Development Of Large Pores Research Articles

Effects of a novel hybrid polymer material on the hydro-mechanical behavior of subgrade silts considering freeze-thaw cycles

Freeze-thaw (FT) cycles are considered to be a potential threat to the hydro-mechanical behavior of subgrade soils in seasonal frozen regions. Enhancing the resistance of the soils to FT cycles therefore becomes a pressing problem that needs to be solved. This paper developed a durable polyacrylate intercalated bentonite superabsorbent polymer (BT-SAP) employing the solution polymerization method, which is a novel hybrid polymer material with the function of reducing the sensitivity of subgrade soils to FT cycles. To evaluate the effects of BT-SAPs on the hydro-mechanical behavior of subgrade silts experiencing FT cycles, the 3D pore structure, volumetric strain (εv), soil-water characteristic curve (SWCC), and resilient modulus (MR) of the soil modified with BT-SAPs were determined using a series of laboratory tests. Specimens with three BT-SAP contents (BC) compacted at their respective optimum moisture content and maximum dry density were first subjected to different numbers of FT cycles (NFT). Then, they were dried or wetted to specific moisture contents (w) before the determination of (i) SWCCs using the filter paper method and (ii) MR from cyclic triaxial tests. Finally, the 3D pore structure of specimens after FT cycles was measured by X-ray μ-CT. Experimental results show that the viscous and micro-swelling effects of the generated BT-SAP-water-gels can inhibit the emergence and development of larger pores and cracks inside the soil after FT cycles. The addition of BT-SAPs significantly reduces the sensitivity of the soil's volume and water retention capacity to FT cycles. The MR decreases with NFT but increases with BC. The important finding is that an optimal BT-SAP content of 0.25% was determined suitable for fine-grained subgrade soils. In addition, an artificial neural network (ANN) model was developed using 1200 sets of the MR measurements obtained in this study and well predicts the MR considering several factors such as BC, NFT, w, dry density, and stress levels. This study provides useful guidelines for the application of BT-SAP materials in subgrade engineering in seasonal frozen regions.

The effects of pulsed electric fields on the quality parameters of freeze-dried apples

In this study, the impact of a pulsed electric field (PEF) treatment on the final quality of freeze-dried apples was investigated. The PEF treatment has been performed at an electric field intensity equal to 1.07 kV/cm and a specific energy input of 0.5, 1 and 5 kJ/kg. The samples were freeze-dried (without a separate pre-freezing step) at varying temperatures (set on 40 °C and 60 °C) and pressures (0.1, 0.25 and 1 mbar). The quality of dried material was evaluated by the analysis of residual moisture content, macro- and microscopic properties, colour, the total content of phenolic compounds and the antioxidant activity as well as texture and acoustic properties. It was found that the residual moisture content of PEF treated samples was reduced by up to ∼82% in comparison to the intact tissue. For electroporated samples, a good preservation of macro-shape, an inhibition of shrinkage and the development of large pores were observed. The PEF treated material exhibited a higher total phenolic content, but a smaller antioxidant activity. Mechanical and acoustic analysis showed a higher crunchiness and brittleness for PEF-treated tissue, whereas untreated tissue was characterised by a harder and rather crackly texture.

Spectroscopic ellipsometry study of thickness and porosity of the alteration layer formed on international simple glass surface in aqueous corrosion conditions

The porosity and pore-size distribution in the glass play an important role in glass corrosion; however, such information is difficult to be obtained non-destructively. Here we report the use of spectroscopic ellipsometry (SE) under controlled humidity environments to determine those structural parameters in the alteration layers formed on international simple glass (ISG), a model nuclear waste glass, in aqueous corrosion conditions. The SE results show that the ISG sample corroded for nearly 4.5 years develops pores larger than 2 nm in diameter, while the alteration layers formed initially in less than 1 month do not have such large pores. The development of larger pores over a long period of corrosion time, while the overall thickness remains relatively constant, implies structural rearrangements of the silicate network occurring within the alteration layer, which could eventually affect the transport of reactants and products as well as the structural stability.

Microstructure of Coal Gangue and Precipitation of Heavy Metal Elements

The microstructure and mineral composition of the gangue play a decisive role in the precipitation of heavy metal elements. In this study, the microstructure, mineral composition, and precipitation of heavy metal elements of coal gangue with different weathering degrees were analyzed through electron microscopy, X-ray diffraction, and static immersion leaching experiments. The following results were derived. (1) After the weathering of the coal gangue, its compactness and integrity changed significantly. The coal gangue structure transformed from relatively dense to relatively loose, and the development of large pores and fractures changed from basically no development to significant development. (2) After weathering, the contents of kaolinite and illite significantly increased, while that of feldspar significantly decreased. Coal gangue contains a small amount of Mn, Cu, Zn, Ti, Ba, Cl, and other elements. After weathering, the contents of each element were reduced. (3) Under the same conditions, a higher number of heavy metal elements precipitated from the weathered coal gangue than from the fresh coal gangue. The results of this research have significant importance in revealing the precipitation mechanism of heavy metals from coal gangue and in perfecting the theory of underground water environmental protection during solid backfilling mining.

Application of X-ray micro-CT for micro-structural characterization of APCVD deposited SiC coatings on graphite conduit

SiC coatings are commonly used as oxidation protective materials in high-temperature applications. The operational performance of the coating depends on its microstructure and uniformity. This study explores the feasibility of applying tabletop X-ray micro-CT for the micro-structural characterization of SiC coating. The coating is deposited over the internal surface of pipe structured graphite fuel tube, which is a prototype of potential components of compact high-temperature reactor (CHTR). The coating is deposited using atmospheric pressure chemical vapor deposition (APCVD) and properties such as morphology, porosity, thickness variation are evaluated. Micro-structural differences in the coating caused by substrate distance from precursor inlet in a CVD reactor are also studied. The study finds micro-CT a potential tool for characterization of SiC coating during its future course of engineering. We show that depletion of reactants at larger distances causes development of larger pores in the coating, which affects its morphology, density and thickness.

Production of char from vacuum pyrolysis of South-African sugar cane bagasse and its characterization as activated carbon and biochar

The potential of vacuum pyrolysis to convert sugar cane bagasse into char materials for wastewater treatment and soil amendment is the focus of this research paper. Vacuum pyrolysis produces both bio-oil and char in similar quantities. Vacuum pyrolysis has the potential to produce high quality chars for wastewater treatment and soil amendment directly during the conversion process, with no further upgrading required. In the present study, chars with the required porous structure was obtained directly from the vacuum pyrolysis process, making it very efficient as adsorbent both in terms of methylene blue (MB) adsorption with a N2-BET surface area of 418m2g−1. Further steam activation of the chars benefited the development of meso- and macroporosity, although this upgrading step was not essential to achieve the required performance of char as an MB adsorbent. The development of large pores during the vacuum pyrolysis favored physisorption of MB, rather than chemisorption. The chemical nature of the vacuum pyrolysis char resulted in a slightly acidic surface (pH 6.56). The biochar from vacuum pyrolysis can be considered as a highly beneficial soil amendment, as it would enhance soil nutrient and water holding capacity, due to its high cation exchange capacity (122cmolckg−1) and high surface area. It is also a good source of beneficial plant macro- and micronutrients and contains negligible levels of toxic elements.

Hydraulic properties of the diagnostic horizon of Latosols of a regional toposequence across the Brazilian Central Plateau

The Brazilian Central Plateau covers about 40% of the Cerrados Biome and represents 24% of the Brazilian territory. The Latosols correspond to about 40% of the Central Plateau. We analyzed the hydraulic properties of a set of Latosols varying according to clay content and mineralogy along a regional toposequence across the Brazilian Central Plateau. We studied the properties of the diagnostic horizon (Bw) of Latosols located on the South American and Velhas Surfaces. We measured the bulk and particle density, the water retention properties at − 1, − 6, − 10, − 33, − 300, and − 1500 kPa by using the centrifugation method, and determined the saturated hydraulic conductivity ( K s) in the field using the Guelph permeameter. Results showed that the total pore volume explained a proportion of the variance of the water retained that decreased with the water potential. On the other hand, the clay content explained a proportion of that variance that increases when the water potential decreased. The great proportion of variance (90.7%) explained for by the clay content alone at − 1500 kPa showed that there is little variability that can be attributed to clay mineralogy variation. The K s value was related to an effective porosity for the Bw of Latosols studied and was defined as the volume proportion of pore with an equivalent diameter of > 300 μm, since it was occupied by air at − 1 kPa. Results showed that water retention properties and K s varied mainly according to the clay content and development of large pores without any close link with the mineralogy of the clay fraction.

Preparation and crystallization characteristics of mesoporous TiO2 and mixed oxides

Mesoporous TiO2 and mixed Ti oxides are prepared by a modified sol-gel method using a block copolymer as a mesoporous template. Calcination of the material at 400 °C for template removal is shown to induce crystallization of pure TiO2, resulting in the destruction of the original mesoporous structure and the development of larger pores (7.5 nm) as inter-particle voids. The addition of tri-, tetra- and penta-valent metals (Al, Zr and Nb) to Ti oxide in the amorphous phase in the ratio Ti : M = 1 : 2 (M = Al, Zr or Nb) increases the thermal stability of the material by elevating the crystallization temperature above that for pure TiO2. The formation of Al2TiO5, TiZr2O6 and TiNb2O7 crystal phases without phase separation is confirmed in these materials, demonstrating the homogeneous mixing of TiO2 and the additive element at the atomic level. The mixed mesoporous oxides are thermally stable at 400 °C, although the porous structure is still destroyed due to crystallization. Thus, a homogeneous mixture of Ti with another element (Al, Zr or Nb) in mesoporous amorphous Ti-mixed oxide is observed.

Cellulose acetate hollow fiber membranes blended with phospholipid polymer and their performance for hemopurification

Commercially available hollow fiber membranes (HFMs) made from synthetic polymers, including cellulose acetate (CA) HFMs, used as hemopurification membranes, need to improve in hemocompatibility, by suppressing protein adsorption and clot formation. In this study, CA HFMs blended with 2-methacryloyloxyethyl phosphorylcholine (MPC) copolymer (PMB30 composed of MPC and n-butyl methacrylate (BMA)) were prepared by a dry-jet wet spinning process. Their performances were evaluated by characterizing their properties such as structure, permeability and protein adsorption. CA/PMB30-blend HFMs showed structure changes such as increase of porosity, development of large pores and decreasing of the thickness of the active layer. And the structure and permeability of CA/PMB30-blend HFMs were controllable by changing preparation conditions. Also, the CA/PMB30-blend HFMs had good permeability, low protein adsorption and low fouling property during the permeability experiment in comparison with CA HFMs, because the hydrophilic and hemocompatible MPC copolymer (PMB30) existed on the surface of the HFM.

Oxygen tracer study of the high-temperature oxidation of pure and impure cobalt

Oxygen tracer experiments were used to examine the role of oxygen movement in the development of CoO scales at 1273 K and 1373 K. Samples were oxidized in various sequences of16O2 and18O2, and the resulting isotope distributions imaged in polished sections of scales using a Camec a SIMS. Scales that were simple (i.e., plane parallel and composed of large, pore-free columnar grains) grew without a significant contribution by movement of oxygen. However, oxygen circulation within the scale was essential to the growth of duplex scales that developed after extended periods of oxidation. The relatively coarsegrained inner oxide on the purer Co grew without macroscopic separation of the scale from the metal. The oxygen for this inner scale came from the development of large pores in the columnar part of the scale. The fine-grained inner oxide on the impure Co had a crudely layered structure due to repeated sequences of scale separation followed by growth of porous oxide on the metal back to the main scale. The oxygen for these inner layers came in part from the development of large pores, but also from a more general dissociation of the base of the columnar scale. Scale failures, which occurred primarily at corners of specimens, did allow penetration of oxygen from the atmosphere to the inner scale. However, these failures sealed and were not essential for continued scale growth.

Mechanisms of proteinuria in diabetic nephropathy: A study of glomerular barrier function

The fractional clearance of neutral dextrans (theta D) with Einstein-Stokes radii between 30 and 64 A was determined in normal subjects (controls, N = 15) and in diabetic patients with heavy proteinuria (advanced nephropathy, N = 16) or trace proteinuria (early nephropathy, N = 8). When plotted on log normal probability coordinates, the correlation between theta D and radius in controls and in early diabetic nephropathy was linear, suggesting that glomerular pores form one population with a normal distribution. In advanced diabetic nephropathy, however, theta D for large molecules (radius greater than 46 A) was elevated and departed from linearity suggesting a bimodal pore size distribution within the glomerular membrane. A mathematical model was devised, which revealed the mean fraction of glomerular filtrate permeating the upper pore mode to be 0.009 +/- 0.002, and the pores to be totally nondiscriminatory toward molecules with radii up to 64 A. We conclude that the development of large pores (or defects) within the glomerular membrane in advanced diabetic nephropathy permits the unrestricted passage of large plasma proteins into the urine.

Porosity of alumina gels prepared from solutions of aluminium nitrate in various alcohols

AbstractMercury porosimetry and nitrogen adsorption measurements have been made on a series of alumina gels prepared by the passage of gaseous ammonia into solutions of aluminium nitrate nonohydrate in various alcohols. The values of surface area calculated from mercury intrusion curves and nitrogen isotherms (BET method) are in reasonable agreement with the macroporous gels, but the restricted penetration of mercury into the mesopore structures results in larger values of areas when calculated by nitrogen adsorption. Marked differences have been obtained in the pore size distribution of gels prepared in various alcohols, including the isomers of propanol and butanol. The alcohol appears to play a double role: (a) by replacing water at the solid‐liquid interface (it promotes aggregation‐cementation); (b) by decreasing the solubility (it reduces the rate of Ostwald ripening). Propan‐1‐ol and propan‐2‐ol tend to promote aggregation‐cementation and hence the formation of a well‐defined mesopore structure, whereas butan‐1‐ol and heptan‐1‐ol appear to favour particle growth and the development of larger pores.