Makale 2020-2029 yılları

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Browsing Makale 2020-2029 yılları by Publisher "MDPI"

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    Descriptive Process Mineralogy to Evaluate Physical Enrich-ment Potential of Malatya/Kuluncak Rare Earth Ore through MLA
    (MDPI, 2023-09-12) Ersoy, Burakhan; Beşirli, Mehmet Umut; Topal, Selim; Soydaş Sözer, Belma; Burat, Fırat
    Rare Earth Elements (REE) are indispensable parts of magnetic, phosphor, metal alloys, catalysts, ceramics, glass, pol-ishing, and defense systems industries due to their unique physical and chemical properties. Currently, China is the largest sup-plier in the world with a production of more than 95% of the world’s Rare Earth Oxides (REO). To reduce the influence of China on the REE market, the countries have started to develop their national strategies for the production and use of REE-bearing resources. Within the scope of this study, particle size, chemical, MLA, XRD, and SEM-EDS analysis were performed for material characterization, and shaking table, centrifugal, and magnetic separations were carried out for the beneficiation of Mala-tya/Kuluncak rare earth ore. The XRD analysis indicated that the representative sample consists of major minerals such as albite, calcite, montmorillonite, muscovite, titanite, kaolinite, clinochlore, and aegirine. Parisite, bastnaesite, Zr-REE-Silicate, Fe-REE-Oxide, and Ca-Ti-Nb-REE-Oxide were detected as REE-bearing minerals by MLA. The chemical analysis resulted in a ∑REO grade of 3,628 g/t and the ore consists of mostly light REE. According to the result of the gravity separation for the coars-est fraction, about 11.3% by weight of the total feed was concentrated as a heavy product assaying 6,437 g/t ∑REO. As a result of magnetic separation, magnetic products with 5,561 g/t and 6,013 g/t ∑REO were obtained at coarse and fine fractions, respective-ly. Finally, the characterization studies and enrichment results were correlated, and very important and meaningful indications about the behavior of REE-bearing minerals were obtained.
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    Scalable Production of Boron Nitride-Coated Carbon Fiber Fabrics for Improved Oxidation Resistance
    (MDPI, 2025-10-14) Yıldırım Elçin; Cennet; Arık; Muhammet Nasuh; Örs; Kaan; Nakaş; Uğur; Yakışık Özgüle; Zeliha Bengisu; Acar; Özden; Aslanlar; Salim; Altay; Özkan; Çelik; Erdal; Şahin; Korhan
    This study aimed to develop an industrially scalable coating route for enhancing the oxidation resistance of carbon fiber fabrics, a critical requirement for next-generation aerospace and high-temperature composite structures. To achieve this goal, synthesis of hexagonal boron nitride (h-BN) layers was achieved via a single wet step in which the fabric was impregnated with an ammonia–borane/THF solution and subsequently nitrided for 2 h at 1000–1500 ◦C in flowing nitrogen. Thermogravimetric analysis coupled with X-ray diffraction revealed that amorphous BN formed below ≈1200 ◦C and crystallized completely into (002)-textured h-BN (with lattice parameters a ≈ 2.50 Å and c ≈ 6.7 Å) once the dwell temperature reached ≥1300 ◦C. Complementary XPS, FTIR and Raman spectroscopy confirmed a near-stoichiometric B:N ≈ 1:1 composition and the elimination of O–H/N–H residues as crystallinity improved. Low-magnification SEM (100×) confirmed the uniform and large-area coverage of the BN layer on the carbon fiber tows, while high-magnification SEM revealed a progressive densification of the coating from discrete nanospheres to a continuous nanosheet barrier on the fibers. Oxidation tests in flowing air shifted the onset of mass loss from 685 ◦C for uncoated fibers to 828 ◦C for the coating produced at 1400 ◦C; concurrently, the peak oxidation rate moved ≈200 ◦C higher and declined by ~40%. Treatment at 1500 ◦C conferred no additional benefit, indicating that 1400 ◦C provides the optimal balance between full crystallinity and limited grain coarsening. The resulting dense h-BN film, aided by an in situ self-healing B2O3 glaze above ~800 ◦C, delayed carbon fiber oxidation by ≈140 ◦C. Overall, the process offers a cost-effective, large-area alternative to vapor-phase deposition techniques, positioning BN-coated carbon fiber fabrics for robust service in extreme oxidative environments.