Coefficient Of Thermal Expansion Matching Research Articles

Multicomponent doping realized superior triple-conducting within cobalt-free Ruddlesden-Popper-type perovskite for Proton-conducting fuel cells cathode

Proton-conducting solid oxide fuel cells (H-SOFCs) are appealing for low-to-intermediate temperature operation due to their intrinsic lower activation energy and better ionic conductivity. Unfortunately, there are currently few acceptable and high-performing cathode materials available for H-SOFCs. Herein, we present a novel high performance multicomponent Ruddlesden-Popper (RP) type cathode Pr3Ni1.5Cu0.3Nb0.05Ta0.05Zr0.05Y0.05O7-δ (PNCNTZY) with superior triple conducting property. The multicomponent co-doping of Nb, Ta, Zr, and Y brings about the enhancement of configurational entropy and cocktail effect for improving H+/O2-/e- triple conductivity and oxygen vacancy concentration. Naturally, the ORR activity is improved by facilitated charge transfer and oxygen surface exchange, exhibiting reduced polarization resistance to just 0.24 Ω cm2 at 550 °C. When used as the cathode in H-SOFC single cells, excellent power production is demonstrated at 550 °C, with a peak power density of up to 0.84 W cm-2. Furthermore, the PNCNTZY sample shows adequate thermal compatibility with proton conductor electrolytes BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb) and then appropriate endurance durability (0.8 A cm-2 at 550 °C for about 250 h) due to their match of thermal expansion coefficient (TEC) brought about by the Co-free and partial replacement of larger-size elements. This extremely promising Co-free RP perovskite cathode for H-SOFCs produced by this work might provide a new type candidate and novel strategy for the commercialization of H-SOFCs.

Enhancing Interfacial Stability and Mechanical Strength of a CoSb3-Based Thermoelectric Junction Using Ti-Based Alloy Barrier Layers.

CoSb3-based filled skutterudites (SKDs) are among the most promising materials for power generation. However, the poor interfacial stability and mechanical strength severely limit their practical application when joined with Cu electrodes. In this study, we propose multiphase Ti-based alloy barrier layers for CoSb3-based thermoelectric junctions to prevent the continuous brittle TiCoSb phase formation. Following the principles of coefficient of thermal expansion matching, we designed three types of Ti80-xNbxCo20 (x = 0, 5, and 10, at.%) barrier layers with the thin intermetallic compound (IMC) layers (<20 μm). Transmission electron microscopy analysis revealed that the interfacial microstructure of the Ti75Nb5Co20/Ce-SKD junction comprises Ti5Sb3, Ti5CoSb3, TiCoSb, and TiSb2 phases, as well as unreacted TiCo, Ti2Co, and Ti(Nb)ss phases, demonstrating a uniform staggered distribution state. After aging tests, the IMC thickness increased gradually from 7 to 12 μm, and the interfacial contact resistivity increased from 7.59 to 15.46 μΩ·cm2. A Cu layer was chosen as a buffer during the brazing process to prevent the formation of cracks and holes. After aging for 360 h at 823 K, the shear strength of the brazed joints remained at ∼21 MPa. Our results demonstrate that the Cu/CuSnP/Cu/Ti75Nb5Co20/Ce-SKD brazed joint exhibits excellent interfacial stability and satisfactory mechanical strength.

Research on Failure Cause and Mechanism of High Temperature Protective Coatings

In the aerospace industry, engines are exposed to extreme stress during long-term operation in high-temperature oxidation atmospheres and gas-corrosive environments. To extend the engine’s service life, it is often necessary to apply high-temperature protective coatings to enhance their resistance to high-temperature oxidation and thermal corrosion. However, in harsh, highly corrosive, and high-temperature environments, such as medium environments, as well as high vibrations and flow rates, these protective coatings can often suffer from damage and failure. This research work aims to summarize the causes of failure in high-temperature protective coatings, discuss the failure mechanisms in detail, and address issues such as interdiffusion, matching of thermal expansion coefficients, wear resistance, and erosion resistance in the design of these coatings. The findings will provide theoretical support for failure analysis, life prediction, and new material design of high-temperature protective coatings.

Low-Permittivity and Low-Temperature Cofired BaSO4-BaF2 Microwave Dielectric Ceramics for High-Reliability Packaged Electronics.

In developing low-temperature cofired ceramic (LTCC) technology for high-density packaging or advanced packaged electronics, matching the coefficient of thermal expansion (CTE) among the packaged components is a critical challenge to improve reliability. The CTEs of solders and organic laminates are usually larger than 16.0 ppm of °C1-, while most low-permittivity (εr) dielectric ceramics have CTEs of less than 10.0 ppm °C1-. Therefore, a good CTE match between organic laminates and dielectric ceramics is required for further LTCC applications. In this paper, we propose a high-CTE BaSO4-BaF2 LTCC as a potential solution for high-reliability packaged electronics. The BaSO4-BaF2 ceramics have the advantages of a wide low-temperature sintering range (650-850 °C), low loss, temperature stability, and Ag compatibility, ensuring excellent performance in LTCC technology. The 95 wt %BaSO4-5 wt %BaF2 ceramic has a εr of 9.1, a Q × f of 40,100 GHz @11.03 GHz (Q = 1/tan δ), a temperature coefficient of the resonant frequency of -11.2 ppm °C1-, a CTE of +21.8 ppm °C1-, and a thermal conductivity of 1.3 W mK-1 when sintered at 750 °C. Furthermore, a dielectric resonant antenna using BaSO4-BaF2 ceramics, a typically packaged component of LTCC and laminate, was designed and used to verify the excellent performance by a gain of 6.0 dBi at a central frequency of 8.97 GHz and a high radiation efficiency of 90% over a bandwidth of 760 MHz. Good match and low thermal stress were found in the packaged components of BaSO4-BaF2 ceramics, organic laminates, and Sn-based solders by finite element analysis, proving the potential of this LTCC for high-reliability packaged electronics.

Interface Design Development for High Durability of SOFC Interconnectors Using Electrodeposition Coating

ENE-FARM type S equipped with solid oxide fuel cell (SOFC) stack has been commercialized since 2012. We have been working on improving the power generation efficiency, reducing costs, and the making them more compact by considering that market expansion and cost reduction are critical for the continued market spread of ENE-FARM type S. However, there is a trade-off between cost reduction and performance improvement and issues related to achieving both have emerged during the development process. In order to reduce costs, significant reduction of the number of cells were required. By reducing the number of cells, the current per cell increased, and the stainless steel connecting the cells as the SOFC interconnector was required to have further improvement in durability at high temperature. The degradation modes of the stainless steel used for SOFC mainly include the growth of an insulating oxide layer such as Cr2O3, Cr poisoning of the SOFC cathode, and anomalous oxidation due to decrease in the Cr concentration in the stainless steel. Therefore, ceramic coating is indispensable for the SOFC interconnector in order to suppress these degradations. Material properties of the coating film and coating manufacturing conditions are critical to the ceramic coating equipped on the SOFC interconnector. In addition, it has excellent physical properties such as high Cr diffusion suppression, barrier performance of oxygen gas diffusion, and good physical properties such as high electrical conductivity and good matching of thermal expansion coefficient with the SOFC components. In general, spinel-based oxide materials have been reported as the coating materials for SOFC interconnector, and many binary oxides containing transition metals such as MnCo2O4, MnCu2O4, and NiCo2O4. We have investigated (Zn, Mn, Co)3O4 because of matching the thermal expansion coefficient to the ferritic stainless steel and improving the sinterability at lower temperature. The total electrical conductivity and the thermal expansion coefficient were changed due to the Mn / Co ratio. In terms of these properties, the optimum composition in ZnMnCoO4 was found to be the Mn / Co ratio of around 1 / 1. We have evaluated the long-term durability of SOFC stack components for 12 years in a short period of time by temperature acceleration evaluation method. The voltage changes with the constant current density of 0.3 A cm-2 at a furnace temperature of 973 K shows no degradation over 45000 hours. Moreover, ZnMnCoO4 coated on the 22Cr-Fe alloy shows higher durability over 20000 hours at 1123 K. In 2016, we released the ENE-FARM type S equipped with the electrodeposition coating technology and achieved the highest power generation efficiency and the smallest size at that time. The electrodeposition coating technology has been used in all of ENE-FARM type S sold in Japan. Furthermore, this electrodeposition technology has contributed significantly to the increase in sales volume since 2016. The electrodeposition coating technology can be applied not only to SOFC but also SOEC and is expected to be used more and more widely in the future.

Development of Multiple Ceramic Coatings on Porous Tubular Metal Support

Micro-tubular metal supported Solid Oxide Fuel Cell (MS-SOFC) has many advantages over traditional ceramic supported SOFC, such as greater mechanical robustness, better thermal and redox cycling along with low cost of starting material. Among the multiple MS-SOFC fabrication methods, the one involving sequential dip-coating followed by co-sintering has the potential to reduce the fabrication cost further, making it attractive from a commercial production standpoint. However, the co-sintering route is challenging because it requires constrained sintering conditions, high temperatures, and inert atmosphere. Other challenges with the co-sintering route are delamination and cracking of layers, warping of cell, diffusion of Fe and Cr away from metal support, diffusion of Ni from anode, coarsening of Ni in the anode, and lack of complete densification of YSZ electrolyte even at temperatures as high as 1350 °C.In this work, we developed a new ceramic multilayer design on a porous tubular 3D-printed metal support. Scandia Stabilized Zirconia (SSZ) and, Ni and SSZ (Ni-SSZ cermet) were used as electrolyte and anode, respectively. Stainless steel 17-4 PH was identified as the metal support material due to its matching coefficient of thermal expansion with SOFC ceramic materials, low cost and corrosion resistance nature. The dip coating steps and the co-sintering process were optimized so that they could be adopted for a cost-effective fabrication of MS-SOFC. The binder-burnout step was optimized to prevent cracking of the multilayers during the co-sintering process. To avoid delamination and to impede the inter-diffusion of elements, a coating of an intermediate layer made of 17-4 PH stainless steel+Ni+YSZ was introduced between the metal support and the succeeding layers. Preliminary results suggest that the intermediate layer has a potential to prevent delamination and inter-diffusion. Introduction of the debinding step and optimized sintering profiles resulted in the formation of the uniform and dense electrolyte coating. However, certain cell warping was observed after electrolyte sintering, suggesting further improvement is still needed in the support design and ceramic processing.

The high temperature oxidation and thermal shock behavior of a dense WSi2–TaSi2 coating on Ta substrate prepared by a novel two-step process

In order to improve the oxidation resistance of the Ta substrate, a novel two-step process including molten salt electrodeposition (Na2WO4-WO3 system) and halide activated pack cementation was adopted to prepare a WSi2–TaSi2 coating on tantalum substrate. During the electrodeposition process, dense tungsten coatings were fabricated at current densities of 30 mA/cm2, 40 mA/cm2 and 50 mA/cm2. It was observed that the grain size exhibited a log-normal distribution. When the current density was 40 mA/cm2, the grain size and flattest surface of the tungsten coating reached 9.50 ± 0.23 μm and 6.792 μm, respectively. When performing the static oxidation test, the WSi2–TaSi2 coating could effectively protect the Ta substrate oxidized at 1600 °C for 30 h. This is attributed to the presence of dense SiO2 and Ta2O5, which acted as a protective layer and suppressed the further penetration of oxygen. Furthermore, due to the matching thermal expansion coefficient between each layer and the sealing ability of semi-molten SiO2, the four-layer SiO2–W5Si3–WSi2–Ta5Si3 coating could successfully pass 721 thermal shock tests from 1600 °C to room temperature.

Study on Tungsten Metallization and Interfacial Bonding of Silicon Nitride High-Temperature Co-Fired Ceramic Substrates

For the first time, Si3N4 HTCC has been prepared using W as the metal phase by high-temperature co-firing (1830 °C/600 KPa/2 h) as a potential substrate candidate in electronic applications. It was discovered that the addition of Si3N4 to the W paste has a significant impact on thermal expansion coefficient matching and dissolution wetting. As the Si3N4 content increased from 0 to 27.23 vol%, the adhesion strength of W increased continuously from 2.83 kgf/mm2 to 7.04 kgf/mm2. The interfacial bonding of the Si3N4 ceramic and the conduction layer was discussed. SEM analysis confirmed that the interface between Si3N4 and W exhibited an interlocking structure. TEM, HRTEM and XRD indicated the formation of W2C and W5Si3 due to the interface reactions of W with residual carbon and Si3N4, respectively, which contributed to the reactive wetting and good adhesion strength between the interface. Suitable amounts of Si3N4 powder and great interfacial bonding were the main reasons for the tough interfacial matching between the Si3N4 ceramic and the conduction layer.

The formation of spinel CuxMn3-xO4 at 750 °C in the designed CuMn layers for solid oxide fuel cell applications

The Cu-Mn based spinel coatings without Cr show good application prospects due to their high conductivity and thermal expansion coefficient matching with metallic interconnectors. Based on the Cu-Mn-O phase diagram, the CuMn alloy layers with different Cu/Mn ratios were designed by electro-deposition and high energy micro-arc alloying (HEMAA) processes. The Mn-33Cu-17Co layer was prepared by HEMAA for thermal growth of the CuMn spinel oxides, and the fine-grained 430 layer was prepared by HEMAA as an interlayer at the interface between the 430 SS substrate and the coating. The microstructure and composition of the composite layers were analyzed. The results show that after oxidation treatment at 750 °C for 500 h, the oxide products of the Mn-33Cu-17Co layer were mainly cubic spinel Cu1.4Mn1.6O4 and CuO, which were different from those of the Mn-35Cu oxide layer, spinel Cu1.2Mn1.8O4 and Mn2O3. The aggregation of Cu-rich oxides was not found in the cross-section and on the top surface of the Mn-33Cu-17Co oxide layer, and the outer spinel layer was uniform and compact. The designed Mn-33Cu-17Co layers, Mn-35Cu layers and Mn1.5Cu1.5 layers showed good high temperature oxidation resistance and electrical conductivity.

Thermal Properties and Joinability Investigation of BaO–SrO–SiO2–B2O3 Glasses for Oxygen Transport Membrane Application

Three new BaO–SrO–SiO2–B2O3 (BS) glasses with different SrO contents (6–25 mol%) are developed for oxygen transport membrane (OTM) joining application. The content of strontium is investigated first in terms of its effect on the glass‐forming tendency, thermal expansion coefficient, crystallization, shrinkage behavior, and viscous flow properties. Differential scanning calorimetry (DSC) is carried out. Dilatometric tests are performed to obtain coefficients of thermal expansion (CTEs) of BS glasses. The crystallization behavior of the BS glasses is investigated by X‐ray powder diffraction (XRD). Sinking dilatometric measurements simulate the joining procedure and observe the shrinkage behavior of the BS glasses. The viscous flow behavior of the BS glasses is examined via hot stage microscopy. The glass with 15 mol% SrO (BS15) glass shows the best glass‐forming tendency, most matching CTE (11.9 × 10−6 K−1), densest microstructure, highest shrinkage rate (24%), and good viscous behavior at high joining temperatures compared with other BS glasses. BS15 glass is chosen for helium leak test and assembly test joining with Aluchrom and SrTi0.75Fe0.25O3−δ membrane (STF25). The sandwiched sample with two Aluchrom plates sealed by BS15 glass at 1075 °C for 5 min achieves good gas‐tightness with low helium leakage rate &lt;10−9 mbar·l s−1.

Investigation of Warpage for Multi-Die Fan-Out Wafer-Level Packaging Process.

This paper focuses on characterizing the evolution of warpage, effects of epoxy molding compound (EMC), and effects of carrier 2 (the second carrier in the process) of 12 inch RDL-first multi-die fan-out wafer-level packaging (FOWLP) during the manufacturing process. The linear viscoelasticity properties of EMC and polyimide (PI) were characterized using dynamic mechanical analysis (DMA) in the frequency domain at different temperatures., The elastic and viscoelastic model were used for PI and EMC, the finite element analyses (FEA) of the cured structure were carried out and the results were compared with the test results. The viscoelastic properties of the EMC in the FEA could predict the wafer warpage more accurately. The FEA and experiments were used to investigate the evolution of warpage. The molding had a great influence on the warpage. The effects of the EMC and carrier 2 were also investigated with FEA. The wafer warpage could be reduced by lowering the thickness of the EMC, increasing the thickness of carrier 2, and selecting EMC and carrier 2 with a matched coefficient of thermal expansion (CTE).

An Overview on the Novel Core-Shell Electrodes for Solid Oxide Fuel Cell (SOFC) Using Polymeric Methodology.

Lowering the interface charge transfer, ohmic and diffusion impedances are the main considerations to achieve an intermediate temperature solid oxide fuel cell (ITSOFC). Those are determined by the electrode materials selection and manipulating the microstructures of electrodes. The composite electrodes are utilized by a variety of mixed and impregnation or infiltration methods to develop an efficient electrocatalytic anode and cathode. The progress of our proposed core-shell structure pre-formed during the preparation of electrode particles compared with functional layer and repeated impregnation by capillary action. The core-shell process possibly prevented the electrocatalysis decrease, hindering and even blocking the fuel gas path through the porous electrode structure due to the serious agglomeration of impregnated particles. A small amount of shell nanoparticles can form a continuous charge transport pathway and increase the electronic and ionic conductivity of the electrode. The triple-phase boundaries (TPBs) area and electrode electrocatalytic activity are then improved. The core-shell anode SLTN-LSBC and cathode BSF-LC configuration of the present report effectively improve the thermal stability by avoiding further sintering and thermomechanical stress due to the thermal expansion coefficient matching with the electrolyte. Only the half-cell consisting of 2.75 μm thickness thin electrolyte iLSBC with pseudo-core-shell anode LST could provide a peak power of 325 mW/cm2 at 700 °C, which is comparable to other reference full cells’ performance at 650 °C. Then, the core-shell electrodes preparation by simple chelating solution and cost-effective one process has a potential enhancement of full cell electrochemical performance. Additionally, it is expected to apply for double ions (H+ and O2−) conducting cells at low temperature.

La1-xCaxFeO3-δ air electrode fabricated by glycine-nitrate combustion method for solid oxide electrolysis cell

As a new type of energy conversion device, solid oxide electrolysis cell (SOEC) has attracted much attention in recent years because of its advantages such as high efficiency and unlimited capacity. At present, SOEC mainly has such issues as the element diffusion or delamination at oxygen electrode/electrolyte interface under high oxygen partial pressure, which limits its operation lifetime. In this paper, La1-xCaxFeO3-δ materials without Sr and Co were prepared by glycine-nitrate combustion method as SOEC oxygen electrodes. It is found that La0.6Ca0.4FeO3-δ (LCF64) has excellent electrical conductivity and has a coefficient of thermal expansion matching with SSZ electrolyte. The hydrogen electrode supported single cells with structure of LCF64-GDC (6:4) | GDC | SSZ | NiO-SSZ active layer | NiO-YSZ transition layer | NiO-YSZ supported layer were prepared by tape casting and co-firing method showed good electrochemical performance in SOEC mode. The electrolysis current density is 457.46 mA cm-2 with 60% H2O-H2 atmosphere and 1.3 V applied voltage at 800 °C. During the constant voltage (1.3V) electrolysis process, the SOEC showed an acceptable stable current density of approximate 280 mA cm-2 for more than 60 h.

Analysis of Pressurized, Tubular, Proton-conducting, Ceramic Reversible Fuel Cells for Efficient, Low-Cost Energy Storage

This work analyzes pressurized, tubular, proton-conducting, ceramic reversible fuel cells (PreTProCRFC) for efficient, low-cost energy storage. PreTProCRFC have the potential to facilitate low carbon energy economies and power-to-gas applications. In the power-to-gas concept, excess electricity from wind turbines and solar photovoltaic arrays is sent to high temperature electrolyzers, like the PreTProCRFC, that store energy as hydrogen (H2) and oxygen (O2) for short or long durations (> 4 hours). When electricity is needed, the PreTProCRFC runs as a fuel cell and consumes the stored H2 and O2 to generate electricity. In this way, PreTProCRFCs have the potential to significantly augment the growth of renewables globally. This research analyzes the potential for PreTProCRFCs as viable short or long-term energy storage devices. This work develops thermodynamic and techno-economic analyses (TEA) for these PreTProCRFC systems and identifies cost drivers important to their R&D and commercialization path. This work also explores the value propositions presented by pressurized, tubular designs, for different segments of the energy storage market.Approach:This work is conducted in close collaboration with project partners Special Power Sources Inc. (SPS), which currently manufactures tubular ceramic fuel cells for research and niche energy applications, and Kansas State University (KSU), which is developing novel, proton-conducting ceramic materials. To execute this research, Gaia works with SPS and KSU to identify and analyze cell, stack, and system engineering performance data. Gaia then develops and deploys custom computer models and data sets that include, but are not limited to, chemical engineering process plant designs of PreTProCRFC systems and detailed TEA models. Gaia also builds on existing U.S. DOE modelling tools, such as the H2A H2 production analysis modelling tools and existing DOE electrolysis case studies.Results:Modelling results indicate that the primary cost drivers for the lifecycle energy storage costs of PreTProCRFC systems include, but are not limited to,(1) the system’s ramp rate in fuel cell mode (i.e. the electric power output per unit time);(2) the system’s ramp rate in electrolysis mode (i.e. the electric power input per unit time);(3) the quantity of effective heat reuse between exothermic fuel cell modes and endothermic electrolysis modes;(4) the efficiency of thermal storage between fuel cell and electrolysis modes;(5) the electricity consumed per unit of hydrogen produced in electrolysis mode;(6) the electricity consumed per unit of oxygen produced in electrolysis mode;(7) the capital costs of the stack;(8) the capital costs of the surrounding balance of plant (BOP) subsystems;(9) the electrolysis outlet pressures for hydrogen and oxygen; and(10) the marginal increase in system cost with higher electrochemical outlet pressures.Regarding (1) and (2), when connected to the electricity grid, and receiving intermittent renewable electricity to store, PreTProCRFC systems need the capability to respond rapidly. Electricity storage devices that can either receive and/or supply electricity more quickly can demand a higher premium ($/kWh price). In particular, the electricity balancing market is a submarket within the overall electricity market responsible for reconciling instantaneous differences in electricity supply and demand, and, consequently, sees the highest prices. The proposed SPS PreTProCRFC stack design is tubular, with less total sealant area, and with a close match of stack material thermal expansion coefficient, so it is expected that this design will more readily electrically ramp compared with other designs. (A main failure mechanism of high temperature electrochemical systems under fast-ramping conditions is mechanical cracking of the stack’s materials, due thermal expansion coefficient mismatches.)Regarding (3), (4), (5), and (6), a unique feature of high temperature electrolysis (compared with low temperature electrolysis) is that electricity consumption by the electrolyzer can be displaced by heat consumption, in a one-to-one ratio. In a PreTProCRFC system, heat released during the exothermic fuel cell reaction can be stored and reused to provide heat for electrolysis. Efficient design of this heat reuse subsystem is crucial to the PreTProCRFC system achieving high round-trip efficiencies, a necessity for the energy storage market.Regarding (7) and (8), primary cost drivers for PreTProCRFC system also include stack capital costs, stack power density, and system BOP costs. Over time, stack capital costs are estimated to decline more rapidly with R&D and more high volume manufacture, compared with BOP capital costs, because the BOP already incorporates many mass-produced components.Regarding (9) and (10), the SPS PreTProCRFC stack is also unique in that it has the capacity to supply hydrogen and oxygen at pressure. Model results indicate that electrochemical compression has the most compelling cost advantage over mechanical compression in the lower pressure range included in the proposed stack design.

Property evolutions of Si/mixed Yb2Si2O7 and Yb2SiO5 environmental barrier coatings completely wrapping up SiCf/SiC composites under 1300 °C water vapor corrosion

A bi-layer environmental barrier coating (EBC) consisting of silicon(Si) bond coat/mixed ytterbium disilicate (Yb2Si2O7) and ytterbium monosilicate (Yb2SiO5) topcoats has been successfully prepared to completely wrap up the SiCf/SiC composites and the protective effects of such EBC have been evaluated by soaking them in a mixed 50% O2 and 50% H2O corrosive gases at 1300 °C for various times. In topcoats, Yb2Si2O7 is the major phase, providing good thermal expansion coefficient (CTE) matching with composite substrate and thus excellent thermal shock resistance, whereas Yb2SiO5 is the dispersing minor phase, providing improved water vapor corrosion resistance. The completely wrapping up of SiCf/SiC composites by above EBC system is employed to avoid direct exposure to the corrosive conditions, making it possible to evaluate the genuine protection effects of current EBCs. Under 1300 °C water vapor corrosion, the mass change, the phase composition and the evolution of microstructure are investigated, which suggest that the bi-layer EBC has excellent performance on protecting SiCf/SiC composites from water vapor corrosion at 1300 °C.

Determining Interface Fracture Toughness in Multi Layered Environmental Barrier Coatings with Laser Textured Silicon Bond Coat

In the high temperature combustion atmosphere inside of aircraft turbines, the currently used ceramic matrix composites require a protective environmental barrier coating (EBC) to mitigate corrosion of the turbine parts. Besides thermomechanical and thermochemical properties like matching thermal expansion coefficient (CTE) and a high resistance against corrosive media, mechanical properties like a high adhesion strength are also necessary for a long lifetime of the EBC. In the present work, the adhesion between an air plasma sprayed silicon bond coat and a vacuum plasma sprayed ytterbium disilicate topcoat was aimed to be enhanced by a laser surface structuring of the Si bond coat. An increase in interface toughness was assumed, since the introduction of structures would lead to an increased mechanical interlocking at the rougher bond coat interface. The interface toughness was measured by a new testing method, which allows the testing of specific interfaces. The results demonstrate a clear increase of the toughness from an original bond coat/topcoat interface (8.6 J/m2) compared to a laser structured interface (14.7 J/m2). Observations in the crack propagation indicates that the laser structuring may have led to a strengthening of the upper bond coat area by sintering. Furthermore, in addition to cohesive failure components, adhesive components can also be observed, which could have influenced the determined toughness.

Fabrication of reaction bonded TiB2/Si/SiC composites for thermal applications

AbstractTitanium diboride (TiB2) is an extremely hard ceramic which has excellent heat conductivity, oxidation stability, and resistance to mechanical erosion. Broader application of this material is inhibited by economic factors, particularly the cost of densifying a material with a high melting point. In this study, reaction bonded TiB2 (RB‐TiB2) composites are fabricated by the reactive infiltration of molten Si into preforms of TiB2 plus carbon. Microstructure analysis indicates uniform distribution of TiB2 particles in the composites. RB‐TiB2 composites with fine particles show higher flex strength and fracture toughness, while composites with larger particles have higher thermal conductivity, measured to be 120 W/(m K) at room. The coefficient of thermal expansion (CTE) of the composites is insensitive to the particle size and can be controlled in the range of 4.0‐5.2 ppm/K (room temperature). RB‐TiB2 shows the potential to be used for electronics thermal management applications with a combination of matching CTE, good thermal conductivity, high melting point, and attractive mechanical properties.

Single layer low-temperature SOFC based on Ce0.8Sm0.2O2-δ- La0.25Sr0.75Ti1O3-δ-Ni0.8Co0.15Al0.05LiO2-δ composite material

This study reports a kind of single layer solid oxide fuel cell (SLSOFC) based on semiconductor-ionic conductor composite material which consists of Ce0.8Sm0.2O2-δ (SDC, ionic conductor), La0.25Sr0.75Ti1O3+δ (LST, n-type semiconductor) and Ni0.8Co0.15Al0.05LiO2-δ (NCAL, p-type semiconductor). It was found that the LST-SDC-NCAL composite based SLSOFC exhibited open circuit voltage (OCV) of more than 1 V and maximum power density of 222 mW cm−2 under 550 °C. In-situ Schottky junction in the device helps to prevent short circuiting as well as promote ion transport. Electrochemical impedance spectroscopy (EIS) analysis revealed that the ionic conductivity of the SLSOFC was about 0.09 S cm−1, and the corresponding activation energy is 0.7 eV. The cell performance was stable during 65 h without any significant degradation. Moreover, the SLSOFC possessed higher tolerance for temperature change than traditional three-layer SOFC due to the well match of thermal expansion coefficient between electrodes and electrolyte. This device is of great significance in preventing fuel cell delamination, simplifying manufacturing process and promoting its commercialization.

Superconducting magnesium diboride films for levitation of laser targets

Inertial confinement fusion targets would benefit from being levitated inside hohlraums to avoid capsule support-related implosion perturbations. Levitation inside a magnetic trap requires coating the capsule with a thin film that is superconducting at 20 K. Such non-epitaxial film growth on non-planar substrates is challenging. Here, we study Mg vapor annealing and solid-phase reactive inter-diffusion methods to form superconducting magnesium diboride (MgB2) films on different planar and spherical carbon substrates, evaluating glassy carbon, polycrystalline diamond made by chemical vapor deposition, and carbon deposited by magnetron sputtering of graphite targets. Thin films of B and Mg are produced by magnetron sputtering onto stationary planar or rolling spherical substrates and annealed at either 600 or 850 ∘C in Mg vapor. The films are characterized by a combination of high-energy ion scattering, electron microscopy, and magnetometry. Results show that the critical superconducting temperature of resultant films depends on film microstructure and oxygen impurity content. The formation of MgB2 films is also strongly substrate dependent, even in this case of non-epitaxial growth. Important factors to consider are oxygen outgassing of the substrate during thermal processing, substrate surface roughness, and the matching of thermal expansion coefficients of different layers in the multilayer structure.

High-Temperature Thermal Conductivity and Thermal Cycling Behavior of Cu–B/Diamond Composites

Diamond particle-reinforced copper matrix (Cu/diamond) composites are currently considered as a promising thermal management material due to their high thermal conductivity and matching coefficient of thermal expansion (CTE) with the semiconductor. In this article, the Cu– <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$x\text{B}$ </tex-math></inline-formula> /diamond ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$x = 0.1$ </tex-math></inline-formula> –1.0 wt%) composites with 67% diamond volume fraction were produced by gas-pressure infiltration. The thermal conductivity of the Cu–B/diamond composites decreases with the increasing temperature from 323 to 673 K, owing to the property change of the composite components. The samples were subjected to 100 thermal cycles from 218 to 423 K to investigate the long-term stability of the Cu–B/diamond composites. The results suggest that the interface structure evolution plays a critical role in determining the high-temperature thermal conductivity and thermal cycling behavior of the Cu–B/diamond composites. By measuring the thermal properties before and after thermal cycling, we found that the Cu–0.5wt%B/diamond composite has the best thermal stability. After 100 thermal cycles, the room temperature thermal conductivity remains almost unchanged at ~740 W/mK, and the CTE increases slightly from 4.88 to 4.97 ppm/K. This article expands the understanding of the thermal properties of the Cu-B/diamond composites and provides a fundamental basis for their electronics packaging applications.