Yttria Layer Research Articles

Tailoring CO2 adsorption and activation properties of ceria nanocubes by coating with nanometre-thick yttria layers

Ceria (CeO2) is a ubiquitous component in catalysts for environmental protection processes, especially those devoted to CO2 valorisation. Aimed at preparing ceria-based nanomaterials with enhanced CO2 adsorption and activation properties, both the surface acid-base and redox features of ceria nanocubes were modulated by a novel, simple, wet chemistry synthetic strategy consisting of their coating with yttria (Y2O3) layers of variable thickness in the nanometre scale. The as-synthesised samples were characterised with special attention to their surface basicity and reducibility. Characterisation results revealed that the surface doping with yttria not only improved both the reducibility at low temperature and CO2 adsorption capacity of ceria nanocubes, but also introduced a variety of basic sites with different strength. Finally, the careful control of the yttria layer thickness allowed to modulate these effects and thereby the ability of nanostructured ceria to adsorb and activate the CO2 molecule.

Cavitation-assisted decontamination of yttria from graphite of different densities

Yttria coated graphite crucibles are widely used to handle molten refractory and radioactive metals like uranium and plutonium. However, the coated layer suffers damages like cracking and peeling off owing to thermal cycles. As a result, removal of the yttria layer from the graphite surface is essential to ensure reuse of the crucible and minimization of radioactive waste. The present work investigates intensified dissolution of yttria from the coated graphite samples using ultrasound as a non-destructive decontamination technique to recycle the graphite substrate. The optimum conditions established for maximum dissolution were 8 M as acid strength, frequency of 30 kHz, temperature of 45 °C and power density of 8 W cm−2 that resulted in maximum dissolution of 52% in 30 min. Use of an oxidant H2O2 to the acid, did not yield any improvement in the dissolution kinetics, instead, increased oxidation of the graphite substrate was observed, leading to the anomalous weight gain of the graphite substrate despite surface erosion. Effect of ultrasound on the dissolution was pronounced, with almost a threefold increase compared to dissolution performed under silent conditions. Rates of dissolution of yttria from the substrate of different densities and pore size distribution were also studied. The dissolution was slowest from graphite of density 1.82 g cm−3 as the pore size distribution was conducive to accommodate the yttria particles. The dissolution in nitric acid followed ash layer diffusion controlled kinetics. The study has demonstrated the efficacy of application of ultrasound for accelerated decontamination of graphite substrates.

Impact of Interfacial SiO2 on Dual Ion Beam Sputtered Y2O3-Based Memristive System

In this article, the effect of the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layer is demonstrated on dual ion beam sputtered yttria-based memristive devices for the first time. It is found that the effect of thickening of SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layer is extremely detrimental for resistive switching (RS) parameters such as endurance and uniformity of current-voltage characteristics. SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> interfacial layer causes the growth of nano stalagmite in the yttria layer. This interfacial layer is also responsible for the origin of pseudo bipolarity in RS characteristics and early failure of the device during endurance testing. The thickness of the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layer has a positive correlation with deposition temperature and oxygen partial pressure. It is found that the deposition temperature of 300°C and a mixture of Ar:O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> with a ratio of 2:3 shows the best RS characteristics.

Effect of Yttria Mould Coating on the Investment Casting of AZ91D-1 wt% CaO Magnesium Alloy

The main objective of the present research is to develop a technique to inhibit the mould–metal interaction in the investment casting of magnesium (Mg) alloys. The use of yttria layers (Y2O3) as an interface mould coating to manufacture thin-walled samples of AZ91D-1 wt% CaO alloy was investigated and the reaction mechanisms were exploited. Additive manufacturing models with thin walls (2 mm thick) were designed to study the casting behaviour of the melt in ceramic moulds (plaster), for both coated and uncoated models. Additionally, the optimal processing parameters were taken into account using a vacuum induction furnace under a flowing argon atmosphere to prevent the ignition of the molten Mg. Regarding uncoated models tests, a considerable content of reaction products was revealed, resulting in large defects all over the castings. In these samples, new phases have been formed around the surface and the matrix due to the mould–metal reactions. On the other hand, the interaction between the liquid metal and the plaster was prevented in those ceramic moulds where yttria was used as an interface protective refractory, which led to a cleaner surface and a more uniform microstructure, improving the effectiveness of this process in the manufacture of Mg structures.

Pack cemented silicon carbide interlayer for plasma sprayed yttria over graphite

ABSTRACTThermodynamically stable and non-reactive yttrium oxide is proposed to be the coating material on high-density graphite (HDG) crucible for melting and consolidating uranium in the pyrochemical reprocessing of spent metallic nuclear fuels. Yttria deposited over HDG by atmospheric plasma spray (APS) process without interlayer cannot withstand temperatures above 1400°C because of large thermal expansion mismatch and high-temperature partial oxidation of underlying graphite substrate through pores and openings in the plasma sprayed yttria layer. To overcome this limitation, a stable oxidation-protective intermediate layer of SiC was developed over graphite by conventional pack cementation process using two different precursor powders. The coated samples were characterized with respect to coating thickness, microstructure, and phase composition. Experimental results revealed that the optimum pack composition for obtaining thick and diffused coating was 70 wt. % Si – 20 wt. % C – 10 wt. % Al2O3. Subsequently, yttria top coat was deposited over pack cemented HDG coupons by APS process with optimized process parameters. The interlayer of SiC developed by pack cementation for yttria top coat facilitated to extend the thermal cycling life of the coating in inert argon environment significantly. The onset of micro-cracking in the top coat with SiC interlayer occurred after 45, 25 and 13 thermal cycles at 1400°C, 1450°C and 1500°C, respectively.

Possibility of Using a Multilayer Target to Reduce Losses of Tritium in a Neutron Tube

The ability of yttria layers to act as barriers to hydrogen desorption is studied. The possibility is discussed of using these layers to reduce losses of tritium from a neutron tube target. The composition of a multilayer target in which tritium desorption is reduced by an accumulator layer (zirconium) and barrier layers (yttria) is described. It is shown that deuterium losses observed in thermal desorption tests over 4 h at 623 K fell by 85–87%. A system is proposed for the renewal of an external barrier layer subjected to sputtering by a deuteron ion flux.

Effect of yttria–titanium shell–core structured powder on strength and ageing of zirconia/titanium composites

Commercially pure titanium powder was modified by a two-step procedure involving attrition milling and subsequent coating with yttria by sol–gel. Lamellar titanium particles with a high aspect ratio were obtained by mechanical grinding. The existence of an yttria layer covering the milled titanium particles (shell–core structure) was corroborated by X-ray photoelectron spectroscopy. Zirconia/titanium (25vol% titanium) compact specimens were processed by a wet route using the modified titanium powder, spark plasma sintered, and then characterized in terms of mechanical strength and ageing. A reinforcement mechanism arises from the special shape and disposition of the metallic particles. The stable Y2O3 barrier prevents excessive formation of side products at the metal–ceramic interface. Hence, our innovative procedure allows to develop a new ceramic–matrix composite in the interesting zirconia/titanium system with improved mechanical properties and controlled ageing compared to the composites made with commercially pure titanium.

Characterization of amorphous yttria layers deposited by aqueous solutions of Y-chelate alkoxides complex

Crack-free amorphous yttria layers were deposited by dip coating in solutions of different Y-chelate alkoxides complex. Three Y-chelate solutions of different concentrations were prepared using yttrium acetate tetrahydrate, yttrium stearic acid as Y source materials. PEG, diethanolamine were used as chelating agents, while ethanol, methanol and tetradecane were used as solvent. Three different combinations of chelating and solvents were used to prepare solutions for Y2O3 dip coating on SUS, electropolished and non-electropolished Hastelloy C-276 substrates. The thickness of the films was varied by changing the number of dipping cycles. At an optimized condition, the substrate surface roughness (rms) value was reduced from ∼50nm to ∼1nm over a 10×10μm2 area. After Y2O3 deposition, MgO was deposited using ion-beam assisted deposition (IBAD), then LaMnO3 (LMO) was deposited using sputtering and GdBCO was deposited using reactive co-evaporation by deposition and reaction (RCE-DR). Detailed X-ray study indicates that LMO/MgO/Y2O3 and GdBCO/LMO/MgO/Y2O3 stack films have good out-of-plane and in-plane textures with strong c-axis alignment. The critical current (Ic) of GdBCO/LMO/MgO/Y2O3 multilayer structure varied from 190 to 420A/cm with different solutions, when measured at 77K. These results demonstrated that amorphous yttria can be easily deposited by dip coating using Y-chelates complex as a diffusion barrier and nucleation layer.

Diode-end-pumped 1.2 W Yb:Y₂O₃ planar waveguide laser.

Fabrication, characterization and laser performance of a Watt-level ytterbium-doped yttria waveguide laser is presented. The waveguide was grown onto a YAG substrate by pulsed laser deposition and features a 6 µm thick ytterbium-doped yttria layer sandwiched between two 3 µm undoped yttria layers. The laser deposited film was characterized by X-ray diffraction, showing a high degree of crystallinity and analyzed spectroscopically, showing performance indistinguishable from previously reported bulk material. When pumped with 8.5 W from a broad area diode laser the waveguide laser produces 1.2 W of output at 1030 nm.

Effect of Microwave Heating on the Mass Transfer, Phase Formation, and Microstructural Transformations in the Y2O3–Al2O3 Diffusion Couple

The phase composition, phase growth kinetics, and structures of diffusion zones formed under microwave heating (24 GHz) (MWH) and conventional heating (CH) in two-layer Al2O3–Y2O3 samples are studied by optical and scanning electron microscopy and electron microprobe analysis. Diffusion annealing was conducted at 1700°C for 5 h in vacuum, the heating rate being 10°C/min in all experiments. The diffusion couples included alumina layers, such as coarse-grained polycore or sintered Al2O3–5 vol.% ZrO2 layers, and yttria layers, such as sintered coarse-grained samples or fine Y2O3 powder layers on the Al2O3 surface. It is shown that the phases formed during reactive diffusion do not uniquely correspond to the phase diagram, but depend on the initial structure of contacting layers and the type of heating. This is attributed to the contribution of kinetic factors to the competitive phase growth, particularly to the structural sensitiveness of diffusion coefficients whereby the diffusive phases grow and the stresses appearing when new phases form. It is found that MWH influences the competitive phase growth in the Al2O3–Y2O3 system, which involves both the change in the phase composition of the diffusion zone compared to that formed under CH and the acceleration of phase growth. The maximum effect of the phase growth acceleration under MWH is observed for the YAG phase, which is 30 times as fast as that under CH. It is suggested that the structure of grain boundaries changes and, accordingly, their permeability increases under MWH. The accelerated GB diffusion under MWH promotes the YAG phase growth in both oxides as a result of opposite diffusion flows of Al and Y ions along GBs. Under TH the YAG phase is formed only in Y2O3 oxide because of the unipolar diffusion of Al3+ ions to Y2O3. The validity of the proposed mechanism is confirmed by numerical evaluations.

Influence of yttria on the cyclic lifetime of YSZ TBC deposited on EB-PVD NiCoCrAlY bondcoats and its contribution to a modified TBC adhesion mechanism

In the present study IN100 substrates have been coated with a 100μm NiCoCrAlY bondcoat (BC) by electron beam physical vapor deposition (EB-PVD). Prior to thermal barrier coating (TBC) deposition the bondcoats have been annealed in vacuum applying various annealing temperatures and durations in order to form a thermally grown oxide (TGO). Subsequently, a 175μm yttria partially stabilized zirconia (YSZ) TBC has been deposited by EB-PVD. Scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) have been used to investigate TGO microstructure and morphology on as coated NiCoCrAlY bondcoats after TBC deposition. Furthermore, the TGO growth during the early stages of TBC deposition has been correlated with TBC thermal cyclic lifetime. STEM investigations reveal the nucleation of an outer yttria TGO layer during different bondcoat pre-treatments that was located between alumina and ceramic topcoat after TBC deposition. The amount of yttria formed as an outer TGO layer increases with annealing temperature and annealing duration. The growth of this yttria layer has been correlated with TBC lifetime. The current results reveal that longer cyclic TBC lifetimes have been observed on those specimens that form a significant quantity of yttria at the TGO outer surface prior to TBC deposition. When disregarding further oxidation during pre-heating of the samples right prior to TBC deposition it is getting obvious that the ceramic topcoat mainly binds to yttria and not to alumina in the initial stages of TBC deposition. It is assumed that the yttria layer acts as a bi-functional primer promoting a) the formation of a chemical compounds such as YAG and YAP between alumina and yttria and additionally b) towards TBC the formation of solid solutions between yttria and YSZ that are indicated by interdiffusion curves. Within a chemical approach a modified TBC adhesion mechanism has been assessed implementing a compound alumina–yttria TGO into the current understanding of TBC adhesion.

Growth of a two-dimensional dielectric monolayer on quasi-freestanding graphene

Integrating graphene into device architectures requires interfacing graphene with dielectric materials. However, the dewetting and thermal instability of dielectric layers on top of graphene makes fabricating continuous graphene/dielectric interfaces challenging. Here, we show that yttria (Y(2)O(3))--a high-κ dielectric--can form a complete monolayer on platinum-supported graphene. The monolayer interacts weakly with graphene, but is stable to high temperatures. Scanning tunnelling microscopy reveals that the yttria layer exhibits a two-dimensional hexagonal lattice rotated by 30° relative to the hexagonal graphene lattice. X-ray photoemission spectroscopy measurements indicate a shift of the Fermi level in graphene on yttria deposition, which suggests that dielectric layers could be used for charge doping of metal-supported graphene.

Infrared Optical and Mechanical Properties of Ceramic Coatings Fabricated by Aerosol Deposition

The possibility and mechanical improvement of the infrared ceramic coatings fabricated on fluoride substrates at room temperature by aerosol deposition (AD) were investigated aiming to optical components for infrared applications and devices. The yttria coating possibility fabricated on barium fluoride substrates by the AD process was found by adjusting one of the deposition conditions. The optical and mechanical properties of the fabricated ceramic coatings, which are important in practical applications, were evaluated by transmittance and hardness measurements respectively. The mechanical hardness of the fabricated yttria single coatings was increased to 4 times higher than that of the barium fluoride substrates. Furthermore, by an additional layer on a barium fluoride substrate, the mechanical properties of the fabricated multi-coatings including an upper yttria layer were improved from that of the single yttria coating on the barium fluoride substrate, retaining the IR transmittance of the single yttria coating at the wavelength of 10μm.

Compilation of mechanical properties for the structural analysis of solid oxide fuel cell stacks. Constitutive materials of anode-supported cells

The mechanical failure of one cell is sufficient to lead to the end of service of a solid oxide fuel cell (SOFC) stack. Therefore, there is growing interest in gaining knowledge on the mechanical properties of the cell materials for stress analysis.This study compiles available data from the literature on the mechanical properties of the most common materials used in intermediate-temperature anode-supported cells: nickel and yttria-stabilized zirconia (Ni–YSZ) anodes, YSZ electrolytes, yttria (YDC) or gadolinia-doped ceria (GDC) compatibility layers and lanthanum strontium manganite (LSM) or lanthanum strontium cobalt ferrite (LSCF) cathodes. The properties for the simulation of stresses, i.e. coefficient of thermal expansion (CTE), Young's modulus, Poisson's ratio, creep behaviour and strength are reported, with an emphasis on temperature and porosity dependence and the evolution upon aging or cycling when available. Measurements of our Ni(O)–YSZ anode material includes the CTE (oxidised and reduced state), Young's modulus and strength at room temperature (oxidised and reduced) and 1073K (oxidised).

High Yield and High Throughput Reactive IBAD MgO Process for Long-length, HTS Wire Production at SuperPower

AbstractSuperPower's IBAD (ion beam assisted deposition) MgO process has been changed to reactive ion beam sputtering of Mg metal target instead of MgO ceramic target, which gives ∼ 60 % increase in deposition rate. The process speed was increased from 195 m/h to 360 m/h. Texture of IBAD MgO tapes by this reactive process was found to degrade faster during long length run. This uniform issue was resolved with feedback control during long run and from run to run. The bottleneck of alumina layer process due to slow ion beam sputtering deposition was removed by new high rate reactive magnetron sputtering at transition mode. The new alumina process speed can be as high as 3,000 m/h in our Pilot Buffer system. The yttria layer process was also changed to high rate reactive magnetron sputtering at transition mode with achievable speed as high as 10,000 m/h in our Pilot Buffer system. The routine production speed of alumina and yttria is 750 m/h due to limitation of tape driving system. The high rate magnetron-sputtered alumina/yttria yields the same texture of IBAD MgO as ion beam sputtered alumina/yttria. Now we are routinely producing IBAD MgO template tapes of ∼ 1.4 km with a uniform in-plane texture ∼ 6-7 degrees. Record high critical current of 813 A/cm over a one meter length and a world record critical current times length value of &gt; 233,8100A-m was obtained with our routinely-produced high throughput IBAD MgO buffers. The requirements for a better IBAD texturing layer than IBAD MgO are also suggested.

Effect of Yttria Nanopowder on Multi-Layer Coatings of Yttria And CVD SiC/Graphite

Nano-yttria powder can be synthesized by yttrium citrate-urea precursor, combusted at 600°C in air. The CVD SiC coated on graphite (CVD SiC/Graphite) infiltrated by the yttrium citrate-urea precursor, combusted at of 600°C, and then sintered at 1450°C, the thin yttria film can be achieved. The SEM morphology and EDS result of the thin yttria film show a mass of needle-shaped pining into the CVD SiC layer, which improves the combination of CVD SiC layer and wash yttria coating. Therefore, it is an effective transition layer between CVD SiC coating and wash yttria layer.

Synthesis of Yttria‐Based Crystalline and Lamellar Nanostructures and their Formation Mechanism

A nonaqueous synthetic route for the preparation of a regular crystalline yttria mesostructure is presented. The reaction between yttrium alkoxides and benzyl alcohol results in the formation of a highly ordered lamellar nanocomposite consisting of yttria layers with a confined thickness of about 0.6 nm, separated from each other by organic layers of intercalated benzoate molecules. Doping with europium leads to strong red luminescence. The nanostructure formation proceeds via two reactions. A C--C bond formation occurs between benzyl alcohol and the isopropanolate ligand. At the same time, yttrium oxide catalyzes two low-temperature hydride-transfer reactions to form benzoic acid and toluene from benzyl alcohol via benzaldehyde, thus limiting the growth of the thickness of the lamellae.

Intermetallic TiAl-based matrix composites: Investigation of the chemical and mechanical compatibility of a protective coating adapted to an alumina fibre

The investigation of both chemical and mechanical compatibility of a TiAl-based matrix with a ceramic fibre has led to the choice of the “Saphikon” single crystal alumina fibre and to develop a double coating concept consisting of an external yttria layer acting as a diffusion barrier and an internal tungsten coating enabling decohesion at the fibre/matrix interface. Tensile tests performed on monofilament composites, i.e. alumina fibres successively coated with W, Y 2O 3 and TiAl, revealed that after the heat treatment (1 h at 1100°C) simulating the consolidation cycle, the double coating provides an 80% increase in the mean tensile strength as compared with a monofilament composite without coating. SEM and TEM observations did not show any evidence of interfacial reaction. Moreover, the absence of cracking in a bulk composite specimen confirms the predictions of the internal stresses calculations and proves the good fibre-matrix thermomechanical compatibility. Finally, push-out tests were used to validate the possibility of fibre/W interface debonding at rather low stresses ( τ d ≈100 MPa).

Experimental evidence of resputtering of the yttria layer in a YBa2Cu3O7−x/Y2O3/YBa2Cu3O7−x trilayer film

Using transmission electron microscopy and energy dispersive x-ray spectroscopy analysis, the microstructure and composition of a YBa2Cu3O7−x/Y2O3/YBa2Cu3O7−x trilayer film deposited on MgO by off-axis sputtering at 670 °C and 100 mTorr was investigated. The YBa2Cu3O7−x layer in contact with the substrate was found to be mainly single phase. However, the top YBa2Cu3O7−x layer was embedded with 5–10 nm crystalline Y2O3 (yttria) particles, which disturbed the local microstructure. The top YBa2Cu3O7−x layer also had barium copper oxide particles covering its surface. The partial decomposition of the top YBa2Cu3O7−x layer may have been due to resputtering of the yttria layer which locally altered the deposition conditions. In particular, the oxygen pressure in the vicinity of the growing film may have increased due to sputtering of the yttria layer by plasma gas atoms and the sputtered target atoms. As a result, deposition occurred under conditions away from the thermodynamic stability line.

YBa2Cu3O7-δ Angle Grain Boundary Junction on Si Bicrystal Substrate

Si bicrystal substrates with angle grain boundaries (AGB) have been fabricated for the first time by a diffusion bonding technique using the hot-press method. YBa2Cu3O7-δ (YBCO) epitaxial thin films are grown on the Si bicrystal substrates with yttria (Y2O3) and yttria-stabilized zirconia (YSZ) buffer layers by rf magnetron sputtering. The properties of bridge-type junctions patterned by excimer laser have been studied from 4.2 K to 77 K and by microwave irradiation. It is found that the critical current density of the AGB junction (JcA) is always less than that of either bridge made on single-crystal grains (JcG). The effects of the temperature and microwave radiation show that the properties of the bridges on the grains are limited by flux creep. In contrast, the properties of the AGB junction with the angle larger than 10° show the Josephson effect.