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Article Citation - WoS: 11Citation - Scopus: 10Synthesis and Characterization of Hydrothermally Grown Potassium Titanate Nanowires(Korean Assoc Crystal Growth, inc, 2015) Kapusuz, Derya; Kalay, Y. Eren; Park, Jongee; Ozturk, Abdullah; Metallurgical and Materials EngineeringPotassium titanate (KT) nanowires were synthesized by a one-step hydrothermal reaction between TiO2 and aqueous KOH solution. The effects of KOH concentration and reaction time on hydrothermal formation and KT nanowire growth were investigated. The nanowire growth mechanism was elucidated using a combined study of powder X-ray diffraction, and scanning and transmission electron microscopy. The results revealed that hydrothermal growth was initiated by the formation of amorphous-like Ti-O-K sheets in anatase. Increasing hydrothermal reaction time caused the transformation of anatase to Ti-O-K sheets, from which potassium hexa-titanate (K2Ti6O13) nuclei formed and grew to establish one-dimensional morphology through preferential growth along the b-axis. It was revealed that the hydrothermal reactions followed a quite different mechanism than the well-known calcination route. Potassium tetra-titanate (K2Ti4O9) crystals formed in the amorphous region using the hexa-titanate phase as a nucleation site for heterogeneous crystallization. Increasing the KOH concentration in the solution accelerated the hydrothermal reaction rate.Article Citation - WoS: 3Citation - Scopus: 4Friction and Wear Behavior of Selected Dental Ceramics(World Scientific Publ Co Pte Ltd, 2009) Park, Jongee; Pekkan, Gurel; Ozturk, AbdullahThe purpose of this study was to determine the friction coefficients and wear rates of six commercially available dental ceramics including IPS Empress 2 (E2), Cergo Pressable Ceramic (CPC), Cercon Ceram (CCS) and Super porcelain EX-3 (SPE). Bovine enamel (BE) was also tested as a reference material for comparison purposes. Samples of the dental ceramics were prepared according to the instructions described by the manufacturers in disk-shape with nominal dimensions of 12 mm x 2 mm. The wear tests were performed by means of a pin-on-disk type tribometer. The friction coefficients and specific wear rates of the materials were determined at a load of 10 N and rotating speed of 0.25 cm/s without lubrication. Surface morphology of the wear tracks was examined using a scanning electron microscope. Statistical analyses were made using one-way ANOVA and Turkey's HSD (P < 0.05).Article Citation - WoS: 4Citation - Scopus: 4Bioactivity of Apatite-Wollastonite Glass-Ceramics Produced by Melting Casting(World Scientific Publ Co Pte Ltd, 2013) Park, Jongee; Ozturk, AbdullahGlass-ceramics containing only apatite and wollastonite crystals were produced in the system MgO-CaO-SiO2-P2O5-F by the melt casting process. The bioactivity of the glass-ceramics was determined by immersing the glass-ceramics in a simulated body fluid (SBF) and by assessing the resulting apatite formation on the free surface after various immersion durations. A 12-mu m-thick apatite layer formed on the surface of the glass-ceramic containing only apatite crystals after 20 days immersion in SBF. However, the thickness of the apatite layer formed on the surface of the glass-ceramic containing apatite and wollastonite crystals was 1 mu m. Results have shown that the bioactivity of glass-ceramic depends strongly on the type of crystal(s) developed during the glass-ceramic process and their proportion in the glassy matrix.
