The carrier dyeing of synthetic fibers

The mode of action of carriers in augmenting the rate of dyeing of disperse dyes with acrylic and polyester fibers is discussed in terms of the plasticizing action of the carrier. It is shown that the effectiveness of a carrier is determined by its ability to reduce the glass transition temperature of the fiber and not by the fiber swelling. The rate of dyeing as measured by the diffusion coefficient of the dye is shown to be uniquely related to the difference between the dyeing temperature and the glass transition temperature (T – T_g). In the light of these results, some aspects of carrier action in dyeing from perchlorethylene are discussed. Treatment of polyester fibers with carrier also increases crystallinity. Changes in diffusion for a series of copolyesters have been correlated with the long spacing obtained from small angle X-ray scattering (SAXS).     

Measurements and Finite-Element Simulations of Residual Stresses Developed in Si3N4/Ni Diffusion Bonds

High-resolution X-ray scanning diffractometry has been used to study the residual strain in Si₃N₄/Ni diffusion bonds. Bonds were made by directly joining Ni and Si₃N₄ samples of same geometry by applying high temperature and enough mechanical pressure. The axial and radial strain profiles have been determined by X-ray diffraction in the ceramic bodies along selected lines perpendicular to the bonding interface. A very small absorption was assured as the X-ray experiments have been performed at the energy of 60 keV, which allowed measurements of the strain and stress fields in the ceramic bulk. The finite-element method calculations carried out showed an excellent agreement with the experimental data.     

Diffusion of lignin macromolecules within the fibre walls of kraft pulp. Part I: Determination of the diffusion coefficient under alkaline conditions

The intrinsic rate of diffusion of soluble lignin from fibre walls to bulk liquor has never been determined previously because of experimental difficulties; for example, the diffusion rate determined in a stirred cell is affected by the mechanical action of stirring. In our work, the intrinsic rate of diffusion of lignin macromolecules from the fibre walls of a softwood kraft pulp was determined under alkaline conditions using a displacement cell which eliminated external heat and mass transfer resistances and pulp fibre disturbances. The effects of such experimental conditions as pulp bed height and liquid flow rate were studied. The diffusion rate can be described by a diffusion model for a hollow cylinder with a very wide range of diffusion coefficients. The diffusion rate increased with increasing pH. Our results provide a new understanding of the lignin diffusion process in fibre walls, which is affected by the size of lignin molecules and the pores, and by the electrostatic interactions between intrafibre pore walls and lignin.     

Measurement technique on the diffusion coefficient of powder flow in a screw feeder by X-ray visualization

Measuring the diffusion coefficient of powder flow, which shows the magnitude of mixing, using X-ray visualization has been developed with the help of image processing techniques. Injecting minute metallic tracers into the powder yielded flow characteristics using the X-ray penetration images. The diffusion coefficient of the flow was determined by tracer figure deformation with time. Using this method, we evaluated four kinds of powder flows transported using different shaped screws in a screw feeder unit. The following results were obtained from this investigation: (i) Increasing the pitch width of the screw yielded decreased transport velocity and a larger diffusion coefficient. (ii) Double screw provided the largest transport velocity and the smallest diffusion coefficient.In addition, uncertainty analysis was applied to the method of measuring the diffusion coefficient to achieve greater bias limit.     

Adsorption of pollutants on to activated carbon in fixed beds

The adsorption of certain pollutants, namely phenol, p-chlorophenol, sodium dodecyl sulphate and mercuric ions, on to activated carbon has been studied using fixed bed systems. There are three main methods of contacting in solid/liquid adsorption systems, namely batch, fixed bed and fluidized bed systems. In fixed bed adsorption the adsorption rate is determined on the basis of adsorption equilibrium (unfavourable, linear, favourable or completely irreversible) and the controlling mechanism (external film mass transport, internal pore diffusion, internal solid phase diffusion or longitudinal diffusion). One or more of the previous transport mechanisms may be rate controlling depending on the solute-adsorbent system. For an adsorbent like activated carbon which is highly porous both external transport and pore diffusion will be very important. An adsorption model, based on external mass transport and internal pore diffusion, has been applied to the systems to predict theoretical breakthrough curves. These curves have then been compared with experimental data and using a ‘best fit’ technique, an effective pore diffusion coefficient can be determined for each sorbate–carbon system.     

Growth of Boric Acid Crystallites on the Surface of Boron-Doped Silicon Carbide Samples

White crystallites were visually observed on fractured or polished surfaces of SiC samples (grain sizes below ∼500 nm) during exposure to air at room temperature for several days. Characterization of the crystallites by scanning electron microscopy, secondary ion mass spectroscopy, and X-ray diffraction identified B(OH)₃ crystals with a strong (002) texture. The rate of boric acid formation was determined by a gravimetric experiment. The rate of weight gain increased significantly after an incubation period of 1 week. Nucleation is initially the rate-limiting process. Subsequently small B(OH)₃ crystals form on the surface, whose growth rate is determined by grain boundary diffusion of boron to the SiC surface. An estimated grain boundary diffusion coefficient of boron in SiC was many orders of magnitude higher than extrapolated literature values.     

Experimental determination of residual stress in silicon nitride diffusion bonds obtained by high-energy X-ray diffraction

High resolution X-ray scanning diffractometry has been used to study the residual strain in binary metal/ceramic (Ni/Si₃N₄) and ceramic/ceramic (Si₃N₄/Ni thin film/Si₃N₄) diffusion bonds. Bonds were fabricated by simultaneous high temperature heating and uniaxial pressing. The axial and radial strain profiles have been determined along selected lines perpendicular to the bonding interface inside the ceramic bodies. The X-ray experiments have been done at the energy of 60 keV, which assured a very small absorption, and therefore, strain fields have been measured in the ceramic bulk. Strains showed higher values near the interface that decreased with the distance.     

Techniques for the experimental determination of liquid permeation data,with particular reference to the n-hexane/polythene system

Permeation rates of n-hexane through polythene membranes have been determined as a function of temperature and pressure. The influence of membrane annealing and of the particular experimental technique adopted was studied. Concentration differences and diffusion coefficients were estimated from measurements of the time lag before a steady permeation rate could be achieved. It was shown that both random and systematic errors were so large that exact estimates of the diffusion coefficient were not possible. It was therefore necessary to use desorption data in conjunction with measurements of the permeation rate to arrive at values for the diffusion coefficient.     

The study of the proton diffusion process in the porous MnO2 electrode

The proton diffusion coefficients in an electrolytic manganese dioxide (EMD) electrode at various stages of the constant current discharge have been determined by means of AC impedance technique. The finite diffusion model was applied in the numerical fitting. The crystallite size of EMD was estimated from (1 1 0), (1 2 1) and (0 2 1) diffraction peaks with both Scherrer equation and Warren-Averbach theory. X-ray diffraction (XRD) peak broadening caused by instrument, crystallite size and microstrain was separated. The crystallite size of ramsdellite was assumed to be the proton diffusion length.     

Determination of Water Diffusion Coefficients and Dynamics in Adhesive/Carbon Fiber-Reinforced Phenolic Resin Composite Joints

Energy-dispersive X-ray spectroscopy analysis (EDX) is an easy and exact method for determination of water diffusion coefficients and dynamics. Here we have calculated the water diffusion coefficients and dynamics in adhesive/carbon fiber-reinforced phenolic resin composite joints subjected to different surface treatments with both EDX and elemental analysis. The water diffusion coefficients and dynamics in the adhesive joints determined with EDX analysis are almost the same as those determined with elemental analysis. The durability of the adhesive joints with carbon fiber-reinforced phenolic resin composites subjected to silane coupling agent treatment is better than those subjected to sandpaper burnishing and chemical oxidation treatment.     

Permeability coefficient of proton-irradiated poly(ethylene terephthalate) thin films

The principle of operation of an apparatus developed to study gas permeation through thin films is described, and the measurement method is discussed. Use is made of diffusion theory to obtain an expression for the permeability coefficient as a function of the rate of increase of the pressure in the receiving volume. The activation energy for permeation of helium through PET is determined. The permeability coefficient for helium is found to increase significantly with the range of the implanted protons although the incident charge has been kept constant. The hypothesis of structural modifications of the proton implanted PET seems to be confirmed by small-angle X-ray scattering experiments on the irradiated samples.     

Étude des caractéristiques de l'ecoulement créé par une turbine à Barreaux croisés dans une cellule de flottation — Influence du nombre de barreaux et de la viscosité Du liquide ii • puissance consommée et analyse spectrale

The effects of the number of bars, of a turbine made of crossed bars, and of the viscosity of the liquid on the spectral analysis of anemometric signals have been studied in a flotation cell: energy spectrum and correlation coefficient, time and spectral integral scales, turbulent diffusion coefficient, viscous energy dissipation rate and micro scale of turbulence have been determined and discussed.     

Adsorption on activated alumina. II — kinetic behaviour

The kinetics of adsorption of water vapour, dimethyl ether, isobutylene, and methanol on activated alumina have been investigated by gravimetric uptake rate and breakthrough curve measurements. Intraparticle diffusivities were determined by matching the experimental response curves to appropriate theoretical models. At low concentration the kinetic-behaviour is straightforward. The sorption rate is controlled by macropore diffusion with contributions from both the Knudsen and molecular mechanisms, depending on the conditions. For water vapour at higher pressures beyond the point of inflection of the isotherm there appears to be a significant contribution from surface diffusion.     

Modeling cat cracker catalyst demetallization

Vanadium and nickel have been identified as the major poisons that lead to the deactivation of cracking catalysts. These metals can be demetallized by a multistage process involving gas solid non-catalytic reactions in porous particles. Mathematical models for predicting the removal rate of vanadium when diffusion, reaction, and reaction and diffusion are controlling have been developed. It is generally accepted that vanadium is deposited on specific sites in the interior of the catalyst. This is verified since a diffusion controlled model for the removal of vanadium is in close agreement with experimental results. The parameters of the diffusion controlled model were estimated by constrained nonlinear regression. A total of five lumped mass transfer parameters for vanadium removal were determined using data from a laboratory demetallization unit. These parameters were then used to predict vanadium removal and compared with experiment.     

Determination of Water Diffusion Coefficients and Dynamics in Adhesive/Carbon Fiber–Reinforced Phenolic Resin Composite Joints

Energy-dispersive X-ray spectroscopy analysis (EDX) is an easy and exact method for determination of water diffusion coefficients and dynamics. Here we have calculated the water diffusion coefficients and dynamics in adhesive/carbon fiber–reinforced phenolic resin composite joints subjected to different surface treatments with both EDX and elemental analysis. The water diffusion coefficients and dynamics in the adhesive joints determined with EDX analysis are almost the same as those determined with elemental analysis. The durability of the adhesive joints with carbon fiber–reinforced phenolic resin composites subjected to silane coupling agent treatment is better than those subjected to sandpaper burnishing and chemical oxidation treatment.     

Kinetic investigation of the carbothermal reduction of an Iranian clay

The kinetics of the carbothermal reduction of clay under argon atmosphere has been investigated by the X-ray diffraction method. The clay-carbon (excess) mixture was formed into 2 cm diameter disks of different thicknesses. Experimental data evidences the significant effect of sample thickness on the reaction rate at 1400 °C. Decreasing thickness promotes mullite dissociation and formation of SiC and alumina powders. Mathematical modeling of the reaction system showed the gas diffusion in the Knudsen regime through the pellet to be the rate controlling step. Diffusivity of CO and reacted core tortuosity factor have been calculated.     

An experimental approach for measuring carbon dioxide diffusion coefficient in water and oil under supercritical conditions

Several direct or indirect approaches have been proposed to measure diffusion coefficient of gases into liquids. The main complexity of indirect techniques such as pressure decay method is interpreting early pressure–time data which strongly affected by incubation period effect or convective instability. In the current approach, accurate apparatus and precise experimental setup including a high pressure and temperature PVT cell, a high precision Sanchez pump, heating and recording sub-system are implemented and a novel data analysis procedure is applied to modify pressure decay method. The effect of incubation period is reduced remarkably and diffusion coefficient of carbon dioxide in water in wide range of pressures and temperatures is determined and the effects of temperature, pressure and carbon dioxide phase alteration from gas to supercritical are investigated and the value of uncertainty is estimated.Furthermore, diffusion coefficient of CO_2 and methane in an oil sample from one of the Iranian southwest oil formations is determined precisely using the experimental approach while no incubation period is detected. The results showed that incubation period duration decreases with increasing diffusion coefficient. Additionally, when CO_2 state is gas, rate of increasing diffusion coefficient with pressure is decreased with temperature and when CO_2 state is supercritical, the rate of increasing diffusion coefficient with pressure is decreased significantly.     

The Degradation of Polyglycolide in Water and Deuterium Oxide. Part I: The Effect of Reaction Rate

The relative importance of the rate of hydrolysis reaction and the rate of water diffusion in the degradation of polyglycolide (PGA) has been investigated. Samples were degraded in standard phosphate-buffered saline, and in fully and partially deuterated buffer solutions. Although the diffusion rate of deuterated water in PGA is similar to that of water, the acid-catalysed hydrolysis of the ester is significantly slower in D₂O because of the kinetic isotope effect. The degradation process was examined using small angle X-ray scattering, mass loss and water uptake measurements, pH measurements and drug release profiles. The results show that the hydrolysis rate has an important effect and that the system is not wholly diffusion controlled. The results are consistent with a four-stage reaction-erosion front model of degradation.     

KINETICS AND MECHANISM OF THE INTERFACIAL MASS TRANSFER OF Zn2+, Co2+, Ni2+ IN THE SYSTEM: BIS(2-ETHYLHEXYL)PHOSPHORIC ACID,n-DODECANE - KNO3, WATER

ABSTRACT

The mass transfer rate of Zn(II), Co(II) and Ni(II) between aqueous nitrate solutions and n-dodecane solutions of the organic soluble ligand HDEHP has been investigated using a forced convection, constant interfacial area stirred cell. The distribution ratios necessary to evaluate the kinetic experiments have been determined and the equilibrium constants which describe the heterogeneous complex formation reaction between Zn²⁺, Co²⁺, Ni²⁺ and HDEHP have been evaluated. The results have been interpreted according to two limiting models: 1) the mass transfer rate is controlled by slow reversible interfacial reactions, 2) the mass transfer is controlled by interfacial film diffusion. Both models are adequate to Interpret the experimental data. The conclusion Is reached that, if interfacial chemical reactions are rate controlling, rate constants of interfacial complex formation reactions independent of the nature of the cation are obtained. This result supports a reaction mechanism which is rate controlled by the microscopic diffusion of the cation through a viscous and structured layer of interfacial water adjacent to the liquid interface