Ceramic Materials Commons^™

Nanostructured Dielectric Materials For High Energy Density Multi Layer Ceramic Capacitors, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

A high energy density multilayer ceramic capacitor, having at least two electrode layers and at least one substantially dense polycrystalline dielectric layer positioned therebetween. The at polycrystalline dielectric layer has an average grain size of less than about 300 nanometers, a particle size distribution of between about 150 nanometers and about 3 micrometers, and a maximum porosity of about 1 percent. The dielectric layer is selected from the group including TiO₂, BaTiO₃, Al₂O₃, ZrO₂, lead zirconium titanate, and combinations thereof and has a breakdown strength of at least about 1100 …

Method For Producing Pressurelessly Sintered Zirconium Diboride/Silicon Carbide Composite Bodies, Shi C. Zhang, Greg Hilmas, William Fahrenholtz

Materials Science and Engineering Faculty Research & Creative Works

A method of sintering a ZrB₂-SiC composite body at ambient pressures, including blending a first predetermined amount of ZrB₂ powder with a second predetermined amount of SiC powder, wherein both powders are characterized by the presence of surface oxide impurities. Next the blended powders are mixed to yield a substantially homogeneous powder mixture and a portion of the substantially homogeneous powder mixture is formed into a green body. The body is fired to a first temperature, wherein substantially all surface oxide impurities are reduced and/or volatilized to substantially eliminate oxides from the green body, and the body …

Deposition, Characterization, And Fabrication Of A Zinc Oxide Piezoelectric Thin Film Microspeaker Using Dc Reactive Sputtering, Adam Olzick

Master's Theses

A piezoelectric microspeaker device that could be used in a variety of acoustic applications was designed and fabricated using a thin film ZnO layer that was reactively DC sputtered onto a single crystalline n-type silicon substrate. When tested the microspeaker did not produce sound due to complications in the etching process, the thickness of the diaphragms, and clamping effects. Instead, a characterization approach was taken and the structural, optical, electrical, and piezoelectric properties of the ZnO were investigated. Scanning electron microscopy, x-ray diffraction, and atomic force microscopy were utilized to discover the ZnO’s structural properties. Using the XRD and SEM, …

Fabricating Replacement Glass Prisms For The Piedras Blancas Lighthouse, Daniel Garcken

Materials Engineering

The objective of this project was to design and create a process for manufacturing replacement glass prisms for the Piedras Blancas lighthouse and several other lighthouses nationwide. The prisms were designed to be in multiple metal arrays spread across the floor of the beacon room (the topmost room of the lighthouses). The prisms functioned to transmit extra, radiant light from the beacon light through the floor of the beacon room and disperse it into the maintenance room below. Using computer aided drafting (CAD) software, an original prism was measured and modeled; the corresponding mold was also modeled. G-codes for controlling …

Glasses For Radiotherapy, Delbert E. Day

Materials Science and Engineering Faculty Research & Creative Works

No abstract provided.

Effective Dielectric Constant Of Two Phase Dielectric Systems, Vladimir Petrovsky, Piotr Jasinski, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

Various theoretical approaches are implemented for electrical characterization of two-phase material systems. Most of these approaches do not include possibility of percolation of the dispersed material. In this article brick wall model is extended on the systems exhibiting percolation. Transition from brick wall geometry to corresponding equivalent circuits provides final equations for effective dielectric constant. Comparison of theoretical results with experimental data shows that developed equations provide good fitting of effective dielectric constant to experimental values. Dielectric constants of both phases and percolation threshold calculated from the fitting match the corresponding experimental values of the phases.

Repairing Mixed-Conducting, Ceramic Electrolyte Films, Kevin Tolman, Izaak Williamson, Kokfoong Chan

College of Engineering Poster Presentations

Ceramatec, Inc. develops ceramic-electrolyte thin films for gas separation/purification technologies. Specific ions (e.g., oxygen) can be selectively diffused through these films in order to obtain a desired product, such as syngas or pure O2. During production, residual stresses develop within the films which induce defects, such as pinholes, micro-cracks, and other sources of leaks, that allow gas contamination. To improve large-scale film production yield, four application techniques were analyzed for their feasibility of restoring the integrity of the films. Controlled, uniform defects were introduced to the films using a microindenter to enable an effective comparison of application techniques …

High-Density Pressurelessly Sintered Zirconium Diboride/Silicon Carbide Composite Bodies And A Method For Producing The Same, Shi C. Zhang, Greg Hilmas, William Fahrenholtz

Materials Science and Engineering Faculty Research & Creative Works

A method of sintering a ZrB₂-SiC composite body at ambient pressures, including blending a first predetermined amount of ZrB₂ powder with a second predetermined amount of SiC powder, wherein both powders are characterized by the presence of surface oxide impurities. Next the blended powders are mixed to yield a substantially homogeneous powder mixture and a portion of the substantially homogeneous powder mixture is formed into a green body. The body is fired to a first temperature, wherein substantially all surface oxide impurities are reduced and/or volatilized to substantially eliminate oxides from the green body, and the body …

Thermal Properties Of Spinel Based Solid Solutions, Kelley R. Wilkerson

Doctoral Dissertations

"Solid solution formation in spinel based systems proved to be a viable approach to decreasing thermal conductivity. Samples with systematically varied additions of MgGa₂O₄ to MgAl₂O₄ were prepared and thermal diffusivity was measured using the laser ash technique. Additionally, heat capacity was measured using differential scanning calorimetry and modeled for the MgAl₂O₄-MgGa₂O₄ system. At 200⁰C thermal conductivity decreased 24% with a 5 mol% addition of MgGa₂O₄ to the system. The solid solution continued to decrease the thermal conductivity by 13% up to 1000⁰C with 5 mol% addition. The decrease in thermal conductivity ultimately resulted in a decrease in heat flux …

Microstructure And Mechanical Properties Of Silicon Carbide-Titanium Diboride Ceramic Composites, Derek Scott King

Masters Theses

"The microstructure, hardness, fracture toughness, Young's modulus, strength and Weibull modulus of silicon carbide-titanium diboride (SiC-TiB₂) ceramics were studied. First, SiC-TiB₂ ceramics with 15 vol.% TiB₂ particles were processed using two green processing methods, spray drying (ST) and ball milling (SiC-15TiB₂). In addition, SiC-TiB2 ceramics with TiB₂ contents ranging from 0 to 100 vol.% were produced to determine a TiB₂ content that produced the best combination of mechanical properties. From spray drying, segregation of the TiB₂ particles in ST led to a granule-like microstructure and spontaneous microcracking in the final ceramic. In ceramics containing 20 and 40 vol.% TiB₂, the …

Sputter Deposition Of Thin-Film Capacitors Onto Low Temperature Co-Fired Ceramic Substrates, Jack Murray

Masters Theses

"Single layer thin film capacitor structures were fabricated on the surface of low temperature co-fired ceramic (LTCC) substrates using sputter deposition. The capacitor structures had areas between ~10⁴ µm² to ~10⁶ µm² and featured ~200 nm Al or Pt electrodes with 150-1500 nm Al₂O₃ dielectric layers. Impedance analysis and current-voltage testing were carried out to determine the effect of electrode material and dielectric thickness upon capacitor performance. Capacitance values for devices with Al electrodes ranged from ~10 to ~700 pF, depending on capacitor area and dielectric thickness, and the fit to expected values was better than devices with Pt or …

Finite Element Analysis Of The Contact Deformation Of Piezoelectric Materials, Ming Liu

Theses and Dissertations--Chemical and Materials Engineering

Piezoelectric materials in the forms of both bulk and thin-film have been widely used as actuators and sensors due to their electromechanical coupling. The characterization of piezoelectric materials plays an important role in determining device performance and reliability. Instrumented indentation is a promising method for probing mechanical as well as electrical properties of piezoelectric materials.

The use of instrumented indentation to characterize the properties of piezoelectric materials requires analytical relations. Finite element methods are used to analyze the indentation of piezoelectric materials under different mechanical and electrical boundary conditions.

For indentation of a piezoelectric half space, a three-dimensional finite element …

Strength Of Polycrystalline Ceramics Under Shock Compression, Jianbin Zhu

Department of Engineering Mechanics: Dissertations, Theses, and Student Research

Determinations of Some polycrystalline ceramics’ strength properties and inelastic deformation mechanisms in the shocked state are critically important to the design and optimization of armor structures involving these materials. In this work, multiscale modeling and simulations have been carried out to study strength of the effects of polycrystalline microstructure, crystal anisotropy, porosity, and their interactions with microscopic deformation/damage mechanisms on the responses of several polycrystalline ceramics under shock compression and to extract their shock strengths from the wave profiles measured in the related plate impact shock wave experiments.

With a mesoscopic computational model, the roles of intragranular microplasticity and deformation …

Processing And Dielectric Properties Of Tio2 Thick Films For High-Energy Density Capacitor Applications, Sheng Chao, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

Nanosized titanium dioxide (TiO₂) powders (∼40 nm) were used for preparation of tape-casting slurries. Effect of various solvents and dispersants on the dispersibility of TiO₂ slurries was studied by sedimentation tests and rheology measurements. TiO₂ green tapes were prepared by tape-casting method and densified at 1000°C with a sintered density >95%. Dielectric properties of TiO₂ tapes were studied by measuring of dielectric constant, loss factor and dielectric breakdown strength (BDS) with respect to their microstructural development. BDS values as high as ∼1400 kV/cm were obtained for sintered tapes so that energy densities up to 14 …

Effect On The Processing Characteristics Of Zno Varistors Produced Using Vibratory Milling, Maura Kelleher, M.S.J. Hashmi

Conference Papers

Abstract. Each manufacturing stage in the production of zinc oxide varistors from powder preparation to the final encapsulated device is important not only for the formation of the varistor component with optimum microstructure and thus electrical characteristics but also for avoiding the introduction of flaws and reduced yield. In this paper the authors describe and discuss the effect of multi-elemental oxide additives having been milled for different durations using a vibratory mill with cylindrical zirconia media on the powder characteristics of the subsequent processing stages. A commercial ZnO varistor formulation was used. The subsequent processing stages that are given particular …

Evaluation Of Cathode Materials For Low Temperature (500-700c) Solid Oxide Fuel Cells, Alexander M. Lassman

Master's Theses

Solid oxide fuel cells (SOFC) have gained a great deal of interest, due to their potential for high efficiency power generation and ability to utilize hydrogen fuel, as well as various hydrocarbon-based fuels. A recent trend in SOFC development has been towards lower operating temperatures (500-700°C), which can substantially reduce the cost and complexity of the system. This thesis presents an investigation into state of the art Ba- and La- based cathode materials for use in low temperature (500-700°C) solid oxide fuel cells.

Synthesis of A-site deficient [A=0.97] Ba_0.5Sr_0.5Co_0.8Fe_0.2O₃ (BSCF) was …

Air Plasma Sprayed Thermal Barrier Coatings: Experiments And Finite Element Analysis, Charles H. Thistle

Master's Theses

The purpose of this research was to examine the primary in-service failure mechanism of an air plasma sprayed thermal barrier coating commonly used in combustor applications, and to use that failure mechanism as a basis in developing a life prediction strategy. The research consisted of an experimental phase, in which the failure mechanism was identified and key features of the coating system measured, and a modeling phase, in which the findings of the experimental phase were used to build a system specific finite element model of the coating in order to extract quantitative data relevant to coating life.

Observations were …

Synthesis, Field Emission And Associated Degradation Mechanisms Of Tapered Zno Nanorods, Gregory M. Wrobel Mr.

Master's Theses

Equation 1..... 4

Equation 2..... 4

Equation 3..... 6

Equation 4..... 7

Equation 5..... 9

Equation 6..... 10

Equation 7..... 11

Equation 8..... 12

Equation 9..... 14

Equation 10..... 40

Equation 11..... 51

Synthesis, Field Emission and Associated Degradation Mechanisms of Tapered ZnO Nanorods

Gregory Michael Wrobel, M.S.

University of Connecticut, 2011

Modern development of field emitter arrays (FEA) has been made possible, partly thanks to the synthesis and development of one-dimensional (1D) nanostructures. High aspect ratio 1D nanostructures effectively amplify the electric field at the emitter tips, allowing electrons to be extracted at relatively low electric field. An inexpensive …

Effect Of Particle Size, Binder Content And Heat Treatment On Mechanical Properties Of 13-93 Bioactive Glass Scaffolds, Krishna C. R. Kolan, Ming-Chuan Leu, Greg Hilmas, Mariano Garcia Velez

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Particle size, binder content and the post-processing schedule are important parameters that affect the microstructure, and, hence, the mechanical properties of parts produced using the indirect selective laser sintering process. 13-93 bioactive glass, with mean particle sizes ranging from 10 μm to 44 μm, is mixed with different amounts of stearic acid binder to fabricate green scaffolds. Through the design of the post-processing schedule, the time required for postprocessing the green scaffolds is reduced from the initial 80 hrs to 12 hrs. The compressive strength varies from 41 MPa for a part with~60% porosity to 157 MPa for a part …

Characterization Of The Oxidation Kinetics Of Fecral Ferritic Stainless Steels At 900°C For Catalytic Converter Applications, Stacy Stamm

Materials Engineering

This study characterized the oxidation kinetics of two types of ferritic stainless steel foils used as substrates for catalytic converters. Catalytic converters rely on an alumina layer on the surface of the foils, which allows the catalyst to attach to the substrate. Because the alumina layer is so important, this study characterized the weight gain, thickness, and composition of the alumina as it grew at 900°C for up to 400 hours. The two foils characterized were an MK foil, used for gasoline engines, and an EMS foil, used for diesel engines. The MK foil showed a percent weight gain of …