Sharif Digital Repository

Electrical behavior of hybrid conductive composites made of phenolic resin, graphite woven, glass woven and graphite nano powder has been studied for the first time in the present research to apply as collecting plates in electro static precipitators. To this purpose, two types of four-layer composites smeared with phenolic resin by different amounts of graphite nano powder then produced at 120°C and 200 bars with proper curing cycle. Finally, electrical resistivity of all the plates undergoing impact loading after different rapping cycles was measured by means of a repetitive rapping tester system particularly manufactured for this task. This study performs changes in mechanical behavior of... 

An experimental study of the. flexural behavior of Reinforced-Concrete (RC) arches strengthened with Glass Fiber-Reinforced Polymer (GFRP) layers was performed. A total of 36 specimens including 3 un-strengthenod (control) and 33 strengthened RC arches were tested under centrally concentrated point load. The variables of this study were steel reinforcement ratio, number of GFRP layers, and location and arrangement of GFRP layers. Failure mode, load-displacement response of specimens, crack propagation patterns, and GFRP debonding were examined. The extrados strengthening method was shown to Ix1 more effective than the intrados strengthening one in improving the failure load and rigidity of... 

Polymer-layered silicate nanocomposites have been noticed recently due to their outstanding properties. The mechanical properties and deformation mechanism of epoxy/montmorillonite nanocomposites under compressive and flexural loadings were investigated. A reduction in compressive and flexural yield stress and also glass transition temperature with increasing the amount of organoclay was observed. This change in mechanical behavior of epoxy can be explained with observation of plastic deformation mechanism. The study of deformation mechanism revealed that presence of organoclay accelerates shear yielding in epoxy. Microscopic evaluation illustrated that nanoparticles in this system act as... 

The effect of etching time scale of glass surface on its statistical properties has been studied using atomic force microscopy technique. We have characterized the complexity of the height fluctuation of an etched surface by the stochastic parameters such as intermittency exponents, roughness, roughness exponents, drift and diffusion coefficients and found their widths in terms of the etching time. © 2006 Elsevier B.V. All rights reserved  

Impact and tensile strength of polystyrene and nylon 6 samples, which have been produced by injection molding before and after annealing in different conditions are obtained. Polystyrene samples that are heated on vacuum conditions can deform highly even in temperatures much less than polystyrene glass temperature. This phenomenon is reduced significantly by heating samples to annealing temperature in atmospheric pressure and then removing air from sample environment in constant temperature. Deformation problems for nylon were not so important but due to high temperature implied for annealing of nylon parts, some color change due to oxidative degradation are observed. So for nylon parts a... 

SiO2-CaO-MgO glass and glass-ceramic powder doped with Nd 3+ were synthesized with sol-gel method. Tetraethylorthosilicate (TEOS), Ca(NO3)2·4H2O, Mg(NO 3)2·6H2O, Nd(NO3) 3·6H2O, ethanol, distilled water, and HNO 3 were used as starting materials. The synthesized powder's properties were examined with simultaneous thermal analysis (STA), X-ray diffraction (XRD), photoluminescence (PL) and scanning electron microscopy (SEM) analysis. The STA curves showed that the softening point and crystallization temperatures were shifted to higher temperatures with increasing dopant content. Regarding XRD patterns of glass samples, Nd was found to act as an intermediate oxide in glass matrix. The XRD... 

A molecular dynamics simulation study has been performed to investigate the solidification and remelting of aluminum using Sutton-Chen many body potential. Different numbers of atoms from 108 to 2048 atoms were considered to find an adequate size for the system. Three different cooling and heating rates, i.e. 10 12 K/s, 10 13 K/s and 10 14 K/s, were used. The structure of the system was examined using radial distribution function. The melting and crystallization temperatures of aluminum were evaluated by calculating the variation of heat capacity during the phase transformation. Additionally, Wendt-Abraham parameters were calculated to determine the glass transition temperature. It is shown... 

Corrosion of lead silicate glass (LSG) contacting 0.5 M aqueous nitric acid (HNO 3) was investigated via scanning electron microscopy, energy-dispersive spectroscopy, inductively coupled plasma analysis, and weight-loss measurement to determine the respective contributions of the ion-exchange vs. the hydrolysis reactions. The LSG having X M ≡ Pb+K+Na/Si mole ratios of less than 0.7 showed very little weight loss with no Si network deterioration. At X M > 0.7, the mechanism changed into the hydrolysis, which caused the formation of a networkless gel layer resting at the solid/liquid interface. Addition of titania (TiO 2) and zirconia (ZrO 2) had disparate effects: X M < 0.7 improved corrosion... 

Processing conditions and final mechanical properties of polymer nanocomposites are affected by their interfacial layers behavior. However, it is impossible to determine directly the properties of these layers by dynamic rheometry tests. In this work, the interfacial layers properties are evaluated for polystyrene containing silica nanoparticles by the concept of glass-transition temperature shift. The samples were prepared via solution-mixing method and dynamic rheometry was used to determine the viscoelastic behavior of filled polymers in the melt state. This initial step showed that addition of silica particles increased the glass-transition temperature. By preference, decrease in the... 

High-temperature (1200-1350°C) corrosion of fused-cast ZrO2-Al2O3-SiO2 (ZAS) refractory contacting lead silicate glass melt (LSG) containing 68.5wt% PbO was investigated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), differential scanning calorimetry (DSC), x-ray diffraction (XRD), thickness measurement and Archimedes density measurement. ZAS durability was improved by baddeliyete content and deteriorated with open porosity proportion, corundum percentage and eutectic mixture presence. Diffusion of lead resulted in fusion-temperature lowering of the glassy layers embedded within the ZAS particles. Heating caused viscosity drop across the interface, loosening the... 

Toughening of epoxy with different types of modifiers produces a bimodal blend that might show better fracture resistance in comparison with single-modified ones. In this research, bimodal epoxy formulations including mixtures of glass microsphere and silica nanoparticles are explored for possible synergistic toughening. The influence of composition on the glass transition temperature (Tg), tensile characteristics, and fracture toughness (KIC) is investigated. Interestingly, a synergism in fracture toughness is observed when mixtures of modifiers were incorporated. For the fixed overall modifier content, KIC is higher when the volume fraction of glass microsphere is lesser than the volume... 

The objective of this study was to evaluate the effects of P 2O5 particle size distribution on the crystalline phases and microstructure of lithium disilicate glass-ceramics derived from the TiO2-ZrO2-Li2O-CaO-Al2O 3-SiO2 system for dentistry applications. The samples were made via fusion and casting procedure. Crystallisation as well as the morphology and microstructure of the samples were investigated using X-ray diffraction, differential scanning calorimetric and scanning electron microscopy. The results showed that the crystallisation of the samples occurred in the range of 500-650°C. The main crystalline phase was lithium disilicate (Li2Si2O5) along with Lithium metasilicate (Li2SiO3),... 

Polyurethane (PU) nanocomposites with 0, 1, 3, 5, and 7 wt-% nanoclay contents were prepared. X-ray diffraction patterns, transmission electron microscopy images, tensile test, and thermogravimetric analysis were utilised to reveal the morphological, mechanical, and thermal-resistant properties of the prepared nanocomposites. The exfoliated structure was obtained for nanoclay contents up to 3 wt-%. Incorporation of nanoclay to the PU matrix prompted the thermal stability of the polymer. A nanocomposite filled with 3 wt-% nanoclay showed the best tensile strength in the prepared nanocomposites. Subsequently, the nanocomposite with the 3 wt-% nanoclay was reinforced with carbon and glass... 

Self-expandable stents are widely used to restore blood flow in a diseased artery segment by keeping the artery open after angioplasty. Despite the prevalent use of conventional crystalline metallic alloys, for example, nitinol, to construct self-expandable stents, new biomaterials such as bulk metallic glasses (BMGs) are being actively pursued to improve stent performance. Here, we conducted a series of analyses including finite element analysis and molecular dynamics simulations to investigate the feasibility of using a prototypical Zr-based BMG for self-expandable stent applications. We model stent crimping of several designs for different percutaneous applications. Our results indicate... 

Molecular dynamics (MD) simulations have been widely used to study the structure of metallic glasses (MGs) at atomic scale. However, ultrafast cooling rates in MD simulations create structures that are substantially under-relaxed. In this study, we introduce long-term pressurized annealing up to 1 μs slightly below the glass-transition temperature, Tg, in MD simulation, which effectively relaxes the structure of Cu64Zr36 MG toward experimental conditions. It is found that applying hydrostatic pressure up to 2 GPa relaxes the MG to low-energy states whereas higher pressures retard relaxation events. In the sample annealed at 2 GPa pressure, equivalent cooling rate reaches to 3.7 × 107 K/s,... 

Polycaprolactone (PCL) is a bioresorbable and biocompatible polymer that has been widely used in long-term implants and controlled drug release applications. However, when it comes to tissue engineering, PCL suffers from some shortcomings such as slow degradation rate, poor mechanical properties, and low cell adhesion. The incorporation of calcium phosphate-based ceramics and bioactive glasses into PCL has yielded a class of hybrid biomaterials with remarkably improved mechanical properties, controllable degradation rates, and enhanced bioactivity that are suitable for bone tissue engineering. This review presents a comprehensive study on recent advances in the fabrication and properties of... 

Mechanism of removal of lead from silicate glass containing 68.5 wt% PbO by 0.5 N HNO3 was investigated by incorporation of the chemical-analyses/weight-loss data into shrinking-core model (SCM) and minimization of the difference. Scanning electron microscopy (SEM), emission spectrometry with inductively coupled plasma (ICP), X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDS) were used to determine the compositional changes of the lead-silicate glass (LSG) samples. Dual inter-diffusion chemical reaction mechanisms having respective activation energies of 83.49 and 47.80 kJ/mol dominated the deleading process. © 2009 Elsevier B.V. All rights reserved  

Carbazole compounds are p-type hole-transporting materials (HTMs) useful for perovskite solar cells (PSCs). In this work, we developed a new class of carbazol based HTMs; non-fused 3-D asymmetric structures (S14 and S12) as HTM of PSCs. To the best of our knowledge, there is no report on non-fused HTMs with a high glass transition temperature (Tg = 165 °C), which reduces crystallization and suppresses grain boundaries in glassy film, resulting in long-term durability. Experimental results show that tuning the carbazole moiety in S14 structure has a constructive influence on geometrical alignment, hole mobility, hydrophobicity, stability as well as efficiency. The resultant power conversion... 

This article presents an investigation on the durability of different glass-fibre-reinforced polymer composites when subjected to harsh outdoor conditions, including freeze/thaw cycles, ultraviolet radiation and moisture, as well as when used with seawater sea-sand concrete for construction applications. To achieve this, the effects of a number of parameters, including the environment of exposure, exposure time, profile cross-sectional configuration and orientation of fibres, on the mechanical properties of different glass-fibre-reinforced polymer composites were studied. To investigate the degradation of the mechanical properties, three-point bending, compression and tension tests were... 

Alkali-activated slag (AAS) binder has been recognized as a suitable material for construction applications owing to its low carbon footprint and good mechanical and durability performance. As a promising alternative to the conventional Portland cement binder, it is important to maximize the performance of AAS composites under normal and harsh environmental conditions such as exposure to fire. The use of fibers in a brittle matrix is a well-known approach to enhance the mechanical strength and cracking behavior under thermal loading. In this study, polypropylene fiber (PPF), glass fiber (GF), and basalt fiber (BF) are used at volume fractions of 0.5%, 1%, and 1.5% in AAS mortar mixes. First,...