Metalurji ve Malzeme Mühendisliği
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ÖgeMelt rheological and bead foaming behavior of recycled polyethylene terephthalate/polybutylene terephthalate blends modified with a joncryl chain extender(American Chemical Society, 2024)This study investigates the melt rheological properties and foamability of recycled polyethylene terephthalate (rPET) and its blends with polybutylene terephthalate (PBT) modified through an epoxy-based Joncryl ADR 4468 chain extender. A twin-screw extruder was used to prepare rPET/PBT blends at various weight ratios (i.e., 100/0, 75/25, 50/50, 25/75, and 0/100) and with varying Joncryl chain extender contents (i.e., 0.25, 0.5, 0.75, and 1.0 wt %). The small-amplitude oscillatory shear rheological experiments were conducted to analyze the melt viscoelastic behavior of the samples. The melt strength and strain-hardening behavior of the compounds were examined by measuring the extensional rheology and Rheotens tests. Crystallization analysis was conducted on the processed samples by using differential scanning calorimetry. The bead foaming behavior of the samples was investigated using a batch-based foaming reactor with supercritical CO2. Both compounding with PBT and Joncryl chain modification increased the complex viscosity, melt strength, and strain-hardening behavior of the blends, while their synergistic effect revealed a more noticeable enhancement. Although direct modification of rPET with Joncryl and its direct compounding with PBT could not generate a meaningful foam structure, a homogeneous microcellular foam structure could successfully be induced when 25 wt % rPET was incorporated in blends with PBT modified with 1.0 wt % Joncryl.
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ÖgeCryo-assisted nitrogen treatment for the fabrication of nanoengineered, mixed transition metal oxide anode from inorganic domestic waste, for lithium-ion batteries(Springer, 2024)A novel method for the fabrication of nanoengineered, mixed transition metal oxide anode active material is proposed based on implementing liquid nitrogen treatment during the chemical precipitation process, for the first time in open literature. Such interference in the precipitation is believed to change the surface energy of the nuclei leading to differentiation in the growth process. To exemplify this hypothesis with an environmentally friendly approach, kitchen scourer pads, an existing waste, are used as a starting material instead of using a mixture of primary quality metals’ salts. Therefore, in this study, firstly, an optimization is realized to leach the scouring pad with 100% efficiency. Then, by applying a conventional chemical precipitation to this leachate at pH 5.5, Sample 1-P is produced. Herein, innovatively liquid nitrogen treatment is carried out during the chemical precipitation to produce Sample 2-P. Lastly, these precipitates (Samples 1-P, 2-P) are calcinated in the air to form mixed transition metal oxide powders: Samples 1 and 2, respectively. Structural, chemical, and morphological characterizations are carried out to examine the effect of liquid nitrogen treatment on the powders’ properties. To discuss the effect of nitrogen treatment on the electrochemical performances of the anode active materials (Sample 1 and Sample 2), galvanostatic tests are realized. The results show that Sample 2 demonstrates a higher 1st discharge capacity (1352 mAh/g) and retains 62% of its performance after 200 cycles when 50 mA/g current load is applied. Moreover, this electrode delivers around 500 mAh/g at 1 A/g current load. The remarkable cycle performance of Sample 2 is believed to be related to the superior chemical, structural, and physical properties of the electrode active material.
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ÖgeSynthesis and characterization of BaIrO3-doped YBCO superconducting thin films via TFA-MOD technique(Springer, 2024)High-temperature superconducting materials (HTS) are characterized by remarkably high critical current density (Jc) values when exposed to low temperatures and magnetic fields. In the realm of such investigations, various crystalline imperfections, including finely dispersed non-superconducting phases, dislocations, vacancies, grain boundaries, twin boundaries, antiphase boundaries, and insulating regions within grain boundaries, have been recognized as potential sources of pinning centers. However, it is essential to acknowledge that Jc values experience a rapid decline as the temperature rises in the presence of a magnetic field. The primary contributing factors to this decline are attributed to the intrinsic crystalline anisotropy of HTS materials and the thermal fluctuations that prevail at elevated temperatures. Nevertheless, a noteworthy factor in the diminishment of Jc values is the scarcity of efficacious pinning centers. In response to these challenges, a pioneering technology has emerged, revolving around nanostructure engineering for the deliberate creation of artificial pinning centers within HTS materials. In alignment with this approach, the present study endeavors to augment the critical current density and enhance the flux pinning properties of YBa2Cu3O6.56 (YBCO) superconducting films. This augmentation is achieved through the integration of BaIrO3 (BIO) perovskite nanodots, nanorods, or nanoparticles as strategically positioned pinning centers. The films are deposited on a SrTiO3 (STO) substrate employing the Trifluoroacetate Metal–Organic Deposition (TFA-MOD) technique. This research initiative seeks to contribute to the advancement of knowledge regarding the controlled manipulation of artificial pinning centers in HTS materials, particularly focusing on YBCO thin films, with the ultimate goal of enhancing their performance under the influence of elevated magnetic fields.
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ÖgeThermodynamic investigations for combustion-assisted synthesis of lithium orthosilicate powders(Springer, 2024)The study investigates the combustion-assisted synthesis of lithium orthosilicate (Li4SiO4) powders for potential CO2 capture applications. Technical-grade lithium carbonate and metallic silicon powders were used as starting materials. Synthesis conditions were explored across temperatures ranging from 500 to 900 °C and different holding durations. Thermodynamic modeling using FactSage 8.2 software suggested that Li4SiO4 production is feasible at temperatures of 700 °C and higher with metallic silicon as the silicon source, which was confirmed experimentally. Characterization of the synthesized powders involved X-ray diffraction, specific surface area determination, particle size distribution analysis, scanning electron microscopy, and CO2 uptake tests. Despite having the lowest Li4SiO4 content as 83.7%, the sample synthesized at 700 °C with 45 min of holding time showed the best CO2 uptake performance as 12.80 wt% while having the lowest crystallite size value (126.58 nm), the highest specific surface area value (4.975 m2/g) and the lowest average particle size value (10.85 µm) which are highly effective on the CO2 uptake performance of such solid sorbents. The study concludes that while challenges remain in achieving optimal CO2 capture performance, it lays a foundation for utilizing lithium orthosilicate in carbon capture applications.
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ÖgeWaste to resource : surface modification of electric arc furnace flue dust by ball milling and in situ carbonization(Springer, 2024)In this article, instead of synthesizing the electrode active material using expensive precursors that lead to high carbon emissions to the atmosphere during fabrication, an alternative engineering approach is presented for the utilization of the electric arc furnace flue dust, which is an industrial waste, as anode material in lithium-ion batteries. In this scope, firstly ball milling of the flue dust with citric acid is applied and then in situ carbonization conditions are optimized by pyrolyzing the mixture at different temperatures (600 °C and 750 °C) and times (4 h and 6 h). Every sample delivers capacities greater than graphite. Structural, morphological, and chemical characterization results demonstrate that the designed method not only promotes the formation of a nanometer-thick carbon layer formation over the particles but also induces partial phase transformation in the structure. The best performance is achieved when citric acid is used as the carbon source and the ball-milled powder is treated at 600 °C for 4 h in nitrogen (C6004): It delivers 714 mAh g−1 capacity under a current load of 50 mA g−1 after 100 cycles. This research is expected to set an example for the utilization of different industrial wastes in high value-added applications, such as energy storage.