Thermal Resistance Properties Research Articles

Multi-site occupancies and dependent photoluminescence of Ca9Mg1.5(PO4)7:Eu2+ phosphors: A bifunctional platform for optical thermometer and plant growth lighting

Herein, we demonstrate an optical thermometer based on single Eu2+ doped Ca9Mg1.5(PO4)7 phosphors, which were prepared by traditional solid-state reaction technique under a reduction atmosphere. Considerations on the bond length obtained by the crystal structure refinement and the dependent photoluminescence performances allow to assign the two distinct emission bands to Eu2+ ions occupied Ca1–Ca3 and Mg2 sites. Moreover, the blue and red emitting bands perfectly match with the photosynthetic action spectrum, which can enhance the indoor plant photosynthesis. The optimal doping content of Eu2+ ions in this Ca9Mg1.5(PO4)7 system is 3 mol%. The corresponding concentration quenching effect is verified as dipole–dipole interaction with the critical distance of 3.315 nm. Furthermore, by exploiting the fluorescence intensity technique, the optical thermal resistance properties of Ca9Mg1.5(PO4)7:Eu2+ are identified based on the temperature dependent emission spectra in a range of 303–523 K. In detail, the maximum absolute and relative sensitivity Sa and Sr of Ca9Mg1.5(PO4)7:Eu2+ thermometer are as high as 0.637%/K and 0.3155 K–1, respectively. Consequently, the Eu2+ doped Ca9Mg1.5(PO4)7 phosphors establish a bifunctional platform for both optical thermometer and plant growth lighting via multi-site occupancies.

Konjac glucomannan/Pullulan films incorporated with cellulose nanofibrils-stabilized tea tree essential oil Pickering emulsions

Biopolymers, such as polysaccharides are increasingly concern in preparation of food packaging. However, those materials have weakness in properties of mechanics, hydrophobicity, and antibacterial, which limit their applications. In this work, we prepared emulsion (K-PL-CEOs) films with double network (DN) matrix by using konjac glucomannan (KGM) and Pullulan (PL), and incorporated with cellulose nanofibrils (CNF)-stabilized tea tree essential oil (TTEO) Pickering emulsions (CEOs). The effect of CEOs content on the structural and physicochemical properties of K-PL films was investigated. The results showed that CEOs were well dispersed in K-PL film forming matrix. The addition of CEOs could improve the thermal stability, UV-shielding, water resistance and mechanical properties of K-PL-CEOs films. Moreover, K-PL-CEOs films exhibited good antibacterial activity against E. coli and S. aureus. This paper demonstrated that K-PL-CEOs films can be potentially applied as food packaging.

A perspective on thermal stability and mechanical properties of 2D Indium Bismide from ab initio molecular dynamics

Identification and synthesis of 2D topological insulators is particularly elusive. According to previous ab initio predictions 2D InBi (Indium Bismide) is a material exhibiting topological properties which are combined with a band gap suitable for practical applications. We employ ab initio molecular dynamics (AIMD) simulations to assess the thermal stability as well as the mechanical properties such as elastic modulus and stress–strain curves of 2D InBi. The obtained new knowledge adds further characteristics appealing to the feasibility of its synthesis and its potential applications. We find that pristine 2D InBi, H-InBi (hydrogenated 2D InBi) as well as 2D InBi heterostructures with graphene are all stable well above room temperature, being the calculated thermal stability for pristine 2D InBi 850 K and for H-InBi in the range above 500 K. The heterostructures of 2D InBi with graphene exhibit thermal stability exceeding 1000 K. In terms of mechanical properties, pristine 2D InBi exhibits similarities with another 2D material, stanene. The fracture stress for 2D InBi is estimated to be ∼3.3 GPa (∼3.6 GPa for stanene) while elastic modulus of 2D InBi reads ∼34 GPa (to compare with ∼23 GPa for stanene). Overall, the thermal stability, elastic, and fracture resistant properties of 2D InBi and its heterostructures with graphene appear as high enough to motivate future attempts directed to its synthesis and characterization.

The microstructure evolution, damage behavior and failure analysis of fine-grained W-Y2O3 composites under high transient thermal shock

Extreme thermal environment, especially transient high thermal load, is one of the great challenges for plasma facing tungsten materials. In this work, the fine-grained W-Y2O3 composites fabricated by nano in-situ composite method were exposed to transient heat loading using electron beams. The microstructure evolution, damage behavior and failure analysis were investigated by experimentally combing with finite element modelling (FEM). Besides, the correlation among thermal shock resistance, microstructure and mechanical properties of the W-Y2O3 composites were initially analyzed. Results show the W-Y2O3 composites obtains superfine microstructure and coherent interface. The surface morphology evolves from smooth to roughness, cracks and melting as the power density increases. Simultaneously, four crack patterns of surface micro-cracks, crack networks, longitudinal cracks and internal transverse cracks were observed. The W-0.3 wt%Y2O3 composites exhibit superior resistance to crack formation attributed to excellent interfacial performance and diffuse Y2O3 hindrance. No obvious damage was found on the surfaces when the power density reached 600 MW/m2. With the increasing Y2O3 contents, the thermal resistance of W-Y2O3 composites significantly decreases. Finite element modelling (FEM) analysis shows that the surface damage is the most serious compared to the interior after thermal shock. The damage, especially cracks, are preferentially formed on the surface, and then migrate and expand to the interior. The damage and its evolution are attributed to the palstic thermal strain on the surface caused by thermal stress. Moreover, the higher the mechanical properties of W-Y2O3 composites, especially the high temperature yield stress and elongation, the better high thermal load resistance. These results should be of relevance for the optimum design of W plasma facing materials in future nuclear fusion reactors.

Effect of Cr, Mo, and V Elements on the Microstructure and Thermal Fatigue Properties of the Chromium Hot-Work Steels Processed by Selective Laser Melting

Thermal fatigue is the main failure mode for chromium hot-work steels. In this study, pre-alloyed chromium hot-work steel powders with three different Cr, Mo, and V addition levels (low content (LH), medium content (MH), and high content (HH)) were used for selective laser melting (SLM). The microstructure and thermal fatigue properties of these SLM-processed materials were investigated. After thermal fatigue tests, LH possessed the lowest hardness (approximately 573 HV5) and longest crack length, MH possessed the highest hardness (approximately 688 HV5) and HH (with the hardness of approximately 675 HV5) possessed the shortest crack length. It can be concluded that the increase of V content in MH is the main reason for the refined grains which result in an enhanced hardness and thermal fatigue resistance compared to LH. The further increase of the Cr and Mo content in HH leads to the grain coarsening and hardness decreasing, which is supposed to degrade the thermal fatigue resistant properties according to the conventional theory. However, HH exhibited an enhanced thermal fatigue resistance compared to MH. That is because the higher stored energy in MH deteriorated its thermal fatigue resistance compared to HH.

Fabricate an inner interface in the W sub-layer to enhance the thermal barrier of the periodic W/Al2O3 nanolaminates on glass slide

Low thermal conductivity and excellent mechanical properties are of great significance for new thermal insulation materials. Periodic nanolaminates can reduce thermal conductivity by scattering phonons at the interface between sub-layers. In this study, we developed an internal interface strategy together with the interlayer interface to jointly improve the thermal resistance and mechanical properties of the materials. Periodic W/Al2O3 and W-WOx/Al2O3 nanolaminates were fabricated on glass slide by magnetron sputtering. The thickness of each sub-layer was ∼5 nm, and the interface between the sub-layers was uniform and continuous. The internal interface in the W was produced by preparing a variety of WOx species in the sub-layer. When the O2/Ar ratio was 0.0125 in the sputtering, the W-WOx sub-layer contained four W species with different valences. The nanolaminates had a thermal resistance of 4.18 × 10−7 m2 K W−1 and nanohardness of 8.22 GPa. Comparatively, the thermal resistance and nanohardness of the W/Al2O3 nanolaminates were 1.72 × 10−7 m2 K W−1 and 7.34 GPa, respectively.

Antioxidant and antibacterial properties of essential oils-loaded β-cyclodextrin-epichlorohydrin oligomer and chitosan composite films

Chitosan (CS) is becoming increasingly popular in food packaging due to its natural degradability and great film-forming properties. Nevertheless, its poor antibacterial properties and inadequate antioxidant properties prevent it from being used effectively. In this study, β-cyclodextrin-epichlorohydrin (β-CD-EP) oligomers were prepared and encapsulated with natural essential oils cinnamaldehyde and thymol, and then the inclusion complexes (IC) were incorporated into chitosan in various contents to afford a series of CS-IC composite films. The impacts of IC on the morphological, mechanical, thermal, and water resistance properties, antioxidant and antibacterial activities of chitosan films, as well as the loading and sustained release behavior of IC, were thoroughly examined. The results turned out that the essential oils were well-loaded with high encapsulation efficiency and showed a significant slow-release effect. It was also found that the tensile strength and the elongation at break decreased with increasing IC contents, while the thermal stability was enhanced. The incorporation of IC dramatically promoted the antioxidant and antibacterial properties of the chitosan films towards Gram-positive bacteria. Based on our findings, chitosan films containing essential oils-loaded β-CD-EP oligomers may serve as an effective food packaging material.

Effect of Biochar Addition on Mechanical Properties, Thermal Stability, and Water Resistance of Hemp-Polylactic Acid (PLA) Composites.

The present study investigated the effect of biochar (BC) addition on mechanical, thermal, and water resistance properties of PLA and hemp-PLA-based composites. BC was combined with variable concentration to PLA (5 wt%, 10 wt%, and 20 wt%) and hemp (30 wt%)-PLA (5 wt% and 10 wt%); then, composites were blended and injection molded. Samples were characterized by color measurements, tensile tests, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and water contact angle analysis. Experimental results showed that adding 5 wt% of BC enhanced the composite’s tensile modulus of elasticity and strength. Hence, the use of optimized loading of BC improved the mechanical strength of the composites. However, after BC addition, thermal stability slightly decreased compared with that of neat PLA due to the catalytic effect of BC particles. Moreover, the water-repelling ability decreased as BC content increased due to the specific hydrophilic characteristics of the BC used and its great porosity.

Polyester and Epoxy Resins with Increased Thermal Conductivity and Reduced Surface Resistivity for Applications in Explosion-Proof Enclosures of Electrical Devices.

Composite materials are still finding new applications that require the modification of various properties and are characterized by the summary impact on selected operational features. Due to the operating conditions of electrical equipment enclosures in potentially explosive atmospheres, the surface resistivity ensuring anti-electrostatic properties, i.e., below 109 Ω and resistance to the flame while maintaining appropriate operational enclosure properties is very important. It is also crucial to dissipate heat while reducing weight. Currently metal or cast-iron enclosures are used for various types of electrical devices. As part of the work, a material that can be used for a composite matrix for the enclosure was developed. The study aimed to assess the influence of selected fillers and chemical modifications on the thermal conductivity coefficient, resistivity, and strength properties of matrix materials for the production of electrical device enclosures used in the mining industry. Selected resins were modified with graphite, copper, and carbon black. Tests were carried out on the coefficient of thermal conductivity, surface resistivity, flammability, and flexural strength. At the final stage of the work, a multi-criteria analysis was carried out, which allowed the selection of a composite that meets the assumed characteristics to the highest degree. It is a vinyl ester composite modified with 15 wt.% MG394 and 5 wt.% MG1596 graphite (W2). The thermal conductivity of composite W2 is 5.64 W/mK, the surface resistivity is 5.2 × 103 Ω, the flexural strength is 50.61 MPa, and the flammability class is V0.

Evaluation of impact, thermo‐physical properties, and morphology of cornhusk fiber‐reinforced polyester composites

AbstractThis study aims to investigate the thermo‐physical and morphological morphology of cornhusk fiber‐reinforced polyester composites. The content of corn husk fiber (CHFs) has been varied, namely 20, 30, 40, and 50 (% vol.) in the polyester composite, respectively. The hot press technique has been used in the manufacture of these composites, then properties were investigated through thermo‐physical tests including differential scanning calorimetry, thermogravimetry, Fourier transforms infrared, impact strength properties, and morphology using SEM. The results showed that the composite containing 30% CHF (KJP2) was found to have the most optimal impact strength (4.25 KJ/m2), and the best thermal resistance properties were found in the KJP3 composite, compared with other composites; due to CHF dispersion and good interfacial adhesion between CHF and polyester. SEM images of the fracture of the impact test specimens of the composites show better interfacial bonding between CHFs and polyester.

Novel Biobased Epoxy Thermosets and Coatings from Poly(limonene carbonate) Oxide and Synthetic Hardeners.

In the area of coating development, it is extremely difficult to find a substitute for bisphenol A diglycidyl ether (DGEBA), the classical petroleum-based raw material used for the formulation of epoxy thermosets. This epoxy resin offers fast curing reaction with several hardeners and the best thermal and chemical resistance properties for applications in coatings and adhesive technologies. In this work, a new biobased epoxy, derived from poly(limonene carbonate) oxide (PLCO), was combined with polyetheramine and polyamineamide curing agents, offering a spectrum of thermal and mechanical properties, superior to DGEBA-based thermosets. The best formulation was found to be a combination of PLCO and a commercial curing agent (Jeffamine) in a stoichiometric 1:1 ratio. Although PLCO is a solid due to its high molecular weight, it was possible to create a two-component partially biobased epoxy paint without the need of volatile organic compounds (i.e., solvent-free formulation), intended for use in coating technology to partially replace DGEBA-based thermosets.

Poly(arylene ether sulfone) containing diphenyl-biphthalazin-dione moieties with excellent thermal resistance

A series of novel poly(arylene ether sulfone)s containing diphenyl-biphthalazin-dione moieties (PPDESs) are synthesized from 4-(4-hydroxyphenyl)-2,3-phthalazin-1-one, 4,4′-dichlorodiphenyl sulfone and diphenyl-biphthalazin-dione. Structural analyses such as NMR, FT-IR, instinct viscosity and XRD, as well as property tests including TGA, DSC, DMA, solubility and mechanical properties were carried out on PPDESs. The Tg of PPDESs is up to 388 °C, suggesting that PPDESs show excellent thermal resistance. The 5% mass loss temperature (Td5) of PPDESs is up to 513 °C. PPDESs possess excellent mechanic and thermo-mechanical performance which Young's modulus above 1.95 GPa, the tensile strength up to 107 MPa and the storage modulus retention up to 51.6% at 300 °C. Additionally, PPDESs exhibit an appropriate solubility in organic solvents such as chloroform, 1,1,2,2-tetrachloroethane, N-methyl pyrrolidone and so on. With the increasing introduction of the diphenyl-biphthalazin-dione, the thermal resistance and mechanical properties of PPDES are improved, while the solubility is slightly reduced.

Development of waste rice husk/PVC/GO nanocomposite using TA–CaO adduct and ESO as green additives

In this study, a biobased composite utilizing waste rice husk ash (RHA) and polyvinyl chloride in a 1:1 ratio was prepared. The composites were prepared in a solventless, green pathway of melt blending using green additives such as tannic acid-calcium oxide (TA–CaO) adduct as a heat stabilizer and epoxidized soybean oil (ESO) as green compatibilizer. The addition of graphene oxide (GO) nanomaterial into the composite improved the thermal, mechanical, chemical and flame resistance properties of the composite. Composite reinforced with 0.5 phr GO, improved the tensile, flexural and, shore D hardness by 34, 37, 14%, respectively. The homogeneous dispersion of the GO layer in reinforced composite was evident from the transmission electron microscopy (TEM) study. Composites with GO as nano reinforcement showed relatively higher flame retardancy due to the synergistic effect of GO and silicon present in RHA. The composite with 0.5 phr loading of GO showed overall improvement in properties among the composites. It is expected that the incorporation of waste RHA along with other renewable bioresource materials will improve biodegradability and decrease the production cost of the composite.

Controlling degradation and recycling of carbon fiber reinforced bismaleimide resin composites via selective cleavage of imide bonds

Carbon fiber reinforced bismaleimide resin (CF/BMI) composites are widely used in aerospace field due to their high thermal stability, chemical resistance and excellent mechanical properties. With the large-scale application of CF/BMI composites, it is inevitable to produce a lot of solid wastes, which have a serious impact on the environment, so people have to recycle waste CF/BMI composites. In view of the physical and chemical properties of BMI resin, we developed a green and friendly chemical recovery method of CF/BMI composites by selectively breaking imide bonds for controlled chemical degradation of BMI resin. In 5 wt% NaOH/H2O reaction system, the controlled chemical degradation of CF/BMI composites can be realized by selective cleavage of imide bonds, and the 4,4′-Diaminodiphenyl methane (DDM) and 2,2′,2″,2‴-((methylenebis(4,1-phenylene))bis(azanetriyl))tetrasuccinic acid (MBTA) can be recovered, and the carbon fiber (CF) can be recycled at the same time. Under the optimal reaction conditions, the yields of DDM and MBTA reached 6.7 wt% and 27.9 wt% at 180 °C for 8 h, respectively. Meanwhile, CF in CF/BMI composites can be completely recovered, and the tensile strength of recovered carbon fiber (rCF) is about 97.6% of that of virgin carbon fiber (vCF). This work provides a very promising strategy for the recycling of CF/BMI composites. The high value-added CF and chemicals (DDM and MBTA) can be recovered by controlled degradation of CF/BMI composites via selective cleavage of imide bonds.

Preparation of Si3N4-BCxN-TiN composite ceramic aerogels via foam-gelcasting

Recently, high-performance ceramic aerogels (CAs) have become a research hotspot because of their multi-functional properties. Compared to their oxide counterparts, non-oxide CAs show better thermal shock resistance and other high-temperature properties, making them suitable for applications in harsh environments. In this work, Si3N4-BCxN-TiN ceramic aerogels (SBCNT CAs) with molar ratios of B/C/Si/Ti = 2:1:5:5 were synthesized at 1623 K for 3 h via foam-gelcasting, from Si, Ti, melamine and boron acid raw materials. The prepared SBCNT CAs containing 91.0% porosity exhibited the highest compressive strength up to 1.0 MPa, and thermal conductivity of 0.144 W/(m·K) at 298 K. They also exhibited excellent service performance at 1473 K in Ar, demonstrating their great potential for high-temperature applications.

Performance Evaluation of Jute/Glass-Fiber-Reinforced Polybutylene Succinate (PBS) Hybrid Composites with Different Layering Configurations.

The hybridization of natural and synthetic fibers leads to composites’ optimum mechanical properties. In this study, an attempt was made to study the effect of the stacking sequence on PBS-based Glass-Jute (GJ) hybrid composites. Six types of hybrid composite, each containing five different layers of jute and glass fabric, were manufactured by the compression molding method. Mechanical properties, such as tensile, flexural, and impact resistance were studied and analyzed in detail. The surface characterization of the composites was performed through scanning electron microscopic images. The moisture absorption properties were also investigated by immersing the composites in distilled water for one week at ambient temperature. The TGA test was conducted to study their thermal properties. The experimental results showed that the stacking sequence of the fiber layers has a significant effect on the overall performance of GJ hybrid composites. Among the hybrid GJ composites, composites with glass fiber layers on their outer surfaces showed optimum mechanical, thermal, and water resistance properties.

Bio-composite Films Based on Alginate and Rice Husk Tar Microparticles Loaded with Eugenol for Active Packaging

This work focused on the valorization of tar derived from rice husk pyrolysis as a precursor of matrices for the encapsulation of active principles. In this regard, the development of novel films based on alginate and eugenol-loaded tar microparticles with suitable mechanical properties and antibacterial activity was studied. Tar microparticles loaded with eugenol were incorporated into sodium alginate films and the effect on the mechanical, thermal and humidity resistance properties were determined, as well as the antimicrobial activity. Films with different crosslinking degrees were also prepared using CaCl2, and the eugenol controlled release profiles were evaluated. Crosslinked films exhibited improved mechanical and humidity resistance properties, as well as a lower release rate of eugenol in water. The antimicrobial studies showed that eugenol-loaded films present a higher antimicrobial activity against Staphylococcus aureus. Alginate/eugenol-loaded tar microparticles composites showed an enhancement of antibacterial properties and suitable physical characteristics to be used in active packaging applications.

Geopolymer concrete with metakaolin for sustainability: a comprehensive review on raw material's properties, synthesis, performance, and potential application.

In the last three decades, the gigantic demand for sustainable and environmentally friendly concrete with reduced environmental footprints has resulted in the development of low carbon concretes such as geopolymer concrete. Metakaolin which is commonly used as an admixture or partial replacement of cement owing to its most effective pozzolanic properties, which improve the microstructure and strengthen the mechanical and durability properties of cement concrete, has been investigated as a precursor in geopolymer concrete. Several studies have been conducted to comprehend the effect of metakaolin as an additive in geopolymer mortar and concrete prepared with various aluminosilicate sources as precursors such as fly ash and rice husk ash to enhance geopolymerization, densify microstructure, and elevate durability. The present paper recapitulates these investigations primarily concentrating on the various properties of metakaolin-based concrete. The effect of various factors such as alkali content, solids/liquids ratio, alkali reactant ratio, molar ratio, water content, and curing regime has been compiled. Most of them revealed that metakaolin is used as a precursor and yields better geopolymer products. XRD studies reported the peaks demonstrating the development of enhancement in hydration products in comparison to other precursors. Examination of SEM graphs reveals that the addition of a smaller quantity of silica-rich materials densifies the microstructure of geopolymers and produces higher mechanical strength. Durability studies reveal that metakaolin geopolymers possess better water resistance, thermal resistance, and anti-corrosion properties. The possible applications of metakaolin-based geopolymeric materials are also pointed out. The comprehensive knowledge presented here is expected to support the prospective researchers to decide their future course of the research area. Graphical abstract.

Improving the oxidation resistance of thermoelectric Mg2Si leg with silica coating

Due to the volatile and oxidation nature of Mg, Mg2Si based thermoelectric legs degrade faster when exposed to ppm level of oxygen during mid-temperature range operation. Here, we have established a modified sol–gel technique to get an oxidation-resistant SiO2 coating on the Mg2Si thermoelectric legs. The cyclic thermal ageing stability, oxidation resistance, and thermoelectric properties of the SiO2 coated Mg2Si have been investigated. The SiO2 coated Mg2Si is stable after ageing for 200 h at 823 K in air, and there is no degradation in the thermoelectric properties due to atmospheric exposure. It is thus a promising technique to increase the life span of Mg2Si based thermoelectric materials for waste heat recovery in automobiles and heavy industries.

Inactivation of vegetative cells, germinated spores, and dormant spores of Bacillus atrophaeus by pulsed electric field with fixed energy input

AbstractIncreasing the electric energy input during pulsed electric field (PEF) treatment is a straightforward technique to boost the efficiency of microbial inactivation. However, drawbacks such as electrode corrosion, arc formation, and high cost are also involved. This study aims to investigate the impact of medium conductivity (), electric field strength (), and the number of pulses () on the inactivation of vegetative cells, germinated spores, and dormant spores of Bacillus atrophaeus with fixed energy input. Our results indicated that (1) vegetative cells were susceptible to PEF treatment, and the relative importance of , , and was ; (2) germinated spores were more resistant to PEF treatment than vegetative cells, and the relative importance of , , and was ; and (3) similar to the thermal resistance property, dormant spores were also highly resistant to PEF treatment and were not significantly inactivated in our experiment setting. It is concluded that the degree of PEF resistance of cell at different physiological states may be related to its structure and size. This study added to the body of knowledge on selecting PEF treatment settings and gave insight into the scaling up of PEF applications in the food processing industry.Practical ApplicationsIn the food processing industry, eliminating contaminants such as bacterial spores is essential, and PEF processing is a common nonthermal technique. While the traditional method of increasing the electric energy input to increase microbial inactivation efficiency is beneficial, it is not cost‐effective. The results of this investigation demonstrated that decreasing spore resistance through germination followed by parameter‐optimized PEF treatments is a practical method for improving pasteurization efficiency. This novel technique might be used in the food sector.