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Lightweight phenolic matrix composites are highly potential in ablative thermal protective materials for future aerospace vehicles, and hybrid modification is considered as one of effective ways to improve the oxidation and ablation resistance of phenolic matrix. Herein, the co-continuous silica zirconium hybrid phenolic resin (SZRx) was synthesized, which can be used to prepare lightweight ablation resistant aerogel composites by the sol-gel method. The SZRx aerogel showed stable porous structure and excellent hydrophobicity, and the silicon zirconium hybrid greatly improved the high temperature carbon residue and oxidation resistance of phenolic resin. The SZRx aerogel composites also possessed excellent integrated characteristics of heat protection and insulation, with a linear ablation rate as low as 0.032 mm/s and a back temperature below 200 °C. The synergistic effect of silicon and zirconium formed the multiphase ceramic layer (C, SiO 2 , SiC and ZrO 2) with the sea-island-like structure on the surface of the composite material, which can effectively resist high-temperature ablation and aerodynamic exfoliation. This can indicate that silicon zirconium dual element hybrid phenolic resin is the highly competitive matrix for lightweight and ablation resistant composite materials. [Display omitted] [ABSTRACT FROM AUTHOR]

In this study, a type of red mud/slag-based cenospheres/geopolymer foam was directly fabricated using the direct foaming method at room temperature. The effects of high-temperature exposure (700–1100 °C) on the phase evolution, pore structure, and properties of the foams were investigated. The results showed that the untreated foam was amorphous structure. The porosity of the foams increased from 36.4 ± 0.6% (1 wt%) to 71.9 ± 0.1% (5 wt%) with the addition of H 2 O 2. The compressive strength of the foams was 1.20–18.15 MPa, which was attributed to the good bond between the cenospheres and red mud/slag-based geopolymer matrix, the fractured spheres, and the crack deflection. After this high-temperature exposure, the foam crystallized mainly into the leucite and mullite phases. The density and compressive strength of the foams decreased as the exposure temperature increased. The thermal conductivity of the foams reached the lowest value of 0.169 W/(m⋅K) and 0.108 W/(m⋅K) with 5 wt% H 2 O 2 before and after the exposure, respectively. These foams have demonstrated good potential for application in the building insulation field. [ABSTRACT FROM AUTHOR]

The porous SiC-Mullite porous ceramics with different pore size were prepared by SiC particles, kaolin, Al(OH) 3 , and flake graphite, V 2 O 5 and AlF 3 were used as mineralizers, the pore size was controllable by adjusting the size of flake graphite. Then the improved empirical formula and grey theory were used to study the effect of the change in pore size on the material properties. The results showed that with the increase of mean pore size from 1.1 μm to 8.5 μm, the cold modulus of rupture and cold crushing strength decreased by 20.8 MPa and 13.7 MPa, respectively. And the thermal conductivity increased from 1.213 W⋅m−1⋅K−1 to 1.721 W⋅m−1⋅K−1 at 800 °C. The <5 μm pores were helped enhance the strength and decreased the thermal conductivity. [ABSTRACT FROM AUTHOR]

Si 3 N 4 -TiN composites have extensive manufacturing applications because of their first-rate mechanical and thermal properties. Conversely, they are very demanding on machines that use conventional practices because of their superior strength and hardness. Electrical discharge machining is a viable substitute for machining of Si 3 N 4 -TiN composites through electrical erosion. However, very few studies have been conducted on the machinability and surface characteristics of electrical-discharge-machined composites. This study focuses on the materials processing characteristics of a Si 3 N 4 -TiNcomposite using rotary EDM and die-sinking EDM performed with a Cu electrode. In addition, the surface and cross section of the subsurface of the composite were examined, along with energy dispersive X-ray analysis, to identify the elements present on the machined surface. It was found that the high level of hardness and low level of toughness of the Si 3 N 4 -TiN composite contributed to the presence of microcracks, globules, pores, recast layers, and craters on the EDMed surface. The recast layer thicknesses of the die-sinking EDM (optimum hole, 106 μm; best hole, 151 μm; worst hole, 166 μm) and rotary EDM (optimum hole, 53 μm; best hole, 55 μm; and worst hole, 58 μm) were examined. In addition, the presence of pores and ablation increased significantly during the rotary EDM process. Rotary EDM parameters capable of producing a minimum white layer thickness were also investigated. Finally, the porosity levels were estimated according to the number of pores using ImageJ software. For the die-sinking EDM, the estimated porosity values for the optimum, best, and worst holes were 14.989%, 19.525%, and 21.706% respectively and for the rotary EDM, these values were 24.873%, 33.04%, and 37.99% respectively. [ABSTRACT FROM AUTHOR]

The porous silicon carbide ceramics with multilevel directional pores were prepared by chemical vapor infiltration (CVI) combined with sacrificial template method. Carbon fiber preform with specific structure was used as template, and silicon carbide was deposited by CVI process. Then, the carbon fiber template was oxidized and removed, so that the porous silicon carbide ceramics were obtained. The influence of deposition time on pore structure, mechanical properties and thermal properties was studied. Compared with the traditional pore-making process, the pores formed by sacrificial template method are more regular, which brings excellent mechanical properties and thermal insulation properties. The porosity and flexural strength of the sample deposited for 72 h can reach 66.00% and 67.52 MPa, respectively, the thermal conductivity can be kept below 1 W/(m·K) from room temperature to 1200 °C. [ABSTRACT FROM AUTHOR]

This article aims to illustrate the influence of the composite micro-powder of α-Al 2 O 3 and zirconium basic carbonate (ZBC) on the microstructure, mechanical and thermal properties, and slag resistance of corundum castable. The results show that the addition of the composite micro-powder to corundum castable sintered at 1550 °C optimized its pore structure, which presented an apparent porosity of 16.8% and a slump in pore size from 10.80-45.72 μm to 0.36–1.83 μm. The ZrO 2 dissolving from ZBC combined with corundum matrix to form "intergranular" and "intragranular" submicron structures, which promoted the densification of matrix structure and improved the strength of castable by 25.8%–42.9%. In terms of slag resistance, castable with composite micro-powder saw an absorption of liquid slag in micropores and a Cr-rich complex spinel blocking layer with high melting point during slag erosion. Moreover, the in-situ ZrO 2 could enter slag to boost its viscosity, thus inhibiting the penetration capacity. Consequently, the penetration and erosion ratios of castable reduced by 6.32% and 83.99%, respectively. [ABSTRACT FROM AUTHOR]

In underground coal gasification (UCG), the backfilling body is utilized to reinforce the isolated coal pillars and provide support for the combustion cavity, but elevated temperatures can lead to a degradation in the carrying capacity. This paper presents an innovative high temperature resistance backfilling material for UCG. The evolution law and high temperature resistance mechanisms of its bearing capacity under high temperatures were mainly investigated, including its thermal expansion, compressive strength, acoustic emission characteristics, thermal stability, phase composition, micromorphology, and pore structure. The result indicates that the calcium aluminate cement (CAC) - fly ash (FA) backfilling body exhibited a non-linear variation in compressive strength with increasing temperature. The compressive strength still maintains 5 MPa at 1000 ℃, meeting the requirements for coal mine backfill. The FA induces secondary hydration in the backfilling body at elevated temperatures, resulting in the formation of a more compact C-A-S-H gel phase. Furthermore, the formation of AlO(OH), C 12 A 7 , and C 6 S 6 H is another reason for the enhancement of the high-temperature resistance of specimens. After 600 ℃ treatment, the porosity of specimens exhibited a significant increase, reaching 30.57 % at 1000 ℃. The thermos-mechanically coupled constitutive equation of the backfilling body was constructed, showing that as temperature rises, the brittleness diminishes and the damage factor experiences a substantial increase after 500 ℃. Experimental results provided strong technical support for strata control of UCG. • A high temperature resistance backfilling material for UCG was proposed for the first time. • The relationship between mechanical properties and thermal physical properties of CAC-FA backfilling body was studied. • The high temperature resistance mechanism of backfilling body was described. • The constitutive model of CAC-FA backfilling body for UCG was established. [ABSTRACT FROM AUTHOR]

Geopolymer materials offer environmental benefits and strong mechanical properties but face limitations such as efflorescence, shrinkage, thermal stability and poor mechanical performance at high temperatures. This study introduces a novel solution using silane-functionalized graphene oxide nanocomposites (GO-APTS) to address these challenges. Experiments on metakaolin-based geopolymers demonstrate that incorporating GO-APTS improves dispersion, enhances mechanical strength, refines pore structures, and boosts resilience to high temperatures while reducing shrinkage and efflorescence, without compromising the workability of the mixes. Although the structural integrity of the material at nanoscale degrades beyond certain temperatures, the overall thermal resistance is significantly increased, with treated geopolymers displaying a ∼6 % improvement in porosity, ∼20 % higher residual compressive strength and ∼15 % reduction in shrinkage compared to control samples after exposure to heat. Our work reveals the promising potential of silanized graphene oxide nanocomposites in crafting cementitious materials suitable for high-temperature applications, paving the way for their broader use in innovative construction and industry solutions. • GO-APTS significantly enhance mechanical strength and thermal properties of geopolymer. • GO-APTS reduces shrinkage and efflorescence in geopolymer. • APTS delays deterioration of GO up to approximately 620 °C – compared to 580 °C for pure GO. • Formation of new geopolymer reaction products at elevated temperatures are observed. • Simultaneously, structural deterioration and nanoscale degradation are evident. [ABSTRACT FROM AUTHOR]

Flexible pressure sensors embody outstanding mechanical and sensing performance, particularly in the fields of personal health monitoring and artificial intelligence, while catering to multifunctional applications resilient against harsh weather conditions. Among these, Ti 3 C 2 T x MXene-based aerogel materials with high surface area and excellent conductivity have attracted a lot of attention. However, there are big challenges in improving the mechanical properties at low densities and designing multi-level pore structures. Herein, the prepared silane monomers (MP) are firstly synthesized by 3-(Trimethoxysilyl) propyl methacrylate (MPTES) and polyethylene glycol diacrylate (PEGDA), then polydopamine-modified silicon dioxide (PDA-SiO 2) nanofibers employed with MXene nanosheets form covalent cross-linking nanofiber aerogels. The multi-level stable structure improves both mechanical strength and elasticity. The assembled MXene/MP/PDA-SiO 2 pressure sensors exhibit a high sensitivity of −0.83 kPa−1, a rapid response time of 48 ms, a minimum 1 % strain detection limit, and reliable stability over 10,000 cycles. Furthermore, these sensors can be used for human motion detection and health diagnostics, and show good personal thermal management performance. This work holds a promising candidate for the next generation of multifunctional flexible electronic devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • A method is developed for the regulation of secondary unstable dendrites during ice crystal growth. • The flexible polyimide (PI) aerogels possesses a micro/nano multi-scale porous skeleton. • The PI aerogels are characterized by ultra-low density and exceptional thermal insulation. The freeze-casting is widely utilized as a tool for regulating micro-scale pore structures in the fabrication of flexible polyimide (PI) aerogels for applications in adsorption, filtration, and fire-retardant. Herein, a confinement-controlled freeze-casting method is developed to fabricate PI aerogels with excellent thermal insulation properties by designing multi-scale structural adaptability. In a confinement-controlled system, the enhanced solid/solid and solid/liquid interface interactions in the solution dispersion system induce dendritic evolution of ice crystals. Under the directional freezing, grown dendritic ice crystals squeeze the loaded particles to form polyamic acid salt (PAAs) cryogels. Followed by template removal and thermal imidization, PI aerogels with a micro/nano-scale slit-like porous structure were obtained. The PI aerogels are characterized by ultra-low density (as low as 9.82 mg/cm3) and exceptional thermal insulation performance (25.0 mW/(m·K) at 25 °C). [ABSTRACT FROM AUTHOR]

BaZrO 3 with the ABO 3 perovskite structure can be doped at the A or B sites to obtain the corresponding properties. In this study, BaZrO 3 was doped with Ca2+, Sr2+, Ti4+, and Ce4+. The structure, phase composition, and mechanical and thermal properties of the composites were investigated. The sintered Ba 1-x Ca x ZrO 3 samples with x = 0.2 and 0.4 exhibited relatively superior comprehensive behaviours; the cold modulus of rupture was increased by 127.36% and 134.59%, while that for BaZr 0 · 8 Ti 0 · 2 O 3 and BaZr 0 · 8 Ce 0 · 2 O 3 was increased by 99.30% and 112.37%, respectively. Further increases in strength and density were obtained in the Ba 0 · 8 Ca 0 · 2 Zr 0 · 8 Ti 0 · 2 O 3 and Ba 0 · 6 Ca 0 · 4 Zr 0 · 8 Ti 0 · 2 O 3 co-doped samples, and the corresponding apparent porosities were greatly decreased from 30.6% to below 1.0%. The thermal conductivities of the doped samples were generally low, achieving a minimum of 0.361 W/(m·K). The combination of high strength and low thermal conductivity demonstrate the significant application potential of BaZrO 3 -based composite materials. [ABSTRACT FROM AUTHOR]

Silver nanoparticles (AgNPs) are grown uniformly on the surface of white porous boron nitride nanofibers (BNNFs) via a thermal reduction method to overcome the issue of nanoparticle aggregation. The optical characteristics of the AgNPs are retained, with different colors present depending on reduction temperature. This mainly depends on the white appearance of BNNFs. In addition, compared to boron nitride (BN) nanosheets and nanospheres, abundant pore structure and high specific surface area of the BNNFs enable superior AgNPs loading without agglomeration. The prepared AgNPs-loaded BNNFs (Ag-BNNFs) are then incorporated into poly (vinyl alcohol) (PVA) hydrogels fabricated through cyclic freeze-thaw techniques to develop antibacterial Ag-BNNFs/PVA composite hydrogels. The addition of 3 wt% Ag-BNNFs increases the tensile strength by 73.1% and compressive strength by 92.8% relative to the unmodified PVA hydrogels. Thermal stability also improves considerably, with the maximum PVA decomposition rate shifting from 280.9°C to 323.6°C in the composite hydrogels. Importantly, a potent bactericidal effect against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) are achieved, with 99.5% and 100% inhibition after 24 h exposure to the Ag-BNNFs/PVA composite hydrogels, respectively. This work demonstrates a new method of dispersing AgNPs with BNNFs, and the resulting Ag-BNNFs effectively enhance the mechanical properties, thermal stability and antibacterial activity of PVA hydrogels. [Display omitted] [ABSTRACT FROM AUTHOR]

High-strength thermal insulation mortar, with its excellent mechanical properties and thermal insulation performance, is commonly used in building structure insulation and reinforcement renovations. In this study, vitrified microbeads and expanded perlite (EP) were used as thermal insulation materials to create high-strength thermal insulation mortar. The effects of the replacement percentage of these materials (50%, 65%, 75%, and 80%) on the density, water absorption, porosity, compressive and flexural strength, and thermal conductivity of the mortar were studied. The results show that increased replacement percentages of vitrified microbead (EP) led to a decrease in the density of the mortar and an increase in the water absorption rate and porosity. Furthermore, when the replacement percentages were increased, the compressive and flexural strength and the thermal conductivity of the mortar were reduced. Comparative analysis of the pore structure of high-strength thermal insulation mortar using scanning electron microscopy and digital microscope revealed the influence of vitrified microbead (EP) on the internal pore structure of high-strength thermal insulation mortar. The influence coefficient (η s) of volume replacement percentage of insulation materials was introduced using the Hamilton and Crosser models. Furthermore, the prediction model of thermal conductivity of high-strength thermal insulation mortar was established under different volume replacement percentages of vitrified microbead (EP). The calculated values of the model matched well with the measured values, with the ratios of the calculated values of the model to the experimental ones ranging from 0.85 to 1.15. • The physical, mechanical, and thermal conductive properties of mortar are found to be influenced by the amount of insulation. • The prediction model of thermal conductivity of high-strength thermal insulation mortar is established. [ABSTRACT FROM AUTHOR]

[Display omitted] • Spherical powders containing Si with tailorable porosity were originally obtained. • Prepared micro-size porous samples consisted of nano-sized channels for reaction. • The energetic kinetics of prepared fuels outperformed Al nanoparticles. • Discrepant reaction mechanism for AlSi@pSi at different circumstances was found. Energetic porous fuels are attractive for their high reactivity. In this study, porous silicon/aluminum–silicon (pSi/AlSi@pSi) powders were prepared via dealloying Al-Si alloy. Results demonstrate that pSi and AlSi@pSi with evenly distributed pores and tailorable porosity were obtained. AlSi@pSi shows a core–shell structure with Al-Si alloy core and porous Si shell. Thermal properties indicate that consistent with its core–shell structure, the oxidation of AlSi@pSi can be considered as a combination of pSi and Al-Si alloy. The main oxidation is kicked in by the reaction of the Al-Si alloy core, followed by the intense reaction of the porous Si shell. The combustion characterization demonstrates that the dramatically improved reactivity of porous samples is attributed to the ultra-high kinetics of porous Si outperforming nano-sized aluminum (n-Al). The shorter ignition delay and combustion duration of porous samples than Al-Si alloy and n-Al result from the lower apparent activation energy (E 0) and the low initiation oxidation temperature for porous Si. The different oxidation processes for AlSi@pSi under thermal oxidation and combustion owe to the high oxidation peak temperature and low E 0 of porous Si. Above all, the prepared porous fuels with tailorable porosity and superior reactivity than n-Al are promising fuels in energetic materials. [ABSTRACT FROM AUTHOR]

As an environmentally friendly material, alkali-activated fly ash-slag (AAFS) is considered as a promising alternative cement because of its excellent mechanical properties and thermal stability. Nevertheless, high temperature induced damage in AAFS can potentially bring serious risks for its practical applications. This paper presents a systematic experimental study on behaviour of AAFS paste subjected to elevated temperatures up to 800 °C in terms of microstructure as well as thermal and mechanical properties. Microstructural evolution was characterised by means of Rietveld-based quantitative X-ray diffraction (QXRD), backscattered scanning electron microscope (BSEM) and X-ray microcomputed tomography (XCT), while thermal and mechanical properties were evaluated from thermogravimetric analysis (TGA), thermal deformation and compressive and flexural strengths. Results indicate that the compressive strength of AAFS paste rises by 77.5 % at 200 °C, followed by a mitigation from 200 to 600 °C and a regain at 800 °C. Different phases in AAFS paste including unreacted particles, reaction products and pores took up 30 %, 67.7 % and 2.31 % at ambient temperature, and 4.95 %, 84.8 % and 10.3 % after exposure to 800 °C, respectively, suggesting the recrystallisation with the formation of nepheline and gehlenite. In addition, the relationships between microstructural characteristics including three-dimensional (3D) pore structure features and thermal and mechanical properties of AAFS paste at elevated temperatures were explored and discussed in depth to gain insights into the underlying degradation mechanisms including pore pressure build-up, thermal gradient and phase transformation. [ABSTRACT FROM AUTHOR]

Monolithic polymer-derived SiC is highly desirable for high temperature applications because of its unique thermal properties in extreme conditions. The current study focuses on the formation, evolution, and stability of polymer-derived SiC at different high temperatures. SiC-based monoliths were pre-pyrolyzed at 1200 °C and then pyrolyzed at 1600 - 2500 °C in a flowing argon atmosphere. The porosity, density, compositions, and phases of the SiC samples were studied. Dense SiC monolith was obtained from 1200 °C to 2200 °C. SiC crystallized at 1900 °C and formed a near stoichiometric composition. β-SiC remained stable even at 2200 °C. However, the SiC monolith experienced continuous mass loss above 1900 °C and disintegrated at 2500 °C with ∼89.5% mass loss. This work opens a pathway for preparing near stoichiometric and dense SiC monoliths through polymer precursor pyrolysis; it also provides fundamental understanding of polymer-derived SiC at different high temperatures. • Dense SiC monolith was prepared by crosslinking and pyrolysis of SMP-10 precursor. • SiC formed at 1900 °C was near stoichiometric. • Pyrolysis at 2200 °C initiated the sublimation of 'Si' and led to excessive carbon. • Pyrolysis at 2500 °C led to disintegration of SiC and a porous graphitic structure. • The work offers a complete map of polymer-derived SiC formation and decomposition. [ABSTRACT FROM AUTHOR]

In this study, a new type of highly porous ceramic was successfully fabricated from α-Al 2 O 3 whiskers and nano-sized Al 2 O 3 particle slurry by vacuum infiltration with the subsequent annealing in air. It was found that with an increase in the alumina slurry amount or sintering temperature, the porosity of the foam ceramic decreased while its compressive strength increased. The optimal alumina slurry content and sintering temperature were equal to 4 g, and 1350 °C, respectively. The as-synthesised porous foam ceramic exhibited a low density of 0.65 g/cm3, high porosity of 83.51%, high compressive strength of 3.84 MPa, and low thermal conductivity of 1.37 W/m⋅K at room temperature, suggesting its potential applications in high-temperature gas filtration and thermal insulation materials. [ABSTRACT FROM AUTHOR]

Pore structure is one of the major factors influencing the failure mechanisms of thermal barrier coatings (TBCs) during high-temperature service. Powders exhibiting different pore structures have been produced using the plasma spheroidization technique. To improve the strain tolerance of an aircraft engine's hot sections, the preparation method of the TBCs material—8-wt% yttria-stabilized zirconia powders—has been continuously optimized. In this paper, the constrained effects of pores on the ceramic top coating of plasma-sprayed lamellar TBCs were investigated. Furthermore, the crystal phase structures, thermophysical properties, porosity, microstructures, and synthesis mechanism of powders and coatings were analyzed. Results revealed that the top ceramic coating, which was made from powders cooled by air and distilled water, can influence the coating porosity. Moreover, thermal insulation was substantiated by the finite element analysis method. Consequently, dense powders cooled by water can be used on the top surface in direct contact with high temperature flame flow to resist the diffusion of oxides, and the porous powder cooled by air can be applied in the middle coating to decrease the thermal conductivity. Hence, TBCs with various layers of different porosities can prolong the service life of thermal barrier coatings. [ABSTRACT FROM AUTHOR]

KLS-1 Lunar regolith simulant was microwave sintered to explore its potential applicability in future lunar construction. The effects of sintering temperature on linear shrinkage, density, porosity, and microstructural, mechanical, and thermal properties were investigated. As the sintering temperature increased, linear shrinkage and density increased and porosity decreased. Structural evolution in the sintered samples was characterized by scanning electron microscopy and X-ray diffraction. Unconfined compressive strength testing showed that mechanical strength increased significantly with increasing sintering temperature, with 1120 °C giving the highest strength of 37.0 ± 4.8 MPa. The sintered samples exhibited a coefficient of thermal expansion of approximately 5 × 10−6 °C−1, which was well-maintained even after cyclic temperature stress between −100 and 200 °C. Therefore, this microwave processing appears promising for the fabrication of building material with sufficient mechanical strength and thermal durability for lunar construction. [Display omitted] [ABSTRACT FROM AUTHOR]

In this investigation, we use pulsed thermography and a multilayer analytical model to critically evaluate the thermal diffusivity and inherent porosity in cold-sprayed Ti-6Al-4V coatings on Al6061-T6 substrates. These coatings are of importance in deploying cold spray as an additive manufacturing technique for the restoration of high-cost alloy components. Our study draws upon experimental data obtained at spray angles from 50°to 90°, illustrating the relationship among the spray angle, porosity within the coating, and the resultant thermal diffusivity. Our results reveal a decrease in porosity and an increase in thermal diffusivity as the spray angle increases from 50°to 90°. In conjunction with our experimental approach, a numerical model was developed, incorporating binary images derived from optical micrographs to simulate transient heat diffusion during pulsed thermography experiments. The congruence between our empirical findings and simulation data affirms the effectiveness of the applied methodology, shedding light on the complex interplay between processing parameters and the resulting thermal properties. This study explores the effects of porosity and thermal gradients introduced during pulsed thermography, providing a profound understanding of the thermal dynamics of cold-sprayed coatings. [Display omitted] • Spray angle affects the porosity and thereby the thermal trait • Microscopic images-based FEM models deepen heat diffusion understanding • Porosity insights enhance cold-sprayed coating thermal dynamics [ABSTRACT FROM AUTHOR]

A novel lightweight foamed cement-based electromagnetic wave (EMW) absorbing material (Density<0.5 g/cm3) is prepared using secondary aluminum ash (SAA) as a foaming agent and carbon black (CB) as an efficient EMW absorbent, providing a new way to recycle SAA. The pore structure parameters, reflection loss (RL), mechanical strength and thermal conductivity are systematically investigated. The experimental test results indicate that the pore structure of cement matrix prepared by SAA exhibits better EMW loss performance than those prepared by traditional foaming agent. The analysis of the pore structure images indicates that the average pore size is reduced, and pore size distribution shifts towards smaller sizes due to the addition of CB. Furthermore, the roundness of pores is increased due to the formation of more irregular pores. Increasing CB content and thickness can reduce RL, enhance absorbing performance at low frequencies, and broaden effective absorbing bandwidth (EAB). The absorbing performance was tested using the arch reflection method in the frequency range of 1.1–18 GHz, the excellent absorbing performance and the widest EAB (RL<−10 dB) reach −36.34 dB and 14.46 GHz, respectively, at a thickness of 4 cm. Benefiting from excellent pore structure, the foamed cement-based material also exhibits better mechanical strength, and good thermal insulation properties are maintained after adding CB. The compressive and flexural strength can reach 2.18 MPa and 1.02 MPa, respectively, while the thermal conductivity remains below 0.122 W/(m·K). • Lightweight cement-based absorber was firstly prepared using SAA as foaming agent. • The effect of CB on pore structure and EMW absorbing property is investigated. • EAB and minimum RL of the developed absorber reach 14.46 GHz and − 36.34 dB. • A new way to recycle SAA is provided. [ABSTRACT FROM AUTHOR]

Concrete infrastructures, such as high-speed railway subgrades, are vulnerable to frost heave in cold regions. Multi-stage phase change material (PCM) aggregate concrete can alleviate frost heave by thermal regulation. This study explored the effect of replacing coarse aggregate with multi-stage PCM aggregate at 0%− 100% on concrete. Firstly, the compressive strength and splitting tensile strength of PCM aggregate concrete were evaluated. Then, the influence of substituting PCM aggregate on the thermal properties was investigated, including thermal conductivity, thermal diffusivity, volumetric heat capacity, and time-temperature curve. Subsequently, the changes in the pore structure were characterized by using a combination of nuclear magnetic resonance (NMR) and computerized tomography (CT). Finally, the interface transition zone (ITZ) of natural aggregate and PCM aggregate was evaluated by using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The results show that the mechanical properties of concrete decrease after the addition of PCM aggregate, but its thermal properties improve. This improvement is not only related to the PCM aggregate but also to the increased pores. It has been confirmed by NMR and CT analysis that the replacement of PCM aggregate leads to an increase in both pore volume and pore number. Only the macropores with a volume larger than 108 μm3 may have an impact on mechanical and thermal properties, although their quantity only accounts for 2%. The SEM and EDS results show that there are no obvious cracks in the ITZ of PCM aggregate, indicating that the PCM aggregate has better compatibility with the cement matrix. Considering the mechanical properties, thermal properties, and porosity, the replacement of 60% PCM aggregate is reasonable in concrete, which provides a theoretical basis for multi-stage PCM aggregate concrete application in cold regions. • The strength of PCM aggregate concrete is descending. • The incorporation of PCM aggregate increases the thermal performance. • The pores increase after the incorporation of PCM aggregate. • A few macropores affect the performance of concrete. • The ITZ of PCM aggregate concrete is not the weakest area. [ABSTRACT FROM AUTHOR]

Incorporation techniques of phase change materials (PCM) in cementitious composites have a significant influence on thermal properties. This study investigated the thermal behavior of low-temperature PCM when subjected to varying temperature change rates and pore confinement inside the porous network of lightweight aggregates (LWA) and encapsulation using melamine-formaldehyde-based polymer. Three categories of thermal energy storage (TES) specimens were prepared: (i) Bulk PCM (i.e., liquid PCM), (ii) micro-encapsulated PCM (MPCM), and (iii) four different LWAs infused with PCM (PCM-LWA). The thermal properties of small-scale individual TES specimens were analyzed using a low-temperature differential scanning calorimeter (LT-DSC) to evaluate the effect of ramp rates. Dynamic vapor sorption (DVS) analysis was utilized to characterize the pore structure of LWAs. LT-DSC results show that undercooling of the PCM significantly increases with the rise in ramp rate for all the specimens; temperature change rate affects the nucleation and crystallization growth process during the phase transition. Pore structure characterization of LWAs indicates that the majority of the pores (> 92 %) were larger than 17.3 nm (i.e., macropores). Confined liquid properties are subjected to modification due to interaction with the confining surfaces, as explained by Gibbs-Thomson theory. PCM incorporated in the LWA porous network experienced variable degree of supercooling during phase transition; magnitude of confinement pressure is dependent on the pore diameter, structure, and tortuosity. Experimental evidence suggested that PCM-LWA will exhibit gradual expulsion of enthalpy of fusion over a larger temperature range (i.e., ∼−5 °C to 4.28 °C) in comparison to MPCM (i.e., ∼4.28 °C). • Effect of temperature change rate on phase transition properties of PCM. • Effect of LWA pore network confinement on phase transition properties of PCM. • Thermal efficiency of latent heat storage specimens. • Correlation of pore size to melting temperature using Gibbs-Thomson theory. [ABSTRACT FROM AUTHOR]

The anisotropic cellulose nanofiber (CNF)/carbon nanotube (CNT) aerogels hold a great promise in directional applications due to their distinct xylem-like aligned penetrating pore structures. The aspect ratio of CNF plays a crucial role in the pore structures of aerogels, directly dominating the final macroscopic properties of materials. Herein, three types of CNF with different aspect ratios were extracted through the 2,2,6,6-tetrmethylpiperidine-1-oxyl radical (TEMPO) oxidation process by changing the doses of oxidant. The corresponding anisotropic CNF/CNT aerogels were prepared by the unidirectional freeze-drying method and then their pore morphologies and properties were investigated in detail. The resulting aerogel with the shortest aspect ratio of CNF exhibited the densest porous structure, thereby obtaining the highest compressive strength of 110 kPa and elastic modulus of 383 kPa, while that containing the longest CNF possessed the highest thermal conductivity coefficient of 0.17 W m−1 K−1 and the worst thermal insulation. This research explored the relationship between the properties of the CNF/CNT aerogels and devisable pore structures caused by various aspect ratios of CNF, thus providing a new insight into the development of CNF/CNT aerogels with tunable performances. [ABSTRACT FROM AUTHOR]

Chemically activated biochar with richer pore structure and higher specific surface area is well suited for loading phase change materials (PCMs). However, the effect of structural characteristics and abundant surface functional groups of chemically activated biochar on the thermal properties of PCMs has not been systematically investigated. Here, shape-stable samples were prepared by introducing biochar obtained by activation with different chemical reagents (ZnCl 2 , H 3 PO 4 , KOH, and K 2 CO 3) into three organic PCMs (paraffin, stearic acid, and polyethylene glycol). The results indicated that the biochar activated by KOH possessed the highest specific surface area of 1344.45 m2/g, followed by biochar activated by ZnCl 2 , H 3 PO 4 , and K 2 CO 3 of 1297.35, 1062.74, and 891.38 m2/g, respectively. The loading capacity of KOH-activated biochar was as high as 82.12 %, 83.13 %, and 80.81 % for the three organic PCMs, and the melting enthalpies of corresponding composite PCMs were 163.82, 168.54, and 139.96 kJ/kg. Additionally, the influence degree on the enthalpies of the three PCMs was only 10.84 %, 12.26 %, and 7.74 %, while that of ZnCl 2 and H 3 PO 4 -activated biochar was as high as 53.61 % and 44.22 %, 52.10 %, and 57.74 %, 55.35 % and 45.79 % indicating the two biochar were not suitable as support materials for PCMs. Moreover, ZnCl 2 -activated biochar has the most apparent upgradation on PCMs' thermal conductivity, which could increase the thermal conductivity of the three organic PCMs by 1.318, 1.34, and 1.229 times, respectively, followed by H 3 PO 4 , K 2 CO 3 , and KOH-activated biochar. • Chemically activated biochar had larger specific surface area. • Encapsulation capacity of KOH-activated biochar for organic were significant. • Influence degree of ZnCl 2 and H 3 PO 4 -activated biochar was obvious. • ZnCl 2 -activated biochar had the most apparent upgradation on thermal conductivity. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) of polyphenylsulfone (PPSU), an amorphous high-performance polymer (HPP), has shown promise in exhibiting structural integrity for many applications. With thermoplastic material extrusion 3D printing, parts consisting of layered melts exhibited voids, where the adhesion quality and void size depend on the processing parameters implemented during printing. However, the structure-process-property (SPP) relationships between the thermal properties and rheological and mechanical behavior of AM PPSU are poorly understood. In this study, a comprehensive analysis of the thermal, thermo-mechanical, and layer-by-layer build-up of PPSU is investigated and correlated with viscosity and extrudate die swell behavior with void fraction volume as confirmed by high-resolution x-ray computed tomography (XCT). Gas chromatography–mass spectrometry (GC–MS) pyrolysis confirmed PPSU composition and degradation at 480 °C, consistent with thermo-gravimetric analysis TGA. A 141% difference in viscosity was observed when processing temperatures increased from 350 °C to 400 °C. Likewise, extrudate die swell decreased with increasing temperatures, resulting in a 17% difference. Tensile and compressive properties confirmed that higher extruding temperatures resulted in lower porosity and higher mechanical strength. In general, higher extruding temperatures lower the viscosity to allow for stronger cohesion between layers; however, increasing the temperature too high results in a below unity extrudate die swell, reducing mechanical properties. Therefore, to optimize the mechanical integrity of 3D printed amorphous PPSU parts, an increase in the viscosity, near unity of the extrudate die swell, and tempered extrusion temperature are needed. [Display omitted] • High Performance Polymers (HPP)s represents polymer materials that compete with metal alloy applications in very demanding applications. s. • Understanding the role of viscosity, die-swell, and the overlap of rasters is crucial in optimizing propoerties of FDM printed HPP Polymers. • Identified three major differences between an amorphous HPP polymer such as polyphenylenesulfone (PPSU) behavior in 3D printing vs semi-crystalline HPPs based on controlled extrusion temperatures. • Correlated the structure-process-property (SPP) relationships between the thermal properties, rheological and mechanical behavior. • An important finding is that tensile and compressive properties with higher extruding temperatures resulted in lower porosity and higher mechanical strength. [ABSTRACT FROM AUTHOR]

To develop light-weight polymer-based multifunctional materials with outstanding electromagnetic wave absorbing/shielding properties and high thermal conductivity, 2D interlinked carbon fiber networks (2D ICFNs) were synthesized via direct pyrolysis of filter papers at 600–900 °C. The pyrolysis temperature (T p) was controlled to modulate the porosity, defects, and the resulting properties of 2D ICFNs. Owing to the co-manipulation of defects and porosity, the 2D ICFNs formed under T p = 900 °C exhibit a larger EABW max /d (3.57 GHz/mm) and stronger absorption (−44.66 dB) at a lower load (15%) compared to most other carbon fiber (CF)-based materials. Their shielding effectiveness is beyond 20 dB over 2.0–18.0 GHz with a maximal value of 76.2 dB at 18 GHz, surpassing the minimum requirement (20 dB) for practical applications. Besides, the 2D ICFNs with moderate porosity and high graphitization bear a larger thermal conductivity (2.69–2.93 W/mK) at a lower filling ratio (20 wt%) in comparison to the majority of previously reported materials. This is primarily due to the shortened phonon/electron transfer paths, decreased phonon-interface/-defect scattering, and continuous paths for thermal transmission in the 2D ICFNs. Overall, it is believed that the 2D ICFNs can be one of the most promising multifunctional fillers for EM absorption applications. Briefs2D interlinked carbon fiber networks were synthesized via direct pyrolysis of filter papers, exhibiting defect/porosity-co-manipulating high thermal conductivity, good electric insulation, and prominent EMI shielding/absorption. [Display omitted] • Direct pyrolysis of filter papers for 2D interlinked carbon fiber networks. • Controlling pyrolysis temperature to modulate the porosity and defects. • Optimizing the thermal, electrical, and EMW absorbing/shielding properties. • Defects and porosity co-manipulating the prominent properties. [ABSTRACT FROM AUTHOR]

• Initial and final setting times of the mixes increase with the seashell ash substitutions. • The spreadability and density properties decrease. • The MSA ash-based LFC exhibits lower capillary sorption, water absorption, and gas permeability. • It was obtained that the 15% MSA replacement in LFC exhibited 15.89%, 17.95% and 12.41% improvement in flexural, split-tensile, and compressive strength. • Moreover, porosity, SEM assessment, and pores distribution indicated that up to 15% replacement, the seashell as-based concrete performed better than the rest of the substitutions. • The thermal conductivity, thermal diffusivity, and specific heat capacity exhibited better performance of sea shell-based specimens. The comprehensive properties of waste seashell ash (Oyster shell ash (OSA), Scallop shell ash (SSA), and Mussel shell ash (MSA)) in lightweight foamed concrete (LFC) are needed to explore for using these aquaculture wastes in light-weight building structures. Therefore, this study's aim is to investigate the fresh, transport, mechanical, pore structure, and thermal properties of OSA, SSA and MSA-based LFC. The seven LFC mixes have been prepared to evaluate the effect of 5, 10, 15, 20, 25, and 30% cement replacement by seashell ash and compared with the control mix. The test findings show that mixes' initial and final setting times increase with the seashell ash substitutions; however, the spreadability and density properties of the fresh test decrease. The MSA ash-based LFC exhibits 0.29–1% lower water absorption than the OSA and SSA ash-based specimens. It was further observed that the 15% MSA replacement in LFC exhibited a maximum of 12.41%, 15.89% and 17.95% enhancement in compressive, flexural and splitting tensile strength compared to the reference mix. Moreover, SEM assessment and pores distribution indicated that up to 15% replacement, the seashell as-based concrete performed better as a pore filler than the rest of the substitutions. The thermal conductivity and specific heat capacity exhibited better performance for all sea shell-based specimens; however, a 15% replacement of MSA seashell-based concrete can be the optimum solution for eco-friendly concrete production considering the overall assessment. [ABSTRACT FROM AUTHOR]

In this work, a facile microwave-assisted foaming and thermal imidization treatment method was proposed to fabricate flexible polyimide (PI)/rGO composite foams with anisotropic pore structures. The PI/rGO composite foams (PIF/rGO) were used as the starting derivatives to prepare carbon foams that demonstrated excellent anisotropic thermal insulation and electromagnetic interference (EMI) shielding applications. The directional growth of pore structures during the foaming period resulted in the formation of aligned ellipsoidal strip-like pore structure in the horizontal direction (i.e., perpendicular to the pore growth direction), which was attributed to the escape of foaming gases such as tetrahydrofuran, methanol and H 2 O. The homogeneous dispersion of rGO in the PI-derived carbon skeleton endowed corresponding carbon foams with excellent mechanical and thermal stability, high thermal insulation and electrical conductivity (σ) as well as absorption dominated EMI shielding performance. The σ and EMI shielding effectiveness (SE) of carbon foams showed an increasing trend with increasing rGO content. The σ, EMI SE and specific EMI SE of the carbon foams reached up to 33.0 S/m, 49.0 dB and 8792.8 dB/(g/cm2) in the horizontal direction, respectively. Therefore, this work provided a facile strategy to fabricate lightweight and anisotropic pore structure rGO-containing PIFs and carbonized derivatives, which demonstrated promising applications in high-end industrial fields. [Display omitted] • A facile strategy was proposed to prepare PIF/rGO and CF/rGO. • The directional growth of pores endowed foams with anisotropic properties. • The foams showed excellent mechanical and thermal insulation properties. • CF/rGO showed absorption-dominated EMI shielding performances. [ABSTRACT FROM AUTHOR]

• The effective young's modulus of U-50Zr alloy was predicted by multi-dimensional elongation modeling and voigt averaging scheme. • The phonon conductivity of U-50Zr alloy was obtained based on reverse non-equilibrium molecular dynamics method. • The semi-empirical correlations for porosity effects on young's modulus and thermal conductivity of U-50Zr were proposed. The U-50Zr alloy is a promising candidate for helical cruciform fuel application, for the superior performance in neutronics and heat transfer properties. Under in-pile conditions, the formation and aggregation of fission gas products would introduce porosity effect, and further degrade the mechanical-thermal physical properties. However, no porosity model has been established for U-50Zr alloy. In this work, the Young's modulus and lattice conductivity for U-50Zr were predicted via molecular dynamics (MD) simulations with modified embedded atom method potential. The effective Young's modulus was obtained by multi-dimensional elongation tests and Voigt averaging scheme, and the phonon conductivity was computed with reverse non-equilibrium molecular dynamics method. The electron conductivity was estimated by Wiedemann-Franz Law with published resistivity data. To fulfill porosity effect modeling, void generation technique was utilized into the MD models, and effective medium theory was incorporated into the approximations of electron conductivity. Good agreements with experimental data were achieved to verify the research methodology. The semi-empirical models on porosity effects for U-50Zr were established, which could provide preliminary predictions of Young's modulus and thermal conductivity. [ABSTRACT FROM AUTHOR]

[Display omitted] • Pitch is treated with nitric acid to produce modified pitch, and the formation mechanism of carbon foam was investigated based on the concentration of nitric acid. • The successful synthesis of carbon foam required pitch modification with a high concentration of nitric acid (60 wt%). • Carbon foam from modified pitch is attributed to the synergistic effect of the functional groups duced onto pitch and the low-molecular-weight components resulting from cracking. • The introduced oxygen-containing functional groups triggered CO 2 production, which could promote pore structure development. Carbon foam is a three-dimensional porous, rigid, and permeable material with applications in many fields owing to its excellent electrical and thermal properties. Pitch is a promising carbon source for carbon foam production, and its modification with nitric and sulfuric acids has been widely investigated. However, the foaming phenomenon resulting from the acid treatment of pitch and the resultant formation of porous structures remain poorly understood. Herein, we clarified the mechanism by which the porous structure of pitch-derived carbon foam is formed by analyzing the components of pitch modified by nitric acid treatment and identifying essential conditions for foam production. Carbon foam was obtained by pitch modification at a high concentration of nitric acid (60 wt%), whereas no carbon foam was formed at low nitric acid concentrations (<60 wt%). Furthermore, at high nitric acid concentrations, carbon foam formation proceeded at a relatively low temperature (280 °C). The formation of carbon foam from modified pitch was attributed to the synergistic effect of the functional groups introduced onto pitch and the low-molecular-weight components resulting from cracking. This work provides new insights into pitch as a precursor and provides a straightforward method for producing carbon foam. [ABSTRACT FROM AUTHOR]

• A novel ternary nitrate-chloride phase change material was prepared. • PCM has good heat storage performance. • Composite phase change material was prepared with EG as adsorption material. • Composite phase change material still has good thermal properties. Nitrate phase change materials (PCM) have important applications in the field of thermal energy storage, but their latent heat value is relatively low. A novel LiNO 3 -NaNO 3 -NaCl ternary molten salt with high latent heat was prepared and studied. LiNO 3 -NaNO 3 -NaCl/expanded graphite (EG) composite phase change material (CPCM) was prepared by using high thermal conductivity EG as the carrier adsorption material. The performance of PCM and CPCM were tested and analyzed. Compared with LiNO 3 -NaNO 3 , the newly prepared ternary nitrate-chloride mixed molten salt has a lower phase change temperature, a higher latent heat value, and a higher thermal decomposition temperature. At the same time, the supercooling degree of LiNO 3 -NaNO 3 -NaCl is about half lower than that of LiNO 3 -NaNO 3. There is no chemical reaction between different molten salts or between mixed molten salts and EG. The mixed molten salt is uniformly dispersed into the pore structure of EG, and no agglomeration occurs. Both LiNO 3 -NaNO 3 -NaCl and LiNO 3 -NaNO 3 -NaCl/EG have good cyclic thermal stability. The addition of EG greatly improves the thermal conductivity of LiNO 3 -NaNO 3 -NaCl. When the addition ratio of EG is 20%, the thermal conductivity of ternary molten salt increases from 1.378 to 5.453 W/m·K. The phase change materials added with EG still have high latent heat of phase change. The results show that LiNO 3 -NaNO 3 -NaCl/EG has broad application prospects in medium temperature heat storage. [ABSTRACT FROM AUTHOR]

Silver (Ag) paste sintering is used as a die-bonding technology for the next generation of power electronic modules as Ag offers a high melting temperature as well as excellent thermal and electrical conductivities. Ag paste sintering is performed using specific conditions depending on the type of paste and the users' specifications (temperature, time, pressure), ending up in a porous joint. As a result, the properties of those joints are heavily influenced by their densities (i.e. porosity). Despite the numerous studies reported in the literature, the relationship between the density of the joint and its thermal conductivity remains an issue since access to the density of an embedded thin joint is very challenging. Furthermore, little is known on the evolution of the thermal conductivity in operating conditions. In this study, these issues were investigated by developing self-standing specimens with microstructures representative of those of real joints. In order to study a wide range of porosity, sintering was performed using a single time/temperature under various pressures. The thermal conductivity was measured using 3D flash method, consisting in applying a short non-uniform laser excitation on the surface of the sample, leading to three-dimensional heat transfer. The relationship between porosity and thermal conductivity is established for the as-sintered state and after aging up to 500 h at temperatures ranging from 150 °C to 350 °C and is compared to existing models. The evolution of the thermal properties during thermal aging is discussed considering both the elaboration conditions and the microstructure evolution. [Display omitted] [ABSTRACT FROM AUTHOR]

This study investigated the impact of the nanostructure design of titanium nitride (TiN x) thin films on their optical, electrical and thermal properties. The growth designs of the films were tailored using conventional sputtering (series 1) and GLancing Angle Deposition (GLAD) geometries (series 2 and 3). The results showed the potential to modify the properties of thin films by adjusting their nanostructure design, rather than changing their composition. TiN x thin films prepared by GLAD, revealed wider and more significant variations in optical and electrical properties, while the thermal properties seemed to be more affected by the structural changes promoted by the N content in the films. GLAD geometries resulted in the reduction of the film's reflectivity, and colour coordinates, as well as an increase in the electrical resistivity. The thermal parameters of effusivity ratio and diffusivity were reduced as the N/Ti ratio increased. • Tailoring of thin films nanostructure design by GLancing Angle Deposition (GLAD). • Correlation between processing parameters and TiN thin films' characteristics. • Influence of roughness, pore density and grain size on the optical, electrical and thermal properties of TiN thin films. • Change thin films' responses by acting on their growing design and their morphological and structural features. • The possibility to extend thin films' responses beyond the conventional composition variation influence. [ABSTRACT FROM AUTHOR]

[Display omitted] • Thermal conductivity and specific heat capacity of pharmaceutical powders were measured. • Effects of moisture content and porosity on the thermal properties were investigated. • Effects of binary mixtures on the thermal properties of the pharmaceutics were determined. • Models were developed to predict thermal properties. Thermal conductivity and specific heat capacity are two important parameters for the drying process of pharmaceutical materials during methods such as wet granulation that can be observed in the overall tablet manufacturing process. In this study, a transient line heat source method was used for the first time to determine the thermal conductivity and volumetric specific heat capacity of common pharmaceutical components and binary mixtures, with moisture content ranging from 0 % to 30 % w.b and active ingredient loading between 0 % and 50 % by weight. A three-parameter least squares regression model relating the thermal properties to moisture content and porosity was evaluated at a 95 % confidence interval, with R2 values ranging from 0.832 to 0.997. Relationships were established between thermal conductivity, volumetric specific heat capacity, porosity, and moisture content for pharmaceutical ingredients including acetaminophen, microcrystalline cellulose, and lactose monohydrate. [ABSTRACT FROM AUTHOR]

• Pore structure is key parameter influencing its properties. • The agglomeration of SiO 2 aerogels modified is significantly improved. • The best way is modified by cation, non-ionic and inorganic surfactant. • The strength and thermal conductivity of the sample are 17.16 MPa and 0.1889 W/(m∙K) SiO 2 aerogel and cement-based cementing materials mixed prone to fragmentation, agglomeration, flying and floating, resulting in SiO 2 aerogel in cement-based cementing materials can not be evenly distributed. In addition, the mixture of hydrophobic SiO 2 aerogel and cement-based cementing materials has low adhesion and poor compatibility. In this study, the SiO 2 aerogels were modified in different ways for improved compatibility with inorganic cementing materials. The results show that the SiO 2 aerogel slurry (A4) modified by cation, non-ionic and inorganic surfactant had superior dispersibility in inorganic cementing materials. When the content of A4 was 30 wt%, the dry density, thermal conductivity and compressive strength of the sample were 1136.4 kg/m3, 0.1889 W/(m∙K), and 17.16 MPa, respectively. [ABSTRACT FROM AUTHOR]

Numerical analogues of non-fractal porous cometary dust particles are generated using a recently introduced model of open-pore solid particles. The refractive index of amorphous silicate is considered and the particle sizes follow a Sekanina-Hanner distribution within the size-range (0.01 μ m- 1 μ m). Using the Discrete Dipole Approximation (DDA) method, we calculate the thermal re-emission spectrum of a population of porous particles in the spectral region 0.2–39.8 μ m and the equilibrium temperature of the particles (when placed at 1 AU distance from Sun). Porosity tends to reduce the temperature of the particles because porous particles radiate heat more effectively than dense particles. A characteristic particle size is determined for which the particle temperature is maximum regardless of the porosity. The temperature of a cloud of polydisperse particles is more homogeneous for highly porous particles. These results are compared with those generated by Mie theory where the Bruggeman mixing rule is applied (EMT method). When agreement between the DDA and the EMT results is achieved, simple approximations are derived from the EMT to analyze and make clear the various behaviors of the spectral thermal re-emission revealed in the numerical data. In particular, the reason why the emission peak around 10 μ m is depressed by porosity and shifted to the smaller wavelength by a steeper particle-size distribution is explained. • a model of small (radius <1 ​μm) non-fractal porous particles made of amorphous silicate is studied in the context of cometary dust. • The profiles of the infrared silicate bands are discussed according to the porosity of the particles. • The temperature of a cloud of polydisperse porous particles is more homogeneous if the particles are porous. • Steeper decrease of the porous-particle size distribution shifts the infrared silicate peaks to shorter wavelengths. • The theory of the effective medium makes it possible to explain qualitatively the various behaviors due to porosity, and approximate formulas are given. [ABSTRACT FROM AUTHOR]

This study used the molecular dynamics (MD) simulation method to assess the effects of different percentages of NPs, sizes, and percentages of porosity on reinforced cement thermal behavior (TB) and mechanical behavior (MB) of samples. The temperature and kinetic energy (KE) converged to 300 K and 35.42 eV after 10 ns, which indicated the thermodynamic equilibrium and the atomic stability in the structures. Increasing the NPs percentage from 1% to 3% increased the maximum temperature from 1364 to 1405 K. By further increasing it to 5%, it was reduced to 1361 K. As the radius of Zn NPs increased to 16 Å, the ultimate strength (US) and Young's Modulus (YM) increased from 1.07 to 0.19 MPa to 1.2 and 0.22 MPa. The increase in the NPs' radius to 16 Å caused an increase in the maximum temperature from 1405 to 1455 K, maintaining atomic stability. As the porosity increased from 1% to 5%, the US and YM reduced from 0.91 to 0.17 MPa to 0.81 and 0.15 MPa. As the porosity increased from 1% to 5%, the maximum temperature was reduced from 1400 K to 1384 K. According to the results, Zn NPs' percentage and size effectively improved the MB of the final cement. [Display omitted] [ABSTRACT FROM AUTHOR]

• Pressureless sintering with cold/hot isostatic pressing is employed. • Thermal conductivity reached 620 W/mK, which is 57 % higher than that of pure copper. • Hot isostatic pressing is employed to eliminate the closed holes and gaps between diamond and copper. • Open pores in copper skeleton closed post high-temperature pressureless sintering. Diamond/copper composites exhibit excellent thermophysical properties and demonstrate wide potential for heat dissipation applications. However, due to high hardness, it's difficult to process complex shape parts. To overcome the challenge, this study proposes the isostatic pressure technique. A pressureless sintering combined with cold and hot isostatic pressing is employed to prepare shaped diamond/copper composites with thermal conductivity reaching 620 W/mK, which is 57 % higher than that of pure copper. Cold isostatic pressing is used to enhance the density of the skeleton, followed by pressureless sintering to change the pore structure from open hole to closed hole. Finally, hot isostatic pressing is employed to eliminate the closed holes, thus improving the comprehensive performance of the composite. [ABSTRACT FROM AUTHOR]

To accommodate the swelling of metallic fuels induced by the fission gas release for a sodium-free fuel option, advanced U-10Zr fuels with controlled porosities were designed and demonstrated by spark plasma sintering (SPS). U-10Zr fuel pellets with manufactured porosities varying from 35% up to fully dense fuel pellets have been fabricated by controlling mechanical attrition of the starting uranium powders, sintering temperature, pressure, and duration, and the correlation among the microstructure control – porosity – sintering conditions has been established. To further mimick the pore structure in irradiated fuels, different pore formers (NaCl and NH 4 HCO 3) were used to control the pore size and distribution. Microstructure characterization indicates a lamellar reaction zone of enriched Zr and U composed of alpha Zr with 2 at% U and distorted alpha U with 13 at% of Zr, respectively, differing from the arc-melted U-10Zr as a result of rapid consolidation of SPS at lower temperatures and short durations. The thermal conductivity of U10Zr with different porosities were also measured. This work demonstrates the success in manufacturing new metallic fuel forms with controlled porosities and pore distribution, which can be used as model systems to investigate the thermal transfer behavior of metallic fuels in the reactor. [ABSTRACT FROM AUTHOR]

• Neural network regression analysis is performed when studying red mud-AAC with different w/s ratios. • Relationship between pore structures and performances of red mud-based AAC is clarified. • A model reflecting pore structures and compressive strength of AAC is proposed with better regression and applicability. • A modified series–parallel model of thermal conductivity is provided in red mud-based AAC. • Neural network regression analysis could be effective based on a mass of measured data. A large amount of red mud needs to be disposed of in China, which causes environmental pollution. The feasibility of using red mud in autoclaved aerated concrete (AAC) has been confirmed, and its strength and thermal properties are highly related to its pore structures. To further clarify the relationship between the pore diameter (shape) and performances of red mud-based AAC, this study aims to establish a quantitative relationship between the compressive strength and the pore structure of AAC with red mud as well as its average shape factor of pores with a diameter above 0.5 mm, which was relied on the principle of elasticity. The experimental results show the strength formula of red mud-based AAC considering its porosity and its pore shape is R = R 0 0.03 1 - 1.21 V p 2 3 + 0.95 S H π 2 - 4 π + 8 + S H 2 π 4 + 16 S H π 2 - 8 S H π 3 16 + S H π 2 - 4 π + 8 + S H 2 π 4 + 16 S H π 2 - 8 S H π 3 . At the same time, to explore the constitutive relationship between the pore structure and thermal properties of red mud-based AAC, the series–parallel model of thermal conductivity is analyzed and modified, indicating that the series model has greater contribution to the effective thermal conductivity of AAC, where the expression is λ eff = 0.9 1 v 1 / λ 1 + v 2 / λ 2 + 0.19 (v 1 λ 1 + v 2 λ 2). Finally, through the neural network regression analysis, it is proved that the established model reveals good accuracy. [ABSTRACT FROM AUTHOR]

Two types of eco-friendly shape-stabilized phase change materials (SSPCMs) were developed in this study. Biobased PCMs were impregnated into the pore structure of recycled expanded glass granules and coated with silica fume particles using a 4-step vacuum impregnation method. The morphological and thermal properties of the fabricated SSPCMs along with their effects on the hydration, microstructural, mechanical, and thermal properties of cement-based composites were characterized through a set of multiphysics tests including isothermal calorimetry, compressive and tensile strength, capillary water absorption, 3D image analysis of μCT scans, and thermoregulating tests. It was found that coating PCM-integrated EG granules with porous silica fume particles can further mitigate the risk of leakage and increase the impregnation capacity of SSPCM composites, thus attaining desirable latent heat capacity. Furthermore, the incorporation of the developed environmentally friendly SSPCMs into concrete can maintain desirable mechanical strength, while achieving considerable thermal energy storage capacity, which can moderate indoor temperature fluctuations, thus yielding substantial HVAC energy savings. • Leak-free ecofriendly biobased SSPCMs with high latent heat capacity successfully fabricated. • TES cement-based composites incorporating SSPCMs developed. • SSPCM inclusion can increase thermal inertia and reduces indoor temperature fluctuation. • SSPCM-integrated cementitious composites can yield significant energy savings in buildings. [ABSTRACT FROM AUTHOR]

A very large amount of fly ash is generated from coal combustion, and the high value-added and efficient utilization conversion of this solid waste into a resource remains an issue to be solved. Among the many methods of waste resource utilization, the preparation of porous geopolymers is an effective way to improve the added value of fly ash. In this review, the processes for obtaining fly ash-based porous geopolymers are divided into two categories: bulk-type (direct foaming, sacrificial template, additive manufacturing, and fast microwave foaming method) and sphere-type (suspension solidification, direct molding, and calcium chloride solution gel method). The synthesis routes, main characteristics (pore structure, porosity), and performance (mechanical and thermal properties as well as adsorption etc.) of fly ash-based porous geopolymers are reviewed, and examples of applications such as heat insulation, filtration, sound absorption, and pH buffering are presented. Moreover, the future development prospects of this field are discussed. [ABSTRACT FROM AUTHOR]

• Tunisian limestones were characterized to investigate their weathering resistance and from thermal shock cycles. • The CRI obtained with a 10-min of IRT survey allowed to predict the major physical and chemical properties of these rocks. • Thermal shock effect was recognized on the CRI and the capillarity as they are related to surface features affected by the fast cooling process. Twenty-one limestone lithotypes from the extreme North of Tunisia (Bizerte region) were characterized in order to investigate their weathering resistance and the resulting damage from thermal shock cycles. An infrared thermography (IRT) monitoring was also conducted to assess the tendencies between the cooling rate index (CRI) and the physical (bulk density, porosity, capillarity and P wave velocity) or the chemical (calcium carbonate, silica and total organic carbon contents) characteristics of the carbonate rocks. Statistical clustering defined four classes in accordance with their different porosity values (1 % < n < 20 %). The obtained CRI within a 10-min of infrared thermography (IRT) survey allowed to forecast not only the total porosity of these rocks but also their major physical properties with a noticeable correlation trends before and even after thermal shock cycles. Similar findings proved the compatibility between the CRI10 and the chemical composition of the limestones due to the different thermal properties of the minerals. The lowest porous samples (n ≤ 5 %) with the highest calcium carbonate content (CaCO3 > 95%) seemed to be the most suitable ones for the infrared thermography (IRT) characterization by its best fitting trends with the CRI10. Thermal shock was very well remarked for all the clusters particularly based on the measures of CRI10 and capillarity, as they are mainly related to surface and subsurface features that are the most affected by the fast cooling process. This study highlighted the validity of the CRI10 as a reliable indirect parameter for the estimation, in laboratory, of low porous stones properties undergoing thermal weathering. [ABSTRACT FROM AUTHOR]

We performed numerical heat conduction analysis for the new proposed functionally graded porosity (FGP) media. Fourier, Cattaneo-Vernotte (C V), dual-phase lag (DPL) and time-fractional heat conduction responses for a porous solid-gas media are compared with the different flux pulse duration experimental results. Four configurations of the FGP domain in which the porosity gradations are controlled by the power-law volume fractions, are introduced. Accordingly, the porosity-dependent effective thermal properties of the domain are estimated and the temperature responses are discussed for different heat conduction models. Even a slight change in the porosity, leads to a different temperature-time history and its gradation affects the temperature distributions through the medium; therefore, by tuning the porosity gradations the desired temperature distributions can be achievable. Finally, the diffusion-like DPL and the classical Fourier models in descending configuration predict about 35% and 41% higher peak temperatures than the constant porosity ones, respectively. Furthermore, these models demonstrate the same temperature distributions in constant porosity; that is, in the case of graded porosity the maximum difference is less than 4% due to not taking into account the time laggings as the function of porosity gradations. • The transient and steady-like DPL model proves the highest accuracy in comparison with experimental data. • Four functionally graded porosity configurations have been proposed. • Fourier, C V, DPL temperature responses have been compared for the FGP media. • The diffusion-like DPL and Fourier models are identical for the constant porosity. [ABSTRACT FROM AUTHOR]

• CP is used to adjust the properties of foamed geopolymers. • The geopolymer foam with 50% CP exhibits excellent performance. • The incorporation of CP is beneficial for the pore structure in foamed concrete. In this study, cenospheres (CP, a lightweight component) was used to replace part of fly ash (FA) to prepare ultra-lightweight foamed geopolymer concrete (UFGC), and the fresh properties of the geopolymer paste was used to control the hardening performance of the UFGC sample. The results show that incorporating CP to the slag-FA system can effectively reduce the reaction rate of the geopolymer paste and increase its fluidity and setting time. Meanwhile, as the CP content increases, the density of the geopolymer foams decreases, and it exhibits better mechanical properties and thermal insulation performance when the substitution ratio of CP is 50%. In addition, a proper amount of CP improves the pore structure of the UFGC sample, reduces its sorptivity coefficient and drying shrinkage deformation. Therefore, a novel building exterior wall insulation material is prepared through CP to optimize the UFGC system, and its (C50) thermal conductivity is reduced by 37.86% compared to the control group, which is beneficial to the development of green and sustainable buildings. [ABSTRACT FROM AUTHOR]

• To achieve the desired printability, the optimal replacement range for silica sand by aerogel in a cementitious mixture is 0–20% by volume. • The thermal conductivities of the SC and 3D printed specimens ranked in the order of 3DCP-X > SC > 3DCP-Y > 3DCP-Z, irrespective of aerogel content. • The weak bonding interfaces between adjacent filaments produce gaps, providing channels for heat to transfer in specimens 3DCP-X. • Under the same thermal and mechanical requirements, walls fabricated by AG-incorporated concrete are 7-cm thinner than traditional concrete walls. This study investigated the properties of fresh and hardened aerogel (AG)-incorporated concrete suitable for 3D concrete printing. After trial and error, it was found, that to achieve the desired printability, the optimal replacement range for silica sand by aerogel in a cementitious mixture is 0–20% by volume. The physical, mechanical, and thermal insulation properties of hardened concrete in three directions were studied, and the influence of anisotropy on these properties was investigated. The results showed that irrespective of the aerogel content, the compressive strength of the cast specimens (avg. 24.90 MPa in A20) was slightly higher than those of the 3D printed specimens, 3DCP-X (avg. 23.63 MPa in A20), 3DCP-Y (avg. 20.77 MPa in A20), and 3DCP-Z (avg. 20.40 MPa in A20). The thermal conductivity of the cast and printed specimens decreased gradually with an increase in the aerogel content. Relative to that of the cast specimens (0.330 W/(m·K) in A20), the thermal conductivity of specimens 3DCP-X (0.405 W/(m·K) in A20) was slightly higher, while those of 3DCP-Y (0.320 W/(m·K) in A20) and 3DCP-Z (0.306 W/(m·K) in A20) were lower. A thermal insulation wall (400 mm × 200 mm × 600 mm) with hollow structures was printed using the AG-incorporated concrete. To satisfy the same thermal and mechanical requirements, walls fabricated using AG-incorporated concrete can be 7 cm thinner than traditional concrete walls. The mechanism for the heat transfer of AG-incorporated concrete in three directions was examined as well. [ABSTRACT FROM AUTHOR]

A novel palmitic acid @ZnO/Expanded graphite composite phase change material (PCM) was prepared. Palmitic acid (PA) was selected as phase change material and ZnO/Expanded Graphite as supporting material. Expanded graphite (EG), which was used to improve the thermal conductivity of PCM, was chemically modified using ZnO derived from ZIF-8. ZnO derived from ZIF-8 has abundant pore structure and large specific surface area. The structure of ZnO/EG additive was characterized by SEM analyzing method. The prepared ZnO/EG has a three-dimensional coupled network and hierarchical porous structure. Meanwhile, EG can effectively prevent the structural collapse and aggregation of Metal-Organic Framework (MOF) derivatives. The morphology and thermal properties of composite PCMs were analyzed with SEM, XRD, FTIR, DSC, TG, and DTG. The melting/solidifying temperatures and corresponding latent heats of composite PCM PA@ZnO/EG-6% are 60.38 °C and 58.46 °C, and 203.35 kJ/kg and 207.87 kJ/kg. Thermal conductivity of the composite PCM PA@ZnO/EG-6% increases by 137.5% than that of PA. The DTG results indicated the composite PCM has superior thermal stability. All test results suggested that this composite is a good PCM and has excellent potential in heat storage due to its excellent thermal properties, good thermal stability, and reliability. • The expanded graphite was modified by ZnO in situ precipitation method. • The prepared ZnO/EG has the three-dimensional coupled network. • The melting phase change enthalpy of the composite PCMs could attain 203.35 kJ/kg. • The thermal conductivity of PCM with 6 wt% ZnO/EG increases by 137.5% than that of PA. [ABSTRACT FROM AUTHOR]

• Thermophysical properties of building materials are reviewed. • The energy transfer and environmental risks in buildings are discussed. • Influence of moisture and temperature on performance of building materials is reviewed. • The effect of salt weathering on building materials is also addressed. • Feasibility of waste added bricks for energy saving and challenges are highlighted. The growing gap between energy demand and supply and the risk of environmental pollution, especially in the developing countries due to population growth and subsequent progress in the construction industry, is a challenging issue of this era. Many studies have been carried out to elucidate the thermophysical properties of building materials in terms of energy transfer and mitigation of environmental risks. This review provides a brief insight into the past literature and ongoing research work on thermophysical properties of building materials to establish the intellectual context of the study. The thermophysical properties of the rocks under the influence of moisture and temperature are reviewed. The influence of salt weathering on building materials' physical and thermal properties is also an important issue to be addressed in building structures. As fired clay bricks undergo several physical and chemical changes during sintering, a review of the existing literature on the effect of the mineralogy of clay, sintering time, and temperature on the physical and thermal properties of the bricks is also presented in this article. The construction of eco-friendly and thermally insulated bricks by adding waste materials is also examined in depth in terms of energy saving capacity and mechanical strength, with a relation to the contemporary challenges. [ABSTRACT FROM AUTHOR]

[Display omitted] • Copolymerization of MAPTMS and acrylate monomer (length 1–12 C atoms) depends on alkyl and perfluoroalkyl chain length. • The presence of the siloxane network increases the thermal conductivity of acrylic coatings. • The coating porosity increases with the increasing length of the acrylate monomer. • Short-chain siloxane-polyacrylic coatings on AA7075-T6 show excellent corrosion resistance in 5 wt% NaCl. • No degradation of coatings was detected by ToF-SIMS and GDOES upon immersion in chloride solution. Siloxane-polyacrylic coatings were synthesized from 3-(trimethoxysilyl)propyl methacrylate, different acrylate derivatives and tetraethyl orthosilicate. Derivatives of different lengths of alkyl and perfluoroalkyl chains were characterized in terms of kinetics of copolymerization during sol synthesis, and of the coatings composition, structure, wettability, thermal properties and porosity using real-time Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry, glow discharge optical emission spectroscopy and photothermal beam deflection spectrometry. The siloxane backbones are surrounded by the organic network identified by characteristic fragments. Coatings are homogeneous. The surface water contact angle is between 70° and 85° for the acrylic chains and 90° for the perfluoroalkyl chain. The coatings thermal conductivity is ca. 0.3 W/m⋅K. The porosity of the coatings increases with the length of the acrylate derivative. Long-term corrosion protection of the coatings deposited on aluminium alloy AA7075-T6 was analysed using electrochemical impedance spectroscopy in 5 wt% NaCl and salt spray chamber test. The coatings containing ethyl and butyl derivatives have superior corrosion resistance accompanied by low porosity compared to long-chain derivatives. A special emphasis was given to the possibility to follow the degradation of these sol–gel coatings upon immersion in chloride solution by surface analytical tools. [ABSTRACT FROM AUTHOR]