Y2O3-Al2O3 System Research Articles

Phase transformation, lattice evolution and microwave dielectric properties of three Y–Al oxides ceramics

The present work begins with the investigation of a large number of studies that give the phase diagram of Y–Al–O ternary compounds. Furthermore, the phase compositions of the Y2O3–Al2O3 system at different temperatures are obtained by high-temperature in situ XRD detection. The constitutive relationships between the lattice properties, grain development, polarizability, internal strain and microwave dielectric properties of the three Y–Al oxides (Y4Al2O9, YAlO3, Y3Al5O12) are elaborated in detail. As an ideal candidate crystalline material for terahertz wave transmission dielectric devices, yttrium-aluminum-garnet ceramics have a dielectric constant of 11.7 in the real part and a Q × f value of 214,735 GHz at high-frequency band (THz).

Photoluminescence of combinatorically sputtered Al2O3–Y2O3 thin films with a Cr3+ and Nd3+ co-doping concentration gradient

The characterization of a wide range of luminescent thin films can be a long and tedious endeavor. With reactive combinatorial sputtering of multiple metal targets, it possible to fabricate thin films with a gradient in composition simply by not rotating the substrate. In this work, combinatorically sputtered thin films of Cr3+ and Nd3+ doped in the Al2O3–Y2O3 system (YAlO) are studied for thin film based luminescent solar concentrators (TFLSCs) application. Contrary to mm's thick plate type LSC's, TFLSCs of just several 100 nm thick require much higher Cr3+ concentration to achieve 40% absorption which can enable several 10's of W/m2 LSC power efficiencies. Our transmission measurements on a Cr2O3 film with a thickness gradient result in an absorption cross section at 460 nm of 1.3 ± 0.7 × 10−19 cm2 showing that the TFLSC absorption requirement can be fulfilled provided that the Cr3+ concentration is in the order of 1022 ions/cm3. The Y:Al ratio of the YAlO host in our films ranged between 0.5 and 3.5, thereby including the monoclinic (Y4Al2O9), perovskite (YAlO3) and garnet (Y3Al5O12) stoichiometry's on a single film. Position dependent XRD, EDX, excitation, emission and lifetime measurements of Cr3+ and Nd3+ show that the unique gradient film sputtering method is able to characterize thin films as a function of host composition and doping concentration. Energy transfer between Cr3+ and Nd3+ in co-doped YAlO films is concluded from Cr3+ excitation bands observed while monitoring Nd3+ emission and from the matching of the rise-time of Nd3+ 1340 nm emission (4F3/2 ->4I11/2) and the decay time of Cr3+ 840 nm emission (4T2 ->4A2). Nd3+ lifetime systematically decreases from 0.24 to 0.05 ms with increasing Cr3+ concentration in Y3Al5-xCrxO12:Nd (0.05 < x < 2). The constraints of heavily doped Cr3+ thin films for enabling adequate absorption and energy transfer to Nd3+ in TFLSC applications are the subjects of the discussion.

Deciphering the glass-forming ability of Al2O3-Y2O3 system from temperature susceptibility of melt structure

Despite its significance in both fundamental science and industrial applications, the glass-forming transition in the Al2O3-Y2O3 (AY) refractory system is not yet fully understood due to the elusive structure evolution upon cooling. Here, atomic-scale structural changes in AY-bearing melts with different compositions and temperatures are tracked by employing in situ high-energy synchrotron X-ray diffraction and empirical potential structure refinement simulation. We find that the glass-forming abilities (GFA) of AY-bearing melts are intriguingly correlated with the dependence of melt structure on temperature. In the case of the Al2O3 and Y3Al5O12 (YAG), the observed large structural changes from superheating to undercooling melt (i.e., higher temperature susceptibility) correspond to a low GFA. Conversely, the 74Al2O3–26Y2O3 (AY26) melt, with the smallest temperature susceptibility, exhibits the highest GFA. Simulation models illustrate that the temperature susceptibility of melt is associated with its atomic arrangement, especially the stability of cation-cation pairs. A balanced network (in AY26 melt), where the unsteady OAl3 tri-clusters are minimized and steady apex-to-apex connections between adjacent network units are abundant, contributes to stabilizing cationic interactions. This, in turn, fosters the formation of large-sized Al-O-Al rings, which topologically facilitates the subsequent glass-forming transition. Our findings provide new structural insight into the GFA of AY-bearing melts and may expand to other unconventional glass-forming systems to accelerate glassy materials design.

The Influence of High Porous Ceramic Implant Based on the ZrO2–Y2O3–Al2O3 System on Vital Indications of Experimental Animals

The Influence of High Porous Ceramic Implant Based on the ZrO2–Y2O3–Al2O3 System on Vital Indications of Experimental Animals

Structure of Nanocomposites in the ZrO2–Y2O3–Al2O3 System and Their Formation under Hydrothermal Conditions

Structure of Nanocomposites in the ZrO2–Y2O3–Al2O3 System and Their Formation under Hydrothermal Conditions

Study on Process Optimization of Sprayable Powders and Deposition Performance of Amorphous Al2O3–YAG Coatings

In this study, the process optimization of sprayed powders and deposition performance for amorphous Al2O3–Y3Al5O12 (YAG) coatings was investigated. The solid-state reaction mechanism of the nano-sized Al2O3 and Y2O3 powders with eutectic molar ratio was studied by multiple step-by-step heating cycle calcination processes. The calcination process could be adjusted according the dominant control factors like chemical reaction rate or ion diffusion rate. Finally, the actual deposition performance of the calcined powders (Al2O3/YAG) was examined by atmospheric plasma spraying (APS). XRD, SEM and DTA were used to characterize the powders and the as-sprayed coatings. The results showed that the reaction of Al2O3–Y2O3 system is a high temperature solid reaction dominated by Al3+ diffusion, the initial reaction process was usually belong to chemical kinetic range, then the reaction will be transformed from chemical kinetic range to diffusion dynamic range with the temperature increasing. The process optimization of powders was very effective, and the deposition effect of coating was effective.

Microstructure and properties evolution of plasma sprayed Al2O3-Y2O3 composite coatings during high temperature and thermal shock treatment

Al2O3-Y2O3 composite powder with TiO2 additive was plasma sprayed to prepare Al2O3-Y2O3 composite coatings. The microstructure and properties evolution of the Al2O3-Y2O3 coatings during high temperature and thermal shock resistance were investigated. The results show that the microstructure of the Al2O3-Y2O3–TiO2 coating is more uniform than that of the Al2O3-Y2O3 coating. Meanwhile, amorphous phase is formed in the two coatings. The Al2O3-Y2O3(–TiO2) coatings were heat treated for 2 h at temperatures of 800, 1000 and 1200 °C, respectively. It is found that the microstructure and properties of the two coatings have no obvious change at 800 °C. Some of the amorphous phase is crystallized at 1000 °C, and meanwhile Y2O3 and Al2O3 react to form YAG phase and YAM phase. At 1200 °C, all of the amorphous phases are crystallized. After heat treatment, the microhardness of the two coatings is increased. The thermal shock resistance of the Al2O3-Y2O3 system coatings can be improved by using TC4 titanium alloy as substrate and with NiCrAlY bonding layer. Moreover, the Al2O3-Y2O3-TiO2 coating exhibits better thermal shock resistance due to the addition of TiO2.

Silicon Carbide Liquid-Phase Sintering with Various Activating Agents

Silicon-carbide materials with 5 – 10 wt.% additions of oxides were prepared by liquid-phase sintering at 1860 – 2100 °C. The highest physicomechanical properties were achieved in SiC material containing 20 wt.% of a three-component eutectic composition in the MgO–Y2O3–Al2O3 system. The mechanical characteristics of liquid phase-sintered materials containing 15 wt.% of the three-component oxides additive exceed those of both the reactive-sintered and the solid-phase sintered materials and approach those of hot-pressed materials. Ill. 5. Ref. 30. Tab. 2.

Silicon carbide liquid-phase sintering with various activating agents

The liquid-phase sintering at 1860‒2100 °C was used to prepare the silicon-carbide materials with the 5‒10 weigh percent of oxide additions. The SiC material with the 20 weigh percent of three-component MgO‒Y2O3‒Al2O3system addition showed the ultimate physical and mechanical properties. The mechanical characteristics of the liquidphase sintered materials with the 15 weigh percent of the three-component oxides addition exceed those of both the reactive-sintered and the solid-phase sintered materials and approach to those of the hot-pressed materials.Ill. 5. Ref. 31. Tab. 2.

Microstructure and properties of Al2O3-Y2O3 ceramic composite coatings fabricated by plasma spraying

The Al2O3-Y2O3 system composite coatings were prepared by plasma spraying Al2O3-Y2O3 composite powders with or without TiO2 addition. The effects of TiO2 on the microstructure and properties of the Al2O3-Y2O3 coatings were investigated. The results show that the composition of the composite powders had great influence on their microstructure evolution. The Al2O3-Y2O3 coatings were composed mainly of α-Al2O3 and c-Y2O3. There were amorphous phase, Y3Al5O12 (YAG) phase and Y4Al2O9 (YAM) phase formed in the Al2O3-Y2O3 coating. The content of Y3Al5O12 in the Al2O3-Y2O3-TiO2 coating increased with addition of 2 wt% TiO2, and the content of Y4Al2O9 and amorphous phases decreased correspondingly. There was no Y3Al5O12 formed in the Al2O3-Y2O3-TiO2 coatings with further increasing of TiO2, while the content of amorphous phase increased. The microhardness of the Al2O3-Y2O3-TiO2 coating was improved with the addition of 2 wt% TiO2, which was attributed to its lower porosity, more uniform microstructure, more YAG phase, and less amorphous phase. The microhardness of the Al2O3-Y2O3-TiO2 coatings decreased significantly with further increasing of TiO2 due to the significant decrease of YAG phase and the increase of the amorphous phase. The Al2O3-Y2O3-TiO2 coating with addition of 2 wt% TiO2 possessed higher toughness, adhesive strength and wear resistance compared with the Al2O3-Y2O3 coating, which was due to its lower porosity, smaller and spherical pores, and more YAG phase.

Synthesis, vaporization and thermodynamic properties of superfine yttrium aluminum garnet

The study of high temperature behavior of Y3Al5O12 is urgently required for development of high temperature materials of the new generation including ultra-high temperature ceramics. The superfine Y3Al5O12 powder was obtained by the glycol-citrate method; the aggregation process of the sample synthesized was investigated under calcination conditions at different temperatures. Using the Knudsen effusion mass spectrometric method vaporization processes and thermodynamic properties of Y3Al5O12 as well as of the melts in the Y2O3-Al2O3 system were studied at temperatures higher than 2270 K. The simultaneous transition to the gaseous phase of both Al2O3 and Y2O3 from the melt under study was observed during isothermal keeping of the Y3Al5O12 sample at the temperature 2675 K with the predominant alumina removal. Analysis of the values of the thermodynamic properties obtained in the Y2O3-Al2O3 system showed negative deviations from ideal behavior despite the possibility of existence of the miscibility gap at the temperature 2675 K.

Oxide Particle Growth During Friction Stir Welding of Fine Grain MA956 Oxide Dispersion-Strengthened Steel

Friction stir welding of an aluminum-containing oxide dispersion-strengthened steel causes significant oxide particle growth visible at both the nano- and microscales. Quantitative stereology of scanning electron images, small-angle X-ray scattering, energy-dispersive X-ray spectroscopy, and atom-probe tomography is used to quantify the degree of particle coarsening as a function of welding parameters. Results show the dispersed oxides are significantly coarsened in the stir zone due to a proposed combination of agglomeration, Ostwald ripening, and phase transformation within the Al2O3-Y2O3 system. This oxide particle coarsening effectively removes all strengthening contribution of the original oxide particles, as confirmed by uniaxial tensile tests and microhardness measurements.

Luminescent Response to the Phase Composition of Nd3+:Y2O3-Al2O3 System

The work demonstrates the luminescent method of identifying the phase composition of Nd3+:Y2O3-Al2O3 system by building calibration curves using standard samples.

Structural studies of Bi2O3-Nb2O5-TeO2 glasses

Bi2O3-Nb2O5-TeO2 glasses show unusual annealing behavior with appearance of spherulites within the matrix glass structure for the Bi0.5Nb0.5Te3O8 composition. The textures resemble those found previously among polyamorphic Al2O3-Y2O3 glasses containing metastably co-existing high- and low-density phases produced during quenching. However the spherulites produced within the Bi2O3-Nb2O5-TeO2 glass are crystalline and can be identified as an “anti-glass” phase related to β-Bi2Te4O11. We used high energy synchrotron X-ray diffraction data to study structures of binary and ternary glasses quenched from liquids within the Bi2O3-Nb2O5-TeO2 system. These reveal a glassy network based on interconnected TeO4 and TeO3 units that is related to TeO2 crystalline materials but with larger Te…Te separations due to the presence of TeO3 groups and non-bridging oxygens linked to modifier (Bi3+, Nb5+) cations. Analysis of the viscosity-temperature relations indicates that the glass-forming liquids are “fragile” and there is no evidence for a LLPT occurring in the supercooled liquid. The glasses obtained by quenching likely correspond to a high-density amorphous (HDA) state. Subsequent annealing above Tg shows mainly evidence for direct crystallization of the “anti-glass” tellurite phase. However, some evidence may exist for simultaneous formation of nanoscale amorphous spherulites that could correspond to the LDA polyamorph. The quenching and annealing behavior of Bi2O3-Nb2O5-TeO2 supercooled liquids and glasses is compared with similar materials in the Al2O3-Y2O3 system.

Phase relations in the SiC–Al2O3–Y2O3 system

Phase relations in the SiC–Al2O3–Y2O3 system were determined by phase analyses of the solid-state reacted samples from powder mixtures of SiC, Al2O3 and Y2O3. The phase diagram at 1700°C of the ternary system was presented. SiC was compatible with each of the three yttrium aluminates of Y4Al2O9 (YAM), YAlO3 (YAP) and Y3Al5O12 (YAG). Stability of the YAP phase and possible effect of the SiO2 impurities on the phase relations in the system were discussed.

Microstructures and characterisation of SiC composites fabricated by liquid-phase sintering at relatively lower temperature

Silicon carbide (SiC) matrix composites have been obtained through liquid-phase sintering in air at temperature below 1600°C by adding three kinds of sintering additives, i.e. BaO–Al2O3, BaO–Al2O3–Y2O3 and BaO–Al2O3–CaO, respectively. Effects of type and content of the sintering additive on microstructures and mechanical properties of the composites were investigated. Among these three types of sintering additives, BaO–Al2O3–Y2O3system was determined to be the most effective. Densification occurs in the sintering process, during which a liquid-phase melt forms through reaction between the sintering additives and SiO2 (the oxidation product of SiC). The melt mostly transforms into crystalline oxides, which act as secondary phases and construct a strong bonding interface by connecting with the SiC particles tightly. By adding 30 wt-% BaO–Al2O3–Y2O3 sintering additives, bending strength and fracture toughness of the SiC composites sintered at 1550°C are up to 520 MPa and 6.7 MPa m1/2, respectively.

Efeito da adição de Nb2O5 na sinterização de Al2O3-Y2O3

A utilização de Y3Al5O12 (YAG - "Ittrium Aluminum Garnet" - Garnet de Alumínio e Ítrio), como reforço em matriz de Al2O3 tem sido estudada desde a década de 1990. As propriedades mecânicas e de resistência à fluência obtidas pelo compóstito Al2O3-YAG têm revelado um grande potencial para seu emprego a temperaturas elevadas por períodos longos de tempo, permitindo a sua utilização na indústria aeroespacial e energética. O objetivo desta pesquisa foi investigar a sinterização do Al2O3 com Y2O3 explorando a presença de fase líquida com o uso do Nb2O5 como aditivo de sinterização para a obtenção do compósito bifásico Al2O3-YAG. No presente estudo, foram produzidas as seguintes composições, utilizando moagem de alta energia: Al2O3 com 4% em peso de Nb2O5 como aditivo de sinterização, Al2O3-YAG também com 4% em peso de Nb2O5 e Al2O3-YAG sem aditivo. Os corpos verdes foram prensados a 70 MPa e sinterizados a 1400 e 1450ºC por 2, 3 e 4 h. Os materiais foram caracterizados por microscopia eletrônica de varredura (MEV) e avaliação de porosidade. O compósito Al2O3-YAG sinterizado a 1400 e 1450ºC apresentou uma porosidade de 40 e 35%, respectivamente, indicando que ainda são necessários mais ajustes em seu processamento.

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.

Study of ceramic pigments based on cobalt doped Y2O3–Al2O3 system

Ceramic pigments based on Y2O3–Al2O3 system doped by cobalt as a colourant agent were synthesized by solid-state reaction at temperatures up to 1,400 °C. The reactivity of initial mixtures of components was improved by the mineralizer LiF and the mechanical activation in a planetary ball mill. The temperature region of the product formation was followed by the method of thermal analysis. The effect of the synthetic method on the phase composition of the products was studied by X-ray diffraction analysis. Studied pigment-application properties of the product include the measurement of optical properties in the visible region of light and particle size distribution. The simple solid-state reaction led to the formation of turquoise samples that contain mainly blue CoAl2O4 spinel and next to it also YAlO3 perovskite and Y3Al5O12 garnet phases. The mineralizer LiF promotes the formation of yttrium aluminium double oxides of sandy-yellow to grey–brown colour hue, although the samples also contain small amount of blue CoAl spinel phase. Intensive milling process did not results in CoAl spinel phase and the samples contain yttrium aluminium perovskite and cobalt oxide. Evaluation of Kubelka–Munk absorption as a function of the pigment concentration was found that hiding is complete by adding of 5 mass% of pigment to the ceramic glaze. Resulting colour hue of all pigment applications into ceramic glaze is blue. The size of particles lies in the range of 7–26 μm.

To melting relations in the La2O3–Y2O3–Al2O3 system

Melting in the La 2 O 3 –Y 2 O 3 –Al 2 O 3 system was investigated using high temperature DTA and microstructures were studied by electron microscopy (SEM/EDX). The experimental results are consistent with calculations based on liquid phase description without ternary interactions and solid phases with limited mutual solubility of La and Y. The thermodynamic description was used to calculate vertical sections at 20 mol% Al 2 O 3 and at fixed ratio of La 2 O 3 /Y 2 O 3 =1 as well as solidus surface. • Melting relations in the La 2 O 3 –Y 2 O 3 –Al 2 O 3 system are investigated up to 2273 K. • Vertical sections and solidus surface are calculated. • Experimental data are reproduced by calculations. • Thermodynamic description of the La 2 O 3 –Y 2 O 3 –Al 2 O 3 system is proved.