Yttria Ceramics Research Articles

Effect of Glass Frit Addition on Characteristics of Yttria Ceramics

Effect of Glass Frit Addition on Characteristics of Yttria Ceramics

Weibull statistical analysis of fracture behavior and Vicker’s hardness of yttria ceramics sintered at various temperatures

Weibull statistical analysis of fracture behavior and Vicker’s hardness of yttria ceramics sintered at various temperatures

Infrared to Visible Upconversion Photoluminescence from Nd-doped Yttria Ceramic for Optical Applications

Upconversion photoluminescence (UCPL) attracts great attention in the field of optics and solid state lightening applications. Thus, in order to understand the underlying mechanisms of UCPL, this work reports on the spectral and kinetic properties of up and down conversion photoluminescence (PL) from Nd-doped Y2O3 ceramic. The energy transition levels and the possible excitation mechanisms are discussed. Nd-doped Y2O3 nanocrystals have been prepared via co-precipitation method then subjected to sintering process for ceramic production. The X-ray diffraction (XRD) and scanning electron microscope (SEM) measurements have been used to reveal the formation of nanocrystals and the crystal phase of the prepared Nd-doped Y2O3 powders. It is found that the PL down conversion (DCPL), from ceramic sample, demonstrates well-resolved narrow emission lines related to the near-infrared transitions in Nd ions, when excited by different UV–visible wavelengths. On the other side, a visible upconversion PL (UCPL) has been detected under excitation by a 1064-nm pulsed laser. In addition, the UCPL together with the photoluminescence excitation (PLE) results have been used to confirm the proposed energy levels for the upconversion process. Moreover, the excitation power dependence of the UCPL and time-resolved photoluminescence (TRPL) have been measured in order to determine the dominant excitation mechanism responsible for the upconversion. our findings suggest that the excited state absorption mechanism (ESA) is likely the possible mechanism of UCPL process in rare earth (Nd) single-doped Y2O3 ceramic.

New Strategy for Preparation of Yttria Powders with Atypical Morphologies and Their Sintering Behavior

A modified precipitation method was used to prepare yttria powers for the fabrication of yttria ceramics in this study. The precipitation behavior, phase evolution, and shape of the yttria precursor were all examined in the presence or absence of an electric field. The findings demonstrate that the phases of the yttria precursor were Y2(CO3)3·2H2O with and without an electric field, while the morphology changed from flake to needle-like under the action of the electric field. After calcining both yttria precursors at 750 °C, yttria powders with similar morphologies were obtained and then densified via conventional sintering (CS) and spark plasma sintering (SPS). The densification and thermal shock resistance of the yttria ceramics were investigated. The yttria ceramics sintered using SPS had higher bulk density and thermal shock resistance than the samples sintered using CS. When the sintering process for the ceramics sintered from needle-like yttria powder was switched from CS to SPS, the bulk density increased from 4.44 g·cm-3 to 5.01 g·cm-3, while the number of thermal shock tests increased from two to six. The denser samples showed better thermal shock resistance, which may be related to the fracture mechanism shifting from intergranular fracture to transgranular fracture.

Highly transparent yttria ceramics with Nb2O5/Ta2O5 as novel sintering additives by pressureless vacuum sintering

AbstractHighly transparent yttria ceramics were fabricated by pressureless sintering with Nb2O5 or Ta2O5 as a novel sintering additive. The optical transmittance, microstructural evolution, and thermo‐mechanical properties of the samples were investigated. The optimal doping concentrations of Nb2O5 and Ta2O5 are 0.3 and 0.2 at.%, respectively, which are much lower compared to those of previously reported counterparts. The transmittance of the sample with 0.3 at.% Nb2O5 reaches 81.6% at 1100 nm and 72.4% at 400 nm (2 mm in thickness), similar transmittance was obtained in the sample with 0.2 at.% Ta2O5. The microhardness (∼7 GPa), fracture toughness (∼0.85 MPa·m1/2), and biaxial strength (∼200 MPa) of the present samples were confirmed to be comparable or even better compared to those of previously reported transparent yttria ceramics fabricated by pressureless sintering. Furthermore, the present samples, by virtue of the low doping concentrations, possessed relatively high thermal conductivity values (>10 W/m·K), which substantially guaranteed high thermal shock resistance.

Preparation, Characterization and Magneto-Optical Properties of Sm-Doped Y2O3 Polycrystalline Material.

In this paper, physicochemical properties of pure Y2O3 and samarium (Sm)-doped Y2O3 transparent ceramics obtained via arc plasma melting are presented. Yttria powder with a selected molar fraction of Sm was first synthesized by a solid-state reaction method. High transparent yttria ceramics were obtained by arc plasma melting from both the pure and Sm oxide-doped powders. The morphological, chemical and physical properties were investigated by X-ray diffraction and scanning electron microscopy. The optical band gap was calculated from the absorption spectra so as to understand the electronic band structure of the studied materials. Samples indicate a series of luminescence bands in the visible region after excitation by laser light in the range from 210 to 250 nm. Magneto-optical measurements were carried out in the 300-800 nm range at room temperature. It can be seen that a maximum Verdet constant ca. 24.81 deg/T cm was observed for 405 nm and this value decreases with increasing wavelength. The potential usefulness of the polycrystalline material dedicated to optics devices is presented.

Impact of Sm ions on microstructure and magneto-optical effects of Y2O3 ceramics obtained by arc plasma melting

Faraday materials based on transparent ceramics are regarded for high power magneto-optical isolators. Pure yttria ceramics with high transmittance were prepared using the raw oxide powders. To enhance the magneto–optical performance of the ceramics, samarium oxide were introduced to yttrium oxide matrix as a paramagnetic ions. The Sm-Y2O3 Faraday ceramic was melted above 2700 °C for 10 min. It is noted that as-prepared ceramic presents the highest in-line transmittance above 61.0% at the high spectrum range of wavelengths from 350 to 1110 nm. Physicochemical properties of the sample were characterized by means of numerous techniques. No secondary phase was detected from the sample using X-ray diffraction. The Verdet constant of Sm-Y2O3 ceramic at 532 nm is as high as 20 rad/m*T, which is higher than that of pure Y2O3 ceramic. The good optical quality and magneto-optical properties make Sm-Y2O3 ceramic an attractive magneto-optical material.

Highly transparent cerium‐doped yttria ceramics for full‐band UV‐shielding window applications

AbstractHighly transparent cerium‐doped yttria ceramics were fabricated via a pressureless sintering method with an addition of 10 at.% La2O3and 1 at.% ZrO2as a binary sintering additive. With an increase in the Ce doping concentration from 0 to 3 at.%, the optical absorption edge of yttria ceramics exhibited a significant red shift from 290 to 380 nm as a result of the 4f–5d transition of Ce3+and the charge transfer of Ce4+(i.e., Ce4++e–→Ce3+). For a 2‐mm thick sample doped with 3 at.% Ce, the total ultraviolet radiation (UV) transmittance (220–400 nm) is only 1.7%, indicating a nearly complete UV absorption. Meanwhile, the specimens possess high in‐line transmittance levels in both the visible and the infrared regions (i.e., >70% at 450 nm and ∼80% at 1100 nm). Additionally, the present specimens were confirmed to have good enough mechanical strength levels (∼165 MPa) and thermal conductivity (∼5 W/m·K), which are comparable or even better compared to those of previously reported transparent yttria ceramics. The results of this work indicate that cerium‐doped transparent yttria ceramics are promising candidate materials for full‐band UV‐shielding window applications.

Neural network-supported study on erosive wear performance analysis of Y2O3/WC-10Co4Cr HVOF coating

In this work, a study was carried out by modifying the conventional Tungsten Carbide Cobalt Chrome (WC–10Co4Cr) powder with a small addition of yttrium-oxide (Y2O3). Reinforcement was done by adding yttria (Y2O3) ceramics in WC–10Co4Cr powder by using a jar ball mill process. The surface microstructure, chemical composition, and phase compositions of coating powder and coatings were examined by using scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffractometry. Silt erosion was evaluated through a pot tester by preparing equi- and multi-sized slurries at different velocities, impact angles, concentrations, and rates. Results show that the WC–10Co4Cr powder coating reinforced by Y2O3 ceramics possesses low porosity, providing higher erosive performance as compared to conventional WC–10Co4Cr coating. The present study reveals that the deposition of conventional WC–10Co4Cr coating helps improve the wear resistance of AISI 316L stainless steel (UNS S31600) by 9.98% for the variation in rotational speed. However, the erosive wear performance of conventional WC–10Co4Cr coating was improved by 45.9% by blending it with the Y2O3 ceramics.

Synthesis of yttria nanopowder with poly acrylic acid as dispersant for highly transparent yttria ceramics

AbstractHighly pure and well‐dispersed yttria nanocrystalline powders were synthesized with a modified coprecipitation method that uses mixed ammonium hydroxide‐carbonate solution as the precipitant and poly acrylic acid (PAA) as the dispersant. Comparing with the yttria powders synthesized using the same route but without PAA dispersant, the PAA‐assisted powders exhibit lower level of agglomeration and better sinterability. Sintering trajectories of the powders with and without PAA dispersant were investigated. Y2O3 ceramics sintered with the PAA‐assisted powders exhibited smaller grain size, homogeneous microstructure, and higher in‐line optical transmittance. The result suggests that the polymer‐assisted coprecipitation could be used to synthesize yttria nanopowders for fabricating high optical quality transparent ceramics.

Hot pressing of Yb:Y2O3 laser ceramics with LiF sintering aid

Transparent ytterbium-doped yttria ceramics, 2 at.% Yb:Y 2 O 3 , were fabricated by hot uniaxial pressing in vacuum at 1550 °C/50 MPa followed by a two-stage Hot Isostatic Pressing (HIPing) at 1200–1400 °C/100 MPa, using nanopowders obtained by self-propagating high-temperature synthesis (with lithium fluoride serving as a sintering aid). The addition of LiF during the powder synthesis markedly changed the morphology of powders, and at the stage of hot pressing, drastically reduced the carbon contamination of ceramics, as well as stimulated sintering without formation of the liquid phase. The spectroscopic properties of ceramics were studied. The stimulated-emission cross-section for Yb 3+ ions is 0.90 × 10 −20 cm 2 at 1030.4 nm and the luminescence lifetime is 797 μs. A continuous-wave 2 at.% Yb:Y 2 O 3 ceramic laser generated an output power of 735 mW at 1027–1034 nm with a slope efficiency of 64.5% and a laser threshold of 0.28 W. • Yb:Y 2 O 3 ceramic is produced by HPing and two-stage HIPing at 1200–1400 °C/100 MPa. • Lithium fluoride is used as a sintering aid improving the optical quality of ceramics. • The microstructure, spectroscopic and laser properties of Yb:Y 2 O 3 ceramic are studied. • The stimulated-emission cross-section for Yb 3+ ions is 0.90 × 10 −20 cm 2 at 1030.4 nm. • Yb:Y 2 O 3 ceramic laser generated 735 mW at 1027–1034 nm with a 64.5% slope efficiency.

Zirconia-doped yttria transparent ceramics via slip casting and sintering

In this work, slurries containing 70 wt % yttria (Y2O3) nanopowder (~90 nm), and 1 wt % zirconium (IV) chloride (ZrCl4) were prepared to fabricate yttria transparent ceramics via slip casting and sintering. To do this, several processing parameters including the pH value of slurries, amounts of Dolapix CE 64 as a dispersant, citric acid, solid load, and de-agglomeration time were optimized. Then, slip-casted samples with the highest relative green density (~65%) were sintered at 1715 °C under vacuum and the microstructure and transmission properties of the obtained samples were investigated. The results showed that with the addition of 1 wt % ZrCl4 to the slurry, the transparency of the fabricated Zr-doped yttria ceramics increased significantly and the highest transmittance (~78%) at a wavelength of 800 nm was obtained for 3 mm-thick sintered samples with a total relative density of 99.4 ± 0.2%.

Influence of process parameters in gel casting of a pure yttria nanopowder to fabricate transparent ceramics

The goal of this research is to fabricate pure transparent yttria ceramics through gel casting and vacuum sintering. A specific processing method has been used and optimized for this purpose. A pure yttria nanopowder was synthesized as the starting material to produce pure transparent ceramics through a low-temperature sintering process. It was attempted to minimize the undesirable nanopowder hydration by using the as-synthesized yttria nanopowder and a rapid deagglomeration and slurry preparation process. The synthesized nanopowders were deagglomerated to enhance the efficiency of both powder shaping and sintering stages. Carrageenan was used as the gelling agent because it is a low-cost and abundant material, and because the temperature is the only catalyst needed for its gelation; therefore, it is possible to control its gelation to obtain high-density and pure optical ceramics. The effect of the deagglomeration method and the processing parameters, including the amounts of dispersant, gelling agent, solid loading, pH, and deagglomeration time, on the rheology of slurry, density, and microstructure of the obtained green yttria ceramics was examined and optimized in order to obtain high solid loading nanoyttria suspensions of 38 vol%, which is more than those obtained in many of the previous investigations. The precise gelling temperature and time were measured, and green gel cast ceramics with a density of 63 % of the theoretical density were produced. A rapid deagglomeration and slurry preparation method was used instead of using a conventional planetary ball-milling approach to minimize the risk of the hydrolysis of yttria nanopowder. No sintering aid was necessary, and transparent yttria ceramics with 99 % of the theoretical density were produced after vacuum-furnace sintering at 10-2 mbar and 1715 °C.

Plasma etching behavior of yttrium‐aluminum oxide composite ceramics

AbstractIn order to get a general regularity of erosion performance in alumina‐strengthened yttria ceramics, High‐quality yttrium‐aluminum oxide composite ceramics with different alumina/yttria molar ratios were fabricated, and the as‐prepared specimens were named Y2O3, YAG, YAGA, and Al2O3. The erosion behavior of the ceramics was examined and explained. The etching morphologies of the ceramics revealed that the multi‐phase composite ceramic (YAGA) was etched selectively, whereas the single‐phase ceramics were corroded homogeneously. The weight loss rate of the ceramics after etching was not proportional to the Al2O3 content, and it conformed to the percolation theory. As the alumina content in yttrium‐aluminum oxide composite ceramics was below the minimum value of percolation transition in two‐phase system the erosion resistance of the strengthened composite ceramics demonstrated excellent as well yttria ceramics.

A novel approach of synthesizing nano Y2O3 powders for the fabrication of submicron IR transparent ceramics

A facile methodology of synthesizing highly reactive, round-edged, Sulfur–free nano Y2O3 powders to fabricate submicron IR transparent yttria ceramics having a unique combination of superior optical and mechanical properties are reported for the first time. Dispersion of yttrium hydroxide into aqueous sol and addition of seed particles produced near-spherical yttria powders having non – aggregated particles with narrow size distribution. The powder exhibited excellent sinterability reaching near-theoretical density at temperatures around 1400 °C in air. Effective inter-particle coordination and traces of Al additives assisted achieving superior densification. Sintered specimens showed average grain sizes closer to 700 nm. Post-sinter hot isostatic pressing eliminated the residual porosity from the sintered samples leading to exhibit IR transmissions up to 84% in the 2.0–9.0 μm regions, equivalent to single crystal Y2O3. Achieving densification through solid-state sintering and retaining the sintered grain sizes in the submicron regions significantly enhanced the mechanical properties. Sintered and HIPed Y2O3 specimens were further characterized for their thermal properties at temperature regions between ambient to 950 °C.

Синтез и исследование свойств двойного карбоната иттрия и аммония.

The paper considers investigation results of yttrium and ammonium double carbonate synthesis. The compound was synthesized and characterized for the first time. It is proposed to use double yttrium and ammonium carbonate as a precursor to ceramic yttria powders.

Zirconia-strengthened yttria ceramics for plasma chamber applications

Yttria (Y2O3) is the most popular lining material for the inner walls of plasma chambers, owing to its well-known resistance against corrosion by reactive fluorinated plasma. Yttria has a relatively lower toughness and strength compared to alumina (Al2O3) and zirconia (ZrO2). The present work aims to explore the strengthening and toughening of yttria by doping with zirconia, while retaining its good corrosion resistance. Ceramics with zirconia to yttria molar ratios of 2:8 and 5:5 (named 20ZY and 50ZY, respectively) were fabricated by pressure sintering in Ar atmosphere. The corrosion of the prepared ceramics in reactive fluorinated plasma (C4F8/CHF3/Ar) was investigated and compared with that of yttria as a control. The results indicated that 20ZY exhibited excellent corrosion resistance, comparable to that of yttria, while the fracture toughness and flexural strength showed increases of 87% and 44%, respectively. 50ZY exhibited a further improvement in fracture toughness and flexural strength, but at the price of a much lower resistance against plasma corrosion. A percolation model was proposed to interpret the observed plasma corrosion behaviors.

Effect of starting materials and sintering temperature on microstructure and optical properties of Y2O3:Yb3+ 5 at% transparent ceramics

Y2O3:Yb3+ 5 at% ceramics have been synthesized by the reactive sintering method using different commercial yttria powders (Alfa-Micro, Alfa-Nano, and ITO-V) as raw materials. It has been shown that all Y2O3 starting powders consist from agglomerates up to 5–7 µm in size which are formed from 25–60 nm primary particles. High-energy ball milling allows to significantly decreasing the median particle size D50 below 500 nm regardless of the commercial powders used. Sintering experiments indicate that powder mixtures fabricated from Alfa-Nano yttria powders have the highest sintering activity, while (Y0.86La0.09Yb0.05)2O3 ceramics sintered at 1750 °C for 10 h are characterized by the highest transmittance of about 45%. Y2O3:Yb3+ ceramics have been obtained by the reactive sintering at 1750–1825°C using Alfa-Nano Y2O3 powders and La2O3+ZrO2 as a complex sintering aid. The effects of the sintering temperature on densification processes, microstructure, and optical properties of Y2O3:Yb3+ 5 at% ceramics have been studied. It has been shown that Zr4+ ions decrease the grain growth of Y2O3:Yb3+ ceramics for sintering temperatures 1750–1775 °C. Further increasing the sintering temperature was accompanied by a sharp increase of the average grain size of ceramics referred to changes of structure and chemical composition of grain boundaries, as well as their mobility. It has been determined that the optimal sintering temperature to produce high-dense yttria ceramics with transmittance of 79%–83% and average grain size of 8 µm is 1800 °C. Finally, laser emission at ∼1030.7 nm with a slope efficiency of 10% was obtained with the most transparent Y2O3:Yb3+ 5 at% ceramics sintered.

The GIPAW approach for the study of local structures and the electric field gradients at Cd and Ta impurity sites. Application to doped yttria ceramics

We report a first-principles study on the structural properties, the electronic structure and the hyperfine properties of the pure, Cd-, and Ta-doped yttria (Y2O3) using the Gauge-Including Projector Augmented Waves (GIPAW) method. The purpose of this work is to assess the accuracy of the GIPAW method for the prediction of the electric field gradient (EFG) at the impurity sites. We analyzed the local structural variations in Y2O3 due to cationic substitution with acceptor (Cd) or donor (Ta) impurities, and how these structural changes modify the electronic structure through the appearance of impurity levels in the density of states. Furthermore, relations between the local structural changes and the variation of the EFGs have been found. From the comparison with available experimental data, we conclude that impurities try to reconstruct local environments similar to those of their respective oxides, and are completely ionized. In addition, this work shows that the GIPAW method is very suitable to calculate accurately the EFG at Cd and Ta impurity sites, as an alternative to the all-electron methods.

Effect of the microstructures of yttria ceramics on their plasma corrosion behavior

To demonstrate the relation between the microstructure of ceramics and their plasma corrosion behavior, sintered yttria (Y2O3) ceramics with various grain sizes and porosities were fabricated under various sintering conditions, and the effect of the microstructures of the Y2O3 ceramics on their plasma corrosion behavior was investigated. The Y2O3 samples were investigated by inductively coupled plasma reactive ion etching using fluorine plasma. After plasma exposure, the plasma corrosion depth and surface roughness (Sa) values of the materials were measured using a laser scanning microscope. The surface microstructures after plasma corrosion were observed by scanning electron microscopy. It was found that the plasma depth showed an almost linear change with plasma exposure time, and all the original surfaces of the samples were corroded by over 0.7 μm during plasma exposure for 60 min. The Sa values of the Y2O3 samples as a result of plasma exposure were significantly different in that although the Sa values of low-density Y2O3 samples increased with an increase in the plasma exposure time, the values of their high-density counterparts did not change and the initial surface roughness was maintained. The fluorine plasma was found to homogeneously corrode the surfaces of the sintered Y2O3 ceramics, regardless of their grain boundaries or grain sizes. However, when internal pores were present in the samples, these internal pores were selectively corroded from their edges, becoming crater-like plasma corrosion marks. Overall, a high-density Y2O3 ceramic was found, which retained its initial surface roughness regardless of plasma exposure time, with an ideal microstructure for use as a plasma-resistant ceramic material that can be used as the inner ceramic components in the plasma etching equipment.