Good Thermal Insulation Performance Research Articles

SiC whiskers nucleated on rGO and its potential role in thermal conductivity and electronic insulation

SiC whisker (SiCw) anchoring on reduced graphene oxide (rGO) is a promising thermal conductive filler, which not only constructs the high-effective phonon transmission pathway but also resolves the agglomeration phenomenon of rGO. However, how to quantificationally anchor SiCw on rGO to build a phonon transmission pathway is incompletely understood. That is, the nucleation mechanism of SiCw requires a full investigation. Here, SiCw@rGO was synthesized by stacking bed method using rGO and rice husk ash as materials, in which SiCw is bridged on the rGO sheets through SiC crystal nucleus (C-Si covalent bonds). The experimental and density functional theoretical results reveal that the oxygen-containing defects (C-O groups) of rGO provide favorable sites for SiC nucleation and promote the yield of SiCw. Additionally, some specific defects of rGO induce the unpaired electrons of the surrounding carbon atoms, which is the prerequisite of the formation of C-Si covalent bonds. The construction of C-Si bonds between SiCw and rGO serves to enhance phonon accessibility, making SiCw@rGO composites achieve good thermal conductivity property and electrical insulation performance. The combination of experimental and theoretical research provides guides for the design of high-efficient thermal conductive materials.

Experimental Study on the Thermal Behavior of Exterior Coating Textures of Building in Hot and Arid Climates

The building envelope is the barrier between the interior and exterior environments. It has many important functions, including protecting the interior space from the climatic variations through its envelope materials and design elements, as well as reduction of energy consumption and improving indoor thermal comfort. Furthermore, exterior building sidings, in addition to their aesthetic appearance, can have useful textures for reducing solar gains and providing good thermal insulation performance. This research examined and evaluated the effect of external siding texture and geometry on energy performance. For this objective, a field in situ testing and investigation of surface temperature was carried out on four samples (test boxes) with different exterior textures and different orientations, under the climate zone of Constantine–Algeria during the summer period. The results indicated significant dependability between the exterior texture geometry, the percentage of shadow projected, and external surface temperature. The second part of the research involved a similar approach, exploring the effect of three types of particles with the same appearance but with different thermal characteristics. It was concluded that the natural plant aggregates “palm particles” had the best performance, which contributed to a significant reduction of external surface temperature reaching 4.3 °C, which meant decreasing the energy consumption.

Thermal insulation TiN aerogels prepared by a combined freeze-casting and carbothermal reduction-nitridation technique

With the rapid development of energy sources and aerospace engineering, high-performance thermal insulation materials with multiple functions are attracting more and more attentions. Non-oxide ceramic aerogels have application potential in thermal insulation under harsh conditions owing to their good thermal insulation performance and chemical stability. In this work, TiN aerogels were prepared by a combined freeze-casting and carbothermal reduction-nitridation method utilizing TiO2 and chitosan as raw materials, at 1473 K for 3 h, with a C/TiO2 molar ratio of 3/1. They showed a specific surface area of 167 m2/g and ultralow density of 0.07 g/cm3 (the relative density of 1.3 %). Their thermal conductivity value was only 0.166 ± 0.0054 W/(m K at 673 K (TiO2 solid content of 5 wt%). Moreover, the prepared aerogels possessed reasonably high mechanical strength and good high-temperature service performance, suggesting that they can be used under high-temperature conditions as an insulation material.

Study on Mechanical and Thermal Performance of Building Energy-saving Wall with Insulation Materials

Sodium alginate and natural fiber were used as modifiers to prepare sodium alginate natural fiber type biological composites. The mechanical properties were characterized by universal testing machine, and the thermal properties were analyzed by conductivity, The effects of wood fiber and straw fiber content on the comprehensive properties of biological composite materials were evaluated by relevant instruments, and the feasibility of biological composite materials as building energy-saving wall insulation materials was evaluated. The results show that the flexural strength, compressive strength and elastic modulus of the composites increase with the increase of wood fiber content. When the wood fiber content is 100%, the mechanical properties of the sample are the best, the flexural strength is 0.573 MPa, and the compressive strength is 1.410 MPa. The results showed that wood fiber and sodium alginate binder were closely combined and had good wettability. The thermal conductivity of biological composite is 0.078-0.089w / (m · K), which means it has good thermal insula tion performance and can be used as thermal insulation material for building energy-saving wall. The results show that the properties of the composite can be improved by adding a higher proportion of wood fiber and a certain amount of glyoxal crosslinking agent.

Effect of slightly cadmium-enriched kenaf straw on the mechanical and thermal properties of cement mortar

The purpose of this paper is to discuss the application of kenaf straw as a building material for phytoremediation of heavy metal-contaminated soil. The kenaf straw core (KSC) content, kenaf fibre content and KSC particle size were used as factors to study the effects of a slightly cadmium-enriched kenaf straw on the mechanical and thermal properties of cement mortar. XRD, thermogravimetry and SEM were also carried out to study the microstructure of the cement mortar. The safety and reliability of the slightly cadmium-enriched kenaf straw in the cement mortar was evaluated by a heavy metal leaching test. The results show that the compressive and flexural strengths of the cement mortar decreased with increasing KSC content, but the 28-day strength of the cement mortar with a maximum KSC content of 8% can still meet engineering requirements. In addition, the cement mortar demonstrated good thermal insulation performance, the thermal conductivity and dry density of the mortar were significantly reduced, and the bond strength and crack resistance of cement mortar were also improved. The cadmium enriched in kenaf straw did not affect the strength of cement mortar, and the leaching concentration of the heavy metal was far below the prescribed safety limit.

High-temperature flexible, strength and hydrophobic YSZ/SiO2 nanofibrous membranes with excellent thermal insulation

A yttria-stabilized zirconia mixed silica nanofibrous membrane (YSZ/SiO2 NFM) was fabricated by the electrospinning method. The well-aligned 3D membrane structure and the composite nanocrystalline-amorphous structure with fine zirconia grain and amorphous silica network, which greatly improved the mechanical properties of YSZ/SiO2 NFMs. The strength of the ceramic fibrous membrane after heat treatment at 1300℃ was reported for the first time, the tensile strength can reach 4.0 ± 0.7 MPa and the strain can reach 5.3 ± 1.1 %. The use temperature of YSZ NFMs was increased by nearly 300℃. The maximum strength was up to 5.9 ± 0.8 MPa, which is currently reported that the highest strength of oxide ceramic nanofibers at the same temperature. The YSZ/SiO2 NFMs after high temperature treatment not only had a good thermal insulation performance, but also had a hydrophobic performance. These attractive properties may provide new opportunities for flexible materials such as high-temperature insulation, fire insulation, and flexible electronics.

Preparation and properties of sulphoaluminate cement-based foamed concrete with high performance

The purpose of this paper is to prepare a foamed concrete with low thermal conductivity from the perspective of raw material selection. According to the results of literature survey, sulphoaluminate cement (SAC) is selected as the cementing material, and the mixture of aluminum nitrate and sodium bicarbonate is selected as the foaming agent. Subsequently, the related properties of the sulphoaluminate cement foamed concrete (SAC-FC) were evaluated. The results show that the SAC-FC not only possesses good thermal insulation performance, but also exhibits excellent mechanical and water-resistant properties. The compressive strength, thermal conductivity, water absorption and softening coefficient of the SAC-FC with 0.3 ~ 1.0 g/cm3 bulk density are 1.2 MPa ~ 15.2 MPa, 0.052 ~ 0.129 W/(m • K), 38.2% ~ 7.6% and 0.764 ~ 0.952, respectively. And the fluctuation ranges of the ratio of flexural strength to compressive strength and the ratio of tensile strength to compressive strength are 20% ~ 30% and 17.5% ~ 22.5%, respectively. In addition, the SAC-FC also presents the early strength characteristic and its 7-day strength is approximately 83% of the 28-day strength.

Multifunctional Coating with Both Thermal Insulation and Antibacterial Properties Applied to Nickel-Titanium Alloy.

BackgroundWith excellent shape memory and superelastic properties, shape memory alloy (SMA) is an ideal actuator, and it can form smart structure for different applications in medical field. However, SMA devices cause apparent thermal damage to the surrounding tissues when it works in vivo, making the application of smart structure that is composed of SMA actuator in vivo is greatly limited.MethodsIn this paper, coating (APA) with PLA as the main body to limit the heat conduction, a multifunctional Ag nanoparticles (AgNPs)/polylactic acid (PLA)/Al2O3 was synthesized. The Al2O3 layer was formed by micro-arc oxidation (MAO) and AgNPs were synthesized by silver nitrate and ethylene glycol. Scanning electron microscopy, transmission electron microscope, and Fourier transform infrared spectra were applied to analyze the morphology and characterization of APA coating. The antimicrobial activity, thermal insulation activity, and biocompatibility of APA coating were furtherly explored and verified through animal experiments and immunohistochemistry.ResultsWith different particle sizes and concentrations of AgNPs, APA multi-functional films were successfully prepared. The Al2O3 layer was closely combined with SMA and formed a porous surface, so the PLA and AgNPs layers can firmly adhere to SMA, thus reducing the release of nickel ions in SMA. AgNPs gave APA coating excellent antibacterial activity and effectively inhibited the growth of Staphylococcus aureus. In addition, coupled with the low thermal conductivity of PLA and Al2O3, AgNPs were tightly anchored on the surface of PLA, which has high infrared reflectivity, making the APA coating obtain good thermal insulation performance.ConclusionWe have successfully prepared the APA coating and obtained the optimum amount of AgNPs, which makes it have good thermal insulation performance, good antibacterial activity and good biocompatibility, which provides a new prospect for the application of SMA.

Preparation and Characterization of Furan-Matrix Composites Blended with Modified Hollow Glass Microsphere.

In this study, a new class of thermal insulation composites was prepared by blending a modified hollow glass microsphere (HGM) with furan resin. The particle dispersion between the microparticles and resin matrix was improved using 3-methacryloxypropyltrimethoxy silane (KH-570). Furthermore, the structure and morphology of the modified HGM were characterised by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). In addition, the effects of the modified HGM on the thermal insulation, flame retardancy, and thermal properties of the composites were investigated. The thermal conductivity of the composites was lower than that of the native furan resin. The minimum thermal conductivity of the composites was 0.0274 W/m·K; the flame retardancy of the composites improved, and the limiting oxygen index become a maximum of 31.6%, reaching the refractory material level. Furthermore, the thermal analysis of the composites demonstrated enhanced thermal stability. This study demonstrates that the composite material exhibited good thermal insulation performance and flame retardancy and that it can be applied in the field of thermal insulation.

Fire-resistance Rating of Square Steel Tubes and Concrete-filled Square Steel Tubular Columns Protected with Ultra-thin Fire-retardant Coating

To promote and criterionize the application of ultra-thin the fireproof coating s to building structures, four concrete-filled square steel tubular (CFSST) pillars as well as two square steel tubes, each protected along with ultra-thin the fireproof coating , were subjected to full-scale fire tests to investigate their fireproof level on the basis of the ISO 834 criterion time�degrees curve. Test results revealed not only the temperature variation characteristics of specimens suffered from inconsistent fire exposure, but also effects of the steel ratio of the test specimen and the number of fire-exposed sides on the fire-refractory level of the test specimen. Test results demonstrated that when protected with an ultra-thin the fireproof coating , the heating rate of the specimens was considerably lower than that of the test furnace, suggesting that the ultra-thin the fireproof coating exhibits good thermal insulation performance. The test results were compared with China�s current criterions for the fire-refractory level of square steel tubes and CFSST pillars, indicating that the criterions would lead to a relatively conservative fire-safe design for four-side fire exposure.

Preparation and Characterization of a Low Density and Low Pressure Sheet Molding Compound

Low Density and Low Pressure Sheet Molding Compounds (LD-LPMC) were prepared by using magnesium oxide paste and crystalline polyester as thickening system to reduce molding pressure and Hollow Glass Microspheres (HGM) as fillers to reduce the density. The molding pressure of LD-LPMC was investigated. The effects of HGM content (0%, 3.8%, 7.6%, 11.4%, 15.2%, 19.0%) on the density, flexural strength and thermal conductivity of LD-LPMC were studied. The results showed that 2-4Mpa was the best molding pressure for the composite materials. With the increase of HGM content, the density, flexural strength and thermal conductivity of LD-LPMC decreased. The thermal conductivity increased with the increase of temperature. When the molding pressure was 3Mpa and the content of the HGM was 7.6%, the density decreased by 13.6%, the flexural strength only decreased by 23.3% and the thermal conductivity (40°C) also decreased by 11.5%, which reflected the low density, high strength and good thermal insulation performance of LD-LPMC.

Lightweight multifunctional polypropylene/carbon nanotubes/carbon black nanocomposite foams with segregated structure, ultralow percolation threshold and enhanced electromagnetic interference shielding performance

Lightweight polypropylene (PP) composite materials are preferred to other polymer-matrix composites, in the conductive and electromagnetic interference (EMI) shielding industries, due to their pronounced advantages. However, facile and high-efficiency fabrication of low-density multifunctional PP composite foams, for EMI shielding, remains a challenge. In this study, we fabricated lightweight polypropylene (PP)/carbon nanotubes (CNTs)/carbon black (CB) nanocomposite foams by combining high-speed mechanical mixing, structural manipulation and solid-state supercritical carbon dioxide (ScCO2) foaming. Due to the “brick and mud” dense structure formed by high-speed mechanical mixing and structure manipulation, we obtained a low density (0.082–0.101 g/cm3) after solid-state ScCO2 foaming in the nanocomposite foams containing hybrid nanofiller (1:1). Specifically, segregated synergistic conductive networks were observed in the nanocomposite foams. With such networks, the nanocomposite foams containing hybrid nanofiller (1:1) exhibited the best electrical properties (~6.67 × 10−3 S/cm at 5 wt% hybrid filler), and the lowest percolation threshold (0.016 vol%) compared with other systems. Moreover, the nanocomposite foams containing 5 wt% hybrid nanofiller (1:1) showed enhanced specific EMI shielding effectiveness (~72.23 dB·cm3/g at X band), and absorption-dominated shielding characteristic. Furthermore, we found a good thermal insulation performance (61.2 mW·m−1·K−1) and compressive properties (~37.1 MPa·g−1·cm3 at 50% strain). Overall, our work provides a simple and versatile strategy for fabricating high-performance PP-based nanocomposite foams. These foams present lightweight, ultra-low percolation threshold, high strength, thermal insulation and good EMI shielding properties.

Porous architectures based on halloysite nanotubes as photothermal materials for efficient solar steam generation

Solar steam generation assisted by photothermal materials has attracted extensive attention due to its advantages of excellent evaporation rate and high photothermal conversion efficiency. In this work, we report a simple method by employment of halloysite (Hal) nanotubes (HNT) and graphene oxide (GO) as raw materials to produce efficient solar photothermal materials (named as GO-HNT). The as-prepared GO-HNT has rich porosity, excellent 90% light absorption and good thermal insulation performance (thermal conductivity 0.162 W m−1 K−1). Based on these characteristics, GO-HNT can be used as a promising solar receiver. Correspondingly, the solar energy conversion efficiency of the GO-HNT solar receiver was measured to be 83.67%, 77.17% and 77.05% respectively under 1 sun, 2 sun and 3 sun irradiations. As a 1D nanocrystalline clay mineral, HNT have great advantages of environmentally friendly, cost-efficient and commercial availability with abundant reserves. In combination with its simple and scalable manufacture method, this GO-HNT-based solar receiver may hold great potentials for a broad range of applications, such as seawater desalination, distillation, sterilization, sewage treatment, etc.

Preparation and properties of silicate inorganic exterior wall insulation based on thermal energy storage

The key to building energy conservation is how to make the exterior wall have good thermal insulation performance, reduce the heat loss of the building?s peripheral structure, develop new exterior wall insulation materials, and effectively achieve energy saving. In this paper, a new type of composite silicate insulation material was prepared by using fly ash, sepiolite fiber, basalt fiber, and cement as raw materials. According to the analysis of the action of each component of the composite silicate thermal insulation material, the composite silicate thermal insulation material is prepared by selecting different raw material ratios, and the fly ash and sepiolite fibers are analyzed by a thermal conductivity measuring instrument and a hydraulic universal testing machine. The influence of water-cement ratio on the thermal conductivity, tensile strength, and compressive strength of composite silicate insulation materials. Through research, it is found that this composite silicate exterior wall insulation material utilizes some abandoned resources to help the building exterior wall to store thermal energy. The preparation process is simple, the insulation performance is good, the mechanical strength is high, and there is great promotion value and application prospect.

Phenolic Resin Foam Composites Reinforced by Acetylated Poplar Fiber with High Mechanical Properties, Low Pulverization Ratio, and Good Thermal Insulation and Flame Retardant Performance.

Phenolic foam composites (PFs) are of substantial interest due to their uniform closed-cell structure, low thermal conductivity, and good thermal insulation performance. However, their disadvantages of a high pulverization rate and poor mechanical properties restrict their application in building exterior insulation. Therefore, the toughening of these composites is necessary. In this paper, poplar fiber was treated with an acetylation reagent, and the acetylated fiber was used to prepare modified phenolic foams (FTPFs); this successfully solved the phenomenon of the destruction of the foam structure due to the agglomeration of poplar fiber in the resin substrate. The foam composites were comprehensively evaluated via the characterization of their chemical structures, surface morphologies, mechanical properties, thermal conductivities, and flame retardant properties. It was found that the compressive strength and compressive modulus of FTPF-5% respectively increased by 28.5% and 37.9% as compared with those of PF. The pulverization ratio was reduced by 32.3%, and the thermal insulation performance and flame retardant performance (LOI) were improved. Compared with other toughening methods for phenolic foam composites, the phenolic foam composites modified with surface-compatibilized poplar fiber offer a novel strategy for the value-added utilization of woody fiber, and improve the toughness and industrial viability of phenolic foam.

Effects of alumina trihydrate (ATH) and organic montmorillonite (OMMT) on asphalt fume emission and flame retardancy properties of SBS-modified asphalt

The objective of this study was to evaluate the flame retardancy and emission properties of asphalt binders containing ATH and OMMT. Limit oxygen index test was performed to evaluate the flame retardancy of each asphalt binder. Volatile organic compound (VOC) emission properties of the asphalt mixture in the mixing process were investigated using a designed test method. Thermogravimetry and Fourier transform infrared spectroscopy were used to evaluate the thermal stability and volatile-release properties of the asphalt binders. The results indicated that both ATH and OMMT effectively suppress the VOC release of the modified asphalt. The flame retardancy and VOC-emission properties of the OMMT/ATH modified asphalt were significantly improved. The addition of ATH/OMMT delayed the thermal decomposition and exhibited good thermal-insulation performance, reducing the heat release during asphalt combustion. Additionally, The ATH/OMMT compounds prevented the breakage of molecular chains in the asphalt, promoting the charring of the asphalt during combustion. According to the engineering-property tests of modified asphalt mixtures, the ATH/OMMT significantly improved the high-temperature performance of the asphalt mixture. However, it slightly reduced the thermal-cracking resistance and moisture susceptibility of the asphalt mixture.

Development of a high-temperature inorganic synthetic foam with recycled fly-ash cenospheres for thermal insulation brick manufacturing

Abstract In this study, a novel inorganic synthetic solid foam composed of recycled fly-ash cenospheres (FACs) is developed with low-density, good thermal insulation performance, and reasonable mechanical strength. The manufacturing process utilizes low-fraction clay binder materials diluted in water, enabling a self-assembling mechanism assisted by natural capillary effect to form minimal contacts among the FACs. The microstructure and minimal contact formation were confirmed by optical and electron microscope imaging. Both thermal and mechanical properties of the fly-ash cenosphere synthetic solid foam (FAC-SSF) materials were experimentally studied as functions of key material parameters including cenosphere particle size and clay content. A numerical model was developed to predict the effective thermal conductivity of FAC-SSF using a three-step homogenization method which takes into account different thermal percolation paths within the material. The inorganic synthetic foam developed has the potential for thermal insulation applications taking advantage of their relatively simple, low-cost, and scalable manufacturing process, minimal use of binder materials, and relatively high mechanical strength and highly tailorable properties.

Effect of Lanthanum Zirconate on High Temperature Resistance of Thermal Barrier Coatings

Thermal barrier coatings (TBCs) typically have low thermal conductivity and high resistance to oxidation at elevated temperatures. TBCs are used to protect the turbine blades of aircraft engines operating at high temperature. The commonly used YSZ (8 wt% Y2O3-stabilized ZrO2) cannot function at temperatures higher than 1200°C for an extended period of time, which hinders the necessary improvement in the aircraft thrust-to-weight ratio. In this work, thermal barrier coatings consisting of a YSZ ceramic layer and of a lanthanum zirconate (LZ) + YSZ composite structure were prepared on a nickel-based high-temperature substrate using atmospheric plasma spraying. Thermal insulation properties and high temperature oxidation performance of TBCs with single layer structure and double layer structure were compared. The growth mechanism and influencing factors of high-temperature oxidation of thermally grown oxide (TGO) were discussed. The results showed that the LZ had good thermal insulation performance and oxygen isolation compared to the YSZ layer. This performance effectively reduces the growth of TGO in TBCs, thereby delaying the coating failure.

Preparation and performance of electromagnetic wave absorbing foamed ceramics with high closed porosity and gradient SiC distribution

Electromagnetic wave absorbing foamed ceramics (FCs) with high closed porosity and gradient SiC distribution were prepared from the powder blend containing quartz, talc, CaCO3, Si3N4 and SiC by sintering at 1200 °C for 1 h in air. The retention in the temperature holding process of the continuous and gradual SiC distribution arising from the inward oxidation of SiC in the temperature rising process is the formation mechanism of the gradient SiC distribution in FCs. As to the FC prepared from the powder blend with 3 wt% of SiC, it shows the best comprehensive performance with low bulk density of 0.48 g/cm3 and relatively high compressive strength of 9.6 MPa, good thermal insulation performance for its high total porosity of 82%, good water resistance performance for its high closed porosity of 80%, and excellent electromagnetic wave absorption performance for its low mean reflectivity of −11.9 dB in the frequency range of 8.0–18.0 GHz and especially low minimum reflectivity of −14.2 dB at 12.7 GHz. More importantly, it is also an excellent high temperature electromagnetic wave absorbing material for its little increased mean reflectivity of −11.3 dB after heat treating at 1000 °C for 20 h in air.

Effect of the thermal insulation wall under the air-conditioning intermittent operation

With the increasing energy consumption, the status of building energy conservation is paid more and more attention. So how to reduce the energy consumption of envelope becomes a hot spot. Self-insulation wall behaves greatly in energy saving, and this paper proposes a self-insulation wall which is filled Expanding Polystyrene(EPS) into the cavities of the sintered shale bricks with different ration. Besides, the condition of intermittent operation of air conditioner in winter is simulated. The results showed that temperature of the wall increased significantly after filling the EPS, and the wall had a good thermal insulation performance. The thermal insulation wall with 50% EPS is recommended, no matter from the aspect of the economy or of thermal physics. Moreover, intermittent operation which is 1 hour interval and 1 hour working was the idealist mode, because the wall performed the best capacity of insulation under this condition.