Grade Graphite Research Articles

High temperature annealing of irradiated nuclear grade graphite

Previous work has shown that the material properties of nuclear grade graphite are substantially affected by the atomic and microstructural changes that occur during neutron-irradiation. The parameters that play a role in these changes are irradiation dose, temperature, graphite composition and the initial microstructure of the graphite. Understanding the details of how these material changes occur and exactly what the changes consists of will enable the prediction of the material property changes as a function of these variables. Other work has shown these atomic level and microstructural changes can be healed or annealed out by raising the irradiated graphite above its irradiation temperature. In this work, experiments were carried out to investigate how the properties of irradiated graphite recover when heated. By showing property recovery as a function of annealing temperature or energy, insight is provided into the type of damage that occurred during neutron-irradiation. The data presented here shows recovery of thermal diffusivity, coefficient of thermal expansion, Young's modulus and electrical resistivity between annealing temperatures of 500 °C and 2380 °C. Graphite grades NBG-18, IG-110 and PCEA are considered that were both stressed and unstressed during irradiation.

Effects of the Electrodes’ Shape and Graphite Quality on the Arc Stability During Hydrogen Plasma Smelting Reduction of Iron Ores

Reducing greenhouse gases (GHG), especially CO2, is necessary to counteract climate change. The European steel industry currently corresponds to 5.7% of the total EU emissions and must therefore minimize their GHG fractions in the future. One of the most promising technologies to eliminate CO2 emissions while directly reducing iron ore to steel in a single step is the hydrogen plasma smelting reduction. The stability of the plasma arc, which is determined by the properties and geometry of the graphite electrode, has a substantial impact on the process’ economic feasibility. To study the arc stability concerning the graphite quality, tip geometry, and electrode gap, a series of experiments is conducted. The results are evaluated to create stability maps and fields to identify stable process parameters. The geometry of the graphite cathode shows the primary influence on arc stability. Tips with a flat end (standard version) offering the most unstable and a machined step on the graphite cathode providing the most stable conditions. However, an additional coating to prevent side arcing leads to the deterioration of the arc. The two graphite grades tested, with different maximum grain sizes and price classes, show no great relevance to the stability of the arc.

Ultrafast synthesis of battery grade graphite enabled by a multi-physics field carbonization

The typical synthesis of graphite requires carbonization at 2800 °C, which consumes a substantial amount of energy. We present a novel, sustainable and cost-effective method for synthesizing high-crystallinity graphite in 13 min at a low temperature of 1100 °C and a multi-physics field (MPF) carbonization coupling with a Ni catalyst. The MPF synergistically benefits from a thermal field, an electric field, and a pressure field in an MPF furnace at the lab scale. Molecular dynamics and differential charge density calculation indicated that the MPF carbonization facilitated exceptional kinetics, and considerably accelerated the breaking of the Ni-metal-catalyzed C-O bonds. The starch-derived graphite anode provided a reversible Li+ storage capacity of 370.7 mAh g−1, matching that of commercial graphite. It also demonstrates exceptional rate performance with a capacity of 103.3 mAh g−1 at an ultra-high current density of 30 A g−1 in diglyme-based Na-ion batteries and ultrastable cycling performance over 10,000 cycles at 2 A g−1. This method will shed some light on how to rapidly fabricate highly crystalline graphite by a energy-saving and low-cost route.

Effect of lithium ion on the separation of electrode materials in spent lithium ion batteries using froth flotation

There is an urgent need to develop a recycling process for spent Lithium-Ion Batteries (LIBs). Amongst the various recycling technologies proposed, froth flotation is considered a cost-effective candidate for the separation of graphite from the lithium metal oxides due to the hydrophobic nature of graphite. However, experimental studies have identified that soluble lithium has a significant impact on the separation efficiency.Two series of experiments were undertaken to understand the influence of lithium ions. The first used a semi-synthetic mixture of spent anode and pure cathode material based on lithium nickel manganese cobalt oxide (LiNi0.33Mn0.33Co0.33O2) or NMC-111 cathode material. The second used mixed samples of spent lithium ion batteries of the same composition. Both the separation efficiency and the flotation kinetics are reported. The soluble lithium concentration is shown to have a significant impact on both. However, if the spent battery material is washed to reduce the lithium ion concentration, the flotation efficiency and kinetics are similar with the graphite recovery exceeding 90% and the graphite grade exceeding 84% in a single flotation stage.

A Study on the Effect of Particle Size on Li-Ion Battery Recycling via Flotation and Perspectives on Selective Flocculation

The recycling of active materials from Li-ion batteries (LIBs) via froth flotation has gained interest recently. To date, recycled graphite has not been pure enough for direct reuse in LIB manufacturing. The present work studied the effect of particle sizes on the grade of recycled graphite. Furthermore, selective flocculation is proposed as a novel approach to control particle sizes and thus improve graphite grade by preventing the entrainment of cathode components. Zeta potential and particle size measurements were performed to find an optimal pH for electrically selective flocculation and to study the interaction of flocculants, respectively. Batch flotation experiments were performed to investigate the effect of particle size on the purity of the recovered graphite. Results suggested that, in the absence of ultrafine fine particles, battery-grade graphite of 99.4% purity could be recovered. In the presence of ultrafine particles, a grade of 98.2% was observed. Flocculating the ultrafine feed increased the grade to 98.4%, although a drop in recovery was observed. By applying a dispersant in addition to a flocculant, the recovery could be increased while maintaining a 98.4% grade. Branched flocculants provided improved selectivity over linear flocculants. The results suggest that particle size needs to be controlled for battery-grade graphite to be recovered.

Development of a novel biocollector for flotation of low grade graphite ore

ABSTRACT Mineral processing plants operate in capacity of hundreds/thousands of tons per day. Accordingly, chemical reagents’ usage also increases proportionally. Stringent norms toward environment sustainability question the usage of chemical reagents, especially in large quantities and tailings disposal in open areas. Hence, bioreagents have gained great interest. Froth flotation is by far the most practiced processing route for fines beneficiation and low-grade ore upgradation especially for naturally hydrophobic minerals. Flotation being a physico-chemical separation technique, flotation reagents selection plays a pivotal role in the process performance. A novel environmental-friendly biocollector, an extract from the leaves of Vitex negundo, was used as flotation collector in the present investigation for beneficiating a low-grade graphite ore with 8.67% fixed carbon. A three-factor and three-level Box-Behnken Design (BBD) under Response Surface Methodology (RSM) was employed to study the effects of important process variables such as grinding time, depressant dosage, and collector dosage on the responses, namely, ash percent of final concentrate and its recovery. A final graphite concentrate with 4.24% ash and 14.42% yield was obtained using the developed biocollector by flotation of low-grade graphite ore with 89.47% ash content. The degree of significance of input variables was determined using ANOVA. Regression models for ash content, % of final concentrate, and its %recovery was obtained from BBD analysis. It showed that the grinding time has a significant influence on the process followed by depressant dosage on the grade of final concentrate and collector dosage on its recovery.

Stereolithography 3-D Printed Electrochemiluminescence Platform With Random Grade Graphite Electrodes: Detection of HO and Cholesterol Using a Smartphone

The growing demand for low-cost mini biosensing platforms combining important features, such as fast performance, rapid prototyping, portability, and easy integration in point-of-care settings, has proven their existence in the field of targeted biomolecule detection. This work encompasses a novel, simple, and ultrafast fabrication of a stereolithographic 3-D printed electrochemiluminescence (GP-SE-ECL) biosensor with a graphite pencil-based single electrode (SE) to detect H2O2 and cholesterol. Graphite pencil electrodes were extensively used as a replacement for screen-printing, laser-induced graphene-based electrodes due to their user-friendliness, ease of availability, excellent electrochemical properties, and cost-efficiency. Different graded graphite electrodes (F, H, HB, 3B, 6B, and 8B) were used to fabricate SE electrochemiluminescence (ECL) devices. Since the conductivity values and surface area for different graded pencils vary, the impact of conductivity and surface area of the electrodes on the effectiveness of the ECL device was confirmed with optimized parameters by sensing H2O2. The lab-made, portable 3-D printed dark room platform integrated with a smartphone was used to capture the ECL signals. The smartphone android application was developed which can not only capture the ECL images, but also calculates the intensities values for the region of interest. Finally, the performance of the fabricated GP-SE-ECL biosensor was corroborated for cholesterol sensing to obtain a linear range (LR) from 50 to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1000 ~\mu \text{M}$ </tex-math></inline-formula> and a detection limit of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$15.71 ~\mu \text{M}$ </tex-math></inline-formula> . Based on the experimental data, it was confirmed that the fabricated device with random grade pencil possesses strong acceptability in the field of biomolecule detection.

Comparative Study of the Compressive Strength of Different Commercial Graphite Grades at Room and High Temperatures

Comparative Study of the Compressive Strength of Different Commercial Graphite Grades at Room and High Temperatures

Estimating the dimensional change behavior of nuclear graphite with heavy-ion irradiation-induced bending

Two promising reactor Generation IV designs employ nuclear graphite as their moderator and reflector. To this end, new graphite grades are being developed, which will require their suitability for reactor design to be established. Understanding graphite irradiation behavior, especially dimensional change, is critical when selecting a particular nuclear graphite grade. This is usually established by fast neutron irradiation experiments in a material test reactor (MTR). However, due to the limited accessibility to the MTR irradiation facility, cost, and the time required for such experiments to be carried out, the development of new nuclear graphite grades is restrictive. Here, a novel approach is proposed to enable suitable grades to be selected from a number of candidates before an MTR program is implemented by estimating the irradiation-induced dimensional change behaviors of several nuclear graphite grades based on the bending of graphite foils under ion irradiation. The method is capable of efficiently distinguishing the most dimensionally stable graphite grades in the laboratory without the need to irradiate many samples in an MTR program.

In English

In the work, carbon nanostructures (CNS) were synthesized on a plasma chemical plant using graphite electrodes SIGE (Special Impregnated Graphite Electrodes) and FGDG-7 (Fine-grained dense graphite) in a helium environment. In the experiments, it was established that graphite electrodes of the SIGE brand are suitable for the synthesis of CNS by the electric arc plasma chemical method. In addition, the experiments indicate that SIGE graphite in electric arc synthesis in a gas environment allows the creation of centimeter composite rods (deposits), where the core consists of graphene sheets rolled into nanotubes that can withstand extremely high temperatures (&gt;4000 K). Studies using scanning microscopy have shown that the synthetic deposit of SIGE graphite can be divided into blocks, which is important for its use in high voltage stations because it is possible to prepare deposits of the required length without mechanical impact and without violating the integrity of its structure. The structure of the synthesized carbon materials was studied by scanning and transmission electron microscopy and it was shown that carbon nanotubes are formed during the evaporation of SIGE brand graphite even without the use of a catalyst. Experiments have confirmed that the mass yield of wall fullerene-containing carbon black during the evaporation of SIGE grade graphite significantly exceeds the results obtained during the evaporation of FGDG-7 grade graphite electrodes. Such results make SIGE graphite more productive for the synthesis of expensive carbon nanoproducts (fullerenes and fullerene-like structures) by the electric arc method. It was also recorded that during the synthesis of carbon nanostructures, single-walled carbon nanotubes are formed, which have a positive charge and are deposited in the form of a core on the surface of the cathode electrode under the action of an electromagnetic field.

Separation of Graphites and Cathode Materials from Spent Lithium-Ion Batteries Using Roasting–Froth Flotation

The separation of graphites and cathode materials from spent lithium-ion batteries (LIBs) is essential to close the loop of material used in LIBs. In this study, the roasting characteristics of the spent LIB materials are carefully analyzed, and the effects of roasting on the surface morphology and elemental chemical states of electrode materials are fully investigated by thermogravimetric analysis, SEM-EDS, and XPS to explore the roasting–flotation enhancement mechanism. Then, froth flotation is utilized to separate the graphites and cathode materials from the spent LIB materials. The optimal roasting temperature is determined by thermogravimetric analysis and the SEM-EDS analysis of the spent LIB materials. The results suggest that the organic binder can be effectively removed from the spent LIB materials at the roasting temperature of 500 °C, and there is almost no loss of graphite. The XPS results indicate that, in the process of roasting, the decomposition products of the organic binder can easily react with valuable metals (Ni, Co, and Mn) to produce corresponding metal fluoride. The flotation results of the spent LIB materials after roasting at the optimal conditions indicate that graphites and cathode materials can be efficiently recovered through roasting–froth flotation. When the dosage of kerosene is 200 g/t and the dosage of methyl isobutyl carbinol (MIBC) is 150 g/t, the cathode materials grade is 91.6% with a recovery of 92.6%, while the graphite grade is 84.6% with a recovery of 82.7%. The roasting–froth flotation method lays the foundation for the subsequent metallurgical process.

Thermophysical characteristics of friction materials based on bronze with 12% tin with the addition of GK-1 graphite powder and foundry coke

The results of measurements of thermal properties in the temperature range from 20 °C to 100 °C of bronze with 12% tin obtained by powder metallurgy and 30 vol. % carbon-containing additive in the form of powders of graphite grade GK-1 (7-10 microns), foundry coke (less than 63 microns). The specific heat capacity of the samples was measured using the differential scanning calorimetry method. Thermal diffusivity and thermal conductivity were studied by two different methods. In the first case, the thermal diffusivity is determined by the laser flash method and the thermal conductivity by the calculation method. In the second case, the coefficients of thermal diffusivity and thermal conductivity were measured by the flat heat source method. It has been established that 30 vol.% of graphite powder GK-1 in the composition of bronze with 12% tin makes it possible to obtain the value of the thermal conductivity coefficient equal to 23,97 W/(m·K) at 20 °C with its further increase to 25,65 W/(m·K) at 100 °C. The specific heat capacity is 376,71 J/(kg·K) at 20°C and 399,26 J/(kg·K) at 100 °C. The addition of 30 vol.% coke powder makes it possible to obtain a thermal conductivity coefficient equal to 9,03 W/(m·K) at 20 ° C and 10,76 W/(m·K) at 100 °C. The specific heat capacity ranges from 391,80 J/(kg·K) at 20 °C to 413,57 J/(kg·K) at 100 °C

Perspective on “code qualifying” new graphite grades for use in advanced nuclear reactors*

The American Society of Mechanical Engineers (ASME) publishes the Boiler and Pressure Vessel (BPV) Code, which include guidance for the safe development, construction, and operation of boilers and pressure vessels. ASME BPV Code Section III “Rules for Construction of Nuclear Facility Components” Division 5 focuses on “High Temperature Reactors”. Subsection HH, subpart A lists the different materials properties that are to be measured and how those properties change due to different environmental conditions (oxidation and irradiation damage) for a graphite to be accepted for use in a high temperature reactor core (i.e., “Code Qualified”). Currently there are no nuclear graphite grades that are “Code Qualified” (i.e., a reactor designer can select a graphite grade and build their reactor without any additional testing), which is due in part to development of new graphite grades in the last 20 years and the lack of comprehensive programs needed to produce the data for the code cases. This perspective is going to discuss the requirements, as called out in the ASME BPV Code, that are necessary to “code qualify” a nuclear graphite grade but will primarily focus on the practical and technical challenges associated with irradiation-induced property changes and how to address these to assist with getting graphite ready for use in advanced nuclear reactors. These same technical challenges can be expected to arise for other materials being developed for advanced reactor concepts.

Infiltration of molten fluoride salts in graphite: Phenomenology and engineering considerations for reactor operations and waste disposal

The possibility and consequences of salt-infiltration in graphite must be evaluated for graphite used in molten salt reactors (MSRs) and fluoride-salt-cooled high-temperature reactors (FHRs), which can be subjected to salt pressures as high as 500 kPa. The volume of graphite porosity infiltrated by salt can be measured by direct infiltration and it can be predicted from the graphite pore size distribution, the surface tension of the salt, and the contact angle between the graphite and the salt. While these three properties are believed to be insensitive to irradiation, the former can be impacted by chronic or acute oxidation, and the latter two are highly sensitive to the chemistry of the salt and to events such as air ingress. For MSRs, predictions based on nominal properties of salt and graphite reveal that few graphite grades would satisfy the 4 vol% limit set in the Molten Salt Reactor Experiment, and even fewer would satisfy the 0.5 vol% design target. For FHRs, infiltration limits have not been defined and depend on the effect of infiltration on graphite properties, which are discussed. A hypothesis is presented for properties that may be impacted by infiltration and for which future studies are needed.

Comparative Analysis of Products of the Fullerenes’ and Carbon-Nanostructures’ Synthesis Using the SIGE and FGDG-7 Grades of Graphite

Comparative Analysis of Products of the Fullerenes’ and Carbon-Nanostructures’ Synthesis Using the SIGE and FGDG-7 Grades of Graphite

Multiscale characterization and comparison of historical and modern nuclear graphite grades

Beginning with Chicago Pile I, graphite has been used as a moderator material in nuclear power stations and is considered a potential material for use in future Generation IV advanced reactors. The microstructure of graphite is responsible for much of its mechanical and thermo-physical properties, and how it responds to irradiation. To understand graphite microstructure, it is necessary to understand its porosity at the macro- and micro-scales; and to understand its porosity, it is necessary to characterize the morphological connectivity of the void content and the two main phases of graphite: filler and binder. Here, using several microscopy and analytical techniques, a detailed examination of the heterogeneity, microstructure and pore structure of different graphite grades and their binder and filler phases is presented. Significant differences were found between coarser and finer nuclear grades. Coarse grades have a more diverse range of filler particles, pores and thermal cracks. Finer grades have a more well-defined pore size distribution, fewer variations of filler particles sizes and do not contain as many large thermal cracks. Fine grades tend to have a well-connected network of pores whereas coarser grades contain a larger content of closed porosity. The framework developed within this work can be applied and used to assess the various graphite grades that would down-select materials for specific use in graphite moderated reactor designs.

Plasma jet printing induced high-capacity graphite anodes for sustainable recycling of lithium-ion batteries

Graphite is an integral part of lithium-ion batteries (LIBs). However, due to limited resources and high production cost, producing battery grade graphite to meet the increasing demands for energy storage devices is becoming a challenge. One viable approach is to recycle the spent graphite anodes from end-of-life LIBs. Importantly, recycling of spent lithium-ion batteries (LIBs) is off utmost importance to address the global challenge of electronic waste management. Herein, we present an environmentally friendly technique of graphite recycling from spent LIB by water leaching, followed by atmospheric plasma jet printing. The major advantage of this method is that it does not require any binders or conductive diluents. Plasma-printed recycled graphite showed a significantly enhanced specific capacity of 402 mAh g−1 at 500 mA g−1 at the end of the 1000th charge-discharge cycle, in comparison to water-washed recycled graphite (112 mAh g−1) and a 23.35 times faster diffusivity of Li+. A detailed experimental investigation revealed that the plasma activation of the graphitic structure resulted in the improved reversible Li+ storage. This work provides a new perspective on the recycling strategy of graphite anodes using in situ plasma functionalization, a significant step towards the sustainable future of LIBs.

Determination of Impurities in Graphite Using Proton Induced Gamma Ray Emission, Total Reflection X-ray Fluorescence and Instrumental Neutron Activation Analysis

Determination of impurities in graphite is very important for its quality control, as their presence even at trace level can affect the performance of graphite in various applications. Graphite with equivalent boron content (EBC) less than 5 mg kg-1 is considered as nuclear grade. Elements with high neutron absorption cross section (boron and rare earths) contribute significantly to EBC. Non-destructive method is preferred as there is no sample processing and probability of loss of volatile elements while digestion. Proton Induced Gamma Ray Emission (PIGE), Instrumental Neutron Activation Analysis (INAA) were utilized for the non- destructive determination of impurities in both nuclear and commercial grade graphite. Low Z elements like Li, B, F, Na, Al and Si were detected in graphite by PIGE whereas Na, K, Sc, Cr, Mn, Fe, Co, Zn, Rb, Zr, Sb, Cs, La, Ce, Nd, Sm, Eu, Tb, Yb, Hf, Ta, Th were determined using INAA. Few elements like Ca, Ti, V, Ni, Sr and Pb remained undetected by both the non-destructive techniques. These elements were determined by Total Reflection X-ray Fluorescence (TXRF) after digestion of the graphite samples by dry ashing. Combinations of these techniques were utilized to get maximum information regarding the impurities present in graphite.

Using porous random fields to predict the elastic modulus of unoxidized and oxidized superfine graphite

Nuclear graphite is a candidate material for Generation IV nuclear power plants. Porous materials such as graphite can contain complex networks of pores that influence the material's mechanical and irradiation response. A methodology known as the random finite element method (RFEM) was adapted to create synthetic microstructures and predict the influence of porosity on the elastic properties of graphite during oxidation. RFEM combines random field theory and the finite element method in a Monte Carlo framework to estimate the mechanical response of a given grade of graphite. In this research, the random fields were verified through experimental characterization to predict the elastic response of three nuclear graphite grades, ETU-10, IG-110, and 2114. Finite element models (FEM) were generated using segmentations of x-ray computed tomography (XCT) data known as image-based models (IBMs) to validate and compare with the RFEM results and better understand the effects of uniform oxidation in these graphite grades. The RFEM predictions appear to correlate well with the experimental values of the measured Young’s modulus of the three graphite grades and display the same trends as IBMs.

Determination of nuclear graphite impurities by prompt gamma activation analysis to support decommissioning operations

Elemental composition of non-irradiated nuclear grade graphite was determined by Prompt Gamma Activation Analysis (PGAA) to quantitively assess some neutron activation precursors. The knowledge of these data is paramount for an accurate radiological characterization of the material before decommissioning of graphite-moderated nuclear reactors. Bulk results of most of the nuclides were consistent with benchmark Inductively Coupled Plasma–Mass Spectrometry (ICP-MS) and literature data. In the case of 14N and 35Cl, depth distribution profiles were observed and quantified for the first time. These outcomes could shine a light on 14C and 36Cl depth distribution profiles and fractional release during leaching experiments.