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Different mechanisms of the brittle fracture of a composite insulator's rod, manufactured by a pultrusion process with a given percentage of fiberglass (70-75% by weight), have been investigated in this research. The epoxy-fiberglass... more
Different mechanisms of the brittle fracture of a composite insulator's rod, manufactured by a pultrusion process with a given percentage of fiberglass (70-75% by weight), have been investigated in this research. The epoxy-fiberglass composites made in this way show high tensile strengths under normal conditions, but they are sensitive to environmental factors while under electrical and mechanical stresses, and thus corrosive environments, temperature and stress can affect their properties with time. This is due to the fact that the composite consists of a large number of fiber-resin interfaces. The occurrence of failure in any of these interfaces will lead to the diffusion of moisture which in turn will be condensed to water. It can be concluded from the results that the following factors greatly influence the brittle fracture of the rod: type and chemical composition of resin and the fiberglass used, and fiber weight percentage in the rod. Thus by changing the chemical composition of fibers and also by increasing the fiber-resin compatibility, the long-term tensile properties of the rod can be significantly improved.
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The crystallization behavior of fluorphlogopite, a glass-ceramic in the MgO–SiO 2–Al2O3–K2O–B2O3–F system, was studied by substitution of Li2O for K2O in the glass composition. DTA, XRD and SEM were used for the study of crystallization... more
The crystallization behavior of fluorphlogopite, a glass-ceramic in the MgO–SiO 2–Al2O3–K2O–B2O3–F system, was studied by substitution of Li2O for K2O in the glass composition. DTA, XRD and SEM were used for the study of crystallization behavior, formed phases and microstructure of the resulting glass-ceramics. Crystallization kinetics of the glass was investigated under non-isothermal conditions, using the formal theory of transformations for heterogeneous nucleation. The crystallization results were analyzed, and both the activation energy of crystallization process as well as the crystallization mechanism were characterized. Calculated kinetic parameters indicated that the appropriate crystallization mechanism was bulk crystallization for base glass and the sample with addition of Li2O. Non-isothermal DTA experiments showed that the crystallization activation energies of base glasses was in the range of 234-246 KJ/mol and in the samples with addition of Li2O was changed to the ra...
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ABSTRACT
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In this work, lithium meta titanate (Li2TiO3) nanocrystallites were synthesized by hydrothermal method and subsequent heat treatment. The shrinkage of the powder compact was measured under constant heating rate in order to study the... more
In this work, lithium meta titanate (Li2TiO3) nanocrystallites were synthesized by hydrothermal method and subsequent heat treatment. The shrinkage of the powder compact was measured under constant heating rate in order to study the sintering behavior of the synthesized powders. Densification curves of the synthesized powders were also constructed via the dilatometry analysis and evaluated at several heating rates. Two separate methods of analytical procedure and master curve sintering were employed to determine the activation energy of the initial sintering stage. The activation energy values were estimated based on these two distinct methods as 229±14 and 230 kJ/mol respectively, consistenting with each other. Moreover, surface diffusion was determined as the dominant mechanism of densification on initial sintering of Li2TiO3 nanocrystallites.
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Nuclear fusion, the process that powers the Sun, can play a big part in our carbon-free energy future. With the intention of generation of electricity the fusion base reactors are being designed and developed. Tritium is the principal... more
Nuclear fusion, the process that powers the Sun, can play a big part in our carbon-free energy future. With the intention of generation of electricity the fusion base reactors are being designed and developed. Tritium is the principal fuel for future fusion power reactors. The breeding blanket is a key component of the fusion reactor because it directly involves tritium breeding and energy extraction, both of which are critical to the development of fusion power [1]. In recent years, there is a general agreement that lithium containing ceramics are the best option for tritium production and release through the 6Li+1n→(He+2.1MeV)+(T+2.7MeV) nuclear transmutation [2]. Hence, worldwide efforts have been devoted to research & development of lithium ceramic breeding blanket. The significant candidate ceramics for this breeding blanket are lithium-containing ternary oxides, such as LiAlO2, Li2ZrO3, Li4SiO4 and Li2TiO3 [3]. Among them, lithium meta titanate (Li2TiO3) has interested multitu...
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The use of proton-recoil proportional and scintillation counters for measurements with 14 MeV neutrons is discussed. Details are given of investigations into their performance and that of the unfolding codes used and examples of their... more
The use of proton-recoil proportional and scintillation counters for measurements with 14 MeV neutrons is discussed. Details are given of investigations into their performance and that of the unfolding codes used and examples of their application in LiF and LiF-Be integral assemblies are presented. Authors: Scott, M.C., Koohi-Fayegh R. and Evans, N. Publication date: October 27-29, 1980 Specialist Meeting on nuclear data and benchmarks for reactor shielding, Paris, France Experimental and computational analysis of neutron flux transmitted from spherical Beryllium shells; Andazehgiri va mohasebe-ye shar norton-e taragosilid-e az pust-e'ha-ye koravi-ye Berilium
Radiation shielding lead glasses can be used in any facility, which requires protection from radiation, for example medical centers, industrial and nuclear sites. Usually, for improvement of optical properties and homogeneity control of... more
Radiation shielding lead glasses can be used in any facility, which requires protection from radiation, for example medical centers, industrial and nuclear sites. Usually, for improvement of optical properties and homogeneity control of these glasses, homogenization process in different ways is applied. One of the important methods, which is also industrially practical for other glass systems, named fritting, is the process of melting and quenching of molten materials to form small glass particles. In the current work, the effect of homogenization on the thermal and physical properties of lead glasses is investigated. In this way, a composition of lead glass was selected. Then fritting procedure applied six times for this composition and the effect of fritting on thermal, physical, properties and homogeneity of glass were discussed. Finally, microstructural analyses of glass specimens were carried out. The results showed that the increase of the fritting period has an unwanted influ...
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Li2TiO3 compound is one of the most important tritium breeding ceramics for industrial application in the nuclear fusion reactor. The use of the hydrothermal method for preparing ceramic composite materials is new trend. In this work,... more
Li2TiO3 compound is one of the most important tritium breeding ceramics for industrial application in the nuclear fusion reactor. The use of the hydrothermal method for preparing ceramic composite materials is new trend. In this work, hybrid nanocomposite microspheres of the nanocrystallites Li2TiO3 were prepared at low temperature 400°C. Nanocomposite powders synthesized by the batch supercritical hydrothermal method for 12 hours under pressure 12MPa. The raw materials were used containing tetrabutyl titanate (Ti(C4H9O)4) as a titanium source, lithium nitrate (LiNO3) as a lithium source, citric acid as a chelating agent and nitric acid as pH controller. The samples were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and X-ray diffraction (XRD). The SEM micrographs showed the synthesized powders have microsphere shape with range size 1 to 3.5 micrometers. XRD result illustrates the microspheres are nanostructure with cubic and monoclin...
Lithium meta titanate (Li2TiO3) is one of the most promising tritium breeding candidate materials. In this study, the nanocrystallites lithium-titanate with hexagonal and cubic crystal structures were synthesized at low temperature, 200°C... more
Lithium meta titanate (Li2TiO3) is one of the most promising tritium breeding candidate materials. In this study, the nanocrystallites lithium-titanate with hexagonal and cubic crystal structures were synthesized at low temperature, 200°C for 12 h by the hydrothermal method. The results showed that the monoclinic phase of Li2TiO3 nanostructure with high purity can be synthesized by further heat treatment of the hydrothermal synthesis powder above 700°C. In despite the heat treatment, electron microscope and X-ray diffraction analysis showed that the synthesized compounds had grain size smaller than 120 nm. Li2TiO3 was also prepared by a solid-state reaction in order to study the influence of the synthesis rout on the morphology and particle size.
ABSTRACT
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Effect of NaF on crystallization kinetics, microstructure and mechanical properties of mica glass-ceramics were investigated by the differential thermal analysis (DTA), X-ray diffractometry (XRD), scanning electron microscopy (SEM) and... more
Effect of NaF on crystallization kinetics, microstructure and mechanical properties of mica glass-ceramics were investigated by the differential thermal analysis (DTA), X-ray diffractometry (XRD), scanning electron microscopy (SEM) and microhardness tester. Non-isothermal DTA experiments showed that the crystallization activation energies of base glasses are changed in the range of 235–246 KJ/mol, while the crystallization activation energies of samples with addition
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ABSTRACT Glasses in ZnO–SiO2–B2O3 ternary system with different ZnO/B2O3 ratios were studied as scintillating materials. Differential thermal analysis and X-ray diffraction patterns showed that nucleation of willemite and zinc oxide was... more
ABSTRACT Glasses in ZnO–SiO2–B2O3 ternary system with different ZnO/B2O3 ratios were studied as scintillating materials. Differential thermal analysis and X-ray diffraction patterns showed that nucleation of willemite and zinc oxide was considerably facilitated with increasing the ZnO/B2O3 ratio. Photoluminescence spectra showed a reduction in intensity over the UV region upon this increment prior to the formation of crystalline phases. Optical basicity as a measure of nonbridging oxygens (NBOs) is elaborated in this study as a major cause of this effect. However, near band edge emission (NBE) after crystallization implied an increase in intensity upon the increment of the ZnO/B2O3 ratio which proved the key role of willemite and zinc oxide as UV emission centers.
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ABSTRACT Glasses in ZnO–SiO2–B2O3 ternary system with different ZnO/B2O3 ratios were studied as scintillating materials. Differential thermal analysis and X-ray diffraction patterns showed that nucleation of willemite and zinc oxide was... more
ABSTRACT Glasses in ZnO–SiO2–B2O3 ternary system with different ZnO/B2O3 ratios were studied as scintillating materials. Differential thermal analysis and X-ray diffraction patterns showed that nucleation of willemite and zinc oxide was considerably facilitated with increasing the ZnO/B2O3 ratio. Photoluminescence spectra showed a reduction in intensity over the UV region upon this increment prior to the formation of crystalline phases. Optical basicity as a measure of nonbridging oxygens (NBOs) is elaborated in this study as a major cause of this effect. However, near band edge emission (NBE) after crystallization implied an increase in intensity upon the increment of the ZnO/B2O3 ratio which proved the key role of willemite and zinc oxide as UV emission centers.
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Abstract Mica-based glasses in the SiO 2-Al 2 O 3-MgO-K 2 OF system were prepared by a sintering method to investigate the effects of different amounts of hematite (Fe 2 O 3) on thermal and sintering behaviors besides machinability of the... more
Abstract Mica-based glasses in the SiO 2-Al 2 O 3-MgO-K 2 OF system were prepared by a sintering method to investigate the effects of different amounts of hematite (Fe 2 O 3) on thermal and sintering behaviors besides machinability of the glasses by means of ...
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Non-isothermal differential thermal analysis (DTA), X-ray diffraction (XRD), and scanning electron microscopy (SEM) were used to study the nucleation and crystallization behavior of mica glass-ceramics with LiF as nucleating agent. The... more
Non-isothermal differential thermal analysis (DTA), X-ray diffraction (XRD), and scanning electron microscopy (SEM) were used to study the nucleation and crystallization behavior of mica glass-ceramics with LiF as nucleating agent. The models enabled establishing the kinetic parameters for crystal growth of individual phases. The activation energies for crystal growth were found to be in the range of 161–301 KJ/mol, 416–424 KJ/mol, and 583–1011 KJ/mol for base glasses, samples with substitution of Li2O for K2O and samples with addition of LiF, respectively. Formation of transparent glass-ceramics from studied glass-samples has been investigated. Transparency is assumed to occur in the samples with nanocrystalline structure.
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In the present study, glasses from the three different compositional triangles in the BaO–B2O3–SiO2 system with fixed B2O3/SiO2 ratio and different BaO/SiO2 molar ratios (designated as Ba32, Ba37, and Ba42) were prepared, and suitability... more
In the present study, glasses from the three different compositional triangles in the BaO–B2O3–SiO2 system with fixed B2O3/SiO2 ratio and different BaO/SiO2 molar ratios (designated as Ba32, Ba37, and Ba42) were prepared, and suitability of them as sealant in solid oxide fuel cells were investigated. Structure of the glasses was characterized with Raman spectroscopy. According to the results, the structure of the glass with 32 % molar BaO (Ba32) predominantly consisted of Q2 structural species. In glasses with 37 and 42 % molar BaO (Ba37 and Ba42), with the substitution of SiO2 by BaO, distribution of Qn units widened, silicate glass network depolymerized, and concentration of Q1 structural units increased at the expense of Q2 units. X-ray diffraction analyses revealed that in samples Ba32 and Ba37, initially, Ba3Si5O13 and Ba5Si8O21 phases were crystallized, respectively, and it seemed they acted as the sites for the subsequent growth of BaSi2O5 phase. In contrast, the dominant pha...
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Easy machining is a characteristic of fluorphlogopite glass–ceramics, that sets them apart from other glass–ceramic systems. However, these materials have low hardness and mechanical strength, which limit their performance as a structural... more
Easy machining is a characteristic of fluorphlogopite glass–ceramics, that sets them apart from other glass–ceramic systems. However, these materials have low hardness and mechanical strength, which limit their performance as a structural ceramic. In this paper, we attempted to overcome this problem by incremental addition of calcium oxide to a base glass composition. In this way, various parameters of the resulting glasses like their sintering and crystallization behavior were investigated, using X-ray diffractometry, differential thermal analysis, and scanning electron microscopy. According to our results, while small amounts of CaO improved the crystallization of fluorphlogopite and induced a decrease in the sinterability of glasses, higher amounts of CaO had the opposite effect, that is, it led to a reduction in the dimensions of mica crystalline particles and caused gehlenite to precipitate.