Formation Of Yttrium Aluminum Garnet Research Articles

Influence of Mechanical Activation on the Formation of Yttrium Aluminum Garnet (YAG) at Lower Temperature

Yttrium aluminum garnet (YAG) is an important material which require high temperature of 1600°C in its solid-state reaction. To lower this temperature, mechanical activation process has applied to the system which make the crystal arrangement broken thus make it more reactive. This process results in homogeneous and fine particle distribution of Al2O3 and Y2O3 compared to manually mixed powders. Moreover, milling process also reduce the particle size of the Al2O3 and Y2O3 from 4694 nm and 349 nm down to 274 nm. This also lessen the crystallite size of Al2O3 and Y2O3 from 1010 and 164 Å to 310 and 50 Å respectively. Then, after calcination at 1100°C, the milled powders form YAG phase in the opposite of manually mixed powders which form YAM phase. YAG formed have nearly round shape with finer grain compared to manually mixed powders which still has large grain of Al2O3 and Y2O3. This formation temperature is much lower than the require conventional solid-state reaction.

Passive filler loaded polysilazane‐derived glass/ceramic coating system applied to AISI 441 stainless steel, part 2: Oxidation behavior in synthetic air

AbstractThis article features the oxidation behavior of ferritic stainless steel grade AISI 441 coated with protective polymer‐derived ceramics (PDC). Two PDC compositions are studied with respect to their oxidation resistance in a flow‐through atmosphere of synthetic air at temperatures of up to 1000°C. The coatings contain a combination of six passive fillers: Y‐containing ZrO2, glass microspheres, alumina‐yttria‐zirconia (AYZ) powder, and three commercial glasses. They are pyrolyzed in air for 1 hour at 800°C with heating and cooling rates of 3 K/min. Detailed microstructural examination of the oxide products formed at the surface of samples after exposure to air at 900°C, 950°C, and 1000°C for 1‐48 hours is analyzed. Both uncoated steel and steel coated with two of the protective systems described in part 1 of this article are investigated. Fe, Cr2O3, TiO2, and a spinel of the composition (Mn,Cr)3O4 are identified at the oxidized surface of the steel substrate using X‐ray diffraction. A significant weight gain of the unprotected steel is measured after all experiments, while oxidation tests of the coated steel show a negligible weight gain after 900°C and 950°C. During the early stages of coating oxidation, the monoclinic‐to‐tetragonal ratio in the zirconia filler is shifted toward the monoclinic modification. Longer exposures and higher temperatures lead to the formation of yttrium aluminum garnet (YAG) due to glass microsphere crystallization and solid state reactions in the AYZ powder. The crystallization of the three commercial glasses functioning as sealants leads to the formation of Ba(AlSiO4)2 also known as hexacelsian, which subsequently transforms to celsian. YZr8O14 is also formed. The protective effect of the PDC coatings applied to the stainless steel is demonstrated up to 950°C.

Combinative effects of Y2O3 and Ti on Al2O3 ceramics for optimizing mechanical and electrical properties

This study aims to combine Y2O3 and Ti to improve the mechanical and electrical properties of Al2O3 ceramics. Al2O3-based composites containing 20 vol% of metallic Ti were chosen. Y2O3 was used as the effective additive to optimize the mechanical and electrical properties of Al2O3/Ti composites. The effects of Y2O3, ranging from 1 to 5 wt%, on mechanical and electrical properties of Al2O3/Ti composites were studied. Energy-dispersive X-ray spectroscopy indicated that the added yttrium was present at the grain boundaries. The formation of yttrium aluminum garnet (Al5Y3O12, YAG) resulting from the solid-state reaction between Y2O3 and Al2O3 was identified by X-ray diffraction (XRD). All Y2O3 doped Al2O3/Ti composites showed an increase in the density. The observation of microstructure revealed that the microstructure was refined and the grain size of Al2O3 decreased. Vickers hardness, Young's modulus, and fracture toughness of the composite having Y2O3 content of 2 wt% reached their maximum values, which were 15.2 GPa, 355.2 GPa, and 4.5 MPa•m1/2, respectively. Ductile fracture mode and transgranular fracture were visible in all the composites. The toughening mechanism, which arises due to the presence of YAG, was demonstrated. In addition, the electrical resistivity of composites increased monotonically with an increase in the Y2O3 content. Nevertheless, the increase was negligible and the composites could be regarded as a good electrical conductor having 5 wt% Y2O3 addition.

Structural, optical and thermal properties of the Ce doped YAG synthesized by solid state reaction method

Powder phosphor yttrium aluminum garnet (YAG), doped with trivalent cerium (Ce3+), is synthesized by using the solid state reaction method. The formation of YAG and YAG:Ce (cerium-doped yttrium aluminum garnet) was investigated by means of X-ray diffraction (XRD) which shows that the powder is a single phase constituted of grains with sizes of about 70nm. From the photoluminescence spectra, it was confirmed that the synthesized YAG:Ce3+‏ phosphor emits typical yellow light peaked at around 550nm under an excitation of 473nm-wavelength. By using the Photo-Thermal Deflection (PTD) technique, heat transfer modes are studied and, thermal conductivity, thermal diffusivity, specific heat and mean free path are determined and obtained respectively in the order of 12Wm−1K−1, 2m2s−1, 800Jmol−1 and 7.5A°, which are in good agreement with literature.

Kinetics and formation mechanism of yttrium aluminum garnet from an amorphous phase prepared by the sol–gel method

Isothermal crystallization kinetics was studied for Y3Al5O12 obtained from amorphous dispersed phases based on aggregately stable sols of yttrium aluminum hydroxides. To describe the formation of yttrium aluminum garnet from the amorphous phases, a mathematical model involving intermediate Y4Al2O9 and YAlO3 phases has been proposed. From the obtained experimental data on the phase composition of the crystallizing system, kinetic parameters of the crystallization process were determined, which allowed us to propose a probable mechanism of YAG crystallization from hydrosols of various composition. The actual mechanism of garnet formation depends not just on the temperature treatment conditions of the amorphous phase, but also on the type of the precursors. The optimization of the time–temperature regimes of YAG crystallization allowed preparation of samples with required properties. Thus, the sol–gel method involving sols of high stability towards aggregation is shown to be promising for the production of high-quality powders and optical ceramics of yttrium aluminum garnet.

Particle size effects on yttrium aluminum garnet (YAG) phase formation by solid-state reaction

Abstract

Influence of hydrolysis method on the sol-gel formation of the yttria-alumina system with use of alcoholates

The influence exerted by hydrolysis methods and introduction of a hydrolyzing agent into the systems formed by the alkoxide technology, which uses yttrium salts and alumium secondary butylate as the initial components, was determined. It was found that the hydrolysis stage affects the conditions of the subsequent thermal treatment, the phase formation in the system, and the granulometric composition of the prepared powders. The most favorable conditions for formation of yttrium aluminum garnet are achieved upon excess water hydrolysis in the presence of an aqueous solution of yttrium salt.

The effect of TiO2 and ZrO2 addition on the crystallization of Ce3+ doped yttrium aluminum garnet from glasses in the system Y2O3/Al2O3/SiO2/AlF3

The crystallization of yttrium aluminum garnet (YAG) doped with Ce3+ from alkali free glasses in the system Y2O3/Al2O3/SiO2/AlF3 has been investigated with and without the addition of ZrO2 and/or TiO2 as nucleation agents. X-ray diffraction (XRD), scanning electron microscopy (SEM) and differential thermal analysis (DTA) were used to characterize the crystallization process. Fluorescence microscopy and fluorescence spectroscopy were used to investigate optical properties. Thermal annealing of the glass was carried out at temperatures in the range from 1100 to 1400°C. In all samples studied, crystallization at temperatures ≥1300°C lead to the formation of YAG as the main crystalline phase. If the glass contained TiO2, the crystallization of YAG occurred at lower temperatures; here, already at 1150°C, YAG was the main crystalline phase. After annealing at 1300°C, the only crystalline phase formed was YAG. The fluorescence intensity showed a maximum at a wavelength of 532nm and was largest in the sample solely doped with 5mol% TiO2. This proves that Ce3+ was incorporated into the YAG crystals.

Synthesis and characterization of photoluminescent cerium-doped yttrium aluminum garnet

Powder phosphor yttrium aluminum garnet (YAG), doped with trivalent cerium (Ce 3+) is synthesized by sol–gel method. The formation of YAG and YAG:Ce (cerium-doped yttrium aluminum garnet) was investigated by means of X-ray diffraction (XRD). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were also used. The purified crystalline phases of YAG and YAG:Ce were obtained at 1000 °C. The maximum average grain size is about 20–23 nm for undoped samples and 28–34 nm for doped samples. The crystalline YAG:Ce emission shows one peak in the range 480–535 nm with the maximum near 520 nm. Photoluminescence (PL) intensity of 5d → 4f transition of Ce 3+ increased with increasing annealing temperature. With increasing the concentration of Ce 3+, the photoluminescence peak shifts towards the red region.

Effect of the aluminum source on the formation of yttrium aluminum garnet (YAG) powder via solid state reaction

The comparison of the different aluminum sources including: α-Al 2O 3, θ-Al 2O 3, γ-Al 2O 3 and boehmite to form the yttrium aluminum garnet (YAG) powder via the solid state reaction method are studied in this article. According to the experimental results, we can conclude that boehmite (AlOOH) is the best aluminum source for the formation of YAG powder. The intermediated phases, such as YAM(Y 2Al 4O 7) and YAP(YAlO 3), were presented at 1200 °C and the impure phase α-Al 2O 3 was formed at 1500 °C for 1 h. A pure YAG phase was successfully formed from the reacting product of yttrium oxide and boehmite after calcining at 1500 °C for 5 h.

Thermal decomposition behavior of precursors for yttrium aluminum garnet

Precursor powders for yttrium aluminum garnet (YAG) were synthesized by solution combustion reactions (nitrate–glycine reaction with stoichiometric and sub-stoichiometric amount of fuel) and simple decomposition of nitrate solution. The TG-DTA, FTIR and XRD analyses of the precursors and the typical heat-treated samples were carried out to understand the processes occurring at various stages during heating to obtain phase pure YAG. Precursors from all the reactions exhibited dehydration of adsorbed moisture in the temperature range of 30 to 300°C. The precursor from nitrate–glycine reaction with stoichiometric amount of fuel (precursor- A) contained entrapped oxides of carbon (CO and CO2) and a carbonaceous contaminant. It exhibited burning away of the carbonaceous contaminant and crystallization to pure YAG accompanied by loss of oxides of carbon in the temperature ranges of 400 to 600 and 880 to 1050°C. The precursor from simple decomposition of nitrates (precursor-B) exhibited denitration cum dehydroxylation and crystallization in the temperature ranges of 300 to 600 and 850 to 1050°C. The precursor from nitrate–glycine reaction with sub-stoichiometric amount of fuel (precursor-C) contained entrapped carbon dioxide and exhibited its release during crystallization in the temperature range of 850 to 1050°C. This study established that, in case of metal nitrate–glycine combustion reactions, crystalline YAG formation occurs from an amorphous compound with entrapped oxides of carbon. In case of simple decomposition of metal nitrates, formation of crystalline YAG occurs from an amorphous oxide intermediate.

Novel synthesis of YAG by solvothermal method

Yttrium aluminum garnet (YAG) powder was synthesized by a mixed solvothermal method under moderate conditions ( 260 – 290 ∘ C , 2–4 h) with inexpensive aluminum and yttrium hydroxides as the precursors, and a low-cost ethanol–water solution (the volume ratio of ethanol to water ⩾ 2 : 1 ) as the solvent. The presence of ethanol in mixed solvent is beneficial to the formation of YAG. The synthesized powder consists of well-dispersed and nearly spherical fine grains (80 nm on average) with a relatively narrow grain size distribution. The powder form is the most desirable for the compacting and sintering of YAG ceramics.

Processing of yttrium–aluminum garnets under non-equilibrium conditions

Polycrystalline yttrium–aluminum garnet (YAG) was processed via mechanical alloying (MA). The powder mixture comprising equal proportions of elemental aluminum and yttria was mechanically alloyed (MA’d) for 5 h and the MA’d powder mixture was heat treated. While MA resulted in aluminum–yttrium solid solution, the reaction leading to the formation of YAG occurs during the subsequent heat treatment of the powder mixture.

Comparison of citrate–nitrate gel combustion and precursor plasma spray processes for the synthesis of yttrium aluminum garnet

The influence of synthesis conditions on the formation of yttrium aluminum garnet (YAG) powders starting from the same solution precursors was investigated by employing a citrate–nitrate gel combustion process and a precursor plasma spraying technique. YAG powders were formed at ≥500 °C, through the citrate–nitrate gel combustion process, without any intermediate phase formation. Time-resolved x-ray experiments were performed for the first time on these citrate–nitrate precursor materials to understand their mode of decomposition. The in situ data confirmed a single-step conversion to YAG from the precursor powder without any intermediate phase formation. Ex situ experiments also produced similar results. However, the use of the same citrate–nitrate precursor solution as a liquid feedstock material in the precursor plasma spraying technique revealed an entirely different transformation mechanism to YAG through intermediate phases like H–YalO3 and O–YalO3.

Low temperature formation of yttrium aluminum garnet from oxides via a high-energy ball milling process

Mechanochemical process has been applied to the mixture of Y 2O 3 and Al 2O 3 in order to increase its reactivity. Yttrium aluminate garnet (YAG, Y 3Al 5O 12) has been synthesized at 1000 °C from the milled mixture, which is significantly lower than that required by the conventional solid-state reaction process and comparable with that required by most of the chemical-based synthesis routes. The reduced formation temperature of the YAG phase is believed to be beneficial from the refined Y 2O 3 and Al 2O 3 as a result of the high-energy ball milling.

Synthesis of YAG powder by aluminum nitrate–yttrium nitrate–glycine reaction

Yttrium aluminum garnet (YAG) powders of controlled size distribution find application in the synthesis of optically transparent solid state laser components, advanced engineering materials and composites, etc. [1, 2]. Solution combustion is one of the simple methods for synthesizing the powder. In this technique, from a very concentrated solution of the metal nitrates a very porous sponge-like oxide compound is formed due to the evolution of a large amount of gaseous products formed in combustion reaction between an oxidizer (nitrate) and a fuel (urea, glycine etc.) present in the reactant system. The salient feature of combustion reaction is that it is exothermic and self sustaining. In this study the fuel, glycine, is chosen for formation of YAG since the amount of heat evolved and kinetics of the reaction are such that the combustion proceeds smoothly without bursting or spilling out of the product, a desirable aspect from the point of view of scaling up. The oxide formed is weakly agglomerated and needs to be ground into a fine powder before forming into shape. Formation of amorphous precursors for yttria–alumina compound phases by the nitrate–glycine reaction (with lean amount of fuel) and evolution of crystalline phases upon heat treatment has been studied by XRD [3]. However a study of the thermal evolution behavior by TG–DTA of the precursors formed by combustion to obtain temperature regimes of weight loss and heat effects (evolution/absorption) before and during crystallization of YAG is essential in obtaining conditions for formation of chemically pure YAG (Y3Al5O12 oxide compound). A study of the grinding behavior of the agglomerated mass formed is important from the point of view of its dispersion behavior, as the presence of coarse agglomerates reduces sinterability and homogeneity of microstructure of the product formed. As no study on these aspects has been reported yet for the precursors formed by the nitrates–glycine reaction (with stoichiometric amount of fuel), a detailed investigation of the same has been carried out. The stock solutions of aluminum nitrate (1.54 M) and yttrium nitrate (1.17 M) in the required molar ratio (5 : 3) for a batch size of 20 g. of YAG were placed in a pyrex beaker and the required amount of glycine was added. The ideal molar ratio of fuel (glycine) to oxidizer (nitrate ion) to be used was calculated using the following reaction and is 5/9 or 0.556 (i.e., 5 moles of glycine requires 9 moles of nitrate ions) [4]

Kinetic model and mechanism of Y3Al5O12 formation in hydrothermal and thermovaporous synthesis

Kinetics and mechanism of fine-crystalline yttrium-aluminum garnet (YAG) formation under hydrothermal and thermovaporous treatment were investigated. It was synthesized from the stoichiomctric mixture of oxides in the temperature range 200-400°C at pressures of water vapor 4.0-26MPa. It was established that in quasiequilibrium with water vapor conditions the synthesis of YAG proceeds with formation of intermediate substance with Y(OH)3 structure and amorphous aluminous component. The diffusion of this aluminous component into the Y(OH)3 matrix resulted in the reorganization of oxygen sublattice accompanied with dehydroxylation. The kinetics of YAG formation is described by the equation of solid-phase transformation with the limiting stage of nucleation. Synthesized YAG contains 5-7% of water, which corresponds to a hydrogarnet structure. The study of luminescence properties of YAG doped with Nd3+ or Cr3+ ions has allowed to determine the positions of hydroxyl groups and oxygen vacancies in the structure.

In situ Raman monitoring of low-temperature synthesis of YAG from different starting materials

Low-temperature formation of yttrium aluminum garnet (YAG) from different starting materials, i.e., alkoxide–acetate, nitrates, and hydroxides by homogeneous precipitation, has been monitored up to 1200°C using in situ Raman spectroscopy. YAG was formed at relatively low temperature around 800°C by the alkoxide method, but at 1100°C by the nitrate and the hydroxide methods. Formation of an intermediate hexagonal YAlO 3 phase was observed for the oxide powders prepared by the latter two methods at about 1000–1100°C, which hindered the lower temperature formation of YAG phase. Additional Raman and X-ray diffraction investigation revealed the presence of impurities and the difference of local homogeneity in the oxide powders prepared by the different methods. Highly homogeneous powders obtained by the alkoxide method enabled the direct and low temperature formation of YAG.

Comparison of Solid‐State and Spray‐Pyrolysis Synthesis of Yttrium Aluminate Powders

The influence of precursor characteristics and synthesis conditions on the formation of yttrium aluminum garnet, Y3Al5O12 (YAG), was investigated using “single‐source” precursors (cohydrolyzed yttrium and aluminum alkoxides and yttrium aluminum glycolates) and “multiple‐source” precursors (mixtures of metal nitrates and mixtures of separately hydrolyzed yttrium and aluminum alkoxides). Phase‐pure YAG was formed only in the solid‐state thermal decomposition experiments. The lack of formation of YAG in all the spray‐pyrolysis experiments was ascribed to the short heating times and fast heating rates, which resulted in the formation of kinetic products. In the case of the metal nitrates, an additional factor that influenced product formation was the difference in thermal reactivity of the precursors. It was concluded that the formation of complex metal oxide materials by conventional or aerosol routes is not necessarily achieved by the use of a chemically homogeneous precursor, such as a single‐source precursor. It also was necessary to ensure that the precursors and intermediates have similar thermal decomposition temperatures to avoid phase segregation in the initial stages of thermal decomposition.

Preparation and Characterization of Y3Al5O12 (YAG) from An Alkoxide-Derived Polymer

ABSTRACTThe controlled hydrolysis of Al(O-sec-Bu)3 and Y(O-iso-Pr)3 or the reaction of Y(OOCCH)3 with partially hydrolyzed Al(O-sec-Bu)3 [AlO0.75(O-sec-Bu)1.5] resulted in the formation of soluble polymeric materials. Pyrolysis of these materials under a flow of oxygen led to the formation of yttrium aluminum garnet (YAG) at 650-1500°C. YAG was the only crystalline phase observed during pyrolysis, and the Al/Y ratio of the pyrolysis products and the starting material was identical. However, infrared spectroscopy indicated that carbonate groups and entrained CO2 existed in the products at temperatures up to 1250°C. The pyrolysis chemistry of the precursors and the microstructure of the products were studied by FT-IR, TGA, XRD, SEM and elemental analyses.