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    Effects of Graphite Incorporation and Annealing on the Structural, Tribological, and Functional Properties of Electroless Ni-B Coatings
    (Springer, 2026) Bulbul, Ferhat; Kara, Adem; Bulbul, Leman Elif; Gunes, Kubra
    This study explores the synergistic effects of graphite nanoparticles (0.1 wt.%) and thermal annealing (100-600 degrees C) on electroless Ni-B coatings for AISI 4140 steel. Graphite-enabled multifunctional performance-crystallization control, friction reduction, and antibacterial activity-are unlike conventional Ni-B systems. XRD showed amorphous-to-crystalline (Ni3B/Ni2B) transformation, with graphite acting as a nucleation agent below 300 degrees C before degrading at 600 degrees C. The 300 degrees C-annealed composite achieved optimal properties: 0.2 friction coefficient (75% lower than uncoated steel), 60% higher wear resistance, and hardness of 777 HV (+ 3.6% over as-deposited), attributed to graphite lubrication and nanocrystalline Ni3B formation. Antibacterial tests revealed a 3.4-mm inhibition zone against E. coli, though efficacy declined at higher temperatures due to graphite oxidation. All composites maintained superhydrophilicity (contact angle approximate to 0 degrees) without mechanical compromise. By correlating annealing temperature with microstructure, this work provides a design framework for Ni-B/graphite coatings combining low friction (mu = 0.2), high hardness (785 HV), and antibacterial functionality-addressing critical needs for wear-resistant, hygienic surfaces in biomedical and industrial applications.
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    Investigation of Pre-service Science Teachers' Self-efficacy Beliefs of Science Teaching
    (Elsevier Science Bv, 2014) Kahraman, Sakip; Yilmaz, Zeynel Abidin; Bayrak, Ramis; Gunes, Kubra
    The scope of the study is to investigate the pre-service science teachers' self-efficacy beliefs of science teaching with respect to gender and grade level. Using the survey approach, the data of the study were gathered from 114 pre-service science teachers enrolled in the Faculty of Education at two universities in Turkey. The data was collected using a likert type scale, science teaching self-efficacy belief scale with 23 items, originally developed by Enochs-Riggs (1990). Variance analyses (two-way ANOVA) was performed on the collected data to reveal whether there are significant differences in science teacher candidates' self-efficacy beliefs of science teaching according to grade level and gender. The results of analysis showed that there was no statistically significant difference in pre-service science teachers' self-efficacy beliefs of science teaching with respect to both gender and grade level. (C) 2014 The Authors. Published by Elsevier Ltd.
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    OPTIMIZATION OF PROCESS PARAMETERS FOR REMOVAL OF Cr(VI) BY HYPNUM CUPRESSIFORME USING RESPONSE SURFACE METHODOLOGY (RSM)
    (Parlar Scientific Publications (P S P), 2012) Ozkan, Esra; Gurses, Ahmet; Acikyildiz, Metin; Gunes, Kubra
    Response surface methodology was applied to optimize the removal of chromium ion by Hypnum cupressiforme from an aqueous solution. Experiments were analyzed using response surface methodology (RSM). The biosorption process was investigated as a function of five independent factors, sorption time, sorption temperature, initial ion concentration, sorbent dosage, and mixing rate. The optimum conditions for the chromium biosorption were found to be 760 min, 313K, 30mg/L, 0.01 mg/100mL, 107 min(-1) respectively, for sorption time, sorption temperature, initial ion concentration, sorbent dosage, and mixing rate.