Sharif Digital Repository

Electrostatic precipitators are widely used in cement plants to remove impurities and dust from the exhaust gases. The filtration mechanism is based on using high intensity electric fields which first ionize the particles and then absorb them toward the collecting electrodes. The corrosion effect is one of the major problems associated with electrostatic precipitators which not only can negatively affect their operation efficiency but also decreases their life-time through breakage occurrence in the corroded electrodes. One of the commonly used methods to suppress this negative effect and increase the total working hours of the device is to cut the bottom part of the first collecting plate... 

One of the best ways to overcome the weaknesses of technology services in different industries is right technology transfer with feasibility in the country. 3D painters have been recently widely used industrially in different countries. The 3D printer is one of the new emerging technologies, enabling the production of every 3D objects with any complexity. 3D printing has provided the possibility of producing, in fastest, more economics and regardless of those complexities. By transfer of this kind of technology and proper management, a huge transformation can created in all industries and factories. To do this, there are several technologies of 3D printing, that each of them used in various... 

At a unit in zirconium production plant under the supervision of Soure Co. nuclear grade zirconium is produced. In the process it is required that hafnium get separated from Zirconium. Zirconium and hafnium separation are performed by nitric acid (4N) and hydrochloric acid (4N). This isolation environment is considerably corrosive and damaging for the equipment. Powder coating is one of the solutions to deal with the corrosion. To do so, electrostatic powder coating method was used for ECTFE polymer. After the coating, according to spark test, roughness analysis, thickness, elasticity and adhesion; temperature and time of the spraying and the spraying of top coating was determined. In... 

The primary objective of this study entails the examination of the impact of lubricants intended for implementation in the compaction process of nano-powders, intending to mitigate friction at the nano scale during compaction. Molecular dynamics modeling is employed to scrutinize this phenomenon and derive the friction parameters within the framework of equations derived from continuum mechanics, based on data acquired from the nanoscale investigations. The manufacturing procedure of metallic components from metal powder compaction necessitates the application of immense pressures, thereby engendering notable friction between the powder particles and the confines of the mold. Consequently,... 

The primary purpose of this study is to perform nonlinear behavior simulations in the compaction and forming of metal powders and their alloys and investigate their behavior in the plastic state. Powder compression is one of the methods of producing metal parts with high precision and improved mechanical properties, which is why it has been considered in addition to its need in the industry.There are various methods for performing these simulations, including multi-scale methods with optimal performance. Given that only the use of high-scale methods or only low-scale methods will have problems and disadvantages in such simulations, multi-scale methods will be a good alternative in which both... 

The present research focuses on the simulation of the metallic powder compaction process with the Peridynamics theory. Various methods are exploited to simulate this process in literature. Studying the nonlinear behavior of powders includes different phenomena such as dislocation and grain boundary, making it complicated. However, numerous research has been shaped to consider these phenomena on the micro-scale. There is also another batch of nano-scale studies underway. In this class of simulations, considering atoms as rigid particles, interatomic potentials, and molecular dynamics methods are used. Because of atomic-scale precision, this approach has very high accuracy. The massive... 

In present research forming process of nanopowders, which is a part of powder metallurgy was investigated by molecular dynamics method. Powder metallurgy is a relatively new method for production of industrial parts by pouring powder into die and compaction to desired density. One can reach parts with higher quality and strength by decreasing size of powder’s particles and entering the nano scale. Particle with smaller size have higher specific surface and due more intensity to react. Classic methods for investigation of this process don’t cover the atomic scale effects, so using newer procedures such as molecular dynamics is highly recommended. In present research, at first compaction of... 

The hierarchical multi-scale approach is one of the most powerful techniques that takes the advantage of different scales and succeeds the limitations of each method in a way that the large systems in coarse-scale can be simulated with atomic precision. In this thesis, the hierarchical atomistic-continuum multi-scale method is developed for modeling the phenomena with non-homogenous deformation, large deformation and plastic behavior. In this regard at first, an atomistic-based higher-order continuum model is formulated in the framework of nonlinear finite element method to present the geometrically nonlinear behavior of nano-structures. The efficiency of higher-order Cauchy-Born hypothesis... 

In present research forming process of nanopowders, which is a part of powder metallurgy was investigated by molecular dynamics method. Powder metallurgy is a relatively new method for production of industrial parts by pouring powder into die and compaction to desired density. One can reach parts with higher quality and strength by decreasing size of powder’s particles and entering the nano scale. Particle with smaller size have higher specific surface and due more intensity to react. Classic methods for investigation of this process don’t cover the atomic scale effects, so using newer procedures such as molecular dynamics is highly recommended. In present research, at first compaction of... 

Performance and mechanical properties of concrete such as tensile strength, compressive strength, conductivity, etc change with creation and emission of cracks. As health monitoring of important structures is a vital subject that demands a large amount of budget annualy. Studying problems and disadvantages of concrete is one of the most important branches of research.
There are many ways to detect damage in concrete. Electrical resistance method that has been used in this thesis. In this study, an instrument called Risistivity Meter is used to measuring the electrical conductivity. This instrument measured the electrical conductivity, that it can be appropriate way to detect cracks... 

Direct metal deposition (DMD) process is an additive manufacturing technology that is rapidly gaining laser importance due to its various capabilities in applications such as coating, repairing high-value damaged parts, rapid prototyping and even production in small quantities. Among the equipment needed for this process, nozzle is perhaps the most important component because its performance affect the efficiency of powders trapped in the molten pool, and is crucial to the quality of the deposited layer. The existing nozzle designs can be categorized in two groups; lateral and coaxial nozzles; and the coaxial ones are divided into continuous and discontinuous types. Coaxial nozzles have... 

Direct Metal Deposition is one of the methods of Additive manufacturing that has seen the most spread in recent years. In this method metal powder is directed towards the free surface of the workpiece through a nuzzle, and is simultaneously heated to become molten in a melting pool by a laser beam and begins the deposition process. One of the parts that make up a DMD system is powder feeding nuzzle. These nuzzles usually encounter a similar fundamental problem: that the effect of gravity on the stream of metal powder and the carrier fluid causes this stream to deviate from its intended position. To prevent this, nuzzles are usually designed with a fixed downward angle and the angle of the... 

Selective laser sintering is an additive manufacturing technique based on fusion of powder bed, wherein after spreading a powder layer, a focused laser beam directs onto selected points of powder bed to fuse powder particles together. This process is repeated layer by layer until the final part is created. Although utilization of blade as a conventional powder spreading (CPS) mechanism has a good compression ability, the fixed contact line between blade and powder bed surface results in improper powder flowability and increasing shear forces applied on underneath layer. In this study, in order to obtain the basis for conducting practical experiments, discrete element simulation of powder... 

Selective laser sintering is a technique which uses a laser as the power source to sintering some selected points at a bed of powder in order to create a solid structure. In this research the SLS mechanisms of powder deposition is simulated and surface smoothness and layer density created by each mechanism is computed. For this purpose roller, blade and hopper mechanisms are simulated. For this simulation, polyamide 12 (PA2200) which is a common material is used. In this simulation at first powder specifications are extracted according to the references and for particle shape instead of using the spherical particle shape we use a certain shape that is more close to reality which created by... 

Additive manufacturing (Simply called A.M.) is a group of manufacturing technologies that is developing rapidly and is being used widely in some industries like car manufacturing, Aerospace and producing Biomedical devices, In a way that some researchers believe that A.M. methods will change the future of manufacturing. One of the most important A.M. techniques is the Selective Laser Sintering (SLS) method that is mostly used in industrial applications. A SLS machine has a lot of sub systems and mechanisms that have key role in the Laser Sintering process. One of the mechanisms of SLS machine is the Powder Dispensing mechanism that produce layers of unsintered powder as thin as 100 microns... 

Successfully bonding nickel-base alloys to titanium-base alloys has proven to be one of the most challenging modern joints. Traditional welding methods for dissimilar titanium/nickel joints often lead to cracking in the fusion and heat-affected(HAZ)zones; due to the formation of brittle intermetallic compounds with low fracture toughnesses. Additionally, the significant difference in thermal expansion coefficients between titanium and nickel introduces significant thermal stress during bonding process, exacerbating the current issue. Creating successful dissimilar Ti/Ni joints requires overcoming the formation of continuous brittle intermetallic compounds (IMCs). Brazing stands out as a... 

Powder production for additive manufacturing processes is one of the daily challenges of researchers. The aim of this research is to produce 316 L stainless steel powder using a new flame spraying method. Flame spraying is the oldest thermal spraying process, which has always been of interest due to its high efficiency and relatively low side costs. 316 L stainless steel wire with a diameter of 3 mm was used to produce the powder; The input material was entered at a temperature of 01°C and was melted with the help of acetylene and oxygen flame and sprayed as a powder, the powder production rate was kg/h0. To collect the produced powder, a cylindrical tank with a diameter of 01 cm and a... 

Methane steam reforming (MSR) is an assuring reaction using steam to produce H2 as clean energy over a nickel-based catalyst. We synthesized monometallic NiMgAl2O4 and bimetallic NiCoMgAl2O4 catalysts in a two-step combustion method using urea, glycine, and sucrose, as fuel. BET-BJH, XRD, TGA, TPR, FESEM, and EDX-mapping characterized surface area, porosity, morphology, crystalline structure, and metal-support interaction behavior. The products exhibited well-structured, simple MgAl2O4 spinel and NiO without NiAl2O4, in both specimens. The MSR evaluation tests at 750℃ under atmospheric pressure, CH4: H2O feed ratio of 1:1.6 showed the bimetallic catalyst has the highest conversion (99.30%)... 

In order to increase the strength of metals such as aluminum, severe plastic deformation processes can be used. Due to the fact that the dimensions of their products are usually small due to limitations, the connection of severely deformed sheets can be considered. Friction stir welding seems to be suitable for this purpose as a solid state process, but due to the significant amount of strain energy stored in this type of sheet, after recrystallization in the stir zone and the surrounding areas often experience severe grain growth. In this research, the 1050 aluminum sheets are severely deformed by constrained groove pressing (CGP) process were subjected to friction stir welding.... 

This research aimed at production of Cu-rGO via the combination of Molecular-Level-Mixing (MLM) method and powder metallurgy route (PM). First, Cu-GO composite powder was produced via MLM method. Subsequently, the resultant powder was mixed with electrolytic copper powder.Synthesis process included adjustment of the solution containing copper sulfate and 2Na.EDTA using NaOH solution. In the next step, GO suspension was added to the aforementioned solution. Finally, reduction of copper powder and formation of nanocomposite powder completed via the addition of Sodium Borohydrate. Nanocomposite powder was washed and dried in vacuum oven in 70˚C. GO reduction process took place using a tube...