Materials Science and Engineering / Malzeme Bilimi ve Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/4719
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Article Citation - WoS: 1Citation - Scopus: 1Effect of Compaction and Fluoride Content on the Remelting Efficiency of Pure Magnesium Chips(Taylor & Francis, 2023) Yörük, Pınar; Gökelma, Mertol; Derin, BoraMagnesium is widely used in industries, such as automotive, aerospace, and medical fields. The demand on magnesium has been growing, although the production and melt treatment is complex due to strong oxidation tendency. Recycling of magnesium scraps is crucial due to the criticality of magnesium-containing raw materials in Europe as well as increasing environmental concerns. Remelting of magnesium is typically conducted under a salt flux which absorbs the impurities and protects the melt against oxidation. This study investigates the effect of compaction, fused salt flux, and salt composition on remelting behavior of magnesium chips. Metal yield and coagulation efficiency were calculated after remelting, and samples were characterized by using Scanning Electron Microscope and X-ray Diffraction. The liquidus temperature and density of fluxes were analyzed by FactSage software. Remelting of compacted chips under a fused salt flux with 5 wt.% CaF2 showed the highest magnesium recovery with a yield of 97.7%. Le magnesium est largement utilise dans une variete d'industries, telles que les domaines de l'automobile, de l'aerospatiale et de la medecine. La demande en magnesium s'est accrue, bien que la production et le traitement du bain soient complexes en raison de sa forte tendance a l'oxydation. Le recyclage des dechets de magnesium est crucial en raison de la criticite des matieres premieres contenant du magnesium en Europe ainsi que des preoccupations environnementales croissantes. La refusion du magnesium est effectuee typiquement sous un flux de sel qui absorbe les impuretes et protege le bain contre l'oxydation. Cette etude examine l'effet du compactage, du flux de sel fondu et de la composition du sel sur le comportement a la refusion des copeaux de magnesium. On a calcule le rendement en metal et l'efficacite de la coagulation apres des experiences de refusion, et l'on a caracterise les echantillons a l'aide d'un microscope electronique a balayage et de la diffraction des rayons X. On a analyse la temperature du liquidus (Tliq) et la densite des flux de sel avec le logiciel FactSage. La refusion des copeaux compactes sous un flux de sel fondu avec 5% en poids de CaF2 a montre la recuperation de magnesium la plus elevee avec un rendement de 97.7%Article A Study on Recyclability of Alsi7mg0.3 Machining Waste(2023) Gökelma, Mertol; Önen Tüzgel, Rabia; Kaya, Ahmet Yiğit; Özaydın, OnurAluminium products are widely used in the automotive industry. One of the important aluminium products in the automotive is wheel production. Turkish wheel production is expected to reach 360000 tons in 2025. The wheels are produced by Low-Pressure Die Casting at the first stage and the machining process in CNC machines is used to create the final form. A significant amount of machining waste (swarf, turnings, and chips) is created during the machining and the importance of secondary aluminium has been increasing due to environmental and economic concerns. This study focuses on the recycling of AlSi7Mg0.3 cast alloy machining waste. The turnings were sorted into two size fractions and remelted separately under a salt flux in a resistance heating furnace. Two different salt mixtures with different melting points and different salt factors were studied in this work. Metal yield and coagulation yield after remelting were discussed.Article Citation - WoS: 5Citation - Scopus: 7Characterization and Separation Behavior of Multi-Layers in Aluminum-Rich Waste Pharmaceutical Blisters(Springer, 2023) Çapkın, İrem Yaren; Gökelma, MertolAl-rich waste pharmaceutical blisters (WPBs) have a multi-layer structure that contains aluminum and polymer-based fractions. Although the aluminum mass in WPBs is less than typical aluminum packaging products such as beverage cans, establishing a feasible recycling procedure is possible by separating the fractions to recover both metal and plastic. Hydrometallurgical methods are mostly preferred for the separation of aluminum and plastic in multi-layered structures. This work reports the characterization of Al-rich WPBs and the separation behavior of aluminum and plastic layers. The effects of hydrochloric acid, acetic acid, formic acid, sulfuric acid, ethanol, acetone, and organic solvent (benzene–ethanol–water) on the separation behavior of layers were studied at different temperatures. Furthermore, the recycling yield of the aluminum fraction was experimentally assessed. © 2023, The Minerals, Metals & Materials Society.Article Citation - WoS: 1Citation - Scopus: 2An Investigation on Inclusions Forming During Remelting of Aluminum and Magnesium Scraps Under a Salt Flux(Springer, 2023) Çapkın, İrem Yaren; Gökelma, MertolDue to increasing environmental and economic concerns, the recycling of metals has been increasing in the last decades. Aluminum saves up to 95% of energy when recycled, and magnesium is one of the most common alloying elements in aluminum alloys, contributing to oxidation behavior. Both aluminum and magnesium have a high oxidation tendency during remelting, which raises the necessity for salt flux usage. Salt fluxes remove oxides and other surface contaminants from the target metal. Salt fluxes allow molten metal pieces to coagulate and form the molten bath. Furthermore, it prevents further oxidation of the metal. The presence of fluorides increases the metal yield by promoting coalescence. Although metals and salts are frequently interacting in such processes, there is still a lack of knowledge of the final and intermediate products of the interaction reactions. This study aims to contribute to the literature by investigating the interaction of aluminum and magnesium scraps with salt flux. As a result of the experiments, AlF3, MgF2, Al2O3, MgO, and MgAl2O4 were observed as the main phases in the aluminum and magnesium scraps dross. The presence of CaF2 in the salt flux, which is insoluble in water, was also observed in the analysis results. In addition, fluorine-containing compounds were observed as a result of chemical interactions among the F-, K-, and oxide layers.Review Citation - WoS: 41Citation - Scopus: 42Review on the Parameters of Recycling Ndfeb Magnets Via a Hydrogenation Process(American Chemical Society, 2023) Habibzadeh, Alireza; Küçüker, Mehmet Ali; Gökelma, MertolRegarding the restrictions recently imposed by China on the export of rare-earth elements (REEs), the world may face a serious challenge in supplying some REEs such as neodymium and dysprosium soon. Recycling secondary sources is strongly recommended to mitigate the supply risk of REEs. Hydrogen processing of magnetic scrap (HPMS) as one of the best approaches for magnet-to-magnet recycling is thoroughly reviewed in this study in terms of parameters and properties. The processes of hydrogen decrepitation (HD) and hydrogenation-disproportio-nation-desorption-recombination (HDDR) are two common methods for HPMS. Employing a hydrogenation process can shorten the production route of new magnets from the discarded magnets compared to other recycling routes such as the hydrometallurgical route. However, determining the optimal pressure and temperature for the process is challenging due to the sensitivity to the initial chemical composition and the interaction of temperature and pressure. Pressure, temperature, initial chemical composition, gas flow rate, particle size distribution, grain size, and oxygen content are the effective parameters for the final magnetic properties. All these influencing parameters are discussed in detail in this review. The recovery rate of magnetic properties has been the concern of most research in this field and can be achieved up to 90% by employing a low hydrogenation temperature and pressure and using additives such as REE hydrides after hydrogenation and before sintering.Article Citation - WoS: 10Citation - Scopus: 7Assessment of Melt Cleanliness of Secondary 5000 Aluminum Alloy Via Non-Metallic Inclusions Characterization(Springer, 2023) Li, Cong; Dang, Thien; Huang, Jinxian; Huang, Chunfa; Li, Jianguo; Friedrich, Bernd; Gökelma, MertolThe extensive energy consumption of primary aluminum production stimulates increasing need of producing primary-quality alloys with secondary sources, during which process amount of non-metallic inclusions (NMIs) in the alloy must be strictly controlled. In the present study funded by AMAP Open Innovation Research Cluster, NMIs generated during remelting a 5000 Al-Mg alloy was investigated to offer benchmarking characters of NMIs with respect to type, morphology, size, composition, and concentration. Under different remelting conditions NMIs formed in the melt ahead of solidification were concentrated using Porous Disc Filtration Apparatus (PoDFA) and characterized microstructurally and quantitatively. Investigated conditions included heating cycle, organic contaminations, and refractory materials. Results suggested oxide films and cuboid particles as typical oxides with, respectively, different compositions. The amount of formed oxides declined with the increase of heating rate. With respect to aluminum carbide (Al4C3), organic contaminations were confirmed to lead to an increased amount of its formation. The carbon-containing refractory material contributed more significantly than organic contaminations on the formation of Al4C3 at melt temperatures over 760 & DEG;C. Formulas were derived based on trial results to enable translation of NMIs PoDFA value [mm(2)/kg] into their mass fraction [ppm] in the melt.Article Citation - WoS: 1Citation - Scopus: 1Investigating Triple Superphosphate for Lead Removal From Aqueous Solutions(Taylor & Francis, 2022) Souley Garba, Mahamane Chapiou; Kaya, Erol; Gökelma, Mertol; Seyrankaya, AbdullahThe aim of this research is to investigate monocalcium phosphate monohydrate [Ca(H2PO4)2. H2O] also called triple superphosphate (TSP) for the removal of lead (Pb) from aqueous solutions. In this study, TSP was selected amongst various phosphate-based materials and fertilizers to act as the source of orthophosphate (PO43-) which is a powerful tool for metal fixation in soil and water. Thermodynamic equilibrium dissolution-precipitation relationships for the systems of Pb-H2O and Pb-PO43--H2O were drawn with the aid of Eh-pH stability diagrams to determine the predominance areas of different species. The lead phosphate compounds, identified through the stability area diagrams, were verified with the batch precipitation tests performed with standard solutions of lead and TSP at different conditions. It was observed that, depending upon solution conditions, TSP can precipitate 99.9% of the lead from the solution. Lead precipitates, analyzed by x-ray diffraction, showed the formation of lead phosphate compounds. The mechanism of TSP for the removal of lead from aqueous solutions is discussed.Conference Object Pre-Study of the Dissolution Behavior of Silicon Kerf Residue in Steel(Springer, 2022) Lazou, Adamantia; Nilssen, David; Gökelma, Mertol; Wallin, Maria; Tranell, GabriellaSilicon kerf residue is generated during the wafering process of pure silicon in the photovoltaic value chain. The generated by-product has a high volume, and the particle size is typically below 1 μm. Although the fine particles are partly oxidized, the material may be beneficial in different metallurgical applications such as grain refining and alloy composition adjustments. This work studies the dissolution behavior of silicon kerf in low alloy steel melts with the aim to upcycle the kerf material in the steel industry for different purposes. In this study, a steel alloy and the kerf residue were melted (at 1580 °C) in an alumina crucible placed in an induction furnace. The amount of added kerf residue was varied. The behavior of the particles in the solidified alloy was characterized by using an optical microscope, electron probe microscope (EPMA), and wavelength-dispersive X-ray spectroscopy (WDS) in order to study the dissolution behavior of the Si-kerf residue in the steel.Article Citation - WoS: 10Citation - Scopus: 11Behavior of Al4c3 Particles During Flotation and Sedimentation in Aluminum Melts(Springer, 2021) Gökelma, Mertol; Storm Aarnaes, Trygve; Maier, Juergen; Renkel, Maria F.; Ekstrom, Kai Erik; Friedrich, Bernd; Tranell, GabriellaAl4C3 particles form during the primary production of aluminum via molten salt electrolysis due to the carbon solubility and direct contact between bath, metal, and carbon anodes. Additional Al4C3 may form during melt processing through direct contact between the melt and carbonaceous materials. As a result of their small size and similar density to aluminum, removal of aluminum carbide particles can be challenging. If not removed, carbides can produce inclusion defects or poor surface condition in aluminum products. The current work studies the removal and behavior of Al4C3 particles during flotation with different gas mixtures, as well as sedimentation. The interaction between carbide particles and Al2O3 films during the melt treatment processes was also studied and reported. Factsage thermochemical software was used to model the interactions at the interface of inclusions and bubbles covered by films. The highest degree of carbide removal was obtained after flotation with an H2O-containing argon gas mixture, where the carbide concentration dropped below the measured solubility limit of carbon at the corresponding temperature. Strong interaction between Al4C3 particles and Al2O3 films was observed during sedimentation which worked as an efficient removal method for the particles. Oxidation of carbides and formation of oxycarbides were suggested as the mechanisms promoting the attachment of carbides on oxide films.Article Citation - WoS: 4Citation - Scopus: 4Rewas 2022: Developing Tomorrow's Technical Cycles(Springer, 2021) Fleuriault, Camille; Gökelma, Mertol; Anderson, Alexandra; Olivetti, Elsa A.REWAS, a sustainability driven conference within The Minerals, Metals & Materials Society (TMS), has a long history of bringing together academia and industry to exchange and reflect on the latest technology developments in the process optimization and waste management fields. The first edition of REWAS (REcycling and WASte symposium) took place in 1999. The scope of the conference has since then broadened to include environmental sustainability, resource management and manufacturing efficiency, liaising these developments to the metallurgical industry in a broader societal and systemic context. The 2022 edition of REWAS which will be hosted at the TMS 2022 Annual Meeting & Exhibition in Anaheim, California, provides a resolute outlook towards Developing Tomorrow's Technical Cycles. Within the metals and materials industry, technical cycles refer to the ensemble of strategies and processes applied to the development of sustainable product loops with the intent to eliminate waste and instead rethink, reuse and upcycle products. The success of technical cycles requires strengthening our circular approach for product life cycle design by providing guidelines and implementation examples to the developers, designers, policy makers and business managers. REWAS promotes such strategies within a priority sector identified for Circular Economy enablement: raw materials supply and management. REWAS 2022 consists of six symposia, and abstract submissions are expected in summer 2021. Topics include recycling and sustainability within the aluminum industry, specifically on casting technologies, recovery of metals from complex products and systems, decarbonization of the metallurgical and manufacturing industry, sustainable production and development perspectives, as well as automatization and digitalization for advanced manufacturing. REWAS 2022 will also include an honorary symposium for Dr. Diran Apelian, whose contributions in metals processing, aluminum and battery recycling, sustainability, education in materials science and more have shaped the path for sustainable materials processing.