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At least 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Experimental evidence for ‘buckle, ruck and tuck’ in neutron irradiated graphite

The current mainstream theory for radiation-induced dimensional change of nuclear graphite is based on the notion that interstitially displaced carbon atoms will coalesce into dislocation loops (i.e., additional basal planes). This standard atomic-displacement model has been challenged by theories based on first principles calculations. Furthermore, the so-called ‘ruck and tuck’ of basal planes has been proposed as an alternative mechanism to explain the observed c-axis expansion under irradiation; however, no such defects have been observed experimentally so far. In this study, the first experimental evidence for the presence of a ‘ruck and tuck’ defect in high-temperature neutron-irradiated nuclear graphite is introduced.

36 MATERIALS SCIENCE↗
DOE OSTI2024

DOE ART Graphite R&D Introduction

Introduction of ART Graphite R&D to include oxidation activities, oxidation resistant graphite, model development, ASME component failure, ASME code development (design rules), ceramic composites, AGC update, molten salt intrusion, split-disk studies, wear testing, and concluding remarks.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2019

Record-Breaking Magnetoresistance at the Edge of a Microflake of Natural Graphite

Placing several electrodes at the edge of a micrometer-size Sri Lankan natural graphite sample at distances comparable to the size of the internal crystalline regions, we found record values for the change of the resistance with magnetic field. At low temperatures and at B ~ 21 T the magnetoresistance (MR) reaches ≈ 10 7 %. The MR values exceed by far all earlier reported ones for graphite and they are comparable or even larger (at T > 50 K) than the largest reported in solids including the Weyl semimetals. The origin of this large MR lies in the existence of highly conducting 2D interfaces aligned parallel to the graphene planes.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Operando Quantification of (De)Lithiation Behavior of Silicon-Graphite Blended Electrodes for Lithium-Ion Batteries

Due to the high lithium capacity of silicon, the composite (blended) electrodes containing silicon (Si) and graphite (Gr) particles are attractive alternatives to the all-Gr electrodes used in conventional lithium-ion batteries. In this Communication, the lithiation and delithiation in the Si and Gr particles in a 15 wt% Si composite electrode is quantified for each component using energy dispersive X-ray diffraction. This quantification is important as the components cycle in different potential regimes, and interpretation of cycling behavior is complicated by the potential hysteresis displayed by Si. The lithiation begins with Li alloying with Si; lithiation of Gr occurs at later stages when the potential dips below 0.2 V (all potentials are given vs. Li/Li + ). In the 0.2 – 0.01 V range, the relative lithiation of Si and Gr is ~58% and 42%, respectively. During delithiation, Li + ion extraction occurs preferentially from Gr in the 0.01 – 0.23 V range and from Si in the 0.23 – 1.0 V range; that is, the delithiation current is carried sequentially, first by graphite and then by silicon. Furthermore, these trends can be used for rational selection of electrochemical cycling windows that limits volumetric expansion in Si particles, thereby extending cell life.

25 ENERGY STORAGE↗
DOE OSTI2022

Mechanistic Elucidation of Electronically Conductive PEDOT:PSS Tailored Binder for a Potassium‐Ion Battery Graphite Anode: Electrochemical, Mechanical, and Thermal Safety Aspects

Potassium-ion batteries (KIBs) are considered more appropriate for grid-scale storage than lithium-ion batteries (LIBs) due to similar operating chemistry, abundant precursors, and compatibility with low-cost graphite anodes. However, a larger ion reduces rate capabilities and exacerbates capacity fading from volumetric expansion. In this report, conductive polymer, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), is substituted for standard insulating polyvinylidene fluoride (PVDF). Half-cells using carbon black (CB) in continuously conductive PEDOT:PSS/CB binder outperforms PVDF/CB by mitigating electrically isolated “dead” graphite, improving 100 cycle capacity retention at C/10 from 63 to 80%. Enhanced electrical contact with PEDOT:PSS/CB also reduces ion impedance and improves rate capabilities. Without CB however, PEDOT:PSS binder performs poorly in electrochemical studies despite promising ex situ electronic conductivity. This discrepancy is mechanistically elucidated through identification of redox activity between PEDOT:PSS and K + which results in high impedances in the anode operating voltage window. Additionally, the impact of conducting binder on mechanical properties and thermal safety of the anode is investigated. Brittleness and poor wettability of PEDOT:PSS are identified as issues, but greater stability against reactive KC 8 reduces overall heat generation. Binder substitution offers a promising means of mitigating issues with current KIB anodes regardless of active material, and the work herein addresses issues towards further improvement.

electrochemical impedance spectroscopy↗
DOE OSTI2025

Linking Lattice Strain and Fractal Dimensions to Non‐monotonic Volume Changes in Irradiated Nuclear Graphite

Graphite's resilience to high temperatures and neutron damage makes it vital for nuclear reactors, yet irradiation alters its microstructure, degrading key properties. We used small- and wide-angle X-ray scattering to study neutron-irradiated fine-grain nuclear graphite (Grade G347A) across varied temperatures and fluences. Results show significant shifts in internal strain and porosity, correlating with radiation-induced volume changes. Notably, porosity volume distribution (fractal dimensions) follows non-monotonic volume changes, suggesting a link to the Weibull distribution of fracture stress.

X-ray scattering↗
DOE OSTI2018

Thermal and Thermophysical Properties of the Radioactive Graphite–Inert Gas System in Heating. Computer Experiment

Consideration has been given to the capabilities of the TERRA software system for modeling thermodynamically the heating of a radioactive graphite–inert gas system in a nuclear reactor. As a result of such modeling, the authors have determined processes occurring in the reactor with the involvement of Eu, Pu, and U actinoids during the heating of the radioactive graphite–argon system at pressures of 10{sup 5} and 10{sup 6} Pa, and also equilibrium constants of chemical reactions and the influence of pressure on them. The thermophysical properties of the system have been studied, and the influence of pressure on its specific volume, the heat capacity, and the molar mass of a gas phase and the weight fraction of a condensed phase has been established.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2018

Ferromagnetism and Persistent Currents in Finely Dispersed Highly Oriented Pyrolytic Graphite Samples

Synthesis of finely dispersed graphite powders is described and results of their investigations by the methods of electron microscopy and magnetometry are presented. The samples have been prepared from crystal highly oriented pyrolytic graphite by grinding in an inert atmosphere for a long time with subsequent annealing at 400°C for 24 h in air or in vacuum. It is demonstrated that annealing of the powder in vacuum leads to a considerable increase in the ferromagnetic component associated with the formation of edge defects of zigzag type. The phenomenon of magnetic flux trapping is manifested in the samples annealed both in air and in vacuum upon cooling down to 10 K in a magnetic field that is indicative of the formation of superconducting regions in the samples.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Wetting and Erosion of ZrO{sub 2}-Graphite Refractory by CaO-SiO{sub 2} and CaO-Al{sub 2}O{sub 3}-Based Mold Slags for Submerged Entry Nozzle

To moderate the erosion in a slag-line zone and extend the service life of a submerged entry nozzle during continuous casting of high-Mn and high-Al steel, the current study developed a low-reaction CaO-Al{sub 2}O{sub 3}-based slag with lower SiO{sub 2} and higher Al{sub 2}O{sub 3} contents than that of conventional CaO-SiO{sub 2}-based slag. The static sessile drop technique and dynamic rotating cylinder method were utilized to investigate the erosion behavior of ZrO{sub 2}-graphite refractory by the above slags. The main results indicated that silicate-based slag could wet the ZrO{sub 2}-graphite substrate completely, while the aluminate-based slag spread rapidly in the first 20 minutes, and then a slag drop with an unchanged profile formed on the substrate. The equilibrium contact angles with the substrate at 1623 K were 0 and 79 deg for the CaO-SiO{sub 2} and CaO-Al{sub 2}O{sub 3} based slags, respectively. The comparison of the influences of the rotating speed and the temperature revealed that the decrease of erosion rate could be realized by the developed slag. An examination of ZrO{sub 2}-saturation limit also indicated that the low-reaction slag could dissolve much more ZrO{sub 2} oxidation, accompanied by a less-negative effect on the viscosity of the molten slag.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Very Hard Corrosion-Resistant Roll-Bonded Cr Coating on Mild Steel in Presence of Graphite

The present work discusses the development of very hard Cr and Cr-carbide coating by roll bonding of Cr powder on a mild steel followed by annealing at 800, 1000, 1100 and 1200 °C with and without the presence of graphite powder packing in argon environment. In addition, the effect of a roll skin pass of 5% prior to the application of coating was studied. The presence of graphite allows diffusion of both carbon and Cr in the mild steel substrate, leading to the formation of Cr-carbide on the outer surface, making the surface very hard (VHN ~ 1800). Depending on the annealing temperature and processing condition, diffusion layer thickness of Cr is found to be in the range of 10-250 μm with Cr content of 12.5-15 wt.% across the diffusion layer. Excellent stable passivity of the coated surface is observed in 0.2 N H{sub 2}SO{sub 4}, which is comparable to a highly passivating 304 stainless steel, and very low corrosion rate of the coating is observed as compared to the substrate mild steel.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Application of Selected Artificial Intelligence Methods in a System Predicting the Microstructure of Compacted Graphite Iron

Intelligent computing tools such as artificial neural network and fuzzy logic are used as predictive modeling tools. The use of these methods, combined with model experimental results, may be an excellent predictive tool, allowing us to forecast the microstructure of the tested cast iron at the level of computer simulation. In this study, the reference training cases collected in one database were used to determine the parameters of the neuro-fuzzy ANFIS model. They mainly include the results of observations and measurements of the content of individual microstructural constituents of the compacted graphite iron, examined as a function of the content of individual alloy additives (molybdenum, nickel and copper introduced in various proportions). The training process of such a fuzzy inference system is done by constantly changing its parameters (parameters of the membership function) and determining new rule conclusions as a result of presenting individual case examples from the training sample. The conducted research has shown the possibility of applying the ANFIS model as a tool to control the chemical composition of compacted graphite iron in the production of castings with high-strength parameters.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Preparation of Nano-SiO{sub 2}-Coated Graphite Films by a Laser-Assisted Sol–Gel Process

Here, we prepared nano-SiO{sub 2}-coated graphite films using a novel laser-assisted sol–gel method. The SiO{sub 2} sol–gel prepositioned on the graphite substrate was irradiated by the fiber laser at different energy densities. The growth mechanism of the coatings under laser irradiation was studied and the effects of processing parameters on the coating structure were systematically investigated. In addition, the high-temperature oxidation resistance of these samples was examined. Surface morphology and elemental composition were examined using scanning electron microscopy and energy-dispersive spectrometer. Phase constituents and microstructure were identified by x-ray diffraction and transmission electron microscopy. The oxidation resistance was analyzed by thermal gravimetric analysis. The results found that laser irradiation significantly modifies the sol–gel-deposited nano-SiO{sub 2} layer. A uniform and compact nano-SiO{sub 2} coating was obtained when irradiated by laser energy density of 14.4 kJ/cm{sup 2}. Optimum high-temperature oxidation resistance was achieved for the two-layer SiO{sub 2}-coated films.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Valuation of Anode Materials for High-Performance Lithium Batteries: From Graphite to Lithium Metal and Beyond

Lithium-ion batteries have revolutionized energy storage, yet advanced technologies such as electric vehicles and eVTOLs demand even higher performance and safety. Anodes, the negative electrodes, are crucial in enhancing batteries’ safety, lifespan, and fast-charging capabilities. This review paper comprehensively evaluates the progression of anode materials from traditional graphite to advanced anodes like lithium metal. Graphite anodes, with a capacity of 372 mAh g −1 , enabled the first commercial lithium-ion batteries, but future applications require higher energy densities and fast-charging capabilities. Emerging anode materials, including alloying, and conversion types, as well as lithium metal, offer significantly higher capacities, with lithium metal offering a theoretical capacity of 3 860 mAh g −1 . However, these advanced anodes face challenges such as volume expansion, high surface reactivity, sluggish Li+ kinetics, and unstable lithium deposition morphologies. Here, this review critically examines the electrochemical performance, interfacial properties, mechanical attributes, and stability issues of various anode materials. It further discusses solid electrolyte interphase (SEI) formation, strategies for enhancing interface stability, and the requirements of anodes for solid-state batteries. Additionally, the review explores potential solutions for limitations with each anode type, highlights innovative anode-free architectures, and evaluates the current and future trends of battery anode industries. Ultimately, this paper aims to guide the development of high-performance anode materials, paving the way for the next generation of efficient, reliable lithium batteries.

Alloying anodes↗
DOE OSTI2021

In situ synchrotron investigation of degenerate graphite nodule evolution in ductile cast iron

Ductile cast irons (DCIs) are of increasing importance in the renewable energy and transportation sectors. The distribution and morphology of the graphite nodules, in particular the formation of degenerate features during solidification, dictate the mechanical performance of DCIs. In situ high-speed synchrotron X-ray tomography was used to capture the evolution of graphite nodules during solidification of DCI, including degenerate features and the effect of the carbon concentration field. The degeneration of nodules is observed to increase with re-melting cycles, which is attributed to Mg-loss. The dendritic primary austenite and carbon concentration gradients in the surrounding liquid phase were found to control nodule morphology by locally restricting and promoting growth. A coupled diffusion-mechanical model was developed, confirming the experimentally informed hypothesis that protrusions form through liquation cracking of the austenite shell and subsequent localised growth. In conclusion, these results provide valuable insights into the solidification kinetics of cast irons, supporting the design of advanced alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Defect-mediated, thermally-activated encapsulation of metals at the surface of graphite

Here, we show that 3 metals – Dy, Ru, and Cu – can form multilayer intercalated (encapsulated) islands at the graphite (0001) surface if 2 specific conditions are met: Defects are introduced on the graphite terraces to act as entry portals, and the metal deposition temperature is well above ambient. Focusing on Dy as a prototype, we show that surface encapsulation is much different than bulk intercalation, because the encapsulated metal takes the form of bulk-like rafts of multilayer Dy, rather than the dilute, single-layer structure known for the bulk compound. Carbon-covered metallic rafts even form for relatively unreactive metals (Ru and Cu) which have no known bulk intercalation compound.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Role of surface diffusion in formation of unique reactivity for graphite oxidation: Time-resolved measurements in a pulsed diffusion reactor

Quantification of oxidation kinetics is essential to develop graphitic materials for diverse applications: from refractories found in gas-cooled nuclear reactors to catalysts needed for chemical manufacturing. In this work, using well-defined highly oriented pyrolytic graphite, low-pressure isotopic transient experiments combined with controlled annealing periods, we resolve the role of surface diffusion and quantify oxidation kinetics with nanomole-precision. We observe an unexpected increase in reactivity following annealing which is explained by the role of surface diffusion increasing the probability for trapping mobile oxygen at more reactive edge sites. Here, the locus of adsorption and spillover to the basal plane is distinct from the trapping location creating a more active oxygen species. Isotopic products reflect the population dynamics of oxygen added at the edge and surface diffusion that relocates basal plane oxygen to more reactive edge sites. Since this process proceeds in parallel with direct oxidation reactions, it is not likely to be observed using steady-state or conventional ‘bulk’ characterization techniques. Our unique time-resolved non-equilibrium measurement in a well-defined transport regime, enables observation of three distinct behaviors: short-term deactivation due to the balance of rates in oxygen supply/product formation, reactivity increases due to surface diffusion and longer-term reactivity increase with oxygen accumulation.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Materials property changes in ETU-10 graphite due to neutron irradiation at elevated temperatures

Graphite grade ETU-10, from IBIDEN Co., Ltd. Has been irradiated in the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory (ORNL). The irradiation program was developed to provide a preliminary study the irradiation-induced property changes to the dimensions/volume, elastic properties, strength, electrical resistivity, coefficient of thermal expansion, and thermal diffusivity/conductivity over a range of temperatures and neutron exposures that may be relevant for future nuclear reactors. The irradiation envelope covers a range of irradiation temperatures (300°C–900 °C) and fluences (up to 40 × 10 25 n/m 2 [E > 0.1 MeV] or ~30 dpa) that would be relevant for advanced nuclear reactors. Further, the dimensional change was observed to be anisotropic for an isotropic graphite, the specimen dimensions, volume, Young's modulus, shear modulus, and strength all displayed a parabolic fluence dependence, the electrical resistivity had a rapid rise followed by a decrease and a later increase, at high fluence the mean coefficient of thermal expansions was similar for all irradiation temperatures, and thermal conductivity rapidly decreased followed by a continued loss.

36 MATERIALS SCIENCE↗