L’objectif de cette thèse est d’élaborer de nouveaux (super)isolants thermiques à partir de silices nanostructurées telles que les Silices Mésoporeuses Organisées et les phyllosilicates. Dans un premier temps, il s’agissait d’élaborer les matériaux en contrôlant les paramètres clé de synthèse, puis de les caractériser en évaluant notamment les propriétés thermiques. Les matériaux étudiés sont des micro- et nanoparticules de silice mésoporeuse d’une part, synthétisées avec des porosités intra- et interparticulaires contrôlées, et des phyllosilicates naturels et synthétiques d’autre part. Dans un deuxième temps, différents traitements post-synthèse ont été réalisés sur ces matériaux pour améliorer significativement leurs propriétés physico-chimiques –en particulier les propriétés d’isolation thermique– et leurs performances mécaniques. Par la suite, dans le cadre de l’étude des phyllosilicates modifiés, des composites peu denses phyllosilicates/polymères et phyllosilicates/tensioactifs intercalés et/ou exfoliés ont été élaborés afin d’améliorer les propriétés obtenues et de réaliser une mise en forme de ces matériaux. Les conductivités thermiques ont été déterminées sur l’ensemble des matériaux utilisés. / This thesis aims at developing new thermal (super)insulators from nanostructured silicas such as Organized Mesoporous Silicas and phyllosilicates. First, new materials were created controlling the key-parameters of the synthesis ; these materials were then finely characterized and especially their thermal properties. On one hand, studied materials are mesoporous silica micro- and nanoparticles synthesized with controlled intra- and interparticular porosities, and on the other hand natural and synthetic phyllosilicates. Then post-synthesis treatments were applied to enhance significantly thermal and mechanical performances of the products. In a further step, in the case of the treated phyllosilicates, low-density phyllosilicates/polymers composites and intercalated and/or delaminated phyllosilicates/surfactant composites were synthesized to improve the properties that were obtained and to process the materials. Thermal conductivity was determined for all the samples.

The positive temperature coefficient of resistivity (PTCR) sensors is resistor materials that undergo a sharp change in resistivity at a designed Curie temperature due to its unique structure and chemical composition. This effect serves important control functions in a wide variety of electronic circuitry and similar applications. Conventional calcining of mixed oxides method (CMO) is used for fabricating lanthanum doped barium titanate (BaTiO3) for PTCR behaviour through solid-state-sintering route, at 1100°C, 1350°C. Two batches of samples were fabricated at low and high sintering temperatures of 1100°C, 1350°C respectively. The effect of different concentrations of donor dopant on BaTiO3 on the electrical properties of Ba(1-x)LaxTiO3 with x= 0.0005, 0.001, 0.002, 0.0025, 0.003 mol%, is investigated at low sintering temperature. The influence of lantanum doping with Al2O3+SiO2+TiO2 (AST) as sintering aids on the electrical properties of Ba(1-x)LaxTiO3 with x= 0.0005, 0.001, 0.003 mol%, is also investigated. The results of the electrical characterization for the first batch of samples showed an increase in room temperature resistance with increaisng donor concentration. Also the results of the electrical characterization for the second batch of samples also showed the same increase in room temperature resistance with increasing donor concentration. For first batch of sensors the high room temperature resistance keeps the jump small and these materials showed V-shaped NTCR-PTCR multifunctional cryogenic sensor behavior with a strong negative coefficient of resistance effect at room temperature.Where as the second batch of sensors showed few orders of magnitude rise in resistivity values. The La-doped BaTiO3 ceramics co-doped with Mn gives an enhanced PTCR effect which can be exploited for various sensor applications.

Nanoporous materials for gas purification and thermal insulation have been studied and developed for application in many areas. It is known that a single adsorbent may not adequately control multiple contaminants. Further the utilization of nanoporous material as thermal insulator in building applications is limited due to high cost. Moreover, in view of the global environmental movement for clean air and reduction of heating energy consumption in built environment, the development of new and better nanoporous materials will not only facilitate major advances in gas adsorption and thermal insulation technology, but also meet the new challenges that cannot be met with the nanoporous materials that are currently available. This thesis presents a synthesis of new nanoporous silica based materials, and the characterization and application of these materials for molecular filtration and thermal insulation. Commercial nanoporous materials have been used for benchmarking for the pore properties, the applicability, and the performance of these new materials. First a double metal-silica adsorbent has been synthesized. The preparation procedure is based on the use of sodium silicate coagulated with various ratios of magnesium and calcium salts which yields micro-meso porous structures in the resulting material. The results show that molar ratios of Mg/Ca influence the pore parameters as well as the structure and morphology. The bimodal pore size can be tailored by controlling the Mg/Ca ratio. In the second synthesis, pure mesoporous silica, SNP has been prepared using glycerol as pore forming agent and monovalent salts as coagulant. This leads to material with large surface area and uniformed pore size centred at 43 or 47 nm.  The materials further exhibits a low bulk density in the range of 0.077 to 0.122 g/ml and possess a high porosity in the range of 95-97%. The influence of acid type (organic or inorganic) on the pore parameters and on the tapped density has also been investigated.   A synthesis method has also been developed for the preparation of carbon-silica composites. The method involves a number of routes, which can be summarised as addition of activated carbon particles to (I) the paste, (II) the salt solution, or (III) with the sodium silicate solution. In route II and III the activated carbon is present before coagulation. The routes presented here leads to carbon-silica composites possessing high micro porosity, meso porosity as well as large surface areas. The results further shows that pore size distribution may be tailored based on the route of addition of the carbon particles. Following route I and III a wide pore size (1-30 nm) was obtained whereas by route II a narrow pore size (1-4 nm) was observed.     MgCa-silica chemisorbents were also developed using either potassium hydroxide or potassium permanganate as impregnate chemicals. A direct or post-impregnation procedure was employed. The results revealed that the impregnate route and amount cause a reduction in both specific surface area and pore volume. Finally the thermal conductivity and dynamic adsorption of H2S, SO2 andtoluene were measured. Results show that at room temperature and atmospheric pressure, a thermal conductivity of 28.4 and 29.6 mW/m.K were obtained for the SNP mesoporous silicas. The dynamic adsorption behaviour of the chemisorbents and composites indicate their ability to absorbed H2S, SO2 andtoluene respectively. The highest H2S uptake corresponds to chemisorbents with 11.2-13.6 wt% KMnO4. The effect of impregnation route, amount of KMnO4 and its location in the pore system are likely the key factors in achieving a large H2S uptake. For SO2 adsorption, the highest uptake capacity was observed for MgCa-68/32-KOH. The results further suggest that the key to large SO2 uptake is as a result of the synergetic effect between large mesopore diameter and extensive mesopore volumes. Carbon-silica composites with carbon content 45 wt % exhibits high toluene adsorption with composite via route I having the highest toluene adsorption capacity (27.6 wt % relative to carbon content). The large uptake capacity of this composite was attributed to the presence of high microporosity volume and a wide (1-30 nm) bimodal pore system consisting of extensive mesopore channels (2-30 nm) as well as large surface area. These capacity values of carbon-silica composites are competitive to results obtained for commercial coconut based carbon (31 wt %), and better than commercial alumina-carbon composite (9.5 wt %). / <p>QC 20130408</p>

The effects of coating formulation on thermal characteristics of coating layers were systematically studied for xerographic toner fusion on coated papers. Model coatings were formulated using three types of ground calcium carbonate and one kaolin pigments, each mixed with 6, 10, 18, and 25 pph of styrene butadiene latex binder. Porosity was found to be a key parameter for coating thermal conductivity adjustment, and was determined by the latex concentration. The particle size distribution and morphology of pigments also affect the overall thermal characteristics of coating layers. Print qualities on model coated papers were evaluated by print gloss measurement, toner adhesion test, and pair-wise visual ranking, and it was proved that print gloss is reduced with increasing bulk thermal conductivity of coating layers. The coating layer consisted of Covercarb HP pigment and 10 pph of latex was found to have the best performance in the three print quality evaluation tests.

The effects of coating formulation on thermal characteristics of coating layers were systematically studied for xerographic toner fusion on coated papers. Model coatings were formulated using three types of ground calcium carbonate and one kaolin pigments, each mixed with 6, 10, 18, and 25 pph of styrene butadiene latex binder. Porosity was found to be a key parameter for coating thermal conductivity adjustment, and was determined by the latex concentration. The particle size distribution and morphology of pigments also affect the overall thermal characteristics of coating layers. Print qualities on model coated papers were evaluated by print gloss measurement, toner adhesion test, and pair-wise visual ranking, and it was proved that print gloss is reduced with increasing bulk thermal conductivity of coating layers. The coating layer consisted of Covercarb HP pigment and 10 pph of latex was found to have the best performance in the three print quality evaluation tests.

No description available.

The present work provides a micromechanics approach based on the generalized self-consistent composite cylinders method as a non-Eshelby approach towards for assessing the impact of carbon nanotubes on the multi-functional nature of nanocom-posites in which they are a constituent. Emphasis is placed on the effective elastic properties as well as electrical and thermal conductivities of nanocomposites con-sisting of randomly oriented single walled carbon nanotubes in epoxy. The effective elastic properties of aligned, as well as clustered and well-dispersed nanotubes in epoxy are discussed in the context of nanotube bundles using both the generalized self-consistent composite cylinders method as well as using computational microme-chanics techniques. In addition, interphase regions are introduced into the composite cylinders assemblages to account for the varying degrees of load transfer between nanotubes and the epoxy as a result of functionalization or lack thereof. Model pre-dictions for randomly oriented nanotubes both with and without interphase regions are compared to measured data from the literature with emphasis placed on assessing the bounds of the effective nanocomposite properties based on the uncertainty in the model input parameters. The generalized self-consistent composite cylinders model is also applied to model the electrical and thermal conductivity of carbon nanotube-epoxy nanocomposites. Recent experimental observations of the electrical conductivity of carbon nanotube polymer composites have identified extremely low percolation limits as well as a per-ceived double percolation behavior. Explanations for the extremely low percolation limit for the electrical conductivity of these nanocomposites have included both the creation of conductive networks of nanotubes within the matrix and quantum effects such as electron hopping or tunneling. Measurements of the thermal conductivity have also shown a strong dependence on nanoscale effects. However, in contrast, these nanoscale effects strongly limit the ability of the nanotubes to increase the thermal conductivity of the nanocomposite due to the formation of an interfacial thermal resistance layer between the nanotubes and the surrounding polymer. As such, emphasis is placed here on the incorporation of nanoscale effects, such as elec-tron hopping and interfacial thermal resistance, into the generalized self-consistent composite cylinder micromechanics model.

Nuclear fuel comes in many forms; oxide fuel is the most commonly used in current reactor systems while metal fuel is a promising fuel type for future reactors due to neutronic performance and increased thermal conductivity. As a key heat transfer parameter, thermal conductivity describes the heat transport properties of a material based upon the density, specific heat, and thermal diffusivity. A material’s ability to transport thermal energy through its structure is a measurable property known as thermal diffusivity; the units for thermal diffusivity are given in area per unit time (e.g., m2/s). Current measurement methods for thermal diffusivity include LASER (or light) Flash Analysis and the hot-wire method. This study examines an approach that combines these previous two methods to characterize the diffusivity of a packed bed of microspheres of depleted uranium (DU) metal, which have a nominal diameter of 250 micrometers. The new apparatus is designated as the Crucible Heater Test Assembly (CHTA), and it induces a radial transient across a packed sample of microspheres then monitors the temperature profile using an array of thermocouples located at different distances from the source of the thermal transient. From the thermocouple data and an accurate time log, the thermal diffusivity of the sample may be calculated. Results indicate that DU microspheres have very low thermal conductivity, relative to solid uranium metal, and rapidly form an oxidation layer. At 500°C, the thermal conductivity of the DU microspheres was 0.431 ± 13% W/m-K compared to approximately 32 W/m-K for solid uranium metal. Characterization of the developed apparatus revealed a method that may be useful for measuring the thermal diffusivity of powders and liquids.

This study provides a re-evaluation of the physical condition of, as well as past and current restoration and conservation work at Ahi Elvan Camii, &Ouml / rtmeli Mesjidi, Sabun&icirc / Mesjidi and Poyraji Mesjidi&amp / #8212 / i.e., one Friday mosque, or camii, and three mesjids, or small neighborhood mosques, located in Ulus, today the historic center of Ankara. All four structures, now registered as historic monuments, have survived intact, preserving most of their original architectural elements. Each structure also represents a different example of a building type which became prevalent in Ankara during the 14th can 15th centuries which have stone foundations, mud brick bearings walls with timber tie-beams, as well as timber ceilings supported by freestanding timber posts. These structures, registered and restored during different periods since the 1920s, were intervened upon in various ways and clad and/or plastered with differing materials (e.g., cement-based or clay-based materials). Although at times past conservation interventions and/or signs of decay may be clearly visible, the effects of these on each structure as a whole&amp / #8212 / whether positive or negative&amp / #8212 / may be more difficult to detect. A micro-climatic investigation program thus provided the primary, non-destructive diagnostic technique for this study. In addition to this, published as well as unpublished documents within the archives of Vakiflar Genel M&uuml / d&uuml / rl&uuml / g&uuml / , or the General-Directorate of Endowments in Ankara, provided visual as well as written information on the history of each structure. Their building materials, as well as past and present restoration and conservation work were also analyzed in situ. Based on long-term meteorological records for Ankara, data were collected at each structure for one year during January, April, July and October using Tiny tag&reg / Plus data loggers on interior and exterior temperatures and relative humidity, as well as surface temperatures at their timber ceilings for one week per season. In addition to this, the distribution of temperature and relative humidity at each structure was measured every m2 within the main prayer hall and women&amp / #8217 / s section, or kadinlar mahfeli at each structure per season, and surface temperature measurements taken of their timber ceilings and interior wall surfaces. Data collected were subsequently analyzed with respect to various relevant factors such as / the physical characteristics of their load-bearing walls and the buffer capacity of materials within these structures and their effects on indoor microclimatic conditions, the risk of surface condensation at the exterior wall surfaces and the timber ceilings of each structure, suggested parameters required for the conservation of their interior timber elements, and materials conservation vis &agrave / vis existing comfort conditions. Past measures taken in the restoration and conservation of the four structures and their present physical condition were thus re-evaluated, and recommendations provided for possible approaches to their sustainable conservation in the long-term.

The thermal conductivities of foamed polymer based materials are much lower thermal conductivity values than unfoamed polymeric materials. Especially, thermal conductivity values of foamed polymers with closed-cell structure decreases to 0.03 W/m.K. The reinforcement of foamed polymeric materials by mixing with bitumen lowers the raw material cost. The main objective of this study is to make a new thermal insulation material with low thermal conductance. In this study, the effects of concentration of calcium carbonate as inorganic filler and the effects of cross-linking on the properties foamed and unfoamed ethylene-vinyl acetate (EVA) copolymer based bituminous blends and composites were investigated. Applications such as thermal, mechanical characteristics of foamed and unfoamed EVA based bituminous composites were investigated. Foamed EVA based bituminous composites were prepared by using Brabender Plastic Coder, PLV 151. Mixing was made at 120 &ordm / C at 60 rpm for 15 minutes. The prepared blends were molded by a technique called Hand Lay-up Self-expanding Batch Molding (HLUSEBM) which was firstly applied by our group. The molding temperature was 170 &ordm / C at which chemical blowing agent and cross-linking agent decomposes. According to test results, at moderate chemical blowing agent and EVA content, the best closed-cell structure with high porosity and low thermal conductivity values were obtained. The compressive properties of foamed polymer based bituminous composites (FPBBCs) increase with increasing CBA and EVA content. With increasing calcium carbonate and EVA concentration, the porosity of FPBBCs increases but thermal conductivity of them decreases. On the other hand, with increasing filler content but with decreasing EVA concentration elastic modulus of FPBBCs increases but elastic recovery decreases.