Water In Porous Materials Research Articles

Kinetics of confined water freezing – An application to the frost-resistance of porous materials

In the manuscript one presents a regular study aiming to determine the relation describing the freezing kinetics as a function of temperature employing the following cooling rates: 2.5 °C/min, 5 °C/min, 7.5 °C/min and 10 °C/min. The increase in ice mass is determined using differential scanning calorimeter by integrating the net heat flow for two building materials: red clay brick and cement paste (w/c = 0.5). The isoconversional method, which states that the transition rate (the rate of ice mass) at constant extent of conversion (ice mass) depends only on temperature, is applied to determine a transition model. We select the most appropriate model and determine the kinetic triplet using the method proposed by Málek and recommended by International Committee for Thermal Analysis and Calorimetry (ICTAC). The activation energy is estimated using the differential Friedman's method. Both analysed materials evinced different microstructures, but the kinetic parameters determined for both of them are relatively similar. Hence, one might conclude that the kinetic of inpore water freezing is not very sensitive to size of voids. The results of experimental analysis enabled one to formulate the general kinetic equations for both analysed materials. The comparison of theoretical and experimental results evinces good agreement. Therefore, the formulas derived in the manuscript might be used for further analysis of the porous building materials durability, which experience significant temperature fluctuations. Furthermore, they can be used to design the most efficient testing procedure for the determination of frost resistance of concrete. The proposed procedure might be used for other problems related with the phase transition of water in porous materials, i.e., food freezing geotechnics, etc.Concluding, the results calculated using the proposed models for both materials are in good agreement with the experimental data. Therefore, the formulas derived in the manuscript might be used for further analysis of the porous building materials durability, which experience significant temperature fluctuations. Furthermore, they can be used to design the most efficient testing procedure for the determination of frost resistance of concrete. The proposed procedure might be used for other problems related with the phase transition of water in porous materials, i.e. food freezing geotechnics, etc.

Investigation of the transport properties for saline water in porous materials - Modeling of the permeability coefficient for saline water-

Salt weathering is a major concern for cultural heritages such as ruins and tombs, and desalination by poulticing is an interesting potential method to efficiently remove contaminating salt. Predicting the degree of achievable desalination is very important. However, many existing models used to consider saline water transport in porous materials have been developed based on the theory of pure water. To understand saline water flow in porous materials, we determined the saline water permeability of a tuff stone by the falling-head method. We found that the permeability of the tuff stone was affected by factors other than the density and dynamic viscosity of the saline water.

Aqueous Flow Reactor and Vapour-Assisted Synthesis of Aluminium Dicarboxylate Metal-Organic Frameworks with Tuneable Water Sorption Properties.

Energy‐efficient indoors temperature and humidity control can be realised by using the reversible adsorption and desorption of water in porous materials. Stable microporous aluminium‐based metal–organic frameworks (MOFs) present promising water sorption properties for this goal. The development of synthesis routes that make use of available and affordable building blocks and avoid the use of organic solvents is crucial to advance this field. In this work, two scalable synthesis routes under mild reaction conditions were developed for aluminium‐based MOFs: (1) in aqueous solutions using a continuous‐flow reactor and (2) through the vapour‐assisted conversion of solid precursors. Fumaric acid, its methylated analogue mesaconic acid, as well as mixtures of the two were used as linkers to obtain polymorph materials with tuneable water sorption properties. The synthesis conditions determine the crystal structure and either the MIL‐53 or MIL‐68 type structure with square‐grid or kagome‐grid topology, respectively, is formed. Fine‐tuning resulted in new MOF materials thus far inaccessible through conventional synthesis routes. Furthermore, by varying the linker ratio, the water sorption properties can be continuously adjusted while retaining the sigmoidal isotherm shape advantageous for heat transformation and room climatisation applications.

Monitoring of the absolute water content in porous materials based on embedded humidity sensors

Moisture transport monitoring may indicate the onset of deterioration in porous building materials prior to damage occurring. Most moisture measurement systems provide only qualitative values, require extensive calibration, or are destructive. Thus, non-destructive and calibration-free monitoring systems are required. Our approach of moisture monitoring is to embed sensors that measure the relative humidity. In our experiment, screed samples are monitored during the hydration and evaporation process. Every test sample is equipped with 10 embedded sensors which measure the relative humidity across the sample thickness. Based on Hillerborg’s approach, the relative humidity is converted into the corresponding pore saturation. In our study, the free water is computed without knowledge of the sorption isotherm. The free water in the pore system is predicted and validated. The predicted weight decrease corresponds conclusively to gravimetrically measured weights. The embedded sensors yield the absolute liquid water content and enable an experimental, non-destructive monitoring of liquid water in porous materials.

Effects of microstructure on water imbibition in sandstones using X‐ray computed tomography and neutron radiography

AbstractCapillary imbibition in variably saturated porous media is important in defining displacement processes and transport in the vadose zone and in low‐permeability barriers and reservoirs. Nonintrusive imaging in real time offers the potential to examine critical impacts of heterogeneity and surface properties on imbibition dynamics. Neutron radiography is applied as a powerful imaging tool to observe temporal changes in the spatial distribution of water in porous materials. We analyze water imbibition in both homogeneous and heterogeneous low‐permeability sandstones. Dynamic observations of the advance of the imbibition front with time are compared with characterizations of microstructure (via high‐resolution X‐ray computed tomography (CT)), pore size distribution (Mercury Intrusion Porosimetry), and permeability of the contrasting samples. We use an automated method to detect the progress of wetting front with time and link this to square‐root‐of‐time progress. These data are used to estimate the effect of microstructure on water sorptivity from a modified Lucas‐Washburn equation. Moreover, a model is established to calculate the maximum capillary diameter by modifying the Hagen‐Poiseuille and Young‐Laplace equations based on fractal theory. Comparing the calculated maximum capillary diameter with the maximum pore diameter (from high‐resolution CT) shows congruence between the two independent methods for the homogeneous silty sandstone but less effectively for the heterogeneous sandstone. Finally, we use these data to link observed response with the physical characteristics of the contrasting media—homogeneous versus heterogeneous—and to demonstrate the sensitivity of sorptivity expressly to tortuosity rather than porosity in low‐permeability sandstones.

A Gravitational Procedure to Measure the Diffusion Coefficient of Water in Porous Materials: A Case Study on Concrete

A new procedure is presented with which the diffusion coefficient of water in partially saturated porous materials can be measured. The first step in the procedure is the creation of a non-equilibrium situation inside a sample by placing it into a centrifuge. In the second step, the mass of the sample is measured by hanging it from two cables, each connected to a balance. The comparison of the time evolutions of the measured masses and the masses as predicted using Fick's second law gives the diffusion coefficient.

Dynamic neutron radiography observations of water migration in porous media

Three examples of application of dynamic neutron radiography in studies of mass and heat transfer in porous media are presented. The self-diffusion coefficient of water in porous material, the imbibition rate parameter in building materials and the power density dependence of boiling of water inside porous medium are discussed. The results were obtained with simple dynamic neutron radiography station employing commercially available components.

Determination of Capillary Motion of Water in Bricks Using Neutron Radiography

Vertical migration of water in several porous materials has been directly observed and recorded with the recently installed neutron and gamma radiography facility at the MARIA reactor of Institute of Atomic Energy, Swierk. The density profiles of water in samples were obtained from the optical density of digitised images. A simple model (representing the porous material as the collection of capillary tubes of various radii) has been introduced to describe the liquid transport in porous materials in terms of capillary motion. The equation for viscous movement of water in porous material in presence of the gravitation is proposed. A good agreement of the calculated density profiles for vertical water migration with the data collected for siliceous bricks suggests that the thinnest capillary tubes determine the upper edge of the water density profile.

Model for the rotational contribution to quasielastic neutron scattering spectra from supercooled water.

A model is proposed for the first-, second-, and third-order rotational correlation functions that are required for the computation of the rotational intermediate scattering function for the calculation of incoherent quasielastic neutron scattering (QENS) spectra from supercooled water. The model is tested against molecular-dynamics data generated from an extended-simple-point-charge model of water and is found to be satisfactory. The model can be used as a practical method for extracting rotational relaxation parameters from QENS spectra measured at large Q from supercooled bulk water or interfacial water in porous materials.

Thermodynamics of frost heaving: A thermodynamic proposition for dynamic phenomena

A phenomenon of up-heaving during the freezing of water in porous materials is reviewed. A unique feature relevant to the phenomenon is that when water and ice are partitioned by a microporous material and are kept in a supercooled state, water moves from below to the ice bottom against a force of gravity, and gravitational potential energy is spontaneously produced. This phenomenon, which is unable to be explained by Newton's laws of dynamics, is found to be consistent with the second law of thermodynamics. It is suggested that matter in a system kept in a thermodynamically nonequilibrium state can move in a direction opposite to a force applied on the matter if the movement produces an increment of entropy in a whole system consisting of the system and local surroundings that interact with the system. The result is generalized and a simple thermodynamic proposition is proposed so as to account for emergence of dynamic motions in nonequilibrium systems. Some of the examples are discussed from this thermodynamic viewpoint.

HEAT, MOISTURE TRANSPORT, AND INDUCED STRESSES IN POROUS MATERIALS UNDER RAPID HEATING

High temperatures and other severe thermal conditions cause release of significant amounts of water in porous materials, and induce pore pressure and temperature gradients under which water is transported through pores. A mathematical model that simulates the coupled heat and mass transfer in heated porous media as well as the resulting stress are discussed. A finite element analysis for the solution of such a model is developed and used to study the temperature and pore pressure distribution and the resulting stresses. A comparison of predicted temperature distribution with experimental data is made, and sensitivity of the coefficient of shrinkage on the induced stress is investigated.

Microbial mechanisms of deterioration of inorganic substrates—A general mechanistic overview

Generally, all types of microorganisms—bacteria and cyanobacteria, algae, fungi, and lichens—are able to attack and degrade materials. Sometimes, the physical presence of microbial cells is sufficient to cause damage. Generally, deterioration is caused by the excretion of metabolic intermediates and/or end-products as well as exoenzymes. Depending on the use of a material, discoloration of a resin or total destruction of a material may result in a serious microbiologically influenced (corrosion) damage. Although many microorganisms are known to participate in these processes, their action may be summarized by nine main categories: 1. (1) physical presence of microbial cells→connection of electric contacts (chips); 2. (2) attack by mineral acids like sulfuric, nitric, carbonic acid→hydrolysis of materials 3. (3) attack by organic acids like acetic, citric, oxalic, gluconic, and other acids→hydrolysis of materials 4. (4) attack by organic solvents like acetic of butyric acid or alcohols like ethanol or propanol or ketons→swelling and hydrolysis of materials 5. (5) salt stress because of reaction products of (2) and (3)→retaining water in porous materials causes increased susceptibility against freeze-thaw attack and furthers crystallisation→swelling attack 6. (6) production of noxious compounds like hydrogen sulfide, nitrogen oxides→production of mineral acids or precipitation of metal sulfides and oxidants/reductants 7. (7) effect of biofouling and biofilm→exopolymers cause localized corrosion cells; retainment of water in porous materials; hydrophobic effects on surfaces; reduced heat transfer efficiency; reduced (flow) velocity or increased pressure 8. (8) attack by exoenzymes→cleavage of insoluble organic compounds to small, water soluble molecules; and 9. (9) production of chelating agents of emulsifying compounds→increased solubility of ‘insoluble’ and/or hydrophobic substances. Usually, the deterioration of a material is caused by a combined action of the above mentioned factors. However, chemical methods often fail to properly detect the mechanisms because some compounds may be subject to metabolic turnover (organic acids, nitrogen compounds, etc.). Microbiological analyses are necessary for elucidating the mechanism of attack.

Small-angle neutron-scattering studies of the fractal-like network formed during desorption and adsorption of water in porous materials.

Small-angle neutron-scattering studies of the fractal-like network formed during desorption and adsorption of water in porous materials.

The frozen earth: fundamentals of geocryology

This book describes the effects of cold climates on the surface of the earth. Using scientific principles, the authors describe the evolution of ground thermal conditions and the origin of natural features such as frost heave, solifluction, slope instabilities, patterned ground, pingos and ice wedges. The thermodynamic conditions accompanying the freezing of water in porous materials are examined and their fundamental role in the ice segregation and frost heave processes is demonstrated in a clear and simple manner. This book concentrates on the analysis of the causes and effects of frozen ground phenomena, rather than on the description of the natural features characteristic of freezing or thawing ground. Its scientific approach provides a basis for geotechnical analyses such as those essential to resource development.

Reply by the author to J. Korringa and R. J. S. Brown

An important feature of the dielectric properties of water in porous materials is that it does not behave like many other dielectric fluids of simpler microscopic structure. As a basis for evaluating the deviance of the dielectric properties of water, an experimental model is used in my paper. This experimental model is the volume fraction model and is determined from direct measurement. It involves no theoretical suppositions about the geometry of the composite dielectric material. This approach is taken to illustrate the unique physical properties of water rather than to adopt some theoretical model which depends upon some extraordinary insight into the “approximate” geometry of the composite dielectrics.

FREEZING AND MELTING TEMPERATURE HYSTERESIS OF WATER IN POROUS MATERIALS: APPLICATION TO THE STUDY OF PORE FORM

SummaryA theory is developed for the influence of pore form on the equilibrium freezing and melting temperatures of water in porous materials. This is supported by calorimetry and uses the hysteresis between freezing and melting temperatures for two clays and undried synthetic organic textile fibres in which the pore geometry is that of intersecting cylinders.For most water‐saturated clay systems, analysis of the low temperature endotherms gives a better appreciation of the pore size distribution than analysis of the exothermic data, unless the width of rectangular pores is known.

Freezing and Thawing Tests and Theories of Frost Damage

Abstract Cyclic freezing and thawing tests on structural clay materials are reported. These results and those of recent studies on the freezing of water in consolidated porous materials and the theories of frost damage are used to discuss the mechanisms of pressure generation and relief mechanism. It is concluded that the major mechanisms of stress generation and relief during the freezing of water in porous materials may be different for small or large cooling rates, and that it is probable that freezing and thawing tests can be accelerated, although it should be done with great caution.

Experimental Determination of Apparent Specific Heats of Frozen Soils

Synopsis A property of water in porous materials is that it freezes at temperatures below 0°C. There is no single freezing temperature for water in soils. As ice is formed the freezing point of the decreasing quantity of unfrozen water falls further below 0°C. Latent heat of fusion is thus involved in temperature changes over a range extending to several degrees below 0°C. The latent heat and specific heat together constitute an apparent specific heat. Apparent specific heats for various silt, clay and organic soils have been measured in a calorimeter. The apparent specific heats generally rise as temperatures approach 0°C, and in a clay soil may be ten times as great at −1°C as at −5°C. The apparent specific heats for a given temperature depend on whether the soil is freezing or thawing, and on various other factors. The precise determination of heat quantities involved in temperature changes in soil in situ is difficult, mainly because of the several factors influencing the freezing of the soil moisture. Une propriété de l'eau dans les corps poreux est qu'elle gèle à des températures inférieures à 0°C. Il n'y a pas de température unique de congélation de l'eau dans le sol. Au fur et à mesure que la glace se forme, le degré de congélation descend au dessous de 0°C. Une chaleur de fusion latente est done en cause lors des changements de température couvrant plusieurs degrés au dessous de 0°C. La chaleur latente et la chaleur spécifique constituent ensemble une chaleur apparente spécifique. Les chaleurs spécifiques apparentes pour des limons, des argiles et des sols organiques divers ont été mesurées dans un calorimètre. D'une manière générale, la chaleur spécifique apparente s'élève lorsque la température s'approche de 0°C, et dans le sol argileux elle peut être dix fois plus grande à −1°C qu'à −5°C. La chaleur spécifique apparente pour une température donnée dépend soit du gel, soit du dégel du sol, et d'autres facteurs divers. La détermination précise des quantités de chaleur en cause lors des channements de température dans le sol, sur place, est difficile, surtout à cause de plusieurs facteurs qui influencent la congélation de l'humidité se trouvant dans le sol.

An Investigation of the Role of Capillary Forces in Laboratory Water Floods

Introduction Capillary forces play a controlling role in waterdrive displacement processes both in laboratory experiments and in actual reservoirs, but their quantitative importance may be quite different in the two cases. Because of the importance of conducting laboratory experiments which are representative of field conditions, it is necessary to understand exactly the role of capillary forces in the displacement process. Though a number of experimental investigations related to this subject are contained in the literature, there appears to be a lack of information pertaining to unsteady-state experiments in water-wet media. This experimental study was conducted to obtain additional laboratory data to clarify further the role of capillary forces in both the macroscopic and microscopic flow of oil and water in porous materials. Theoretical Considerations The capillary pressure is defined as the difference in pressure between a continuous oil phase and a continuous water phase in a porous material. The magnitude of this pressure difference depends on the interfacial curvature and the interfacial tension. The interfacial curvature is determined by the geometry of the pore spaces, the wettability of the rock surfaces, and the quantity of each phase present. Capillary forces are involved in a water-drive displacement process in that they exert a controlling influence on the microscopic fluid distribution which in turn is reflected in the saturation or macroscopic flow behavior. Microscopic Fluid Distribution Because of the microscopic nature of the displacement of oil by water, it is necessary to consider the flow and the fluid distribution in individual pores. On this microscopic scale the capillary forces, which act over a distance of one or two sand grain diameters, control the distribution of oil and water under static equilibrium conditions. When an external force is applied to the fluids, such as in a water-injection experiment, the applied forces tend to distort the oil-water interfaces. However, in most fine-grained, water-wet sands, the applied pressure difference across one or two grain diameters is usually several orders of magnitude less than the capillary pressure difference.

Interaction of Water and Porous Materials

A GENERAL Discussion of the Faraday Society on "The Interaction of Water and Porous Materials" was held at University College, Southampton, during March 31-April 2. The four groups of papers on the programme were concerned with (a) fundamental, (6) botanical, (c) zoological, mainly entomological, and (d) industrial aspects of the penetration and movement of water in porous materials. They were well chosen to provide topics on which physical chemists, botanists, zoologists, agriculturists and those interested in fibrous materials such as textiles, wood and leather, could discuss problems common to two or more groups.