Emulsion explosives have become the preferred choice as blasting agents for numerous industries including mining, agriculture, and construction. One of the most important components in such an emulsion is an emulsifier, which controls the emulsification properties of the explosive. The present study involves the production of one such emulsifier, which is produced by reacting two immiscible liquids, PIBSA (polyisobutylene succinic anhydride) and MEA (monoethanolamine). The study examines the effect of design variable such as the impeller speed, impeller type and the dispersed phase volume fraction on interfacial area. Experiments were carried out in a 0.15 m diameter fully baffled stirred tank using a 6-bladed Rushton turbine impeller and a marine propeller. Drop size was determined using a microscope with a video camera and image processing system. The transient concentration of PIBSA was determined using FTIR analysis and used to estimate the volume fraction of the dispersed phase (ƒÖ). The effective interfacial area was calculated using the Sauter mean drop diameter, d32 and ƒÖ. Impeller speeds ranging from 150 to 600 rpm and dispersed phase volume fractions, ƒÖ ranging from 0.01 to 0.028 were examined in the experimental study. It was found that that the evolution of Sauter mean drop diameter, d32 has four different trends depending on ƒÖ and impeller speed. At high impeller speeds and high ƒÖ, d32 values decrease initially and reach constant values after a long period of time. This trend is consistent with the findings in previous investigations. Under certain operating conditions, d32 values increase initially with stirring time to reach a maximum value and then decrease to reach a steady state value. The presence of these trends has been attributed to the effect of changing physical properties of the system as a result of chemical reaction. Results indicate that, in general, Sauter mean drop diameter d32 decreases with an increase in agitation intensity. However a decrease in the dispersed phase volume fraction is found to increase d32. These trends are found to be the same for both impeller types studied. Comparing the drop size results produced by the two impellers, it appears that low-power number propeller produces s ignificantly smaller drops than the Rushton turbine. It was found that the concentrations of reactants decrease with time for all impeller speeds thereby leading to a decrease in interfacial area with the progress of the reaction. Interfacial area values obtained at higher impeller speeds are found to be lower in spite of lower d32 values at these speeds. Also, these values decrease with time and become zero in a shorter duration indicating the rapid depletion of MEA. The interfacial area values obtained with the propeller at a given impeller speed are lower as compared to those for Rushton turbine. They also decrease and become zero in a shorter duration as compared to those for Rushton turbine suggesting propeller¡¦s performance is better in enhancing the reaction rate.

<p>Due to the small dimensions, nanoparticles and materials consisting of nano-sized building blocks exhibit unique — mostly superior — properties, well differing from their bulk counterpart. Most of the novel properties of nanoparticles (and nanomaterials) are size-dependent, while the majority of the common gasphase methods used for generation of nanopowders result in different, usually wide, size-dispersions. Further understanding of the fundamental processes leading to particle formation is therefore required, leading to better control of size and distribution of the nanoparticles, thus allowing engineering of the desired properties for both nanoparticles and nanomaterials.</p><p>In this present thesis, nanoparticles were produced by two different gasphase techniques activated by lasers, namely laser chemical vapor deposition (LCVD) and pulsed laser ablation (PLA). Optical emission spectroscopy (OES) was performed on thermal (blackbody-like) radiation originating from laser-excited particles during LCVD and coupled to measured size-distributions. In-situ monitoring of size-distributions by a differential mobility analyzer (DMA) was employed during PLA. In addition, deposited nanoparticles were characterized by a variety of standard techniques.</p><p>Different cooling mechanisms of the laser-excited gasphase particles were identified based on temperature and emitted intensity data extracted from OES measurements. The strong evaporation at elevated temperatures also allowed direct size manipulation of the particles. By monitoring the intensity of the emitted thermal radiation and the scattered laser line, strong indications about the so called coagulation limit, where a broadening of the size-distribution occurred, was obtained. The DMA monitoring, supported by modeling, gave information about different mechanisms (thermal and photochemical) of the ablation process, and particle condensation well below the ablation threshold was also found.</p>

Thesis (M.Sc. (Pharmaceutics))--North-West University, Potchefstroom Campus, 2007.

The determination of the atmospheric aerosol size distribution is an inverse illposed problem. The shape and the material composition of the air-carried particles are two substantial model parameters. Present evaluation algorithms only used an approximation with spherical homogeneous particles. In this paper we propose a new numerically efficient recursive algorithm for inhomogeneous multilayered coated and absorbing particles. Numerical results of real existing particles show that the influence of the two parameters on the model is very important and therefore cannot be ignored.

Due to the small dimensions, nanoparticles and materials consisting of nano-sized building blocks exhibit unique — mostly superior — properties, well differing from their bulk counterpart. Most of the novel properties of nanoparticles (and nanomaterials) are size-dependent, while the majority of the common gasphase methods used for generation of nanopowders result in different, usually wide, size-dispersions. Further understanding of the fundamental processes leading to particle formation is therefore required, leading to better control of size and distribution of the nanoparticles, thus allowing engineering of the desired properties for both nanoparticles and nanomaterials. In this present thesis, nanoparticles were produced by two different gasphase techniques activated by lasers, namely laser chemical vapor deposition (LCVD) and pulsed laser ablation (PLA). Optical emission spectroscopy (OES) was performed on thermal (blackbody-like) radiation originating from laser-excited particles during LCVD and coupled to measured size-distributions. In-situ monitoring of size-distributions by a differential mobility analyzer (DMA) was employed during PLA. In addition, deposited nanoparticles were characterized by a variety of standard techniques. Different cooling mechanisms of the laser-excited gasphase particles were identified based on temperature and emitted intensity data extracted from OES measurements. The strong evaporation at elevated temperatures also allowed direct size manipulation of the particles. By monitoring the intensity of the emitted thermal radiation and the scattered laser line, strong indications about the so called coagulation limit, where a broadening of the size-distribution occurred, was obtained. The DMA monitoring, supported by modeling, gave information about different mechanisms (thermal and photochemical) of the ablation process, and particle condensation well below the ablation threshold was also found.

This study focuses on the analysis of atmospheric particles sampled from two different field campaigns: the field study at a cattle feeding facility in the summer from 2005 to 2008 and the Indirect and Semi-Direct Aerosol Campaign (ISDAC) in 2008. A ground site field study at a representative large cattle feeding facility in the Texas Panhandle was conducted to characterize the particle size distributions, hygroscopicity, and chemical composition of agricultural aerosols. Here, a first comprehensive dataset is reported for these physical and chemical properties of agricultural aerosols appropriate for use in a site-specific emission inventory. The emission rate and transport of the aerosols are also discussed. In addition, mixing ratios of total and gaseous ammonia were measured at the same field in 2007 and 2008. Measurements such as these provide a means to determine whether the fugitive dust emitted from a typical large feedlot represents a health concern for employees of the feeding operation and the nearby community. Detailed chemical composition of aircraft-sampled particles collected during ISDAC was studied. Filter samples were collected under a variety of conditions in and out of mixed phase and ice clouds in the Arctic. Specifically, particles were sampled from a mixed-phase cloud during a period of observed high concentrations of ice nuclei (IN), a biomass plume, and under relatively clean ambient conditions. Composition of particles was studied on a particle-by-particle basis using several microspectroscopy techniques. Based on the elemental composition analysis, more magnesium was found in Arctic cloud residues relative to ambient air. Likewise, based on the carbon speciation analysis, high IN samples contained coated inorganics, carbonate, and black or brown carbon particles. In the samples collected during a flight through a biomass burning plume, water-soluble organic carbon was the dominant overall composition. Due to their hygroscopic nature, these organics may preferably act as cloud condensation nuclei (CCN) rather than IN. Other ambient samples contained relatively higher fractions of organic and inorganic mixtures and less purely water-soluble organics than found in the biomass particles. The most likely source of inorganics would be sea salt. When present, sea salt may further enhance ice nucleation.

Volcanogenic lightning has a long documented history in the scientific field, though its origins are still poorly understood. The interactions leading to electrification of ash plumes is essentially a function of the microphysics controlling and affecting ash particle collisions. This thesis presents measurements made on charged particle interactions in a fluidized bed, with large-scale applications to the phenomenon of volcanogenic lightning and charged particle dynamics in volcanic plumes. Using a fluidized bed of ash samples taken from Ecuador's Volcán Tungurahua, particles are introduced to a collisional environment, where they acquire an associated polarity. A charged copper plate is used to collect particles of a given polarity, and particle size distributions are obtained for different weight fractions of the ash. It is observed that relatively smaller particles acquire a net negative charge, while larger particles in the sample charge positively. This is a well-documented occurrence with perfectly spherical, chemically identical samples, but this work represents one of the first applications of the principle to volcanic ash. Image analysis is preformed to determine the size distribution associated with specific polarities, and the associated minimum charge on each particle is calculated based on the plate collection height and particle size. We also present results that demonstrate the relationship between particle collisions and the amount of charge exchanged. Using techniques developed to examine the collision rate within a flow, combined with the charging rates determined from this experiment, we determine a maximum charge exchange rate of 1.28±0.23 electrons transferred per collision.

<p>Fatigue and ductility properties in various tool steels, produced by powder metallurgy, spray forming or conventionally ingot casting, have been analysed experimentally and successfully compared to developed models. The models are able to predict the fatigue limit and cause for fatigue fracture, and strain- and stress-development until fracture during the ductile fracture process respectively. Total fracture in a tool steel component, both in fatigue and ductility testing, is caused by a propagating crack initiated by particles, i.e. carbides or non-metallic inclusions. The models are based on experimentally observed size distributions.</p><p>The axial fatigue strength at two million cycles was determined for various tool steels. The fracture surface of each test bar broken was examined in SEM to determine the cause for fatigue failure, i.e. a single carbide or inclusion particle or a cluster of carbides, and the size of the particle. The particles act as stress concentrators where a crack is easily initiated when the material is subjected to alternating stresses. The developed models calculate the probability that at least one particle will be present in the material which is larger than the threshold level for crack initiation at a certain stress range.</p><p>The ductility testing was performed on various tool steels by four-point bending under static load. The load and displacement until total fracture were recorded and the maximum strain and stress acting in the material were calculated. The fracture surface of each broken test bar was examined in SEM, though the crack initiating area appears different compared to a fatigue failure. Ductile fracture is caused by a crack emanating from voids nucleated around many particles in a joint process and then linked together. By finite element modelling of void initiation and propagation in 2D of an experimentally observed carbide microstructure for each tool steel, successful comparisons with experiments were performed. Carbides were modelled as cracked when larger than a certain size, based on fracture surface observations, and the matrix cracked above a pre-defined plastic deformation level. The stresses and strains at total failure were in good agreement between model and experiments when evaluated.</p><p>The use of these developed models could be a powerful tool for optimisation of fatigue and ductility properties for tool steels. With good fatigue and ductility properties normal failures appearing during operation of a tool steel product could be minimised. By theoretical tests in the developed models of various carbide microstructures the optimum mechanical properties could be achieved with a minimum of experiments performed.</p>

Για τον προσδιορισμό της πορομετρικής καμπύλης των γεωυφασμάτων διατίθενται σήμερα τρία πρότυπα (ASTM D6767, EN ISO 12956 και ASTM D4751) που θεωρούνται “διεθνούς” αποδοχής. Το πιο πρόσφατο από αυτά (ASTM D6767) εγκρίθηκε το 2002, ορίζει μέθοδο με βάση τη ροή σε τριχοειδή και αποτελεί το κύριο αντικείμενο της παρούσας διατριβής. Ελέγχθηκαν 52 μη υφασμένα γεωυφάσματα κατασκευασμένα από ίνες πολυπροπυλενίου τόσο κατά ASTM D6767 όσο και κατά EN ISO 12956 (υγρό κοσκίνισμα) και ASTM D4751 (ξηρό κοσκίνισμα). Τα αποτελέσματα που προέκυψαν συγκρίθηκαν τόσο μεταξύ τους όσο και με φυσικές ιδιότητες των γεωυφασμάτων, με τιμές μεγεθών που παρέχουν οι κατασκευαστές αυτών των προϊόντων και με τιμές μεγεθών που υπολογίζονται θεωρητικά. Τα μεγέθη πόρων και οι πορομετρικές καμπύλες που προκύπτουν εργαστηριακά με εφαρμογή κάθε μίας από τις τρεις μεθόδους είναι διαφορετικά. Αυτό οφείλεται στις διαφορετικές παραδοχές ή υποθέσεις κάθε μεθόδου αλλά και στις διαδικασίες που προβλέπει η κάθε μέθοδος. Ειδικότερα, οι δύο βασικές υποθέσεις του προτύπου ASTM D6767 αφορούν τη γωνία επαφής, θ, μεταξύ ρευστού και στερεού (τίθεται ίση με μηδέν) και τη μορφή της διατομής των πόρων των γεωυφασμάτων (κυλινδρική). Λόγω της δομής των μη υφασμένων γεωυφασμάτων οι δύο παραπάνω υποθέσεις δεν είναι δυνατόν να επαληθευθούν. Για τον λόγο αυτό στην εξίσωση προσδιορισμού των μεγεθών πόρων του προτύπου ASTM D6767 εισάγεται διορθωτικός συντελεστής. Από την επεξεργασία των αποτελεσμάτων της παρούσας διατριβής προέκυψε ότι ο συντελεστής αυτός πρέπει να έχει τιμή ίση με 1/3 (για τη συγκεκριμένη συσκευή που χρησιμοποιήθηκε και τις διαδικασίες που εφαρμόστηκαν για την εκτέλεση των δοκιμών) ώστε τα αποτελέσματα να προσεγγίζουν ικανοποιητικά αυτά της δοκιμής κατά EN ISO 12956. / Three internationally accepted standards (ASTM D6767, EN ISO 12956 and ASTM D4751) are available today for determing the pore size distribution of geotextiles. The most recently approved standard (2002) is ASTM D6767 which defines a method based on capillary flow. Laboratory testing according to this standard is the main subject of this thesis. Fifty two nonwoven geotextiles, made of polypropylene fibers, were tested according to the three standardized methods (ASTM D6767, EN ISO 12956 – wet sieving and ASTM D4751 – dry sieving). Comparisons were made between the results obtained from each standardized method as well as between measured pore sizes and geotextile physical properties, manufacturer provided pore sizes and values obtained theoretically. Different pore sizes and pore size distribution curves are obtained when different laboratory standard methods are applied. This is due to the different assumptions on which each method is based and also due to the procedures that each method specifies. The two main assumptions of the Standard ASTM D6767 concern the contact angle, θ, between liquid and solid (equal to zero) and the pore shapes of the geotextiles (cylindrical). Due to the structure of the nonwoven geotextiles the effect of these assumptions is different to quantify. Accordingly, the computation of pore sizes according standard ASTM D6767 is based on the introduction of a correction coefficient in the pertinent equation. The results obtained during this correction coefficient should have a value equal to 1/3 for the particular device used and the procedures applied. Use of this correction coefficient fields results that approximate very well the results obtained from wet sieving tests according to Standard EN ISO 12956.

科学研究費補助金 研究種目:一般研究(C) 課題番号:04640413 研究代表者:藤吉 康志 研究期間:1992-1993年度