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DEMİRCİ, SELİM

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Author: TÜNÇAY, MEHMET MASUM × Has files: false ×

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    Synthesis, characterization, thermal, and antibacterial activity studies on MgO powders
    (SPRINGER, 2021) GÜLLÜOĞLU, ARİF NİHAT; Demirci, Selim; Yildirim, Bercem Kiran; Tuncay, Mehmet Masum; Kaya, Nusret; Gulluoglu, Arif Nihat
    In this study, MgO particles were synthesized via sol-gel technique and calcined at 600 degrees C for 2 h with heating rates of 2, 5, 10, and 20 degrees C/min, respectively, for the first time. Comprehensive characterizations were performed by TGA-DTA, XRD, SEM, Raman spectroscopy, BET analysis, photoluminescence techniques. The kinetic parameters were determined by employing four popular model-free methods: Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sonuse (KAS), Starink, and Tang methods. MgO powders had a high crystalline structure regardless of different heating rates based on XRD results. Surface morphologies and surface areas of MgO powders did not change with heating rates. Surface morphologies of MgO powders were found to be nearly spherical with some rounded shape and exhibiting faceted edges in some regions. The specific surface area of MgO powders was found to be 5.9179, 5.6883, 3.6617, and 4.1942 m(2)/g with increasing heating rate, respectively. According to Raman analysis, MgO particles produced at 2 degrees C/min possessed higher surface defects like oxygen vacancies. The PL emission signals for MgO particles were observed at similar to 500 nm consisting of broad peaks, which might be attributed to oxygen defects on the surface of particles. The antibacterial performances of MgO particles were carried out against gram-negative E. coli and gram-positive B. subtilis by means of the agar disc diffusion method. MgO particles produced at a heating rate of 2 degrees C/min possessed the biggest inhibition zone against gram-positive B. subtilis. Having better antibacterial performances for MgO particles produced at 2 degrees C/min heating rate might be attributed to surface oxygen vacancies and surface area, which led to the generation of more reactive oxygen species (ROS). [GRAPHICS] .
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    Effect of surface modifications of additively manufactured Ti-6Al-4V alloys on apatite formation ability for biomedical applications
    (ELSEVIER SCIENCE SA, 2021) GÜLLÜOĞLU, ARİF NİHAT; Demirci, Selim; Dalmis, Ramazan; Dikici, Tuncay; Tuncay, Mehmet Masum; Kaya, Nusret; Gulluoglu, Arif Nihat
    In this study, Ti-6Al-4V alloys were additively manufactured (AM) with different laser powers. The goal was to investigate the effect of different surface modifications on apatite formation ability. Four types of surface modifications, namely, sandblasting (S), acid etching (E), anodic oxidation (AO) and anodic spark oxidation (ASO), were achieved on the Ti-6Al-4V samples. The microstructure, phase, morphology, roughness and wettability properties were examined by optical microscope (OM), scanning electron microscope (SEM), Xray diffraction (XRD), surface profilometer and contact angle techniques. The bioactivity analysis was performed in simulated body fluid (SBF) for 2 weeks. The results indicated that the microstructure, surface topography, roughness and wettability influenced the apatite formation were affected by the production laser power. Generally, the samples 3 showed higher Ca and P ion ratio value because of percentage of beta phase amount, the presence of bioactive phases on the surfaces. The E3 sample resulted in the best apatite formation theoretically. The etching procedure of AM Ti-6Al-4V in the acidic solution can be applied to improve the apatite formation ability of Ti-6Al-4V alloys. (c) 2021 Elsevier B.V. All rights reserved.
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    Effect of heating rate on structure, morphology and photocatalytic properties of TiO2 particles: thermal kinetic and thermodynamic studies
    (SPRINGER, 2021) KIRAN YILDIRIM, BERÇEM; Dikici, Tuncay; Demirci, Selim; Tuncay, Mehmet Masum; Yildirim, Bercem Kiran; Kaya, Nusret
    In this study, TiO2 powders were produced via sol-gel route at 500 degrees C for 2 h with distinct heating rates. TGA-DTA, XRD, SEM, Raman spectroscopy, XPS, UV-vis spectroscopy and photoluminescence characterization techniques were carried out for TiO2 powders. Photocatalytic efficiency of TiO2 powders on degradation of methylene blue (MB) solution was examined in terms of different heating rates. Thermodynamic and non-isothermal kinetic study of TiO2 powders were estimated. TiO2 powders showed anatase phase based on XRD results. Surface morphology of TiO2 powders did not change with different heating rates. It can be concluded that heating rate played important role on band gap and photocatalytic activity. The band gap of the TiO2 particles decreased from 3.25 to 2.95 with increasing heating rate. The photocatalytic activity results exhibit that T1 powders have the highest photocatalytic performances. The kinetic constant and photocatalytic degradation rate were 0.00678 min(-1) and 83.48%, respectively. This could be attributed to high crystalline structure and low bulk vacancies or defects. Furthermore, TiO2 powders showed good stability. This study exhibited a new way to enhance the photocatalytic performances of pure TiO2 powders. [GRAPHICS]