Papers by Keyword: Pore Size Distribution

Abstract: An important practical and fundamental problem in the production of porous polymer membranes is the study of the porous structure and the detection of "defects" or large pores in the area of ​​the membrane. Known porosimetry methods cannot solve this problem. This work proposes a new non-destructive express method for studying the porous structure of asymmetric polymer membranes in high-intensity electric fields. This method can be successfully implemented on both flat sheet and hollow fiber membranes with a known porous structure. On the example of hollow fiber membranes made of polyacrylonitrile and polysulfone an assessment of the chemical structure effect of the membrane material on the high-voltage discharge currents in a highly inhomogeneous electric field through hollow fiber membranes with a given pore size was made. Under normal conditions and an average intensity of an inhomogeneous electric field E = 5 kV/cm, the results obtained allow us to conclude about a certain practical potential of the developed express method.

Abstract: The design and dimensional characteristics of the spinneret affect not only the geometry of the hollow fiber, but also the transport properties of the hollow fiber membranes. In the literature available today, there is a limited number of works in which the influence of the design and dimensional characteristics of the spinneret is studied. In this work, using the example of polysulfone hollow fiber membranes, it was shown that the use of a spinneret with smaller annular diameters leads to an increase in the gas permeability of the hollow fiber membrane with a decrease in the value of the ideal selectivity for the He/CO₂ gas pair. It was found that using the spinneret with large annular diameters, the hollow fiber membrane is obtained with a smaller value of the average pore size of the flow, which is in agreement with the obtained data on gas permeability.

Abstract: This article proposes the differential BJH equation based on the principles of multilayer adsorption and capillary condensation, which was simplified by theoretical investigation and experiments. This work indicates that the differential function of isotherm and the differential function of pore size to relative pressure determine the pore size distribution of porous media. The differential BJH model can be used to explain the source of the false peak in pore size distribution and to calculate the pore size distribution of different shapes of pores in a porous media with a porous structure. It has an excellent application prospect in the characterization of complex pore structure represented by shale.

Abstract: Contemporary demand after high-quality ceramics leads to the depletion of raw material deposits. The industry also produces waste secondary materials that cannot be used directly for the desired purposes. It is therefore necessary to find other uses for these materials. It is common practice in the ceramics industry to stockpile fine fractions of refractory clays prior to their firing in a shaft kiln. These fractions have the size of 35 mm and less and when stored in a mound are facing a risk of weathering. Finding a purpose for these unused materials will markedly slow down fresh clay mining and make the production more eco-friendly and cost-effective. This paper seeks a suitable technology of treating fine fractions of BC (Brezina Clay), sometimes called FBC (Fine Brezina Clay), prior to its being fired into grog. The stockpiles hold tens of thousands of tons of these fractions. The properties of the fired clay are determined by the length of time for which the material has been stockpiled, moisture content, of the clay, as well as the briquetting pressure before firing in a shaft kiln. FBC contains approx. 41 % of aluminium oxide. This amount is not high enough for certain applications. The aluminium oxide content can be increased by the addition of bauxite, corundum, mullite, kaolin, clays rich in Al₂O₃, or technical Al₂O₃. The experiment described in this paper tested how the addition of technical Al₂O₃ affects the pore structure of fired FBC, which is later used as a grog in both shaped and non-shaped refractory products. The influence of firing temperature on the material's mineralogy was examined as well

Abstract: This paper deals with the use of computed tomography (CT) images and analytical software for the nondestructive evaluation of the texture of autoclaved aerated concrete (AAC) with 20% fluidized bed combustion fly ash as a substitute for quartz sand. The samples of AAC, made in the laboratory with the same composition but different ways of curing in the fresh stage (before autoclaving), were subjected to observation of the differences in the texture of the silicate matrix, such as inhomogenity, defects, and pore size distribution. The curing conditions with limited drying resulted in formation of larger, locally-connected pores and additional cracking after autoclaving, which led to a decrease in compressive strength up to 1.32 MPa, compared to samples cured in conditions that allowed complete drying reaching 1.95-1.96 MPa. Also there were problems identified related to imperfect laboratory preparation of the samples, such as agglomeration of individual mixture compounds and larger air void formation, due to the absence of vibrating, cracking and weak spots formation. CT provided sufficient contrasting images for consequent software evaluation of pore size distribution, however a higher resolution of the images is needed for determination of pores smaller than 0,125 mm.

Abstract: Pozzolanic additives are widely applied as components of cementitious composites as well as mortars based on white lime. They are generally recognized as components improving the durability of resulting material – concrete or mortar. The mechanism responsible for this favorable effect lies in physical and chemical modification of initial binding system. The present paper deals with influence of a pozzolanic additive – ceramic dust (CD) – on pore system of lime – based mortar. The CD was characterized by means of elementary and phase analysis. The range of mortars of varying CD/lime ratio was prepared; their pore size distribution, strength and rate of liquid water and water vapor were determined. The presence of CD caused change in the pore size distribution while the total porosity did not changed significantly. The volume of large pores was reduced and amount of fine pores was increased as consequence of growing CD content. It had positive effect on rate of liquid water transport. Diffusion resistance factor was influenced by the presence of CD towards the lower values; in opposite to the liquid sorptivity the diffusion resistance was controlled by the total porosity. The strength was improved by addition of pozzolanic additive as could be expected. It is in accordance with the reduced volume of capillary pores but obviously the presence of pozzolanic additive in lime converts the binding system to hydraulic and thus the effect of CD on strength cannot be explained just by its influence on pore size distribution.

Abstract: The behavior of concrete under severe loading is of interest, especially for problems like ballistic impact and penetration and near distance explosions, where very high pressures are developed. For these problems the behavior of concrete at very high hydrostatic pressures is of importance. There is very little data available on concrete behavior at that high pressure level. Therefore there is much need for an extensive experimental work in order to provide necessary data and illuminate the rather obscure area of concrete behavior at high pressures. However high pressure controlled testing requires special and expensive equipment, and the testing is associated with a wide variety of technical problems. Recently published experimental data, obtained by utilizing a high-capacity tri-axial press, indicates that concrete that is subjected to high pressures behaves differently than concrete under low uniaxial loading. When uniaxial loading is applied, without any confining pressure, the concrete specimen demonstrates a well-known brittle behavior where failure is caused by a localized damage. Quite to the contrary, at high levels of confining pressures, the concrete behaves like a ductile material, and its failure is associated with diffuse material damage. The experimental data at the very high pressure range is most important to understand the processes of damage evolution that governs the characteristics of the equation of state. This paper presents the development of an experimental setup that is capable of performing confined compression tests of mortar and concrete specimens at high pressures up to 400MPa. The experimental study aims at investigating the effect of water/cement ratio as well as the ratio of fine aggregate on the different branches of the equation of state: active loading and unloading/reloading. The paper presents some of the test results as well as a new equation of state that is based on the multi scale approach. The model is applicable for dry materials; cementitious paste and concrete in which the pores are filled with water should be treated differently to account for the liquid phase.

Abstract: In this study the effect of age, w/c ratio on mean distribution radius and dispersion of pores in Ordinary Portland Cement (OPC) sand mortar was determined through Mercury Intrusion Porosimetry (MIP) test. For this purpose the cement sand mortar specimens were prepared from two different types of OPC with varied w/c ratios such as 0.2, 0.3, 0.4, 0.5 and 0.6 and tested at different curing ages from 1 day to 90 days. Separate relationships relating the mix parameters such as w/c ratio and age with mean distribution radius (r_0.5) and coefficient (d) representing dispersion of pores, are developed for OPC sand mortars.

Abstract: Pore size plays a key role in the performances, such as transportation, filtration and separation, of bicomponentspunbond nonwoven geotextiles which fibrillated by hydroentanglement method. In this research work, samples of polyester (PET) - nylon6 (PA6) hollow segmented-pie bicomponentspunbond nonwoven materials were selected. A modified pore size prediction model has been proposed to predict the pore properties, and comparisons between theoretical and experimental results also discussed. The results show that the bicomponent fibers has been splitting into ultrafine fibers under the effect of the hydroentanglement method, and ultrafine fibers oriented mainly in the X-Y directions (plane direction). There is a good agreement between experimental results and experimental results, and the model of the pore size distribution is suit for the PET/PA6 bicomponentspunbond nonwoven geotextiles can be determined. The model provides a quantitative description of pore distribution for those nonwoven materials claimed to constitute with a series of types fiber.

Abstract: The properties and microstructure of concrete containing 0-6wt% metakaolin (MK) were studied by analytical techniques. The compressive strength increased with the content of MK and reached the maximum by 5wt% MK addition, where the compressive strength increased by 33% at 28 days comparing to the control. The pore structure was refined in the concrete containing MK due to the increase of amount of pores smaller than 10 nm. There is a relationship between average pore diameter and compressive strength.