The improved understanding of adsorption chemistry which has arisen from the development of new surface analytical techniques during the last twenty years has had a major effect on the understanding of catalytic reaction mechanisms. However, there are many other areas of technology where Interfacial chemistry has a determining role but where the understanding is much less developed. In this paper examples are presented of the role of interfacial chemistry in adhesion. In particular, It Is shown that modification of a surface to the extent of just a few atomic layers in depth can have dramatic effects on the performance of adhesive bonds, particularly when exposed to hostile environmental conditions. These examples will be used to highlight a need for greater fundamental understanding of the interfacial chemistry of adhesion and also other technologies where interface effects are dominant. 相似文献
Plasma spraying and pack-aluminising processes were combined and applied to the nickel-base superalloy Mar-M247 to improve its cyclic oxidation resistance. The performance tests of duplex ZrO2-8 wt.%Y2O3/MCrAlY thermal barrier coatings (TBCs) were conducted at 1050 °C, 1075 °C, 1100 °C, 1150 °C and 1200 °C. The results of the experiments in this study showed that TBC specimens with the aluminised MCrAlY bond coat exhibited higher cyclic lives (except for the Ni-22Cr-10Al-1Y bond coat), at all the temperatures tested, than specimens on which the bond coat was not aluminised. The microstructures of the Co-29Cr-6Al-1Y, Co-32Ni-21Cr-8Al-0.5Y and Ni-22Cr-10Al-1Y bond coats with or without aluminising treatment were examined in detail using a scanning electron microscope equipped with an electron probe microanalyzer. 相似文献
The nature of ultrafast energy dissipation in poly(n-hexylsilyne), a prototypical σ-delocalized alkysilicon network polymer, is explored. This disordered silicon backbone material exhibits strong near-UV to visible band-edge absorption and a high quantum yield of visible emission. The time evolution of the emission band is studied over four decades of time using time-resolved luminescence as a probe. The data indicate that while there is an ‘intrinsic’ Stokes shift after photoexcitation due to kinetic energy relaxation (<10ps), thermalization within a dense band of vibronic states via intramolecular phonon-assisted hopping on a nanosecond timescale is the dominant mechanism for excited-state decay. The data can be understood in terms of theoretical predictions for energy relaxation in disordered materials. 相似文献
The absorption spectrum of poly(3-alkylthiophene) gel changes drastically in association with a volume instability upon changing the solvent composition and also the temperature. In the expanded state in chloroform and at high temperature, the photoluminescence is much enhanced compared with the shrunken state in ethanol and at low temperature. This gel chromism and anomalous luminescence are discussed in terms of the change of effective conjugation length induced by the steric hindrance and the dynamics of the photoexcited species. 相似文献
Photoinduced phase transitions have been observed between the two phases in single crystals of polydiacetylenes with side-groups of alkylurethanes. The threshold of the excitation intensity for the photochromism is extremely low, one absorbed photon per 140 repeated backbone units, indicating a collective nature of the photoconversion. The excitation spectra for the converted fraction clearly show that the photoinduced phase transition is mediated by photogeneration of polaronic species and not of singlet excitons. 相似文献
Significant economic savings can be achieved by improving the wear lifetime of precision manufacturing tools through nitrogen-ion implantation. This near-ambient temperature, surface modification process preserves dimensional integrity and surface finish while eliminating delamination problems that are often associated with overlay coatings. Conventional ion implantation is a line-of-sight process which requires elaborate manipulation and masking to uniformly implant components of complex shapes. A recently developed process, plasma source ion implantation (PSII), circumvents this line-of-sight restriction and makes ion implantation more attractive economically. In this article, the effects of PSII of nitrogen at a target bias of 50 kV, to a dose of 0.3 × 1018 atoms/cm2 on the surface microstructure and mechanicalproperties of AISI S1 tool steel are presented. 相似文献
Chiroptical luminescence and circular dichroism measurements are reported for single crystals of Ho2Ge2O7. These crystals belong to the tetragonal space group P4,2,2 (or P43212) with Z=4. Each Ho3+ ion in the crystal structure is coordinated to seven oxygens to form a distorted pentagonal bipyramid. The Ho3+ ions exhibit luminescence from several excited multiplet levels; chiroptical luminescence spectra are reported for 6I8 → 6F6, 6S2, and 6F3 at a sample temperature of 10 K. Room-temperature absorption and circular dichroism measurements are reported for the 6I8 → 6F6, 5S2, 6F4, and 6F3 transition regions. 相似文献
We have studied theoretically and experimentally the fluorescence enhancement in fluoroborate glasses, doped with the ion Eu3+, containing small silver particles. The model developed shows that the gain coefficient has quenching and enhancement regions. The absorption peak of the metallic particles occurs at 425 nm, which is not in resonance with the 5L6 level of the ion Eu3+. For this reason it is not possible to make a complete comparison between theoretical and experimental results, but the structure of the absorption spectra allows us to check some crucial aspects of the problem, such as energy transfer, enhancement of the local field and the high absorption by the particle system. Results of electronic microscopy have revealed non-uniformity of the particle distribution with average radii of approximately 20 Å and 35 Å and a measured localized mean filling factor of 0.02. 相似文献
The inner filter effect is observed in luminescence whenever a second substance is present that has absorptions which overlap the luminescence. This results in a diminution of the luminescence at those wavelengths and is generally observed in solution. In the present communication we show that this effect can be observed when a solid rare earth complex is physically mixed with a solid luminescent organic matrix with which it does not interact. The resulting luminescence is reduced in emission intensity at those wavelengths corresponding to the absorptions of the rare earth ion. This is illustrated with a mixture of Na3[Ho(ODA)3] ·2NaClO4·6H2O and pyrene at 77 K, and it is shown that the absorption spectrum of the holmium complex can be extracted from the luminescence spectrum of pyrene. This absorption spectrum is in good agreement with that obtained by conventional spectroscopy with a single crystal. 相似文献
This paper deals with the role of dispersed lanthana as an active phase in several catalytic reactions: CO hydrogenation, CO oxidation, and oxidative dimerization of methane.
Characterization of the prepared catalysts indicates that lanthana can be effectively dispersed on silica and on ceria. While in the case of silica-supported catalysts lanthana appears at the surface, leading to an almost full coverage for loadings higher than 40%, in the case of ceria-based systems, lanthana forms a solid solution with the support.
In all the reactions studied, the presence of lanthana can be related to significant changes in the catalytic properties of the bare supports. Thus, the selectivity towards the total oxidation products observed on pure ceria is decreased, and the low activity shown by silica is enhanced. For the CO+H2 reaction, the addition of lanthana also generates upgraded products. 相似文献