Search results for: Bon Heun Koo

Items from 1 to 20 out of 87 results

article

Electronic structure and defect‐induced luminescence study of phase‐stabilized t‐ZrO₂ nanocrystals

Maneshwar Thakur, Ankush Vij, Akshay Kumar, Bon Heun Koo, more

Luminescent tetragonal‐ZrO₂ (t‐ZrO₂) nanocrystals were synthesized using an optimized combustion method without post‐synthesis annealing and characterized using X‐ray diffraction, electron microscopy, Raman spectroscopy, X‐ray photoelectron spectroscopy, UV–Vis. spectroscopy, photoluminescence spectroscopy, thermoluminescence (TL), and vibrating sample magnetometry. The as‐synthesized t‐ZrO₂ nanocrystals...

article

Research status of bond coats in environmental barrier coatings

Zhenya Zhang, Youngjin Park, Zhaolu Xue, Shihong Zhang, more

International Journal of Applied Ceramic Technology > 19 > 4 > 1841 - 1859

Bond coats in environmental barrier coatings (EBCs) prevent oxidants from penetrating the substrate, mediate the mismatch of the coefficient of thermal expansion (CTE), and improve the adhesion strength between adjacent layers. However, the development of bond coats is rarely studied systematically. In this paper, the research status of the bond coats in EBCs is introduced in detail, including the...

article

Investigation of Mixed-Type Craters and the Role of Bifluoride Additives to Produce Zirconia-Toughened Alumina-Based PEO Coating

Zeeshan Ur Rehman, Seong Hun Shin, Tanveer Ahmad, Bon Heun Koo

Journal of Materials Engineering and Performance > 2018 > 27 > 5 > 2430-2437

Al₂O₃-ZrO₂ composite ceramic coatings were prepared on Al6061 aluminum alloy by plasma electrolytic oxidation in Na₃PO₄-K₂ZrF₆-Na₂SiF₆-based alkaline electrolyte. Optimum processing time for the coating formation was found to be ~ 50 min. Cross section and surface morphology of the coatings were analyzed using scanning electron microscope. From the phase and elemental composition analysis, the presence...

article

Nb modified structural, magnetic and magnetocaloric properties of double perovskite Ba2FeMo1−xNbxO6

Imad Hussain, S.N. Khan, Eun Ji Kim, So Eun Jeon, more

Ceramics International > 2018 > 44 > 3 > 2892-2899

A systematic study focusing on the effect of Niobium (Nb) doping on the structural, magnetic and magnetocaloric properties of Ba₂FeMoO₆ samples is presented here. The samples of interest Ba₂FeMo_1−xNb_xO₆ (0 ≤ x ≤ 0.4) were prepared using the solid state reaction method and were confirmed to possess a cubic structure with Fm-3m space group using the X-ray diffraction analysis and Rietveld refinement...

article

Structural and electrochemical properties of the catalytic CeO2 nanoparticles-based PEO ceramic coatings on AZ91 Mg alloy

Zeeshan Ur Rehman, Muhammad Uzair, Hyung Tae Lim, Bon Heun Koo

Journal of Alloys and Compounds > 2017 > 726 > C > 284-294

CeO₂ nanoparticles are highly recognized for their catalytic role in various energy applications. The phenomenon of switching between the stable oxidation states (+4, +3) of cerium is considered as the main cause of its catalytic activity. In this report cerium rich ceramic coating was prepared on AZ91D magnesium alloy. From the EDS analysis, it was confirmed that CeO₂ particles were preferentially...

article

Towards a compact coating formed on Al6061 alloy in phosphate based electrolyte via two-step PEO process and K2ZrF6 additives

Zeeshan Ur Rehman, Seong Hun Shin, Mosab Kaseem, Muhammad Uzair, more

Surface and Coatings Technology > 2017 > 328 > C > 355-360

In this work oxide coatings were prepared on Al6061 aluminum alloy using one and two-step plasma electrolytic oxidation (PEO) process. Under various conditions K₂ZrF₆ was added to the phosphate based electrolyte solution which was used to prepare one and two-step PEO coatings. Microstructure and phase composition of the final coatings were examined using SEM and XRD. The investigation revealed that...

article

Magnetocaloric effect and magnetic properties of the isovalent Sr2+ substituted Ba2FeMoO6 double perovskite

Imad Hussain, M.S. Anwar, S.N. Khan, Aga Shahee, more

Ceramics International > 2017 > 43 > 13 > 10080- 10088

Fine-tuning the charge distribution in Ba₂FeMoO₆ obtained via “isovalent” substitution at the A-site (i.e., Ba) is expected to bring about changes in the physical properties of the system that can be manipulated in magnetic refrigerants. With this motivation, the phase formation, crystal structure, microstructure, magnetic and magnetocaloric properties of the Ba_2−xSr_xFeMoO₆ (0≤x≤0.4) samples fabricated...

article

Synthesis and Microstructural Analysis of Magnetic CaFe_0.5Co_0.5O_3−δ Using Rietveld Method

Zeeshan Ur Rehman, Muhammad Uzair, Noh Tae Hwan, Kim Min Soo, more

Journal of Superconductivity and Novel Magnetism > 2018 > 31 > 3 > 833-839

Perovskite cobaltates are widely recognized as potential candidates for their applications in magnetic and magnetoresistive applications. In this report, pseudo-magnetic CaFe_0.5Co_0.5O_3−δ was synthesized at ambient pressure. Various calcinations, heating times, and sintering temperatures were applied in order to achieve the optimized conditions. The optimal sintering temperature with excellent phase...

article

Investigation of hybrid PEO coatings on AZ31B magnesium alloy in alkaline K₂ZrF₆–Na₂SiO₃ electrolyte solution

Zeeshan Ur Rehman, Seong Hun Shin, Imad Hussain, Bon Heun Koo

Protection of Metals and Physical Chemistry of Surfaces > 2017 > 53 > 3 > 495-502

Detail study of the PEO coatings produced on AZ31B magnesium alloy in Na₂SiO₃–K₂ZrF₆-based electrolyte solution was carried out in this work. ZrO₂, MgF₂, MgO and Mg₂SiO₄ were observed as the major phases in the coatings. Electrolytic decomposition and then the severe thermochemical environment provoked various Zr–F–Mg based complexes in the coatings. From the surface analysis, various structures e...

article

Effect of Na2SiO3·5H2O concentration on the microstructure and corrosion properties of two-step PEO coatings formed on AZ91 alloy

Zeeshan Ur Rehman, Bon Heun Koo

Surface and Coatings Technology > 2017 > 317 > C > 117-124

In this study, effect of Na₂SiO₃·5H₂O (Na₂SiO₃) concentration on the two-step peo coating was investigated. The specimens were primarily processed in a solution composed of (NaOH+Na₂SiF₆+Na₂SiO₃·5H₂O) for 900s. The pre-coated specimens were then immersed into secondary solutions containing various Na₂SiO₃ concentrations and processed for a constant time of 900s. Scanning electronic microscope (SEM),...

article

Transformation of plasma electrolytic oxidation coatings from crater to cluster–based structure with increase in DC voltage and the role of ZrO2 nanoparticles

Zeeshan Ur Rehman, Seong Hun Shin, Hyung-Tae Lim, Bon Heun Koo

Surface and Coatings Technology > 2017 > 311 > C > 383-390

Two step PEO ceramic coatings were formed on AZ91 magnesium alloy in ZrO₂ nanoparticles and K₂ZrF₆ based colloidal electrolyte solution for various voltages. Surface and layer structure of the coatings was analyzed using SEM (Scanning Electron Microscope). Structure analysis revealed that surface of the coating was transferred from individual pancake or craters-based structure to cluster-based structure...

article

Effects of electron injection on the magnetic and magnetocaloric behavior of Sr2FeMoO6 double perovskite

Imad Hussain, M.S. Anwar, S.N. Khan, Jong Woo Kim, more

Journal of Alloys and Compounds > 2017 > 694 > C > 815-822

With the aim of determining and distinguishing the influence of rare-earth doping on the strength of magnetic interactions, magnetic and magnetocaloric properties of Sr_2-xPr_xFeMoO₆ (x = 0.0, 0.1, 0.2, 0.3) double perovskite were investigated. The X-ray diffraction analysis revealed that all the samples crystallized in a tetragonal structure with I4/mmm space group. The temperature dependent magnetization...

article

Structure and corrosion properties of the two-step PEO coatings formed on AZ91D Mg alloy in K2ZrF6-based electrolyte solution

Zeeshan Ur Rehman, Seong Hun Shin, Imad Hussain, Bon Heun Koo

Surface and Coatings Technology > 2016 > 307 > PA > 484-490

In this work, PEO (plasma electrolytic oxidation) coatings were produced on AZ91D magnesium alloy using two-step PEO (plasma electrolytic oxidation) technique. Microstructure and phase composition of the two-step coatings were analyzed using SEM, and XRD, respectively. From the microstructural analysis, it was found that the microstructural features of the primary coatings significantly influenced...

article

Low temperature growth of ZnO nanotubes for fluorescence quenching detection of DNA

Faheem Ahmed, Nishat Arshi, Saurabh Dwivedi, Bon Heun Koo, more

Journal of Materials Science: Materials in Medicine > 2016 > 27 > 12 > 1-9

In this work, large-scale and single-crystalline ZnO nanotubes were fabricated by a simple technique from an aqueous solution at a low temperature of 65 °C. According to detailed morphology, structural and compositional analyses showed that the ZnO nanotubes [diameter ~200 nm (wall thickness ~50 nm); length ~1 µm] have single-crystallite with wurtzite structure. As-prepared ZnO nanotubes showed an...

article

Reversible magnetocaloric response in Sr2FeMoO6 double pervoskite

M.S. Anwar, Imad Hussain, Bon Heun Koo

Materials Letters > 2016 > 181 > C > 56-58

In the present work, polycrystalline Sr₂FeMoO₆ double perovskite sample has been synthesized by solid state reaction. The magnetization-temperature curve shows the transition temperature at 358K, which is lower than normal; this is attributed to the anti-site defects and oxygen vacancies present in the sample. A low maximum magnetic entropy change−∆SMmax, and the relative cooling power equal to 0...

article

Influence of La addition on the structural, magnetic and magnetocaloric properties in Sr2−xLaxFeMoO6 (0≤x≤0.3) double perovskite

Imad Hussain, M.S. Anwar, Jong Woo Kim, Kook Chae Chung, more

Ceramics International > 2016 > 42 > 11 > 13098- 13103

We report the effect of carrier doping via partial substitution of La³⁺ for Sr²⁺ on the structural, magnetic and magnetocaloric properties of Sr₂FeMoO₆ double perovskite. Polycrystalline Sr_2−xLa_xFeMoO₆ (x=0.0, 0.1, 0.2, 0.3) samples were prepared using the conventional solid state reaction method. Using the X-ray diffraction (XRD) analysis it was established that all the samples crystallized in a...

article

Combined Effect of Long Processing Time and Na₂SiF₆ on the Properties of PEO Coatings Formed on AZ91D

Zeeshan Ur Rehman, Bon Heun Koo

Journal of Materials Engineering and Performance > 2016 > 25 > 8 > 3531-3537

In this study, protective ceramic coatings were prepared on AZ91D magnesium alloy by plasma electrolytic oxidation (PEO) to improve the corrosion and mechanical properties of AZ91D magnesium alloy. The process was conducted in silicate-fluoride-based electrolyte solution. It was found that the average micro-hardness of the coating was significantly increased with an increase in the PEO processing...

article

Cr doping assisted tuning of functional properties of ZnO nanorods prepared by fast solution route

Faheem Ahmed, Nishat Arshi, Bon Heun Koo, Iflah Laraib, more

Journal of Sol-Gel Science and Technology > 2016 > 77 > 1 > 179-185

In this work, single-crystalline Zn_1−xCr_xO (0.0 ≤ x ≤ 0.05) nanorods were prepared by a facile microwave-assisted solution method, and their significant correlation between structural, optical, morphological and magnetic properties was investigated. X-ray diffraction and transmission electron microscopy (TEM) results showed that Cr-doped ZnO was comprised of single-phase...

article

Effect of annealing temperature and layer thickness on the opto-electrical properties of transparent conducting Zn/SnO₂/Zn multilayer thin films

Sung Jae Kim, M. S. Anwar, Eun Ji Kim, Hyeon Ji Cho, more

Journal of the Korean Physical Society > 2016 > 68 > 1 > 154-158

Highly transparent Zn/SnO₂/Zn conducting multilayer films are prepared on quartz glass substrates by using RF sputtering. The deposited films were annealed at various temperatures for thermal diffusion. The influences of annealing temperature, annealing time and the zinc thickness on the structural, electrical and optical properties of the multilayer films were studied. X-ray diffraction results showed...

article

Influence of Zn on magnetocaloric effect in (0.95)La0.7Sr0.3MnO3/Ni1−xZnxFe2O4 ceramic composites

M.S. Anwar, Azmat Ali Khan, K.Y. Park, Seung Rok Lee, more

Materials Research Bulletin > 2015 > 69 > Complete > 41-45

We report the magnetic and magnetocaloric properties of (0.95)La _0.7 Sr _0.3 MnO ₃ /(0.05)Ni _1−x Zn _x Fe ₂ O ₄ (x=0.0, 0.1, 0.3, and 0.5) ceramic composites. The composite samples with nominal compositions were prepared using the conventional solid-state reaction method. The phase purity and structure were confirmed by using X-ray diffraction...

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INFONA - science communication portal

Search results for: Bon Heun Koo

Electronic structure and defect‐induced luminescence study of phase‐stabilized t‐ZrO₂ nanocrystals

Research status of bond coats in environmental barrier coatings

Investigation of Mixed-Type Craters and the Role of Bifluoride Additives to Produce Zirconia-Toughened Alumina-Based PEO Coating

Nb modified structural, magnetic and magnetocaloric properties of double perovskite Ba2FeMo1−xNbxO6

Structural and electrochemical properties of the catalytic CeO2 nanoparticles-based PEO ceramic coatings on AZ91 Mg alloy

Towards a compact coating formed on Al6061 alloy in phosphate based electrolyte via two-step PEO process and K2ZrF6 additives

Magnetocaloric effect and magnetic properties of the isovalent Sr2+ substituted Ba2FeMoO6 double perovskite

Synthesis and Microstructural Analysis of Magnetic CaFe_0.5Co_0.5O_3−δ Using Rietveld Method

Investigation of hybrid PEO coatings on AZ31B magnesium alloy in alkaline K₂ZrF₆–Na₂SiO₃ electrolyte solution

Effect of Na2SiO3·5H2O concentration on the microstructure and corrosion properties of two-step PEO coatings formed on AZ91 alloy

Transformation of plasma electrolytic oxidation coatings from crater to cluster–based structure with increase in DC voltage and the role of ZrO2 nanoparticles

Effects of electron injection on the magnetic and magnetocaloric behavior of Sr2FeMoO6 double perovskite

Structure and corrosion properties of the two-step PEO coatings formed on AZ91D Mg alloy in K2ZrF6-based electrolyte solution

Low temperature growth of ZnO nanotubes for fluorescence quenching detection of DNA

Reversible magnetocaloric response in Sr2FeMoO6 double pervoskite

Influence of La addition on the structural, magnetic and magnetocaloric properties in Sr2−xLaxFeMoO6 (0≤x≤0.3) double perovskite

Combined Effect of Long Processing Time and Na₂SiF₆ on the Properties of PEO Coatings Formed on AZ91D

Cr doping assisted tuning of functional properties of ZnO nanorods prepared by fast solution route

Effect of annealing temperature and layer thickness on the opto-electrical properties of transparent conducting Zn/SnO₂/Zn multilayer thin films

Influence of Zn on magnetocaloric effect in (0.95)La0.7Sr0.3MnO3/Ni1−xZnxFe2O4 ceramic composites

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