Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Amorphous”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Effects of Microwave-Assisted Annealing on the Structure and Magnetic Properties of (Nd{sub 0.75}Pr{sub 0.25}){sub 9}Fe{sub 72}Ti{sub 1}Zr{sub 3}Mn{sub x} Mo{sub 4−x}B{sub 10.5}C{sub 0.5} Amorphous Ribbons

The amorphous as-spun ribbons with nominal composition (Nd{sub 0.75}Pr{sub 0.25}){sub 9}Fe{sub 72}Ti{sub 1}Zr{sub 3}Mn{sub x}Mo{sub 4−x}B{sub 10.5}C{sub 0.5}(x = 1, 2, 3) were annealed by microwave-assisted annealing. The effects of the Mn-doped alloys on glass-forming ability (GFA), crystallization, and magnetic properties of the Nd{sub 2}Fe{sub 14}B/α-Fe nanocomposite magnets were examined by thermal differential scanning calorimetry (DSC), X-ray diffraction (XRD), and vibrating sample magnetometry (VSM). An appropriate amount of Mn was beneficial to the optimization of the structure and magnetic properties. Compared with conventional annealing, the microwave-assisted annealing has contributed to the precipitation of hard magnetic phases and adjusted the proportion of hard and soft magnetic phases. The optimum magnetic properties with coercivity up to 805 kA/m were found for ribbons (with composition x = 1) annealed under the microwave power of 2000 W for 10 min.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Magnetic, Magnetocaloric Properties, and Phenomenological Model in Amorphous Ni{sub 80−x}Fe{sub x}(SiB){sub 20} Alloys with (x = 0, 2.4, 8, and 16)

Amorphous Ni{sub 80−x}Fe{sub x}(SiB){sub 20} ribbons with different Fe concentrations (0 ≤ x ≤ 16) were fabricated by melt spinning technique, and their magnetic and magnetocaloric properties were investigated and a phenomenological model was also applied. The Curie temperature (T{sub C}), magnetic moment of transition metal and maximum magnetic entropy change (− ΔS{sub M}) increase with increasing Fe content. At a magnetic field change of 2 T, the (− ΔS{sub M}) and relative cooling power (RCP) show the highest values of 0.53 J/kg K and 85 J kg{sup −1} respectively for Fe{sub 16}Ni{sub 64}(SiB){sub 20} alloys. In addition, a satisfactory agreement between the experimental and Hamad’s phenomenological model is reported.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Amino Acids as Additives against Amorphous Aggregation: In Vitro and In Silico Study on Human Lysozyme

The effect of 16 amino acids (AA) with various physicochemical properties was investigated on human lysozyme (HL) heat-induced amorphous aggregation. UV-Visible spectrophotometry was used to monitor the kinetics of aggregation in the absence and presence of AA, and transmission electron microscopy (TEM) images were taken from the aggregates. To conduct in silico experiments, Autodock vina was used for docking of AA into protein (via YASARA interface), and FTmap information was checked for an insight onto putative binding sites. Prediction of aggregation-prone regions of lysozyme was made by AGGRESCAN and Tango. Among all tested AA, phenylalanine had the best anti-aggregation effect, followed by lysine. In addition, based on in silico tests, Trp 109 and Val 110 of lysozyme are suggested to be of importance in the aggregation process of the enzyme. In conclusion, phenylalanine, arginine, and lysine were found to affect the nucleation phase of lysozyme aggregation and could be considered as suitable stabilizing structures for this enzyme.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2019

A novel liquid-mediated nucleation mechanism for explosive crystallization in amorphous germanium

We report a novel mechanism for explosive crystallization in amorphous germanium (a-Ge), which operates through liquid-mediated nucleation occurring under extreme thermal gradient conditions. The crystallization kinetics of sputter-deposited films with thicknesses ranging from 30 to 150 nm were characterized using in situ movie-mode dynamic transmission electron microscopy (MM-DTEM). After localized heating from a short laser pulse, explosive liquid phase nucleation (LPN) was observed to occur during the early stage (<2 μs) of crystallization in the thicker (>50 nm) films deposited on silicon nitride substrates. The crystallization front propagated at ~12–15 m/s and produced nanocrystalline microstructure with ~50 nm grains. A mechanism involving the existence of a relatively thick (>100 nm) transient liquid layer and a high nucleation rate is proposed to explain the behavior. In conclusion, the key thermodynamic and kinetic features as well as the feasibility of the mechanism are further explored by employing parametric and systematic phase-field modeling and simulations.

36 MATERIALS SCIENCE↗
DOE OSTI2018

A thermal study of amorphous and textured carbon and carbon nitride thin films via transient grating spectroscopy

Here in this study, we are considering a novel way of growing carbon nitride (CN) films by using High Power Impulse Magnetron Sputtering (HiPIMS). Carbon and CN thin films were grown on silicon substrate with varying nanocrystalline texturing: some samples were amorphous while others were either nanocrystalline graphite (for the carbon sample) or fullerene-like (for the CN sample), with both samples having a graphitic nanostructure vertically ordered throughout the film. Their thermal diffusivity was computed using transient grating spectroscopy in order to compare the impact of the material's nanostructure on its thermal property as well as benchmarking the performance of CN. It was found that the thermal properties of carbon thin films were decreased when doped with nitrogen, which is attributed to the increased atomic disorder introduced by the nitrogen cross-linking, impacting the phonon propagation. The impact of nitrogen doping on thermal properties opens new avenues in engineering materials with tailored and varying thermal properties at the microscale.

42 ENGINEERING↗
DOE OSTI2023

Mechanisms of Zn removal from water by amorphous geopolymer: Molecular-level insights from X-ray absorption spectroscopy, isotope fractionation, and surface complexation modeling

Porous geopolymers have attracted widespread attention as promising heavy metal adsorbents that can be synthesized from aluminosilicate solid wastes. However, the precise microstructural evidence for adsorbed heavy metals on geopolymers remains unclear due to the insensitivity of conventional characterization techniques on minerals with amorphous structure and surface disorder. Batch adsorption and column experiments coupled with X-ray absorption spectroscopy (XAS), Zn stable isotope, and surface complexation model (SCM) were employed to reveal the Zn removal mechanisms with coal fly ash porous geopolymer (CFAPG) at a molecular scale. The macroscopic kinetic and isothermal adsorption of Zn on CFAPG were well described by the pseudo-second-order model and Bi_Langmuir equation, respectively, indicating the presence of abundant heterogeneous active sites on the CFAPG surface. Further, two types of active sites on the CFAPG surface were identified by XAS coupled with Zn isotopes in batch experiments at pH <= 6.0: one is pH-dependent and associated with tetrahedral zinc coordi-nation, and the other is pH-insensitive and associated with octahedral zinc coordination; these sites were confirmed by the bidentate SCM as the variable charge site (surface complexation, >S-OH) and the permanent negative charge site (cation exchange, >X - ), respectively. Furthermore, the important contribution of surface co -precipitation besides surface complexation and cation exchange to the Zn adsorption on CFAPG was identified by XAS coupled with SCM in a flow-through column experiment at pH >6.0. These investigations provide a systemic understanding of the Zn adsorption mechanisms on CFAPG and an SCM reference for the application and prediction of geopolymers in heavy metal-contaminated water remediations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Amorphous-crystalline transition-driven synthesis of Co single-atom catalysts on MoO 3 for enhanced hydrogen evolution in acidic and alkaline media

Single atom catalysts (SACs) dispersed in metal oxide supports offer not only maximized catalyst utilization but also extended modulation capabilities through interactions between the SA and its support. However, achieving facile preparation and ensuring electrochemical durability of such SACs, particularly for hydrogen evolution reaction (HER) applications, remain formidable challenges. Here, our study addresses these issues by employing an amorphous-to-crystalline phase transition in MoO 3 to synthesize a cobalt (Co) SA catalyst. This method facilitates the production of highly selective SA catalysts at low temperatures and ensures their enhanced stability in HER applications. The Co SA MoO 3 catalyst exhibits superior performance in HER, operating effectively in both acidic and alkaline environments. Significantly, it maintains stable HER activity across these diverse electrolytic conditions. Our Density Functional Theory (DFT) calculations provide insights into the exceptional HER performance of Co SA MoO 3 . These calculations reveal that the strong affinity for hydrogen and water, facilitated by the modulation of the p-band orbitals at specific oxygen sites adjacent to the Co SA, establishes a thermoneutral pathway for HER. This study represents a pivotal advancement, showcasing a highly practical and robust single-atom catalyst, marking a significant stride towards sustainable energy solutions.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Mechanochemical formation of highly stable amorphous calcium carbonate in calcium silicates: Potential long-term storage of CO 2 in cement

Here, we have investigated mechanochemical reactions with the calcium silicate wollastonite to probe potential mechanisms of sequestration and long-term storage of CO 2 as mineral carbonates in cement pastes. Wollastonite, CaSiO 3 , was milled under ambient and 13 C enriched CO 2 atmospheres. Milling induced a structure change from monoclinic wollastonite-2M to triclinic-1T, consistent with high pressure treatment. The results from solid-state 13 C nuclear magnetic resonance (NMR) spectroscopy shows this process forms an extraordinarily stable amorphous calcium carbonate (ACC) phase that remains despite a high temperature dehydration treatment (130 °C) and persists in the same form after 3 yrs. of storage at ambient conditions. Thermogravimetric analysis (TGA) of these samples indicates that ACC is produced at the similar solid concentrations in both CO 2 -enriched and ambient atmospheres. The observation of meta-stable ACC due to wollastonite carbonation may play an important role in further exploration and optimization of mineral carbonation reactions for CO 2 capturing cement formulations.

13C solid-state NMR↗
DOE OSTI2020

Molecular scale insight of pore morphology relation with mechanical properties of amorphous silica using ReaxFF

Porous materials are typically heterogeneous and they contain large variations of micro-/nano-pore structures, causing complicated behaviors. In continuum models, most mechanical properties of porous materials are estimated based on porosity, while the variations of micro/nano structures are ignored. That could be problematic as the microscopic heterogeneity may affect the mechanical response of porous materials. Thus, understanding micro/nano heterogeneity impact has been the focus in many scientific and engineering subjects. In the present study, we investigated the effect of nanopore structure (including pore shape and orientation) as well as porosity on mechanical properties of amorphous silica (a-SiO 2 ). The pore sizes in our simulations are comparable to the corresponding ones observed in a-SiO 2 based materials. We found that the existing of nanopores strongly influences Young’s modulus (E) and critical energy release rate (G IC ). These properties decrease with increasing porosity. Importantly, the impact of nanopores was characterized by structural parameters of porous materials. In addition to dependency on porosity, Young’s modulus also was found to vary as a function of potential energy per atom, which highly depends on nanopore shape. Furthermore, critical energy release rate was found to increase with increasing ligament length (also known as pore wall thickness). Finally, the results highlighted the importance of nanopore structures, which must be taken into account when studying fracture mechanisms in porous materials. Based on our findings, it was proposed that mechanical properties of porous materials can be controlled by nano-engineering pore structures.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Nanomechanical investigation of the interplay between pore morphology and crack orientation of amorphous silica

Porous amorphous silica (a-SiO 2 ) is of both fundamental and practical interests, as they exhibit a large specific surface area and tunable porous network. However, the brittle nature of a-SiO 2 and the presence of pre-existing cracks at both micro- and nano-scales lead to complex mechanical behavior. Here, we systematically investigate the effects of pre-existing crack and its orientation on the mechanical properties of a-SiO 2 with varying pore shapes using reactive molecular dynamics simulations. We demonstrate that pore shape will primarily influence the Young’s modulus (E) and critical energy release rate (G IC ). We further investigate the impact of pore shape and crack orientation by local characterization of the structural parameters. By defining the high stress and inter-mediate regions, the overall mechanical properties are found to be greatly influenced by the pore shape which can be reflected through the spatial distribution of von Mises stress. Overall, G IC is found to increase with the increase of ligament length (also known as pore wall thickness). Meanwhile, the effect of the pre-existing crack on the crack propagation process is confirmed by analyzing the density distribution evolution. These results highlight the interplay between pore morphology and crack orientation in controlling the fracture behaviors in brittle porous materials.

42 ENGINEERING↗
DOE OSTI2025

Mechanisms and stability of Li dynamics in amorphous Li-Ti-P-S-based mixed ionic–electronic conductors: A machine learning molecular dynamics study

Mixed ionic–electronic conductors (MIECs) exhibit both high ionic and electronic conductivity to improve the battery performance. In this work, we investigate the mechanism and stability of transport channels in our recently developed MIEC material, amorphous Ti-doped lithium phosphorus sulfide (LPS), using molecular dynamics (MD) simulations with a 99% accurate machine-learning force field (MLFF) trained on ab initio MD data. The achieved MLFF helps efficient large-scale MD simulations on LPS with three Ti concentrations (10%, 20%, and 30%) and six temperatures (25°C to 225°C) to calculate ionic conductivity, activation energy, Li-ion transport mechanism, and configurational entropy. Results show that ionic conductivities and activation energies are consistent with our recent experimental values. Moreover, Li-ion transport occurs via free-volume diffusion facilitated by the formation of disordered Li-S polyhedra. The enhanced stability of transport channels at 10% and 20% Ti doping, compared to 0% and 30%, is observed by analyzing the vibrational and configurational entropy of these disordered Li-S polyhedra. Overall, this study highlights the utility of MLFF-based large-scale MD simulations in explaining the transport mechanism and the stability of Li-ion in Ti-doped LPS electrolyte with significant computational efficiency.

And configuration entropy↗
DOE OSTI2025

Exceptional radiation resistance of hardened amorphous SiC under high-temperature hydrogen ion implantation

This study provides a compelling comparison of the structural and mechanical responses of single-crystal silicon carbide (sc-SiC), nanocrystalline silicon carbide (nc-SiC), and amorphous silicon carbide (am-SiC) to hydrogen ion implantation at 650 °C across three distinct fluences: low, medium, and high (LF, MF, HF). While both sc-SiC and nc-SiC exhibit blistering, microcracking, and exfoliation, am-SiC remains free of blisters, demonstrating superior resilience. Notably, nc-SiC, with its high density of stacking faults (SFs), requires a higher fluence to initiate blistering compared to sc-SiC. At high fluences, hydrogen accumulation at grain boundaries (GBs) in nc-SiC elevates internal gas pressure, intensifying exfoliation. In sc-SiC, blistering leads to increased hardness, whereas in nc-SiC, the degradation of the SF structure results in a reduction in hardness. In contrast, am-SiC undergoes structural relaxation during irradiation, resulting in a significant increase in hardness while maintaining its structural integrity, with only the formation of nano-sized spherical bubbles observed. Furthermore, these findings highlight the exceptional suitability of am-SiC for nuclear applications, where resistance to radiation-induced microcracking is critical.

36 MATERIALS SCIENCE↗
DOE OSTI2019

High-dose temperature-dependent neutron irradiation effects on the optical transmission and dimensional stability of amorphous fused silica

The primary concern for implementing amorphous fused silica (a-SiO 2 ) fiber optic sensors in a nuclear environment is the radiation-induced attenuation (RIA) of the light signal due to the formation of radiation-induced color centers. In addition, Bragg grating sensors drift under irradiation due to radiation-induced compaction of the a-SiO 2 structure. This work provides new data regarding RIA and radiation-induced compaction of a-SiO 2 samples irradiated to a fast neutron fluence of 2.4 × 10 21 n/cm 2 at temperatures of 95, 298, and 688 °C. Results show that RIA may be approaching saturation for the range of photon energies evaluated in this paper and that the hydroxyl content has a significant impact on RIA when the irradiation temperature is increased to 688 °C. Furthermore, a model was developed for predicting radiation-induced compaction, and the resulting signal drift for Bragg grating sensors, as a function of neutron fluence and temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Synthesis of magnesiowüstite nanocrystallites embedded in an amorphous silicate matrix via low energy multiple ion implantations

The synthesis process is presented for experimentally simulating modifications in cosmic dust grains using sequential ion implantations or irradiations followed by thermal annealing. Cosmic silicate dust analogues were prepared via implantation of 20–80 keV Fe - , Mg - , and O - ions into commercially available p-type silicon (100)wafers. The as-implanted analogues are amorphous with a Mg/(Fe+Mg) ratio of 0.5 tailored to match theoretical abundances in circumstellar dusts. Before the ion implantations were performed, Monte-Carlo-based ion-solid interaction codes were used to model the dynamic redistribution of the implanted atoms in the silicon substrate. 600 keV helium ion irradiation was performed on one of the samples before thermal annealing. Two samples were thermally annealed at a temperature appropriate for an M-class stellar wind, 1000 K, for 8.3 h in a vacuum chamber with a pressure of 1 x 10 -7 torr. The elemental depth profiles were extracted utilizing Rutherford Backscattering Spectrometry (RBS) in the samples before and after thermal annealing. X-ray diffraction (XRD)analysis was employed for the identification of various phases in crystalline minerals in the annealed analogues. Transmission electron microscopy (TEM) analysis was utilized to identify specific crystal structures. RBS analysis shows redistribution of the implanted Fe, Mg, and O after thermal annealing due to incorporation into the crystal structures for each sample type. XRD patterns along with TEM analysis showed nanocrystalline Mg and Fe oxides with possible incorporation of additional silicate minerals.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Virtual bound states elements and their effects on magnetic and electrical properties of Fe-Ni based metal amorphous nanocomposites

Metal amorphous nanocomposite alloys, with compositions (Fe 70 Ni 30 ) 80-x Nb 4 Si 2 B 14 TE x (0 ≤ x ≤ 5), where TE is a transition element, and (Fe 70 Ni 30 ) 80-y Nb 4+y Si 2 B 14 (0.5 ≤ y ≤ 2) were synthesized. Samples were annealed at 440 °C and strain-annealed at 440 °C and 300 MPa. Resistivity was found to increase with small substitutions of TE elements. Increasing V resulted in reduced B s from 1.2 T to 0.5 T. Further Mo additions lowered B s to 0.6 T, and consistently reduced the permeability. For Cr and Nb, resistivity increased, and strain-annealed permeability was lower than the annealed permeability. Finally, toroidal core losses on (Fe 70 Ni 30 ) 79.5 Nb 4 Si 2 B 14 V 1 yielded W1.0/400 = 2.1 W/kg, and W1.0/1 k = 6.0 W/kg.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Reactive flash sintering of the complex oxide Li 0.5 La 0.5 TiO 3 starting from an amorphous precursor powder

We report the transformation of an amorphous mixture of Li 0.5 La 0.5 TiO 3 (LLTO) directly into a single phase dense polycrystal, all within a few seconds at about 800°C by the flash method. The starting material is a chemically-prepared precursor powder that experiences concurrent crystallization and densification to cubic LLTO during the flash event, as shown by in-situ X-ray measurements. The experiments were conducted at a constant heating rate with fields from 80 to 120 V cm –1 and a current limit of 60 mA mm –2 . Here, the resulting polycrystal yielded a bulk conductivity of 0.5 mS cm –1 .

36 MATERIALS SCIENCE↗
DOE OSTI2022

How arsenic makes amorphous GeSe a robust chalcogenide glass for advanced memory integration

The 3D integration technology in semiconductor fabrication requires a key component, the ovonic threshold switching (OTS) selector, to suppress the current leakage. The As doped amorphous (a-) GeSe glass is a commercialized OTS material in 3D phase-change memory, but the understanding of such a doping mechanism is still inadequate. Here we systematically explore the effect of As doping on the structural, bonding, and dynamics properties of a-GeAsSe using ab initio molecular dynamics simulations. The results reveal that As atoms form strong bonds with both Ge and Se atoms. The distorted octahedral structures and the 5-fold rings linked by atoms are increased. All of these structural features lead to a more disordered configuration. Moreover, as atoms have notably slowed down the atomic mobility, rendering a-GeAsSe a high stability. Overall, our studies offer insightful understanding of As-doping in OTS materials, paving the way for the design and application of advanced selector devices.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Probing Li ion dynamics in amorphous xLi 2 SO 4 ∙(1-x)LiPO 3 by quasielastic neutron scattering

The diffusion dynamics of a series of lithium sulfate substituted phosphate glass materials xLi 2 SO 4 ∙(1-x)LiPO 3 has been probed by quasielastic neutron scattering. Amorphous Li ion conductors are attractive as electrolyte materials for all-solid state batteries because they are highly isotropic and chemically stable. Local disorder is expected to reduce barriers to ion migration – leading to improved ionic conductivity relative to their crystalline counterpart – while minimizing unwanted electron transport. We report Li self-diffusion in these materials on a length scale comparable to the interatomic spacings, obtaining values D ≃ 55 ± 4 × 10 -8 cm 2 /s at 450 K. Elastic neutron scattering measurements show an alteration of the phosphate chain backbone of the glass material.

36 MATERIALS SCIENCE↗