Thermal Insulation Performance Research Articles

First-principles characterization of thermal conductivity in LaPO4 -based alloys

Alloys based on lanthanum phosphate (LaPO4) are often employed as thermal barrier coatings, due to their low thermal conductivity and structural stability over a wide temperature range. To enhance the thermal-insulation performance of these alloys, it is essential to comprehensively understand the fundamental physics governing their heat conduction. Here, we employ the Wigner formulation of thermal transport in conjunction with first-principles calculations to elucidate how the interplay between anharmonicity and compositional disorder determines the thermal properties of La1−xGdxPO4 alloys, and discuss the fundamental physics underlying the emergence and coexistence of particlelike and wavelike heat-transport mechanisms. We also show how the Wigner transport equation correctly describes the thermodynamic limit of a compositionally disordered crystal, while the Boltzmann transport equation does not. Our predictions for microscopic vibrational properties (temperature-dependent Raman spectrum) and for macroscopic thermal conductivity are validated against experiments. Finally, we leverage these findings to devise strategies to optimize the performance of thermal barrier coatings. Published by the American Physical Society 2024

Study on preparation and thermal insulation properties of curing foam

The thermal insulation performance of curing foam is a critical factor affecting fire extinguishing efficiency. In this study, sodium dodecyl sulfate was used as the foaming agent, and then combined with foam stabilizers, foam thickeners and inorganic powders to prepare the curing foam extinguishing agents. The result demonstrated that the addition of PEG and Xanthan gum could prolonge the 50 % drainage time of foam solution to 1.98 times compared with the foam solution without foam additives. The composite powders imparts an excellent thermal insulation and high-temperature stability to curing foam, especially the mass fractionratio of loess to cement equals to 4:6 and the water cement ratio is 0.7. Moreover, the thermal insulation tests showed that when the test temperature equalled 500 °C, the curing foam could reduce the temperature of the covered surface by 234.2 °C. Compared with the water-based foam, the thermal insulation performance was improved by 58.1 %. Finally, fire extinguishing test showed that the fire extinguishing time of curing foam is 0.47 s and 33.99 s shorter than that of water-based foam and water, respectively. The consumption of water-based foam and water fire extinguishing consumption is 1.46 times and 4.37 times that of curing foam, respectively. The excellent structural stability is due to the addition of Xanthan gum and PEG additives, which provide a more uniform distribution of bubbles and denser pores. At the same time, the mixture of loess and cement acts as a skeleton in curing foam thereby improving the stability of the integral structure and further preventing the heat transfer.

Designing a Microstructure of NiCo-LDH@CNTs@Carbon Foam for Efficient Electromagnetic Wave Absorption and Excellent Environmental Tolerance.

The constantly evolving environment imposes increasingly stringent demands on the mechanical qualities of materials employed for absorbing electromagnetic waves (EMWs). Therefore, there is an urgent need for advanced materials capable of efficiently absorbing EMWs and withstanding harsh electromagnetic conditions. In this study, the electrodeposition method was effectively used to synthesize nickel-cobalt layered double hydroxides (NiCo-LDHs) in a controlled manner on a composite structure of carbon nanotubes and carbon foam, creating an exquisite construction. The manipulation of the electrodeposition time facilitated the regulation of the density of the layered structure within the composite material, thereby significantly enhancing its polarization relaxation performance. Increased defect sites and interface polarization enhance impedance matching and the attenuation constant, resulting in greatly improved absorption performance. The optimized sample demonstrated exceptional wave-absorbing performance in comparative experimental analysis, attaining a maximum reflection loss of -58.18 dB. It also has an effective absorption bandwidth of 5.36 GHz at a wavelength of 2.28 mm. The exceptional isolation effect of LDH, coupled with the outstanding insulation ability of the porous carbon skeleton, confers remarkable corrosion resistance and thermal insulation performance on the composite material. Hence, this discovery offers novel insights into designing environmentally tolerant absorbent materials.

Fabrication of low conductivity and high strength MgO-MgAl2O4 aggregates with sub-micron pore structure

Lightweight MgO-MgAl2O4 refractory aggregates were fabricated by using fine MgO and spherical Al(OH)3 powders as starting materials. The evolutions of microstructure and pores and their effects on the properties of the specimens were investigated. During heating process, MgO crystallites diffused into the formed Al2O3 pseudomorph, producing sub-micron intra-particle pores in both MgAl2O4 cores and MgO matrix. Besides, larger inter-particle pores between the MgAl2O4 cores and MgO matrix were occurred, attributing to the Kirkendall effect resulting from in-situ spinalization. As MgO content increased from 50 wt% to 80 wt%, due to reduction of the number of the porous MgAl2O4 cores, the inter-particle pores caused by Kirkendall effect decreased sharply in both number and size, while no obvious changes occurred in the intra-particle pores as the porous MgO matrix amount increased simultaneously. The decrease of large inter-particle pores caused obvious improvement in strength but slight increase in thermal conductivity. With a further increase of MgO to 90 wt%, as the number of the porous MgAl2O4 cores reduced further and the MgO matrix densification improved obviously, intra-particle pores and thermal insulation performance reduced significantly. The specimen with 80 wt% MgO showed the best performance, with a median pore diameter of 0.26 μm, apparent porosity of 36.0 %, flexural strength of 23.9 MPa, and thermal conductivity of 2.1 W/(m·K) at 500 °C.

From Mg(OH)2 to lightweight closed-pore MgO refractory aggregates: The role of NiO additive

MgO refractory aggregates with high closed porosity were prepared using light-burned MgO and Mg(OH)2 with adding NiO additive. The evolutions of microstructure and pores and their effects on the properties were investigated. The introduction of NiO effectively enhanced growth of MgO grains and transformation of large open pores into small closed ones, attributing to the lattice distortion caused by MgxNi1-xO solid solution formation. Due to the occurrence of more closed pores and lattice distortion, thermal insulation performance was improved significantly. Moreover, the formed circular closed pores and MgxNi1-xO could absorb thermal stress, lower thermal expansion coefficient and induce crack deflection, thus effectively enhancing thermal shock resistance. The specimen with 4.0 wt% NiO showed the best performance, with a median pore diameter of 5.69 μm, closed/apparent porosity of 9.4 %/3.6 %, thermal conductivity of 9.9 W/(m·K) (500 °C), flexural strength of 68.5 MPa, and residual flexural strength of 10.8 MPa after thermal shock.

The electrically controlled dimming film of thiol-vinyl ether system with low-voltage and high contrast ratio for smart windows

As a type of smart window, polymer dispersed liquid crystal (PDLC) electrically controlled dimming film can respond to external electrical stimuli to regulate the optical flux of sunlight, reducing energy consumption. Herein, a PDLC film was prepared by systematically studying the functionalities and structural compatibility of vinyl ether and thiol compounds, and the optimal PDLC film possesses a superior contrast ratio (CR) of 196.9. When the film thickness is adjusted to 8 μm, the film saturation voltage is reduced to 6.7 V, still maintaining a high CR of 48.4. The well-designed PDLC films exhibited excellent modulation of light. The temperature difference between PDLC film and bare ITO glass can reach 4 °C under the simulated sunlight test, demonstrating the good thermal insulation performance. This smart films with low power consumption and high CR can meet the demand for active regulation of optical flux on smart windows.

Optimizing sustainable construction: enhancing thermal insulation performance and energy savings with surface-modified cellulose nanofiber aerogels

Optimizing sustainable construction: enhancing thermal insulation performance and energy savings with surface-modified cellulose nanofiber aerogels

A novel phosphogypsum based self-produced gas expansion slurry for preventing coal spontaneous combustion

In order to solve the coal spontaneous combustion disaster in the upper layer goaf during the slicing mining process, a slurry that can expand by self-produced gas was developed using phosphogypsum and sodium bicarbonate as raw materials. The effect of different factors on the performance of phosphogypsum based self-produced gas expansion slurry (PSES) was analyzed. The optimal ratio and conditions of PSES were determined through orthogonal experiments. The thermal insulation performance and cooling and fire extinguishing performance of PSES were studied. Finally, it was applied in Luwa coal mine in Shandong province. The research results indicated that the optimal experimental conditions and ratios for PSES were phosphogypsum content of 56 wt%, sodium bicarbonate content of 21 wt%, water temperature of 25 ℃, and mixing time of 65 s. Under these conditions, the expansion performance of the slurry was good, and the setting time and compressive strength can meet the requirements for sealing the coal and rock cracks in the goaf. Under the same heat source, the thicker the slurry, the better its thermal insulation effect. Under the same thickness, the higher the heat source temperature, the shorter the effective insulation time(EIT). After the slurry was injected into the cracks of the broken coal, it wrapped around the broken coal from bottom to top. The temperatures of A-layer, B-layer, and C-layer of the coal pile decreased in sequence. After half an hour of grouting, the temperatures at all points dropped below 50 ℃ without any reignition phenomenon. After injecting PSES into the coal spontaneous combustion dangerous area in the upper layer goaf, the concentrations of CO and O2 in the monitoring borehole decreased to a safe range, and the generated CO2 concentration finally stabilized at around 4.6 %. It showed that PSES can seal the coal and rock cracks in the goaf, suppress the coal spontaneous combustion, and guarantee the lower layer working face can be mined.

Polyvinyl alcohol/boron nitride aerogels for radiative cooling

AbstractDaytime radiative cooling material provides a low‐energy way of cooling because it can reflect sunlight and radiate heat without consuming any energy. However, there are still great difficulties in manufacturing low‐cost, high‐efficiency, sustainable, and biodegradable daytime radiative cooling materials. In this paper, poly (vinyl alcohol)/boron nitride (PVA/BN) composite aerogels were prepared by freeze‐drying technology. By adjusting the PVA concentration and BN content, the aerogel can achieve high sunlight reflectivity (96%), high mid‐infrared emissivity (96%) and good thermal insulation performance. Therefore, the temperature of the aerogel can be reduced to 12.5°C lower than the ambient temperature at night, and 5.5°C lower than the ambient temperature under the direct sunlight of 900 W/m2. This aerogel opens an environmentally sustainable pathway for radiative cooling applications.

Heat transfer inhibition of corundum–mullite insulation tiles through composition regulation

AbstractThe increase in size and efficiency of gas turbines leads to higher temperature in the combustion chamber, putting greater demands on the performance of the thermal insulation tiles. Corundum–mullite has been used because of its high‐temperature resistance, thermal shock resistance, and low thermal conductivity. However, how to inhibit heat transfer through composition regulation while ensuring the safe use of high‐temperature insulation tiles is the key to improving the heat conversion efficiency of gas turbines. In this study, thermal insulation tiles were prepared by casting molding. On the basis of determining the optimal corundum/mullite ratio (22:45 wt%) in the aggregate, the thermal conductivity of the sample was reduced by adding MgO (2 wt%). The results show that phonon intrinsic and defect scattering, caused by changes in phase composition, effectively reduce the thermal conductivity of the insulation tile sample to 2.05 W·m−1·K−1, which is 34.71 % lower than the maximum value before regulation. During 30 cycles of thermal shock (air‐cooling at 1000°C), the residual strength gradually decreased and tended to be stable, with a minimum of 8.6 MPa, indicating that the thermal insulation tile can provide better thermal insulation without affecting the safety of gas turbines, providing new ideas and methods for improving the thermal insulation performance of high‐temperature thermal insulation materials.

Heat insulation and thermal insulation method of passive low energy consumption residential building exterior envelope structure based on BIM

With the improvement of economic level, a continuous rise in building energy consumption brings about serious environmental problems. Therefore, this study proposes a passive energy-consuming residential building envelope thermal insulation and heat preservation method based on building information modeling technology for building energy consumption increasing and envelope structure's performance improving. Firstly, it is a study on the passive low-energy residential building envelope's thermal insulation materials and architecture, and secondly, it is a study on the improvement of the thermal insulation and heat preservation performance of the passive low-energy residential building envelope on the foundation of building information modeling. These experimental results show that in the residential building, the indoor temperature averages around 27.8 °C, of which the highest indoor ambient temperature is found at 21 o'clock, with a temperature value of 28.4 °C, which reduces 2.1 °C when comparing with the indoor temperature under the traditional residential building. Under the exterior wall construction utilizing this technology, the temperature change of the indoor environment is smoother, which satisfies people's requirements for the indoor living environment. At the same time, the area parameters of the ventilation area of the building and the area of the envelope obtained after the analysis of BIM technology have a significant effect on the cooling of the interior. This method reduces the use of resources and lays a good foundation for the further development of building informatization, which is significant in realizing the informatization developing in construction.

Composite silica aerogel based on HNTs-modified APP with enhanced thermal insulation and flame retardancy performance for organosilicon resin

Efficient thermal insulation and flame-retardant materials are crucial in reducing energy consumption and minimizing fire hazards. This work presents a novel method for preparing a composite aerogel: a silane coupling agent was used as a chemical bridge to synthesize a new flame retardant AKH (modified APP with HNTs). AKH was incorporated into the silica sol to fabricate the SA-AKH composite aerogel. SA-AKH features a dense three-dimensional network skeletal structure, excellent thermal stability, and a high specific surface area. When integrated into organosilicon resin, SA-AKH significantly enhances the flame resistance of composite materials. During cone calorimetry testing (CCT), SSAKH4 exhibited a peak heat release rate (PHRR) of 281.88 kW/m2 and total smoke production (TSP) of 5.52 m2, representing a decrease of 30.8 % and 4.5 %, respectively, compared to SSA4. The composite material, derived from the unique mesoporous structure of aerogel combined with the flame retardant and hollow characterization of AKH, demonstrates exceptional flame retardancy and smoke suppression. SA-AKH is expected to make novel advancements in the field of high-efficiency insulation and flame-resistant composites.

Green building material with superior thermal insulation and energy storage properties fabricated by Paraffin and foam cement composite

In the field of architecture and construction, foam cement has been gradually gaining popularity due to its outstanding attributes of reduced weight, carbon footprint, and potential thermal insulation effects. However, relying solely on the thermal insulation provided by the foam in foam cement lacks the capability to store and release heat. In this paper, a novel approach is proposed by directly incorporating paraffin into foam cement with non-continuous pores, creating a phase change foam cement. The addition of paraffin to foam cement, facilitated by the presence of surfactants in foam, allows the paraffin to disperse. In contrast, if paraffin is directly added to cement without the foam, it tends to aggregate. The internal pore structure, thermal performance, phase change temperature, and relaxation distributions were investigated through equipment such as scanning electron microscope (SEM), thermal conductivity meter, differential scanning calorimetry (DSC), and H1 nuclear magnetic resonance (NMR). Results indicate that paraffin/foam cement plays a dual function, effectively storing and releasing energy, significantly enhancing its thermal insulation performance. Particularly, the incorporation of 10 vol% paraffin content results in a notable 21.8 % reduction in the thermal conductivity, for foam cement with a density of 600 kg/m3. This is attributed to the heat storage capability of the phase-change paraffin, which absorbs heat as the surrounding temperature rises, synergistically collaborating with the foam. This presents a novel perspective for the development of green and energy-efficient building materials, contributing to the realization of sustainable energy utilization in the construction industry.

Synergistic design of C/SiC@SiC aerogel for enhanced thermal insulation and electromagnetic wave absorption

High-performance SiC aerogels are sought after for their superior thermal insulation and absorption properties, especially in applications such as electromagnetic stealth for aero engines and high-temperature radar stealth. However, achieving SiC aerogel with both temperature resistance and strong wave absorption while controlling their properties remains a significant challenge. This study investigates the influence of reactant concentrations on the structure, thermal insulation, and absorption performance of SiC aerogels synthesized via the sol-gel method. The aerogel synthesized with a n(C):n(Si) ratio of 1:2 showed superior thermal insulation. Additionally, it showed excellent electromagnetic wave absorption, with a minimum reflection loss of −53.80 dB at 6.16 GHz and a maximum effective absorption bandwidth of 3.10 GHz at a thickness of 2.40 mm. Furthermore, the maximum compressive strength of C/SiC@SiC reached 0.98 MPa, a notable improvement of 81.48 % compared to the pristine C/SiC matrix. The maximum effective absorption bandwidth of C/SiC@SiC was increased to 6.06 GHz at 2.35 mm, and the surface center temperature decreased from 183.1 °C for C/SiC to 130.1 °C for C/SiC@SiC. Overall, this study offers valuable insights into the development of advanced absorption and thermal insulation materials, providing a foundation for further research and innovation in this field.

Metal-organic framework incorporated polybenzimidazole aerogel fibers with dual protections for thermal hazards and chemical warfare agents

Aerogel fibers possess the flexibility of fiber materials and the high porosity and low thermal conductivity of aerogel materials, which hold great promising for applications in thermal insulation and personal protection. However, the inferior mechanical performance and the lack of functionality have impeded the wider applications of these fascinating materials. Herein, we report a novel kind of MOF/polybenzimidazole composite aerogel fibers (CAFs) with both physical and chemical protection functions. The CAFs are fabricated by an oxidation induced sol–gel transition spinning method that utilized the transition of labile imidazole/Co2+ coordination bonds to stable imidazole/Co3+ coordination bonds upon oxidation. The incorporation of MOF has obviously improved the strength and ductility of CAFs due to the good interfacial interactions with matrix and increased crosslinking among polymer chains. The CAFs maintain the high thermal stability and flame retardancy of polybenzimidazole matrix, while the increased porosity and surface area with the addition of MOF have lowered the thermal conductivity and improved the thermal insulation performance of CAFs. The uniform porous skeleton also facilitates the access of chemical warfare agents (CWAs) to MOF inside the fiber. The catalytic experiments show that the CAFs have better degradation effect on CWAs than pure MOF powder, dense composite fiber, and MOF coated fiber. This work is expected to provide an efficient strategy for strong and multifunctional aerogel fibers.

Enhanced Fire Safety of Energy-Saving Foam by Self-Cleavage CO2 Pre-Combustion and Phosphorus Release Post-Combustion.

Rigid polyurethane foam (RPUF) is widely utilized in construction and rail transportation due to its lightweight properties and low thermal conductivity, contributing to energy conservation and emission reduction. However, the inherent flammability of RPUF presents significant challenges. Delaying the time to ignition and preventing flame spread post-combustion is crucial for ensuring sufficient evacuation time in the event of a fire. Based on this principle, this study explores the efficacy of using potassium salts as a catalyst to promote the self-cleavage of RPUF, generating substantial amounts of CO2, thereby reducing the local oxygen concentration and delaying ignition. Additionally, the inclusion of a reactive flame retardant (DFD) facilitates the release of phosphorus-oxygen free radicals during combustion, disrupting the combustion chain reaction and thus mitigating flame propagation. Moreover, potassium salt-induced catalytic carbonization and phosphorus derivative cross-linking enhance the condensed phase flame retardancy. Consequently, the combined application of potassium salts and DFD increases the limiting oxygen index (LOI) and reduces both peak heat release rate (PHRR) and total heat release (THR). Importantly, the incorporation of these additives does not compromise the compressive strength or thermal insulation performance of RPUF. This integrated approach offers a new and effective strategy for the development of flame retardant RPUF.

Investigation of double-PCM based PV composite wall for power-generation and building insulation: Thermal characteristics and energy consumption prediction

The integration of phase change material (PCM) with building-integrated photovoltaic (BIPV) presents a compelling approach to enhance solar energy utilization and mitigate indoor thermal loads, contributing to energy-efficient and low-carbon building development. Traditional BIPV-PCM structures, however, struggle to balance PV efficiency and thermal insulation, particularly with varying PCM wall positions. To address this situation, this study introduces a novel double-PCM BIPV composite envelope (BIPV-dPCM). An experimentally validated dynamic heat transfer model was developed and used to perform a comparative simulation analysis with three reference systems to quantify the energy-saving potential of the BIPV-dPCM, focusing on PV output and wall insulation effectiveness metrics. Further dimensionless parametric analysis were carried out to investigate the systematic performance of the two PCMs at different relativities. In addition, the coupled working mechanism of the BIPV-dPCM system concerning the power generation performance and thermal insulation performance under transient variations is explored. It was found that the BIPV-dPCM showcases superior thermoelectric coupling performance compared to three alternative enclosures. Incorporating two PCMs significantly enhances electrical exergy efficiency by 11.66 % and thermal exergy efficiency by 1.54 %, surpassing other reference systems. The increase in PCM latent heat ratio has a limited effect on performance gain. Notably, as the PCM thickness ratio exceeds 1, the decline in P value decelerates, for every 0.5 increment in the g, the P value diminishes by merely 0.2 %. The ideal h is identified between 1 and 1.5, with 1.5 being optimal for energy conservation objectives. Additionally, the self-sufficiency coefficient (SSC) of the BIPV-dPCM remains robust, sustaining a range of 55 % to 65 % over prolonged periods. This study offers novel perspectives and serves as a design reference for optimizing building energy systems and enhancing cooling efficiencies in subtropical climates.

Ultrathin aerogel-structured micro/nanofiber metafabric via dual air-gelation synthesis for self-sustainable heating

Incorporating passive heating structures into personal thermal management technologies could effectively mitigate the escalating energy crisis. However, current passive heating materials struggle to balance thickness and insulating capability, resulting in compromised comfort, space efficiency, and limited thermoregulatory performance. Here, a dual air-gelation strategy, is developed to directly synthesize ultrathin and self-sustainable heating metafabric with 3D dual-network structure during electrospinning. Controlling the interactions among polymer, solvent, and water enables the microphase separation of charged jets, while adjusting the distribution of carbon black nanoparticles within charged fluids to form fibrous networks composed of interlaced aerogel micro/nanofibers with heat storage capabilities. With a low thickness of 0.18 mm, the integrated metafabric exhibits exceptional thermal insulation performance (15.8 mW m−1K−1), superhydrophobicity, enhanced mechanical properties, and high breathability while maintaining self-sustainable radiative heating ability (long-lasting warming of 8.8 °C). This strategy provides rich possibilities to develop advanced fibrous materials for smart textiles and thermal management.

Effects of NIR-reflective pigments on waterborne polyurethane coatings and their thermal insulation performance

Waterborne coatings have garnered much attention and gradually occupied the coating market recently due to the significant advantages in volatile organic compound emissions compared with solvent-borne coatings. Waterborne polyurethane coatings are a majority portion of waterborne coatings. Unlike solvent-borne coatings, the film formation of waterborne coatings occurs in an inhomogeneous phase, which brings a challenge for pigmentation in waterborne coatings. However, the influence of pigment on film formation and the property of waterborne polyurethane coating remain unclear. In this study, the different contents of commercial black near-infrared (NIR) reflective pigments were incorporated into both commercial and synthetic waterborne polyurethane systems. The film formation process was monitored by multispeckle diffusing wave spectroscopy. The impact of the pigment content on dry films was assessed through scanning electron microscope, color and gloss measurements, dynamical thermal analyzer, and tensile testing. Furthermore, the thermal insulation performance of the waterborne polyurethane coatings was evaluated to study the function of the NIR reflective pigments. Our findings reveal that the addition of black NIR reflective pigments yields a multifaceted effect on film formation and coating morphology and improves thermal insulating property. Elevated pigment content correlated with increased crosslinking density, tensile stress, and Young's modulus.

Betulin Enables Multifunctional Cellulose-Based Insulative Foams with Low Environmental Impacts.

The significance of synthetic foams as insulative materials stems from their mechanical and water resistance as well as their cost-effectiveness. Broadly, the design of building envelopes should also consider fire and mold resistance and the impacts on the environment (end of life and compostability). This study addresses these issues considering the ever-increasing demand for sustainable sources to develop highly porous insulative materials. We introduce a versatile strategy based on wet-foam laying of cellulosic fibers that leads to hierarchical structures whose performance is tailored by the surface incorporation of betulin (BT), a bioactive molecule extracted from tree bark, combined with poly(dimethylsiloxane) (PDMS) after installation of urethane linkages. As such, we introduce an eco-friendly alternative to traditional polyurethane foams with competitive mechanical and thermal insulation performance. The modification of the fiber foams at low BT loading simultaneously endows superhydrophobicity (water contact angle >150°), fire retardancy (self-extinguish within 10 s), microbial resistance, and durability (no degradation in soil conditions after 3 months). BT plays a critical role as an antimicrobial and hydrophobic agent that synergizes with PDMS to achieve fire resistance. The life cycle assessment of the BT-modified foams reveals a significant reduction in greenhouse gas emission and human toxicity compared with rigid polyurethane foams by 96 and 92%, respectively. Overall, the valorization of the bark-derived BT is demonstrated by considering the scalability and cost-effectiveness of solid foams designed to substitute petroleum-derived counterparts.