The oxidative resistance of polymeric geosynthetic barriers (GBR-P) used for road and railway tunnels

The results of autoclave tests according to DIN EN ISO 13438 (method C) and conventional oven tests in line with DIN EN 14575 are presented for the evaluation of the resistance to oxidation of geosynthetic barriers GBR-P based on polyethylene. These GBR-P products are used as a barrier layer against water in road and railway tunnels. The residual mechanical stability of the exposed materials was determined by tensile testing. The remaining activity of the stabiliser was investigated using the OIT method. The results of both accelerating test methods are discussed and compared in detail. Based on autoclave tests at three temperatures (e.g. 60, 70 and 80 °C) and 50 bar oxygen pressure, and additionally two more measurements at 80 °C and 10 and 20 bar oxygen pressure, a modified Arrhenius extrapolation is used for an assessment of the expected service time of one of the GBR-P products.     

Concealed Cyclotrimeric Polymorph of Lithium 2,2,6,6‐Tetramethylpiperidide Unconcealed: X‐Ray Crystallographic and NMR Spectroscopic Studies

Lithium 2,2,6,6‐tetramethylpiperidide (LiTMP), one of the most important polar organometallic reagents both in its own right and as a key component of ate compositions, has long been known for its classic cyclotetrameric (LiTMP)₄ solid‐state structure. Made by a new approach through transmetalation of Zn(TMP)₂ with tBuLi in n‐hexane solution, a crystalline polymorph of LiTMP has been uncovered. X‐ray crystallographic studies at 123(2) K revealed this polymorph crystallises in the hexagonal space group P6₃/m and exhibited a discrete cyclotrimeric (C_3h) structure with a strictly planar (LiN)₃ ring containing three symmetrically equivalent TMP chair‐shaped ligands. The molecular structure of (LiTMP)₄ was redetermined at 123(2) K, because its original crystallographic characterisation was done at ambient temperature. This improved redetermination confirmed a monoclinic C2/c space group with the planar (LiN)₄ ring possessing pseudo (non‐crystallographic) C_4h symmetry. Investigation of both metalation and transmetalation routes to LiTMP under different conditions established that polymorph formation did not depend on the route employed but rather the temperature of crystallisation. Low‐temperature (freezer at ?35 °C) cooling of the reaction solution favoured (LiTMP)₃; whereas high‐temperature (bench) storage favoured (LiTMP)₄. Routine ¹H and ¹³C NMR spectroscopic studies in a variety of solvents showed that (LiTMP)₃ and (LiTMP)₄ exist in equilibrium, whereas ¹H DOSY NMR studies gave diffusion coefficient results consistent with their relative sizes.     

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Catalytic and seeded shape-selective synthesis of II–VI semiconductor nanowires

We demonstrate catalytic and seeded shape-selective growth of CdSe nanostructures by a steady-state vapor-transport process. By varying the powder and sample temperatures, we observe a transition from a regime where catalytic growth is dominant to a metal-free self-induced nucleation regime. We then show that the best structural and optical quality are obtained by using CdSe colloidal nanocrystals as seeds for metal-free growth, as indicated by electron microscopy, X-ray diffraction and photoluminescence.     

Solution-phase synthesis of ICG-001, a β-turn peptidomimetic molecule inhibitor of β-catenin–Tcf-mediated transcription

The solution-phase synthesis of the β-turn peptidomimetic ICG-001, a selective inhibitor of Wnt/β-catenin signalling, which has been found to be important for both initiation and progression of cancers of different tissues and has been exploited as an extremely useful chemogenomic tool, was developed. This route is particularly suitable for the multigram scale preparation of ICG-001.     

Crystal structures of dibenzo[ce]‐1,2‐dithiine and its related oxides

The X‐ray structures of dibenzo[ce]‐1,2‐dithiine, dibenzo[ce]‐1,2‐dithiine‐5,5‐dioxide, diben‐ zo[ce]‐1,2‐dithiine‐5,5,6‐trioxide, and dibenzo[ce]‐1, 2‐dithiine‐5,5,6,6‐tetraoxide are reported and compared with the related “constrained'' naphthalene deri‐ vatives. The S‐S distances vary upon oxidation of the S centers in the order S‐S < SO‐S > SO₂‐S < SO₂‐SO > SO₂‐SO₂ i.e. the most oxidized sulfur atoms do not lead to the longest bond lengths. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:346–351, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20101     

Relating inhomogeneous deformation to local texture in zirconium through grain-scale digital image correlation strain mapping experiments

The effect of local texture on inhomogeneous plastic deformation is studied in zirconium subjected to uniaxial compression. Cross-rolled commercially pure Zr 702 plate that had a strong basal (0 0 0 1) texture through the plate thickness, and a non-basal texture in cross-section, was obtained. At a compressive strain rate of 1 s^?1, samples loaded either in the through-thickness or in-plane directions exhibited significant differences in yield strength, hardening response and failure mechanisms. These macroscopic differences are related to microstructural features by combining information from electron backscattered diffraction with real time in situ imaging and subsequent full-field strain measurements obtained using digital image correlation. Experimental results indicate that the through-thickness loaded zirconium samples, which show a strong basal-texture in the loading direction, do not deform homogeneously – implying the lack of a representative volume element. The detailed surface deformation fields provided by digital image correlation allow for a qualitative and quantitative analysis of the relationship between grain orientation and patterns of deformation bands that form as the precursors to development of an adiabatic shear band in the through-thickness loaded sample. For the in-plane loaded samples, inhomogeneities still exist at the microscale, but the collective behavior of several grains leads to a homogeneous response at the macroscale. It is observed that local texture for hcp polycrystals, which are significantly slip restricted, can directly affect both local and global response, even at low to moderate plastic strains.