Browsing by Author "Park, Jongee"

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Citation Count: 10
Alkaline Hydrothermal Synthesis, Characterization, and Photocatalytic Activity of TiO₂ Nanostructures: The Effect of Initial TiO₂ Phase
(Amer Scientific Publishers, 2019) Erdogan, Nursev; Park, Jongee; Choi, Woohyuk; Kim, Soo Young; Ozturk, Abdullah; Metallurgical and Materials Engineering
One-dimensional (1D) titanate nanostructures were synthesized by hydrothermal route, using commercially available TiO2 (P25) and anatase powders as precursor materials and strong NaOH solution as catalyzer. The prepared titanates were calcined, followed by protonation to produce TiO2 nanostructures having enhanced photocatalytic and photovoltaic properties. The synthesized TiO2 1D nanostructures were characterized using field-emission scanning electron microscope, high-resolution electron microscope, X-ray diffraction analysis, and UV-Vis photospectroscopy to understand the effect of initial TiO2 phase on morphological and crystallographic features, and bandgap. Methylene blue degradation test was applied to evaluate the photoactivity of the products obtained after different stages of the process. The findings indicate that 1D TiO2 nanostructures form by different mechanisms from dissolved aggregates during hydrothermal process, depending on the crystal structure of the initial precursor used. Photocatalytic test results reveal that protonated titanates have considerable adsorption capability, while photocatalytic degradation depends on TiO2 transformation.
Alumina ve Titanya eş-doplanmış zirkonya seramiklerinin mekanik ve biyolojik özellikleri
(2017) Ağaç, Özlem; Park, Jongee; Metallurgical and Materials Engineering
Günümüzde daha doğala yakın göründüğünden dolayı zirkonya diş hekimliğinde oldukça yaygın olarak kullanılmaktadır. Ayrıca, zirkonya‟nın yüksek sertliği ve kırılma tokluğu, biyolojik uyumluluğu ve estetik görünümü sebebiyle de en çok tercih edilen seramik malzemelerin arasında yer alır. Bu çalışmada, mekanik öğütme yöntemi ile katkı maddeleri farklı oranlarda (0 ve % 2.0) % 3 mol yttria (Y2O3) içeren zirkonya içerisine sırasıyla katılmıştır. Şekillendirilen numuneler sırasıyla 1350, 1450 ve 1550 °C‟ de 2 saat süresince sinterlenmiş olup, katkı maddelerinin etkilerini gözlemlemek için yoğunluk, sertlik, kırılma tokluğu ve hücre tutunma oranı hesaplanmıştır. Sertlik ve kırılma tokluğu hesapları için Vicker‟s sertlik yöntemi kullanılmıştır. X Ray Kırınım Yöntemi (XRD) ile yalnızca titanya içeren ve hem titanya hem de alumina içeren numunelerin kristal faz analizleri yapılmıştır. Taramalı Elektron Mikroskobu (SEM) kullanılarak numunelerin tane boyutları hesaplanmıştır ve yüzey morfolojisi incelenmiştir. Deney sonuçlarına göre katkı malzemelerinin oranı arttıkça, yoğunluğun düştüğü görülmüştür. Mekanik özellikler göz önünde bulundurulduğunda en yüksek sertlik ve tokluk değerleri % 0.5 TiO2 ve % 1.0 Al2O3 numunelerinde elde edilmiştir. Titanya ve aluminanın zirkonya içerisine katılması faz değişimine sebep olmamıştır ancak tane boyutunu küçültmüştür. Ayrıca, katkı maddeleri numune yüzeyine hücrelerin tutunmasını ve büyümesini de olumlu yönde etkilemiştir.
Citation Count: 12
Antisolvent-fumigated grain growth of active layer for efficient perovskite solar cells
(Pergamon-elsevier Science Ltd, 2021) Sajid, Sajid; Khan, Suliman; Khan, Ayub; Khan, Danish; Issakhov, Alibek; Park, Jongee; Metallurgical and Materials Engineering
High efficiency of perovskite solar cell can be obtained through various approaches, including materials and interface engineering, device modification and fabrication techniques. In all approaches, the quality of the perovskite layer has a significant impact on the efficiency of the perovskite solar cell. Antisolvent dripping is widely used in almost all fabrication methodologies to achieve a high-quality perovskite layer. However, in the conventional antisolvent dripping, there are several factors (antisolvent volume, time and point of dripping, etc.) to be strictly followed. Due to these difficult and critical tricks, researchers often get perovskite layers with pinholes, small grains, and wide grain boundaries that deteriorate the performance of the perovskite solar cells. In order to produce perovskite films with large-scale grains, narrow boundaries and smooth surface morphology, a sealed antisolvent-fumigated process is implemented. There is no need to make any substantial efforts to achieve optimal conditions for the fabrication of high-quality perovskite layers using the antisolvent-fumigated strategy. Consequently, the efficiency of perovskite solar cell improves dramatically from 18.65% to 21.45%. Our findings present a new and convenient method for fabricating highly efficient perovskite solar cells.
Citation Count: 2
Approximation of oscillatory Bessel integral transforms
(Elsevier, 2023) Khan, Suliman; Zaman, Sakhi; Arshad, Muhammad; Alhazmi, Sharifah E.; Khan, Feroz; Park, Jongee; Metallurgical and Materials Engineering
The numerical treatment of oscillatory integrals is a demanding problem in applied sciences, particularly for large-scale problems. The main concern of this work is on the approximation of oscillatory integrals having Bessel-type kernels with high frequency and large interpolation points. For this purpose, a modified meshless method with compactly supported radial basis functions is implemented in the Levin formulation. The method associates a sparse system matrix even for high frequency values and large data points, and approximates the integrals accurately. The method is efficient and stable than its counterpart methods. Error bounds are derived theoretically and verified with several numerical experiments.(c) 2023 International Association for Mathematics and Computers in Simulation (IMACS). Published by Elsevier B.V. All rights reserved.
Citation Count: 2
BIOACTIVITY OF APATITE-WOLLASTONITE GLASS-CERAMICS PRODUCED BY MELTING CASTING
(World Scientific Publ Co Pte Ltd, 2013) Park, Jongee; Ozturk, Abdullah; Metallurgical and Materials Engineering
Glass-ceramics containing only apatite and wollastonite crystals were produced in the system MgO-CaO-SiO2-P2O5-F by the melt casting process. The bioactivity of the glass-ceramics was determined by immersing the glass-ceramics in a simulated body fluid (SBF) and by assessing the resulting apatite formation on the free surface after various immersion durations. A 12-mu m-thick apatite layer formed on the surface of the glass-ceramic containing only apatite crystals after 20 days immersion in SBF. However, the thickness of the apatite layer formed on the surface of the glass-ceramic containing apatite and wollastonite crystals was 1 mu m. Results have shown that the bioactivity of glass-ceramic depends strongly on the type of crystal(s) developed during the glass-ceramic process and their proportion in the glassy matrix.
Citation Count: 29
Boron and zirconium co-doped TiO₂ powders prepared through mechanical ball milling
(Elsevier Sci Ltd, 2013) Tokmakci, Tolga; Ozturk, Abdullah; Park, Jongee; Metallurgical and Materials Engineering
A titania photocatalyst co-doped with boron and zirconium was prepared by mechanical ball milling. The resulting powder was characterized by XRD, XPS, SEM, and EDS. The photocatalytic performance of the powder was evaluated by degradation of methylene blue (MB) solution under UV illumination. XRD patterns were refined by Rietveld analysis to obtain accurate lattice parameters and positions of the atoms in the crystal structure of the photocatalyst. XRD, XPS, and Rietveld analysis results indicated that mechanical ball milling successfully weaved the dopant elements into the crystal structure and distorted the lattice of TiO2. Also, SEM micrographs confirmed that mechanical ball milling led to a decrease in average particle size of the photocatalyst. Boron and zirconium co-doped TiO2 particles exhibited a better visible light response and photocatalytic activity than those of the mono-element doped TiO2 (i.e. B-TiO2 and Zr-TiO2) and undoped TiO2 particles. The enhanced photocatalytic activity is attributed to the synergistic effects of boron zirconium co-doping and particle size reduction. (C) 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Citation Count: 0
Computational analysis of TiC3 as a high-efficiency anode for calcium-ion batteries
(Elsevier, 2024) Park, Jongee; Fatima, Syeda Afrinish; Metallurgical and Materials Engineering
A comprehensive analysis of the structural, electronic, and thermal properties of TiC3 has been conducted. The calculated thermal expansion coefficient throughout a significant portion of the temperature range leads to a negative value underscoring the material's significance. The carbon-rich polytype of titanium carbide (TiC3) is being proposed for the first time as an anode material for calcium-ion batteries (CIB). The adsorption of Ca2+ ions has been determined to be favorable, with high accommodation of guest atoms and sufficiently rapid ionic mobility. The total volume expansion for a maximum Ca2+ adsorbed TiC3 configuration is calculated to be 8.2 %, which is lower compared to other anode materials for CIBs. Through the calciation of TiC3 up to the highest Ca2+ concentration (Ca7TiC3), an exceptionally high theoretical capacity of 2236 mAh/g has been achieved. Regarding battery rate capability, the lowest diffusion barrier calculated is 0.13 eV, with a remarkably high diffusion coefficient along the corresponding pathway equal to 10-3 cm2/s, indicating the ease of Ca ion movement within the host material. Furthermore, the equilibrium distance (2.5 & Aring;) between our host and guest atoms indicates a robust interaction between them. These findings lay the groundwork for the development of high-performance anode materials for CIBs.
Citation Count: 1
Computational insight of lithium adsorption and intercalation in bilayer TiC3
(Pergamon-elsevier Science Ltd, 2024) Park, Jongee; Fatima, Syeda Afrinish; Metallurgical and Materials Engineering
Lithium-ion batteries (LIBs) have gained significant attention owing to their long lifespan. However, these batteries offer unmatched energy storage capacity and suffer from restricted lithium-ion mobility within the electrodes. Here, we employ first-principles calculation to investigate the two-dimensional TiC3 bilayer material. The results exhibit a remarkably high specific capacity of 1277 mAh/g and a low diffusion energy barrier of 0.12 eV. The TiC3 bilayer is anticipated to show high electrical conductivity, maintaining its metallicity due to strong bonding with four Li atoms. Additionally, its high thermal and dynamic stabilities are expected to significantly enhance the battery performance. Notably, the AB stacking bilayer TiC3 experiences a mere 6.01 % increase in volume, considerably smaller compared to the 28 % increase observed in the SiC bilayer. This suggests that TiC3 bilayers remain intact even at the highest concentration of lithium adsorptions. We also explored the solidelectrolyte interface (SEI) formation at the outset of battery operation using reactive force field molecular dynamics simulation. The reactive products of SEI are nicely matched with previous experimental and theoretical findings. All these intriguing properties position the TiC3 bilayer as an exceptionally promising material for use in LIBs.
Citation Count: 13
Control of the Crystal Growth Shape in CH₃NH₃PbBr₃ Perovskite Materials
(Amer Scientific Publishers, 2017) Le, Quyet Van; Shin, Jong Wook; Jung, Jin-Hee; Park, Jongee; Ozturk, Abdullah; Kim, Soo Young; Metallurgical and Materials Engineering
CH3NH3PbBr3 (MAPbBr(3)) materials with perovskite structure were grown by a two-step process using Pb(CH3COO)(2). 3H(2)O and methyl amine bromide (MABr). By changing the concentration of MABr in isopropyl alcohol (IPA) solvent and the annealing temperature, the shape of CH3NH3PbBr3 materials can be controlled to afford nanocubes, nanowires, nanorods, and wrinkled structures. MAPbBr3 with single cubic structure was obtained at a MABr concentration of 3 mg/mL in IPA, and a nanorod array of MAPbBr3 was realized at a MABr concentration of 9 mg/mL in IPA at room temperature. Uniformly wrinkled shapes were formed after the synthesis temperature was increased to 60 and 90 degrees C. The X-ray diffraction patterns, Fourier transform infrared spectra, and X-ray photoelectron spectra of CH3NH3PbBr3 nanorods confirmed that the pure perovskite phase was obtained by dipping Pb(CH3COO)(2). 3H(2)O in MABr/IPA solution. The optical bandgap of the CH3NH3PbBr3 nanorods was estimated from the Tauc plot as 2.2 eV. The evolution of perovskite shapes is expected to lead to improvements in the electrical properties and surface contact, which are important factors for realizing high-performance devices.
Citation Count: 13
A DFT study of TiC3 as anode material for Li-ion batteries
(Elsevier, 2023) Park, Jongee; Fatima, Syeda Afrinish; Metallurgical and Materials Engineering
Two-dimensional monolayer titanium carbide (TiC3) was used to study as a suitable electrode material for lithium-ion batteries with first principles calculation. The monolayer TiC3 showed excellent structural stability, high mechanical stiffness and good electronic conductance behaviour. The adsorption of Li on the carbon rich composition of titanium carbide monolayer is predicted to be favourable. TiC3 structure has remained the same, preserving its metallicity after Li adsorption with attaining high electrical conductivity during lithiation/delithiation process. Especially, the theoretical specific capacity of TiC3 monolayer is high, up to 1916 mAh/g, which is five times higher than the practical graphite. The low open circuit voltage (0.26 V) and diffusion energy barrier (0.25 eV) are also beneficial for overall performance of LIBs. Importantly, during lithiation the change in area is very small and reaches only 8.1 % for full lithiation indicating that it can avoid the large volume expansion during charge/discharge cycles. Its excellent performance, including high melting temperature, dynamical and mechanical stability, can be credited to the rigidness of the TiC3. Given these advantages, that is, high specific capacity, low Li diffusion energy barrier, low open circuit voltage and high in-plane stiffness, TiC3 monolayer can be a promising anode material for lithium-ion batteries.
Citation Count: 1
Diethanolamine Modified Perovskite-Substrate Interface for Realizing Efficient ESL-Free PSCs
(Mdpi, 2023) Sajid, Sajid; Alzahmi, Salem; Wei, Dong; Ben Salem, Imen; Park, Jongee; Obaidat, Ihab M.; Metallurgical and Materials Engineering
Simplifying device layout, particularly avoiding the complex fabrication steps and multiple high-temperature treatment requirements for electron-selective layers (ESLs) have made ESL-free perovskite solar cells (PSCs) attractive. However, the poor perovskite/substrate interface and inadequate quality of solution-processed perovskite thin films induce inefficient interfacial-charge extraction, limiting the power conversion efficiency (PCEs) of ESL-free PSCs. A highly compact and homogenous perovskite thin film with large grains was formed here by inserting an interfacial monolayer of diethanolamine (DEA) molecules between the perovskite and ITO substrate. In addition, the DEA created a favorable dipole layer at the interface of perovskite and ITO substrate by molecular adsorption, which suppressed charge recombination. Comparatively, PSCs based on DEA-treated ITO substrates delivered PCEs of up to 20.77%, one of the highest among ESL-free PSCs. Additionally, this technique successfully elongates the lifespan of ESL-free PSCs as 80% of the initial PCE was maintained after 550 h under AM 1.5 G irradiation at ambient temperature.
Citation Count: 5
Effect of H₂O/TEOT ratio on photocatalytic activity of sol-gel-derived TiO₂ powder
(Ice Publishing, 2013) Agartan, Lutfi; Kapusuz, Derya; Park, Jongee; Ozturk, Abdullah; Metallurgical and Materials Engineering
Effect of water/tetraethyl orthotitanate molar ratio (R) on the formation and morphology of sol-gel-derived titania powder has been studied. Solutions for R of 3 and 5 have been prepared. Initial viscosity of the solutions and viscosity of the gels prepared by aging the solutions for some time were measured. Results revealed that lower gel viscosities lead to better crystallization of the aerogel. Aerogels were dried at 80 degrees C for 24 h and then calcined at 300 degrees C for 1 h to obtain titania powders. The structural and morphological analyses of the powders were performed using X-ray diffraction and scanning electron microscopic characterization techniques. Titania particles obtained after calcination composed of only anatase phase and were in the size range of 9-50 nm. The photocatalytic activity of the powders was evaluated in terms of the degradation of methylene blue (MB) solution under UV (ultraviolet) illumination. A diffuse reflectance spectroscopy was used for the band gap energy measurements. Results revealed that R had a profound effect on the particle morphology and photocatalytic activity of sol-gel-derived titania powders. The titania powders prepared from the solution for R of 5 degraded 99.47% of MB solution under UV illumination in 90 min.
Citation Count: 28
Effect of initial water content and calcination temperature on photocatalytic properties of TiO₂ nanopowders synthesized by the sol-gel process
(Elsevier Sci Ltd, 2015) Agartan, Lutfi; Kapusuz, Derya; Park, Jongee; Ozturk, Abdullah; Metallurgical and Materials Engineering
The effects of initial water content and calcination temperature on sol gel synthesized TiO2 powders were studied. Mother solutions had water/Ti-precursor mole ratios (R ratio) of 1, 5, 10, and 50. Dried aerogels were calcined for 3 h at temperatures of 300, 400, and 500 degrees C to obtain crystallized TiO2 nanopowders in the range of 15-30 nm. PE-scanning electron microscopy and X-ray diffraction techniques were employed to investigate the morphological and structural properties of the nanopowders synthesized. Profound effect of gel viscosity was observed on the formation mechanism and extent of crystallinity in the powders. Methylene blue degradation test results suggest, photocatalytic performance is enhanced as initial water content and calcination temperature increased. Band-gap energy of the powders ranged from 3.09 to 3.27 eV. Overall, this study shows that initial water content and calcination regime have a profound effect on the phase assembly, crystallite size, band-gap energy, and photocatalytic performance of sol gel synthesized TiO2 nanopowders. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Citation Count: 0
Effect of porosity on the efficiency of DSSC produced by using nano-size TiO2 powders
(2014) Bilgin,N.; Park,J.; Ozturk,A.; Metallurgical and Materials Engineering; English Translation and Interpretation
The effect of porosity on the energy conversion efficiency of dye-sensitized solar cells (DSSCs) prepared by using pastes formed by mixing 20 nm and 200 nm TiO2 particles in different ratios is investigated. XRD and SEM analysis have been done to investigate the microstructure of pastes. The energy conversion efficiency of DSSCs was determined by drawing complete current density-voltage curve. The DSSC prepared using the mixture composed of 40 wt% 20 nm and 60 wt% 200 nm TiO2 particles maintained best energy conversion efficiency of 6.74%. The energy conversion efficiency of the DSSCs prepared by using pastes based on the mixture of two different size of TiO 2 particles is much better than that of the DSSCs prepared by using pastes composed of either only 20 nm or only 200 nm of TiO2 particles. The improved energy conversion efficiency is attributed to the establishment of further porous structure that lets more dye absorption from the surface through interior which provides enhancement of light absorption and multiple scattering.
Citation Count: 11
Effects of fluorination and thermal shock on the photocatalytic activity of Bi₂O₃ nanopowders
(Elsevier, 2021) Bouziani, Asmae; Park, Jongee; Ozturk, Abdullah; Metallurgical and Materials Engineering
Fluorinated Bi2O3 (F-Bi2O3) nanopowder was prepared via fluorination followed by thermal shock of alpha-Bi2O3 nanopowder. The XRD, FTIR, SEM, and DRS characterization techniques were employed to investigate the effects of fluorine (F) insertion into the alpha-Bi2O3 host and the thermal shock from different temperatures. The crystal structure, optical and photocatalytic properties of the F-Bi2O3 nanopowders prepared were researched. The XRD results confirmed the substitution of O2- with F-. The FTIR results revealed that the coordination of Bi atoms changed upon F- substitution. The incorporation of F into the alpha-Bi2O3 host and thermal shock did not influence the morphology but modified the band structure of alpha-Bi2O3, leading to a red-shift in the optical absorption edge. Also, the bandgap narrowed from 2.8 eV to 2.6 eV. The density functional theory calculation proved that the F 2p orbitals were positioned in the valence band (VB), resulting in broader and more spread bands for F-Bi2O3. The results suggested that the photoexcited charge carrier mobility in the valence band (VB) and conduction band (CB) are enhanced upon F insertion into alpha-Bi2O3. The photocatalytic efficiency of the synthesized nanopowders was assessed by the degradation of Bromocresol Green (BG) under visible light illumination. Photocatalytic activity improved upon fluorination. The F-Bi2O3 nanopowders thermally shocked from higher temperatures showed negligible photocatalytic performance. The best photocatalytic performance of 70% BG degradation was realized after 180 min visible irradiation for the F-Bi2O3 nanopowder thermal shocked from 500 degrees C.
Citation Count: 0
Effects of Graphene Transfer and Thermal Annealing on Anticorrosive Properties of Stainless Steel
(Amer Scientific Publishers, 2017) Oh, Jeong Hyeon; Han, Sangmok; Kim, Tae-Yoon; Park, Jongee; Ozturk, Abdullah; Kim, Soo Young; Metallurgical and Materials Engineering
Stainless steel (STS) films were annealed in a thermal quartz tube and covered with graphene to improve their anticorrosive properties. Graphene was synthesized via the chemical vapor deposition method and transferred onto the surface of the STS film by the layer-by-layer approach. The structure of the STS film changed from alpha-Fe to gamma-Fe after annealing at 700 C for 1 h, resulting in an increase of 82.72% in the inhibition efficiency. However, one-layer graphene acted as a conductive pathway and therefore deteriorated the anticorrosive properties of the STS film. To overcome this problem, graphene was transferred layer by layer onto the STS film. It was found that transfer of three layers of graphene onto the STS film resulted in a 91.57% increase in the inhibition efficiency. Therefore, thermal annealing and transfer of multilayer graphene are considered to be effective in enhancing the anticorrosive properties of STS films.
Citation Count: 5
Enhanced bioactivity and low temperature degradation resistance of yttria stabilized zirconia/clay composites for dental applications
(Elsevier Sci Ltd, 2022) Tufan, Yigithan; Park, Jongee; Ozturk, Abdullah; Ercan, Batur; Metallurgical and Materials Engineering
Yttria stabilized zirconia (YSZ)/clay composites were produced to improve osseointegration and undesired tetragonal-to-monoclinic phase transformation (low temperature degradation, LTD) of YSZ ceramics so that long-term clinical success of YSZ implants is achieved. Various amounts (0.5,1,2, and 4 wt%) of clay was incorporated to YSZ. Predetermined amounts of clay and YSZ were mixed and pressed uniaxially at 15 MPa into compacts that were subsequently pressureless sintered at 1450 degrees C. Density, compressive strength, hardness and indentation crack resistance of 4 wt% clay incorporated YSZ/clay composite were 5.77 +/- 0.01 g/cm3, 1188 +/- 121 MPa, 1223 +/- 9 HV, and 4.4 +/- 0.1 MPa root m, respectively. Additionally, biological properties of YSZ/clay composites were assessed in vitro using bone cells. Incorporation of 4 wt% clay significantly enhanced bone cell prolifer-ation, spreading, and functions. Moreover, a significant increase in the LTD resistance of YSZ was achieved upon 4 wt% clay incorporation. The findings collectively suggest that YSZ/clay composites have a potential to be used as an alternative material for dental applications.
Enjekte edilebilir poli (Metil metakrilat) (PMMA) zirkonya kompozitlerin hazırlanması ve karakterizasyonu
(2020) Abdullah, Hamad Farhan; Şaşmazel, Hilal Türkoğlu; Park, Jongee; Metallurgical and Materials Engineering
Çalışmanın amacı, üç boyutlu (3B) yazıcı ile biyomateryaller üretmektir. PMMA/Zirkonya biyomateryalleri, ağırlıkça farklı zirkonya tozlarının PMMA solüsyonlarına ısıtma ocağı üzerinde manyetik balık ile 75 ˚C karıştırılması ile üretilmiştir. Hazırlanan malzemeler şırınga ile istenilen şekle sokulmuştur ve farklı sinterleme sıcaklıkları ile sinterlenmiştir. PMMA örneklerinin kimyasal yapı analizi ATR-FTIR ile tayin edilmiştir. Hazırlanan örneklerin morfolojik özellikleri taramalı elektron mikroskobu (SEM) ile incelenmiştir. Kristalinite ve faz değişimleri X-ışını Kırınım (XRD) ile tayin edilmiştir. Mekanik testler ise sıkıştırma dayanımı testleri ile gerçekleştirilmiştir. ATR-FTIR analizi sonuçlarına göre PMMA ~ 70% oranında polimer dönüşümü göstermiştir. SEM görüntülerine göre; porozite, PMMA miktarı ile artma, sinterleme sıcaklığı ile ise azalma göstermiştir. Sinterleme sıcaklığına bağlı olarak tanelerde (grain) topaklanma görülmüştür. XRD sonuçlarına göre, sinterleme sıcaklığındaki artış tetragonal fazın yüzde hacminde düşüşe sebep olmuş; malzemenin kristalit boyutunu ise artırmıştır. Mekanik testler sonucunda ise, sıkıştırma dayanımı; sinterleme sıcaklığı ile birlikte artmış, PMMA miktarı ile azalmıştır. Anahtar kelimeler: Biyomalzemeler, üç boyutlu (3B) baskı, PMMA, Zirkonya
Citation Count: 21
Facile synthesis of CsPbBr₃/PbSe composite clusters
(Taylor & Francis Ltd, 2018) Thang Phan Nguyen; Ozturk, Abdullah; Park, Jongee; Sohn, Woonbae; Tae Hyung Lee; Jang, Ho Won; Kim, Soo Young; Metallurgical and Materials Engineering
In this work, CsPbBr3 and PbSe nanocomposites were synthesized to protect perovskite material from self-enlargement during reaction. UV absorption and photoluminescence (PL) spectra indicate that the addition of Se into CsPbBr3 quantum dots modified the electronic structure of CsPbBr3, increasing the band gap from 2.38 to 2.48 eV as the Cs:Se ratio increased to 1:3. Thus, the emission color of CsPbBr3 perovskite quantum dots was modified from green to blue by increasing the Se ratio in composites. According to X-ray diffraction patterns, the structure of CsPbBr3 quantum dots changed from cubic to orthorhombic due to the introduction of PbSe at the surface. Transmission electron microscopy and X-ray photoemission spectroscopy confirmed that the atomic distribution in CsPbBr3/PbSe composite clusters is uniform and the composite materials were well formed. The PL intensity of a CsPbBr3/PbSe sample with a 1:1 Cs: Se ratio maintained 50% of its initial intensity after keeping the sample for 81 h in air, while the PL intensity of CsPbBr3 reduced to 20% of its initial intensity. Therefore, it is considered that low amounts of Se could improve the stability of CsPbBr3 quantum dots.
Citation Count: 4
FRICTION AND WEAR BEHAVIOR OF SELECTED DENTAL CERAMICS
(World Scientific Publ Co Pte Ltd, 2009) Park, Jongee; Pekkan, Gurel; Ozturk, Abdullah; Metallurgical and Materials Engineering
The purpose of this study was to determine the friction coefficients and wear rates of six commercially available dental ceramics including IPS Empress 2 (E2), Cergo Pressable Ceramic (CPC), Cercon Ceram (CCS) and Super porcelain EX-3 (SPE). Bovine enamel (BE) was also tested as a reference material for comparison purposes. Samples of the dental ceramics were prepared according to the instructions described by the manufacturers in disk-shape with nominal dimensions of 12 mm x 2 mm. The wear tests were performed by means of a pin-on-disk type tribometer. The friction coefficients and specific wear rates of the materials were determined at a load of 10 N and rotating speed of 0.25 cm/s without lubrication. Surface morphology of the wear tracks was examined using a scanning electron microscope. Statistical analyses were made using one-way ANOVA and Turkey's HSD (P < 0.05).