Graphite Blocks Research Articles

New Thermochemical Salt Hydrate System for Energy Storage in Buildings

This paper introduces an innovative design for an “inorganic salt-expanded graphite” composite thermochemical system. The storage unit is made of a perforated, compressed, expanded graphite block impregnated with molten CaCl2∙6H2O; the humid air passes through the holes that allow the moisture to diffuse and react with the salt. The prepared block underwent 90 hydration-dehydration cycles. Although most of the performed cycles were carried out with salt overhydration and deliquescence, the treated samples have remained mechanically and thermally stable with no drop in energy density. The volumetric energy density of the composite ranged from 135.5 to 277.6 kWh/m3, depending on airflow rate and absolute humidity. To ensure composite material cycling stability, the energy density of the block was measured during hydration at similar conditions of absolute humidity, inlet temperature, and airflow rate (0.01 kgwater/kgair, 20 °C, 400 l/min). The average energy density at these conditions was sustained at 219 kWh/m3. The block integrity was monitored by visual inspection after removing it from the reactor chamber every few cycles. Both the composite material and its manufacturing process are simple and easy to scale up for future commercialization.

Trash to treasure: A general strategy to prepare high performance graphite block via constructing interfacial transition layers with highly chemically active on recyclable graphite powder

Recently, the cycling of graphite residuum generated in the machining process of isostatic graphite has aroused great interest in both academia and industry as it offers an important solution to reduce the waste of resources and environmental disruption. However, conventional method of simple backfilling of residuum suffers drawbacks of low added-value and environmental pollution owing to the high graphitization degree and low chemical activity of these graphite powders. Herein, we report a general strategy to prepare high-performance graphite block (GBB) while using recyclable graphite powder (RGP) as starting compound via constructing highly chemical active interfacial transition layers (ITLs) on the surface of RGP by impregnated pitch (IP). The ITLs decorated recycled graphite powder (RGP@SC), as reflected in FT-IR, ESR, TG-DTG and EA, contains abundant surface functional groups, free radicals, and heteroatoms which ensures the high chemical activity, thus obviously improving the self-sintering and self-adhesion properties of GBB. As a result, GBB with RGP@SC as the main aggregate display a high homogeneity and mechanical properties. The average open porosity, flexural and compressive strength are determined to 9.90%, 56.60 MPa and 123.50 MPa, respectively, which even outperforms most reported graphite blocks. Impressively, due to the absence of impregnating and multiple calcinating, the process has a short production cycle, which not only saves energy, but also is environmentally friendly. The current work displays benchmark example of the employment of RGP for synthesis of high-performance graphite block.

Core Optimization for Extending the Graphite Irradiation Lifespan in a Small Modular Thorium-Based Molten Salt Reactor

The lifespan of core graphite under neutron irradiation in a commercial molten salt reactor (MSR) has an important influence on its economy. Flattening the fast neutron flux (≥0.05 MeV) distribution in the core is the main method to extend the graphite irradiation lifespan. In this paper, the effects of the key parameters of MSRs on fast neutron flux distribution, including volume fraction (VF) of fuel salt, pitch of hexagonal fuel assembly, core zoning, and layout of control rod assemblies, were studied. The fast neutron flux distribution in a regular hexagon fuel assembly was first analyzed by varying VF and pitch. It was demonstrated that changing VF is more effective in reducing the fast neutron flux in both global and local graphite blocks. Flattening the fast neutron flux distribution of a commercial MSR core was then carried out by zoning the core into two regions under different VFs. Considering both the fast neutron flux distribution and burnup depth, an optimized core was obtained. The fast neutron flux distribution of the optimized core was further flattened by the rational arrangement of control rod channels. The calculation results show that the final optimized core could reduce the maximum fast neutron flux of the graphite blocks by about 30% and result in a more negative temperature reactivity coefficient, while slightly decreasing the burnup and maintaining a fully acceptable core temperature distribution.

‘Accurate proton range shift verification by using a two-layer dense-pixel LYSO compton camera prototype

ObjectiveCompton camera (CC)-based prompt gamma imaging (PGI) is promising to realize real-time in-vivo range verification during proton therapy. Lutetium–yttrium orthosilicate (LYSO)-based CC has advantages in high detection efficiency and position resolution. However, few LYSO CC-based PGI experimental evaluations have been investigated. ApproachWe built a 46 × 46 two-layer dense-pixel LYSO CC prototype for PGI. We attempt the first-ever effort to conduct the proton range shift verification experiments with the LYSO CC prototype. A 13 MeV proton beam with a cross-section of 1 mm2 produced by the Compact Pulsed Hadron Source (CPHS) and a lead collimator irradiates a block of graphite, a block of polymethacrylates (PMMA) and a block of fresh pork, respectively. A range shift varied from 1 mm to 5 mm of the proton beam is used to evaluate the performance of the prototype in PGI. The peak current intensity was about 640 nA. The pulse width and frequency were 100 μs and 1 Hz, respectively. The rate of incident protons in each measurement is about 3.6 × 108/s, and the corresponding delivered dose is about 5.8 Gy. Main resultsThe built LYSO CC prototype can distinguish the displacement of the Bragg peak in 2 mm (reaching 1 mm) at a distance of about 13 cm, and can accurately reconstruct the positions of the Bragg peak with a mean deviation of 0.2 mm in the eighteen groups of experiments. SignificationThe experiments demonstrate the feasibility of the developed two-layer dense-pixel LYSO CC in realizing accurate range shift monitoring and show its potential in range verification during clinical proton therapy and high particle rate proton therapy (e.g., FLASH proton therapy).

A new planar capacitive sensor with high sensitivity for proximity sensing of an approaching conductor

PurposeWith the development of artificial intelligence, proximity sensors show their great potential in intelligent perception. This paper aims to propose a new planar capacitive sensor for the proximity sensing of a conductor.Design/methodology/approachDifferent from traditional structures, the proposed sensor is characterized by sawtooth-structured electrodes. A series of numerical simulations have been carried out to study the impact of different geometrical parameters such as the width of the main trunk, the width of the sawtooth and the number of sawtooths. In addition, the impact of the lateral offset of the approaching graphite block is investigated.FindingsIt is found that sensitivity is improved with the increase of the main trunk with, sawtooth width and sawtooth number while a larger lateral offset leads to a decrease in sensitivity. The performance of the proposed planar capacitive proximity sensor is also compared with two conventional planar capacitive sensors. The results show that the proposed planar capacitive sensor is obviously more sensitive than the two conventional planar capacitive sensors.Originality/valueIn this paper, a new planar capacitive sensor is proposed for the proximity sensing of a conductor. The results show that the capacitive sensor with the novel structure is obviously more sensitive than the traditional structures in the detection of the proximity conductor.

Numerical simulation and optimization of compact latent heat exchanger with micro-channel plate in shape-stabilized composite phase change material

To enable the rapid provision of domestic hot water, this study presents the independent design of a plate heat exchanger featuring a large heat exchange area and a compact structure. Utilizing a sandwich structure, the thermal storage unit integrates two shaped composite phase change materials (CPCM), namely sodium acetate trihydrate (SAT)/expanded graphite (EG) blocks of identical thickness — in conjunction with a micro-channel heat exchange plate. Multiple thermal storage units are stacked to create the heat exchanger. Experimental validation of the heat transfer performance of this thermal energy storage heat exchanger is conducted, accompanied by the establishment of a heat transfer model elucidating the interaction between the phase change material (PCM) and the fluid. The investigation explores the impact of varying thicknesses of shape-stabilized CPCM, thermo-physical parameters of CPCM, and flow rates on enhancing the thermal efficiency of the thermal energy storage heat exchanger. Results indicate a competitive relationship between the phase change enthalpy and thermal conductivity of CPCM under constant density. Increasing the mass fraction of SAT effectively boosts its heat storage density. However, this improvement is counterbalanced by a reduction in CPCM's thermal conductivity, resulting in diminished heat transfer rates within the material and reduced efficiency in transferring heat between the material and the fluid. Optimal performance is achieved when the mass fraction of sodium acetate trihydrate is 80 wt% and the CPCM thickness is 20 mm. At these parameters, the thermal energy storage heat exchanger exhibits the highest heat transfer efficiency. Furthermore, the heat exchanger is capable of producing 197.86 kg of hot water in 1365 s at an inlet flow rate of 300 L/h, achieving an impressive discharging efficiency of 82.73 %. These findings underscore the feasibility of employing the mini-channel plate thermal energy storage heat exchanger for the rapid preparation of domestic hot water.

Changes in Functional Groups and Crystal Structure of Coal Tar Pitch with Respect to Carbonization Temperature

In this study, changes in the microstructure of coal-tar pitch (CTP) during successive processes, including pyrolysis, polycondensation, and crystallization, were examined in connection with the resulting variations in structure factors, as measured by X-ray diffraction (XRD) analysis, and functional groups, as confirmed by Fourier transform infrared (FTIR) spectroscopy. To this end, four zones were defined based on variations in crystallinity, which were indicated by d002 and Lc. Each zone was further characterized by interpreting crystallinity development in relation to changes in functional groups and specimen height. At around 400 °C, polycondensation occurred as the C-Har and C-Hal peaks decreased in intensity. These peak reductions coincided with the formation of mesophase spheres, resulting in enhanced crystallinity. Subsequently, at around 500 °C, the peak intensity of C-H and COOH decreased, which was attributed to the release of large amounts of gases. This led to sharp volume changes and a temporary reduction in crystallinity. All these results suggest that changes in the functional groups of CTP at lower temperatures (600 °C or less) during the carbonization process are closely associated with variations in its crystallinity. The major findings of the present study provide valuable insights for designing highly effective processes in the manufacturing of synthetic graphite blocks using CTP as a binder material, including by selecting appropriate temperature ranges to minimize volume expansion and crystallinity degradation and determining the lowest possible carbonization temperature to ensure adequate binder strength.

Effect of Impregnation and Graphitization on EDM Performance of Graphite Blocks Using Recycled Graphite Scrap

In the present study, graphite scrap powder from machining of commercial graphite blocks for electrical discharge machining (EDM) applications was recycled as a filler material for manufacturing graphite blocks, and its suitability for use as EDM electrodes was thoroughly assessed. The effects of process parameters applied in EDM electrode manufacturing, including the number of impregnations and graphitization temperatures, on the physical properties of the resulting graphite blocks, were examined. Additionally, EDM performance was evaluated with respect to the above process parameters. In blocks subjected to three impregnation treatments, followed by graphitization at 2200 °C, surface protrusions formed during the EDM process, indicating that the EDM process did not proceed smoothly. On the other hand, in blocks that underwent three impregnation treatments, followed by graphitization at 2800 °C, no surface protrusions were observed, indicating successful EDM operation. This observation further confirms the suitability of these recycled materials for use in EDM electrodes. The graphite block electrodes fabricated using recycled graphite scrap exhibited inferior cyclic stability, with an electrode wear rate of 0.82%, higher than that of a commercial graphite block electrode (0.04%). Nevertheless, using recycled graphite scrap contributes to reducing product costs and CO2 emissions, making the developed graphite electrodes a favorable choice.

The Influence of Scratches on the Tribological Performance of Friction Pairs Made of Different Materials under Water-Lubrication Conditions

Water-lubricated bearings are widely used in marine equipment, and the lubricating water often contains hard particles. Once these particles enter the gap between the bearing and the shaft, they can scratch the smooth surfaces of the shaft and bearing, influencing the working performance of the bearing system. To investigate the effect of scratch parameters on tribological performance, this paper conducts multiple block-on-ring experiments and constructs a mixed-lubrication model under water-lubrication conditions. The results show that among the three commonly used bearing materials, the tribological performance of graphite block is the most sensitive to scratches on the test ring surface. Under the condition of one scratch (N = 1), the loading area of water film pressure is divided into two separate zones (a trapezoidal pressure zone and an extremely low-pressure zone). In addition, the variation of maximum water film pressure is determined by the positive effect (hydrodynamic pressure effect of fluid) and negative effect (“piercing effect” of the asperities). Compared with the scratch depth and scratch location, the scratch width has the most significant effect on the tribological performance of the block-on-ring system. The maximum contact pressure is located at both edges of the scratch due to the formation of a water sac structure. The scratch has a great influence on the transition of the lubrication state of the block-on-ring system. The existence of scratches increases the critical speed at which the lubrication state transits from mixed-lubrication to elastohydrodynamic lubrication, and the critical speed is directly proportional to the scratch width.

Evaluation of Mason’s Empirical Formula Using a Chain Model of Polycrystalline Graphite

The dependence of the temperature of minimum electrical resistivity on the size of the mosaic blocks of artificial graphite of GMZ grade based on isotropic coke was calculated. A chain model of the electrical connection of lamellar structural elements (graphite flakes) was used. Compliance of the calculated results with Mason’s empirical formula was shown. Two cases were considered: the case of independence of the dimensions of mosaic blocks and the anisometry of the lamellar structural elements and the case when the dimensions of the mosaic blocks were proportional to the anisometry of the lamellar structural elements.

Structure evolution at the gate-tunable suspended graphene-water interface.

Graphitic electrode is commonly used in electrochemical reactions owing to its excellent in-plane conductivity, structural robustness and cost efficiency1,2. It serves as prime electrocatalyst support as well as a layered intercalation matrix2,3, with wide applications in energy conversion and storage1,4. Being the two-dimensional building block of graphite, graphene shares similar chemical properties with graphite1,2, and its unique physical and chemical properties offer more varieties and tunability for developing state-of-the-art graphitic devices5-7. Hence it serves as an ideal platform to investigate the microscopic structure and reaction kinetics at the graphitic-electrode interfaces. Unfortunately, graphene is susceptible to various extrinsic factors, such as substrate effect8-10, causing much confusion and controversy7,8,10,11. Hereby we have obtained centimetre-sized substrate-free monolayer graphene suspended on aqueous electrolyte surface with gate tunability. Using sum-frequency spectroscopy, here we show the structural evolution versus the gate voltage at the graphene-water interface. The hydrogen-bond network of water in the Stern layer is barely changed within the water-electrolysis window but undergoes notable change when switching on the electrochemical reactions. The dangling O-H bond protruding at the graphene-water interface disappears at the onset of the hydrogen evolution reaction, signifying a marked structural change on the topmost layer owing to excess intermediate species next to the electrode. The large-size suspended pristine graphene offers a new platform to unravel the microscopic processes at the graphitic-electrode interfaces.

Experimental Simulation of Decay Heat of Corium at the Lava-B Test-Bench

During the development of a severe accident at a nuclear power plant (NPP), corium is formed—a melt of core materials. A distinctive feature of corium, due to the content of fuel elements in its composition, is the presence of decay heat, which makes a significant contribution to the nature of the interaction of the corium melt with the structural materials of the reactor plant. In this regard, the decay heat should be taken into account when conducting computational studies and physical experiments. For this reason, certain requirements are imposed on the methods of simulating decay heat in the corium prototype, which relate to both the uniformity of the volume distribution and its intensity. This paper presents the results of calibration experiments to substantiate the operability of the induction heating system of the Lava-B test bench, which is used to simulate decay heat in the study of processes occurring during an accident with the NPP core meltdown. So, in order to obtain optimal characteristics of the heating system, a series of experiments was conducted on heating the graphite block in the experimental section of the Lava-B test bench. In the experiments, the capacitance of the used oscillating circuit capacitor banks and the electrical power on the inductor varied. As a result of the analysis of the data obtained, the most optimal parameters of the inductor-load simulator system were determined. In general, the performed experiments confirmed the operability of the induction heater and the possibility of its use in experimental studies of the interaction of corium with the various structural elements of the NPP reactor core at the Lava-B test bench.

Improvement of Ball Mill Performance in Recycled Ultrafine Graphite Waste Production for Carbon Block Applications.

A carbon block is a carbonaceous material used in various applications such as bearings, mechanical seals, and electrical brushes. This work aims to fabricate carbon blocks from industrial graphite waste, a residue from the cutting and tooling process of graphite block production. The ball milling process was used to fabricate ultrafine graphite waste to enhance the packing of carbon blocks. The milling performance was profoundly affected by dispersing agents in which sodium dodecyl sulfate (SDS), lignosulfonate (LS), and mixed dispersant (LS-SDS) were applied. The results showed that LS-SDS had the best milling performance, the greatest grinding index, and a flowable slurry, indicating the potentiality of this formulation for the environmentally friendly manufacture of ultrafine graphite waste. Carbon blocks were prepared from oven-dried ultrafine graphite waste, which was mixed with amorphous carbon and pitch. This carbon mixture was formed a block by compaction before carbonization and impregnation. The density of the fabricated carbon blocks increased from 1.76 to 1.83 g/cm3 after impregnation along with the increase in hardness, flexural strength, and reduction in electrical resistivity from 83, 62 MPa, and 40 μΩ m to 88, 81 MPa, and 39 μΩ m, respectively. The physical properties of carbon blocks prepared from ultrafine graphite waste were comparable to the properties of typical pristine carbon products.

CRUCIBLE ATOMIZER WITH THE FUNCTION OF SEPARATING MATRIX COMPONENTS FOR ATOMIC ABSORPTION DETERMINATION OF ELEMENTS IN SOLID SAMPLES

A design is proposed for a crucible electrothermal atomizer with a vertical arrangement of evaporation, condensation, and atomization zones in graphite cylindrical blocks with transverse heating. In such a cylindrical column, heat treatment was carried out – the evaporation of a solid sample and the condensation of vapors, and then the evaporation of the condensate into the atomization zone, in which vapors are filtered through the porous medium of the graphite filter into the analytical zone. Due to the separation of matrix components and the reduction of interference, the metrological characteristics of the determination of elements in solid organomineral samples are improved.

Changes in Mechanical Properties of Graphite Blocks Fabricated Using Natural Graphite as a Filler by Adding 3-mm Chopped Carbon Fiber

Changes in Mechanical Properties of Graphite Blocks Fabricated Using Natural Graphite as a Filler by Adding 3-mm Chopped Carbon Fiber

Improved Oxidation Resistance of Graphite Block by Introducing Curing Process of Phenolic Resin.

The purpose of this study is to improve the oxidation resistance of graphite blocks after graphitization at 2800 °C by introducing a curing process of phenolic resin, used as a binder to control the pore size. Using the methylene index obtained from FTIR, the curing temperature was set to 150 °C, the temperature at which cross-linking most highly occurs. Graphite blocks that had undergone curing, and were carbonized with a slow heating rate, showed increased mechanical and electrical properties. Microstructural observation confirmed that the curing process inhibited the formation of large pores in the graphite block. Therefore, the cured graphite block showed better oxidation resistance in air than a non-cured graphite block. Oxidation of the graphite block was caused by pores created by pyrolysis of the phenolic resin binder, which acted as active sites.

Control of the properties of a binder pitch to enhance the density and strength of graphite blocks

Control of the properties of a binder pitch to enhance the density and strength of graphite blocks

Effect of heating rate, temperature, and residence time during graphitization on the mechanical and electrical properties of isotropic graphite blocks

The present study aimed to determine the correlation between graphitization parameters during the manufacturing of isotropic graphite blocks, including temperature, residence time, and heating rate, and the physical properties of the obtained graphite blocks. It was found that during graphitization, nitrogen- and sulfur-containing gases were generated, and the isotropic graphite blocks exhibited volume shrinkage, and their apparent density and bulk density increased, regardless of any changes in the process parameters, due to the intrinsic microstructure of the isotropic coke. Graphite blocks with varying graphitization temperatures and residence time exhibited increased bulk density and open porosity but decreased flexural strength and electrical resistivity compared to carbonized blocks. It was also confirmed that the heating rate process parameter was related to gas release rates and crystallization. In addition, it was observed that micron-sized pores were created around the developed graphite layered structure with increasing graphitization degree.

Preliminary Neutronics Design and Analysis of the Fast Modular Reactor

General Atomics is developing a new 100-MW(thermal) fast modular reactor (FMR) that provides safe, carbon-free electricity and is capable of incremental capacity additions. The modular design allows it to be factory built and assembled onsite to keep the capital cost low, while the use of dry cooling facilitates siting to complement renewables in nearly any location. The FMR uses high-assay low-enriched uranium-dioxide fuel encapsulated by recognized irradiation-resistant silicon carbide composite (SiGA®) cladding that is derisked in the current accident-tolerant fuel program. The FMR fuel assembly is a hexagonal fuel bundle of 120 fuel rods. The total length of the fuel assembly is less than 4 m, with an active fuel length of 1.8 m. The fuel assemblies are configured in an annular core that is located and supported by the reactor internals. The coolant material is helium at a normal operating pressure of 7 MPa. The core is surrounded by zirconium silicide (Zr3Si2) and graphite reflector blocks. The fuel, coolant, internals, and reflectors are contained within a reactor pressure vessel. The preliminary nuclear design and analysis established the arrangement of the active core and reflector blocks. The nuclear design analyses of the FMR defined the design parameters, such as fuel enrichments, excess reactivity, fueling scheme, fuel cycle, power distribution, and control rod worth. The preliminary conceptual design determined the three-batch fueling scheme with the allowable total power peaking factor of 1.5. The average discharge burnup is 100 GW days per ton of uranium.

Changes in Mechanical and Electrical Properties as a Function of Unidirectional Pressure Changes in Preforming While Isostatic Pressing for Graphite Block Fabrication

Changes in Mechanical and Electrical Properties as a Function of Unidirectional Pressure Changes in Preforming While Isostatic Pressing for Graphite Block Fabrication