Oxide film on metal substrate reduced to form metal-oxide-metal layer structure

Electrically conductive layer of zirconium on a zirconium-oxide film residing on a zirconium substrate is formed by reducing the oxide in a sodium-calcium solution. The reduced metal remains on the oxide surface as an adherent layer and seems to form a barrier that inhibits further reaction

Should Labor Defend Worker Rights as Human Rights? A Debate

The authors debate the relative merits and drawbacks of defining the labor movement under the umbrella of human rights, and the virtues of the rights of the individual versus the solidarity of the community

Instrumentation for potentiostatic corrosion studies with distilled water

Corrosion is studied potentiostatically in the corroding environment of distilled water with an instrument that measures the potential of the corroding specimen immediately after interruption of the polarizing current. No current is flowing. The process permits compensation for IR drops when potentiostatic control is used in high resistance systems

Method and apparatus for dissipating remanent fields and preserving diamagnetism of ceramic superconductors

A method for dissipating a remanent field, created when a magnetic field is brought into contact with a superconductor, while preserving the diamagnetism of a superconductor comprises the steps of (1) providing a ceramic superconductor; (2) continuously or intermittently generating an AC current to the ceramic superconductor; and (3) gradually decreasing the AC current until the undesired remanent field is dissipated

Directional isothermal growth of highly textured Bi2Sr2CaCu2Oy

For Bi2Sr2CaCu2Oy (2212), it is shown that an oxygen gradient, as opposed to a temperature gradient, can be used to produce large bulk forms of the 2212 superconductor with highly textured microstructures from an oxygen‐deficient melt held at a constant temperature. Material produced in this manner was found to have transition temperatures between 85 and 92 K, high critical current densities below 20 K, and modest critical current densities at 77 K

Development of commercially viable high-{Tc} Bi-2223 superconductor tapes

Long lengths of flexible Ag-clad Bi-2223 Superconductors have been fabricated by the powder-in-tube technique using prereacted, poly-phase, Pb-doped Bi-Sr-Ca-Cu-O powders. At liquid helium (4.2 K) temperature, improved process conditions yielded transport critical current density (J{sub c}) values greater than 10{sup 5} A/cm{sup 2} at zero field; at liquid nitrogen (77K) temperature, the J{sub c} values of short tape samples exceeded 4 {times} 10{sup 4} A/cm{sub 2}. Rolled tapes are cut into lengths up to 2 - meters long and are used in parallel to fabricate small superconducting pancake coils by the ``wind-and-react`` technique. The cots are characterized at 77K and 4.2 K. The J{sub c} of the coils are up to 80% of the short, rolled sample result at 77 K. The coils exhibited these results even after being cooled and warmed several times between ambient, 77 K and 4.2 K, indicating their stability following thermal cycling

Processing and properties of hot-forged bulk superconductors

(Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} (Bi-2223) and TlBa{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} (Tl-1223) bars were hot forged in air at 820--850C. Final stresses of 2--3 MPa were sufficient to produce >95% dense Bi-2223 bars. In contrast, stresses to {approx}42 MPa were able to produce only 75--80% dense Tl-1223 bars. The Bi-2223 bars were more phase-pure and exhibited much stronger c-axis textures than the Tl-1223. Maximum critical current densities at 77 K were 8 {times} 10{sup 4} A/cm{sup 2} for the Bi-2223 and 2 {times} 10{sup 4}/cm{sup 2} for the Tl-1223. Fracture strength and toughness values were 140 MPa and 2.9 MPa{radical}m for the Bi-2223 and 50 MPa and 0.5 MPa{radical}m for the Tl-1223

Teaching Matters, Volume 2: Essays by the faculty and staff at the University of Maine at Farmington

Essays by the faculty and staff at the University of Maine at Farmington.https://scholarworks.umf.maine.edu/publications/1087/thumbnail.jp

Mechanical properties of nanocrystalline metals, intermetalics and multiphase materials determined by tension, compression and disk-bend techniques

The mechanical behavior of nanocrystalline metallic, intermetallic, and multiphase materials was investigated using tension, compression, and disk-bend techniques. Nanocrystalline NiAl, Al-Al{sub 3}Zr, and Cu were synthesized by gas condensation and either resistive or electron beam heating followed by high temperature vacuum compaction. Disk- bend tests of nanocrystalline NiAl show evidence of improved ductility at room temperature in this normally extremely brittle material. In contrast, tension tests of multiphase nanocrystalline Al- Al{sub 3}Zr samples show significant increases in strength by substantial reductions in ductility with decreasing grain size. Compression tests of nanocrystalline copper result in substantially higher yield stress and total elongation values than those measured in tensile tests. Implications for operative deformation mechanisms in these materials are discussed

Visualizing size-dependent deformation mechanism transition in Sn

Displacive deformation via dislocation slip and deformation twinning usually plays a dominant role in the plasticity of crystalline solids at room temperature. Here we report in situ quantitative transmission electron microscope deformation tests of single crystal Sn samples. We found that when the sample size was reduced from 450 nm down to 130 nm, diffusional deformation replaces displacive plasticity as the dominant deformation mechanism at room temperature. At the same time, the strength-size relationship changed from “smaller is stronger” to “smaller is much weaker”. The effective surface diffusivity calculated based on our experimental data matches well with that reported in literature for boundary diffusion. The observed change in the deformation mode arises from the sample size-dependent competition between the Hall-Petch-like strengthening of displacive processes and Coble diffusion softening processes. Our findings have important implications for the stability and reliability of nanoscale devices such as metallic nanogaps.National Science Foundation (U.S.) (CMMI-0728069)National Science Foundation (U.S.) (DMR-1008104)National Science Foundation (U.S.) (DMR-1120901)United States. Air Force Office of Scientific Research (FA9550-08-1-0325