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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.
41

PTCR effect in La2CO3 doped BaTiO2 ceramic sensors

Puli, Venkata Sreenivas Unknown Date (has links)
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.
42

Construction and testing of compact low noise hydrophones with extended frequency response / Construction and testing of low-noise hydrophones

Bakas, Konstantinos 06 1900 (has links)
Approved for public release; distribution is unlimited / A simple low-noise hydrophone design with internal preamplifier is presented. This design is similar to published designs and is a variation of the design developed in the NPS thesis by Miguel Alvarado [2003], except that several improvement features are included. These include a simplification of the structure and its modes of vibration, a large reduction in package diameter and the effect its acoustic diffraction has on the sensitivity, and an extended upper frequency response of 42 kHz resulting from the simplified structure and reduced diameter. Furthermore, the modified geometry along with its orientation in the water should produce a very omni-directional response in the horizontal plane at the higher frequencies. Finally, an new feedback preamplifier design developed by Hofler and Alvarado was discovered to have some subtle but serious performance problems. These problems were resolved in this research and the resulting preamplifier performance was tested and documented herein. / Lieutenant, Hellenic Navy
43

An automated environment for applying rapid prototyping techniques to ceramic material manufacturing.

04 June 2008 (has links)
The past few years have delivered a great deal of development in the area of Layered Manufacturing. The challenge is to apply the existing technologies to existing and/or new manufacturing systems, thereby adding value to these systems. The advances in the field of Layered Manufacturing range from the process of slicing to the actual building process. The main achievements in the arena of slicing have been in the advances of Adaptive Slicing. By not using a uniform slice thickness, not only is the stair stepping effect minimized, but the build time is also shortened. Many advances have been made in terms of the actual materials used and the process of building, thereby expanding the range of uses for the technology as a whole. With the extension in the variety of materials available for use with the technology, new uses become more than mere possibility and actually become viable. The use of Layered Manufacturing in the case of the CSIR was not the focus of the original experiment, but was a method to test the results of their main experiments – namely, research into the properties of ceramic materials and their use in the realm of medicine. The research of the CSIR focuses on the use of ceramic materials for the purpose of bone implants, which is a problem area in medicine. The machine they built in order to test the properties of the new materials they invent, uses Layered Manufacturing as a building process. What the CSIR lacks are the backend systems to enable the building of more complex experimental parts, as they have no way of going from design to a full build. This research project focuses on proving that the technologies involved in Layered Manufacturing will add value to the CSIR’s research. By implementing a system that takes advantage of existing software, and by using custom software to make it applicable to the environment the CSIR is currently operating in, their research could be speeded up tremendously without putting too much strain on their budget. What has been achieved is a simple system which employs the use of available technologies and software packages, and which requires no changes to the hardware of the current process used, such as the Rapid Prototyping machine. / Ehlers, E.M., Prof.
44

Synthesis of fine ceramic powders and the making of ceramic matrix composite materials =: 精細陶瓷粉末之合成及以陶瓷為基質的複合材料之製造. / 精細陶瓷粉末之合成及以陶瓷為基質的複合材料之製造 / Synthesis of fine ceramic powders and the making of ceramic matrix composite materials =: Jing xi tao ci fen mo zhi he cheng ji yi tao ci wei ji zhi de fu he cai liao zhi zhi zao. / Jing xi tao ci fen mo zhi he cheng ji yi tao ci wei ji zhi de fu he cai liao zhi zhi zao

January 1999 (has links)
by Fung-luen Kwong. / Thesis submitted in: August 1998. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1999. / Includes bibliographical references (leaves 130-131). / Text in English; abstract also in Chinese. / by Fung-luen Kwong. / Acknowledgements --- p.i / Abstract --- p.ii / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Development of ceramic materials --- p.1 / Chapter 1.2 --- Alumina-Zirconia advanced ceramics --- p.2 / Chapter 1.3 --- About this thesis --- p.3 / Chapter 2 --- Related work and Motivation --- p.6 / Chapter 2.1 --- Introduction --- p.6 / Chapter 2.2 --- Powder synthesis --- p.7 / Chapter 2.2.1 --- Mechanical milling --- p.7 / Chapter 2.2.2 --- Sol-gel methods --- p.8 / Chapter 2.2.3 --- CVD methods --- p.12 / Chapter 2.2.4 --- Hydrothermal processing --- p.12 / Chapter 2.2.5 --- Wear of Zr02 milling media --- p.14 / Chapter 2.3 --- Powder fabrication --- p.14 / Chapter 2.3.1 --- Dry pressing --- p.14 / Chapter 2.3.2 --- Isostatic pressing --- p.19 / Chapter 2.3.3 --- Hot pressing --- p.23 / Chapter 2.4 --- Sintering mechanism --- p.26 / Chapter 2.4.1 --- Solid state sintering --- p.26 / Chapter 2.4.2 --- Liquid state sintering --- p.36 / Chapter 2.5 --- Toughening mechanism --- p.39 / Chapter 2.5.1 --- Stress-induced transformation toughening --- p.39 / Chapter 2.5.2 --- Microcrack toughening --- p.42 / Chapter 2.6 --- Motivation --- p.42 / Chapter 3 --- Experiments --- p.45 / Chapter 3.1 --- Methodology --- p.45 / Chapter 3.1.1 --- Procedures --- p.45 / Chapter 3.1.2 --- Verified parameters and potential difficulties --- p.53 / Chapter 3.2 --- Instrumentation --- p.56 / Chapter 3.2.1 --- Electronic balance --- p.56 / Chapter 3.2.2 --- Instron 4486 loading machine --- p.60 / Chapter 3.2.3 --- High temperature furnace --- p.63 / Chapter 3.2.4 --- Scanning electron microscope (SEM) --- p.65 / Chapter 3.2.5 --- Hardness tester --- p.67 / Chapter 3.2.6 --- X-ray powder diffraction --- p.69 / Chapter 4 --- Results ´ؤ The effects of conditions in fabrication --- p.71 / Chapter 4.1 --- Wet chemical reaction --- p.71 / Chapter 4.2 --- Pressure dependence analysis --- p.75 / Chapter 4.3 --- Sintering behavior --- p.80 / Chapter 4.3.1 --- Sintering temperature analysis --- p.80 / Chapter 4.3.2 --- Sintering duration analysis --- p.85 / Chapter 4.3.3 --- Program for counting pores --- p.94 / Chapter 5 --- Results ´ؤ The effects of Additives to Al203 - ZrO2 --- p.96 / Chapter 5.1 --- Introduction --- p.96 / Chapter 5.1.1 --- Effects of adding metal aluminum --- p.97 / Chapter 5.1.2 --- Effects of adding magnesium oxide --- p.103 / Chapter 6 --- Conclusions --- p.108 / Source code of the programs for counting pores --- p.111 / TIFF 6.0 --- p.124 / Bibliography --- p.131
45

Optimizing the performance of a glass-ceramic storage phosphor as an imaging plate for medical use

Vu, Manh 01 May 2011 (has links)
Europium-doped-fluorochlorozirconate glass ceramics, known as ZBLAN, were produced in a glove box which has a controlled environment of argon gas. For imaging applications BaCl2 is used instead of BaF2. Their properties after different thermal processing and different amounts of europium-doping were investigated. After annealing the ZBLAN glass, BaCl2 nanoparticles are precipitated in the glass matrix. These glass ceramic storage phosphors are strong candidates for replacing traditional x-ray screen film system and commercial storage phosphors such as Agfa MD-30. Differential scanning calorimetry (DSC) was used to determine the crystallization temperature of the hexagonal phase of BaCl2, and orthorhombic BaCl2 this in turn determines the subsequent annealing temperature. X-ray diffraction (XRD) and photoluminescence (PL) show that the hexagonal phase of BaCl2 was formed upon annealing at temperatures between 250 °C and 280 °C for 5 minutes. The orthorhombic phase of BaCl2, which has storage properties, was formed at higher annealing temperatures, at approximately 290 °C and above. Secondary ion mass spectroscopy (SIMS) was used to determine adsorbed/diffused oxygen content of the glass. The weight loss of fluorine and chlorine is 3-5 % and was determined using ion chromatography (IC). The concentration of other cations was determined using inductively coupled plasma spectroscopy (ICP). Transmission electron microscopy (TEM) was used to take high resolution pictures and verify the composition of BaCl2 nanoparticles. The relative concentration of Eu2+ to Eu3+ of heated EuCl3 and ZBLAN was studied using Mössbauer spectroscopy. The oxidation of Eu2+ to Eu3+ was also observed during the experiment. This study has reinforced the strong potential for application of glass-ceramic storage phosphors for medical imaging.
46

Phase stability and defect structure determination of polytitanate compunds in the BaO-TiO2 system

Javadpour, Jafar 01 1900 (has links) (PDF)
Ph.D. / Materials Science and Engineering / Polytitanates in the BaO- TiO2 system with Ba:Ti ratios ranging from 1:2 to 1:5 were prepared using a low temperature technique developed by Pechini. The samples were heated at 600 to 1300°C in oxygen. Room temperature Raman spectroscopy was used to investigate the phase relations in this system. Results of this study indicate the following: except for BaTi4O9, the powders of these compounds were amorphous when heated at 600°C for 4hrs; the compound BaTi2O5 is a low temperature stable phase; Ba6Ti17O40 forms only at temperatures above 1100°C; Ba4Ti13O30 does not form below 1000°C; the single phase BaTi4O9 structure was observed at 1200°C'; the Ba2Ti9O20 phase is obtained only after long heat treatment at 1200°; BaTi5O11 was stable up to 1200°C, at which it decomposes into Ba2Ti4O20 and TiO2. After determination of stability relationships in this system, the electrical conductivities of these compounds were examined as a function of temperature and oxygen partial pressure. For all the temperatures (850-1150°C) studied, the conductivities of these compounds increased with decreasing oxygen partial pressure resulting in n-type properties throughout the whole P[subscript O2] range (10[superscript -19 - 1atm). The P[subscript O2] dependencies of the electrical conductivity were found to be linear for an extensive range of oxygen partial pressures. On the basis of structural considerations the conductivity data was described by a majority defect model consisting of both singly and doubly ionized oxygen vacancies. For lower oxygen partial pressure values a drastic change in the electrical conductivity was observed. This is believed to result from increasing defect interaction for larger departures from stoichiometry. A defect model based on this interaction is proposed to account for the observed sharp change in the electrical conductivity values.
47

Examination of particle/particle interactions and their impact on rheology and mixedness of an alumina/titania system

August, Cari R., January 2009 (has links)
Thesis (Ph. D.)--Rutgers University, 2009. / "Graduate Program in Materials Science and Engineering." Includes bibliographical references (p. 244-249).
48

Reactive processing and mechanical properties of polymer derived silicon nitride matrix composites and their use in coating and joining ceramics and ceramic matrix composites /

Stackpoole, Margaret Mary. January 2002 (has links)
Thesis (Ph. D.)--University of Washington, 2002. / Vita. Includes bibliographical references (leaves 240-248).
49

Hilda Ditchburn : a teacher and pioneer of stoneware ceramics in Southern Africa.

Vurovecz, Candice. January 2008 (has links)
The candidate's investigation of Hilda Ditchburn (nee Rose) (1917 - 1986) attempts to historically place the subject as a teacher and pioneer of stoneware ceramics within the context of studio ceramics in South Africa in the second half of the 20th Century. Through an analysis, discussion and documentation of Ditchburn's life and works on a personal, technical and professional level, her discoveries and advances in studio ceramics in South Africa in the 1950's and 60's will be determined. In the light of Ditchburn's ceramic background, I shall discuss the ceramic pieces she made from the 1940's to late 1970's, focusing on selected stoneware pieces, and including examples of her earthenware and porcelain pieces. I shall discuss her experiments and discoveries with glaze chemistry and clay bodies as well as their different firing methods. I shall highlight her achievement in being the first studio potter in South Africa to design and build an oil fired kiln for high fired stoneware. This kiln was successfully fired in 1954, a time when stoneware was not being made in South Africa, thus predating any stoneware kiln made by a studio potter in the country and pioneering the growth of stoneware ceramics in South Africa. This dissertation is divided into four chapters, each with sub-headings pertaining to the information contained. The first and second chapters give background and foundational information for placing Hilda in context. The third and fourth chapters map out Hilda's personal, academic and professional information. This includes archival material and Hilda's works of art. / Thesis (M.A.)-University of KwaZulu-Natal, Pietermaritzburg, 2008.
50

Characterization of metal/ceramic interfaces on aluminum nitride

Papageorge, Marc Vasilios 12 1900 (has links)
No description available.

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