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Description: Under the commonly employed experimental conditions of a significant upstream concentration of H and c{sub H} {approx} 0 downstream, expressions are given for obtaining the concentration-independent D*{sub H} from the concentration dependent D{sub H} employing the known non-ideality. A procedure is given for determining the concentration profile for a given upstream concentration for an alloy where the non-ideality is known as a function of H concentration. For the Pd{sub 0.81}Ag{sub 0.19} alloy (423 K) the nonideality, f(r)<1 decreases the flux but for alloys where the non-ideality is in the opposite direction, f(r)>1, the flux will be greater which would be an advantage for the experimental purification of H{sub 2}.
Date: July 13, 2006
Creator: Shanahan, K; Ted B. Flanagan, T & D. Wang, D
Partner: UNT Libraries Government Documents Department

Pressure dependence of defect emissions and the appearance of pressure-induced deep centers in chalcopyrite alloys AgxCu1-xGaS2

Description: We present the pressure dependence of the defect emissions in the chalcopyrite alloy semiconductor Ag{sub x}Cu{sub 1-x}GaS{sub 2} for values of the alloy concentration x varying between 0 and 1. A large variation in the pressure coefficients of the different defect emissions with x was found. In one alloy concentration x=0.25 deep levels were found to appear under pressure. Plausible explanations of our results have been proposed.
Date: December 31, 2000
Creator: Choi, In-Hwan & Yu, Peter Y.
Partner: UNT Libraries Government Documents Department

Dymalloy: A composite substrate for high power density electronic components

Description: High power density electronic components such as fast microprocessors and power semiconductors must operate below the maximum rated device junction temperature to ensure reliability. function temperatures are determined by the amount of heat generated and the thermal resistance from junction to the ambient thermal environment. Two of the Largest contributions to this thermal resistance are the die attach interface and the package base. A decrease in these resistances can allow increased component packing density in MCMs, reduction of heat sink volume in tightly packed systems, enable the use of higher performance circuit components, and improve reliability. The substrate for high power density devices is the primary thermal link between the junctions and the heat sink. Present high power multichip modules and single chip packages use substrate materials such as silicon nitride or copper tungsten that have thermal conductivity in the range of 200 W/mK. We have developed Dymalloy, a copper-diamond composite, that has a thermal conductivity of 420 W/mK and an adjustable coefficient of thermal expansion, nominally 5.5 ppm/C at 25 C, compatible with silicon and gallium arsenide. Because of the matched coefficient of thermal expansion it is possible to use low thermal resistance hard die attach methods. Dymalloy is a composite material made using micron size Type I diamond powder that has a published thermal conductivity of 600 to 1000 W/mK in a metal matrix that has a thermal conductivity of 350 W/mK. The region of chemical bonding between the matrix material and diamond is limited to approximately 1000 A to maintain a high effective thermal conductivity for the composite. The material may be fabricated in near net shapes. Besides having exceptional thermal properties, the mechanical properties of this material also make it an attractive candidate as an electronic component substrate material.
Date: June 29, 1995
Creator: Kerns, J.A.; Colella, N.J.; Makowiecki, D. & Davidson, H.L.
Partner: UNT Libraries Government Documents Department

Bi-2212 and Bi-2223 wire development

Description: The results of innovative processing of Bi-2212 by isothermal melt processing and by controlled oxygen pressure cooling yield improved properties over the conventional routes. The addition of large grains of Ag has resulted in improved core/interface geometry and better performance in Bi-2212 and Bi-2223. A deformation processing study of Bi-2223 showed the effects of sheath material, relative core thickness, and reduction per pass on core/interface uniformity.
Date: December 1, 1995
Creator: Willis, J.O.; Ray, R.D. II & Holesinger, T.G.
Partner: UNT Libraries Government Documents Department

Self dressing resistance welding electrode. Technical progress report, first quarter 1992

Description: This grant was divided four tasks. Task one was to produce prototype electrodes and test to establish optimum weld parameters for a variety of applications. Task two was to expand the concept application--design it into a broader range of electrodes and produce prototype electrodes for test to establish the optimum electrode parameters. Task three was to develop a process to produce the refractory reinforced embodiment. Produce prototypes employing a variety of electrically conductive materials, test to verify performance improvement, and establish weld parameters. Task four was to write a final report. Progress made on each task is described.
Date: December 31, 1992
Creator: Prucher, B.
Partner: UNT Libraries Government Documents Department

Strength and flexibility of bulk high-{Tc} superconductors

Description: Strength, fracture toughness, and elastic modulus data have been gathered for bulk high-temperature superconductors, commercial 99.9% Ag, and a 1.2 at.% Mg/Ag alloy. These data have been used to calculate fracture strains for bulk conductors. The calculations indicate that the superconducting cores of clad tapes should begin to fracture at strains below 0.2%. In addition, residual strains in Ag-clad (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} tapes have been measured by neutron diffraction. An explanation is offered for why many tapes appear to be able to tolerate large strains before exhibiting a reduction in current transport.
Date: August 1, 1996
Creator: Goretta, K.C.; Jiang, M.; Kupperman, D.S.; Lanagan, M.T.; Singh, J.P.; Vasanthamohan, N. et al.
Partner: UNT Libraries Government Documents Department

Nonmagnetic crystal-electric-field ground state in the heavy-fermion compound PrInAg{sub 2}

Description: The authors have performed inelastic neutron scattering measurements that confirm that the crystal-electric-field split ground state in the heavy-fermion compound PrInAg{sub 2} is a nonmagnetic, non-Kramers doublet. This implies that a quadrupolar Kondo interaction is responsible for the enhanced thermodynamic properties observed at low temperatures. They also observe anomalous broadening of the inelastic peaks and suggest two possible causes for this broadening.
Date: June 18, 1998
Creator: Kelley, T.M.; Beyermann, W.P.; Robinson, R.A.; Nakotte, H.; Canfield, P.C. & Trouw, F.
Partner: UNT Libraries Government Documents Department

Rapid fabrication of materials using directed light fabrication

Description: Directed light fabrication (DLF) is a rapid fabrication process that fuses gas delivered metal powders within a focal zone of a laser beam to produce fully dense, near-net shape, 3-dimensional metal components from a computer generated solid model. Computer controls dictate the metal deposition pathways, and no preforms or molds are required to generate complex sample geometries. The focal zone of the laser beam is programmed to move along or across a part cross-section, and coupled with a multi-axis sample stage, produces the desired part. By maintaining a constant molten puddle within the focal zone, a continuous liquid/solid interface is possible while achieving constant cooling rates that can be varied between 10 to 10{sup 4} K s{sup -1} and solidification growth rates (that scale with the beam velocity) ranging up to 10{sup 2} m s{sup -1}. The DLF technique offers unique advantages over conventional thermomechanical processes in that many labor and equipment intensive steps can be avoided. Moreover, owing to the flexibility in power distributions of lasers, a variety of materials can be processed, ranging from aluminum alloys to rhenium, and including intermetallics such as Mo{sub 5}Si{sub 3}. As a result, the rapid fabrication of conventional and advanced materials are possible.
Date: October 1, 1997
Creator: Thoma, D.J.; Lewis, G.K.; Milewski, J.O.; Chen, K.C. & Nemec, R.B.
Partner: UNT Libraries Government Documents Department


Description: We have measured the Ag and Pd M{sub 5}VV Auger spectrum in coincidence with Ag and Pd 4d{sub 5/2} photoelectrons for the Ag/Cu(100) and Pd/Cu(100) systems, respectively, as a function of admetal coverage. These systems form surface alloys (i.e. random substitutional alloys in the first atomic layer) for impurity concentrations in the 0.1 monolayer range. For these systems, the centroid of the impurity 4d levels is expected to shift away from the Fermi level by {approx}1 eV [Ruban et al., Journal of Molecular Catalysis. A 115 (1997) 421], an effect that should be easily seen in coincidence core-valence-valence Auger spectra. We find that the impurity Auger spectra of both systems shift in a manner that is consistent with d-band moving away from EF. However, the shift for Pd is considerably smaller than expected, and a shift almost absent for Ag. The disagreement between theory and experiment is most likely caused by the neglect of lattice relaxations in the calculations.
Date: October 8, 2001
Creator: Arena, D. A.; Bartynski, R. A. & Hulbert, S. L.
Partner: UNT Libraries Government Documents Department

De-alloying and stress-corrosion cracking. Final report

Description: This research program has had two major areas of focus that are related: (1) alloy corrosion and (2) the role of selective dissolution in the stress corrosion cracking of alloy systems. These interrelated issues were examined using model systems such as Ag-Au and Cu-Au by conventional electrochemical techniques, in situ scanning tunneling microscopy (STM), in situ small angle neutron scattering (SANS), ultrahigh speed digital photography of fracture events, and computer simulations. The STM and SANS work were specifically aimed at addressing a roughening transition known to occur in alloy systems undergoing corrosion at electrochemical potentials greater than the so-called critical potential. Analytical models of de-alloying processes including the roughening transition were developed that specifically include curvature effects that are important in alloy corrosion processes. Stress-corrosion experiments were performed on the same model systems using rapid optical and electrochemical techniques on 50 {micro}m--250 {micro}m thick sheets and small diameter wires. The primary goal of this work was to develop a fundamental understanding of the corrosion and electrochemistry of alloys and the stress-corrosion cracking processes these alloys undergo. Computer simulations and analytical work identified surface stress and an important parameter in environmentally assisted fracture. The major results of the research on this program since the summer of 1993 are briefly summarized.
Date: September 1, 1998
Creator: Sieradzki, K.
Partner: UNT Libraries Government Documents Department

Age hardening in rapidly solidified and hot isostatically pressed beryllium-aluminum-silver alloys

Description: Three different alloys of beryllium, aluminum and silver were processed to powder by centrifugal atomization in a helium atmosphere. Alloy compositions were, by weight, 50% Be, 47.5% Al, 2.5% Ag, 50% Be, 47% Al, 3% Ag, and 50% Be, 46% Al, 4% Ag. Due to the low solubility of both aluminum and silver in beryllium, the silver was concentrated in the aluminum phase, which appeared to separate from the beryllium in the liquid phase. A fine, continuous composite beryllium-aluminum microstructure was formed, which did not significantly change after hot isostatically pressing at 550 C for one hour at 30,000 psi argon pressure. Samples of HIP material were solution treated at 550 C for one hour, followed by a water quench. Aging temperatures were 150, 175, 200 and 225 C for times ranging from one half hour to 65 hours. Hardness measurements were made using a diamond pyramid indenter with a load of 1 kg. Results indicate that peak hardness was reached in 36--40 hours at 175 C and 12--16 hours at 200 C aging temperature, relatively independent of alloy composition.
Date: July 1, 1995
Creator: Carter, D.H.; McGeorge, A.C.; Jacobson, L.A. & Stanek, P.W.
Partner: UNT Libraries Government Documents Department

Landau-Ginzburg model of interphase boundaries in CsCl-type ferroelastics due to M{sup -}{sub 5} mode instability: LaAg{sub 1-x}In{sub x}

Description: We have constructed a Landau-Ginzburg model of ferroelastic domain walls in the tetragonal phase of CsCl-type intermetallic compounds. This improper ferroelastic phase transition is driven by the condensation of a degenerate zone-edge phononmode of M{sup -}{sub 5} symmetry and can be described by a six-component order parameter. Analytic and numerical kink-type soliton solutions for the order parameter profile and the strain distribution are obtained for three different interphase boundaries: a twin boundary and two antiphase boundaries. The stability, merging and splitting of various domain types are also studied. Specifically, a symmetry-allowed product phase of I4/mmm (D{sup 17}{sub 4h}) symmetry has been experimentally observed in pseudobinary rare earth alloys of composition RAg{sub 1-I} In{sub I} (R=La, Ce, Pr) and in related systems (YCu, LaCd).
Date: July 1, 1995
Creator: Hatch, D.M.; Saxena, A. & Barsch, G.R.
Partner: UNT Libraries Government Documents Department

Capillary flow solder wettability test

Description: A test procedure was developed to assess the capillary flow wettability of solders inside of a confined geometry. The test geometry was comprised of two parallel plates with a controlled gap of constant thickness (0.008 cm, 0.018 cm, 0.025 cm, and 0.038 cm). Capillary flow was assessed by: (1) the meniscus or capillary rise of the solder within the gap, (2) the extent of void formation in the gap, and (3) the time-dependence of the risen solder film. Tests were performed with the lead-free solders.
Date: January 1, 1996
Creator: Vianco, P.T. & Rejent, J.A.
Partner: UNT Libraries Government Documents Department

Zintl cluster chemistry in the alkali-metal-gallium systems

Description: Previous research into the alkali-metal-gallium systems has revealed a large variety of networked gallium deltahedra. The clusters are analogues to borane clusters and follow the same electronic requirements of 2n+2 skeletal electrons for closo-deltahedra. This work has focused on compounds that do not follow the typical electron counting rules. The first isolated gallium cluster was found in Cs{sub 8}Ga{sub 11}. The geometry of the Ga{sub 11}{sup 7{minus}} unit is not deltahedral but can be described as a penta-capped trigonal prism. The reduction of the charge from a closo-Ga{sub 11}{sup 13{minus}} to Ga{sub 11}{sup 7{minus}} is believed to be the driving force of the distortion. The compound is paramagnetic because of an extra electron but incorporation of a halide atom into the structure captures the unpaired electron and forms a diamagnetic compound. A second isolated cluster has been found in Na{sub 10}Ga{sub 10}Ni where the tetra-capped trigonal prismatic gallium is centered by nickel. Stabilization of the cluster occurs through Ni-Ga bonding. A simple two-dimensional network occurs in the binary K{sub 2}Ga{sub 3} Octahedra are connected through four waist atoms to form a layered structure with the potassium atoms sitting between the layers. Na{sub 30.5}Ga{sub 60{minus}x}Ag{sub x} is nonstoichiometric and needs only a small amount of silver to form (x {approximately} 2--6). The structure is composed of three different clusters which are interconnected to form a three-dimensional structure. The RbGa{sub 3{minus}x}Au{sub x} system is also nonstoichiometric with a three-dimensional structure composed of Ga{sub 8} dodecahedra and four-bonded gallium atoms. Unlike Na{sub 30.5}Ga{sub 60{minus}x}Ag{sub x}, the RbGa{sub 3} binary is also stable. The binary is formally a Zintl phase but the ternary is not. Some chemistry in the alkali-metal-indium system also has been explored. A new potassium-indium binary is discussed but the structure has not been completely characterized.
Date: March 27, 1998
Creator: Henning, R.
Partner: UNT Libraries Government Documents Department

Mechanical properties of Pb-free solder alloys on thick film hybrid microcircuits

Description: The technology drivers of the electronics industry continue to be systems miniaturization and reliability, in addition to addressing a variety of important environmental issues. Although the Sn-Pb eutectic alloy is widely used as a joining material in the electronics industry, it has drawn environmental concern due to its Pb content. The solder acts both as an electrical and mechanical connection within the different packaging levels in an electronic device. New Pb-free solders are being developed at Sandia National Laboratories. The alloys are based on the Sn-Ag alloy, having Bi and Au additions. Prototype hybrid microcircuit (HMC) test vehicles have been assembled to evaluate Pb-free solders for Au-Pt-Pd thick film soldering. The test components consist of a variety of dummy chip capacitors and leadless ceramic chip carriers (LCCC`s). The mechanical properties of the joints were evaluated. The reflow profiles and the solid state intermetallic formation reaction will also be presented. Improved solder joint manufacturability and increased fatigue resistance solder alloys are the goals of these materials.
Date: March 10, 1998
Creator: Hernandez, C.L.; Vianco, P.T.; Rejent, J.A. & Hosking, F.M.
Partner: UNT Libraries Government Documents Department

Processing and fabrication of high-{Tc} superconductors for electric power applications

Description: Recent developments in the powder-in-tube fabrication of (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} tapes include identification of high current transport regions of the superconductor core, optimization of conductor design and processing to take advantage of these high current regions, optimization of superconductor powders and heat treatments, and incorporation of flux pinning defects into the superconductor grains. These developments are briefly discussed and their implications are assessed.
Date: September 1997
Creator: Balachandran, U.; Iyer, A. N.; Goretta, K. C. & Haldar, P.
Partner: UNT Libraries Government Documents Department