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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/3
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Publication Metadata only Surface hardening of Ti-AL-V superalloy spinal implant by using the boronization method(IOS Press, 2024) Hekimoğlu, Mehdi; Özer, Hidir; Onursal, Ceylan; Department of Chemistry; Kiraz, Kamil; Özer, Ali Fahir; Department of Chemistry; College of Sciences; School of MedicineBackground: We compared the raw Ti-Al-V super alloy transpedicular implant screws with boronized and surfacehardened transpedicular implant screws. OBJECTIVE: To improve patients' postoperative prognosis with the production of harder and less fragile screws. METHODS: Surface hardening was achieved by applying green-body encapsulation of the specimen with elemental boron paste which is sintered at elevated temperatures to ensure the boron-metal diffusion. Boron transported into the Ti-Al-V super alloy matrix gradually while suppressing aluminum and a homogeneously boronized surface with a thickness of similar to 15 microns was obtained. The uniform external shell was enriched with TiB2, which is one of the hardest ceramics. The Ti-Al-V core material, where boron penetration diminishes, shows cohesive transition and ensures intact core-surface structure. RESULTS: Scanning electron microscope images confirmed a complete homogeneous, uniform and non-laminating surface formation. Energy-dispersive X-ray monitored the elemental structural mapping and proved the replacement of the aluminum sites on the surface with boron ending up the TiB2. The procedure was 8.6 fold improved the hardness and the mechanical resistance of the tools. CONCLUSIONS: Surface-hardened, boronized pedicular screws can positively affect the prognosis. In vivo studies are needed to prove the safety of use.Publication Metadata only Nanoparticle silicalite-1 crystallization from clear solutions: nucleation(Elsevier Science Bv, 2009) Tokay, Begüm; Erdem-Şenatalar, Ayşe; Schueth, Ferdi; Thompson, Robert W.; Department of Chemistry; Somer, Mehmet Suat; Faculty Member; Department of Chemistry; College of Sciences; 178882Despite much effort spent by various research groups, there remain many aspects of nanoparticle silicalite-1 crystallization from clear solutions which require further investigation. In order to shed light, especially on the nucleation of silicalite-1, particle growth at 100 degrees C from several starting compositions known to yield colloidal silicalite-1, which have been studied previously by other researchers using various techniques, was followed in this study by laser light scattering using scattering angles of 90 degrees and 173 degrees, and zeta potential and pH measurements. Crystallinity was monitored by X-ray diffraction, Fourier transform infrared analysis and transmission electron microscopy. Thermogravimetric analyses and density measurements were also used to characterize the products obtained at various times during the syntheses. The results demonstrate that the distinct time of sudden jump in the effective diameter of the nanoparticles in solution, as observed more clearly by using the back-scattering device, and which marks the beginning of the constant linear growth rate of the particles, corresponds to the nucleation of the silicalite-1 crystal structure. This time was also shown to coincide with the exo-endo thermal switch time of the reaction mechanism, which has been observed previously by another research group. Nucleation was accompanied by an aggregation of a population of smaller particles, as indicated by the broadening of the particle size distribution, and the variation of the pH and zeta potential values during synthesis.Publication Metadata only Strain modulated band gaps of semiconducting zigzag single walled carbon nanotubes(Natl Inst Optoelectronics, 2015) Eyecioğlu, Önder.; Mısırlıoğlu, Banu Süngü; Department of Physics; Dereli, Gülay; Other; Department of Physics; College of Sciences; N/AStrain can alter the electronic properties of materials. At the nanoscale, small displacements of atoms could have large effects. In this study, we have examined how elastic strain can modify the energy band gaps of semiconducting zigzag Single Walled Carbon Nanotubes (SWCNTs). The electronic structure of SWCNTs have been computed for each deformed configurations by means of real space, Order(N) Tight Binding Molecular Dynamic (O(N) TBMD) simulations. During the applications of uniaxial strain, carbon atoms are moved slightly from their equilibrium positions, but their atomic bonds are not broken. Three different kinds of semiconducting zigzag SWCNTs are chosen. (12,0) SWCNT, although a semiconducting SWCNT, is quasi-metallic in its pristine state. Application of stretching and compression opens its band gap. Thus under strain (12,0) SWCNT shows metallic-semiconducting transitions. (13,0) and (14,0) zigzag SWCNTs are semiconductors having energy band gap values of 0.44eV and 0.55eV in their pristine state. The energy band gap of (13,0) SWCNT decreases with increasing absolute value of compression. On the other hand, the energy band gap of (14,0) SWCNT decreases with increasing value of tension. So in both cases, the energy band gap closes and semiconducting metallic transitions are observed. Flexibilities of the stretched hexagonal network of SWCNTs are displayed in terms of carbon-carbon bond-lengths, bond-angles and radial distribution functions. Correlations between the strain induced structural changes and the electronic properties of SWCNTs are discussed.Publication Metadata only A microstructure-sensitive model for simulating the impact response of a high-manganese austenitic steel(Asme, 2016) N/A; N/A; Department of Mechanical Engineering; Mirzajanzadeh, Morad; Canadinç, Demircan; PhD Student; Faculty Member; Department of Mechanical Engineering; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; College of Engineering; N/A; 23433Microstructurally informed macroscopic impact response of a high-manganese austenitic steel was modeled through incorporation of the viscoplastic self-consistent (VPSC) crystal plasticity model into the ANSYS LS-DYNA nonlinear explicit finite-element (FE) frame. Voce hardening flow rule, capable of modeling plastic anisotropy in microstructures, was utilized in the VPSC crystal plasticity model to predict the micromechanical response of the material, which was calibrated based on experimentally measured quasi-static uniaxial tensile deformation response and initially measured textures. Specifically, hiring calibrated Voce parameters in VPSC, a modified material response was predicted employing local velocity gradient tensors obtained from the initial FE analyses as a new boundary condition for loading state. The updated micromechanical response of the material was then integrated into the macroscale material model by calibrating the Johnson-Cook (JC) constitutive relationship and the corresponding damage parameters. Consequently, we demonstrate the role of geometrically necessary multi-axial stress state for proper modeling of the impact response of polycrystalline metals and validate the presented approach by experimentally and numerically analyzing the deformation response of the Hadfield steel (HS) under impact loading.Publication Metadata only Resistive hydrogen sensors based on nanostructured metals and metal alloys(Amer Scientific Publishers, 2013) N/A; Department of Electrical and Electronics Engineering; Kılınç, Necmettin; Researcher; Department of Electrical and Electronics Engineering; College of Engineering; 59959Hydrogen (H-2), as a renewable energy source, has numerous applications such as chemical production, fuel cell technology, rocket engines, fuel for cars etc. The detection of H-2 is so important in safety issue due to the flammable and explosive properties of H-2 gas, in a H-2 source for leak detection and in H-2 production process because of real-time quantitative analysis of production. This paper reviews resistive type H-2 sensor based on palladium (Pd), platinum (Pt) and their alloy nano-structures in the forms of thin films, nanoporous films, nanowires, nanoparticles, nanotubes, etc. The sensing mechanism of the nanostructured Pd and Pt resistive sensor is discussed in separated section. Nanostructured Pd sensors show a decrease or an increase in their resistance towards H-2 gas depending on continuity of the nanostructure and will be examined in two parts: discontinuous (nano-gap based) and continuous Pd and Pd alloy nanostructure sensors. on the contrary to Pd nanostructure sensor, nanostructured Pt sensors require oxygen (O-2) to operate. There are limited numbers of publications about nanostructured Pt and Pt alloy sensors, so further investigation are needed to well understand sensing mechanism of the Pt sensors.