Search for: silicones
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    Effects of tool rake angle and tool nose radius on surface quality of ultraprecision diamond-turned porous silicon

    , Article Journal of Manufacturing Processes ; Volume 37 , 2019 , Pages 321-331 ; 15266125 (ISSN) Heidari, M ; Akbari, J ; Yan, J ; Sharif University of Technology
    Elsevier Ltd  2019
    This paper presents an investigation of the effects of tool rake angle and nose radius on the surface quality of ultraprecision diamond-turned porous silicon. The results showed that as rake angle decreases, the high-stress field induced by the tool edge increases, causing microcracks to propagate extensively near the pore walls. As a result, the ductile-machined areas shrank under a negative tool rake angle. On the other hand, brittle fracture occurred around pores released cutting pressure significantly. These trends of rake angle effects are distinctly different from those in the cutting of non-porous silicon. Finite element simulation of stress in the cutting area agreed with the... 

    Efficiency improvement of solar stills through wettability alteration of the condensation surface: An experimental study

    , Article Applied Energy ; Volume 268 , 2020 Zanganeh, P ; Soltani Goharrizi, A ; Ayatollahi, S ; Feilizadeh, M ; Dashti, H ; Sharif University of Technology
    Elsevier Ltd  2020
    The condensation process is of great importance in many heat transfer devices in which a large amount of energy must be transferred. Furthermore, condensation is a crucial part of energy conversion and affects the energy efficiency of thermal desalination plants and solar stills. During the condensation process in solar stills, an essential part of the energy is transferred through the condensation surface to produce fresh water. Therefore, the condensation surface plays a significant role in the working efficiency of solar stills. The wettability of the condensation surface influences the condensation mechanism, which, in turn, affects the efficiency of solar stills. This study aims to... 

    Investigation into the effect of substrate material on microstructure and optical properties of thin films deposited via magnetron sputtering technique

    , Article Ceramics International ; 2021 ; 02728842 (ISSN) Mashaiekhy Asl, J ; Nemati, A ; Hadi, I ; Mirdamadi, Sh ; Sharif University of Technology
    Elsevier Ltd  2021
    This study aims at investigating the effect of the substrate material on growth mechanism and also microstructure of Ta2O5 thin films. For this purpose, atomic force microscopy, scanning electron microscopy, and interferometry analyses were implemented to reveal the influence of silicon wafer and amorphous BK7 glass substrates on the nucleation and growth mechanisms of Ta2O5 thin films deposited via the radio frequency magnetron sputtering technique. Results indicated that those films with finer morphologies had relatively higher nucleation densities. Compared with BK7 glass substrate, crystals formed on the silicon wafer were shown to be finer and had lower mean areas in more nucleation... 

    Optimization of nano HA-SiC coating on AISI 316L medical grade stainless steel via electrophoretic deposition

    , Article Materials Letters ; Volume 285 , 2021 ; 0167577X (ISSN) Hosseini, M. R ; Ahangari, M ; Johar, M. H ; Allahkaram, S. R ; Sharif University of Technology
    Elsevier B.V  2021
    Biocompatible nanostructured coating plays an important role in enhancement of osseointegration ability of metallic implants. This study sets out to obtain optimized SiC concentration in Hydroxyapatite (HA) coating on AISI 316L stainless steel alloy through electrophoretic deposition method. Effect of SiC concentrations (1, 2, and 3%.wt) on the morphology, corrosion behaviour, and mechanical properties of the HA coating is investigated. Results show that SiC could obstruct the formation and growth of micro cracks in the HA coating where HA-3%SiC is considered as a crack free coating. Electrochemical tests reveal that SiC has improved the corrosion resistance of HA coating, and HA-3%SiC... 

    Coefficient of performance of mono-and multi-crystalline silicon photovoltaic panels

    , Article Solar World Congress 2005: Bringing Water to the World, Including 34th ASES Annual Conference and 30th National Passive Solar Conference, Orlando, FL, 6 August 2005 through 12 August 2005 ; Volume 2 , 2005 , Pages 1045-1050 ; 9781622762637 (ISBN) Bahadori, M. N ; Zamzamian, K ; Sharif University of Technology
    The coefficient of performance (COP) of a photovoltaic panel or module is defined as the ratio of the total electrical energy produced by the panel during its life to the total energy spent for its manufacture. All processes involved for the manufacture of photovoltaic panels were considered and the energy spent per unit mass of the final product during each process was determined. The total electrical energy spent for the manufacture of a photovoltaic module of 1×0.5 m dimensions, employing 340 micron wafers, with the net wafer area of 0.36 m2, was then determined. Monocrystalline and multicrystalline silicon cells were employed. It was found that for the manufacture of the PV module... 

    A general model for multicomponent transport in nonporous membranes based on Maxwell-Stefan formulation

    , Article Chemical Engineering Communications ; Volume 191, Issue 4 , 2004 , Pages 460-499 ; 00986445 (ISSN) Ghoreyshi, A. A ; Farhadpour, F. A ; Soltanieh, M ; Sharif University of Technology
    Taylor and Francis Ltd  2004
    A "general" model of membrane transport was formulated using the mechanistic Maxwell-Stefan approach and generalized driving forces, which included the contribution from the various internal and external driving forces. Transient models of dialysis and pervaporation were developed that used exactly the same general model to describe the transport through the membrane. In this model, the bulk solution/polymer equilibria were described by a modified Flory-Huggins model, and the concentration dependence of ternary Maxwell-Stefan diffusivities was described by a natural extension of the binary Vignes relationship to a multicomponent system. A notable advantage of the general model lies in the... 

    Multicomponent transport across nonporous polymeric membranes

    , Article Desalination ; Volume 144, Issue 1-3 , 2002 , Pages 93-101 ; 00119164 (ISSN) Ghoreyshi, S. A. A ; Farhadpour, F. A ; Soltanieh, M ; Sharif University of Technology
    Elsevier  2002
    The theoretical description of multicomponent transport across nonporous polymeric membranes was investigated using two alternative frameworks: the phenomenological approach of irreversible thermodynamics and the mechanistic Stefan-Maxwell formulation. The transport models developed account for potential equilibrium and/or kinetic coupling of fluxes and the contribution of diffusion induced non-selective flow within the polymer. The models were validated against transient dialysis and pervaporation data for the {ethanol-water}/silicone rubber system. A critical assessment was obtained by recovering the model parameters from the dialysis data and using the same parameters to predict the... 

    Drug release from silicon polymer matrices containing an osmotic agent or a water-swelling additive

    , Article Iranian Journal of Science and Technology, Transaction B: Technology ; Volume 26, Issue 2 , 2002 , Pages 197-204 ; 03601307 (ISSN) Abdekhodaie, M. J ; Sharif University of Technology
    Potassium chloride, as an osmotic agent and poly methacrylic acid, as a water-swelling additive have been incorporated in polydimethyl siloxane. By using caffeine as a model drug, the results of release experiments from two systems have been compared. Because of osmotic rupturing pseudo-zero-order release kinetics preceded by marked burst effect were observed. Since osmotic pressure of PMAA is higher than that of KCI, drug release rate from PMAA-PDMS matrices is higher than that from KCI-PDMS matrices. Since KCI is release along with the drug, but PMAA is not, therefore water-swelling additives may provide efficient drug release without releasing undesirable substances  

    Microstructural evolution of Al-20Si-5Fe alloy during rapid solidification and hot consolidation

    , Article Rare Metals ; Volume 28, Issue 6 , 2009 , Pages 639-645 ; 10010521 (ISSN) Rajabi, M ; Vahidi, M ; Simchi, A ; Davami, P ; Sharif University of Technology
    Al-20Si-5Fe melt was rapidly solidified into particles and ribbons and then consolidated to near full density by hot pressing at 400°C/250 MPa/1 h. According to the eutectic-growth and dendritic-growth velocity models, the solidification front velocity and the amount of undercooling were estimated for the particles with different sizes. Values of 0.43-1.2 cm/s and 15-28 K were obtained. The secondary dendrite arm spacing revealed a cooling rate of 6 × 105 K/s for the particles with an average size of 20 μm. Solidification models for the ribbons yielded a cooling rate of 5 × 107 K/s. As a result of the higher cooling rate, the melt-spun ribbons exhibited considerable microstructural... 

    Thermal residual stresses in silicon thin film solar cells under operational cyclic thermal loading: A finite element analysis

    , Article Solar Energy ; Volume 135 , 2016 , Pages 366-373 ; 0038092X (ISSN) Namvar, A ; Dehghany, M ; Sohrabpour, S ; Naghdabadi, R ; Sharif University of Technology
    Elsevier Ltd  2016
    In manufacturing amorphous silicon solar cells, thin films are deposited at high temperatures (200-400 °C) on a thick substrate using sputtering and plasma enhanced chemical vapor deposition (PECVD) methods. Since the thin films and substrate have different thermal expansion coefficients, cooling the system from deposition temperature to room temperature induces thermal residual stresses in both the films and substrate. In addition, these stresses, especially those having been induced in the amorphous silicon layer can change the carrier mobility and band gap energy of the silicon and consequently affect the solar cell efficiency. In this paper, a 2D finite element model is proposed to... 

    Improvement of Mechanical Properties of a Mg-Zn alloy using the Micro Alloying Elements

    , M.Sc. Thesis Sharif University of Technology Cheraghi Heyvedi, Hamid (Author) ; Karimi Taheri, Ali (Supervisor)
    The development of new wrought magnesium alloys for automotive industry has increased in recent years due to their high potential as structuralmaterials for low density and high strength/weight ratio demands. However, the poor mechanical properties of the magnesium alloys have led tosearch a new kind of magnesium alloys for better strength and ductility.In this research,a new type of magnesium alloy based on Mg-Zn-Si-Ca system has been developed using the permanent gravity casting process. For comparison, an alloy without Siby the same method was also produced. The effects of trace Si addition on the microstructure and mechanical properties in magnesium alloy with composition of... 

    SiC Production by Chemical Vapor Deposition Method

    , M.Sc. Thesis Sharif University of Technology Habibian Nejad, Ali (Author) ; Farhadi, Fathola (Supervisor)
    Silicon carbide due to its noticeable mechanical and thermal properties, uses in various industries either main substrate or reinforcement. SiC has low specific surface area according to its resistivity against sintering. Recently, a lot of scientists have been worked on SiC in order to fabricating small ones ; subsequently, better sintering will be achieved. Chemical vapor deposition method (CVD) is a method to produce fine SiC with deposition of products by reacting of initial materials from gas environment. In this study normal CVD as proper method and hydrogen, silicon tetrachloride and activated carbon as initial materials are chosen. Using of iron and nickel catalysts in temperature... 

    Modeling and technical-economic optimization of electricity supply network by three photovoltaic systems

    , Article Journal of Solar Energy Engineering, Transactions of the ASME ; Vol. 136, issue. 2 , 2014 ; ISSN: 0199-6231 Safarian, S ; Khodaparast, P ; Kateb, M ; Sharif University of Technology
    To attain an ongoing electricity economy, developing novel widespread electricity supply systems based on diverse energy resources are critically important. Several photovoltaic (PV) technologies exist, which cause various pathways to produce electricity from solar energy. This paper evaluates the competition between three influential solar technologies based on photovoltaic technique to find the optimal pathways for satisfying the electricity demand: (1) multicrystalline silicon; (2) copper, indium, gallium, and selenium (CIGS); and (3) multijunction. Besides the technical factors, there are other effective parameters such as cost, operability, feasibility, and capacity that should be... 

    Use of atomistic phonon dispersion and boltzmann transport formalism to study the thermal conductivity of narrow Si nanowires

    , Article Journal of Electronic Materials ; Volume 43, Issue 6 , 2014 , Pages 1829-1836 ; ISSN: 03615235 Karamitaheri, H ; Neophytou, N ; Kosina, H ; Sharif University of Technology
    We study the thermal properties of ultra-narrow silicon nanowires (NW) with diameters from 3 nm to 12 nm. We use the modified valence-force-field method for computation of phononic dispersion and the Boltzmann transport equation for calculation of phonon transport. Phonon dispersion in ultra-narrow 1D structures differs from dispersion in the bulk and dispersion in thicker NWs, which leads to different thermal properties. We show that as the diameter of the NW is reduced the density of long-wavelength phonons per cross section area increases, which increases their relative importance in carrying heat compared with the rest of the phonon spectrum. This effect, together with the fact that... 

    Nanocrystallization kinetics and magnetic properties of the melt spun amorphous (Fe0.5Co0.5)77Si11B 9Cu0.6Nb2.4 alloy

    , Article Thermochimica Acta ; Vol. 575, issue , 2014 , p. 64-69 Shivaee, H. A ; Samadi, M ; Alihosseini, H ; Madaah Hosseini, H. R ; Sharif University of Technology
    Kinetics of crystallization in an amorphous (Fe0.5Co 0.5)77Si11B9Cu0.6Nb 2.4 (at.%) alloy was investigated using differential scanning calorimetry (DSC). Transformed fraction as a function of temperature was obtained by accurate DSC measurement and the experimental data analyzed with Vyazovkin model-free kinetic method. Reconstructed form of the experimental kinetics model, g(α), clearly showed the crystallization mechanism do not belongs to a single model but almost follows the Avrami-Erofe'ev. Magnetic coercivity and hysteresis loss values of the annealed samples at 823 K were 7.5 A m-1 and 1.2 J m-3, compared to 17.1 A m-1 and 37.1 J m-3 for as spun samples. Magnetic measurements show the... 

    A new energy-based isothermal and thermo-mechanical fatigue lifetime prediction model for aluminium-silicon-magnesium alloy

    , Article Fatigue and Fracture of Engineering Materials and Structures ; Volume 36, Issue 12 , 2013 , Pages 1323-1335 ; 8756758X (ISSN) Farrahi, G. H ; Azadi, M ; Winter, G ; Eichlseder, W ; Sharif University of Technology
    In this paper, a new fatigue lifetime prediction model is presented for the aluminium-silicon-magnesium alloy, A356.0. This model is based on the plastic strain energy density per cycle including two correction factors in order to consider the effect of the mean stress and the maximum temperature. The thermal term considers creep and oxidation damages in A356.0 alloy. To calibrate the model, isothermal fatigue and out-of-phase thermo-mechanical fatigue (TMF) tests were conducted on the A356.0 alloy. Results showed an improvement in predicting fatigue lifetimes by the present model in comparison with classical theories and also the plastic strain energy density (without any correction... 

    The effect of melt quality and filtering on the Weibull distributions of tensile properties in Al-7%Si-Mg alloy castings

    , Article Materials Science and Engineering A ; Volume 579 , 2013 , Pages 64-70 ; 09215093 (ISSN) Eisaabadi B., G ; Davami, P ; Kim, S. K ; Tiryakioglu, M ; Sharif University of Technology
    The effects of melt quality and the placement of a filter in the filling system on Weibull distributions of tensile strength and elongation of Al-7%Si-Mg alloy castings were investigated. Three different combinations of melt quality and filtering were used: (a) unstirred, with filter in the filling system, (b) stirred to produce and entrain surface oxide films with no filter in the filling system to emulate poor initial melt preparation and melt handling, and (c) stirred and with a filter placed in the filling system. The results showed that the highest elongation and tensile strength values were obtained from the unstirred, filtered condition and lowest values were from stirred and... 

    On the effect of cooling rate during melt spinning of FINEMET ribbons

    , Article Nanoscale ; Volume 5, Issue 16 , 2013 , Pages 7520-7527 ; 20403364 (ISSN) Gheiratmand, T ; Hosseini, H. R. M ; Davami, P ; Ostadhossein, F ; Song, M ; Gjoka, M ; Sharif University of Technology
    The effect of quenching wheel speed on the structure and Curie temperature of Fe73.5Si13.5B9Nb3Cu1 alloy has been investigated using X-ray diffraction, differential scanning calorimetry, transition electron microscopy and a SQUID magnetometer. Ribbons were melt-spun at different wheel speeds and then were annealed to nucleate nano crystals embedded in the amorphous matrix. The results indicated that the thickness of the ribbons was inversely proportional to the wheel speed following the power law of the type t ∝ Vs -1.231. DSC and XRD results showed that at higher wheel speeds the greater potential energy triggers the formation of Fe (Si) crystallites and thus, increases the crystallinity.... 

    Microstructure based modelling of flow behaviour of Al-Mg-Si alloy at different temper conditions

    , Article Materials Science and Technology (United Kingdom) ; Volume 29, Issue 8 , 2013 , Pages 968-974 ; 02670836 (ISSN) Anjabin, N ; Karimi Taheri, A ; Sharif University of Technology
    A new integrated physically based constitutive model was developed for an age hardenable Al- Mg-Si alloy. The kinetics of precipitation during various stages of aging was modelled. The precipitate features consisted of particle radius and volume fraction obtained from the kinetics model, which was used to compute the alloy yield strength/hardness. A published multiinternal variable workhardening model was improved to take into account the effects of solute solution and precipitates on the alloy hardening capacity after performing different cycles of aging treatment. The flow curves and hardness predicted by the model were in good agreement with the experimental results. The model is able to... 

    Calculation of confined phonon spectrum in narrow silicon nanowires using the valence force field method

    , Article Journal of Electronic Materials ; Volume 42, Issue 7 , 2013 , Pages 2091-2097 ; 03615235 (ISSN) Karamitaheri, H ; Neophytou, N ; Taheri, M. K ; Faez, R ; Kosina, H ; Sharif University of Technology
    We study the effect of confinement on the phonon properties of ultra-narrow silicon nanowires of side sizes of 1 nm to 10 nm. We use the modified valence force field (MVFF) method to compute the phononic dispersion and extract the density of states, the transmission function, the sound velocity, the ballistic thermal conductance and boundary-scattering-limited diffusive thermal conductivity. We find that the phononic dispersion and the ballistic thermal conductance are functions of the geometrical features of the structures, i.e., the transport orientation and confinement dimension. The phonon group velocity and thermal conductance can vary by a factor of two depending on the geometrical...