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Atomistic simulations of brittle crack growth.

Description: Ceramic materials such as lead zirconium titanates (PZT), low temperature co-fired ceramics and silica glasses are used in several of Sandia's mission critical components. Brittle fracture, either during machining and processing or after many years in service, remains a serious reliability and cost issue. Despite its technological importance, brittle fracture remains poorly understand, especially the onset and propagation of sub-critical cracks. However, some insights into the onset of fracture can be gleaned from the atomic scale structure of the amorphous material. In silica for example, it is well known [1] that the Si-O-Si bonds are relatively weak and, in angle distribution functions determined from scattering experiments, the bonds exhibit a wide spread around a peak at 150. By contrast the O-Si-O bonds are strong with a narrow peak in the distribution around the 109 dictated by the SiO{sub 4} tetrahedron. In addition, slow energy release in silica, as deduced from dissolution experiments, depends on the distribution of 3-fold and higher rings in the amorphous structure. The purpose of this four month LDRD project was to investigate the atomic structure of silica in the bulk and in the vicinity of a crack tip using molecular dynamics simulations. Changes in the amorphous structure in the neighborhood of an atomically sharp tip may provide important clues as to the initiation sites and the stress intensity required to propagate a sub-critical crack.
Date: April 1, 2007
Creator: Hoyt, Jeffrey John
Partner: UNT Libraries Government Documents Department
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Fabrication of Ceramic Shapes

Description: Abstract: "This report indicates some of the methods employed at Los Alamos for the fabrication of refractory products."
Date: December 23, 1946
Creator: Mullen, Terence & Taub, James M.
Partner: UNT Libraries Government Documents Department
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FWP executive summaries: basic energy sciences materials sciences and engineering program (SNL/NM).

Description: This report presents an Executive Summary of the various elements of the Materials Sciences and Engineering Program which is funded by the Division of Materials Sciences and Engineering, Office of Basic Energy Sciences, U.S. Department of Energy at Sandia National Laboratories, New Mexico. A general programmatic overview is also presented.
Date: July 1, 2006
Creator: Samara, George A. & Simmons, Jerry A.
Partner: UNT Libraries Government Documents Department
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A micromechanical basis for partitioning the evolution of grainbridging in brittle materials

Description: A micromechanical model is developed for grain bridging inmonolithic ceramics. Specifically, bridge formation of a single,non-equiaxed grain spanning adjacent grains is addressed. A cohesive zoneframework enables crack initiation and propagation along grainboundaries. The evolution of the bridge is investigated through avariance in both grain angle and aspect ratio. We propose that thebridging process can be partitioned into five distinct regimes ofresistance: propagate, kink, arrest, stall, and bridge. Although crackpropagation and kinking are well understood, crack arrest and subsequent"stall" have been largely overlooked. Resistance during the stall regimeexposes large volumes of microstructure to stresses well in excess of thegrain boundary strength. Bridging can occur through continued propagationor reinitiation ahead of the stalled crack tip. The driving forcerequired to reinitiate is substantially greater than the driving forcerequired to kink. In addition, the critical driving force to reinitiateis sensitive to grain aspect ratio but relatively insensitive to grainangle. The marked increase in crack resistance occurs prior to bridgeformation and provides an interpretation for the rapidly risingresistance curves which govern the strength of many brittle materials atrealistically small flaw sizes.
Date: October 9, 2006
Creator: Foulk, J. W., III; Cannon, R. M.; Johnson, G. C.; Klein, P. A. & Ritchie, R. O.
Partner: UNT Libraries Government Documents Department
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Ceramic Coatings for Components Exposed to Coal-Gas Environments : a Review

Description: The corrosive and erosive environments at high temperatures and pressures in coal gasifiers impose severe requirements on the alloys of fabrication. A concise review of the application of ceramic coatings to resist coal-gas environments has been conducted. The purpose of this review is to explore suitable ceramic or cermet materials that may resist or retard the degradation of metal components and to summarize the state of the art of various methods of producing such coatings.
Date: December 1976
Creator: Swaroop, Robert
Partner: UNT Libraries Government Documents Department
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NGNP Composites R&D Technical Issues Study

Description: This study identifies potential applications and design requirements for ceramic materials (CMs) and ceramic composite materials (CCMs) in the NGNP hightemperature gas-cooled reactor (HTGR) primary circuit. Components anticipated for fabrication from non-graphite CMs and CCMs are identified along with recommended normal and off-normal operating conditions. The evaluation defines required dimensions and material properties of the candidate materials for normal operating conditions (NOC), anticipated transients, abnormal events, and design basis events. The report also identifies additional activities required for codifying the selected materials. The activities include ASTM Standard and ASME Code development and other work to support NRC licensing of the plant. Evaluation of the NGNP baseline design indicates components requiring either CMs or CCMs depend upon the reactor operating temperatures. For a reactor outlet temperature of 900 oC, four of the five evaluated components would benefit from either CMs or CCMs. Although some thermal and mechanical data exist for most of the candidate materials, they all need additional irradiation, thermal, and mechanical testing. The codification process must take into account the type of material and the geometry of components using either CMs or CCMs. The process requires close integration of the design and the research and development (R&D) program, which has already started by using preliminary control rod component designs as the basis for establishing specimen geometry and test conditions. The remaining time and budget for completing the R&D program need further assessment.
Date: September 1, 2008
Creator: Services, AREVA Federal
Partner: UNT Libraries Government Documents Department
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Viscosity of Molten Alumina

Description: In the analysis of LMFBR core-containment and heat-removal problems associated with hypothetical core-disruptive accidents, viscosity data on molten ceramics are needed to help analyze the convective heat transfer and flow patterns within liquid pools. An oscillating cup viscometer has been used to measure the viscosity of molten alumina in the temperature range from 2400 to 2750/sup 0/K. The data are represented by the equation: log eta = 11448/T - 8.2734 where the viscosity, eta, is given in Pascal seconds and the temperature, T, is in Kelvins.
Date: 1978?
Creator: Blomquist, R. A.; Fink, J. K. & Leibowitz, L.
Partner: UNT Libraries Government Documents Department
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Evaluation of Ceramic Refractories for Slagging Gasifiers : Summary of Progress to Date

Description: Commercial refractories were tested for up to 500 h in both basic and acidic slags. The slag compositions typify those expected in slagging coal gasifiers. The slag temperatures ranged up to 1600 degrees C. Compositions tested have included silicon carbides, chrome-alumina-magnesia spinels, and alumina and magnesia-based refractories with various amounts of chromia and silica. In some tests, the cold faces were water cooled. With water cooling, the silicon carbides showed virtually no attack after 500 h. In the absence of water cooling, the chrome-alumina-magnesia spinels were the most resistant to slag attack but were subject to thermal-shock cracking. Alumina-chrome refractories performed well in acid slags when water cooled, are probably more stable than silicon carbide in coal-gasification atmospheres, and, in the form of ramming mixes, showed excellent thermal-shock resistances. Plans for future testing are described.
Date: September 1978
Creator: Kennedy, C. R.; Swaroop, R.; Jones, D. J.; Fousek, R. J.; Poeppel, R. B. & Stahl, D.
Partner: UNT Libraries Government Documents Department
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Revolutionary systems for catalytic combustion and diesel catalytic particulate traps.

Description: This report is a summary of an LDRD project completed for the development of materials and structures conducive to advancing the state of the art for catalyst supports and diesel particulate traps. An ancillary development for bio-medical bone scaffolding was also realized. Traditionally, a low-pressure drop catalyst support, such as a ceramic honeycomb monolith, is used for catalytic reactions that require high flow rates of gases at high-temperatures. A drawback to the traditional honeycomb monoliths under these operating conditions is poor mass transfer to the catalyst surface in the straight-through channels. ''Robocasting'' is a unique process developed at Sandia National Laboratories that can be used to manufacture ceramic monoliths with alternative 3-dimensional geometries, providing tortuous pathways to increase mass transfer while maintaining low-pressure drops. These alternative 3-dimensional geometries may also provide a foundation for the development of self-regenerating supports capable of trapping and combusting soot particles from a diesel engine exhaust stream. This report describes the structures developed and characterizes the improved catalytic performance that can result. The results show that, relative to honeycomb monolith supports, considerable improvement in mass transfer efficiency is observed for robocast samples synthesized using an FCC-like geometry of alternating rods. Also, there is clearly a trade-off between enhanced mass transfer and increased pressure drop, which can be optimized depending on the particular demands of a given application. Practical applications include the combustion of natural gas for power generation, production of syngas, and hydrogen reforming reactions. The robocast lattice structures also show practicality for diesel particulate trapping. Preliminary results for trapping efficiency are reported as well as the development of electrically resistive lattices that can regenerate the structure by combusting the trapped soot. During this project an ancillary bio-medical application was discovered for lattices of hydroxyapatite. These structures show promise as bone scaffolds for the reparation …
Date: December 1, 2004
Creator: Stuecker, John Nicholas; Witze, Peter O.; Ferrizz, Robert Matthew; Cesarano, Joseph, III & Miller, James Edward
Partner: UNT Libraries Government Documents Department
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Nuclear Magnetic Resonance Imaging of Green-State Ceramics

Description: Proton (¹H) nuclear magnetic resonance (NMR) imaging techniques are investigated as a means to nondestructively characterize green-state (unfired) Si{sub 3}N{sub 4} ceramic components. Spectroscopic results indicate that the organic additives used in the injection molding of ceramics behave as soft solids, with broad spectral peak widths (T₂ <0.5 ms) and moderate multicomponent spin-lattice relaxation rates (T{sub 1} ranging from 11 ms to 1 s). Because of the intrinsically different spectral characteristics of the organic additives, conventional-solution NMR imaging techniques cannot be applied to these materials. Hence, the authors developed specialized NMR imaging accessories capable of applying high magnetic field gradients in a back-projection protocol. NMR images were acquired of injection-molded test bars that had been fabricated with different mixing and molding parameters. Organic concentrations determined from the NMR images were correlated with results obtained through destructive testing. The correlation suggests that NMR imaging is a viable technique for quantifying organics in injection-molded green-state ceramics.
Date: August 1990
Creator: Gopalsami, Nachappa; Dieckman, S. L.; Ellingson, W. A.; Botto, Robert E.; Wong, P. S.; Yeh, H. C. et al.
Partner: UNT Libraries Government Documents Department
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Three-Dimensional Nuclear Magnetic Resonance Imaging of Green-State Ceramics

Description: Objective is the development of nuclear magnetic resonance imaging techniques and technology applicable to the nondestructive characterization of green-state ceramics. To this end, a three-dimensional (3-D) NMR imaging technique has been developed, based on a back-projection acquisition protocol in combination with image reconstruction techniques that are based on 3-D Radon transform inversion. The method incorporates the experimental flexibility to overcome many of the difficulties associated with imaging of solid and semisolid broad-line materials, and also provides contiguously sampled data in three dimensions. This technique has been evaluated as a nondestructive characterization method for determining the spatial distribution of organic additives in green-state injection-molded cylindrical Si₃N₄ tensile specimens. The technique has been evaluated on the basis of providing moderate image resolution over large sample volumes, high resolution over smaller specimen volumes, and sensitivity to variations in the concentration of organics. Resolution of 200 micrometers has been obtained with excellent sensitivity to concentration. A detailed account of the 3-D imaging results obtained from the study, a discussion of the difficulties and limitations of the imaging technique, and suggestions for technique and system improvements are included.
Date: September 1991
Creator: Dieckman, S. L.
Partner: UNT Libraries Government Documents Department
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Study of methods for automated crack inspection of electrically poled piezoelectric ceramics.

Description: The goal of this project was to identify a viable, non-destructive methodology for the detection of cracks in electrically poled piezoelectric ceramics used in neutron generator power supply units. The following methods were investigated: Impedance Spectroscopy, Scanning Acoustic Microscopy, Lock-in Thermography, Photo-acoustic Microscopy, and Scanned Vicinal Light. In addition to the exploration of these techniques for crack detection, special consideration was given to the feasibility of integrating these approaches to the Automatic Visual Inspection System (AVIS) that was developed for mapping defects such as chips, pits and voids in piezoelectric ceramic components. Scanned Vicinal Light was shown to be the most effective method of automatically detecting and quantifying cracks in ceramic components. This method is also very effective for crack detection in other translucent ceramics.
Date: June 1, 2004
Creator: Yang, Pin; Hwang, Stephen C.; Jokiel, Bernhard, Jr. & Burns, George Robert
Partner: UNT Libraries Government Documents Department
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Materials Science Division Coal Technology Quarterly Report: January-March 1976

Description: Quarterly report of the Argonne National Laboratory Materials Science Division regarding the evaluation of ceramic refractories to withstand abrasion-corrosion by coal slag that will be encountered in the Bituminous Coal Research (BCR) Bi-Gas coal-gasification pilot plant, development of computer models to predict corrosion and erosion behavior of materials, and analysis of pilot-plant components that have failed or are removed from service for other reasons.
Date: 1976?
Creator: Argonne National Laboratory
Partner: UNT Libraries Government Documents Department
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X-ray Computed Tomography for Structural Ceramic Applications : Beam Hardening Corrections

Description: Beam hardening (BH), caused by the energy dependence of x-ray attenuation in materials, reduces the reliability of images generated by computed tomographic (CT) when polychromatic x-ray sources are used. The magnitude of the BH effect was calculated, and four different approaches to BH correction for CT imaging of ceramics were investigated: the ''water bag'' approach, pre-hardening of the beam by use of a filter, linearization correction, and dual-energy methods. The dual-energy approach appears to be a promising means of BH correction for CT imaging of ceramics.
Date: May 1987
Creator: Ellingson, William A.; Segal, E. & Vannier, M. W.
Partner: UNT Libraries Government Documents Department
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Materials Science Division Coal Technology Quarterly Report: April-June 1976

Description: Quarterly report of the Argonne National Laboratory Materials Science Division regarding coal technologyresearch and development. This report summarizes the work performed in six major tasks: evaluation of ceramic refractories, evaluation of ceramic coatings and refractories, development of nondestructive testing methods for use in coal plant fabrication, development of computer models to predict corrosion behavior, computer models to predict erosion behavior, and analysis of pilot-plant components that have failed or are removed from service.
Date: 1976?
Creator: Argonne National Laboratory
Partner: UNT Libraries Government Documents Department
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Materials Science Division Coal Technology Quarterly Report: July-September 1976

Description: Quarterly report of the Argonne National Laboratory Materials Science Division regarding coal technology research and development, including studies on both ceramic and metallic materials in order to facilitate the economical conversion of coal into cleaner and more usable fuels.
Date: 1976?
Creator: Argonne National Laboratory
Partner: UNT Libraries Government Documents Department
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Materials Science Division Coal Technology Quarterly Report: October-December 1976

Description: Quarterly report of the Argonne National Laboratory Materials Science Division regarding coal technology research and development. This report discusses a project for the economical conversion of coal into cleaner and more usable fuels: evaluation of ceramic-refractories exposed to abrasion-corrosion caused by coal slag, evaluation of ceramic coatings and refractories exposed to erosive environments, development of nondestructive evaluation methods applicable to coal-conversion systems, development of analytical models to predict corrosion behavior, and analysis of failed coal-gasification plant components.
Date: 1977?
Creator: Argonne National Laboratory
Partner: UNT Libraries Government Documents Department
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