The effect of Zn on precipitation in Al–Mg–Si alloys

Effects of addition of Zn (up to 1 wt%) on microstructure, precipitate structure and intergranular corrosion (IGC) in an Al–Mg–Si alloys were investigated. During ageing at 185?°C, the alloys showed modest increases in hardness as function of Zn content, corresponding to increased number densities of needle-shaped precipitates in the Al–Mg–Si alloy system. No precipitates of the Al–Zn–Mg alloy system were found. Using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), the Zn atoms were incorporated in the precipitate structures at different atomic sites with various atomic column occupancies. Zn atoms segregated along grain boundaries, forming continuous film. It correlates to high IGC susceptibility when Zn concentration is ~1wt% and the materials in peak-aged condition.     

Lattice disorder in germanium by boron ion bombardment

Abstract

The lattice disorder produced in germanium by 56keV boron-ion bombardment has been measured using the channeling-effect technique. The dependence on dose (10¹⁴-10¹⁶ ions/cm²) and implantation temperature (?90 °C to +130°C) has been studied. It is found that at room-temperature, each incident boron ion creates ?10 times more disorder in germanium than in silicon. It is remarked that, contrary to the present results, previously established anneal stages generally occur at significantly lower temperatures in germanium than in silicon.     

Two‐Dimensional Oligo(phenylene‐ethynylene‐butadiynylene)s: All‐Covalent Nanoscale Spoked Wheels

Round and round : Covalently bound spokes induce an efficient template‐directed cyclization towards a rigid molecular wheel (see figure) and afford dramatically increased shape‐persistence properties compared with non‐strutted macrocycles.

     

Shape-persistent macrocycles: building blocks for complex organic and polymeric architectures

Alkyl- and Oligostyrene substituents were attached to shape-persistent macrocycles based on a phenyl-ethynyl backbone. In good solvents for both the rigid core and the flexible corona no aggregation occurred. Whereas, addition of a solvent that selectively solubilizes the corona induced a solvophobic aggregation. For alkyl substituted rings the experimental data were described by a monomer-dimer equilibrium. In contrast, the oligostyrene substituted rings formed more expanded aggregates which were investigated by scattering and by imaging methods. The superstructures are consequently described as hollow supramolecular cylindrical brushes.     

A superquadratic indefinite elliptic system and its Morse–Conley–Floer homology

We study critical points of the indefinite functional by applying Floer's homology construction to the ordinary gradient flow of the functional f on a suitable Sobolev space. One of our main observations is that even though this flow is well posed in both time directions and lacks any kind of smoothing property one can still obtain compactness of connecting orbit spaces and thus define the Floer homology for . Received November 11, 1997; in final form March 12, 1998     

Electron microscopy investigations of the morphology of a polyester-polyurethane

In the current paper the morphology of a slightly crosslinked polyester-polyurethane (hard-segment content ca. 33 wt.-%) is studied by means of transmission electron microscopy (TEM). A new staining technique based on ruthenium tetroxide was applied. This new technique allows the unambiguous visualization of the typical microdomain structure of the polyurethane and also of a wide size spectrum of globular hard-segment-rich domains which result from phase separation in the early stage of preparation. The hard-segment-rich microdomains have a size between 1.5 and 10 nm while the globular domains span a size spectrum from 10 to 2000 nm.     

Electron microscopy investigations of polyester-polyurethane elastomers stained with ruthenium tetroxide

Microphase separation of as-reacted polyester-polyurethane samples based on α-hydro-ω-hydroxypoly(oxyethyleneoxyadipoyl)/4,4′-methylenedi(phenyl isocyanate)/1,4-butanediol/2-ethyl-2-hydroxymethyl-1,3-propanediol (mole ratio 1:3,2:1,9:0,1) was studied using transmission electron microscopy. A new staining technique was applied which uses ruthenium tetroxide vapour for the treatment of the polymer. Ruthenium tetroxide reacts preferably with the hard-segment-rich microdomains of the polyester-polyurethane. Therefore, a well-contrasted pattern is formed by staining which reflects the microdomain structure of the polymer. The hard-segment-rich microdomains have irregular, mostly globular shape, and their sizes range from about 2 to 8 nm.