Excellent Thermal Properties Research Articles

Novel wet transfer technology of manufacturing flexible suspended two-dimensional material devices

With the rise of two-dimensional (2D) materials, their excellent optical, electronic, and thermal properties different from bulk materials make them increasingly widely studied and commercialized. 2D materials’ exceptional physical properties and unique structures make them an ideal candidate for next-generation flexible and wearable devices. In this work, we created a manufacturing method to successfully transfer monolayer, bilayer, and trilayer graphene onto the flexible substrate, with trenches of micron size to suspend graphene. Thermal transport measurements have been characterized to prove the suspended region. The achievement of manufacturing 2D materials in suspended condition will allow us to study their intrinsic physical properties at a mechanical strain, as well as contribute to novel flexible and wearable electronic devices and sensors.

Hot-Pressed Super-Elastic Graphene Aerogel with Bidirectional Thermal Conduction Properties as Thermal Interface Materials

Traditional graphene-based films normally possess high thermal conductivity (TC) only along a single direction, which is not suitable for thermal interface materials (TIMs). Here, a graphene film with excellent bidirectional TC and mechanical properties was prepared by hot-pressing super-elastic graphene aerogel (SEGA). Thermal annealing at 1800 °C improves the further restacking of graphene sheets, bringing high structure stability to SEGA for enduring the hot-pressing process. The junctions and nodes between the graphene layers in the hot-pressed SEGA (HPSEGA) film provide bidirectional heat transport paths. The in-plane TC and through-plane TC of HPSEGA film with a thickness of 101 μm reach 740 Wm−1K−1 and 42.5 Wm−1K−1, respectively. In addition, HPSEGA film with higher thickness still maintains excellent thermal transport properties due to the interconnected structure reducing the effect of the defects. The infrared thermal images visually manifest the excellent thermal-transfer capability and thermal-dissipation efficiency of the HPSEGA films, indicating the great potential as advanced bidirectional TIMs.

Improving thermal conductivity of reduced-activation ferritic/martensitic steel using three-dimensional woven copper fiber

Reduced-activation ferritic/martensitic (RAFM) steel is a primary candidate for blanket modules in nuclear-fusion reactors. Blanket modules transfer thermal energy generated by nuclear-fusion reactions to the coolant; therefore, blanket materials must have high thermal conductivity. RAFM steel is suitable for fusion reactors owing to its high strength, toughness, and resistance to neutron irradiation; however, its thermal conductivity is lower than that of other metals. This study fabricates RAFM steel–copper composites using three-dimensional (3D) woven copper fibers with different volume fractions as a preform to improve the thermal conductivity of RAFM steel around the coolant pipes. The microstructural, mechanical, and thermal properties of the developed composites and the correlations between them are experimentally investigated. Finite element simulations were also conducted on the composites comprising 3D woven copper fibers to evaluate the effective thermal conductivity. The factors that improve the effective thermal conductivity of RAFM steel–copper composites are discussed through a comparison with copper-powder composites with comparable volumes. This study demonstrates the manufacturing of composites with excellent thermal and mechanical properties using various 3D woven structures as preforms.

Mechanical properties evolution of clays treated with rice husk ash subjected to freezing-thawing cycles

Rapidly growing urbanization and industrialization drive the continued development of soil stabilization and ground improvement techniques. Rice husk ash (RHA) is widely regarded as a highly promising construction material in civil engineering due to its excellent pozzolanic properties and has garnered significant attention from researchers. This paper presents an experimental study and a micro-mechanical discussion on the role of RHA in the mechanical improvement of soil. RHA was mixed with the native soil in varying proportions, ranging from 0% to 12%. Several laboratory tests were conducted, including standard proctor compaction tests, Atterberg limit tests, freeze-thaw tests, unconfined compression tests, X-ray diffraction (XRD) analysis, and scanning electron microscopy (SEM). The results indicated that the optimal moisture content (OMC) of the soil mixture increased while the maximum dry density (MDD) decreased with higher RHA dosage. The Atterberg limits of the soil mixture exhibited a positive correlation with the RHA content. A substantial enhancement in the soil's strength, stiffness, and ductility was observed upon the incorporation of RHA. It was noted that the strength loss of the untreated samples and those with 12% RHA was 34.91% and 12.89%, respectively, following 12 freeze-thaw cycles. Furthermore, XRD test results revealed that the treated specimen had an identical mineral composition to the control specimen, with no generation of hydration products. SEM analysis also highlighted that the filling effect of RHA significantly reduced pore content and pore connectivity within the soil, accompanied by a shift in the specimen's pores from mesopores to small and micropores. The excellent thermal insulation and heat retention properties of RHA, along with its pore-refining effect, make a positive contribution to enhancing the frost resistance of the specimens. These findings contribute to guiding the effective application of RHA in civil engineering, offering eco-friendly solutions for biomass waste management, and promoting the sustainable development of construction materials.

Preparation of DOPO coated conjugated microporous polymer hollow nanospheres with excellent flame retardancy and thermal insulation

Materials with thermal insulation and flame retardant properties are highly sought after in construction industry. In this study, two hollow-structured conjugated microporous polymer spheres (HCMPs) were successfully synthesized via the template method by polymerizing 1,3,5-triethynylbenzene with 3-amino-2,6-dibromopyridine and 2-amino-3,5-dibromopyridine respectively. To enhance flame retardant properties, HCMPs were impregnated with ethanol-soluble 6 H-dibenzo (C, E) (1,2) phosphine oxide-6-oxide (DOPO) (named as HCMP-FR), which maintains a hollow structure, enabling it to serve as a heat insulator, as observed under transmission electron microscope (TEM). The two types of HCMP-FR with a thermal conductivity of 0.047 W m−1 K−1 and 0.051 W m−1 K−1 respectively, exhibit excellent thermal insulation property. HCMP-FRs were added in to epoxy resin (EP) composites to further investigate the property of it. Under addition of 1.3%wt HCMP1-FR and HCMP2-FR, the thermal conductivity of EP composites (0.159 W m−1 K−1 and 0.146 W m−1 K−1) decreased by 25.3% and 31.4% compared with pure EP composites respectively, and the density (0.651 g cm−3 and 0.8 g cm−3) decreased by 42.1% and 22.5%, significantly reducing EP's thermal conductivity and density. The cone calorimeter (CC) tests show that the pHRR of EP composites at 0.6%wt addition was 859.04 kW m−2 and 904.35 kW m−2, respectively, which were 17.5% and 13.1% lower than that of pure EP, and the TSP decreased by 44.9% and 41.3% when 1.3% HCMP-FRs was added, which shows an excellent smoke depressing property. Therefore, the HCMP-FRs synthesized have highly promising for application in thermal insulation and flame retardancy of energy saving building.

Controllable large-scale processing of temperature regulating sheath-core fibers with high-enthalpy for thermal management

Temperature regulating fibers (TRFs) with high enthalpy and high form stability are the key factors for thermal management. However, the enthalpies of most TRFs are not high, and the preparation methods are still at the laboratory scale. It remains a great challenge to use industrial spinning equipment to achieve continuous processing of TRFs with excellent thermal and mechanical properties. Here, polyamide 6 (PA6) based TRFs with a sheath-core structure were prepared by bicomponent melt-spinning. The sheath-core TRF (TRFsc) are composed of PA6 as sheath and functional PA6 as core, which are filled with the shape stable phase change materials (ssPCM), dendritic silica@polyethylene glycol (SiO2@PEG). With the aid of the sheath structure, the filling content of SiO2@PEG can reach 30 ​%, so that the enthalpy of the TRFs can be as high as 21.3 ​J/g. The ultra-high enthalpy guarantees the temperature regulation ability during the alternating process of cooling and heating. In hot environment, the temperature regulation time is 6.59 ​min, and the temperature difference is 12.93 ​°C. In addition, the mechanical strength of the prepared TRFsc reaches 2.26 cN/dtex, which can fully meet its application in the field of thermal management textiles and devices to manage the temperature regulation of the human body or precision equipment, etc.

ZrC-SiC closed-cell ceramics with low thermal conductivity: Exploiting unique spherical closed-cell structure through tape casting and CVI techniques

Porous ultra-high temperature ceramics (UHTCs) are recognized as novel candidates for fulfilling the requirements of thermal protection systems of hypersonic aircrafts, as they possess excellent high-temperature resistance and low thermal conductivity. Currently, the reported porous UHTCs predominantly exhibit an open pore structure. By contrast, closed-cell UHTCs, formed by employing ceramic hollow microspheres (HMs) as pore-forming agents, hold great potential for achieving superior thermal insulation performance. Unfortunately, the implementation of this strategy has been hindered by the scarcity of raw materials and preparation techniques.In this paper, ZrC-SiC closed-cell ceramics were first successfully prepared through a combination of tape casting and chemical vapor infiltration (CVI) techniques, utilizing the self-developed ZrC HMs as the primary raw material. The morphology, microstructure, and thermal insulation properties of the obtained ZrC-SiC closed-cell ceramics were investigated. The results indicate that when the content of ZrC HMs is 30 vol.%, the density of the prepared porous ceramics is 2.09 g cm–3, with a closed porosity of 14.05% and a thermal conductivity of 1.69 W (m K)–1. The results clearly prove that the CVI process can successfully convert ZrC HMs into closed pore structures within porous ceramics. The introduction of ZrC HMs suppresses the contribution of free electrons to thermal conductivity and brings about a large number of solid-gas interfaces, which increases the interfacial thermal resistance and significantly reduces the phonon thermal conductivity. Consequently, the as-prepared ZrC-SiC closed-cell ceramics show excellent thermal insulation properties. This study provides a new idea and method for the development of porous UHTCs and offers a more reliable material choice for thermal protection systems.

Hydrosilylation Adducts to Produce Wide-Temperature Flexible Polysiloxane Aerogel under Ambient Temperature and Pressure Drying.

Despite incorporation of organic groups into silica-based aerogels to enhance their mechanical flexibility, the wide temperature reliability of the modified silicone aerogel is inevitably degraded. Therefore, facile synthesis of soft silicone aerogels with wide-temperature stability remains challenging. Herein, novel silicone aerogels containing a high content of Siare reported by using polydimethylvinylsiloxane (PDMVS), a hydrosilylation adduct with water-repellent groups, as a "flexible chain segment" embedded within the aerogel network. The poly(2-dimethoxymethylsilyl)ethylmethylvinylsiloxane (PDEMSEMVS) aerogelis fabricated through a cost-effective ambient temperature/pressure drying process. The optimizedaerogel exhibits exceptional performance, such as ultra-low density (50mg cm-3), wide-temperature mechanical flexibility, and super-hydrophobicity, in comparison to the previous polysiloxane aerogels. A significant reduction in the density of these aerogels is achieved while maintaining a high crosslinking density by synthesizing gel networks with well-defined macromolecules through hydrolytic polycondensation crosslinking of PDEMSEMVS. Notably, the pore/nanoparticle size of aerogels can be fine-tuned by optimizing the gel solvent type. The as-prepared silicone aerogels demonstrate selective absorption, efficient oil-water separation, and excellent thermal insulation properties, showing promising applications in oil/water separation and thermal protection.

Enhancing the mechanical and dielectric properties of high thermally stable polyimides via a crosslinkable bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride monomer

Polyimides (PIs) have attracted great attention because of their excellent properties and applications in areas such as flexible display substrates, microelectronics, and integrated circuits. The effects of crosslinking on the thermal, mechanical, and dielectric properties of PIs, however, still require further investigation. In this work, we introduce a crosslinkable monomer, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic acid dianhydride (BTA), which contains double bonds, into the system consisting of cyclobutane-1,2,3,4-tetracarboxylic dianhydride (CBDA) and 4,4′-oxydianiline (ODA) for the synthesis of PI films. The obtained PIs are further crosslinked by free radical reactions using a crosslinking agent, 1,3,5-triallyl-1,3,5-triazine-2,4,6(1H,3H,5H)-trione (TAIC) to form three crosslinked PI materials, PI-TAIC-5%, PI-TAIC-10%, and PI-TAIC-15%. The resulting all three crosslinked PI films exhibit excellent thermal properties with their glass transition temperatures (Tg) higher than 400 °C. For the mechanical properties, the formation of the rigid network structure leads to an improvement in their tensile strengths and Young's moduli. The introduction of 10 mol% TAIC in the PI (PI-TAIC-10%) shows the highest tensile strength (114.77 MPa), representing an 18.6% enhancement in comparison with that of the original PI material. In terms of dielectric properties, the crosslinking reactions effectively increase the free volumes between the polymer chains and reduce the molecular dipole moments. As a result, PI-TAIC-15% significantly reduces the dielectric properties, resulting in a decrease in the dielectric constant (Dk, from 3.42 to 3.15) and the dielectric loss (Df, from 3.67 × 10−2 to 2.58 × 10−2) under 10 GHz frequency. As far as the coefficient of thermal expansion (CTE) results, the formation of the network structure in PI-TAIC-15% restricts the movement of the polymer chains, leading to a 15% reduction in the CTE value than that of the non-crosslinked PI film. Overall, this work provides a promising strategy to optimize the mechanical and dielectric properties of high thermally stable PIs via crosslinking reactions.

Novel YAGG: Cr garnet phosphor ceramic with broadband near infrared (NIR) emission and luminescence thermal stability for plant growth

In recent years, NIR (Near-Infrared) phosphor-converted LEDs (pc-LEDs) have played an indispensable role in the field of plant lighting. This study presents the development of a novel garnet-based phosphor ceramic, YAGG:0.035Cr3+, obtained through a high-temperature solid-state method. Through optical and structural performance analysis, it was found that the sample can be effectively excited by a commercial 450 nm blue LED, emitting near-infrared light in the range of 650–850 nm. This emission spectrum overlaps with approximately 74% of PFR spectrum absorbed by plant growth, and it achieves QY of around 40%. Notably, this ceramic demonstrates excellent thermal luminescence properties, maintaining approximately 96% of its integrated emission intensity at 423 K compared to room temperature. To explain this outstanding thermal performance, we analyzed that the gradual substitution of the 4T2 level for the 2E level leads to the dominance of the 4T2-4A2 transition process in PL. Furthermore, the YAGG:0.035Cr3+ phosphor ceramic was packaged with a 450 nm LED, and the emitted light intensity exhibited a linear relationship with the driving current. Even under high-power driving conditions of 1000 mA, the luminescence did not reach saturation. These results effectively demonstrate the potential application of YAGG:0.035Cr3+ phosphor ceramic in the field of plant lighting.

Recovering AlN from secondary aluminum ash using a novel triboelectric separation

ABSTRACT Secondary aluminum ash is a byproduct in the aluminum industry that contains valuable components, such as aluminum nitride (AlN) and aluminum oxide (Al2O3). AlN has excellent thermal and electrical properties and is widely used in various applications, making the recovery of AlN from secondary aluminum ash essential for both economic and environmental reasons. In this study, we developed a novel triboelectric separation technique to recover AlN from aluminum ash by investigating the tribocharging characteristics of the main components of secondary aluminum ash, Al2O3 and AlN. We studied the effects of tribocharging ball ratio, friction time, and stirring speed on the tribocharging of pure Al2O3 and AlN, using various materials such as polytef (PTFE), polypropylene (PP), polyvinyl chloride (PVC), copper (Cu), and stainless steel (SS) as tribocharging materials. We also examined the effects of friction medium ball ratio, friction medium material, rotational speed, and voltage on the triboelectric separation process. Our results showed that the charge-to-mass ratio for Al2O3 and AlN was 1.96 and −15.56 nC/g, respectively, the difference is largest, with a PTFE ball, a 1:5 ratio, a stirring speed of 290 n/min, and a tribocharging duration of 30 s. The triboelectric sequence of these friction materials was (+)PTFE, PP, Al2O3, SS, Cu, PVC, and AlN (-). To recover AlN from aluminum ash, PTFE should be chosen as the friction medium, and a friction medium ball ratio of 1:3, rpm rotation speed of 50, and voltage of 40kV should be used, resulting in an AlN grade of 89.25% and a significant increase in the recovery rate of AlN in the positive and negative electrode. Our findings demonstrate the feasibility of effective triboelectric separation of Al2O3 and AlN.

Flexible and photo-responsive composite phase change materials for thermal therapy

The medical dressings with appropriate temperature can relieve body pain by promoting blood circulation. In order to endow the thermal compress dressings with multifunction and facilitate their application in different scenarios, the flexible films employing paraffin (PF) as thermal energy storage medium, styrene-ethylene/butylene-styrene (SEBS) triblock copolymer as matrix and graphene as photo-thermal conversion agents were fabricated. The film containing 77 wt% of PF has high latent heat of 157.26 J·g−1 and exhibits smooth and dense morphology. The film also exhibits tensile strain of 2576.75 %, photothermal conversion efficiency of 70.52 % and enviable self-healing properties, which makes it possible to meet the needs of different body parts and reuse in practical applications. In addition, under natural sunlight, the thickness of 3 mm thermal film can maintain the temperature ranging from 40 °C to 50 °C for more than 25 min; under the action of an electrically heated film, the film can maintain at 40 °C to 50 °C for about 22 min. The extraordinarily long thermal therapy time and suitable thermal therapy temperature are remarkable. In summary, the excellent thermal storage properties, mechanical properties, self-healing properties and photothermal conversion properties make it a good application prospect for thermal therapy.

Moisture resistant polyimide aerogel membranes with low dielectric constant and super thermal insulation for electronic device under harsh environment

Membranes with low dielectric constant and high moisture resistance are the key material for miniaturized and integrated communication equipment as an interlayer dielectric layer. Here, a series of cross-linked PI aerogel membranes were prepared by co-polymerization and scraping coating technology. The introduction of the fluorinated blocks and benzimidazole ring structures can consequently garner novel PI aerogel membranes with fascinating dielectric properties and outstanding moisture resistance. The dielectric constants of the sample membranes are as low as 1.33 at 1 KHz and 1.32 at 1 MHz with dielectric loss as low as 0.0079 at 1 KHz and 0.0035 at 1 MHz. The water contact angle can reach 107.35° with a surface roughness value of 30.428 nm. Moreover, the PI aerogel membranes have high specific surface area and excellent thermal and mechanical properties. The thermal conductivity as low as 35.4 mW m−1 K−1 at room temperature indicates excellent thermal insulation performance. PIAM-2 is suitable as an interlayer dielectric layer for electronic components under harsh environment. In addition, the influence of surface roughness on surface wettability was also elaborated on which can provide a feasible method for the preparation of low dielectric materials with moisture resistance.

Multi-scale modeling in thermal conductivity of Polyurethane incorporated with Phase Change Materials using Physics-Informed Neural Networks

Polyurethane (PU) possesses excellent thermal properties, making it an ideal material for thermal insulation. Incorporating Phase Change Materials (PCMs) capsules into Polyurethane has proven to be an effective strategy for enhancing building envelopes. This innovative design substantially enhances indoor thermal stability and minimizes fluctuations in indoor air temperature. To investigate the thermal conductivity of the Polyurethane-Phase Change Materials foam composite, we propose a hierarchical multi-scale model utilizing Physics-Informed Neural Networks (PINNs). This model allows accurate prediction and analysis of the material’s thermal conductivity at both the meso-scale and macro-scale. By leveraging the integration of physics-based knowledge and data-driven learning offered by Physics-Informed Neural Networks, we effectively tackle inverse problems and address complex multi-scale phenomena. Furthermore, the obtained thermal conductivity data facilitates the optimization of material design. To fully consider the occupants’ thermal comfort within a building envelope, we conduct a case study evaluating the performance of this optimized material in a detached house. Simultaneously, we predict the energy consumption associated with this scenario. All outcomes demonstrate the promising nature of this design, enabling passive building energy design and significantly improving occupants’ comfort. The successful development of this Physics-Informed Neural Networks-based multi-scale model holds immense potential for advancing our understanding of Polyurethane-Phase Change Material’s thermal properties. It can contribute to the design and optimization of materials for various practical applications, including thermal energy storage systems and insulation design in advanced building envelopes.

Thermal storage characteristics of microencapsulated phase change material coatings in low-energy rural prefabricated building walls

ABSTRACT Prefabricated buildings in rural areas of China waste a large amount of energy due to poor thermal insulation. Phase change materials (PCMs) are able to stabilize room temperature by latent heat absorption and release during the phase change process. This study incorporated PCMs in the form of microcapsules into the interior wall coatings of prefabricated buildings, and by taking advantage of PCMs’ energy storage capacity, the thermal storage characteristics of PCM-coated bricks were investigated. The results show that microencapsulated phase change material(MPCM) coatings for prefabricated walls exhibit excellent thermal stability properties and effectively reduce the heat flux of prefabricated walls, with coatings having a MPCM mass fraction of 15% and a thickness of 5 mm providing the highest overall benefits. By fitting the numerical simulation results with experimental data, a novel multifunctional passive solar phase change heat collection and storage wall system was developed. This study innovatively combines energy storage materials with interior wall coatings in prefabricated walls of modular buildings investigating how it enhances the thermal stability of the external insulation walls and effectively reduces the reliance on heating equipment for auxiliary heating in rural residences. This essay aims to provide feasible recommendations for optimizing the dual-stage energy-saving and carbon reduction goals in both the construction and operation of rural areas.

Investigation on the Interface Structure, Mechanical Properties, and Thermal Stability of TiAlSiN/TiAlN Multilayers.

Recently, the TiAlSiN/TiAlN coatings with excellent mechanical and thermal properties have great potential for protective applications that face deteriorated service environments. Here, we systematically investigate the interface structure, mechanical properties, and thermal stability of TiAlSiN/TiAlN multilayers with varied Al and Si contents of TiAlSiN sublayer. Both Ti0.53Al0.38Si0.09N/Ti0.52Al0.48N (ML_1) and Ti0.48Al0.38Si0.14N/Ti0.52Al0.48N (ML_2) exhibit the face-centered cubic structure through epitaxial growth, whereas the Ti0.43Al0.48Si0.09N/Ti0.52Al0.48N (ML_3) shows a mixed cubic/wurtzite (c/w) structure. This mechanism is explored by first-principles calculations that the increased content of Al and Si within the TiAlSiN sublayer is detrimental to the formation of a coherent interface. Meanwhile, the change of interfacial structure leads to a variation in hardness from ∼35.6 GPa of ML_1 to ∼35.4 GPa of ML_2 and then to ∼30.9 GPa of ML_3. In addition, ML_1 presents a delayed thermal decomposition by ∼100 °C, compared to those of ML_2 and ML_3 multilayers.

High‐Resolution Intaglio Transfer Printing of Silver Nanowires for Wearable Electrophysiological Sensors

Silver nanowires (NWs) are promising materials for flexible electronics, such as electronic skins due to their excellent electrical, thermal, and mechanical properties. Achieving precise patterning of Ag NWs is essential for the successful integration and miniaturization of the electronic device system, but the high aspect ratio (AR) of NWs and the high porosity of NW networks pose challenges in forming high‐resolution patterns. Herein, the intaglio transfer printing technique to create high‐resolution patterning of ultralong Ag NWs (AR≈1000) is presented. During the pattern formation process, the external force becomes concentrated specifically at the edge of the intaglio trench, resulting in the breaking of the entangled Ag NW network in the corresponding region. This simple yet effective technique enables precise high‐resolution (minimum line width: 7 µm) and complicated Ag NW patterns on flexible substrates. The patterned Ag NWs are conformally attached to the various curvilinear surfaces and show high mechanical stability under continuous bending conditions. Wearable electrophysiological sensors are demonstrated to monitor electromyography and electrocardiogram signals in real‐time for continuous healthcare monitoring. This patterning strategy offers an effective approach for achieving high‐resolution patterns of highly anisotropic nanomaterials and highlights the potential of patterned Ag NWs in wearable electronics.

Multicomponent Si–Zr-based lightweight nanofiber films with a hollow structure exhibiting excellent thermal insulation properties

Hollow-structured ceramic fibers with multiple components are ideal as lightweight insulation materials. In this study, tetraethyl orthosilicate, boric acid, and zirconia octahydrate were used as raw materials for fabricating SiZrBOC hollow ceramic fibers through coaxial electrospinning. These ceramic fibers exhibit a low thermal conductivity and an excellent temperature resistance. The electrospun SiZrBOC hollow ceramic fibers display a clean and compact morphology with internal folds. Fourier-transform infrared spectroscopy and thermogravimetric analysis (TGA) were used to assess the transformation process and thermal behavior of the hollow ceramic fibers. The results suggest that the incorporation of B promotes the formation of Si–O–B bonds within the system, leading to a maximum yield of 75.49 wt% for the production of the SiZrBOC hollow ceramic fibers. The phase composition and microstructure of the SiZrBOC hollow ceramic fibers were analyzed via X-ray diffraction (XRD) measurements. The pyrolysis at 1000 °C resulted in the appearance of diffraction peaks corresponding to SiO2 and SiC in the XRD patterns of the SiZrBOC hollow ceramic fibers. Laser thermal conductivity measurements reveal that the SiZrBOC hollow ceramic fibers exhibit a thermal conductivity of only 0.06 W‧m−1K−1 at 25 °C and 0.124 W‧m−1K−1 at 500 °C, indicating a significantly superior thermal insulation performance compared with conventional solid SiZrBOC ceramic fibers.

Polyimide aerogel/aramid fiber composite with high mechanical strength and thermal insulation for thermal protective clothing

Polyimide (PI) aerogel, as a new organic aerogel material, has the excellent thermal properties of polyimide and the characteristic of high thermal insulation of aerogels, and has gained increasing attention. In this work, using PI aerogel as the matrix material and aramid fiber as the reinforcement material, controllable flexible PI aerogel/aramid fiber composite insulation materials were successfully prepared by freeze-drying and soft treatment. This study sought to determine how the mass percentage of PI aerogel affected the microstructure, mechanical characteristics, thermal insulation capabilities, and thermal comfort of clothes in PI aerogel/aramid fiber composites. To achieve this, the preparation process of PI aerogel was optimized, and the effects of different mass fractions of PI aerogel on the properties of the composite material were evaluated. The results demonstrated that increasing the mass fraction of PI aerogel led to improvements in the mechanical properties, flexibility, and heat insulation properties of the composite material. Furthermore, the PI aerogel/aramid fiber composite offered enhanced thermal comfort to the wearer in hot and humid environments, indicating that the composite material is particularly suited for thermal insulation applications.

Double Carbon Networks Reinforce the Thermal Storage and Thermal Transfer Properties of 1-Octadecanol Phase Change Materials.

Using thermal storage materials with excellent thermal properties in the energy utilization system enables efficient use of renewable energy sources. Organic phase change materials (PCMs) have the advantages of high heat storage density, no corrosion, and low cost, but low thermal conductivity and insufficient heat transfer capacity have always been the bottlenecks in their application. In this paper, melamine foam@ reduction graphene oxide (MF@rGO) and carbon foam@ reduction graphene oxide (CF@rGO) composite foams with double carbon networks were prepared by self-assembly method and further employed in 1-octadecinal (OD) PCMs. The microstructure, chemical composition, phase change behavior, thermal conductivity, and photothermal conversion performance of MF@rGO/OD and CF@rGO/OD were studied in detail using SEM, FTIR, Raman DSC, and LFA. The melting and solidification enthalpies of CF@rGO/OD composite PCMs were 208.3 J/g and 191.4 J/g, respectively, its thermal conductivity increased to 1.54 W/m·K, which is 6.42 times that of pure OD. The porous structure and high thermal conductivity of the double carbon network substantially enhance the efficiency of energy storage and release in composite PCMs. CF@rGO/OD composite PCMs have excellent heat storage performance and heat transfer capacity, and a wide range of application prospects in the fields of low-temperature solar heat storage, precision instrument temperature control, and intelligent buildings.