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Densification and properties of Fe2O3 nanoparticles added CaO refractories
, Article Ceramics International ; 2016 ; 02728842 (ISSN) ; Nemati, A ; Shahraki, A ; Farooghi, M ; Sharif University of Technology
Elsevier Ltd
2016
Abstract
Up to 8wt. % of Nano-iron oxide was added to CaO refractory matrix. The crystalline phases and microstructure characteristics of specimens sintered at 1650°C for 5h in an electric furnace were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The physical properties are reported in terms of bulk density, apparent porosity and hydration resistance. The mechanical behavior was studied by a cold crushing strength (CCS) and flexural strength at 1200°C test. As a result, it was found that the presence of Nano-iron oxide in the CaO refractory matrix induced 2CaO.Fe2O3 (C2F), CaO.Fe2O3 (CF) and 3CaO.Al2O3 (C3A) phase's formation, which improved the sintering...
Performance improvement of MgO-CaO refractories by the addition of nano-sized Al2O3
, Article Materials Chemistry and Physics ; Volume 198 , 2017 , Pages 354-359 ; 02540584 (ISSN) ; Ghasemi kahrizsangi, S ; Nemati, A ; Sharif University of Technology
2017
Abstract
Magnesia-dolomite refractories have advantages such as stability in the basic environments, clean steel production, high corrosion resistance, proper covering in the cement furnace, and low production costs. However, their application is restricted due to low hydration resistance. In this research, the effects of nano and micro alumina particles on the microstructure, sintering behavior, and properties of magnesia-dolomite refractories were studied. For this purpose, MgO-CaO refractories were formulated using dolomite and magnetite and 0, 2, 4, 6 and 8 wt percentage nano and micro alumina were added to the formulation. Phase and microstructure analysis of the samples were performed using...
Air quenching as a reliable technique to obtain colossal dielectric constant with low loss in (In, Nb)-co doped TiO2
, Article Materials Letters ; Volume 267 , May , 2020 ; Mahmoudi, P ; Karimi, A ; Sharif University of Technology
Elsevier B. V
2020
Abstract
In this research, for the first time, the effect of air quenching on the microstructural and electrical properties of (In, Nb) co-doped TiO2 was investigated. The FE-SEM images showed that the air quenching has no effect on microstructure of co-doped TiO2. However, air quenching affected the electrical properties so that the dielectric constant in the frequency of 1 kHz at room temperature sharply enhanced from 21*103 to 26*104 and the dielectric loss surprisingly decreased from 0.6 to 0.1. This incredible improvement in the dielectric properties is attributed to the electron-pined defect dipoles which has been activated through air quenching. © 2020 Elsevier B.V
Grain growth kinetics and electrical properties of CuO doped SnO2-based varistors
, Article Journal of Alloys and Compounds ; Volume 770 , 2019 , Pages 784-791 ; 09258388 (ISSN) ; Nemati, A ; Maleki Shahraki, M ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
Up to now, attempts for developing coarse-grained SnO2-based varistors which exhibit high nonlinearity property at lower voltage have become a challenge without any prominent result because of its unknown grain growth mechanism. In this study, the effect of CuO addition to SnO2-based varistors as a grain growth enhancer additive on microstructural development, grain growth kinetics, and electrical properties was investigated. The characterization of grain growth kinetics showed that CuO addition encouraged grain growth and enhanced the grains size as it could be seen in the activation energy which decreased from 594 kJ/mol to 364 kJ/mol. In the samples with a low amount of CuO, the solute...
High voltage SnO2 varistors prepared from nanocrystalline powders
, Article Journal of Materials Science: Materials in Electronics ; Volume 21, Issue 2 , 2010 , Pages 199-205 ; 09574522 (ISSN) ; Shojaee, S. A ; Nemati, A ; Sani, M. A. F ; Sharif University of Technology
2010
Abstract
In this study, SnO 2-based varistors were prepared from mechanically activated nanocrystalline powders. Nanocrystalline powders were derived by subjecting the initial powders to intensive high-energy activation with different times and ball to powder ratio. The effect of activation parameters on the powder properties and sintering temperature, as well as microstructural, micro-electrical and macro-electrical properties of the final specimens was evaluated. Varistors derived from high-energy mechanical activation exhibit a higher density (98.3% relative density) and more refined microstructure upon sintering at 1,300 °C in comparison varistors prepared from conventional powders. Breakdown...
Novel multifunctional capacitor-varistor ceramics based on SnO2
, Article Ceramics International ; Volume 44, Issue 16 , 2018 , Pages 20386-20390 ; 02728842 (ISSN) ; Alipour, S ; Mahmoudi, P ; Karimi, A ; Sharif University of Technology
Elsevier Ltd
2018
Abstract
Up to now, multifunctional varistor-capacitor materials were based on TiO2, even though these materials failed to have practical applications. For the first time, in this research, multifunctional varistor-capacitor properties are observed in the CuO-doped SnO2-CoO-Sb2O3 system. The XRD analysis showed that this system has a single phase microstructure. SEM images indicated that the CuO addition resulted in a better densification and larger grain size. The very low electric breakdown field of the CuO-doped SnO2-CoO-Sb2O3 system (12 V/mm, similar to TiO2), is a consequence of coarse-grained microstructure. This varistor had a suitable surge withstand capability as well. The colossal...
A Comparison of the Effects of Additives Alumina Nanoparticles and Microparticles on Microstructure and Properties of Magnesia-Doloma Refractory
, M.Sc. Thesis Sharif University of Technology ; Nemati, Ali (Supervisor)
Abstract
Magnesia-Doloma refractories has advantages such as stability in alkaline environments, clean steel production, resistance to acid slag, good cement kiln coating flexibility, low production cost. It also has some weaknesses such as low resistance to thermal shock and quick hydration. In the present study using Birjand Mines Magnesite powders and Dolomites from Zefreh, Esfahan, Magnesia-Doloma clinkers were pressed under the pressure 90 MP and prepared at 1650⁰C in furnace under air atmosphere. The effect of adding 0, 2, 4, 6, and 8% of the Microparticles and Nanoparticles of α-Alumina on microstructure, physical properties, hydration resistance and Thermal shock resistance was studied. Phase...
Two-step sintering of ZnO varistors
, Article Solid State Ionics ; Volume 190, Issue 1 , 2011 , Pages 99-105 ; 01672738 (ISSN) ; Shojaee, S. A ; Faghihi Sani, M. A ; Nemati, A ; Safaee, I ; Sharif University of Technology
2011
Abstract
In this research, effects of two-step sintering parameters, such as first and second step sintering temperatures (T1 and T2, respectively) and soaking time in the second step, on microstructure and electrical properties of ZnO varistors have been studied. In addition, slow rate of grain growth in the second step of sintering has also been investigated. Near fully dense (higher than 99%) and sub-micron grain size (1-0.75 μm) ZnO varistors have been fabricated by different two-step sintering cycles. Decreasing T1 and T2 result in longer necessary time in the second step to reach near full density with smaller final grain size. The superior electrical properties of varistors (VB: 2050-1022 V/mm...
Microstructural and electrical properties of varistors prepared from coated ZnO nanopowders
, Article Journal of Materials Science: Materials in Electronics ; Volume 21, Issue 6 , June , 2010 , Pages 571-577 ; 09574522 (ISSN) ; Maleki Shahraki, M ; Faghihi Sani, M. A ; Nemati, A ; Yousefi, A ; Sharif University of Technology
2010
Abstract
This paper describes a solution-based technique for fabrication of varistor grade composite nanopowders. The method consists of coating major varistor dopants on the surface of the ZnO nanoparticles. As a result, a homogenous mixture of dopants and ZnO nanoparticles will be achieved. TEM results indicated that a composite layer of dopants with the average particle size of 9 nm on the surface of ZnO nanoparticles has been successfully prepared. Sintering of the coated powders was performed in temperatures as low as 850 °C and final specimens with average particle size of 900 nm and density of 98.5% were achieved. In comparison to conventional mixing, varistors prepared from coated nanopowders...
Facile synthesis and self-assembling of transition metal phosphide nanosheets to microspheres as a high-performance electrocatalyst for full water splitting
, Article Journal of Alloys and Compounds ; Volume 875 , 2021 ; 09258388 (ISSN) ; Golmohammad, M ; Shahraki, M. M ; Simchi, A ; Sharif University of Technology
Elsevier Ltd
2021
Abstract
The development of noble-metal-free electrocatalysts with enhanced active sites is of great significance for the production of renewable energy on large scale. Ultrathin transition metal compounds (e.g., phosphides and sulfides) have unique structural features but their stability and electroactivity must still be improved for practical applications. We propose a new strategy to synthesis ultrathin sheets of Ni-Cu-Co transition metals on porous nickel and self-assemble them into yarn-shaped microspheres. Enhance catalytic activity and stability are then attained by thermochemical phosphorization without morphological modifications. We employed various analytical techniques including XRD, SEM,...
Novel hot milling approach for the synthesis of fine PbZr0.95Ti0.05O3 powders
, Article Ceramics International ; Volume 45, Issue 18 , 2019 , Pages 24176-24181 ; 02728842 (ISSN) ; Hojaji Najafabadi, A. R ; Safaei, S ; Sadrnezhaad, Kh ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
A new and effective hot milling system was designed and applied to the synthesis of PbZr0.95Ti0.05O3 (PZT) powder. PbO, ZrO2 and TiO2 powders were used as starting materials and hot milled at various temperatures ranging from 10 ̊°C to 800 ̊°C. The obtained powders were characterized by X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). Results indicated that pure, crystalline, and fine PZT powders with the average particle size of 170 nm can be successfully synthesized directly after a relatively short synthesis time of 12 h at lower temperature of 800 ̊°C by the hot milling technique. In contrast to this method, this study demonstrates that conventional solid-state...
The effect of nano-TiO2 additions on the densification and mechanical properties of SiC-matrix composite
, Article Ceramics International ; Volume 46, Issue 5 , April , 2020 , Pages 6477-6483 ; Yaghobizadeh, O ; Baharvandi, H. R ; Alipour Shahraki, A ; Mohammadi, H ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
This research studied the effect of adding TiO2 nanoparticles along with Al2O3 and Y2O3 additives on the physical and mechanical properties of a SiC-matrix composite. The samples were fabricated through a pressureless process at 1900 °C. The results showed that the addition of TiO2 nanoparticles up to 4.5 wt% inhibited the excessive growth of SiC grains. According to the investigations, the microstructure and final properties of composites were affected by density, synthesized phases as well as their distribution in the matrix, and grain size. The highest density, Young's modulus, hardness, indentation fracture resistance, and flexural strength, alongside with the lowest brittleness index...
Analogies and Differences Between Auantum Mechanics and Quanmtum Field Theory (Causality and Locality)
, M.Sc. Thesis Sharif University of Technology ; Golshani, Mehdi (Supervisor)
Abstract
Causality and locality are two of the fundamental problems in physics and physicists have different interpretations of them. In new physics theories like Quantum mechanics and Quantum field theory, the main point of discussion is that whether these two theories are local and causal or not? In first chapter, we introduce the principle of causality. The second and third chapters cover causality in Quantum mechanics and Quantum field theory.The last chapter is about locality
Behavior Patterns Analysis of Cavity Quantum Electro-Dynamics in Complex Systems for Different Coupling Regimes
, M.Sc. Thesis Sharif University of Technology ; Khorasani, Sina (Supervisor)
Abstract
In this M.Sc. thesis the behavior patterns of the cavity quantum electrodynamics of complex systems are analyzed, such systems are quantum optic multi-partite systems and consist of an arbitrary number of quantum dots in interaction with arbitrary number of cavity modes.
First, the coefficients matrix of the ket sate of the system was measured, in order to achieve it; the general time-dependent state of the most general possible system was specified. Its related Hamiltonian was written, and finally the Schrodinger equation was measured in different coupling regimes. It was done in Schrodinger picture without any approximation.Second, the presence probabilities of the quantum dots of any...
First, the coefficients matrix of the ket sate of the system was measured, in order to achieve it; the general time-dependent state of the most general possible system was specified. Its related Hamiltonian was written, and finally the Schrodinger equation was measured in different coupling regimes. It was done in Schrodinger picture without any approximation.Second, the presence probabilities of the quantum dots of any...
Investigation on MBBR with Suspended Biomass and Recycled Sludge
,
M.Sc. Thesis
Sharif University of Technology
;
Borgheei, Mahdi
(Supervisor)
Abstract
There is a growing demand for efficient treatment plans which can deal with high loading of organic pollutant, considering the population growth in communities. Our country is going toward industrialization; hence, it requires more effective and efficient treatment plans as well as innovative ones. Moving Bed Biological Reactors are accounted amongst appropriate methods in removing various pollutant which has been used in recent decades. In regard to increasing demand for new treatment plans, one of the options can be upgrading of existing activated sludge systems. Two bioreactors with 10 liter volume each in parallel lines were used in this work. One of them was a regular MBBR as a blank...
Hydrogen distribution in refinery with non-linear programming
, Article International Journal of Engineering, Transactions B: Applications ; Volume 18, Issue 2 , 2005 , Pages 165-176 ; 1728-144X (ISSN) ; Kashi, E ; Rashtchian, D ; Sharif University of Technology
Materials and Energy Research Center
2005
Abstract
Growth of the world population, increasing demand for fossil fuel consumption and consequently increasing threat of global warming, has extended the need for production and use of clean fuels and normal hydrogen is an important utility in the production of clean fuels. In this paper, a mathematical optimization method is applied which is based on non-linear programming of superstructure for minimizing the consumption of hydrogen. The method considers all the pressure constraints and is suited for revamping industrial systems. The optimum placement of new equipments like purification unit has been also considered. It is tried to verify the method adopted, in addition, an industrial case study...
Fabrication of AZ31/Al2O3 nanocomposites by friction STIR processing
, Article Reviews on Advanced Materials Science ; Volume 28, Issue 1 , 2011 , Pages 85-89 ; 16065131 (ISSN) ; Kim, H. S ; Kokabi, A. H ; Abachi, P ; Shahraki, B. K ; Sharif University of Technology
2011
Abstract
The aim of this paper is to fabricate AZ31/Al2O3 nanocomposites by friction stir processing (FSP). Due to severe plastic deformation, dynamic recrystallization, and grain growth retardation by nanoparticles during the FSP processing, ultrafine grained microstructures with homogeneous distribution of the nanoparticles were produced. With increasing rotational speed, as a result of the increased plastic deformation and heat generation, increased grain size of the matrix, and simultaneously shattering effect of rotation cause a uniform nanoparticle distribution. By the large plastic deformation, texture of the matrix evolved and especially the (0002) basal plane was developed
Densification and properties of ZrO2 nanoparticles added magnesia–doloma refractories
, Article Ceramics International ; Volume 42, Issue 14 , 2016 , Pages 15658-15663 ; 02728842 (ISSN) ; Barati Sedeh, M ; Gheisari Dehsheikh, H ; Shahraki, A ; Farooghi, M ; Sharif University of Technology
Elsevier Ltd
2016
Abstract
In this work the effect of nano- and microZrO2 addition on the densification and hydration resistance of MgO–CaO refractories was investigated. 0, 2, 4, 6 and 8 wt% ZrO2 was added to MgO–CaO refractories that contain 35 wt% CaO. The crystalline phases and microstructure characteristics of specimens sintered at 1650 °C for 5 h in an electric furnace were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The physical properties are reported in terms of bulk density, apparent porosity and hydration resistance. Results show that with addition of ZrO2 the bulk density and hydration resistance of the samples increased while apparent porosity decreased. Also...
Stable high dielectric properties in (Cr, Nb) co-doped SnO2 ceramics
, Article Materials Chemistry and Physics ; Volume 246 , May , 2020 ; Golmohammad, M ; Chermahini, M. D ; Mahmoudi, P ; Moghadam, H. A ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
In this research, the microstructure, dielectric, and non-Ohmic properties of (Cr, Nb) co-doped SnO2 ceramics, (Cr0.5, Nb0.5)xSn1-xO2 with x% = 0, 0.5, 1.0, 2.0, 5.0, and 10.0, as a colossal dielectric material and a prospective alternative to co-doped TiO2 ceramics were studied. The X-ray diffraction results indicated that in all compositions, the cassiterite phase was achieved without any secondary phases. Moreover, field-emission secondary electron microscopy showed that the microstructure of samples has different morphologies including typical grains, enlarged grains and prism-like grains microstructure for various sintered samples. The maximum dielectric constant (2737) accompanied by...
A Semisupervised Classification Algorithm for Data Streams Using Decision Tree Algorithm
, M.Sc. Thesis Sharif University of Technology ; Beigy, Hamid (Supervisor)
Abstract
Nowadays, living in information era has forced us to face with a great deal of problems of which the input data is received like a nonstop endless stream. Intrusion detection in networks or filtering spam emails out of legal ones are instances of such problems. In such areas, traditional classification algorithms show function improperly, thus it is necessary to make use of novel algorithms that can tackle these problems. Among classification algorithms, decision trees have significant advantages such as being independent of any parameter and acting robust against outliers or unrelated attributes. Moreover, results of a decision tree are quite easy to interpret and extract rules from....