Papers by Keyword: Nanoparticle

Abstract: Alloy 625 is a Ni-based superalloy with the main alloying elements being Nb, Cr, and Mo. It is known for its excellent corrosion resistance, good weldability, both high heat and creep resistance, and good strength. The current work presents the microstructure of Alloy 625-nTiC metal matrix composites (MMC) fabricated through suction casting. The microstructure and chemical composition of strengthening phases were investigated by light microscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy. The results showed that fabricated MMC composites are characterized by a dendritic microstructure with irregular distribution of the strengthening precipitates. Based on chemical composition analysis, the strong enrichment in Nb and Ti was revealed.

Abstract: Silver nanoparticles (AgNPs) have attracted attention due to their unique properties and potential application. This research aimed to do green synthesis of AgNPs with Syzygium aromaticum leaves extract (SALE) and evaluate their antibacterial and antioxidant activities. Syzygium aromaticum leaves were extracted using distilled water at 70 °C for 30 min and the results were characterized with FTIR. AgNPs were synthesized by mixing AgNO₃ precursor with SALE. The effects of parameters such as volume ratio of AgNO₃ precursor to SALE, AgNO₃ concentrations, and synthesis times were investigated. The synthesized AgNPs were characterized using UV-Vis spectrophotometer, FTIR, and TEM. Antibacterial activity of SALE and AgNPs was investigated against Escherichia coli (E.coli) and Bacillus subtilis (B. subtilis) with disc diffusion method and antioxidant activity was tested with DPPH method. The FTIR characterization revealed that SALE and resulting AgNPs contain O-H, C-H, C=O, C=C, C-O, and C≡C functional groups. The UV-Vis characterization demonstrated that AgNPs exhibited an absorption peak at λ = 420 nm indicating surface plasmon resonance. The optimal volume ratio of AgNO₃ to SALE, AgNO₃ concentrations, and synthesis time for AgNPs synthesis was achieved at 10:3, 5 mM, and 60 min respectively. TEM characterization indicated that AgNPs have spherical form and sizes ranging from 14 to 32 nm. The antibacterial testing revealed that AgNPs have antibacterial activities against E. coli and B. subtilis with inhibition zone values are 8,38 ± 0,48 and 6,88 ± 1,47 respectively. Additionally, antioxidant testing presented that the IC₅₀ values were 85.05 µg/mL for SALE and 34.71 µg/mL for AgNPs. The results indicate that green synthesis of AgNPs from AgNO₃ precursor with SALE was done successfully and this nanoparticle has good antibacterial and antioxidant activities.

Abstract: This study proposes a simple method for fabricating metal particles. Metal nanoparticles are synthesized in an aqueous solution. The synthesis method is based on the galvanic replacement of one metal with another, i.e., the deposition of a metal on the surface of another metal using difference between the standard electrode potentials of the metals under ultrasonication. An aqueous colloidal solution of metallic copper (Cu) nanoparticles is prepared using Cu acetate and a metallic zinc (Zn) plate. A similar colloidal solution of metallic Cu nanoparticles is prepared using Cu acetate and a metallic iron plate. No metallic nanoparticles are obtained using metallic aluminum and nickel (Ni) plates because of the formation of passivated layers. An aqueous colloidal solution of metallic Ni nanoparticles is prepared using Ni acetate and a metallic Zn plate; however, Ni_0.7Zn_0.3O is also formed. The results of the study show that the proposed method can be used to produce metallic particles in a simple manner.

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: In this study, we proposed a method for fabricating diagnostic imaging nanoparticles composed of Au nanoparticles and silica shells (Au/SiO2). The proposed method consisted of two steps. The first step was the synthesis of Au nanoparticles. In sodium hydroxide (NaOH) solution, hydrogen tetrachloroaurate (III) trihydrate was reduced with tetrakis(hydroxymethyl)phosphonium chloride to synthesize Au nanoparticles with a diameter of 1.7 ± 0.3 nm. The Au nanoparticles were then coated with silica in the following step. The silica coating was achieved via a sol–gel reaction of tetraethyl orthosilicate in the presence of Au nanoparticles in water/ethanol dissolved in NaOH. The Au/SiO2 nanoparticles degraded faster in saline or phosphate-buffered saline than in water, and the X-ray imaging capability was retained.

Abstract: In the ultrasonic bonding process, oxides existing on the metal surfaces are removed, and bonding is achieved by bringing clean surfaces to be in contact with each other. However, the bonding process with microstructure variation is not well understood due to experimental difficulties. In this study, using a newly developed sample holder, which enables ultrasonic bonding in a TEM, we directly observed the bonding process at the nanoscale. The bonding process of Au foils with a clean surface was investigated and compared to that of Al foils with a stable oxide film, a bonding inhibitor, on the surface. During the Al ultrasonic bonding process, the nanoparticles generated dispersed over the entire bonding interface and finally formed a fine grain region at the interface. In contrast, in Au bonding, the nanoparticles generated tended to accumulate at the local area of the Au surface and form bridge-like connections between Au foils. It was considered that these differences in bonding behavior were caused by the surface conditions of the materials to be bonded.

Abstract: Nanosilica is a nanotechnology product with many substantial functions in many industries. Previous research showed that nano silica can be synthesized from geothermal silica, that caused silica scaling in injection well and turbine in geothermal power plant, reducing its power plant capacity by 40%. This research used geothermal silica as a precursor for nanosilica production with co-precipitation to recover amorphous silica from silica geothermal to reduce scaling while also increasing its economic value. The objectives of this study were to determine the model to represent the co-precipitation method for nano-silica by using nucleation and growth modelling, therefore help the scale-up process of nanosilica production. The experiment was conducted in four steps. (1) Silica washing utilized distillate water with a ratio of water to silica of 10:1 and sulfuric acid of 20% with a ratio of acid to silica of 4:1, both as a washing agent. (2) Preparation of HCl with concentrations of 3% and 9%. (3) Preparation of sodium silicate solution by reacting washed silica and NaOH to obtain sodium silicate. (4) Preparation of primary and secondary sodium silicate by diluting sodium silicate by two and four times to obtain primary and secondary sodium silicate, respectively. (5) Precipitation of sodium silicate with HCl consists of two steps using primary and secondary sodium silicate. The result showed that the model fit concentration data, with Sum of Squared Error (SSE) 1.9297.10-4, mass transfer coefficient rate is 9.8.10-3 dm/min, and the average relative error is 3.5%.

Abstract: Banana peels are considered one of the most abundant biowastes while Saba banana (Musa acuminata × balbisiana) is one of the most consumed fruit varieties in the Philippines. This research focused on the synthesis and characterization of carbon quantum dots (CQDs) from ripe and unripe Saba banana peels (SBP) via hydrothermal carbonization using low (100°C) and high (200°C) carbonization temperatures. Transmission electron microscopy revealed that ripe CQDs synthesized at these temperatures (rCQDs-100 and rCQDs-200, respectively) possessed disk-shaped and quasi-spherical structures with particle size range of 1.71-5.05 nm and 1.55-4.66 nm, respectively. However, unripe CQDs (uCQDs-100 and uCQDs-200, respectively) could not be considered as quantum dots due to their flake-like morphology and relatively large particle size (>40 nm and 2.21-21.24 nm, respectively). Likewise, Fourier-transform infrared spectroscopy identified the presence of enormous functional groups in all samples. Interestingly, C=N group was found only in uCQDs corresponding to the presence of chlorophyll in the samples. Moreover, all the CQDs emitted blue-green color under UV light illumination, with rCQDs-200 exhibited the best fluorescence emission. Thus, the approach of synthesizing CQDs using ripe SBP at higher temperature offers higher reacted precursors, better morphology, and greater fluorescence emission.

Abstract: The sulfur content present in graphene oxide prepared by Hummers' method has only been addressed by few papers so far. By modified Hammers method we synthesized thermally stable in ambient environment multilayer sulphur-doped graphene oxide. The samples were heat treated in an electrical furnace setup at different ambient temperatures and their crystallite size and linear coefficient of thermal expansion were extracted from Raman band intensity peak ratio as a function of temperature. We found unusually large (in comparison with graphene oxide) contraction on heating of multilayer two weight percent sulphur-doped graphene oxide with carbon to oxygen ratio of 2.3 in a narrow temperature range (308-318 K) with the lowest value of the linear thermal expansion coefficient of -18 ppm 1/K. Based upon an examination of the synthesized sulphur-doped graphene diffractograms, it is suggested that negative thermal expansion stems from the phonon backscattering by the sulphur impurity sites and the edges of the layers. The obtained experimental results have potential practical applications for fabrication of solar cells, sensors, lubricators, thermal actuators and also wavelike (second sound) thermal transport structures.

Abstract: The features of the dependence of the dielectric constant and the specific volume resistance of the composite "80 wt. % SKI-3 + 20 % wt. % LDPE" from the content of nanosized filler particles - aluminum and black carbon. The use of modern methods for studying macroscopic properties and electron microscopy made it possible to study the structure and morphology of the supramolecular formations of the composite. Models and possible physical mechanisms leading to extreme changes in εʹ and ρ_V at low concentrations of nanoparticles are presented.