647 Matching Results

Search Results

Advanced search parameters have been applied.

Project Calcium

Description: Fouling problems in utility boilers have been classified into two principal types: high-temperature and low-temperature fouling. A multiclient-sponsored program was initiated at the Energy and Environmental Research Center (EERC) to better understand the causes of low-temperature fouling when burning high-calcium western US coals. The goals of Project Calcium were to define the low-temperature deposition problem, identify the calcium-based components that are responsible for the formation of the deposits, develop ways to predict their formation, and identify possible methods to mitigate the formation of these deposits. To achieve the goals of Project Calcium, detailed sampling of utility boilers and laboratory-scale studies coupled with state-of-the-art methods to determine the inorganic components in coals and coal ash-derived materials were conducted. Boiler Sampling was also performed. The work involved sampling coal, entrained ash, deposits and slags from five full-scale utility boilers combined with detailed advanced characterization of the materials. The results of this work aided in identifying the key phenomena to focus the laboratory studies and in model verification. Field testing was conducted at three utilities.
Date: September 1, 1992
Creator: Hurley, J.P.; Benson, S.A.; Erickson, T.A.; Allan, S.E. & Bieber, J.
Partner: UNT Libraries Government Documents Department

The interpretation of HRTEM images of partially amorphized pyrochlore structure types

Description: Results of image simulations on partially amorphous microlite (Ca{sub 2}Ta{sub 2}O{sub 7}, pyrochlore structure) are presented. Results indicate that HRTEM images are not sensitive to position of amorphous layers within a crystalline matrix. It is also observed that the limit of detection of amorphous material within a crystalline matrix is dependent on total thickness. In thin crystals (<150{Angstrom}), up to 75 vol% crystalline material can give rise to aperiodic images, yet addition of a small amount of crystalline material (80 vol% crystalline) produces a periodic image. Images calculated for isolated spheres of amorphous material distributed within crystalline microlite suggest that isolated domains of amorphization are observable at sample thicknesses less than 3x the diameter of the feature. Image contrast of amorphized domains is enhanced by imaging at defocus settings significantly different than Scherzer focus. This indicate that interpretation of HRTEM images of partially amorphized crystalline materials should be undertaken with caution, and estimates of the volume of damage considered only qualitative.
Date: December 31, 1990
Creator: Miller, M.L. & Ewing, R.C.
Partner: UNT Libraries Government Documents Department

Calculated electronic structure and transport properties of La{sub .67}Ca{sub .33}MnO{sub 3}

Description: We have calculated the electronic structure, total energy, magnetic moments, and electrical resistivities of LaMnO{sub 3} and La{sub . 67}Ca{sub .33}MnO{sub 3} using mean field band theory. The magnetic and structural properties seems to be in good agreement with experiment. Calculations predict that La{sub .67}Ca{sub .33}MnO{sub 3} is metallic for the majority spins and semiconducting for the minority spins.
Date: December 31, 1995
Creator: Butler, W.H.; Zhang, X.G. & MacLaren, J.M.
Partner: UNT Libraries Government Documents Department

Engineering process instructions and development summary MC3642 thermal battery

Description: The MC3642 is a dual channel thermal battery used on the DE1010/W85 Command Disable Controller. It utilizes the CalCaCrO{sub 4} electrochemical system. The electrical requirements of this battery are as follows: RISE TIME PEAK VOLTAGE ACTIVE LIFE LOAD Channel 1 - 1.0 Sec. Max. 34 Volts 10 Sec. Min. 40.0 Ohms to 20 Volts above 20 Volts Channel 2 - .350 Sec. Max. 42 Volts 10 MSec. Min. 6.5 Ohms to 23 Volts above 23 Volts The battery consists of 14 cells connected in series (Channel 2) and 12 cells connected in series (Channel 1). Each cell is composed of an anode fabricated from a bimetallic sheet (0.005{double_prime} thick calcium on 0.005{double_prime} thick iron substrate), a depolarizer-electrolyte-binder (DEB) pellet and a heat pellet. Activation is achieved by mechanical primer. Optimum battery performance is achieved with a 35155/10 DEB pellet weighing .80g and a heat pellet, weighing 1.30 grams, of 88/12 heat powder.
Date: June 1, 1981
Creator: Jacobs, D.
Partner: UNT Libraries Government Documents Department

Lattice effect in perovskite and pyrochlore CMR materials

Description: Colossal magnetoresistance (CMR) in doped La manganite thin films (La{sub 1-x}M{sub x}MnO{sub 3}, where M = divalent ion, either Ca or Pb) has been shown to result in a factor of 10{sup 6} suppression of the resistance. The driving force for the CMR transition is thought to be the double-exchange interaction. Many studies of both the crystal structure and the local structure of the La{sub 1-x}M{sub x}MnO{sub 3} (M = Ca, Sr, Ba, Pb) system have now been carried out. As expected, these systems all show a strong coupling of the lattice to the CMR transition. On the other hand, neutron diffraction and x-ray absorption for the Tl{sub 2}Mn{sub 2}O{sub 7} pyrochlore, which also exhibits CMR, shows no deviations from ideal stoichiometry, mixed valency, or Jahn-Teller distortions of the MnO{sub 6} octahedron. We present results of crystallographic and local structural studies of these two important classes of CMR materials, compare the differences in structural response, and discuss the implications of these findings to our understanding of these materials.
Date: September 1997
Creator: Kwei, G. H.; Argyriou, D. N.; Lawson, A. C.; Neumeier, J. J.; Thompson, J. D.; Billinge, S. J. L. et al.
Partner: UNT Libraries Government Documents Department

Computational modeling of materials processing and processes

Description: This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Anisotropic mechanical properties of densified BSCCO powders are of paramount importance during thermo-mechanical processing of superconducting tapes and wires. Maximum current transport requires high relative density and a high degree of alignment of the single crystal planes of the BSCCO. Unfortunately this configuration causes high stresses that can lead to cracking, and thus reduce the density, and the conductive properties of the tape. The current work develops a micromechanical material mode to model is calibrated and compared to experimental results, and then employed to analyze the effects of initial texture and confinement pressure and shear strains in the core of oxide powder-in-tube (OPIT) processed tapes are calculated by finite-element analysis. The calculated deformations were then applied as boundary conditions to the micromechanical model. Our calculated results were used to interpret a set of prototypical rolling experiments. 11 refs., 5 figs.
Date: December 31, 1998
Creator: Lowe, T.C.; Zhu, Yuntian & Bingert, J.F.
Partner: UNT Libraries Government Documents Department

Molecular modeling of the structure and dynamics of the interlayer and surface species of mixed-metal layered hydroxides: Chloride and water in hydrocalumite (Friedel's salt)

Description: The dynamical behavior of Cl{sup {minus}} and H{sub 2}O molecules in the interlayer and on the (001) surface of the Ca-aluminate hydrate hydrocalumite (Friedel's salt) over a range of temperatures from {minus}100 to 300 C is studied using the technique of isothermal-isobaric molecular dynamics computer simulations. This phase is currently the best available model compound for other, typically more disordered, mixed-metal layered hydroxides. The computed crystallographic parameters and density are in good agreement with available X-ray diffraction data and the force field developed for these simulations preserves the structure and density to within less than 2% of their measured values. In contrast to the highly ordered arrangement of the interlayer water molecules interpreted from the X-ray data, the simulations reveal significant dynamic disorder in water orientations. At all simulated temperatures, the interlayer water molecules undergo rapid librations (hindered hopping rotations) around an axis essentially perpendicular to the layers. This results in breaking and reformation of hydrogen bonds with the neighboring Cl{sup {minus}} anions and in a time-averaged nearly uniaxial symmetry at Cl{sup {minus}}, in good agreement with recent {sup 35}Cl NMR measurements. Power spectra of translational, vibrational, and vibrational motions of interlayer and surface Cl{sup {minus}} and H{sub 2}O were calculated as Fourier transforms of the atomic velocity autocorrelation functions and compared with the corresponding spectra and dynamics for a bulk aqueous solution. The ordered interlayer space has significant effects on the motions. Strong electrostatic attraction between interlayer water molecules and Ca atoms in the principal layer makes the Ca{hor_ellipsis}OH{sub 2} bond direction the preferred axis for interlayer water librations. The calculated diffusion coefficient of Cl{sup {minus}} as an outer-sphere surface complex is almost three times that of inner-sphere Cl{sup {minus}}, but is still about an order of magnitude less than that of Cl{sup {minus}} in bulk aqueous solution at ...
Date: January 17, 2000
Creator: KALINICHEV,ANDREY G.; KIRKPATRICK,R. JAMES & CYGAN,RANDALL T
Partner: UNT Libraries Government Documents Department

Effects of localized holes on charge transport, local structure and spin dynamics in the metallic state of CMR La{sub 1{minus}x}Ca{sub x}MnO{sub 3}

Description: The authors review resistivity, x-ray-absorption fine-structure (XAFS) and muon spin relaxation ({mu}SR) data which provide clear evidence for localized holes causing polaron distortion and unusual spin dynamics below {Tc} in ``colossal magnetoresistive`` (CMR) La{sub 1{minus}x}Ca{sub x}MnO{sub 3}. Resistivity measurements for x = 0.33 under an applied field H have shown that ln[{rho}(H,T)] {infinity}-M, where M is the magnetization. The XAFS data show a similar functional dependence for the polaron distortions on M The data from these two measurements are interpreted in terms of some fraction of the available holes x remaining localized and some increasing fraction becoming delocalized with increasing M Finally, this polaron-induced spatial inhomogeneity yields anomalously slow, spatially inhomogeneous spin dynamics below {Tc}, as shown in the {mu}SR data. These experiments individually probe the charge, lattice and spin degrees of freedom in this CMR system and suggest that the polarons retain some identity even at temperatures significantly below {Tc}.
Date: March 1, 1998
Creator: Heffner, R.H.; Hundley, M.F. & Booth, C.H.
Partner: UNT Libraries Government Documents Department

Observations on the Radiation Decomposition of Some C14 LabeledCompounds

Description: Varying amounts of radiation decomposition during storage in the dry form have been found in the cases of C{sup 14}-labeled valine, norvaline, norleucine, choline chloride, calcium glycolate and cholesterol. These data indicate that investigators using labeled organic compounds should make frequent checks of the purity of these compounds in order to exclude the possibility of the presence of decomposition products.
Date: February 27, 1953
Creator: Tolbert, B.M.; Adams, P.T.; Bennett, Edward L.; Hughes, Ann M.; Kirk, Martha R.; Lemmon, R.M. et al.
Partner: UNT Libraries Government Documents Department

Oxalate co-precipitation synthesis of calcium zirconate and calcium titanate powders.

Description: Fine powders of calcium zirconate (CaZrO{sub 3}, CZ) and calcium titanate (CaTiO{sub 3}, CT) were synthesized using a nonaqueous oxalate co-precipitation route from Ca(NO{sub 3}){sub 2}{center_dot}4 H{sub 2}O and group(IV) n-butoxides (Ti(OBu{sup n}){sub 4} or Zr(OBu{sup n}){sub 4}). Several reaction conditions and batch sizes (2-35 g) were explored to determine their influence on final particle size, morphology, and phase. Characterization of the as-prepared oxalate precursors, oven dried oxalate precursors (60-90 C), and calcined powders (635-900 C) were analyzed with TGA/DTA, XRD, TEM, and SEM. Densification and sintering studies on pressed CZ pellets at 1375 and 1400 C were also performed. Through the developed oxalate co-precipitation route, densification temperatures for CZ were lowered by 125 C from the 1500 C firing temperature required for conventional mixed oxide powders. Low field electrical tests of the CZ pellets indicated excellent dielectric properties with dielectric constants of {approx}30 and a dissipation factor of 0.0004 were measured at 1 kHz.
Date: June 1, 2009
Creator: Hernandez-Sanchez, Bernadette A. & Tuttle, Bruce Andrew
Partner: UNT Libraries Government Documents Department

Surfactant development for enhanced oil recovery. Seventh quarterly report, April 1--June 30, 1995

Description: The overall objective of the project is to develop surfactant system(s) that will enhance projects on tertiary oil recovery. Such surfactant systems will be expected to be stable at high temperatures and exhibit high salinity tolerance. The authors have shown in previous reports that double-tailed surfactants show very good promise as well as remarkable potential for effective tertiary oil recovery. For this reason they have continued to devote research activities on this class of surfactants. In this report two additional double-tailed surfactants were synthesized and their critical micelle concentration (CMC) determined. These surfactants are sodium dihexadecyl phosphate (SDDP) and calcium ditetradecyl sulfonate CaDTDS. These are all anionic surfactants with different head groups. The observed critical micelle concentration for these surfactants are 0.78 {times} 10{sup {minus}5} M and 0.81 {times} 10{sup {minus}5} M, respectively. These CMC values were obtained using conductometric and surface tensiometric methods.
Date: November 1, 1995
Partner: UNT Libraries Government Documents Department

MERCURY CONTROL WITH CALCIUM-BASED SORBENTS AND OXIDIZING AGENTS

Description: The initial tasks of this DOE funded project to investigate mercury removal by calcium-based sorbents have been completed, and initial testing results have been obtained. Mercury monitoring capabilities have been obtained and validated. An approximately 1MW (3.4 Mbtu/hr) Combustion Research Facility at Southern Research Institute was used to perform pilot-scale investigations of mercury sorbents, under conditions representative of full-scale boilers. The initial results of ARCADIS G&amp;M proprietary sorbents, showed ineffective removal of either elemental or oxidized mercury. Benchscale tests are currently underway to ascertain the importance of differences between benchscale and pilot-scale experiments. An investigation of mercury-capture temperature dependence using common sorbents has also begun. Ordinary hydrated lime removed 80 to 90% of the mercury from the flue gas, regardless of the temperature of injection. High temperature injection of hydrated lime simultaneously captured SO{sub 2} at high temperatures and Hg at low temperatures, without any deleterious effects on mercury speciation. Future work will explore alternative methods of oxidizing elemental mercury.
Date: June 1, 2002
Creator: Gale, Thomas K.
Partner: UNT Libraries Government Documents Department

The influence of fiber/matrix interface on the mechanical behavior of Nicalon SiC fiber reinforced glass-ceramic composites

Description: Mechanical properties of unidirectional Nicalon SiC fiber reinforced Ca aluminosilicate (CAS/SiC) and Mg aluminosilicate (MAS/SiC) glass-ceramic composites were investigated by tensile testing and nondestructive laser-ultrasound technique. The Ba-stuffed MAS was either undoped or doped with 5% borosilicate glass. Degradation of elastic stiffness constant C{sub 11} in transverse direction due to interface damage was monitored in situ by measuring the laser- generated ultrasound wave velocity. The three composite materials show different characteristics of macroscopic deformation behavior, which is correlated strongly to interface degradation. A stronger reduction trend of the elastic constant C{sub 11} is associated with a larger degree of inelastic deformation. The fracture surfaces also reveal the close relation between fiber pullout length and interfacial characteristics. Interfaces of these composites were studied by TEM; their influence on inhibiting and deflecting matrix cracks is discussed.
Date: November 1, 1996
Creator: Liu, Y.M.; Mitchell, T.E. & Wadley, H.N.G.
Partner: UNT Libraries Government Documents Department

Interface modification during oxidation of a glass-ceramic matrix/SiC fibre composite

Description: Oxidation heat treatments between 375{degrees}C and 600{degrees}C for 100 hours in air, have been performed on the calcium aluminosilicate glass-ceramic matrix/SiC fibre reinforced composite CAS/Nicalon (manufactured by Coming, USA). Using a commercial nano-indentation system to perform fibre push-down tests, the fibre-matrix interfacial debond fracture surface energy (G{sub i}) and frictional shear stress ({tau}) have been determined. Modification of interface properties, compared to the as fabricated material, was observed at heat treatment temperatures as low as 375{degrees}C, where a significant drop in G{sub i} and an increase in {tau} were recorded. With 450{degrees}C, 525{degrees}C and 600{degrees}C heat treatments, an increase in G{sub i} but a dramatic increase in {tau} were recorded. Under four-point flexure testing, the as fabricated and the 375{degrees}C heat treated materials displayed tough, composite behaviour with extensive fibre pull out, but at {le}450{degrees}C, brittle failure with minimal fibre pull out, was observed. This transition from tough mechanical response to one of brittleness is due to the large increase in {tau} reducing fibre pull out to a minimum and therefore reducing the total required work of fracture. The large increases in {tau} and G{sub i} have been attributed to the oxidative removal of the lubricating, carbon interface and the compressive residual stresses across the interface.
Date: April 1, 1996
Creator: Daniel, A.M.; Martin-Meizoso, A.; Plucknett, K.P. & Braski, D.N.
Partner: UNT Libraries Government Documents Department

Heteroepitaxy of perovskite ferroelectrics on silicon: a path to silicon-integrated ferroelectrics

Description: We have studied the thin-film heteroepitaxy between simple perovskite oxides and Si as it is accomplished with molecular beam epitaxy growth. Interface chemistry and electrostatics play critical roles in determining whether a commensurate interface develops. Submonolayer silicides are the required precursors for the transition to commensurate epitaxial oxide structures in these systems. This approach is illustrated with BaTiO{sub 3}; high crystalline perfection is achieved and resistivities as high as 10{sup 13} ohm-cm can be developed for BaTiO{sub 3} MOS capacitors on (001) Si. The epitaxy is (100)BaTiO{sub 3}//(001)Si with [0001]BaTiO{sub 3} aligned in plane with the polar axis along the [110] of Si. This epitaxy is dominated by a strong propensity for Ba to order along the [110] of Si during the submonolayer silicide formation. This commensurate heteroepitaxial growth leads to a truly monolithic crystal and attendant properties. 9 figs, 23 refs.
Date: October 1, 1996
Creator: McKee, R.A.; Walker, F.J. & Chisholm, M.F.
Partner: UNT Libraries Government Documents Department

Critical current density enhancement in rolled multifilament Bi-2223 HTS composites

Description: At 77 K and self-field, we report transport critical density (J{sub c}) of 58 kA/cm{sup 2} in rolled 19 and 85 filament Bi-2223 HTS tapes. For an 85-filament tape with transport J{sub c} of 50 kA/cm{sup 2}, transport J{sub c} of greater than 80 kA/cm{sup 2} electrical performance, increasing the number of the strong links between the 2223 colonies is believed to be the most important factor. Microstructure studies on these samples suggest that there is still great potential for further J{sub c} enhancement.
Date: December 31, 1997
Creator: Li, Q.; Riley, G.N. Jr. & Parrella, R.D.
Partner: UNT Libraries Government Documents Department

Transuranium Removal from Hanford AN-107 Simulants using Sodium Permanganate and Calcium

Description: Removal of strontium from the complexant-containing wastes (AN-102 and AN-107) had previously been acceptably accomplished by isotopic dilution. Actinide removal using ferric co-precipitation, however, was very problematic from both a processing and a decontamination standpoint. Therefore, a series of tests were performed to identify other potential actinide removal agents and to test these agents at various concentrations.
Date: August 30, 2000
Creator: Wilmarth, W.
Partner: UNT Libraries Government Documents Department

Growth-related magnetic and physical structures in CMR films

Description: Scanning tunneling microscopy (STM), atomic force microscopy (AFM), and magnetic force microscopy (MFM) have proven to be powerful tools for revealing property-sensitive structures in magnetic materials. With the renewed interest in perovskite films as materials for read-heads in high density magnetic data storage, the same challenges faced by high temperature superconductor (HTS) film fabrication are repeated for these materials. To begin addressing these challenges, we used vapor phase epitaxy to fabricate La (Sr, Ca,) based manganate films on single crystal perovskite substrates under different conditions and characterized them with scanning probe microscopies, x-ray diffraction, and temperature-dependent magnetization and resistivity measurements (M(T) and {rho}(T)). The as-grown films were polygranular with grain sizes increasing with increasing temperature (T). The post-deposition annealed films consisted of coalesced layers with improved transport properties. The room temperature magnetic structure of the Sr-based films appeared to be related to defects and/or strain.
Date: September 1, 1997
Creator: Hawley, M.E.; Brown, G.W. & Hundley, M.F.
Partner: UNT Libraries Government Documents Department

Laser-ultrasonic evaluation of damage in unidirectional ceramic matrix composites

Description: Ceramic matrix composites (CMCs) have attracted great attention because of their potential for high temperature structural applications. Among these materials, calcium aluminosilicate (CAS) glass ceramic and similar composites reinforced by Nicalon{trademark} SiC fiber with carbon-rich interface have been under active investigation because of their {open_quotes}notch-insensitivity{close_quotes}: stress near holes and notches can be redistributed by inelastic deformation in the form of multiple matrix cracking. Therefore, stress concentration is alleviated near these sites. Understanding the damage mechanism in these composites is very important for the development of constitutive modeling. To achieve this goal, monitoring damage initiation and accumulation in-situ are especially critical. In most of the previous work, the change of elastic modulus along loading direction was used to characterize the damage. However, the overall anisotropic damages such as fiber-matrix debonding or shear deformation were unknown. In this study, we have pursued an in-situ nondestructive laser-ultrasonic technique to assess the overall anisotropic stiffness degradation under loading. When a laser pulse is brought to sample surface, high frequency acoustic waves can be generated by thermal or ablation mechanisms depending on the incident power intensity. The propagation of the elastic waves through anisotropic media is characterized by the well-known Christoffel equation.
Date: April 1, 1996
Creator: Liu, Y.M.; Mitchell, T.E. & Wadley, H.N.G.
Partner: UNT Libraries Government Documents Department

Microstructural study of CMR films as a function of growth temperature as-deposited and annealed

Description: The properties encompassed by the family of complex metal oxides span the spectrum from superconductors to insulating ferroelectrics. Included in this family are the new colossal magneto-resistive perovskites with potential applications in advanced high density magnetic data storage devices based on single or multilayer thin films units of these materials fabricated by vapor phase deposition (PVD) methods. The realization of this potential requires solving basic thin film materials problems requiring understanding and controlling the growth of these materials. Toward this end, we have grown La{sub 0.7}Ca{sub 0.3}MnO{sub 3} and La{sub 0.7}Sr{sub 0. 3}MnO{sub 3} on LaAIO{sub 3} single crystal substrates by pulsed laser and RF sputter deposition at 500 to 900 C and annealed at over 900 C for about 10 hours. The evolution of the microstructure of these films was studied by scanning probe microscopies and transmission electron microscopy (TEM). Results of SPM characterization showed that at the lower end of the growth temperature range, the as-grown films were polygranular with grain size increasing with temperature. The 500 C as-grown films appeared to be amorphous while the 750 C film grains were layered with terrace steps often one unit cell high. In contrast, films grown at 900 C consisted of coalesced islands with some 3-D surface crystals. After annealing, all films had coalesced into very large extended layered islands. The change in microstructure was reflected in a decreased resistivity of coalesced films over their unannealed granular precursors. Previous reported work on the growth of La{sub 0. 84}Sr{sub 0.16}MnO{sub 3} and La{sub 0.8}Sr{sub 0.2}CoO{sub 3} grown demonstrated the sensitivity of the microstructure to substrate and deposition conditions. Films grown on an ``accidental`` vicinal surface grew by a step flow mechanism.
Date: December 1995
Creator: Hawley, M. E.; Wu, X. D.; Arendt, C. D.; Adams, M. F.; Hundley & Hefner, R. H.
Partner: UNT Libraries Government Documents Department