Graphite Content Research Articles

Analysis of the Impact of Graphite Addition on the Tribological Properties of Composites with Polyester–Glass Recyclate

Composites are increasingly being modified with various types of fillers and nanofillers. These materials have attracted much attention due to the improvement in their properties compared to traditional composite materials. In the case of advanced technologies, adding additives to the matrix has created a number of possibilities for use in many industries, from electronics to mechanics. Mechanical recycling of composites allows them to be reused as a filler in new composite materials; however, a decrease in their strength parameters is observed, and hence, new possibilities of their use are sought. The main objective of this research was to analyze the effect of the graphite content on the tribological and structural properties of composites with polyester–glass recyclate. Composite materials with 10% polyester–glass recyclate and an additive in the form of graphite in the amounts of 0%, 2%, 5%, 10% were made using the hand lamination method and their mechanical properties were verified. Then, using a universal tribometer operating in rotational motion with friction without lubrication, the influence of nanoadditives on the change in the coefficient of friction (µ) and the change in the coefficient K (the rate of a mass wear) of the obtained composites was investigated. This study showed that adding graphite in the amount of 2%, 5%, and 10% changes the nature of tribological wear of the obtained composite material. The coefficient K (mass wear rate) also changes. The addition of 10% graphite significantly changes the coefficient of friction without lubrication in a pair with a steel counter-sample.

Transition Metal-Mediated Preparation of Nitrogen-Doped Porous Carbon for Advanced Zinc-Ion Hybrid Capacitors

Carbon is predominantly used in zinc-ion hybrid capacitors (ZIHCs) as an electrode material. Nitrogen doping and strategic design can enhance its electrochemical properties. Melamine formaldehyde resin, serving as a hard carbon precursor, synthesizes nitrogen-doped porous carbon after annealing. Incorporating transition metal catalysts like Ni, Co, and Fe alters the morphology, pore structure, graphitization degree, and nitrogen doping types/proportions. Electrochemical tests reveal a superior capacitance of 159.5 F g−1 at a scan rate of 1 mV s−1 and rate performance in Fe-catalyzed N-doped porous carbon (Fe-NDPC). Advanced analysis shows Fe-NDPC’s high graphitic nitrogen content and graphitization degree, boosting its electric double-layer capacitance (EDLC) and pseudocapacitance. Its abundant micro- and mesopores increase the surface area fourfold compared to non-catalyzed samples, favoring EDLC and fast electrolyte transport. This study guides catalyst application in carbon materials for supercapacitors, illuminating how catalysts influence nitrogen-doped porous carbon structure and performance.

Modification of the Surface Layer of Grey Cast Iron by Laser Heat Treatment

This paper presents possible modifications to the properties of grey cast iron by laser heat treatment. These modifications are analyzed especially with regard to wear properties as a result of graphite content, which is a well-known solid lubricant. Examples of applications of grey cast iron in cases where good wear resistance is required are presented. Laser hardening from the solid state, laser remelting, and laser alloying are characterized. In this study, changes in the surface layer caused by these treatments were analyzed (especially the influence on the microstructure—including graphite content—and wear properties). It was shown that all of these treatments enable the wear resistance of the surface layer to be enhanced, mostly due to the increase in the hardness and microstructure homogeneity. It was also proven that it is possible to retain the graphite phase (at least partially) in the modified surface layer, which is crucial in the case of friction wear resistance. In particular, laser hardening from the solid state does not eliminate graphite. Laser remelting and alloying cause the dilution of carbon from the graphite phase to the melted metal matrix, but, in the case of nodular cast iron, it is possible that not all of the valuable graphite in the surface layer is lost.

Graphite-enhanced methanogenesis in coal measure shale anaerobic digestion: Implications for increasing gas yield and CO2 utilization

Anaerobic digestion (AD) of coal measure shale (CMS) for methane production is a promising technology for increasing yield of coal measure gas (CMG) wells. However, improving methane production efficiency of CMS remains a challenge. Conductive material has been shown to promote biogas production in different AD systems, but its effectiveness in CMS requires investigation. In this study, graphite was selected as conductive material due to its low cost and suitability for field applications, and its effects on methane production was investigated. The results indicate that as graphite concentration increases from 0 to 1.6 g/L, the methane production of CMS increases. However, when the graphite concentration reaches 2.0 g/L, the methanogenesis is inhibited, resulting in lower methane production compared to the control group. In the group with a graphite concentration of 1.6 g/L, the abundances of Romboutsia and Pseudomonas increase, which improves the compatibility of the microbial community with the CMS AD system and causes the amount of the substrates for methanogenesis to increase. Also, the direct interspecies electron transfer between Methanobacterium, Methanosaeta and Pseudomonas is strengthened, which enhances the methane production. However, excessive addition of graphite (2.0 g/L) intensifies the competitions from dissimilatory iron reduction and sulfate reduction reactions for substrates and electrons with the methanogenesis, causing the methane production to decrease. This study confirms the effectiveness of graphite in enhancing methane production of CMS, and the promoted hydrogenotrophic methanogenesis enhances the CO2 methanation, which offers an efficient pathway for increasing CMG well yield and enabling CO2 underground utilization.

(Keynote) Electrocatalysts Design for Carbon Dioxide Reduction and Valorization

There are several materials design strategies that have been utilized with various levels of success for CO2 reduction reaction (CO2RR) to C1, C2 and occasionally, C3 products (Ci denotes the number of carbon atoms in the product of CO2RR). Among those Cu based materials take leading role as this class of catalysts is relatively simple to synthesize and implement.1 Adding co-catalyst in the composite materials allow for regulating of selectivity towards a specific product while sustaining some simplicity of the synthesis and deployment strategies.2 Alternatively, CO2RR can be carried on carbon-based electrocatalysts with atomically dispersed transition metals, stabilized by nitrogen (known as M-N-C). We synthesized a library of nitrogen-doped carbonaceous materials with atomically dispersed 3d transition metals and corresponding metal-free electrocatalysts. The sacrificial support method (SSM) was used yielding catalyst materials of high dispersity and high graphitic content. The resulting electrocatalysts were impurity free, hence allowing a better understanding of the mechanism of CO2 reduction. By combining the electrochemical results with density functional theory, we were able to separate the electrocatalysts into several categories, based on their CO2 → COOHads free energy and their COads binding strength.3 The ‘strong-CO binder’ electrocatalysts (e.g. Cr, Mn and Fe – N – C) achieved a Faradaic efficiency up to 50% at – 0.35 V vs. RHE (at pH = 7.5, in 0.1 M phosphate buffer). Such Faradaic efficiency was also achieved for a metal-free electrocatalyst, therefore showing the high activity of the metal-free, N-containing, moieties toward the CO2 reduction reaction. A separate study showed materials hydrophobicity as one of the major factors of metal-free catalysts selectivity.4 Among the many practical products of CO2RR syngas (an H2/CO mixture) attracts special attention. Appropriate electrocatalysts, such as the metal–nitrogen–carbon (M-N-C) materials, allow for the production of CO alongside H2(from the hydrogen evolution reaction), and thus leads to syngas generation.5 Selectivity of mono- and bi-metallic (M-N-C, M = Fe, Mo or FeMo) electrocatalysts towards syngas production have been extensively studied.6 The ratio of the CO:H2 in the syngas was tuned by modifying the ratio of metallic precursors in the bi-metallic FeMo-N-C catalysts, tailoring the catalysts’ selectivity towards the CO2RR or the hydrogen evolution reaction (HER).Further development of CO2RR towards valorization of its products may lay through its integration with bioprocesses.7 Success of that strategy will rely on the ability of such systems to result in highly selective synthesis of formate, acetate, or propionate as major products.8,9 Those examples show the path to designer catalyst materials for a desired scalable CO2RR-based electrosynthesis technology. References S. Ozden et al., Journal of Catalysis 404 (2021) 512-517M. Ferry et al., ACS Energy Letters, 7 (2022) 2304-2310T. Asset et al., ACS Catalysis, 9 (2019) 7668-7678D. Hursán et al., Joule, 3 (2019) 1719-1733L. Delafontaine et al., ChemSusChem, 13 (2020) 1688-1698L. Delafontaine et. al, ChemElectroChem, 9 (2022) e202200647S. Guo et. al, ACS Catalysis, 11 (2021) 5172-5188S. Guo et. al, Applied Catalysis B – Environmental, 316 (2022) 121659S. Guo et. al, ACS Energy Lett., 8 (2023) 935-942

Effects of Carbon Type and Composition on the Properties of Carbon-Copper Composite as Pantograph Slide in Railway Application

Carbon-copper composites have wide application prospects as high-speed railway pantograph slides due to the self-lubricating ability of carbon and good conductivity of copper. However, carbon-copper composites produced through powder metallurgy may still encounter challenges, such as poor wettability and lower conductivity. The experimental approach in this work involved the fabrication of carbon-copper composites using the warm compaction method, with different types and proportions of carbon materials, namely local carbon from palm kernel shells (PKS) and graphite. Characterisation and testing of hardness, density, resistivity, transverse rupture strength (TRS), and microstructure of the composites have been conducted. An increase in graphite content was found to improve the electrical conductivity of the carbon-copper composite, while the addition of local carbon has enhanced its hardness. Furthermore, the addition of graphene oxide (GO) as filler has significantly improved the mechanical strength of this composite by up to 61.34%. This research has highlighted the potential of locally sourced carbon for developing advanced pantograph slide materials for railway applications. The findings provided valuable insights into the optimisation of composite compositions to achieve the desired balancebetween electrical conductivity and mechanical performance. These carboncopper composites hold the promise of more efficient and durable pantograph slides, which can contribute to the overall reliability and sustainability of railway systems.

Boosted the thermal conductivity of liquid metal via bridging diamond particles with graphite

The liquid metal (LM) composite is regarded as having potential and wide-ranging applications in electronic thermal management. Enhancing the thermal conductivity of LM is a crucial matter. Herein, a novel LM composite of eutectic gallium-indium (EGaIn)/diamond/graphite was developed. A highest thermal conductivity of 133 ± 3 W m−1 K−1 was achieved, 411 % higher than that of the matrix. The bonding mechanism reveals that the interfacial adsorption energy (ΔE) of graphite and EGaIn can be effectively decreased by the functional groups of graphite (by −108 % for –OH and −125 % for −CO) and the oxide of EGaIn (by −64 %). Furthermore, the ΔE of diamond and EGaIn can be significantly reduced through the oxidation of EGaIn (by −83 %) and the H-terminal of diamond (by −187 %). The thermal conductance mechanism suggests that a 3 vol% graphite content in the EGaIn/40 vol% diamond/graphite composite can form an excellent thermal conductance bridge among diamond particles. However, the thermal conductivity of the composite significantly decreased when too much graphite was added due to the tendency of the graphite to coat the diamond particles. There was no significant change in the melting point of EGaIn after being mixed with diamond and graphite. The EGaIn/diamond/graphite composite also demonstrated excellent thermal management performance in LED lamps and CPU heat dissipation as a thermal interface material, particularly in high-power electronic devices. This work presents the potential to enhance the thermal conductivity of LM-based composite by bridging spheroidal particles with a flaky material.

Research on the fabrication of high-quality patterned diamond using femtosecond laser

Diamond, known for its exceptional thermal, electrical, and mechanical properties, is widely used in precision machining tools, MEMS, and electronic devices. However, because of its extreme hardness and chemical inertness, diamond machining is highly challenging. Femtosecond laser technology, with its high instantaneous energy and minimal heat-affected zone, has emerged as an effective method for the precision machining of diamond. This study explores the application of 1026 nm and 513 nm femtosecond lasers in diamond grooving. The experimental results indicate that with increasing laser energy density, both groove width and depth increase, accompanied by a rise in amorphous carbon and graphite contents, resulting in increased tensile stress and decreased crystallinity in the machined region. Notably, the 513 nm laser demonstrates higher precision, achieving narrower grooves suitable for fine machining of diamond. Molecular dynamics simulations and experimental data reveal that the formation of amorphous carbon and graphite phases is the primary mechanism for deep ablation, and no significant anisotropy is observed during the process, allowing for the uniform fabrication of micro-nanostructures. TEM analysis confirms the presence of amorphous carbon and nanocrystalline diamond at the groove bottom, indicating phase transformation and also the formation of nanoscale diamond particles in regions of concentrated femtosecond laser energy. This study provides experimental and theoretical support for the high-quality fabrication of micro-nano structures on diamond, with significant implications for its advanced applications.

SEGREGATED ELECTRICALLY CONDUCTIVE NANOCOMPOSITES BASED ON THERMOPLASTIC ELASTOMERS AND GRAPHITE

The paper presents the results of a study of the electrical conductive characteristics and a complex of physical-mechanical properties of graphite-based nanocomposites, a wide range of polyolefins - low-density polyethylene, high-density polyethylene, isotactic polypropylene, random copolymer of polypropylene, block copolymer of propylene with ethylene, ethylene/hexene copolymer and ethylene/butene-1 copolymer. For the considered nanocomposites based on polyolefins, the optimal concentrations of graphite were determined, at which the maximum values of electrical conductivity are achieved, within the range of 10–2–10–3 (Ωm)–1. A detailed description of the mechanism of tunneling and electronic electrical conductivity in the nanocomposites under consideration is given. Thermoplastic elastomers (TPE) based on polyolefins and ethylene-propylene-diene rubber have been developed. In a wide concentration range, the regularities of changes in the electrical conductivity of nanocomposites based on thermoplastic elastomers and nanodispersed graphite have been determined. When studying the physical-mechanical properties of TPE nanocomposites, the tensile strength, yield strength, elongation at break, bending strength, Vicat softening temperature, melt flow rate, and Young's modulus were determined. The regularity of the change in the dependence "stress-strain" for TPE depending on the content of ethylene-propylene-diene rubber has been established. Using the methods of derivatography, X-ray phase and SEM analyses, and electron microscopy, studies were carried out to assess the structural features of nanocomposites of thermoplastic elastomers depending on the ratio of the mixture components used. For visual interpretation, a schematic representation of the processes occurring in the interfacial region of thermoplastic elastomers is given. The method of X-ray phase analysis shows the regularity of the change in the degree of crystallinity of thermoplastic elastomers depending on the content of rubber and graphite. The principal possibility of obtaining flexible electrically conductive materials with predetermined properties by controlling the ratio of components in the composition of thermoplastic elastomers is shown. For citation: Kakhramanov N.T., Allahverdiyeva Kh.V., Gahramanli Yu.N., Mustafayeva F.A., Sadikhov N.M., Martynova G.S., Valimatova N.I., Gurbanova R.V. Segregated electrically conductive nanocomposites based on thermoplastic elastomers and graphite. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 11. P. 122-137. DOI: 10.6060/ivkkt.20246711.7045.

Study on the thermal field material of FZ-Si crystal waste graphite purified by ultrasonic enhanced acid leaching

This study examines the acid-leaching and purification process of waste graphite in the production of Czochralski monocrystalline silicon. The optimal leaching conditions are identified as a liquid-to-solid ratio of 6, a leaching temperature of 70 °C, an acid concentration of 8 mol, and a leaching time of 60 min. The use of hydrofluoric acid, sulfuric acid, and nitric acid in the acid-leaching process increases the fixed carbon content of waste graphite from ∼94 % to ∼98.5 %. To address the low fixed carbon content that cannot be achieved through conventional acid-leaching, a method combining ultrasonic intensification with hydrofluoric and hydrochloric acid leaching is proposed and successfully implemented. Under ultrasonic enhancement conditions, the leaching effect is optimal at a temperature of 60 °C, acidity of 4 mol, and leaching time of 60 min. These results demonstrate that the introduction of ultrasound significantly strengthens the acid-leaching process. The method proposed in this study not only purifies waste graphite through acid-leaching but also elucidates the reaction behavior of various impurity elements during the leaching process. Overall, these findings provide a foundational basis for the recovery of waste graphite in the thermal field.

Optimization of the performance of copper/graphite system for GIL Tri‐post grounding electrode based on plasma sintering technology

Grounding electrodes, as crucial components of GIL bushings, experience friction with the GIL shell during long-term operation, generating metal particles that induce partial discharge. This phenomenon can lead to internal insulation breakdown, severely compromising GIL operation. This study focuses on enhancing the wear resistance of grounding electrodes by proposing a solution involving copper-graphite composites. Copper/graphite composite materials were fabricated using Spark Plasma Sintering technology. Additionally, the impact of graphite content and particle size on wear resistance, hardness, and electrical conductivity was comprehensively analyzed. Performance evaluation using radar chart analysis identified the optimal solution. The results indicate that at a sintering temperature of 960 °C, pressure of 45 MPa, and holding time of 15 min, with a graphite mass fraction of 7 %, the grounding electrode material exhibits a smooth surface and uniform distribution of graphite. Furthermore, when the graphite particle size is 4 μm, the friction coefficient remains approximately 0.7 with minimal fluctuations. The abrasion produces scratches measuring only 190 μm, and the wear rate is recorded at 2.1128 × 10−4 mm³/N·m, while the hardness reaches 59.6 HV, an increase of 19.6 HV compared to a particle size of 40 μm. In conclusion, an appropriate graphite content effectively enhances the wear resistance of the grounding electrode, and a reduction in graphite particle size optimizes overall performance. When the composite material contains 7 % graphite with a particle size of 4 μm, the performance is optimal, allowing the grounding electrode to maintain its original properties while demonstrating excellent wear resistance. This study provides a significant approach to optimizing the performance of grounding electrodes.

The deteriorated tribological and noise performances of copper-based brake pads induced by the increased content of flake graphite

Enhancing the lubricity of copper-based brake pads has been viewed as a crucial strategy to boost braking performance. Flake graphite and the oxide film are two substances that are widely concerned with providing lubrication at the friction interface. However, the results from full-scale dynamometer in this work indicate that the increased content of flake graphite with stronger lubrication and iron particles that accelerate the generation of oxide film lead to a deterioration in tribological and noise performance. This is manifested by high sensitivity to clamping force, significant fading behavior, increased sound pressure level and high-frequency noise. The evidence from the worn surface suggests that flake graphite is susceptible to peeling off from the friction surface, thereby amplifying the instability of the friction surface. The unstable existence of both flake graphite and oxide film during emergency braking actually diminishes the lubrication of the friction interface, likely resulting in the degraded braking performance. The indication suggests that the development of high-performance copper-based brake pads should aim to achieve a harmonization of diverse properties, rather than emphasizing only specific aspects.

Recovery of Lithium, Cobalt, and Graphite Contents from Black Mass of LCO-Based Discarded Li-Ion Batteries

Recovery of Lithium, Cobalt, and Graphite Contents from Black Mass of LCO-Based Discarded Li-Ion Batteries

Microstructure and properties behavior of in situ synthesized with high content (Ti, W) C reinforced In625 by two step-laser direct energy deposition

The formation of sensitive interface cracks and the difficulty in processing high-concentration Ni-based ceramic coatings via direct energy deposition (LDED) present major engineering challenges. To address these, high-quality In625/ceramic coatings with various mass contents of Ti, nickel-coated graphite (Ni3C), and WC were fabricated on QT250 using two-step laser directed energy deposition (TsLDED). The influence of the Ti/C: WC molar mass ratio on the bonding interface, microstructure, phase composition, and mechanical properties of the coatings was analyzed. The results indicated that grains at the In625/ceramic coating interface formed epitaxial growth, ensuring a robust bond. In situ synthesis of (Ti, W) C, WCx (WC and W2C), M23C6, and other precipitated phases were uniformly distributed, enhancing nucleation, refining microstructure, and improving mechanical properties. The addition of Ti facilitated the transformation of WCx to (Ti, W) C. High Ti and C concentrations promoted eutectic structure formation in the matrix phase, enhancing performance. The In625 + 56 % Ti – 14 % Ni3C – 30 % WC composite coating exhibited the highest microhardness and the lowest friction coefficient, with microhardness 5.61 and 3.6 times that of QT250 and In625 coatings, respectively, and a friction coefficient 0.3 times that of In625. Variations in the Ti/C: WC molar mass ratio directly affected the content, proportion, and type of (Ti, W) C, WCx, γ-Ni, and eutectic structures comprising M23C6, NiTix, Ni2W4C, Cr2Ti, and γ-Ni, influencing microstructure evolution and mechanical properties. The TsLDED process thus enables the preparation of In625/ceramic reinforced coatings with improved mechanical properties.

Assessment of impact load effect on self-sensing of cement composites incorporating hybrid silicon carbide-graphite under various environmental conditions

This study investigates the self-sensing abilities of hybrid silicon carbide-graphite cement composites (HSCGC) under various environmental conditions, focusing on dynamic impacts. Integrating silicon carbide (SiC) and graphite enhances the mechanical and electrical properties of these composites. Tests showed that composites with 30 % SiC and 2 % graphite had a 14.1 % increase in compressive strength and up to 85 % decrease in electrical resistivity. Water absorption reduced by 3.25 %, indicating better durability. Impact resistance ratios (IRR) varied with humidity and impact angles, with the highest IRR observed at 70 % humidity and a 30-degree angle. Self-sensing responses indicated that higher SiC and graphite content maintained stable conductivity, especially at 60 and 90-degree angles. Temperature changes affected resistivity, negligible at −10°C and increased at 45°C. The study concludes that HSCGCs are suitable for smart construction materials, capable of real-time environmental and structural monitoring, advancing predictive models and control systems.

Effect of graphite on microstructure and friction-wear properties of yttria-stabilized zirconia coatings

Yttria-stabilized zirconia and flake graphite composite (C/YSZ) coatings were successfully prepared on a TC4 substrate by electrophoretic co-deposition and sintering at 1100 °C using YSZ nanopowder and flake graphite. The effects of the graphite content on the microstructure and friction-wear properties were investigated. The results indicated that flake graphite agglomerated in the C/YSZ coating. The YSZ coating with 0.6wt.% graphite exhibited the highest toughness with the plastic resistance index (H/E) of 0.0172, which was 6.8 % higher than that of the YSZ coating, and effectively inhibited the formation of coating cracks. However, an increase or a decrease in the graphite content led to a decrease in the toughness of the C/YSZ composite coating. The agglomerated graphite in the C/YSZ composite coating acted as a solid lubricant and affected friction and wear properties. The coefficient of friction (COF) of the 0.6C/YSZ sample was 0.45, which was 40 % lower than that of the YSZ sample. The reason for this was that graphite effectively inhibited the falling-off of debris from the coating surface and reduced abrasive wear. However, an excessive amount of graphite, i.e., in case of the 0.8C/YSZ coating, decreased the roughness of the wear surface, leading to a reduction in the H/E and COF by 24.4 % and 29.7 %, respectively.

A novel paraffin/graphite PCM backfill for PHC energy pile: Numerical and experimental analysis on thermal performance

A novel paraffin/graphite phase change material was proposed as backfills for prestressed high-performance concrete piles. An experimental device for high-performance concrete energy pile was established to access the thermal performance of paraffin/graphite phase change material backfill and a finite element method numerical simulation based on the experiment was conducted. Two theoretical models, Multiphase-Effective Medium Theory and Maxwell-Eucken with parallel, were proposed to calculate the thermophysical parameters of paraffin/graphite phase change material. The results show that Multiphase-Effective Medium Theory achieves enhanced reliability than Maxwell-Eucken with parallel in the thermophysical parameters calculation of multi-phase composites. Paraffin/graphite phase change material can enhance the heat storage capacity of paraffin/graphite phase change material and reduce the temperature fluctuation of the piles, while graphite can accelerate the heat transfer within the pile system. A “transition point” in dynamic competition between the graphite and paraffin of paraffin/graphite phase change material was first discovered during the heat transfer process, which can be employed as an indicator for the operational patterns of the prestressed high-performance concrete energy pile. The thermal performance of prestressed high-performance concrete energy piles can be improved by reasonably controlling the graphite and paraffin contents in paraffin/graphite phase change material backfills.

Assessment of thermal-hydraulic-mechanical-chemical (THMC) performances of Ca-type bentonite-graphite mixtures as buffer materials for a high-level radioactive waste repository

The bentonite buffer material is the most important element of the engineered barrier system (EBS) used to dispose of high-level radioactive waste. Therefore, there are functional criteria or performance targets for the bentonite buffer material to maintain the long-term performance of the EBS for the entire disposal system. Thermal conductivity is a key parameter in the design of an EBS as it has the greatest influence on the buffer temperature. As the peak temperature of the buffer should not exceed the thermal design criterion, it is necessary to increase the thermal conductivity of the bentonite buffer material. Therefore, in this study, a small portion of graphite was added to Ca-type bentonite and thermal, hydraulic, and mechanical properties were measured separately, along with overall THMC (thermal-hydraulic-mechanical-chemical) properties. Additionally, while thermal conductivity was examined for varying graphite contents, other properties such as hydraulic conductivity, swelling pressure, and unconfined compressive strength were tested with a 3 % graphite addition. In particular, the thermal conductivity was measured for 3 % graphite addition to the pure bentonite under the different dry densities and saturation conditions and a regression analysis was performed to predict thermal conductivity based on the dry density and degree of saturation values. Furthermore, the saturated hydraulic conductivity, swelling pressure, unconfined compressive strength, and sorption efficiency of cesium (Cs) ions in bentonite and bentonite-graphite mixtures were measured. Moreover, prototype buffer blocks for bentonite-graphite mixtures were manufactured to evaluate viability of production. The addition of 3 % graphite to pure bentonite satisfied the functional criteria of saturated hydraulic conductivity and swelling pressure when the dry density was 1.63 g/cm3 or higher, and the thermal conductivity of the bentonite-3 % graphite mixtures was 10–30 % higher than that of pure bentonite.

Highly thermally conductive and shape-stabilized phase change materials with desirable solar/electric-to-thermal conversion performance based on high-modulus graphite/PVA foam

The widespread utilization of phase change materials (PCMs) has been impeded by challenges such as leakage, low thermal/electrical conductivity, and inadequate light absorption. Although constructing interconnected three-dimensional (3D) carbon networks within PCMs can mitigate these issues, their complex and energy-intensive fabrication processes, coupled with insufficient mechanical strength causing significant leakage and collapse of liquefied PCMs under external loads or impacts, hinder their practical application. Herein, we present a novel approach for the preparation of 3D graphite/polyvinyl alcohol foam (GPF) through a simple vacuum foaming combined with air-drying method. The obtained GPF-5 exhibits impressive compression strength (4.46 MPa) and compression modulus (93.1 MPa) at low density of 0.30 g/cm3. Upon impregnation with polyethylene glycol (PEG), GPF-5/PEG exhibits notable mechanical strength (7.62 MPa), contributing to its thermal shape stability and resistance to leakage. Even when subjected to temperatures above the melting point of PEG under external loads, GPF-5/PEG maintains its original shape without any liquid leakage. Due to the efficient construction of 3D thermal conductivity pathways within GPF, GPF-5/PEG demonstrates a high thermal conductivity of up to 3.48 W/m K−1 with graphite contents of 21.1 wt%, representing an increase of 136 % and 1640 % compared to graphite/PEG (with equivalent graphite content) and pure PEG, respectively. Additionally, GPF-5/PEG displays high latent heat of melting (136.8 J/g) and superior thermal cycling stability. Moreover, GPF-5/PEG demonstrates high solar-to-thermal and electric-to-thermal energy conversion capabilities, highlighting their potential for diverse applications. The work offers a rational strategy for fabricating high-modulus carbon foam, which can be used for PCMs-based multi energy conversion and storage systems with high thermo-mechanical properties.

Optimization of laser cladding powder ratio and process parameters based on MOGWO algorithm

Optimizing the process parameters is crucial to obtaining a high-quality fusion coating. The fitted regression model for each response was then analyzed by creating a central composite test with process parameters and power ratios (laser power, scanning speed, and Ni-clad graphite content) as inputs and the quality of the fused coating (dilution rate, microhardness, and width of the fused coating) as responses. The laser cladding process parameters and power ratios were optimized using the multi-objective Gray Wolf Optimization (MOGWO) algorithm. The best combinations of process parameters and power ratios were laser power of 1596 W, scanning speed of 21.7 mm/s, and Ni-clad graphite percentage of 18.4 %. Experimental validation demonstrates the superiority and accuracy of the MOGWO algorithm. The dilution rate of the optimized fusion-clad coating is increased by 47.4 % and the microhardness is increased by 17.8 %.