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    Contribution of galvanic coupling with TiN, TiAlN, and CrN to the corrosion of steel in neutral and acidic chloride solutions
    (Wiley-V C H Verlag Gmbh, 2023) Avci, Burcak; Kazmanli, Kursat; Evren, Burak; Urgen, Mustafa
    The inherent defective morphology of the physical vapor deposition (PVD) hard coatings limits their corrosion protective ability. We examined the impact of nitride-based PVD coatings, including TiN, TiAlN, and CrN deposited on inert substrates by cathodic arc PVD method (CA-PVD), on the galvanic corrosion of carbon steel. Their contribution was evaluated by zero-resistance ammeter (ZRA) and electrochemical impedance spectroscopy (EIS) in 3.5 wt.% NaCl at pH 2 and 6, with and without aeration. The results indicated the prominent role of the coating type and the coupling environment on the generated galvanic currents. Immersion tests for the TiN-, TiAlN-, and CrN-coated steel cross-sections visually verified these results. The galvanic current contribution was distinct in environments where oxygen reduction is the dominant cathodic reaction. However, the layers' contribution to galvanic corrosion was minimal in deaerated acidic solutions, which is attributed to the high bonding strength of adsorbed intermediates to the coating surfaces.
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    Enhanced interface structure of electroformed copper/diamond composites for thermal management applications
    (Walter De Gruyter Gmbh, 2024) Evren, Burak; Evren, Gokce; Kincal, Cem; Solak, Nuri; Urgen, Mustafa
    As the power density of electronic devices increases, the requirement for heat sinks with enhanced thermal properties becomes imperative for advanced heat dissipation. Copper/diamond composites are next-generation heat dissipators with high thermal conductivities, yet fabrication of these composites requires high energy and complex instruments. In this study, copper/diamond composites are fabricated by electroforming. The sediment co-deposition process is modified to obtain uniform diamond particle distribution with tailorable volume fraction. Diamond particles were initially settled on the cathode surface outside the electrolyte, and then the setup was immersed in an acidic copper sulfate electroforming bath. Varying amounts (0-100 mg l(-1)) of thiourea are introduced to the electrolyte to enhance the matrix-particle interface. The gaps between diamond particles are filled with electrodeposited copper using optimized deposition conditions. The composite structure detaches from the cathode by itself after the production with desired shape and dimensions. The effect of operating conditions on cathodic polarization, composite microstructure, and thermal properties are investigated. Thermal conductivity of 49 vol.% diamond containing sample fabricated with optimized parameters exceeds 667 W m(-1) K-1. The increase in thermal conductivity and enhanced interface structure is attributed to the excellent void-filling ability of the optimized electrolyte.
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    Morphological, microstructural and photocatalytic characterization of undoped and Ni, Co doped Fe2O3 particles synthesized by sonochemical method
    (Scientific & Technical Research Council Turkey-TUBITAK, 2022) Kaya, Elif Emil; Evren, Burak; Erdöl, Zeynep; Ekinci, Duygu; İpekoğlu, Mehmet; Özenler, Sibel
    In this study, an abundant and eco-friendly photocatalytic material, Fe2O3 particles were synthesized by sonochemical method. Morphological and microstructural investigations of synthesized undoped and Ni, Co-doped Fe2O3 particles were performed. The effect of particle morphology and microstructure on its photocatalytic performance was further investigated. Comparative studies for evaluating particle crystallite sizes were conducted by Williamson-Hall (W-H) method and modified Debye-Scherrer (MDS). Crystallite sizes and lattice strains of Fe2O3 induced by process parameters were calculated by W-H method based on uniform deformation model (UDM). The crystallite sizes of the synthesized powders were calculated in the range of 200 nm and 76 nm by Williamson-Hall analysis. In addition to structural investigation, dislocation density of the synthesized particles was calculated by Williamson-Smallman relation. Afterwards, photocatalytic performance of Fe2O3 particles was investigated in detail. The photodegradation of methylene blue solutions in the presence of light in 20 min with samples 3,4, and 5 in 20 min were 0.937, 0.896, and 0.855, respectively. Moreover, the photodegradation of methylene blue solution with sample 5 for 15, 30, and 45 min were 0.9, 0.828, and 0.757, respectively. A photocatalytic activity of 24.25% has been observed under optimum conditions for the time interval of 45 min.
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    Spreading behavior of droplets impacting over substrates with varying surface topographies
    (Elsevier, 2020) Çetiner, Arda; Evren, Burak; Budaklı, Mete; Arık, Mehmet; Özbek, Arif
    Droplet interaction with solid surface plays an important role in a number of practical applications such as thermal management systems, steel production, painting, prevention of impurit deposition, and formation of corrosion. In this study, droplet impact on different surface topographies was experimentally investigated. A major part of this work was to devoted to developing supherhydrophobic surfaces using a combination of two conventional manufacturing techniques in order to study the droplet dynamics with the aim of preventing liquid attachement at the wall. Five surfaces were manufactured for which the methods such as mechanical polishing, Ylaser-ablation, anodization, superhydrophobic spray-coating, and combination of laser-ablation and anodization were applied. Deionized water was used as the working liquid. The effects of velocity and surface temperature on spreading dynamics were investigated by impacting single droplets for Weber numbers between 67 and 565. Experiments are performed at 25 degrees C ambient temperature with a constant droplet temperature of 25 degrees C, while the effect of surface temperature has been studied for 25 degrees C and 2 degrees C. Maximum spreading factor data was obtained and compared with theoretical models and experimental data found in the literature. Through the combination of laser-ablation and anodization methods, superhydrophobicty is obtained with static contact angles similar to that measured on the superhydrophobic coating. Experiments at 25 degrees C surface temperature show that the droplet impacting on the combined surface had greater maximum spreading factor values than only laser-ablated and anodized surfaces and lower than those determined at the cotaed surface. At low surface temperature, the smallest maximum spreading factor was measured at the substrate with its surface treated by the combined method. The mathematical models found in literature show a good agreement concerning the maximum spreading factor values determined at the polished, anodized and laser-ablated surfaces. However, the maximum spreading factor at both spray-coated and combined surfaces is larger than the model predictions.