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Missouri University of Science and Technology

Series

Materials Science and Engineering

1998

Articles 1 - 8 of 8

Full-Text Articles in Engineering

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 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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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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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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