Low Coefficient Of Thermal Expansion Research Articles

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.

Melt‐reprocessable linear low‐density polyethylene/cyclic olefin copolymer blends with low dielectric constant and low thermal expansion

AbstractInsulation materials with low dielectric constants, low coefficients of thermal expansion (CTE), low densities, renewability, and low cost are urgently needed in the fields of communication, control and signal cables. Here we report that combining cyclic olefin copolymer (COC) with linear low‐density polyethylene (LLDPE) by melt blending achieves the above goals. The dielectric constant and CTE of LLDPE/COC blends are minimized at 20 wt% COC content, reaching a value of 2.23 at 1000 Hz and 1.21 × 10−4 K−1, respectively. The density of the blend increases by only 1.6% compared with LLDPE, whereas the tensile modulus increases by 56%, which is conducive to the blends to improve mechanical strength while preserving lightweight. The rheological tests show that the zero‐shear viscosity, storage modulus, and loss modulus of the LLDPE/COC blends do not change much compared with pristine LLDPE, maintaining their good melt processability at 160°C. The cyclic rigid structure of COC causes a decrease in CTE, and the increase in free volume between molecular chains is responsible for the reduced dielectric constant. The present work provides a promising route to the design and fabrication of melt‐reprocessable polymer composites with low dielectric constant and low thermal expansion.

Investigation of Photosensitive Polyimide With Low Coefficient of Thermal Expansion and Excellent Adhesion Strength for Advanced Packaging Applications

Investigation of Photosensitive Polyimide With Low Coefficient of Thermal Expansion and Excellent Adhesion Strength for Advanced Packaging Applications

Effects of mechanical properties of carbon-based nanocomposites on scaffolds for tissue engineering applications: a comprehensive review.

Mechanical properties, such as elasticity modulus, tensile strength, elongation, hardness, density, creep, toughness, brittleness, durability, stiffness, creep rupture, corrosion and wear, a low coefficient of thermal expansion, and fatigue limit, are some of the most important features of a biomaterial in tissue engineering applications. Furthermore, the scaffolds used in tissue engineering must exhibit mechanical and biological behaviour close to the target tissue. Thus, a variety of materials has been studied for enhancing the mechanical performance of composites. Carbon-based nanostructures, such as graphene oxide (GO), reduced graphene oxide (rGO), carbon nanotubes (CNTs), fibrous carbon nanostructures, and nanodiamonds (NDs), have shown great potential for this purpose. This is owing to their biocompatibility, high chemical and physical stability, ease of functionalization, and numerous surface functional groups with the capability to form covalent bonds and electrostatic interactions with other components in the composite, thus significantly enhancing their mechanical properties. Considering the outstanding capabilities of carbon nanostructures in enhancing the mechanical properties of biocomposites and increasing their applicability in tissue engineering and the lack of comprehensive studies on their biosafety and role in increasing the mechanical behaviour of scaffolds, a comprehensive review on carbon nanostructures is provided in this study.

TZM Alloy Job Carrier for High Temperature Vacuum Furnace

RRCAT has a cold walled dry pumped controlled atmosphere furnace for brazing, diffusion bonding and heat treatment of components required for particle accelerators. This furnace has a work zone of 500 mm diameter and 1.5 meter length and it can be operated up to a temperature of 1100 deg C. A Titanium-Zirconium-Molybdenum (TZM) alloy job carrier has been designed for a load carrying capacity of 400 kg for better utilization of the vertical space. Due to alloy’s outstanding combination of properties e.g. high electrical and thermal conductivity, low coefficient of thermal expansion and high rupture as well as creep strength; it is a preferred choice in a wide variety of high-temperature applications in spite of its higher cost. The structural design of the job carrier needs optimization in order to reduce its weight as well as its cost without compromising on design constraints. In this paper, a detailed design of job-carrier has been presented using plate theory and Euler beam theory. Subsequently, finite element analysis (FEA) in ANSYSTM Workbench is performed to ensure that resultant stresses and deformation are within acceptable limits. Additionally, a limit load analysis has been performed to determine the maximum load capacity and factor of safety. FEA results are then used for fatigue life and creep assessment. The job-carrier has been successfully installed inside RRCAT’s controlled atmosphere furnace and has been tested at full load. The effort has also led to 70% reduction in the procurement cost with respect to commercially available products.

Influence of the temperature changes on stresses in carbon composite fastening bolts

High joint strength of composite structures can be achieved by using mechanical fasteners. The materials used for rivets and bolts have lower coefficients of thermal expansion than composites in the direction perpendicular to the reinforcement fibers. It is suspected, therefore, that temperature changes can cause stress changes in mechanical fasteners. The purpose of this study was to experimentally determine and analytically substantiate the values of stress changes resulting from a change in temperature in the range from -20 to 60°C in M8 steel bolts fastening carbon composite. The value of stress changes was estimated to be around 100 MPa, which can consequently lead to joint unsealing or plastic deformation of the mechanical fastener.

Investigation of WBG based Power Converters used in E-Transportation

Nowadays, Uses for transportation are evolving in the direction of getting more electrified due to rising fuel costs and environmentally hazardous pollutants due to which The grid’s need for power is increasing dramatically. As the only solution for this is to diminish the power consumption of Electric Vehicles (EV). Enhanced component efficiency can lead to improved electric vehicle performance. Wide band gap (WBG) semiconductors, in particular silicon carbide (SiC) and Gallium Nitride (GaN), are ideal candidates of choice to address the recent growing demand in both high efficiency and great power density converters about electric vehicles. Due to their the capacity to switch at a high frequency, high temperature, high voltage, reduced size and reduced conduction losses makes them superior than Si semi-conductors. WBG devices have some properties which include rapid electron mobility, high breakdown field, and big band gap low on-state resistance and capacitance, lower co-efficient of thermal expansion (CTE) and high stability. This paper includes a study on WBG devices, their properties, and the increased efficiency of power converters i.e DC-DC boost converter and single-phase full bridge inverter using LTSpice simulation tool.

Silicon carbide single crystals for high-temperature supercapacitors.

Designing advanced electrode materials that can be reliably cycled at high temperatures and used for assembling advanced energy storage devices remain a major challenge. As a representative of novel wide bandgap semiconductors, silicon carbide (SiC) single crystals have broad prospects in high-temperature energy storage due to their excellent characteristics such as low thermal expansion coefficient, high temperature radiation resistance and stable chemical properties. In this work, an N-type SiC single-crystal material with a high-density porous structure was successfully designed and prepared by using an improved electrochemical anodic oxidation strategy. Besides, the N-type SiC single crystals were used in electrochemical energy storage as an integrated electrode material, exhibiting superior electrochemical performance. In addition, the high-temperature supercapacitor device assembled with ionic liquids has a wide operating temperature range and maintains a capacity of 88.24% after 5000 cycles at 150 °C. The reasons for its high energy storage performance are discussed through electrochemical tests and first-principles calculation methods. This study proves that the application of SiC single crystals in supercapacitor devices has great potential in the field of high-temperature energy storage, providing a reference for the further development of novel semiconductors in the field of energy storage and optoelectronic devices.

Fabrication of low thermal expansion coefficient electrodeposited Invar alloy films by hydrogen annealing for OLED fine metal masks

This study unveils the dependence of the Invar effect on grain size. An electrodeposited Invar alloy film was prepared with near-zero inclusions and near-zero thermal expansion, which will advance its application in OLED fine metal masks.

Rapid Solidification of Invar Alloy.

The Invar alloy has excellent properties, such as a low coefficient of thermal expansion, but there are few reports about the rapid solidification of this alloy. In this study, Invar alloy solidification at different undercooling (ΔT) was investigated via glass melt-flux techniques. The sample with the highest undercooling of ΔT = 231 K (recalescence height 140 K) was obtained. The thermal history curve, microstructure, hardness, grain number, and sample density of the alloy were analyzed. The results show that with the increase in solidification undercooling, the XRD peak of the sample shifted to the left, indicating that the lattice constant increased and the solid solubility increased. As the solidification of undercooling increases, the microstructure changes from large dendrites to small columnar grains and then to fine equiaxed grains. At the same time, the number of grains also increases with the increase in the undercooling. The hardness of the sample increases with increasing undercooling. If ΔT ≥ 181 K (128 K), the grain number and the hardness do not increase with undercooling.

Innovative pathways to high-performance glass ceramics: Harnessing nature's treasures with chromium and zirconium nucleation catalysts

This study explores the novel production of high-performance glass ceramics (GCs) by harnessing readily available and cost-effective raw materials schist, dolomite, and magnesite for the first time. The nominal composition for the base glass, G(30), was designed based on the eutectic composition of the diopside-anorthite ratio with 30% enstatite content within the quaternary CaO-MgO-Al2O3-SiO2 system. To enhance nucleation, chromium (Cr2O3) and zirconium (ZrO2) oxide were separately introduced into the base glass batch in two ratios (0.5% and 1%), producing four additional batches-Cr(0.5), Cr(1), Zr(0.5), and Zr(1), orderly. All these batches were melted at temperatures ranging from 1450 °C to 1550 °C then cast into glass discs and rods. Double-stage heat treatment schedule, 750 °C /2 h followed by 950 °C and 1050 °C/1 h separately, was employed to induce the transformation of prepared glass into GCs. X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) techniques were applied to orderly investigate the developed crystalline phases and the prevailing micro-structures of the prepared GCs. The glass ceramic with the highest Cr2O3 ratio, Cy(1) which was treated at 1050 °C/1 h, displayed the most adequate microstructure and minimal pore formation in comparison with other GCs. As well, the favorable physicochemical properties, Vickers microhardness (6.43 GPa), low thermal expansion coefficient (0.171 ×10 −6 °C−1) at 29–100 °C, and the exceptional resistance for acid and alkali corrosion (95%), nominate such GS sample, Cy(1), for several architectural applications.

Enter the multifunctional trifluoromethylated epoxy Resin: Excellent flame retardant, better dielectric, low thermal expansion, etc

In order to obtain epoxy resins with flame retardant, dielectric properties, and easier industrialization, thus meeting the future development requirements in the field of electronic encapsulation, a trifluoromethylated epoxy resin (DGEBAF) was synthesized by using a two-step method, and the cured epoxy resin (DGEBAF/DDM) was prepared with DDM as the curing agent. Detailed studies of DGEBAF/DDM including curing kinetics, mechanical properties, and dielectric properties, etc. were conducted by using DGEBA/DDM (with dimethyl structure in DGEBA) and DGEBF/DDM (with dihydrogen structure in DGEBF) as the comparative samples. The results indicate that DGEBAF/DDM has higher storage modulus and strength, better dielectric properties, and hydrophobicity, and lowest thermal expansion coefficient, due to the existence of trifluoromethyl. Importantly, deeply study about the flame retardancy and its mechanism of DGEBAF/DDM was processed, which was of great significance for its application in the field of electronic packaging. Its vertical combustion level reaches UL-94 V-0. The limiting oxygen index of DGEBAF/DDM is 34.5 %, which is improved by 35.8 % and 30.2 % compared to DGEBA/DDM and DGEBF/DDM, respectively. The thermal decomposition mechanism of DGEBAF was explored by Py-GC/Mass, XPS, and FTIR analysis. It can be inferred that trifluoromethylated epoxy resin releases •CF3 at high temperatures and effectively enhances the flame retardant of the epoxy resin through radical trapping. The smoke toxicity of DGEBAF/DDM combustion was detected in real time by conical thermal method combined with gas infrared analysis. In addition, we have found that DGEBAF/DDM decomposes at first but produces most residual carbon among the three epoxy resins. Based on the characteristics, an intelligent fire alarm system was designed.

Microstructural, Phase, and Thermophysical Stability of CrMoNbV Refractory Multi-Principal Element Alloys

Structural survivability of refractory multi-principal element alloys (RMPEAs) at high temperatures hinges on a combination of microstructure, phase, and thermophysical stabilities. In this study, we investigate the high-temperature stability of three compositions from the CrMoNbV system: Cr7Mo18Nb35V40, Cr25Mo25Nb25V25, and Cr40Mo45Nb10V5. The microstructure, high-temperature phase stability, coefficient of thermal expansion (CTE), and yield strength were evaluated up to 1300oC. Results show that all three as-cast compositions have dendritic microstructures with an average grain size of ~100µm and no preferred texture. High-temperature analysis of phase stability shows that Cr7Mo18Nb35V40 maintains a single-phase BCC structure from room temperature up to 1300oC, while Cr25Mo25Nb25V25 forms an undesirable C15 Laves phase and Cr40Mo45Nb10V5 exhibits BCC phase separation. The CTE measured was 9.58, 9.52 and 8.80 ppm/oC, and the yield strength at 1250oC was 503, 629 and 628MPa for Cr7Mo18Nb35V40, Cr25Mo25Nb25V25 and Cr40Mo45Nb10V5, respectively. The low density, CTE and high-temperature yield strength of the three alloys sets the CrMoNbV system above current superalloys. More importantly, the microstructural, phase, and thermophysical stabilities of the Cr7Mo18Nb35V40 alloy over the equiatomic and Cr-rich alloys highlight the importance of high-temperature survivability over yield strength as an RMPEA design principle.

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.