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51.
52.
Synthesis and properties of polybenzoxazine modified polyurethanes as a new type of electrical insulators with improved thermal stability 总被引:1,自引:0,他引:1
Hamid Yeganeh Mohammad Razavi‐Nouri Mehdi Ghaffari 《Polymer Engineering and Science》2008,48(7):1329-1338
A new class of electrical insulating materials with improved thermal stability was prepared from combination of polybenzoxazine with epoxy terminated polyurethane prepolymer (EPU). EPU was prepared by the reaction of glycidol with NCO‐terminated urethane prepolymer. The prepolymer was prepared from polycaprolactone polyol (molecular weight 1000), and hexamethylene diisocyanate. Bisphenol‐A and aniline were used for preparation of benzoxazine monomer. Mode of reactions and optimum curing condition were determined by DSC and FTIR analysis. Upon these analysis as well as DMTA findings, formation of interpenetrating polymer networks was suggested for blends consisted different weight ratios of two components. Viscoelastic behavior, mechanical, thermal, and electrical properties of the prepared samples was studied and their relation to the chemical structure and composition of blends were elucidated. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers 相似文献
53.
Alireza Valizadeh Haleh Mikaeili Mohammad Samiei Samad Mussa Farkhani Nosratalah Zarghami Mohammad kouhi Abolfazl Akbarzadeh Soodabeh Davaran 《Nanoscale research letters》2012,7(1):1-14
Ferrite nanoparticles of basic composition Ni0.7-x Zn x Cu0.3Fe2O4 (0.0 ?? x ?? 0.2, x = 0.05) were synthesized through auto-combustion method and were characterized for structural properties using X-ray diffraction [XRD], scanning electron microscopy, transmission electron microscopy, and Fourier transform infrared spectroscopy [FT-IR]. XRD analysis of the powder samples sintered at 600°C for 4 h showed the cubic spinel structure for ferrites with a narrow size distribution from 28 to 32 nm. FT-IR showed two absorption bands (v 1 and v 2) that are attributed to the stretching vibration of tetrahedral and octahedral sites. The effect of Zn doping on the electrical properties was studied using dielectric and impedance spectroscopy at room temperature. The dielectric parameters (??', ????, tan??, and ?? ac) show their maximum value for 10% Zn doping. The dielectric constant and loss tangent decrease with increasing frequency of the applied field. The results are explained in the light of dielectric polarization which is similar to the conduction phenomenon. The complex impedance shows that the conduction process in grown nanoparticles takes place predominantly through grain boundary volume. PACS: 75.50.Gg; 78.20; 77.22.Gm. 相似文献
54.
55.
Mohammad Razavi‐Nouri 《应用聚合物科学杂志》2012,124(3):2541-2549
This paper is devoted to the preparation of thermoplastic nanocomposites of polypropylene (PP) and different amounts of single‐walled carbon nanotubes (SWNTs) in the range 0.25–2 wt %. The effect of SWNT content on the dynamic mechanical behavior, thermal degradation, crystalline structure, and the kinetic crystallizability of PP were studied. The results obtained from dynamic mechanical thermal analyzer (DMTA) showed that the maximum storage modulus was achieved when 1 wt % SWNT was added into the pristine polymer. Thermal stability of the nanocomposites was measured by thermogravimetric analyzer (TGA). From the TGA results, it was found that the weight fraction of PP which was located at the interface for the nanocomposite containing 0.5% SWNT was about 60%, and this value did not change much with the addition of higher amounts of SWNT. Moreover, the thickness of the interface between PP and SWNT was estimated to be of the order of 101 nm which is very close to the radii of gyration of PP molecular chains. Wide angle X‐ray diffractometer (WAXD) was used to explore the crystalline structure of water and slow‐cooled samples. It was found that the crystallization of PP in 040 lattice plane increased for the nanocomposites compared with PP for both cooling rates studied. It was also found that the kinetic crystallizability values were nearly the same for PP and the nanocomposites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 相似文献
56.
Mehdi Javani Amir Abdolmaleki Amin Nouri Khorasani 《Journal of Adhesion Science and Technology》2013,27(10):975-985
Crosslinking reaction of polymer by ultraviolet (UV) irradiation has been important in industries. In this work, photocrosslinking of styrene–isoprene–styrene (SIS) triblock copolymer in the presence of benzoin photoinitiator and a dimethacrylate monomer as crosslinking agent was investigated. Curing of samples was initiated under UV irradiation. Benzoin was used as photoinitiator because it contains chromophore group that could absorb UV irradiation. Ethylene glycol dimethacrylate (EGDMA) was used as crosslinking agent, since it has alkene functional groups that could react with the alkene group of SIS. ATR-FTIR spectra of samples show that absorption band of double bond at 1500–1600?cm?1 decreases after UV exposure. Increasing the concentration of benzoin (0.1–1?phr) and EGDMA (1–10?phr) leads to an increase in gel content and hardness, while swelling ratio decreases. After 5?min heating at 150?°C, about 20%wt of the unirradiated compound became insoluble, because heating of compound at 150?°C causes crosslinking reaction without any irradiation. 相似文献
57.
Moez Kthiri Hassen Loukil Ahmed Ben Atitallah Patrice Kadionik Dominique Dallet Nouri Masmoudi 《Journal of Signal Processing Systems》2012,68(2):273-285
Motion estimation is a highly computational demanding operation during video compression process and significantly affects
the output quality of an encoded sequence. Special hardware architectures are required to achieve real-time compression performance.
Many fast search block matching motion estimation (BMME) algorithms have been developed in order to minimize search positions
and speed up computation but they do not take into account how they can be effectively implemented by hardware. In this paper,
we propose three new hardware architectures of fast search block matching motion estimation algorithm using Line Diamond Parallel
Search (LDPS) for H.264/AVC video coding system. These architectures use pipeline and parallel processing techniques and present
minimum latency, maximum throughput and full utilization of hardware resources. The VHDL code has been tested and can work
at high frequency in a Xilinx Virtex-5 FPGA circuit for the three proposed architectures. 相似文献
58.
The present paper is a contribution to the phenomenological modelling of fatigue non-linear cumulative diffuse damage in short glass fibre reinforced thermoplastic matrix composites. In such materials, fatigue damage kinetic exhibits three stages, namely: (i) material softening and damage initiation, (ii) coalescence and propagation of micro-cracks and (iii) macroscopic cracks propagation and material failure. The proposed model is built in the framework of the continuum damage mechanics and aims at predicting these three stages of the damage evolution. This model is based on the approach initially proposed by Ladevèze and Le Dantec [Ladevèze P, Le Dantec E. Damage modelling of the elementary ply for laminated composites. Comp Sci Technol 1992;43:257–67]. It extends the previous approach and takes into account the important stiffness reduction observed during the first damage stage. The above is modelled by the integration of a combined Norton-like power law and an exponential law expressing the damage rates as a function of the associated thermodynamic dual forces. The model has been formulated in terms of strain energy, so that makes easy its numerical implementation into the finite element code Abaqus/Standard through a user defined material subroutine UMAT. Numerical simulations are performed on a short glass fibre reinforced thermoplastic described by a given set of damage parameters. Damage evolutions predicted by the developed model reproduce well those observed for this kind of composites under cyclic loading. A parametric study is performed to understand the effects of the model parameters on the damage accumulation and their sensitivity on its kinetic. The sensitivity study would be useful since it contributes to optimise the ongoing experimental procedure aimed at identifying the damage model parameters. 相似文献
59.
Hessameddin Yaghoobi Abdolhossein Fereidoon Mohammad Khaksari Nouri Soraya Mareishi 《先进材料力学与结构力学》2015,22(10):864-875
In this study, the thermal buckling analysis of hybrid laminated plates made of two-layered functionally graded materials (FGMs) that are integrated with surface-bonded piezoelectric actuators referred to as (P/FGM)s are investigated. Material properties for both substrate FGM layers and piezoelectric layers are temperature-dependent. Uniform temperature rise as a thermal load and constant applied actuator voltage are considered for this analysis. By definition of four new analytic functions, the five coupled governing stability equations, which are derived based on the first-order shear deformation plate theory, are converted into fourth-order and second-order decoupled partial differential equations (PDEs). Considering a Levy-type solution, these two PDEs are reduced to two ordinary differential equations. One of these equations is solved using an accurate analytical solution, which is named as power series Frobenius method. The effects of parameters, such as the plate aspect ratio, ratio of piezoelectric layer thickness to thickness of FGM layer, gradient index, actuator voltage, and the temperature dependency on the critical buckling temperature difference, are illustrated and explained. The critical buckling temperatures of (P/FGM)s with six various boundary conditions are reported for the first time and can be served as benchmark results for researchers to validate their numerical and analytical methods in the future. 相似文献
60.