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  • 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.
191

Processing, structure and properties of composites based on natural fillers and strereoregular polyolefins : environmentally benign concept

Berková, Kristýna 18 October 2013 (has links) (PDF)
This doctoral thesis is focused on composites based on polypropylene and wood flour. Firstly, the experimental work deals with preparation of composites based on wood flour with various concentrations and isotactic polypropylene with various melt flow indexes. In terms of this study, one polypropylene, which can have also practical use, was chosen. Further, this polypropylene is investigated with various types and concentrations of wood flour. Also, the attention is devoted to the modification of polypropylene by a specific β-nucleating agent. The differences are compared and described between the composites with neat and nucleated polypropylene. Further, the work is focused on solvent extraction of wood flour. The effect of extraction and solvent of wood flour is also examined in composites with neat and nucleated polypropylene. On prepared composites, the rheological, structural and thermal properties are studied. These properties differ depending on specific type of wood flour, its concentration and specific type of polypropylene.
192

The Solubility and Metal-silicate Partitioning of Some Highly Siderophile Elements: Implications for Core-formation and Planetary Accretion

Bennett, Neil 19 June 2014 (has links)
Understanding Earth’s accretion and primary differentiation is a long-standing goal of geology. The segregation of FeNi metal from molten silicate to form Earth’s core is expected to deplete and fractionate the highly siderophile elements (HSEs). Estimates of the primitive upper mantle (PUM) composition however, reveal only modest HSE depletions and chondritic element ratios. Past experiments to determine if the mantle composition is set by high-temperature metal-silicate equilibrium have involved measuring the solubility of HSEs in silicate melt at conditions more reducing than the iron-wustite (IW) buffer. Accurate determination of solubilities at such conditions has been hindered by the formation of dispersed metal inclusions; this work describes methods to circumvent the problem. Results of three separate studies are presented which document the solubility of Re, Pt and Au in molten silicate which is demonstrably nugget-free. Data obtained from experiments done at 0.1 MPa–2 GPa, 1573–2573 K and ~ IW -1.5 to +3 reveal: 1) Re, Pt and Au solubility increases with increasing temperature, 2) Re solubility increases with increasing oxygen fugacity (fO2), consistent with dissolution as oxide species, 3) Below ~ IW +3, Pt and Au solubility increases with decreasing fO2, consistent with dissolution as neutral or silicide species, and 4) that Au is amongst the most soluble HSE in molten silicate, with values increasing with temperature, but insensitive to changes in P, fO2 and melt composition, making it well suited as a geothermometer for core formation. Partition coefficients calculated from these and previous solubility measurements indicate that metal-silicate equilibrium is unable to reproduce the Re/Os and Pt/Os ratios required by PUM Os isotope systematics if simultaneously accounting for the observed absolute element abundances. Instead, results support late accretion of material following core formation, elevating element abundances and endowing chondritic inter-element ratios. Experimental results are incorporated into a terrestrial accretion model, which differs from the standard approach by explicitly accounting for the distribution of oxygen. Model results show siderophile element abundances in PUM are best reproduced if the mantle undergoes oxidation during accretion and metal-silicate equilibrium occurs near the peridotite solidus.
193

The Solubility and Metal-silicate Partitioning of Some Highly Siderophile Elements: Implications for Core-formation and Planetary Accretion

Bennett, Neil 19 June 2014 (has links)
Understanding Earth’s accretion and primary differentiation is a long-standing goal of geology. The segregation of FeNi metal from molten silicate to form Earth’s core is expected to deplete and fractionate the highly siderophile elements (HSEs). Estimates of the primitive upper mantle (PUM) composition however, reveal only modest HSE depletions and chondritic element ratios. Past experiments to determine if the mantle composition is set by high-temperature metal-silicate equilibrium have involved measuring the solubility of HSEs in silicate melt at conditions more reducing than the iron-wustite (IW) buffer. Accurate determination of solubilities at such conditions has been hindered by the formation of dispersed metal inclusions; this work describes methods to circumvent the problem. Results of three separate studies are presented which document the solubility of Re, Pt and Au in molten silicate which is demonstrably nugget-free. Data obtained from experiments done at 0.1 MPa–2 GPa, 1573–2573 K and ~ IW -1.5 to +3 reveal: 1) Re, Pt and Au solubility increases with increasing temperature, 2) Re solubility increases with increasing oxygen fugacity (fO2), consistent with dissolution as oxide species, 3) Below ~ IW +3, Pt and Au solubility increases with decreasing fO2, consistent with dissolution as neutral or silicide species, and 4) that Au is amongst the most soluble HSE in molten silicate, with values increasing with temperature, but insensitive to changes in P, fO2 and melt composition, making it well suited as a geothermometer for core formation. Partition coefficients calculated from these and previous solubility measurements indicate that metal-silicate equilibrium is unable to reproduce the Re/Os and Pt/Os ratios required by PUM Os isotope systematics if simultaneously accounting for the observed absolute element abundances. Instead, results support late accretion of material following core formation, elevating element abundances and endowing chondritic inter-element ratios. Experimental results are incorporated into a terrestrial accretion model, which differs from the standard approach by explicitly accounting for the distribution of oxygen. Model results show siderophile element abundances in PUM are best reproduced if the mantle undergoes oxidation during accretion and metal-silicate equilibrium occurs near the peridotite solidus.
194

Ter Blend Of Poly (ethylene Terephthalate), Polypropylene And Low Density Polyethylene

Dogan, Erkan 01 January 2003 (has links) (PDF)
This study covers the recycling of waste poly(ethylene terephthalate) (PET) bottles through melt blending with low density polyethylene (LDPE) and polypropylene (PP). In general, polymer blends are known to be immiscible and incompatible with poor mechanical properties. This problem is due to the low intermolecular forces between the components of the immiscible blends. In order to enhance the interaction and compatibility between these matrices, some reactive or non-reactive copolymers were used. In this work / PET was treated with silane coupling agent (SCA) (low molecular weight reactive additive) for compatilization of LDPE-PP-PET blends. LDPE-PP-PET blends were prepared in different compositions (by weight) with and without silane coupling agent at high temperatures by a single screw extrusion and injection molding. Mechanical properties of treated and non-treated blends were studied in terms of tensile strength, strain at break and impact strength. Melt flow properties of blends were investigated by melt flow index. The impact fractured surfaces and thermal behaviour of the blends were examined with Scanning Electron Microscope (SEM) and Differential Scanning Calorimeter (DSC), respectively. Through out the studies, good adhesion between PET and LDPE-PP matrix was successfully achieved by the surface treatment of PET particles. The adhesion was also observed in SEM studies. Also the variation in mechanical properties was found to be highly dependent on the number of extrusion.
195

Chaotic pattern dynamics on sun-melted snow

Mitchell, Kevin A. 11 1900 (has links)
This thesis describes the comparison of time-lapse field observations of suncups on alpine snow with numerical simulations. The simulations consist of solutions to a nonlinear partial differential equation which exhibits spontaneous pattern formation from a low amplitude, random initial surface. Both the field observations and the numerical solutions are found to saturate at a characteristic height and fluctuate chaotically with time. The timescale of these fluctuations is found to be instrumental in determining the full set of parameters for the numerical model such that it mimics the nonlinear dynamics of suncups. These parameters in turn are related to the change in albedo of the snow surface caused by the presence of suncups. This suggests the more general importance of dynamical behaviour in gaining an understanding of pattern formation phenomena.
196

A new perspective on melt inclusions: development of novel in-situ analytical protocols

Paul, Bence Timothy Unknown Date (has links) (PDF)
Novel techniques for in-situ lead isotope analysis of melt inclusions using multicollector inductively coupled plasma mass spectrometry, and parallel Faraday cup and ion counter detection have been developed. These provide for measurement of the critical 204Pb isotope, which has been unavailable in melt inclusion Pb isotope studies, but requires on-line determination of 200Hg to correct for 204Hg isobaric interferences. External standardisation allows for effective mass fractionation correction and ion counter gain calibration. An off-line Tau correction was applied and standard glass analyses suggest that this correction provides more accurate and precise results.
197

Thermal homogeneity and energy efficiency in single screw extrusion of polymers : the use of in-process metrology to quantify the effects of process conditions, polymer rheology, screw geometry and extruder scale on melt temperature and specific energy consumption

Vera-Sorroche, Javier January 2014 (has links)
Polymer extrusion is an energy intensive process whereby the simultaneous action of viscous shear and thermal conduction are used to convert solid polymer to a melt which can be formed into a shape. To optimise efficiency, a homogeneous melt is required with minimum consumption of process energy. In this work, in-process monitoring techniques have been used to characterise the thermal dynamics of the single screw extrusion process with real-time quantification of energy consumption. Thermocouple grid sensors were used to measure radial melt temperatures across the melt flow at the entrance to the extruder die. Moreover, an infrared sensor flush mounted at the end of the extruder barrel was used to measure non-invasive melt temperature profiles across the width of the screw channel in the metering section of the extruder screw. Both techniques were found to provide useful information concerning the thermal dynamics of the extrusion process; in particular this application of infrared thermometry could prove useful for industrial extrusion process monitoring applications. Extruder screw geometry and extrusion variables should ideally be tailored to suit the properties of individual polymers but in practise this is rarely achieved due the lack of understanding. Here, LDPE, LLDPE, three grades of HDPE, PS, PP and PET were extruded using three geometries of extruder screws at several set temperatures and screw rotation speeds. Extrusion data showed that polymer rheology had a significant effect on the thermal efficiency on the extrusion process. In particular, melt viscosity was found to have a significant effect on specific energy consumption and thermal homogeneity of the melt. Extruder screw geometry, set extrusion temperature and screw rotation speed were also found to have a direct effect on energy consumption and melt consistency. Single flighted extruder screws exhibited poorer temperature homogeneity and larger fluctuations than a barrier flighted screw with a spiral mixer. These results highlighted the importance of careful selection of processing conditions and extruder screw geometry on melt homogeneity and process efficiency. Extruder scale was found to have a significant influence on thermal characteristics due to changes in surface area of the screw, barrel and heaters which consequently affect the effectiveness of the melting process and extrusion process energy demand. In this thesis, the thermal and energy characteristics of two single screw extruders were compared to examine the effect of extruder scale and processing conditions on measured melt temperature and energy consumption. Extrusion thermal dynamics were shown to be highly dependent upon extruder scale whilst specific energy consumption compared more favourably, enabling prediction of a process window from lab to industrial scale within which energy efficiency can be optimised. Overall, this detailed experimental study has helped to improve understanding of the single screw extrusion process, in terms of thermal stability and energy consumption. It is hoped that the findings will allow those working in this field to make more informed decisions regarding set conditions, screw geometry and extruder scale, in order to improve the efficiency of the extrusion process.
198

A Raman spectroscopic study of solid dispersions and co-crystals during the pharmaceutical hot melt extrusion process

Banedar, Parineeta Namdeo January 2015 (has links)
Process Analytical Technology (PAT) is framed with the objective of the design and development of processes to ensure predefined quality of the product at the end of manufacturing. PAT implementation includes better understanding of process, reduction in production time with use of in-line, at-line and on-line measurements, yield improvement and energy and cost reductions. Hot Melt Extrusion process (HME) used in the present work is proving increasingly popular in industry for its continuous and green processing which is beneficial over traditional batch processing. The present work was focused on applications of Raman spectroscopy as off - line and in - line monitoring techniques as a PAT for production of pharmaceutical solid dispersions and co-crystals. Solid dispersions (SDs) of the anti-convulsant Carbamazepine (CBZ) with two pharmaceutical grade polymers have been produced using HME at a range of drug loadings and their amorphous nature confirmed using a variety of analytical techniques. Off-line and in-line Raman spectroscopy has been shown to be suitable techniques for proving preparation of these SDs. Through calibration curves generated from chemometric analysis in-line Raman spectroscopy was shown to be more accurate than off-line measurements proving the quantification ability of Raman spectroscopy as well as a PAT tool. Pure co-crystals of Ibuprofen-Nicotinamide and Carbamazepine-Nicotinamide have been produced using solvent evaporation and microwave radiation techniques. Raman spectroscopy proved its superiority over off-line analytical techniques such as DSC, FTIR and XRD for co-crystal purity determination adding to its key advantage in its ability to be used as an in-line, non-destructive technique.
199

Analyse de la fonte glaciaire et nivale dans les Andes tropicales à partir d’un bilan d’énergie : Glacier de l’Antisana, Equateur (0°28’S) / Analysis of the melting from ice and snow in the tropical Andes using the energy balance approach : Glacier Antisana, Ecuador (0 ° 28'S).

Maisincho Guagrilla, Luis 09 November 2015 (has links)
Ce travail a permis de modéliser le bilan de masse superficiel sur le bassin versant du Glacier 15 du massif Antisana (0.28 km2; 0°28'S, 78°09'W), dans les Andes tropical de l'Equateur. Le bilan de masse superficiel (MBS) entre 2000 et 2008 sur le glacier 15a de l'Antisana a été modélisé en utilisant deux approches parallèles : un modèle empirique de type degré-jour et un modèle physique de type bilan d'énergie.Dans un premier temps, la fonte a été calculée à l'aide de la température moyenne et des cumuls de précipitations alors que le calcul de la sublimation a été réalisé grâce à la vitesse du vent. Ce modèle a été appliqué au pas de temps journalier et a été calé à 4900 m d'altitude entre mars 2002 et août 2003 et validé entre janvier et novembre 2005. Un lien significatif entre la température et la fonte apparaît lorsqu'une distinction entre neige et glace est effectuée. La relation entre la fusion et la température est expliquée essentiellement par le lien significatif existant entre le bilan radiatif de courtes longueurs d'onde et la température, car le rayonnement solaire est aussi le principal moteur de la fonte. Néanmoins, cette relation disparaît dès lors que le vent devient intense. Ce point a cependant peu de conséquences sur les calculs effectués, car les périodes ventées sont marquées par des températures faibles. Le modèle a été appliqué pour évaluer dans quelle mesure cette approche est appropriée pour modéliser le bilan de masse superficiel, l'ablation, et les altitudes de la ligne de neige et de la ligne d'équilibre. Les résultats montrent qu'un modèle empirique de type degré-jour permet une modélisation précise du MBS à l'échelle d'un glacier en Equateur. Néanmoins, ce modèle ne devrait pas être appliqué à d'autres régions tropicales, en particulier là où la sublimation est importante (grâce à une saison sèche prononcée) ou lorsque les glaciers sont situés au-dessus de l'altitude moyenne de l'isotherme 0°C.Dans un deuxième temps, un modèle de bilan d'énergie superficiel (BES) distribué développé initialement pour des applications en Terre d'Adélie (Antarctique) a été appliqué sur le site du glacier 15a de l'Antisana pour quantifier l'ablation de la glace et de la neige. Ce modèle a été adapté pour les conditions tropicales puis forcé à l'aide des mesures météorologiques obtenues à proximité et sur glacier 15a. Le modèle a tout d'abord été appliqué à une altitude de référence à 4900 m pour une pente de 28° et avec un azimut NO (45°). La spatialisation du bilan d'énergie a ensuite été effectuée en discrétisant le glacier par tranches de 50 m d'altitude, puis en calculant la pente et l'azimut moyen de chaque tranche à l'aide de un modèle numérique de terrain (MNT) précis du glacier. Les données d'entrées ont été distribuées sur la langue du glacier 15a en supposant que les forçages météorologiques varient selon des gradients verticaux constants. Ces gradients ont été établis à partir de mesures de terrain. Le modèle a été calé à partir des données de bilan de masse mensuel et d'albédo journalier mesurées sur le glacier 15a entre mars 2002 et août 2003, puis validé à partir de mesures obtenues entre janvier 2005 et décembre 2008. Le modèle reproduit précisément les variations spatiales et temporelles du bilan de masse entre 4850 m et 5700 m d'altitude. Les résultats inédits de bilan d'énergie de surface distribués sur le glacier 15a ont ainsi permis d'analyser les processus physiques à l'origine des variations spatio-temporelles de l'ablation. Enfin, cette étude explique pour la première fois pourquoi les modèles de type degré-jour donnent systématiquement des résultats de bonne qualité dans cette région, venant contredire les résultats d'études antérieures. Cette thèse constitue ainsi une étape importante dans la compréhension de la sensibilité des bilans de masse aux variations de température dans cette région. / Antisana Glacier 15 basin surface mass balance (SMB) (0.28 km2;0°28'S,78° 09'W, 5750 m), located in the tropical Andes of Ecuador, between 2000 and 2008 has been modeled using two models: an empirical positive degree-day (PDD) and other physical surface energy balance approach..As a first stage, melting was calculated using daily temperature and the cumulative precipitation while sublimation was computed as wind-speed function. The PDD was applied at daily-time step and calibrated at 4900 m a.s.l. The period time to calibrate was March 2002 - August 2003 and validated was January - November 2005. A significant link between melting rates and temperature was revealed when model discriminates snow and ice surface. This relationship is explained by the link between the short-wave radiation and air temperature. However, this relationship disappears under intense wind-speed events, however this events show low air temperature, therefore they are not affect the final results. The PDD model was applied for modeling SMB, ablation, snow-line position and equilibrium line altitude. The results show this model type fits to SMB measures over Antisana glacier. However, it should not apply to other tropical regions, particularly where there are high sublimation rates (pronounced dry seasons) or where glaciers are located under the isotherm 0 ° C.A second stage, a distributed surface energy balance (DBES) model over glacier 15a of the Antisana was applied to quantify ice and snow ablation. For this task was used a model adapted to tropical conditions from Adélie Land-Antarctica BES model. Initially, the model was applied at 4900 m.a.s.l. , with a slope of 28º and NW (45 °) azimuth. For computing DBES, the glacier was divided in 18 altitude strips ( 50m/level). The model generated slops and azimuths from a digital elevation model (DEM). The meteorological vertical gradients were measured in the study zone. This values was used into de model as constants during both periods calibration and validation. The DBES model reproduced the spatial variation and temporal of SMB between 4850 m.a.s.l. and 5700 m.a.s.l.. The unpublished results of SEB distributed on the glacier 15a allowed to analyze the physical processes that to generate the spatio-temporal variation of the ablation.The DBES results show that the model applied in a former research was based on wrong assumptions and inaccurate. The results of DBES and PDD models show that the accumulated precipitation measured at the bottom of the glacier are greatly underestimated. It implies the need for new protocols for improving the precipitation measurement. Both the former research and SEB confirm the crucial role of shortwave radiation and albedo values over glacier melt. It puts also in evidence that snow metamorphism in the study zone occurs faster than other latitudes, associated with accelerated degradation of surface albedo. Finally, this research explains the reason why the PDD model provides good quality results in this region, which contradicted the results of previous study. This research contributes a better understanding about sensibility of SMB with temperature variations in the inner tropics.
200

Characterization of a refractory cement and sensor development for temperature measurements in molten steel

Sandin, Pierre January 2018 (has links)
In steel manufacturing, temperature control is a critical parameter,as it is extremely important for the steel quality. In general,disposable sensors are regularly immersed in the melt for temperaturemeasurements. There are commercially available sensors for continuoustemperature measurements. In this study, a refractory cement is used for encapsulation andcarrier of a resistive temperature detector, for continuoustemperature measurements in molten steel. This cement is normallyused for manufacturing of steel melt crucibles. The work in thisstudy is mostly experimental and consist of characterization of thecement and development of the sensor. The characterization includesthe mechanical properties, the thermal shock resistance, the steelmelt resistance and obtainable surface roughness, for differentpowder fractions, water-to-cement ratio, firings and mixing method.Process developments were also done for the manufacturing of thesensor element and its carrier system. The end goal for continuous temperature measurement in molten steelfor more than 60 minutes was not reached. However, functional sensorswere developed where temperatures up to 1000 °C were measured duringcalibrations, and the cement was well characterized. This work has been carried out within the Strategic innovationprogram "Smartare Elektroniksystem", a joint investment of Vinnova,Formas and Energimyndigheten.

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