Material science
Zahra Amirsardari; Babak Afzali; Mohammad Reza Amirsoleimani
Abstract
To discuss the potential role of iridium (Ir) nanoparticles loaded under atmospheric conditions, we prepared a series of catalysts with the same active phase but different contents of 10wt%, 15wt%, and 20wt% on gamma-alumina for decomposition of hydrazine. The performance of the catalysts was better ...
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To discuss the potential role of iridium (Ir) nanoparticles loaded under atmospheric conditions, we prepared a series of catalysts with the same active phase but different contents of 10wt%, 15wt%, and 20wt% on gamma-alumina for decomposition of hydrazine. The performance of the catalysts was better with 15wt% and 20wt% of the Ir nanoparticles, and also the selectivity to hydrogen was about 27%. An increase in the reaction rate from 181 h-1 to 218 h−1 was observed in the loading of 15% by weight of iridium particles due to the good dispersion of the active phases by preventing surface agglomeration. As a satisfactory result of this investigation, Ir catalysts with different weight percentage (15wt% and 20wt%) showed the same activity and selectivity, and are suitable substitutes for each other. Using a catalyst with a lower weight percentage of the active phase and high activity is economically acceptable due to its low cost.
Material science
mojtaba forghani; Maedeh sadat Zoei; Mohammad Reza Pakmanesh; mohammad chiani; Saeed Asghari
Abstract
The sandwich panel is an important element of the satellite structure which various metal and composite materials are used to make its faces. Anodizing is used as a conversion coating in order to achieve the final properties of the panel surface and stability in the space environment. Anodizing is an ...
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The sandwich panel is an important element of the satellite structure which various metal and composite materials are used to make its faces. Anodizing is used as a conversion coating in order to achieve the final properties of the panel surface and stability in the space environment. Anodizing is an electrochemical process in which an oxide layer is formed using electricity. During the anodizing process, concentration polarization is created and the process is stopped when the limiting current resulting from the movement of electrical charges between the surface of the anodic layer and the electrolyte is increased. By stopping the process without spending enough time to obtain a thickness sufficient for colorability, a black anodic layer for use in space coatings is not obtained. In this research, by performing the anodizing process in four container of 250, 500, 2000 and 40000 cm3, the effect of the volume of the electrolyte on the wear and corrosion and optical-thermal properties of the layer obtained in each of the processes was investigated. The results showed that with the increase in the volume of the electrolyte caused by the increase in the volume of the container, the stopping time of the process increases. The evaluation of optical-thermal properties, wear resistance and corrosion resistance was done by infrared emission coefficient and solar absorption test, pin on disk test and salt spray test, respectively. The results of measuring optical-thermal and wear and corrosion properties for three container with volume of 500, 2000 and 40000 cm3 showed that with the increase in the volume of electrolyte and the process completion time of the process, the thickness of the anodic layer increased, which improved the optical-thermal properties, corrosion and wear resistance.
Material science
Maedeh sadat Zoei; S. Javid Mirahmadi; Mojtaba Forghani; mohammad chiani; Saeed Asghari
Abstract
Thermal barrier coatings (TBCs), are advanced ceramic systems that are usually applied to the surface of hot industrial parts to improve equipment performance at higher temperatures. During each thermal cycle, due to the mismatch in the coefficients of thermal expansion of TBC layers, these layers expand ...
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Thermal barrier coatings (TBCs), are advanced ceramic systems that are usually applied to the surface of hot industrial parts to improve equipment performance at higher temperatures. During each thermal cycle, due to the mismatch in the coefficients of thermal expansion of TBC layers, these layers expand and contract unbalanced. The resulting thermal stresses cause the nucleation and growth of microcracks in the TBC system. After several hundreds of thermal cycles, the microcracks eventually combine and form a relatively large crack that causes spallation and separation of the coating, exposing the parts to high temperatures and ultimately leading to catastrophic failure of the entire equipment. The creation of self-healing capability provides the ability to repair cracks spontaneously. In this article, various types of technologies for achieving self-healing in YSZ thermal barrier coatings and the structure and properties of the resulting coatings have been introduced and reviewed. After extracting the technologies of applying self-healing thermal barrier coating and comparing them with each other, it is possible to obtain coatings with self-healing properties according to the needs of each industry and then determined the proper composition of the self-healing coating, the proper thickness of the self-healing coating layer, the proper arrangement of the self-healing coating layer and the parameters of the coating process
Material science
maryam salvatifar
Abstract
One of the most serious problems of the industrialized world is heavy metal contamination. As a heavy metal, lead has very harmful effects on human health even in small amounts. Therefore, removing it from water is one of the most important challenges in public health system. Microorganism application ...
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One of the most serious problems of the industrialized world is heavy metal contamination. As a heavy metal, lead has very harmful effects on human health even in small amounts. Therefore, removing it from water is one of the most important challenges in public health system. Microorganism application is very useful and safe in this field. Creatures living on Earth are constantly under the influence of gravity, and if it changes, they will be affected by a unique shock. Such a change has effects on the structure and function of cells by interfering with biochemical pathways and gene expression. Investigating these changes, in addition to maintaining the health of astronauts, will also be useful for improving the quality of human life on earth. In this study, the efficiency of Lactobacillus acidophilus ATCC 4356 bacteria in the bioremoval of lead from aqueous solution was investigated in microgravity and Mars gravity conditions. The results showed a decrease in lead concentration after 24-hour treatment by 82.1% under microgravity conditions, 79.6% under simulated Mars gravity conditions and 70.6% under natural Earth gravity conditions. Therefore, by reducing the gravity, it is possible to increase the efficiency of L. acidophilus in the bioremoval of lead metal
Material science
Sajede Aghasi; Seyed Hassan Jafari; Mahdi Golriz
Abstract
One of the methods for improving thermal conductivity of epoxy adhesives is the incorporation of conductive ceramic, metal or carbon fillers. As the main goal of this research is to improve the thermal conductivity of epoxy resin and keep its electrical insulating property, the effect of Alumina (Al2O3) ...
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One of the methods for improving thermal conductivity of epoxy adhesives is the incorporation of conductive ceramic, metal or carbon fillers. As the main goal of this research is to improve the thermal conductivity of epoxy resin and keep its electrical insulating property, the effect of Alumina (Al2O3) ceramic filler individually, and in combination with Boron Nitride (BN) ceramic filler with high thermal conductivity and electrical resistivity is investigated. Scanning Electron Microscopy (SEM) observations showed a proper dispersion and an acceptable connection between fillers. The results of the thermal diffusivity measurements revealed that by incorporating conductive ceramic fillers, either individually or in combination, regardless of the type of the hardener, thermal diffusivity would increase due to 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 showed that the thermal conductivity of hybrid system of Alumina/BN has raised to 1.7 (W/mK), which is about 0.4 (W/mK) for epoxy system without filler. The most important achievement of this research is to achieve proper thermal conductivity while keeping mechanical properties, dielectric constant, and lap shear strength of Alumina/BN hybrid system within acceptable range of thermal conductive adhesive for space applications
Electric power
Mohammad Zarei-Jelyani; Mohammad Mohsen Loghavi; Mohsen Babaiee; Rahim Eqra; Masood Masoumi
Abstract
In 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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In 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 its high proton conductivity and remarkable chemical stability. In the present study, the Nafion 117 membrane was subjected to 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 up to 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 the 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
The use of thermal knives as holding mechanism and non-explosive release in the field of space mechanisms has always been considered. In these mechanisms, the use of materials with high melting points and low weight, as well as the possibility of production on a small scale is a major challenge. Therefore, ...
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The use of thermal knives as holding mechanism and non-explosive release in the field of space mechanisms has always been considered. In these mechanisms, the use of materials with high melting points and low weight, as well as the possibility of production on a small scale is a major challenge. Therefore, the use of platinum / alumina catalysts can be a good solution to the leading problems in this field.The purpose of this paper is to prepare a high specific surface alumina base using the process of anodizing aluminum and coating it with platinum particles. Thus, the present study consists of two stages; In the first stage, aluminum is anodized in oxalic acid solution and its parameters are optimized in order to achieve aluminum nanotubes with various diameters and wall thicknesses, as well as the applied voltage, electrolyte concentration and anodizing conditions. In the next step, platinum nanoparticles were precipitated in different amounts using metal salt and suitable solvent using electrochemical method. The results showed that the obtained nanowires have a diameter of about 200 nm and a length of several micrometers. All samples were mechanically polished and it was shown that the aluminum anode oxide membranes were completely filled with a combination of metals. Also, the performed analyzes showed that the obtained nanowires are stable inside the membrane
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, a highly filled suspension with optimal rheological properties makes it possible to transfer to the mold and complete filling in complex geometries. In this dynamic ...
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Achieving a flawless solid composite propellant requires proper processability of its corresponding filled polymer slurry. In other words, a highly filled suspension with optimal rheological properties makes it possible to transfer to the mold and complete filling in complex geometries. In this dynamic study, the rheological properties of the obtained suspensions have been investigated after adding molybdenum disulfide nanoparticles to the model materials. In order to study the effect of molybdenum disulfide nanosheets on the rheological behavior of the suspensions, polyethylene glycol matrix and glass beads, with particle distribution of 60 to 103 microns were used as a model.Single- layer and multi- layer molybdenum disulfide nanosheets with thickness of 50 to 100 nm was obtained using 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. The results of frequency sweep and temperature sweep tests showed that by increasing the percentage of molybdenum disulfide nanosheets by less than 0.1%,The mixed viscosity has a significant decreasing in all microfiller values while maintaining the storage modulus and increasing the loss modulus. Finally, the dynamic shear flow test demonstrated that the dynamic viscosity also decreased significantly after the 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 is effective. The physical parameters of wear resistance, adhesion and surface microhardness are impressive and could avoid occurance of cold weld. Therefore, in the present study, by applying plasma nitriding on chromium layer on titanium used in space structures, its tribological behavior (wear resistance, adhesion and surface microhardness) has been investigated. The results confirmed the formation of nitride chromium thin layer on titanium substrate due to the applying plasma nitriding on the chromium layer , which increasing the surface microhardness up to 1109 HV and improving the wear resistance and adhesion subsequently. The coefficient of friction is also decreased to 0.16,which can well prevent the occurrence of cold weld
Structure
Maedeh sadat Zoei; hadi gorabi; mohammadreza asharf khorasani; saeed asghari; S. Javid Mirahmadi
Abstract
Space systems in Low Earth Orbit (LEO) expose 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) expose 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 has 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 has used by DC plasma equipment. Initially, the parameters of the atomic oxygen corrosion ground test 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. 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 has achieved
