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排序方式: 共有697条查询结果,搜索用时 531 毫秒
51.
Yanfeng Wang Li ZhengxianDu Jihong Hua YunfengWang Baoyun 《Applied Surface Science》2011,258(1):456-460
Materials’ surface service property could be enhanced by transition metal nitride hard coatings due to their high hardness, wear and high temperature oxidation resistance, but the higher friction coefficient (0.4-0.9) of which aroused terrible abrasion. In this work, quinternary (Ti,Al,Si,C)N hard coating 3-4 μm was synthesized at 300 °C using plasma enhanced magnetron sputtering system. It was found that the coating's columnar crystals structure was restrained obviously with the increase of C content and a non-columnar crystals growth mode was indicated at the C content of 33.5 at.%. Both the XRD and TEM showed that the (Ti,Al,Si,C)N hard coatings had unique nanocomposite structures composed of nanocrystalline and amorphous nc-(Ti,Al)(C,N)/nc-AlN/a-Si3N4/a-Si/a-C. However, the coatings were still super hard with the highest hardness of 41 GPa in spite of the carbon incorporation. That a-C could facilitate the graphitization process during the friction process which could improve the coating's tribological performance. Therefore, that nanocomposite (Ti,Al,Si,C)N coatings with higher hardness (>36 GPa) and a lower friction coefficient (<0.2) could be synthesized and enhance the tribological performance and surface properties profoundly. 相似文献
52.
In the present paper, we deal with the complex Szasz-Durrmeyer operators and study Voronovskaja type results with quantitative estimates for these operators attached to analytic functions of exponential growth on compact disks. Also, the exact order of approximation is found. 相似文献
53.
This paper is concerned with the construction of globally smooth solutions near a given global Maxwellian to the Cauchy problem of the Vlasov-Poisson-Boltzmann system for non-cutof hard potentials in three space dimensions without the neutral condition imposed on the initial perturbation.Our analysis is based on the time-weighted energy method and some delicate estimates. 相似文献
54.
《Physics and Chemistry of Liquids》2012,50(1):51-58
Abstract A general proof is given that the classical second virial coefficient satisfies the requirement for the non-existence of a termination point of any locus of Cv extrema. This validity criterion is applied to some proposed forms for the second virial coefficient. The order of the termination temperatures is verified for a fairly general intermolecular potential. In particular a proof is given that TF lies between TC and TA. Also the hard-core limit of the ratio TD/TA(~2) is examined briefly. 相似文献
55.
Amphiphilic urethane acryale hydrogels containing ionic groups (dimethylolpropionic acid) were prepared by varying the molecular
weight of the soft segment (polyether type) and the type of diisocyanate, and their mechanical properties were examined. They
showed heterophasic gel structure composed of ionic hard domains induced by aggregation of the ionic groups and polyether
soft domains comprising the urethane acrylate network. This heterophasic structure could be confirmed by dynamic mechanical
analysis (DMA) and by wide-angle X-ray scattering analysis (WAXS); the crystallinity detected by WAXS and the transition peak
of the ionic hard domains detected by DMA strongly suggested that there were ionic aggregates. These ionic aggregates acted
as reinforcing fillers in the network, which eventually enhanced the tensile strength of the hydrogels. Above all, the tensile
properties of the hydrogels were of interest in that the trends of the stress-strain curves were consistent with the rubbery
ones. It is believed that the higher purity of the polyether soft domains resulted from the heterophasic gel structure imparting
further elastomeric properties on the network.
Received: 31 July 1998 Accepted in revised form: 15 October 1998 相似文献
56.
57.
A procedure for predicting thermodynamic, dynamic, and rheological properties of polymerically stabilized colloidal dispersions
in good solvents by mapping onto an effective hard sphere dispersion is investigated and evaluated for its range of applicability.
Configurational pressures and energies, calculted by Monte Carlo simulations, are used to assess the model's accuracy for
predicting thermodynamic data. Similarly, long-time self-diffusivities, calculated by equilibrium Brownian Dynamic simulations,
are used to assess the model's feasibility for predicting dynamic properties. Finally, zero shear viscosities are calculated
by the method of hydrodynamic preaveraging and compared to rheological measurements. The various testing methods demonstrate
the effectiveness of the procedure and suggest the model's range of applicability.
Received: 13 March 2000 Accepted: 28 June 2000 相似文献
58.
59.
Dong Ya Yang Chun Pu Hu Sheng Kang Ying 《Journal of polymer science. Part A, Polymer chemistry》2005,43(12):2606-2614
A series of polyester‐based poly(urethane urea) (PUU) aqueous dispersions with well‐defined hard segments were prepared from polyester polyol, 4,4′‐diphenylmethane diisocyanate, dimethylolpropionic acid, 1,4‐butanediol, isophorone diisocyanate, and ethylenediamine. These anionic‐type aqueous dispersions had good dispersity in water and were stable at the ambient temperature for more than 1 year. For these aqueous dispersions, the particle size decreased as the hard‐segment content increased, and the polydispersity index was very narrow (<1.10). Films prepared with the PUU aqueous dispersions exhibited excellent waterproof performance: the amount of water absorption was as low as 5.0 wt %, and the contact angle of water on the surface of this kind of film was as high as 103° (this led to a hydrophobic surface). The water‐resistant property of these waterborne PUU films could be well correlated with some crystallites and ordered structures of the well‐defined hard segments formed by hydrogen bonding between the urethane/urethane groups and urethane/ester groups, as well as the degree of microphase separation between the hard and soft segments in the PUU systems. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2606–2614, 2005 相似文献
60.
“Laser-assisted magnetic recording”, in which a recording media is heated by a laser beam while writing data, is attracting
attention as a technology that enables a recording density of 1 Tb/in.2. There exists another technology for media in which the recording layer is constructed with many small projections that enable
high magnetic coercivity. This is called “patterned media”. For developing hard disk drives using these methods, we developed
a simulator that analyzes the optical intensity distribution from the optical head for laser-assisted recording and the temperature
profile on the patterned media. The simulator calculates the optical model using the finite-difference time-domain (FDTD)
method. The thermal analysis of the three-dimensional model allows fast calculations using the alternating direction implicit
(ADI) method. The heat source distribution data for thermal analysis is calculated in order to use the results of optical
analysis. The optical and thermal analyses of the laser-assisted recording model were investigated with the simulator. 相似文献