Dissertations / Theses on the topic 'Particulates'

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The optical properties of motor aluminum oxide are required inputs to current plume signature prediction codes, such as SIRRM. Accurate predictions are possible only if variations in the particle emissivity due to changes in particle size, contamination, and changing temperature, etc. , are known . This investigation demonstrated a simplified method for determination of the emissivity of rocket motor generated alumina. Plume particulate material was collected on tungsten alloy wire during motor firings. A DC circuit was used to resistively heat the material, and the temperature was determined at various points by relating the wire resistivity to circuit current and voltage. An Agema Thermovision infrared (3.5-5 (j.) camera and microscope were used to observe the material during heating, and broad-band emissivity was computed using system software. It was estimated that the emissivity could be measured with an accuracy of ± 3%. Motor alumina was found to have significantly greater emissivity than pure alumina in the temperature range of 500-1200K.

The effect of particulate matter on the climate depends on its scattering properties (influenced by morphology) and refractive index (dependent on microstructure). The morphology and microstructure of particulates from two different engines were studied. The first set of soot samples was collected from a 1.9L Volkswagen Turbo Direct Injection engine with or without a catalytic converter, using two different fuel types (ULSD and B20) and six speed/load combinations. The second set of the samples was taken from a Cummins ISX heavy-duty engine using the Westport pilot-ignited direct injection natural-gas fuelling system for three different speed/load combinations. The soot morphology was investigated using transmission electron microscopy (TEM), emphasizing the fractal properties. A Matlab-based image processor was used to extract geometrical properties of soot. Thirty-five aggregates were analyzed for each sample. The fractal dimensions (Di) were computed using the aggregate dimension and pair correlation methods. For the soot collected from VW engine, it was found that fuel type (ULSE) and B20) and the presence of a catalytic converter did not affect the fractal dimensions of soot aggregates, while engine load conditions had slight influence on Df. At constant engine RPM, fractal dimensions started to decline as the engine torque was significantly increased. For the soot produced by the natural gas engine, similar changes in the fractal dimension with respect to the engine load were also observed. Both methods of computing Df produced similar trends. Raman spectroscopy was used to quantify the degree of structural disorder present in soot. The Raman spectral analysis was done using two-band (“G” at ~1578 and “D” ~l340 cm⁻­­­¹ and five-band (U, Dl, D2, D3, D4 at about 1580,1350, 1500, 1620 and 1200 cm⁻­­­¹ respectively) combinations. For the soot sampled from VW engine, the results from both methods showed that B20 soot exhibited much greater structural disorder and the degree of graphitization of the soot increased as the engine load increased. Likewise, the Raman analysis of the soot from the Cummins engine also showed that the increased in engine load condition caused increases in the degree of the structural order of soot.

Airborne particulates are one of the most complex air pollutants and considerable concern surrounds their environmental impact especially with regards to human health. An investigation of the efficiency of various total inhalable and respirable dust samplers has been conducted to identify the most convenient way of collecting dust particles to examine their physical characteristics. The efficiency of a variety of dust samplers were investigated using limestone dust clouds generated inside an environmental dust chamber. Various sampling periods were employed to establish dust concentrations in the environmental dust chamber. The experimental dust cloud was found to contain on average 55.74 % of respirable dust as defined by different instruments while a consistent dust concentration of approx 200 mg/m3 was repeatedly produced. The methods for collecting and estimating airborne asbestos fibre concentrations were studied and found to be extremely limited. Standard optical techniques grossly underestimated both airborne fibre concentrations and respirable dimensions of fibres. The size and dimensions of respirable asbestos fibres are defined by their ability to gain access to the lungs and there is no instrument or technique available at present, which will allow collection and estimation of respirable fibrous dust clouds. A comparison of coal dust particles with similar particles retained in the lungs has shown a difference from the predicted respirable fractions as proposed by the British Medical Research Council (BMRC) and other conventions. Respirable dust sampling instruments may therefore be under sampling larger particles. The difficulty in estimating the characteristics of airborne particulate material has been demonstrated by illustrating urban particulate collection and analysis. The extremely large differences in terms of physical size, and aerodynamic properties of dust particles formed by different materials have been demonstrated.

Thesis (M.S.)--West Virginia University, 2003.
Title from document title page. Document formatted into pages; contains vii, 112 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 109-112).

Thesis (Ph. D.)--Ohio State University, 2004.
Title from first page of PDF file. Document formatted into pages; contains xvii, 260 p.; also includes graphics (some col.). Includes bibliographical references (p. 242-260).

Thesis (M.S.)--West Virginia University, 2007.
Title from document title page. Document formatted into pages; contains ix, 69 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 59-64).

Thesis (M.S.) -- University of Maryland, College Park, 2004.
Thesis research directed by: Dept. of Biological Resources Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

Urban particulate matter (UPM) is known to be a causative agent in a number of diseases including cancers of the respiratory system. Toxicological analysis has implicated particle size, surface area, metal ions, free radical induction, and organic chemistry as potential drivers of human health effects; however the relative importance of these factors is unclear. This project attempts to determine the factors responsible for the in vitro toxicity of particulate air pollution. The importance of fuel type on exhaust particle characteristics was examined through the collection of engine exhaust particles (EEP) produced by a heavy diesel engine operating using conventional diesel and rapeseed oil based biofuels. The effects of particle aging in the atmosphere, and the contributions of sources other than engine exhausts were determined through the collection of UPM from a roadside site. The genotoxic potential of particulate samples was determined using the comet assay, and particle free radical induction was measured with the plasmid strand break assay. Particle organic chemistry was determined using gas chromatography mass spectrometry. Particular emphasis was placed on the accurate quantification of polycyclic aromatic hydrocarbons (PAH), a class of carcinogenic hydrocarbons known to be present on the surface of particulate matter. Engine particulate samples were collected from a heavy duty diesel engine using conventional petrodiesel, rapeseed oil (RSa) or rapeseed oil with a fuel additive (RSaAd). Analysis of particulate specific emissions indicated that Rsa combustion generated a significantly greater mass of particulate matter than the combustion of diesel. This increase in particulate mass output was attributed to poor RSa combustion characteristics due to coking of fuel injectors during engine operation. ' This could be corrected through the use of a fuel additive, which bought Rsa particulate emissions into line with diesel. In all fuels the majority of the particulate mass collected had an aerodynamic diameter of less than one 1 urn, indicating that they may potentially deposit within the lower respiratory tract in humans, and as such are relevant to human health. Analysis of total suspended particle and size fractionated samples of engine particulate material showed that engine exhaust particles produced through diesel combustion were significantly more genotoxic than those produced whilst operating with biofuels. A statistically significant size dependency was found in diesel exhaust particles, with finer material inducing a greater level of DNA damage. Finer rapeseed oil exhaust particles were also shown to be more genotoxic than coarser material, although this trend was not as pronounced as in diesel exhaust particles, and was not statistically significant. Free radical analysis of exhaust particles showed that for all fuels the coarsest fraction of PM induced the largest level of radical activity. In most fractions diesel and Rsa EEP induced similar levels of damage, whereas coarse RSaAd induced significantly greater levels of free radicals. Free radical induction was indicated to be a result of particle phase metals present due to engine wear. Diesel EEP P AH levels were higher than Rsa or RSaAd samples in most size fractions of particles examined. Diesel EEP showed finer fractions to have the greatest P AH concentrations, with P AH concentration being roughly in line with v what might be expected based on projected surface area, suggesting absorption from the vapour phase as the mechanism by which P AH arrive on diesel PM. RSO and RSOAd EEP contained significantly lower P AH concentrations than diesel EEP. A correlation was found between particle phase P AH concentrations and observed DNA damage in the comet assay, suggesting PAH as potential drivers of genotoxicity. The concentration and distribution of n-alkane species was shown to be independent of fuel type, which is in line with previous studies that have indicated that engine lubricating oil is the major source of particle n-alkanes. Qualitative analysis of compounds other than P AH and n-alkanes in EEP showed differences in composition between diesel and RSO derived EEP, with the latter containing a greater number of oxygenated compounds. Size fractionated samples of UPM were collected from the Kirkstall Road air monitoring enclosure, located on a busy road servicing Leeds city centre. As in engine experiments the majority of particulate mass was found to be present in finer particles. In addition to particle size seasonal effects were observed with higher particle mass concentrations observed during colder sampling periods. Comet assay analysis of size fractionated UPM indicated that the majority of DNA damage was observed in the finest fraction of particles. However this damage was lower than that observed in the finest fraction of diesel EEP. In general particles collected during colder periods exhibited greater levels of DNA damage than those collected during warm sampling periods. As in diesel EEP the majority of the particle phase P AH detected were in the finest fractions of particulate material. Coarse UPM fractions contained a greater proportion of total particle phase P AH contributions than was observed in diesel EEP, possibly indicating particle agglomeration in the atmosphere. Additionally, a seasonal component was observed, with particles collected during colder seasons generally containing greater levels of PAH. A strong correlation between particle PAH concentrations and DNA damage in the comet assay was observed, indicating that the mechanism by which DNA damage occurs may involve PAH. Free radical analysis showed that the trend observed in EEP was reversed in UPM, with the finest fractions of UPM inducing greater levels of plasmid unwinding. This was at odds with the results of analysis of free radicals by EEP. The reason for this difference was unclear; however this may be a result of UPM and EEP inducing free radical activity by different mechanisms. The use of PAH diagnostic ratios and analysis of n-alkane species distribution indicated that the anthropogenic sources of particulate matter predominate at the roadside. There was evidence that UPM represented a more complex chemical mixture than EEP, with a greater number of particle bound organic compounds. The majority of these species were oxygenates, indicating oxidative processing of particles during atmospheric residence.

A new process was developed to fabricate particulate metal matrix composites (MMCs). The process involves three steps: (1) modifying the particulate surface by metal coating, (2) forming a particulate porous compact; and (3) introducing metal into the channel network by vacuum infiltration. MMCs with different reinforcements, volume fractions, and sizes can be produced by this technique. Powders of alumina and silicon carbide were successfully coated with nickel and copper in preparation for infiltration with molten aluminum. Electroless Ni and Cu deposition was used since it enhances the wettability of the reinforcements for composite fabrication. While Cu deposits were polycrystalline, traces of phosphorous co-deposited from the electroless bath gave an amorphous Ni-P coating.
The effect of metal coating on wetting behavior was evaluated at 800ºC on plain and metal-coated ceramic plates using a sessile drop technique. The metallic films eliminated the non-wetting behavior of the uncoated ceramics, leading to equilibrium contact angles in the order of 12º and below 58º for Ni and Cu coated ceramics, respectively. The spreading data indicated that local diffusion at the triple junction was the governing mechanism of the wetting process. Precipitation of intermetallic phases in the drop/ceramic interface delayed the formation of Al4C3.
Infiltration with molten Al showed that the coated-particulates are suitable as reinforcing materials for fabricating MMCs, giving porosity-free components with a homogeneously distributed reinforcing phase. The coating promoted easy metal flow through the preform, compared to the non-infiltration behavior of the uncoated counterparts. Liquid state diffusion kinetics due to temperature dependent viscosity forces controlled the infiltration process. Microstructural analysis indicated the formation of intermetallic phases such as CuAl 2, in the case of Cu coating, and Ni2Al3 and NiAl 3 when Ni-coated powders were infiltrated. The overall Ni and Cu content increased from bottom to top of the samples due to dissolution of the metal film by the stream of liquid Al during infiltration. The strengths of the Al/Ni-SiC composites, measured by four-point bending, were 205 and 225 MPa for samples reinforced with 78 mum and 49 mum Ni-SiC, respectively. The mode of fracture was mainly controlled by SiC particle fracture.

Particles of a variety of orthopaedic materials have been implicated with bone resorption both in vivo and in vitro. The polymer investigated in this study is poly(L-lactide), a bioresorbable material which has been used in orthopaedics to manufacture screws and pins for fracture fixation. Poly(L-lactide) implants degrade and release particulate debris prior to their resorption. So far, the particles generated during the degradation of poly(L-lactide) implants have not been implicated with bone resorption in human clinical trials however, osteolysis in the vicinity of degrading resorbable implants made of a similar material known as poly(glycolide) has been observed radiographically. The biocompatibility of poly(L-lactide) particles was investigated using both in vitro and in vivo techniques in this project and the findings can be summarised as follows: 1. Exposure of fibroblasts to poly(L-lactide) particulates caused an increase in prostaglandin E₂ (PGE₂) release from intact viable cells whereas exposure of macrophages to these particles caused PGE₂ release due to cell death. 2. The presence of lactate monomer [the ultimate degradation product of poly(L-lactide)], caused alterations in cell mortality, percent lactate dehydrogenase (LDH) release and increases in PGE₂ release which were not attributable to osmolarity changes alone. 3. An in vitro transformation assay revealed that poly(L-lactide) particles have the capacity to transform C3H/10T1/2 cells, although there is no evidence to suggest that these particles would cause tumours in humans or other animals. 4. Finally, a "rat pin" model did not show up any evidence of bone resorption in the vicinity of a loaded metallic pin implant, caused by high molecular weight poly(L-lactide) particles although fluorescence microscopy indicated that mineralisation may have been reduced.

The Discrete Element Method (DEM) has been applied to numerical modelling of the bulk compression of low modulus particulates. An existing DE code for modelling the contact mechanics of high modulus particles using a linear elastic contact law was modified to incorporate non-linear viscoelastic contact, real containing walls and particle deformation. The new model was validated against experimental data from the literature and physical experiments using synthetic spherical particles, apple and rapeseed. It was then used to predict particle deformation, optimum padding thickness in a handling line and bulk compression parameters during oilseed expression. The application of DEM has previously been limited to systems of hard particles of high compressive and shear modulii with relatively low failure strain. Material interactions have therefore commonly been modelled using linear contact law. For high modulus particles, particle shape change resulting from deformation is a not a significant factor. Most agricultural particulates however deform substantially before failure and their interaction is better represented with non-linear hysteretic viscoelastic contact relationship. Deformation of geometrically shaped particles in DEM is usually treated as "virtual" deformation, which means that particles are allowed to overlap rather than deform due to contact force. Change to particle shape has not previously been possible other than in the case of particles modelled as 2-D polygons or where each particle is also modelled concurrently with an FE mesh. In this work a new approach has been developed which incorporates a non-linear deformation dependent contact damping relationship and a shape change while maintaining sufficient geometrical symmetry to allow the problem to be handled by the same DE algorithms as used for true spheres. The method was validated with available experimental results on impact behaviour of rubber and the variations with different damping coefficients were simulated for a selected fruit. A fruit handling process dependent on the impact process was then simulated to obtain data required in the design of a fruit processing line. Changes in shape of spherical synthetic rubber particles and rapeseeds under compression were predicted and validated with physical experiments. Images were taken and analysed using image processing techniques with 1: 1 scaling. The method on shape change entails a number of simplifying assumptions such as uniform stress distribution and homogeneous material properties and uniform material distribution when deformed, which are not observed in real agricultural materials and will tend to overestimate the true contact area between particles. In reality for fruits and vegetables, material redistribution is a complex process involving a combination of compaction and movement. However with the new method a better approximation of bed voidage (which standard DEM approaches underestimate) and stress were obtained in the compression of a synthetic material. This is a significant improvement on existing methods particularly with respect to stress distribution within a bulk particulate system comprising deforming elements where the size and orientation of contact surface between particles has a strong influence on the bulk modulus. The new model was used for prediction of mechanical oil expression in four oilseed beds. Similar patterns in the variation of the characteristic parameters were obtained as observed in existing experimental data. The data could not be matched exactly as the quantity and arrangement of seeds in the initial seedbeds were not the same as those used in the experimental work. However the DE model gave approximate oil point data for seedbeds with the same physical properties and initial conditions as in the experiment. This suggests that the new model may be a useful tool in the study of mechanical seed-oil expression and other agricultural particulate compression processes.

Particulate adsorption by Mucor flavus and Neurospora crassa is a physical property of the cell wall, independent of both cellular metabolism and the production of extracellular polymers. Initial attractive forces responsible for particulate adsorption by N. crassa are mainly electrostatic in nature and this mechanism probably holds for M. flavus also. The outer glucan layer of the cell wall of N. crassa, although able to adsorb particulates, was not as efficient as the underlying protein layer at particle adsorption. Young, growing mycelium generally adsorbs the , -, largest amount of particles, due to the continued production of adsorption sites and the entrapment of particulates by hyphae. Factors increasing adsorption include nutrient starvation of mycelium and incubation with low concentrations of magnesium ions. Relatively high concentrations of mercury and copper ions decrease adsorption perhaps due to the precipitation and adsorption of the corresponding metal sulphides on the mycelial surface thereby effectively physically interfering with further particulate adsorption. Optimum conditions for adsorption are a temperature of 250C and a slightly acid pH value. Also, small particles are more readily adsorbed than large particles. Mucor flavus can adsorb clays and this ability may be used to treat industrial effluents which contain large amounts of clay minerals. An acid pH and a temperature of 250C are optimum conditions for clay adsorption by the fungus. Low concentrations of montmorillonite and kaolinite increase biomass production by Aspergillus niger in submerged culture, due to the inhibition of pellet formation by the fungus. The clays cause A. niger to grow in a more filamentous form and presumably would affect other fungi in a similar way. The use of clays to control fungal morphology may be important in several industrial fermentations. Low concentrations of the fungicide thiram stimulated the growth of Aspergillus niger in the presence of montmorillonite. Immobilization of fungi by magnetic means is possible due to their ability to adsorb magnetite. This method could also be used to remove fungi from fermentation media as an alternative to filtration or centrifugation. Even though older hyphae of Penicillium chrysogenum are unable to adsorb magnetite, this fungus can still be magnetically immobilized if it is grown from a spore suspension in the presence of magnetite. Either the spores or young hyphae of this fungus adsorb magnetite, producing pellets with magnetic properties. Magnetite adsorption occurs optimally at a temperature of 250C and is constant over a wide range of pH values. Waste mycelium of A. niger from the surface fermentation method of citric acid production can be magnetically removed from solution after adsorbing magnetite. Dilute solutions of sodium hydroxide and sodium bicarbonate desorbed magnetite attached to mycelial surfaces. Silver is accumulated selectively by A. niger waste mycelium produced by the surface fermentation method of citric acid production. The process is rapid, maximum uptake occurring twenty minutes after initial exposure of the mycelium to a silver solution. Silver accumulation by the mycelium is relatively insensitive to changes in pH and temperature, a slight decrease in uptake only occurring at a temperature of 800C. Dilute solutions of H2S04 and HNO3 desorb silver from the mycelial surface. However, this process is relatively inefficient and more effective desorbents need to be found to make the silver accumulation process economically viable.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, February 2004.
Includes bibliographical references (p. 227-237).
Fluidic actuation offers a facile method to move large quantities of small solids, often referred to as fluid-bed movement. Applications for fluid bed processing are integral to many fields including petrochemical, petroleum, chemical, pharmaceutical, biochemical, environmental, defense, and medical. Thermal vapor microbubbles have been shown to be a low power input with high work output fluidic actuation technique with demonstrated commercial applications in ink jet printing and optical switching. This thesis further develops microbubble actuation (BA) as an arrayed particulate actuation technology for active sorting in particulate fluid beds. Numerical and analytical models of flows, forces, and fields affecting a tBA-based system are presented. The design and fabrication of an arrayed pBA-powered device are delineated with notation of specifications that may focus future design iterations. Performance testing and characterization of CpBA technology, including over a hundred in-plane and out-of-plane nucleation site geometries, serve as the impetus for the technical guidelines that are presented, which include a detailed comparison of in-plane and out-of-plane nucleation site geometry performance.
by Antimony L. Gerhardt.
M.Eng.

Urban environmental pollution is of increasing concern. There is a need for improved analytical methods to assess risk from potentially toxic elements in urban soils and related material. This thesis focuses on development and application of such methods, notably the modified BCR sequential extraction procedure. The analytes studied were Cr, Cu, Fe, Mn, Ni, Pb and Zn, and quantification was by ICP-AES and ICP-MS. Results obtained by BCR extraction of urban allotment soils were compared with those from aqua regia digestion, 0.05 M EDTA extraction, and the SBET. Correlation analysis and principal component analysis (PCA) grouped analytes into a set mainly of lithogenic origin (Cr, Fe, Mn,Ni) and another of mainly anthropogenic origin (Cu, Pb, Zn). The PCA indicated relationship between amounts of analytes released in step 1 of the sequential extraction and EDTA-extractable analytes, and between results of the SBET method and those obtained with EDTA. The BCR extraction was then mini aturised for application to urban airborne particles. The fractionation pattern was not affected by reducing the sample mass from 1 g to 0.0625 g for particles < 45 μm and 500 - 1000 μm in diameter, but changing the size of vessel used did have an effect. When the miniaturised extraction was applied to test samples presented on filter dynamics measurement system (FDMS) filters a significant Zn blank was found. Despite this, recoveries within 30 % of certified values were obtained when 0.1 g test portion of BCR CRM 701, loaded onto FDMS filters, were extracted. Finally, the chemometric identification of substrates and element distribution (CISED) method was miniaturised and adapted for application to particulate samples on FDMS filters. Four distinct physicochemical components were extracted from BCR 701 using the traditional CISED method, but 11 components when the CRM was loaded onto a filter. The mobilities of the PTE as predicted by the CISED were in good agreements with fractionation patterns obtained using the BCR sequential extraction protocol.

Doutoramento em Ciência e Engenharia de Materiais
As propriedades funcionais dos materiais ferroeléctricos tais como a polarização reversível, piroelectricidade, piezoelectricidade, elevada actividade óptica não linear e comportamento dieléctrico não linear são fundamentais para a sua aplicação em sensores, microactuadores, detectores de infravermelhos, filtros de fase de microondas e memórias não-voláteis. Nos últimos anos, motivado pelas necessidades industriais de redução do tamanho dos dispositivos microelectrónicos, aumentando a eficiência volumétrica, tem sido feito um grande esforço ao nível da investigação para desenvolver estruturas ferroeléctricas à escala micro- e nano- métrica. É sabido que a redução de tamanho em materiais ferroeléctricos afecta significamente as suas propriedades. Neste sentido e considerando que foi previsto teoreticamente por cálculos ab initio que estruturas do tipo nanocilindros e nanodiscos apresentariam um novo tipo de ordem ferroeléctrica e, na expectativa de alcançar conhecimento para o desenvolvimento de uma nova geração de dispositivos microelectróncos, existe um grande interesse em desenvolver métodos de fabrico de nanoestruturas ferroeléctricas unidimensionais (1D) tais como nanocilindros e nanotubos. As estratégias de fabrico de nanoestruturas 1D até agora descritas na literatura indicam claramente as dificuldades inerentes à sua preparação. Existem duas grandes vias de síntese destas nanoestruturas: i) o método “topdown” que consiste na redução de tamanho de um dado material até à obtenção duma estrutura 1D; e ii) o método “bottom-up” em que átomos, iões e moléculas são agrupados para formar um material 1D. O método “top down” envolve em geral técnicas de desgaste, como o uso do feixe de electrões, que apesar de permitirem elevada precisão no posicionamento e no controlo do tamanho, falham em termos de resolução, exigem muito tempo e causam facilmente defeitos que deterioram as propriedades físicas destes materiais. Na metodologia “bottom up” a utilização de moléculas ou estruturas “molde” tem sido a mais explorada. As estructuras 1D podem também ser preparadas sem recorrer a “moldes”. Neste caso a agregação orientada é promovida pelo recurso a aditivos que controlam o crescimento dos cristais em direcções preferenciais. Neste contexto, neste trabalho utilizaram-se duas estratégias “bottom up” de baixo custo para a preparação de nanopartículas de titanato de bário (BaTiO3) com morfologia controlada: 1) síntese química (em solução e em fase vapor) com utilização de nanotubos de titanato TiNTs) como “moldes” e precursores de titânio 2) síntese química em solução com presença de aditivos. Os nanotubos de titanato de sódio foram preparados por síntese hidrotermal. Como existiam muitas dúvidas acerca da natureza estrutural e do mecanismo de formação dos NTs, a parte inicial do trabalho foi dedicada à realização de um estudo sistemático dos parâmetros intervenientes na síntese e à caracterização da sua estrutura e microestrutura. Foi demonstrado que os NTs têm a fórmula geral A2Ti2O5 (A = H+ or Na+), e não TiO2 (anátase) com defendido por vários autores na literatura, e podem ser preparados por método hidrotermal em meio fortemente alcalino usando como fonte de titânio TiO2 comercial na forma de anátase ou rútilo. A menor reactividade do rútilo exige temperaturas de síntese superiores ou tempos de reacção mais longos. A forma tubular resulta do tratamento hidrotermal e não de processos de lavagem e neutralização subsequentes. Se os NTs forem tratados após a síntese hidrotérmica em água a 200 ºC, transformam-se em nanocilindros. Uma das partes principais desta tese consistiu na investigação do papel dos NTs de titanato no crescimento anisotrópico de BaTiO3. O potencial funcionamento dos NTs como “moldes” para além de precursores foi testado em reacção com hidróxido de bário em síntese em solução e por reacção com um precursor orgânico de bário em fase vapor. Tendo por base os estudos cinéticos realizados, bem como as alterações estruturais e morfológicas das amostras, é possível concluir que a formação do BaTiO3 a partir de NTs de titanato de sódio, ocorre por dois mecanismos dependendo da temperatura e tempo de reacção. Assim, a baixa temperatura e curto tempo de reacção verifica-se que se formam partículas dendríticas de BaTiO3 cuja superfície é bastante irregular (“wild”) e que apresentam estrutura pseudo-cúbica. Estas partículas formam-se por reacção topotáctica na fronteira dos nanotubos de titanato de sódio. A temperaturas mais altas e/ou reacções mais longas, a reacção é controlada por um mecanismo de dissolução e precipitação com formação de dendrites de BaTiO3 tetragonais com superfície mais regular (“seaweed”). A microscopia de força piezoeléctrica mostrou que as dendrites “seaweeds“ possuem actividade piezoeléctrica superior à das dendrites “wild”, o que confirma o papel desempenhado pela estrutura e pela concentração de defeitos na rede na coerência e ordem ferroeléctrica de nanoestruturas. Os nossos resultados confirmam que os NTs de titanato não actuam facilmente como “moldes” na síntese em solução de BaTiO3 já que a velocidade de dissolução dos NTs em condições alcalinas é superior à velocidade de formação do BaTiO3. Assumindo que a velocidade de reacção dos NTs com o precursor de bário é superior em fase vapor, efectuou-se a deposição de um precursor orgânico de bário por deposição química de vapor sobre um filme de NTs de titnato de sódio depositados por deposição electroforética. Estudou-se a estabilidade dos NTs nas diferentes condições do reactor. Quando os NTs são tratados a temperaturas superiores a 700 ºC, ocorre a transformação dos NTs em nanocilindros de anatase por um mecanismo de agregação orientada. Quando se faz a deposição do precursor de bário, seguida de calcinação a 700 ºC em atmosfera oxidante de O2, verifica-se que a superficie dos NTs fica coberta com nanocristais de BaTiO3 independentemente da concentração de bário. O papel dos NTs de titanato no crescimento anisotrópico de BaTiO3 em fase vapor é assim descrito pela primeira vez. Em relação à metodologias de crescimento de partículas na ausência de “moldes” mas com aditivos fez-se um estudo sistemático utilizando 5 aditivos de natureza differente. As diferenças entre aditivos foram sistematizadas tendo em conta as diferenças estruturais e morfológicas verificadas. Está provado que os aditivos podem funcionar como modificadores de crescimento cristalino por alteração do seu padrão de crescimento ou por alteração da cinética de crescimento das faces cristalográficas do cristal. Entre os aditivos testados verificou-se que o ácido poliacrilíco adsorve em faces específicas do BaTiO3 alterando a cinética de crescimento e induzindo a agregação orientada das partículas. O polivinilpirrolidona, o docecilsulfato de sódio e hidroxipropilmetilcelulose actuam mais como inibidores de crescimento do que como modificadores do tipo de crescimento. A D-frutose aumenta a energia de activação da etapa de nucleação não ocorrendo formação de BaTiO3 para as mesmas condições dos outros aditivos. Esta tese clarifica o papel dos NTs de titanato de sódio enquanto precursores e “moldes” no crescimento anisotrópico de BaTiO3 em solução e em fase vapor. É feita também a abordagem do controlo morfológico do BaTiO3 através do uso de aditivos. As estratégias de preparação de BaTiO3 propostas são de baixo custo, reprodutíveis e fáceis de efectuar. Os resultados contribuem para uma melhor compreensão da relação tamanho – morfologia – propriedade em materiais ferroeléctricos nanométricos com vista à sua potencial aplicação.
For applications as sensors, microactuators, infrared detectors, microwave phase filters and non-volatile memories, functional properties of ferroelectric materials such as switchable polarization, piezoelectricity, high non-linear optical activity, pyroelectricity, and non-linear dielectric behavior are indispensable. More recently and motivated by the industrial need of reduction of size of microelectronics devices to increase volumetric efficiency, many efforts have been dedicated to the development of micro- and nano- scale ferroelectric structures. This is because as dimensions decrease, ferroelectric materials exhibit a pronounced size effect, which is manifested in a significant deviation from bulk properties. In this sense, interest in the fabrication of one-dimensional (1D) ferroelectric nanostructures such as nanowires (NWs) and nanotubes (NTs) has increased in the recent years for two important reasons. First, the study of these systems can provide useful information for the fabrication of the next generation, fully three-dimensional FeRAM structures with the required bit density. Second, detailed ab initio calculations have predicted a new kind of ferroelectric order in nanorods and nanodisks. Nevertheless, the fabrication strategies proposed in the literature clearly indicate that the synthesis of 1D nanostructures is non trivial. There are two main approaches for the preparation of 1D materials. The so called top-down methods that consist in the size reduction until 1D nano structures are obtained and bottom-up methods when atoms, ions or molecules are assembled to form a 1 D nano structure. The top-down methods based on electron-beam (EB) assisted fabrication although they provide high-precision positioning and size control they are limited in resolution, time-consuming and are prone to processing damages. Among the bottom-up procedures, template assisted methods have been the most tried and tested for the preparation of 1D ferroelectrics. There are two main template based methods, denoted as ‘physical’ and ‘chemical’ templating. Other bottom-up approaches used for the 1D nanostructure fabrication include non-template additive assisted methods. In this case the assembling is achieved via the control of the crystal growth along preferential directions in the presence of specific additives. Within this context in this work two low cost bottom-up synthesis strategies for the morphology control of BaTiO3 are exploited: 1) a chemical template methodology, sarting from TiO2 NTs as templating agents and 2) a non template additive assisted syntheses. For the chemical templated approach TiO2 NTs were fabricated by an hydrothermal method. Because there are still questions to be answered regarding the anisotropic growth of titanium based NTs, namely the structure and the formation mechanism, the initial part of the present work is dedicated to systematic studies of titanium based NTs to be used as template for the further growth of BaTiO3. It is demonstrated that layered titanate nanotubes (TiNTs) with general formula H2Ti2O5 (and not anatase as others claimed) can be prepared by hydrothermal method in high alkaline medium starting from commercial TiO2 (anatase and rutile). Concerning the formation mechanism of the NTs it is shown that the tubular shape is formed during the hydrothermal synthesis and it is not related with the after synthesis washing process, clarifying the under going discussion on the topic. Moreover, the NTs to anatase nanorods (NRs) transformation during the post synthesis hydrothermal treatment is explained and finally the present work demonstrates that both commercial anatase and rutile are transformed in layered titanate nanotubes under high alkaline hydrothermal conditions, but because of the low reactivity of rutile, high temperatures or long reaction times were required. As a main part of this work, the effective template role of TiNTs for the anisotropic growth of BaTiO3 is systematicaly addressed. For that the potential template role of TiNTs is ellucidated in two low cost chemical template methods: i) solution based hydrothermal treatment of TiNTs in the presence of Ba(OH)2 as barium precursor and ii) vapor phase reaction of metal-organic barium compound in the presence of TiNTs. By a kinetic analysis and structural and morphological studies, it is demonstrated that during hydrothermal synthesis from layered titanate nanotubes, anisotropic BaTiO3 forms via two mechanisms depending on the temperature and time. At low temperatures (90°C) and short reaction time (# hours) “wild” type BaTiO3 dendritic particles with pseudo cubic structure are formed through a phase boundary topotactic reaction. At higher temperatures and/or for longer times, the reaction is controlled by a dissolution precipitation mechanism and “seaweed” type BaTiO3 dendrites with tetragonal structure are formed. By piezoresponse force microscopy measurements it is demonstrated that the “seaweed” type BaTiO3 dendrites have higher piezoactivity then the “wild” type and it is clearly revealed the role of the structure and the lattice defect concentration on the polarization coherency and ferroelectric order of the dendritic particles. Our results unambiguously elucidated why TiNTs do not routinely act as templates for the hydrothermal formation of 1D BaTiO3. This is because the dissolution rate of the TiNTs under high alkaline hydrothermal conditions is higher than the barium titanate formation. Consequently and assuming that the reaction of TiNTs with barium precursor in vapor phase is faster than the NTs transformation an original approach based on chemical vapor deposition of a metal-organic barium precursor (MoCVD) on TiNTs is proposed in this work. It is demonstrated that TiNTs are stable under MoCVD conditions and temperature. When the TiNTs are subsequently thermal treated at temperatures higher than 700 °C in O2 atmosphere they transform into TiO2 anatase nanorods (NRs) by an oriented attachment mechanism. After the barium precursor deposition on TiNTs and followed by annealing at 700 °C in O2 atmosphere round shaped BaTiO3 nanocrystals are covering the TiNTs surface independently on barium concentration. When the annealing temperature and titanium concentration increase the barium titanate nanoparticles seem to be segregated and NRs of barium deficient phases are formed. The role of the TiNTs on the anisotropic growth of barium titanate in vapor phase reaction is described for the first time in this work. Regarding the non template additive assisted syntheses the effect of additives on the morphological control of BaTiO3 particles is systematically addressed. Different types of additives were tested on the synthesis of BaTiO3 and the structural changes of the nanoparticles assessed and related with the nature of the additive. It is prooved that additives can be used as crystal growth modifiers by changing the growth habit or kinetically controlling the growth rate of the various crystallographic facets of the crystals. All the tested additives influence the growth of BaTiO3, but their role is distinctly different; poly(acrylic acid) (PAA) adsorbs on specific crystallographic faces changing the growth kinetics and inducing the oriented attachment of the particles; poly(vinyl pyrrolidone) (PVP), sodium dodecylsulfate (SDS) and hydroxypropylmethylcellulose (HPMC) act as growth inhibitors rather than crystal habit modifiers resulting in small crystals (26 nm); and D-Fructose appears to increase the activation energy for nucleation and no crystalline BaTiO3 is formed under the same conditions used for the other additives. In conclusion, the role of TiNTs as template agents for the growth of anitsotropic BaTiO3 in solution is clarified and the concept in vapour phase reaction is proved. In addition the effect of selected additives on the morphology control of BaTiO3 nanoparticles is presented. The proposed preparation strategies for anisotropic BaTiO3 nanostructures are low cost, reproducible and “user friendly”. The results clearly contribute to a better understanding of the size – shape - properties relationship in nano ferroelectrics envisaging future applications.
FCT - SFRH/BD/23375/2005

This thesis examines the particle capture, fibre wetting and droplet flow processes within wet filters collecting solid and liquid aerosols and within filters collecting only liquid aerosols. The processes involved in this type of filtration were examined through a series of experiments and models developed to describe the behaviour of fibre/liquid systems. This work can be summarized in 4 categories: (1) The bounce and immediate re-entrainment of liquid and solid monodisperse aerosols under a stable filtration regime (pre cake formation) by wet and dry fibrous filters. In this work it was found that the solid particles generally exhibited a lower fractional filtration efficiency than liquid particles (of the same size), although this difference decreased in the smaller size fractions. However, for the wet filtration regime (each fibre of the filter was coated by a film of water), no significant difference in filtration efficiency was detectable between solid and liquid aerosols. Either the bounce effect of the particles is inhibited by the liquid film, or the filtration conditions in the wet filter are so different that the aerosol properties are less significant with respect to capture. (2) A microscopic study of the effect of fibre orientation on the fibre wetting process and flow of liquid droplets along filter fibres when subjected to airflow and gravity forces was conducted. The flow of the liquid collected by the fibres was observed and measured using a specially developed micro-cell, detailed in the thesis. The experimental results were compared to a theoretical model developed to describe the flow of droplets on fibres. The theory and experimental results showed a good agreement. A sensitivity analysis of the model was performed which showed the droplet radius to be the most significant parameter. The model has the potential to improve filter self-cleaning and minimise water use. (3) An experimental study of the capture of solid and liquid (oil) aerosols on fibrous filters wetted with water. Variable quantities of liquid irrigation were used, and the possibility for subsequent fibre regeneration after clogging or drying was also studied. It was found that self-cleaning (removal of solid aerosols by water) occurred even under heavily dust-laden conditions, and post evaporation of water. With the collection of oil aerosols on fibres wetted with water, a predominance of the barrel shaped droplet on the fibre was observed, with oil droplets displacing water droplets (if the oil and fibre combination created a barrel shaped droplet), creating various compound droplets of oil and water not previously reported in literature. (4) An extensive experimental investigation of the wetting processes of fibre/liquid systems during air filtration (when drag and gravitational forces are acting) has shown many important features, including droplet extension, oscillatory motion, and detachment from fibres as airflow velocity increases. The droplet oscillation is believed to be induced by the onset of the transition from laminar to turbulent flow as droplet size increases. To model such oscillation it was necessary to create a new conceptual model to account for the forces both inducing and preventing such oscillation. The agreement between the model and experimental results is satisfactory for both the radial and transverse oscillations.

This thesis examines the particle capture, fibre wetting and droplet flow processes within wet filters collecting solid and liquid aerosols and within filters collecting only liquid aerosols. The processes involved in this type of filtration were examined through a series of experiments and models developed to describe the behaviour of fibre/liquid systems. This work can be summarized in 4 categories: (1) The bounce and immediate re-entrainment of liquid and solid monodisperse aerosols under a stable filtration regime (pre cake formation) by wet and dry fibrous filters. In this work it was found that the solid particles generally exhibited a lower fractional filtration efficiency than liquid particles (of the same size), although this difference decreased in the smaller size fractions. However, for the wet filtration regime (each fibre of the filter was coated by a film of water), no significant difference in filtration efficiency was detectable between solid and liquid aerosols. Either the bounce effect of the particles is inhibited by the liquid film, or the filtration conditions in the wet filter are so different that the aerosol properties are less significant with respect to capture. (2) A microscopic study of the effect of fibre orientation on the fibre wetting process and flow of liquid droplets along filter fibres when subjected to airflow and gravity forces was conducted. The flow of the liquid collected by the fibres was observed and measured using a specially developed micro-cell, detailed in the thesis. The experimental results were compared to a theoretical model developed to describe the flow of droplets on fibres. The theory and experimental results showed a good agreement. A sensitivity analysis of the model was performed which showed the droplet radius to be the most significant parameter. The model has the potential to improve filter self-cleaning and minimise water use. (3) An experimental study of the capture of solid and liquid (oil) aerosols on fibrous filters wetted with water. Variable quantities of liquid irrigation were used, and the possibility for subsequent fibre regeneration after clogging or drying was also studied. It was found that self-cleaning (removal of solid aerosols by water) occurred even under heavily dust-laden conditions, and post evaporation of water. With the collection of oil aerosols on fibres wetted with water, a predominance of the barrel shaped droplet on the fibre was observed, with oil droplets displacing water droplets (if the oil and fibre combination created a barrel shaped droplet), creating various compound droplets of oil and water not previously reported in literature. (4) An extensive experimental investigation of the wetting processes of fibre/liquid systems during air filtration (when drag and gravitational forces are acting) has shown many important features, including droplet extension, oscillatory motion, and detachment from fibres as airflow velocity increases. The droplet oscillation is believed to be induced by the onset of the transition from laminar to turbulent flow as droplet size increases. To model such oscillation it was necessary to create a new conceptual model to account for the forces both inducing and preventing such oscillation. The agreement between the model and experimental results is satisfactory for both the radial and transverse oscillations.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Environmental Engineering
Faculty of Environmental Sciences
Full Text

Fluid-to-particle heat transfer coefficients (h$ rm sb{fp}$) associated with food and model particles under simulated aseptic processing conditions were experimentally evaluated, and verified using measured inactivation kinetic parameters of the enzyme trypsin. Convective heat transfer coefficients were determined initially using two methods: a rate method based on evaluated heating/cooling rate indices (f$ rm sb c$/f$ rm sb h$) and a ratio method based on the ratio of temperature difference between the medium and particle locations.
Carrot and potato tissue in the form of finite cylinders of different lengths (0.02-0.04 m) and diameters (0.016-0.023 m) were used for evaluating h$ rm sb{fp}$ associated with aqueous CMC solutions (0-1.0% w/w) at temperatures ranging from 50 to 80$ sp circ$C and at relatively low fluid flow (0.2 to $0.7 times10 sp{-3}$ m/s) conditions. Carrots generally gave higher h$ rm sb{fp}$ values (100-550 W/m$ sp2$C) compared to potatoes (80-450 W/m$ sp2$C). Laminar flow natural convection dominated the flow regime. Hence, the Nusselt number was modeled as a function of Rayleigh's number which resulted in coefficients of determination (R$ sp2$) greater than 0.80.
A pilot scale holding tube simulator was designed and fabricated for routine/rapid gathering of heat penetration data which may be experienced in high temperature short time processing conditions.
Using the simulator under conditions comparable to industrial applications, and a full factorial experimental design, h$ rm sb{fp}$ values were estimated using finite cylinders of Teflon and potato tissue of different sizes (length: 0.020-0.0254 m; diameter: 0.0159-0.0254 m), and spherical Teflon particles (diameter 0.0191 m) in food grade CMC solutions (0-1.0% w/w). Operating temperatures were 90, 100 and 110$ sp circ$C, and flow rate was varied from 1.0-$1.9 rm times10 sp{-4} m sp3$/s. Average h$ rm sb{fp}$ values ranged from 56 to 966 W/m$ sp2$C depending on size, shape, fluid concentration, particle orientation, and tube diameter. Differences caused by different particle materials were accounted for by introducing a thermal diffusivity ratio in developed dimensionless correlations for both mixed and forced convective heat transfer to spherical and finite cylindrical particles under simulated aseptic processing conditions.
Thermal inactivation of trypsin (bovine pancreas type III) in low and high pH media was studied at temperatures ranging from 90-130$ sp circ$C. Comparative studies of its kinetic data with other bioindicators indicated the enzyme to be suitable for HTST verification/validation purposes. Further studies revealed, probably depending on pH, that trypsin was more susceptible to thermal inactivation at temperatures around 70$ sp circ$C. (Abstract shortened by UMI.)

CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
Ensaios imunológicos em amostras biológicas são baseados em métodos que quantificam a ligação antígeno-anticorpo através de um marcador ligado ao anticorpo. Recentemente, métodos magnéticos de detecção têm sido aplicados através da utilização de marcadores contendo nanopartículas magnéticas em seu interior. Isto pode levar a um diagnóstico precoce de determinadas patologias como tumores, doenças auto-imunes, etc. Com este objetivo, construímos um magnetômetro para realizar esta caracterização. Utilizamos uma sonda Hall triaxial, um eletroímã alimentado por uma fonte de corrente bipolar e um sistema posicionador de precisão. Todos os componentes do magnetômetro foram controlados utilizando a linguagem LabView®. A interface com o usuário é extremamente versátil e é realizada através de um arquivo texto onde qualquer seqüência de campos magnéticos aplicado (de 0,2 mT à 1 T) a serem aplicados à amostra pode ser especificada. A performance do magnetômetro construído foi comparada com a de um magnetômetro comercial SQUID e um erro médio quadrático de 0.43% foi encontrado na magnetização da partículas de níquel para momentos magnéticos na ordem de 10-4 Am2. Finalmente, como exemplo de aplicação, nanopartículas de ferrita de cobalto com momento magnéticos na ordem de 10-5 Am2 foram recobertas com vários surfactantes e sua caracterização foi realizada utilizando o magnetômetro construído.
Immunoassays in biological samples are based on methods that quantify the antigen-antibody link using a magnetic marker attached to the antibody. Recently, magnetic methods of detection have been applied using markers with magnetic nanoparticles in its interior. This can lead to early diagnosis of certain pathology such as tumors, autoimmune diseases etc. With this objective, built a magnetometer to perform this characterization. We use a tri-axial Hall probe, an electromagnet powered by a bipolar current source and a accurate positioner system. All components of the magnetometer were controlled using Lab View language. The interface with the user is extremely versatile and is made through a text file where any sequence of magnetic fields (from 0,2 mT to 1 T) to be applied to the sample can be specified. The performance of the built magnetometer was compared with a commercial SQUID magnetometer and an mean squared error of 0.43% was found in the magnetization of the particles of nickel for magnetic moments in the order of 10-4 Am2. Finally, as an example of application, nanoparticles of cobalt ferrite with magnetic moments in the order of 10-5 Am2 were coated with various surfactant and its characterization was performed using the built magnetometer.

In spite of the widely perceived importance of suspended particulate material (SPM) , its distribution in the shelf seas and the processes controlling its variation are little known. This thesis reports an exploratory study of the spatial and time dependant variability of SPM in an area of the northern Irish Sea. SPM was determined both directly by gravimetric methods and via measurements of beam attenuation (c). Spatial distributions were determined from grid surveys using a profiling transmissometer. In addition a six month record of beam attenuation and current velocity was obtained from a site off the north coast of Anglesey. A clear spatial pattern in the surface distribution of c was observed which was similar to the distribution of h/ta, suggesting that concentrations of SPM are determined by the availability of TKE from tidal stirring. A strong seasonal cycle of c was observed in mixed water, with values decreasing in June, July and August which suggested a reduction in the supply of SPM during summer. In stratified water, high concentrations of SPM remained confined to the dense layer below the thermocline. The seasonal cycle was observed in the time series from the mooring, but in addition there was a marked response to tidal currents in the spring and in autumn. Close analysis of the record in April and May-showed signals at M% and M4frequencies. These variations in c were attributed to a local response to tidal currents causing erosion of the sea-bed and to the oscillation of a horizontal gradient in c in the region. A regression model was found to explain 35% of the variance in data from a5 week time series. 70% of the variance was explained for four day time series, near spring tides. The relationship between c and tidal flows was more marked at spring tides than at neaps.

Thesis (M.Sc.)--City University of Hong Kong, 2002.
At head of title: City University of Hong Kong, Department of Physics and Materials Science, Master of Science in materials technology and management dissertation. Title from title screen (viewed on Sept. 4, 2006) Includes bibliographical references.

Thesis (M.S.)--West Virginia University, 2008.
Title from document title page. Document formatted into pages; contains iv, 87 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 83-86).

In the context of the safety of nuclear installations, there is general concern over the release and dispersal of radioactive pollutants in particulate form into the atmosphere. Such a release may lead to radiation exposure to individuals under radioactive fall-out conditions in the form of direct gamma exposure, through inhalation or by the particulate material being deposited on internal and external surfaces of buildings. This project addresses the protection offered by buildings to the occupants, against such exposure pathways. A computer model (BHOUSE) has been developed to simulate the exchange and transport of pollution in aerosol form for a building. A particular aspect investigated, mainly through modelling, has been the protection afforded by buildings through the deposition indoors of aerosols which might infiltrate into the buildings in question. On the one hand this process is likely to reduce indoor air concentrations, thus reducing inhalation dose, on the other hand it may lead to the problem of long-term contamination inside buildings. A related consideration is the safety provided by the building, to the occupants inside, against the direct radiation emitted by the externally deposited activity. Various benchmarking exercises have been carried out to investigate the indoor air and contaminant dispersal. These exercises have included: pollution ingress rate to a building under a variety of conditions; effect of wet external deposition on mechanical transport rate; variation of indoor pollution level with and without vacuum cleaner operating and the calculation of inhalation dose rates. Measures to obtain higher protection factors against particulate inhalation have also been suggested. Predictions obtained with the model have been compared with an existing model. This comparison aimed to identify common features and significant differences between models. Such studies clearly relate to other non-nuclear aspects of indoor air quality research. A better understanding of the importance of individual parameters affecting indoor air quality has been achieved. The thesis also reports results obtained through participation in a joint experimental programme between Imperial College, the Danish Riso National Laboratory and the Building Research Establishment (BRE) which yielded measured indoor deposition velocities in an experimental terraced house using monodisperse aerosol labelled with a stable tracer. The deposition behaviour of particles with different sizes have also been studied. Neutron activation analysis was used to estimate aerosol concentration levels on air filters inside rooms, with the use of the Imperial College nuclear reactor. The resulting average deposition velocities were used in the model in order to illustrate the protection afforded by buildings against inhalation dose, for the aerosol sizes which were investigated. A critical review has also been conducted on aerosol test chamber studies.