Low Coefficient Of Thermal Expansion Research Articles

The Effect of Graphite Flake Volume Fraction on the Thermophysical Proper Ties of Graphite Flake/Aluminum Composites

A vacuum hot‐press sintering process is utilized to manufacture graphite flake/aluminum composites, and the influence of graphite flake volume fraction on the microscopic structure, hardness, thermal conductivity (TC), and coefficient of thermal expansion (CTE) of the composites is investigated. The results indicate that the graphite flakes are neatly aligned along the in‐plane direction in the composites and exhibit a strong bond with the aluminum matrix interface. The in‐plane TC of the composite significantly increases with the addition of graphite flakes, whereas hardness, through‐plane TC, and CTE decrease. As the volume fraction of graphite flakes in the composites increases from 15% to 60%, in‐plane TC improves from 278.8 to 353.8 W m−1 K−1, through‐plane TC decreases from 164.4 to 33.2 W m−1 K−1, and the CTE decreases to 13.7 × 10−6 K−1, achieving high thermal conductivity and a low CTE.

Poly(ester imide)s with Low Linear Coefficients of Thermal Expansion and Low Water Uptake (VII): A Strategy to Achieve Ultra-Low Dissipation Factors at 10 GHz.

In this study, a series of ester-linked tetracarboxylic dianhydrides (TCDAs) with 2,6-naphthalene-containing longitudinally extended structures consisting of different numbers of aromatic rings (NAr = 6-8) was synthesized to obtain novel modified polyimides, poly(ester imide)s (PEsIs). These TCDAs were fully compatible with the conventional manufacturing processes of conventional polyimide (PI) systems. As an example, the PEsI film obtained from the ester-linked TCDA (NAr = 8) and an ester-linked diamine achieved unprecedented outstanding dielectric properties without the support of fluorinated monomers, specifically an ultra-low dissipation factor (tan δ) of 0.00128 at a frequency of 10 GHz (50% RH and 23 °C), in addition to an extremely high glass transition temperature (Tg) of 365 °C, extremely low linear coefficient of thermal expansion (CTE) of 6.8 ppm K-1, suppressed water uptake (0.24%), requisite film ductility, and a low haze. Consequently, certain PEsI films developed in this study are promising candidates for heat-resistant dielectric substrates for use in 5G-compatible high-speed flexible printed circuit boards (FPCs). The chemical and physical factors denominating tan δ are also discussed.

Laser deposition of titanium layer to enhance two-way shape memory behavior of Nitinol sheet

One of the long-standing mechanical challenges associated with shape memory alloys (SMAs) is achieving and stabilizing an evolving two-way shape memory effect (TWSME) through thermomechanical training/cycling. In most martensitic NiTi SMAs that exhibit zero TWSME at room temperature, the TWSMEs typically require hundreds of cycling repetitions to track trivial values. This demonstrates a promising solution to overcome this challenge. The surface of NiTi SMA sheets was treated by depositing a certain number of titanium (Ti) powder layers on the NiTi surface using a laser beam. The results showed that a unique TWSME of approximately 12% with good stability was achieved after 100 cycles when the optimum number of five Ti layers was deposited, which was much higher than that of the NiTi sheet (0.3% TWSME) and the sample with a single-time laser path irradiation (1.8%). This was attributed to the low coefficient of thermal expansion of the Ti vs. NiTi sheet, which prevented reverse bending during heating, and the formation of Ti-rich intergranular Ti2Ni(Ox) precipitates, which hindered dislocation movement. Meanwhile, in this sample, owing to the generation of a large residual tensile stress and a large heat-affected zone that led to a reduction in plastic zones, the one-way shape memory effect (OWSME) was retained at values above 90% with good stability over cycling. However, the introduction of additional Ti layers can cause problems in terms of oxygen accumulation within the NiTi sheet, which should be considered when designing a product.

Ultra-high-performance graphene-based bulk materials strengthened by Y-type connection structure

The strategic design and assembly of bulk graphene materials represent a pivotal advancement for harnessing the inherent properties of graphene in practical applications. However, fabricating high-strength graphene-based bulk materials from graphene powders presents a significant challenge, primarily due to interlayer slippage between the graphene layers. Here, a unique Y-type connection structure was found in few-layer graphene synthesized by self-propagating high-temperature synthesis (SHS) and subsequently retained in graphene-based bulk materials prepared by spark plasma sintering (SPS) process. The Y-type connection structure and defect-induced linkages serve to cross-link the graphene-based bulk materials. Consequently, the bulk material exhibited an ultra-high compressive strength, reaching 2.14 GPa, supported by Molecular dynamics (MD) simulations which demonstrated that the Y-type connection structure increases the shear modulus and the load transfer rate. The Y-type connection structure plays a vital role in reinforcing the strength of graphene-based bulk materials, offering valuable insights for the microstructural design and property augmentation of other graphene-derived materials. Besides it’s ultra-high compressive strength, the graphene-based bulk material also performs a low thermal expansion coefficient (0.5 × 10−6 K−1), high electrical conductivity (1.47 × 105 S·m−1) and exceptional EMI shielding capability.

A rapid and precise approach to predicting the cure‐induced warping of T‐shaped composite parts with inconsistent layup

AbstractThis work involved the precise prediction and in‐depth analysis of cure‐induced warping of T‐shaped parts with inconsistent layup. First, the warping mechanism of this kind of part was studied. Then, a finite element analysis (FEA) that considered the parts' structural characteristics and inconsistent layup using the curing mechanical constitutive model was developed to predict the warping. Following verification of the model's accuracy, the effects of material and structural characteristics on warping were investigated. When designing T‐shaped parts, selecting materials with lower thermal expansion coefficients can help minimize warping. Additionally, increasing the radius of the chamfer at the rib and flange connections is also effective. By taking into account the effects of structural parameters and inconsistent layup by using both classical laminated plate theory and artificial neural networks (ANN), a rapid and accurate surrogate model for warping prediction was finally developed. It was discovered that the two‐layer ANN model performed better than the other two models and could predict warping with accuracy and speed. For the parts analyzed in this work, this model is able to identify the fluctuations of warping captured by FEA. Moreover, by defining deviation as the difference between the predicted values of the surrogate model and the FEA, it can be observed that the majority of deviations for the validation set are within ±1.5 mm. This demonstrates that the two‐layer ANN possesses strong generalization ability and high accuracy in predicting warping.Highlights The inconsistent layup could significantly affect the T‐shaped part's warping. Cutting off a part's rib may significantly reduce its warping. A rapid and accurate model for warping prediction was developed. The layup and structure's influence could be identified by the two‐layer ANN.

Preparation of Li2O–Al2O3–SiO2–B2O3（LASB）glass-ceramic with low thermal expansion coefficient from spent hydrogenation catalysts and crystallization kinetics

The recovery of spent hydrogenation catalysts occupies advantages in both alleviating environmental burden and resource shortage. Whereas, the development of conventional hydrometallurgical recovery of molybdenum (Mo) and nickel (Ni) from spent MoNi/Al2O3 catalysts has been limited by the numerous processes and the accompanying generation of waste liquids and residues. Herein, A new recycling route for the preparation of spent hydrogenation catalysts with low thermal expansion coefficients (CTE) was proposed, which has the advantages of short process, green environment and high value utilization. The Li2O–Al2O3–SiO2–B2O3 (LASB) parent glass containing Mo and Ni were obtained by melting with different contents of the spent catalysts. The thermal expansion coefficient of the glass was minimized to 6.08 × 10−6/°C at an addition of 25 wt% of the spent catalysts. Moreover, according to the crystallization peak in DTA curve, glass-ceramics were prepared by one-step crystallization heat treatment at different crystallization temperatures. The main crystalline phase of the glass-ceramic precipitated by heating at 685 °C is β-quartz (Li2Al2Si3O10), which gives the glass-ceramics the lowest coefficient of thermal expansion (0.96 × 10−6/°C) of glass-ceramic as well as the maximum density (2.45 g/cm3) and Vickers hardness (705.8 Hv). Furthermore, the activation energy (354.65 ± 17.42) kJ/mol) and Avrami index (5.39) associated with crystallization were extracted from the fitting of different theoretical model, indicating the three-dimensional crystallization of the LASB glass-ceramics. This technology provides a waste-to-material strategy for hazardous waste and a clean production route for the preparation of the functional glass-ceramics.

Interfacial Stability between High-Entropy (La0.2Yb0.2Sm0.2Eu0.2Gd0.2)2Zr2O7 and Yttria-Stabilized Zirconia for Advanced Thermal Barrier Coating Applications

(La0.2Yb0.2Sm0.2Eu0.2Gd0.2)2Zr2O7 (HEZ) has shown considerable promise as a novel thermal barrier coating material for temperatures exceeding 1300 °C. This study systematically investigates the interfacial stability of (La0.2Yb0.2Sm0.2Eu0.2Gd0.2)2Zr2O7 with yttria-stabilized zirconia (YSZ), which is of paramount importance for its application in double-layer thermal barrier coatings. Our findings highlight that rare earth elements with a smaller radius diffuse more easily into the YSZ lattice, resulting in a broader diffusion zone. Simultaneously, the incorporation of rare earth elements into the YSZ lattice inhibits tetragonal-to-monoclinic phase transformation. Compared to La2Zr2O7/YSZ, HEZ/YSZ demonstrates superior high-temperature stability, which could be attributed to the higher fracture toughness and lower thermal expansion coefficient of HEZ, the absence of t-m transformation and the formation of a continuous gradient diffusion layer that minimizes interface stress. This study offers a practical strategy for designing materials for durable double-layer thermal barrier coating systems.

Kinetic analysis of the crystallization of Y2O3 and La2O3 doped Li2O-Al2O3-SiO2 glass.

Li2O-Al2O3-SiO2 (LAS) glass ceramics have a low coefficient of thermal expansion, high mechanical strength, and excellent chemical stability. With advancements in glass ceramics, researchers have explored using LAS glass ceramics with transition metal doping and rare earth doping. Most previous studies have studied the impact of rare earth element doping on crystallization primarily in the context of conventional nucleating agents present in glass. In this study, we aimed to investigate the impact of Y2O3 and La2O3 on LAS glasses in the presence of undoped nucleating agents. The crystallization mechanism of La2O3 and Y2O3 doped LAS glass ceramics was studied using differential scanning calorimetry. The crystallization kinetics of the glasses were analyzed using model-free and modeling methods. Moreover, the activation energy of crystallization and the indices of crystallization and growth of glass ceramics were calculated, and the crystalline phase and microstructure of the samples were characterized. All three fractions of the LAS glass showed consistent crystallization under different calculation methods. The glass doped with La2O3 and Y2O3 exhibited two- or three-dimensional growth during crystallization, promoting crystallization in the LAS glass. The Y3La0 sample demonstrated the most favorable crystallization effect. In the presence of an undoped nucleating agent, rare earth elements can enhance glass crystallization; this new idea can be utilized for the development of new materials.

Fabrication of Sr-feldspar/cordierite and Sr-feldspar/Sr-osumilite composites through sintering of Mg–Sr-cordierite and borosilicate glass for electronic applications

The main objective of this study is to fabricate composite materials having excellent thermal, mechanical and electrical properties for thermal and electronic applications. In this work, strontium feldspar-containing composites (Sr-feldspar/cordierite and Sr-feldspar/Sr-osumilite) were prepared by solid-state sintering of SrO-containing cordierite (MgSrAl4Si5O18)/borosilicate glass powder mixtures. The phase composition, physical properties and microstructure of sintered composites were investigated by X-ray diffraction technique, water displacement method and scanning electron microscope, respectively. Moreover, the thermal expansion coefficient, hardness, and electrical properties were also measured. The results of X-ray patterns revealed the crystallization of Sr-feldspar and cordierite in the composites that contain up to 20% borosilicate glass. On the other hand, the composites that include more than 20% glass, displayed the crystallization of Sr-feldspar and Sr-osumilite with little amount of cristobalite. The bulk density values of sintered composites were decreased from 2.41 to 1.84 g/cm3 with increasing the amount of added glass. The microhardness values were increased from 519 to 710 kg/mm2 with increasing the glass content. Low thermal expansion coefficient (2.65 × 10−6, 2.22 × 10−6, 3.45 × 10−6 and 4.26 × 10−6 K-1 for C0, CG91, CG73, CG55, respectively) and low dialectic constant (7–8.5) were obtained for the prepared composites.

Enhancing the dielectric and thermal properties of polytetrafluoroethylene-based composites through designing and constructing a novel interfacial structure

Polytetrafluoroethylene (PTFE) is widely used as a fundamental core material for high-frequency and high-speed signal transmission fields due to its excellent dielectric properties. However, the high coefficient of thermal expansion (CTE) characteristic of PTFE severely limits its practical application. The CTE of PTFE can be reduced by filling with SiO2, which is always accompanied by a rapid deterioration of dielectric properties due to the poor interfacial compatibility between SiO2 and PTFE matrix. In this paper, the challenge of synergistic regulation of dielectric and CTE properties for PTFE-based composites is overcome by constructing an interfacial structure with physical interactions. Micro-mesoporous SiO2 (mSiO2) is prepared and introduced as a filler, compared with smooth surface SiO2 (sSiO2), the presence of micro-mesoporous in mSiO2 allows PTFE molecular chains to be adsorbed on the surface or in the pore channels of mSiO2, which improves the interfacial combination of the mSiO2/PTFE composites through the physical interaction between mSiO2 and PTFE. The results show that mSiO2/PTFE composite exhibits a lower CTE (58 ppm °C−1) while maintaining a lower dielectric constant (εr, 2.29, 30 GHz) with dielectric loss (tan δ, 2.31 × 10−3, 30 GHz) at a filler addition of 30 vol%, as compared with that of the sSiO2/PTFE composites. This work provides a new strategy for fabricating PTFE-based composites with low CTE as well as low εr and tan δ.

A review on gas permeability of polymer matrix composites for cryogenic applications

Fiber-reinforced polymer matrix composites are increasingly considered for lightweight cryogenic pressure vessels due to their excellent combination of tailorability, specific mechanical properties, and relatively low coefficients of thermal expansion. However, significant challenges must be overcome to fully utilize PMCs for cryogenic fuel tanks in terms of transverse microcracking and subsequent permeation of cryogenic fuel. Gas permeation and microcrack densities of cryogenically cycled composites are highly influenced by their layup, ply thickness, load case, and manufacturing defects like voids and resin rich zones. There has been a significant amount of research on measuring gas permeation of composites fatigued under pure thermal or uniaxial thermo-mechanical stresses. However, results demonstrate that the gas permeability should be measured under biaxial thermo-mechanical stresses to properly gauge the leakage characteristics of damaged composites. This paper summarizes the results from over a hundred papers on the key parameters that influence the gas permeability of composites, appropriate testing methods to cycle composites for permeability measurement, methods to limit the evolution of transverse microcracks, and materials traditionally used for the fabrication of all-composite cryogenic fuel tanks. Thin plies and nanofiller-toughening of the matrix have been shown to provide significant improvements in transverse microcrack suppression within cryogenically cycled composites.

Microstructural characterization of 15Cr steel after quenching and slow cooling rates

Abstract Ferritic 15 %-Cr steels have better oxidation resistance, due to their higher chromium content, and creep strength, their lower dislocation density and lack of lath microstructure than conventional martensitic steels such as MarBN. Their mechanical properties are sensitive to chemical composition and heat treatment. In this study, we first simulated the formation of stable phases in two ferritic steels containing 2 % nickel (wt.%) and an alloy without nickel using the thermomechanical software MATCALC. Microstructural analysis using scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS) reveals the formation of carbides and intermetallic phases after diffusion annealing, both during rapid cooling in oil and slow cooling in the furnace. Dilatometry and XRD studies confirm the gradual phase transformation of ferrite to austenite from 650 °C onwards during heating. Dilatometry also shows that ferritic steels have a lower coefficient of thermal expansion than martensitic steels, austenitic steels, and superalloys, which results in lower thermal stresses during frequent start-up and shutdown of power plants.

Enhanced Mechanical and Thermal Properties of Polyimide Films Using Hydrophobic Fumed Silica Fillers.

Polyimide (PI) composite films with enhanced mechanical properties were prepared by incorporating modified fumed silica (FS) particles while preserving their optical and thermal characteristics. The PI matrix was synthesized using a fluorinated diamine, a fluorinated dianhydride, and a rigid biphenyl dianhydride via chemical imidization. Commercially available FS particles, including unmodified FS particles (0-FS) and particles modified with dimethyl (2-FS), trimethyl (3-FS), octyl (8-FS), octamethylcyclotetrasiloxane (D4-FS), and polydimethylsiloxane (PDMS-FS) were used. Scanning electron microscope images and nitrogen adsorption-desorption isotherms revealed well-defined porous structures in the FS particles. The water contact angles on the composite films increased compared to those of the pristine PI films, indicating improved water resistance. The PI/0-FS films exhibited a typical trade-off relationship between tensile modulus and elongation at break, as observed in conventional composites. Owing to the poor compatibility and agglomeration of the PDMS-FS particles, the PI/PDMS-FS composite films exhibited poor mechanical performance and diminished optical characteristics. Although the longer-chained FS particles (8- and D4-FS) improved the tensile modulus of the PI film by up to 12%, a reduction of more than 20% in toughness was observed. The PI composite films containing the methylated FS particles (2- and 3-FS) outperformed 8- and D4-FS in terms of mechanical properties, with PI/3-FS films showing an over 10% increased tensile modulus (from 4.07 to 4.42 GPa) and 15% improved toughness (from 6.97 to 8.04 MJ/m3) at 7 wt. % silica loading. Except for the PI/PDMS-FS composites, all composite film samples exhibited more than 86% transmittance at 550 nm. Regarding thermal properties, the glass transition temperature (Tg) and thermal stability remained stable for most composite films. In addition, PI/3-FS films demonstrated enhanced dimensional stability with lower coefficients of thermal expansion (from 47.3 to 34.5 ppm/°C). Overall, this study highlights the potential of incorporating specific modified FS particles to tailor the mechanical, optical, and thermal properties of PI composite films.

Mg2Al4Si5O18 as a novel bond coat material for advanced thermal/environmental barrier coatings on SiCf/SiC composites

This study proposes cordierite (Mg2Al4Si5O18, MAS) as a novel bond coat material for thermal/environmental barrier coatings (T/EBC), deposited using atmospheric plasma spray on SiC fiber reinforced SiC matrix composites (SiCf/SiC-CMCs) coupons, forming a Mg2Al4Si5O18/Yb2Si2O7/Yb2SiO5/LaMgAl11O19 coating system. The phase composition and thermal properties of the as-sprayed MAS coating were investigated, revealing cordierite as the primary phase in the as-sprayed coating with minor amounts of spinel and quartz phases which disappeared after heat treatment. Additionally, the as-sprayed MAS coating exhibited a low thermal expansion coefficient (3.19 × 10−6 K−1). The thermal cycling behavior and steam corrosion performance of the T/EBC coating system with cordierite as the bond coat were studied. Detailed analysis revealed that during thermal cycling tests, the coating failure was primarily related to liquid-phase sintering caused by eutectic reactions. In steam corrosion tests, the coating delamination was linked to the formation and growth of cracks and corrosion voids due to the residual stress release.

Additively manufactured multi-functional metamaterials: low coefficient of thermal expansion and programmable Poisson’s ratio

ABSTRACT By using Invar 36 alloy as the constituent material, a series of multi-functional metamaterials, integrating low coefficient of thermal expansion (CTE) and programmable Poisson’s ratio (PR), were originally designed and additively manufactured by laser powder bed fusion (PBF-LB). The densification, relative density, microstructures, CTE and PR were systematically characterised and analysed by experiments and numerical modelling. Specifically, the fabricated metamaterials demonstrate uniform microstructures, resulting in isotropic low CTEs ranging from 1.79 to 1.85 ppm/°C. Besides, the designed metamaterials achieve PR tuning in the range of −0.54∼+0.58, which is close to the theoretical predictions, confirming the PR programmability. The underlying mechanism is disclosed that the variable θ 1 dominates the transverse deformation behaviour of the metamaterial, achieving programmable PR. Summarily, these metamaterials achieve the integration of the low CTE and programmable PR, and provide a wider operating temperature range and superior mechanical performances than polymer-based multi-functional metamaterials, exhibiting a broader application prospect.

Polyphenylene oxide/boron nitride–alumina hybrid composites with high thermal conductivity, low thermal expansion and ultralow dielectric loss

AbstractTraditional integrated circuit (IC) packaging materials and printed circuit board substrate materials suffer from several limitations including low thermal conductivity, high coefficient of thermal expansion (CTE), and poor dielectric properties. Although significant efforts have been made to enhance these properties, achieving a single composite system with simultaneous high thermal conductivity, extremely low CTE, and dielectric loss remains a formidable task. In this study, we propose a hybrid polymer composite system that addresses these challenges. Our approach involves utilizing a thermosetting polyphenylene oxide (PPO) as the resin matrix, while incorporating boron nitride (BN) sheets with high thermal conductivity and alumina (Al2O3) spheres with favorable fluidity as fillers. To optimize the composite properties, the filler surfaces are modified using dopamine and silane coupling agents, ensuring proper interface control. The composites exhibit significant improvements in thermal conductivity, reduced dielectric loss and CTE, while maintaining excellent processibility. Specifically, with a composition of 25 vol% BN and 25 vol% Al2O3, the thermal conductivity of the composite reaches 2.18 W·m−1 K−1, surpassing neat PPO resin by a factor of 10.9. Simultaneously, the CTE decreases from 2.27% to 1.18% between 50 and 260°C, and the dielectric loss reduces from 0.0024 to 0.0011 at 10 GHz, as compared to neat PPO resin.Highlights The reported novel hybrid composite offers a promising solution to the limitations of traditional IC packaging materials. The reported hybrid composite exhibits significantly improved thermal conductivity, ultralow dielectric loss, and reduced coefficient of thermal expansion, while maintaining excellent processibility. The thermal conductivity of the composites reaches 2.18 W·m−1 K−1, surpassing that of the neat resin by a factor of 10.9, meanwhile the dielectric loss is as low as 0.0011 at 10 GHz, which is extremely difficult to achieve simultaneously for thermosetting polymer composites. Synergetic effects were realized with the hybridization of fillers with different dimensionality, and proper filler surface modification.

Investigation of Shape Memory Polyurethane Properties in Cold Programming Process Towards Its Applications.

Thermoresponsive shape memory polymers (SMPs) with the remarkable ability to remember a temporary shape and recover their original one using temperature have been gaining more and more attention in a wide range of applications. Traditionally, SMPs are investigated using a method named often "hot-programming", since they are heated above their glass transition temperature (Tg) and after that, reshaped and cooled below Tg to achieve and fix the desired configuration. Upon reheating, these materials return to their original shape. However, the heating of SMPs above their Tg during a thermomechanical cycle to trigger a change in their shape creates a temperature gradient within the material structure and causes significant thermal expansion of the polymer sample resulting in a reduction in its shape recovery property. These phenomena, in turn, limit the application fields of SMPs, in which fast actuation, dimensional stability and low thermal expansion coefficient are crucial. This paper aims at a comprehensive experimental investigation of thermoplastic polyurethane shape memory polymer (PU-SMP) using the cold programming approach, in which the deformation of the SMP into the programmed shape is conducted at temperatures below Tg. The PU-SMP glass transition temperature equals approximately 65 °C. Structural, mechanical and thermomechanical characterization was performed, and the results on the identification of functional properties of PU-SMPs in quite a large strain range beyond yield limit were obtained. The average shape fixity ratio of the PU-SMP at room temperature programming was found to be approximately 90%, while the average shape fixity ratio at 45 °C (Tg - 20 °C) was approximately 97%. Whereas, the average shape recovery ratio was 93% at room temperature programming and it was equal to approximately 90% at 45 °C. However, the results obtained using the traditional method, the so-called hot programming at 65 °C, indicate a higher shape fixity value of 98%, but a lower shape recovery of 90%. Thus, the obtained results confirmed good shape memory properties of the PU-SMPs at a large strain range at various temperatures. Furthermore, the experiments conducted at both temperatures below Tg demonstrated that cold programming can be successfully applied to PU-SMPs with a relatively high Tg. Knowledge of the PU-SMP shape memory and shape fixity properties, estimated without risk of material degradation, caused by heating above Tg, makes them attractive for various applications, e.g., in electronic components, aircraft or aerospace structures.

Garnet-type lithium sensors for the monitoring and control of Pb-Li alloys in tritium breeding modules

During the EU-DEMO conceptualization, eutectic Pb-Li was considered as the prime candidate liquid breeding material. Nonetheless, the conversion of lithium into tritium through the breeding reaction will result in a decrease in the lithium concentration within the alloy. Then, the monitoring of the lithium concentration in Pb-Li alloys is critical for the optimal Tritium Breeding Blanket (TBB) performance, as lithium affects dissolution of structural materials, tritium inventory and extraction rates. Garnet-like ceramics possess desirable properties for their use in lithium sensors, like high lithium-ion conductivity, good chemical stability, low thermal expansion coefficient, and great mechanical strength. For these reasons, electrochemical sensors based on garnet-type ceramics offer advantages for measuring lithium in molten Pb-Li alloys, such as high selectivity and fast response. This work presents the development of lithium sensors based on the garnet-type ceramic Li6BaLa2Ta2O12. The material was characterized by XRD and SEM, exhibiting good crystallinity and a homogeneous microstructure. The sensors were evaluated in a potentiometric configuration in molten Pb-Li alloys with lithium concentrations ranging from 3 to 35 at% Li. Potentiometric measurements were used to obtain correlations that allow the determination of the lithium activity in the lead–lithium alloys studied.

Synthesis of colorless transparent poly(amide-imide) with high modulus and low thermal expansion coefficient and its performance study

To meet the needs of high dimensional stability and high transparency of colorless polyimide (CPI) films, a series of poly(amide-imide) (PAI) films were synthesized by copolymerization of 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), terephthaloyl chloride (TPC) and 2,2′-bis(trifluoromethyl)benzidine (TFDB). By adjusting the ratio of 6FDA and TPC, the resulting PAI films exhibited high glass transition temperature (Tg) ranging from 347 to 366 °C, low coefficient of thermal expansion (CTE) values of 4–48 ppm/K, excellent optical performance with transmittances at 400 nm (T400) of 79–83 %, and sufficient mechanical performance. The rigid rod-like amide bonds in the molecular chains increased with the introduction of TPC, which increased the hydrogen bonding between the molecular chains, significantly reduced the CTE and improved the tensile strength and modulus. In particular, PAI-7 exhibited excellent comprehensive performance with a high Tg of 366 °C, a relatively low CTE value of 13 ppm/K, excellent transmittance of 81 % at 400 nm and high tensile modulus of 6.5 GPa, which was expected to be used in the field of flexible displays.

Review on Fe-based double perovskite cathode materials for solid oxide fuel cells

As a clean and efficient energy conversion device, solid oxide fuel cells have been garnering attention due to their environmentally friendly and fuel adaptability. Consequently, they have become one of the current research directions of new energy. The cathode, as the electrochemical reaction site of an oxidation atmosphere in solid oxide fuel cells, plays a key role in determining the output performance. In recent years, the development of double perovskite cathode materials with mixed ionic and electronic conductors has made significant progress in intermediate-temperature (600-800 °C) fuel cells. These materials have the potential to deliver higher power densities and improved stability, making them promising candidates for future fuel cell applications. The Fe-based double perovskite structure cathode material has gained extensive attention due to its adjustable crystal structure and performance, as it has A(A’) or B(B’) positions in its AA’BB’O6 structure. This material has several advantages, such as high oxygen catalytic activity, low thermal expansion coefficient, and compatibility with the thermal expansion of the electrolyte. An increasing number of researchers have been exploring the performance reaction mechanism of double perovskite by modifying and adjusting its material microstructure, crystal structure, and electronic structure. In this paper, the research progress of LnBaFe2O5 and Sr2Fe2-xMoxO6 double perovskite cathode materials is reviewed to highlight the effects of various modification methods developed on electrochemical performance of these materials. Furthermore, the potential future research directions of double perovskite cathode materials are prospected.