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Publication Metadata 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/ACutting 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.Publication Metadata only Assessment of impressed/moulded ceramic wares excavated during the 2018-2019 seasons at the Iznik Tile Kilns Excavation and analysis results with a pXRF instrument on selected samples(İstanbul Üniversitesi Yayınevi, 2020) Arlı, Vesile Belgin Demirsar; Kaya, Şennur; Franci, Gülsu Şimşek; Researcher; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); N/AIznik reached the peak of its ceramic and tile production between the 14th- and 17th- centuries. Recent findings at the Iznik Tile Kilns Excavation carried out in the BHD coded excavation area in Iznik District center revealed that ceramics had been produced there using an impressed/moulded technique , which was widely used in non-Anatolian Islamic ceramic art. These types of ceramics, which are thought to have been intensively produced after Iznik passed into Ottoman administration in 1331, were classified into two main groups in terms of their forms and decorations. Moreover, during the 2019 excavation season, characterization studies were carried out using a portable XRF (pXRF) instrument on seven selected samples in order to determine the body, slip and glaze composition. The results showed that the sample without a slip contained calcium-rich clay (high calcium and high alumina). The analyses of the molding materials confirmed earlier studies which had determined that the paste used (the third type of paste) had been calcareous or calcium-rich clay. Moreover, the sample with slip contains a greater amount of quartz (55.4 wt%) than the sample without slip (44.2 wt%). of interest is that the sherd which is covered with a turquoise glaze contains 24.6 wt% lead-oxide (PbO) and 6 wt% tin oxide (SnO2). This glaze composition may indicate that the artifact was produced in the earlier period of Iznik production, namely at the end of the 15th century. Another glazed mold from among the samples analysed does not contain any tin oxide and has a higher amount of PbO which indicates a later production date (17th- century). The pXRF measurement results suggest that the mold may have been produced in an earlier period, and then glazed later for decorative and/or technical purposes. / 14-17. yüzyıllar arasında çini ve seramik üretiminde zirve yapan İznik’te, Anadoludışı İslam seramik sanatında yaygın kullanılan baskı/kalıba baskı tekniğindeseramiklerin de üretildiği, İznik İlçe merkezinde BHD kodlu kazı alanındayürütülen İznik Çini Fırınları Kazısı’nda ele geçen bulgularla netleştirilmiştir.İznik’in Osmanlı idaresine geçtiği 1331 yılından sonra yoğun olarak üretildiğidüşünülen bu seramikler, form ve bezeme açısından iki temel grupta toplanmıştır.Diğer yandan 2019 kazı sezonunda, bu tip seramiklerin karakterizasyonlarınıntespiti amacıyla seçilen yedi örnek üzerinde pXRF (Taşınabilir X-ışınlarıflüoresansı) cihazı ile hamur, astar ve sır bileşimlerine dair ölçümler yapılmıştır.Yapılan ölçüm sonuçlarına göre astarı olmayan örnekte hamur bileşiminin kilve kalsiyumca zengin olduğu anlaşılmıştır. Kalıp malzemeleri üzerinde yapılananalizlerle, kireçli veya kireç katkılı kil içeren hamur karışımının (3. tip) kullanıldığıdoğrulanmıştır. Astarlı örnekte ise kuvars miktarı (% ağ. 55.4), astarsız örneğegöre (% ağ. 44.2) daha fazladır. Firuze sırlı örneğin sırında %24.6 kurşun oksit(PbO) ve %6 kalay oksit (SnO2) tespit edilmiştir. Bu ölçümden bu örneğin erkendönem üretimi (15. yüzyıl sonu) olabileceği düşünülmektedir. Diğer sırlı kalıpörneğinin ölçüm sonucu ise (yüksek kurşun oksit içeren kalaysız sır), kalıbınmuhtemelen geç dönem (17. yüzyıl) üretimi veya önceden sırsız olarak kullanılankalıp malzemesinin sonradan dekoratif veya işlevsel olarak sırlanmış olabileceğinidüşündürür.Publication Metadata 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/ABoron 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.Publication Metadata 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; 150017In 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.Publication Metadata 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/AIn 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.Publication Metadata only Effects of different milling conditions on the properties of lanthanum hexaboride nanoparticles and their sintered bodies(Elsevier, 2019) Ağaoğulları, Duygu; Akçamlı, Nazlı; Duman, İsmail; Oveçoğlu, M. Lutfi; Department of Chemistry; Balcı, Özge; Researcher; Department of Chemistry; College of Sciences; 295531Publication Metadata 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/AIn 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.Publication Metadata only Effects of milling parameters on the microstructural and thermal properties of nanocrystalline lanthanum hexaboride powders(Australian Ceramic Society, 2018) Agaogullari, Duygu; Ovecoglu, M. Lutfi; Duman, Ismail; Department of Chemistry; Balcı, Özge; Researcher; Department of Chemistry; College of Sciences; 295531This study reports the effects of some milling parameters (duration, ball-to-powder weight ratio (BPR), process control agent (PCA)) on the fabrication of nanocrystalline LaB6 powders via a combined process of mechanochemical synthesis (MCS) and acid leaching, starting from La2O3-B2O3-Mg powder blends. MCS was carried out in a high-energy ball mill (SPEX (TM) 8000D Mixer/Mill, at 1200 rpm) using hardened steel vial and balls under Ar atmosphere. As-synthesized products were leached out with 4 M HCl from unwanted MgO phase and probable Fe impurities. When a BPR of 18:1 was used, 5 h of MCS and leaching yielded LaB6 powders with an average particle size of 100 nm, containing a very small amount of FeB49 phase. Pure LaB6 powders were obtained with an average particle size of 53 nm after 12 h of MCS of the 0.5 wt% PCA added La2O3-B2O3-Mg powder blends with a BPR of 10:1 and after leaching.Publication Metadata only Effects of solvent on TEOS hydrolysis kinetics and silica particle size under basic conditions(Springer, 2013) Malay, Ozge; Menceloglu, Yusuf Z.; Department of Chemistry; Yılgör, İskender; Faculty Member; Department of Chemistry; College of Sciences; 24181In-situ liquid-state Si-29 nuclear magnetic resonance was used to investigate the temporal concentration changes during ammonia-catalyzed initial hydrolysis of tetraethyl orthosilicate in different solvents (methanol, ethanol, n-propanol, iso-propanol and n-butanol). Dynamic light scattering was employed to monitor simultaneous changes in the average diameter of silica particles and atomic force microscopy was used to image the particles within this time frame. Solvent effects on initial hydrolysis kinetics, size and polydispersity of silica particles were discussed in terms of polarity and hydrogen-bonding characteristics of the solvents. Initial hydrolysis rate and average particle size increased with molecular weight of the primary alcohols. In comparison, lower hydrolysis rate and larger particle size were obtained in the secondary alcohol. Exceptionally, reactions in methanol exhibited the highest hydrolysis rate and the smallest particle size. Ultimately, our investigation elaborated, and hence confirmed, the influences of chemical structure and nature of the solvent on the formation and growth of the silica particles under applied conditions.Publication Metadata only Fabrication and gas sensing properties of C-doped and un-doped TiO2 nanotubes(Elsevier, 2014) Sennik, Erdem; Işık, Müge; Ahsen, Ali Şems; Öztürk, Osman; Öztürk, Zafer Ziya; Department of Electrical and Electronics Engineering; Kılınç, Necmettin; Researcher; Department of Electrical and Electronics Engineering; College of Engineering; 59959In this work, un-doped and carbon (C) doped TiO2 nanotubes were fabricated and their hydrogen sensing properties were investigated. A Ti foil was anodized in an aqueous hydrofluoric acid (H:F) electrolyte (0.5 wt%) at room temperature to form TiO2 nanotube arrays. C-doped TiO2 nanotubes were obtained through two methods; a chemical process and thermal acetylene (C2H2) treatment. In the chemical method, a Ti foil was anodized 'in-situ' in aqueous solution of 0.5 wt% polyvinyl alcohol (PVA)+0.5 wt% HF. In the heat treatment method, a Ti foil was anodized in an aqueous (HF) electrolyte (0.5 wt%) to obtain TiO2 nanotubes, and then C-doped TiO2 nanotubes were obtained by heating as-prepared nanotubes at 500 degrees C in a quartz tube under a continuous N-2 and C2H2 flux (1:1). The obtained un-doped and C-doped TiO2 nanotubes were characterized by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and X-ray photoelectron spectroscopy (XPS). The H-2 sensing properties of the nanotubes exposed to 5000 ppm H-2 were investigated at 100 degrees C. C-doped TiO2 nanotubes showed a lower response to H-2 than the undoped TiO2 nanotubes.