Yttrium Aluminum Garnet Phase Research Articles

Preparation of AlN–Al2O3 composites exhibiting antibacterial and water purification properties

This study aimed to develop new antibacterial and water purification materials without heavy metal contamination. Herein, AlN–Al2O3 composites were prepared by changing the content of AlN in raw material. The results showed that AlN, Al2O3, aluminum oxynitride, and yttrium aluminum garnet phases were generated by adjusting the AlN: Al2O3 ratio. The difference in the ability of AlN and aluminum oxynitride to release substances such as ammonium ions and aluminum hydroxide when reacting with water resulted in remarkably different pH values of the sample immersion solution, which led to an increase in the material antibacterial efficiency with the addition of AlN. Similar results were also obtained with zinc ion absorption. Therefore, AlN–Al2O3 composite ceramics can potentially be used as novel antibacterial and water purification materials without heavy metal contamination through the release of ammonium ions for conferring antibacterial effects and of aluminum hydroxide for absorbing heavy metals and suspended impurities.

Structure, thermal properties and crystallization behavior of binary Y2O3–Al2O3 glasses with high alumina content

Five compositions in the system Al2O3–Y2O3 with high level of homogeneity were prepared in the form of glass microspheres by flame synthesis. The amorphous nature of prepared glasses with highly disordered structure was confirmed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman and nuclear magnetic resonance (NMR) spectroscopy. In the NMR spectra, typical signals with chemical shifts of 75, 42 and 12 ppm were observed, which were attributed to the presence of AlO4, AlO5 and AlO6 motifs in the glass structure. The ratio of individual motifs in glass samples did not change significantly with the composition. The crystallization of yttrium-aluminium garnet (YAG) phase was observed as a major process in the glasses thermally treated up to 1450 °C, with slow crystallization of θ- and α-Al2O3 phases detected in the temperature interval 980–1450 °C. IR and Raman spectra of the microspheres crystallized at 998, 1300 and 1500 °C for 4 h contained typical bands, that were assigned to the vibrations of AlO4 and AlO6 groups in YAG and Al2O3 structures. The comparison of 27Al and 89Y magic angle spinning (MAS) NMR spectra showed the presence of only YAG and α-Al2O3 phase in the samples crystallized at 1500 °C and the presence of a trace amount of θ-Al2O3 in the sample crystallized at 998 and 1300 °C. The yttrium aluminium perovskite (YAP) and yttrium aluminium monoclinic (YAM) phases, expected in this system, were no detected.

Influence of Er3+ doping on the mechanical and thermophysical properties of (ErxY1-x)3Al5O12 ceramics

In this work, Er3+ was selected to replace Y3+ in the yttrium aluminium garnet (YAG) in order to improve its mechanical and thermophysical properties. A series of (ErxY1-x)3Al5O12 (x = 0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1.0) ceramics were prepared by solid-state synthesis method at 1000 ?C and finally sintered at 1600 ?C for 5 h. The microstructure and morphology of the prepared ceramics were investigated. The results showed that all Er3+ doped Y3Al5O12 ceramics exhibited single garnet-type YAG phase and good compactness. With the increase of Er3+ doping concentration, the thermal conductivity of the (ErxY1-x)3Al5O12 ceramics decreased slowly and then increased subsequently. Among the investigated specimens, the (Er0.7Y0.3)3Al5O12 had the lowest thermal conductivity (1.51W/m?K, at 1000 ?C), which was about 28% lower than that of the pure YAG (2.1W/m?K, at 1000 ?C). As the Er3+ doping concentration increased, the thermal expansion coefficient of the (ErxY1-x)3Al5O12 ceramics hardly changed, remaining around 9.08 ? 10?6 K?1 at 1200 ?C. Moreover, when the Er3+ doping concentration exceeded 0.5, the mechanical properties of the (ErxY1-x)3Al5O12 ceramics increased suddenly. Specifically, the hardness increased from 14.28 to 16.53GPa and the bending strength increased from 231.74 to 324.49MPa.

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.

A new hybrid suspension and solution precursor thermal spray for wear-resistant silicon carbide composite coatings

Silicon Carbide (SiC) coatings offer exceptional wear resistance and excellent tribological characteristics; however, it is a challenging material to be thermally sprayed due to a lack of melting point. In this study, a hybrid, single-step suspension and solution precursor feedstock design is proposed, consisting of a SiC suspension modified with Yttrium Aluminium Garnet (YAG) precursors, for thermal spraying of SiC/YAG coatings. The decomposition of SiC was restricted in all spray campaigns. The solid loading of SiC (from 10 wt% to 20 wt%) and YAG phase (from 20 wt% and up to 50 wt%) were varied in an attempt to improve wear performance, enhance coating cohesion, and minimise porosity of the studied coatings. Among all studied coatings, 60 wt% SiC/40 wt% YAG and 50 wt% SiC/50 wt% YAG coatings at a 10 wt% solid loading were the best-performing coatings, demonstrating a promising wear resistance up to a sliding distance up of 1000 m, a dense coating structure with porosity at 0.4 ± 0.2%. The feedstock design opens up a new method to process materials which are difficult, if not impossible, to process using a conventional thermal route.

Controlled crystallization of BaO–B2O3–Bi2O3 Glass in the temperature range of a supercooled melt in the presence of additional nucleation centers

To use the promising BaO–B2O3–Bi2O3 glass-forming system in the formation of glass-ceramic material, for example, with the yttrium aluminum garnet phase, a study of the crystallization behavior of bulk glasses and samples with additional nucleation centers acquired as a result of their crushing is carried out. In this work, the kinetics of crystallization combined with the subsequent melting of the formed phases with a change in the composition of the glass-forming system of 20Bi2O3 – (80-х)B2O3 – хBaO for x = 5, 10, 15, 20 mol% is investigated by means of differential scanning calorimetry. The crystalline phases, isolated at the established temperatures, are characterized by XRD method. A theoretically substantiated method for processing thermograms in the region of combined crystallization-melting peaks made it possible to establish the dependences of the crystallization parameters on the composition of crushed glass samples simulating nucleation centers, to find the compositions with highest stability against crystallization, and to recommend the time-temperature modes for the synthesis of glass-ceramics.

A suspension high velocity oxy-fuel thermal spray manufacturing route for silicon carbide – YAG composite coatings

Silicon carbide (SiC) coatings obtained through thermal spraying represent a major engineering challenge due to the high tendency of SiC to decompose during the spraying process. In order to avoid this decomposition, suspension high velocity oxy-fuel (SHVOF) thermal spray was used in combination with a novel SiC powder modified by addition of yttrium aluminium garnet (YAG) as the feedstock. The colloidal stability of the feedstock in water was optimised in order to obtain stable and well-dispersed suspensions suitable for SHVOF spraying. Dense SiC-YAG coatings with ~80 μm thickness were obtained and the coatings showed promising results in terms of porosity, microstructure, phase distribution and mechanical properties. Energy dispersive X-ray spectroscopy and X-ray diffraction showed a lack of degradation of the SiC phase in the coatings, thanks to the formation of a molten YAG phase during the spray process, which prevents SiC decomposition.

Study of the Effect of Injection Currents on White Light Emission of Ce-Doped YAG Phosphor Powder Prepared by Microwave Combustion

The behaviors of yttrium aluminum garnet (YAG) phosphor powder doped by cerium (YAG:Ce3+) was studied. Here, the YAG:Ce3+ nanopowders have been synthesized using microwave combustion (MW) according to the formula, Y(3-0.04) Al5O12: 0.04Ce3+ to produce white light emitting diode (WLEDs) by conversion from blue indium gallium nitride light emitting diode (InGaN LED, 445 nm) chips; the whole process took only 20 min. Pure YAG phase was obtained after annealing at 1050 °C for 5 h with nonaggregated and spherical particles. Thermogravimetry and derivative thermogravimetry (TG/DTG), X-ray powder diffraction (XRPD), transmission electron microscope (TEM), photoluminescence (PL), electroluminescence (EL) emissions and standard CIE 1931 chromaticity diagrams have been used to characterize the samples. The highest WLEDs emission was achieved for the annealed YAG:Ce3+, together with proper color rendering index (CRI), and tunable correlated color temperature (CCT). Finally, we conclude that the decreasing EL intensity at increased injection current is caused by the thermal ionization from the 5d1 level to the conduction band.

The effects of ball milling time on the rheological, optical, and microstructural properties of YAG transparent ceramics

AbstractStable slurries dispersed mixture of commercial Al2O3 and Y2O3 powders, ammonium poly meta acrylate (Dolapix CE64) as the dispersant, and tetraethyl orthosilicate (TEOS) as the sintering aid were prepared by ball milling process. The effects of the milling time on the fabrication of transparent polycrystalline yttrium aluminum garnet (YAG) ceramics were investigated by slip casting and vacuum sintering. The results showed that the best milling time for the deagglomeration of the powder mixture was 16 hours and the slurry prepared during this time showed a near‐Newtonian behavior due to the better deagglomeration and lower viscosity. X‐ray patterns also showed that all samples were pure YAG phase. The results also revealed that the sample prepared by 16 hours ball milling time suspensions exhibited higher relative green and final density, as well as the maximum transmittance at 1064 nm (≈ 77%). These samples had a more uniform microstructure too.

Influence of Yb and Si on the fabrication of Yb:YAG transparent ceramics using spherical Y2O3 powders

Abstract Yb:YAG (yttrium aluminum garnet) transparent ceramics were fabricated by the solid-state method using monodispersed spherical Y2O3 powders as well as commercial Al2O3 and Yb2O3 powders. Pure YAG phase was obtained at low temperature due to homogeneous mixing of powders. Under the same sintering conditions, the Yb:YAG ceramics with different doping contents of Yb3+ had similar morphologies and densification rates. After being sintered at 1700 °C in vacuum, the ceramic samples had high transparencies. The Yb:YAG ceramics doped with 0.5 wt% SiO2 formed Y–Si–O liquid phase and nonstoichiometric point defects that enhanced sintering. Compared with Nd doping, Yb doping hardly affected the YAG grain growth, sintering densification or optical transmittance, probably because Yb3+ easily entered the YAG lattice and had a high segregation coefficient.

Preparation of YAG nano-fibers using polyvinyl butyral from nitrate solution

Yttrium aluminum garnet (YAG) nano-fibers were obtained by electrospinning using aluminum and yttrium nitrates as initial materials. Coordination agent and spinning additive influences on sol spinnability were analyzed. A stable spinning precursor sol was prepared using citric acid as a coordination agent and polyvinyl butyral as a spinning additive. Linear links were formed in precursor sol ∼4 nm in diameter. Spinning voltage effect on the fiber diameter was also studied. YAG phase was obtained after the gel fibers were sintered at 800 °C. The nano-fibers with diameter of 80–200 nm were prepared at 24 kV. YAG crystal grains were linked together forming nano-fibers.

Crystallization kinetics of glass microspheres with yttrium aluminium garnet (YAG) composition

A combination of sol–gel Pechini method and flame synthesis was used to prepare yttrium aluminate glass microspheres with the garnet composition (YAG, 62.5 mol% aluminium oxide, 37.5 mol% yttrium oxide). Prepared glass microbeads were studied by optical microscopy, SEM, X-ray diffraction (XRD), differential scanning calorimetry (DSC) and high-temperature (HT) XRD analysis. Formation of YAG as the only crystalline phase was observed during HT XRD experiment in the temperature interval (750–1200 °C), with the onset of YAG phase crystallization in the temperature interval 860–870 °C and most prominent increase in the YAG phase content between 905 and 910 °C. The experimental data obtained by DSC analysis and the Johnson–Mehl–Avrami–Kolmogorov model were used for determination of crystallization behaviour of the studied system. The frequency factor A = 5.2 × 1048 ± 9.6 × 1048 min−1, apparent activation energy E app = 1100 ± 10 kJ mol−1 and the Avrami coefficient m = 4 were determined. The linear temperature dependence of nucleation rate, reaction-controlled crystal growth interface and a 3-D crystal growth were confirmed in the studied system.

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.

Spectroscopic properties of Nd3+ ions in YAP nano-perovskites

Yttrium aluminium nano-perovskite doped with different concentrations of Nd3+(YAP: Nd3+) were successfully synthesized by the Pechini sol-gel method at 1200°C and 1550°C. X-ray powder diffraction patterns confirmed the monoclinic and orthorhombic structure space group P2/m and Pnma for the samples treated at 1200°C and 1550°C respectively. Yttrium aluminium garnet phase was detected in both treatments, being more noticeable at 1200°C treated samples. The non-equivalent center nature of these samples was observed performing site selection spectroscopy, confirming the presence of two different sites for the Nd3+ ions in the samples, associated with perovskite and garnet phases, previously detected in XRD measurements. The study of the luminescence dynamics of YAP: Nd3+ nano-perovskites treated at 1550°C for all concentrations was carried out, confirming the existence of the energy transfer between Nd3+ ions. Time resolved spectroscopy allowed to confirm that the thermal treatment at 1550°C was the proper one in order to obtain nano-perovskites.

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.

Advanced TEM characterization of oxide nanoparticles in ODS Fe–12Cr–5Al alloys

The oxide nanoparticles present in three oxide-dispersion-strengthened (ODS) Fe–12Cr–5Al alloys containing additions of (1) Y2O3 (125Y), (2) Y2O3 + ZrO2 (125YZ), and (3) Y2O3 + HfO2 (125YH), were investigated using transmission and scanning transmission electron microscopy. In all three alloys nano-sized (<3.5 nm) oxide particles distributed uniformly throughout the microstructure were characterized using advanced electron microscopy techniques. In the 125Y alloy, mainly Al2O3 and yttrium–aluminum garnet (YAG) phases (Y3Al5O12) were present, while in the 125YZ alloy, additional Zr(C,N) precipitates were identified. The 125YH alloy had the most complex precipitation sequence whereby in addition to the YAG and Al2O3 phases, Hf(C,N), Y2Hf2O7, and HfO2 precipitates were also found. The presence of HfO2 was mainly due to the incomplete incorporation of HfO2 powder during mechanical alloying of the 125YH alloy. The alloy having the highest total number density of the oxides, the smallest grain size, and the highest Vickers hardness was the 125YZ alloy indicating, that Y2O3 + ZrO2 additions had the strongest effect on grain size and tensile properties. High-temperature mechanical testing will be addressed in the near future, while irradiation studies are underway to investigate the irradiation resistance of these new ODS FeCrAl alloys.

Influence of yttria and zirconia additions on spark plasma sintering of alumina composites

Abstract

Synthesis of spherical yttrium aluminum garnet via a mixed solvothermal method

Yttrium aluminium garnet (YAG) powders were synthesized by a mixed solvothermal method. The crystal structure of the YAG powders was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). The impacts of the mixed solvents, the synthesis temperature and the polymer additive on the spherical grain formation and the crystal structure of the YAG has been researched by changing the synthetic conditions. The results show that spherical YAG powders were obtained using ethylenediamine–ethanol as mixed solvents with polyethylene glycol as additive at 220 °C for 20 h. Pure spherical YAG particles of 100–200 nm in diameter are formed directly in the process of mixed solvothermal reaction. The degree of crystallization and the crystal structure of the YAG phase have been improved with the increase of the synthesis temperature. The particles tend to be spherical and the distribution of particle size is homogeneous as expected. Finally, in this paper we investigated the formation mechanism of spherical YAG particles.

Ethanol-dependent solvothermal synthesis of monodispersed YAG powders with precursor obtained through bubbling ammonia

Yttrium aluminum garnet (YAG) precursor precipitates, which were produced through bubbling ammonia gas approach, were solvothermally treated in alcoholic solution to synthesize monodispersed YAG powders in this paper. A variety of techniques, such as thermogravimetry/differential scanning calorimetry (TG/DSC), X-ray diffraction (XRD), Fourier transform infrared spectra (FT-IR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed to characterize the as-synthesized YAG precursor and powders. The results showed that the crystallization temperature of the YAG phase was largely dependent on the ethanol. Increasing the ethanol content in the solvent could decrease the YAG crystallization temperature. When the ratio of ethanol to water was 3:1, single-phase YAG was accurately available at a relatively lower temperature of 320°C. Moreover, the obtained YAG powders were well-defined monodispersed spheres with mean particle size of about 274nm, and showed excellent sinterability.

Flame aerosol deposition and annealing of Y3Al5O12:Tb phosphor coatings

Sub-micrometer-sized powders of Y3Al5O12:Tb phosphor (dSEM = 320 nm) were prepared by flame-assisted spray pyrolysis of aqueous precursors in a premixed propane/air flame and in situ deposited onto quartz substrates. Phosphor screens with densities of up to 0.7 mg cm−2 could be produced within 20 min. As-deposited coatings were amorphous and required a thermal post-treatment. After annealing in an oven for 2 h (T ≥ 900 °C), the yttrium aluminum garnet phase (YAG:Tb) was obtained. Alternatively, the phosphor coatings were treated by an impinging flame in the same setup used for the deposition. Quasi-amorphous Y3Al5O12:Tb coatings demonstrated bright green photoluminescence upon flame annealing at T ≈ 1100 °C for just several minutes and could outperform YAG:Tb when excited in the wavelength ranges 205–220 nm and 230–260 nm. For example, brightness of emission from the quasi-amorphous coatings was up to five times higher than that of the fully crystalline YAG:Tb phosphor at a technically important wavelength of 254 nm.