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Studium slinování nanočásticových keramických materiálů / Study of Sintering of Nanoceramic MaterialsDobšák, Petr January 2010 (has links)
The topic of the Ph.D. thesis was focused on the process of sintering alumina and zirconia ceramic materials with the aim to compare kinetics of sintering sub-micro and nanoparticle systems. Zirconia ceramic powders stabilized by different amount of yttria addition in the concentration range of 0 – 8 mol% were used. The different crystal structure (secured by yttria stabilization) of zirconia, as found, did not play statistically proven role in the process of zirconia sintering. The possible influence was covered by other major factors as particle size and green body structure, which does affect sintering in general. According to the Herrings law, the formula predicting sintering temperature of materials with different particle size was defined. The predicted sintering temperatures were in good correlation with the experimental data for zirconia ceramic materials prepared from both, coarser submicrometer, and also nanometer powders. In case of alumina ceramics the predicted and experimentally observed sintering temperature values did not match very well. Mainly the nanoparticle alumina materials real sintering temperature values were markedly higher than predicted. The reason was, as shown in the work, strong agglomeration of the powders and strong irregularities of particle shape. The major role of green body microstructure in the sintering process was confirmed. The final density of ceramic materials was growing in spite of sintering temperature, which was decreasing together with pore - particle size ratio (materials with similar particle size were compared). Sintering temperature was increasing together with growing size of pores trapped in the green body structure. Clear message received from the above mentioned results was the importance of elimination of stable pores with high coordination number out off the green body microstructure during shaping ceramic green parts. Same sintering kinetics model was successfully applied on the sintering process of submicro- and also nanometer zirconia ceramics. Activation energy of nanometer zirconia was notably lower in comparison to submicrometer material. For the sintering of nanoparticle zirconia was typical so called “zero stage” of sintering, clearly visible on kinetic curves. It was found out, that processes running in zirconia “green” material during zero stage of sintering are heat activated and their activation energy was determined. Pores of submicrometer zirconia were growing in an open porosity stage of sintering just a slightly (1.3 times) compared to the nanoparticle zirconia, where the growth was much higher (5.5 times of the initial pore diameter). This difference was most probably caused by preferential sintering of agglomerates within the green bodies and by particle rearrangement processes which appears in the zero stage of sintering of nanoparticular ceramics. The technology of preparation of bulk dense ytria stabilized zirconia nanomaterial with high relative density of 99.6 % t.d. and average grain size 65nm was developed within the thesis research.
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Polymer Matrix Composite: Thermally Conductive GreasesPreparation and CharacterizationAdhikari, Amit 29 August 2019 (has links)
No description available.
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Nové nanoprvky pro elektroniku – příprava a charakterizace / New nanodevices for electronics - fabrication and characterizationMárik, Marian January 2021 (has links)
Táto práca sa zaoberá technikou výroby samousporiadaných nanoštruktúr pre elektrické aplikácie. Prototypy boli pripravené anodickou oxidáciou v dvoch dĺžkach a tromi rôznymi tepelnými úpravami. Štrukturálna charakterizácia bola spravená pomocou techniky SEM, TEM a EDX a vyhodnotenie nielen z štrukturálneho, ale aj z materiálového hľadiska. Jedinečná koreňová štruktúra samousporiadaných nanotyčiniek bola vyhodnotená a porovnaná po troch rôznych tepelných úpravách: po anodizácii, po vákuovom žíhaní, a po žíhaní vo vzduchu. Všetky prototypy obsahujú nanotyčinky s amorfnou štruktúrou, ale našli sa však aj nanokryštály pod koreňovými štruktúrami. Elektrická charakterizácia prototypov ukázala: odporové spínacie správanie (RS), diódové charakteristiky a charakteristiku podobnú pre diódy s kapacitorom. Aktívny povrch pre spínací mechanizmus je v hornej časti nanoštruktúr na rozhraní nanotyčiniek a zlatej elektródy. Výška Schottkyho bariéry na rozhraní Ti / TiO2 bola vypočítaná dvoma spôsobmi a pre všetky tri zariadenia bola nižšia ako 1,11 eV.
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Design and Testing of a Top Mask Projection Ceramic Stereolithography System for Ceramic Part ManufacturingDe Caussin, Dylan Robert 01 June 2016 (has links) (PDF)
Ceramic manufacturing is an expensive process with long lead times between
the initial design and final manufactured part. This limits the use of ceramic as a viable material unless there is a large project budget or high production volume associated with the part. Ceramic stereolithography is an alternative to producing low cost parts through the mixing of a photo curable resin and ceramic particles. This is an additive manufacturing process in which each layer is built upon the previous to produce a green body that can be sintered for a fully dense ceramic part.
This thesis introduces a new approach to ceramic stereolithography with a top mask projection light source which is much more economical compared to current vector scanning methods. The research goes through the design and development of a stereolithography printer prototype capable of handling ceramics and the testing of different mixtures to provide the best printing results with varying viscosities. The initial testing of this printer has created a starting point for top mask projection as an economical alternative to current ceramic manufacturing techniques.
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Sodium Solid Electrolytes: NaxAlOy Bilayer-System Based on Macroporous Bulk Material and Dense Thin-FilmHoppe, Antonia, Dirksen, Cornelius, Skadell, Karl, Stelter, Michael, Schulz, Matthias, Carstens, Simon, Enke, Dirk, Koppka, Sharon 05 May 2023 (has links)
A new preparation concept of a partially porous solid-state bilayer electrolyte (BE) for high-temperature sodium-ion batteries has been developed. The porous layer provides mechanical strength and is infiltrated with liquid and highly conductive NaAlCl4 salt, while the dense layer prevents short circuits. Both layers consist, at least partially, of Na-β-alumina. The BEs are synthesized by a three-step procedure, including a sol-gel synthesis, the preparation of porous, calcined bulk material, and spin coating to deposit a dense layer. A detailed study is carried out to investigate the effect of polyethylene oxide (PEO) concentration on pore size and crystallization of the bulk material. The microstructure and crystallographic composition are verified for all steps via mercury intrusion, X-ray diffraction, and scanning electron microscopy. The porous bulk material exhibits an unprecedented open porosity for a NaxAlOy bilayer-system of ≤57% with a pore size of ≈200–300 nm and pore volume of ≤0.3 cm3∙g−1. It contains high shares of crystalline α-Al2O3 and Na-β-alumina. The BEs are characterized by impedance spectroscopy, which proved an increase of ionic conductivity with increasing porosity and increasing Na-β-alumina phase content in the bulk material. Ion conductivity of up to 0.10 S∙cm−1 at 300 °C is achieved.
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Nano-Characterization of Ceramic-Metallic Interpenetrating Phase Composite Material using Electron CrystallographyMoro, Marjan 11 July 2012 (has links)
No description available.
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Mesoporous Inorganic Membranes for Water PurificationSchillo, Melissa C. 12 September 2011 (has links)
No description available.
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Gas-Phase Epoxidation of Ethylene and PropyleneGaudet, Jason 07 December 2010 (has links)
Catalysts consisting of silver on α-Al₂O₃, α-SiC, and β-SiC supports were synthesized and tested for catalytic performance in the gas-phase direct oxidation of ethylene to ethylene oxide. For this study, which used no promoters, ethylene oxidation selectivity of SiC-supported catalysts ranged from 10 to 60% and conversion from 0-4.5%. Silicon carbide supported catalysts exhibited poor performance except for a surface-modified β-SiC-supported catalyst, which demonstrated conversion and selectivity similar to that of an α-Al₂O₃-supported catalyst. This Ag/β-SiC catalyst was further investigated with a kinetic study, and the reaction orders were found to be 0.18 with respect to ethylene and 0.34 with respect to oxygen. The kinetic results were consistent with Langmuir-Hinshelwood rate expressions developed from single-site and dual-site reaction mechanisms.
Gold nanoparticles on titanium oxide and titania-silica supports are active for the formation of propylene oxide by the oxidation of propylene with hydrogen and oxygen mixtures. This study investigates the effect of cyanide treatment on gold supported on titanosilicate zeolite supports (Au/TS-1). Catalysts treated with weak solutions of sodium cyanide resulted in preferential removal of small gold particles, while catalysts treated with strong solutions resulted in dissolution of the gold and re-precipitation as gold (+1) cyanide. X-ray absorption spectroscopy demonstrated that catalysts which produce propylene oxide in the presence of hydrogen and oxygen mixtures had supported gold (+3) oxide nanoparticles of 3 nm size after synthesis, which were reduced to gold metal at reaction conditions. Samples treated with strong solutions of sodium cyanide resulted in supported gold (+1) cyanide particles of large size, 9-11 nm. These particles did not produce propylene oxide but, surprisingly, showed high selectivity toward propylene hydrogenation. Increasing gold (+1) cyanide particle size resulted in a decrease in hydrogenation activity.
TS-1 and Au/TS-1 surfaces were studied with laser Raman spectroscopy. Surface fluorescence was substantially reduced with a low-temperature ozone treatment, allowing observation of titanosilicate framework bands. Hydrocarbon vibrations are observed for TS-1 and Au/TS-1 under propylene. Density functional theory models indicated that propylene adsorbed to a metal site along the Ï bond would show a Raman spectrum very similar to gas-phase propylene except for out-of-plane C-H vibrations, which would be moved to higher energy. This adsorption spectrum, with out-of-plane vibrations shifted to higher energy, was observed for both TS-1 and Au/TS-1. Langmuir adsorption isotherms were generated for both TS-1 and Au/TS-1, and a scaling factor derived from propylene uptake experiments allowed these isotherms to be scaled to propylene coverage of titanium. / Ph. D.
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Development and Evaluation of Transparent, Aligned Polycrystalline Alumina as an Infrared Window Candidate for Hypersonic FlightAshwin Sivakumar (18437757) 28 April 2024 (has links)
<p dir="ltr">Hypersonic flight is the key to unlocking a nation’s strategic advantage in this century’s military theater. Military powerhouses such as the United States, Russia, India, China, Australia, and the EU publicly possess hypersonic weapons capabilities. Such technology enables intercontinental travel orders of magnitude faster than conventional flights. A trip halfway across the world would take not twenty hours, but two. However, the level of thermal and chemical load the aircraft and these electronic equipment experience while at such high speeds cause them to fail. Thus, ceramic window materials are used to act as a barrier between the hypersonic flight environment and this sensitive electronic equipment. Such materials need to be both mechanically robust, but transparent within the relevant infrared ranges used for target detection. Single-crystal sapphire (alumina) is an infrared window material readily available, plentiful, and easy to microstructurally control and manufacture, but not optimal. Its transparency range is limited to the optical and near-infrared, while it exhibits poor mechanical and dielectric strength. Polycrystalline alumina (PCA) has recently been shown to possess more favorable infrared window characteristics as opposed to its single-crystal counterpart. This is achieved by processing using a platelet powder morphology in a single processing step – hot-pressing. Full densification (> 99.5%) of PCA samples was achieved, demonstrating maximum of 84% optical transparency, but accompanied by grain growth (60+µm), resulting in lower mechanical strength. This research thus works on a two-fold approach to minimizing the grain growth of PCA. Optical tests demonstrated favorable results for lowering isothermal temperatures to reduce grain growth. Weibull values of m = 28.8 and m = 9.7 from 4 point-flexure tests were obtained (ASTM 1161a). Thermal loading via ablation testing compared PCA samples to industry alternatives (single-crystal sapphire) and (equiaxed alumina). Ablation tests revealed the benefit of polycrystalline alumina over sapphire. The benefit of lower isothermal sintering temperatures for reduced grain growth resulted in higher peak load before failure, resulting in greater characteristic strength and minimal transmission lost during a minute of oxyacetylene heat flux exposure. Finally, additional work was done on nanoceramic MgO-Y<sub>2</sub>O<sub>3</sub>, in a ceramic-processing method like that of PCA. These findings will also be discussed.</p>
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Desenvolvimento de membrana nas cerâmicas tubulares obtidas a partir de um resíduo da produção de alumina. / Development of membrane in tubular ceramics obtained from a residue of alumina production. / Développement d'une membrane en céramique tubulaire obtenue à partir d'un résidu de production d'alumine. / Desarrollo de membrana en las cerámicas tubulares obtenidas a partir de un residuo de la producción de alúmina. / 由氧化铝生产残渣获得的管状陶瓷膜的开发。GUIMARÃES, Iliana de Oliveira. 06 April 2018 (has links)
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Previous issue date: 2014-08-29 / Capes / O processo Bayer, utilizado para a obtenção de alumina, usa bauxita como matériaprima.
Este processo abrange quatro estágios: digestão, clarificação, precipitação e
calcinação. O resíduo gerado na etapa de calcinação é um produto com pequeno
tamanho de partícula, conhecido como ESP dust. Esta pesquisa teve como objetivo
desenvolver membranas cerâmicas tubulares utilizando em sua composição o ESP
dust, um pó de alumina do precipitador eletrostático, e uma argila bentonítica.
Inicialmente, foi realizada a caracterização dos precursores. Foram analisadas duas
amostras do resíduo, uma do resíduo bruto e outra do resíduo calcinado a 1200°C.
Essas amostras apresentaram um alto teor de alumina nas suas composições
químicas. As fases gibbsita e α-alumina foram identificadas no resíduo bruto e, após
sua calcinação, a gibbsita foi totalmente transformada em α-alumina. Observou-se
que não houve alterações significativas no tamanho e morfologia das partículas após
a calcinação, mas durante este processo, as partículas tornaram-se porosas,
provavelmente devido às mudanças de fase cristalina da alumina e a saída de água
dos cristais. Dentre vinte formulações diferentes testadas para produzir membranas
cerâmicas, quatro composições apresentaram os melhores resultados com relação
ao processamento por extrusão: duas composições com o resíduo bruto e duas com
o resíduo calcinado. Neste trabalho, as membranas tubulares compostas pelo
resíduo de alumina e pela argila bentonítica foram produzidas por extrusão e foram
sinterizadas a 900, 1000 e 1100°C. Foi observado que as membranas produzidas
apresentaram superfícies com poros distribuídos. A porosidade aparente variou
entre 47,70% (composição com 60% de resíduo calcinado e 40% de argila
bentonítica sinterizada a 1000°C) e 58,40% (composição com 70% de resíduo bruto
e 30% de argila bentonítica sinterizada a 1000°C). Foram realizados ensaios de
fluxo tangencial com água deionizada em pressões de 1,0; 1,5 e 2,0 Bar. O maior
fluxo permeado (909,24L/h.m2) foi observado para as membranas feitas da
composição contendo 70% de resíduo bruto e 30% de argila bentonítica sinterizadas
a 1100°C, aplicando pressão de 1 Bar. / The Bayer process uses bauxite as raw material to obtain alumina. This process
includes four stages: digestion, clarification, precipitation and calcination. The waste
generated during the calcination step is a product with small particle size, known as
ESP dust. This research aimed to develop tubular ceramic membranes using in its
composition the ESP dust, an alumina powder from electrostatic precipitator, and a
bentonite clay. Initially, the characterization of the precursors was performed. Two
samples were studied, one from crude residue and other from calcined residue at
1200°C. These samples showed a high content of alumina in chemical compositions.
The gibbsite and α-alumina phases were identified in crude residue and after
calcination gibbsite was completely transformed into α-alumina. Were observed no
significant changes in particles size and morphology after calcination, but during this
process, the particles become porous, probable due changes in crystalline phase of
alumina and the water outlet of crystals. Among twenty different formulations tested
to produce ceramic membranes, four compositions showed better results with regard
to the extrusion processing: two compositions with crude residue and two with
calcined residue. In this paper, tubular membranes produced from alumina residue
and bentonite clay were sintered at 900, 1000 and 1100°C. It was observed that the
produced membranes had surfaces with distributed pores. The apparent porosity was
between 47.70% (composition with 60% of calcined residue and 40% of bentonite
clay sintered at 1000°C) and 58.40% (composition with 70% of crude residue and
30% of bentonite clay sintered at 1000°C). Tangential flow tests were performed with
deionized water at pressures of 1.0; 1.5 and 2.0 Bar. Higher permeate flow rate
(909,24L/h.m2) was observed for membranes made of a composition containing
crude residue (70%) and bentonite clay (30%) sintered at 1100°C, applying pressure
of 1 bar.
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