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Surface and interface modification science and technology.

Description: Surface modification of solids is of scientific and technological interest due to its significant benefits in a wide variety of applications. Various coatings applications such as corrosion protection and electrical insulators and conductors are required for proper engineering design based on geometrical relationships between interfaces and on thermodynamic/kinetic considerations for the development of surface modifications. This paper will explore three basic examples: the proton conductor BaCeO{sub 3}, high-temperature protective coatings, and epitaxial relationships between interfaces.
Date: July 19, 1999
Creator: Park, J.-H.
Partner: UNT Libraries Government Documents Department

CaO insulator and Be intermetallic coatings on V-base alloys for liquid-lithium fusion blanket applications

Description: In the period of April 1, 1995 to June 30, 1995, a computational model for simulating particle motions turbulent flow condition is developed. The model was applied to the analysis of particle transport and deposition processes in a circular duct and in a plane recirculating region. The mean gas velocity and turbulence intensity fields were first estimated using the available experimental data, as well as those obtained from an earlier developed CFD code. A model for evaluating particle deposition rate in the presence of gravitational and electrical forces in turbulent flows was also formulated. Results concerning the deposition velocity of particles under various conditions were obtained. It was shown that the model predictions are in good agreement with the available experimental and digital simulation data. Experimental study of glass fiber transport and deposition rate is also initiated.
Date: August 1, 1995
Creator: Park, J.H. & Kassner, T.F.
Partner: UNT Libraries Government Documents Department

Fabrication of intermetallic coatings for electrical insulation and corrosion resistance on high-temperature alloys

Description: Several intermetallic films were applied to high-temperature alloys (V alloys and 304, 316 stainless steels) to provide electrical insulation and corrosion resistance. Alloy grain growth at 1000 C for the V-5Cr-5Ti alloy was investigated to determine stability of the alloy substrate during coating formation by CVD or metallic vapor processes at 800-850 C. Film layers were examined by optical and scanning electron microscopy and by electron-energy-dispersive and XRD analysis; they were also tested for electrical resistivity and corrosion resistance. Results elucidated the nature of the coatings, which provided both electrical insulation and high-temperature corrosion protection.
Date: November 1, 1996
Creator: Park, J.-H. & Cho, W.D.
Partner: UNT Libraries Government Documents Department

Insulator coating for high temperature alloys method for producing insulator coating for high temperature alloys

Description: A method for fabricating an electrically insulating coating on a surface is disclosed comprising coating the surface with a metal, and reacting the metal coated surface with a nonmetal so as to create a film on the metal-coated surface. Alternatively, the invention provides for a method for producing a noncorrosive, electrically insulating coating on a surface saturated with a nonmetal comprising supplying a molten fluid, dissolving a metal in the molten fluid to create a mixture, and contacting the mixture with the saturated surface. Lastly, the invention provides an electrically insulative coating comprising an underlying structural substrate coated with an oxide or nitride compound. This invention has applications to breeding blankets for fusion reactors as well as to alkali metal thermal to electric converters.
Date: December 31, 1994
Creator: Park, J.H.
Partner: UNT Libraries Government Documents Department

Self-healing of defects in CaO coatings on V-5%Cr-5%Ti in liquid lithium

Description: In-situ electrical resistance of CaO coatings produced on V-5%Cr-5%Ti by exposure of the alloy to liquid Li that contained 0.5-85 wt % dissolved Ca was measured as a function of time at temperatures between 250 and 600{degrees}C. Examination of the specimens after cooling to room temperature revealed no spallation, but homogeneous crazing cracks were present in the CaO coating. Additional tests to investigate the in-situ self-healing behavior of the cracks indicated that rapid healing occurred at >360{degrees}C.
Date: November 1, 1994
Creator: Park, J.H. & Kassner, T.F.
Partner: UNT Libraries Government Documents Department

Electrically insulating films deposited on V-4%Cr-4%Ti by reactive CVD

Description: In the design of liquid-metal blankets for magnetic fusion reactors, corrosion resistance of structural materials and the magnetohydrodynamic forces and their influence on thermal hydraulics and corrosion are major concerns. Electrically insulating CaO films deposited on V-4%Cr-4%Ti exhibit high-ohmic insulator behavior even though a small amount of vanadium from the alloy become incorporated into the film. However, when vanadium concentration in the film is > 15 wt.%, the film becomes conductive. When the vanadium concentration is high in localized areas, a calcium vanadate phase that exhibits semiconductor behavior can form. The objective of this study is to evaluate electrically insulating films that were deposited on V-4%Cr-4%Ti by a reactive chemical vapor deposition (CVD) method. To this end, CaO and Ca-V-O coatings were produced on vanadium alloys by CVD and by a metallic-vapor process to investigate the electrical resistance of the coatings. The authors found that the Ca-V-O films exhibited insulator behavior when the ratio of calcium concentration to vanadium concentration R in the film > 0.9, and semiconductor or conductor behavior when R < 0.8. However, in some cases, semiconductor behavior was observed when CaO-coated samples with R > 0.98 were exposed in liquid lithium. Based on these studies, they conclude that semiconductor behavior occurs if a conductive calcium vanadate phase is present in localized regions in the CaO coating.
Date: April 1, 1998
Creator: Park, J.H.
Partner: UNT Libraries Government Documents Department

Surface modification of high-temperature alloys: A protective and adhesive scale-forming process

Description: To develop a high-quality protective/adhesive scale-forming surface modification technique, several stepwise experiments were performed on the alloys of Fe-25Cr, Fe-25Cr-(0.3-1)Y, and Fe-25Cr-(O.3-1)Ce: alloy grain-growth behavior, surface coatings by ion-beam-assisted deposition (IBAD) and high-temperature chemical vapor deposition (CVD), and oxidation/sulfidation tests. Silicon-based oxide, nitride, and oxinitride coatings were prepared by IBAD. During annealing, the silicon diffuses into and reacts with the substrate to form a metal-silicide. To verify the scale-forming mechanism, oxidation tests (at temperatures of 700--1000{degrees}C and oxygen partial pressure of 10{sup {minus}4} atm) were performed on substrates with and without the coating layer. The results showed that Cr{sub 2}O{sub 3} was formed as the outer scale and that a thin SiO{sub 2} layer was observed at the alloy/scale interface. Based on these results, an alternative surface-modification approach was tried. A durable protective coating for high-temperature alloys was achieved by CVD followed by chemical reaction in a controlled environment. By thermogravimetric analysis with a microbalance, several oxidation/sulfidation tests (at 700 and 1000C) were performed with and without the coating on Fe-25Cr-1Ce and Fe-25Cr-1Y. After each run, samples were examined by scanning electron microscopy, energy-dispersive X-ray analysis, and Auger and X-ray photoelectron spectroscopy. The results elucidated the nature of the protective coating that provides high-temperature corrosion protection.
Date: December 31, 1995
Creator: Park, J.H. & Cho, W.D.
Partner: UNT Libraries Government Documents Department

CaO insulator coatings and self-healing of defects on V-Cr-Ti alloys in liquid lithium

Description: Electrically insulating and corrosion-resistant coatings are required at the liquid metal/structural interface in fusion first-wall/blanket applications. The electrical resistance of CaO coatings produced on V-5%Cr-5%Ti by exposure of the alloy to liquid Li that contained 0.5--85 wt.% dissolved Ca was measured as a function of time at temperatures between 250 and 600{degrees}C. The solute element, Ca in liquid Li, reacted with the alloy substrate at 400--420{degrees}C to produce a CaO coating. Resistance of the coating layer measured in-situ in liquid Li was {approx}10{sup 6} {Omega} at 400{degrees}C. Thermal cycling between 300 and 700{degrees}C changed the coating layer resistance. which followed insulator behavior. These results suggest that thin homogeneous coatings can be produced on variously shaped surfaces by controlling the exposure time, temperature, and composition of the liquid metal. The technique can be applied to various shapes(e.g., inside/outside of tubes, complex geometrical shapes) because the coating is formed by liquid-phase reaction. Examination of the specimens after cooling to room temperature revealed no spallation, but homogeneous crazing cracks were present in the CaO coating. Additional tests to investigate the in-situ self-healing behavior of the cracks indicated that rapid healing occurred at {ge}360{degrees}C.
Date: February 1996
Creator: Park, J. H. & Kassner, T. F.
Partner: UNT Libraries Government Documents Department

CaO insulator coatings and self-healing of defects on V-Cr-Ti alloys in liquid lithium system

Description: Electrically insulating and corrosion-resistant coatings are required at the liquid metal/structural interface in fusion first-wall/blanket applications. Electrical resistance of CaO coatings that were produced on V-5%Cr-5%Ti by exposure of the alloy to liquid Li containing 0.5-85 wt.% dissolved Ca was measured as a function of time at temperatures between 250 and 600{degrees}C. The solute element, Ca in liquid Li, reacted with the alloy substrate at 400-420{degrees}C to produce a CaO coating. Resistance of the coating layer measured in-situ in liquid Li was {approx}10{sup 6} {Omega} at 400{degrees}C. Thermal cycling between 300 and 700{degrees}C changed the coating layer resistance, which followed insulator behavior. These results suggest that thin homogeneous coatings can be produced on variously shaped surfaces by controlling the exposure time, temperature, and composition of the liquid metal. The technique can be applied to various shapes (e.g., inside/outside of tubes, complex geometrical shapes) because the coating is formed by liquid-phase reaction. Examination of the specimens after cooling to room temperature revealed no spallation, but homogeneous crazing cracks were present in the CaO coating. Additional tests to investigate the in-situ self-healing behavior of the cracks indicated that rapid healing occurred at {>=}360{degrees}C.
Date: September 1, 1995
Creator: Park, J.H. & Kassner, T.F.
Partner: UNT Libraries Government Documents Department

Fabrication of intermetallic coatings for electrical and corrosion resistance on high-temperature alloys

Description: Several intermetallic films were fabricated to high-temperature alloys (V-alloys and 304 and 316 stainless steels) to provide electrical insulation and corrosion resistance. Alloy grain-growth behavior at 1000{degrees}C for the V-5Cr-5Ti was investigated to determine the stability of alloy substrate during coating formation by chemical vapor deposition (CVD) or metallic vapor processes at 800-850{degrees}C. Film layers were examined by optical and scanning electron microscopy and by electron-energy-dispersive and X-ray diffraction analysis and tested for electrical resistivity and corrosion resistance. The results elucidated the nature of the coatings, which provided both electrical insulation and high-temperature corrosion protection.
Date: October 1, 1994
Creator: Park, J.H. & Cho, W.D.
Partner: UNT Libraries Government Documents Department

Oxidation behavior of iron-chromium alloys at elevated temperatures: A reactive-element effect

Description: Oxidation tests were conducted on samples of Fe-25Cr, Fe-25Cr,-0.3-1.0Y, and Fe-25Cr-1Ce at temperatures of 700 to 1000{degrees}C and oxygen partial pressures of 1 to 20 atm for time periods of 19 to 160 h. In some tests, oxidized samples were quenched from test temperature to room temperature in {approximately}20 min to examine characteristics of the spallation scales. The results showed that the scales, even though of the same composition, spalled totally when developed on Fe-25Cr alloy, while those on Ce- and Y-containing alloys exhibited good scale adherence and no spallation. After removal of the spalled scales, specimens of Fe-25Cr alloy were reoxidized to gain insight into development and morphology of thermally grown scales and their spallation characteristics. The reoxidized samples formed complex scale layers that had iron oxide phase at the gas side of the interface; the scale layer was adherent and no spallation was noted. Experiments were conducted to evaluate the roles of alloy grain size and grain growth rate in development and spallation of oxide scales. Results showed that excessive alloy grain growth is the primary cause of spallation of thermally grown scales. Additions of reactive elements such as Y and Ce minimize alloy grain growth and thus improve the adhesion of scales to the substrate and virtually eliminate spallation.
Date: March 1, 1992
Creator: Park, J.H. & Natesan, K.
Partner: UNT Libraries Government Documents Department

Oxidation/sulfidation behavior of Fe-Cr alloys: A reactive-element effect

Description: Corrosion resistance of a number of structural alloys in high-temperature environments is achieved by the formation of a continuous chromium oxide scale. Research on high-temperature corrosion of structural alloys has been in progress to reduce the rate of oxidation, improve the adhesion of oxide scale to the substrate alloy, and to stabilize the oxide scale against other corrosive agents such as sulfur, chlorine, alkalies, and ash/sorbent deposits. Extensive research is being conducted at Argonne National Laboratory to (1) evaluate mechanisms of oxidation, sulfidation, and break-away corrosion of chromia- and alumina-forming alloys exposed to mixed-gas atmospheres that span a wide range of oxygen, sulfur, and chlorine activities typical of combustion and gasification systems; (2) develop an understanding of the role of several microalloy constituents (e.g., Zr, Nb, Y, Ce, V) in oxidation/sulfidation processes and scale breakdown; (3) characterize the physical, chemical and mechanical properties of surface scales that are resistant to sulfidation attack; and (4) evaluate the role of deposits, such as alkali sulfates, alkali chlorides, ash, and sulfur sorbents, in the corrosion behavior or metallic alloys, selected coatings, and ceramic materials.
Date: April 1, 1992
Creator: Natesan, K. & Park, J.H.
Partner: UNT Libraries Government Documents Department

Electronic/ionic conductivity and oxygen diffusion coefficient of Sr-Fe-Co-O system

Description: Oxides in the system Sr-Fe-Co-O exhibit both electronic and ionic conductivities. Recently, Sr-Fe-Co-O system attracted great attention because of the potential to be used for oxygen permeable membranes that can operate without the electrodes or external electrical circuitry. Electronic and ionic conductivities at various temperatures have been measured on two compositions in Sr-Fe-Co-O system named SFC-1 and SFC-2. The electronic transference number is much greater than the ionic transference number in SFC-1 sample, while the electronic and ionic transference numbers are very close in SFC-2 sample. At 800{degrees}C, the electronic conductivity and ionic conductivity are {approx}76 S{center_dot}cm-1 and =4 S-cm-1, respectively, for SFC-1. While, for SFC-2, the electronic and ionic conductivities are =10 S-cm-1 and {approx}7 S-cm-1, respectively. By a local fitting to {sigma}{center_dot}T = A exp(-E{sub {alpha}}/{kappa}{Tau}), we found that the oxide ion activation energies are 0.92 eV and 0.37 eV respectively for SFC-1 and SFC-2 samples. Oxygen diffusion coefficient of SFC-2 is {approx}{times}10{sup {minus}7} cm{sup 2}/sec at 900C.
Date: March 1, 1995
Creator: Ma, B.; Park, J.H.; Balachandran, U. & Segre, C.U.
Partner: UNT Libraries Government Documents Department

Electrical properties and defect structure in the Sr-Fe-Co-O system

Description: The ceramic Sr-Fe-Co-O has potential use as a membrane in gas separation. This material exhibits high conductivity of both electrons and oxygen ions. It allows oxygen to penetrate at high flux rates without other gas components. Electrical properties are essential to understanding the oxygen transport mechanism and defect structure of this material. By using a gas-tight electrochemical cell with flowing air as the reference environment, we were able to achieve an oxygen partial pressure ({sub p}O{sub 2}) as low as 10{sup -16} atm. Total and ionic conductivities of Sr-Fe-Co-O have been studied as a function of {sub p}O{sub 2} at elevated temperature. In air, both total and ionic conductivities increase with temperature, while the ionic transference number is almost independent of temperature, with a value of {approx}0.4. Experimental results show that ionic conductivity decreases with decreasing {sub p}O{sub 2} at high {sub p}O{sub 2} ({ge}10{sup -6} atm). This suggests that interstitial oxygen ions and electron holes are the dominant charge carriers. At 800{degrees}C in air, total conductivity and ionic conductivity are 17 and 7 S/cm, respectively. Defect dynamics in this system can be understood by means of the trivalence-to-divalence transition of Fe ions when {sub p}O{sub 2} is reduced. By using the conductivity results, we estimated oxygen permeation through a ceramic membrane made of this material. The calculated oxygen permeability agrees with the experimental value obtained directly from an operating methane conversion reactor.
Date: November 1, 1995
Creator: Ma, B.; Chao, C.C. & Park, J.H.
Partner: UNT Libraries Government Documents Department

Use of high-temperature gas-tight electrochemical cells to measure electronic transport and thermodynamics in metal oxides

Description: By using a gas-tight electrochemical cell, the authors can perform high-temperature coulometric titration and measure electronic transport properties to determine the electronic defect structure of metal oxides. This technique reduces the time and expense required for conventional thermogravimetric measurements. The components of the gas-tight coulometric titration cell are an oxygen sensor, Pt/yttria stabilized zirconia (YSZ)/Pt, and an encapsulated metal oxide sample. Based on cell design, both transport and thermodynamic measurements can be performed over a wide range of oxygen partial pressures (pO{sub 2} = 10{sup {minus}35} to 1 atm). This paper describes the high-temperature gas-tight electrochemical cells used to determine electronic defect structures and transport properties for pure and doped-oxide systems, such as YSZ, doped and pure ceria (Ca-CeO{sub 2} and CeO{sub 2}), copper oxides, and copper-oxide-based ceramic superconductors, transition metal oxides, SrFeCo{sub 0.5}O{sub x}, and BaTiO{sub 3}.
Date: October 1, 1997
Creator: Park, J.H.; Ma, B. & Park, E.T.
Partner: UNT Libraries Government Documents Department

Pressure effect on ionic conductivity in yttrium-oxide-doped single-crystal zirconium oxide

Description: In this study, the authors investigated the effect of pressure on the ionic conductivity of a 9.5 mol% yttria-stabilized zirconia (YSZ) single crystal. The experiment was conducted in the elastic region, and the oxygen ion transport number was unity (t{sub ion} > 0.99999). A conventional four-probe DC method was used to measure the ionic conductivity of the rectangular-shaped sample under uniaxial pressures up to 600 atm at 750 C in air. Measured ionic conductivity decreased as applied pressure increased. Based on henry Eyring`s absolute reaction rate theory, which states that the calculated activation volume has a positive value ({Delta}V{sup 2} = 2.08 cm{sup 3}/mol of O{sup {minus}2}) for oxygen ion transport in the fluoride cubic lattice, they concluded that the results they obtained could be explained by an oxygen ion transport mechanism. This mechanism can explain the fact that the interionic distance increases during oxygen ion transport from one unit cell to neighboring unit cells.
Date: June 1, 1998
Creator: Park, E.T. & Park, J.H.
Partner: UNT Libraries Government Documents Department

Mechanical properties of, and phase transformation in, V-Cr-Ti-O solid solutions

Description: Incorporation of O in the surface of V-Ti-Cr alloys has been investigated in controlled environments at 550-750{degrees}C. and tests were performed to determine the physical properties of V-Cr-Ti-O solid solutions. The amount of O in the alloys has been determined by weight-change measurements. Microhardness was used to determine O depth profiles in the alloys. X-ray, diffraction indicated a phase transformation from body-centered-cubic (bcc) to tetragonal in the highly stressed lattice because of O incorporation. Cr depletion was observed near alloy grain boundaries, based on back-scattered-electron images and electron-energy-dispersive spectra. Elastic modulus and Vickers hardness also increased in O-enriched V-Cr-Ti alloys. Hardening in the alloys results from O atoms on face-centered interstitial sites in the bcc sublattice and the formation of very fine coherent oxide particles. O or N diffusion occurs via the interstitial sublattice of the bcc V-base alloys and is accompanied by the formation of homogeneous oxide or nitride phases via internal oxidation or nitridation. The O,N-enriched surface region exhibited the extraordinarily high Vickers hardness of -18 GPa (1800 kg/mm{sup 2}). A value typical of oxides, nitrides, or carbides, or obtainable by ion-beam irradiation of metals.
Date: November 1, 1995
Creator: Park, J.H.; Kuppermann, D. & Park, E.T.
Partner: UNT Libraries Government Documents Department

Hydrogen transport and embrittlement for palladium coated vanadium-chromium-titanium alloys

Description: Vanadium based alloys have been identified as a leading candidate material for fusion first-wall blanket structure application because they exhibit favorable safety and environmental characteristics, good fabricability, potential for high performance and long-time operation lifetime in a fusion environment. As part of a study of the thermodynamics, kinetics and embrittlement properties of hydrogen in vanadium based alloys, experiments were conducted to determine the rate of hydrogen transport through the vanadium reference alloys, V-7.5Cr-15Ti and V-4Cr-4Ti, and to determine these alloys` hydrogen embrittlement, they were exposed to hydrogen pressures of 3 and 300 kPa (0.03--3 atm) at temperatures between 380 and 475 C. To facilitate hydrogen entry and egress, tubes of these alloys were coated with palladium on the inside and outside faces. Observed permeabilities were 0.015 to 0.065 {micro}moles/(m{sup 2}sPa{sup 0.5}) for the V-7.5Cr-15Ti alloy and 0.02 to 0.05 {micro}moles/m{sup 2}sPa{sup 0.5} for the V-4Cr-4Ti alloy depending on the quality of the coat and the operating temperature. At 1.7 atm hydrogen, V-7.5Cr-15Ti embrittled at temperatures below 380 C while V-4Cr-4Ti embrittled around 330 C.
Date: September 1, 1995
Creator: Buxbaum, R.E.; Subramanian, R.; Park, J.H. & Smith, D.L.
Partner: UNT Libraries Government Documents Department

Electronic Transport Properties in Copper Oxides

Description: Oxidation of copper and electronic transport in thermally grown large-grain poly-crystals of non-stoichiometric copper oxides were studied at elevated temperatures. Thermogravimetric copper oxidation was studied in air and oxygen at temperatures between 350 and 100 C. From the temperature-dependence of oxidation rates, three different processes can be identified for the oxidation of copper: bulk diffusion, grain-boundary diffusion, and surface control with whisker growth; these occur at high, intermediate, and low temperatures, respectively. Electrical conductivity measurements as a function of temperature (350 - 1134 C) and pO2 (10(sup⁻⁸-1.0 atm) indicated intrinsic electronic conduction in CuO over the entire range of conditions. Electronic behavior of non-stoichiometric Cu(sub 2)O indicates that the charge defects are doubly ionized oxygen interstitials and holes. The calculated enthalpy of formation of oxygen ((Delta)H(sub O(sub 2))) and the hole conduction energy (E(sub H)) at constant composition for non-stoichiometric Cu2O are 2.0 (plus minus) 0.2 eV and 0.82 (plus minus) 0.02 eV, respectively.
Date: July 1991
Creator: Park, J.-H. & Natesan, K.
Partner: UNT Libraries Government Documents Department

Korea Research Reactor -1 & 2 Decommissioning Project in Korea

Description: Korea Research Reactor 1 (KRR-1), the first research reactor in Korea, has been operated since 1962, and the second one, Korea Research Reactor 2 (KRR-2) since 1972. The operation of both of them was phased out in 1995 due to their lifetime and operation of the new and more powerful research reactor, HANARO (High-flux Advanced Neutron Application Reactor; 30MW). Both are TRIGA Pool type reactors in which the cores are small self-contained units sitting in tanks filled with cooling water. The KRR-1 is a TRIGA Mark II, which could operate at a level of up to 250 kW. The second one, the KRR-2 is a TRIGA Mark III, which could operate at a level of up 2,000 kW. The decontamination and decommissioning (D & D) project of these two research reactors, the first D & D project in Korea, was started in January 1997 and will be completed to stage 3 by 2008. The aim of this decommissioning program is to decommission the KRR-1 & 2 reactors and to decontaminate the residual building structure s and the site to release them as unrestricted areas. KAERI (Korea Atomic Energy Research Institute) submitted the decommissioning plan and the environmental impact assessment reports to the Ministry of Science and Technology (MOST) for the license in December 1998, and was approved in November 2000.
Date: February 24, 2003
Creator: Park, S. K.; Chung, U. S.; Jung, K. J. & Park, J. H.
Partner: UNT Libraries Government Documents Department

Defect structure of the mixed-conducting Sr-Fe-Co-O system

Description: Electrical conductivity of the mixed-conducting Sr-Fe-Co-O system was investigated at high temperatures and various oxygen partial pressures (pO2). The system exhibits not only high combined electrical and oxygen ionic conductivities but also structural stability in both oxidizing and reducing environments. Conductivity of SrFeCo{sub 0.5}O{sub x} increases with temperature and pO2, within the experiment pO2 range (1-10{sup -18} atm). p-type conduction was observed, the activity energy of which decreases with pO2. A model of the defect chemistry in the Sr-Fe-Co-O system is proposed. The pO2- dependent conducting behavior can be understood by considering the trivalent-to-divalent transition of the transition metal ions in the system.
Date: November 1, 1996
Creator: Ma, B.; Balachandran, U.; Chao, C.-C. & Park, J.-H.
Partner: UNT Libraries Government Documents Department