Low Coefficient Of Thermal Expansion Research Articles

From waste to value: Utilising waste foundry sand in thermal energy storage as a matrix material in composites

Waste foundry sand (WFS) is a by-product of the casting industry, which poses increasing economic and environmental issues due to the costs associated with landfill maintenance and stricter environmental regulations. This study proposes a novel solution for WFS as a material for thermal energy storage. The approach involves blending WFS with NaNO3 and a proprietary additive, X, to fabricate a composite phase change material (CPCM). The CPCM is found to be structurally stable up to 400 °C, and an optimal composition with a mass ratio of NaNO3:WFS:X = 0.6:0.3:0.1 is achieved. This composition yields an energy storage density of 628 ± 27 kJ/kg, and an average thermal conductivity of 1.38 W/mK over the temperature range of 25–400 °C. The CPCM also exhibits good mechanical strength and a low coefficient of thermal expansion compared to NaNO3. Currently, only a small portion of WFS is recycled, most commonly in building applications. The CPCM presented in this study has the potential for medium-to-high temperature heat storage in waste heat recovery applications, offering a sustainable solution for upcycling WFS.

Strengthand operational reliabilityofbimetallicthermoconverters

As a result of different physical and mechanical characteristics of the components, the bimetallic contact thermoconverter deforms when heated, and its displacement carryinformation aboutthe measured temperature of anobject or environment. However, thermal stresses often lead to a violation of the bond strength between the component plates of the thermoconverter and cause a partial or complete break between them. In order to increase the operational reliability of the thermometric system, it is proposed to make a gap between the plates, to make the plate with a higher coefficient of thermal expansion in the form of sections that abut against the edges made on a plate with a lower coefficient of thermal expansion, thanks to which the thermoconverter maintains its integrity. Due to this structural design, the thermoconverter has significantly higher reliability and performance under long-term cyclic heat load. Using the means of mathematical and computer modeling within the limits of the theory of thermoelasticity, the strength of the proposed design of the bimetallic heat exchanger was investigated. It is shown that due to such a design, the thermoconverter maintains its integrity up to temperatures of the order of 850 °C.

Influence of the Carbon Fiber Length Distribution in Polymer Matrix Composites for Large Format Additive Manufacturing via Fused Granular Fabrication.

Many studies assess the suitability of fiber-reinforced polymer composites in additive manufacturing. However, the influence of the fiber length distribution on the mechanical and functional properties of printed parts using these technologies has not been addressed so far. Hence, in this work we compare different composites based on Acrylonitrile Styrene Acrylate (ASA) and carbon fiber (CF) suitable for large format additive manufacturing (LFAM) technologies based on fused granular fabrication (FGF). We study in detail the influence of the CF size on the processing and final properties of these materials. Better reinforcements were achieved with longer CF, reaching Young's modulus and tensile strength values of 7500 MPa and 75 MPa, respectively, for printed specimens. However, the longer CF also worsened the interlayer adhesion of ASA to a greater extent. The composites also exhibited electrical properties characteristic of electrostatic dissipative (ESD) materials (105-1010 Ω/sq) and low coefficients of thermal expansion below 15 µm/m·°C. These properties are governed by the CF length distribution, so this variable may be used to tune these values. These composites are promising candidates for the design of elements with enhanced mechanical and functional properties for ESD protection elements or molds, so the products can be manufactured on demand.

Synthesis of Aptes-Capped Self-Adsorption Pd Nanoparticles and Application in Metallization on Glass Substrate with High Adhesion

Palladium is the most used catalysts in the electroless deposition process. The technology that use the amino silane compound (3-Aminopropyl) Triethoxysilane (APTES) as surface modifier is quite mature. Therefore, an innovative idea that one step palladium catalyst APTES-Pd with APTES as capping agent and surface modifier appeared. APTES-Pd is capable to adsorb on surface of glass substrate by forming Si-O covalent bond. Comparing to commercial palladium catalysts, the process is complex and need to work at high concentration, APTES-Pd has easier process and able to work at low concentration. The particle size of APTES-Pd is characterized by transmission electron microscopy (TEM) and dynamic light scattering (DLS). The configuration of APTES-Pd as well as the effect of modification on glass substrate is explained by X-ray photoelectron spectroscopy (XPS).Glass substrate is a good option as an interposer substrate. It has serval advantages, such as low k, high resistivity, high stability, low coefficient of thermal expansion (CTE) mismatch with copper material and good mechanical properties. However, because glass substrate (SiO2) is stable and surface is smooth, it’s hard to electroless deposit Cu layer with high adhesion on it. The adhesion that using commercial palladium catalysts Sn/Pd for electroless copper deposition is too low to pass tape test. Because interaction between Sn/Pd and substrate is electrostatic adsorption which is lower than covalent bond. Using APTES-Pd for electroless copper deposition is capable to improve the interaction between glass and Cu layer. APTES-Pd can pass tape test on glass substrate. But its adhesion is still too low to be measured by T-Peel. To enhance the adhesion of the metal films on glass substrates, we coat titanium dioxide (TiO2) as adhesion promoter. TiO2 can not only bond to glass substrate but increase surface roughness. After coating TiO2 film, the adhesion of metal film increases to 122 gf/cm.

Application in Self-Adsorption Pd Nanoparticles with High Adhesion

Electroless plating (ELP) is widely used to metallize non-conductive substrates in printed circuit board industry. Due to the complexity of commercial palladium catalysts activation procedure and the high price of palladium, we synthesized a type of palladium catalyst with polyvinyl alcohol (PVA) as protector, formaldehyde (HCHO) as reducing agent. We used polyethylimine (PEI) to modify the surface of the substrate in advance.In this study, we developed a one-step catalyst by adding PEI into PVA-Pd. In addition to its stability, the catalyst has self-adsorption property. The process can be operated at low concentrations, which can effectively reduce the cost. Because of these characteristics, it can not only control the catalyst better than the commercial palladium catalyst but also simplify the process. The effect of self-adsorption was tested on Rogers RO3003 laminates. RO3003 high frequency laminates are ceramic-filled PTFE composites for use in printed circuit boards in commercial microwave and RF applications. The substrate has excellent characteristics such as stable dielectric constant over various temperatures and frequency and low coefficient of thermal expansion. Due to these properties, RO3003 has a great potential to be applied in 5G generation products. After activating, we used electroless copper plating to metallize the substrate.The study focused on the Cu/Pd ratio of the self-adsorption catalyst PEI+PVA-Pd to quantitatively analyze the adsorption capacity by ICP-OES, and the adhesion was analyzed by T-peel. The results indicates that the process is cost-effective, and the adhesion between substrate and copper foil is also higher. The copper layer by using self-adsorption catalyst will also have a better compactness and the surface will be pinhole-free. Therefore, this process can be successfully applied to electroless copper deposition with self-adsorption catalysts.

Effect of Ferric Catalyst on Chemical Decomposition of Polyimide-Film-Surface for Enhancing Chemical–Mechanical-Planarization Polishing-Rate

In semiconductor devices, flexible displays and microelectromechanical systems (MEMS), polyimide has been utilized as a protecting layer, interlayer dielectric polymer for thin-film metallization and low-stress polymer for wafer-level packaging. Since, it has low stress, low thermal coefficient of expansion, low moisture, high modulus, good ductility, thermal stability, high glass transition temperature, and low process cost. However, the applications of polyimide required estentially chemical-mechanical-planarization (CMP) of the polyimide-film-surface. that can be challenging to enhance the polishing rate of the polyimide-film-surface because of the hard and covalently bonded nature of the polyimide-film surface.In this study, to enhance chemical dominant CMP, the chemical decomposition of the polyimide-film-surface was performed by hydrolysis reaction between ferric ions and oxygen atoms covalently bonded with pyromellitimide on the polyimide-film-surface during CMP, as shown in Fig. 1. The polyimide-film polishing rate was estimated as a function of ferric catanylst concentration in the CMP slurry;surprisingly, the polyimide film polishing rate(i.e., 1465A/min) peaked at a specific(i.e., 0.05wt%) ferric catalyst concentration, as shown in Fig. 2. This result indicates that the degree of chemical decomposition during CMP could be principally determined by ferric nitrate concentration. The details of both chemical and mechanical dominant polishing mechanisms will be presented. In addition, the evidence of the chemical composition of the polyimide-film-surface will be demonstrated, depending on the ferric catalyst concentation in the CMP slurry. Figure 1

Thermal Expansion of Polypropylene Part II: Depression of In‐Plane Linear Thermal Expansion of Polypropylene by Elastomer Incorporation and Elucidation of Its Mechanism Through Temperature‐Variable X‐ray Scattering

AbstractIn this study, the in‐plane linear thermal expansion behaviors from −20 °C to 100 °C along the flow direction (FD) for injection molded isotactic homo polypropylene (hPP) and their elastomer blends are thoroughly investigated. The elastomers used in this study are two different poly(ethylene‐co‐octene)(EO) thermoplastic elastomers which have the same density but different melt flow rate (MFR), 5.0 and 30 (dg/10 min). Thus, the blends are designated as hPP‐EO5.0 having the EO with 5.0 of MFR and hPP‐EO30 having the EO with 30 of MFR. It is found that from −20 °C to 40 °C, the linear thermal expansion profiles for neat hPP, hPP‐EO5.0, and hPP‐EO30 overlapped, indicating that with or without the EO, their linear thermal expansions proceeded under the same mechanism. On the other hand, above 40 °C, their thermal expansion behaviors greatly changed; the linear thermal expansions of hPP‐EO5.0 and hPP‐EO30 are suppressed to be much lower than that of neat hPP. The morphological observation by a transmission electron microscope (TEM) reveals that the shapes of the EO domains in the blend systems are found to be elongated along the FD. Thus, it would be expected that the suppressed linear thermal expansions of the hPP‐EO blends are attributed to the suppression of the linear thermal expansions of the hPP amorphous layers in the lamellae due to the retraction of the elongated EO domains caused due to the instability of the interfacial tension at elevated temperatures. Yet, temperature variable small‐angle X‐ray scattering (SAXS) results reveal that the linear thermal expansions of the hPP amorphous layers in the EO blends, on the contrary, increase. One of the plausible mechanisms is proposed to elucidate seemingly contradictory phenomenon that the EO blends have their suppressed bulk linear thermal expansions while enhanced linear thermal expansions of the hPP amorphous layers. Finally, the suitable elastomer design for low coefficient of linear thermal expansion (CLTE) PP is proposed.

Study of thermal properties of TiCN by Debye Einstein model, Debye Grüneisen model and quasiharmonic approximation

Thermodynamic properties of ternary ceramic TiCN are studied by first-principles calculation combined with the Debye Einstein model, which considers the contribution of 3n−3 optical frequencies at the Γ point; Debye Grüneisen model, which treats optical frequencies as acoustic ones; and quasiharmonic approximation(QHA), which is the most prevalent method in prediction of phonon dispersion and thermal properties. No imaginary frequency shows that TiCN has dynamic stability, and negative formation energy indicates the thermodynamic stability. Particularly, TiCN has low thermal expansion coefficient, which rises quickly firstly and then gradually as temperature rises. The study of bulk modulus shows that TiCN possess excellent resistance to the volume thermal deformation. For temperature effects of thermal expansion coefficient, heat capacity and entropy, the obtained results show that Debye Einstein model are apparently closer to the QHA at low temperatures. Our present results provide guideline for exploration of thermal properties of multicomponent materials.

Preparation and characterization of colorless and transparent semi‐alicyclic fluoro‐containing polyimide nanocomposite films with enhanced high‐temperature dimensional stability via incorporation of colloidal silica nanofillers

AbstractColorless and transparent semi‐alicyclic fluoro‐containing polyimide (PI) nanocomposite films with enhanced high‐temperature dimensional stability and sustained optical transparency were designed and prepared via incorporation of nano‐sized colloidal silica (SiO2) fillers into the PI matrix derived from hydrogenated pyromellitic dianhydride (HPMDA) and 2,2′‐bis[(4‐aminophenoxy)phenyl]hexafluoropropane (BDAF). The derived PI composite films, abbreviated as 6FCPI‐X in which X stands for the weight percent of the SiO2 in the composite films, exhibited superior thermal and comparable optical properties to the pristine 6FCPI‐0 (6FDA‐BDAF) matrix film. For example, as for the thermal properties, 6FCPI‐35 composite film showed a glass transition temperature (Tg) of 279.1°C and a residual weight ratio at 750°C (Rw750) of 66.1%, which were apparently higher than those of 6FCPI‐0 matrix (Tg = 272.2°C; Rw750 = 47.1%). More importantly, the 6FCPI/SiO2 nanocomposite films showed obviously lower linear coefficients of thermal expansion (CTE) values as compared with that of the 6FCPI‐0 matrix. 6FCPI‐35 composite film showed a CTE value of 36.1 × 10−6/K in the temperature range of 50–250°C, which was lower than half of that of the 6FCPI‐0 matrix (CTE = 77.9 × 10−6/K) in the same range of temperature. In addition, incorporation of nano‐sized colloidal SiO2 particles basically maintained the intrinsically good optical properties of the pristine 6FCPI‐0 matrix film. 6FCPI‐35 composite film showed the optical transmittances of 81.7%, 85.3%, and 87.2% at the wavelength of 400 nm (T400), 450 nm (T450), and 500 nm (T500), respectively, which were in the same level with those of the 6FCPI‐0 film (T400 = 84.0%; T450 = 86.3%; T500 = 87.6%). The 6FCPI series of nanocomposite films also exhibited similar CIE Lab color parameters, including the yellow indices (b*) lower than 2.0 and haze values lower than 1.0%.

A Computational Study of Solid Si Target Dynamics under ns Pulsed Laser Irradiation from Elastic to Melting Regime

The dynamic behavior of solid Si targets irradiated by nanosecond laser pulses is computationally studied with transient, thermοmechanical three-dimensional finite element method simulations. The dynamic phase changes of the target and the generation and propagation of surface acoustic waves around the laser focal spot are provided by a finite element model of a very fine uniformly structured mesh, able to provide high-resolution results in short and long spatiotemporal scales. The dynamic changes in the Si material properties until the melting regime are considered, and the simulation results provide a detailed description of the irradiated area response, accompanied by the dynamics of the generation and propagation of ultrasonic waves. The new findings indicate that, due to the low thermal expansion coefficient and the high penetration depth of Si, the amplitude of the generated SAW is small, and the time and distance needed for the ultrasound to be generated is higher compared to dense metals. Additionally, in the melting regime, the development of high nonlinear thermal stresses leads to the generation and formation of an irregular ultrasound. Understanding the interaction between nanosecond lasers and Si is pivotal for advancing a wide range of technologies related to material processing and characterization.

Tuning the ORR catalytic activity of LaFeO3-δ-based perovskite cathode for solid oxide fuel cells by doping with alkaline-earth metal elements

Co-based perovskite cathodes have demonstrated impressive catalytic activity for oxygen reduction reaction (ORR) at intermediate temperatures. However, these cathodes face the challenges such as high cost and thermal expansion coefficient (TEC) mismatch. On the other hand, Fe-based perovskite oxides like LaFeO3 exhibit more stable properties and lower TEC, but their ORR activity is not as remarkable as that of Co-based cathodes. In this study, La3+ at the A-site of LaFeO3 was substituted by aliovalent alkaline-earth metal cations. The research findings reveal that the doping of alkaline-earth metal ions induces the formation of structural defects and alters the valence state of Fe. This leads to an increase in the conductivity and oxygen vacancy concentration, which are critical for ORR kinetics in both H–SOFC and O–SOFC. Among the various dopants, Sr doped LaFeO3 (LSrF) exhibits the most outstanding ORR catalytic activity. This can be attributed to its highest total conductivity, O2− conductivity, oxygen surface exchange coefficient, and oxygen bulk diffusion coefficient. At 700 °C, single cell with LSrF cathode achieves peak power densities of 0.781 and 0.894 W cm−2, for O2--conducting solid oxide fuel cell (SOFC) and H+-conducting SOFC, respectively. These performances are essentially twice that of single cell with LaFeO3 cathode. The findings of this study provide valuable insights into doping strategies for Fe-based perovskite cathodes and contribute to the advancement of IT-SOFC cathode research.

Effect of Combining Nano- and Microfillers for the Assessment of Thermal Class of Glass Fiber-Reinforced Epoxy Composites for Outdoor Insulation

The present work was taken up with the objective to develop a compact and reliable hybrid composite insulation, investigate the thermal properties of the developed composites and correlate the experimental data with results of mathematical modelling. A composite material made of unidirectional glass fibers reinforced with epoxy resin, and containing silica, alumina, and aluminatrihydrate fillers, was fabricated using the pultrusion technique. Thermogravimetric analysis, thermal conductivity, and coefficient of thermal expansion were conducted on the developed composites. The energy of activation was estimated from the thermograms using mathematical models to assess the thermal class of the composites. Though G-E composite is typically classified under class F insulation, the study has established that due to the unique filler combination, has a higher temperature index ranging between 156 °C - 166 °C. The improvement in thermal performance was observed when each filler is present in a weight percentage of 10%. The hybrid composites have excellent thermal conductivity (0.43 W/mK), a low coefficient of thermal expansion (22.1 μm/m°C), and hence useful for high-temperature insulation applications like circuit breakers, vacuum interrupters, transformers, switching gear etc.

In-situ growth of diamond/Ag as hybrid filler for enhancing thermal conductivity of liquid crystal epoxy

To meet the higher requirements posed by high-power chips on packaging materials, designing and fabricating a multi-functional integrated composite is an effective solution. In this work, the diamond/Ag hybrid filler was prepared (in-suit growth) using the “Ball milling-Heating” approach in the absence of any solvent or external force. Furthermore, the nano-micro hybrid filler was combined with the inherently high thermal conductivity liquid crystal epoxy resin to create composites through a hot-press curing. In this process, there is a synergistic interaction between fillers and matrix and Ag nanoparticles serve as bridging elements in nano-scale. Ultimately, the hybrid filler with a nano-microstructure effectively constructs “phonon-electronic-phonon” pathways in the liquid crystal epoxy matrix. When the hybrid filler content reached 80 wt%, the composites demonstrated a range of integrated advantages including high thermal conductivity (4.65 W/m·K), low coefficient of thermal expansion (CTE), high volume resistivity, and excellent thermal stability. The era of high-power devices is approaching, and this study offers a novel perspective on the application of epoxy-based composite materials in the realm of advanced packaging.

Effect of lattice distortion on thermal conduction behavior in a novel high-entropy rare-earth tantalates

In this study, seven types of thermal protection coating materials (high-entropy rare-earth tantalates 5RETaO4, RE= Nd, Sm, Eu, Gd, Dy, Ho, Y, Eu, Tm, and Y) were synthesized by solid-phase reaction and high-throughput experiment. Results showed that 5RETaO4 exhibits excellent thermophysical properties owing to its unique high-entropy and lattice distortion effects. Namely, (Nd0.2Dy0.2Ho0.2Y0.2Eu0.2)TaO4 ceramics perform low thermal conductivity and suitable thermal expansion coefficient. The low thermal conductivity of 5RETaO4 is mainly due to the difference of RE3+-O2- bond caused by different rare-earth cation radius, which further changes the length of an ionic bond between O2- and Ta5+, resulting in severe lattice distortion and increased phonon scattering coefficient. These excellent properties indicate that (Nd0.2Dy0.2Ho0.2Y0.2Eu0.2)TaO4 can be used as a new generation of thermal protection coating material.

Magnet selection for permanent magnet synchronous machines by decision science

This work investigates magnet selection for permanent magnet synchronous machines (PMSMs) by decision science. 20 multiple-attribute decision-making (MADM) methods ranked a list of 45 industrial-grade permanent magnets based on eight property requirements―high energy density (BHMAX), high coercivity (HC), high magnetic remanence (BR), high electrical resistivity (ρ), high Curie temperature (TC), high maximum service temperature (TS), low linear thermal expansion coefficient (α), and low density (d)―targeted to selecting magnets for PMSMs. The Shannon's entropy method evaluated the objective attribute weights of ρ, BHMAX, and HC, as ∼46%, ∼24%, and ∼23%, respectively, and the rest—BR, TC, TS, d, and α―combined as ∼7%; equal weights (∼12.5% each) to all the attributes were the subjective weights. Principal component analysis (PCA) consolidated ranks from various MADM methods, and hierarchical clustering (HC) grouped magnets based on their similarities. For PMSMs in applications where ρ, BHMAX, and HC, are more critical compared to the rest of the properties, the eight top-ranked magnets are N35 (Neodymium® 35), N35H (Neodymium® 35H), N30 (Neodymium® 30), N30H (Neodymium® 30H), N27H (Neodymium® 27H), N27 (Neodymium® 27), F5–S (Ferrite 5, Sintered Iron Strontium Oxide), and F3–S (Ferrite 3, Sintered Iron Barium Oxide) in that order. On the other hand, for PMSMs in applications where all the attributes are equally important, the eight top-ranked magnets are N35 (Neodymium® 35), N35H (Neodymium® 35H), N30H (Neodymium® 30H), N30 (Neodymium® 30), N27H (Neodymium® 27H), N27 (Neodymium® 27), CS4 (Samarium Cobalt 4), and F5–S (Ferrite 5, Sintered Iron Strontium Oxide) in that order. The consolidated ranks of the magnets obtained by assigning objective and subjective attribute weights showed a strong correlation of ∼0.94. This investigation targeted magnet selection for PMSMs from a comprehensive dataset of industrial-grade permanent magnets, utilizing several property requirements, applying both objective and subjective attribute weights identified Neodymium® 35 as the top-ranked magnet.

Low‐Loss Sr2Ti9O20‐Filled Butyl Rubber Composites for Miniaturized Flexible Microwave Substrate Applications

Low‐loss Sr2Ti9O20 (STO)/butyl rubber (BR) composites have been prepared by mixing and hot pressing. X‐ray diffraction and energy‐dispersive spectroscopy are employed to investigate the phases contained in the STO filler, and the microstructural characteristics of the composites are discovered using scanning electron microscopy. The STO/BR composites demonstrate a high relative permittivity of 10.98 and a low loss of 0.003 at 10 GHz, corresponding to an optimum filler volume fraction of 45%. In addition, a low coefficient of thermal expansion of 50.72 ppm °C−1 and a high thermal conductivity of 0.9603 W m−1 K−1 have been found for the optimum composition, with an acceptable moisture absorption of 0.071%. The obtained composites can be employed for miniaturized, flexible radio‐frequency substrate applications.

Developing Creep and Stress Relaxation Models to Assess the Service Life of an Additive Manufactured Industrial-Scale Recuperator Utilizing Inconel 625 and AISI 310S Materials.

This work is focused on the development of creep and stress relaxation models on Inconel 625 and Stainless Steel 310 materials for additive manufacturing. At the end, the operational lifespan of an industrial-scale additive manufactured recuperator is evaluated. An industrial-scale recuperator for burners with a highly complex geometry is manufactured using Continuous Wave SLM and Pulsed Wave Selective Laser Melting techniques. The recuperator operates under steady but high thermal loads, reaching temperatures of up to 875 °C. Therefore, its service life is assessed, considering creep and stress relaxation phenomena. Two different materials are evaluated: Inconel 625 and Stainless Steel 310. Tensile testing has been conducted on samples at various temperatures to acquire material parameters, incorporating appropriately the anisotropic nature of the materials. Creep parameters were determined through creep experiments and data from the literature, and the recuperator response was simulated by FEA modelling. Analytical creep and stress relaxation models were proposed based on the simulation results for each material to predict their creep response. The service life was determined by applying a custom failure criterion based on the creep testing data. The Inconel 625 recuperator exhibits a service life that is significantly higher compared to any burner's life, while the Stainless Steel 310 recuperator exhibits approximately 27 years of service life. Both materials are considered suitable; however, Inconel 625 offers higher resistance to creep according to creep tests, and due to its lower thermal expansion coefficient, the resulting thermal stresses are lower.

Multiscale Engineered Waste Wood Particles toward a Sustainable, Scalable, and High‐Performance Structural Material

AbstractDeveloping sustainable and lightweight structural materials is a promising strategy for reducing carbon emissions in transportation and buildings. However, producing high‐performance bulk structural materials from sustainable biomass materials while maintaining excellent mechanical strength remains a major challenge, especially for further scale‐up. Herein, a scalable and robust bottom‐up strategy is reported to fabricate bulk wooden plate (W‐plate) with a typical “brick‐and‐mortar” structure from engineered wood particles via moderate delignification and in situ LiCl/DMAc treatment followed by hot‐pressing. The W‐plate constructed by delignified wood particles and regenerated cellulose nanofibers can achieve a confluence of mechanical strengthening and toughening by the ordered lamination structure and multiscale cellulose micro/nanofiber crosslinking interactions, resulting in high flexural strength (225.17 ± 12.18 MPa) and high fracture toughness (4.01 ± 0.53 MPa m0.5) while maintaining a low density (1.34 g cm−3), superior to typical metals and ceramics. Moreover, the W‐plate exhibits advantageous thermal properties, including a low thermal expansion coefficient (<19 × 10−6 K−1) and a high storage modulus (>7.5 GPa) compared to those of petroleum‐based polymers. Coupled with abundant and renewable raw materials, all‐cellulose components, and scalable and recyclable fabrication, the W‐plate can potentially be used as a high‐performance, cost‐effective, and environmentally friendly alternative for engineering applications.

Measurements of stresses in β‐(Y,Yb)2Si2O7 environmental barrier coating layers using Raman spectroscopy

AbstractResidual stress measurements in environmental barrier coatings (EBCs) can help in understanding coating durability and potential damage mechanisms. We demonstrate the capability of Raman spectroscopy to measure average residual stresses in two different β‐RE2Si2O7 (RE = rare earth or Y3+, denoted as REDS) EBCs with a nominal (Yb,Y)2Si2O7 composition, focusing on macroscopic residual stresses acting at macroscopic length scales. Uniaxial compression measurements of dense β‐(Yb,Y)2Si2O7 ceramics are used for calibration curves for applied stress versus Raman peak shift. We use these calibration curves to evaluate the macroscopic thermoelastic residual stress in the (Yb,Y)2Si2O7 layers from coefficient of thermal expansion (CTE) mismatch of two different (Yb,Y)2Si2O7‐based EBCs on SiC‐based substrates. Microscopic stress contributions to Raman peak shifts are subtracted using reference free‐standing coatings and analytic estimates for inclusion stresses when (Yb,Y)2Si2O7 coatings have a high, variable volume fraction of (Yb,Y)2SiO5. The macroscopic thermal residual stress in these (Yb,Y)2Si2O7 EBCs is compressive, as expected from the smaller CTE of β‐REDS versus SiC. These thermal residual stresses can vary between different YbYDS EBC coatings by more than a factor of three with a measured layer residual stress of approximately –180 MPa (compressive) for a high modulus, low CTE coating, and our measured values generally agree with calculated estimates.

Spray pyrolysis-based synthesis of pure molybdenum powder with nanoscale primary particles and its sintering characteristics

Molybdenum (Mo) is a refractory metal with exceptional high-temperature stability, resistance to creep, and low coefficient of thermal expansion, it thus has great potential for various high-temperature applications. Nevertheless, conventional methods of synthesizing Mo powder, such as mechanical milling and wet chemical processing, have encountered limitations in producing sintered bodies with high relative density and a fine grain structure while maintaining a low sintering temperature. Therefore, it is crucial to develop an efficient powder synthesis method that enables precise and uniform control over the powder's size and shape while minimizing contamination. Such an approach would contribute to achieving excellent formability and sinterability for the resulting Mo sintered body. In this study, we successfully demonstrated the ultrasonic spray pyrolysis (USP) technique in combination with hydrogen reduction for synthesizing pure Mo powder. The resulting Mo powder exhibited micro-sized secondary particles composed of nanoscale primary particles, leading to improved formability and sinterability, essential for fabricating high-quality sintered bodies. In order to comprehensively understand the properties of the as-prepared molybdenum oxide and hydrogen-reduced Mo powder, we employed various methods to analyze its physicochemical characteristics systematically. Subsequently, the fine Mo particles were subjected to a pressureless sintering process after a conventional uniaxial powder molding. Due to its excellent formability and sinterability, we achieved a Mo sintered body with a grain size of approximately 3 μm while maintaining a relatively high sintering density of 98.3% at a comparatively low sintering temperature of 1400 °C. The resulting microstructure contributed to a relatively high hardness of around 234 Hv. These results indicate the successful synthesis of pure Mo powder with desirable properties and highlight its potential in various applications, particularly those requiring high-quality sintered bodies with enhanced hardness.