Graphite Content Research Articles

Rapid and Cost-Effective Fabrication and Performance Evaluation of Force-Sensing Resistor Sensors

In this study, we developed a cost-effective and rapid method for fabricating force-sensing resistor (FSR) sensors as an alternative to commercial force sensors. Our aim was to achieve performance characteristics comparable to existing commercial products while significantly reducing costs and fabrication time. We analyzed the material composition of two widely used commercial force sensors: Interlink FSR-402 and Flexiforce A201-1. Based on this analysis, we selected 4B and 9B pencils, which contain high concentrations of graphite, and silicone sealant to replicate these material properties. The fabrication process involved creating piezoresistive sheets by shading A4 copy paper with 4B and 9B pencils to form a uniform layer of graphite. Additionally, we prepared a mixture of 9B pencil lead powder and silicone sealant, ensuring a consistent application on the paper substrate. Measurement results indicated that the force sensor fabricated using a mixture of 9B pencil powder and silicone sealant exhibited electrical and mechanical characteristics closely resembling those of commercial sensors. Load tests revealed that the hand-made sensors provided a proportional voltage output in response to increasing and decreasing loads, similar to commercial FSR sensors. These results suggest that our fabrication method can produce reliable and accurate FSR sensors suitable for various applications, including wearable technology, robotics, and force-sensing interfaces. Overall, this study demonstrates the potential for creating cost-effective and high-performance FSR sensors using readily available materials and simple fabrication techniques.

Insights into chemical aging of urban aerosols over Delhi, India

Atmospheric particles can undergo aging as they are transported over long distances and mix with particles from other sources. This can lead to the accumulation of pollutants and the formation of complex aerosol mixtures with diverse chemical and physical properties. To investigate the process of aging in ambient atmosphere, 24h sampling of PM2.5 aerosol particles on Quartz microfiber filter with a tin substrate was carried out from November 2020 to March 2021 at CSIR-National Physical Laboratory, New Delhi (28°38'10″ N and 77°10′17" E), using fine particle sampler. Based on the observations of weather and meteorological parameters, a few episodic cases have been selected, and samples were analyzed at bulk and individual particle level. The objective of the present study is to investigate the aging characteristics of aerosols, enabling us to understand the mixing of aerosols (at both bulk and individual particle levels) and the variation in fresh and deformed (aged with other species) graphitic content in the episodic cases. The Raman Spectroscopy technique employed measures the intensity of graphitic (G band; around 1580 cm−1) and disordered graphitic (D band; around 1320 cm−1) content of aerosols. Individual particle microscopic observations reveal the occurrence of open chain fractals of black carbon in variable monomer sizes, sometimes agglomerated with metals like Cu, Cr, Ca etc., along with the presence of S- rich and organic aerosols while the Raman Spectrum (bulk sample analysis) highlights graphitic and disordered (when graphite interacts with other chemical species) graphitic intensities. Comparing the intensities of heavy haze and moderate haze with non-haze days (for comparison purpose, March 23, 2021 with the lowest PM2.5 concentration ∼ 62 μg/m3, has been considered as a non-haze day), it was observed that the intensities recorded on haze days were 45 to 200 times higher for the G band and 43 to 93 times higher for the D band; while for moderate haze days, the intensities were 4 to 61 times higher for the G band and 2 to 29 times higher for the D band. These findings suggest chemical processing of BC during haze days.

Evaluation of Shape Recovery Performance of Shape Memory Polymers with Carbon-Based Fillers.

This study focuses on enhancing the thermal properties and shape recovery performance of shape memory polymers (SMPs) through the application of carbon-based fillers. Single and mixed fillers were used to investigate their effects on the glass transition temperature (Tg), thermal conductivity, and shape recovery performance. The interaction among the three-dimensional (3D) structures of mixed fillers played a crucial role in enhancing the properties of the SMP. These interactions facilitated efficient heat transfer pathways and conserved strain energy. The application of mixed fillers resulted in substantial improvements, demonstrating a remarkable 290.37% increase in thermal conductivity for SMPCs containing 60 μm carbon fiber (CF) 10 wt% + graphite 20 wt% and a 60.99% reduction in shape recovery time for SMPCs containing CF 2.5 wt% + graphite 2.5 wt%. At a content of 15 wt%, a higher graphite content compared to CF improved the thermal conductivity by 37.42% and reduced the shape recovery time by 6.98%. The findings demonstrate that the application of mixed fillers, especially those with high graphite content, is effective in improving the thermal properties and shape recovery performance of SMPs. By using mixed fillers with high graphite content, the performance of the SMP showed significant improvement in situations where fast response times were required.

Cycle performance analysis of hybrid battery thermal management system coupling phase change material with liquid cooling for lithium-ion battery module operated at high C-rates

High performance battery thermal management system (BTMS) is urgently needed to satisfy the severe cooling demand of battery modules operated at high C-rates during continuous charging-discharging cycles. Hybrid BTMS coupling phase change material (PCM) with liquid cooling is a promising solution which attracts great attention in recent years. Here, cycle performance of the hybrid system is analyzed in detail via comparison with the pure PCM system to examine its reliability and demonstrate its superiority during continuous 3C-charging and 4C-discharging cycles. Effects of PCM melting temperature are studied and RT44HC is found a suitable PCM choice with appropriate melting temperature. Analysis of the first three cycles is proved important and basically sufficient as system thermal behavior stabilizes afterwards. Further, interacting mechanisms of expanded graphite (EG) content and battery distance on system cooling performance are elucidated and their possible combinations satisfying temperature requirements of battery module in both temperature rise and temperature uniformity are presented. Optimal combination of EG content and battery distance is 3 % and 3 mm. Effects of coolant velocity are also investigated and suitable velocity for the optimized hybrid system is set at 0.01 ms−1 to achieve balance between cooling performance and auxiliary energy cost.

Prediction of thermo-physical properties and evaluation of thermal energy storage performance of phase change materials based on silicone rubber/graphite (Q/G) composites

ABSTRACT Phase change composite materials (PCCMs) are a type of thermal energy storage system known for their high latent heat of fusion. In this study, PCCM samples based on peroxide-cured silicone rubber (Q) were prepared using a simple soaking procedure in molten Paraffin Wax (PW). At any fixed amount of peroxide, the rubber base samples were filled with varying amounts of graphite powder (G), 4 to 8 Wt.%, to improve the thermo-physical properties. The effect of peroxide and graphite content was then evaluated on the PW loading, PW leakage, and thermal storage performance of the resulting Q/G/PW composites. It was found that the highest ratio of the PW loading to PW leakage occurs at a peroxide content of 6 Wt.%. Moreover, the graphite particles demonstrate a significant role in PW trapping inside the rubber structure and lowering the PW leakage. Finally, the thermal studies showed that the Q/G/PW composite containing 6 wt.% of peroxide and 4 wt.% of graphite has the highest latent heat of 111.5 J/g with a PW loading of 15.2%. This sample also had the lowest thermal diffusivity and the slowest cooling and heating rate.

Modifying Polymer-Based Hard Carbons for Enhanced Understanding of Sodium Storage Properties

Numerous theories on the storage of sodium in hard carbons can be found in the literature. In particular, understanding the contributions of (heteroatom) doping, porosity and graphitic layers is of great importance. Much of the current literature on hard carbons uses different biomaterials as precursors in order to improve the sustainability of the synthesis. However, large differences in the composition of the starting materials and the presence of foreign atoms make a systematic investigation of the storage process extremely difficult.Therefore, a hard carbon material based on furan resins was used in this work to obtain a well-defined starting material that can be modified systematically. This allows a detailed investigation of the effects caused by those modifications. Modifications can be achieved by directly adding various template materials to the polymerization process. Both doping with heteroatoms by adding template chemicals such as boric acid and the introduction of graphitic layers by adding high-purity graphite during polymerization were investigated.Addition of boron and phosphorus heteroatoms led to an increase in reversible capacity up to 240 mAh g-1 from 150 mAh g-1 for carbonization temperatures as low as 650°C. Formation of a potential plateau was observed for boron doping, which is usually found at higher carbonization temperature surpassing 1000°C. Utilizing Raman and XRD spectroscopy, crystallite size was found to be decreasing with phosphorus doping, while boron doping led to an increase. This increase could be a possible explanation for the observed capacity plateau.The addition of high-purity carbon samples, such as KS6L graphite or graphene, allowed for a targeted introduction of single- and multi-layer graphitic domains without alteration of additional properties. Increasing graphite content up to 5 wt-% during polymerization resulted in enhanced electrochemical characteristics, including increased sodium intercalation into the lattice and shift of the sloping proportion to lower potentials. Further increase up to 10 wt-% led to a vanishing of the plateau potential and a lowering of the reversible capacity. The results indicate that the interlayer spacings has now decreased below a threshold, which prohibits the sodium from intercalation between the graphitic layers. Additionally, doping Hard Carbons with graphene revealed a capacity decrease at content ratios as low as 2 wt-%, emphasizing the significance of both the stacking and interlayer spacing of the graphitic lattice, as well as the chemical composition, for efficient sodium storage.In summary the results presented provide an enhanced understanding into the sodium storage properties of Hard Carbons, which help improve the design of synthesis processes for more cost-efficient and high-performance carbon materials. Figure 1

One facile route to prepare high‐performance radiation resistant EPDM rubber composites through graphite modification technology

AbstractModification and improvement of aging resistance in nuclear power environment for the ethylene‐propylene‐diene (EPDM) rubber has been attracting the attention of scientists. In this article, graphite modified EPDM composites (ultrafine graphite [UG]/EPDM) were prepared, and effect of graphite with sizes of 13, 2.6, and 1.3 μm on the processability, vulcanization parameters, mechanical properties, stability of radiation aging of EPDM composites were investigated, respectively. The results showed that EPDM rubber was an irradiated crosslinked polymer. The Mooney viscosity and crosslinking density of EPDM gradually increased with increasing graphite content under the effect of physical and chemical cross‐linking of graphite. The lamellar structure of graphite particles in the rubber matrix is beneficial to improvement of the mechanical properties and aging resistance of the EPDM composites and play a reinforcing role, and the sp2 hybrid structure of graphite can trap and quench free radicals, delayed the irradiation aging of EPDM. UG/EPDM composites irradiation stability was improved with increasing graphite dispersion in EPDM matrix. Under the cumulative irradiation dose of 1000 kGy, the tensile strength of blank sample and UG‐2.6 μm−10 decreased by 51.1% and 17.7%, respectively, and the hardness increased by 8.7% and 4.9%, respectively. The energy storage modulus and the corresponding glass transition temperature (Tg) of UG/EPDM composites enhanced with graphite, while the thermal stability of the composites was improved.

Effect of graphite concentration on the electrochemical performance of a novel α-MnO2-expanded graphite-PVDF composite cathode material based on FTO substrate

A facile chemical reduction method is employed for the synthesis of α-MnO2 followed by ultrasonication with synthetic graphite and poly (vinylidene pyrrolidone) PVDF for the development of α-MnO2-expanded graphite-PVDF (MGP) composite. Known masses of MGP composite are drop-casted on a fluorine-doped tin oxide (FTO) conducting glass substrate for the fabrication of composite electrodes to use as the cathode. The compositional effects of various weight percentages of graphite on the electrochemical performance of the MGP composite are studied. The increase in graphite’s weight percentage is always accompanied by an equal reduction in the weight of MnO2 by maintaining a constant amount of PVDF. We demonstrate a maximum electrochemical performance for the composite containing 80% MnO2, 10% expanded graphite, and 10% PVDF, further increases in graphite concentration (reduction in that of MnO2) have detrimental effects on the performance. The basis characterisation of the composite is carried out using XRD, FTIR, UV–vis, AFM, and SEM and the electrochemical studies are done using CV, GCD and EIS. We observe both faradaic and non-faradaic charge storage mechanisms in the composite samples with a 35% capacitive contribution and a 65% diffusive contribution to the total capacitance. Moreover, the composite electrode demonstrates a maximum specific capacitance of 358 F g−1 at 10 mV s−1 with an outstanding power density of 2.8 KW Kg−1.

Incoming Inspection of Lithium‐Ion Batteries Based on Multi‐cell Testing

Incoming inspections of battery cells prior to module assembly help to ensure the quality of the battery system and prevent the installation of anomalous cells. Depending on the area of application, identifying deviations in the electrical behavior of the battery cells under test can be essential for downstream assembly processes like cell matching and algorithm adaptations of the battery management software. In this work, the use of a multi‐cell testing procedure involving differential voltage analysis, incremental capacity analysis, direct current internal resistance tests, and electrochemical impedance spectroscopy is investigated to reveal differences in cell properties and identify anomalous cells while economizing on the required cell test channels. The results obtained from 20 model‐identical 21700 cylindrical cells from four different batches demonstrate that this methodology can detect material variations, such as differing silicon and graphite content, which are not disclosed by the supplier or indicated in the data sheet. A teardown with elemental analysis of two cells from different batches is carried out as verification. Finally, prospects for potential application scenarios and raw measurement data are provided.

Carbon dots with tunable excitation-independent fluorescence and organelle-specific targeting via core graphitization and surface groups engineering

Single-emission fluorescence and non-specific cellular organelle-targeting limit the application of carbon dots (CDs) in bio-imaging. Here, we proposed an adjustable strategy for synthesis of four CDs: Tm1-, Tm2-, Tma-, and Tp-CDs. The synthetic scheme was designed with tartaric acid and m-/p-phenylenediamine as precursors and water/acetone as solvent through hydrothermal/solvothermal synthesis and (or) column chromatography isolation. The maximum productivity of the CDs was 56.2 % and the highest fluorescence quantum yield was 47.8 %. These CDs emitted excitation-independent blue, green, and yellow fluorescence, respectively. The red shift of CDs fluorescence was caused by increasing graphitized conjugated sp2 domain and graphitic nitrogen content of carbon core. The hydrophilicity/lipophilicity and protonation ability of CDs determined their cellular uptake, intracellular trafficking and subcellular targets, including endoplasmic reticulum, lysosomes and nucleus. These CDs have the potential application in fluorescence visualization of live bacteria and in the organelle-targeted imaging of living mammalian, fungal, and plant cells. The study provides novel insights into rational design of CDs with multi-color fluorescence and organelle-specific targeting in live cells.

The Effect of Expanded Graphite Content on the Thermal Properties of Fatty Acid Composite Materials for Thermal Energy Storage.

The mass content of expanded graphite (EG) in fatty acid/expanded graphite composite phase-change materials (CPCMs) affects their thermal properties. In this study, a series of capric-myristic acid/expanded graphite CPCMs with different EG mass content (1%, 3%, 5%, 8%, 12%, 16%, and 20%) were prepared. The adsorption performance effect of EG on the PCMs was observed and analyzed. The structure and thermal properties of the prepared CPCMs were characterized via scanning electron microscopy, differential scanning calorimetry, thermal conductivity measurements, and heat energy storage/release experiments. The results show that the minimum mass content of EG in the CPCMs is 7.6%. The phase-change temperature of the CPCMs is close to that of the PCMs, at around 19 °C. The latent heat of phase change is equivalent to that of the PCM at the corresponding mass content, and that of phase change with an EG mass content of 8% is 138.0 J/g. The CPCMs exhibit a large increase in thermal conductivity and a significant decrease in storage/release time as the expanded graphite mass content increases. The thermal conductivity of the CPCM with a mass content of 20% is 418.5% higher than that with a mass content of 5%. With an increase in the EG mass content in CPCMs, the heat transfer mainly transitions from phase-change heat transfer to thermal conductivity.

The influence of trace vanadium on the solidification process, microstructure, and mechanical properties of gray cast iron

This study employed optical microscopy (OM), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) to investigate the impact of vanadium (V) on the microstructure and mechanical properties of gray cast iron (GCI) HT250. Additionally, Thermo-Calc software was employed to explore the influence of V on the solidification process. The results indicate that adding trace amounts of V in GCI forms a face-centered cubic VC phase, with the precipitation temperature of the VC phase gradually increasing. When the V content reaches 0.28 wt%, the VC phase begins to precipitate during the eutectic reaction. The incorporation of V consumes carbon, reducing the graphite content and promoting the formation of type D graphite. As the V content increases, there is an enlargement in the pearlite area ratio, a decrease in the pearlite layer spacing, and a reduction in the size of eutectic cells. These microstructural alterations lead to enhanced mechanical properties. The tensile strength peaks at 336 MPa with a V content of 0.77 wt%, representing a 29% increase compared to samples without added V. Similarly, the Vickers hardness increases with increasing V content, reaching a peak of 373 HV at 0.92 wt% V, a 27% increase compared to samples without V addition. However, at this point, the tensile strength decreases to 322 MPa.

ANALYZING THE PROPERTIES OF A COMPOSITE OF PCL-GRAPHITE BY THE INJECTION MOLDING

Coral reefs are vulnerable to several natural phenomena such as ocean warming, acidification, coral diseases, and plastic pollution. In order to tackle these problems, scientists are now working on the development of biocomposites utilizing biodegradable polymers such as polycaprolactone (PCL). Graphite can be used in conjunction with PCL to enhance its characteristics. The work is centered around conducting water absorption experiments on a composite material consisting of PCL and graphite. The investigation employs PCL granular and graphite powdered materials. The materials undergo heating, crushing, and weighing processes to ascertain weight ratios. Next, the mixture is shaped into specimens. The product's shape and distribution of chemical constituents are analyzed using water absorption, hydrophobicity, FTIR, and SEM testing. The findings indicate that the water absorption diminishes as the concentration of graphite powder increases. An alloy containing 10% graphite had the highest water absorption rate. The hydrophobicity test assesses the ability of a specimen's surface to repel water by introducing NaCl droplets and observing droplet production. The contact angle value exhibits a direct correlation with the increase in graphite content. The FTIR study indicates that there are no changes in the functional groups, resulting in a limited connection between the PCL matrix and the graphite filler. The temperature during the injection molding process affects the microstructure of the polymer. Lower temperatures lead to reduced crystallization, whereas higher temperatures result in denser molecular groupings. Graphite is a highly suitable choice for use as a filler in a PCL matrix because of its layered structure, large surface area, and excellent capacity to effectively fill voids within the matrix.

Dynamic failure of magnesia-carbon refractories under uniaxial compressive load

The thermo-mechanical stress, which was a combination of thermal stress from rapid temperature changed and dynamic mechanical stress from scrap impact, accelerated the damage to MgO–C refractories during service. The influence of graphite content (8 wt% and 16 wt%), heat treatment temperature, and oxidation level (partially oxidized or not) on dynamic mechanical stress damage behavior was investigated using the Split-Hopkinson pressure bar test at various loading velocities. The results indicated the SHPB test could form dynamic stress, and the parameters obtained post-test could characterize the dynamic mechanical properties of MgO–C refractories. Furthermore, all of the specimens' dynamic compressive strength clearly demonstrated the strain rate hardening effect; this phenomenon was particularly evident in the low-graphite specimens. Additionally, the thermally treated specimens dissipated impact energy by destroying the whole volume, whereas the oxidized specimens suffered damage layer by layer, and the specimens’ dynamic mechanical characteristics were weakened by oxidization or heat treatment.

Exploring the Impact of Spray Process Parameters on Graphite Coatings: Morphology, Thickness, and Tribological Properties

This study explores, through a full factorial experimental design, the effects of graphite concentration and spray flow rate on the morphology, thickness, and tribological performance of graphite coatings for potential tribological applications. Coatings were applied to rough substrates using varying concentrations and flow rates, followed by analysis of their morphological characteristics, roughness, thickness, coefficient of friction (COF), and wear behavior. The results revealed distinct differences in the coating morphology based on flow rate, with low-flow-rate coatings exhibiting a porous structure and higher roughness, while high-flow-rate coatings displayed denser structures with lower roughness. A COF as low as 0.09 was achieved, which represented an 86% reduction compared to uncoated steel. COF and wear track measurements showed that thickness was influential in determining friction and the extent of wear. Flow rate dictated the coating structure, quantity of transfer film on the ball, and the extent of graphite compaction in the wear track to provide a protective layer. SEM and elemental analysis further revealed that graphite coatings provided effective protection against wear, with graphite remaining embedded in the innermost crevices of the wear track. Low flow rates may be preferable for applications requiring higher roughness and porosity, while high flow rates offer advantages in achieving denser coatings and better wear resistance. Overall, this study highlights the importance of optimizing graphite concentration and spray flow rate to tailor coating morphology, thickness, and tribological performance for practical applications.

The effect of different powder mixtures used in the boriding process on the surface properties of AISI 304 stainless steel material

AISI 304 stainless steel, which is used in many areas such as chemistry, petrochemistry, storage tanks and food storage, attracts attention in terms of surface hardness and wear resistance, especially when its industrial applications are evaluated. In this study, it was aimed to improve the surface properties of the AISI 304 stainless steel material used as the substrate material. To develop the best surface properties, boriding layers of varying percentages were created. In order to create these layers, B4C, KBF4, SiC and graphite powders were compared using variable ratios. Microhardness and wear tests were performed on the borided samples and microstructure examinations were carried out using optical, SEM, XRD and EDX. It has been determined that the B4C used as boron source should not be less than 20% for the formation of the boriding layer and the double phase FeB/Fe2B. The powder mixture ratio with the highest thickness and hardness value of the boriding layer formed is the powder mixture with 20% B4C, 50% KBF4, 10% SiC and 20% graphite content. It was observed that the layer thickness increased by 63% and the hardness value increased by 11%. It was observed that this powder mixture gave the lowest wear rate compared to the other powder mixtures in the study. The difference between the highest and lowest wear rate is more than 3 times greater.

Effects of Adding Graphite to Epoxy Resin on its Mechanical Properties and Mild-to-Severe Wear Performance at its Heat Distortion Temperature

In this study, epoxy/graphite composites were fabricated based on different weight fractions (0, 3, 6, and 9 wt.%) of graphite powder for bearing applications. The mechanical and tribological properties were assessed. Adhesive wear tests covered the severe regions, where the interface temperature (IFT) exceeded the heat distortion temperature (HDT) of the epoxy. Graphite additions improved elastic modulus and hardness but decreased fracture strain and toughness of the composites. The tribological behaviors in the mild wear region were improved as the graphite content increased. In the mild wear region, the increase in graphite additions showed a good improvement by reducing the specific wear rate (SWR) and coefficient of friction (COF). In the severe wear region, the neat epoxy and higher graphite concentrations exhibited a dramatic increase in SWR, whereas the lowest addition of 3 wt.% exhibited good wear performance. For epoxy, the reason was that IFT exceeded its HDT, while the aggregation of graphite particles was the main reason in the case of higher graphite concentrations. SEM examinations showed severe wear signs—high ploughing and fracture—when IFT exceeded the HDT. However, by reducing the IFT, graphite additions did not show such severe wear features due to the accelerated heat dissipation.

Graphite-enhanced foam cement-based materials: Mechanical properties, pore structure and electromagnetic wave absorption performance

To reduce the environmental pollution caused by electromagnetic waves (EMW), graphite-enhanced foam cement-based electromagnetic wave-absorbing materials were prepared. The effects of hydration products and pore structure on the mechanical strength and microstructure have been investigated. The results show that at a graphite content of 10 wt%, resulting in a reduction in pore size and concentration within 400μm. This led to improved material compactness, resulting in an increase in compressive strength of 32.01 % and 29.13 % for 3-day and 28-day foamed concrete, along with a 35.40 % and 29.27 % increase in flexural strength. For the 10 mm thick foamed concrete, the reflection loss is −24.08 dB with an effective absorption bandwidth of 0.466 GHz (3.762–4.228 GHz). The impedance matching increased by 129 %, moving from 8.3 to 10 mm up range to 6.1–10 mm, while the frequency range increased by 61.35 %, moving from 3.37 to 5 GHz up range to 2.37–5 GHz, compared to the control group.

Preparation of a novel foamed concrete modified with carbon fiber and graphite: Mechanical, electro-magnetic and microstructural characteristics based on X-CT

In this paper, foam concrete is modified using graphite and carbon fiber as absorbents. The mechanical properties are analyzed in conjunction with hydration products, pore size distribution based on XCT test. Additionally, the resistivity, complex permittivity and complex permeability are tested. The results demonstrate that carbon fiber enhances the proportion of pores with diameters less than 200 μm in foam concrete, thereby significantly enhancing its flexural strength. Furthermore, incorporating graphite helps offset the initial retardation of sulfoaluminate cement hydration induced by carbon fibers, leading to an increase in the average pore size and a reduction in compressive strength. The incorporation of carbon fibers at a concentration of 0.6 wt% achieves the percolation threshold, akin to scenarios with singular fiber incorporation. Exceeding 2 wt% graphite content results in negligible influence on the conductivity. The synergistic integration of graphite and carbon fibers significantly improves the electromagnetic wave absorption performance of the composite. At a thickness of 6 mm, the material exhibits an effective bandwidth where the reflection loss is less than −10 dB, extending up to 2.5 GHz, which constitutes 52.08 % of the tested frequency spectrum.

Leaching kinetics of ash impurities from aphanitic graphite by combining dual-ultrasound and hydrochloric acid–potassium hydrogen fluoride

The hydrochloric acid-fluoride salt is useful for purifying graphite. Ultrasonic-assisted technique can significantly reduce the leaching time and improve the leaching efficiency. Compared with single-frequency, dual-frequency ultrasound has the advantages of high energy efficiency and wide cavitation area. In this study, the combination of a dual-frequency ultrasound-assisted technique and hydrochloric acid–potassium hydrogen fluoride leaching agent was proposed for the leaching of aphanitic graphite to remove impurity minerals. First, the effects of probe-type ultrasonic power, tank-type ultrasonic power, temperature, HCl concentration, ultrasonication time, and KHF2 concentration on the purification efficiency of impurities from aphanitic graphite with the assistance of dual-frequency ultrasound were investigated. It was found that the combination of dual-frequency ultrasound and hydrochloric acid–potassium hydrogen fluoride can reduce the ash content of aphanitic graphite from 13.02 % to 1.02 % with an ash removal rate of 94.17 %. Second, volumetric reaction models and unreacted shrinkage nucleation models were used to fit the kinetics of impurities from aphanitic graphite with dual-frequency ultrasound-assisted HCl-KHF2 leaching. Kinetic analysis shows that the volumetric reaction model with chemical control was better to fit the leaching process. This is consistent with the calculation results of the activation energy of the reaction (Ea = 58.13 kJ/mol). Finally, laser particle size analyzer, X-ray diffraction (XRD), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), X-ray fluorescence spectroscopy (XRF), transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDS) were used to analyze the fugacity of impurity minerals during the process of dual-frequency ultrasound-assisted HCl-KHF2 leaching. It was revealed that combining ultrasonic cavitation fragmentation with chloric acid–potassium fluoride generated SiF4 with high solubility, thereby removing silica-bearing impurities more efficiently. The challenges in further reducing ash content from 1.02 % in the leached concentrate of aphanitic graphite could be attributed to the existence of titanium-bearing mineral impurities on the surface of graphite particles and the presence of silica-bearing minerals between graphite carbon layers.