• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 78
  • 43
  • 26
  • 24
  • 16
  • 13
  • 8
  • 6
  • 5
  • 3
  • 2
  • 2
  • 2
  • 1
  • 1
  • Tagged with
  • 266
  • 56
  • 50
  • 49
  • 43
  • 35
  • 30
  • 26
  • 24
  • 24
  • 23
  • 22
  • 22
  • 22
  • 20
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
211

Caractérisation des interactions entre un plasma non-thermique et des matériaux / Characterization of interactions between a non-thermal plasma and materials

Rodrigues, Anthony 08 November 2013 (has links)
L'étude des interactions entre les espèces actives générées par un plasma non thermique et diverses surfaces de matériaux font l'objet de ce travail.Dans un premier temps, des polymères provenant de la biomasse ont été le sujet de nos recherches. Ils représentent une source importante de molécules plateforme telle que le glucose à partir desquelles peuvent être générés des produits de haute valeur ajoutée. Plus précisément, les effets d'un plasma à décharge à barrière diélectrique sur la structure et la dépolymérisation de l'inuline, de la cellulose et de l'amidon ont été étudiés. Une variation des paramètres électriques et chimiques de la décharge plasma a été effectuée et leurs effets sur les biopolymères évalués afin de comprendre les mécanismes de réaction. Nos résultats ont montré qu'un traitement initial par le plasma permettait d'augmenter considérablement le rendement final en sucre monomère (fructose ou glucose) par rapport au même produit de départ non traité par le plasma (84 et 54% de glucose à partir réciproquement de l'amidon et de la cellulose traités par plasma, au lieu de 65 et 1 % pour les mêmes produits non traités). Cet effet pourrait être du en partie à une dépolymérisation par attaque acide induite au sein du plasma sur les zones amorphes des biopolymères.Dans un second temps, l'étude a porté sur l'élimination des COV par couplage plasma non-thermique et catalyseur. Pour cette étude, nous avons conçu et mis en oeuvre un appareillage original formé par un réacteur plasma-catalyseur permettant une analyse sous atmosphère contrôlée de la surface du catalyseur par spectroscopie IR (DRIFT). Cet appareillage a permis d'étudier la décomposition de quatre COV (isopropanol, acétone, éthanol et toluène) adsorbé sur différents oxydes métalliques (g-Al2O3, CeO2 et TiO2) placés dans la zone de décharge en temps réel (in-situ). Les premiers résultats ont permis d'élucider certaines voies de décomposition de ces différents COV. / The interactions between the active species generated by a non thermal plasma and various material surfaces have been studied in this work. In a first part, biopolymers coming from biomass have been the subject of our investigations as they offer a great reservoir for a platform molecule, glucose, from which valuable chemicals can be generated. More specifically, the effects of a dielectric barrier discharge plasma on the structure and depolymerization of inulin, cellulose and starch were evaluated. For that purpose, the electrical and chemical characteristics of the plasma discharge were varied and their effects on the biopolymers evaluated in order to understand the reaction mechanisms. Our results showed that a plasma pre-treatment increased considerably the final monomer yield (in glucose and fructose) compared to the untreated starting material (84 and 54 % yield in glucose from plasma treated starch and cellulose, instead of 65 and 1 % for the same untreated samples). This effect could be partly explained by the depolymerization of the amorphous areas of the polymers by and acid attack within the plasma discharge.In a second part, the study focused on the removal of VOCs by coupling non-thermal plasma and inorganic materials. For this purpose, we designed and implemented an innovative apparatus. It consists of a plasma-catalyst reactor with controlled atmosphere that allows the analysis of the catalyst surface by IR spectroscopy (DRIFT). The decomposition of four VOCs (isopropanol, acetone, ethanol and toluene) adsorbed on different metallic oxides (y-Al2O3, CeO2 and TiO2) placed within the discharge area have been studied in situ using this method. The first results have enlightened the decomposition pathways of the different VOCs.
212

Detection of harmful microbes and their metabolites with novel methods in the agri-food production chain

Nieminen, T. (Timo) 12 January 2009 (has links)
Abstract This thesis aimed at developing methods for tracking the environmental origins of microbial contaminants of the food chain. We worked on three targets: i) environmental mycobacteria ii) toxinogenic Bacillus species iii) post-harvest fungi in strawberry jam. Our aim was to develop methods for early detection of the above contaminants, which have the potential to endanger consumer health. We developed a novel method based on 16S rRNA hybridization for tracking the reservoirs of potentially pathogenic environmental mycobacteria in piggeries and soil. From 1010 to 1012 16S rRNA molecules of environmental mycobacteria were found per gram of peat, wood shavings and straw in piggeries with a high prevalence of infections. These beddings may thus be a source of mycobacteria for pigs. We found 1010–1011 of mycobacterial 16S rRNA molecules per gram of Finnish forest soil, indicating that the soil contained 107–109 mycobacteria per gram. These numbers exceed the previous cultivation-based estimates of mycobacterial content in Finnish soils. To elucidate the role of mastitis in the input of toxinogenic Bacillus into the dairy production chain, milks were sampled from mastitic cows. Twenty-three Bacillus isolates were screened for toxins using the sperm cell motility inhibition assay. Four of the six toxinogenic isolates found were identified as Bacillus pumilus and two as Bacillus licheniformis. The isolates produced toxic substances that were heat-stable (100 °C) and soluble in methanol, thus being of non-protein nature. The extracts prepared from the toxin-producing isolates disrupted the plasma membrane of exposed sperm cells at concentrations 1–15 μg ml-1 (B. pumilus) 20–30 μg ml-1 (B. licheniformis). The toxic action of the mastitis-associated B. licheniformis strains was similar to that of the lipopeptide lichenysin A. The genes for lichenysin synthetase were found in these strains by PCR. This study revealed that heat-stable toxin-producing strains of B. pumilus and B. licheniformis occur in milk of mastitic milking cows. They may enter the dairy production chain when milk of clinically healthy cows recovered from mastitis is sent to dairies. Many foodborne contaminant fungi are known to produce volatile organic compounds. We investigated the suitability of such metabolites as early indicators of fungal contamination of strawberry jam. We found that volatile organic compounds commonly produced by the contaminant fungi in strawberry jam were 2-pentanone, styrene, 3-methyl-1-butanol, 1,3-pentadiene and ethanol. The results indicate that these compounds could be used to detect fungal contamination of jam.
213

Trådlös Övervakning av Inomhusklimat och PIR-baserad Passageräkning : En Demonstrationsanläggning åt Sweco Position AB

Svensson, Joakim, Yalda, Milad January 2017 (has links)
Denna rapport är ett tekniskt komplement till Johanna Hernnäs och Linnea Martinssons rapport AerQ - Ett produktutvecklingsprojekt för att läsa av inomhusklimatet. I denna rapport beskrivs designen av en demonstrationsanläggning för inomhusklimat och passageräkning bestående av två trådlösa och batteridrivna enheter för inomhusklimat respektive passageräkning och en mobilapplikation till vilket datan presenteras. Klimatenheten mäter temperatur, relativ luftfuktighet och koldioxid samt kommunicerar via Wi-Fi och BLE och visuellt via RGB-LED:s. passageräknaren detekterar passager m h a en PIR-sensor och kommunicerar via BLE. I rapporten presenteras utförandet av demoanläggninen och en undersökning av PIR-sensorer. Resultatet visar att det är möjligt att detektera riktning med en PIR-sensor samt en lösning för långvarig batteridrift av en sensornod utrustad med ljusdiodslinga, Wi-Fi och VOC-sensor(MEMS metalloxidsensor). Systemets roll kan vara att återkoppla till behovsstyrd ventilation och/eller uppmärksamma användare om sitt inomhusklimat. / This report is a technical complement to Johanna Hernnäs and Linnea Martinssons bachelor work paper AerQ - Ett produktutvecklingsprojekt för att läsa av inomhusklimatet. This report describes the design of an indoor climate and people counting demo facility consisting of two wireless and battery-powered units for indoor climate and people counting and a mobile application to which the data is presented. The climate unit measures temperature, relative humidity and carbon dioxide, and communicates via Wi-Fi and BLE and visually via RGB LEDs. The people counter detects a passage with a PIR sensor and communicates via BLE. The report presents the implementation of the demo facility and a investigation of PIR sensors. The result shows that it is possible to detect direction with a PIR sensor as well as a long-term battery operation of a sensor node equipped with RGB LEDs, Wi-Fi and VOC Sensor (MEMS Metal Oxide Sensor). The system's role may be to feedback demand-driven ventilation and / or to alert users about their indoor climate.
214

Étude cinétique de la dégradation photocatalytique de composés organiques volatils (COV) et modélisation par une approche numérique de la mécanique des fluides / Kinetic study of VOC photocatalytic remediation and modelling with a computational fluid dynamics approach

Queffeulou, Amélie 05 November 2009 (has links)
Les COV présents en air intérieur sont une source d’inconfort pour les occupants et peuvent être nocifs pour la santé. La photocatalyse apparaît comme un procédé prometteur pour l’abattement de ces polluants. ArcelorMittal Liège Research développe à cet effet des films minces de TiOB2B déposé sur acier qui peuvent être intégrés dans des systèmes de purification d’air. Les objectifs de cette recherche sont, d’une part, identifier les paramètres influençant la dégradation photocatalytique de ces COV avec ce type de catalyseur et d’autre part, valider la possibilité de prédire les performances d’un réacteur photocatalytique par un modèle couplant l’écoulement et la réaction photocatalytique. Pour réaliser l’étude cinétique à des teneurs de quelques ppm, un dispositif expérimental adapté a été conçu ; il utilise un réacteur annulaire continu. L’acétaldéhyde a été choisi comme polluant modèle. La conversion dépend de la concentration en polluant, du taux d’humidité, de la température, de l’intensité lumineuse en UV et de la présence d’autres COV. La réaction est modélisée avec un modèle théorique surfacique de la réaction photocatalytique. Afin de prédire les performances d’un réacteur photocatalytique utilisant des films minces de TiOB2B, une méthodologie consistant à coupler l’écoulement et la réaction photocatalytique a été développée et validée. La distribution spatio-temporelle de la concentration en polluant est alors déterminée par une approche de mécanique des fluides numériques. La comparaison des résultats expérimentaux et des simulations obtenus avec un réacteur photocatalytique de laboratoire et un autre à l’échelle semi-pilote est très satisfaisante / VOCs are a source of discomfort for occupants and can have harmful effects on health. Photocatalysis is a promising process to remove these compounds. ArcelorMittal Liège Research has indeed developed TiOB2 Bthin film coated on steel which can be easily integrated into purification air systems. Objectives of this research are firstly, identifying parameters which influence the photocatalytic degradation of these VOCs using of such catalyst. Secondly, validate the possibility to predict performances of the photocatalytic reactor by combining fluid flow and photocatalytic reaction. An experimental set-up including an annular reactor has been designed and realized in order to conduct kinetic studies. Acetaldehyde has been chosen as a pollutant model and studied mainly with concentrations of few ppm ranges. Its conversion yield depends on pollutant concentration, relative humidity, temperature, UV light intensity and presence of others VOCs. Based on a theoretical surface model of the photocatalytic reaction, and using experimental data, this reaction is modelled. In order to predict performances of the photocatalytic reactor packed thin film of TiOB2B, a methodology which consists to combine fluid flow and photocatalytic reaction has been developed and validated. Space-time distribution of pollutant concentration is then determined with a computational fluid dynamics approach. Comparison between experimental data and numerical simulations obtained with a photocatalytic reactor at the laboratory scale and another one in semi-pilot scale are well satisfactory
215

Elaboration d’un microsystème d’analyse de l’air destiné à la détection rapide d’un développement fongique dans les espaces clos / Elaboration of a rapid and continuous air analyzing macrosystem for fungal contamination detection in enclosed spaces

Joblin, Yaël 12 May 2011 (has links)
Les champignons sont des biocontaminants courants des environnements intérieurs. De nombreuses études ont démontré leur rôle dans la dégradation des supports que ces microorganismes colonisent tels que les matériaux de construction, les ouvrages ou les œuvres d'art. De plus, ces biocontaminants sont susceptibles d'induire des allergies, des infections, des toxi-infections ou encore des irritations. Depuis 2005, une technique de détection de la croissance fongique, basée sur la recherche de traceurs chimiques spécifiques dans l'air, et un indice de contamination fongique (ICF), ont été développés et validés au cours de différentes campagnes de mesures dans l'habitat, les bureaux, les écoles, les crèches… L'objectivation d'une croissance fongique dans un environnement s'appuie sur des prélèvements par adsorption, une analyse chromatographique au laboratoire (GC/MS) et le calcul de l'ICF. Dans le cadre de la surveillance de la qualité microbiologique de l'air des environnements intérieurs, cette thèse a pour ambition de prolonger ces travaux en développant notamment un système de microcapteurs chimiques adapté à la mesure in situ. Cette recherche repose à la fois sur la méthode de détection fongique développée au CSTB et sur l'expertise scientifique et technique de l'ESIEE en matière de miniaturisation d'instruments de mesure, grâce à l'apport des microtechnologies. Le premier axe de cette étude a consisté à identifier expérimentalement les COV du métabolisme fongique spécifiques d'un développement sur des matériaux du patrimoine. Ces molécules ont permis de consolider l'ICF et de définir deux indices spécifiques à la problématique des sites patrimoniaux, validés dans des châteaux, musées, bibliothèques, grottes ornées… Le second axe porte, d'une part, sur la conception la réalisation et la caractérisation des briques élémentaires du microsystème d'analyse, à savoir un module de préconcentration (adsorption TENAX), un module de séparation (microGC) et un module de détection (capteurs polymères) et d'autre part sur les intégrations et pilotage de ces briques / Fungi are common microbial contaminants of indoor environments. Many studies have demonstrated their role in the partial or total degradation of materials they colonize such as building materials, or works of art. Moreover, those microbial contaminants are likely to lead to allergies, infections, poisoning or irritation. Since 2005, a new technique based on researching specific chemical tracers in the air, was developed and validated during different measurement campaigns. This approach is now applied to various indoor environments (houses, offices, schools, child care centers…) and allows the detection of recent and/or hidden contamination. The purpose of this work is to study and characterize a rapid and continuous air analysing microsystem for detection of fungal contamination in closed spaces. This study falls within the field of monitoring air microbiological quality in indoor environments. In addition to the time saved by the absence of any laboratory analysis, this system must provide a permanent monitoring of environments frequented by people, such as museums, schools, hospitals... This research is based both on the fungal detection method developed by CSTB and on scientific and technical expertise of ESIEE : specialised in design and manufacturing of miniaturized analysis systems obtained using microtechnology. The first step of this study was to define the compounds' nature to be detected for different cases of contamination along with the sampling strategy for the system. The second step focuses on the microstructures design and fabrication to be used in microanalytical system based on gas chromatography and the development of a miniaturised analysis system. So the first part of the study consisted in defining specific fungal contamination tracers for heritage conservation sites. This list allowed to reinforce a fungal contamination index for indoor environments and to define two specific indexes designed for heritage conservation sites. The validation of these different indexes allowed checking their compliance with those types of environments (castles, museums, libraries, decorated caves...) by detecting all cases of contamination, along with the control remediation of former contaminated environments. The second part of the study enabled the design and validation of three main modules constitutive of the microanalytical system based on gas chromatography. A miniaturised analysis system based on three modules has been developed
216

Microstructural Control in Fabricating Multifunctional Carbon Fibers

January 2020 (has links)
abstract: Precursors of carbon fibers include rayon, pitch, and polyacrylonitrile fibers that can be heat-treated for high-strength or high-modulus carbon fibers. Among them, polyacrylonitrile has been used most frequently due to its low viscosity for easy processing and excellent performance for high-end applications. To further explore polyacrylonitrile-based fibers for better precursors, in this study, carbon nanofillers were introduced in the polymer matrix to examine their reinforcement effects and influences on carbon fiber performance. Two-dimensional graphene nanoplatelets were mainly used for the polymer reinforcement and one-dimensional carbon nanotubes were also incorporated in polyacrylonitrile as a comparison. Dry-jet wet spinning was used to fabricate the composite fibers. Hot-stage drawing and heat-treatment were used to evolve the physical microstructures and molecular morphologies of precursor and carbon fibers. As compared to traditionally used random dispersions, selective placement of nanofillers was effective in improving composite fiber properties and enhancing mechanical and functional behaviors of carbon fibers. The particular position of reinforcement fillers with polymer layers was enabled by the in-house developed spinneret used for fiber spinning. The preferential alignment of graphitic planes contributed to the enhanced mechanical and functional behaviors than those of dispersed nanoparticles in polyacrylonitrile composites. The high in-plane modulus of graphene and the induction to polyacrylonitrile molecular carbonization/graphitization were the motivation for selectively placing graphene nanoplatelets between polyacrylonitrile layers. Mechanical tests, scanning electron microscopy, thermal, and electrical properties were characterized. Applications such as volatile organic compound sensing and pressure sensing were demonstrated. / Dissertation/Thesis / Masters Thesis Materials Science and Engineering 2020
217

Medhåll, motstånd eller samtycke : En teoriprövande granskning av remissvaren på SOU 2020:30 ”En moderniserad arbetsrätt”

Malmros, Carl January 2020 (has links)
No description available.
218

Étude et développement d'un procédé de traitement des odeurs par oxydation à l'ozone : application aux effluents gazeux d'usines de production de superphosphate / Study and development of an odor treatment process by ozone oxidation : application to gaseous effluents from superphosphate production plants

Vitola Pasetto, Leticia 18 July 2019 (has links)
Dans le procédé de production d’engrais à base de superphosphate, l’attaque de la roche phosphatée par l’acide sulfurique génère des sous-produits gazeux odorants. Bien que leurs émissions se situent dans les limites réglementaires, les usines d’engrais à base de superphosphate sont susceptibles de causer des nuisances olfactives pour les riverains. Cette thèse propose d’étudier la faisabilité d’un procédé de traitement des odeurs par l’ozonation en phase gazeuse homogène. Une première étape de priorisation des composés chimiques ayant le potentiel odorant le plus important a été réalisée. Ce classement a été effectué à partir d’un rapport technique fourni par notre partenaire industriel basé sur une campagne de mesure olfactométrique et de caractérisation chimique des gaz émis par la cheminée d’une usine de production des engrais superphosphate. À partir du calcul de la valeur d’activité odorante (OAV), deux familles de composés ont été ciblées : les composés soufrés – représentés par le sulfure d’hydrogène (H2S), le sulfure d’éthylméthyle (MES) et le disulfure de diméthyle (DMDS) – et les aldéhydes (représentés par le propanal et le butanal). Deux techniques analytiques (GC/FID et SIFT/MS) ont été mises en œuvre afin d’évaluer les performances d’élimination de ces composés, la difficulté d'analyser une matrice gazeuse contenant de l'ozone ayant été mise en évidence. Ainsi, une interférence de l'ozone sur l'analyse des aldéhydes par GC/FID a été identifiée. La technique SIFT/MS a, quant à elle, nécessité un développement important. L’ozonation d’effluents gazeux modèles a été réalisée en suivant l’élimination des composés cibles dans différentes conditions de fonctionnement (temps de résidence, température du réacteur, concentration en ozone et taux d’humidité) dans un domaine expérimental compatible avec les contraintes industrielles. Les composés soufrés ont présenté des taux d’élimination élevés, particulièrement dans le cas de H2S, dont les conversions ont atteint environ 80%. Les monosulfures (MES) et disulfures organiques (DMDS) se sont montrés moins réactifs à l’ozone, puisque les conversions sont restées assez faibles (de l’ordre de 30% pour un ratio O3/soufrés similaire). Dans la gamme de conditions opératoires utilisées, ni l'humidité, ni le temps de résidence dans le réacteur n’ont montré d'influence considérable. La concentration d'ozone s’avère être le paramètre du procédé le plus influant, ayant un effet positif sur les taux de conversion des trois composés soufrés étudiés. Parallèlement, pour le DMDS, une augmentation de la température du réacteur a aussi amélioré la conversion. De manière globale, les taux de conversion les plus importants ont été obtenus pour les ratio O3/soufrés et la température du réacteur les plus élevés. A l’inverse, même lorsque les conditions de réaction les plus favorables ont été appliquées (température et concentration d’ozone les plus élevées), les aldéhydes se sont montrés non réactifs vis-à-vis de l’ozone. Malgré les faibles conversions obtenues, l’utilisation du SIFT/MS a permis d’identifier les principaux sousproduits de la réaction ozone-composés soufrés en phase gazeuse comme étant le méthyléthylsulfoxyde (MESO), le méthyléthylsulfone (MESO2), le diméthyl thiosulfinate (DMSOS), les isomères de diméthyl thiosulfonate (DMSO2S), le diméthyldisulfoxyde (DM(SO)2) et également le dioxyde (SO2) et le trioxyde de soufre (SO3). Le procédé de traitement des odeurs par ozonation directe des gaz en sortie de cheminée industrielle apparaît donc difficilement envisageable en raison de la faible efficacité d’élimination des composés malodorants démontrée dans nos essais. En revanche, cette technique couplée avec une absorption chimique pourrait s’avérer intéressante pour éliminer les nuisances olfactives avec une bonne efficacité / In the superphosphate-based fertilizers production process, the attack of phosphate rock by sulfuric acid generates odorous gaseous by-products. Although their emissions are within regulatory limits, superphosphate fertilizer plants are likely to cause odor nuisance to residents. This thesis proposes to study the feasibility of a process of odor treatment by ozonation in homogeneous gas phase. A first step of prioritization of the chemical compounds with the most important odorous potential has been realized. This ranking was established from a technical report provided by our industrial partner based on a campaign of olfactometric measurement and chemical characterization of the gases emitted by the chimney of a superphosphate fertilizer production plant. From the calculation of the odor activity value (OAV), two families of compounds were targeted: sulfur compounds - represented by hydrogen sulphide (H2S), ethylmethyl sulphide (MES) and dimethyl disulfide (DMDS) - and aldehydes (represented by propanal and butanal). Two analytical techniques (GC/FID and SIFT/MS) were applied in order to evaluate the elimination performance of these compounds, the difficulty of analyzing a gaseous matrix containing ozone having been demonstrated. Thus, ozone interference on GC/FID analysis of aldehydes has been identified. The SIFT/MS technique, in turn, required significant development. The ozonation of model gaseous effluents was carried out following the elimination of the target compounds under different operating conditions (residence time, reactor temperature, ozone concentration and moisture) in an experimental field compatible with the industrial constraints. The sulfur compounds exhibited high removal rates, particularly in the case of H2S, whose conversions reached about 80%. Organic monosulfides (MES) and disulfides (DMDS) were less reactive to ozone, as conversions remained quite low (around 30% for the same level of O3/sulfur ratio). In the range of operating conditions used, neither the moisture nor the residence time in the reactor showed considerable influence. The ozone concentration is the most influential process parameter, having a positive effect on the conversion rates of the three sulfur compounds studied. Meanwhile, for DMDS, an increase in reactor temperature also improved the conversion. Overall, the highest conversion rates were obtained for the highest O3/sulfur ratios and reactor temperature. Conversely, even when the most favorable reaction conditions have been applied (highest temperature and ozone concentration), the aldehydes have been inert to ozone. Despite the low conversions obtained, the use of SIFT/MS has identified the main by-products of the ozone-sulfur compounds gas phase reaction as methylethylsulfoxide (MESO), methylethylsulfone (MESO2), dimethyl thiosulfinate (DMSOS), isomers of dimethyl thiosulfonate (DMSO2S), dimethyldisulfoxide (DM(SO)2) and also sulfur dioxide (SO2) and trioxide (SO3). The odors treatment process by direct ozonation of the gases at the outlet of industrial chimney thus appears difficult to envisage because of the low efficiency of malodorous compounds elimination demonstrated in our tests. On the other hand, this technique coupled with chemical absorption could be interesting to eliminate the olfactory nuisances with a good efficiency
219

Hochempfindliche resonante Gassensoren auf der Basis von einkristallinen Silizium-Plattenschwingern

Grahmann, Jan 08 May 2008 (has links)
Die vorliegende Arbeit beschäftigt sich mit der Modellerstellung und Technologie eines gravimetrischen Gassensors für organische Gase. Die Besonderheit liegt in dem verwendeten Resonatortyp. Es handelt sich um einen lateral elektrostatisch angeregten quadratischen Plattenresonator, der mit einer Rezeptorschicht versehen wird. Mit Hilfe von FEM-Berechnungen werden die Eigenfrequenzen und Eigenformen berechnet. Für die untersuchte Lamé- und Square-Mode wird die Sensorgüte unter Berücksichtigung des "Squeeze-Film-Damping" sowie der viskoelastischen Rezeptorschichteigenschaften bestimmt. Die Sensormoden werden durch ein Feder-Masse-Modell mit einem Freiheitsgrad modelliert und durch ein elektrisches Ersatzschaltbild repräsentiert. Die berechneten Nachweisgrenzen für Oktan und Toluol bei 6-facher Rauschgrenze liegen im zweistelligen ppb-Bereich. Für die technologische Umsetzung werden SOI-Wafer verwendet. Die ≤ 100 nm betragenden Spaltbreiten zwischen Elektroden und Resonator werden durch das RIE-Ätzen von Siliziumgräben mit senkrechten Seitenwänden, der Abscheidung von SiO2 als Opferschicht und dem Füllen der Gräben mit hochdotiertem Polysilizium hergestellt. Die Kontaktierung der Resonatoren erfolgt über einen leitenden Stamm, der aufgrund von selbstjustierenden Prozessen die Resonatorplatte zentriert einspannt. / The following work is concerned with the modelling and fabrication technology of a gravimetric sensor for volatile organic compounds (VOC). Novelty is the combination of a lateral electrostatic driven square plate resonator with a gas sensitive detection layer. The eigenfrequencies and -modes are calculated with FEM simulations. Especially suited for gas sensors are the Lamé- and Square eigenmodes which are studied more closely. The quality factor is determined considering "squeeze film damping" and the viscoelastic properties of the gas sensitive detection layer. To present the sensor oscillation modes a spring mass model with one degree of freedom is determined and extended by an equivalent circuit diagram. The calculated limits of detections for octane and toluene are in the binary ppb-range, working with six times the limit of frequency noise. SOI-wafers are the base material for the sensor process flow. Electrode gaps ≤100 nm, essential for the electrostatic drive, are fabricated by RIE-etching vertical trenches into the device layer down to the buried oxide and by depositing a silicon dioxide as sacrifical layer and by refilling the trenches with highly doped polysilicon. The electrical contact of the resonator plate is ensured through an electrical conducting polysilicon stem. The developed process flow enables a self alignment ot the stem, clamping the plate centered.
220

IMPROVING WORKER SAFETY AND ENVIRONMENTAL PROTECTION BY UNDERSTANDING CHEMICAL EMISSIONS FROM PLASTIC COMPOSITES DURING MANUFACTURE AND USE

Seyedeh-Mahboobeh Teimouri-Sendesi (8755941) 21 June 2022 (has links)
<p>This dissertation focused on cured-in-place-pipe (CIPP) technology, which is being used to repair sewer pipes across the globe. The CIPP process involves the manufacture of a new fiber-reinforced composite plastic pipe inside an existing damaged pipe. By 2022, the global CIPP market will exceed $2.5 billion and constitute 40% of the U.S. pipe rehabilitation market. In recent years, concerns about the type, magnitude, and toxicity of chemical air emissions associated with CIPP installations have markedly increased. CIPP installations in Asia, Europe, Oceania, and North America have been associated with indoor and ambient air contamination incidents, afflicted schools, daycare centers, homes, and offices and prompted building evacuations. This research program was designed to better understand chemical release into the air during CIPP composite manufacture and the human health risks. Principles and techniques from the environmental engineering, air quality, material science, and risk analysis were applied. This dissertation contains three chapters and each chapter is a stand-alone manuscript, with the first chapter already having been published.</p><p>Chapter 1 involved the characterization of chemical emissions for steam-cured CIPP installations in Indiana (IN, sanitary sewer) and California (CA, storm sewer). It was discovered that a complex multiphase mixture of organic vapor, water vapor, and particulate (condensable vapor and partially cured resin) was emitted. Chemicals captured included a variety of hazardous air pollutants, carcinogens, endocrine disrupting compounds, and other chemicals with little toxicity data. The materials captured in California during 4 CIPP installations, when normalized against styrene concentration, exhibited different toxicity towards mouse cells. This toxicity indicated that non-styrene compounds were probably responsible for toxicity. Testing revealed significant and previously unreported worker and public safety chemical risks existed with CIPP installations.</p><p>Chapter 2 describes experiments conducted to determine which CIPP manufacturing conditions (i.e. curing pressure, temperature, time and ventilation) influenced chemical air emissions during and after composite manufacture. During thermal manufacture, approximately 8.87 wt% volatile organic compounds (VOC) was released into the air at standard pressure. For the CIPP styrene-based resin examined, chemical volatilization during manufacture was influenced by pressure, but temperature and heating time did not influence the composition of chemical residual inside the new composite. All cured composites, regardless of temperature or heating time, contained approximately 3 wt% VOC. No statistical difference was found for either: (1) VOC loading across cured composites or (2) styrene emission into the air across cured composites despite different curing temperature and heating times. Styrene was the most abundant compound detected in the composite and in air. High styrene air concentration signals inhibited the author’s ability to determine if other non-styrene compounds were emitted into the air. Short-term ventilation (2 hr) of the new composite reduced styrene air concentration to near zero in 10 min, but styrene levels rebounded when ventilation was halted. Due to the high styrene loading in the cured composite, it is expected that ventilation will only temporarily reduce VOC air levels in pipes, manholes, and other affected spaces.</p><p>Chapter 3 includes inhalation health risk assessment due to chemical emission from CIPPs during manufacture and use. Publicly available worksite data for ultraviolet (UV)-light and steam-CIPP installations were utilized and Monte Carlo simulation was applied. Data-gaps were also identified. Health risks associated with newly manufactured (post-cured) chemical emission from lab scale CIPPs were also evaluated. For CIPP resins and post-cured CIPPs 31 chemicals have been quantified among which many are unique volatile organic chemicals VOCs, but only 8 air testing studies were found. At a steam-CIPP worksite, VOCs were found in a condensed multiphase mixture discharged into air, 4 VOCs were detected in the vapor phase, while only styrene vapor phase results could be used for risk assessment. Worksite styrene levels (1,825 ppm<sub>v</sub>, 1,070 ppm<sub>v</sub>, 220-270 ppm<sub>v</sub>, 140 ppm<sub>v</sub>) have been reported indicating a health risk can exist. Monte Carlo simulation using literature data revealed that for the single UV-CIPP and single steam-CIPP study negligible styrene HQs were found, while unacceptable styrene LECRs% > 10<sup>−4</sup> (i.e. 37-38%) were obtained. Monte Carlo simulation on laboratory data showed that post-cured emissions from the composite cured longer increased the unacceptable styrene LECR (from 17.86% to 21.12%) and HQ (0.95% to 8.04%). Whereas curing the composite at greater temperature reduced the styrene LECR and HQ to 0.89%. and 0, respectively. Ventilation also diminished the acceptable LECR% in all composites but did not reduce the carcinogenic health risk to an acceptable level. Health risk can exist as evidenced by limited air testing data. More studies are needed to examine inhalation health risks associated with the CIPP manufacturing process and newly manufactured plastics.</p>

Page generated in 0.0562 seconds