Discovery of Super-Li Rich Red Giants in Dwarf Spheroidal Galaxies

Stars destroy lithium (Li) in their normal evolution. The convective envelopes of evolved red giants reach temperatures of millions of K, hot enough for the 7Li(p,alpha)4He reaction to burn Li efficiently. Only about 1% of first-ascent red giants more luminous than the luminosity function bump in the red giant branch exhibit A(Li) > 1.5. Nonetheless, Li-rich red giants do exist. We present 15 Li-rich red giants--14 of which are new discoveries--among a sample of 2054 red giants in Milky Way dwarf satellite galaxies. Our sample more than doubles the number of low-mass, metal-poor ([Fe/H] <~ -0.7) Li-rich red giants, and it includes the most-metal poor Li-enhanced star known ([Fe/H] = -2.82, A(Li)_NLTE = 3.15). Because most of these stars have Li abundances larger than the universe's primordial value, the Li in these stars must have been created rather than saved from destruction. These Li-rich stars appear like other stars in the same galaxies in every measurable regard other than Li abundance. We consider the possibility that Li enrichment is a universal phase of evolution that affects all stars, and it seems rare only because it is brief.Comment: 6 pages, 3 figures, accepted to ApJ Letters, version 3 includes additional references and minor typographical change

Combustion Synthesis of Large Bulk Nanostructured Ni 65

A large bulk nanostructured Ni65Al21Cr14 alloy with dimensions of Φ 100 mm × 6 mm was produced by combustion synthesis technique followed with rapid solidification. The Ni65Al21Cr14 alloy was composed of γ′-Ni3Al/γ-Ni(Al, Cr) eutectic matrix and γ-Ni(Al, Cr) dendrite. The eutectic matrix consisted of 80–150 nm cuboidal γ′-Ni3Al and 2–5 nm γ-Ni(Al, Cr) boundary. The dentrite was comprised of high-density growth twins with about 3–20 nm in width. The nanostructured Ni65Al21Cr14 alloy exhibited simultaneously high fracture strength of 2200 MPa and good ductility of 26% in compression test

Combustion synthesis of bulk nanocrystalline iron alloys

The controlled synthesis of large-scale nanocrystalline metals and alloys with predefined architecture is in general a big challenge, and making full use of these materials in applications still requires greatly effort. The combustion synthesis technique has been successfully extended to prepare large-scale nanocrystalline metals and alloys, especially iron alloy, such as FeC, FeNi, FeCu, FeSi, FeB, FeAl, FeSiAl, FeSiB, and the microstructure can be designed. In this issue, recent progress on the synthesis of nanocrystalline metals and alloys prepared by combustion synthesis technique are reviewed. Then, the mechanical and tribological properties of these materials with microstructure control are discussed

Ultrafine Eutectic-Dendrite Composite Bulk Fe-B Alloy with Enhanced Ductility

Bulk Fe 2 B and Fe 3 B alloys have been prepared by a self-propagating high temperature synthesis combining rapid solidification technique. The Fe 2 B and Fe 3 B alloys are composed of t-Fe 2 B dendrite and ultrafine eutectic matrix with t-Fe 2 B and -Fe, and the dendrites are rounded by the matrix. The volume fractions of the dendrite of the Fe 2 B and Fe 3 B alloys are 90% and 20%, respectively. The fracture strength reduces from 3400 MPa to 2660 MPa with the increase of dendrite content, but the strain at fracture rises markedly from 3% to 19%. The result indicates that a small quantity of dendrites embedded in the ultrafine eutectic matrix can reinforce the ductility

Wear Behaviour of Nanocrystalline Fe88Si12 Alloy in Water Environment

Wear behaviour of nanocrystalline Fe88Si12 alloy has been investigated in water environment compared with the coarse grained counterpart. The friction coefficient of the Fe88Si12 alloy changes slightly with the grain size. The wear resistance is enhanced as the grain size decreases first and then reduces when the grain size continues to decrease, although the hardness of the Fe88Si12 alloy decreases monotonically with the grain size. It is contrary to the predications of Archard’s formula. The best wear resistance of Fe88Si12 alloy with grain size of 40 nm in our present work is attributed to the proper grain boundary volume fraction and composite phase structures of disordered B2 and ordered D03

Friction and Wear Behavior of an Ag–Mo Co-Implanted GH4169 Alloy via Ion-Beam-Assisted Bombardment

Ag, Mo, and Ag–Mo were respectively implanted into GH4169 alloy substrates without heating via ion-beam-assisted bombardment technology (IBAB). In addition, the wear performance under low sliding speed and applied load were researched at room temperature (RT). A small amount silver molybdate phase could be detected on the surface of the co-implanted GH4169 alloy bombarded by a high-energy ion beam. The average friction coefficients under the steady wear state had almost no change at all. Compared with the un-implanted GH4169 alloys, the wear rate of the GH4169 alloys with co-implantation of Ag and Mo was reduced by 75%. A large amount of the silver molybdate phase could be generated due to the tribo-reaction on the worn surface during sliding. It benefits the formation of continuous oxide layers as lubrication and protected layers, leading to the change in the predominant wear mechanism from abrasion and adhesion wear to oxidation wear

Excellent Tribological Properties of Lower Reduced Graphene Oxide Content Copper Composite by Using a One-Step Reduction Molecular-Level Mixing Process

Reduced graphene oxide (RGO) composite copper matrix powders were fabricated successfully by using a modified molecular-level mixing (MLM) method. Divalent copper ions (Cu2+) were adsorbed in oxygen functional groups of graphene oxide (GO) as a precursor, then were reduced simultaneously by one step chemical reduction. RGO showed a distribution converting from a random to a three-dimensional network in the copper matrix when its content increased to above 1.0 wt.% The tribological tests indicated that the friction coefficient of the composite with 1.0 wt.% RGO decreased markedly from 0.6 to 0.07 at an applied load of 10 N, and the wear rate was about one-third of pure copper. The excellent tribological properties were attributed to a three-dimensional and uniform distribution, which contributes to improving toughness and adhesion strength

Low‐Temperature Preparation Copper‐Doped Nickel Chloride Cathode for Thermal Battery Overcomes the Energy‐Power Trade‐Off

Nickel chloride (NiCl2) is a typical hexagonal layered semiconductor material with wide application. However, it is mainly restricted by complicated technological process within ultrahigh dehydration temperature. Utilizing copper doping, a sort of high purity and remarkable crystallinity NiCl2 is fabricated using a simple low‐temperature calcination technique. The dehydration temperature is decreased from 600 to 400 °C because the adsorbed copper ions on NiCl2 dihydrate surface can weaken NiO bond strength. Serving for thermal battery cathode, copper‐doped NiCl2 exhibits remarkable discharge ability at 500 mA cm−2, equipped with supernormal power density of 16.27 kW kg−1 and energy density of 717 Wh kg−1 simultaneously. Its energy density is increased by 28% compared to NiCl2. Copper doping optimizes thermodynamics process of discharge reaction and modifies local electronic structure of NiCl2. For copper‐doped NiCl2, the shift of Ni 3d and Cl 3p to lower energy level results in elevated redox potential, and the reduction of bandgap accelerates the carrier mobility, further promoting discharge degree. Utilizing metal ions dopant, this research surmounts the low‐temperature synthesis of NiCl2 and addresses its inferior electrochemical performance, ensuring high energy‐power output. This will expand the application scenarios of NiCl2‐based cathode materials