Papers by Keyword: Nanostructure

Abstract: The impact of cooling rates on the microstructural evolution of an Al-Sr eutectic alloy was investigated. Two distinct cooling rates, 0.02 and 57.12 °C/s, were employed during the solidification process. To elucidate the characteristics of phase transformations and microstructural evolution during solidification, thermal analyses were conducted on the recorded cooling curves. Both the first and second derivatives of these curves were examined. At the slower cooling rate, the microstructure predominantly consisted of the eutectic Al phase and the eutectic Al-Sr phase, as identified by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Conversely, at the higher cooling rate of 57.12 °C/s, primary Al phases were observed, indicating a significant departure from equilibrium solidification conditions. Additionally, a substantial quantity of nanosized eutectic Al-Sr particles was detected, resulting in a markedly refined microstructure.

Abstract: Mechanical tests and electron microscopic structural studies of low-carbon copper-steels quenched after austenitization and tempered at different temperatures are carried out to clarify the decomposition mechanism of α-Fe based substitution solid solutions. With the onset of decomposition, limited nanosize (4–7 nm) precipitates of so-called ε-phase (solid solution of iron in copper with fcc structure) appear on dislocations. The substructure formed from the austenitic region during quenching determines the nature of such decomposition. In alloys with martensitic structure, the decomposition is heterogeneous. Both the formation of precipitates of the copper-rich ε-phase and their growth primarily occur on dislocations and grain boundaries. In supersaturated alloys with polyhedral ferrite structure, on the contrary, the decomposition is homogeneous, and the growth of the copper-rich phase occurs mainly in the defect-free part of the bcc matrix. Supersaturated iron begins to decompose, forming copper-rich zones isomorphic α-Fe. When a sufficiently high copper concentration is reached, these zones create mechanical stresses that cause local tetragonal distortions of the crystal lattice leading to its reconstruction. When a dislocation loop is formed around this zone, compensating for the elastic deformation, the coherence of the structure is destroyed and fcc precipitates are formed in the matrix. Satisfactory agreement between the theoretical estimate of 8 nm of the critical displacement required for the formation of a dislocation of inconsistency and the initial incoherent precipitates size determined experimentally – by electron microscopy, confirms the proposed mechanism based on the nucleation of nanoinclusions of the ε-phase copper in the bcc iron matrix.

Abstract: Production of nanoscale catalytic materials is an urgent technological challenge. Catalysts have a wide range of applications, such as for neutralizing nuclear waste, decontaminating water polluted with mercury, purifying the atmosphere from various micro-particles, in molecular sieves, and in chemical synthesis, oil refining, etc. Another important application of nanostructured materials is in rechargeable batteries and fuel cells, where their high specific surface area is essential to ensure the speed and effectiveness of the interactions between different materials. Active nanostructured materials with a sufficiently high density of controlled surface defects meet these requirements well and, therefore, offer significant potential for optimizing the high energy consumption in batteries. Currently, the particle size of natural and industrially synthesized manganese oxide materials is typically in the micron range or larger. From perspectives, the most developed and promising methods for synthesizing manganese dioxide are ion exchange, hydrothermal, electrolytic, and chemical synthesis. In this work, a distinctive method for synthesizing nanostructured manganese dioxide is proposed, described, and analyzed. Experiments were conducted to determine the optimal synthesis routes using the Self-propagating High-temperature Synthesis (SHS) method, as a distinctive technological approach that uses manganese ore enrichment waste as raw material and ammonium chloride as a pretreatment chemical agent.

Abstract: Cassava peels (CP) are agricultural-industrial co-products, better means of generating wealth that have recently attracted the attention and efforts of scientists due to their vitality in achieving a higher standard of living in a variety of industrial applications and human health care. Hence, an urgent demand for low-cost, non-toxic nanostructure material that can host, deliver, and transmit light with improved optical properties. In this work, β-cyclodextrins (β-CDs) was produced from cassava starch using US132 Cyclodextrins glucanotransferase enzyme (CGTase), converting it to cyclic oligosaccharides using experimental designs. The β-CDs produced by US132 CGTase are subsequently refined to a high level (67.26 g L-1) and homogenized using an eco-friendly, straightforward crystallization process that yielded a 40% purification yield. Gold nanoparticles (AuNPs) was effectively synthesized from Kahaya senegalenses plant, as a natural reducing agent. The Uv-visible and SEM evaluations revealed the plasmon resonance bands and spherical cap-shaped morphology of the developed hybridized β-CDs/AuNPs. However, the functional groups contained in the developed nanohybrids were validated by the FT-IR analysis. The size and crystallinity of the developed sample was found within the nano range as deduced from XRD and TEM (20-20 nm) analysis. The successful formation the developed nanostructured β-CDs/AuNPs was confirmed employing Uv-Visible, XRD, FT-R and SEM analysis. Therefore, the developed nanostructured β-CDs/AuNPs displayed significant and noticeable advantages which can withstand present drifts, due to its environmental friendliness, biocompatibility and encapsulating effect.

Abstract: The effects of cooling rates on the microstructure development of an Al-Fe eutectic alloy were studied. Two different cooling rates of 0.03 and 61.00 °C/s were applied to the solidifying alloys. To unfold the characteristics of phase changes and the microstructure evolution taking place during solidification, the recorded cooling curves based on temperature measurements were analyzed by thermal analyses, in which the first and second differences of the cooling curves were derived. The slow cooling resulted in the formation of only the eutectic Al phase and the eutectic Al-Fe phase in the microstructure identified by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). With the cooling rate increasing to 61.00 °C/s, the primary Al phase appeared, as the solidification became strongly non-equilibrium. A large quantity of the nanosized eutectic Al-Fe particles were detected. Overall, the microstructure refined substantially.

Abstract: Carbon nanotube (CNT) is an innovative material with significant potential for a wide range of applications, including but not limited to the development of lightweight composite materials or superconductors. A single CNT demonstrates an exceptional degree of tensile strength. CNTs are commonly employed in a structure of yarn, wherein several CNT strands are arranged and aligned together. CNT yarns, on the other hand, have a lower tensile strength than individual CNTs due to the different parameters of the yarn. This study aimed to investigate the effect of different structural parameters on the mechanical properties of CNT yarn. Sixty CNT yarn models with different structures were simulated with the molecular dynamic (MD) simulation. The varied parameters are the chirality of the CNTs, CNTs’ inner diameter, number of walls, crosslink density, and yarn twist angle. Tensile strength results from the simulations were compared concerning the varied parameters, and their influence on the nominal tensile strength of the CNT yarn was studied. It was found that the parameters for the CNT yarn that yields a higher tensile strength are the armchair type CNT with a small diameter, a large number of walls, crosslink density higher than approximately 1%, and a low twist angle.

Abstract: Nd³⁺ ion-doped ZnO nanomaterial was prepared using chemical synthesis method and its fluorescence spectra have been investigated at room temperature. From SEM images of the synthesized ZnO: Nd³⁺ nanoparticles it is observed that an increase in concentration of Nd³⁺ ions leading to the decrease in the particle size. Nearly hexagonal shapes for the dark spots in the SAED images indicate that the ZnO nanoparticles are almost hexagonal. The oscillator strengths leading to 4f ↔ 4f transitions are characterized by different Judd-Ofelt intensity parameters Ω_λ (λ = 2, 4 and 6). These Ω_λ parameters along with the fluorescence data and various radiative properties viz., spontaneous emission probability (A), radiative life time (t), fluorescence branching ratio (b) and stimulated emission cross-section (s_p) were evaluated and compared with the reported values. The values of these parameters indicate that the observed transitions ⁴F_3/2 → ⁴I_11/2, ⁴F_3/2 → ⁴I_13/2 and ⁴F_3/2 → ⁴I_15/2 can be considered to be good laser transitions in the near infrared region for different optoelectronic and spintronic uses.

Abstract: Titanate nanosheets are a type of 2-dimensional nanomaterial with vast applications in electronics, energy storage, and photocatalysis due to their superior properties, such as their large specific surface area and excellent electrical conductivity. Titanate nanosheets are expected to be the material precursor of TiO₂ nanostructures with further treatment. The current research aims to synthesize titanate nanosheets using the natural mineral ilmenite from Indonesia through the hydrothermal method. X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM), and Brunaeur-Emmett-Teller (BET) analysis were used to characterize the chemical composition, crystal structure, shape, size, and specific surface area of the prepared samples. The structure phase of the as-synthesized sample is known to be layered titanate. The as-synthesized nanosheet sample has a diameter ranging from 2.5 to 4 μm and BET surface areas of approximately 40 m²/g. This concise hydrothermal method could create 2-dimensional structured nanomaterials from Indonesian local minerals.

Abstract: One of the most important challenges of modern materials engineering is to improve the efficiency and durability of materials, which directly translates into reducing the consumption of raw materials. In many applications, these goals are achieved by strengthening and functionalizing the surface, especially in the case of nanocoatings. The material for the study is the Ta/TaN multilayer systems obtained with the ALD technique (Atomic Layer Deposition, R200 by Picosun). For their structure characterisation electron microscopy (HR STEM, electron diffraction, EDS, EELS) was used. Geometrical parameters (thickness of the constituent Ta and TaN layers, ratio of thicknesses of metallic and ceramic layers) were determined, and their chemical and phase compositions were verified. The obtained results will be used to model mechanical properties and interpret the results of experimental nanoindentation measurements.

Abstract: Sea urchin zinc oxide (SU-ZnO) nanostructures were successfully synthesized using the sol-gel method and characterized by various analytical techniques. The present work reports a facile and straightforward route for synthesizing sea urchin ZnO nanostructures consisted of self-assembled ZnO nanorods with sharp tips yielding the sea urchin-like shape. The SU-ZnO nanostructures were characterized using Scanning electron microscopy and Energy dispersive X-ray spectroscopy (SEM-EDS), Fourier transform infrared (FTIR) spectroscopy, particle size analysis (dynamic light scattering technique), and ultraviolet-visible (UV-vis) spectroscopy. The result of energy dispersive X-ray spectroscopy shows that the SU-ZnO nanostructure contains 77.30% zinc and 22.70% oxygen content. Scanning electron microscopy shows that the synthesized ZnO exhibits a sea urchin-like structure with a homogeneous and consistent size. FTIR spectroscopy confirmed the structural features and functional groups that are present in ZnO nanostructures. The particle size analysis shows that the synthesized SU-ZnO nanostructures have an average particle size of 812.62 ± 55.92 nm. The growth of SU-ZnO nanostructure was also investigated by recording the UV-Vis absorption spectra at different reaction times.