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Publication Date: 2021
Ceramics International (02728842) 47(21)pp. 29977-29987
The goal of this research is to fabricate pure transparent yttria ceramics through gel casting and vacuum sintering. A specific processing method has been used and optimized for this purpose. A pure yttria nanopowder was synthesized as the starting material to produce pure transparent ceramics through a low-temperature sintering process. It was attempted to minimize the undesirable nanopowder hydration by using the as-synthesized yttria nanopowder and a rapid deagglomeration and slurry preparation process. The synthesized nanopowders were deagglomerated to enhance the efficiency of both powder shaping and sintering stages. Carrageenan was used as the gelling agent because it is a low-cost and abundant material, and because the temperature is the only catalyst needed for its gelation; therefore, it is possible to control its gelation to obtain high-density and pure optical ceramics. The effect of the deagglomeration method and the processing parameters, including the amounts of dispersant, gelling agent, solid loading, pH, and deagglomeration time, on the rheology of slurry, density, and microstructure of the obtained green yttria ceramics was examined and optimized in order to obtain high solid loading nanoyttria suspensions of 38 vol%, which is more than those obtained in many of the previous investigations. The precise gelling temperature and time were measured, and green gel cast ceramics with a density of 63 % of the theoretical density were produced. A rapid deagglomeration and slurry preparation method was used instead of using a conventional planetary ball-milling approach to minimize the risk of the hydrolysis of yttria nanopowder. No sintering aid was necessary, and transparent yttria ceramics with 99 % of the theoretical density were produced after vacuum-furnace sintering at 10-2 mbar and 1715 °C. © 2021 Elsevier Ltd and Techna Group S.r.l.
Publication Date: 2019
Computational Condensed Matter (23522143) 19
The electronic structure of γ-Al 2 O 3 in the presence of the Al and O defects is investigated within the density functional theory using the PBE-GGA and TB-mBJ schemes. The formation of the Al vacancy produces acceptor-like sublevels above the valence band maximum, consistent with the previous G 0 W 0 calculations. Furthermore, the formation of the oxygen vacancy generates donor-like sublevels below the conduction band minimum, which is consistent with experiment. The donor sublevels are predicted more accurately by TB-mBJ than PBE-GGA, as electron charge density is calculated to be larger at the O vacancy site by TB-mBJ within its optimized c-factor. © 2019 Elsevier B.V.
Publication Date: 2018
Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers (13474065) 57(12)
The nanocrystallization stage was performed in a reductive hydrogen atmosphere to prevent surface oxidation and improve the soft magnetic properties of the amorphous, Fe73.5Si13.5B9Nb3Cu1 alloy through annealing. Both the amorphous and nanocrystalline Fe73.5Si13.5B9Nb3Cu1 ribbons were characterized by differential scanning calorimetry, transmission electron microscopy, X-ray diffraction, alternative gradient field magnetometry, and AC susceptometry techniques. To reduce the processing cost, commercially available industrial gas sources were used at the atmospheric pressure, instead of high purity inert gas or high vacuum ambient. The surface oxidation completely stopped after using a 70% Ar-30% H2 mixture of such gases, also the period of the nanocrystallization stage decreased. Moreover, it was observed that the soft magnetic parameters of the nanocrystalline samples depend on the annealing time. Both the in-plane permeability and coercive field of the ribbons improved through nanocrystallization and the optimum annealing time was determined. © 2018 The Japan Society of Applied Physics.
Publication Date: 2016
Journal of Ceramic Processing Research (12299162) 17(4)pp. 394-400
The aim of this article is to decrease the crystallization temperature of the tetragonal perovskite PbTiO3 nanopowders below the PbTiO3 Curie temperature (~ 500 °C). At the beginning of our study, the calcination temperature was selected based on the thermal analysis of the PbTiO3 gels, came out at 680 °C. However, detailed investigation of the thermal properties of the PbTiO3 gel revealed possibility of the formation of single tetragonal perovskite phase at lower temperatures. Pb-partitioning phenomenon (section 3.2) was investigated in detail in PbTiO3 nanopowders in order to reach good crystallization below 500 °C. Both X-Ray diffraction and transmission electron microscopy investigations showed that well crystalline pure phase PbTiO3 nanopowders have been synthesized after calcination of the PbTiO3 gel at 460 °C, which is quite close to the Curie temperature of the PbTiO3 nanoparticles. To improve crystallization of the samples prepared at 460 °C, the effects of the heat treatment parameters and Pb content on gel crystallization were investigated in detail. © 2016, Hanyang University. All rights reserved.
Publication Date: 2015
IEEE Sensors Journal (1530437X) 15(11)pp. 6454-6459
Here, a generalized induction coil sensor model (more generalized than other models) has been considered at low frequencies (within 0.1-100 Hz), and the equivalent magnetic field of the coil's thermal noise and the sensor's signal-to-noise ratio (SNR) were calculated theoretically based on the dimensions and geometry of the coil winding and its core. In our suggested theoretical consideration, all involved parameters were considered and optimized without any assumption and constraint, while some authors in their latest reports, have been used some assumptions and constraints in their sensor calculations (such as holding constant the sensor's volume and aspect ratio). Our calculations indicated that the equivalent magnetic field of the thermal noise can be minimized by the coil-to-core weight ratio. Moreover, it was found that the sensor's SNR can be maximized with only a special value of core aspect ratio (length to diameter of core ratio). The obtained theoretical results were evaluated experimentally by fabricating a search coil magnetometer model, using the optimum parameters. The resonance frequency and the parasitic capacitance of the coil were measured. Moreover, the variations of the transfer function of the magnetometer, with respect to frequency, were studied. Thus, it was shown that, at low frequencies, our experimentally measured noise data exhibit better agreement with our suggested theoretical results with respect to the state of the art. © 2001-2012 IEEE.
Papi h., ,
Jalali asadabadi, S. ,
Nourmohammadi abadchi, A. ,
Ahmad, I. ,
Nematollahi, J. ,
Yazdanmehr m., M. Publication Date: 2015
RSC Advances (20462069) 5(68)pp. 55088-55099
The optical properties of pure γ-Al2O3 and in the presence of oxygen point defects are investigated by the density functional theory approach using the PBE-GGA and TB-mBJ-GGA schemes. The optical properties of the modeled imperfect crystal show closer agreement with the experimental results than the ideal crystal. The defects produce extra sharp bands and sub-bands, in the bandgap region. The TB-mBJ scheme provides better descriptions of the bandgaps and positions of the sub-bands compared to the experiments than the PBE-GGA scheme. The imaginary part of the dielectric function reveals that the sub-bands produced by the oxygen point defects act as trapping centers. The real part of the dielectric function and the index of refraction are also strongly affected by these defects and increase at 0 eV, decrease at 5 eV and remain constant at 80 eV with the defects. The intensities of the optical spectra are calculated by PBE-GGA to be higher than those of TB-mBJ. The higher intensities are mainly ascribed to the matrix elements of the linear momentum operator. © The Royal Society of Chemistry.
Publication Date: 2014
Journal of Materials Research (08842914) 29(20)pp. 2432-2440
The aim of this research study is to produce high-quality TiO2 nanotube arrays using porous alumina templates. The templates are fabricated through anodizing bulk aluminum foils which can be utilized for the production of thick alumina templates. To produce the nanotube arrays, the alumina template pores are filled with the precursor sol by applying a DC electric field. Then, the deposited nanotubes are heat treated at 320 °C for 2 h and, subsequently, sintered for 2 h at 400 and 750 °C to obtain nanotubes with pure anatase and rutile phases, respectively, as confirmed by x-ray diffraction data. Scanning and transmission electron microscopy (SEM and TEM) investigations show that the nanotubes have been deposited in the channels of the nanoporous alumina template. Also, SEM investigations show the existence of a vast area of TiO2 nanotube arrays when we use semiconductor alumina templates. Copyright © Materials Research Society 2014.
Publication Date: 2014
Materials Research Society Symposium - Proceedings (02729172) 1601(January)pp. 8-11
The aim of this research study is to produce high quality TiO2 nanotube arrays. It is shown that sol-gel electrophoresis is a suitable one to obtain vast-area TiO2 nanotube arrays when nanoporous alumina templates are used. To fabricate TiO2 nanotube arrays, alumina templates were produced via a two-step anodizing by a homemade anodizing cell using high purity phosphoric acid as the electrolyte with aluminum and platinum as electrodes. The semiconductor behavior of these templates can also be employed when producing conducting substrates for the grown TiO2 nanotubes. Stabilized titanium sol was prepared by modified hydrolysis of the titanium precursor using acetic acid. In order to produce TiO2 nanotube arrays, the template pores were filled with the precursor sol by applying a DC electric field. Then, the filled template was heat treated to crystallize the desired TiO2 phase. Scanning electron microscopy of TiO2 nanotube arrays showed that the nanotubes have been deposited in the channels of the nanoporous alumina template. X-ray diffraction data confirmed phase structure and composition of TiO2 nanotube arrays after heat treatment. To reach pure anatase phase, the samples were heated at 320°C and 400°C for two hours. To obtain pure rutile phase, the samples were heated at 320°C and 750°C for two hours. © 2013 Materials Research Society.
Publication Date: 2013
Ferroelectrics (15635112) 448(1)pp. 123-133
Pb-partitioning phenomenon was investigated in PbTiO3 nanopowders produced via sol-gel processing in order to achieve highly crystalline and single phase tetragonal perovskite PbTiO3 nanoparticles. The calcination conditions were selected based on the simultaneous thermal analysis of the PbTiO3 gels, including complete burn out of the contained carbon and crystallization of the desired perovskite structure. X-Ray diffraction investigations confirmed key contributions of Pb stoichiometry and the gel calcination conditions to aid in improving formation of single tetragonal phase as well as avoiding formation of toxic lead compounds. Transmission electron microscopy investigations showed that well crystallized PbTiO3 nanoparticles have been synthesized after calcination of the PbTiO3 gel. © 2013 Copyright Taylor and Francis Group, LLC.
Publication Date: 2013
Ferroelectrics (15635112) 448(1)pp. 134-144
Sol-gel electrophoresis technique has been used as a usual method merely for preparing PbTiO3 thin film and nanowires with high quality and more condense layers. In this research, initially we used this technique to grow PbTiO3 nanotubes in porous anodic alumina template channels. Firstly, templates are prepared via two-step anodizing of pure aluminum foils in phosphoric acid. Then, the templates were filled with a highly stabilized PbTiO3 sol prepared and we used titanium tetra-butoxide and lead acetate trihydrate as precursors. An electric field (DC) was applied to drive the sol into the template channels. Nanotubes were formed after the etching of the porous template with 5 wt.% caustic soda solution. The heat treatment condition was evaluated based on the simultaneous thermal analysis results of the prepared and crystallization of the tetragonal perovskite structure by the X-ray diffraction of the grown nanotubes. Scanning electron microscopy investigations showed that close-packed PbTiO3 nanotubes have been grown in the template channels. © 2013 Copyright Taylor and Francis Group, LLC.
Publication Date: 2013
Journal of K-Theory (18652433) 1587(1)
In the current research, we have utilized sol-gel electrophoresis technique to grow PbTiO3 nanotube arrays in porous anodic alumina template channels. By using this method high quality and more condense nanotubes are obtained compared with other usual sol-gel methods. Also, the effect of the anodizing parameters on the diameter of the template pores, and effect of electrophoresis voltage on wall thickness were investigated. © 2013 Materials Research Society.
Publication Date: 2012
Nanoscale Research Letters (1556276X) 7
γ-Al2O3 is a porous metal oxide and described as a defective spinel with some cationic vacancies. In this work, we calculate the electronic density of states and band structure for the bulk of this material. The calculations are performed within the density functional theory using the full potential augmented plan waves plus local orbital method, as embodied in the WIEN2k code. We show that the modified Becke-Johnson exchange potential, as a semilocal method, can predict the bandgap in better agreement with the experiment even compared to the accurate but much more expensive green function method. Moreover, our electronic structure analysis indicates that the character of the valence band maximum mainly originates from the p orbital of those oxygen atoms that are close to the vacancy. The charge density results show that the polarization of the oxygen electron cloud is directed toward aluminum cations, which cause Al and O atoms to be tightly connected by a strong dipole bond. © 2012 Yazanmehr et al.; licensee Springer.
In the current research, we have utilized sol-gel electrophoresis technique to grow Lead Titanate (PbTiO 3) nanotubes in porous anodic alumina template channels. The templates were prepared through two-step anodizing of pure aluminum foils in phosphoric acid. The porous templates were filled with a highly stabilized PbTiO 3 sol prepared using titanium tetra-butoxide and lead acetate trihydrate, as the Ti and Pb precursors. A DC electric field was applied to drive the sol into the template channels. Tube formation was realized after etching of the template pores with 5wt. % caustic soda solution. Sol-gel electrophoresis method has already been used for preparing PbTiO 3 thin films and nanowires, and by using it, high quality and more condenses layers than other usual sol-gel methods have been produced. But, to the best of our knowledge, this method has not been used for growth of PbTiO 3 nanotubes. The heat treatment condition was evaluated based on the simultaneous thermal analysis (STA) results of the prepared and crystallization of the tetragonal perovskite structure by the X-ray diffraction (XRD) of the grown nanotubes. Scanning electron microscopy (SEM) investigations showed that close-packed PbTiO 3 nanotubes have been grown in the template channels. © 2012 IEEE.
Publication Date: 2012
International Journal of Engineering, Transactions B: Applications (1728144X) 25(4)pp. 343-349
In the current research project, sol-gel electrophoresis technique was utilized to grow titanium dioxide (TiO2) nanotubes. A titanium sol was prepared using organometallic precursors of titanium to fill the template channels. The prepared sol was driven into nanopores of porous anodic aluminum oxide templates under the influence of a DC electric field to form nanotubes on the pore walls. Successful deposition on the template pore walls was achieved after broadening the pores through chemical etching using phosphoric acid. The simultaneous thermal analysis (STA) of the samples determined the onset temperature of the anatase TiO2 crystallization. After calcination, the phase structure of the produced nanotubes was evaluated based on the X-ray diffraction (XRD) investigations. Scanning electron microscopy and energy dispersive X-ray (SEM and EDX) studies showed that TiO2 nanotubes with uniform size and shape have been electrophoretically grown in the aluminum oxide template channels.
In the current research, we have synthesized PbTiO 3 nanopowders via a sol-gel process and investigated Pb-partitioning in the produced nanopowders. Highly stabilized PbTiO 3 sols, with various Pb/Ti ratios, were prepared through chemical modification of the organometallic precursors of titanium by acetic acid. The calcination conditions were selected based on the simultaneous thermal analysis (STA) of the PbTiO 3 gels, including complete burnout of the contained carbon and crystallization of the desired perovskite structure. X-Ray diffraction (XRD) investigation demonstrated role of Pb/Ti ratio as well as the gel calcination conditions in improving formation of the tetragonal perovskite phase PbTiO 3 nanopowders and avoiding Pb-partitioning. Transmission electron microscopy (TEM), with uniform morphology, investigations showed that well crystallized PbTiO 3 nanoparticles have been synthesized after calcination the best selected PbTiO 3 gel under the optimum heat treatment conditions. © 2012 IEEE.
Publication Date: 2012
Nanoscale Research Letters (1556276X) 7(1)pp. 1-7
The photoluminescence emission of nanoporous anodic aluminum oxide films formed in phosphoric acid is studied in order to explore their defect-based subband electronic structure. Different excitation wavelengths are used to identify most of the details of the subband states. The films are produced under different anodizing conditions to optimize their emission in the visible range. Scanning electron microscopy investigations confirm pore formation in the produced layers. Gaussian analysis of the emission data indicates that subband states change with anodizing parameters, and various point defects can be formed both in the bulk and on the surface of these nanoporous layers during anodizing. © 2012 Nourmohammadi et al.; licensee Springer.
Publication Date: 2012
Reaction Kinetics, Mechanisms and Catalysis (18785204) 107(1)pp. 79-88
We have produced zinc oxide (ZnO) photocatalyst nanostructure films by the deposition of ZnO onto indium tin oxide (ITO) glass substrates. A polyethylene glycol (PEG) aided sol-gel route using zinc acetate, 2-methoxyethanol and monoethanolamine, followed by spin coating and heat treatment, was utilized to form these photocatalyst films. The obtained interface nanostructure films were characterized with X-ray diffraction, scanning electron microscopy and UV-Vis spectroscopy. The photocatalytic activity of the films were also investigated using Direct Sky Blue 5B (C. I. Direct Blue 15) as a model organic compound under UV light irradiation. The influence of operating parameters, including the pH of the solution and the number of ZnO layers on Direct Sky Blue 5B degradation, were examined. An interesting decolorization performance was observed in the ZnO/ITO thin films produced using 2 % PEG. © 2012 Akadémiai Kiadó, Budapest, Hungary.
Publication Date: 2011
Journal of Nanoscience and Nanotechnology (discontinued) (15334899) 11(10)pp. 8689-8694
In this article, we present a sol-gel method to synthesize hybrid nanocomposite films of Zinc oxide (ZnO)/methylcellulose (MC) on microscope glass slides. The zinc/MC solutions were prepared, using different weight ratios of zinc acetate dihydrate to MC, in the presence of acetic acid. Fourier transform infrared spectroscopy (FTIR) investigation of the Zn sol/MC mixture showed coordinating interaction between zinc ions and MC. Thermal gravimetry analysis (TGA) results showed rapid decomposition of organic compounds in the composites at the temperature range of 200-450 °C. The UV-Vis spectroscopy was also utilized to identify ZnO nanoparticles in the MC matrix. The generation of ZnO nanoparticles in the MC matrix was then observed to proceed in situ through the annealing of the gel phase at 200 °C. Nanocrystalline films of ZnO/MC were subsequently obtained by the calcinations of ZnO/MC nanocomposites at 550 °C. The nanocomposite films were transparent in the visible light and showed a higher energy absorption edge compared with the bulk ZnO. Nanocrystallite sizes of ZnO particles were estimated from scanning electron microscopy (SEM) and the X-ray diffraction (XRD) investigations. Copyright © 2011 American Scientific Publishers. All rights reserved.
Publication Date: 2010
Journal of Sol-Gel Science and Technology (15734846) 53(2)pp. 342-346
Lead zirconate (PbZrO3) nanotubes have been grown using porous anodic alumina templates. Sol-gel electrophoresis technique was utilized to form the nanotubes on the pore walls. The alumina templates were prepared using various anodizing voltages and times to achieve different pore diameters and lengths. Phosphoric acid solution was employed as the anodizing electrolyte. Stabilized lead zirconate sols were prepared using lead acetate trihydrate and an alkoxide precursor of zirconium. Acetic acid was used as the modifier. The prepared sols were driven into the template channels under various electrophoretic voltages and times, and the effect of the electrophoresis parameters on the formation of nanotubes was investigated. The filled templates were dried at 100 °C and sintered at 700 °C. Scanning and transmission electron microscopy (SEM and TEM) investigations demonstrated the tubular form of the lead zirconate arrays. The SEM investigations also showed the nanotubes have been efficiently grown in the template pores. The TEM studies further confirmed the polycrystalline nature of the tubes. © Springer Science+Business Media, LLC 2009.
Publication Date: 2009
Journal of Alloys and Compounds (09258388) 473(1-2)pp. 467-472
Template-based electrophoretic deposition of perovskite lead zirconate titanate (PZT) nanotubes was achieved using anodic alumina (AA) membranes and sols, containing lead, zirconium and titanium precursors. The effect of various anodizing voltages on the size of the channels in the anodic alumina template was investigated. The prepared sol was driven into the channels under the influence of various electric fields and subsequently sintered at about 700 °C. The effects of the initial heating rates and the burn-out temperature on the phase evolution of the samples were studied and a modified firing process was employed. The effects of the electrophoretic voltage and the deposition time on the average wall thickness of the tubes were investigated. Scanning and transmission electron microscopy (SEM and TEM) revealed the efficiency of electrophoresis in the growth of lead zirconate titanate nanotubes in a close-packed array. The X-ray diffraction analyses indicated the presence of perovskite as the principal phase after a modified firing schedule. © 2008 Elsevier B.V. All rights reserved.
Publication Date: 2008
Journal of Materials Science (15734803) 43(14)pp. 4753-4759
Lead zirconate titanate (PZT) nanotubes have been grown using porous anodic alumina templates. Sol-gel electrophoretic deposition method was utilized to form the nanotubes on pore walls. The templates were prepared using various anodizing voltages to achieve different pore diameters. Phosphoric acid solution was employed as the electrolyte. Stabilized PZT sols were prepared using lead acetate trihydrate and modified precursors of zirconium and titanium with acetic acid. The filled templates were then sintered at 700 °C. Scanning electron microscopy (SEM) shows that tubular PZT arrays have been efficiently grown in the alumina templates. Transmission electron microscopy (TEM) further confirms the tubular form and polycrystalline nature of the tubes. Energy dispersive X-ray (EDX) analyses also confirm the composition of the tubes. X-ray diffraction (XRD) spectra indicate the presence of the perovskite PZT as the main phase. © 2008 Springer Science+Business Media, LLC.
Publication Date: 2008
Materials Letters (18734979) 62(19)pp. 3349-3351
Sol-gel electrophoretic deposition was utilized to grow lead zirconate titanate (PZT) nanotubes through a template-based process, using porous anodic alumina templates and an acetic acid-based PZT sol. The templates were prepared employing various anodizing voltages and times to achieve different pore diameters and lengths. The PZT sol was deposited into the template channels under the influence of a DC electric field. A single-firing process was developed to transform the dried precursor gels into the perovskite PZT phase. Scanning and transmission electron microscopy show the applicability of electrophoresis technique for the deposition of tubular PZT arrays. Electron diffraction patterns also indicate the amorphous nature of the template and polycrystalline structure of the tubes. X-ray diffraction studies indicate the perovskite structure of the grown PZT nanotubes. © 2008.
Publication Date: 2007
pp. 608-611
Lead zirconate titanate (PZT) is a solid solution system with high spontaneous polarization, dielectric permittivity and piezoelectric coefficients. In the current study, we have grown lead zirconate titanate nano tubes through the template-based synthesis process. Porous anodic alumina membranes were prepared using various anodizing voltages for the templates in a cooled anodizing cell at 1° C. Phosphoric acid solution was employed as the electrolyte. The templates were then filled with prepared PZT sols. To prepare the PZT sol, lead acetate trihydrate, zirconium (IV) butoxide and titanium (IV) butoxide were used as precursor materials. SEM and EDX investigations show that nano-sized lead zirconate titanate tubes are efficiently grown in porous anodic alumina templates. XRD investigations have also shown that the grown nanotubes have ferroelectric perovskite structure.
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