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241.
Using a photoemission spectroscometer that operates close to ambient conditions of pressure and temperature we have determined the Pd-O phase diagram and the kinetic parameters of phase transformations. We found that on the (111) surface oxidation proceeds by formation of stable and metastable structures. As the chemical potential of O2 increases chemisorbed oxygen forms followed by a thin surface oxide. Bulk oxidation is a two-step process that starts with the metastable growth of the surface oxide into the bulk, followed by a first-order transformation to PdO.  相似文献   
242.
The sorption of hydrogen between the layers of the multilayered wall of nanotubular TiO2 was studied in the temperature range of -195 to 200 degrees C and at pressures of 0 to 6 bar. Hydrogen can intercalate between layers in the walls of TiO2 nanotubes forming host-guest compounds TiO2 x xH2, where x < or = 1.5 and decreases at higher temperatures. The rate of hydrogen incorporation increases with temperature and the characteristic time for hydrogen sorption in TiO2 nanotubes is several hours at 100 degrees C. The rate of intercalate formation is limited by the diffusion of molecular hydrogen inside the multilayered walls of the TiO2 nanotube. 1H NMR-MAS and XRD data confirm the incorporation of hydrogen between the layers in the walls of TiO2 nanotubes. The nature and possible applications of the observed intercalates are considered.  相似文献   
243.
The synthesis of molecular composites where rigid polymer molecules are reinforcing elements in a thermoset bisimide matrix has been investigated. The approach has been designed to avoid phase separation by selecting systems where reaction of amine-terminated rigid and semiflexible oligomers with maleimide unsaturation occurs prior to crosslinking of the thermoset. This objective has been met for some compositions. The concentration and molecular weight of the rigid oligomers have been varied. The structure of the reinforcing polymer, the reactivity of the maleimide and the conditions for composite synthesis are variables of critical importance, and further work must determine the promise and limitations of this approach.  相似文献   
244.
Several independent synthetic routes are described leading to the formation of a novel unsaturated tetracyclic phosphorus carbon cage compound tBu4C4P6 (1), which undergoes a light-induced valence isomerization to produce the first hexaphosphapentaprismane cage tBu4C4P6 (2). A second unsaturated isomer tBu4C4P6 (9) of 1 and the bis-[W(CO)5] complex 13 of 1 are stable towards similar isomerization reactions. Another starting material for the synthesis of the hexaphosphapentaprismane cage tBu4C4P6 (2) is the trimeric mercury complex [(tBu4C4P6)Hg]3 (11), which undergoes elimination of mercury to afford the title compound 2. Single-crystal X-ray structural determinations have been carried out on compounds 1, 2, 9, 11, and 13.  相似文献   
245.
246.
Ellipticine and a number of ellipticine analogs were converted to Reissert compounds. Alkylation of the 6-benzylellipticine Reissert compound gave a series of 1-substituted-6-benzylellipticines. 1-Cyanoellipticine, obtained through the Reissert compound, was hydrolyzed to ellipticine-1-carboxamide hydrochloride which was active against P388 lymphocytic leukemia. Other aspects of the chemistry of the ellipticine Reissert compound are presented.  相似文献   
247.
The FAKE method of approximate molecular-orbital calculations is presented and illustrated by application to a number of molecules. The method is of the extended Huckel type but uses accurately computed kinetic-energy matrix elements and avoids scale factors of the Wolfsberg—Helmholtz type. It also includes neighbor-atom charge effects and single-center off-diagonal matrix elements. These features permit FAKE occupied-orbital energies and charge distributions to come into close agreement with corresponding ab initio quantities.  相似文献   
248.
In ternary water-oil-nonionic alkyl polyglycol ether (C(i)E(j)) microemulsions, an increase in efficiency is always accompanied by the formation of a lamellar (L(alpha)) phase. The addition of an amphiphilic block copolymer to the ternary base system increases the efficiency of the microemulsion drastically while suppressing--at least partly--the formation of the L(alpha) phase. However, amphiphilic block copolymers can be used not only to suppress the formation of lyotropic liquid crystals but also for the opposite effect, namely, to induce their formation. To understand to what extent the increase in efficiency is accompanied by the formation of lyotropic liquid crystals, we studied phase diagrams of water-n-alkane-n-alkyl polyglycol ethers (C(i)E(j))-PEPX-PEOY at a constant volume fraction of oil in the water/oil mixture. Using polymers of the poly(ethylene propylene)-copoly(ethylene oxide) type, with M(PEP) = X kg mol(-1) and M(PEO) = Y kg mol(-1), we determined phase diagrams as a function of the polymer concentration, size, and symmetry. Moreover, the influence of a particular polymer mixture was studied, which turned out to be the best system if both a high efficiency and a low tendency to form an L(alpha) phase are needed.  相似文献   
249.
On the Preparation of Arsenic Dichloride Trifluoride, AsCl2F3 AsCl2F3 is prepared by pyrolysis of [AsCl4]+ [AsF6]?. The vibrational spectra of the new low temperature compound are reported and the valence force constants are calculated. The formation of AsCl2F3 by ligand exchange reactions is discussed.  相似文献   
250.
The composition range and (composite modulated) structure of compounds within the wide range non-stoichiometric LaSb2Snx, 0.1?x?0.75, solid solution is carefully investigated via a combined electron diffraction, XRD and electron probe microanalysis study. Evidence for metastability of the LaSb2Snx phase at the low x composition end of the solid solution is presented. Direct evidence is found for a reasonably (although by no means perfectly) well ordered Sn sub-structure which is, in general, mutually incommensurable with respect to a very well ordered underlying LaSb2 sub-structure along both a and c directions. The overall (3+2)-d superspace group symmetry is given along with a discussion of the consequences as regards the arrangement of the Sn atoms. The Sn sub-structure c-axis cell dimension shows very little variation with composition x providing direct experimental evidence of the importance of Sn-Sn metallic bonding (along one-dimensional [001] Sn strings) for the stability of the phase.  相似文献   
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