Showing 1–12 of 135 results
A simple thermodynamic model for the doping and alloying of nanoparticles
Impurity incorporation into nanoparticles is modeled using thermodynamics. For small particles, entropically driven impurity incorporation is reduced, rendering doping difficult. We show that the free energy of surface impurities in small nanoparticles is lower than core impurities, surface doping therefore occurs preferentially. A critical size for core doping is identified, below which it is energetically unfavorable. In all cases, core impurity concentration is reduced as particle size decreases. We show larger than bulk impurity concentrations are possible, corresponding to increased alloying.
Antimicrobial Properties of Socks Protected with Silver Nanoparticles
Antimicrobial properties of socks containing silver nanoparticles were investigated. Two types of socks were used for testing. The first were linen (100%) socks impregnated with a specimen containing silver nanoparticles. The second type were commercially available cotton (55%) socks containing nanosilver. An antimicrobial effect was assayed against selected Gram-positive and Gram-negative bacteria as well as yeasts. It was found that the specimen used for impregnating linen socks has a wide range of antimicrobial activity against some Gram-positive, Gram-negative bacteria and yeasts – Candida albicans. Antimicrobial effectiveness depended on the type of microorganism, cell number and concentration of silver nanoparticles. Commercially available cotton socks presented antibacterial properties against Staphylococcus epidermidis.
Assessment of Nucleation Kinetic Mechanisms in Gas Hydrate Crystallization Processes
Nucleation is one ofرایگان!
Nucleation is one of the most important steps in the process of crystallization of gas hydrates. In the present work the nucleation mechanism of gas hydrate formation process using the propane as a sII gas hydrate former is investigated at isothermal operating conditions. Effects of variations of supersaturation and impeller speed on the kinetics of hydrate nucleation are also presented. Differente expressions for dependence of induction time with degree of supersaturation are employed. The accuracy of the predicted induction times for the case of progressive nucleation are always much higher than those obtained through instantaneous nucleation assumption at all ranges of impeller speeds. It is found that the heterogeneous progressive nucleation is the most probable nucleation mechanism at the early stages of gas hydrate formation processes
Batch Emulsion Polymerization of Vinyl Chloride: Application of Experimental Design to Investigate the Effects of Operating Variables on Particle Size and Particle Size Distribution
In this article, theرایگان!
In this article, the influences of operating variables on the particle size (PS) and particle size distribution (PSD) of emulsion poly(vinyl chloride) in batch reactor were investigated using Taguchi experimental design approach. The variables were temperature (T), water to monomer weight ratio (R), concentrations of initiator ([I]) and emulsifier ([E]), and agitation speed (S). Scanning electron microscope was used together with image analysis software to determine the PS and PSD. Statistical analysis of results revealed that the PS of emulsion poly(vinyl chloride) strongly depends on emulsifier and initiator concentrations, respectively, whereas the other factors have no significant effects in the range of levels investigated in this study. Except initiator concentration, all factors have important influence on the PSD (significance sequence: S > R > T > [E]). It is implied from the greater influence of agitation speed relative to temperature on PSD that the shear coagulation predominates the Brownian coagulation in this system. The relative optimum condition for a typical paste application was also determined using overall evaluation criteria.
Biopolishing of cotton fabric with fungal cellulase and its effect on the morphology of cotton fibres
Attempt has been madرایگان!
Attempt has been made to analyse structural changes in cotton fibres occurred during biopolishing using cellulases obtained from Trichoderma reesei. Cellulase hydrolysis results in weight loss of the samples, which, in turn, results in the splitting of fibres and removal of surface irregularities of the fibres as revealed by SEM images. Degree of crystallinity is not influenced by the biopolishing process due to random hydrolysis of the cellulase enzymes on cotton fibres. Lateral order of the crystallites, measured between (101) and (10 1 ) peaks of the x-ray diffraction reduces from 0.662 to 0.667 on account of the hydrolysis though the crystallite thickness measured perpendicular to (002) plane remains unchanged. FTIR results reveal the increased -OH bending, CH2 in-plane bending, and C-H vibrations of the cellulose chains in the biopolished cotton samples using cellulase.
Characterization and Identification of Gas Hydrate Bearing Sediments of Oman Sea Using Seismic Methods
Gas hydrates attractرایگان!
Gas hydrates attracted worldwide attention due to their potential as huge energy resource in the recent decades. Therefore identifying and prospecting them is essential for strategic hydrocarbon reservoir management. Seismic methods are known as a powerful gas hydrate exploration methodology. In this research pre-stack seismic attributes have been used to identify elastic properties and qualitative hydrate saturation of sediments. Using AVO analysis on pre-stack seismic data, occurrence of gas hydrate has been confirmed in the Oman Sea. Also post-stack seismic meta-attributes (applying pattern recognition and classification methods on several attribute planes) have been successfully used to make separation between hydrate and non-hydrate sediments. Joint use of pre- and post-stack seismic attributes will be a good evaluation techniques for confirmation of this study.
Characterization of Nanocrystals Using Spectroscopic Ellipsometry
First applications oرایگان!
First applications of ellipsometry to the measurement of poly- and nanocrystalline thin films date back to many decades. The most significant step towards the ellipsometric investigation of composite thin films was the realization of the first spectroscopic ellipsometers in the ’70s , which allowed the measurement of the dielectric function, the imaginary part of which is directly related to the joint density of electronics states sensitively depending upon the changes of the crystal structure. The first models were based on the effective medium approach using constituents of known dielectric functions , whereas the volume fraction of the components can be related to the crystal properties of the thin films. This approach is popular ever since, based on its robustness.
Characterization of poly(vinyl chloride) powder produced by emulsion polymerization
The effect of emulsiرایگان!
The effect of emulsion process formulation ingredients on the morphology, structure, and properties of polyvinyl chloride (PVC) powder has been considered in this study. PVC powder was extracted with ethanol and films were obtained by solvent casting from tetrahydrofurane. Characterization of powders, films, and ethanol extract was performed through FTIR spectroscopy, DSC, AFM, SEM, EDX analysis, methylene blue, and nitrogen adsorption. PVC powder was composed of spheres of a large particle size range from 10 nm to 20 lm as shown by SEM. The specific surface area of the PVC powder was determined as 16 and 12 m2 g-1 from methylene blue adsorption at 25 C and from N2 adsorption at -196 C, respectively. AFM indicated the surface roughness of the films obtained by pressing the particles was 25.9 nm. Density of PVC powder was determined by helium pycnometry as 1.39 g cm-3. FTIR spectroscopy indicated that it contained carbonyl and carboxylate groups belonging to additives such as surface active agents, plasticizers, and antioxidants used in production of PVC. These additives were 1.6% in mass of PVC as determined by ethanol extraction. EDX analysis showed PVC particles surfaces were coated with carbon-rich materials. The coatings had plasticizer effect since, glass transition temperature was lower than 25 C for PVC powder and it was 80 C for ethanol extracted powders as found by using differential scanning calorimetry. These additives from polymerization process made PVC powder more thermally stable as understood from Metrom PVC thermomat tests as well.
Computational Modeling of Natural Gas Production From Hydrate Dissociation
This paper providesرایگان!
This paper provides an overview of computational modeling of hydrate dissociation. A simplified axisymmetric model for natural gas roduction rom the dissociation of methane hydrate in a confined reservoir by a depressurizing well was first described. During the hydrate dissociation, the heat and mass transfer in the reservoir were analyzed, assuming a sharp dissociation front. The system of governing
equations was solved by a finite difference scheme, and the distributions of temperature and pressure in the reservoir, as well as the natural gas production from the well were evaluated. The numerical results were compared with those obtained by the linearization method. Hydrate dissociation in a porous sandstone core was then studied using a kinetic model. The ANSYSFLUENT code was used for analyzing hydrate dissociation in an axisymmetric core. When the core was opened exposing the core to low pressure, the hydrate in the core dissociates and the methane gas and liquid water begin to flow in the pores. A Users’ Defined function (UDF) for analyzing hydrate dissociation was developed and included in the FLUENT code. The New UDF used the Kim-Bishnoi kinetic model for hydrate dissociation. Variations of relative permeability of the core were included in the model. Sample simulation results were presented and discussed
Dependence of the Laminar Burning Velocity of Methane, Propane and Ethylene on Initial Temperature and Inert Diluent Concentration
Through its influencرایگان!
Through its influence on flamelet combustion, the laminar burning velocity is a crucial parameter in describing turbulent combustion. Calculations with a single chemical kinetics mechanism have determined the effect of equivalence ratio and initial temperature on the burning velocities of methane, ethylene and propane in air at atmospheric pressure. These results have been checked against available data in the literature, and then used to extrapolate to the much higher temperatures that are generally of interest in recirculating flows. Simple correlations have been developed to describe them to within 10% over the temperature range from 300K to 1100K in a convenient form for modeling purposes. Dilution of fuel by carbon dioxide is of interest in the context of synthetic and biogas fuels, and so its effect has also been computed. Comparison with dilution by nitrogen indicates the extent of CO2’s role as a reactive species.
Determination of Structure and Formation Conditions of Gas Hydrate by Using TPD Method and Flash Calculations
In this work, satbilرایگان!
In this work, satbility calculations and determination of gas hydrate structure in equilibrium conditions by using minimization of TPD function for ethane-water system (SI), propane-water system (SII) and methane-methyl cyclo pentane-water system (SH) were performed. Based on results, at 274 K and 275 K temperatures, the liquid phase of methane-water system at 27 bar and 30 bar pressures, propane-water system at .7 bar and 2.5 bar pressures and methane-methyl cyclo pentane-water system at 9.6 bar and 10.1 bar pressures was decomposed. As a result of decomposition of liquid phase for these systems, two new phases, a new liquid phase and hydrate phase were formed. Subsequently, multiphase flash calculations in order to determine the amount and composition of stable phases in equilibrium state were performed. For minimization of TPD function, Algorithm Genetic was used. The results Show good accuracy with data of Heriot Watt university hydrate model (HWHYD)