Larger Particle Diameter Research Articles

Influence of smectite suspension structure on sheet orientation in dry sediments: XRD and AFM applications

The structure-building phenomena within clay aggregates are governed by forces acting between clay particles. Measurements of such forces are important to understand in order to manipulate the aggregate structure for applications such as dewatering of mineral processing tailings. A parallel particle orientation is required when conducting XRD investigation on the oriented samples and conduct force measurements acting between basal planes of clay mineral platelets using atomic force microscopy (AFM). To investigate how smectite clay platelets were oriented on silicon wafer substrate when dried from suspension range of methods like SEM, XRD and AFM were employed. From these investigations, we conclude that high clay concentrations and larger particle diameters (up to 5 μm) in suspension result in random orientation of platelets in the substrate. The best possible laminar orientation in the clay dry film, represented in the XRD 0 0 1/0 2 0 intensity ratio of 47 was obtained by drying thin layers from 0.02 wt.% clay suspensions of the natural pH. Conducted AFM investigations show that smectite studied in water based electrolytes show very long-range repulsive forces lower in strength than electrostatic forces from double-layer repulsion. It was suggested that these forces may have structural nature. Smectite surface layers rehydrate in water environment forms surface gel with spongy and cellular texture which cushion approaching AFM probe. This structural effect can be measured in distances larger than 1000 nm from substrate surface and when probe penetrate this gel layer, structural linkages are forming between substrate and clay covered probe. These linkages prevent subsequently smooth detachments of AFM probe on way back when retrieval. This effect of tearing new formed structure apart involves larger adhesion-like forces measured in retrieval. It is also suggested that these effect may be enhanced by the nano-clay particles interaction.

Controlling synthesis of well-crystallized mesoporous TiO2 microspheres with ultrahigh surface area for high-performance dye-sensitized solar cells

In this study, well-crystallized mesoporous anatase TiO2 spheres were prepared by hydrothermal treatment of the titanium diglycolate precursors. These spheres are submicrometer-sized and consist of packed nanocrystallites with diameters of ∼8 nm, and possess a specific surface area of 193 m2 g−1 and main pore sizes of ∼5 nm. We demonstrated that due to the large particle diameters and ultrahigh specific surface areas, mesoporous TiO2 microspheres can enhance the light harvesting within the photoanodes for dye-sensitized solar cells (DSSCs), and meanwhile, their good crystallinity and better interparticle connections caused by partially oriented attachment of primary particles result in the effective charge transport through the film of mesoporous TiO2 spheres. A high light-to-electricity conversion of 8.20% has been achieved, indicating a 40% increase in the conversion efficiency compared to the standard Degussa P25 photoanode.

Relationship of Particle Content and Size of Spherical Silica with the Flowability of Epoxy Molding Compounds for Large-Scale Integrated Circuits Packaging

The melting viscosities of different kinds of epoxy resins have been investigated in this paper. The results showed that tetramethyl biphenyl epoxy resin(TMBP) has very low melting viscosity(0.02Pa•s at 150°C) and can be blended with ortho-cresol novolac epoxy resin(ECN) in order to decrease the melting viscosity of epoxy molding compound(EMC). When the content of TMBP in the blend of ECN/TMBP was up to 40wt%, the viscosity of the blend decreased to 0.15 Pa•s from 0.8 Pa•s of ECN. In addition, the effects of the content, particle size of silica on the flowability of EMC have been researched systematically in the paper. The results showed that the melting viscosity of EMC increased greatly with the filling increasing of silica, and the particle size and the match of silica with different particle diameter had markedly influenced on the flowability of EMC. The melting viscosity of system with higher filling content of silica changed complicatedly with the increasing of shear rate, i.e., the viscosity of the system decreased with the increasing of shear rate in the range of low shear rate, then increased with the increasing of shear rate in the range of high shear rate, but decreased again with the increasing of shear rate in the range of higher shear rate. The system filled by silica with small particle diameter had low melting viscosity at low shear rate and high melting viscosity at high shear rate, but the melting viscosity of the system filled by silica with large particle diameter changed by contraries.

Preparation, Characterisation and Mechanical Properties of Environmentally Friendly Waterborne Polyurethane and Polyurethane-Acrylate

The waterborne polyurethane (PU) prepolymer was prepared based on the polyester polyol (N220), isophorone diisocyanate (IPDI), and dimethylol propionic acid (DMPA). The waterborne polyurethane-acrylate (PUA) dispersions were prepared with different proportions of acrylate by in situ dispersion technique. The structures and properties of prepared PU and PUA were analysed and characterised with FT-IR spectroscopy, etc. The results indicated that compared with PU, the PUA dispersions had larger particle diameters, narrower particle-size distribution, lower surface tension, high temperature stability and freeze-thaw stability. The PUA films showed better optical transparency, higher tensile strength and lower elongation at break. The prepared PUA have potential application such as coatings, leather finishing, adhesives, sealants, plastic coatings and wood finishes.

Synthesis of ZnO Nanoparticles by Solvothermal Method and Their Ammonia Sensing Properties

ZnO nanoparticles were prepared by a simple solvothermal route by using a ethylene glycol (EG)-ethanol (E) solvent system. The shape and size of ZnO nanoparticles were tuned by changing the volume composition of the solvents and the synthesis temperature. Phase purity was confirmed by X-ray diffraction (XRD) and crystal size was determined by transmission electron microscopy (TEM). Ellipsoidal and spherical nanoparticles were obtained by varying the volume ratio of the solvents. Mostly spherical nanoparticles with average diameter of 4 nm was synthesized with higher volume fraction of EG at a lower synthesis temperature. The blueshift of room-temperature photoluminescence measurement from free exciton transition are observed for the smallest nanoparticle size that is ascribed to the quantum confinement effect. The ammonia gas sensing characteristics of the smallest diameter nanoparticles showed better sensitivity at a relatively lower temperature than that of large diameter particles.

Facet-Selective Platinum Electrodeposition at Free-standing Polycrystalline Boron-Doped Diamond Films

In the present investigation, electrochemical deposition of platinum particles was carried out on boron doped diamond (BDD) films by using cyclic voltammetry at different potential sweep rates while maintaining the Pt concentration and number of potential cycles during the deposition as constant for all samples. The BDD film surfaces were studied using Raman spectroscopy, X-ray diffraction, and scanning electrochemical microscopy. The deposited particles were characterized by scanning electron microscopy/X-ray energy dispersive analysis, X-ray photoelectron spectroscopy, and cyclic voltammetry before and after methanol oxidation. The platinum nanoparticles are found to be selectively electrodeposited on the (111) facets of the BDD. In addition, the location of the Pt particles on the diamond facets was affected by the potential sweep rate. For higher sweep rates, the particle size was dependent on the facet on which the particles are electrodeposited with smooth (110) facets exhibiting a smaller number of particles but with a larger particle diameter. After methanol oxidation studies using cyclic voltammetry and controlled potential electrolysis for several hours, the platinum particles remained attached to the (111) facets of the BDD, while the particles on the (110) facets of the BDD became agglomerated along grain boundaries. Functional groups present on the (111) facet of the diamond surface play an important role on the stability of the particles attached to the diamond surface. After methanol oxidation, the particles deposited on other facets appeared to lose their adhesion leading to agglomeration on the grain boundaries. BDD appears to be a promising electrocatalyst support material that can help to resist platinum nanoparticle agglomeration in direct methanol and other low temperature fuel cell applications.

Pharmaceutical quality evaluation of lipid emulsions containing PGE 1: Alteration in the number of large particles in infusion solutions

There are two generics of a parenteral lipid emulsion of prostaglandin E1 (PGE 1) (Lipo-PGE 1) in addition to two innovators. It was reported the change from innovator to generic in clinical practice caused the slowing of drip rate and formation of aggregates in the infusion line. Thus, we investigated the difference of pharmaceutical quality in these Lipo-PGE 1 formulations. After mixing with some infusion solutions, the mean diameter and number of large particles were determined. Although the mean diameter did not change in any infusion solutions, the number of large particles (diameter >1.0 μm) dramatically increased in generics with Hartmann's solution pH 8 or Lactec ® injection with 7% sodium bicarbonate. Next, we investigated the effect of these infusion solutions on the retention rate of PGE 1 in lipid particles. The retention rate of PGE 1 in these two infusion solutions decreased more quickly than that in normal saline. Nevertheless, there were no significant differences among the formulations tested. Our results suggest that there is no difference between innovators and generics except in mixing with these infusion solutions. Furthermore, that monitoring the number of large particles can be an effective means of evaluating pharmaceutical interactions and/or the stability of lipid emulsions.

Effect of strong shot peening cleaning and hot galvanizing on fatigue strength of steel welded joint

The soiling of the slag, spatter and the fume, etc., which come into contact with the steel sheet surface with welding, is cleaned making use of steel sphere shot material of large particle diameter, high projection pressure with strong peening processing (below, called strong peening cleaning). In this research, the cleaning state of the soiling with welding and improvement of fatigue strength of the hot galvanized welded joint was inspected, when the surface of a SM490A welded joint was cleaned with strong peening cleaning. The following experimental results were obtained: 1. The fatigue limit of smooth base metal which received strong peening cleaning at about 320 MPa was remarkably high in comparison with smooth base metal at about 245 MPa. 2. The fatigue limit of a welded joint which received strong peening cleaning at about 300 MPa was remarkably high in comparison with a welded joint at about 170 MPa. 3. The strong peening cleaning was highly efficient and the cleaning state was satisfactory. 4. The cause of the remarkable rise of the fatigue limit (300 MPa) of the welded joint which received strong peening cleaning was because the fatigue limit (about 170 MPa, 57%) of the welded joint was improved (about 130 MPa, 43%) with peening cleaning. It was considered that improvement effects were: a rise (about 68 MPa, 23%) of hardness of the weld toe; relief (about 43 MPa, 14%) of stress concentration; increase (about 136 MPa, 45%) of compressive residual stress; and the decrease (about − 96 MPa, − 32%) by increase of surface roughness. 5. The fatigue strength of the hot galvanized welded joint decreased remarkably. This was thought to be due to the decrease (about HV40) of hardness of the surface, the decrease (about 188 MPa) of the compressive residual stress and the influence of many factors which accompanied hot galvanizing.

Numerical simulation of chemical looping combustion process with CaSO 4 oxygen carrier

Chemical-looping combustion (CLC) is a promising technology for the combustion of gas or solid fuel with efficient use of energy and inherent separation of CO 2. The technique involves the use of an oxygen carrier which transfers oxygen from combustion air to the fuel, and hence a direct contact between air and fuel is avoided. A chemical-looping combustion system consists of a fuel reactor and an air reactor. A metal oxide is used as oxygen carrier that circulates between the two reactors. The air reactor is a high velocity fluidized bed where the oxygen carrier particles are transported together with the air stream to the top of the air reactor, where they are then transferred to the fuel reactor using a cyclone. The fuel reactor is a bubbling fluidized bed reactor where oxygen carrier particles react with hydrocarbon fuel and get reduced. The reduced oxygen carrier particles are transported back to the air reactor where they react with oxygen in the air and are oxidized back to metal oxide. The exhaust from the fuel reactor mainly consists of CO 2 and water vapor. After condensation of the water in the exit gas from the fuel reactor, the remaining CO 2 gas is compressed and cooled to yield liquid CO 2, which can be disposed of in various ways. With the improvement of numerical methods and more advanced hardware technology, the time needed to run CFD (Computational fluid dynamics) codes is decreasing. Hence multiphase CFD-based models for dealing with complex gas-solid hydrodynamics and chemical reactions are becoming more accessible. Until now there were a few literatures about mathematical modeling of chemical-looping combustion using CFD approach. In this work, the reaction kinetics model of the fuel reactor (CaSO 4 + H 2) was developed by means of the commercial code FLUENT. The bubble formation and the relation between bubble formation and molar fraction of products in gas phase were well captured by CFD simulation. Computational results from the simulation also showed low fuel conversion rate. The conversion of H 2 was about 34% partially due to fast, large bubbles rising through the reactor, low bed temperature and large particles diameter.

Size and composition distribution dynamics of alloy nanoparticle electrocatalysts probed by anomalous small angle X-ray scattering (ASAXS)

Anomalous small angle X-ray scattering (ASAXS) is shown to be an ideal technique to investigate the particle size and particle composition dynamics of carbon-supported alloy nanoparticle electrocatalysts at the atomic scale. In this technique, SAXS data are obtained at different X-ray energies close to a metal absorption edge, where the metal scattering strength changes, providing element specificity. ASAXS is used to, first, establish relationships between annealing temperature and the resulting particle size distribution for Pt25Cu75 alloy nanoparticle electrocatalyst precursors. The Pt specific ASAXS profiles were fitted with log-normal distributions. High annealing temperatures during alloy synthesis caused a significant shift in the alloy particle size distribution towards larger particle diameters. Second, ASAXS was used to characterize electrochemical Cu dissolution and dealloying processes of a carbon-supported Pt25Cu75 electrocatalyst precursor in acidic electrolytes. By performing ASAXS at both the Pt and Cu absorption edges, the unique power of this technique is demonstrated for probing composition dynamics at the atomic scale. These ASAXS measurements provided detailed information on the changes in the size distribution function of the Pt atoms and Cu atoms. A shift in the Cu scattering profile towards larger scattering vectors indicated the removal of Cu atoms from the alloy particle surface suggesting the formation of a Pt enriched Pt shell surrounding a Pt-Cu core. Together with XRD and TEM, ASAXS is proposed to play an increasingly important role in the mechanistic study of degradation phenomena of alloy nanoparticle electrocatalysts at the atomic scale.

Novel electrohydrodynamic preparation of porous chitosan particles for drug delivery

Uniform spherical chitosan particles of size <10 microm in diameter are important in drug delivery applications due to their excellent biocompability and biodegradability. A high concentration of chitosan in the particles can help to control the release of drugs and methods for processing high viscosity chitosan solutions are therefore required. In principle, any type of polymer, whether hydrophobic or hydrophilic, can be electrosprayed to obtain monodisperse particles of diameter <10 microm. In practice, however, electrospraying of biopolymers having viscosities of >100 mPa s results in particles >10 microm diameter. In this study, by reducing surface tension of a high viscosity chitosan suspension, it was found that smaller diameter particles could be prepared. Chitosan solutions were electrosprayed in the stable cone-jet mode to systematically study the relationship between particle diameter, viscosity and surface tension. Increasing viscosity resulted in larger diameter particles with a broad size distribution, but decreasing surface tension had the opposite effect. Results show that a chitosan solution having a viscosity of approximately 80 mPa s can be used to prepare chitosan particles of diameter approximately 2.5 microm which on drying reduced to particles of 500 nm.

Dual‐Function Growth Medium and Structural Soil for Use as Porous Pavement

Permeable grass-covered surfaces can reduce the quantity of storm water runoff and filter out potentially harmful chemicals. The objective of this study was to develop permeable structural soils that sustained healthy turf growth and filtered heavy metals from contaminated pavement runoff. The basic soil medium was a 50:50 mixture (v/v) of expanded shale (ExSh) and quartz sand (QS). The ExSh component consisted of (i) large-diameter particles (3-6 mm), (ii) small-diameter particles (1-3 mm), or (iii) a 50:50 mixture (v/v) of the two. The basic blends were mixed with 0, 10, and 20% sphagnum peat moss (v/v) and 0, 10, and 20% natural zeolites (v/v) and placed in 15-cm-diameter pots in a greenhouse. Bermudagrass plugs were planted in each pot. The addition of sphagnum peat moss to the basic ExSh/QS blend increased bermudagrass growth and improved plant response to added fertilizer. Zeolites had no significant effect on plant growth in the absence of sphagnum peat moss. Growing mediums that contained 10 to 20% sphagnum peat moss and 10 to 20% zeolites consistently produced more bermudagrass biomass than the unamended ExSh/QS mixture. Changing the ratio of small- to large-diameter ExSh in the basic medium did not affect bermudagrass yield. Very low amounts of Cd, Cu, Pb, and Zn were recovered in leachate after the addition of 10 mg metal per pot, suggesting that most heavy metals (>99%) were retained in the growing mediums. Zeolites reduced the amount of Cd and Pb in leachate water, but not Cu or Zn.

Tempo de operação para limpeza de linhas laterais em função da velocidade da água e de duas condições topográficas

The cleaning of the pipes with water is an essential activity for success in trickle irrigation, because it contributes to the clogging of emitters, that is a serious problem found in these irrigations systems, because clogging complete or partially can reduce application uniformity. Therefore, the purpose of this paper was to establish operation time for cleaning of lateral lines, for different particle size and sample weights under flat and -2% slope condition, considering different velocities of water. Samples of a clay soil were inserted at the beginning of the lateral line of a 20 m polyethylene pipe. At the end of pipe, particle recovery was realized using a cloth filter. It was observed that the initial amount of clay material did not present significant effect in displacement time, considering the water speed of 0.3 m s-1. The condition of -2% of slope, for speed of 0.7 m s-1 did not present risk for obstruction of the water flow, considering that the particles of larger diameter took a greater time to be collected than the smaller ones. In all condition studied, a period of 15 min is enough for cleaning the pipe. The water speed of 2 m s-1, in a plane condition and of maximum length, considering an operation time of 1 min, can be adopted in field conditions, for cleaning the drip irrigation system.

Influence ofn-dodecyl mercaptan as chain transfer agent in dispersion polymerization of styrene

Dispersion polymerization of styrene with n-dodecyl mercaptans (DDM) as the chain transfer agent was investigated. PS particles with various molecular weight, molecular weight distribution (MWD), and particle diameter were prepared by varying the concentration of DDM and also the addition time of DDM before and after the particle nucleation. The average particle diameter was increased, whereas polymerization rate, molecular weight, and MWD were decreased with increasing DDM concentrations from 0 to 10 wt %. The effect of addition of DDM before and after particle nucleation was studied at 0.4, 0.8, and 1.0 wt % DDM. The addition of DDM before particle nucleation produced PS particles of relatively large particle diameter and low molecular weight when compared with the addition of DDM after particle nucleation. This study shows that particle nucleation occurs in about 5–6 min, which corresponds to the 15–16% conversion, 372–378 nm in Dn, and provides a facile way to control the particle size and interesting information about the particle formation using the delayed addition of DDM. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6612–6620, 2008

Streamline-Based Microfluidic Devices for Erythrocytes and Leukocytes Separation

In this paper, we report two devices for the continuous size-based separation of particles, such as blood cells, which is an important step for on-chip blood preparation. Unlike previously demonstrated passive fluidic devices for particle separation, the local geometry of the bifurcated side channels was used as a design parameter. The design of the devices was based on 2-D fluidic simulation of a T-shaped model. This novel approach was proved to be effective in predicting device performance. The critical particle size for separation was clearly defined in the bifurcated region by simulation under the established theoretical framework. We validated the operation principle of the devices by separating 5- and 10-mum polystyrene beads. Human leukocytes were also successfully separated from erythrocytes with 97% efficiency. The separation region of the device had a small footprint for the separation of particles in micrometer range, which makes this device a good candidate to be integrated into a lab-on-a-chip system. The particles were collected in different exit channels after they were separated, which facilitated further sensing and processing. Similar to cross-flow filters, particles were separated perpendicular to the flow direction. The filtering effect was achieved with the collection zones established by the fluidic field. Clogging was minimized by designing the minimal channel width of the devices larger than the largest particle diameter. Solvent exchange could be accomplished for particles.

Experimental study of the performance of porous materials to moderate the roof surface temperature by its evaporative cooling effect

The change of urban surfaces from permeable to impermeable materials, i.e. asphalt or concrete, has caused the rising of surface temperatures, particularly in densely developed cities. The consequences of this problem lead to higher energy consumption, especially for cooling purposes and other environment related issues. This paper aims to investigate the performance of several non-porous and porous potential roofing materials, to determine which ones might best be used to create a more effective system by utilizing their moisture absorption and evaporation capabilities. Here, four kinds of materials—pebbles, silica sand, volcanic ash, and siliceous shale—were tested to evaluate their moisture and thermal performance, including the effects from different particle sizes. First, the necessary physical properties and pore characteristics were obtained. Thus, each material, under simple boundary conditions, was evaluated in an evaporation experiment, to determine comparative moisture and thermal behavior. Next, cyclic experimentation was conducted, in which variations of temperature, relative humidity and simulated solar radiation were included. The measurement results showed that porous materials can satisfactorily lower surface temperature. Among the tested samples, siliceous shale of both small and large particle diameter was found to lower the daily average surface temperature by up to 6.8 and 8.6 °C, respectively. The better performance of large size particles could possibly be caused by the ventilation occurring within the material layers and high solar penetration through the large gaps between particles, which would release more latent heat when compared to materials of smaller particle size. Finally, analysis of surface energy balance suggested that water contents, solar absorptivity, and wind effects all have significant influences on cooling the surface temperature.

Nanoparticle Spectroscopy: Plasmon Coupling in Finite-Sized Two-Dimensional Arrays of Cylindrical Silver Nanoparticles

This study provides new data for interpreting plasmon coupling in finite two-dimensional arrays, which are important in plasmonic devices and sensing applications. Finite square arrays of cylindrical silver nanoparticles with two different nanoparticle diameters (339 and 163 nm) and two different interparticle spacings (400 and 450 nm) were fabricated by e-beam lithography. The plasmonic properties of these arrays were obtained by UV−visible−near-IR extinction spectroscopy and compared with isolated particle spectra. In the case of the large-diameter particle arrays, the semi-infinite array resonance is quite blue-shifted from the isolated particle resonance; the resonant wavelength of the 2 × 2 particles and successively larger blocks keeps blue-shifting relative to the isolated particle resonance and converges to that of a semi-infinite array. For the small-diameter particle arrays, the semi-infinite resonance is red-shifted from the isolated particle resonance; the resonant wavelength of the 2 × 2 particles and successively larger blocks keeps red-shifting and converges to the semi-infinite array. The experimental resonances for progressively increasing array sizes show systematic resonance shifts consistent with increasing numbers of particles, and the bandwidth trends require models and more experiments to obtain better insight into trends.

Topography and functional information of plasma membrane

By using atomic force microscope (AFM), the topography and function of the plasmalemma surface of the isolated protoplasts from winter wheat mesophyll cells were observed, and compared with dead protoplasts induced by dehydrating stress. The observational results revealed that the plasma membrane of living protoplasts was in a state of polarization. Lipid layers of different cells and membrane areas exhibited distinct active states. The surfaces of plasma membranes were unequal, and were characterized of regionalisation. In addition, lattice structures were visualized in some regions of the membrane surface. These typical structures were assumed to be lipid molecular complexes, which were measured to be 15.8+/-0.09 nm in diameter and 1.9+/-0.3 nm in height. Both two-dimensional and three-dimensional imaging showed that the plasmalemma surfaces of winter wheat protoplasts were covered with numerous protruding particles. In order to determine the chemical nature of the protruding particles, living protoplasts were treated by proteolytic enzyme. Under the effect of enzyme, large particles became relatively looser, resulting that their width was increased and their height decreased. The results demonstrated that these particles were likely to be of protein nature. These protein particles at plasmalemma surface were different in size and unequal in distribution. The diameter of large protein particles ranged from 200 to 440 nm, with a central micropore, and the apparent height of them was found to vary from 12 to 40 nm. The diameter of mid-sized protein particles was between 40-60 nm, and a range of 1.8-5 nm was given for the apparent height of them. As for small protein particles, obtained values were 12-40 nm for their diameter and 0.7-2.2 nm for height. Some invaginated pits were also observed at the plasma membrane. They were formed by the endocytosis of protoplast. Distribution density of them at plasmalemma was about 16 pits per 15 microm(2). According to their size, we classified the invaginated pits into two types--larger pits measuring 139 nm in diameter and 7.2 nm in depth, and smaller pits measuring 96 nm in diameter and 2.3 nm in depth. On dehydration-induced dead protoplasts, the degree of polarization of plasma membranes decreased. Lipid molecular layers appeared relatively smooth, and the quantity of integral proteins reduced a lot. Invaginated pits were still detectable at the membrane surface, but due to dehydration-induced protoplast contraction, the orifice diameter of pits reduced, and their depth increased. Larger pits averagely measuring 47.4 nm in diameter and 31.9 nm in depth, and smaller pits measuring 26.5 nm in diameter and 43 nm in depth at average. The measured thickness of plasma membranes of mesophyll cells from winter wheat examined by AFM was 6.6-9.8 nm, thicker in regions covered with proteins.

EFFECT OF AMMONIUM PERCHLORATE GRAIN SIZE ON COMBUSTION OF A SELECTED COMPOSITE SOLID PROPELLANT

The heterogeneous propellants consisting of Ammonium Perchlorate (AP) particles imbedded in a Hydroxyl Terminated Polybutadience (HTPB) are widely used in solid rocket industries. In this study, the effect of AP particles diameter and the random distribution with the HTPB on the burning of such propellant is presented. A mathematical model which describes the unsteady burning of a heterogeneous propellant by simultaneously solving the combustion fields in the gas phase and the thermal field in the solid phase with appropriate jump condition across the gas/solid interface is developed. The gas-phase kinetics is represented by a two-step reaction mechanism for the primary premixed flame and the primary diffusion flame between the decomposition products of the HTPB and the oxidizer AP. The propagation of the unsteady non-planer regression surface is described, using the Essentially-Non-Oscillatory (ENO) scheme with the aid of the level set strategy. The results show that the large AP particle diameter has a marked effect on the combustion surface deformation and on the burning rate as well. Therefore, modeling of the condensed phase process is mostly conducted on AP. Moreover, the effect of various parameters on the surface propagation speed, flame structure, and the burning surface geometry is obtained.

Comparison of Mixing Technologies for the Production of Concentrated Emulsions

The generation of surfactant stabilized water-in-oil emulsions has been studied using different mixing technologies ranging from a simple magnetic stirrer in a beaker to continuous processing with static mixers. Experiments were conducted with a diesel cut as the continuous phase, distilled water as the dispersed phase, and a mixture of three non-ionic surfactants as used in the patented formulation of Aquazole™. It is shown that water droplets in the submicron range can be obtained by means of very low energy input if the appropriate physical chemistry conditions prevail. As a result, at dispersed phase concentrations over 35%, the droplet size depends mostly on the surfactant concentration and is insensitive to the mixing technology used. When the dispersed phase concentration is further increased, stable dense packed emulsions with large particle diameter are produced and behave as gels. The physical chemistry parameters derived from the batch experiments are successfully applied to fine emulsion production using static mixers under creeping flow conditions.