Crack-Growth Behavior in Thermal Barrier Coatings with Cyclic Thermal Exposure

Crack-growth behavior in yttria-stabilized zirconia-based thermal barrier coatings (TBCs) is investigated through a cyclic thermal fatigue (CTF) test to understand TBCs’ failure mechanisms. Initial cracks were introduced on the coatings’ top surface and cross section using the micro-indentation technique. The results show that crack length in the surface-cracked TBCs grew parabolically with the number of cycles in the CTF test. Failure in the surface-cracked TBC was dependent on the initial crack length formed with different loading levels, suggesting the existence of a threshold surface crack length. For the cross section, the horizontal crack length increased in a similar manner as observed in the surface. By contrast, in the vertical direction, the crack did not grow very much with CTF testing. An analytical model is proposed to explain the experimentally-observed crack-growth behavior

Crack-Resistance Behavior of an Encapsulated, Healing Agent Embedded Buffer Layer on Self-Healing Thermal Barrier Coatings

In this work, a novel thermal barrier coating (TBC) system is proposed that embeds silicon particles in coating as a crack-healing agent. The healing agent is encapsulated to avoid unintended reactions and premature oxidation. Thermal durability of the developed TBCs is evaluated through cyclic thermal fatigue and jet engine thermal shock tests. Moreover, artificial cracks are introduced into the buffer layer’s cross section using a microhardness indentation method. Then, the indented TBC specimens are subject to heat treatment to investigate their crack-resisting behavior in detail. The TBC specimens with the embedded healing agents exhibit a relatively better thermal fatigue resistance than the conventional TBCs. The encapsulated healing agent protects rapid large crack openings under thermal shock conditions. Different crack-resisting behaviors and mechanisms are proposed depending on the embedding healing agents

Germanium coating boosts lithium uptake in Si nanotube battery anodes

Si nanotubes for reversible alloying reaction with lithium are able to accommodate large volume changes and offer improved cycle retention and reliable response when incorporated into battery anodes. However, Si nanotubes electrode exhibits poor rate capability because of its inherently low electron conductivity and Li ion diffusivity. Si/Ge double-layered nanotubes electrode show promise to improve structural stability and electrochemical kinetics, as compared to homogeneous Si nanotube arrays. The mechanism explaining the enhancement in the rate capabilities is here revealed by means of electrochemical impedance methods. Ge shell efficiently provides electrons to the active materials which increase the semiconductor conductivity thereby assisting Li+ ion incorporation. The charge transfer resistance which accounts for the interfacial Li+ ion intake from the electrolyte is reduced by two orders of magnitude, implying the key role of Ge layer as electron supplier. Other resistive processes hindering the electrode charge/discharge process are observed to show comparable values for Si and Si/Ge array electrodes

WO 3 nanofibrous backbone scaffolds for enhanced optical absorbance and charge transport in metal oxide (Fe 2 O 3 , BiVO 4 ) semiconductor photoanodes towards solar fuel generation

Producing clean fuel (O2 and H2) using semiconductors through solar driven water splitting process has been considered as a promising technology to mitigate the existing environmental issues. Unlike the conventional single photoabsorbers, heterostructured semiconductors exhibit the merits of improved solar light photon harvesting and rapid charge separation, which are anticipated to result in high quantum yield of solar fuel generation in photoelectrochemical (PEC) cells. In this report, we demonstrate the electrospun derived WO3 backbone fibrous channel as heteropartner to the primary photoabsorber (Fe2O3 and BiVO4) for promoting the electron transport from charge injection point to charge collector as well as photoholes to the electrolyte. We examine structure, optical, photoelectrochemical and charge transfer property of Fe2O3/WO3 and BiVO4/WO3 electrodes. These results were compared with directly coated Fe2O3 and BiVO4 photoabsorber onto conducting substrate without WO3 backbone. The optical results showed that the absorbance and visible light activity of Fe2O3 and BiVO4 is significantly improved by WO3 backbone fibers due to high amount of photo absorber loading. In addition, one dimensional (1-D) WO3 fibers beneficially enhance the optical path length to the photoanode through light scattering mechanism. The electrochemical impedance analysis exhibits WO3 nanofiber backbone reduces charge transfer resistance at Fe2O3 and BiVO4 by rapid charge collection and charge separation compare to backbone-free Fe2O3 and BiVO4. As a result, Fe2O3/WO3 and BiVO4/WO3 fibrous hetero interface structures showed fourfold higher photocurrent generation from PEC cell

Graphene-Tapered ZnO Nanorods Array as a Flexible Antireflection Layer

Flexible solar cells have drawn a great deal of attention due to their various advantages including deformable and wearable characteristics. In the solar cells, the antireflection layer plays an important role in the improvement in the conversion efficiency by increasing the light transmission and suppressing the Fresnel refraction. For the successful implantation of the antireflection layer into the flexible solar cells, the flexible mechanical property of the antireflection layer is also necessary. However, the study on flexible antireflection layer for the flexible solar cells or optoelectronics is still lacking. In this study, we report the graphene-tapered ZnO nanorods array as a flexible antireflection layer for the application in flexible solar cells. Flexible two-dimensional graphene sheet and the tapered morphology of ZnO nanorods enable conformal coverage on the flexible substrate with curved surface and significant improvements in antireflection properties, respectively

Freestanding rGO-SWNT-STN Composite Film as an Anode for Li Ion Batteries with High Energy and Power Densities

Freestanding Si-Ti-Ni alloy particles/reduced graphene oxide/single wall carbon nanotube composites have been prepared as an anode for lithium ion batteries via a simple filtration method. This composite electrode showed a 9% increase in reversible capacity, a two-fold higher cycle retention at 50 cycles and a two-fold higher rate capability at 2 C compared to pristine Si-Ti-Ni (STN) alloy electrodes. These improvements were attributed to the suppression of the pulverization of the STN active material by the excellent mechanical properties of the reduced graphene oxide-single wall carbon nanotube networks and the enhanced kinetics associated with both electron and Li ion transport

High capacity monoclinic Nb₂O₅ and semiconducting NbO₂ composite as high-power anode material for Li-Ion batteries

Niobium pentoxide, Nb2O5, is an intercalation-type material with a high theoretical capacity of ∼404 mAh g−1 for Li-ion batteries. However, electrochemical properties of Nb2O5 largely depend on its various polymorphs with different crystal structures, and their low electrical conductivity acts as the main obstacle. Here, we report high-temperature calcined monoclinic Nb2O5 and semiconducting NbO2 composite as a high-power anode material. Monoclinic Nb2O5 itself as a main active material shows a high capacity of ∼280 mAh g−1, and NbO2 with a small band gap of ∼0.5 eV not only improves electrical conductivity but also gives a capacity of ∼110 mAh g−1. To have a synergic effect of these two materials, the Nb2O5/NbO2 composite is prepared via simple post-calcination of as-prepared Nb2O5 under a reduction atmosphere. It shows a discharge capacity of ∼214 mAh g−1 at 0.05 C, a high initial Coulombic efficiency of 94.7%, a superior rate capability of ∼40 mAh g−1 at 100 C, and a robust cycle performance of 81% retention over 900 cycles.This work was supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP) and the Ministry of Trade, Industry and Energy of the Republic of Korea through the research on Li-ion batteries (No. 20168510050080), Basic Science Research Program through the National Research Foundation of Korea funded by the Ministry of Science, ICT (2016R1C1B2007299) and the research fund of Hanyang University (HY-2017)

Synthesis of carboxymethyl cellulose lithium by weak acid treatment and its application in high energy-density graphite anode for Li-ion batteries

Carboxymethyl cellulose lithium (CMC-Li) has recently been explored as a promising binder for Li-ion batteries because of enhanced Li+ ion flux. CMC-Li has been generally prepared by CMC acid form (CMC-H) as an intermediate product treated with a strong acid, which considerably causes a polymer degradation. Here, we report a synthesis method of CMC-Li through the use of a weak acid (acetic acid) and its application in a high energy-density graphite anode. CMC-Li synthesized by acetic acid (CMC-Li (A)) exhibits enhanced physicochemical properties including an appropriate viscosity of ∼3000 mPa·s at a shear rate of 10 s-1, good slurry stability, and strong adhesion force of 1.4 gf/mm compared to those of CMC-Li synthesized by hydrochloric acid. The high energy-density graphite anode prepared with CMC-Li (A) shows higher charge/discharge capacities and capacity retentions in various rates of 0.05-2 C than those of the electrode prepared with CMC-Na that might be due to the enhanced Li+ ion flux upon cycling

Highly Graphitic Carbon Nanofibers Web as a Cathode Material for Lithium Oxygen Batteries

The lithium oxygen battery is a promising energy storage system due to its high theoretical energy density and ability to use oxygen from air as a “fuel”. Although various carbonaceous materials have been widely used as a cathode material due to their high electronic conductivity and facial processability, previous studies mainly focused on the electrochemical properties associated with the materials (such as graphene and carbon nanotubes) and the electrode configuration. Recent reports demonstrated that the polarization associated with cycling could be significantly increased by lithium carbonates generated from the reaction between the carbon cathode and an electrolyte, which indicates that the physicochemical properties of the carbon cathode could play an important role on the electrochemical performances. However, there is no systematic study to understand these phenomena. Here, we systematically explore the electrochemical properties of carbon nanofibers (CNF) webs with different graphitization degree as a cathode for Li oxygen batteries. The physicochemical properties and electrochemical properties of CNF webs were carefully monitored before and after cycling. CNF webs are prepared at 1000, 1200 and 1400 °C. CNF web pyrolyzed at 1400 °C shows lowered polarization and improved cycle retention compared to those of CNF webs pyrolyzed at 1000 and 1200 °C

Engineering SiO2 Nanoparticles: A Perspective on Chemical Mechanical Planarization Slurry for Advanced Semiconductor Processing

Chemical mechanical polishing (CMP) is a process that uses mechanical abrasive particles and chemical interaction in slurry to remove materials from the surface of films. With advancements in semiconductor device technology applying various materials and structures, SiO2 (silica) nanoparticles are the most chosen abrasives in CMP slurries. Therefore, understanding and developing silica nanoparticles are crucial for achieving CMP performance, such as removal rates, selectivity, decreasing defects, and high uniformity and flatness. However, despite the abundance of reviews on silica nanoparticles, there is a notable gap in the literature addressing their role as abrasives in CMP slurries. This review offers an in-depth exploration of silica nanoparticle synthesis and modification methods detailing their impact on nanoparticles characteristics and CMP performance. Further, we also address the unique properties of silica nanoparticles, such as hardness, size distribution, and surface properties, and the significant contribution of silica nanoparticles to CMP results. This review is expected to interest researchers and practitioners in semiconductor manufacturing and materials science