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DOE OSTI2022

Calibrating uncertain parameters in melt pool simulations of additive manufacturing

Melt pool scale numerical modeling of additive manufacturing (AM) processes can provide predictive capabilities and theoretical insight into the process-property-structure-performance relationships for AM parts. Despite capabilities of numerical models to solve complex multi-physics problems, it is often important to consider a tradeoff between detailed physics and computational cost. Therefore, sources of uncertainty in both experimental conditions and the parameters needed for modeling require models to be validated against empirical evidence. Here, a method is proposed to calibrate uncertain parameters used in continuum-scale melt pool models for powder bed fusion (PBF) AM. Both a simplified heat transfer model and a heat transfer and fluid flow model were investigated. A surrogate model and Markov chain-based optimization algorithm calibrated melt pool geometry for models within experimental variation of the target melt pool width and depth from the NIST AM-Bench 2018-02 dataset. The melt pool temperature distributions, solidification parameters, and simulated multi-layer solidification microstructures were compared between the two models. Similar results from both models indicate that calibrated, lower fidelity numerical models may be used in place of higher fidelity models to generate melt pool solidification data. Finally, these calibrated models therefore enable lower computational cost melt pool simulations without a noticeable decrease in simulation accuracy for grain-scale microstructure simulations.

36 MATERIALS SCIENCE↗

DOE OSTI2024

Compact and accurate chemical mechanism for methane pyrolysis with PAH growth

In this study, a reliable and compact chemical mechanism of gas-phase methane pyrolysis leading to formation of large polycyclic aromatic hydrocarbon (PAH) molecules has been developed. This model is designed for studies of carbon nanostructure synthesis such as carbon black and graphene flakes, including soot growth kinetics. Methane pyrolysis with carbon nanostructure synthesis is a two-stage process where conversion of CH 4 to C 2 H 2 precedes the growth of PAH molecules from acetylene. We present a single chemical mechanism that accurately describes both stages. We have constructed a compact and accurate chemical mechanism capable of modeling both stages of methane pyrolysis based on the ABF mechanism which was expanded with the most prominent reaction pathways from the mechanism by Tao for small PAH molecules and HACA pathways for larger PAH molecules, up to 37 aromatic rings. The resulting mechanism was validated through comparison to multiple available sets of experimental data. Good agreement with the experimental data for both processes was obtained. Performance of the mechanism was tested for pyrolysis of methane-rich mixtures under long residence times leading to abundant formation of PAH molecules. It is shown that the inclusion of larger PAH species (up to A37) in the chemical mechanism is important for accurate prediction of the fraction of carbon converted to PAH molecules and, correspondingly, the residual fraction of acetylene in the mixture. The mechanism file is available upon request.

08 HYDROGEN↗

DOE OSTI2024

Rapid mapping of electrochemical processes in energy-conversion devices

Electrochemical impedance spectroscopy (EIS) is ubiquitously applied to identify physicochemical processes governing the performance of energy-conversion devices. However, deconvolution and interpretation of impedance phenomena are limited by measurement throughput and a dearth of scalable analysis methods. Here, we demonstrate an approach to quickly collect and coherently analyze large volumes of electrochemical data. In this study, we accelerate impedance characterization by combining rapid measurements in time and frequency domains, which are interpretably transformed using the distribution of relaxation times (DRT) and a new distribution of phasances (DOP) model. This method provides excellent agreement with EIS and decreases measurement time by an order of magnitude. High-throughput spectra are then distilled into detailed electrochemical maps. This approach is applied to a Li-ion battery and a protonic ceramic electrochemical cell as practical case studies, demonstrating how mapping can richly characterize physicochemical relationships that are difficult to decipher with conventional measurement and analysis methods.

25 ENERGY STORAGE↗

DOE OSTI2020

Exploring the relationship between solvent-assisted ball milling, particle size, and sintering temperature in garnet-type solid electrolytes

Garnet-type solid electrolytes, such as Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 (LLZTO), are promising materials for solid-state batteries, but processing remains a challenge, in part due to the high sintering temperature required for densification. Additionally, this temperature can be lowered by decreasing the initial particle size via solvent-assisted ball milling, but the relationship between solvent choice, particle properties, sintering behavior, and ionic conductivity is not well understood. In this work, we systematically explore these parameters, showing that milling in commonly used protic solvents, such as alcohols, effectively decreases the particle size but results in lithium loss (through Li + /H + exchange) that leads to poor sintering. By contrast, milling in aprotic solvents with surfactant reduces the particle size to ~220 nm without lithium loss, enabling the fabrication of dense samples (5.1 g/cm 3 ) with good ionic conductivity (0.43 mS/cm at 25 °C) at a lower sintering temperature (1000 °C). We compare ionic conductivities and activation energies for samples prepared with different particle sizes and sintering temperatures and use multiphase-field simulations to identify the mass transport and microstructural mechanisms responsible for the observed sintering dependence on particle size. These results further clarify the relationship between processing parameters and performance and represent important progress toward overcoming fabrication challenges for these materials.

25 ENERGY STORAGE↗

DOE OSTI2018

Electrochemically reduced graphene oxide nanosheet coatings as solid lubricants in humid air

Highlights: • A facile, low cost and green approach to fabricate ERGO coatings is reported. • The feasibility of using ERGO coatings as solid lubricants is demonstrated. • ERGO coatings reduce copper’s COF to 1/6 and wear rate to more than 1/260. - Abstract: A facile, low cost and green approach to fabricating graphene nanosheet coatings is reported. It is composed of spraying graphene oxide (GO) suspension to form GO nanosheet coatings followed by a low voltage electrochemical reduction process. The tribological performance of the as-prepared electrochemically reduced graphene oxide (ERGO) nanosheet coatings on copper disk are evaluated by sliding against steel ball in humid air. The friction coefficient of copper is reduced to 1/6 its value, and its specific wear rate is reduced more than two orders of magnitude when copper disk is coated with ERGO nanosheet coatings. These improved tribological performance are attributed to the presence of ERGO nanosheets in the sliding interface of steel vs. copper friction pair. They not only provide easy shearing, reducing the friction coefficient, but also effectively suppress abrasive wear and adhesive wear, decreasing the wear rate of copper disk.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2025

Phase-field modeling of diffusion bonding in 316H stainless steel: Impact of processing conditions on grain morphology and bonding quality

A novel multi-phase, multi-component phase‐field model is presented to study the diffusion bonding of 316H stainless steel. Combined with targeted experimental investigations, this model simulates the bond-growth process and predicts the bonding quality. Unlike previous models, our approach captures the simultaneous evolution of voids and grain structures, while quantifying bonding quality using defined bonding ratio. A comprehensive analysis of bond process control is performed by changing temperature, pressure and surface roughness observing the resulting bond structure, which is consistent with experimental observations and analytical predictions. Temperature is determined to be the dominant factor, with the transition from a flat to a robust bond occurring between 1000 °C and 1050 °C. At the ideal bonding temperature of 1050 °C, a surface roughness exceeding 0.6 μm or an applied stress below 4 MPa results in poor bonding quality. Beyond this, higher pressures and smoother surfaces reduce void size, accelerate void shrinkage, and lead to improved bond integrity. This diffuse-interface model can be extended to other material systems if supplied with appropriate thermodynamic and kinetic data. In conclusion, this makes it an effective modeling platform for optimizing high-temperature diffusion bonding and developing reliable bonded components such as compact heat exchangers.

Diffusion bonding↗

DOE OSTI2025

Effects of magnetic field assisted heat treatment on the microstructure and mechanical properties of Fe-0.63 %C alloy

This study investigates the influence of an applied magnetic field on the microstructural evolution and mechanical properties of hypoeutectoid steels subjected to heat treatment. Tensile tests and microstructural analysis were performed on samples processed under varying magnetic field strengths (0 T, 5 T, and 9 T) and different austenitization incubation times. The results indicate that the application of a magnetic field alters the fraction of proeutectoid ferrite phase without changing the cooling rates and heat treatment process. Additionally, pearlite microstructural features such as lamellar spacing and misorientation angles exhibit variations under different field strengths. While the pearlite nodule diameter remains largely unaffected, an increase in percentage elongation and strength is observed in the 5 T treated sample, attributed to changes in microstructural features with the magnetic field. Additionally, the percentage elongation is reduced in the samples heat treated with reduced austenitization incubation times. The study further demonstrates that low-angle misorientations increased in the samples taken parallel to the magnetic field direction, influencing the mechanical response. These findings suggest that applying a magnetic field during heat treatment provides an additional driving force for phase transformations, offering a manufacturing process for tailoring microstructures and optimizing mechanical properties. Moreover, integrating magnetic fields in heat treatment processes has potential benefits in energy efficiency.

High magnetic field↗

DOE OSTI2020

Rechargeable alkaline zinc–manganese oxide batteries for grid storage: Mechanisms, challenges and developments

Rechargeable alkaline Zn–MnO 2 (RAM) batteries are a promising candidate for grid-scale energy storage owing to their high theoretical energy density rivaling lithium-ion systems (~400 Wh/L), relatively safe aqueous electrolyte, established supply chain, and projected costs below $100/kWh at scale. In practice, however, many fundamental chemical and physical processes at both electrodes make it difficult to achieve commercially competitive energy density and cycle life. In this paper, we present a detailed and timely analysis of the constituent materials, current commercial status, electrode processes, and performance-limiting factors of RAM batteries. We also examine recently reported strategies in RAM and related systems to address these issues through additives and modifications to the electrode materials and electrolyte, special ion-selective separators and/or coatings, and unconventional cycling protocols. We conclude with a critical summary of these developments and discussion of how future studies should be focused toward the goal of energy-dense, scalable, and cost-effective RAM systems.

25 ENERGY STORAGE↗

DOE OSTI2026

Additively manufactured refractory high-entropy alloys with superior radiation resistance

Refractory high-entropy alloys (RHEAs) are promising candidates for next-generation nuclear and high-temperature applications. Among many approaches to manufacture RHEAs, additive manufacturing (AM) represents the most recent and advanced metal manufacturing method which allows near-net-shape manufacturing to reduce material waste and post-processing time. However, performance of AM RHEAs under complex irradiation conditions remains largely unexplored. Here, in this study, we demonstrate for the first time the response of directed energy deposition (DED) AM quaternary RHEAs (HfTaVW, CrTaVW) subjected to sequential dual-beam ion irradiation, consisting of helium pre-implantation followed by high-dose heavy ion bombardment. Compositions of DED AM RHEAs were selected using Monte Carlo (MC) simulations based on a cluster expansion (CE) Hamiltonian parameterized by density functional theory (DFT). Post-irradiation microstructural characterization revealed that the AM RHEA maintained remarkable stability, with suppressed helium bubble growth and reduced defect accumulation compared to conventional alloys. Even at high doses (∼100 dpa), the alloy exhibited no void swelling, a low density of dislocation loops, and no evidence of severe degradation. These results highlight the intrinsic ability of AM-derived microstructures and multicomponent chemistry to synergistically mitigate irradiation effects. Our findings establish AM RHEAs as a class of materials with superior resistance to radiation damage under conditions relevant to advanced fusion and fission environments and demonstrate the importance of sequential ion beam studies in evaluating their long-term performance.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Synthesis and thermomechanical characteristics of zwitterionic poly(arylene ether sulfone) copolymers

Charge-containing polymeric materials have been widely studied for a range of applications. The fundamental relationships between the charge species, charge density, and the microscale morphology of charge-containing polymers are critical for defining the application in which they may be used. In this work, a series of thermoplastic poly(arylene ether sulfone) (PAES) copolymers with controllable sulfobetaine charge contents (0~100 mol%) and high molecular weights (Mw ~ 65 kDa) were prepared. All the zwitterionic PAESs synthesized showed thermal stability up to 250 °C. DSC and tensile tests showed a decreased T g and mechanical strength with the incorporation of increasing charge density, which suggests a plasticization effect by the charged group. Electron microscopy and X-ray scattering data confirmed the absence of microphase separation in the ion-containing random copolymer system, which corroborated with the observation of a single T g for all zwitterionic copolymers studied. Furthermore, the relative hydrophilicity of the samples was evaluated by water uptake measurements, which revealed that the water uptake of the zwitterionic PAESs can reach up to 64% for the 72 mol% zwitterion copolymer while the free-standing film in the wet state still maintains a Young's modulus of 185 MPa. Here, the thermoplastic charge-containing copolymers in this work demonstrated potential for applications such as coatings or water purification membranes, in which balancing hydrophilicity, processibility, and thermomechanical performance are important.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2022

Elucidating the challenges in extracting ultra-slow flame speeds in a closed vessel - A CH 2 F 2 microgravity case study using optical and pressure-rise data

Refrigerants with a low global warming potential (GWP) possess mild flammability. Hence, a fundamental understanding of their combustion characteristics is required to assess their fire-hazardous potential. The laminar burning velocity is one fundamental property to describe these under safety evaluation aspects. However, measuring laminar burning velocities for slow-burning components, such as low-GWP alternatives, is challenging. This is due to influencing effects such as buoyant flame deformation, stretch, radiation, and confinement, especially at the flammability limits. Here, in the present study, we investigated near-limit flames of the representative refrigerant difluoromethane (CH 2 F 2 ) with nitrogen-enriched oxidizer mixtures to elucidate the potentials and limitations at ultra-slow flame speeds of two widely used flame speed measurement methods in the closed vessel configuration: the optical flame speed measurement in the early quasi-isobaric regime and the flame speed determination from the pressure-rise during the later phase of the isochoric combustion process. Experiments were performed under terrestrial- and microgravity, conducted in a specially designed setup suitable for drop tower applications, using both methods in parallel. Recommendations for the extraction of flame speed data are derived from the non-buoyant reference investigations under microgravity and transferred to ultra-slow flames at terrestrial gravity. Near-limit flames under microgravity were found to be significantly affected by stretch effects for the optical method so that flame speed extrapolations to unstretched conditions are prone to errors. Stretch also affects the pressure method’s lower evaluation limit, and errors can be estimated by combining flame speed data from the pressure method and Markstein lengths from optical experiments.

42 ENGINEERING↗

DOE OSTI2019

Time-resolved ionization measurements with intense ultrashort XUV and X-ray free-electron laser pulses

Abstract Modern free-electron lasers (FEL) operating in XUV (extreme ultraviolet) or X-ray range allow an access to novel research areas. One instance is the ultrafast ionization of a solid by an intense femtosecond FEL pulse in XUV which consequently leads to a change of the complex index of refraction on an ultrashort timescale. The photoionization and subsequent impact ionization resulting in electronic and atomic dynamics are modeled with our hybrid code XTANT(X-ray thermal and non-thermal transitions) and a Monte Carlo code XCASCADE(X-ray-induced electron cascades). The simulations predict the temporal kinetics of FEL-induced electron cascades and thus yield temporally and spatially resolved information on the induced changes of the optical properties. In a series of experiments at FERMI and LCLS, single shot measurements with spatio-temporal encoding of the ionization process have been performed by a correlation of the FEL pump pulse with an optical femtosecond probe pulse. An excellent agreement between the experiment and the simulation has been found. Furthermore, we demonstrate that such kind of experiments forms the basis for pulse duration and arrival time jitter monitoring as currently under development for XUV-FELs.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2021

Material Design Strategy for Halide Solid Electrolytes Li 3 MX 6 (X = Cl, Br, and I) for All-Solid-State High-Voltage Li-Ion Batteries

Although several solid electrolyte (SE) candidates have been explored, achieving the necessary combination of performance, stability, and processability has been challenging. Recently, several lithium ternary halides have attracted increasing attention for SEs because of their favorable combination of high ionic conductivity and wide electrochemical window. This study aims to provide a material design strategy for lithium halides Li 3 MX 6 (X = Cl, Br, and I) for high-voltage all-solid-state Li-ion batteries, achieved by the systematic investigation of crystal structures, phase and electrochemical stabilities, electronic and mechanical properties, and ionic conductivities. Calculation results reveal that the electronegativity difference between M and X affects structural properties and stabilities. Weak Coulomb interactions in Li 3 MX 6 result in the preference of the monoclinic phase, and the oxidation potential and chemical stability against the cathode materials of Li 3 MX 6 increase for relatively small X. Chlorides exhibit the highest oxidation potential (~4.3 V) among Li 3 MX 6 , suggesting that chlorides are appropriate SEs for high-voltage cathodes. The band gap and elastic moduli increase for relatively small X, suggesting the relatively low electronic conductivity and elastic deformability of chlorides. Chlorides with transition metals typically exhibit trigonal phases, a wider electrochemical stability window, a larger band gap, and higher elastic moduli compared to other types of halides. Additionally, chloride Li 3 MCl 6 is expected to have relatively high ionic conductivities with the aliovalent substitution of M 3+ to Zr 4+ and the anion mixing of Cl with Br. The findings of this study will provide fundamental guidelines for the development of lithium halide SEs for high-voltage all-solid-state Li-ion batteries.

25 ENERGY STORAGE↗

DOE OSTI2020

Nucleation Effects in the Atomic Layer Deposition of Nickel–Aluminum Oxide Thin Films

Atomic layer deposition (ALD) has become an important technique to synthesize a wide variety of materials on the subnanometer length scale. Expanding the library of ALD for ternary materials is vital for applications in which ternary materials allow for tuning of physical, optical, and electronic properties. In this work reported herein, we demonstrate the first report of nickel–aluminum oxide (Ni–Al–O) films deposited by ALD using nickeloceneozone and trimethylaluminum-water as reactants. While deposition of a wide range of compositions is achieved, the observed growth per cycle (GPC) did not follow the simple combination of GPCs measured for the binary ALD processes. Nucleation studies performed to better understand this behavior reveal that the deposition of aluminum oxide is greatly enhanced on a NiO surface prepared by nickelocene and ozone. A model is developed that considers nucleation effects to predict composition and thickness as a function of supercycle recipe. Characterization of the deposited films shows that Al-doping of NiO results in contraction of the NiO lattice, decreased crystallinity, and reduced density, and that films become completely amorphous at compositions with less than 50% Ni. In addition, Al-doped NiO films deposited by ALD are investigated as a hole-selective transport layer in lead-based perovskite solar cells. An Al doping of ~4% improves power conversion efficiency of the perovskite-based devices over that of NiO primarily through increases in fill factor.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Nitroxide Radical Polymer–Solvent Interactions and Solubility Parameter Determination

Redox-active polymers such as macromolecular nitroxide radicals have been studied as electrode materials for organic batteries and electronics. Polymer–solvent interactions are essential to processing and device performance, but macromolecular nitroxide radical–solvent interactions are currently not well described. In this work, the Hildebrand and Hansen solubility parameters of poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl methacrylate) (PTMA), oxidized PTMA (PTMA + ), and PTMA’s precursor (PTMPM) are determined using both experimental and group contribution methods for the first time. This work indicates that the hydrogen-bonding Hansen solubility parameter (δ h ) and the solubility sphere radii (R) provide the best prediction of the macromolecular radical’s interaction with solvents. From these solubility parameters, the group contribution values for the nitroxide and oxoammonium cation were then calculated. It is shown that this information allows for the prediction of polymer–solvent interactions for other nitroxide-based macromolecular radicals. Lastly, the discovered solubility parameters are used to predict PTMA electrode formulations for batteries that outperform controls.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Ethanol Upgrading to n -Butanol Using Transition-Metal-Incorporated Poly(triazine)imide Frameworks

The upgrading of ethanol to n-butanol was performed using a molecular catalyst integrated into a carbon nitride support, one of the first examples of a supported molecular catalyst performing the Guerbet process. Initial studies using crystalline poly(triazine)imide (PTI) with lithium or transition-metal cations imbedded in the support together with a base as the catalyst system did not produce any significant amounts of n-butanol. However, when using the catalyst material formed by treatment of PTI-LiCl with [(Cp*)IrCl 2 ] 2 (Cp* = pentamethylcyclopentadienyl) along with sodium hydroxide, a 59% selectivity for butanol (13% yield) was obtained at 145 °C. This PTI-(Cp*)Ir material exhibited distinct UV–vis absorption features and powder X-ray diffractions which differ from those of the parent PTI-LiCl and [(Cp*)IrCl 2 ] 2 . Here, the PTI-(Cp*)Ir material was found to have a metal loading of 27% iridium per empirical unit of the framework. Along with the formation of n-butanol from the Guerbet reaction, the presence of higher chain alcohols was also observed.

Guerbet↗

DOE OSTI2024

Machine Learning Accelerated First-Principles Study of the Hydrodeoxygenation of Propanoic Acid

The complex reaction network of catalytic biomass conversions often involves hundreds of surface intermediates and thousands of reaction steps, greatly hindering the rational design of metal catalysts for these conversions. Here, we present a framework of machine learning (ML)-accelerated first-principles studies for the hydrodeoxygenation (HDO) of propanoic acid over transition metal surfaces. The microkinetic model (MKM) is initially parametrized by ML-predicted energies and iteratively improved by identifying the rate-determining species and steps (RDS), computing their energies by density functional theory (DFT), and reparameterizing the MKM until all the RDS are computed by DFT. The Gaussian process (GP) model performs significantly better than the linear ridge regression model for predicting both the adsorption free energies and transition state free energies. Parameterized with energies from the GP model, only 5–20% of the full reaction network has to be computed by DFT for the MKM to possess DFT-level accuracy for the TOF and dominant reaction pathway. While the linear ridge regression model performs worse than the GP model, its performance is greatly improved when only transition states are predicted by the regression model and adsorption energies are computed by DFT. Overall, we find that a high accuracy in adsorption free energies is more important for a reliable MKM than a high accuracy in TS free energies. Lastly, based on the GP model with GOH and GCHCHCO as catalyst descriptors, we build two-dimensional volcano plots in activity and selectivity that can help design promising alloy catalysts for HDO reactions of organic acids.

adsorption↗

DOE OSTI2026

Restoring Escaped Zincate in Rechargeable Alkaline Zinc Batteries with a Seed-in-Nanoshell Design

Rechargeable alkaline zinc batteries are promising candidates for safe and low-cost energy storage, but suffer from ZnO dissolution that causes irreversible active material loss and rapid capacity decay. Here, we report a seed-in-nanoshell ZnO anode architecture that mitigates dissolution by combining physical confinement with electrochemical restoration of dissolved zincate species. ZnO particles are encapsulated within an ion-sieving carbon nanoshell that restricts zincate diffusion, maintains electrical conductivity, and stabilizes repeated solid–solution–solid transformations. Silver (Ag) nanoparticles incorporated into the nanoshell act as zincophilic nucleation seeds, lowering the Zn deposition barrier and directing the redeposition of dissolved zincate back to metallic Zn during charging. This confinement-enabled restoration mechanism converts zincate dissolution from an irreversible loss pathway into a recoverable process, enabling improved performance under harsh test conditions. The anode also delivers 227.9 mAh g −1 at −40 °C. Finally, a scalable tens-of-gram synthesis of ZnO@Ag is demonstrated, underscoring the practical potential of this strategy for advanced aqueous zinc batteries.

25 ENERGY STORAGE↗