Good Thermal Conductivity Research Articles

The effects of substitution of yttrium for Ce-rich mischmetal on the mechanical properties and thermal conductivity of Mg–4Al–4Zn–4RE alloy

Mechanical properties and thermal conductivity are the key parameters for Mg alloys used as the structural components for heat dissipation, balancing good mechanical properties and high thermal conductivity is still a long-term challenge. Here, we investigated the influence of Y contents on the microstructure and mechanical properties of the as-cast Mg–4Al–4Zn–(4–x)RE–xY (x: 0, 1, 2, 3, 4 wt%), where RE was the Ce-rich misch metal. Compared with Mg–4Al–4Zn–4RE alloy, the strength and ductility were significantly enhanced due to the well-optimized microstructure by the suitable substitution of Y for Ce-rich RE. Especially, the ultimate tensile strength and elongation were significantly improved from 201 MPa to 244 MPa and 8.0% to 16.8%, respectively, when the Y content was increased from 0 to 3.0 wt%. Meanwhile, the thermal conductivity still kept a high level within the range of 84.2–89.6 W(m·K)−1. The significantly improved elongation was mainly attributed to the reduction and refinement of coarse lamellar Al11RE3 intermetallic phases with increasing Y contents. The as-cast Mg–4Al–4Zn–1RE–3Y alloy exhibited high performance with a combination of high tensile properties and good thermal conductivity.

Sustained-release of essential oils by polyvinyl alcohol-based nanofibers

Flavored cigarettes are very popular among consumers. However, many essential oils in cigarettes are lost during storage, and the utilization rate of the essential oils during use is low. Therefore, effective packaging and stable sustained release are urgently needed. In this study, a composite electrospun stable nanofiber storage material was prepared for sustained release. Polyethylene glycol, which has good heat storage properties, was selected as the heat storage material to inhibit the release of essential materials during storage. Porous graphene with good thermal conductivity and a porous structure was selected as the heat conductive component to ensure rapid and uniform release. Polyethylene glycol/porous graphene polyvinyl alcohol-mint essential oil sustained-release composite electrospun nanofibers membrane was prepared by electrospinning, and the morphology, composition, thermal properties, and sustained-release properties were tested. The results showed that the composite electrospun nanofiber membrane reduced the loss of mint oil during storage and enabled the rapid release of mint oil at high temperatures. At room temperature, the retention rate of the mint oil was still more than 90% after 120 h, and at a high temperature (75°C) the retention rate was less than 20% after 10 min; that is, 80% of the essential oil material was released within 10 min.

Vertically aligned and conformal BN-coated carbon fiber to achieve enhanced thermal conductivity and electrical insulation of a thermal interface material

Due to excellent thermal conductivity, high aspect ratio, and low density, mesophase pitch-based carbon fibers (MPCFs) are highly desired in electronic packaging. However, their thermal conductivity is hard to present in the polymer matrix because of the disordered stacking and low filling. Moreover, few researches are focused on the enhancement of the electrical insulation performance for MPCFs. Herein, we report vertically aligned and insulating boron nitride (BN) coated carbon fiber (CF) powders as significant fillers for polymer composites, endowing markedly improved thermal conductivity and electrical insulation. The high-quality BN coating layer on the surface of the CF is produced by a cooling precipitation method and high-temperature treatment with ingenious use of solubility properties, exhibiting a conformal, dense, and highly crystalline structure. This preparation method overcomes the limitations of coating thickness and particle agglomeration, resulting in a 31-fold enhancement of the electrical resistivity of the CF powders. After orientation treatment in a silicone rubber matrix, such CF@BN-filled pads exhibit good thermal conductivity, significantly improved insulation performance, and excellent mechanical properties. Among them, the optimized pad achieves a thermal conductivity of 12.06 W m−1 K−1, a volume resistivity of 50 × 108 Ω cm and a breakdown voltage of 3100 V mm−1, exceptional flexibility, and a favorable compression ratio (@45 psi) of 41.7 %. This work provides unique insights into constructing carbon fiber fillers as well as the preparation of high thermal conductivity composites, thereby expanding the application scenarios of carbon fiber powder in electronic packaging.

Adsorption Structures, Vibrational Raman Spectra and Chemical Binding Properties of Thioglycolic Acid on Cu(111) Surfaces: A DFT Study.

Copper is widely used in everyday life and industrial production because of its good electrical and thermal conductivity. To overcome copper oxidation and maintain its good physical properties, small organic molecules adsorbed on the surface of copper make a passivated layer to further avoid copper corrosion. In this work, we have investigated thioglycolic acid (TGA, another name is mercaptoacetic acid) adsorbed on copper surfaces by using density functional theory (DFT) calculations and a periodical slab model. We first get five stable adsorption structures, and the binding interaction between TGA and Cu(111) surfaces by using density of states (DOS), indicating that the most stable configuration adopts a triple-end binding model. Then, we analyze the vibrational Raman spectra of TGA adsorbed on the Cu(111) surface and make vibrational assignments according to the vibrational vectors. Finally, we explore the temperature effect of the thermodynamically Gibbs free energy of TGA on the Cu(111) surface and the antioxidant ability of the small organic molecular layer of copper oxidation on the copper surface. Our calculated results further provide evidences to interpret the stability of adsorption structures and antioxidant properties of copper.

Development of hBN/natural fibres reinforced polymer composites using grey relation grade analysis for thermal and electrical applications

The objective of this work is to enhance the thermal conductivity and electrical properties of polymer hybrid composites through a systematic novel grey relation grade analysis (GRGA) optimization approach. This involves reinforcing the hybrid composites with hexagonal boron nitride (hBN) and various kinds of natural fibers or fillers. The development of a unique technology to produce multiphase composites using 2% of natural fibers or fillers such as coir fiber, rice husk filler, wood filler (WF), banana fiber (BF) and sugarcane fiber along with hBN (1, 3, 5 wt.%) particulates as reinforcements in epoxy matrix. The Taguchi L15 matrix array is utilized to fabricate interlaced composite samples via hand layup molding. Ultrasonic waves are used to ensure the uniform distribution of hBN filler into the matrix. Analysis of variance and GRGA reveal the significant results. It shows that the multiphase hybrid composites exhibit good thermal conductivity when higher content of hBN (5 wt.%) particulate for all the micro particulate polymer (MPP) composites. Multi-response optimization shows that the micro BF (2 wt.%) interlaces with hBN (5 wt.%) composite exhibits the higher thermal conductivity and electrical resistance compared to all other natural fiber interlaced composites. The aforementioned MPP composite has thermal conductivity of 1.03 W (m·K)−1 and electrical resistance of 279.88 Giga Ohms. Besides, the WF interlaced hBN (5 wt.%) composite shows the minimum dielectric constant compared to all other natural fiber composites. This desirable result is caused by the proper dispersion of hBN with the matrix which encourages interlocking with the fiber and the matrix. Maximum electrical resistance is observed for composite containing 5 wt.% of h-BN and 2 wt.% of BF. The developed MPP composite could be used in heat shields, electrical insulation components, and interior automotive components like dashboards, luggage compartments and interior walls.

Preparation and characterization of eicosane-paraffin/expanded graphite/polyurethane as form-stable composite phase change materials with wide phase change temperature range

Phase change materials (PCMs) with wide phase change temperature range, high latent heat, good thermal conductivity, and shape stability are essential for applications such as solar energy conservation and thermal management of electronic devices. Form-stable composite PCMs (FSCPCMs) with a broad phase change temperature range of 18–65 °C were successfully developed by using a mixture of eicosane and paraffin mixture along with cross-linking polyurethane as PCM, expanded graphite as thermally conductive filler and supporting material. The prepared FSCPCMs demonstrated excellent thermal stability and thermal conductivity with a latent heat up to 142.5 J/g. In conclusion, the synthesized FSCPCMs exhibit promising potential for practical applications in thermal energy storage.

Review on manufacturability and strengthening mechanisms of particulate reinforced Mg composites

The further development of lightweight and energy-saving engineering materials is a great challenge for scientists in the 21st century. Magnesium and its composites, as the metal materials with the lowest density among metal structural materials, have good thermal conductivity, good dimensional stability, high specific strength, good biocompatibility, which can meet the requirements of energy-saving, emission reduction, environmental protection. In recent years, magnesium and its composites have found the major applications in various fields such as aerospace, automotive industry, electronics and medical industry. However, the fabrication of magnesium matrix composites is difficult, and the deformation behaviors and strengthening mechanisms of particulate reinforced magnesium matrix composites have unique characteristics. This article reviews the recent research progress of the magnesium matrix composites, including different fabrication methods and strengthening mechanisms. According to the classification of solidification rate, the advantages and disadvantages of various techniques used to fabricate magnesium matrix composites were introduced. The traditional and novel fabrication techniques were discussed. The influence mechanisms of particulates on solidification microstructures, recrystallization behaviors, texture strength and twin behaviors of magnesium matrix composites during solidification and extrusion were summarized, and the roles of particulates in solidification and extrusion of magnesium matrix composites were analyzed. The strengthening mechanisms of particulates on the mechanical properties, corrosion resistance, fatigue resistance and creep resistance of magnesium matrix composites were revealed. Finally, the development prospect and research direction of magnesium matrix composites were prospected. It is hoped that this paper can provide a reference for the further development of magnesium matrix composites.

Mechanical and thermal properties for corrosion products of lutetium silicates against CMAS

AbstractRare earth silicates are promising environmental/thermal barrier coating (E/TBC) materials facing severe CMAS (CaO‐MgO‐Al2O3‐SiO2) corrosion. Previous studies mainly focused on the intrinsic properties of precorrosion coatings, but there were few studies on their CMAS corrosion products that play a crucial role in the performance of coatings in postservice stage. In this work, the mechanical and thermal properties of nine corrosion products between lutetium silicates and CMAS are studied using first‐principles calculations. Their differences of elastic stiffness are attributed to the different crystal structures and bonding strength. The T:O ratio is identified as a factor of the crystal structure for silicate products, and it has a good correlation with their elastic stiffness. Moreover, the divergences of thermal conductivity are dominated by three essential factors, that is, atomic vibration intensity, lattice vibrational anharmonicity, and complexity of crystal structure. Compared with rare earth silicates, six products, that is, the α‐CaSiO3, β‐CaSiO3, Ca2MgSi2O7, Ca2Al2SiO7, CaAl2Si2O8, and Ca2Lu8(SiO4)6O2, showing good damage tolerance and low thermal conductivities, are predicted to be advantageous to E/TBCs. These discoveries reveal the mechanical/thermal properties of corrosion products between lutetium silicates and CMAS and are expected to support the future researches on the performance of E/TBC in the postservice stage.

Characterization and utilization of sawdust waste generated from advanced manufacture for its application as a thermal insulation in sustainable buildings using the blowing technique

The construction industry is vital for economic development, but it accounts for 40% of energy consumption and 45% of global greenhouse gas emissions. In this context, research has focused on reducing energy demand in homes, particularly through the development of insulation materials. Sawdust is a byproduct available annually in Chile in quantities exceeding 4.5 million tons. Therefore, the objective of this study was to characterize the physical and thermal properties of this waste to evaluate its use as a thermal insulation material. Stability and thermal conductivity tests, as well as density and moisture content measurements, were conducted on the sawdust. Additionally, to assess the functionality of this thermal insulator, the material was applied using the blowing technique in partitions, followed by physical tests. The results indicate that the proposed insulation material has thermal stability up to 270 °C. The thermal conductivity was comparable to conventional mineral wool and fiberglass (0.042–0.048 [W/mK]). The density ranged from 123.77 to 198.15 [kg/m³] depending on the filling time of the specimens but remained low compared to other organic materials. The moisture content was 11.31%, suitable for maintaining good thermal conductivity. This study concludes that sawdust is a viable alternative for thermal insulation, especially when applied through blowing. Its stability and thermal conductivity are comparable to conventional materials, while its thermal inertia is 200% higher than that of glass wool. Furthermore, the low moisture content suggests that there would be no proliferation of pathogens, making it a promising thermal insulator for sustainable construction development. Finally, it is mentioned that the material carbonizes within a limited time, leading to self-extinguishment of the flame.

Low-temperature synthesis and properties of high-purity boron nitride microspheres

Boron nitride (BN) has excellent high temperature resistance, thermal conductivity, strong insulation, and wave-transparent properties. Spherical BN is an essential filler in polymer matrix composites due to good particle mobility and high filler content. In this paper, we present a large-scale preparation for BN microspheres with uniform particle size distribution in the range of 1.0–2.8 μm via solvothermal method at low cost and high yield (∼90%), which is two orders of magnitude lower than the diameter of the spherical BN prepared by other methods. BN microspheres can achieve good crystallinity (>70%) and high purity (>99.9%) at 800 °C. The temperature resistance study showed that the BN microspheres could maintain the dense particle morphology at 1200 °C. In addition, the prepared BN microspheres have good dielectric and thermal conductivity properties (dielectric constant ∼3.4, dielectric loss ∼2.0 × 10−3, and thermal conductivity of 9.8 W m−1 K−1), which show great potential in the field of wave-transparent and thermal conductive composites. The synthesis process of BN microspheres proposed in this study provides a new idea for the preparation of ceramic micro or nano materials by polymer-derived ceramics.

The effect of temperature variation on Aluminum Matrix Composite (AMC) Sintering with CNT

Material selection is a very important part of the design due to the variety of functions and extreme applications. There is always a need for materials that are light, strong, hard, with good thermal conductivity. Aluminum matrix composites (AMC) are potential candidates for applications that require proper material selection. The most popular AMC processing technique is the powder metallurgy/PM method to produce products with precise dimensions. Powder metallurgy for the mass production of components is the most promising and versatile method. carbon Nanotube (CNT) particle reinforced AMC fabrication is an advanced material for the automobile, aircraft, aerospace, defense, petroleum, chemical industries at a relatively low price with high performance. Al powder 4.98 gr, CNT 0.02 gr with a mixing time of 8 hours at 650 rpm. The specimens were made using a cold uniaxial pressing process at room temperature 27°C. Aluminium – CNT powder is compacted in a rigid molding with a compaction pressure of 160 MPa. Variation of sintering 100°C, 200°C, 300°C, 400°C, 500°C with a time of 60 minutes. The PM method proves that the mechanical properties and physical properties of the material are improved. Material shrinkage after sintering is large by forming shrinkage. Hardness test results with Rockwell, 26.5HR, 27.9HR, 28.8HR 29.9HR, 32.5HR. Wear rate 0.196 mm3/m, 0.078mm3/m, 0.054mm3/m, 0.052mm3/m 0.049mm3/m. Porosity values are 6.30%, 6.28%, 5.98%, 4.51%, 4.58%. The higher the sintering tem-perature, the higher the hardness value, the lower the porosity and wear.

Performance of Stainless-Steel Bipolar Plates (SS-BPPs) in Polymer Electrolyte Membrane Water Electrolyser (PEMWE): A Comprehensive Review

Bipolar Plates (BPPs) play a critical role in Polymer Electrolyte Membrane Water Electrolysers (PEMWEs) for effective hydrogen generation. The performance and longevity of the system can be considerably impacted by choosing the suitable material for these components. Polymer electrolyte membrane water electrolysis technology relies on cost-effective and corrosion-resistant BPPs. Tantalum, niobium, and titanium are low-cost, easy-to-machine materials that have good electrical and thermal conductivity; however, they exhibit low corrosion resistance. Noble metal and metal nitride coatings are usually investigated to minimize corrosion and interfacial contact resistance. Because of its performance-to-cost ratio, Stainless Steel (SS) based materials are among the most popular materials for BPP development. This study recommends material and operating parameters to improve PEMWE systems for sustainable hydrogen production’s efficiency, durability, and economic viability.

Numerical investigation of the thermal and acoustic effect of material variations on the exhaust muffler

Exhaust mufflers are used in automobiles to prevent the noise arising from exhaust gases resulting from internal combustion engines. With the advancement of the automotive industry, exhaust mufflers have become more complex over time to reduce noise and increase driving comfort. Within the scope of this study, exhaust muffler geometries with different geometries have been designed, and harmonic acoustic analyses have been carried out. In the analysis, the airflow speed has been accepted as 30 m/s. Acoustic pressure and transmission loss data obtained because of analyses performed with 1Pa pressure input have been evaluated. As a result of the evaluations, it has been concluded that the muffler modeled in a complex structure has been better acoustically. Although the main task of exhaust muffler is to reduce the sound level at the exit of exhaust gases, it is also important to reduce the temperature of the air in the exhaust system and have good thermal conductivity so as not to jeopardize the thermal safety of the system. For this reason, CFD thermal flow analysis has been carried out with 4 different materials using a complex design with high acoustic efficiency. Gray cast iron, stainless steel, 1020 steel, and aluminum have been used as materials. In this part of the study, it has been determined that the use of aluminum material has been better in terms of thermal efficiency.

Editorial for the Special Issue on Carbon Fiber Composites

Carbon fibers (CFs) have received tremendous attention since their discovery in the 1860s due to their unique properties, including outstanding mechanical properties, low density, excellent chemical resistance, good thermal conductivity, etc [...]

Failure analysis on the abnormal cracking of Si3N4 ceramic substrates for SiC power modules in new energy vehicles

Si3N4 ceramic with good thermal conductivity, high mechanical strength and low thermal expansion coefficient is an advanced thermal management material which has been applied to new energy vehicles. At present, with the rapid development of the electric driving technology for new energy vehicles, Si3N4 ceramic has been gradually used in SiC power modules so as to efficiently achieve the functions of heat dissipation, insulation and voltage resistance. Due to its important role in the power conversion process, the reliability of Si3N4 ceramic was vital, and any factor that might lead to its premature failure must be attached importance to. In this paper, a case about abnormal cracking of Si3N4 ceramic substrates during the high and low temperature cycling tests was reported. To solve this problem, various characterization methods were conducted to analyze the density, thermal conductivity, flexural strength, phase structure, morphology characteristics. Finally, through comprehensive analysis, the root cause that resulted in abnormal cracking of Si3N4 ceramic substrates was determined and meanwhile corresponding countermeasures were also proposed. Hopefully, the achievements of this paper will have positive significance for upgrading the quality of Si3N4 ceramic substrates and improving the service reliability of power modules.

Irradiation resistance of thermo-optical properties of zirconium diboride by 3 MeV electrons

Due to good thermal conductivity and thermal shock resistance, ultra-high temperature ceramics such as zirconium diboride (ZrB2) have been investigated as promising materials to be used in reusable thermal protection systems TPSs are vital to the heat balance of a spacecraft during atmospheric reentry and subsequent operation in space. Hence, the thermal and optical properties are especially critical for such applications. Meanwhile, radiation exposure in space can pose risks of degrading such material properties, especially over a prolonged mission duration. The interaction of electron radiation-which can be found in the outer Van Allen belt, with ZrB2 has not been studied previously and was chosen as the main scope of this study. An electron source of 3 MeV with different radiation exposure time was used. The response of thermo-optical properties of ZrB2 to increasing electron radiation fluences was investigated. ZrB2 samples were made through spark plasma sintering into sintered pellets and then exposed to 3 MeV electron irradiation. These ZrB2 samples were characterized by their microstructure, thermal conductivity, coefficient of thermal expansion (CTE), emittance, absorptivity, and surface roughness before and after irradiation. It was found that ZrB2’s thermo-optical properties showed high radiation resistance at these fluences, and no apparent microstructural change was observed after irradiation. However, the irradiated samples had, on average, a 29% lower surface roughness than the unirradiated samples, possibly originating from electron sputtering.

Unravelling formation mechanism, thermal and oxidation stabilities of layered sub-micron MAB phase WAlB synthesized at open atmosphere

With the high melting point, good thermal and electrical conductivities, a less explored layered MAB phase WAlB may prove beneficial for futuristic applications. In this present paper, a successful synthesis method of highly pure WAlB phase under an open atmosphere following the molten salt route is reported. In this method, a two-step heating profile was used to produce sub-micron sized particles. Template growth of layer WAlB from layered W–Al intermetallics is revealed after careful examination using XRD, SEM, and thermal analysis. The WAlB phase was found thermally stable until 800 °C under an inert atmosphere and until 500 °C under an open atmosphere after investigating the respective XRD, thermal analysis, and SEM data.

Preparation of Sustainable Composite Materials from Bio‐Based Domestic and Industrial Waste: Progress, Problems, and Prospects‐ A Review

AbstractBio‐based waste from households and industries is a big problem for the world, however, turning it into valuable composite materials can offer a promising approach to deal with it. It involves the conversion of waste from different bio‐based sources such as cellulose waste from farming and forestry leftovers, chitin waste from seafood and mushrooms, and keratin waste from hair, nails, and feathers into natural fibers. These fibers are then effectively mixed with other materials to create composite materials having unique properties, such as high strength and stiffness, good thermal and electrical conductivity, and better barrier properties. Developing these materials is not just good for the environment because it reduces landfill waste and the reliance on non‐renewable resources, but it can also make economic sense for producers. In this review, the basic compounds of natural fibers and the development of composite materials from them are explored and discussed in detail. Furthermore, their chemical and mechanical properties are discussed and summarized. In the final section, a brief overview of the challenges and the future research needed in this fast‐evolving field is given.

Research Progress and the Prospect of Damping Magnesium Alloys.

As the lightest structural metal material, magnesium alloys possess good casting properties, high electrical and thermal conductivity, high electromagnetic shielding, and excellent damping properties. With the increasing demand for lightweight, high-strength, and high-damping structural materials in aviation, automobiles, rail transit, and other industries with serious vibration and noise, damping magnesium alloy materials are becoming one of the important development directions of magnesium alloys. A comprehensive review of the progress in this field is conducive to the development of damping magnesium alloys. This review not only looks back on the traditional damping magnesium alloys represented by Mg-Zr alloys, Mg-Cu-Mn alloys, etc. but also introduces the new damping magnesium materials, such as magnesium matrix composites and porous magnesium. But up to now, there have still been some problems in the research of damping magnesium materials. The effect of spiral dislocation on damping is still unknown and needs to be studied; the contradiction between damping performance and mechanical properties still lacks a good balance method. In the future, the introduction of more diversified damping regulating methods, such as adding other elements and reinforcements, optimizing the manufacturing method of damping magnesium alloy, etc., to solve these issues, will be the development trend of damping magnesium materials.

Preparation of ZrP2O7-based fiber composites by in situ synthesis method

ZrP2O7-based fiber composites were prepared by in situ synthesis and their microstructure, thermal conductivity, mechanical and dielectric properties were determined. The chemical reaction with BPO4 as the phosphorus source and nano-ZrO2 as the zirconium source was initiated at 900°C, which promotes liquid-phase sintering and reduces the sintering densification temperature of the ZrP2O7-based fiber composites by generating small ZrP2O7 grains and low-melting B2O3. The lower sintering densification temperature and the appropriate amount of network formers effectively suppressed the high-temperature crystallization phenomenon of the high-silica-oxygen fibers, strengthened the interfacial bonding between the fibers and the matrix, and improved the interfacial debonding problem of the ZrP2O7-based fiber composites. It is found that the ZrP2O7-based fiber composites possess low dielectric constant, low dielectric loss, good thermal conductivity, and acceptable mechanical properties, which can meet the relevant application requirements of centimeter-wave technology.