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Articles 871 - 900 of 1011

Full-Text Articles in Materials Science and Engineering

High-Temperature Defect Structure Of Nb-Doped Lacro3, Chikung J. Yu, Harlan U. Anderson, Don M. Sparlin Jan 1989

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 LaCr0.98Nb0.02CrO3 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.

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

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Oxidation-Reduction Behavior Of Undoped And Sr-Doped Lamno3 Nonstoichiometry And Defect Structure, J. H. Kuo, Harlan U. Anderson, Don M. Sparlin Jan 1989

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 …

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Glass Microspheres, D. E. Day, Gary J. Ehrhardt Dec 1988

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.

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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 Aug 1988

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, In0.1Y0.9Ba2Cu3O9-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 …

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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. Apr 1988

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 …

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South East Missouri Lead Belt - A Review 1987, Johh L. Watson Jan 1988

South East Missouri Lead Belt - A Review 1987, Johh L. Watson

Materials Science and Engineering Faculty Research & Creative Works

The south-east Missouri Lead Belt is, and has been for many years, a major world producer of lead concentrate. This paper reviews the current mill operations in the area and presents detailed information on equipment, operating parameters and metallurgical performance. © 1988.

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Microstructural Analysis In Processing Of The High‐Tc Superconductor Ba2ycu3o7‐X In Air, Jyoti P. Guha Jan 1988

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 Ba2YCu3O7‐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 Ba2YCu3O7‐x–BaCuO2–CuO. The implication of this finding for the processing of Ba2YCu3O7‐x is discussed. Copyright © 1988, Wiley Blackwell. All rights reserved.

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Sealing Glasses For Titanium And Titanium Alloys, Richard K. Brow, R. D. Watkins Jan 1988

Sealing Glasses For Titanium And Titanium Alloys, Richard K. Brow, R. D. Watkins

Materials Science and Engineering Faculty Research & Creative Works

Glass compositions containing calcium oxide, alumina, boric oxide, strontium oxide and barium oxide in various mole % combinations were studied. These compositions are capable of forming stable glass to metal seals with titanium and titanium alloys for use as seals for battery headers.

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Comments On A Paper By No, Esnouf, San Juan, And Fontozzi, Hollis P. Leighly Jan 1988

Comments On A Paper By No, Esnouf, San Juan, And Fontozzi, Hollis P. Leighly

Materials Science and Engineering Faculty Research & Creative Works

No abstract provided.

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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 Jan 1988

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[(Mg1/3Nb2/3)0.92Ti0.08]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 …

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Nucleation And Growth Of Zinc Electrodeposited From Acidic Zinc Solutions, A. C. Beshore, B. J. Flori, G. Schade, Thomas J. O'Keefe Jul 1987

Nucleation And Growth Of Zinc Electrodeposited From Acidic Zinc Solutions, A. C. Beshore, B. J. Flori, G. Schade, Thomas J. O'Keefe

Materials Science and Engineering Faculty Research & Creative Works

The nucleation and initial crystal growth kinetics by electrodeposition from acidic zinc solutions was studied in the absence and presence of antimony and glue on a glassy carbon electrode. Zinc exhibits instantaneous nucleation under the experimental conditions employed in the potential region from -1600 to -2000 mV (mercurous sulphate reference). At low overpotentials antimony and glue increase the number of nuclei. © 1987 Chapman and Hall Ltd.

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Calculation Of Mass Transfer Coefficients In Metal Deposition Using Electrochemical Tracer Techniques, Thomas J. O'Keefe, J. S. Cuzmar, S. F. Chen Jan 1987

Calculation Of Mass Transfer Coefficients In Metal Deposition Using Electrochemical Tracer Techniques, Thomas J. O'Keefe, J. S. Cuzmar, S. F. Chen

Materials Science and Engineering Faculty Research & Creative Works

A modification of the tracer technique of Ettel has been developed for determining mass-transfer coefficients in electrolytes for both electrowinning and electrorefining systems. The method involves the direct measurement of the limiting current density of a more noble tracer ion at low concentration by cyclic voltammetry techniques in an electrolyte of choice. A Ag+tracer in acid copper sulfate is used as the example. Additional tests were made by code positing the tracer with copper to compare the results of the two methods. The effect of copper ion concentration and temperature on the electrochemical and transport properties of the solution were …

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Microstructural Inhomogeneity In Sintered Pb(Mg1/3nb2/3)O3‐Pbtio3 Based Dielectrics, Jyoti P. Guha, Harlan U. Anderson Jan 1987

Microstructural Inhomogeneity In Sintered Pb(Mg1/3nb2/3)O3‐Pbtio3 Based Dielectrics, Jyoti P. Guha, Harlan U. Anderson

Materials Science and Engineering Faculty Research & Creative Works

The sintering behavior and microstructural development of dielectric ceramics based on Pb(Mg1/3Nb2/3)O3‐PbTiO3 solid solutions are greatly affected by the formation of a liquid phase at ∼ 1290°C. Prolonged sintering at and above this temperature gives rise to an excessive PbO loss and the resultant variation in composition leads to an inhomogeneous microstructure. The inhomogeneity is characterized by the formation of a dense, localized region containing a PbO‐rich liquid near the surface with a porous interior region in the bulk of the sample. Copyright © 1987, Wiley Blackwell. All rights reserved

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The Mg-Sb System, A. A. Nayeb-Hashemi, J. Beverley Clark Dec 1986

The Mg-Sb System, A. A. Nayeb-Hashemi, J. Beverley Clark

Materials Science and Engineering Faculty Research & Creative Works

No abstract provided.

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Discussion Of "Lime-Enhanced Reduction Of Sulfide Concentrates: A Thermodynamic Discussion", Arthur E. Morris, Harry Flynn Dec 1986

Discussion Of "Lime-Enhanced Reduction Of Sulfide Concentrates: A Thermodynamic Discussion", Arthur E. Morris, Harry Flynn

Materials Science and Engineering Faculty Research & Creative Works

No abstract provided.

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Electrochemical Monitoring Of Electrogalvanizing Solutions, Thomas J. O'Keefe, S. F. Chen, E. R. Cole, M. Dattilo Nov 1986

Electrochemical Monitoring Of Electrogalvanizing Solutions, Thomas J. O'Keefe, S. F. Chen, E. R. Cole, M. Dattilo

Materials Science and Engineering Faculty Research & Creative Works

The corrosion resistance of steel is vastly improved when a zinc cathodic protective layer is applied. In recent years there has been renewed interest in producing this galvanized coating electrolytically. As with many deposition processes, the control of the operating parameters is very important in order to produce good quality zinc coatings. The homogeneity, ductility and smoothness of the zinc layer are critical. These factors are usually influenced by the electrochemical nature of the solution and organic additives are often used to assist in control. Studies on the polarization behavior of solutions for electro galvanizing electrolytes were made. Cyclic voltammetry …

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Reply, Paul W. Angel, Chandra S. Ray, Delbert E. Day Jan 1986

Reply, Paul W. Angel, Chandra S. Ray, Delbert E. Day

Materials Science and Engineering Faculty Research & Creative Works

No abstract provided.

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Preparation Of Perovskite Pb(Mg1/3nb2/3)03 Using Pb3nb208 And Mgo, Jyoti P. Guha, Harlan U. Anderson Jan 1986

Preparation Of Perovskite Pb(Mg1/3nb2/3)03 Using Pb3nb208 And Mgo, Jyoti P. Guha, Harlan U. Anderson

Materials Science and Engineering Faculty Research & Creative Works

The synthesis of perovskite Pb(Mg1/3Nb2/3)O3 from an equimolar mixture of Pb3Nb208 and MgO was studied by solid‐state reaction techniques. An addition of 1 wt% excess MgO to the stoichiometric composition enhances the formation of the cubic perovskite phase. The absence of free PbO in the initial starting materials minimizes the volatilization loss during firing, thereby reducing the possibility of any compositional change and resulting in a substantial improvement of the perovskite phase purity over the conventional mixed‐oxide processing. Copyright © 1986, Wiley Blackwell. All rights reserved

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Tspc/Dc Measurements On Barium Titanate, Harlan U. Anderson, Wayne Huebner Jan 1986

Tspc/Dc Measurements On Barium Titanate, Harlan U. Anderson, Wayne Huebner

Materials Science and Engineering Faculty Research & Creative Works

Thermally-stimlated polarization / depolarization current (TSPC / DC) measurements were made on high-purity doped and undopod BaTiO3 as a function of applied field, heating rate, dopant level, and Ba:Ti ratio. The form of the TSPC/DC curves is dependent upon both the resistive and ferroelectric properties of BaTiO3. For TSPC spectra, current peaks are exhibited due to the change in in magnitude and direction of the spontaneous polarization with changing crystal structure. In particular, whether the phase transition is first or seoond order influsnaes the existence and magnitude of the current peaks. TSDC measurements are essentially dynamic pyroelectric measurements and as …

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Reaction During Sintering Of Barium Titanate With Lithium Fluoride, Jyoti P. Guha, Harlan U. Anderson Jan 1986

Reaction During Sintering Of Barium Titanate With Lithium Fluoride, Jyoti P. Guha, Harlan U. Anderson

Materials Science and Engineering Faculty Research & Creative Works

The reactions occurring during sintering of stoichiometric BaTiO3 with small additions of LiF were studied at temperatures between 700° and 900°C. BaTiO3 reacts with LiF to form a cubic solid solution and Li2TiO3 During sintering, the cubic solid solution coexists with Li2Ti03 and forms a liquid phase at 740°± 5°C. The occurrence of a liquid phase at this temperature results in an enhancement of the sintering process and leads to the development of a highly dense microstructure. Copyright © 1986, Wiley Blackwell. All rights reserved

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Glass Experiments In Space, Norbert J. Kreidl Jan 1986

Glass Experiments In Space, Norbert J. Kreidl

Materials Science and Engineering Faculty Research & Creative Works

Current and potential glass research under microgravity includes studies of minimum cooling rate, homogeneous nucleation, diffusion, surface tension and enrichment, fining without buoyancy, avoidance of liquid phase separation, gel synthesis, composites and uniform micro balloons. The experiments do not just anticipate space fabrication but will also provide information and innovation encouraging advanced processing on earth. © 1986.

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High-Temperature Redox Behavior Of Doped Srtio3 And Lacro3, Harlan U. Anderson, M. M. Nasrallah, B. K. Flandermeyer, A. K. Agarwal Mar 1985

High-Temperature Redox Behavior Of Doped Srtio3 And Lacro3, Harlan U. Anderson, M. M. Nasrallah, B. K. Flandermeyer, A. K. Agarwal

Materials Science and Engineering Faculty Research & Creative Works

The stability of high-temperature fuel cell electrodes to their ambient environment is important for the long-term reliability of fuel cells. In this report the behavior of oxide electrode materials as a function of oxygen activity and temperature is considered. Models for the oxidation-reduction behavior of both p- and n-type oxides are presented. These models take into account the absorption and evolution of oxygen which take place as oxygen activity is varied. The resulting instability in electrical conductivity is explained as a consequence of changes in carrier concentration due to variability in ionic defect concentration. The proposed models are applied to …

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Comment On “Dielectric Properties Of Lead‐Magnesium Niobate Ceramics”, Jyoti P. Guha Jan 1985

Comment On “Dielectric Properties Of Lead‐Magnesium Niobate Ceramics”, Jyoti P. Guha

Materials Science and Engineering Faculty Research & Creative Works

No abstract provided.

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Feasibility Study Of Fabricating Composite Ceramic Chamber Liners For Small Caliber Automatic Weapons, P. D. Ownby, D. V. Stewart Jan 1985

Feasibility Study Of Fabricating Composite Ceramic Chamber Liners For Small Caliber Automatic Weapons, P. D. Ownby, D. V. Stewart

Materials Science and Engineering Faculty Research & Creative Works

No abstract provided.

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Screening Design Test For Cyclic Voltammetric Evaluation Of Zinc Sulfate Electrolyte, R. K. Singh, Thomas J. O'Keefe Jan 1985

Screening Design Test For Cyclic Voltammetric Evaluation Of Zinc Sulfate Electrolyte, R. K. Singh, Thomas J. O'Keefe

Materials Science and Engineering Faculty Research & Creative Works

A statistical screening design program was conducted to determine the effects of certain operating parameters in the cyclic voltametric evaluation of zinc sulfate electrolyte. The variables studied included solution temperature, sulfuric acid and zinc concentrations, and scan rate. Solution temperature was found to be the most significant factor affecting the initial potential, followed by scan rate and zinc concentration. Based on screening design data, mathematical equations were developed to predict polarization behavior of addition-free zinc sulfate electrolytes. A few preliminary tests on the effect of impurities and organic additives, such as Sb(III) and glue, on potential, deposit morphology, and crystal …

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The Oxidation Of Dilute Alloys Of Magnesium In Aluminium, Hollis P. Leighly, A. Alam Dec 1984

The Oxidation Of Dilute Alloys Of Magnesium In Aluminium, Hollis P. Leighly, A. Alam

Materials Science and Engineering Faculty Research & Creative Works

The oxide layers developed during the oxidation of aluminum alloys containing 500 and 1000 PPM of magnesium at 850K were examined with the aid of electron spectroscopy for chemical analysis. The magnesium content of the oxide layers was relatively high because of the preferential depletion of the magnesium atoms from the base alloys. Near the outer surfaces of the oxide layers, spinel (MgAl2O4) was the predominant magnesium-bearing compound. At depth, MgO was more dominant. The preferential depletion of magnesium from the alloys injected vacancies into the material. This led to the formation of defect clusters. The presence of these defect …

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Oxygen Activity Dependence Of The Defect Structure Of La-Doped Batio3, M. M. Nasrallah, Harlan U. Anderson, A. K. Agarwal, B. F. Flandermeyer Oct 1984

Oxygen Activity Dependence Of The Defect Structure Of La-Doped Batio3, M. M. Nasrallah, Harlan U. Anderson, A. K. Agarwal, B. F. Flandermeyer

Materials Science and Engineering Faculty Research & Creative Works

A model for the behavior of donor doped BaTiO3 as a function of oxygen activity is proposed. Thermogravimetric measurements show good agreement with the proposed model. The results show that donor-doped BaTiO3 is stoichiometric with electronic compensation of the donor at low oxygen activity, but with increasing oxygen activity, compensation becomes ionic as excess oxygen is absorbed. The possible compensation mechanisms are discussed. © 1984 Chapman and Hall Ltd.

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Oxidation-Reduction Behaviour Of La-Doped Srtio3, B. F. Flandermeyer, A. K. Agarwal, Harlan U. Anderson, M. M. Nasrallah Aug 1984

Oxidation-Reduction Behaviour Of La-Doped Srtio3, B. F. Flandermeyer, A. K. Agarwal, Harlan U. Anderson, M. M. Nasrallah

Materials Science and Engineering Faculty Research & Creative Works

Thermogravimetric measurements as a function of oxygen activity were performed in the temperature range of 1200 to 1400° C on a series of lanthanum SrTiO3 compounds. A model which assumes the absorption of excess oxygen in the structure which compensates the donors by formation of cationic defects is postulated. Comparison of this model with the experimental results show reasonable agreement. © 1984 Chapman and Hall Ltd.

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Oxygen Activity Dependence Of The Electrical Conductivity Of Li‐Doped Cr2o3, R. F. Huang, A. K. Agarwal, Harlan U. Anderson Jan 1984

Oxygen Activity Dependence Of The Electrical Conductivity Of Li‐Doped Cr2o3, R. F. Huang, A. K. Agarwal, Harlan U. Anderson

Materials Science and Engineering Faculty Research & Creative Works

The electrical conductivity of Li‐doped Cr2O3 was investigated as a function of PO2, temperature, and dopant content. Results show that the electrical conductivity remains almost unchanged with decreasing P O2 in the high‐P O2 region but decreases rapidly at low P O2. A second phase was found in samples which contained more than 0.85 mol% Li. The results are explained by a model in which the concentration of charge carriers is dependent on the acceptor dopant and oxygen vacancy concentration. Copyright © 1984, Wiley Blackwell. All rights reserved

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