Growth of zinc oxide nanostructures on carbon fibers: Production, characterization and photocatalytic properties Çinko oksit nanoyapıların karbon fiber üzerinde büyütülmesi: Üretimi, karakterizasyonu ve fotokatalitik özellikleri

xiv, 88 pages29 cm. 1 CDÖZETSon yıllarda, karbon fiber üzerine büyütülmüş çinko oksit nano yapıları, üstünyapısal, elektriksel ve optik özellikle dolayısı ile yoğun olarak çalışılmaktadır. ZnO, geniş band aralığı (3.37 eV) nedeniyle morötesi ışık altında aktive olabilen bir yarı iletken fotokatalizördür. Ancak, çinko oksidin karbon temelli malzemeler üzerinde büyütülmesi veya yapısına metallerin katkılanması ile yasak band aralığının daraltılması ve görünür bölge ışığı altında aktive edilmesi sağlanabilir. Bu bilgiler ışığında, yapılacak çalışmada, çinko oksit nanotellerin, karbon fiber üzerinde hidrotermal yöntem ile büyütülmesi amaçlanmıştır. Fotokatalizör olarak en etkin yapıyı elde etmek için, hidrotermal yöntem koşulları olan sıcaklık, konsantrasyon ve süre optimize edilmiştir. Hidrothermal sentez parametlerinin, ZnO nanotellerin boyutları üzerine etkileri yanıt yüzey yöntemi ve merkezi kompozit yöntemi ile incelenmiştir. Hidrotermal yöntem parametrelerinin, üretilen yapılar üzerindeki etkilerinin anlaşılabilmesi için, yapısal, morfolojik, optik ve fotokatalitik özellikleri detaylı bir şekilde analiz edildi.ABSTRACTOver the last decades, zinc oxide nanostructures on flexible carbon fibers have been extensively studied due to their superior structural, electrical and optical properties. ZnO is a wide band gap (3.37 eV) metal oxide semiconductor photocatalyst activating under ultraviolet light. However, as ZnO nanowires are grown on carbon based substrates, due to synergistic effect, narrower band gap structures could be obtained and catalysts become active under visible light irradiation. Owing to this motivation, ZnO nanowires were grown successfully on carbon fibers by hydrothermal method. To obtain most effective photocatalyst, the effects of hydrothermal synthesis parameters, temperature, concentration and growth time, on dimensions of zinc oxide nanowire structures on carbon fibers were evaluated via response surface methodology and central composite design. Morphological, structural, photocatalytic properties of fabricated structures were analyzed by scanning electron microscopy, X-ray diffraction, and UV-Visible spectrophotometer

A study on the corrosion behavior of 7072/3004/7072 clad aluminum alloy in different media

Cladding is an easy and economical method to design multifunctional aluminum structures with improved corrosion resistance, mechanical strength, and physical appearance. In this study, the electrochemical properties and corrosion behavior of an aluminum-clad product made of 7072/3004/7072 aluminum alloys were investigated by Tafel extrapolation and impedance spectroscopy. 3004 aluminum sheet was used as core, and it was cladded with 7072 aluminum sheets on both sides. The long-term corrosion behavior of clad samples was examined after being immersed in tap water, rainwater, and 3.5 wt.% NaCl solution for 4 weeks. The results show that because of the potential difference between 7072 and 3004 aluminum alloys, 7072 alloy behaves more anodic and corrodes preferentially (with a slower rate) compared to 3004 aluminum alloy. Cladding 3004 with embossed 7072 alloy improves the corrosion resistance of the alloy. Moreover, the electrolyte comparison demonstrates that the carbonate-forming ions (such as Ca) in tap water and HCO3-, NO3-, and SO(4)(2-)in rainwater decelerate the corrosion rate

Development of high luminous efficacy red-emitting CaAl12O19:Mn4+ phosphor using Al- and K-doped ZnO NWs/CFs

CaAl12O19:Mn4+&nbsp;phosphor (CAO:Mn), which has advanced color rendering and high productivity for white light-emitting diodes (wLEDs), is an important candidate for red-emitting materials due to its large absorption band from the visible region to the deep-red region based on the d-d transitions of manganese ions. For this reason, it is widely used especially in wLEDs, and in recent years, many researchers have aimed to improve the optical properties of the aforementioned red phosphor material with the use of different dopants and additives. In this study, the observed enhancements in the photoluminescence based optical properties of sol-gel synthesized CAO:Mn phosphor were described in detail in the presence and absence of pristine zinc oxide nanowires grown on carbon fibers (ZnO NWs/CFs), Al-doped ZnO NWs/CFs (Al-ZnO NWs/CFs) and K-doped ZnO NWs/CFs (K-ZnO NWs/CFs) additives. The addition of pristine ZnO NWs/CFs and Al- and K-doped ZnO NWs/CFs to CAO:Mn phosphor in the ethyl cellulose (EC) matrix resulted in an increase in emission intensity of 74%, 81%, and 84%, respectively. Additionally, the features of the synthesized phosphor’s emission/excitation spectra and decay times were examined on both the nano- and microsecond time scales. The presented material can be shown as a new candidate for improving the properties of red phosphors related to brightness, stability, and degradation times.</p