排序方式: 共有69条查询结果,搜索用时 31 毫秒
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Ilenia CarpentieriValentina Brunella Pierangiola BraccoMaria Cristina Paganini Elena Maria Brach del PreverMaria Paola Luda Sara BonomiLuigi Costa 《Polymer Degradation and Stability》2011,96(4):624-629
The radiation-induced oxidative degradation of polyethylenes (PEs) with different degrees of crystallinity was characterized after electron-beam irradiation and during storage at room temperature.UHMWPE, HDPE, LDPE, LLDPE and an ethylene-octene copolymer (Engage) were e-beam irradiated to 30 or 60 kGy in vacuum or in air and stored at room temperature in air. EPR spectroscopy was used to investigate macro-radicals produced during irradiation and their post-irradiation changes. FTIR spectroscopy was used to monitor changes in the polymer structure, induced by irradiation, and to follow post-irradiation oxidation.We found that the crystallinity and the size of the crystalline lamellae, in particular, play a major role on the post-irradiation effects. The low-crystallinity polyethylenes showed no oxidation or oxidation only to a small extent, even when irradiated and stored in air. On the contrary, development of post-irradiation oxidation was observed in HDPE and UHMWPE. We attribute these results to a different reactivity of the macro-alkyl radicals formed upon irradiation in the amorphous or in the crystalline phase. While the radicals formed in the amorphous phase decay in short time, the migration time of the radicals trapped in the crystalline phase to the amorphous one is a key factor, governing the oxidation process. 相似文献
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Czoska AM Livraghi S Paganini MC Giamello E Di Valentin C Pacchioni G 《Physical chemistry chemical physics : PCCP》2011,13(1):136-143
Nitrogen boron co-doped TiO(2) prepared via sol-gel synthesis and active under visible light, contains two types of paramagnetic extrinsic defects, both exhibiting a well resolved EPR spectrum. The first center is the well characterized [N(i)O]˙ species (i = interstitial) also present in N-doped TiO(2), while the second one involves both N and B. This latter center (labeled [NOB]˙) exhibits well resolved EPR spectra obtained using either (14)N or (15)N which show a high spin density in a N 2p orbital. The structure of the [NOB]˙ species is different from that previously proposed in the literature and is actually based on the presence of interstitial N and B atoms both bound to the same lattice oxygen ion. The interstitial B is also linked to two other lattice oxygen ions reproducing the trigonal planar structure typical of boron compounds. The energy level of the [NOB]˙ center lies near the edge of the valence band of TiO(2) and, as such, does not contribute to the visible light absorption. However, [NOB]˙ can easily trap one electron generating the [NOB](-) diamagnetic center which introduces a gap state at about 0.4 eV above the top of the valence band. This latter species can contribute to the visible light activity. 相似文献
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Chen D Albuquerque IF Baublis VV Bondar NF Carrigan RA Cooper PS Lisheng D Denisov AS Dobrovolsky AV Dubbs T Endler AM Escobar CO Foucher M Golovtsov VL Goritchev PA Gottschalk H Gouffon P Grachev VT Khanzadeev AV Kubantsev MA Kuropatkin NP Lach J Lang Pengfei Lebedenko VN Li Chengze Li Yunshan Mahon JR McCliment E Morelos A Newsom C Pommot Maia MC Samsonov VM Schegelsky VA Shi Huanzhang Smith VJ Sun CR Tang Fukun Terentyev NK Timm S Tkatch II Uvarov LN Vorobyov AA Yan Jie Zhao Wenheng 《Physical review letters》1992,69(23):3286-3289
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Foucher M Albuquerque IF Bondar NF Carrigan R Chen D Li Chengze Cooper PS Denisov AS Dobrovolsky AV Dubbs T Endler AM Escobar CO Tang Fukun Golovtsov VL Goritchev PA Gottschalk H Gouffon P Grachev VT Shi Huanzhang Yan Jie Khanzadeev AV Kubantsev MA Kuropatkin NP Lach J Luksys M Lebedenko VN Dai Lisheng Mahon JR McCliment E Morelos A Newsom C Lang Pengfei Pommot Maia MC Samsonov VM Zheng Shuchen Smith VJ Terentyev NK Timm S Tkatch II Uvarov LN Vorobyov AA Zhao Wenheng Zhong Yuanyuan 《Physical review letters》1992,68(20):3004-3007
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Some cases of formation and stabilization of charge carriers (electron and holes) at the surface of solid oxides are discussed. Charge carriers can be simultaneously or independently stabilized at the surface metal oxides. In the former case, they usually derive from a process of charge separation in the solid triggered by above band gap irradiation. In the second case, the charge carrier isolation is the result of a chemical alteration of the stoichiometric equilibrium of the solid either by matter addition or by effect of chemical impurities (valence induction). Electron paramagnetic resonance (EPR) is highly suited to monitor the process of charge separation and to characterize electron or hole centers stabilized in the solid or at its surface. In this paper examples of trapped electron and/or trapped hole centers as detected by continuous-wave EPR at the surface of simple binary oxides are discussed with particular emphasis to the formation mechanism, the EPR parameters and the chemical reactivity. 相似文献
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Robert M. Adlington Jack E. Baldwin William MC Coull Gareth J. Pritchard Christopher J. Schofield Nicholas J. Westwood 《合成通讯》2013,43(21):3803-3813
N-Arylsulfonylation of 2-azetidinones can lead to the diastereoselective formation of oligomerization products. However, a simple increase of arylsulfonyl chloride concentration minimized oligomerization and allowed preparation of 1-arylsulfonyl-2-azetidinones in good yield. 相似文献
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