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41.
42.
近年来沥青混凝土作为防渗材料,在我国水工建筑中得到了广泛应用。与道路工程的沥青混凝土不同的是,水工沥青混凝土具有良好的粘弹性及抗渗性。目前,国家规范对填充料的细度尚无明确规定,通过调整沥青混凝土的填充料细工,对沥青混凝土的各项性能进行了系统的试验和分析,研究表明:适宜的填充料细度及掺量,能有效地改善沥青混凝土性能,提高其抗渗性。 相似文献
43.
S. Gratch 《International Journal of Thermophysics》1985,6(6):541-544
Historical developments regarding the realization of the importance of reliable thermophysical properties data in engineering applications are presented. The events leading to the establishment of the Symposium on Thermophysical Properties in 1959 and the accomplishments of the symposia series since then are discussed. Contributions of the National Bureau of Standards to the thermophysical properties field are described.Welcoming address presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A. 相似文献
44.
In this paper we report the evolution of the polar cluster like behavior with the incorporation of Ti4+ ion in BaZrO3 Ceramics. Dielectric behavior of BaZrxTi(1−x)O3 (x = 1.00, 0.95, 0.90, 0.85) ceramics is studied in the temperature range from 300 to 30 K. Polar cluster like behavior becomes more prominent with the increase in content of Ti4+ ion. The dielectric relaxation is analyzed by Vogel–Fulcher relation and Arrhenius law. Frequency dependence of dielectric constant and low loss tangent of these materials can be useful for the potential applications at low temperature. 相似文献
45.
Thermoplastic starch (TPS), as opposed to dry starch, is capable of flow and hence when mixed with other synthetic polymers can behave in a manner similar to conventional polymer-polymer blends. This paper presents an approach to preparing polyethylene/thermoplastic starch blends with unique properties. A one-step combined twin-screw/single screw extrusion setup is used to carry out the melt-melt mixing of the components. Glycerol is used as the starch plasticizer and its content in the TPS is varied from 29 to 40%.Under the particular one-step processing conditions used it is possible to develop continuous TPS (highly interconnected) and co-continuous polymer/TPS blend extruded ribbon which possess a high elongation at break, modulus and strength in the machine direction. The PE/TPS (55:45) blend prepared with TPS containing 36% glycerol maintains 94% of the elongation at break and 76% of the modulus of polyethylene. At a composition level of 71:29 PE/TPS for the same glycerol content, the blend retains 96% of the elongation at break and 100% of the modulus of polyethylene. These excellent properties are achieved in the absence of any interfacial modifier and despite the high levels of immiscibility in the polar-nonpolar TPS-PE system. The 55:45 blend possesses a 100% continuous or fully interconnected TPS morphology, as measured by hydrolytic extraction. This highly continuous TPS configuration within the blend should enhance its potential for environmental biodegradation. The elongation at break in the cross direction of these materials, although lower than the machine direction properties, also demonstrates ductility at high TPS concentrations. At a glycerol content of 36% in the TPS, the blends demonstrate only very low levels of sensitivity to moisture. A high degree of transparency is maintained over the entire concentration range due to the similar refractive indices of PE and TPS and the virtual absence of interfacial microvoiding.Effective control of the glycerol content, TPS concentration and processing conditions can result in a wide variety of morphological structures including spherical, fiber-like, highly continuous and co-continuous morphologies. These various blend morphologies are shown to be the determining parameters with respect to the observed mechanical properties.This material has the added benefit of containing large quantities of a renewable resource and hence represents a more sustainable alternative to pure synthetic polymers. 相似文献
46.
Dielectric relaxation measurements are reported over a frequency range from 10−1 to 109 Hz as a function of exposure time for an epoxy resin-carbon fibre composite, ageing at 60 °C in water. Investigation of the nature of the dipole relaxation of the water molecules, indicates the nature of their interaction with the polymer matrix. Analysis of the dielectric relaxation spectra allow identification of processes that can be attributed to ‘free’ and ‘bonded’ water, water in micro-cracking, located in carbon fibre disbonds and plasticizing the polymer matrix. Identification of the various types of location in which water exists was aided by use of the Ng factor from the Kirkwood-Frölich equation, which describes the constraints on free dipole ration nature imposed by the environment in which it is located. These data indicate the power of the dielectric technique for quantitative analysis of water ingress into epoxy composites. 相似文献
47.
用自蔓燃高温合成(SHS)技术及电弧熔融法制备的(Nb,Ti)C固溶体作基体,制备(Nb,Ti)C-35Ni金属陶瓷。结果表明用电弧熔融法制备的(Nb,Ti)C为基的试样具较优的室温力学性能(σ=1630MPa,KIC=18.0MPa),其陶瓷颗粒均匀分行粘结相之中并是包裹结构;而用SHS法制备的(Nb,Ti)C为基的试样其力学性能相对较差,其陶瓷颗粒无包裹结构. 相似文献
48.
Oxide films formed by water oxidation at 360°C on ZrNb(1%)O(0.13%) for several durations (50-300 days) were studied by impedance spectroscopy (IS) in gaseous atmosphere. The electrical behavior of oxide layers was investigated as a function of the temperature (25-300°C) at constant oxygen partial pressure (0.3 Pa). Cole-Cole diagrams suggest a frequency-temperature equivalence. A simple electrical model has been derived from the as-deduced 14 decade master curve. Equivalent circuit includes a series association of two layers exhibiting different dielectric properties: a dense layer near the oxide-metal interface and a porous layer at the waterside. Electronic conductivity is predominant within the whole temperature range, but ionic contribution was proposed to increase for temperature higher than 170°C. During the parabolic oxidation step, the oxide thickness of the barrier layer increases but oxide growth would not be only a geometrical one. The kinetic modification to a constant oxidation rate was observed to be correlated to the increase of the dense layer thickness. Such a behavior suggests that the mechanism controlling oxidation rate is not a pure mechanism of oxygen diffusion through this layer. Finally, a qualitative model of activated electrons transport based on an hopping mechanism was proposed in order to take into account that the Arrhenius diagrams of both total conductivity and dispersion factor are characterized by a break point with two activation energy values. 相似文献
49.
Solid solutions of the GdFeO3–GdInO3 system were prepared at 1550 °C by ceramic powder processing. The formulated composition was Gd(Fe1−xInx)O3 (GFI) with the indium contents at x = 0, 0.25, 0.5, 0.75, and 1.0. A stable phase of Gd(Fe1/3In2/3)O3 in our system was identified by X-ray diffraction and phase composition analysis. Multi-phase morphologies were observed for GFI bulks with x = 0.5 and 0.75. Dielectric and electrical properties of the GFI bulks were investigated. The addition of 25% In3+ in GdFeO3 had an obvious enhancement in polarization and led to an elevated resonance frequency. Dielectric properties of GFI bulks except GdInO3 were strongly dependent upon the test frequency, which corresponded to the response of polarization mechanism. GdInO3 displayed as a stable dielectric, which was frequency- and temperature-insensitive. GdInO3 was thermally activated and became leaky until above 600 °C. 相似文献
50.
Jiang-Li Chen Zhuo Xu Shao-Bo Qu Xiao-Yong Wei Xiao-Hui Liu 《Ceramics International》2008,34(4):803-807
The NiFe2O4 and Pb(Zr0.52Ti0.48)O3 ceramic composites are prepared by conventional solid state reaction method. The microstructural and morphological properties of the composites are studied by X-ray diffraction analysis and scanning electron microscopy. Results indicate that the ferrite and piezoelectric phases can co-exist in the composites. The relationship between the dielectric constant and frequency (40 Hz–40 MHz) as well as temperature is also investigated. It is noted that the transition temperature of the composites is about 380 °C. A double electric hysteresis loop is observed in our composites. The magnetic properties are relatively weak according to the magnetic hysteresis loop. With increase in the content of the ferrite phase, the permeability increases. The electromagnetic properties of the as-prepared composites are tunable according to the content of the NiFe2O4 phase. 相似文献