Thermodynamics of hydrogen in graphite at high temperature and the effects of oxidation, irradiation and isotopics
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Vergari, Lorenzo (ORCID:0000000275489678)↗
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Results for “Graphite Oxidation”
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Crystallographic data on selected artificial graphites with comments on the role of the degree of crystal development in oxidation
X ray crystallographic measurements of selected grades of commercial nonpyrolitic artificial graphite
Maahs, H. G.↗
Highly Concentrated Electrolytes: Electrochemical and Physicochemical Characteristics of LiPF 6 in Propylene Carbonate Solutions
Highly concentrated electrolytes (HCEs) based on LiPF 6 in propylene carbonate (PC) have been examined as lithium-ion battery electrolytes. These HCEs have lower ionic conductivities and higher viscosities than ethylene carbonate (EC) electrolytes with 1.2 M LiPF 6 , but they have higher Li + ion transference numbers. Electrochemical cycling behaviour of LiNi 0.8 Co 0.015 Al 0.05 O 2 //graphite cells with 3.2 M LiPF 6 in PC resembles that of cells with EC-based electrolytes; the HCE cells have higher impedance, which can be lowered by increasing test temperature. By employing Raman and infrared spectroscopy, combined with density functional theory and ab initio molecular dynamics simulations, we reveal that the Li + solvation structure and speciation are key factors that determine cell performance. Two distinct regimes are observed as a function of salt concentration—in the conventional regime, the solvation number (SN) is mostly constant, while in the HCE regime it decreases linearly. Graphite exfoliation is suppressed only at very high salt concentrations ( > 2.4 M), where [ PC ] free /[Li + ] < 1 and P F 6 − f r e e > P C f r e e . Results from the Advanced Electrolyte Model indicate that Li + desolvation improves at higher LiPF 6 concentrations, thereby mitigating PC co-intercalation into the graphite. However, Li + ion transport is hindered in the HCEs, which increases impedance at both the oxide-positive and graphite-negative electrodes.
25 ENERGY STORAGE↗
Thermo-oxidative stability studies of Celion 6000/PMR-15 unidirectional composites, PMR-15, and Celion 6000 fiber
Experimental results on the influence of the thermooxidative resistance characteristics of the fiber and matrix resin on the thermal stability of isothermally aged Celion 6000/PMR-15 matrix resin composites are presented. SEM studies reveal that extreme oxidative erosion of the graphite fiber occurs at elevated temperatures in the presence of the polyimide matrix. The activation energy of oxidation of the composite was shown to be greater than those of the fiber and the matrix resin.
Bowles, Kenneth J.↗
Carburization of metals by a chemical mechanism of carbon transport through molten fluoride salts
Carburization of structural alloys used in Fluoride Cooled High Temperature Reactors (FHR) can result from the interaction between the metal and graphite components and cause changes in alloy properties. However, carburization requires transport of carbon from graphite to alloy surfaces through the molten fluoride coolant. This work introduces an alternative to previously proposed carbon transport mechanisms. The new mechanism is based on the generation of carbonate ions (CO 3 2- ) by oxide impurities in the salt reacting with graphite. CO 3 2- is then reduced on metal surfaces to deposit carbon. This work demonstrates the reduction of dissolved CO 3 2- on pure Fe, Ni, Cr, Mo, and W surfaces without an applied potential in molten FLiNaK at 700 °C. Finally, we also demonstrate that the interaction between oxide and graphite in molten FLiNaK media produces CO 3 2- .
36 MATERIALS SCIENCE↗
Carbon Nanostructure Examined by Lattice Fringe Analysis of High Resolution Transmission Electron Microscopy Images
The dimensions of graphitic layer planes directly affect the reactivity of soot towards oxidation and growth. Quantification of graphitic structure could be used to develop and test correlations between the soot nanostructure and its reactivity. Based upon transmission electron microscopy images, this paper provides a demonstration of the robustness of a fringe image analysis code for determining the level of graphitic structure within nanoscale carbon, i.e. soot. Results, in the form of histograms of graphitic layer plane lengths, are compared to their determination through Raman analysis.
VanderWal, Randy L.↗
Carbon Nanostructure Examined by Lattice Fringe Analysis of High Resolution Transmission Electron Microscopy Images
The dimensions of graphitic layer planes directly affect the reactivity of soot towards oxidation and growth. Quantification of graphitic structure could be used to develop and test correlations between the soot nanostructure and its reactivity. Based upon transmission electron microscopy images, this paper provides a demonstration of the robustness of a fringe image analysis code for determining the level of graphitic structure within nanoscale carbon, i.e., soot. Results, in the form of histograms of graphitic layer plane lengths, are compared to their determination through Raman analysis.
VanderWal, Randy L.↗
Completion of Level 3 Milestone M3AT-20IN0305040333
This item is an interoffice memo documenting the completion of of Level 3 Milestone M3AT-20IN0305040333. The status and progress made in the studies on irradiated graphite using thermogravimetric analysis (TGA) for isothermal oxidation of irradiated buttons, non-irradiated companions, and same-grade specimens are detailed.
36 MATERIALS SCIENCE↗
Comprehensive characterization of ball-milled powders simulating a tribofilm system
A model system was used to simulate the properties of tribofilms which form during automotive braking. The model system was prepared by ball milling of a blend of 70 vol.% iron oxides, 15 vol.% molybdenum disulfide and 15 vol.% graphite. The resulting mixture was characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and various transmission electron microscopic (TEM) methods, including energy dispersive X-ray spectroscopy (EDXS), high resolution investigations (HRTEM) with corresponding simulation of the HRTEM images, diffraction methods such as scanning nano-beam electron diffraction (SNBED) and selected area electron diffraction (SAED). It could be shown that the ball milling caused a reduction of the grain size of the initial components to the nanometer range. Sometimes even amorphization or partial break-down of the crystal structure was observed for MoS{sub 2} and graphite. Moreover, chemical reactions lead to a formation of surface coverings of the nanoparticles by amorphous material, molybdenum oxides, and iron sulfates as derived from XPS. - Highlights: • Ball milling of iron oxides, MoS{sub 2}, and graphite to simulate a tribofilm • Increasing coefficient of friction after ball milling of the model blend • Drastically change of the diffraction pattern of the powder mixture • TEM & XPS showed the components of the milled mixture and the process during milling. • MoS{sub 2} and graphite suffered a loss in translation symmetry or became amorphous.
36 MATERIALS SCIENCE↗
Semi-supervised learning approach for crack detection and identification in advanced gas-cooled reactor graphite bricks - 111
One of the life-limiting components of an Advanced Gas cooled Reactor (AGR) is its graphite core. The bricks present in the core undergo radiolytic oxidation throughout their lifetime which causes graphite weight loss and irradiation which can result in some of the bricks developing cracks. Understanding the nature and extent of brick cracking within the core is key to ensuring continued and extended operation of the AGR fleet. A semi-supervised machine learning classification algorithm is proposed as a method for improving the detection of cracked graphite bricks, by combining the labels derived from infrequent, detailed inspections of the core, with unlabeled, more frequent monitoring measurements taken during refueling operations. Semi-supervised machine learning, which is an emerging field in nuclear power condition monitoring, is the combination of ideas from both supervised and unsupervised machine learning whereby the data that is used to train the algorithm is a combination of labeled and unlabeled data. This paper introduces the initial research that has been undertaken in creating a semi-supervised self-training algorithm to detect the presence of graphite brick cracks and then proceeds to show that there is an improvement in the classification of graphite bricks using a semi-supervised machine learning classifier compared to supervised machine learning classifiers. This improved classification performance is encouraging as it does not require time consuming and costly human analysis to obtain extra learning information from available data. (authors)
21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
Heterogeneous Electrochemical Ammonia Oxidation with a Ru-bda Oligomer Anchored on Graphitic Electrodes via CH−π Interactions
Not Available
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Liquid crystallinity driven highly aligned large graphene oxide composites
Graphene is an emerging graphitic carbon materials, consisting of sp{sup 2} hybridized two dimensinal honeycomb structure. It has been widely studied to incorporate graphene with polymer to utilize unique property of graphene and reinforce electrical, mechanical and thermal property of polymer. In composite materials, orientation control of graphene significantly influences the property of composite. Until now, a few method has been developed for orientation control of graphene within polymer matrix. Here, we demonstrate facile fabrication of high aligned large graphene oxide (LGO) composites in polydimethylsiloxane (PDMS) matrix exploiting liquid crystallinity. Liquid crystalline aqueous dispersion of LGO is parallel oriented within flat confinement geometry. Freeze-drying of the aligned LGO dispersion and subsequent infiltration with PDMS produce highly aligned LGO/PDMS composites. Owing to the large shape anisotropy of LGO, liquid crystalline alignment occurred at low concentration of 2 mg/ml in aqueous dispersion, which leads to the 0.2 wt% LGO loaded composites. - Graphical abstract: Liquid crystalline LGO aqueous dispersions are spontaneous parallel aligned between geometric confinement for highly aligned LGO/polymer composite fabrication. - Highlights: • A simple fabrication method for highly aligned LGO/PDMS composites is proposed. • LGO aqueous dispersion shows nematic liquid crystalline phase at 0.8 mg/ml. • In nematic phase, LGO flakes are highly aligned by geometric confinement. • Infiltration of PDMS into freeze-dried LGO allows highly aligned LGO/PDMS composites.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Research on graphite reinforced glass matrix composites
A broad group of fibers and matrices were combined to create a wide range of composite properties. Primary material fabrication procedures were developed which readily permit the fabrication of flat plate and shaped composites. Composite mechanical properties were measured under a wide range of test conditions. Tensile, flexure mechanical fatigue, thermal fatigue, fracture toughness, and fatigue crack growth resistance were evaluated. Selected fiber-matrix combinations were shown to maintain their strength at up to 1300 K when tested in an inert atmosphere. Composite high temperature mechanical properties were shown to be limited primarily by the oxidation resistance of the graphite fibers. Composite thermal dimensional stability was measured and found to be excellent.
Prewo, K. M.↗
Automotive Lithium-ion Cell Manufacturing: Regional Cost Structures and Supply Chain Considerations
Manufacturing capacity for lithium-ion batteries (LIBs)--which power many consumer electronics and are increasingly used to power electric vehicles--is heavily concentrated in east Asia. Currently, China, Japan, and Korea collectively host 88% of all LIB cell and 79% of automotive LIB cell manufacturing capacity. Mature supply chains and strong cumulative production experience suggest that most LIB cell production will remain concentrated in Asia. However, other regions--including North America--could be competitive in the growing automotive LIB cell market under certain conditions. To illuminate the factors that drive regional competitiveness in automotive LIB cell production, this study models cell manufacturing cost and minimum sustainable price, and examines development of LIB supply chains and current LIB market conditions. Modeled costs are for large format, 20-Ah stacked pouch cells with lithium-nickel-manganese-cobalt-oxide (NMC) cathodes and graphite anodes suitable for automotive application. Production volume is assumed to be at commercial scale, 600 MWh per year.
25 ENERGY STORAGE↗
Manufacturing of Dysprosium-Iron Alloys by Electrolysis in Fluoride-Based Electrolytes. Electrolysis in a Laboratory-Scale Cell
Electrolytic production of light rare earth elements and rare earth alloys with transition elements takes place in a fluoride-based electrolyte using rare earth oxides as raw material. The optimization of this method, mainly in terms of the energy efficiency and environmental impact control, is rather challenging. Anode effects, evolution of fluorine-containing compounds and side cathode reactions could largely be minimized by good control of the amount of rare earth oxide species dissolved in the fluoride-based electrolyte and their dissolution rate. The Dy{sub 2}O{sub 3} feed rate needed for stable cell operation was studied by following up the anode voltage and gas analysis. On-line analysis of the cell off-gases by FTIR showed that the electrochemical reaction for the formation of Dy-Fe alloy gives mainly CO gas and that CF{sub 4} is starting to evolve gradually at anode voltages of ca. 3.25 V. The limiting current density for the discharge of the oxide ions at the graphite anode was in the range of 0.1 to 0.18 A cm{sup −2} at dissolved Dy{sub 2}O{sub 3} contents of ca. 1 wt pct. Modeling of the laboratory cell reactor was also carried out by implementing two models, i.e., an electrical model simulating the current density distribution at the electrodes and a laminal bubbly flow model that explains the electrolyte velocity induced by gas bubble production at the anode.
36 MATERIALS SCIENCE↗
Comparison of NBG-18, NBG-17, IG-110 and IG-11 oxidation kinetics in air
In this paper, the oxidation rates of several nuclear-grade graphites, NBG-18, NBG-17, IG-110 and IG-11, were measured in air using thermogravimetry. Kinetic parameters and oxidation behavior for each grade were compared by coke type, filler grain size and microstructure. The thickness of the oxidized layer for each grade was determined by layer peeling and direct density measurements. The results for NBG-17 and IG-11 were compared with those available in the literature and our recently reported results for NBG-18 and IG-110 oxidation in air. The finer-grained graphites IG-110 and IG-11 were more oxidized than medium-grained NBG-18 and NBG-17 because of deeper oxidant penetration, higher porosity and higher probability of available active sites. Variation in experimental conditions also had a marked effect on the reported kinetic parameters by several studies. Finally, kinetic parameters such as activation energy and transition temperature were sensitive to air flow rates as well as sample size and geometry.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
High-temperature tensile cell for in situ real-time investigation of carbon fibre carbonization and graphitization processes
A new high-temperature fibre tensile cell is described, developed for use at the Advanced Photon Source at Argonne National Laboratory to enable the investigation of the carbonization and graphitization processes during carbon fibre production. This cell is used to heat precursor fibre bundles to temperatures up to ~2300°C in a controlled inert atmosphere, while applying tensile stress to facilitate formation of highly oriented graphitic microstructure; evolution of the microstructure as a function of temperature and time during the carbonization and higher-temperature graphitization processes can then be monitored by collecting real-time wide-angle X-ray diffraction (WAXD) patterns. As an example, the carbonization and graphitization behaviour of an oxidized polyacrylonitrile fibre was studied up to a temperature of ~1750°C. Real-time WAXD revealed the gradual increase in microstructure alignment with the fibre axis with increasing temperature over the temperature range 600–1100°C. Above 1100°C, no further changes in orientation were observed. The overall magnitude of change increased with increasing applied tensile stress during carbonization. As a second example, the high-temperature graphitizability of PAN- and pitch-derived commercial carbon fibres was studied. Here, the magnitude of graphitic microstructure evolution of the pitch-derived fibre far exceeded that of the PAN-derived fibres at temperatures up to ~2300°C, indicating its facile graphitizability.
Behr, Michael↗