Yttria-stabilized Zirconia Layer Research Articles

Performance of Atmospheric Plasma-Sprayed Thermal Barrier Coatings on Additively Manufactured Super Alloy Substrates

This work represents a preliminary study of atmospheric plasma-sprayed (APS) Yttria-Stabilized Zirconia (YSZ)-based thermal barrier coatings (TBCs) deposited on forged and additive manufactured (AM) HAYNES®282® (H282) superalloy substrates. The effect of different feedstock morphologies and spray gun designs with radial and axial injection on APS-deposited YSZ layer characteristics such as microstructure, porosity content, roughness, etc., has been investigated. The performance of TBCs in terms of thermal cycling fatigue (TCF) lifetime and erosion behaviour were also comprehensively investigated. In view of the high surface roughness of as-built AM surfaces compared to forged substrates, two different types of NiCoCrAlY bond coats were examined: one involved high-velocity air fuel (HVAF) spraying of a finer powder, and the other involved APS deposition of a coarser feedstock. Despite the process and feedstock differences, the above two routes yielded comparable bond coat surface roughness on both types of substrates. Variation in porosity level in the APS topcoat was observed when deposited using different YSZ feedstock powders employing axial or radial injection. However, the resultant TBCs on AM-derived substrates were observed to possess similar microstructures and functional properties as TBCs deposited on reference (forged) substrates for any given YSZ deposition process and feedstock.

Design and analysis of a planar and multilayer metamaterial with the dual-functions of an ultra-broadband and high absorptivity absorber and a multi-wavelength resonator

This absorber exhibits a hierarchical structure, featuring layers of ZnO, Zr, yttria-stabilized zirconia (YSZ), Zr, YSZ, Al, YSZ and Al from top to bottom. Simulation analyses were conducted using COMSOL Multiphysics® simulation software (version 6.1). The primary innovation of this multilayer metamaterial lies in its entirely planar configuration, enabling switchable functionality: one ultra-broadband with high absorptivity (facilitated by the ZnO layer) and three narrowband absorption peaks (achieved through the Al layer). The simulation results clearly demonstrate that when light was incident from the ZnO direction onto this designed structure, the investigated planar and multi-functional absorber exhibited excellent absorber characteristics. Over an ultra-wide broadband range from 395 to 2070[Formula: see text]nm, the average absorptivity reached an impressive 95.03%. When light was incident from the Al direction onto the investigated planar and dual-functional absorber, three narrowband absorption peaks were observed at wavelengths 355, 550 and 1200[Formula: see text]nm. The second innovation highlights the effectiveness of ZnO as an anti-reflection layer, elevating the absorptivity of the ultra-broadband absorber. The third innovation establishes that Al is the optimal metal choice. It is worth noting that while using no Al layer or substituting Al with other metals did not diminish the absorptivity of the ultra-broadband absorber, alternative metals might adversely affect the absorptivity of the multi-wavelength absorber.

Mullite/YSZ hybrid thermal barrier coatings plasma sprayed on IN-738LC: Microstructure, phase analysis and oxidation resistance

In the current study, the low carbon Ni-based superalloy Inconel-738 (IN-738LC) was used as the substrate and a metallic bond coat (NiCrAlY) was deposited on the substrate by air plasma spray (APS) method. Subsequently, the layer was coated by a ceramic interlayer Yttria-stabilized zirconia (YSZ) by APS. Finally, as the last ceramic layer, a hybrid ceramic top layer containing mullite and YSZ was plasma deposited on the YSZ interlayer in various compositions such as: 25 wt% mullite/75 wt% YSZ, 50 wt% mullite/50 wt% YSZ, 75 wt% mullite/25 wt% YSZ, and 100 wt% mullite. In order to investigate the oxidation resistance of the produced TBCs, they were heated at 1000 °C for 50 and 100 h. The results showed that the presence of mullite phase is advantageous to hybrid coatings, so that in the 50 wt% mullite/50 wt% YSZ hybrid coating, the percentage of destructive spinel oxides forming the thermally grown oxide (TGO) layer reduced compared to the 25 wt% mullite/75 wt% YSZ coating. Moreover, aluminum oxide is the dominant oxide in the 50 wt% mullite/50 wt% YSZ hybrid coating. However, the further increase in the mullite percentage had no noticeable effect on the reduction of spinel oxides. In addition, the presence of mullite alongside YSZ led to an increase in the hardness of the 25 wt% mullite/75 wt% YSZ hybrid coating (845 HV) compared to the conventional coating including a YSZ layer (680 HV) or a mullite layer (655 HV). The X-ray diffraction (XRD) analysis revealed that the presence of mullite beside YSZ in the coating increases the stability of the coating after oxidation test so that, in the XRD pattern, monoclinic phase was not detected in the hybrid coatings. In general, 50 wt% mullite/50 wt% YSZ hybrid coating provided the best results compared to other coatings. Moreover, with increasing thickness of the hybrid ceramic layer containing 50 wt% mullite to 350 μm, the thickness of the TGO layer decreased to approximately 7 μm. Additionally, it was shown that due to the decrease of chromium and nickel elements in the TGO layer, the level of the spinel oxides in the thick coatings decreases. This led to an increase in the stability of the TGO layer and an extension of the thermal system's lifespan.

Comparative corrosion performance of YSZ-coated Ti-13Zr-13Nb alloy and commercially pure titanium in orthopedic implants

This study delves into the corrosion performance and wear behavior of orthopedic implant alloys, particularly the Ti-13Zr-13Nb alloy and commercially pure titanium (cp-Ti), both coated with Yttria-Stabilized Zirconia (YSZ) nanoceramic. The research utilizes the Taguchi design of experiments (DOE) approach and employs electrophoretic deposition (EPD) techniques to create thin, well-adhering YSZ layers on these alloys. Employing an orthogonal Taguchi L9 array, the study investigates how various EPD parameters, including electrical voltages, YSZ concentration, deposition duration, and grinding intensity, influence the deposition yield on both Ti alloys. To optimize the EPD parameters for these Ti alloys, the coated substrates underwent thickness and adhesion tests. The optimal conditions established are as follows: for commercially pure Ti, YSZ coating thickness and adhesion were achieved using 60 Vs, 7 min of deposition, 15 % concentration, and 400° of grinding. Meanwhile, for Ti-13Zr-13Nb, the ideal parameters were 60 Vs, 7 min of deposition, 20 % concentration, and 400° of grinding. Comprehensive characterization techniques were employed, including high-resolution scanning electron microscopy (FE-SEM) for alloy analysis, optical microscopy and atomic force microscopy (AFM) for surface microstructure and thickness evaluation, energy-dispersive X-ray spectroscopy (EDAX) for composition analysis, and X-ray diffraction (XRD) for phase analysis.The research goes on to assess corrosion resistance by subjecting the optimal coated Ti alloys to simulated body fluid (SBF) using electrochemical methods such as polarization (Tafel) and cyclic polarization. Additionally, adhesion force was measured using a tip tester. Notably, both cp-Ti and Ti-13Zr-13Nb coatings showcased enhanced corrosion resistance in Ringer's solution at 37 °C. Importantly, the corrosion rate of the coated Ti-13Zr-13Nb alloy (1.888 × 10–3) was found to be lower than that of the coated cp-Ti alloy (3.013 × 10–3)..

Investigation of Corrosion Resistance of YSZ Coating with Sacrificial Aluminum Oxide Protective Layer against CMAS and Composite Corrosives

An Al film was deposited onto the surface of yttria-stabilized zirconia (YSZ) coating using magnetron sputtering, followed by in situ oxidized to form Al2O3, referred to as Al2O3-YSZ (A-YSZ). The corrosion behavior of the A-YSZ coating against the attacks of calcium–magnesium–aluminum–silicon (CMAS) and a composite corrosive agent containing salt (NaVO3/Na2SO4/NaCl) and CMAS (CMAS + salt). Results demonstrate the excellent resistance of the investigated coating to the corrosion of CMAS and CMAS + salt. The Al2O3 layer plays a crucial role as sacrificial protection in effectively isolating the composite corrosive agents, substantially extending the service life of YSZ coatings. NaVO3, Na2SO4, and NaCl promote the formation of high-melting-point products, reducing their penetration into the YSZ layer. The reaction mechanisms of Al2O3 with CMAS and CMAS + salt were clarified.

Feasibility evaluation of low-temperature deposited thin-film electrolyte with successive post-annealing for solid oxide fuel cells

During the past decade, thin-film-based solid oxide fuel cells (TF-SOFCs) have demonstrated remarkable performance at a low operating temperature of ∼500 °C by reducing ohmic resistance with vacuum-deposited thin electrolytes. However, a high-temperature deposition process at approximately 700 °C is employed in TF-SOFCs, which is only available at a laboratory scale and is not appropriate for commercial deposition equipment. To address this issue, we investigate the feasibility of depositing electrolytes at relatively low temperatures (≤300 °C) accompanied with post-annealing. A TF-SOFC comprising a trilayer thin-film electrolyte, i.e., yttria-stabilized zirconia (YSZ) sandwiched between gadolinia-doped ceria (GDC), fabricated at low-temperature deposition with subsequent post-annealing is selected and tested. Based on a thorough examination using X-ray diffraction and scanning electron microscopy, the appropriate growth conditions for the YSZ and GDC thin-film layers are selected. Through the optimization, we successfully create a low-temperature deposited 750 nm-thick GDC/350 nm-thick YSZ/150 nm-thick GDC (CZC) trilayer electrolyte exhibiting comparable performances with that deposited at 700 °C. High performance of a single cell, a peak power density of 890 mW/cm2 at 500 °C, is achieved. This result suggests the potential of fabricating high-quality TF-SOFCs with commercial equipment.

Characterization and Performance Evaluation of Yttria-Stabilized Zirconia (YSZ) Thickness on ZnO Nanorods-Based Photoelectrochemical Cell

Photoelectrochemical cell (PEC) has the same working principle as solar cell which convert solar energy into electricity. PEC consists of photoanode, electrolyte, and counter electrode, where electrolyte plays an important role in determining PEC performance. Yttria-stabilized zirconia (YSZ) is the most suitable electrolyte used due to its high ionic conductivity and chemically stable. In this study, YSZ was deposited to ZnO Nanorods (NRs) by doctor blade method with thickness variation of 100 μm (PEC10) and 120 μm (PEC12). X-ray diffraction (XRD), scanning electron microscope (SEM), and UV-Vis spectroscopy were used to distinguish the phase, morphology, and band gap of the formed materials, respectively. Moreover, I-V test was also conducted to evaluate the performance of the fabricated PEC with different YSZ thickness. SEM image confirmed the deposition thickness of YSZ layer on NRs which formed rough and irregular interface due to grain boundary fusion of YSZ and NRs. In addition, there is little difference XRD pattern from PEC10 and PEC12 which shows ZnO and YSZ peaks with peak shifting observed. Meanwhile, slightly difference noticed on band gap value where PEC10 has 3.25 eV and PEC12 has 3.58 eV. Even though, the characteristic of PEC10 and PEC12 is similar, the I-V test shown a significant difference of solar efficiency where PEC10 has higher efficiency of about 0.328% than PEC12. This difference is contributed by smaller grain size which has higher specific surface area and porosity. Based on this study, the thickness of electrolyte layer YSZ doesn’t affect the basic characteristic of PEC but affect the efficiency of PEC significantly.

Electrophoretic deposition of dense anode barrier layers of doped ZrO2 and BaCeO3 on a supporting Ce0.8Sm0.2O2-δ solid electrolyte: Problems and search for solutions in SOFC technology

This work is aimed at the formation of dense anode coatings of yttria-stabilized zirconia (YSZ) and samarium-doped barium cerate BaCe0.8Sm0.2O3-δ (BCS) on the Ce0.8Sm0.2O2-δ electrolyte to increase the performance of a single fuel cell on its base. Materials are obtained by precipitation from a nitrate solution (YSZ-disp), by laser vaporization-condensation (YSZ-lec) and citrate-nitrate method (BCS). YSZ and BCS coatings on SDC substrates were obtained by electrophoretic deposition (EPD) followed by sintering at 1300–1500 °C. Two methods are applied to ensure surface conductivity of the SDC substrates for successful EPD: by synthesizing a conducting polymer - polypyrrole and by depositing a buffer layer of finely dispersed Pt. The main problem of the formation of the dense YSZ layers on the SDC substrates has been revealed, which is associated with their delamination during high-temperature sintering due to thermal expansion mismatch. It is shown that the use of a Pt buffer sublayer makes it possible to avoid delamination during sintering at a temperature of 1500 °C. The BCS barrier layers are shown to be completely compatible with SDC. The influence of the YSZ and BCS barrier layers on the ohmic and polarization resistance values and the open circuit voltage (OCV) values is discussed.

Functional coatings made of eco-friendly materials

Thermal barrier coatings protect alloys (for example, in turbine blades) from extreme temperatures. There is a pressing need to find better materials than currently used yttria-stabilized zirconia (i.e. materials with better thermal stability, lower thermal conductivity, higher thermal expansion coefficient matching that of the alloy). Here we explore gehlenite (Ca2Al2SiO7) for possible application as a material for thermal barrier coatings. We found that gehlenite can indeed be used in next-generation thermal barrier coatings, as a top coat on a thin layer of yttria-stabilized zirconia.

Electrophoretic deposition of YSZ layers on pyrolytic graphite and a porous anode substrate based on NiO-YSZ

Solid oxide fuel cells are promising hydrogen energy devices. The goal of this research was to create ceramic layers for SOFCs based on yttria-stabilized zirconia (YSZ) and to investigate their parameters. YSZ ceramic layers with a thickness of 5.14 μm on a porous NiO–YSZ substrate and 7 μm on pyrolytic graphite were obtained by electrophoretic deposition. X-ray diffraction and electron microscopy were used to determine the composition, structure, and morphological features of ceramic layers. The effects of the substrate's nature, the degree of dispersion of the initial YSZ powder, and the heat treatment conditions on the properties of the ceramic layer YSZ were considered.

Solid Oxide Fuel Cells with 3D Inkjet Printing Modified LSM-YSZ Interface

Solid oxide fuel cells (SOFCs) have drawn attention as an alternative power generation technology due to demonstrated high efficiency and low emissions. The lanthanum strontium manganite (LSM)-yttria-stabilized zirconia (YSZ) cathode is utilized widely for SOFCs due to its high performance and stability. The electrochemical oxygen reduction reaction that occurs in the cathode can be enhanced by the porous LSM-YSZ cathode with good electronic and ionic conductivity. With sufficient electrochemically active reaction sites, the oxygen ion transfer processes in the mixed ionic conductor (YSZ) and at the interface of cathode and electrolyte (LSM-YSZ) become critical for the activity of the cathode. Thus, the pillar shape YSZ microstructure with ~ 150 μm×150 μm×10 μm (L×W×H) size can be fabricated by 3D inkjet printing on the interface of electrolyte and cathode to increase the TPB area and enhance the connection between the dense YSZ electrolyte and mixed YSZ ionic conductor. Scanning Electron Microscopy (SEM) is utilized to assess the morphology and microstructure of the YSZ interface. To investigate the influence of the modified interface on the performance of the SOFC, electrochemical performance testing and characterization are conducted for the SOFCs with/without the modified YSZ layer. The microstructures with different pillar central spacing are also fabricated by 3D inkjet printer to optimize the geometry of the LSM-YSZ interface.

Solid Oxide Fuel Cells with 3D Inkjet Printing Modified LSM-YSZ Interface

The geometry of the electrode/electrolyte interface is critical to solid oxide fuel cell (SOFC) performance. Adding 3D microstructures on electrode/electrolyte interface may enhance the performance of SOFCs potentially. In this study, the pillar shape yttria-stabilized zirconia (YSZ) 3D microstructures with ~ 60 m to 90 m diameter were fabricated by 3D inkjet printing on the interface of electrolyte and cathode to increase the TPB area and enhance the connection between the dense YSZ electrolyte and mixed YSZ ionic conductor. Scanning Electron Microscopy (SEM) is utilized to assess the morphology and microstructure of the YSZ interface. To investigate the influence of the modified interface on the performance of the SOFC, electrochemical performance testing and characterization are conducted for the SOFCs with/without the modified YSZ layer. SOFCs performance is investigated with a different number of printed interfacial layers fabricated with the 3D inkjet printer.

Thermal shock performance and microstructure of advanced multilayer thermal barrier coatings with Gd2Zr2O7 topcoat

Thermal shock behavior of multilayer thermal barrier coatings with yttria-stabilized zirconia (YSZ) and gadolinium zirconate (GZO) top layers was comprehensively investigated to compensate the demand for higher efficiency gas turbine engines. Here, four types of coatings comprised of three-layer and advanced four-layer with HVOF and LPPS bondcoats along with two types of topcoats (YSZ and GZO) were produced and exposed to thermal shock tests at 1100 and 1200 °C. In this regard, the microstructure of GZO, interlamellar and interfacial TGO morphologies, the ratcheting rate and its features, consumption of aluminum, the interdiffusion between bondcoat and the substrate and, ultimately, the performance of layers and their constitutions were evaluated in the multilayered coatings. According to the results, the bimodal microstructure of the top layer GZO assists with improving the sintering resistance and durability of the coating. Moreover, although the four-layer advanced coating with a GZO top layer exhibited a much higher lifetime, for the enhanced performance to keep on, the strength of GZO/YSZ interface and the structure of bondcoat-APS must be improved.

Investigation of Thermal Shock Behavior of Multilayer Thermal Barrier Coatings with Superior Erosion Resistance Prepared by Atmospheric Plasma Spraying

Gadolinium zirconate (GZ) has become a promising thermal barrier coating (TBC) candidate material for high-temperature applications because of its excellent high-temperature phase stability and low thermal conductivity compared to yttria-stabilized zirconia (YSZ). The double-ceramic-layered (DCL) coating comprised of GZ and YSZ was confirmed to possess better durability. However, the particle-erosion resistance of GZ is poor due to its low fracture toughness. In this study, a novel erosion-resistant layer, an Al2O3-GdAlO3 (AGAP) amorphous layer, was deposited as the top layer to resist erosion. Three triple-ceramic-layer (TCL) coatings comprised of an Al2O3-GAP layer as the top layer, a GZ layer, a GZ/YSZ composite layer, and a rare-earth-doped gadolinium zirconate (GSZC) layer as the intermediate layer, and a YSZ layer as the base layer. For comparison, an AGAP-YSZ DCL coating without a middle layer was prepared as well. Under the erosion speed of 200 m/s, only a small amount of spallation occurred on the surface of the Al2O3-GAP layer, indicating a superior particle-erosion resistance. In the thermal shock test, the Al2O3-GAP layer experienced glass transition and the glass transition temperature was close to 1500 °C. The hardness of the Al2O3-GAP coating after glass transition increased ~170% compared to the as-sprayed Al2O3-GAP coating. Moreover, The DCL TBC and TCL TBCs exhibited different failure mechanisms, which illustrated the necessity of the middle layer. The finite element model (FEM) simulation also shows that the introduction of the GZ layer can obviously reduce the thermal stress at the TC/BC interface. In terms of coating with a modified GZ layer, the AGAP-GZ/YSZ-YSZ coating and AGAP-GSZC-YSZ coating showed a similar failure model to the AGAP-GZ-YSZ coating, and the AGAP-GSZC-YSZ coating exhibited better thermal shock resistance.

Heterogeneous Integration of Doped Crystalline Zirconium Oxide for Photonic Applications

Hybrid integration of new materials will play a key role in the next photonics revolution, unlocking the development of advanced devices with outstanding performances and innovative functionalities. Functional oxides, thanks to the richness of their physical properties are promising candidates to build active reconfigurable elements in complex circuits. We review in this article our recent work regarding the hybrid integration of Yttria-Stabilized Zirconia (YSZ), a crystalline oxide with transparency from the visible to the mid-IR range with refractive index of about 2.15. YSZ is mostly studied for its high ionic conductivity, epitaxial growth on Si as buffer layer and its chemical stability but we demonstrated that it also holds a great potential in photonics for the development of low-loss waveguides ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$&lt; $</tex-math></inline-formula> 2 dB/cm) and complex passive structures. Kerr refractive index of YSZ is in the same order of magnitude than well-known nonlinear materials such as silicon nitride. We explored the implementation of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$Er^{3+}$</tex-math></inline-formula> ions as an active element providing outstanding luminescence in correspondence with C-band of telecommunications. The optical properties of active layers of Er-doped YSZ grown on waveguides in different platforms and under resonant pumping and its propagation losses, modal gain and signal enhancement will be discussed in this paper.

On the catalytic effect of zirconia on flash sintering of alumina

AbstractFlash sintering of alumina is more difficult than of yttria‐stabilized zirconia (YSZ). Whereas (MgO doped) alumina requires fields greater than 1 kVcm–1 and temperatures often significantly higher than 1000°C, YSZ can be flashed sintered at ∼100 Vcm–1 at temperatures below 800°C. Mixed powders of such bi‐phasic ceramics, on the other hand, can be flashed under conditions below those for alumina. This effect is usually subscribed to the influence of YSZ on the overall electrical conductivity of the composite. However, such rationalization leaves open the mechanism by which YSZ catalyzes the flash event in alumina. Here, we present results for the onset of flash in a layered structure of YSZ and alumina where both constituents extend from one electrode to the other. We find that the flash initiates, at first, exclusively in the YSZ layer, under conditions identical to those in usual voltage‐to‐current experiments in single phase YSZ, and then, after a brief incubation period, spreads transversely through the thickness of the alumina layer at a speed of ∼3.3 mm s–1, while the power supply is held at constant current. This observation opens a new question as to how flash once initiated in an “easy” phase can migrate normal to itself into a second ceramic, which is nominally more‐difficult‐to flash. (In the present experiments, the alumina layer sintered to full density with all the shrinkage being accommodated in the thickness direction, consistent with an earlier study that articulated that flash obviates constrained sintering.) It is noteworthy that the catalytic effect depends not only on the volume fraction of YSZ, but also on the architecture of the green state (for example a two‐phase powder mixture vs. layered structure), which may affect the initiation of the flash in YSZ but, likely, not its migration behavior into the second phase.

Hot corrosion behavior of hybrid double-layered LZ/LZC + YSZ thermal barrier coatings made using powder and solution precursor feedstock

Lanthanum zirconate (La2Zr2O7; LZ) and cerium doped lanthanum zirconate (La2(Zr0.7Ce0.3)2O7; LZC) has gained immense attention as thermal barrier coating (TBC) materials because of their superior thermophysical properties, high-temperature phase stability and chemical inertness than yttria-stabilized zirconia (YSZ). In the present study, LZ and LZC double-layered TBCs are prepared by solution precursor plasma spray process (SPPS) as a top layer over the atmospheric plasma sprayed YSZ coatings, and their hot corrosion behavior is studied. The as-deposited SPPS coatings exhibited single phases, and the microstructural morphologies reveal a hierarchically structured surface with vertically cracked microstructure. Exposure to the high temperature corrosion process results in damage of the morphology and microstructure within the SPPS layer by forming lanthanum vanadate (LaVO4) and lanthanum cerium vanadate ((LaCe)VO4) in LZ and LZC coatings, respectively, while leaching out zirconia (ZrO2). In the case of conventional YSZ, the corrosive salts infiltrate entirely through the coating and result in complete densification and associated phase changes. While combining the above aspects, the hybrid double-layered architecture of LZ/YSZ and LZC/YSZ coatings can be beneficial to protect the underlying YSZ layer against the detrimental infiltration of molten corrosive salt.

Solution precursor thermal spraying of gadolinium zirconate for thermal barrier coating

Gadolinium zirconate (GZ) is an attractive material for thermal barrier coatings (TBCs). However, a single layer GZ coating has poor thermal cycling life compared to Yttria Stabilized Zirconia (YSZ). In this study, Solution Precursor High Velocity Oxy-Fuel (SP-HVOF) thermal spray was used to produce a double layer GZ/YSZ TBC and compared the thermal cycling performance with the single layer YSZ TBC. The temperature behaviour of the solution precursor GZ was studied, and single splat tests were carried out to obtain an optimised spray parameter. In thermal cycling tests, the single-layer YSZ reached 20 % failure at 85 ± 5 cycles, whereas the double-layer GZ/YSZ was at 70 ± 15 cycles. The single-layer failed at the topcoat/TGO interface, whereas the double-layer failed at GZ/YSZ interface and topcoat/TGO interface. Moreover, Gd diffusion occurred near the GZ/YSZ interface, resulting in porosities in the GZ layer.

Enhancement of high-temperature oxidation resistance of CoCrNiAlY–yttria-stabilized zirconia–LaMgAl11O19 dual-ceramic coating by arc Al plating

A novel Al plating was developed to enhance the oxidation resistance of CoCrNiAlY–yttria-stabilized zirconia (YSZ)–LaMgAl11O19 dual-ceramic coating. The results indicated that the lanthanum magnesium hexaaluminate (LMA) layer without the Al plating sustained severe volume shrinkage, consequently initiating the formation and propagation of longitudinal micro-cracks. These micro-cracks behaved as channels that accelerated the inner diffusion of oxygen. The rapid growth of the thermally grown oxide (TGO) layer induced high interface stress, resulting in the severe fracturing of the interface between the CoCrNiAlY and YSZ layers. However, the Al plating not only effectively suppressed the volume shrinkage of the LMA layer and the initiation of large-size longitudinal micro-cracks but also induced the formation of an in-suit Al2O3 barrier layer. The strong synergistic effect of the dense ceramic layer and Al2O3 layer effectively inhibited the inner diffusion of oxygen, consequently reducing the interface stress and rapid TGO layer growth. Accordingly, a considerably effective anti-oxidation performance was achieved by the dual-ceramic coating with the Al plating.

Thin-Film SOFC Enabling Low-Temperature and Low-Hydrogen-Concentration Operation

Solid oxide fuel cells (SOFCs), which have the highest power-generation efficiency among generators, are key in achieving a low-carbon society. To reduce the cost of an SOFC system including mounting cost, thereby, expand its application, we have been developing a thin-film SOFC suitable for low-temperature operations.Since the anode, solid-electrolyte, and cathode layers are formed by sputtered thin films, the internal resistance of the cell decreases; thus, the operating temperature can be lowered [1, 2]. Figure 1 shows a cross-sectional micrograph of the developed SOFC. In this study, nanoporous anodic aluminum oxide (AAO) was used as a support substrate [3, 4, 5]. The pore diameter was 55 nm and thickness was 100 μm. On the AAO substrate, a stack of dense (70 nm) and porous-platinum (80 nm) layers was deposited for the anode. Pores were formed in the dense platinum layer because the surface of the underlying AAO support substrate has 55-nm pores. A dense yttria-stabilized zirconia (YSZ) was used for the solid electrolyte layer (290 nm). The density of the YSZ layer is significant for inhibiting both gas and electron/hole leakage between the anode and cathode sides. Reactive sputtering by using a metal Zr84-Y16 target under a DC bias condition was key to deposit the dense YSZ layer on the porous-platinum anode layer. The interfacial layer (40 nm) of gadolinia-doped ceria (GDC) was deposited on the YSZ layer. The cathode layer (20 nm) of GDC-platinum composite material was then deposited on the interfacial layer. The characteristics of our SOFC was measured at 453°C, as shown in Fig. 2. The air was flowed to the cathode, and wet 3%-hydrogen of nitrogen base was flowed to the anode. An open circuit voltage of 1.049 V and output power density of 203 mW/cm2 were achieved using 3% hydrogen. At the cathode side, the polarization resistance was reduced by forming a gadolinium-doped ceria layer at the interface [5]. In addition, the GDC-platinum cathode was found to reduce the polarization resistance compared to the porous platinum cathode. At the anode side, the hydrogen diffused through the pores of the AAO substrate and reached the anode layer of the SOFC. The triple-phase boundaries formed among gas-, porous-anode-, and solid-electrolyte phases arguably enhanced the performance of the anode. The water vapor produced at the anode side diffused through the pores of the AAO and joined the exhaust gas. The power density at 453°C is expected to increase by using high-concentration hydrogen [6], which we plan to demonstrate for future study. Apart from operation in high-concentration hydrogen, our SOFC has another application. The experimental results indicate that our SOFC can generate high power by using the low-concentration hydrogen from hydrous bioethanol even at low temperatures.