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DEVELOPMENT OF TITANIUM NITRIDE/MOLYBDENUM DISULPHIDE COMPOSITE TRIBOLOGICAL COATINGS FOR CRYOCOOLERS
Title
DEVELOPMENT OF TITANIUM NITRIDE/MOLYBDENUM DISULPHIDE COMPOSITE TRIBOLOGICAL COATINGS FOR CRYOCOOLERS.
Creator
Pai, Anil, Dhere, Neelkanth, University of Central Florida
Abstract / Description
Hydrogen is a clean and sustainable form of carrier of energy that can be used in mobile and stationary applications. At present hydrogen is produced mostly from fossil sources. Solar photoelectrochemical processes are being developed for hydrogen production. Storing hydrogen can be done in three main ways: in compressed form, liquid form and by chemical bonding. Near term spaceport operations are one of the prominent applications for usage of large quantities of liquid hydrogen as a...
Show moreHydrogen is a clean and sustainable form of carrier of energy that can be used in mobile and stationary applications. At present hydrogen is produced mostly from fossil sources. Solar photoelectrochemical processes are being developed for hydrogen production. Storing hydrogen can be done in three main ways: in compressed form, liquid form and by chemical bonding. Near term spaceport operations are one of the prominent applications for usage of large quantities of liquid hydrogen as a cryogenic propellant. Efficient storage and transfer of liquid hydrogen is essential for reducing the launch costs. A Two Stage Reverse Turbo Brayton Cycle (RTBC) CryoCooler is being developed at University of Central Florida. The cryocooler will be used for storage and transport of hydrogen in spaceport and space vehicle application. One part in development of the cryocooler is to reduce the friction and wear between mating parts thus increasing its efficiency. Tribological coatings having extremely high hardness, ultra-low coefficient of friction, and high durability at temperatures lower than 60 K are being developed to reduce friction and wear between the mating parts of the cryocooler thus improving its efficiency. Nitrides of high-melting-point metals (e.g. TiN, ZrN) and diamond-like-carbon (DLC) are potential candidates for cryogenic applications as these coatings have shown good friction behavior and wear resistance at cryogenic temperatures. These coatings are known to have coefficient of friction less than 0.1 at room temperature. However, cryogenic environment leads to increase in the coefficient of friction. It is expected that a composite consisting of a base layer of a hard coating covered with layer having an ultra-low coefficient of friction would provide better performance. Extremely hard and extremely low friction coatings of titanium nitride, molybdenum disulphide, TiN/MoS2 bilayer coatings, DLC and DLC/MoS2 bilayer coatings have been chosen for this application. TiN film was deposited by reactive DC magnetron sputtering system from a titanium target and MoS2 film was deposited by RF magnetron sputtering using a MoS2 target. Microwave assisted chemical vapor deposition (MWCVD) technique was used for preparation of DLC coatings. These composite coatings contain a solid lubricating phase and a hard ceramic matrix phase as distinctly segregated phases. These are envisioned as having the desired combination of lubricity and structural integrity. Extremely hard coatings of TiN and DLC were chosen to provide good wear resistance and MoS2 was chosen as the lubricating phase as it provides excellent solid lubricating properties due to its lamellar crystal structure. This thesis presents preparation; characterization (SEM and XRD), microhardness and tribological measurements carried out on TiN and TiN/MoS2 coatings on aluminum and glass substrate at room temperature. It also presents initial development in preparation of DLC coatings.
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Date Issued
2004
Identifier
CFE0000326, ucf:46305
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0000326
PREPARATION OF EFFICIENT CUIN1-XGAXSE2-YSY/CDS THIN-FILM SOLAR CELLS BY OPTIMIZING THE MOLYBDENUM BACK CONTACT AND USING DIETHYLSELENIDE AS SELENIUM PRECURSOR
Title
PREPARATION OF EFFICIENT CUIN1-XGAXSE2-YSY/CDS THIN-FILM SOLAR CELLS BY OPTIMIZING THE MOLYBDENUM BACK CONTACT AND USING DIETHYLSELENIDE AS SELENIUM PRECURSOR.
Creator
Kadam, Ankur, Dhere, Neelkanth, University of Central Florida
Abstract / Description
High efficiency CuIn1-xGaxSe2-ySy (CIGSS)/CdS thin-film solar cells were prepared by optimizing the Mo back contact layer and optimizing the parameters for preparing CIGSS absorber layer using diethylselenide as selenium source. The Mo film was sputter deposited on 2.5 cm x 10 cm soda-lime glass using DC magnetron sputtering for studying the adhesion and chemical reactivity with selenium and sulfur containing gas at maximum film growth temperature. Mo being a refractory material develops...
Show moreHigh efficiency CuIn1-xGaxSe2-ySy (CIGSS)/CdS thin-film solar cells were prepared by optimizing the Mo back contact layer and optimizing the parameters for preparing CIGSS absorber layer using diethylselenide as selenium source. The Mo film was sputter deposited on 2.5 cm x 10 cm soda-lime glass using DC magnetron sputtering for studying the adhesion and chemical reactivity with selenium and sulfur containing gas at maximum film growth temperature. Mo being a refractory material develops stresses, nature of which depends on the deposition power and argon pressure. It was found that the deposition sequence with two tensile stressed layers deposited at 200W and 5 x 10-3 Torr argon pressure when sandwiched between three compressively stressed layers deposited at 300 W power and 0.3 x 10-3 Torr argon pressure had the best adhesion, limited reactivity and compact nature. An organo-metallic compound, diethylselenide (DESe) was developed as selenium precursor to prepare CIGSS absorber layers. Metallic precursors Cu-In-Ga layers were annealing in the conventional furnace in the temperature range of 475oC to 515 oC and in the presence of a dilute DESe atmosphere. The films were grown in an indium rich regime. Systematic approaches lead to the optimization of each step involved in the preparation of the absorber layer. Initial experiments were focused on obtaining the range of maximum temperatures required for the growth of the film. The following experiments included optimization of soaking time at maximum temperature, quantity of metallic precursor, and amount of sodium in terms of NaF layer thickness required for selenization. The absorber surface was coated with a 50 to 60 nm thick layer of CdS as hetero-junction partner by chemical bath deposition. A window bi-layer of i:ZnO/ZnO:Al was deposited by RF magnetron sputtering. The thickness of i:ZnO was increased to reduce the shunt resistance to improve open circuit voltage. The cells were completed by depositing a Cr/Ag front contact by thermal evaporation. Efficiencies greater than 13% was achieved on glass substrates. The performance of the cells was co-related with the material properties.
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Date Issued
2006
Identifier
CFE0001035, ucf:46822
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0001035
Effects of Allotropic Transformations on Interdiffusion Behavior in Binary Systems
Title
Effects of Allotropic Transformations on Interdiffusion Behavior in Binary Systems.
Creator
Ewh, Ashley, Sohn, Yongho, Suryanarayana, Challapalli, Coffey, Kevin, University of Central Florida
Abstract / Description
Diffusion plays a significant role in most materials systems by controlling microstructural development. Consequently, the overall properties of a material can be largely dependent upon diffusion. This study investigated the interdiffusion behavior of three binary systems, namely, Mo-Zr, Fe-Mo, and Fe-Zr. The main interest in these particular metals is for application in nuclear fuel assemblies. Nuclear fuel plates generally consist of two main components which are the fuel and the cladding....
Show moreDiffusion plays a significant role in most materials systems by controlling microstructural development. Consequently, the overall properties of a material can be largely dependent upon diffusion. This study investigated the interdiffusion behavior of three binary systems, namely, Mo-Zr, Fe-Mo, and Fe-Zr. The main interest in these particular metals is for application in nuclear fuel assemblies. Nuclear fuel plates generally consist of two main components which are the fuel and the cladding. Due to diffusional interactions that can occur between these two components, a third is sometimes added between the fuel and cladding to serve as a diffusion barrier layer. Fe, Mo, and Zr can act as either cladding or barrier layer constituents and both Mo and Zr also serve as alloying additions in uranium based metallic fuels. Therefore, a fundamental understanding of the diffusional interactions in these systems is critical in predicting the performance and lifetime of these fuels. In order to study this diffusion behavior, a series of solid-to-solid diffusion couples were assembled between Fe, Mo, and Zr. These couples were then diffusion annealed isothermally for various predetermined times over a range of temperatures, including some both above and below the allotropic transformation temperatures for Fe and Zr. Following the diffusion anneal, the couples were water quenched, cross-sectioned, and prepared for microstructural and compositional characterization. A combination of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and electron probe microanalysis (EPMA) were used to obtain micrographs showing the microstructure and to collect compositional data for identifying intermediate phases and determining concentration profiles across the interdiffusion zone.Based on this characterization, the phases that developed in the diffusion zones were identified. In the Mo-Zr system, a large Zr solid solution layer developed in the couples annealed at and above 850(&)deg;C and a thin (~1-2 ?m) layer of Mo2Zr formed in all couples. Growth constants and concentration dependent interdiffusion coefficients were calculated for the Mo2Zr and Zr solid solution phases, respectively. In the Fe-Mo system, both the ?-Fe2Mo and ?-Fe7Mo6 phases were observed in couples annealed at 900(&)deg;C and below while ?-Fe7Mo6 and ?-Fe solid solution layers were observed in couples annealed above 900(&)deg;C. The relevant growth constants and activation energies for growth were calculated. In the Fe-Zr system, the couple annealed at 750(&)deg;C developed an FeZr2 and an FeZr3 layer while the couple annealed at 850(&)deg;C developed an Fe2Zr and Fe23Zr6 layer in the diffusion zone. The results of this analysis were then compared to available information from literature and the corresponding binary phase diagrams for each system. The results are discussed with respect to the effects of the allotropic transformations of Fe and Zr on the interdiffusion behavior in these systems.
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Date Issued
2012
Identifier
CFE0004374, ucf:49422
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0004374
Phase Transformations and Microstructural Evolution in the U-10 wt.% Mo Alloy with Various Zr Additions at 900C and 650C
Title
Phase Transformations and Microstructural Evolution in the U-10 wt.% Mo Alloy with Various Zr Additions at 900C and 650C.
Creator
Eriksson, Nicholas, Sohn, Yongho, Challapalli, Suryanarayana, Coffey, Kevin, University of Central Florida
Abstract / Description
The Reduced Enrichment for Research and Test Reactor (RERTR) now known as the Material Minimization and Management Reactor Control program (MMMRC) seeks to replace the use of highly enriched uranium (HEU) fuels used in research and test nuclear reactors around the world. The low enriched uranium (LEU) fuels must have fissionable uranium densities comparable to the HEU fuels. After extensive investigation by various researchers around the world, the U-Mo alloys were selected as a promising...
Show moreThe Reduced Enrichment for Research and Test Reactor (RERTR) now known as the Material Minimization and Management Reactor Control program (MMMRC) seeks to replace the use of highly enriched uranium (HEU) fuels used in research and test nuclear reactors around the world. The low enriched uranium (LEU) fuels must have fissionable uranium densities comparable to the HEU fuels. After extensive investigation by various researchers around the world, the U-Mo alloys were selected as a promising candidate. The Mo alloyed with U allows for the stabilization of the face-centered cubic ?-U phase, which demonstrated favorable irradiation behavior. However, deleterious diffusional interaction between the fuel and the cladding, typically Al-base alloy, remain a challenge to overcome for application of U-Mo alloys as the LEU fuel. Zr has been identified as a potential diffusion barrier between monolithic U-10 wt.% Mo (U10Mo) metallic fuel and AA6061 cladding alloys for the development of a LEU fuel system. However, interdiffusion and reaction between the Zr barrier and U10Mo fuel can produce phases such as Mo2Zr, and promote the destabilization of ?-U phase into ?'-U (U2Mo) and ?-U. In order to better understand this phenomenon, this study examined the phases that are present in the U10Mo alloys with varying Zr concentration, 0, 0.5, 1.0, 2.0, 5.0, 10.0, 20.0 wt.% at room temperature after heat treatment at 900(&)deg;C for 168 hours and 650(&)deg;C for 3 hours. These two temperatures are relevant to fuel plate fabrication process of homogenization and hot-rolling, respectively. Scanning electron microscopy and X-ray diffraction were employed to identify and quantitatively document the constituent phases and microstructure to elucidate the nature of phase transformations. For U10Mo alloys containing less than 1.0 wt.% Zr, there was no significant formation of Mo2Zr after 900?C homogenization and subsequent heat treatment at 650?C for 3 hours. The ?-U phase also remained stable correspondingly for these alloys containing less than 1.0 wt.% Zr. For U10Mo alloys containing 2 wt.% or more Zr, a significant amount of Mo2Zr formation was observed after 900?C homogenization and subsequent heat treatment at 650?C for 3 hours. For these alloys, destabilization of ?-U into ?'-U (U2Mo), UZr2 and ?-U was observed. The alloy containing 20 wt.% Zr, however, did not demonstrate ?-U decomposition even though Mo2Zr was observed after heat treatments. The formation of Mo2Zr effectively reduced the stability of the metastable ?-U phase by depleting the ?-stabilizing Mo. The destabilization of ?-U phase into the ?-U phase is not favorable due to anisotropic and poor irradiation behavior of ?-U phase. Therefore the formation of Mo2Zr at the interface between U10Mo fuel and Zr diffusion barrier must be carefully controlled during the fabrication of monolithic LEU fuel system for successful implementation.
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Date Issued
2015
Identifier
CFE0005943, ucf:50812
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0005943
Redox-Active Solid State Materials and its Biomedical and Biosensing Applications
Title
Redox-Active Solid State Materials and its Biomedical and Biosensing Applications.
Creator
Gupta, Ankur, Seal, Sudipta, Dong, Yajie, Cho, Hyoung Jin, Zhai, Lei, Schulte, Alfons, University of Central Florida
Abstract / Description
Reactive oxygen species (ROS) are byproducts of physiological processes in human body, and strengthened production of ROS is known to cause acute conditions such as inflammation, aging, Alzheimer's disease, melanoma and ovarian cancer, fibrosis and multiple sclerosis. Therefore, early detection of ROS at nanomolar concentration (at cellular level) and developing more potent antioxidants is essential for regular health monitoring. As an example, ROS are also responsible for inflammation...
Show moreReactive oxygen species (ROS) are byproducts of physiological processes in human body, and strengthened production of ROS is known to cause acute conditions such as inflammation, aging, Alzheimer's disease, melanoma and ovarian cancer, fibrosis and multiple sclerosis. Therefore, early detection of ROS at nanomolar concentration (at cellular level) and developing more potent antioxidants is essential for regular health monitoring. As an example, ROS are also responsible for inflammation reactions at orthopedic implants-tissue interface triggered by wear debris. Inflammation induced by ROS results in revision surgery. Coatings of redox-active materials exhibiting antioxidant properties on implants have potential to mitigate the inflammation and delay the need of revision surgery. This dissertation focus on developing advanced functional nanomaterials by tailoring the surface chemistry of existing materials. Surface chemistry of materials can be altered by introducing surface and edge defects in the lattice structure Three materials system doped cerium oxide nanoparticles (d-CNPs), cerium oxide thin films (CeOx) and molybdenum disulfide (MoS2) nanoparticles, have been studied for its surface and edge contributions in potential biomedical and biosensing applications. Surface (d-CNPs and CeOx thin films) and edge chemistry (MoS2) have been tailored to understand its role and specific response.Surface Ce3+/Ce4+ oxidation state in CNPs controls the bio-catalytic activity. Higher superoxide dismutase (SOD) is demonstrated by high Ce3+/Ce4+ oxidation state. On the other hand, improved catalase mimetic activity is observed for low Ce3+/Ce4+ CNPs. Different CNPs preparation results in different Ce3+ to Ce4+ ratio, particle size, surface coating, and agglomeration, thus significantly varying the antioxidant properties of CNPs. In the first section of the dissertation, sustainable one-step room temperature synthesis of rare earth element (La, Sm, and Er) d-CNPs have been developed to effectively control the Ce3+ to Ce4+ ratio for specific biological application. Substitution of Ce4+ ions by trivalent dopants from ceria lattice increases the oxygen vacancies and density of catalytic sites. Uniform distribution of trivalent dopant in ceria lattice confirmed by EFTEM is attributed to enhanced SOD mimetic activity, ROS scavenging and tuning surface Ce3+/Ce4+ oxidation state in CNPs. Surface chemistry of redox-active cerium oxide coating on orthopedic implants also plays a vital role in scavenging ROS and mitigating inflammation. Thus, surface chemistry of CeOx thin films deposited by atomic layer deposited (ALD), have also been tailored by controlling the film thickness. CeOx film of 2 nm thickness has high Ce3+/Ce4+ (ratio 1) whereas higher thickness films (6-33 nm) have lower Ce3+/Ce4+ (ratio 0.30-0.37). These films have been further tested for catalase mimetic activity and hydrogen peroxide (H2O2) detection. Sensor selectivity is always a key issue. Most often, ascorbic acid found in the biological system, interfere in the electrochemical detection of H2O2 resulting in selectivity issue, thus protective Nafion layer is required to prevent cerium oxide-ascorbic acid interaction.To improve the selectivity of electrochemical sensors, Sulfur-deficient redox-active MoS2 have been utilized for electrochemical detection of pharmaceutically relevant chemical species. S-deficient MoS2 nanoparticles have been prepared by liquid exfoliation method to increase Mo-edge density and tested as sensing materials for detection of pharmaceutically relevant H2O2, hypochlorous acid (HOCl) and reactive nitrogen (NO*) species. The addition of ascorbic acid and uric acid have shown no interference during H2O2 detection. Change in S to Mo ratio have been studied using x-ray photoelectron spectroscopy. Density functional theory (DFT) have been employed to understand the detection mechanism and size-dependent sensitivity of MoS2. DFT study further reveals the role of S-deficiency and Mo- and S-edges in the higher catalytic activity of 5-7 nm MoS2 particles.Through these studies, the importance of defects in nanomaterials and their exotic properties at the nanoscale have been demonstrated. Understanding developed from these studies have provided the framework to develop more advanced functional nanomaterials for biomedical and biosensing applications.
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Date Issued
2017
Identifier
CFE0006944, ucf:51655
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0006944
Precision Metrology of Laser Plasmas in the XUV Band
Title
Precision Metrology of Laser Plasmas in the XUV Band.
Creator
Szilagyi, John, Richardson, Martin, Sundaram, Kalpathy, Abdolvand, Reza, Baudelet, Matthieu, Shivamoggi, Bhimsen, University of Central Florida
Abstract / Description
The XUV band, a region of light spanning the wavelength range of 5 - 200 nm, is located between the Ultraviolet and X-ray regions of the electromagnetic spectrum. It is further divided into a 100 - 200 nm region called the Vacuum Ultraviolet (VUV), and a 5 (-) 100 nm region called the Extreme Ultraviolet (EUV). Applications of this light have been slow to develop due to the lack of suitable sources, efficient optics, and sensitive detectors. Recently, many industries such as the semiconductor...
Show moreThe XUV band, a region of light spanning the wavelength range of 5 - 200 nm, is located between the Ultraviolet and X-ray regions of the electromagnetic spectrum. It is further divided into a 100 - 200 nm region called the Vacuum Ultraviolet (VUV), and a 5 (-) 100 nm region called the Extreme Ultraviolet (EUV). Applications of this light have been slow to develop due to the lack of suitable sources, efficient optics, and sensitive detectors. Recently, many industries such as the semiconductor manufacturing industry, medical surgery, micromachining, microscopy, and spectroscopy have begun to benefit from the short wavelengths and the high photon energies of this light. At present, the semiconductor chip industry is the primary reason for the investment in, and development of, XUV sources, optics, and detectors. The demand for high power EUV light sources at 13.5 nm wavelength is driven by the development of the next generation of semiconductor lithography tools. The development of these tools enables the continued reduction in size, and the increase in transistor density of semiconductor devices on a single chip. Further development and investigation of laser produced plasma EUV light sources is necessary to increase the average optical power and reliability. This will lead to an increase in the speed of EUV lithographic processes, which are necessary for future generations of advanced chip design, and high volume semiconductor manufacturing. Micromachining, lithography, and microscopy benefit from improvements in resolution due to the shorter wavelengths of light in the VUV band. In order to provide adequate illumination for these applications, sources are required which are brighter and have higher average power. Laser produced plasma (LPP) VUV light sources are used extensively for lithography and defect detection in semiconductor manufacturing. Reductions in the wavelength and increases in the average power will increase the rate and yield of chip manufacture, as well as reduce the costs of semiconductor manufacture.The work presented in this thesis, describes the development of two laser plasma source facilities in the Laser Plasma Laboratory at UCF, which were designed to investigate EUV and VUV laser plasma sources. The HP-EUV-Facility was developed to optimize and demonstrate a high power 13.5 nm EUV LPP source. This facility provides high resolution spectroscopy across 10.5 - 20 nm, and absolute energy measurement of 13.5 nm +/- 2% in 2? sr. The VUV-MS-Facility was developed to investigate VUV emission characteristics of laser plasmas of various target geometries and chemistries. This facility provides absolute calibrated emission spectra for the 124 - 250 nm wavelength range, in addition to, at wavelength plasma imaging. Calibrated emission spectra, in-band power, and conversion efficiency are presented in this work for gas targets of Argon, Krypton, and Xenon and solid targets of Silicon, Copper, Molybdenum, Indium, Tantalum, Tin, and Zinc, across the laser intensity range of 8.0x10^6 (-) 3.2x10^12 W/cm2.
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Date Issued
2017
Identifier
CFE0006805, ucf:51793
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0006805
Growth and doping of MoS2 thin films for electronic and optoelectronic applications
Title
Growth and doping of MoS2 thin films for electronic and optoelectronic applications.
Creator
Abouelkhair, Hussain, Peale, Robert, Kaden, William, Stolbov, Sergey, Coffey, Kevin, University of Central Florida
Abstract / Description
MoS2 high absorption coefficient, high mobility, mechanical flexibility, and chemical inertness is very promising for many electronic and optoelectronic applications. The growth of high-quality MoS2 by a scalable and doping compatible method is still lacking. Therefore, the suitable dopants for MoS2 are not fully explored yet. This dissertation consists mainly of four main studies. The first study is on the growth of MoS2 thin films by atmospheric pressure chemical vapor deposition. Scanning...
Show moreMoS2 high absorption coefficient, high mobility, mechanical flexibility, and chemical inertness is very promising for many electronic and optoelectronic applications. The growth of high-quality MoS2 by a scalable and doping compatible method is still lacking. Therefore, the suitable dopants for MoS2 are not fully explored yet. This dissertation consists mainly of four main studies. The first study is on the growth of MoS2 thin films by atmospheric pressure chemical vapor deposition. Scanning electron microscope images revealed the growth of microdomes of MoS2 on top of a smooth MoS2 film. These microdomes are very promising as a broadband omnidirectional light trap for light harvesting applications. The second study is on the growth of MoS2 thin films by low pressure chemical vapor deposition (LPCVD). Control of sulfur vapor flow is essential for the growth of a pure phase of MoS2. Turning off sulfur vapor flow during the cooling cycle at 700 (&)#186;C leads to the growth of highly textured MoS2 with a Hall mobility of 20 cm2/Vs. The third study was on the growth of Ti-doped MoS2 thin films by LPCVD. The successful doping was confirmed by Hall effect measurement and secondary ion mass spectrometry (SIMS). Different growth temperatures from 1000 to 700 ? were studied. Ti act as a donor in MoS2. The fourth study is on fluorine-doped SnO2 (FTO) which has many technological applications including solar cells and transistors. FTO was grown by an aqueous-spray-based method. The main objective was to compare the actual against the nominal concentration of fluorine using SIMS. The concentration of fluorine in the grown films is lower than the concentration of fluorine in the aqueous solution.?
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Date Issued
2017
Identifier
CFE0006847, ucf:51767
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0006847
INTERDIFFUSION BEHAVIOR OF U-MO ALLOYS IN CONTACT WITH AL AND AL-SI ALLOYS
Title
INTERDIFFUSION BEHAVIOR OF U-MO ALLOYS IN CONTACT WITH AL AND AL-SI ALLOYS.
Creator
Perez, Emmanuel, Sohn, Yong-Ho, University of Central Florida
Abstract / Description
U-Mo dispersion and monolithic fuels embedded in Al-alloy matrix are under development to fulfill the requirements of research reactors to use low-enriched molybdenum stabilized uranium alloys as fuels. The system under consideration in this study consisted of body centered cubic (gamma) U-Mo alloys embedded in an Al structural matrix. Significant interaction has been observed to take place between the U-Mo fuel and the Al matrix during manufacturing of the fuel-plate system assembly and...
Show moreU-Mo dispersion and monolithic fuels embedded in Al-alloy matrix are under development to fulfill the requirements of research reactors to use low-enriched molybdenum stabilized uranium alloys as fuels. The system under consideration in this study consisted of body centered cubic (gamma) U-Mo alloys embedded in an Al structural matrix. Significant interaction has been observed to take place between the U-Mo fuel and the Al matrix during manufacturing of the fuel-plate system assembly and during irradiation in reactors. These interactions produce Al-rich phases with physical and thermal properties that adversely affect the performance of the fuel system and can lead to premature failure. In this study, interdiffusion and microstructural development in the U-Mo vs. Al system was examined using solid-to-solid diffusion couples consisting of U-7wt.%Mo, U-10wt.%Mo and U-12wt.%Mo vs. pure Al, annealed at 600°C for 24 hours. The influence of Si alloying addition (up to 5 wt.%) in Al on the interdiffusion microstructural development was also examined using solid-to-solid diffusion couples consisting of U-7wt.%Mo, U-10wt.%Mo and U-12wt.%Mo vs. pure Al, Al-2wt.%Si, and Al-5wt.%Si annealed at 550°C for 1, 5 and 20 hours. To further clarify the diffusional behavior in the U-Mo-Al and U-Mo-Al-Si systems, Al-rich 85.7Al-11.44U-2.86Mo, 87.5Al-10U-2.5Mo, 56.1Al-18.9Si-21.9U-3.1Mo and 69.3Al-11.9Si-18.8U (at.%) alloys were cast and homogenized at 500°C to determine the equilibrium phases of the system. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron probe microanalysis (EPMA) and X-ray diffraction (XRD) were employed to examine the phase development in the diffusion couples and the cast alloys. In ternary U-Mo-Al diffusion couples annealed at 600°C for 24 hours, the interdiffusion microstructure consisted of finely dispersed UAl3, UAl4, U6Mo4Al43, and UMo2Al20 phases while the average composition throughout the interdiffusion zone remained constant at approximately 80 at.% Al. The interdiffusion microstructures observed by EPMA, SEM and TEM analyses were correlated to explain the observed morphological development in the interdiffusion zones. The concept of thermodynamic degrees of freedom was used to justify that, although deviations are apparent, the interdiffusion zones did not significantly deviate from an equilibrium condition in order for the observed microstructures to develop. Selected diffusion couples developed periodic bands within the interdiffusion zone as sub-layers in the three-phase regions. Observation of periodic banding was utilized to augment the hypothesis that internal stresses play a significant role in the phase development and evolution of U-Mo vs. pure Al diffusion couples. The addition of Si (up to 5 wt.%) to the Al significantly reduced the growth rate of the interdiffusion zone. The constituent phases and composition within the interdiffusion zone were also modified. When Si was present in the Al terminal alloys, the interdiffusion zones developed layered morphologies with fine distributions of the (U,Mo)(Al,Si)3 and UMo2Al20 phases. The U6Mo4Al43 phase was observed scarcely in Si depleted regions within the interdiffusion zone. The phase development and evolution of the interdiffusion zone was described in terms of thermodynamic degrees of freedom with minimal deviations from equilibrium.
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Date Issued
2011
Identifier
CFE0003747, ucf:48778
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0003747