Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Surface Modification of Chitosan Films/Meshes for Biomaterial Applications(Izmir Institute of Technology, 2019) Işıklı, Berçin; Tıhmınlıoğlu, FundaModification of surface of biomaterials is a great interest for many years due to first contact of surface of materials with the biological fluids. This thesis aims to investigate surface modification effect on the chemical, surface wettability, protein adsorption as well biodegradability properties of dense chitosan (Ch) and asymmetric chitosan films (ACh). The surfaces of chitosan dense and asymmetric films were modified by ion implantation technique using carbon and carbon-nitrogen hybrid ions at a fluence of 1x1015 ions/cm2 and ion energy of 20kV. Chemical compositions of the film surfaces were analyzed by Fourier transform infrared spectroscopy (FTIR-ATR). Surface hydrophobicity measurements were conducted by static contact angle measurements. Protein adsorption on unmodified and modified surfaces on films was investigated as a function of time at various pH conditions. After ion implantation on chitosan films, both C and C-Nitrogen ion implantation, the surfaces become rougher and hydrophobic having moderate wettability (����� values in the range of 72-85°) and in good agreement with FTIR-ATR data findings. It was found pH dependence of the amount of protein adsorbed on the dense chitosan films as a function of time for both un-implanted and implanted films. BSA and fibrinogen were more adsorbed on the chitosan films at pH 5. The amount of BSA and fibrinogen protein adsorption was 0.97 and 1.33 gprotein/gfilm, respectively for 60 min incubation period. Protein adsorption enhanced for C and C+N2 ion implanted samples for BSA and fibrinogen, respectively due to the hydrophobic protein surface interaction effect. In vitro degradation results showed that ACh films degrade much faster (mass loss 57 %) than Ch films (40 %) due to the porous structure at the end of 3 weeks. However, the ion implanted Ch samples degraded much slower having mass loss of 30% and 17.7% for C+N2 and C implanted samples, respectively at the end of 3 weeks compared to un-implanted Ch films as 40 %. The results are in good agreement with water sorption and surface hydrophobicity of the implanted films. This study demonstrated that surface modification, as well as structure, changes the protein sorption, wettability and biodegradation properties of the chitosan films.Master Thesis Structural and Nanohardness Behavior of Low Energy, High Flux Nitrogen Implanted Austenitic Stainless Steel(Izmir Institute of Technology, 2018) Dal, Refika; Öztürk, Orhan316 austenitic stainless steels (SSs) are one of the most commercial and technological alloys and extensively used in the field of defence, nuclear and biomedical applications due to its excellent corrosion resistance in abrasive and erosive environment. However, this type of steel is rather soft, and these results in poor durability, in particular when this material (316 SS) is in contact with other surfaces. In addition, 316 SS is nonmagnetic at room temperature. In order to make the surface of 316 SS harder, nitrogen ion beam implantation and wear resistant method is applied. Earlier studies of high dose nitrogen ion implantation into the surface of austenitic SSs around 400 °C substrate temperature showed that an expanded austenite phase (The Nitrogen phase in the FCC lattice of 316 SS) gives excellent wear resistance with high hardness value. In this study, type 316 stainless steel (SS) was implanted with low energy (700 eV), high flux (2.9 mA/cm2) nitrogen ions at 400 °C substrate temperature in order to harden its surface. Microhardness and nanohardness measurements were carried out on the nitrogen implanted surface and on the nitrogen implanted cross-section under the applied loads ranging from 6 mN to 30 mN. Both microhardness and nanohardness data suggest that the hardness of the N implanted 316 SS significantly increases compared to the hardness of the substrate material (by a factor of 3 to 4).The hardness increase is believed to be due to the high amount of nitrogen, the thick nitrogen implanted layer and macroscopic residual compressive stresses, the formation of which is verified by θ/2θ XRD scans as lattice expansions about 10 at. %. SIMS profiles suggest concentration-dependent diffusion behavior for the N implanted layers. Based on SIMS and SEM/EDX data, nitrogen implanted layers are 4-5 micron thick and constituting about 28 %.Master Thesis Magnetic Characterization of Expanded Austenite Phase Formed on Nitrogen Ion Implanted 316 Stainless Steel Alloy(Izmir Institute of Technology, 2015) Karataş, Özgün; Öztürk, Orhan; Selamet, YusufAustenitic stainless steels (SSs) are technologically important alloys and highly resistant to corrosion in a variety of environments. Nevertheless, these materials have a few drawbacks; they are rather soft materials and susceptible to wear. Correspondingly, an improvement of the surface properties is often desirable. Ion beam techniques are widely used to enhance surface properties of these alloys. Surface modification of austenitic SSs by nitrogen ion beams at moderate substrate temperatures near 400 ºC, leads to the formation of a high N content phase. This phase, known as an expanded austenite phase, γN, creates a hard and wear resistant layer on the stainless steel. Additional property of this phase is related to its magnetic structure due to the large amount of nitrogen insertion and corresponding lattice expansion. In the current study, new data corresponding to structural and magnetic nature of the expanded austenite layers on austenitic 316 SS by low-energy, high-flux nitrogen ion implantation are presented. Phase and compositional analyses, surface topography and magnetic features of the nitrogen ion implanted layers were studied by a combination of experimental techniques involving XRD, SEM, AFM, MFM, VSM and MOKE. Nitrogen implantations were performed for 30, 90 and 240 minutes of processing time, at a fixed temperature near 400 °C. Relatively low-energy (0.7 keV) and high-flux (2 mA/cm2) ion beam conditions were carried out during the implantation. Combination of the aforementioned techniques provides strong evidence for the formation of the γN phase with mainly ferromagnetic characteristics. MFM imaging reveals stripe-like domain structures of the nitrogen ion implanted layers. Both VSM and MOKE analyses display hysteresis loops of the layers. Ferromagnetism in the γN layers are manifested by MFM, M and MOKE analyses. Ferromagnetic structure is linked to large lattice expansions 0 due to high nitrogen contents at. . s an interstitial impurity, nitrogen dilates fcc lattice of 316 SS i.e. Fe-Fe distance is increased, which strongly influences the magnetic interactions.Master Thesis Characterization of Ion Implanted Surfaces by Laser Induced Breakdown Spectroscopy, Libs(01. Izmir Institute of Technology, 2008) Örer, Sabiha; Yalçın, ŞerifeLaser Induced Breakdown Spectroscopy, LIBS, is a versatile atomic emission spectrometric technique for the determination of the elemental composition of solids, liquids, gases and aerosols with the need for little or no sample preparation.In this study, an optical LIBS system from its conventional parts was designed, constructed and optimized for spectrochemical analysis of solid materials. Specifically, the 2-D elemental distribution of Ge ions on silicon oxide surfaces, prepared by the method of ion implantation, with differing atomic concentrations between 1016 - 1017 ions/cm2 have been investigated by LIBS. For this purpose a Nd: YAG laser operating at the second harmonic wavelength, 532 nm, was used to create a plasma on the material surfaces. Spatially and temporally resolved atomic emission from the luminous plasma was detected by an Echelle spectroctrograph and Intensified Charged Coupled Device (ICCD) detector combination. Spectral emission intensity from the LIBS measurements has been optimized with respect to time, crater size, ablation depth and laser energy. Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) coupled with Energy Dispersive X-Ray Spectroscopy (EDX) have been utilized to obtain crater depth, morphology and elemental composition of the sample material, respectively. LIBS spectral data revealed the possibility of performing 2-D distribution analysis of Ge ions over the silicon oxide substrate at Ge ion concentrations lower than 0.5% (atomic). LIBS as a fast semi-quantitative analysis method with 50.m lateral and 800 nm depth resolutions has been evaluated. In this wok, elemental analysis of some metal surfaces, such as Al and Cu, was also performed by LIBS.Keywords: LIBS, surface analysis, Ge ion implantation, lateral resolution,Master Thesis Microstructural and Mechanical Characterization of Nitrogen Ion Implanted and Plasma Ion Nitrided Plastic Injection Mould Steel(Izmir Institute of Technology, 2003) Onmuş, Ortaç; Öztürk, OrhanIn this study, high-chromium ferritic plastic injection mould steel (X36CrMo17, similar to AISI-420F) was subjected to plasma nitriding and nitrogen ion beam implantation under various conditions. The effectiveness of conventional plasma nitriding and nitrogen ion beam implantation conditions in improving the tribological properties and mechanical performance was investigated.The experimental results clearly show that plasma nitriding and nitrogen ion beam implantation lead to the development of the various near-surface microstructures and enhanced mechanical properties.Plasma nitriding was performed at a temperature range between 520-540 °C, with a bias voltage of 500 V for 15 to 18 hours under various gas mixtures of N2+H2 in an industrial nitriding facility (micro-pulsed DC). Nitrogen ion beam implantation was carried out with 2x1017 and 1x1018 ion doses with an 85 kV nitrogen ion energy at temperatures 200 a1C. Near-surface phases, compositions, plasma nitrided and nitrogen implanted layer thicknesses and the strength of these layers were studied by a combination of symmetric (0-2.) and grazing incidence x-ray diffraction (XRD and GIXRD), conversion electron and x-ray Mössbauer spectroscopies (CEMS and CXMS), cross-sectional scanning electron microscopy (SEM) and cross-sectional nanohardness measurements. The corrosion behaviour was investigated by a salt spray method and by observation of acid etching during SEM sample preparation. The tribological properties (friction and wear) were examined by a ball-on-disc tribometer.Combined Mössbauer, XRD, and SEM analyses clearly indicate that (Fe,Cr,Mn)-nitrides and CrN are distributed in the top nitrided layers of several micron thickness. The CEMS and CXMS analyses show the nearly complete decomposition of the near surface and deeper crystal structures into pure bcc (Fe), (Fe,Cr,Mn)-nitrides, consisting of Fe3N and Fe4N, and CrN. The XRD, CEMS and CXMS results also show an Fe3C-like carbide phase, (Fe,Cr,Mn)3C, in the nitrided layers, whose presence is attributed to C segregation to the near-surface region and to extra carbon being present in the nitriding system. The nitriding conditions with the gas composition N2/H2.1 produces the thickest nitrided layer (about 135 .m) with an excellent resistance to corrosion. The nanohardness measurements indicate that the cross sectional hardness-depth profiles under all nitriding conditions is found to be plateau-shaped, and the nitrided layer surface hardness values are found to be increased by a factor of about three in comparison to that of the substrate material. This study also showed that the hardening effect in plasma nitrided specimens was due to a fine and homogeneous chromium nitride precipitation. The wear analysis results showed that the nitrided layers have reduced friction coefficient values (20 to 25%) and possess excellent wear resistance in comparison to that of the bulk material.It was also found that nitrogen ion implantation into plastic injection mould steel produces N content rich layers (less than 0.1 .m thick) with enhanced wear and corrosion properties. The surface nanohardness measurements of the low and high dose implanted specimens indicate that the hardness values increase by factors of about 1.4 and 1.6, respectively, compared to the substrate material. The salt spray corrosion analysis (2% NaCl solution in distilled water) experiments showed enhanced corrosion behaviour for the N implanted layers, and that nitrogen ion implantation is a viable method for improving corrosion resistance of plastic injection mould steel.Combined Mössbauer and XRD data reveal that the N implanted layers consist of nitride phase, (Fe,Cr,Mn)2+xN, with both magnetic (x-1) and paramagnetic (x-0) characteristics. Based on the CEMS results, the N implanted layer thicknesses are found to be - 40 and 65 nm for the low dose (2x1017 ions/cm2) and high dose (1x1018 ions/cm2) dose N implanted specimens, respectively.Master Thesis Characterization of Ultra High Molecular Weight Polyethylene (uhmwpe) Modified by Metal-Gas Hybrid Ion Implantation Technique(Izmir Institute of Technology, 2006) Urkaç Sokullu, Şadiye Emel; Tıhmınlıoğlu, FundaThe aim of this work was the characterization of the surface modified Ultra High Molecular Weight Polyethylene (UHMWPE) in order to understand the effect of ion implantation technique on the properties of this material. The samples were Ag and Ag+N hybrid ion implanted by using MEVVA (Metal Vapour Vacuum Arc) ion implantation technique with a fluence of 10 17 ions/cm2, extraction voltage of 30 kV.Untreated and surface treated samples were investigated by Stopping andRange of Ions into Matters (SRIM), Rutherford Back Scattered Analysis (RBS), Attenuated Total Reflection - Fourier Transform Infrared (ATR/FT-IR) Spectroscopy, Raman Spectroscopy, Optical Absorption Photospectroscopy (OAP), Thermo Gravimetry Analysis (TGA), Differential Scanning Calorimetry (DSC), X-Ray Diffraction (XRD) Analysis, Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), Optical Microscopy (OM), Micro-hardness and Contact Angle Measurement. The results of RBS analysis show that Ag ions were detected up to 32 +15 nm after Ag implantation, and 42 +15 nm after Ag+N implantation., underneath the surface. ATR- FTIR chemical characterization analyses results indicated that the effect of implantation on UHMWPE surfaces caused dehydrogenation of polymer with an increase of C.C bond formation which results in enriching the crosslinking carbon atoms on the surface. Optical Absorption Photospectroscopy and Raman spectrum suggests that the chemical structure of UHMWPE has changed after implantation. The characterization results showed that the ion bombardment induced an increase in the % crystallinity, onset and termination degradation temperatures of UHMWPE obtained by thermal analyses, an increase in hardness, and surface wettability and a decrease in roughness of the polymer. The surface topography results can be attributed to the implantation inducing surface roughness decreasing due to the better wettability properties of surfaces obtained after implantation. In conclusion, this study has shown that ion implantation represents a powerful tool on modifying key properties on UHMWPE surfaces.Master Thesis Biocompatibility and Microstructural Characterization of Pvd Coated and Nitrogen Implanted Co-Cr Alloy(Izmir Institute of Technology, 2004) Türkan, Uğur; Öztürk, OrhanIn this study, the effectiveness of nitrogen ion implanted and TiN coated layers on CoCrMo alloy (ISO 5832-12) in preventing metal ion release during in vitro exposure of these layers to simulated body fluid (SBF) was investigated. The experimental results clearly show higher levels of cobalt ion release from nitrogen implanted CoCrMo material surfaces into simulated body fluid as compared to the as-polished CoCrMo alloy. The results clearly indicate that nitrogen ion implantation used for modification of fcc CoCrMo alloy surfaces lead to the development of various near surface microstructures. Nitrogen ion implantation was carried out at 60 and 30 keV ion energies with the corresponding current densities of 0.1 and 0.2 mA/cm2, respectively, for the substrate temperatures of 100, 200 and 400 °C and implantation time of 30 minutes. Near surface crystal structures and phases, nitrogen ion implanted and TiN coated layer thicknesses were characterized by a combination of symmetric (.-2.) and grazing incidence x-ray diffraction (XRD and GIXRD) and cross-sectional scanning electron microscopy (SEM). Metal ion release into the simulated body fluid was analyzed by atomic absorption spectrometry (AAS) and inductively coupled plasma optical emission spectrometry (ICP-OES). The experimental XRD results clearly show the formation of a metastable, fcc, high-N phase (.N) in mainly fcc CoCrMo alloy for the ion beam conditions at 400 °C. The lower implantation temperatures, 100 and 200 °C, for both 60 and 30 keV ion energies, result in a nitride phase, (Co, Cr, Mo)2+xN. The cross sectional SEM results for the specimens implanted at the 60 and 30 keV ion energies at 400 °C reveal quite clearly the uniform nature of the .N layers. The .N layer thicknesses, based on the SEM data, were found to be 450 and 540 nm for the 60 and 30 keV implanted specimens, while the (Co, Cr, Mo)2+xN nitride layer has a thickness range from 150 to 250 nm for the 60 and 30 keV at 100 and 200 °C implantation conditions. The SEM results also indicate that the (Co, Cr, Mo)2+xN nitride and .N phase layers on the CoCrMo alloys have high etch resistance suggesting enhanced corrosion resistance for the N implanted specimens compared to the substrate material. The XRD and SEM results for the TiN coated (via PVD) specimens show that the fcc TiN coatings exhibit (111) preferred orientation and have a coating thickness of . 3 µm with a columnar type of growth mode. The experimental AAS results show that in vitro exposure of the N implanted layers result in higher levels of cobalt ion release into the SBF than the as-polished substrate CoCrMo alloy. This was attributed to the rougher surfaces of the N implanted specimens compared to that of the substrate material (i.e, rougher surface implying a larger area is available for metal ion release). It was also found that the specimens implanted at the lower substrate temperatures of 100 and 200 °C have lower levels of Co ion release compared to those specimens implanted at the substrate temperature of 400 °C. The limited dissolution of cobalt, in this case, was explained by the stronger bonds of metal-N in the nitride phase than those of .N phase. Furthermore, the AAS data indicate higher cobalt ion release rate for the N implanted specimens compared to the substrate alloy and suggest transport (diffusion) controlled dissolution reaction mechanism. The AAS results show no cobalt ions are released from the TiN coated specimens (i.e, the release levels were below the analytical detection limit of the AAS apparatus). This indicates that the TiN coated layer can be an effective barrier for reducing the metal ion release from the substrate alloy. The SEM/EDX study of the surface morphologies of the N implanted, TiN coated and as-polished CoCrMo alloy test specimens after the static immersion test clearly indicate calcium phosphate formation on the as-polished alloy, while there was almost no phosphate precipitates on the surface of N implanted and TiN coated specimens. While the experimental results show higher levels of cobalt ion release for the N implanted specimens compared to the substrate material, the overall release levels are found to be below toxic levels for the human body.