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GÜLTEKİN, ZAFER

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    Effect of mn doping on structural, optical and magnetic properties of zno films fabricated by sol-gel spin coating method
    (Springer, 2023-02-01) GÜLTEKİN, ZAFER; ALPER, MÜRSEL; Akay, Cengiz; AKAY, CENGİZ; Hacıismailoğlu, M. Cüneyt; Bursa Uludağ Üniversitesi/Fen Edebiyat Fakültesi/Fizik Bölümü.; 0000-0002-0781-3376; 0000-0002-8037-0364; K-7950-2012; W-1656-2017
    We have fabricated undoped ZnO and Mn-doped ZnO thin films on glass substrates using sol-gel spin coating method and investigated their structural, optical, magnetic and magnetoresistance properties depending on the Mn doping ratio. X-ray diffraction (XRD) patterns showed that all the films under study are predominantly crystalized in a single-phase wurtzite structure. Scanning electron microscope (SEM) images revealed that the films become more homogeneous, continuous and pinhole-free coatings as the Mn content of the films increases. Optical characterizations by UV-visible spectrometer indicated that transmittance spectra of all films have a high transmittance above 85% in visible region, while they show the absorbance spectra in 300-400 nm range. In addition, it was observed that the optical energy band edges shift to red with increasing Mn content, due to probably increasing the carrier concentration. The refractive index and the dielectric constant are also affect by the Mn content. Magnetic measurements by vibrating sample magnetometer showed that the film magnetic properties change from diamagnetic to ferromagnetic as the Mn content increases. Furthermore, it was found that the magnetoresistance measurements support their magnetic behavior of the films.
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    Synthesis of di- and tricationic surfactants and comparison of their activity on oxidation of metal in hcl media
    (Maik Nauka/interperiodica/springer, 2023-11-02) Öztürk, Serkan; ÖZTÜRK, SERKAN; Gültekin, Zafer; GÜLTEKİN, ZAFER; Akgül, Gülsen; Alper, Mürsel; ALTINÖLÇEK GÜLTEKİN, NURAY; ALPER, MÜRSEL; Bursa Uludağ Üniversitesi/Fen Edebiyat Fakültesi/Kimya Bölümü.; Bursa Uludağ Üniversitesi/Fen Edebiyat Fakültesi/Psikoloji Bölümü.; Bursa Uludağ Üniversitesi/Yenişehir Meslek Yüksekokulu.
    In this study, two surfactants with the same long chain were synthesized. One shows dicationic and the other tricationic properties. Various spectroscopic methods such as FT-IR, H-1 NMR and C-13 NMR were used to confirm the structures of the synthesized surfactants. The inhibition activities of two synthesized surfactants against mild steel corrosion in 1.0 M HCl solution were determined using the weight loss method. The 24-h corrosion tests on metal coupons immersed in acidic solutions were carried out using different inhibitor concentrations and similar and successful inhibition was obtained for both surfactants. Current density was determined by potentiodynamic polarization at a single inhibitor concentration to compare with the inhibition efficiency results obtained by decrease in weight method. Based on the current density, the inhibition efficiencies of the surfactants were calculated by Tafel extrapolation method. The inhibition efficiency results obtained by both weight loss and Tafel method were close and consistent. According to both methods, the corrosion inhibition of dicationic surfactant was slightly better than that of tricationic surfactant. By determining the critical micelle concentration for the two surfactants, some physicochemical parameters such as surface tensions and free energy of micelle formation at this concentration were calculated and correlated with their corrosion inhibitory activity. Scanning electron microscopy was used to ascertain the surface roughness conditions of metals submerged in an acidic solution, thus visually proving that surfactants protect the metal surface from corrosion.