Interpore Spacing Research Articles

Parametric Control via the Algebraic Expression of Lotus-Type Pore Shapes in Metals

Lotus-type porous metals, characterized by low densities, large surface areas, and directional properties, are contemporarily utilized as lightweight, catalytic, and energy-damping materials; heat sinks; etc. In this study, the effects of dimensionless working parameters on the morphology of lotus-type pores in metals during unidirectional solidification were extensively investigated via general algebraic expressions. The independent dimensionless parameters include metallurgical, transport, and geometrical parameters such as Sieverts’ law constant, a partition coefficient, the solidification rate, a mass transfer coefficient, the imposed mole fraction of a solute gas, the total pressure at the top free surface, hydrostatic pressure, a solute transport parameter, inter-pore spacing, and initial contact angle. This model accounts for transient gas pressure in the pore, affected by the solute transfer, gas, capillary, and hydrostatic pressures, and Sieverts’ laws at the bubble cap and top free surface. Solute transport across the cap accounts for solute convection at the cap and the amount of solute rejected by the solidification front into the pore. The shape of lotus-type pores can be described using a proposed fifth-degree polynomial approximation, which captures the major portions between the initial contact angle and the maximum radius at a contact angle of 90 degrees, obtained by conserving the total solute content in the system. The proposed polynomial approximation, along with its working parameters, offers profound insights into the formation and shape of lotus-type pores in metals. It systematically provides deep insights into mechanisms that may not be easily revealed with experimental studies. The prediction of a lotus-type pore shape is thus algebraically achieved in good agreement with the available experimental data and previous analytical results.

Design and preparation of a massive trimodal porous silver by the combinational process of Gasar and dealloying

This study introduces a combined way of Gasar and dealloying process for fabricating massive three-level hierarchically porous silver (MTHPS). The key contributions of this research lie in improving the dimension of obtained hierarchical porous metals. The thickness of the de-alloyed precursor can be skillfully characterized by the inter-pore spacing l in Gasar porous metals utilizing Gasar process. By effectively adjusting the phase in as-cast Mg82.43Ag17.57 and the corrosion solution, the MTHPS samples with different morphologies are obtained. After dealloying the as-cast Gasar porous Mg82.43Ag17.57, hierarchical porous Ag which consists of lotus-type macropores (a diameter of 376 ± 86 μm), honeycomb submicron pores (a diameter of 360 ± 78 nm), and continuous ligament/channel structures (with pore diameters less than 56 ± 23.9 nm) were obtained. The Mg4Ag phase was observed in the T4-treated Gasar porous Mg82.43Ag17.57, which contributes to the formation of a novel tertiary porous structure. In addition, the catalytic performance of MTHPS for formaldehyde was evaluated in an alkaline environment, and the results showed that three-level porous silver with small pore size and well-continuous ligament/channel structured nanopores exhibited excellent electrocatalytic properties.

Ion Concentration Polarization Tunes Interpore Interactions and Transport Properties of Nanopore Arrays

AbstractBiological processes require concerted function of many channels embedded in the cell membrane. While single solid‐state nanopores are already designed to mimic properties of individual biological channels, it is not yet known how to connect the pores to achieve biomimetic ionic circuits with interacting components. To identify fundamental processes that control interactions between nanopores embedded in the same membrane, a model system of minimal arrays consisting of two and three nanopores in silicon nitride films is designed. The constituent nanopores have an opening diameter <10 nm, and the interpore spacing is tuned between 15 and 200 nm. The experimental and modeling results reveal that nanopores in an array interact with each other via overlapping depletion zones created by the process of concentration polarization. The interactions can be further controlled by salt concentration and voltage. These results showcase a possibility of tuning interactions between nanopores and transport properties of arrays by chemical modification of the pore walls. Arrays consisting of nanoporous ionic diodes feature depletion zones with higher concentrations, and lower current suppression than homogeneously charged pores. These experiments and modeling provide the first steps to leave the constraints of single nanopores and to design biomimetic ionic circuits.

Fabrication of ZnO/ZnAl2O4/Au Nanoarrays through DC Electrodeposition Utilizing Nanoporous Anodic Alumina Membranes for Environmental Application.

In this study, anodic aluminum oxide membranes (AAOMs) and Au-coated AAOMs (AAOM/Au) with pore diameters of 55 nm and inter-pore spacing of 100 nm are used to develop ZnO/AAOM and ZnO/ZnAl2O4/Au nanoarrays of different morphologies. The effects of the electrodeposition current, time, barrier layer, and Au coating on the morphology of the resultant nanostructures were investigated using field emission scanning electron microscopy. Energy dispersive X-ray and X-ray diffraction were used to analyze the structural parameters and elemental composition of the ZnO/ZnAl2O4/Au nanoarray, and the Kirkendall effect was confirmed. The developed ZnO/ZnAl2O4/Au electrode was applied to remove organic dyes from aqueous solutions, including methylene blue (MB) and methyl orange (MO). Using a 3 cm2 ZnO/ZnAl2O4/Au sample, the 100% dye removal for 20 ppm MB and MO dyes at pH 7 and 25 °C was achieved after approximately 50 and 180 min, respectively. According to the kinetics analysis, the pseudo-second-order model controls the dye adsorption onto the sample surface. AAOM/Au and ZnO/ZnAl2O4/Au nanoarrays are also used as pH sensor electrodes. The sensing capability of AAOM/Au showed Nernstian behavior with a sensitivity of 65.1 mV/pH (R2 = 0.99) in a wide pH range of 2-9 and a detection limit of pH 12.6, whereas the ZnO/ZnAl2O4/Au electrode showed a slope of 40.1 ± 1.6 mV/pH (R2 = 0.996) in a pH range of 2-6. The electrode's behavior was more consistent with non-Nernstian behavior over the whole pH range under investigation. The sensitivity equation was given by V(mV) = 482.6 + 372.6 e-0.2095 pH at 25 °C with R2 = 1.0, which could be explained in terms of changes in the surface charge during protonation and deprotonation.

Scaling of inter-pore spacing of lotus-type pores

Abstract The present study is to scale the inter-pore spacing and bubble radius required for controlling the porosity of the lotus-type pores in the solid during a unidirectional solidification. The porosity in solid degrade properties of material in welding, casting and additive manufacturing, etc. On the other hand, the ordered cylindrical pores in the material are often used to improve the functional properties, such as the tensile and compression stresses, the impact and acoustic energy absorption, the permeability, and the thermal and electrical conductivity, etc. Different from the traditional minimum undercooling criterion to estimate the porosity and size of lotus-type pores, this study relevantly combines the Gibbs-Thomson equation, the Young-Laplace equation, the nucleation theory, and the Henry’s law or Sieverts’ law to scale the inter-pore spacing and the critical radius of the lotus-type pores, which are considered as the same order of the wavelength and the amplitude of the morphological instability of the solidification front, respectively. This work revises the minimum undercooling criterion which ignores the nucleating bubble on the solidification front, and conducts irrelevant evaluation of the curvature of the solidification front. The present work finds the revised scaling results and available experimental data to be in good agreement. The sizes of the pores and the porosity in the solid can be successfully controlled in advance.

Parametric study of lotus-type pore shape in solid subject to Henry's laws at interfaces

Mechanisms of the length and maximum radius of lotus-type or single pores in ice or nonmetals satisfied by Henry's law at gas-liquid interfaces dissolved by a gas during unidirectional solidification are rigorously investigated and supported by a Table from algebraic predictions involving different dimensionless working parameters. Lotus-type porous materials characterized by directional properties have been often used as functional materials in food, biomedical, and micro- and nano-technologies. Following previous work taking into account solute amount and transport within the pore, and concentration boundary layers on the advancing solid-liquid interface and bubble cap, and the Young-Laplace equation and Henry's law at liquid-gas interfaces, the algebraic study further provides a Table for a quantitative and extensive understanding of different mechanisms of length and maximum radius. Dimensionless parameters include solute transport parameters of Henry's law constant, mass transfer coefficient, partition coefficient, solute gas amount in imposed ambient, and solute transport parameter, and fluid and thermal parameters of solidification rate, imposed gas pressure, hydrostatic pressure, and geometrical parameter of inter-pore spacing. The controlling of the shapes of lotus-type pores is achieved by a good comparison between predicted maximum diameter and inter-pore spacing during freezing of water dissolved by oxygen gas.

FACING BUILDING MATERIAL BASED ON MECHANICALLY ACTIVATED CULLET MODIFIED WITH SODIUM HYDROXIDE

The technology of facing material based on mechanically activated cullet modified with sodium hydroxides has been developed. The phase composition, macro- and microstructure of the lining material are investigated. It is established that the microstructure of a composite modified with sodium hydroxide in the interpore space is represented by lamellar crystals of sodium meta-, di- and orthosilicates. The optimal composition for obtaining a facing material with a compressive strength of 24.7 MPa and a softening coefficient of 0.91 has been established.

Modeling the process of biological deferrization of underground waters in contact loading of bioreactor

The conducted analysis of modern biotechnologies in the field of groundwater treatment showed that one of the development trends is the direction of biological iron removal, which has not only a long history and fundamentality of research into the physiology, ultrastructure and life mechanisms of ferrobacteria, but also a wide implementation of the method at water treatment plants in Europе, Australia, Canada, USA, Japan. The introduction of modern technological equipment at such stations calls for the need to forecast their work using methods of mathematical modeling of processes with their subsequent computer implementation. The work provides a brief analysis of existing mathematical models, most of which are based on the kinetics of enzymatic reactions and are presented as modifications of the Michaelis-Menten and Monod equations.
 Despite the large number of studies on this topic, until now there is no comprehensive model that would take into account all the processes that take place in the contact loading of bioreactors, in contrast to the physicochemical mechanisms in the filtering process, for which modern multicomponent mathematical models have been developed.
 The aim of the work is to development of a mathematical model of the kinetics of the process of biological iron removal groundwater in bioreactors and verification of its computer implementation with the data of experimental studies. The mathematical model is represented by the Cauchy problem for a nonlinear system of differential equations in partial derivatives of the first order. The system of the Cauchy problem consists of five equations with five unknown functions, which describe the distribution the concentration of ferrum cations, bacteria and the matrix structures in two phases (movable and immobilized) both in space and time The inverse influence of the characteristics of the process, in particular, the concentration of matrix structures in the inter-pore space, as well as characteristics of the medium with the help of coefficients of mass exchange and porosity, were taken into account. The model makes it possible to predict changes in cleaning efficiency depending on the duration of the filter cycle, filtration speed, Fe2+ concentration, the content of iron bacteria and their matrix structures in the interpore space, and to determine the optimal time of operation of the bioreactor between washings

DILATATION OF THE METHOD OF THE FIXATION OF MOVEABLE SANDS

A new method of physicochemical blocking deflation of movable sands has been developed that represents their fixation in a wet state with binders. It is proposed to carry out sand-fixing works during rainy periods or after preliminary moistening of the sandy surface in order to intensify and reduce the cost of sand-fixing works. The substantiation is carried out on the example of some of the approved and recommended binders based on the express method of studying the possibility of their application to obtain a polymer sandy protective crust on wet sand. The emerging defensive hull is characterized by resistance to wind-sand stream and evaluated by plastic quality and thickness. The impregnation of damp sand with a smaller sum of cover than dry sand is related to an alteration within the nature of impregnation from gravity to capillary. With a decrease in the specific surface of the bulk material and an increase in the pore space, gravitational forces are predominant. The process of wet sand impregnation is associated with the acceleration of the adsorption of the dispersed phase and a reduction in the hole covered due to the partial occupation of the interpore space with water. As a result, in wet sand, the depth of sand impregnation with the binder increases at a lower consumption per unit volume of sand. The following has been established: the possibility of impregnation of approved and recommended binders into wet sand, the inverse dependence of the binder concentration in emulsion forms on the humidity of the sandy surface, the time of application of various binders after moistening the sand and the possible savings of binders.

Growth of Highly-Ordered Metal Nanoparticle Arrays in the Dimpled Pores of an Anodic Aluminum Oxide Template.

A reliable, scalable, and inexpensive technology for the fabrication of ordered arrays of metal nanoparticles with large areal coverage on various substrates is presented. The nanoparticle arrays were formed on aluminum substrates using a two-step anodization process. By varying the anodization potential, the pore diameter, inter-pore spacing, and pore ordering in the anodic aluminum oxide (AAO) template were tuned. Following a chemical etch, the height of the pores in the AAO membrane were reduced to create a dimpled membrane surface. Periodic arrays of metal nanoparticles were subsequently created by evaporating metal on to the dimpled surface, allowing for individual nanoparticles to form within the dimples by a solid state de-wetting process induced by annealing. The ordered nanoparticle array could then be transferred to a substrate of choice using a polymer lift-off method. Following optimization of the experimental parameters, it was possible to obtain cm2 coverage of metal nanoparticles, like gold and indium, on silicon, quartz and sapphire substrates, with average sizes in the range of 50-90 nm. The de-wetting process was investigated for a specific geometry of the dimpled surface and the results explained for two different film thicknesses. Using a simple model, the experimental results were interpreted and supported by numerical estimations.

Solution combustion synthesis of iron-deficient Sc2-xFexO3 (x = 0.17-0.47) nanocrystals with bixbyite structure: The effect of spatial constraints

In this paper, nanopowders based on iron-deficient Sc2-xFexO3 (x = 0.17–0.47) nanocrystals with bixbyite structure and crystallite size of 3.7–38.9 nm were successfully synthesized via solution combustion. Variable glycine-to-nitrate (G/N) ratio was the main controlling factor. A wide range of experimental and computational methods were used to analyze the impact of spatial constraints on the resulting solid-state products. It was found that solution combustion mode greatly influenced on the temperature and gaseous products in the reaction zone. Volume (G/N = 0.4–0.8, Tmax = 1179–1511 °C), self-propagating (G/N = 1.0–1.4, Tmax = 614–957 °C) or smoldering (G/N = 0.2, Tmax = 443 °C) combustion modes were acquired during the synthesis depending on G/N ratio. It was shown that the formation of impurity phases of am-Fe2O3 (Tmax < 850 °C), c-Fe3O4 (900 °C < Tmax < 1500 °C) or c-FeO (Tmax > 1500 °C) was possible, depending on the combustion temperature. Besides, the combustion mode affected the porous and surfacial structure of resulting mesoporous nanopowders – specific surface area and total pore volume varied in ranges of 1.7–82.8 m2/g and 0.0088–0.1538 cm3/g, consequently. Chemical composition and unit cell parameters of Sc2-xFexO3 showed the positive deviation from Vegard's law. The average sizes of the interpore thickness (h) depending on G/N ratio were found from values of specific surface area and pycnometric density of nanopowders, which made it possible to establish the presence of spatial constraints for the crystals' growth of Sc2-xFexO3 at h values below 10 nm. Analysis of aspect (h/D) ratio allowed to determine synthetic parameters which led to mono- or polycrystalline structure of interpore space in resulting Sc2-xFexO3-based nanopowders. The results and patterns established in this paper allowed to synthesize a new type of foam-like functional materials based on rare-earth ferrites.

К ВОПРОСУ ВЫБОРА ОПТИМАЛЬНОГО ВОДОЦЕМЕНТНОГО ОТНОШЕНИЯ ПРИ ПРОИЗВОДСТВЕ ТЕПЛОИЗОЛЯЦИОННОГО ПЕНОБЕТОНА

The article considers the influence of the water-cement ratio on the formation of the structure of thermally insulating foam concrete, having the D300 average density grade. The basis for the analysis is the contradiction between the experimentally obtained direct dependence of the strength of foam concrete on the water-cement ratio and the practice of improving the structure of the material due to water reduction. The computation of the optimal amount of water in the foam concrete mixture based on the method of absolute volumes is presented. The calculation includes a formula for determining the volume of the interpore space depending on the thickness of the interpore partition, the cell diameter and the type of packing. The actual indicators collected during the experiment confirm the results of the calculations. The influence of the amount of water in the foam concrete mixture on the quality of the foam concrete is evaluated by the compressive strength and the macrostructure character of the material. The strength is determined by the destructive method. The structure is studied using an optical microscope in combination with image processing software. The greatest strength is possessed by a material with a partition thickness exceeding the maximum size of the cement grain, provided that the volume of the interpore space and the sum of the absolute volumes of the components of the foam concrete mixture are equal. A structure with closed pores and dense interpore partitions is observed in foam concrete on a protein foam former with a water-cement ratio, taking into account water in the foam, equal to 0.7.

The influence of foams, having different expansion ratios, on the structurization of thermal insulation foam concrete

Introduction. The article addresses the influence of foams, having different origins and expansion ratios, on the structurization of thermal insulation foam concrete. The study is focused on solving the problem of the binder hydration conditions in the interpore space of the foam concrete mixture and maintaining its stability. The goal is to design an economically effective composition. Materials and methods. To analyze the structurization process, foam concrete samples, featuring average density grades D300 and D500, were made using ordinary Portland cement. The nature of the surfactant substance of the foam, its expansion ratio and the water-cement ratio of the solution are the variable factors determining parameters of the material structure. The strength of the foam concrete was used to evaluate the cement hydration conditions. The strength was identified according to GOST 10180. Parameters of the macrostructure were measured using the Levenhuk optical microscope and the LevenhukLite software. Results. It is found that hydration in the interpore space of the mixture is implemented to the fullest extent when a protein foaming agent, featuring a low foam expansion ratio, is used. The foam concrete, thus made, has closed pores, whose diameter varies in a small range of values, while the partition thickness exceeds the maximum size of the cement grain. An increase in the foam expansion ratio and a low value of the water-cement ratio of the solution lead to the uneven distribution of air in the mixture and reduce the thickness of the interpore partition. In this case, the structure of the foam concrete is “friable”; it represents conglomerates of interconnected pores. Conclusions. Since the geometry of the macrostructure of the material has a significant influence on the heat transfer process and strength, the protein foaming agent, featuring a low foam expansion ratio, is preferable for the production of thermal insulation foam concrete using standard Portland cement without re-grinding. Otherwise, a higher foam expansion ratio foam requires an increase in the specific surface area of the binder.

Unified algebraic expression of lotus-type pore shape in solid

Algebraic expressions for the shapes of lotus-type or isolated pores after bubbles completely entrapped in solid during unidirectional solidification are provided in this study. Functional materials of lotus-type porous metals are fabricated by unidirectional solidification of molten metals dissolving gasses such as hydrogen, oxygen or nitrogen. In view of superior and anisotropic features of mechanical, thermal and electrical properties, unidirectional lotus-type pore materials have been widely used in bio-, micro- and nano-technologies. The present model is based on a previous work by accounting for transient gas pressure in the pore affected by solute transfer and balance of gas, capillary and hydrostatic pressures, and physico-chemical equilibrium at the bubble cap. Solute transport across the bubble cap during solidification can be in different directions as previously denoted by Cases 1 and 2 due to relative magnitude between height of bubble cap and thickness of the concentration boundary layer on the solidification front. Proposing the self-consistently unified model combining Cases 1 and 2 and introducing a solute transport parameter, algebraic expressions of lotus-type pores and isolated pore can be obtained. Predicted and measured maximum radius, total length, inter-pore spacing, aspect ratio and porosity of lotus-type pores subject to Henry's law and Sievert's law as well as shape of an isolated pore during unidirectional solidification of water containing oxygen gas, liquid copper containing hydrogen, and water containing carbon dioxide, respectively, agree quite well.

FORECASTING THE GROUNDWATER TREATMENT PROCESS IN A BIOREACTOR USING FERROBACTERIA

The monitoring of water quality parameters in 90 settlements of eight regions of Ukraine made it possible to state that groundwater is a complex multicomponent system. Existing deironing stations using simplified aeration-filtration technology are not able to remove Fe (II) compounds from water in the presence of humic complexes. Therefore, in modern conditions, the urgent task is to intensify their work through the introduction of new technologies, including biotechnology with the development of appropriate mathematical models. It is shown that much less attention was paid to modeling the kinetics of groundwater treatment processes in bioreactors than to traditional physicochemical methods, for which modern mathematical models were developed.&#x0D; The aim of the work is to develop a mathematical model of the kinetics of the process of groundwater treatment in bioreactors. The mathematical model is represented by the Cauchy problem for a nonlinear system of differential equations in partial derivatives of the first order. The system of the Cauchy problem consists of five equations with five unknown functions, which describe the distribution the concentration of ferrum cations, bacteria and the matrix structures in two phases (movable and immobilized) both in space and time. The inverse influence of the characteristics of the process, in particular, the concentration of matrix structures in the inter-pore space, as well as characteristics of the medium with the help of coefficients of mass exchange and porosity, were taken into account. The model allows determining the optimum operation time of a bioreactor between washings

(Invited) Growth of Self-Ordered Porous Anodic Oxide Nanomaterials By Coupled Ion Migration and Viscous Flow

Porous anodic oxide (PAO) films are self-organized porous oxide nanomaterials formed by electrochemical oxidation. PAO includes porous anodic alumina and TiO2 nanotube layers. These films eventually evolve into a hexagonally-ordered array of parallel cylindrical pores or nanotubes of order 100 nm diameter, with a characteristic interpore spacing that scales directly with the cell voltage.We explore the roles of mechanical stress and oxide flow in self-ordering, through a modeling analysis of stress-driven viscous flow of oxide (1). The model is based on coupled viscous flow of oxide and stress- and electric field-driven migration of metal and oxygen ions (2). Stress at the film interfaces is generated by ion-transfer processes and relaxed by viscous flow, resulting in layers with elevated compressive or tensile stress within a few nm of the interfaces (3,4). Experimental evidence for these layers has been found from in situ stress measurements (5,6). We present linear stability analysis incorporating the surface stress boundary conditions in the coupled oxide flow-electrical migration model of Houser and Hebert (2).For porous alumina, the calculations reveal self-organized pattern formation with steady-state pore spacing-voltage scaling ratios that compare favorably to those found experimentally (1). The scaling ratios are independent of oxide viscosity or uncertainties in the values of any other model parameters. The stress driving oxide flow arises at the oxide-solution interface due to strong electrolyte anion adsorption, which blocks direct oxide deposition on the surface itself. New results for TiO2 nanotube layers are presented. Near-surface stress is not present in TiO2 nanotube layers (6); instead, compressive stress driving flow arises at the metal-oxide interface from the volume change upon conversion of metal to oxide.REFERENCES P. Mishra and K. R. Hebert, Electrochim. Acta, 340, 135879 (2020).J. E. Houser and K. R. Hebert, Nature Mater., 8, 415 (2009).K. R. Hebert, P. Mishra, J. Electrochem. Soc., 165, E737 (2018).K. R. Hebert, P. Mishra, J. Electrochem. Soc., 165, E744 (2018).Ö. Ö. Çapraz, P. Shrotriya, P. Skeldon, G. E. Thompson, K. R. Hebert, Electrochim. Acta, 167, 404 (2015).Q. Dou, P. Shrotriya, W. F. Li, K. R. Hebert, Electrochim. Acta, 292, 676 (2018).Q. Dou, P. Shrotriya, W. F. Li, K. R. Hebert, Electrochim. Acta, 295, 418 (2019).

Prospects for Evaluating the Damageability of Asphalt Concrete Pavements During Cold Recycling

The article considers improvement of the methodology for accounting for the degradation of asphalt concrete working in the upper layers of the pavement. Development of recycling technologies for road structures is an ongoing process; it allows reaching a higher quality of reclaimed materials and using them for subsequent construction of structural layers, including the upper layers without the protective ones, as well as during repair and reconstruction of roads of various technical categories. At the same time, the system of pre-project assessment (diagnostics) of the state of asphalt concrete pavements cannot be considered optimal and effective because the determined indicators demonstrate that, firstly, various surface and structural defects are present, and, secondly, that the indicators mentioned above are more relevant to the road structure as a whole. The joint handling of the theoretical and experimental data allows concluding that damageability level depends on the physical, mechanical and structural properties, the main being maximal structural strength and the number of elastic bonds involved in the deformation process. A variant of modelling of asphalt concrete damageability depending on the work capacity is proposed, when the reduced amount of dissipated energy is replaced with sufficient accuracy for practice by the ratio of the actual number of load application cycles (freezing and thawing cycles) to the limit. A correlation between the level of damageability and the kinetics of changes of the interpore space of asphalt concrete under the influence of strain (temperature, climatic factors) has been established. Results allow fixing (predicting) the level of damageability by measuring the level of water permeability. The research methodology and equipment for implementation thereof was developed earlier, it can be effectively used at the stage of pre-project diagnosis.

Pore structure analysis of directionally solidified porous copper

Directionally solidified porous copper is considered as a potential candidate in the field of microchannel heat sinks. By the Bridgman-type directional solidification method, a porous copper ingot was fabricated. Evolution of the porosity, pore number density, average pore diameter and average interpore spacing at different ingot heights was investigated. The results show that with the increase of ingot height, the porosity firstly increases and then basically remains unchanged from the ignot height of 65 mm; the pore number density rapidly decreases at first, and the decreasing speed becomes slower when the ignot height higher than 85 mm; the average pore diameter increases and then remains unchanged from the ingot height of 85 mm; the average interpore spacing increases, and the increasing speed of average interpore spacing becomes slower with the increase of height to higher than 85 mm. In order to study the evolution of diameter and spatial distribution of pores, the distribution ranges of pore diameter, nearest-neighbor distance and radial cumulative pore number were analyzed. As the ingot height increases, the distribution ranges of pore diameter and nearest-neighbor distance firstly increase and then tend to be stable. There are no pore clusters and for long distance, the spatial distribution of pores is uniform at different ingot heights. Pore structure and 3D pore morphology of porous copper were observed with the help of light illumination and X-ray tomography. Pore nucleation, pore interruption, pore coalescence, diameter change of pores and lateral displacement of pores were found to exist in the pore structure.

Bacteria transport and deposition in an unsaturated aggregated porous medium with dual porosity.

Bacterial transport and deposition play an important role in the assessment and prediction of subsurface pollution risks. Bacteria transport experiments were performed under unsaturated flow conditions in an aggregated porous medium at the laboratory column scale, to investigate how the inter- and intra-aggregated pore space of this medium could affect transport and deposition under unsaturated flow conditions, where inter- and intra-pore spaces are not fully activated. The results obtained through experimental observations and numerical simulations showed that some intra- and inter-pore space of this medium was excluded from bacteria transport and retention, as confirmed by the non-uniform transport of bacteria pathways in the aggregated porous media under unsaturated flow conditions. Capillary energy was higher the than other forces acting at bacteria air-water-solid interfaces. If this energy should contribute in increasing bacteria deposition under unsaturated conditions, similar to what has been reported for sandy media, similar overall retention of E. coli and R. rhodochrous was obtained under unsaturated flow conditions, suggesting that capillary energy was not the driving force for bacteria deposition.

Prediction of the process of biological deferrization of underground water in a bioreactor

Research in the field of groundwater treatment indicates the prospects for the development of its complex purification involving various morphological types of microorganisms, fixed on inert contact materials. It was indicated that at certain parameters of water quality (pH 6–7; Eh 50...200 mV, in the presence of dissolved carbon dioxide and at magnitudes of permanganate oxidation of up to 5 mg О 2 /dm 3 ), development of bacteria of genus Gallionella prevails in groundwater, and development of bacteria of genera Lepthothrix, Crenothrix prevails at pH values of 6.5–7.5; Eh=–200...300 mV and PО>5 mg О 2 /dm 3 . This provides a series of advantages in the use of the biochemical method over conventional physical and chemical methods, in particular, acceleration of the process of water purification from ferrite compounds. It was shown that much less attention was paid to modeling the kinetics of the processes of treatment of underground water in bioreactors than to conventional physical-chemical methods, for which modern mathematical models were developed. That is why the development of the direction of modeling the biochemical process of water purification from iron compounds is a relevant task. The mathematical model is represented by the Cauchy problem for a nonlinear system of differential equations in partial derivatives of the first order. The system of the Cauchy problem consists of five equations with five unknown functions, which describe the distribution the concentration of ferrum cations, bacteria and the matrix structures in two phases (movable and immobilized) both in space and time. When constructing the model, we used both technological (maximum contamination capacity (2.6 kg/m 3 ), boundary magnitude of the bacteria biomass in the matrix structures (9.5 g/m 3 ), maximum specific rate of their growth (0.17–0.18 h –1 ), saturation coefficient (0.65–0.7 g/m), flow rate in the range of 5–20 m/h), and design parameters (the height of contact load of a bioreactor – 1.3 m). In the considered model, the time of effective operation of a bioreactor depends on the concentrations of cations of Fe 2+ , which in natural waters can be in the range of 0.5–20 mg/dm 3 , the number of ferrobacteria (10 2 –10 4 kl/dm 3 ), as well as the water flow rate. The inverse influence of the characteristics of the process, in particular, the concentration of matrix structures in the inter-pore space, as well as characteristics of the medium with the help of coefficients of mass exchange and porosity, were taken into account. The model allows determining the optimum operation time of a bioreactor between washings