Browsing by Author "Gokce, Hasan"

Filter results by typing the first few letters
Now showing 1 - 2 of 2
  • Thumbnail Image
    Article
    Powder Metallurgical Synthesis, Thermochemical Calculations and Characterization Studies of HfB2 Powders
    (Springer India, 2025) Akbari, Amir; Suzer-Cicek, Ilayda; Mertdinc-Ulkuseven, Siddika; Gokce, Hasan; Ovecoglu, M. Lutfi; Agaogullari, Duygu
    This study reports on the thermochemical calculations, mechanochemical synthesis, purification process, and characterization studies of the HfB2 powders by using native sources. Firstly, HfO2, native B2O3, and Mg starting powders were prepared with a multi-axial vibratory ball mill (NanoMultimix) in stoichiometric and excess amounts. The milling process was optimized by varying the time (2, 4, 6, 8, 10, 12 h). Then, unwanted by-products (HfO2, MgO) were removed by leaching with 4 and 6 M HCl. Phase and Rietveld analysis, microstructure investigations with scanning electron microscopy/energy dispersion spectroscopy and transmission electron microscopy, and particle size measurement were conducted. The purest HfB2 was obtained in the powders milled for 8 h in stoichiometric ratios and leached with 6 M HCl. The resulting optimum powder has an average particle size of 135 nm. Oxidation kinetics (500, 600, 700, 800, and 900 degrees C) were also investigated. As the temperature increased, the amount of oxidation increased based on the TG result. As a result of the characterization studies, the synthesis of single-phase, high-purity HfB2 was achieved using domestic resources.
  • Thumbnail Image
    Article
    Γ-Type High-Entropy Disilicates (Y0.2er0.2tm0.2yb0.2x0.2)2si2o7 (X = Dy, Gd, Ho): Phase Stability, Thermal Behavior, and CMAS Corrosion Resistance
    (Elsevier Ltd, 2026) Kavak S.; Yüksek A.N.; Gökçe H.; Lütfi Öveçoğlu M.; Ağaoğulları D.; Yuksek, Ahmet Numan; Ovecoglu, M. Lutfi; Gokce, Hasan; Kavak, Sina; Agaogullari, Duygu; Lütfi Öveçoğlu, M.
    Three quinary high entropy disilicate (HEDS) compositions namely, (Y0.2Er0.2Tm0.2Yb0.2Dy0.2)2Si2O7, (Y0.2Er0.2Tm0.2Yb0.2Gd0.2)2Si2O7 and (Y0.2Er0.2Tm0.2Yb0.2Ho0.2)2Si2O7 were synthesized via ball milling and sintering using commercially available oxides for environmental barrier coating (EBC) applications. XRD, SEM, and EDS analyses confirmed the formation of single-phase γ-type pyrosilicates with dense and homogenous elemental distribution. Moreover, it was found that the newly developed (5RE0.2)2Si2O7 high entropy disilicate materials exhibit low thermal conductivities, high temperature phase stability and similar coefficients of thermal expansion (CTE) with SiC. CMAS corrosion resistances of HEDS samples were investigated at 1300 °C for 2, 12, and 24 h. The findings highlight the potential of high entropy engineering to enhance the high-temperature corrosion resistance, high temperature phase stability and improved thermal properties making these materials promising candidates for advanced EBC systems for gas turbine applications. © 2026 Elsevier B.V.