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Densification, solid solution formation, and microstructural investigation of reactive pressureless sintered HfB2-TiB2-SiC-MoSi2 quadruplet composite

S Ghadami, E Taheri-Nassaj, HR Baharvandi, F Ghadami
Journal PapersCeramics International , 2021 February 27, {Pages }

Abstract

Dense HfB2-TiB2-SiC-MoSi2 quadruplet composite was produced by a reactive pressureless sintering method at 2050 ?C for 5 h. The relative density was improved and reached 98% by in situ formations of SiC and MoSi2 phases. Microstructural studies proved that SiC and MoSi2 second phases were mostly formed during the sintering process. Moreover, the Sintering mechanism of the composite was investigated by HSC software. TiB2 co-matrix was improved the sinterability of the composite by the formation of (Hf,Ti,Mo)-B and (Hf,Ti,Mo)-C solid solutions.Mechanical properties such as Vickers hardness (23.2 GPa), fracture toughness (5.4 MPa m1/2), and elastic modulus (430 GPa) were effectively enhanced by tailoring the composite.

Structural, magnetic, and gigahertz-range electromagnetic wave absorption properties of bulk Ni–Zn ferrite

M Derakhshani, E Taheri-Nassaj, M Jazirehpour, SM Masoudpanah
Journal PapersScientific Reports , Volume 11 , Issue 1, 2021 May 4, {Pages 13-Jan }

Abstract

Nickel–zinc ferrite (Ni 0.5 Zn 0.5 Fe 2 O 4) powders were prepared by the conventional solid-state route and sintered at 1100 and 1300 C for utilization as a tile electromagnetic wave absorber. Structural, magnetic, and microwave absorption properties were investigated by characterization techniques of X-ray diffraction, thermogravimetric analysis, Raman spectroscopy, electron microscopy, vibrating sample magnetometry, and vector network analyzer. The samples sintered at 1300 C showed high magnetic saturation of 87 emu/g and low coercivity of 4 Oe. Electromagnetic investigations exhibit high reflection losses up to− 48.1 dB at certain high and low gigahertz frequencies, as clearly depicted in the 3D contour plot. The optimized condition

Microwave absorption properties of porous NiZn ferrite powders synthesized by solution combustion method: Effect of fuel contents

M Derakhshani, E Taheri-Nassaj, M Jazirehpour, SM Masoudpanah
Journal Papers , , {Pages }

Abstract

Improvement of mechanical properties of HfB 2-based composites by incorporating in situ SiC reinforcement through pressureless sintering

S Ghadami, E Taheri-Nassaj, HR Baharvandi, F Ghadami
Journal Papers , , {Pages }

Abstract

Effect of synthesis and sintering technique on the long-range 1: 3 cation ordering and microwave dielectric loss of Li2ZnTi3O8 ceramics

Zohreh Tajik, Ahmad Sayyadi-Shahraki, Ehsan Taheri-Nassaj, Amirhossein Meysami, Kai Xin Song, Hadi Barzgar Bafrooei
Journal PapersCeramics International , 2020 May 18, {Pages }

Abstract

This study first reports the synthesis of Li 2 ZnTi 3 O 8 (LZTO) system by microwave (MW) and conventional (CS) sintering techniques. The effects of both synthesis and sintering technique on the structure, degree of ordering and microwave dielectric properties of LZTO ceramics were investigated. Based on XRD data analysis, a single phase Li 2 ZnTi 3 O 8 is obtained for both synthesis techniques. However, fully ordered LZTO system can only be obtained by the CS method. All the samples display nearly non-homogenous grain growth with an average grain size of 7 μm (MW sintering) and 38 μm (CS sintering), respectively. The calculated activation energy of the grain growth for LZTO ceramics was reduced from 329 kJ/mol (MW process) to 233 kJ/mol

Effect of SiC and MoSi2 in situ phases on the oxidation behavior of HfB2-based composites

S Ghadami, E Taheri-Nassaj, HR Baharvandi, F Ghadami
Journal PapersCeramics International , 2020 May 11, {Pages }

Abstract

Monolithic HfB2 and HfB2-15vol%SiC-15vol%MoSi2 composite samples were oxidized by a conventional electric furnace at 1700 ?C for 5 h. Microstructural and phase analysis of the oxidized samples were performed by X-ray diffraction (XRD) analysis and field emission scanning electron microscope (FESEM) equipped with energy-dispersive spectroscopy (EDS). Besides, for analyzing the oxidation mechanism of the samples, thermodynamic calculations were also accomplished by HSC software. The changes in weight and thickness of the oxide scale were measured and the oxide growth rate of the oxidized samples was subsequently calculated. The results showed that HfB2-15vol%SiC-15vol%MoSi2 composite was much more resisted than that monolithic HfB2 due to

Effect of in situ SiC and MoSi2 phases on the oxidation behavior of HfB2-based composites

S Ghadami, E Taheri-Nassaj, HR Baharvandi, F Ghadami
Journal PapersCERAMICS INTERNATIONAL , Volume 46 , Issue 12, 2020 August 15, {Pages 20299-20305 }

Abstract

Monolithic HfB2 and HfB2-15vol%SiC-15vol%MoSi2 composite samples were oxidized by a conventional electric furnace at 1700 degrees C for 5 h. Microstructural and phase analysis of the oxidized samples were performed by X-ray diffraction (XRD) analysis and field emission scanning electron microscope (FESEM) equipped with energydispersive spectroscopy (EDS). Besides, for analyzing the oxidation mechanism of the samples, thermodynamic calculations were also accomplished by HSC software. The changes in weight and thickness of the oxide scale were measured and the oxide growth rate of the oxidized samples was subsequently calculated. The results showed that HfB2-15vol%SiC-15vol%MoSi2 composite was much more resisted than that monolithic HfB2 due

Synthesis of meso-porous gamma-alumina membrane: effect of yttria addition on the thermal stability

Shirin Khanmohammadi, Ehsan Taheri-Nassaj, Morteza Farrokhi-Rad
Journal PapersSurfaces and Interfaces , Volume 21 , 2020 December 1, {Pages 100683 }

Abstract

In this study supported meso-porous gamma-alumina membrane with a thickness of 2.5?m was synthesized on a macro-porous alpha-alumina substrate via colloidal sol-gel route. To evaluate the improvement in the thermal stability of alumina by yttria addition, unsupported alumina membranes with various amounts of yttria (0, 2.5, 5 and 10%mol) were investigated by XRD and TG-DTA analyses. Based on XRD results and considering transitional alumina stabilization effect, the optimum concentration of yttria was determined to be 5%mol. The results of DTA analysis showed that 5%mol yttria addition shifted the gamma to alpha phase transformation to higher temperatures.

Characterization and estimation of dielectric constant of electrospun BaTiO3 nanofibers at different calcination temperatures using theoretical models

Mehdi Hedayati, Ehsan Taheri-Nassaj, Amin Yourdkhani, Mario Borlaf, Shahed Rasekh, Parisa Amirkhizi, Tutu Sebastian, Seyedhosein Payandeh, Frank J?rg Clemens
Journal PapersJournal of the European Ceramic Society , 2020 October 2, {Pages }

Abstract

The main aim of this work was to estimate the dielectric constant of electrospun BaTiO3 nanofibers (BT NFs) using theoretical models. The effect of calcination temperatures on morphology and crystal structure of BT NFs was also investigated by using SEM, TEM, XRD and Raman spectroscopy. The dielectric constant of BT NFs was calculated by applying modified Maxwell Garnett and Yamada models on polymer nanocomposite films comprising stearic acid modified BT NFs in Polyvinylidene difluoride (PVDF) matrix. The results showed that although it was detected low tetragonality (1.0041) at lowest calcination temperature (850 ?C), the better crystallization of BT and high tetragonality could be achieved at a calcination temperature of 1000 ?C and above

Effect of in situ VSi 2 and SiC phases on the sintering behavior and the mechanical properties of HfB 2-based composites

Soheil Ghadami, Ehsan Taheri-Nassaj, Hamid Reza Baharvandi, Farzin Ghadami
Journal PapersScientific Reports , Volume 10 , Issue 1, 2020 October 6, {Pages 13-Jan }

Abstract

In situ HfB 2–SiC–VSi 2 composite was fabricated by reactive pressureless sintering at the temperature of 2150 C for 4 h under a vacuum atmosphere. In situ SiC and VSi 2 reinforcements were formed using VC and Si powders as starting materials according to the following reaction: VC+ 3Si= SiC+ VSi 2. Microstructural studies and thermodynamic calculations revealed that in situ VSi 2 and SiC phases were mostly formed and homogeneously distributed in HfB 2 skeleton. The results showed that the density of in situ HfB 2–SiC–VSi 2 composite was 98%. Besides, the mechanical properties of the composite were effectively enhanced by the formation of in situ second phases. The Vickers hardness and the fracture toughness of the composite reached

Co-electrophoretic deposition of Co3O4 and Graphene nanoplates for supercapacitor electrode

AA Sadeghi Ghazvini, E Taheri-Nassaj, B Raissi, R Riahifar, M Sahba Yaghmaee, Majid Shaker
Journal PapersMaterials Letters , 2020 December 11, {Pages 129195 }

Abstract

In this work, we used the electrophoretic deposition (EPD) technique for the fabrication of Co3O4-Graphene nano-composite as the binder-free electrode for electrochemical supercapacitors. Cobalt nitrate salt was used as the charging agent for EPD of graphene, Co3O4, and their co-deposition. Characterization of the obtained layer by optical microscopy and scanning electron microscopy (SEM) revealed that there was no deposition in the suspension without additive such as nitrate cobalt salt, whereas a uniform layer was formed in the presence of nitrate cobalt salt. Energy dispersive spectroscopy (EDS) analysis of the graphene coating deposited via EPD approved the successful electrodeposition of Co nano-petals between graphene nano-plates. Cyc

Effect of in situ SiC and MoSi2 phases on the oxidation behavior of HfB2-based composites

S Ghadami, E Taheri-Nassaj, HR Baharvandi, F Ghadami
Journal Papers , , {Pages }

Abstract

Study on structure, microstructure and microwave dielectric characteristics of CaV2O6 and (Ca0.95M0.05)V2O6 (M=Zn, Ba) ceramics

Atousa Pirvaram, Ehsan Taheri‐Nassaj, Hamid Taghipour‐Armaki, Wen‑Zhong Lu, Wen Lei, Hadi Barzegar Bafrooei
Journal PapersJournal of the American Ceramic Society , Volume 102 , Issue 9, 2019 September , {Pages 5213-5222 }

Abstract

In this study, the (Ca0.95M0.05)V2O6 (M = Zn, Ba) and the CaV2O6 ceramics were synthesized through a solid‐state reaction method, and the effects of Zn2+ and Ba2+ substitution on the structure, sintering temperature, densification, microstructure and microwave dielectric properties of CaV2O6 ceramic were analysed. The XRD patterns of the sintered samples indicated a single‐phase of CaV2O6 in all temperatures. Substitution of Zn2+ caused a lower sintering temperature and improved the densification of the CaV2O6 ceramic. While the dielectric properties of the (Ca0.95Ba0.05)V2O6 compound were not desirable, the (Ca0.95Zn0.05)V2O6 sample sintered at 650?C for 4?hours showed significant dielectric properties, with εr?=?10.29, Q?× f?~? 53

Densification behaviour and microstructure of spark plasma sintered alumina–mullite nanocomposite

Ali Sedaghat Ahangari Hossein Zadeh, Ehsan Taheri-Nassaj
Journal PapersMicro & Nano Letters , 2019 April 11, {Pages }

Abstract

Spark plasma sintering (SPS) is a consolidation technique that combines high heating and cooling rates with a uniaxial applied pressure which results in short processing time. SPS is successful in producing ceramics with novel microstructures, which are often reported to be made at temperatures lower than ones used in conventional densification techniques. In this work, the densification and microstructure development sequences of the alumina–15 vol% mullite composite during the SPS and the conventional process were compared. Through SPS technique, the fully dense 0.5 ?m grain sized alumina composite (99.5% T.D.) was obtained at 1600?C and its microstructure exhibited nanocrystalline in submicron-sized grains. The nanocrystalline grains w

Novel HfB2-SiC-MoSi2 composites by reactive spark plasma sintering

S Ghadami, E Taheri-Nassaj, HR Baharvandi
Journal PapersJournal of Alloys and Compounds , Volume 809 , 2019 November 15, {Pages 151705 }

Abstract

In situ HfB2-SiC-MoSi2 composites were fabricated using HfB2, Si, Mo, and C powders as starting materials. Fully-dense composites achieved by Reaction Spark Plasma Sintering (RSPS) method at 1850 ?C under 40 MPa for 5 min. Thermodynamic calculations and microstructural studies proved that SiC and MoSi2 second phases were formed and homogeneously distributed according to the following reactions: Si+CSiC and Mo+2SiMoSi2. In addition, the presence of in situ SiC and MoSi2 reinforcement phases have also confirmed by field emission scanning electron microscopy, X-ray diffraction pattern and considering thermodynamics calculations made by HSC software. Besides, the mechanical investigations revealed that in comparison with monolithic HfB2,

BaTiO3 nanotubes by co-axial electrospinning: Rheological and microstructural investigations

Mehdi Hedayati, Ehsan Taheri-Nassaj, Amin Yourdkhani, Mario Borlaf, Jian Zhang, Michel Calame, Tutu Sebastian, Seyedhosein Payandeh, Frank J?rg Clemens
Journal PapersJournal of the European Ceramic Society , 2019 November 27, {Pages }

Abstract

BaTiO3 (BT) nanotubes (NTs) were synthesized using a co-axial electrospinning process. BT precursor/PVP-ethanol and heavy mineral oil were used as the shell solution and core liquid, respectively. The rheological studies indicated that NTs could be formed by a stable jet at a range of viscosities of the shell solution. Due to the shear thinning behavior of the shell solutions, their actual viscosity values at the time of jet formation will be lower than the viscosity of the core liquid. The morphology of the obtained NTs was strongly influenced by the viscosity of the shell solution. By increasing the concentration of BT precursor, the morphology of the BT NTs was changed from porous to more dense structure. XRD analysis revealed that the c

Co-deposition of Co3O4 and graphene via electrophoretic technique

AA Sadeghi Ghazvini, E Taheri-Nassaj, B Raissi, R Riahifar, M Sahba Yaghmaee
Journal PapersMaterials Letters , Volume 213 , 2018 February 15, {Pages 75-78 }

Abstract

In this research, co-depositions of cobalt oxide nanopowders (NPs) and graphene (G) nanoplates in the acetone medium in presence of polyethylenimine (PEI) as a charging agent was investigated. Scanning electron microscopy (SEM) results confirmed the uniformity and nanostructures of obtained layers from all three suspensions containing 4 g/l Co3O4-G (1, 0.5, and 0.25 wt% G). Moreover, SEM results demonstrated that the porosity of the structure increased by elevating the deposition time. Comparison between results showed that the suspension containing 0.25 wt% G gave rise to the most uniform three dimensional (3D) nanoporous structure.

Effect of polyethylenimine addition and washing on stability and electrophoretic deposition of Co3O4 nanoparticles

Ali Asghar Sadeghi Ghazvini, Ehsan Taheri‐Nassaj, Babak Raissi, Reza Riahifar, Maziar Sahba Yaghmaee
Journal PapersJournal of the American Ceramic Society , Volume 101 , Issue 2, 2018 February , {Pages 553-561 }

Abstract

In this work, the parameters of cobalt oxide suspension such as conductivity, zeta potential, particle size, stability, and finally the electrophoretic behavior of particles in the absence and presence of polyethylenimine (PEI) in acetone medium were investigated. Also, the effects of washing on the stability and electrophoretic deposition of Co3O4 were studied. Characterization of the obtained layer by optical microscopy revealed that there was no deposition in the suspension without PEI, while a uniform layer was formed in the presence of PEI additive. Scanning electron microscopy (SEM) results confirmed the uniformity of layer obtained in acetone using PEI additive. Moreover, SEM results demonstrated that more porous microstructures wer

Effect of Ti-ion non-stoichiometry on microstructure and microwave dielectric characteristic of Li2ZnTi3O8 ceramics

Younes Sadin, Ehsan Taheri Nassaj, Hamid Taghipour Armaki, Wen-Zhong Lu, Wen Lei, Hadi Barzegar Bafrooei
Journal PapersJournal of Materials Science: Materials in Electronics , Volume 29 , Issue 16, 2018 August 1, {Pages 13516-13525 }

Abstract

This paper studies the microwave dielectric properties, microstructure, vibration and densification of Li2ZnTi3+xO8+2x () ceramics, manufactured via a conventional mixed oxide route. The X-ray diffraction and Raman spectroscopy revealed the unit cell parameter and cation ordering in LZT non-stoichiometry in their vibrational modes. The densification and phase composition were characterized by the EDX and SEM methods. It was found that a slight Ti vacancy can improve the relative density to the maximum value (96.2%). The XRD results showed that the second phase of TiO2 in the Li2ZnTi3.06O8.12 composition is formed. The sintered samples were detected in the microwave frequency range by using the resonance technique. The values

Study on cytotoxicity and photocatalytic properties of different titania/hydroxyapatite nanocomposites prepared with a combination of sol–gel and precipitation methods

Motahare S Mohseni-Salehi, Ehsan Taheri-Nassaj, Maryam Hosseini-Zori
Journal PapersResearch on Chemical Intermediates , Volume 44 , Issue 3, 2018 March 1, {Pages 1945-1962 }

Abstract

Abstract In the present study different titania/hydroxyapatite nanocomposites were successfully synthesized via a combination of sol–gel and precipitation methods. Titanium-tetra-isopropoxide, 1-propanol, calcium nitrate tetra-hydrate and orthophosphoric acid were the starting materials. In order to characterize samples, several techniques such as XRD, Raman spectroscopy, FE-SEM, and BET–BJH were used. The photocatalytic activity of nanocomposites was investigated by photodegradation of 10 mg?L−1 methylene blue aqueous solution under UV irradiation for 120?min. The dye adsorption of titania in darkness was enhanced from 2.5 to 11.6% for 40 wt% titania/hydroxyapatite nanocomposite. The best photocatalyt

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