Material science
Sajede Aghasi; Seyed Hassan Jafari; Mahdi Golriz
Abstract
One of the methods for improving thermal conductivity of epoxy adhesives is the incorporating of conductive ceramic, metal or carbon fillers. As the main goal of this research, is to improve thermal conductivity of epoxy resin and keep its electrically insulating property, Alumina (Al2O3) ceramic filler, ...
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One of the methods for improving thermal conductivity of epoxy adhesives is the incorporating of conductive ceramic, metal or carbon fillers. As the main goal of this research, is to improve thermal conductivity of epoxy resin and keep its electrically insulating property, Alumina (Al2O3) ceramic filler, individually and in combination with Boron Nitride (BN) ceramic filler with high thermal conductivity and electrical resistivity. Scanning Electron Microscopy (SEM) observations showed a good dispersion and an acceptable connection between fillers. Thermal diffusivity measurements revealed that by incorporating conductive ceramic fillers, either individually or in combination with each other, regardless of the type of the hardener, thermal diffusivity would increase as a result of the formation of thermal conductive networks. Although, in hybrid system, because of bridging effect between particles, thermal diffusivity will notably increase. Therefore, using hybrid system of Alumina/BN along with long chain polyamine curing agent is a suitable choice for the preparation of thermally conductive yet electrically insulating epoxy adhesives in space industries. The results show that the thermal conductivity of hybrid system of Alumina/BN have been raised to 1.7 (W/mK) instead of 0.4 (W/mK) which is belong to pure epoxy system. The most important point of this work is that the good thermal conductivity obtained by kept of mechanical properties, dielectric constant, as well as lap shear strength of Alumina/BN hybrid system meet all acceptable range of thermal conductive adhesive for space application.
Electric power
Mohammad Zarei-Jelyani; Mohammad Mohsen Loghavi; Mohsen Babaiee; Rahim Eqra; Masood Masoumi
Abstract
]n recent years, extensive research has been focused on the key materials of vanadium redox flow batteries (VRFBs) to improve the power and energy density. In a VRFB system, the ion-exchange membrane is an important component, because it is used to separate the positive and negative electrolytes and ...
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]n recent years, extensive research has been focused on the key materials of vanadium redox flow batteries (VRFBs) to improve the power and energy density. In a VRFB system, the ion-exchange membrane is an important component, because it is used to separate the positive and negative electrolytes and to allow the transfer of ions. Nafion membrane is now widely used in VRFBs due to their high proton conductivity and remarkable chemical stability. In the present study, the Nafion 117 membrane was subjected to an acid-heat pretreatment for utilizing in VRFBs. Three-cell stacks of VRFB were assembled using bare and pretreated membranes, and their performances were evaluated during charge/discharge cycles. The results indicate that acid and heat pretreatment on the Nafion 117 membrane improves the VRFB energy density by 30%. In addition, the average discharge voltage, which is one of the key parameters in the VRFB performance, is increased from 3.57 V (for the bare membrane) to 3.9 V (for the pretreated membrane). This helps to reduce the weight of the VRFB stack as well as the cost of the battery manufacturing. On the other hand, the acid and heat pretreatment of membrane improves the energy and voltage efficiencies of VRFB from 66.9% and 76.8% to 73% and 87%, respectively.
Material science
shahab khameneh asl; reza golzarian; behnam salahimehr; ali fardi
Abstract
Platinum nanoparticles are widely used in the oil and gas industries, electronics, space tools, pharmaceutical industries, biomaterials and etc.Platinum catalysts are more active and selective than the other catalysts. In this regard, the preparation of a suitable alumina catalyst base and more effective ...
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Platinum nanoparticles are widely used in the oil and gas industries, electronics, space tools, pharmaceutical industries, biomaterials and etc.Platinum catalysts are more active and selective than the other catalysts. In this regard, the preparation of a suitable alumina catalyst base and more effective coating of platinum particles are presenting an important role in increasing the quality and efficiency of the catalyst. The purpose of this research is to prepare a high Specific surface area alumina base via aluminum anodizing and coating them with platinum particles. As a result, two steps of the work have been carried out, which are as follows: anodizing aluminum in an oxalic acid solution and optimizing its parameters to reach alumina nanotubes with controlled diameter, thickness and height. Subsequently, the research is resumed using scanning electron microscopy and data related to the special surface.In the next step, different amounts of platinum coatings using a suitable metal salt and solvent is deposited via an optimized electrochemical method.Finally, nanotubes with a diameter, thickness, height of about 60 nm, 20 nm, 15 μm, respectively were produced as the catalyst base.The optimized parameters include: applied voltage of 40 v DC and temperature range of 0-4 °C and the duration of anodizing for 7 h.The platinum coat array is masked on the substrate lithographically. The Samples are prepared using H2PtCl6.6H2O under an electrochemical 12V AC of 200 Hz with a sinusoidal waveform in a solution at a concentration of 8 mM in 150 seconds.The specific surface area was 3.16 m2/g and the absorbed gas volume was 0.728 cm3/g, absorption and desorption isotherm had a hysteresis suitable for catalytic activity.This knowledge was acquired in order to optimize the synthesis and coating conditions of the substrate with a suitable coating for catalytic applications and thermal knives.
Material science
Majid Haghgoo; Ahmad Ramezani Saadat Abadi
Abstract
Achieving a flawless solid composite propellant requires proper processability of its corresponding filled polymer slurry. In other words, the optimal rheological properties of highly filled suspensions after mixing process, ensure its transfer to the mold and complete filling of complex geometries. ...
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Achieving a flawless solid composite propellant requires proper processability of its corresponding filled polymer slurry. In other words, the optimal rheological properties of highly filled suspensions after mixing process, ensure its transfer to the mold and complete filling of complex geometries. In this dynamic study, after adding molybdenum disulfide nanoparticles to the model materials, rheological properties of the obtained suspensions have been investigated.In order to study the effect of molybdenum disulfide nanosheets on the rheological behavior of the suspensions, polyethylene glycol matrix and glass beads, as model, with particle distribution of 60 to 103 microns were employed.Single-layer and multi-layer molybdenum disulfide nanosheets with thickness of 50 to 100 nm was obtained after acid washing, oxidation and heat shock of raw molybdenum disulfide. Then, after preparation of suspensions containing 10-40 vol% glass beads, the effect of obtained molybdenum disulfide (less than 0.1 vol% of the matrix) on the rheological properties of the mixture was studied. Results of frequency sweep and temperature sweep tests showed that complex viscosity of the suspensions had a significant decrease with increasing nanoparticles, while simultaneously, storage modulus was fixed and loss modulus was increased. The test also confirmed this. Finally, the dynamic shear flow test demonstrated that the dynamic viscosity also decreased significantly after addition of nanoparticles.
Structure
Arvin Taghizadeh Tabrizi; Hossein Aghajani; Farhad Farhang Laleh
Abstract
Although regarding low density and high ratio of strength to weight of titanium, the application of this metal is restricted in space industry due to its low surface properties including low wear resistance which could lead to the cold weld. For improving this property of titanium, applying protective ...
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Although regarding low density and high ratio of strength to weight of titanium, the application of this metal is restricted in space industry due to its low surface properties including low wear resistance which could lead to the cold weld. For improving this property of titanium, applying protective coatings are effective. Physical parameters, wear resistance, adhesion of applied layer, and surface microhardness are impressive and could avoid occurrence of the cold weld. Therefore, by applying plasma nitriding on chromium layer in titanium used in space constructions, tribological properties (wear resistance, adhesion and surface microhardness) were studied. Results confirmed the formation of nitride chromium phase on titanium substrate due to the applying plasma nitriding on chromium layer and increasing the surface microhardness up to 1109 HV and improving the wear resistance and adhesion subsequently. The value of the friction coefficient was decreased down 0.16 which could avoid the cold weld occurrence.
Structure
Maedeh sadat Zoei; hadi gorabi; mohammadreza asharf khorasani; saeed asghari; S. Javid Mirahmadi
Abstract
Space systems in Low Earth Orbit (LEO) are exposed to the destructive parameter of atomic oxygen. In long-term missions, the rate of degradation of the material resulting from the reaction with atomic oxygen is significant and reduces the performance of the structure. Due to the harmful effects of atomic ...
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Space systems in Low Earth Orbit (LEO) are exposed to the destructive parameter of atomic oxygen. In long-term missions, the rate of degradation of the material resulting from the reaction with atomic oxygen is significant and reduces the performance of the structure. Due to the harmful effects of atomic oxygen on materials, the choice of atomic oxygen resistant materials or the use of durable surface coatings is very common. In this study, the corrosion resistance of atomic oxygen of an interconnector part of a solar cell was studied by applying a silicone base coating. In order to investigate the corrosion behavior of atomic oxygen, ground test method with equivalent conditions of LEO orbit was used by DC plasma equipment. Initially, the parameters of the atomic oxygen corrosion ground test were determined under the equivalent conditions of the LEO orbit. The results of atomic oxygen application in this study showed that the amount of atomic oxygen erosion yield of silicon coating is significantly lower than the amount of atomic oxygen erosion yield of silver substrate. Also, the study of the coating surface after applying atomic oxygen by SEM images led to the determination of the optimal coating thickness. EDX results showed that after applying atomic oxygen, no significant change in the chemical composition of the coating was achieved.
