Engineering Commons^™

Oxidation-Reduction Behavior Of Undoped And Sr-Doped Lamno3 Nonstoichiometry And Defect Structure, J. H. Kuo, Harlan U. Anderson, Don M. Sparlin

Materials Science and Engineering Faculty Research & Creative Works

Undoped and Sr-doped LaMnO₃ showed reversible oxidation-reduction behavior. These perovskites can be excess, stoichiometric or deficient in oxygen content depending on the specific conditions. Under very reducing conditions decomposition into new phases occurs. Phase stabilities for these oxides were determined. The results showed that Sr doping caused the LaMnO₃ to dissociate at higher oxygen activities than those necessary for undoped LaMnO₃. Defect models are proposed to interpret the thermogravimetric results in which metal vacancies are assumed for the oxygen excess condition and oxygen vacancies are assumed for the oxygen deficient condition. Thermodynamic properties were calculated which …

High-Temperature Defect Structure Of Nb-Doped Lacro3, Chikung J. Yu, Harlan U. Anderson, Don M. Sparlin

Materials Science and Engineering Faculty Research & Creative Works

Electrical conductivity and Seebeck measurements on LaCr_0.98Nb_0.02CrO₃ show that the defect structure of the material is mainly controlled by the extrinsic electrons formed by the Nb donors through the electronic compensation process. The experimental results also indicate that this material conducts electricity via a small polaron mechanism with an electron mobility around 0.004-0.01 cm2/V sec between 1100 and 1300°C. © 1989.

Effect Of Volatilization On The Conduction Behavior Of Acceptor‐Doped Chromium Oxide, Rong‐Fong ‐F Huang, Harlan U. Anderson

Materials Science and Engineering Faculty Research & Creative Works

The effect of volatilization on the conduction behavior of Li‐ or Mg‐doped Cr₂O₃ was studied. The Po2 dependence on conduction changed from 1/4 to 3/8 when volatilization occurred. The high‐temperature conduction mechanism of Cr₂O₃ may be dominated by the formation of Cr vacancies due to the volatilization effect. Copyright © 1989, Wiley Blackwell. All rights reserved

Gaas Photoconductive Closing Switches With High Dark Resistance And Microsecond Conductivity Decay, M. S. Mazzola, K. H. Schoenbach, V. K. Lakdawala, R. Germer, G. M. Loubriel, F. J. Zutavern

Electrical & Computer Engineering Faculty Publications

Silicon-doped n-type gallium arsenide crystals, compensated with diffused copper, were studied with respect to their application as photoconductive, high-power closing switches. The attractive features of GaAs:Cu switches are their high dark resistivity, their efficient activation with Nd:YAG laser radiation, and their microsecond conductivity decay time constant. In the authors' experiment, electric fields are high as 19 kV/cm were switched, and current densities of up to 10 kA/cm² were conducted through a closely compensated crystal. At field strengths greater than approximately 10 kV/cm, a voltage `lock-on' effect was observed.

Nucleation Of Electrodeposited Copper On Anodized Titanium, J. L. Delplancke, M. Sun, Thomas J. O'Keefe, R. Winand

Materials Science and Engineering Faculty Research & Creative Works

A study has been made to determine the effect of an electrochemically produced titanium-oxide film on the nucleation of copper. The oxide films were made galvanostatically at 25°C in 1 M sulphuric acid on pure titanium metal. Potentiodynamic, potential step and current step experiments were performed in an additive-free copper sulphate-sulphuric acid electrolyte at 25°C. It was found that the oxide film played an important role during nucleation. By increasing the thickness of the anodic film, it was possible to decrease the diameter and to increase the surface density of copper nuclei. The kinetics of nucleation and growth of the …

Nanosecond Optical Quenching Of Photoconductivity In A Bulk Gaas Switch, M. S. Mazzola, K. H. Schoenbach, V. K. Lakdawala, S. T. Ko

Electrical & Computer Engineering Faculty Publications

Persistent photoconductivity in copper-compensated, silicon-doped semi-insulating gallium arsenide with a time constant as large as 30 µs has been excited by sub-band-gap laser radiation of photon energy greater than 1 eV. This photoconductivity has been quenched on a nanosecond time scale by laser radiation of photon energy less than 1 eV. The proven ability to turn the switch conductance on and off on command, and to scale the switch to high power could make this semiconductor material the basis of an optically controlled pulsed-power closing and opening switch.

Optical Recording Aspects Of Rf Magnetron Sputtered Iron-Garnet Films, J.P. Krumme, V. Doormann, P. Hansen, H. Baumgart, J. Petruzzello, M.P.A. Viegers

Electrical & Computer Engineering Faculty Publications

The intrinsic magneto-optical readout performance in reflection is calculated for bismuth and cobalt-substituted iron-garnet films on a multilayer interference mirror at 800-, 633-, 488-, and 420-nm wavelengths and is compared with that of a trilayer medium composed of an antireflection layer, a rare-earth transition-metal film, and a metallic mirror. It is found, when disregarding inhomogeneities, like irregular domain shape, ripple of the magnetic anisotropy, and surface roughness, that iron garnets are superior to rare-earth transition-metal films at blue to near-ultraviolet wavelengths if operated at thicknesses where optical interference occurs in the magnetic layer. Optical transmittance at these thicknesses is sufficiently …

Relationships Between Chemistry Variations And The Morphology And Nodular Formation Of Carbon Nodules In Ductile Cast Iron, Donald Francis Cassel

Dissertations and Theses @ UNI

The purpose of this study was to determine what relationships exist between the chemistry and the morphology and nodular formation of carbon nodules in commercially produced ductile cast iron. Additionally, the effects of chemistry on the hardness of produced castings from net shake processes were investigated. According to pertinent information in current literature, the hardness of castings has a direct bearing on the final cost of products.

The method of gathering this information and developing a correlation between the chemistry variations and the morphology and nodular formation was facilitated by the cooperation of a commercial producer of ductile cast iron …

Behavior Of Ductile Materials Under Impulsive Loading, M. Y. Brunner

Tanzania Journal of Engineering and Technology (TJET)

Ductile materials under dynamic loading are known to be able to absorb energy and thereby delay or even prevent structural failure. This paper is concerned with such behaviour in the case of impulsive loads of short duration. It is shown that even when the feared, unstable, labile condition is attained, failure may not necessarily occur. This behaviour is particularly impressive for structures with large mass, because it is essentially the mass which slows down the attainment of the failure strains. If the impulsive load dies away quickly enough, the constant plastic resistance will be adequate to bring the increasing deformations …

Relationship Between Magnetic Ageing, Metallographic Evidence Of Ageing And Composition For Cold Rolled Si-Fe Electrical Sheets, J .V .Tesha

Tanzania Journal of Engineering and Technology (TJET)

The cold rolled Si-Fe sheets used for the production of the current cores for electricity meters suffer from ageing which causes an irreversible change in the magnetic properties. The ageing process is due to the precipitation of mixed iron silicon carbides in the microstructure. There exists already a thermal treatment and magnetic properties measurements method to detect the susceptibility to ageing. This requires a minimum of 1000 hours. In order to find the correlation between magnetic ageing, composition and metallographical evidence of ageing, different Si-Fe sheet compositions were investigated using the optical microscope to observe the time to appearance of …

Glass Microspheres, D. E. Day, Gary J. Ehrhardt

Materials Science and Engineering Faculty Research & Creative Works

A radioactive microsphere for radiation therapy of a mammal comprising a biologically compatible glass material containing a beta or gamma emitting radioisotope distributed substantially uniformly throughout the glass. Advantageously, the radioisotope is produced by irradiation of the microsphere.

Anomalous Temperature Dependence Of The Electric Field Gradient At The Y Site In In₀.₁Y₀.₉Ba₂Cu₃O9- Δ, Gary L. Catchen, Michael Blaszkiewicz, Anthony Baratta, Wayne Huebner

Materials Science and Engineering Faculty Research & Creative Works

Perturbed angular correlation (PAC) spectroscopy has been used to measure a well-defined static electric quadrupole interaction in a superconducting ceramic, In_0.1Y_0.9Ba₂Cu₃O_9-δ. Perturbation functions, Fourier transforms, and the derived PAC parameters are given for data taken at temperatures ranging from 77 to 1070 K. Indirect evidence is presented for the occupation of the Y site by the ¹¹¹In-¹¹¹Cd PAC probe. The derived electric field gradients were found to increase linearly with temperature. This result suggests the presence of soft, anisotropic vibrations in the structure. Additional evidence is presented …

30th Rocky Mountain Conference

Rocky Mountain Conference on Magnetic Resonance

Program and abstracts from the 30th annual meeting of the Rocky Mountain Conference, co-sponsored by the Rocky Mountain Section of the Society for Applied Spectroscopy and the Rocky Mountain Chromatography Discussion Group. Held in Denver, Colorado, July 31 - August 5, 1988.

Reactions Of Diketones With Phosphorous Ylides, Amal Mohamed Lakany

Archived Theses and Dissertations

No abstract provided.

Effect Of Fabric On Stress-Strain Relation, Volume Change, And Dynamic Shear Modulus Of Ottawa Sand, Ming-Tarng Chen

Civil & Environmental Engineering Theses & Dissertations

To evaluate the effect of fabric on stress-strain behavior, volume change, and the dynamic shear modulus of Ottawa sand, four series of tests on hollow cylindrical specimens were performed by a torsional simple shear/resonant apparatus. All specimens were first isotropically consolidated, and then sheared along the different stress paths while keeping the mean effective stress constant. The test results showed that depositional fabric had a slight influence on the stress-strain behavior, and one half-cycle of pre-shearing created a clear anisotropy on the stress-strain response. The intermediate principal stress had a dominant effect on volume change characteristics but it might not …

Effect Of The Variations Of The Mobile Dislocation Density On The Thermally Activated Cyclic Deformation Behavior, J. S. Mshana

Tanzania Journal of Engineering and Technology (TJET)

The application of the transition state theory of rate processes to describe tension-tension, strain controlled cyclic deformation BEHAVIOUR was extended to describe the effect of the variations of the mobile dislocation density on the cyclic deformation BEHAVIOUR. It was shown from the derived constitutive relation that due to the net increase in the mobile dislocation density during strain controlled cyclic deformation the stress change per cycle (or in function of time) increases.

The Relationship Of Pore Volume And Pore Size Distribution To The Development Of Gloss And Scattering Coefficient, John A. Cook

Masters Theses

This study describes in a quantitative manner the relationships between coating structure and optical properties. Gloss, scattering coefficient and void volume were measured after applying different blends of polystyrene spheres to mylar film. Each coating was modeled using large spherical particles of the same size ratios to measure pore size distribution. The coating structure followed well with theoretical packing characteristics of spheres. Optical properties were related to changes in coating structure. Scattering coefficient and gloss correlated better with pore size distribution than particle size. Gloss increased when total void volume was reduced, while the scattering coefficient decreased.

Premartensitic Anelasticity In Indium-Thallium Alloys., Manfred Wuttig, C. Y. Lei, Tetsuro Suzuki

Materials Science and Engineering Faculty Research & Creative Works

The linear and nonlinear low frequency internal friction of In-24 at. pct Tl displays a Curie-Weiss type behavior in the temperature range above the transformation temperature. The critical temperature equals the martensite start temperature. It is proposed that the origin of the observed internal friction is the diffusion-controlled interaction of substitutional atoms with the premartensitic strain modulation, tweed.

Structural Characterization Of A High-Temperature, Ionic Conducting Ceramic Using Perturbed Angular Correlation Spectroscopy, Gary L. Catchen, Michael Blaszkiewicz, Khalid Jamil, Dinesh K. Agrawal, Wayne Huebner, Herbert A. Mckinstry, Lorenz H. Menke Jr.

Materials Science and Engineering Faculty Research & Creative Works

Perturbed angular correlation (PAC) spectroscopy has been used to characterize several structural aspects of a high-temperature, ionic conducting ceramic, CaZr3.95Hf0.05P6O24. Hafnium was introduced into the material to provide the PAC probe nuclei, 181Hf/181Ta, which were located primarily at Zr sites. PAC measurements were made over a range of temperatures from 77 to 1180 K, and they have been analyzed and interpreted using several simple models. The distorted octahedral crystal field at the Zr site produced a (low-frequency) static electric quadrupole interaction which can be accurately described by the point-charge model. But, the temperature dependence of the associated electric field gradient …

Effect Of Excess Pbo On The Sintering Characteristics And Dielectric Properties Of Pb(Mg1/3nb2/3)O3–Pbtio3‐Based Ceramics, Jyoti P. Guha, Dyllan J. Hong, Harlan U. Anderson

Materials Science and Engineering Faculty Research & Creative Works

Additions of excess PbO to the perovskite Pb[(Mg_1/3Nb_2/3)_0.92Ti_0.08]O₃ solid solution enhanced the formation of a liquid phase at 840°C, which served as a densification aid for the ceramics. The liquid phase allowed elimination of pores and promoted grain growth during sintering. With additions of 1 to 2 wt% excess PbO, densities in excess of 97% of theoretical were obtained at a sintering temperature of 950°C. The peak dielectric constants of the resulting ceramics were over 18 000 at 30°C and dissipation factors less than 1%. Additions of PbO in excess of …

Microstructural Analysis In Processing Of The High‐Tc Superconductor Ba2ycu3o7‐X In Air, Jyoti P. Guha

Materials Science and Engineering Faculty Research & Creative Works

In the synthesis of the superconducting compound Ba₂YCu₃O_7‐x from a stoichiometric mixture containing BaCO₃, Y₂O₃, and CuO In air, a low‐melting liquid phase is formed at about 890°C. The liquid phase was identified as a ternary eutectic located within the compatibility triangle Ba₂YCu₃O_7‐x–BaCuO₂–CuO. The implication of this finding for the processing of Ba₂YCu₃O_7‐x is discussed. Copyright © 1988, Wiley Blackwell. All rights reserved.

An Investigation Of The Micro-Surfaces Of Fiber Glass, Window Glass, Bottle Glass, And Quartz Crystal Through The Use Of Scanning Electron Microscopy, Raymond C. Friedrichsen

Graduate Research Papers

The problem of this study is to investigate the surfaces of quartz crystal, bottle glass, window glass, and fiber glass, to determine if there are any substantial differences in their structures when compared to a fiber optic material. The investigation will be done with the aid of the scanning electron microscope {SEM).

Effects Of 0.5 Weight Percent Boron On Cobalt Aluminide, Kevin Thomas Slattery

Masters Theses

"A study was made on the effects of adding 0.5 weight percent boron to the ordered intermetallic Cobalt Aluninide. Thirty gram (30g) specimens were induction melted in an pure argon atmosphere and cast into a copper alloy bar mold. The addition of boron raised the modulus of rupture from 30.1 to 44.3 ksi; increased the Knoop microhardness from 543 to 693; reduced the average grain size from 190 to 70 microns; and gave a more equiaxed grain structure. X-ray diffraction detected the presence of a second phase, AlB , 12 in the material containing boron. Scanning electron micro-scopy revealed that …

Influence Of Prior Deformation On Structure And Properties Of Heat Treated Aluminum Casting Alloy, Chungwei Hsia

Masters Theses

"A1 356 alloy is extensively used for a wide variety of casting applications. The structure is composed of primary dendrites and eutectic silicon formed during the eutectic reaction. It has long been recognized that the shape of the eutectic silicon significantly affects the ductility of the alloy. Traditionally, the morphology of the silicon is changed by certain chemical and/or thermal processes to improve the ductility. Mechanically deforming the castings to "modify" the shape of silicon has been shown by this research to be an effective alternative method to improve the spheroidization rate of eutectic silicon during heat treatment. The best …

Glass Formation And Properties In The Sm₂O₃·Al₂O₃·Sio₂ System, Erik M. Erbe

Masters Theses

"The purpose of this investigation was to develop a samarium containing aluminosilicate glass with properties suitable for use in the treatment of rheumatoid arthritis. Microspheres made from these compositions would be neutron activated to produce radioactive Sm-153 which has beta-particle energies suitable for treating rheumatoid arthritis as well as appropriate gamma-ray emission for nuclear imaging. The properties of Sm₂O₃ · AI₂O₃ · SiO₂ glasses containing 10 to 25 mole% Sm₂O₃ were evaluated as a function of composition. The density, refractive index, thermal expansion coefficient, and microhardness increased with increasing Sm …

The Effect Of Phosphate Additives On Alumina, Alumina-Calcia, Alumina-Silica Refractory Castable Systems, Sukendro Widjaja

Masters Theses

The effects of the addition of phosphate chemicals to Al₂O₃, Al₂O₃-CaO, and Al₂O₃-SiO₂ systems have been studied concentrating on selected dry and fired properties. The various refractories evaluated were formulated from all alumina aggregate systems based on 1) a mix of tabular and calcined fine aluminas, 2) a combination of calcium aluminate cement bonded-tabular and calcined fine aluminas, and 3) an alumina aggregate-silica fume mixture. Specimens were vibration-cast, dried at 110°C and fired at 1450°C. It was found that each system has different property responses to different …

Sessile Drop Studies Of Aluminum On Sapphire, Ke Wen K. Li

Masters Theses

A sessile drop technique employing a drop placement method has been used to investigate the wetting behavior and interfacial phenomena between aluminum and single crystal α-alumina. Measurements were made under a flowing mixture of H₂ and He atomsphere from 1200°C to 1600°C. Acute contact angles decreased continuously in all cases during the 8-hour experimental time. Neither the oxygen partial pressure of the flowing gas nor the orientation of the single crystal alumina substrate affected the contact angles, but the shapes of crystals grown at the substrate-metal interfaces were dependent on the orientation of the substrate surface to some extent. …

Processing And Characterization Of Ceramic Fiber Reinforced Porous Matrix Composites, Wen-Chiang Tu

Masters Theses

"The development of ceramic fiber reinforced ceramic matrix composites has been shown to be a promising approach for high toughness ceramic materials. The purpose of this work was to develop a new ceramic matrix composite(CMC) system based on a porous mullitic matrix reinforced with ceramic fibers. Unidirectional alligned fiber reinforced mullitic matrix composites were fabricated by a filament winding process. Prepregs were laminated and thermal processed in air. SEM fractographs of the composites were characterized and related to the observed load-deflection behaviors under 3-point flexure. The fracture surface expositions changed from extensive fiber tear-out to limited fiber pull-out as the …

Fabrication And Mechanical Property Analysis Of A Transparent, Glass Fiber Reinforced Polymer Matrix Composite, James R. Olson

Masters Theses

"A "transparent” composite was produced by reinforcing poly(methyl methacrylate) (PMMA) with unidirectional borosilicate glass fibers. Composites with 40 volume percent fiber had a modulus of rupture of 600 MPa which is six times greater than that of pure PMMA. Young's modulus for the same composite was 18 MPA which is nine times greater than the 2 MPa measured for pure PMMA. Work of fracture was 110 kJ/m² or more than double the 45 kJ/m² required to fracture pure PMMA. The optical transmission of the composite with 30 volume percent fiber was approximately 40 percent through a 10 mm …

The Effect Of Additives On Properties Of Pfn-Pfw Dielectric Materials, Weih-Min Liao

Masters Theses

"The purpose of this study was to investigate the effect of processing and additives on the properties of the Pb(Fe_1/2Nb_1/2)O₃-PB(Fe_2/3W_1/3)O₃ solid solutions. The basic composition was 70 m% Pb(Fe_1/2Nb_1/2)O₃ and 30 m% Pb(Fe_2/3W_1/3)O₃. The additives used were MnO, PbO and ZnNbO₆. Pressed compacts were sintered over the temperature range 900'C to 1050°C for 1 to 5 hours.

The influence of processing and composition on the properties was determined by measurement of density, shrinkage, dielectric constant, dissipation factor and …