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At least 1,081 records · Page 60
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Effect of Fe Substitution on Microstructure and Magnetic Properties of Ni{sub 1−x}Fe{sub x}O{sub 2} Nanoparticles

Fe-substituted NiO nanoparticles (Ni{sub 1−x}Fe{sub x}O{sub 2}) (x= 0.00, 0.03, 0.05, 0.07, and 0.09) were synthesised using ball-milling method followed by vacuum sintering and studied for their microstructural and magnetic properties. All the samples show a cubic structure with a crystallite size of 17–26 nm. Secondary phases related to Fe{sub 2}O{sub 3} were identified from XRD, indicating that the observed ferromagnetism may be due to the dopants. The doping of Fe ions does not cause any significant variation in the crystal structure. The pure NiO nanoparticles were weak ferromagnetic in nature, and Fe-doped NiO nanoparticles exhibit room temperature ferromagnetism. The strength of magnetization increased from 0.57 to 0.94 emu/g with an increase of Fe concentration from 3 to 7 at.%, respectively. A high coercive field of 173 Oe was observed for the Ni{sub 1−x}Fe{sub x}O{sub 2} nanoparticles at x= 0.09. The results and the process of development of ferromagnetism at room temperature in the Ni{sub 1−x}Fe{sub x}O{sub 2} nanoparticles were presented and discussed in detail.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Evolution of Micro-structure and Magnetic Properties in L1{sub 0} CoPt Nanoparticles by Au Addition

L1{sub 0} CoPt-Au nanoparticles with face-centered tetragonal (FCT) structure were synthesized by sol-gel technique at 700°C. The micro-structure and magnetism of L1{sub 0} CoPt-Au were measured by different measuring technologies. The influences of Au on the micro-structure and magnetism of L1{sub 0} CoPt nanoparticles were investigated. The Au addition promoted the formation of ordered L1{sub 0} phase CoPt nanoparticles and improved the grain size of L1{sub 0} CoPt nanoparticles When the Au content increased to 10 at.%, coercivity increased and saturation magnetization decreased, which may be originated from the increased order degree and ferrimagnetic nature of L1{sub 0} CoPt nanoparticles. Interestingly, when the Au addition was more than 10 at.%, the coercivity decreased due to the decrease of the order degree.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Complex Electric Modulus Spectroscopy of (MnFe{sub 2}O{sub 4}){sub x}/CuTl-1223 Nanoparticles-Superconductor Composites

Manganese ferrite (MnFe{sub 2}O{sub 4}) nanoparticles and Cu{sub 0.5}Tl{sub 0}.{sub 5}Ba{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10−δ}(CuTl-1223) superconducting phase were synthesized by sol-gel and solid-state reaction methods, respectively. Different contents of MnFe{sub 2}O{sub 4} nanoparticles were added in CuTl-1223 superconducting matrix to get (MnFe{sub 2}O{sub 4}){sub x}/CuTl-1223; x = 0∼2.0 wt% nanoparticles-superconductor composites. Complex electric modulus spectroscopy measurements of (MnFe{sub 2}O{sub 4}){sub x}/CuTl-1223 composites were carried out at different test frequencies from 20 Hz to 10 MHz and at different operating temperatures from 78 to 253 K to analyze and interpret the dynamical aspects of electrical transport phenomena (i.e., such as carrier hopping rate, conductivity, and blocking factor). The complex electric modulus spectra showed the effects of both grains and grain-boundaries on electrical properties. The capacitance of grain-boundaries was found higher than that of grains. The capacitive behavior of grains was increased and that of grain-boundaries was decreased with increasing operating temperature for all these samples. Blocking factor of these composites was increased with increasing contents of MnFe{sub 2}O{sub 4} nanoparticles. Shifting of peaks in imaginary part of modulus spectra towards lower frequency with increasing contents of these nanoparticles showed non-Debye type relaxation phenomenon in the material.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Tuning the Magnetic Properties of ZnFe{sub 2}O{sub 4} Nanoparticles Through Partial Doping and Annealing

The aim of this study was to investigate the effect of annealing temperature and cobalt cation (Co{sup 2+}) doping on the magnetic properties of zinc ferrite (ZFO) nanoparticles. The nanoparticles were prepared through sol-gel combustion process with citric acid as the fuel. The obtained nanoparticles were annealed at several temperatures from 300 to 1000 °C for 2 h. Spinel formation was proved by X-ray diffraction (XRD) patterns, and the average crystallite size in all samples was estimated between 22 and 32 nm. It is worthwhile to mention that Fe{sub 2}O{sub 3} and ZnO are detected as the medium phases. Meanwhile, Fe{sub 2}O{sub 3} phase transformation to the other allotropes has happened around 400 °C and was characterized via the simultaneous thermal analysis (STA) and XRD. For higher annealing temperatures, diffusion has gradually been completed and, finally, the single phase of spinel structure was prepared at 1000 °C. In addition, field-emission scanning electron microscopy (FESEM) images revealed that the nanoparticle size after annealing was between 30 and 200 nm for the whole samples. The formation of the spinel phase was considered the most important factor on the magnetic properties of ZFO. Cobalt doping, annealing temperature, and also Fe{sub 2}O{sub 3} phase were the main factors on changing magnetic properties. Paramagnetic nanoparticles with higher coercivity for doped samples rather than un-doped samples have been obtained.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Thermal Decomposition Synthesis of MgFe{sub 2}O{sub 4} Nanoparticles for Magnetic Hyperthermia

In this work, the effects of the thermal decomposition temperature and time on the structure, cation distributions, magnetic properties, and AC magnetically induced heating characteristics of MgFe{sub 2}O{sub 4} nanoparticles were investigated. The structure and cation distributions between the tetrahedral and octahedral sites determined by X-ray diffraction method showed single-phase MgFe{sub 2}O{sub 4} nanoparticles had a partially inverse structure. The inversion coefficient increased using high reaction temperature and time. The square-like shape and small magnesium ferrite nanoparticles with narrow particle size distribution were synthesized at high reaction temperatures, as observed by transmission electron microscopy. Magnetic properties of MgFe{sub 2}O{sub 4} nanoparticles studied by vibrating sample magnetometry showed the ferrimagnetic characteristics with the highest saturation magnetization of 24 emu/g at a reaction temperature of 300 °C for 60 min. Furthermore, the AC magnetically induced heating characteristics of MgFe{sub 2}O{sub 4} nanoparticles were correlated to the saturation magnetization and coercivity.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Influence of Particle Size on the Spin Pinning Effect in the fcc-FePt Nanoparticles

In this work, the Fe{sub 60}Pt{sub 40} nanoparticles were synthesized through the chemical reduction method by using the Fe(CO){sub 5} and the Pt(acac){sub 2} as the metallic precursor. The particle size of the synthesized FePt nanoparticles was controlled by adjusting the reaction conditions involving of the Fe(CO){sub 5}-injecting temperature and the soak time of reaction. The structure, morphology, and magnetic properties of the synthesized FePt nanoparticles were characterized by XRD, TEM, and vibrating sample magnetometer (VSM), respectively. The synthesized nanoparticles exhibit uniform size and good dispersity. The magnetization behaviors indicate that the nanoparticles present the core-shell magnetic structure including the ferromagnetic core part and the spin-disorder shell part. There exists a spin pinning effect of the shell part on the core part. The increase of particle size weakens the spin pinning effect.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Synthesis of TiO{sub 2} Nanoparticles from Ilmenite Through the Mechanism of Vapor-Phase Reaction Process by Thermal Plasma Technology

Synthesis of nanoparticles of TiO{sub 2} was carried out by non-transferred arc thermal plasma reactor using ilmenite as the precursor material. The powder ilmenite was vaporized at high temperature in plasma flame and converted to a gaseous state of ions in the metastable phase. On cooling, chamber condensation process takes place on recombination of ions for the formation of nanoparticles. The top-to-bottom approach induces the disintegration of complex ilmenite phases into simpler compounds of iron oxide and titanium dioxide phases. The vapor-phase reaction mechanism was carried out in thermal plasma zone for the synthesis of nanoparticles from ilmenite compound in a plasma reactor. The easy separation of iron particles from TiO{sub 2} was taken place in the plasma chamber with deposition of light TiO{sub 2} particles at the top of the cooling chamber and iron particles at the bottom. The dissociation and combination process of mechanism and synthesis are studied briefly in this article. The product TiO{sub 2} nanoparticle shows the purity with a major phase of rutile content. TiO{sub 2} nanoparticles produced in vapor-phase reaction process shows more photo-induced capacity.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

The Tribological Behavior of Hybrid Graphene/Tungsten Disulfide Nanoparticle Coatings

Environmental concerns regarding the disposal of fluid lubricants have led to the application of green technologies to metalworking processes in the form of dry lubricants. These dry lubricants are typically applied as spray coatings that employ the use of nanoparticles. The possible use of graphene in the form of graphene/tungsten disulfide (G/WS{sub 2}) nanoparticle spray coatings has been examined in this research. The investigation was performed through the use of ball-on-disk tests at ambient temperatures to ascertain the possible application of the aerosol spray coatings to the aluminum forming processes. The coatings proved to possess good adhesion to the Al-Mg alloy substrate. The nanoparticle spray coatings were tested at various graphene to WS{sub 2} concentrations and under varying loads. A low steady-state COF was noted for all graphene concentrations during sliding contact under all the loads examined. The durability of the coatings was observed to improve with increasing loads. The low COF was attributed to the formation of wear-induced transfer layers on the steel balls and tribolayers on the coated Al-Mg surfaces. The coating durability was related to the concentration of graphene within the nanoparticle spray coatings and the stability of the tribolayers during sliding contact. The results highlight that the G/WS{sub 2} nanoparticle spray coatings could be considered for aluminum metalworking processes.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Mitigating keyhole pore formation by nanoparticles during laser powder bed fusion additive manufacturing

Keyhole pore formation is one of the most detrimental subsurface defects in the laser metal additive manufacturing process. However, effective ways to mitigate keyhole pore formation beyond tuning laser processing conditions during keyhole mode laser melting are still lacking. Here we report a novel approach to mitigate keyhole pore formation during laser powder bed fusion (LPBF) process by using stable nanoparticles. The critical keyhole depth for keyhole pore generation (i.e., the largest keyhole depth without keyhole pore formation) during LPBF of Al6061 increases from 246 µm to 454 µm (85% increase) after adding TiC nanoparticles. In-depth x-ray imaging studies and thermo-fluid dynamics simulation enable us to identify that two mechanisms work together to mitigate keyhole pore generation: (1) adding nanoparticles prevents the keyhole from collapsing by increasing the liquid viscosity to impede the protrusion development; (2) adding nanoparticles slows down the keyhole pore movement by increasing the liquid viscosity, resulting in the recapturing of the pore by the keyhole. We further demonstrate that adding TiC nanoparticles can also eliminate the keyhole fluctuation induced keyhole pore during LPBF of Al6061. Our research provides a potential way to mitigate keyhole pore formation for defect lean metal additive manufacturing.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Impact of hydrogen bonding pendant groups in polymer grafted nanoparticles on interlayer adhesion and mechanical properties in material extrusion printing

The addition of nanoparticles or copolymer grafted nanoparticles (CPGNPs) to polymeric matrices greatly improves thermomechanical properties of the resulting nanocomposite, but corresponding studies of nanocomposite systems created by 3D printing are few, especially in the realm of functional polymeric materials. Here we describe how silica nanoparticle-grafted, random copolymers of poly(methyl methacrylate-random-2-uriedo-[1H]-pyrimidinone methacrylate) (P(MMA-r-UPyMA) dramatically increases the mechanical properties of poly(methyl methacrylate) (PMMA) based nanocomposite specimens created by melt extrusion printing. Most notably, when these novel CPGNPs are combined with PMMA matrix chains via a solution-based process, printed specimens containing only 0.5 wt% additive show significant increases in Young’s modulus (90%), storage modulus (93%), tensile modulus (148%) and ultimate tensile strength (110%). These improvements are ascribed to strengthening of adhesion across interfaces due to multi-point hydrogen bonding between UPyMA groups, the reinforcement effect of the P(MMA-r-UPyMA)-grafted silica nanoparticles, as well as hydrogen bonding interactions and entanglements between graft and matrix chains. Imaging of fracture surfaces after tensile testing reveals that in comparison to nanocomposites created by simple mechanical mixing of solids, the solution-casting process improves the dispersion of nanoparticles and reduces the void spaces between printed roads. These studies demonstrate that introducing functionality into polymer grafts, such as hydrogen bonding interactions, and intimate mixing of polymer-modified nanomaterials can greatly improve interlayer adhesion and mechanical properties, thereby advancing this method of polymer additive manufacturing

36 MATERIALS SCIENCE↗
DOE OSTI2025

Effect of grafting density on the two-dimensional assembly of nanoparticles

Employing grazing-incidence small-angle X-ray scattering (GISAXS) and X-ray reflectivity (XRR), we demonstrate that films composed of polyethylene glycol (PEG)-grafted silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs), as well as their binary mixtures, form highly stable hexagonal structures at the vapor–liquid interface. These nanoparticles exhibit remarkable stability under varying environmental conditions, including changes in pH, mixing concentration, and PEG chain length. Short-chain PEG grafting produces dense, well-ordered films, while longer chains produce more complex, less dense quasi-bilayer structures. AuNPs exhibit higher grafting densities than AgNPs, leading to more ordered in-plane arrangements. In binary mixtures, AuNPs dominate the population at the surface, while AgNPs integrate into the system, expanding the lattice without forming a distinct binary superstructure. In conclusion, these results offer valuable insights into the structural behavior of PEG-grafted nanoparticles and provide a foundation for optimizing binary nanoparticle assemblies for advanced nanotechnology applications.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Coiled-coil forming peptides for the induction of silver nanoparticles

Biopolymers with defined sequence patterns offer an attractive alternative for the formation of silver nanoparticle (AgNP). A set of coiled-coil dimer forming peptides was tested for their AgNP formation ability. Seventeen of those peptides mediated the formation of AgNPs in aqueous solution at neutral pH, while the formation of a coiled-coil dimer inhibited the nanoparticle generation. A QSAR regression model on the relationship between sequence and function suggests that in this peptide type the patterns KXQQ and KXEE are favorable, whereas Ala residues appear to have an inhibitory effect. UV–VIS spectra of the obtained nanoparticles gave a peak at around 420 nm, typical for AgNPs in the size range around 40 nm, which was confirmed by dynamic light scattering and transmission electron microscopy. Peptide-induced AgNPs exhibited good antibacterial activity, even after a 15 min contact time, while they had low toxicity to human cells at the same concentrations. These results show that our designed peptides generate AgNPs with antibacterial activity at mild conditions and might be used for antibacterial coatings. - Highlights: • 17 of the 30 tested coiled-coil forming peptides induce AgNP formation. • Coiled-coil dimer formation suppresses AgNP generation of individual peptides. • Size of the peptide-induced silver nanoparticles is around 40 nm. • QSAR analysis points to the importance of KXQQ and KXEE motifs for AgNP generation. • Peptide-induced silver nanoparticles exhibit antibacterial activity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Preparation, characterization of Fe3O4 at TiO2 magnetic nanoparticles and their application for immunoassay of biomarker of exposure to organophosphorus pesticides

Novel Fe3O4 at TiO2 magnetic nanoparticles were prepared and developed for a new nanoparticle-based immunosensor for electrochemical quantification of organophosphorylated butyrylcholinesterase (BChE) in plasma, a specific biomarker of exposure to organophosphorus (OP) agents. The Fe3O4 at TiO2 nanoparticles were synthesized by hydrolysis of tetrabutyltitanate on the surface of Fe3O4 magnetic nanospheres, and characterized by attenuated total reflection Fourier-transform infrared spectra, transmission electron microscope and X-ray diffraction. The functional Fe3O4 at TiO2 nanoparticles were performed as capture antibody to selectively enrich phosphorylated moiety instead of phosphoserine antibody in the traditional sandwich immunoassays. The secondary recognition was served by quantum dots (QDs)-tagged anti-BChE antibody (QDs-anti-BChE). With the help of a magnet, the resulting sandwich-like complex, Fe3O4 at TiO2/OP-BChE/QDs-anti-BChE, was easily isolated from sample solutions and the released cadmium ions were detected on a disposable screen-printed electrode (SPE). The binding affinities were investigated by both surface plasmon resonance (SPR) and square wave voltammetry (SWV). This method not only avoids the drawback of unavailability of commercial OP-specific antibody but also amplifies detection signal by QDs-tags together with easy separation of samples by magnetic forces. The proposed immunosensor yields a linear response over a broad OP-BChE concentrations range from 0.02 to 10 nM, with detection limit of 0.01 nM. Moreover, the disposable nanoparticle-based immunosensor has been validated with human plasma samples. It offers a new method for rapid, sensitive, selective and inexpensive screening/evaluating exposure to OP pesticides.

biomarker↗
DOE OSTI2021

Enhancing functionalities in carbon fiber composites by titanium dioxide nanoparticles

Carbon fiber composite's high specific strength makes it incredibly useful for structural applications. However, their low strain-to-failure can be problematic in structural applications that can potentially see high strain conditions or high fatigue cycles resulting in sudden, catastrophic failure. This is further complicated by damage manifesting within the composite thus not showing damage indicators on the surface. Therefore, monitoring the structural integrity and strain history of the composite in application by itself—while maintaining positive composite performance—is vital to ensure safe operation. In this study, a homogeneous dispersion of TiO 2 nanoparticles on carbon fiber is demonstrated to generate a piezoresistive carbon fiber polymer matrix composite with enhanced self-sensing capabilities. The nanoparticle-embedded composites also exhibited superior strength and damping potential compared to the nanoparticle-free composites. The apparent interlaminar shear strength increased by up to 15% and the damping loss factor increased by an average of 150% while the piezoresistive sensitivity increased by up to 180% with the addition of a small weight fraction of nanoparticles to the fiber surface. These results demonstrate an approach to simultaneously improve the sensing capabilities, damping behavior and mechanical strength of carbon fiber composites by simply adding nanoparticles in the fiber sizing using a commercially scalable deposition method.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Growth of encapsulating carbon on supported Pt nanoparticles studied by in situ TEM

Carbon deposition on MgO-supported Pt nanoparticles from ethylene decomposition was explored by in situ transmission electron microscopy (TEM) at the atomic level. An imaging strategy was established for controlling beam-gas-sample interactions that minimizes beam-induced changes of the reaction. Using this strategy, it was possible to observe how carbon encapsulation occurs on Pt nanoparticles and the role of the Pt surface morphology. The evidence indicates that multiple partial layers grew simultaneously prior to full encapsulation of the nanoparticle. The growth of carbon on Pt nanoparticles was discovered to induce significant changes in the nanoparticle shape, resulting in particles becoming rounder as coking progressed. Closer examination of the surface structure revealed that in some cases carbon growth induced step formation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Photoactivatable fluorescent probes reveal heterogeneous nanoparticle permeation through biological gels at multiple scales

Diffusion through biological gels is crucial for effective drug delivery using nanoparticles. Here, we demonstrate a new method to measure diffusivity over a large range of length scales – from tens of nanometers to tens of micrometers – using photoactivatable fluorescent nanoparticle probes. We have applied this method to investigate the length-scale dependent mobility of nanoparticles in fibrin gels and in sputum from patients with cystic fibrosis (CF). Nanoparticles composed of poly(lactic-co-glycolic acid), with polyethylene glycol coatings to resist bioadhesion, were internally labeled with caged rhodamine to make the particles photoactivatable. We activated particles within a region of sample using brief, targeted exposure to UV light, uncaging the rhodamine and causing the particles in that region to become fluorescent. We imaged the subsequent spatiotemporal evolution in fluorescence intensity and observed the collective particle diffusion over tens of minutes and tens of micrometers. We also performed complementary multiple particle tracking experiments on the same particles, extending significantly the range over which particle motion and its heterogeneity can be observed. In fibrin gels, both methods showed an immobile fraction of particles and a mobile fraction that diffused over all measured length scales. In the CF sputum, particle diffusion was spatially heterogeneous and locally anisotropic but nevertheless typically led to unbounded transport extending tens of micrometers within tens of minutes. Lastly, these findings provide insight into the mesoscale architecture of these gels and its role in setting their permeability on physiologically relevant length scales, pointing toward strategies for improving nanoparticle drug delivery.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Synthesis of UO 2 nanoparticles via coulometric titration: influence of electrolytes and ligands on synthesized particle properties

Here, this study investigates the controlled synthesis of uranium oxide nanoparticles (UO 2 NPs) via coulometric titration under ambient conditions, focusing on the impact of electrolyte anions, salt concentrations, and strongly complexing ligands on particle formation and properties. Using dilute solutions of mineral acids (HNO 3 , HCl, and HClO 4 ), we demonstrate that the choice of electrolyte anion affects particle size, polydispersity, and surface charge. Particle characterization using dynamic light scattering and transmission electron microscopy shows that particles synthesized in perchlorate are largest and show a high degree of polydispersity. In comparison, particles synthesized in chloride are smaller and more uniform in size. Synthesis in nitrate yields a wide variety of particle sizes, with the major fraction (>65 %) having a smaller size than that obtained in the other two electrolytes. The presence of more strongly coordinating ligands such as sulfate and acetate modulate hydrolysis and condensation reactions, with sulfate suppressing nanoparticle formation across a wide concentration range ([SO 4 2- ] > 5 mM) and acetate enabling stable colloidal suspensions at [HOAc] ≤ 0.1 M. Synthesis in concentrated electrolytes (2 M NaNO 3 , NaCl, or NaClO 4 ) accelerates reaction kinetics but introduces challenges, as particles showed increased polydispersity and aggregation, and were more prone to oxidation. Electrolyte effects on actinide oxide nanoparticle formation are discussed and a short comparison to established nanoparticle syntheses is drawn. This work underscores the importance of tailoring synthesis parameters to achieve desired nanoparticle properties, providing valuable insights for optimizing UO 2 NP production for various applications.

Actinide hydrolysis↗
DOE OSTI2014

Gamma ray irradiated AgFeO{sub 2} nanoparticles with enhanced gas sensor properties

AgFeO{sub 2} nanoparticles were synthesized via a facile hydrothermal method and irradiated by various doses of gamma ray. The products were characterized with X-ray powder diffraction, UV–vis absorption spectrum and transmission electron microscope. The results revealed that the crystal structure, morphology and size of the samples remained unchanged after irradiation, while the intensity of UV–Vis spectra increased with irradiation dose increasing. In addition, gamma ray irradiation improved the performance of gas sensor based on the AgFeO{sub 2} nanoparticles including the optimum operating temperature and sensitivity, which might be ascribed to the generation of defects. - Graphical abstract: Gamma ray irradiation improved the performance of gas sensor based on the AgFeO{sub 2} nanoparticles including sensitivity and optimum operating temperature, which might be ascribed to the generation of defects. - Highlights: • AgFeO{sub 2} nanoparticles were synthesized and irradiated with gamma ray. • AgFeO{sub 2} nanoparticles were employed to fabricate gas sensors to detect ethanol. • Gamma ray irradiation improved the sensitivity and optimum operating temperature.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗