Montmorillonite polymer concrete: Zero-shrinkage and expanding polymer concrete with enhanced strength

Conventional polymer concrete (PC) suffers from setting stresses, generated during the cure of the resin binder, when polymerization shrinkage is hindered by the close packing of filler and aggregate particles. Setting stresses impair significantly the strength of the cured PC. Current zero-shrinkage and expanding PC formulations achieve these properties with a sacrifice in strength. Here we present a novel method for producing zero-shrinkage and expanding PC systems with concomitant enhancement in strength. This is achieved by dispersing small amounts of the mineral montmorillonite (MMT) into the resin. As the system cures, the resin interacts with the hydrated mineral: at temperatures above 100°C some of the hydration water is released, creating expansion forces, which counteract resin shrinkage. MMT contents of 0.2 percent or less give rise to zero-shrinkage polyester PC systems with flexural strength 30 percent greater than the corresponding conventional PC; higher MMT contents create PC systems that expand upon curing or generate hydrostatic pressure during constant-volume cure. We discuss the effects of MMT content and cure temperature on the volume change and strength of the resulting PC. We then propose a mechanism for the action of MMT as a highstrength expansion agent, based on differential scanning calorimetry and thermomechanical analysis of these systems.     

Preparation and properties of plasma-deposited films with surface energies varying over a wide range

Polymer surfaces have been modified by chemical reaction or thin film deposition using a capacitatively coupled plasma RF-discharge system. This has allowed the production of a graded, reproducible series of surfaces with surface energies ranging from low to high. Three gases, hexafluoroethane (C₂F₆), perfluoropropane (C₃F₈), and hexafluoropropene (CF₃CF?CF₂), were used to prepare the low-energy surfaces. Ethylene oxide (C₂H₄O) was used to prepare the higher energy surfaces. Intermediate values of surface energy were obtained by using gas mixtures of perfluoropropane and ethylene oxide. The plasma-deposited films were characterized by ESCA and contact-angle studies. In the low-energy range, the critical surface tension (γ_c) values of the films prepared were found to be lower than those for Teflon. For the higher energy surfaces, values up to about 45 dyn/cm were obtained. Addition of oxygen to the plasma permitted the production of films with still higher γ_c values. ESCA studies indicate that, under the reaction conditions used, C₃F₈ and CF₃CF?CF₂ form a fluoropolymer deposit on glass that is at least 100 Å thick. For the same reaction parameters, C₂F₆ resulted in more etching and deposition of a much thinner film.     

The effect of sorption on the tensile creep and strength reduction of desiccated concrete

The influence of sorption of fluids of differing molecular size on the strength and tensile creep of desiccated concrete and mortar are investigated. It is shown that the desiccated tensile strength is significantly reduced by sorption in accordance with the molecular sieve concept; compressive and splitting tensile strengths are also reduced but to lesser extent. For specimens subjected to a constant applied tensile load, strength reduction increases the effective stress-strength ratio thereby contributing to creep. In some cases, the concomitant effect of strength reduction and sorption induced deformations results in specimen fracture.     

Reduction of iron ore fines by coal fines in a packed bed and fluidized bed apparatus—A comparative study

Reduction of iron ore fines by coal fines in packed and fluidized beds has been studied. The investigation includes study of the kinetic aspects of reduction, carbon and sulfur content of the direct reduced iron (DRI) produced, and metallography of the products. For both processes, the kinetic data fit the first-order reaction model. Reduction in a fluidized bed is much faster than in a packed bed system. In both cases, DRI contains a substantial amount of free carbon at the initial stages of reduction. At the later stages of reduction, the carbon present in the DRI is mainly in the combined state. For identical temperatures and particle sizes, reaction in fluidized bed is much faster compared to that in a packed bed. At any particular degree of reduction, sulfur content in DRI samples produced by fluidized bed reduction is always more than that of DRI samples produced by packed bed reduction. Scanning electron microscopy (SEM) micrographs reveal that metallic whiskers formed during reduction in packed beds only. These whiskers become more prominent at higher temperatures and longer times.     

Studies with inorganic precipitate membranes—XI: Evaluation of the thermodynamically effective fixed charge density by various methods

Thermodynamically effective fixed charge densities of parchment supported membranes were estimated by methods of (a) Teorell—Meyer—Sievers, (b) Altug and Hair, and (c) the most recent one of Kobatake based on the thermodynamics of irreversible processes. The two limiting forms of Kobatake's equation for dilute and concentrated ranges gave identical values of charge densities. It is interesting to note that these two values of limiting cases are closer to the Teorell—Meyer—Sievers and Altug and Hair values. The theoretical prediction for membrane potential by the Kobatake's equation were borne out quite satisfactorily by experimental results obtained with both the membranes.     

Studies with inorganic precipitate membranes—XII: Consideration of membrane field strength and energetics of permeation

Electrolytic transfort processes occuring across parchment supported membranes have been described by Nernst Planck flux equation taking into account the membrane resistance R_m, membrane potential E_metc.E_m values for various electrolytes display very interesting phenomena. In the case of 1:1 electrolyte the E_m values are all positive, while in the case of (2:1) and (3:1) electrolytes surface charge reversal takes place. The diffusion rate sequence and selectivity of the membrane for different uni- bi- and trivalent cations was found to be primarily dependent on the difference in the hydration energies of counter ions in the external solution. On the basis of Eisenman-Sherry theory the diffusion rate sequence of alkali metal cations point towards the weak field strength of the fixed charge groups. Various thermodynamic parameters, ΔH^≠, ΔF^≠ and ΔS^≠ were evaluated by applying the theory of absolute reactions rates to the diffusion process through parchment supported membranes. The values of ΔS^≠ were found to be negative, indicating that diffusion takes place with partial immobilization in the membrane phase. The relative partial immobility was found to increase with increase in the valence of the ions constituting the electrolyte. A formal relation between ΔH_hydration, ΔF_hydration and ΔS_hydration of cations with the corresponding values of ΔH^≠, ΔF^≠ and ΔS^≠ for diffusion, was also found to exist for these membranes.     

Atmospheric corrosion of clad palladium and palladium-silver alloys: film growth and contamination effects

Claddings of Pd, Pd-40 Ag and Pd-60 Ag on CA725² copper alloy, exposed for up to 40 months in certain air-conditioned telephone central offices, do not show significant film growth or surface contamination effects. When exposed for similar periods in a non-air-conditioned room of a central office, these claddings had dust particles containing salts of Ca, Na and Cl on a hydrated palladium dichloride film for Pd, and on a mixed hydrated PdCl₂ and silver chloride film for Pd-40 Ag and Pd-60 Ag. The growth rate of the chloride film was parabolic with rate constants of 1.11 × 10^?11 cm²/month for Pd, 2.77 × 10^?12 cm²/month for Pd-60 Ag and 5.82 × 10^?13 cm²/month for Pd-40 Ag. The Pd-60 Ag alloy also reacted with other contaminants and was the most degraded with respect to total film growth, followed by Pd and Pd-40 Ag.     

Extraction of motion parameters of gravity-wave structures from all-sky OH image sequences

We describe the application of a motion model to OH images collected by CCD cameras during three nights in February and April 1995 (3 February, 1 April, and 4 April) at the StarFire Optical Range, New Mexico. We used the instrument to take broadband images of OH Meinel bands at an altitude of 87 km to record the footprints of dynamics created by acoustic gravity waves in the mesosphere. We used the motion model to extract the velocity of the gravity waves from the images. The results of a total of 181 observations with the motion model were compared with a total of 189 observations obtained by manual estimation. We used these results to extract the intrinsic properties of the gravity waves. The mean intrinsic velocity for the three nights under consideration was 61.5 +/- 17.0 m/s with the motion model and 61.1 +/- 23.3 m/s with manual estimation.     

PSO Based Multi-Objective Approach for Controlling PID Controller

CSTR (Continuous stirred tank reactor) is employed in process control and chemical industries to improve response characteristics and system efficiency. It has a highly nonlinear characteristic that includes complexities in its control and design. Dynamic performance is compassionate to change in system parameters which need more effort for planning a significant controller for CSTR. The reactor temperature changes in either direction from the defined reference value. It is important to note that the intensity of chemical actions inside the CSTR is dependent on the various levels of temperature, and deviation from reference values may cause degradation of biomass quality. Design and implementation of an appropriate adaptive controller for such a nonlinear system are essential. In this paper, a conventional Proportional Integral Derivative (PID) controller is designed. The conventional techniques to deal with constraints suffer severe limitations like it has fixed controller parameters. Hence, A novel method is applied for computing the PID controller parameters using a swarm algorithm that overcomes the conventional controller's limitation. In the proposed technique, PID parameters are tuned by Particle Swarm Optimization (PSO). It is not easy to choose the suitable objective function to design a PID controller using PSO to get an optimal response. In this article, a multi-objective function is proposed for PSO based controller design of CSTR.     

Biosynthesis of Flower-Shaped CuO Nanostructures and Their Photocatalytic and Antibacterial Activities

Copper oxide nanoflowers(CuO-NFs)have been synthesized through a novel green route using Tulsi leaves-extracted eugenol(4-allyl-2-methoxyphenol)as reducing agent.Characterizations results reveal the growth of crystalline singlephase CuO-NFs with monoclinic structure.The prepared CuO-NFs can effectively degrade methylene blue with 90%efficiency.They also show strong barrier against E.coli(27±2 mm)at the concentration of 100μg mL−1,while at the concentration of 25μg mL−1 weak barrier has been found against all examined bacterial organisms.The results provide important evidence that CuO-NFs have sustainable performance in methylene blue degradation as well as bacterial organisms.