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Open Access. Powered by Scholars. Published by Universities.®

Missouri University of Science and Technology

1998

Articles 1 - 16 of 16

Full-Text Articles in Materials Science and Engineering

Vacancy Clustering In Quenched Al-Li Solid Solution Alloys Studied By Doppler Broadening Spectroscopy, Hollis P. Leighly, P. G. Coleman Nov 1998

Vacancy Clustering In Quenched Al-Li Solid Solution Alloys Studied By Doppler Broadening Spectroscopy, Hollis P. Leighly, P. G. Coleman

Materials Science and Engineering Faculty Research & Creative Works

The clustering of vacancies in severely quenched Al-Li solid solution alloys, with Li content between 230 and 2760 ppm, has been studied using Doppler broadening spectroscopy. The alloy samples were initially annealed at 873 K in dry air or dry, pure nitrogen. The onset temperature for vacancy clustering in samples initially annealed in air was found to be 150 ± 10 K, 40 ± 15 K lower than for the nitrogen-annealed samples. This result is consistent with the migration of divacancies, formed as a result of the significant increase in vacancy concentration caused by Li migration to, and oxidation at, …

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Specific Heat And Transport “Anomalies” In Mixed Alkali Glasses, Peter F. Green, Richard K. Brow, James J. Hudgens Nov 1998

Specific Heat And Transport “Anomalies” In Mixed Alkali Glasses, Peter F. Green, Richard K. Brow, James J. Hudgens

Materials Science and Engineering Faculty Research & Creative Works

We show that changes in the relative mole fractions of Li2O and Na2O in alkali metaphosphate glasses lead to “anomalies” in the specific heat and structural relaxations. The heat capacity change between the liquid and glassy states, Δcp(Tg), at the calorimetric glass transition temperature, Tg, exhibits a minimum when the mole fractions of Li2O and Na2O are comparable. Moreover, systematic changes in the temperature dependence of the viscosity, η, i.e., changes in the “fragility” of the system, accompany these changes in mole fraction. This observed dependence …

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Mixed Electron Emission From Doped Pb(Zr,Ti)O₃ Ceramics: Microstructural Aspects, Weiming Zhang, Wayne Huebner Jun 1998

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 …

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Mixed Electron Emission From Lead Zirconate-Titanate Ceramics, Weiming Zhang, Wayne Huebner, Stephen E. Sampayan, Mike L. Krogh Jun 1998

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 …

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Iron Phosphate Compositions For Containment Of Hazardous Metal Waste, D. E. Day May 1998

Iron Phosphate Compositions For Containment Of Hazardous Metal Waste, D. E. Day

Materials Science and Engineering Faculty Research & Creative Works

An improved iron phosphate waste form for the vitrification, containment and long-term disposition of hazardous metal waste such as radioactive nuclear waste is provided. The waste form comprises a rigid iron phosphate matrix resulting from the cooling of a melt formed by heating a batch mixture comprising the metal waste and a matrix-forming component. The waste form comprises from about 30 to about 70 weight percent P205 and from about 25 to about 50 weight percent iron oxide and has metals present in the metal waste chemically dissolved therein. The concentration of iron oxide in the waste form along with …

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Regarding The Correlation Of Nuclear Spin Relaxation And Electrical Conductivity Relaxation In Ionic Glasses, David L. Sidebottom, Peter F. Green, Richard K. Brow Apr 1998

Regarding The Correlation Of Nuclear Spin Relaxation And Electrical Conductivity Relaxation In Ionic Glasses, David L. Sidebottom, Peter F. Green, Richard K. Brow

Materials Science and Engineering Faculty Research & Creative Works

Much attention has been focused recently on the apparent differences between ion dynamics in ion-containing glasses as probed by electrical conductivity relaxation (ECR) and by nuclear spin relaxation (NSR) techniques. In both relaxation processes, a power law frequency dependence is observed. Based upon fluctuation-dissipation arguments, the power law exponents should be equivalent. However, experimentally, it appears that the conductivity exponent is generally smaller than the NSR exponent. While an explanation for this discrepancy based upon fundamental differences in the correlation functions probed by the two techniques has been proffered, we show how this discrepancy may simply arise from differing analyses …

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Incommensurate Magnetic Fluctuations In Yba₂Cu₃O₆.₆, Pengcheng Dai, Herbert A. Mook, Fatih Dogan Feb 1998

Incommensurate Magnetic Fluctuations In Yba₂Cu₃O₆.₆, Pengcheng Dai, Herbert A. Mook, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

We use inelastic neutron scattering to demonstrate that the low-frequency magnetic fluctuations in YBa2Cu3O6.6 (Tc = 62.7 K) change from commensurate to incommensurate on cooling with the incommensurability first appearing at temperatures above Tc. For the energies studied, the susceptibility at incommensurate positions increases on cooling below Tc, accompanied by a suppression of the spin fluctuations at the commensurate points. These results suggest that incommensurate spin fluctuations may be a common feature for all cuprate superconductors.

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Deuterium Nmr Of Adsorbed Poly(Methyl Acrylate)-D₃, Frank D. Blum, Wuu-Yung Lin Jan 1998

Deuterium Nmr Of Adsorbed Poly(Methyl Acrylate)-D₃, Frank D. Blum, Wuu-Yung Lin

Chemistry Faculty Research & Creative Works

The dynamics of polymers at interfaces are important in a variety of applications, especially where those applications depend on the mechanical or surface properties. Unfortunately, the surface properties of interfacial species like polymers used in composites are not easily measured macroscopically. Microscopic techniques, especially spectroscopic ones, have been successful. In our laboratory we have been successful in applying NMPR to determine the behavior of absorbed polymers. NMR has several advantages for this kind of study, the principal ones being that it can be used on opaque materials, different nuclei can be used as probes, and interfacial material can sometimes be …

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Metal-Organic Chemical Vapor Deposition Of Sr-Co-Fe-O Films On Porous Substrates, C.-F. Xia, P. Atanasova, Robert W. Schwartz, T. L. Ward Jan 1998

Metal-Organic Chemical Vapor Deposition Of Sr-Co-Fe-O Films On Porous Substrates, C.-F. Xia, P. Atanasova, Robert W. Schwartz, T. L. Ward

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Aerosol-assisted chemical vapor deposition using the b-diketonate precursors Sr(tmhd)2•2H2O, Fe(tmhd)3 and Co(tmhd)3 was investigated for depositing thin films of the mixed-conducting ceramic SrCoyFe1-yO3-d onto porous a-Al2O3 substrates. Single-phase SrCoyFe1-yO3-d perovskite films were obtained at a deposition temperature of 550°C and pressure of 15 mm Hg, whereas deposition at atmospheric pressure produced mixed-phase films. The Co/Fe elemental ratios in the films reflected those in the precursor solution, but the films were depleted in Sr. Reduced-pressure deposition provided a more uniform film morphology than atmospheric-pressure, and led to a supported film which was leak-tight to N2 flow.

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Magnetoresistance Of Magnetic Tunnel Junctions In The Presence Of A Nonmagnetic Layer, Shi C. Zhang, P. M. Levy Jan 1998

Magnetoresistance Of Magnetic Tunnel Junctions In The Presence Of A Nonmagnetic Layer, Shi C. Zhang, P. M. Levy

Materials Science and Engineering Faculty Research & Creative Works

We find that electron propagation across a uniform nonmagnetic metallic layer di in a magnetically layered structure is coherent up to a critical length dc. This provides a possible explanation for the slow decay of the magnetoresistance of magnetic tunnel junctions when a layer of Cu or Ag is inserted between the magnetic electrode and the barrier. However, for many (most) structures the roughness of the interfaces breaks the coherence for di ≪ dc. While the loss of coherence is not fatal for the magnetoresistance of metallic multilayers, it is for tunnel junctions. The quantum well states arising from the …

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Organically Deposited Metallic Films For Device Fabrication, Thomas J. O'Keefe, M. Stroder, Matthew O'Keefe Jan 1998

Organically Deposited Metallic Films For Device Fabrication, Thomas J. O'Keefe, M. Stroder, Matthew O'Keefe

Materials Science and Engineering Faculty Research & Creative Works

Advances in integrated circuit density, speed and complexity are dependent on lower resistance, finer line width on-chip interconnections. Methods for incorporating copper interconnects into IC fabrication processes have been developed which accomplish this objective but most of these methods use some form of blanket metal deposition that requires mechanical and/or chemical removal of excess material. To date, investigations into the selective deposition of conductor materials for device fabrication have met with limited success. A new process for selectively depositing metallic conductors using inexpensive, organic-based chemical solutions could potentially force a paradigm shift in the deposition of metals for microelectronic applications. …

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Electrodeposition Of Copper On Thermally Oxidized 316 L Stainless Steel Substrates, Z. Zhou, Thomas J. O'Keefe Jan 1998

Electrodeposition Of Copper On Thermally Oxidized 316 L Stainless Steel Substrates, Z. Zhou, Thomas J. O'Keefe

Materials Science and Engineering Faculty Research & Creative Works

The effect of thermal oxidation of 316 L stainless steel cathode blanks used in copper electrodeposition was studied. Current and potential step experiments were performed to evaluate electrochemical changes caused by the oxidation treatments. SEM and AES were used to characterize the stainless-steel substrates and the deposited copper films. Particular emphasis was given to the initial stages of copper nucleation and growth. The copper electro crystallization process was strongly influenced by the temperature employed in oxidizing the stainless steel. Dense, uniform and fine copper nuclei were obtained on the stainless-steel substrate oxidized in air at 200°C and 300°C for 3 …

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Maskless, Direct Deposition Of Copper Onto Aluminum Bond Pads For Flip Chip Applications, M. Fang, Thomas J. O'Keefe, M. Stroder, W. Shih, Matthew O'Keefe, R. Strawser, D. Via Jan 1998

Maskless, Direct Deposition Of Copper Onto Aluminum Bond Pads For Flip Chip Applications, M. Fang, Thomas J. O'Keefe, M. Stroder, W. Shih, Matthew O'Keefe, R. Strawser, D. Via

Materials Science and Engineering Faculty Research & Creative Works

Flip chip interconnection of integrated circuits (IC) for packaging applications such as direct chip attachment use Pb-Sn solders as the connection between the die and the substrate. Under bump metallization is typically used to transition from the non-solderable Al bond pad on the IC to a solderable surface such as copper using traditional blanket metal deposition, photolithography and etching procedures. In this study, we report for the first time the use of a novel process for selectively depositing adherent copper directly onto aluminum thin films, eliminating the need for adhesion promoting transition layers and additional patterning steps. Utilizing copper bearing …

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Analysis Of The Value Of The Fe Examination For The Assessment Of Student Learning In Engineering And Science Topics, John L. Watson Jan 1998

Analysis Of The Value Of The Fe Examination For The Assessment Of Student Learning In Engineering And Science Topics, John L. Watson

Materials Science and Engineering Faculty Research & Creative Works

This paper presents the results of a project, which investigated the potential of fully using previously unreleased data from the nationally normed Fundamentals of Engineering (FE) examination to assess learning in key engineering and science topics. In the past, very limited information was released by the National Council of Examiners for Engineers and Surveyors (NCEES) for the eight hour FE examination, which is composed of 150-200 questions in ten morning and five afternoon topics. For the purposes of this project the NCEES agreed to release information to the University of Missouri-Rolla (UMR) to permit the value of the FE data …

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Electrochemical Characterization Of Copper Deposited On Plasma And Thermally Modified Titanium Surfaces, K. S. Teng, J. L. Delplancke, Jiangfan Zhang, T. J. O'Keefe Jan 1998

Electrochemical Characterization Of Copper Deposited On Plasma And Thermally Modified Titanium Surfaces, K. S. Teng, J. L. Delplancke, Jiangfan Zhang, T. J. O'Keefe

Electrical and Computer Engineering Faculty Research & Creative Works

Thin oxide films were grown at temperatures from 373 to 1073 K in plasma and in air on commercially pure titanium substrates. It was determined that the color, thickness, composition, phase, and polarization behavior in a copper electrolyte varied with operating conditions: temperature, oxygen partial pressure, and plasma composition. High-temperature and high oxygen partial pressure plasma produced a thick oxide film. The surface film structure transformed from TiO2 (anatase) to TiO2 (rutile) at a temperature of 600 °C. A lower oxide of the form TinO2n-1, such as Ti2O3 (which may be porous) or possibly Ti3O5, was formed on a thermally …

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Evolution Of In Situ Refractories In The 20th Century, William E. Lee, Robert E. Moore Jan 1998

Evolution Of In Situ Refractories In The 20th Century, William E. Lee, Robert E. Moore

Materials Science and Engineering Faculty Research & Creative Works

A common theme over the past 100 years in refractories science and technology has been to generate a protective refractories layer in a high-temperature container, often by reaction of the refractory materials with the contents (glass, slag, or atmosphere). The history of refractories during the 20th century is used in this review to illustrate how techniques - such as slag splashing, in situ spinel generation in castables, magnesia dense layer formation in magnesia-carbon brick in steelmaking, clinker adhesion in cement kilns, and viscous boundary layer generation in glass tanks - have evolved to their present status.

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