Engineering Commons^™

Oxidation Of Additively Manufactured Zrb2–Sic In Air And In Co2 At 700–1000 °C, Marharyta Lakusta, Nicholas M. Timme, Abid H. Rafi, Jeremy Lee Watts, M. (Ming) C. (Chuan) Leu, Gregory E. Hilmas, William G. Fahrenholtz, David W. Lipke

Materials Science and Engineering Faculty Research & Creative Works

Oxidation behavior of additively manufactured zrb2–sic in air and in co2 is reported in the temperature range of 700–1000 °c. Observed scale morphologies in air and in co2 were similar, featuring an outer borosilicate layer and an inner porous zirconia layer containing partially oxidized silicon carbide particles and remnant borosilicate products. Oxide scale thicknesses and parabolic scaling constants in air were approximately twice those observed in co2 across all studied temperatures. Activation energies for oxidation of 140 ± 20 kj/mol in air and 110 ± 20 kj/mol in co2 were determined, indicating similar diffusion processes that appear to be rate-limiting. …

Ac Conductivity Relaxation Processes In Cacu₃Ti₄O₁₂ Ceramics: Grain Boundary And Domain Boundary Effects, Wei Li, Robert W. Schwartz

Materials Science and Engineering Faculty Research & Creative Works

The ac conductivity of CaCu₃Ti₄O₁₂ ceramics associated with electrical charge carrier motion (ions or vacancies) was investigated as a function of frequency at different temperatures. The long range migration of charge carriers within the ceramic is restricted by two kinds of insulating barriers, namely, grain boundaries and domain boundaries. The potential barriers associated with these boundaries lead to two anomalies in conductivity response and three frequency-dependent contributions to conductivity: long range diffusion of carriers, carrier migration localized within grains, and carrier migration localized within domains.

Influence Of Nanocrystalline Grain Size On The Breakdown Strength Of Ceramic Dielectrics, Yang Ye, Fatih Dogan, E. Schamiloglu, J. Gaudet, P. Castro, M. Roybal, M. Joler, C. Christodoulou, Shi C. Zhang

Materials Science and Engineering Faculty Research & Creative Works

In an effort to develop transmission lines with higher energy storage capabilities for compact pulsed power applications, the University of Missouri-Rolla (UMR) and the University of New Mexico (UNM) have undertaken a collaborative approach to developing and studying ceramic dielectrics. At UMR, the electrical breakdown strength (BDS) of TiO2-based materials is investigated for high energy density applications. The results of research to-date show that dense titania ceramics with nanocrystalline grain size (~200 nm) exhibit significantly higher BDS as compared to ceramics made using coarse grain materials. Processing-microstructure-property relationships in TiO2 systems are found to play a role with respect to …

High Energy Density Dielectrics For Symmetric Blumleins, Wayne Huebner, Shi C. Zhang

Materials Science and Engineering Faculty Research & Creative Works

Multilayer, tape cast ceramics are being developed for use in large area, high voltage devices in order to achieve high specific energy densities (>10⁶ J/m³) and physical size reduction. In particular, symmetric Blumleins are desired with the following properties:

• High voltage hold off (≥ 300 kV)
• High, nondispersive permittivity: ≈100 to 900
• Ability to be fabricated into various shapes and sizes
• Surface flashover inhibition at the edge
• Ability to be triggered by surface flashover switching

The compositions being pursued are based on pure BaTiO₃ dielectrics. Our approach is to add glass phase additions which result …

High Breakdown Strength, Multilayer Ceramics For Compact Pulsed Power Applications, Wayne Huebner, Brian L. Gilmore, Shi C. Zhang, Mike L. Krogh, B. C. Schultz, R. C. Pate, L. F. Rinehart, J. M. Lundstrom

Materials Science and Engineering Faculty Research & Creative Works

Advanced ceramics are being developed for use in large area, high voltage devices in order to achieve high specific energy densities (greater than 10^6/ J/m^3/) and physical size reduction. Initial materials based on slip cast TiO2 exhibited a high bulk breakdown strength (BDS greater than 300 kV/cm) and high permittivity with low dispersion (epsilon approximately equal to 100). However, strong area and thickness dependencies were noted. To increase the BDS, multilayer dielectric compositions are being developed based on glass/TiO2 composites. The addition of glass increases the density (approximately equal to 99.8% theoretical), forms a continuous grain boundary phase, and also …

Measurement Of The Dielectric Strength Of Titanium Dioxide Ceramics, Wayne Huebner, J. M. Lundstrom, L. F. Rinehart, R. C. Pate, T. L. Smith, Mike L. Krogh

Materials Science and Engineering Faculty Research & Creative Works

Titanium dioxide ceramics (TiO2) are candidate materials for high energy density pulsed power devices. Experiments to quantify the dielectric strength of TiO2 have been performed on a limited number of unoptimized samples. A high voltage test set was constructed to test the titanium dioxide. All samples had a relative dielectric constant of 100, all samples were of 3 mm nominal thickness, and all tests were performed in water dielectric to reduce the effect of the triple point field enhancement at the electrode edge. Both single layer and laminated samples were tested and the breakdown field strengths were recorded. Voltage risetimes …

Mixed Electron Emission From Doped Pb(Zr,Ti)O₃ Ceramics: Microstructural Aspects, Weiming Zhang, Wayne Huebner

Materials Science and Engineering Faculty Research & Creative Works

A mixed type electron emission, i.e., simultaneous ferroelectric and plasma emission, was observed with a negative driving pulse applied to doped Pb(Zr,Ti)O₃ ceramics in the absence of any external potential on the electron collector. During these emission studies, significant microstructural changes on the emission surface were observed, and corresponded to the different emission modes. Erosion craters at the edge of the electrode and small particles near these craters reflected the formation of a dense plasma there. Comparatively, cavities, i.e., grain pullouts, accumulated on the bare ferroelectric surface, the frequency of which depended upon its distance from the grid. This …

Mixed Electron Emission From Lead Zirconate-Titanate Ceramics, Weiming Zhang, Wayne Huebner, Stephen E. Sampayan, Mike L. Krogh

Materials Science and Engineering Faculty Research & Creative Works

Simultaneous ferroelectric and plasma emission from Pb(Zr,Ti)O₃ was observed with only a negative driving pulse applied to the sample, and without an extraction potential on the electron collector. Plasma emission was a strong, inconsistent, and self-destructive process. In addition, a positive ion current was detected. Comparatively, ferroelectric emission was a relatively stable self-emission process, exhibiting no apparent delay time, and no positive ion current. The relationship between the switching and emission current of ferroelectric samples measured simultaneously cannot only be used to determine the existence of ferroelectric emission, but can also give direction to choosing suitable ferroelectric materials for …

Correlation Of Wettability And Interfacial Reaction To The Densification And Dielectric Properties Of Fluxed-Batio₃, Sea-Fue Wang, Wayne Huebner, Joseph P. Dougherty

Materials Science and Engineering Faculty Research & Creative Works

Reducing the sintering temperature of BaTiO3 has typically been achieved through the use of a fluxing agent to promote densification by liquid phase sintering. Liquid phase formation in these systems is due either to the melting of the flux or to the formation of a eutectic liquid between the flux and BaTiO3. In this paper, the correlation between the wettability and interfacial reactions between fluxes and BaTiO3 with respect to the densification behavior associated with liquid phase sintering, and the resulting dielectric properties is presented. Fluxes used in this study include 5ZnO*2B2O3, 5CdO*2SiO2, Pb5Ge3O11, CuO*TiO2, 3Bi2O3*B2O3, and LiF.

Grain Size Effect On The Induced Piezoelectric Properties Of 0.9pmn-0.1pt Ceramic, U. Kumar, Wayne Huebner, P. Marsh, H. Kankul, S. F. Wang, Clyde G. Oakley

Materials Science and Engineering Faculty Research & Creative Works

Lead magnesium niobate-lead titanate (Pb(Mg_1/3Nb_2/3)O₃ - PbTiO₃ (PT) solid solutions have been widely researched to produce devices that can be used in low- and high-electric-field applications. For some applications, such as medical ultrasonic transducers, it is necessary to prepare the ceramic with high density and small average grain size. The effect of grain size on the low- and high-field properties of 0.9-PMN-0.10-PT ceramics is described in the present work. To prepare highly dense ceramic, vibratory and attrition milled powders were sintered between 1000 and 1250 ⁰C. The average grain sizes of the sintered ceramics …

Design Considerations For 1-3 Composites Used In Transducers For Medical Ultrasonic Imaging, Wayne Huebner, Kuiming Liang, Clyde G. Oakley

Materials Science and Engineering Faculty Research & Creative Works

Ceramic polymer piezoelectric composites with 1-3 connectivity have become an important tool in the design and manufacture of thickness-mode transducers for medical diagnostic ultrasonic imaging. The authors compare annular array transducers made from ceramics alone to those made with these composites to demonstrate the advantages of composites. They examine some of the trade-offs involved in optimizing composite designs for this application. The effects of varying Young's modulus and Poisson's ratio of the polymer phase on the coupling coefficient and high-frequency lateral resonances of the composite are presented