sorption phenomena, water vapour and liquid water transfer are considered. The multiscale approach is based on the concept of examining the porous space at different levels of magnification. The conservation of the water vapour permeability of dry material is used as scaling criterion to link the different pore scales. A macroscopic permeability is deduced from the permeabilities calculated at the different levels of magnification. Each level of magnification is modelled using an isotropic nonplanar 2D cross-squared network. The multiscale network simulates the enhancement of water vapour permeability due to capillary condensation, the hysteresis phenomenon between wetting and drying, and the steep increase of moisture permeability at the critical moisture saturation level. The calculated network permeabilities are compared with experimental data for calcium silicate and ceramic brick and a good agreement is observed.     

Effect of Net Stress on Hydraulic Conductivity of Unsaturated Soils

This note presents results of a laboratory test program that examines the influence of pore volumes on soil water coefficient of permeability in different saturation conditions. Comparing the results, it is observed that the dependency of water coefficient of permeability to void spaces in unsaturated soils follow a different trend than associated in saturated state. The shift of the soil?Cwater characteristic curve within the change of pore spaces is utilized to qualify the opposite detected response of unsaturated water permeability to the change of pore spaces.     

纳米LaF3微粒对聚酰亚胺粘结固体润滑涂层摩擦学性能及抗腐蚀性能的影响

采用MHK-500型摩擦磨损试验机考察了含纳米LaFa微粒的聚酰亚胺粘结固体润滑涂层在干摩擦条件下同GCr15钢环配副时的摩擦学性能，评价了涂层的耐腐蚀性能，重点探讨了纳米LaFa填料对涂层耐磨性及耐腐蚀性能的影响．结果表明：含1％～2％纳米LaF3的涂层的耐磨性最佳，而纳米LaF3填料对涂层减摩性能的影响不大；含2％纳米LaF3的涂层的耐腐蚀性最好．     

等离子喷涂纳米和常规喂料WC-Co涂层在干摩擦和水环境中的摩擦磨损性能研究

采用大气等离子喷涂法分别以纳米和常规喂料制备出2种WC—Co涂层,在SRV摩擦磨损试验机上考察了2种涂层在干摩擦和水环境中的摩擦磨损性能．结果表明：在干摩擦和水环境中,纳米WC—Co涂层的摩擦系数和磨损率均小于常规WC—Co涂层;纳米和常规WC—Co涂层的磨损机制差异不大,在干摩擦下其磨损机制主要以粘着磨损、剥落和磨粒磨损为主;在水环境中,WC—Co涂层与Si3N4配副时的摩擦系数和磨损量较与不锈钢球配副时高,2种摩擦副的磨损机理有所不同,前者主要以剥落和疲劳磨损为主,后者主要以粘着磨损为主,伴有轻微的磨粒磨损．     

Map of regimes of pressure oscillations induced by absorption during gas jet injection through a submerged nozzle

Map of regimes of pressure oscillations induced by absorption during rapid injection of a soluble gas jet through a submerged nozzle into liquid, namely, oscillations during absorption, bubbling, internal chugging and small chugging, is suggested. Boundaries between various pressure oscillations regimes occurring when rapidly soluble gas is absorbed in water are investigated theoretically. It is showed that these boundaries are determined by four equations. It is showed that regime of high-frequency pressure oscillations during absorption occurs due to gas bubble oscillations, and other regimes of oscillations occur due to pressure oscillations in the whole system comprising the header, vent tubes and gas bubble. The conditions for excitation of high-frequency and low-frequency oscillations and boundaries between different regimes of pressure pulsations are determined. In a case when Henri's law for soluble gases is valid the developed model predicts that oscillations during absorption are not excited.     

纳米和微米TiO2对聚四氟蜡/聚氨酯复合涂层摩擦磨损性能的影响

制备出纳米和微米TiO2改性聚四氟蜡/聚氨酯复合涂层,采用傅立叶红外光谱仪分析其结构,在MHK-500型摩擦磨损试验机上考察复合涂层的摩擦磨损性能,采用扫描电子显微镜和光学显微镜观察分析复合涂层的磨损表面和偶件转移膜的分布情况.结果表明:纳米和微米TiO2可以增加聚四氟蜡/聚氨酯复合涂层的摩擦系数;5%纳米TiO2提高了聚四氟蜡/聚氨酯复合涂层的耐磨性;而添加微米TiO2则降低了聚四氟蜡/聚氨酯复合涂层的耐磨性能;同时,载荷和速度对纳米TiO2改性聚四氟蜡/聚氨酯复合涂层的摩擦磨损性能有很大影响,在低载荷、中速条件下复合涂层具有较好的耐磨性能.     

Experimental study of the osmotic behaviour of reverse osmosis membranes for different NaCl solutions and hydrostatic pressure differences

The osmotic behaviour of five different present-day reverse osmosis membranes was studied, using different NaCl solutions (<6 wt.%) and applying different hydrostatic pressure differences (<5.2 bar) between the high and low concentration sides. The osmotic water flux through the membranes was found to increase non-linearly with respect to the increasing concentration difference over the membrane, leading to non-constant values for apparent water permeability. The polyamide composite membranes studied resulted only in very weak osmosis for even relatively small hydrostatic pressure differences and for strong NaCl solutions. Asymmetric cellulose acetate membranes showed somewhat better osmotic behaviour. However, all the osmotic water fluxes measured were still far too small for practical application in the production of energy.     

Relative Permeability of Gas for Unconventional Reservoirs

Relative permeability of gas gains great significance in exploring unconventional gas. This paper developed a universal relative permeability model of gas, which is applicable for unconventional gas reservoirs such as coal, tight sandstone and shale. The model consists of the absolute relative permeability of gas and the gas slippage permeability. In the proposed model, the effects of water saturation and mean pore pressure on gas slippage permeability are taken into account. Subsequently, the evaluation of the model with existing model is done and then the validation of the model is made with data of tight sandstones, coals and shales from published literatures. The modeling results illustrate that a strong power-law relationship between relative permeability of gas and water saturation and the contribution of gas slippage permeability to relative permeability is determined by water saturation and mean pore pressure simultaneously. Furthermore, a sensitivity analysis of the impact of the parameters in the model is conducted and their effects are discussed.     

Investigation of Various Pressure Transient Techniques on Permeability Measurement of Unconventional Gas Reservoirs

Chloride ingress into concrete is a major cause for material degradation, such as cracking due to corrosion-induced steel reinforcement expansion. Corresponding transport processes encompass diffusion, convection, and migration, and their mathematical quantification as a function of the concrete composition remains an unrevealed enigma. Approaching the problem step by step, we here concentrate on the diffusivity of cement paste, and how it follows from the microstructural features of the material and from the chloride diffusivity in the capillary pore spaces. For this purpose, we employ advanced self-consistent homogenization theory as recently used for permeability upscaling, based on the resolution of the pore space as pore channels being oriented in all space directions, resulting in a quite compact analytical relation between porosity, pore diffusivity, and the overall diffusivity of the cement paste. This relation is supported by experiments and reconfirms the pivotal role that layered water most probably plays for the reduction of the pore diffusivity, with respect to the diffusivity found under the chemical condition of a bulk solution.     

A Numerical Model of Tracer Transport in a Non-isothermal Two-Phase Flow System for {\text{ CO}}_2 Geological Storage Characterization

For the purpose of characterizing geologically stored $\text{ CO}_{2}Air sparging is an in situ soil/groundwater remediation technology, which involves the injection of pressurized air through air sparging well below the zone of contamination. To investigate the rate-dependent flow properties during multistep air sparging, a rule-based dynamic two-phase flow model was developed and applied to a 3D pore network which is employed to characterize the void structure of porous media. The simulated dynamic two-phase flow at the pore scale or microscale was translated into functional relationships at the continuum-scale of capillary pressure?Csaturation (P ^c?CS) and relative permeability??saturation (K _r?CS) relationships. A significant contribution from the air injection pressure step and duration time of each air injection pressure on both of the above relationships was observed during the multistep air sparging tests. It is observed from the simulation that at a given matric potential, larger amount of water is retained during transient flow than that during steady flow. Shorter the duration of each air injection pressure step, there is higher fraction of retained water. The relative air/water permeability values are also greatly affected by the pressure step. With large air injection pressure step, the air/water relative permeability is much higher than that with a smaller air injection pressure step at the same water saturation level. However, the impact of pressure step on relative permeability is not consistent for flows with different capillary numbers (N _ca). When compared with relative air permeability, relative water permeability has a higher scatter. It was further observed that the dynamic effects on the relative permeability curve are more apparent for networks with larger pore sizes than that with smaller pore sizes. In addition, the effect of pore size on relative water permeability is higher than that on relative air permeability.