The syntheses and properties of the iodotrisilanes (IH2Si)2SiH2, (IH2Si)2SiHI, I3SiSiI2SiH3, (I3Si)2SiH2 and Si3I8 are reported. All trisilanes were synthesized from the appropriate phenyltrisilanes and hydrogen iodide, with the exception of I5Si3H3, which was prepared by thermolysis of I3SiSiH3. The 29 Si-chemical shifts and 29Si29Si-coupling constants are reported. ab]Die Synthesen und Eigenschaften der Iodtrisilane (IH2Si)2SiH2, (IH2Si)2SiHI, I3SiSiI2SiH3, (I3Si)2SiH2 und Si3I8 werden beschrieben. Bis auf I5Si3H3, das während der Thermolyse von I3SiSiH3, entstand, wurden alle Iodtrisilane aus den entsprechenden Phenyltrisilanen mit Iodwasserstoff hergestellt. Die 29Si-Verschiebungen und 29Si29Si-Kopplungskonstanten werden mitgeteilt. 相似文献
Elemental mapping of freeze-dried cryosections from biological cells was done using the energy window mode and the quantitative mode. Quantitative mapping requires long measuring times and high electron exposure resulting in inhomogeneous shrinkage and distortion of the cryosection. Collection of X-ray spectra for quantitative analysis of intracellular structures and compartments combined with energy window mapping was found to be sufficiently fast and reliable to reveal inhomogeneities of the element distribution in cells. However, this method is suitable only for mapping elements without overlapping peaks in the X-ray spectrum. 相似文献
Carbon nanotubes (CNTs) show exceptional properties that render them attractive for incorporation in a new generation of high‐performance engineering composites with tailored properties. While a great deal of work has been done toward using CNTs as a reinforcing agent in polymer composites, the full potential of CNTs has yet to be reached. In this work, two case studies were proposed in order to analyze the effectiveness of CNTs and carbon fibers (CFs) as reinforcing agents. Micromechanics models for the stiffness and strength of hybrid composites, comprising CNTs and CFs are derived by considering the concept of effective fiber. In addition, the 2009 prices of commercially available CNTs are reviewed. The strongest, the stiffest, and the cheapest CFs commercially available are compared with single walled CNTs (SWCNTs) and multiwalled CNTs (MWCNTs). The simulated results from the micromechanics models show that the use of CFs makes the acquisition of composites with maximum tensile strengths of 4.18 GPa possible. Analysis of the cost versus property relation showed that CNTs are the most viable strengthening option for achieving composites with strengths of up to 11.61 GPa. It is also shown that CFs are the most viable stiffening option, making composites with Young's moduli of up to 383 GPa possible at the expense of the material's toughness. Moreover, it is shown that, in order to achieve CNT's true potential, several challenges have to be faced. CNTs have to be produced with higher purity, longer lengths, better integrity, in larger amounts, and at lower cost. Moreover, issues such as orientation of the CNTs, their concentration, interfacial adhesion, distribution, and dispersion have to be overcome.