Research Outputs

Permanent URI for this communityhttps://hdl.handle.net/20.500.14288/2

Browse

Filters

2010 - 2019142020 - 20228

Advanced Search

Filter by

Settings

Department: search.filters.department.N/ASubject: search.filters.subject.Ceramics

Search Results

Now showing 1 - 10 of 22
  • Placeholder
    PublicationMetadata only
    A numerical approach to the heat transfer in monolithic and SiC reinforced HfB2, ZrB2 and TiB2 ceramic cutting tools
    (Elsevier Sci Ltd, 2019) Moghanlou, Farhad Sadegh; Vajdi, Mohammad; Sha, Jianjun; Shokouhimehr, Mohammadreza; Asl, Mehdi Shahedi; N/A; Motallebzadeh, Amir; Researcher; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); N/A; N/A
    Cutting tools are widely used in industry and must be hard enough for machining processes, which should work appropriately at low temperatures to improve cutting speed and productivity. In this research, a numerical method was employed to calculate the temperature distribution in the cutting tools made of different diborides. Monolithic and SiC reinforced HfB2, ZrB2 and TiB2 ceramics were selected for investigation and comparison studies. In this regard, 3-dimensional heat conduction equation was solved in a cutting tool with radiative, convective and heat flux boundary conditions by finite element method using COMSOL Multiphysics. This study clarifies that the maximum temperature in the tools made of ZrB2 and TiB2 among the monolithic ceramics is lower than that of HfB2. Moreover, the temperature variation slope versus time is the highest in HfB2. All composite materials reinforced with SiC showed lower maximum temperature than the monolithic ones. The thermal performance of TiB2-SiC and ZrB2-SiC composites was acquired to be better than that of the other investigated materials. The dominant heat transfer mechanism in the cutting tools was conduction.
  • Placeholder
    PublicationMetadata only
    Boron mining and enrichment waste: a promising raw material for porcelain tile production
    (Wiley, 2020) N/A; N/A; N/A; Karadağlı, Emirhan; Çiçek, Buğra; Researcher; Researcher; Koç University Boron and Advanced Materials Application and Research Center (KUBAM) / Koç Üniversitesi Bor ve İleri Malzemeler Uygulama ve Araştırma Merkezi (KUBAM); Koç University Boron and Advanced Materials Application and Research Center (KUBAM) / Koç Üniversitesi Bor ve İleri Malzemeler Uygulama ve Araştırma Merkezi (KUBAM); N/A; N/A; N/A; N/A
    Boron mining and enrichment waste (BW) from boric acid (H3BO3) production is a by-product of the boron industry. BW exhibits B2O3 contents of 16-31 wt%, and therefore, could be used to effectively lower the sintering temperature of ceramics without increasing their thermal expansion coefficient. Herein, we introduced 3-10 wt% of BW to a formulation used for commercial porcelain tile production, and achieved a sintering temperature decrease of 38 degrees C (to 1195 degrees C). The resulting porcelain tiles exhibited a strength of 44.80 MPa and water absorption percentage of 0.01%, and therefore, met TS ISO EN 10545 requirements. Thus, this study paves the way for the use and valorization of BW in the production of porcelain tiles and could inspire the search for other opportunities to utilize BW in ceramic production.
  • Placeholder
    PublicationMetadata only
    Effect of yttrium doping on structural and electrical properties of Bi2Sr1.9Ca0.1-xYxCu2O7+delta (Bi-2202) cuprate ceramics
    (Elsevier, 2016) Boudjadja, Yazid; Amira, Abderrezak; Saoudel, Abdelmalek; Mahamdioua, Nabil; Varilci, Ahmet; Terzioğlu, Cabir; N/A; Polat-Altıntaş, Sevgi; Researcher; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); N/A; 150017
    In this work, we report on the effect of Y3+ doping on structural, mechanical and electrical properties of Bi-2202 phase. Samples of Bi2Sr1.9Ca0.1-xYxCu2O7+delta with x=0, 0.025, 0.05, 0.075 and 0.10 are elaborated in air by conventional solid state reaction and characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM) combined with EDS spectroscopy, density, Vickers microhardness and resistivity measurements. A good correlation between the variations of the bulk density and the Vickers microhardness with doping is obtained. The SEM photograph shows that the samples are composed of grains with a flat shape that characterizes the Bi-based cuprates. Quantitative EDS analysis confirms the reduction of Ca content and the increase of Y content when xis increased. The variation of resistivity with temperature shows that only samples with x=0, 0.025 and 0.05 present an onset transition to the superconducting state. The higher onset transition temperature is obtained for x= 0.025 and is about 93.62 K. The transition is wide and is realized in two steps confirming then the presence of the low T-c Bi-2201 phase in the samples. For x=0.075 and 0.10, a transition to a semiconducting state is seen at low temperatures. Some physical parameters are extracted from these curves and discussed.
  • Placeholder
    PublicationMetadata only
    Effects of ceramic-based CrN, TiN, and AlCrN interlayers on wear and friction behaviors of AlTiSiN+TiSiN PVD coatings
    (Elsevier Sci Ltd, 2021) Ozkan, Dogus; Yilmaz, M. Alper; Szala, Miroslaw; Turkuz, Cenk; Chocyk, Dariusz; Tunc, Cihan; Goz, Onur; Walczak, Mariusz; Pasierbiewicz, Kamil; N/A; Yağcı, Mustafa Barış; Researcher;  Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); N/A; N/A
    In this study, the wear and friction behavior of cathodic arc physical vapor deposited AlTiSiN+TiSiN coatings on H13 tool steels were investigated by using CrN, TiN and AlCrN interlayers with tribometer tests both under unlubricated and boundary lubricated conditions. 6 mm alumina balls were used as counter surfaces to test ceramic hard coatings. Surface coatings were characterized through nanoindentation, scanning electron microscopy coupled with an energy-dispersive X-ray spectrometer (SEM/EDXS), optical profilometry, and atomic force microscopy (AFM) techniques. The results showed that especially AlTiSiN+TiSiN coating with TiN interlayer resulted in a much more enhanced tribological performance of the tool steels at both unlubricated and the boundary lubricated conditions even at elevated contact pressures.
  • Placeholder
    PublicationMetadata only
    Effects of graphite nano-flakes on thermal and microstructural properties of TiB2–SiC composites
    (Elsevier Sci Ltd, 2020) Moghanlou, Farhad Sadegh; Nekahi, Sahar; Vajdi, Mohammad; Ahmadi, Zohre; Shokouhimehr, Ali; Shokouhimehr, Mohammadreza; Jafargholinejad, Shapour; Asl, Mehdi Shahedi; N/A; Motallebzadeh, Amir; Researcher; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); N/A; N/A
    In the last decades, the production of ultra-high temperature composites with improved thermo-mechanical properties has attracted much attention. This study focuses on the effect of graphite nano-flakes addition on the microstructure, densification, and thermal characteristics of TiB2-25 vol% SiC composite. The samples were manufactured through spark plasma sintering process under the sintering conditions of 1800 degrees C/7 min/40 MPa. Scanning electron microscopy images demonstrated a homogenous dispersion of graphite flakes within the TiB2-SiC composite causing a betterment in the densification process. The thermal diffusivity of the specimens was gained via the laser flash technique. The addition of graphite nano-flakes as a dopant in TiB2-SiC did not change the thermal diffusivity. Consequently, the remarkable thermal conductivity of TiB2-SiC remained intact. It seems that the finer grains and more interfaces obstruct the heat flow in TiB2-SiC-graphite composites. Adding a small amount of graphite nano-flakes enhances the densification of the mentioned composite by preventing the grain growth.
  • Placeholder
    PublicationMetadata only
    Halloysite clay nanotube in regenerative medicine for tissue and wound healing
    (Elsevier, 2022) Same, Saeideh; Samee, Golshan; Navidi, Golnaz; Jahanbani, Yalda; Davaran, Soodabeh; N/A; Nakhjavani, Sattar Akbar; Researcher; Koç University Research Center for Translational Medicine (KUTTAM) / Koç Üniversitesi Translasyonel Tıp Araştırma Merkezi (KUTTAM); N/A; N/A
    The vital necessity of effective treatment at damaged tissue or wound site has resulted in emerging tissue en-gineering and regenerative medicine. Tissue engineering has been introduced as an alternative approach for common available therapeutic strategies in the terms of restoring deformed tissue structure and its functionality via the developing of new bio-scaffold. Designed three-dimensional (3D) scaffolds, alone or in combination with bioactive agents, should be able to stimulate and accelerate the development of engineered tissues and provide proper mechanical support during in-vivo implantation and later regeneration process. To cover it up, a series of new bio-structures with higher mechanical strength were designed through the combination of halloysite nanotubes (HNTs) into 3D bio-polymeric networks. HNTs clay mineral with its unique rod-like structure and distinctive chemical surface features, exhibits excellent biocompatibility and biosafety for doping into regen-erative scaffolds to enhance their mechanical stiffness and biological performance. In this paper, the ongoing procedures of bone/cartilage tissue engineering and wound healing strategies focusing on the designing of 3D-HNTs bio-composites and their multi-cellular interactions in-vitro and in-vivo preclinical studies are reviewed. Furthermore, the challenges and prospects of 3D-HNTs and HNTs-based functional bio-devices for regenerative medicine are also discussed.
  • Placeholder
    PublicationMetadata only
    Heat transfer, thermal stress and failure analyses in a TiB2 gas turbine stator blade
    (Elsevier Sci Ltd, 2019) Vaferi, Kourosh; Nekahi, Sahar; Vajdi, Mohammad; Moghanlou, Farhad Sadegh; Shokouhimehr, Mohammadreza; Sha, Jianjun; Asl, Mehdi Shahedi; N/A; Motallebzadeh, Amir; Researcher; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); N/A; N/A
    Gas turbine stator blades do not experience centrifugal force contrary to the rotor blades; but they are exposed to high-temperature combustion gases causing thermal stresses. In the present work, a series of numerical simulations were carried out to clarify the feasibility of TiB2 utilization as an appropriate material for gas turbine stator blades. The governing equations of heat transfer and solid mechanics were discretized by the finite element method and solved using Comsol Multiphysics software. The boundary conditions were applied, and temperature, displacement and maximum principle stress were obtained. The results showed that using ceramics such as TiB2 instead of conventional alloys can enhance the maximum displacement. Temperature distribution in the blade is more uniform than that of alloys, and consequently, the thermal stresses are reduced. The TiB2 can withstand the applied stresses according to the Coulomb-Mohr theory with a safety factor of 2.4.
  • Placeholder
    PublicationMetadata only
    Numerical analyses of heat transfer and thermal stress in a ZrB2 gas turbine stator blade
    (Elsevier Sci Ltd, 2019) Moghanlou, Farhad Sadegh; Vajdi, Mohammad; Sha, Jianjun; Shokouhimehr, Mohammadreza; Asl, Mehdi Shahedi; N/A; Motallebzadeh, Amir; Researcher; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); N/A; N/A
    Temperature of burned gases is a key parameter in output works of gas turbines. Nevertheless, high temperatures cause metallurgical problems in the turbine parts, specially the blades. Hence, ZrB2 as an ultra-high temperature ceramic (UHTC) with a melting point of 3246 degrees C, considerable high-temperature strength and relatively high thermal conductivity can be a proper candidate for manufacturing of gas turbine parts. In the present work, heat transfer and related thermal stresses of a gas turbine stator blade made of ZrB2 ceramic is investigated numerically by means of Comsol Multiphysics software and the obtained data are compared with M152 (UNS S64152) alloy. The results showed that ZrB2 has more uniform temperature distribution than M152, which is corresponded to its lower thermal gradient. Due to its lower thermal expansion coefficient, ZrB2 showed lower total displacement than M152 which is an important parameter in blade performance. Also, the Von Mises stress of ZrB2 showed higher value than M152.
  • Placeholder
    PublicationMetadata only
    On-site pXRF analysis of body, glaze and colouring agents of the tiles at the excavation site of Iznik kilns
    (Elsevier, 2019) Demirsar Arli, Belgin; Kaya, Sennur; Colomban, Philippe; N/A; Franci, Gülsu Şimşek; Researcher; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); N/A; N/A
    The excavation at Iznik tiles kilns continues as the third period of the field mission. We present here the first on-site, non-invasive analyses performed with portable XRF instrument on twenty-five excavated tiles and two residue materials of the kiln. The shards studied were attributed to the productions from 14th- to 17th-centuries. The comparison was made by the discussion of characteristic elemental ratios selected from the ceramic technology criteria and PCA/Euclidean distances analysis. Three groups of body and glaze technologies were evidenced. We encountered that the amount of tin oxide in the glaze decreased over the centuries. Besides, two different types of fluxes were used in the glaze, some containing only potassium, and the others having potassium and calcium. The decors, which were investigated in this study were blue, turquoise, green, red colours, and black lines. A copper-iron mixture in the red areas was documented, which reflects the use of bornite.
  • Placeholder
    PublicationMetadata only
    Reduction of viscosity of alumina nanopowder aqueous suspensions by the addition of polyalcohols and saccharides
    (Wiley, 2010) Akinc, Mufit; N/A; Department of Chemistry; Department of Chemistry; Department of Chemistry; Yar, Yasemin; Acar, Havva Funda Yağcı; Yurtsever, İsmail Ersin; PhD Student; Faculty Member; Faculty Member; Department of Chemistry; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; N/A; 178902; 7129
    Flow behavior of nanosize alumina suspensions in the presence of polyalcohols was investigated. Viscosity of high solids content (35 vol%) alumina nanopowders was measured at room temperature. It was shown that after the first advancing shear rate branch, viscosity measurements show excellent reproducibility. All the suspensions showed the formation of large clusters, which are broken down as shear rate increases indicating reversible cluster breaking and reforming. Viscosity of suspensions decreases dramatically with up to 10 wt% polyalcohol addition. Only ethylene glycol showed an increase in viscosity indicating no interaction with the particle surface. The addition of polyalcohols is believed to prevent the formation of large and/or strong clusters by modifying the alumina particle surface. The exact nature and quantitative description of viscosity reduction by polyalcohol addition have yet to be established.