Yttrium Aluminum Garnet Powders Research Articles

Synergistic effect of YAG particulate reinforcement on microstructural and thermo-mechanical properties of pressureless sintered MgAl2O4 spinel ceramic composites

Yttrium aluminum garnet (YAG) powders, synthesized through a partial wet chemical process, exhibit controlled morphology, high phase purity, and uniform homogeneity etc. This process involves the precipitation of aluminum ions onto Y2O3 particles. The transformation process of the Al-compound/Y2O3 precursor structure leads to the direct crystallization of pure YAG at 900 °C, passing through an intermediate stage where hexagonal YAH phase forms. A comprehensive study was conducted on the impact of preformed YAG as a reinforcing phase on the densification, mechanical, and thermo-mechanical properties of MgAl2O4-YAG composite, sintered under pressureless sintering in temperature range of 1500 °C–1600 °C. The inclusion of YAG particulate up to 5.0 wt% significantly enhances the densification, hardness, fracture toughness, flexural strength and high-temperature mechanical behavior of magnesium aluminate spinel (MAS) ceramics, however, increasing the YAG content beyond 5.0 wt% causes a reduction in these properties. The optimized addition of YAG particulate contributes to reducing the average grain size and refining the microstructure of the spinel ceramic matrix.

Improved microstructure and optical properties of Nd:YAG ceramics by hot isostatic pressing

Hot isostatic pressing (HIP) has unique advantages in the preparation of high-density, fine-grained ceramics. In this work, 1.0 at.% neodymium-doped yttrium aluminum garnet (Nd:YAG) powders were prepared via solid-state reaction (SSR) and co-precipitation (CP) methods, and differences in their microstructure after being subjected to the same sintering process were compared. After calcination of raw materials at different temperatures, there was significant phase change at 800 °C-1400 °C for SSR powders. However, this process did not occur for CP powders. Average grain size of Nd:YAG ceramics prepared via CP method was smaller than that of ceramics prepared via SSR method. HIP provided significant improvement in both microstructure and in-line transmittance of ceramics. Ceramics pre-fired under vacuum at 1700 °C showed slight increase in grain size after HIP, with densities close to 100%, and clean, narrow grain boundaries. Moreover, in-line transmittance of ceramics increased from 69.91% to 80.37% (at 1064 nm) via HIP.

Fabrication of Yb:YAG Transparent Ceramic by Vacuum Sintering Using Monodispersed Spherical Y2O3 and Al2O3 Powders

In the present work, Yb:YAG (yttrium aluminum garnet) transparent ceramics were fabricated using monodispersed spherical Y2O3, Al2O3 powders and commercial Yb2O3 nano-powder as raw materials, adding 0.5 wt% tetraethyl orthosilicae (TEOS) through the solid-state method and vacuum sintering technology. The prepared monodispersed Y2O3 and Al2O3 powders adopted by homogeneous co-precipitation showed improved mixing uniformity and lead to the reduced defect of the YAG powders. After sintering in vacuum at 1700 °C for 10 h, the (Y1−xYbx)AG (x = 0, 0.01, 0.10) ceramics with high transparency were obtained. Analysis of the densification rate, micromorphology, and optical properties of the ceramics suggests that the performance of the Yb:YAG ceramics is independent of the doping amount of Yb. Moreover, when the Y2O3, Al2O3, and Yb2O3 mixtures were laid aside for some time in the air after milling and drying, the performances of the as-prepared Yb:YAG ceramics would be affected distinctively. It is likely because the Y2O3 is easily hydrolyzed to Y(OH)3, Y(OH)2+ and Y2(OH)24+, which impinged the sintering activity of the powder mixture.

Solution combustion synthesized micron sized yttrium aluminum garnet (Y3Al5O12) powder: A promising feedstock source for plasma spraying

Yttrium aluminum garnet (YAG) is a well-known high-temperature ceramic material that is used in a plethora of applications such as solid-state laser materials, cathode-ray tubes, field emission displays, scintillators, phosphors, electro-luminescent devices, etc. In recent years, plasma-sprayed yttrium aluminum garnet (YAG) has been explored as an alternative ceramic topcoat for thermal barrier coatings (TBCs) as it is known to prevent the oxidation of the bond coat. Also, it possesses high resistance to calcium magnesium aluminosilicate (CMAS) attack compared to conventional yttria-stabilized zirconia (YSZ) TBC topcoat material. In the current investigation, an attempt is made to fabricate plasma-sprayed YAG coating. The flowable powders required for plasma spraying are synthesized by the versatile solution combustion method after optimizing the process with two different fuels. The powders synthesized using hexamine fuel possess blocky angular-shaped particles and very good flowability. The flowability of the powders is correlated to the heat of combustion, adiabatic flame temperature and shape of the particles. The YAG powder synthesized from hexamine fuel is used for plasma spray application as the process results in higher yield and better flowability. The influence of different plasma spray powers (20, 30 and 40 kW) on the phase purity and crystallinity of the YAG coatings is studied using X-ray diffractometry. The influence of three different plasma powers on the microhardness and microstructure of the coatings is explored. The YAG coating plasma-sprayed at 30 kW is relatively a dense coating and exhibits a higher microhardness value of 1342 ± 9 HV at a load of 100 mN. The CMAS resistance of the YAG coatings is also reported.

Dosimeter Based on YAG: Ce Phosphor via Sol-Gel Method for Online X-ray Radiation Monitoring

This paper focuses on the preparation of cerium-doped yttrium aluminum garnet (YAG: Ce) powder with several concentration gradients via the sol-gel method by detecting its structural characteristics via X-ray diffraction (XRD) patterns and scanning electron microscope (SEM) to verify the generation of a complete crystal phase and evenly distributed nanopowder. On this basis, the luminescence characteristics of Ce3+ are explored, the mechanism and model are discussed based on the spectra, and the ideal doping concentration was obtained by comparing the luminescence intensity along with the fluorescence quenching theory and fluorescence decay spectra of samples with different doping concentrations. Several radiation dosimeters based on YAG: Ce phosphors were made; the online radiation monitoring function was realized under the exposure of a standard X-ray source; the repeatability, accuracy, and sensitivity of the system were verified by experiments; and the factors affecting dosimeter response are discussed. This paper verifies the possibility of adhibiting YAG: Ce fluorescent powder for online X-ray monitoring, and lays the foundation for further research.

Synthesis of yttrium aluminum garnet (Y3Al5O12, YAG) powder with nano and submicro size and high infrared transmittance using flame aerosol synthesis method

In this study, the flame aerosol synthesis (FAS) method was used to synthesize a yttrium aluminum garnet (Y3Al5O12, YAG) nanopowder. The dominant reaction route in the FAS method is the liquid route; this shaped the primary morphology of the YAG nanopowder into hollow and solid spheres. The effects of precursor concentration and annealing parameters were systematically investigated. At a precursor concentration of 0.4 mol L−1 and an annealing temperature of 1400 °C, the YAG nanopowder exhibited excellent infrared transmittance. Compared to other conventional synthesis methods, the FAS method has the advantages of high yield, low cost, and ease of obtaining a nanosized powder. The FAS method is thought to be one of the best choices for the large-scale production of YAG powders.

Oxidation resistance, residual strength, and microstructural evolution in Al2O3-MgO–C refractory composites with YAG nanopowder

The decisive role of nanostructured yttrium aluminium garnet (YAG;Y3Al5O12) powder addition on oxidation resistance, residual strength and microstructural evolution were studied in Al2O3-MgO–C refractory composites. Oxidation index and rate constant calculations indicated that the oxidation resistance was almost 70 % improved for the nano-YAG containing refractories oxidized in air at 1600 °C. Residual compressive strength (Rc) estimations showed that there was nearly 75 % strength retained in these oxidized refractories fortified with nano-YAG. Residual bending strength (Rb) estimations based on cyclic thermal shock, exhibited that there was almost 70 % thermal shock resistance enhancement in refractories reinforced with nano-YAG, showed a good agreement between Rb and Rc values. These beneficial properties were attributed to the formation of a well-sintered framework of YAG/Spinel bonding grains throughout the dense oxidized layer microstructure of these new class of refractories. The concept of interfacial toughening and implications of these results to practical applications are discussed.

Pulverization and Densification Behavior of YAG Powder Synthesized by PVA Polymer Solution Method

YAG (Yttrium Aluminum Garnet, Y3Al5O12) has excellent plasma resistance and recently has been used as an alternative to Y2O3 as a chamber coating material in the semiconductor process. However, due to the presence of an impurity phase and difficulties in synthesis and densification, many studies on YAG are being conducted. In this study, YAG powder is synthesized by an organic-inorganic complex solution synthesis method using PVA polymer. The PVA solution is added to the sol in which the metal nitrate salts are dissolved, and the precursor is calcined into a porous and soft YAG powder. By controlling the molecular weight and the amount of PVA polymer, the effect on the particle size and particle shape of the synthesized YAG powder is evaluated. The sintering behavior of the YAG powder compact according to PVA type and grinding time is studied through an examination of its microstructure. Single phase YAG is synthesized at relatively low temperature of 1,000 oC and can be pulverized to sub-micron size by ball milling. In addition, sintered YAG with a relative density of about 98 % is obtained by sintering at 1,650 oC.

Yttrium Aluminum Garnet Powder Feedstock for Atmospheric Plasma Spray

High demands for higher turbine efficiency bring attention to newer and more advanced insulating materials for the high temperature components in the turbine. Yttrium aluminum garnet (YAG) has shown good insulating properties in the previous published research, such as higher temperature limitation and better resistance to calcium–magnesium–alumina–silicate environmental contaminant penetration than the more conventional yttria-stabilized zirconia systems. Whereas in literature, coatings of YAG are typically prepared by solution deposition processes, in the present work YAG powder has been prepared for more conventional thermal spraying methods. The goal is to show the potential YAG powders have as a thermal barrier coating. Different approaches for obtaining a successful deposition and a good coating have been explored. Small-sized industrial-supplied powder and larger in-house-made powder have been compared, emphasizing the importance of energy used for deposition and crystallinity in the final coating. Highly crystalline material has successfully been produced with F4 atmospheric plasma spray system without post-treatment or substrate heating.

Preparation of translucent YAG glass/ceramic at temperatures below 900 °C

The work presented here deals with the preparation of bulk yttrium aluminium garnet (YAG) glass-ceramics and YAG ceramics from glass microspheres with a YAG composition. Sol-gel prepared YAG powder was fed into a high temperature methane-oxygen flame where the particles melted and glass microspheres, with a YAG composition, were formed. Viscous flow sintering of the microspheres was then performed to prepare bulk YAG glass-ceramics or ceramics in a hot press.Rapid crystallization of YAG glass was traced during hot pressing through a change in the heating rate slope due to release of latent (crystallization) heat. This allowed control of crystallization and enabled preparation of YAG-based materials with different amounts of residual glass. YAG ceramic with relative density of 94.2 % was prepared at 891 °C without isothermal heating; additionally, YAG glass-ceramic reached relative density > 99 % at temperature 815 °C without isothermal heating.

Ce-doped YAG phosphor powder synthesized via microwave combustion and its application for white LED

Cerium-doped yttrium aluminum garnet (YAG : Ce3 + ) powder phosphor have been extensively studied as phosphors for blue to white light conversion. Y(3 − x)Al5O12 : x Ce3 + (x = 2.0 at. %) were successfully synthesized by microwave-assisted combustion (MW) using the organic fuel urea. A direct conversion from the amorphous phase to the cubic one was obtained at 1050°C for 5 h, together with an increase in the particle size into the range of 50 to 60 nm and decrease in the specific surface area. The as-prepared precursors and powder sintered at 1050°C were characterized for their structure, particle size, morphology, electroluminescence properties, and chromaticity by x-ray diffraction, Brunauer–Emmett–Teller method, Fourier transform infrared spectroscopy, field emission-scanning electron microscopy, transmission electron microscopy, electroluminescence, and standard CIE 1931 chromaticity analysis (CIE) chromaticity diagram, respectively. The results show that the obtained sintered YAG : Ce3 + phosphor powder has spherical-shaped particles and strong yellow emission compared to as-prepared phosphor powder. White light emitting diodes with proper color rendering index, and tunable correlated color temperature properties can be produced by controlling the injection currents and coating thickness of the sample, offering daylight white and neutral white LEDs.

A comparative study of synthesis and spark plasma sintering of YAG nano powders by different co-precipitation methods

Pure yttrium-aluminum-garnet (YAG) nano particles were synthesized via normal and reverse co-precipitation methods using nitrate starting solutions and ammonium hydrogen carbonate (AHC) as precipitator agent. The impact of titration method on the phase evolution, thermal behavior, precipitate's composition, morphology and chemical bonds of powders were studied by XRD, TG-DTA, FTIR, FESEM, TEM, EDS and BET analysis. The results revealed that in the normal method, the precipitates were composed of relatively dense particles compared with more homogenous fluffy precipitates with higher carbonate content obtained by the reverse method. The precursors achieved by the reverse method formed less agglomerated and smaller size YAG powders after calcination at 900 °C. Calcined nano powders were processed by spark plasma sintering (SPS) technique at 1350 °C for 10 min without any sintering aids or dispersive agents. The sintering of both powders led to a highly dense and fine submicron-structured YAG ceramic. However, the YAG ceramic produced by SPS of reverse co-precipitated nano powders showed higher transparency (43% at 680 nm and 58% in near-infrared range) and finer micro-structure (about 210 nm in grain size) as compared with normal co-precipitated nano particles.

Solid-state synthesis of YAG powders through microwave coupling of oxide/carbon particulate mixtures

The rapid synthesis of yttrium aluminum garnet (Y3Al15O12, YAG) powder was investigated through the use of microwave irradiation of the oxide precursor system. For this investigation, an external hybrid heating source was not used. Instead, the rapid heating of the precursor materials (yttria and alumina powders, which are typically transparent to 2.45 GHz microwaves) was initiated by mixing an intrinsic absorbing material (carbon) into the original oxide precursors. The effect of the carbon characteristics, such as carbon source, concentration, particle size, and agglomerate microstructure were evaluated on the efficiency of coupling and resultant oxide reaction. The microwave power was varied to optimize the YAG conversion and eliminate intermediate phase formation. Interactions between the conductive carbon particles and the dielectric oxides within the microwave exposure produced local arching and micro-plasma formation within the powder bed, resulting in the rapid formation of the refractory YAG composition. This optimal conduction led to temperatures of 1000 °C that could be achieved in less than 5 min resulting in the formation of > 90 vol% YAG. The understanding of a conductor/dielectric particulate system in this work, provided insight into possible application of similar systems where microwave irradiation could be used for enhanced solid-state formation, local melting events, and gas phase reactions with a composite powder media.

The effects of chelating agent type on the morphology and phase evolutions of alumina nanostructures

In this work, pure aluminum oxide nanoparticle was obtained by the chemical method at low temperature. In this approach, alpha-alumina nanoparticle was prepared by aluminum nitrate nonahydrate and triethanolamine (TEA) as the Al3+ and both gel agent, respectively. FESEM images show that TEA has better efficiency in controlling particle size and agglomeration as compared with citric acid as a chelating agent. Then, yttrium aluminum garnet (YAG) powder was prepared by yttrium nitrate, urea, and tetraethyl orthosilicate (TEOS) as a Y3+, precipitation agent, and flux agent, respectively. Furthermore, results show that by using TEOS, the YAG particles were obtained, while in the absence of this agent, the impurely YAG phase was achieved at the simillar annealing temperature.

Modified Pechini method for the synthesis of weakly-agglomerated nanocrystalline yttrium aluminum garnet (YAG) powders

Modification of Pechini method for synthesis of weakly agglomerated yttrium aluminum garnet powder has been presented. Modified synthesis procedure is based on an additional calcination process in KCl melt at 1000 °C and allows obtaining weaker agglomeration of nanoparticles. Structure, morphology and particle size have been defined using scanning electron microscopy technique, X-ray diffraction, and static light scattering. Adsorption ability of powders has also been studied. Diffraction patterns of samples confirm existence of only one YAG phase; the average size of particles is about 200 nm. The size of coherent-scattering regions was determined to be 40–50 nm. Steady-state luminescence properties and lifetimes of nanocrystalline YAG:Eu3+ powders synthesized by standard and modified Pechini techniques were compared.

Anion-Exchange Synthesis of Yttrium-Aluminum Garnet Powders

A new method is proposed for synthesizing yttrium-aluminum garnet Y3Al5O12 powder. The method consists in anion exchange coprecipitation of yttrium and aluminum from chloride solutions by the anionite Purolite A-300 in the OH-form and calcination at 900 °C of the precursor formed. The product was investigated by means of XPA, DSC, IR-spectroscopy, and electron microscopy. The Y3Al5O12 particle size was 300 nm.

Ammonium citrate-assisted combustion synthesis and photoluminescence properties of Dy:YAG nanophosphors

Dy3+-doped yttrium aluminum garnet (YAG) nanocrystalline powders were synthesized by employing a sol–gel combustion process, in which triammonium citrate was used as both fuel reagent and dispersant. The influence of citrate-to-nitrate molar ratio (0–2) on slurry rheology, phase formation, composition, morphology, and particle size distribution of the Dy:YAG powders was evaluated systematically. The effects of Dy3+ dopant concentration (various from 1 to 3 at.%) and annealing temperature (1000–1300 °C) on the structural and optical properties of Dy:YAG phosphors were also investigated, and the chromaticity coordinates of the phosphor were calculated. Results show that pure Dy:YAG nanopowders were produced by calcining the combustion synthesis products with a citrate–nitrate ratio of 1 at or above 850 °C. Study of the luminescence behavior of the synthesized powders reveals that the phosphors exhibit greenish-blue emission pre-annealing and red emission post-annealing. Furthermore, emission band intensity is increased with an increase in both the Dy3+ dopant concentration and annealing temperature. The Dy:YAG phosphor’s temperature-dependent variation between greenish-blue and red luminescence emission makes it attractive as a potential candidate for applications in temperature monitoring of fuel sprays.

Effect of Gallium and Indium Co-Substituting on Upconversion Properties of Er/Yb:Yttrium Aluminum Garnet Powders Prepared by the Co-Precipitation Method.

Gallium and Indium co-substituted Yb, Er:YAG was fabricated through the chemical co-precipitation method. The formation process and structure of the Ga3+ and In3+ substituted phosphor powders were characterized by the X-ray diffraction, thermo-gravimetry analyzer, infrared spectra, and X-ray photoelectron spectroscopy, and the effects of Ga3+ and In3+ concentration on the luminescence properties were investigated by spectrum. The results showed that the blue shift occurred after the substitution of Ga3+ and In3+ for Al3+ in matrix, and the intensity of emission spectrum was affected by the concentration of Ga3+ and In3+.

Role of flux on synthesis of poly single crystals of Ce3+ doped yttrium aluminum garnet

Yttrium aluminum garnet powders of good morphology are composed of tiny single crystals of regular faces. However, the growth mechanism of those ploy single crystals remains unknown. This paper provides morphology images of particles uncrushed, and it is found that those tiny crystals grow from large clusters in a pomegranate‐like manner. The morphology change occurs after phase transition, and is driven by flux, which provides a semi‐liquid environment around the crystals. This paper is beneficial for understanding growth mechanism of poly tiny single crystals of yttrium aluminum garnet powders.

Synthesis, Characterization, and Sintering of Yttrium Aluminum Garnet Powder Through Double Hydrolysis Approach

A double hydrolysis approach is first adopted to prepare yttrium aluminum garnet (YAG) powders using Y(NO3)3 · 6H2O and NaAlO2 as raw materials. A variety of techniques, such as thermogravimetry/differential scanning calorimetry (TG/DSC), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) are employed to characterize the as-synthesized samples. The results show that pure-phase YAG powders are accurately available at 900 °C and above. Among these, the YAG powders, produced at 1100°C, are elliptic in shape, with an average particle size of ~44 nm. Pellets of pressed YAG powders are sintered in vacuum at 1700°C for 8 h, resulting in a dense and nearly pore-free microstructure with an average grain size of ~7 μm.