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    Cellular response to calcium phosphate cements
    (Elsevier, 2020) Cecen, Berivan; Kalemtaş, Ayşe; Topates, Gulsum; Kozaci, Leyla Didem
    Calcium orthophosphate (COP) ceramics have been investigated as bone repair materials for many decades. The first in vivo application of these materials was accomplished in 1920 to test tricalcium phosphate performance as a bone substitute. Since this first attempt, various COPs were investigated on animals to shed light on their effect on the healing behavior of bones. Calcium phosphate cements are currently receiving a great deal of interest especially for the hard tissue repair, augmentation, and regeneration applications due to their attractive characteristics such as biocompatibility, ease of shaping, osteoconductivity, and biodegradability.
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    Production of Si3N4 porous beads via carbothermal reduction and nitridation technique
    (Taylor & Francis Ltd, 2020) Topates, Gulsum; Kalemtaş, Ayşe
    Si(3)N(4)porous beads were produced from direct carbothermal reduction and nitridation of spheres composed of carbon+SiO(2)mixtures. A simple one-step sol-gel templating technique was used to prepare carbon+SiO2(molar ratio of carbon/SiO(2)was set as 4) containing spheres with a diameter of 2 mm. A natural and abundant biopolymer, alginate, is used as a sacrificial template to produce porous Si(3)N(4)ceramic beads. Carbothermal reduction and nitridation process was conducted at two different temperatures (1500 and 1550 degrees C) and atmospheres (pure nitrogen and 5% hydrogen in nitrogen) to observe the effect of process parameters on the yield of Si3N4. Porous beads with a smooth shape and without any deformation were successfully obtained after the carbothermal reduction and nitridation process. X-ray powder diffraction studies showed that the use of H(2)increased the amount of Si(3)N(4)formed by accelerating the reduction and nitridation reactions. Microstructural investigations revealed oxide addition changed grain morphology from fiber-like to short, angular geometry. This microstructural development showed that the addition of oxide powder increased the amount of liquid phase formed during the heat treatment process and changed carbothermal reduction and nitridation mechanism from vapor-solid to vapor-liquid solid.
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    Starch consolidation of SiC ceramics: processing and low-temperature sintering in an air atmosphere
    (Taylor & Francis Ltd, 2020) Kalemtaş, Ayşe; Topates, Gulsum; Aydin, M. Turkay Aytekin; Ozey, Nigar
    Highly porous SiC ceramics containing borax decahydrate were produced by a starch consolidation method in which corn starch was used as a shaping and pore-forming additive. Four different compositions were prepared with different SiC:borax decahydrate ratios and corn starch content. Mixtures with a solid ratio of 55 wt.% were cast in non-porous molds and heated at 80 degrees C for shaping. The starch consolidation technique enabled the shaping of SiC ceramics with different forms and sizes. Simultaneous thermogravimetry and differential thermal analysis of the SiC-borax decahydrate mixture showed that melting took place at below 600 degrees C, as a result of which sintering was carried out at the relatively low temperature, of 600 degrees C in the air using borax decahydrate as a sintering additive. Phase analysis showed that oxidation of SiC did not take place, since no cristobalite phase was detected. Density measurement and mercury porosimetry studies showed that highly porous (70-89% porosity) SiC ceramics with pore size values ranging from 14 to 18 mu m were produced. SEM microstructures of each composition revealed that a strong neck had been formed between the SiC particles in spite of the low sintering temperature.