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71.
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
72.
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
73.
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
74.
A. A. Vladimirov 《Mathematical Notes》2006,79(3-4):342-355
In this paper, we study the problem of the boundary accumulation of a discrete spectrum, which is essential for a boundary-value problem of fourth order arising in the theory of small transverse vibrations in an inhomogeneous viscoelastic rod (a Kelvin—Voigt body). We establish conditions for such an accumulation and its asymptotics, which are expressed in terms of the coefficients defining the problem posed by the differential expression. The results obtained are illustrated by numerical computation data. 相似文献
75.
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
76.
The primary interest of this study concerns the use of an inexpensive photographic digital camera as the detection system, using its own flash as the source of light to present a new analytical procedure to measure disposable multianalyte optical sensors for potassium, magnesium, hardness and conventional pH test strips. The camera arrangement was designed in a fixed position over an optical board with controllable ambient conditions. After acquiring the digital image, the analytical information contained in each test zone is analyzed using theRGB colour space. Reflectance measurements were developed to study the colourimetric and spectral characteristics of the test zones. We obtained the following application ranges and precision in terms of relative standard deviation (RSD %): for potassium from 3.2 × 10−7 to 0.1 M with a precision between 3.3 and 4.0%, for magnesium from 2.7 × 10−6 to 1.5 M showing a precision between 4.7 and 7.8% and finally for hardness from 4.3 × 10−2 to 200,000 mg L−1 CaCO3 and between 5.1 and 7.0%. Moreover, the analytical characteristics of several optical procedures were compared with the results presented here. The proposed method was statistically validated against a reference procedure using samples of water from different sources and beverages, indicating that there are no significant statistical differences at a 95% confidence level. 相似文献
77.
78.
为了减少混响室时域全波仿真的计算量,首次对混响室时域响应的预测做出探索研究。以改良矩阵束方法为基础,提出一种计算效率更高的矩阵束方法,并验证了该方法的正确性与稳定性。用复指数幂求和式对混响室的时域波形进行拟合,利用该方法能够高效求解出拟合式中的各极点,实现了对混响室时域响应的近似外推。由电场强度的前20 000步计算结果,可快速预测得到后20 000步响应,发现束参数比例取0.62左右时,对多个采样点的电场均可得到良好的预测效果,可保证仿真与预测相结合得到的结果与真实结果的频域相对误差小于15%。这种结合预测的仿真算法可节省计算量约50%。 相似文献
79.
Sundaramoorthy Malathi Devi Durairajan Madhavan Kadarkaraithangam Jeyasubramanian Ayyappan Vimalraj Osannal Hikku Gnanadhas Sobhin 《先进技术聚合物》2024,35(2):e6321
The fabrication of activated carbon dispersed polybenzoxazine (BXP) composite through a single step melt condensation technique is reported. Employing green strategy, activated carbon (AC) was obtained from various types of worn-out plastics such as computer keyboard, sponge, electrical switches, and automobile tyres. Structural features of all the polymeric composites were explored using Fourier transform infrared (FTIR) spectroscopy, Field Emission Scanning Electron Microscope (FESEM) with Energy Dispersive X-ray Analysis (EDAX). Thermal stability and hardness of the composites was analyzed by recording thermogravimetric analysis (TGA) and Rockwell hardness measurements. The results of thermal studies revealed that AC–BXP composites show higher thermal stability (301.98°C) than BXP (220.71°C). Rockwell hardness study (RHN) for ACWCKB@BXP is 71 whereas pristine BXP showed only 20. The corrosion protection ability of coated steel was examined through potentiodynamic polarization and electrochemical impedance spectroscopy analysis. From the Tafel plot, more shift in Ecorr value (from −0.6286 to −0.5065 V) towards positive side confirms its corrosion protection ability. Furthermore, the Icorr, the corrosion rate and the corrosion protection efficiency of the ACWTYR@BXP composite are 0.83 × 10−6 A/cm2, 0.0098 mm/year, and 99.54%, respectively, which inhibit the rate of corrosion to a greater extent in 3.5% NaCl solution. The current study applies principles of green chemistry like minimum number of synthesis steps, non-usage of solvents and simply adoptable coating procedure. 相似文献
80.