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31.
Physical Properties of Sol-Gel Coatings 总被引:3,自引:0,他引:3
One of the most important applications of sol-gel technology is the fabrication of coatings. This is because of the possibility of applying oxide coatings with practically all types of chemical compositions at low ambient temperatures on many substrates of various shapes through the use of liquid solutions. Both oxides and different types of organic-inorganic hybrid coatings have been reported. Both oxides and hybrid coatings are usually amorphous at ambient temperatures but some oxides can be converted to the crystalline phase with heating. Regardless of the intended applications of the coatings their physical properties are always of importance. For instance, an anti-reflective coating for an automobile mirror is of little practical value unless it is fairly scratch-resistant. In this review which covers published information in the past fifteen years, some of the more important results of physical properties of sol-gel derived coatings are discussed firstly for oxides and then for organic-inorganic hybrids. It appears that properties such as the hardness of oxide coatings are inadequate unless the heat-treatment temperatures are in excess of about 400°C. The hybrid coatings, especially when they contain a dispersed phase of a hard solid like colloidal silica, can be processed at temperatures below about 150°C and can improve the performance of organic plastics such as the polycarbonates. There is insufficient scientific understanding of the relationship between physical properties and other interdependent variables such as processing conditions, chemistry and coating thickness. More research in this area will undoubtedly contribute to the availability of better and new coatings via the sol-gel approach. 相似文献
32.
Allyl alcohol (AA), acrylonitrile (AN), methyl methacrylate (MMA), monomers and monomer mixtures AA+AN, AA+MMA were used to conserve and consolidate Beech and Spruce. After impregnation, copolymerisation and polymerisation were accomplished by gamma irradiation. The fine structure of wood+polymer(copolymer) composites was investigated by Scanning Electron Microscopy (SEM). It was observed that copolymer obtained from AA+MMA monomer mixture showed the optimum compatibility. The compressional strength and Brinell Hardness Numbers determined for untreated and treated wood samples indicated that the mechanical strength of wood+copolymer composites was increased. It was found that the mechanical strength of the wood samples containing the AA+MMA copolymer was higher than the others. In the presence of P(AA/MMA), at highest conversion, the compressive strength perpendicular to the fibres in Beech and Spruce increased approximately 100 times. The water uptake capacity of wood+copolymer composites was observed to decrease by more than 50% relative to the original samples, and biodegradation did not take place. 相似文献
33.
Tzonka Mineva 《Journal of Chemical Sciences》2005,117(5):485-490
The third term in the Taylor expansion of the total energy functional around the number of electronsN is evaluated as the second-order derivative of orbital Kohn-Sham energies with respect to orbital occupancy. Present approach
is an extension of an efficient algorithm to compute densityfunctional based orbital reactivity indices. Various energy derivatives
used to approximate orbital reactivity indices are defined within the space spanned by the orbital occupation numbers and
the Kohn-Sham one-electron energies. The third-order energy functional derivative has to be considered for singular hardness
tensor ([η]). On the contrary, this term has negligible influence on the reactivity index values for atomic or molecular systems
with positively defined hardness tensors. In this context, stability of a system in equilibrium state estimated through the
eigenvalues of [η] is discussed. Numerical illustration of the Kohn-Sham energy functional derivatives in orbital resolution
up to the third order is shown for benchmark molecules such as H2O, H2S, and OH−. 相似文献
34.
A. Fonseca N.A. Sobolev E. Alves N.D. Zakharov A.A. Tonkikh 《Journal of luminescence》2006,121(2):417-420
In this work we studied the influence of high-energy proton irradiation on the optical and structural properties of an Si/Ge superlattice (SL) with embedded Ge quantum dots (QDs). The presence of QDs in the as-grown samples was established by transmission electron microscopy and photoluminescence (PL). The samples were irradiated with 2.0 MeV protons to fluences in the range 2×1012-2×1014 cm-2. The structural characterization made by X-ray reciprocal space mapping, X-ray reflection and Rutherford backscattering/channelling has shown no changes in the as-grown heterostructure due to the irradiation. In spite of the expected high concentration of nonradiative recombination centres caused by the proton-induced damage, the PL emission from the Ge dots has been observed even for the highest irradiation fluence. The studied QD-in-SL structure has shown an extraordinarily high radiation hardness when compared with previously studied QD heterostructures. 相似文献
35.
M. N. Vereshchagin S. N. Dub V. G. Shepelevich O. M. Ostrikov 《Journal of Applied Mechanics and Technical Physics》2004,45(3):449-452
The formation of shear bands in Fe–Cr–Mo–V–B–Si amorphous alloy under nanoindentation Is studied. The indentation process is considered against the background of shear band formation in the amorphous material. 相似文献
36.
纳米压痕过程的三维有限元数值试验研究 总被引:15,自引:3,他引:15
采用有限元方法模拟了纳米压痕仪的加、卸载过程,三维有限元模型考虑了纳米压痕仪的标准Berkovich压头.介绍了有限元模型的几何参数、边界条件、材料特性与加载方式,讨论了摩擦、滑动机制、试件模型的大小对计算结果的影响,进行了计算结果与标准试样实验结果的比较,证实了模拟的可靠性.在此基础上,重点研究了压头尖端曲率半径对纳米压痕实验数据的影响.对比分析了尖端曲率半径r=0与r=100nm两种压头的材料压痕载荷—位移曲线.结果表明,当压头尖端曲率半径r≠0时,基于经典的均匀连续介质力学本构理论、传统的实验手段与数据处理方法,压痕硬度值会随着压痕深度的减小而升高. 相似文献
37.
E.T. Lilleodden J.A. Zimmerman W.D. Nix 《Journal of the mechanics and physics of solids》2003,51(5):901-920
Nanoindentation experiments have shown that microstructural inhomogeneities across the surface of gold thin films lead to position-dependent nanoindentation behavior [Phys. Rev. B (2002), to be submitted]. The rationale for such behavior was based on the availability of dislocation sources at the grain boundary for initiating plasticity. In order to verify or refute this theory, a computational approach has been pursued. Here, a simulation study of the initial stages of indentation using the embedded atom method (EAM) is presented. First, the principles of the EAM are given, and a comparison is made between atomistic simulations and continuum models for elastic deformation. Then, the mechanism of dislocation nucleation in single crystalline gold is analyzed, and the effects of elastic anisotropy are considered. Finally, a systematic study of the indentation response in the proximity of a high angle, high sigma (low symmetry) grain boundary is presented; indentation behavior is simulated for varying indenter positions relative to the boundary. The results indicate that high angle grain boundaries are a ready source of dislocations in indentation-induced deformation. 相似文献
38.
Microindentation hardness testing was applied to five types of highly-crosslinked ultrahigh molecular weight polyethylenes (UHMWPEs) for total joint replacements. UHMWPE's were crosslinked using the same total radiation dose (75 kGy; γ-radiation) either by the standard, single-step irradiation (one-step crosslinking) or by the newer, several-step irradiation (sequential crosslinking). Each irradiation step was followed by thermal treatment (annealing at 110 °C or remelting at 150 °C) in an inert atmosphere. We showed that: (i) the micromechanical properties were determined by the last thermal treatment step, while the number of irradiation cycles was insignificant and (ii) the values of microhardness, microcreep and microplasticity from the microindentation experiments were in excellent agreement with the changes of UHMWPE structure, characterized by IR and DSC. Statistical evaluation of the results, the agreement with theoretical predictions and the comparison with previous studies on similar systems demonstrated that microindentation was a reliable and sensitive method of UHMWPE characterization. 相似文献
39.
Influence of substrate temperature and N2/Ar flow ratio on the stoichiometry,structure and hardness of TaNx coatings deposited by DC reactive sputtering 下载免费PDF全文
K. Valdez D. G. Espinosa‐Arbeláez J. E. García‐Herrera J. Muñoz‐Saldaña M. H. Farias W. De la Cruz 《Surface and interface analysis : SIA》2015,47(11):1015-1019
The effect of substrate temperature and N2/Ar flow ratio on the stoichiometry, structure and hardness of TaNx coatings prepared on (111) Si substrates by DC reactive sputtering was investigated. For the structural, chemical and morphological analysis, X‐ray diffraction (XRD), Auger electron scanning and atomic force microscopy were respectively used. Hardness values of thin films were determined using the work of indentation model from nanoindentation measurements. TaN stoichiometric coatings were obtained for samples deposited at room temperature. The stoichiometric TaN phase was not obtained by increasing the temperature up to 773 K, even when increasing the N2/Ar flow ratio. Even when a saturation in nitrogen content was achieved, nitrogen vacancies are still present in those samples. For coatings prepared at 773 K and low N2/Ar flow ratio, a phase mixture between TaNx and cubic α‐Ta was observed, while a cubic structure δ‐TaN was formed by increasing the N2/Ar flow ratio. A maximum in hardness and (38 GPa) was obtained for the sample deposited at 773 K and a N2/Ar flow ratio of 0.2, which presented a δ‐TaN cubic crystalline structure and a roughness value of 1.6 nm. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
40.
Enhancement of water barrier properties and tribological performance of hybrid glass fiber/epoxy composites with inclusions of carbon and silica nanoparticles 下载免费PDF全文
Water barrier properties and tribological performance (hardness and wear behavior) of new hybrid nanocomposites under dry and wet conditions were investigated. The new fabricated hybrid nanocomposite laminates consist of epoxy reinforced with woven and nonwoven tissue glass fibers and two different types of nanoparticles, silica (SiO2) and carbon black nanoparticles (C). These nanoparticles were incorporated into epoxy resin as a single nanoparticle (either SiO2 or C) or combining SiO2 and C nanoparticles simultaneously with different weight fractions. The results showed that addition of carbon nanoparticles with 0.5 and 1 wt% resulted in maximum reduction in water uptake by 28.55% and 21.66%, respectively, as compared with neat glass fiber reinforced epoxy composites. Addition of all studied types and contents of nanoparticles improves hardness in dry and wet conditions over unfilled fiber composites. Under dry conditions, maximum reduction of 47.26% in weight loss was obtained with specimens containing 1 wt% carbon nanoparticles; however, in wet conditions, weight loss was reduced by 17.525% for specimens containing 0.5 wt% carbon nanoparticles as compared with unfilled fiber composites. Diffusion coefficients for different types of the hybrid nanocomposites were computed using Fickian and Langmuir models of diffusion. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献