Browsing by Subject "Chemical compositions"

Now showing 1 - 11 of 11

Open Access
Bias in bonding behavior among boron, carbon, and nitrogen atoms in ion implanted a-BN, a-BC, and diamond like carbon films
(2011) Genisel, M. F.; Uddin, M. N.; Say, Z.; Kulakci, M.; Turan, R.; Gulseren, O.; Bengu, E.
In this study, we implanted Nþ and Nþ 2 ions into sputter deposited amorphous boron carbide (a-BC) and diamond like carbon (DLC) thin films in an effort to understand the chemical bonding involved and investigate possible phase separation routes in boron carbon nitride (BCN) films. In addition, we investigated the effect of implanted Cþ ions in sputter deposited amorphous boron nitride (a-BN) films. Implanted ion energies for all ion species were set at 40 KeV. Implanted films were then analyzed using x-ray photoelectron spectroscopy (XPS). The changes in the chemical composition and bonding chemistry due to ion-implantation were examined at different depths of the films using sequential ion-beam etching and high resolution XPS analysis cycles. A comparative analysis has been made with the results from sputter deposited BCN films suggesting that implanted nitrogen and carbon atoms behaved very similar to nitrogen and carbon atoms in sputter deposited BCN films. We found that implanted nitrogen atoms would prefer bonding to carbon atoms in the films only if there is no boron atom in the vicinity or after all available boron atoms have been saturated with nitrogen. Implanted carbon atoms also preferred to either bond with available boron atoms or, more likely bonded with other implanted carbon atoms. These results were also supported by ab-initio density functional theory calculations which indicated that carbon-carbon bonds were energetically preferable to carbon-boron and carbon-nitrogen bonds.
Open Access
Compositional homogeneity in a medical-grade stainless steel sintered with a Mn-Si additive
(Elsevier, 2012-06-09) Salahinejad, E.; Hadianfard, M.J.; Ghaffari, M.; Mashhadi, S.B.; Okyay, Ali Kemal
In this paper, chemical composition uniformity in amorphous/ nanocrystallization medical-grade stainless steel (ASTM ID: F2581) sintered with a Mn-Si additive was studied via scanning electron microscopy, energy dispersive X-ray spectroscopy, and transmission electron microscopy. The results show that as a result of sintering at 1000 °C, no dissociation of Mn-Si additive particles embedded in the stainless steel matrix occurs. In contrast, sintering at 1050 °C develops a relatively homogeneous microstructure from the chemical composition viewpoint. The aforementioned phenomena are explained by liquation of the Mn-Si eutectic additive, thereby wetting of the main powder particles, penetrating into the particle contacts and pore zones via capillary forces, and providing a path of high diffusivity.
Open Access
Effect of milling time on the structure, micro-hardness, and thermal behavior of amorphous/nanocrystalline TiNiCu shape memory alloys developed by mechanical alloying
(Elsevier Ltd, 2014) Alijani F.; Amini, R.; Ghaffari, M.; Alizadeh, M.; Okyay, Ali Kemal
In the present paper, the effect of milling process on the chemical composition, structure, microhardness, and thermal behavior of Ti-41Ni-9Cu compounds developed by mechanical alloying was evaluated. The structural characteristic of the alloyed powders was evaluated by X-ray diffraction (XRD). The chemical composition homogeneity and the powder morphology and size were studied by scanning electron microscopy coupled with electron dispersive X-ray spectroscopy. Moreover, the Vickers micro-indentation hardness of the powders milled for different milling times was determined. Finally, the thermal behavior of the as-milled powders was studied by differential scanning calorimetery. According to the results, at the initial stages of milling (typically 0-12. h), the structure consisted of a Ni solid solution and amorphous phase, and by the milling evolution, nanocrystalline martensite (B19') and austenite (B2) phases were initially formed from the initial materials and then from the amorphous phase. It was found that by the milling development, the composition uniformity is increased, the inter-layer thickness is reduced, and the powders microhardness is initially increased, then reduced, and afterward re-increased. It was also realized that the thermal behavior of the alloyed powders and the structure of heat treated samples is considerably affected by the milling time.
Open Access
Fabrication of polymer micro needles for transdermal drug delivery system using DLP based projection stereo-lithography
(Elsevier, 2016) Ali, Z.; Türeyen, E. Buğra; Karpat, Yiğit; Çakmakcı, Melih
Fabrication of micro needles, which reduce pain during insertion and lessen tissue injury, has recently attracted great interest. Different manufacturing systems have been utilized for the advancement of micro needles such as two-photon photo polymerization, bulk lithography, droplet-borne air blowing and injection molding [1]. This paper proposes a micro fabrication process for polymer micro needles, using DLP based projection-based stereo lithography that is capable of fabricating micro-needles using biocompatible polymers. The fabrication in the experimental setup is performed with continuous movement of the platform in the vertical direction hence good surface quality is obtained. The influence of polymerization time, light intensity of DLP projector and chemical composition of the resins on the production speed and the geometrical accuracy of the micro needles have been studied. The length and the tip diameter of the micro needle are shown to be controlled through these factors. The length and tip diameter of the fabricated micro needles were observed using SEM and optical microscope and measured to be around 520 μm and 40 μm, respectively. The results indicate that polymer micro needles with appropriate geometry can be fabricated using this technique. © 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license.
Open Access
Increasing Ti-6Al-4V brazed joint strength equal to the base metal by Ti and Zr amorphous filler alloys
(2012) Ganjeh, E.; Sarkhosh H.; Bajgholi, M.E.; Khorsand H.; Ghaffari, M.
Microstructural features developed along with mechanical properties in furnace brazing of Ti-6Al-4V alloy using STEMET 1228 (Ti-26.8Zr-13Ni-13.9Cu, wt.%) and STEMET 1406 (Zr-9.7Ti-12.4Ni-11.2Cu, wt.%) amorphous filler alloys. Brazing temperatures employed were 900-950 °C for the titanium-based filler and 900-990 °C for the zirconium-based filler alloys, respectively. The brazing time durations were 600, 1200 and 1800 s. The brazed joints were evaluated by ultrasonic test, and their microstructures and phase constitutions analyzed by metallography, scanning electron microscopy and X-ray diffraction analysis. Since microstructural evolution across the furnace brazed joints primarily depends on their alloying elements such as Cu, Ni and Zr along the joint. Accordingly, existence of Zr 2Cu, Ti 2Cu and (Ti,Zr) 2Ni intermetallic compounds was identified in the brazed joints. The chemical composition of segregation region in the center of brazed joints was identical to virgin filler alloy content which greatly deteriorated the shear strength of the joints. Adequate brazing time (1800 s) and/or temperature (950 °C for Ti-based and 990 °C for Zr-based) resulted in an acicular Widmanstätten microstructure throughout the entire joint section due to eutectoid reaction. This microstructure increased the shear strength of the brazed joints up to the Ti-6Al-4V tensile strength level. Consequently, Ti-6Al-4V can be furnace brazed by Ti and Zr base foils produced excellent joint strengths. © 2012 Elsevier Inc. All rights reserved.
Open Access
Microstructural characterization of medical-grade stainless steel powders prepared by mechanical alloying and subsequent annealing
(Elsevier, 2013) Salahinejad, E.; Hadianfard, M. J.; Ghaffari, M.; Amini, R.; Mashhadi, S. B.; Okyay, Ali Kemal
The harmful effect of nickel ions released from conventional stainless steel implants has provided a high level of motivation for the further development of nickel-free stainless steels. In this paper, the microstructure of medical-grade nickel-free stainless steel powders, with the chemical composition of ASTM F2581, is studied during mechanical alloying and subsequent annealing. Rietveld X-ray diffraction and transmission electron microscopy evaluations reflect nanocrystallization, austenitization and amorphization of the powders due to mechanical activation. It is also realized that annealing of the as-milled powder can develop a single austenitic structure with nanometric crystallite sizes, implying a considerable inherent resistance to grain growth. This study demonstrates the merit of mechanical alloying and subsequent annealing in the development of nanostructured medical-grade stainless steels.
Open Access
Phase transformation during mechano-synthesis of nanocrystalline/amorphous Fe–32Mn–6Si alloys
(Elsevier, 2013) Amini, R.; Shamsipoor, A.; Ghaffari, M.; Alizadeh, M.; Okyay, Ali Kemal
Mechano-synthesis of Fe-32Mn-6Si alloy by mechanical alloying of the elemental powder mixtures was evaluated by running the ball milling process under an inert argon gas atmosphere. In order to characterize the as-milled powders, powder sampling was performed at predetermined intervals from 0.5 to 192 h. X-ray florescence analyzer, X-ray diffraction, scanning electron microscope, and high resolution transmission electron microscope were utilized to investigate the chemical composition, structural evolution, morphological changes, and microstructure of the as-milled powders, respectively. According to the results, the nanocrystalline Fe-Mn-Si alloys were completely synthesized after 48 h of milling. Moreover, the formation of a considerable amount of amorphous phase during the milling process was indicated by quantitative X-ray diffraction analysis as well as high resolution transmission electron microscopy image and its selected area diffraction pattern. It was found that the α-to-γ and subsequently the amorphous-to-crystalline (especially martensite) phase transformation occurred by milling development.
Open Access
A photoelectron spectroscopic investigation of conducting polypyrolle-polyamide composite film
(Elsevier, 1995-04) Süzer, Şefik; Toppare, L.; Allen, G. C.; Hallam, K. R.
X-ray photoelectron spectrum of the electrochemically prepared polypyrrole and polypyrrole-polyamide composite films exhibit an additional strong high binding energy peak at 402.0 eV corresponding to N+ moieties. Intensity of this peak is significantly reduced upon electrochemical reduction. Atomic concentrations derived from the observed N+ and F (stemming from the dopant BF4-) peaks reveal a slightly higher cation/anion ratio for this composite and suggest that the composite has a different chemical composition than the corresponding polymers. © 1995 Elsevier Science B.V.
Open Access
Self-limiting low-temperature growth of crystalline AlN thin films by plasma-enhanced atomic layer deposition
(2012) Ozgit, C.; Donmez I.; Alevli, M.; Bıyıklı, Necmi
We report on the self-limiting growth and characterization of aluminum nitride (AlN) thin films. AlN films were deposited by plasma-enhanced atomic layer deposition on various substrates using trimethylaluminum (TMA) and ammonia (NH 3). At 185 °C, deposition rate saturated for TMA and NH 3 doses starting from 0.05 and 40 s, respectively. Saturative surface reactions between TMA and NH 3 resulted in a constant growth rate of ∼ 0.86 Å/cycle from 100 to 200 °C. Within this temperature range, film thickness increased linearly with the number of deposition cycles. At higher temperatures (≤ 225 °C) deposition rate increased with temperature. Chemical composition and bonding states of the films deposited at 185 °C were investigated by X-ray photoelectron spectroscopy. High resolution Al 2p and N 1s spectra confirmed the presence of AlN with peaks located at 73.02 and 396.07 eV, respectively. Films deposited at 185 °C were polycrystalline with a hexagonal wurtzite structure regardless of the substrate selection as determined by grazing incidence X-ray diffraction. High-resolution transmission electron microscopy images of the AlN thin films deposited on Si (100) and glass substrates revealed a microstructure consisting of nanometer sized crystallites. Films exhibited an optical band edge at ∼ 5.8 eV and an optical transmittance of > 95% in the visible region of the spectrum. © 2011 Elsevier B.V. All rights reserved.
Open Access
Structural, microstructural and thermal properties of lead-free bismuth-sodium-barium-titanate piezoceramics synthesized by mechanical alloying
(2013) Amini, R.; Ghazanfari, M.R.; Alizadeh, M.; Ardakani H.A.; Ghaffari, M.
Bismuth-sodium-barium-titanate piezoceramics with a composition of (Bi 0.5Na0.5)0.94Ba0.06TiO3 (BNBT) were prepared by mechanical alloying (MA). Structural analysis and phase identification were performed by X-ray diffraction (XRD). Microstructural studies and chemical composition homogeneity were performed by scanning electron microscope (SEM) coupled with energy dispersive X-ray analysis (EDX). Furthermore, thermal properties of the as-milled powders were evaluated by thermogravimetry/differential thermal analysis (TG/DTA). During the initial milling, the constituents were transformed to the perovskite, pyrochlore, and BNT phases; in addition, partial amorphization of the structure appeared during the milling cycle. As MA progressed, transformation of pyrochlore-to-perovskite and crystallization of the amorphous phase occurred and also, the BNBT phase was significantly developed. It was found that the MA process has the ability to synthesize the BNBT powders with a submicron particle size, regular morphology, and uniform elemental distribution. © 2012 Elsevier Ltd.
Open Access
Substrate temperature influence on the properties of GaN thin films grown by hollow-cathode plasma-assisted atomic layer deposition
(AIP Publishing LLC, 2016-02) Alevli, M.; Gungor, N.; Haider A.; Kizir S.; Leghari, S. A.; Bıyıklı, Necmi
Gallium nitride films were grown by hollow cathode plasma-assisted atomic layer deposition using triethylgallium and N2/H2 plasma. An optimized recipe for GaN film was developed, and the effect of substrate temperature was studied in both self-limiting growth window and thermal decomposition-limited growth region. With increased substrate temperature, film crystallinity improved, and the optical band edge decreased from 3.60 to 3.52 eV. The refractive index and reflectivity in Reststrahlen band increased with the substrate temperature. Compressive strain is observed for both samples, and the surface roughness is observed to increase with the substrate temperature. Despite these temperature dependent material properties, the chemical composition, E1(TO), phonon position, and crystalline phases present in the GaN film were relatively independent from growth temperature.