Browsing by Subject "Carbon fibers"
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Item Open Access Atomic layer deposition of NiOOH/Ni(OH) 2 on PIM-1-based N-Doped carbon nanofibers for electrochemical water splitting in alkaline medium(Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim, 2019) Patil, Bhushan; Satılmış, Bekir; Khalily, Mohammad Aref; Uyar, TamerPortable and flexible energy devices demand lightweight and highly efficient catalytic materials for use in energy devices. An efficient water splitting electrocatalyst is considered an ideal future energy source. Well‐aligned high‐surface‐area electrospun polymers of intrinsic microporosity (PIM‐1)‐based nitrogen‐doped carbon nanofibers were prepared as a free‐standing flexible electrode. A non‐noble‐metal catalyst NiOOH/Ni(OH)2 was precisely deposited over flexible free‐standing carbon nanofibers by using atomic layer deposition (ALD). The morphology, high surface area, nitrogen doping, and Ni states synergistically showed a low onset potential (ηHER=−40 and ηOER=290 mV vs. reversible hydrogen electrode), small overpotential at η10 [oxygen evolution reaction (OER)=390.5 mV and hydrogen evolution reaction (HER)=−147 mV], excellent kinetics (Tafel slopes for OER=50 mV dec−1 and HER=41 mV dec−1), and high stability (>16 h) towards water splitting in an alkaline medium (0.1 m KOH). The performance was comparable with that of state‐of‐the‐art noble‐metal catalysts (e.g., Ir/C, Ru/C for OER, and Pt/C for HER). Post‐catalytic characterization with X‐ray photoelectron spectroscopy (XPS) and Raman spectroscopy further proved the durability of the electrode. This study provides insight into the design of 1D‐aligned N‐doped PIM‐1 electrospun carbon nanofibers as a flexible and free‐standing NiOOH/Ni(OH)2 decorated electrode as a highly stable nanocatalyst for water splitting in an alkaline medium.Item Open Access Effects of thermoplastic coating on interfacial interactions in advanced engineering composites for aerospace applications(2023-05-03) Yavuz, Zelal; Khaligh, Aisan; Öz, Y.; Tuncel, DönüşDelamination due to an inferior adhesion between reinforcement material and matrix in carbon fiber-reinforced thermoplastic (CFRTP) composites is a crucial problem to be solved. To this end, this study aims to overcome poor wettability between reinforcing phase, i.e., carbon fiber (CF), and thermoplastic matrix, i.e., polyetherether ketone (PEEK). Herein, CF’s surface was tailored by application of different polymeric sizing agents which have different chemical structures. Morphology and topology analyses were performed by Scanning Electron Microscope and 3D laser scanning, respectively. Later, a variety of wettability results were obtained by the sessile drop method used in Contact Angle (CA) measurements for CFs throughout application of each sizing agent applied by dip coating. Sizing materials were designed such that the chemical structure of CF’s surface could exhibit compatibility with the matrix itself. Consequently, complete wettability (CA: 0°) was achieved for CFs sized by HPEEK (CF/hydroxylated PEEK (HPEEK)) and the surface free energy (SFE) of CF was enhanced from 5.43 to 72.8 mJ/m2 while the SFE of the PEEK matrix is 40.1 mJ/m2. Moreover, sizing by HPEEK improved the average surface roughness of CF by 32% which enables optimized adhesion. Afterward, repetitive tensile tests were carried out to observe effects of improved interfacial interlocking on the mechanical properties of the final CFRTP composite. Stress–strain curves revealed that the tensile strength of CFRTP improved from 473 to 508 MPa through the sizing of CF by HPEEK whereas pristine PEEK has a much smaller tensile strength (98 MPa) than the aforementioned CF-reinforced composites.Item Open Access The investigation of advanced thermoplastic composite materials in aerospace applications(Bilkent University, 2023-05) Yavuz, ZelalThe development of load-carrier reinforced composites is crucial in terms of a wide range of applications, such as aerospace, automotive, sports industry and so on. When these fields are taken into consideration, reducing the excessive weight of structural materials without any sacrifice in the performance is required. Thus, using reinforcement materials (e.g. carbon fibers) for polymeric matrices in composites is the most convenient way to follow. In this study, carbon fiber (CF) was used as a reinforcement material for thermoplastic based composites. Since bare CFs are too fragile to process they must be coated / sized such that the brittleness of CFs can be avoided during industrial applications. Therefore, sizing of carbon fibers is crucial for guiding them into service by protecting the CF’s surface. Yet, the traditional sizing agent (i.e. epoxy) is not suitable for handling continuous CF reinforced thermoplastic composites (CFRTPs) with high processing temperatures above 300 ℃. In this study a novel sizing agent was developed for this purpose. The effects of this sizing on the CFs’ physicochemical as well as surface properties were investigated. As a result, the impact on fiber-matrix interphase behavior can be analyzed. Moreover, the main problem for thermoplastic based composites which is the delamination between the reinforced fiber and thermoplastic matrix can be solved throughout the development of novel coating material so that inert carbon fibers can be made compatible with the matrix. In this thesis, the activation of carbon fiber’s surface, then providing a functional sizing agent and method in order to expel the present voids because of incompatibility between CF and thermoplastic matrix (i.e. Polyetherether ketone) were carried out by enhancing the adhesion. Hence, the wettability of CF by polyetherether ketone (PEEK) matrix was enhanced by altering the surface free energy of CF resulting in optimized adhesion. Thus, the delamination problem in thermoplastic based composites was solved throughout the sizing of CFs. The first part of this work consists of the elimination of current epoxy coating on the aerospace grade commercial carbon fibers. Then, the application of surface activation method was performed by acidic modification to make CFs ready for sizing process. The formation of functional groups (-COOH, -OH) on CF’s surface was achieved after degrading of present epoxy coating throughout CFs. As a result, the developed sizing agents could be binded easily onto CF’s activated surface through the hydrogen bonding. In the second part, four different polymeric sizing agents were prepared by taking the chemical compatibility with the matrix into consideration. The sizing process was performed via dip-coating method for the surface-activated CFs. The chemical and physical analyses for neat and treated CFs were carried out via microscopic and spectroscopic techniques. As a result of sizing process, the enhanced compatibility between the matrix and reinforcement material was proved by the Contact Angle Analysis and surface free energy calculations according to Young’s equation.Item Open Access Milling force modelling of multidirectional carbon fiber reinforced polymer laminates(Elsevier, 2012) Karpat, Yiğit; Bahtiyar, O.; Deger, B.Carbon fiber reinforced polymer (CFRP) usage in the aerospace industry has been steadily increasing due to its superior material properties such as high strength, low weight, high resistance to corrosion, and a low thermal expansion coefficient. In addition, CFRP parts are produced near-net-shape, a process that eliminates rough machining operations. However, machining operations such as drilling, side milling, and slotting are still necessary to give the CFRP parts their final shape. A majority of the studies on machining of CFRP laminates are on drilling. The number of studies on milling of CFRPs is quite limited. In this study, a mechanistic cutting force model for milling CFRPs is proposed based on experimentally collected cutting force data during slot milling of unidirectional CFRP laminates using a polycrystalline diamond cutter. Cutting force coefficients in radial and tangential directions are calculated as a function of fiber cutting angle. The mechanistic model is shown to be capable of predicting cutting forces during milling of multidirectional CFRP laminates and capable of investigating stability of machining. © 2012 The Authors.