Effect of ammonium on the hydraulic conductivity of geosynthetic clay liners

Hydraulic conductivity and swell index tests were conducted on a conventional geosynthetic clay liner (GCL) containing sodium-bentonite (Na-B) using 5, 50, 100, 500, and 1000 mM ammonium acetate (NH₄OAc) solutions to investigate how NH₄⁺ accumulation in leachates in bioreactor and recirculation landfills may affect GCLs. Control tests were conducted with deionized (DI) water. Swell index of the Na-B was 27.7 mL/2 g in 5 mM NH₄⁺ solution and decreased to 5.0 mL/2 g in 1000 mM NH₄⁺ solution, whereas the swell index of Na-B in DI water was 28.0 mL/2 g. Hydraulic conductivity of the Na-B GCL to 5, 50, and 100 mM NH₄⁺ was low, ranging from 1.6–5.9 × 10^?11 m/s, which is comparable to the hydraulic conductivity to DI water (2.1 × 10^?11 m/s). Hydraulic conductivities of the Na-B GCL permeated with 500 and 1000 mM NH₄⁺ solutions were much higher (e.g., 1.6–5.2 × 10^?6 m/s) due to suppression of osmotic swelling. NH₄⁺ replaced native Na⁺, K⁺, Ca²⁺, and Mg²⁺ in the exchange complex of the Na-B during permeation with all NH₄⁺ solutions, with the NH₄⁺ fraction in the exchange complex increasing from 0.24 to 0.83 as the NH₄⁺ concentration increased from 5 to 1000 mM. A Na-B GCL specimen permeated with 1000 mM NH₄⁺ solution to chemical equilibrium was subsequently permeated with DI water. Permeation with the NH₄⁺ converted the Na-B to “NH₄-bentonite” with more than 80% of the exchange complex occupied by NH₄⁺. Hydraulic conductivity of this GCL specimen decreased from 5.9 × 10^?6 m/s to 2.9 × 10^?11 m/s during permeation with DI water, indicating that “NH₄-bentonite” can swell and have low hydraulic conductivity, and that the impact of more concentrated NH₄⁺ solutions on swelling and hydraulic conductivity is reversible.     

Mechanical behavior of the membrane during the polymer electrolyte fuel cell operation

A computational modeling framework is developed to represent the transport phenomena, electrochemistry and the mechanical stresses in a polymer electrolyte fuel cell (PEFC). The model is able to predict the mechanical stresses developed in the polymer electrolyte due to hydration changes, and restriction of the membrane swelling as a result of these hydration changes in the PEFC assembly. Anisotropy in the mechanical properties of the gas diffusion layers is accounted in the stress calculations. It is seen that hydration variations during the PEFC operation can cause significant mechanical stresses. The effects of operating voltage and relative humidities of reactants are investigated. It is observed that high inlet humidities result in a better performance; however, it can potentially cause the polymer electrolyte membrane to go through plastic deformation irreversibly. Thermal stresses due to temperature variations are also calculated and compared with hygral stresses; and it is found that thermal stresses are not negligible but are typically a fraction of the hygral stresses in a typical PEFC operation.     

Equations of anomalous absorption onto swelling porous media

Absorption is a very common process which takes place on various types of materials ranging from porous media to new nano-materials and biological tissues. The majority of studies reported on absorption to date are concentrated on “rigid” porous media, which contradict the properties of real porous media which undergo swelling and shrinking changes. Here we present new absorption equations derived from a fractional diffusion-wave equation (fDWE) for absorption onto swelling porous media in a material coordinate. We show that the cumulative anomalous absorption is I(t) = St^β/2 and the absorption rate , where S is the anomalous sorptivity and β the order of fractional derivative in fDWE. Using published data on cumulative absorption against time, the two adsorption parameters are determined: β = 1.2448 and S = 2.7775 cm²/h. The value of β = 1.2448 implies that absorption onto this swelling porous media belong to the category of super-diffusion, which is a phenomenon unknown to us before. In comparison, the traditional absorption equations do not have such features. When S is determined, the anomalous diffusivity, D_m, is calculated using its relation with S. We expect that the proposed new absorption equations will be valuable for explaining new phenomena and processes encountered in broader disciplines of science and engineering applications.     

Evaluation of Water Retention Functions and Computer Program “Rosetta” in Predicting Soil Water Characteristics of Seasonally Impounded Shrink–Swell Soils

Soil water retention is a critical factor influencing irrigation decisions and hence agricultural crop yields. However, information on soil water retention characteristics (SWRC) is seldom available for irrigation planning, crop yield modeling, or hydrological simulations, especially for problematic soils, such as seasonally impounded shrink-swell soils. As large scale direct measurement of SWRC is not viable due to a number of reasons, researchers have developed pedotransfer functions (PTFs) to estimate SWRC from easily measured soil properties, such as texture, organic matter content, bulk density, etc. However, PTF applicability in locations other than those of data collection has been rarely reported. One of the most recent PTFs that has shown overall reasonable predictions in evaluation studies is Rosetta, a numerical code for estimating soil hydraulic parameters with hierarchical pedotransfer functions. Relatively, the development of large databases makes it one of the widely used PTFs. If validated for spatial application, it has immense use potential in countries like India, where data on soil hydraulic properties are seldom available, a deficiency that hampers better simulations in processes, like partitioning runoff and infiltration, assessing evapotranspiration, irrigation scheduling, etc. Rosetta is also relatively flexible allowing estimation of hydraulic properties from easily available minimum input of textural fractions. This study was conducted to evaluate (1) an applicability of four widely used soil water retention functions to describe SWRC; and (2) the computer program Rosetta for its validity. Statistical indices, i.e., root mean square error (RMSE), mean absolute error, maximum absolute error, and degree of agreement (d) were computed to evaluate “goodness-of-fit” of the four functions to the measured SWRC data. These indices were also used to compare measured SWRC with estimates of SWRC by Rosetta. For soil samples collected from 41 profiles, 175 SWRC were measured in the laboratory. The van Genuchten function fitted relatively better (RMSE = 0.052?m3?m?3) to SWRC of clay soils, whereas the Brooks–Corey (BC) function was better in expressing SWRC of clay loam and sandy clay loam soils with RMSE = 0.06 and 0.07?m3?m?3, respectively. Campbell and Cass–Hutson (CH) functions were of intermediate value. Worst performing functions were BC (clay soils), Campbell (clay loam), and CH (sandy clay loam) with corresponding RMSE = 0.059, 0.065, and 0.077?m3?m?3. Estimates of two important points on the SWRC curve, i.e., field capacity and permanent wilting point were predicted with relatively better accuracy for clay and sandy clay loam soils by all the four functions. RMSE and d ranged from 0.027?to?0.043?m3?m?3 and from 0.73 to 0.88 for clay soils. Corresponding values for sandy clay loam soils were 0.008?–0.019?m3?m?3, and 0.92–0.98. However, in clay loam soils, only two functions were found suitable. Estimates of SWRC obtained by applying hierarchical rules in Rosetta were reliable (RMSE<0.05?m3?m?3). Magnitude of average RMSE increased progressively in clay loam, clay and sandy clay loam soils (0.028<0.035<0.042?m3?m?3). The study established that SWRC of the “Haveli” soils could be estimated using generic PTF and thus information that is prerequisite in simulating hydrological processes occurring in seasonally impounded soils could be acquired.     

Properties of protease-treated maize starches

Commercially produced maize starches were treated with protease (Promod 25P) and their composition and properties were compared with untreated controls. It was found that, although protease treatment reduced the starch protein contents by 41%, 21% and 37% for the waxy, normal and amylomaize starches, respectively, it also caused some pits on the granule surfaces, which were evident by scanning electron microscopy (SEM), but no obvious decrease in granule dimensions (Coulter Counter Multisizer). The protein extraction was associated with decreases in starch lipid content by 42%, 40% and 45% (waxy, normal and amylomaize starches, respectively) and a decrease in total amylose content (30.7–26.0%) for the normal maize starch. The gelatinisation parameters of the starches by differential scanning calorimetry (DSC) in water, 0.001 M HCl or NaOH were less obviously affected by protease treatment in common with the swelling factors at 80 °C. The amount of α-glucan leached by the swollen (80 °C) granules was, however, increased by the protease treatment by factors of 3.8, 1.4, and 1.1, for the waxy, normal and amylomaize starches, respectively. Although proteases provide a useful tool for the purification of native starches, commercial protease preparations need to be controlled in terms of amylase content to prevent modifications to starch structure and properties during industrial processing.     

Methanol permeability and performance of Nafion-zirconium phosphate composite membranes in active and passive direct methanol fuel cells

Methanol crossover through polymer electrolyte membranes represents one of the major problems to be solved in order to improve direct methanol fuel cell (DMFC) performance. With this aim, Nafion/zirconium phosphate (ZrP) composite membranes, with ZrP loading in the range 1-6 wt%, were prepared by casting from mixtures of gels of exfoliated ZrP and Nafion 1100 dispersions in dimethylformamide. These membranes were characterised by methanol permeability, swelling and proton conductivity measurements, as well as by tests in active and passive DMFCs in the temperature range 30-80 °C. Increase in filler loading results in a decrease in both methanol permeability and proton conductivity. As a consequence of the reduced conductivity the power density of active DMFCs decreases with increasing ZrP loading (from 46 to 32 mW cm⁻² at 80 °C). However, due to the lower methanol permeability, the room temperature Faraday efficiency of passive DMFCs, with 20 mA cm⁻² discharge current, nearly doubles when Nafion 1100 is replaced by the composite membrane containing 4 wt% ZrP.     

Process and formulation variables affecting the performance of a rupturable capsule-based drug delivery system with pulsatile drug release

The objective of this study was to optimize several process and formulation parameters, which influence the performance of a rupturable, pulsatile drug delivery system. The system consisted of a drug-containing hard gelatin capsule, a swelling layer of croscarmellose (Ac-Di-Sol®) and a binder, and an outer ethylcellulose coating. Polyvinyl pyrrolidone (Kollidon 90F) was superior to HPMC and HPC as a binder for the swelling layer with regard to binding (adherence to capsule) and disintegration properties of the swelling layer. The capsule-to-capsule uniformity in the amount of swelling layer and outer ethylcellulose coating, which significantly affected the lag time prior to rupture of the capsule, was optimized by decreasing the batch size, and by increasing the rotational pan speed and the distance between the spray nozzle and the product bed. The type of baffles used in the coating pan also affected the layering uniformity. Fully-filled hard gelatin capsules had a shorter lag time with a higher reproducibility compared to only half-filled capsules, because the swelling pressure was directed primarily to the outer ethylcellulose coating and not to the inner capsule core. Stability studies revealed that the lag time of the capsules was stable over a 240-day period when the moisture content was kept unchanged.     

Geomechanical characterization of a tectonized shaley complex in the hilly area around Florence

In a typical unit of structurally complex, mainly shaley and highly tectonized terrain, two different levels of shaley clayey materials in the same site were identified and analyzed. These lithotypes were characterized in terms of their behaviour as a result of swelling phenomena connected with the mineralogy, stress history and variation in water content. The aim of the study was to assess, in particular, the problems caused by cutting and altering the slope composed of these heterogeneous terrains.     

A swelling model for stoichiometric SiC at temperatures below 1000°C under neutron irradiation

A simple phenomenological model for the saturation swelling below 1000°C of neutron-irradiated silicon carbide (SiC) is presented in this paper. Under fast neutron irradiation, SiC is known to undergo volumetric expansion (swelling) which quickly saturates at a fast fluence of approximately 10²⁵ n/m² for irradiation temperatures below 1000°C. A previous model due to Balarin attributes swelling to lattice dilation as a result of single point defects. We show in this paper that the experimentally observed linear temperature dependence of saturation swelling can be explained in terms of the formation and growth of small interstitial clusters, resulting directly from collision cascades initiated by energetic neutrons. These loops grow by absorption of mobile carbon interstitials and their composition is subject to stoichiometry constraints, requiring absorption of slower silicon interstitials. Because of cascade re-solution events, the density of loops decreases sharply with temperature as a result of overlap of cascades with larger size loops at higher temperatures. The average radius of these loops increases with temperature. Volumetric swelling is shown to obey a linear temperature dependence as a consequence of the strong decrease in density and the simultaneous increase in average radius, and to saturate with fluence. The model is shown to be consistent with experimental observations. In the temperature range below 500–600°C, swelling seems to be dominated by single point defects, or defect clusters containing only a few atoms, in accordance with the explanation offered by Balarin.     

碱—碳酸盐骨料反应及膨胀机理和抑制效果探讨

本文根据宝珠寺水电工程人工骨料料场粘土质白云岩夹层岩样碱一碳酸盐反应的试验鉴定结果，结合有关资料对其膨胀机理提出了探讨性意见。并综合评述了抑制碱一碳酸盐骨料反应的措施。