Browsing by Author "Akbari, Amir"

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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.
Citation - WoS: 3
Citation - Scopus: 3
Powder metallurgy processing of seven/eight component multi-phase (HfTiZr-Mn/Mo/W/Cr/Ta)B₂ high entropy diboride ceramics
(Elsevier, 2024) Suzer, Ilayda; Akbari, Amir; Ates, Semih; Bayrak, Kuebra Gurcan; Mertdinc-Ulkuseven, Siddika; Arisoy, C. Fahir; Agaogullari, Duygu; Öveçoğlu, M. Lutfi
This study aims to show the possibility of synthesizing seven- and eight-component high entropy diboride (HEB) ceramics using high energy ball milling-assisted spark plasma sintering (SPS). Metal boride powders, synthesized in laboratory conditions from metal oxide-boron oxide-magnesium powder blends, were combined equimolarly as seven and eight components containing systems. Afterwards, hybridized powders were mechanically alloyed (MA) for 6 h and subjected to spark plasma sintering (SPS) at 2000 degrees C and under 30 MPa. Detailed phase analysis and physical, microstructural, and mechanical characterization of the samples were performed. in the sintered products, the main phase belongs to the HEB, and also low amounts of Hf/Zr oxides and secondary phases (W or Ti-rich) occurred. The highest hardness was observed at the (HfTiZrMoWCrTa)B-2 with 25 GPa, and the lowest hardness was seen at the (HfTiZrMnCrMoWTa)B2 with 17 GPa. Also, the highest wear resistance was calculated for the (HfTiZrMnCrMoTa)B-2 as 6.05 x 10(-7) mm(3)/Nm. Additionally, (HfTiZrMnMoWTa)B-2 and (HfTiZrMnMoCrTa)B-2 have the highest and lowest Archimedes' densities, with 7.94 g/cm(3) and 6.91 g/cm(3), respectively.
Room-Temperature Synthesis of Refractory Borides: a Case Study on Mechanochemistry and Characterization of Mo-Borides and W-Borides
(Elsevier Sci Ltd, 2025) Süzer, İlayda; Akbari, Amir; Kaya, Faruk; Mertdinç Ülküseven, Sıddıka; Derin, Bora; Öveçoğlu, M. Lütfi; Ağaoğulları, Duygu
Mo-boride and W-boride powders were produced from native boron oxide, magnesium, and related metal oxide starting materials by mechanochemical synthesis (MCS) followed by an purification treatment. The reaction formation mechanisms and the products were predicted with the FactSageTM thermochemical simulation program. Different conditions were tested to determine the optimum synthesis parameters. MCS was conducted at stoichiometric ratios and different milling durations, using excess reactant amounts over the determined optimum time. After MCS, unwanted phases were removed by HCl acid leaching. Detailed phase analyses of the final powders were obtained by X-ray diffractometer (XRD), whereas detailed microstructure characterization was conducted by scanning electron microscope/energy dispersion spectrometer (SEM/EDS), transmission electron microscope (TEM) and particle size analyzer. Among the utilized parameters, the ideal composition chosen for Mo boride synthesis was 6 h milled and leached MoO3-100 wt% B2O3-50 wt% Mg (1.41 mu m), including alpha-MoB, beta-MoB, MoB2, Mo2B, Mo2B5, and Mo phases. For the synthesis of W boride, the proper composition was found as WO3-100 wt% B2O3-50 wt% Mg (0.37 mu m) containing W2B5, WB, beta-WB, WB4, W2B, and W phases after milling for 20 h and leaching. Besides, as a result of the oxidation resistance measurements at 700 and 800 degrees C, phases belonging to MoO2 and WO2 were found along with boride phases.