Ternary phase equilibria in the Ga-As-Cr system and its relevance to diffusion and solubility studies

The phase equilibria in the Ga-As-Cr system were determined for As ? 50 a/o from room temperature to 1300°C by calorimetric and x-ray examination of appropriately prepared samples. Several corrections were made in the literature values for properties of Cr-As binary compounds. The ternary diagram shows that GaAs is not a dominant compound in the system and GaAs and Cr cannot coexist under equilibrium conditions. From one ternary tie triangle region and a solid plus liquid region, appropriate solubility and diffusion sources for Cr in GaAs for most temperatures can be obtained.     

Eisen und Stab

Ohne Zusammenfassung     

Synthesis and Molecular Structures of Hydrotris(dimethylpyrazolyl)borate Complexes of the Lanthanides

The reaction of lanthanide triflates with 2 equiv of potassium hydrotris(dimethylpyrazolyl)borate (Tp(Me)()2) gives good yields of complexes of composition Ln(Tp(Me)()2)(2)OTf. For La (2), Ce (3), Pr (4), and Nd (5) the complexes are seven-coordinate in the solid state with the triflate group coordinated to the metal in unidentate fashion. Complex 5 crystallizes in the monoclinic space group P2(1)/c with a = 17.629(3) ?, b = 12.740(2) ?, c = 18.163(3) ?, beta = 107.35(1) degrees, V = 3893(1) ?(3), Z = 4, and R(w) = 0.0458. For the complexes of Y (1), Sm (6), Eu (7), Gd (8), Dy (9), Ho (10), and Yb (11), the smaller size of the metal ion leads to ejection of the triflate from the coordination sphere and the complexes are ionic in the solid state with a six-coordinate metal center. Complex 11 crystallizes in the monoclinic space group C2/m with a = 16.593(7) ?, b = 13.671(5) ?, c = 8.746(2) ?, beta = 91.66(3) degrees, V = 1983(1) ?(3), Z = 2, and R(w) = 0.0416. In solution, however, complex 6 adopts a seven-coordinate molecular structure with the triflate ion within the first coordination sphere.     

The crosslinking of epoxy resins at interfaces. III. At a carbonized polyacrylonitrile surface

The crosslinking chemistry of an anhydride-cured epoxy resin, in the first 200–400 nm adjacent to a carbonized polyacrylonitrile (PAN) surface (a model for the surface of a carbon fiber), is significantly affected by the humidity history of that surface. Prior humid aging of the carbonized PAN surface increases the subsequent rate of consumption of anhydride curing agent, and decreases the yield of ester crosslinked products. The crosslinking chemistry of an amine-cured epoxy resin appears unchanged by the presence of the carbonized surface. Dynamic mechanical analysis (DMA) of unidirectional composites made from carbon fibers and the above epoxy resin matrices shows that the damping characteristics of composites made with an epoxy–anhydride matrix are sensitive to the preconditioning history of the carbon fibers, while composites made with an epoxy–amine matrix are unaffected by the preconditioning history of the fibers. Partial removal of the carbon fiber surface coating by dichloromethane extraction does not change the sensitivity of the composites to fiber preconditioning history. These results are rationalized on the basis of the effect moisture adsorbed by the carbonized PAN and by the carbon fiber has on the epoxy resin crosslinking processes.     

Air and water free solid-phase synthesis of thiol stabilized au nanoparticles with anchored, recyclable dendrimer templates

Solid-phase synthetic templates for Au nanoparticles were developed using Merrifield resins and polyamidoamine (PAMAM) dendrimers. This synthetic scheme affords the opportunity to prepare metal nanoparticles in the absence of air and water, and it does not necessitate phase transfer agents that can be difficult to remove in subsequent steps. Amine-terminated generation 5 PAMAM (G5NH2) dendrimers were grafted to anhydride functionalized polystyrene resin beads and alkylated with 1,2-epoxydodecane to produce G5C12anch. The anchored dendrimers bound both CoII and AuIII salts from toluene solutions at ratios comparable to those of solution phase alkyl-terminated PAMAM dendrimers. The encapsulated AuIII salts could be reduced with NaBH4 to produce anchored dendrimer encapsulated nanoparticles (DENs). Treatment of the anchored DENs with decanethiol in toluene extracted the Au nanoparticles from the dendrimers as monolayer protected clusters (MPCs). After a brief NaCN etch, the anchored dendrimers were readily recycled and a subsequent synthesis of decanethiol Au MPCs was performed with comparable MPC yield and particle size distribution.