Yttria Powders Research Articles

Characteristics of oxide-dispersion strengthened alloys produced by high-temperature severe deformation

This study is to explore an economically attractive and technically feasible processing method for oxide-nanoparticle strengthened alloys for fusion reactor application. Despite many scientific merits of the advanced oxide-dispersion strengthened (ODS) alloys, such as the nanostructured ferritic alloy (NFA) 14YWT, the only viable production path for a high-quality NFA is the high-power mechanical alloying process. This process is often a multi-day high-speed ball milling of alloy powder with a small quantity of yttria (Y2O3) powder, followed by the milled-powder consolidation using extrusion or other methods and additional thermomechanical processing (TMP) for property control. This complex production path, including the low-temperature mechanical alloying in particular, has limited technical advancement toward the cost-effective and scale-up production of ODS alloy components. To overcome such a practical limitation, we proposed to explore alternative low-cost processing routes using traditional thermomechanical processing (TMP) method only. A series of continuous TMP cycles, which were designed to impose high-temperature severe plastic deformation (HT-SPD) conditions to the consolidated powder mixtures, were applied to achieve the effective distribution of oxide particles in nanograin structure and thus desirable mechanical properties. Since the reduced-activation ferritic-martensitic (RAFM) alloy powders (Fe-10Cr and Fe-14Cr alloys with various Y contents) are available in our inventory, we focused to utilize the new solid-state synthesis approach for controlling oxide (oxygen source) dissolution and nanoscale clustering in nanograin structure in those alloys. A combination of powder consolidation at 900 °C and continuous thermomechanical activation at 600 °C yielded two essential ODS alloy microstructure contents–nanograin structure and nanoparticle distribution–and thus demonstrated a good combination of strength and ductility.

P/M 18Cr ODS steels produced by mechanical alloying and hot powder forging

Mechanical alloying in attritor mill and powder consolidation through hot forging were employed to produce 18Cr ODS steels. Elemental powders were mechanically alloyed with nano-size yttria powder for up to 12 h. The effect of milling time on powder morphology, crystallite size and lattice strain were studied. Optimum milling time of mechanical alloying was determined for dissolution of constituents in the ferrite matrix. Further milling led to peak broadening. TEM confirmed the presence of fine crystallites in milled powders. HRTEM fringes were taken on the oxide particles. Their FFT confirmed that Y2O3 and TiO2 particles were present in the milled powders. The milled powders were consolidated through hot powder forging. Addition of Ti and Y2O3 significantly reduce the grain size in forged alloys. It also leads to formation of fine complex Y-Ti-O oxides. The powder forged alloys exhibited fine grained recrystallized microstructure. Reasons for this are discussed.

Building up europium thulium co-doped yttria nanoparticles with electron paramagnetic resonance response by colloidal synthesis

In the radiation dosimetry field the research for new materials is a continuos demand with the aim to provide highly improvement procedures where ionizing radiation is used. Considering this challenge, the present work reports the colloidal synthesis of europium-thulium-co-doped yttria powders (YET) and evaluates the dopants effect on the promotion of EPR response of yttria. The powdered compositions prepared with up to 2at.%Tm and 2at.%Eu (at.%, atomic percentage) were evaluate by XRD, PCS, SEM, and EPR. Based on the results, the proposed synthesis method provided ceramic powders with cubic C-type form and mean particle size (d50) less than 160nm. The most significant EPR dose-response was noticed for the powdered composition prepared with 0.5at.%Tm (YET0.5) as irradiated with 5kGy (60Co). These findings are key parameters to advance toward the formation of new materials for radiation dosimetry.

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.

Influence of SHS Precursor Composition on the Properties of Yttria Powders and Optical Ceramics

This study looked at optimizing the composition of precursors for yttria nanopowder glycine-nitrate self-propagating high-temperature synthesis (SHS). Based on thermodynamic studies, six different precursor compositions were selected, including with excesses of either oxidant or fuel. The powders from the precursors of all selected compositions were highly dispersed and had specific surface areas ranging from 22 to 57 m2/g. They were consolidated by hot pressing (HP) with lithium-fluoride sintering additive and subsequent hot isostatic pressing (HIP). The 1 mm thick HPed ceramics had transmittance in the range of 74.5% to 80.1% @ 1μm, which was limited by optical inhomogeneity due to incomplete evaporation of the sintering additive. Two-stage HIP significantly improves optical homogeneity of the ceramics. It was shown that an excess of oxidizer in the precursor decreases the powders' agglomeration degree, which forms large pore clusters in the ceramics.

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.

Nano oxide particles in 18Cr oxide dispersion strengthened (ODS) steels with high yttria contents

Oxide dispersion strengthened (ODS) steels containing yttria are candidate materials for fuel cladding tubes in future nuclear reactors. Their performance is determined by the size, distribution and volume fraction of the oxide dispersoids. The addition of yttria leads to a significant loss in ductility of steel limiting the yttria content in most ODS steels to 0.35%. This limitation may be overcome by powder forging of ODS steel powders. Two steels having nominal compositions (in wt%) of Fe-18Cr-2W-0.285Ti-0.5Y 2 O 3 and Fe-18Cr-2W-0.571Ti-1Y 2 O 3 were prepared by mechanical alloying of elemental powders with yttria powder in a Simoloyer attritor. The alloy powders were consolidated by powder forging at 1473 K in a flowing hydrogen atmosphere. The microstructure of powder forged ODS steels was characterized by electron microscopy. Both the steels exhibited a fine-grained recrystallized microstructure after forging. Fine (<10 nm) cuboidal oxide particles were found to be present in a ferrite matrix. A few coarse oxide particles were also observed. These coarse (>10 nm) oxide particles were present mainly along the ferrite grain boundaries. The crystal structure of oxide particles was determined by applying fast fourier transformation (FFT) on the fringes observed by high resolution transmission electron microscopy. The extracted FFTs were indexed to identify the crystal structure. The coarse particles were found to be Y 2 O 3 , TiO 2 and Cr 2 O 3 . The fine particles were identified as Y 2 TiO 5 and Y 2 Ti 2 O 7 . The face centre cubic Y 2 Ti 2 O 7 oxide particles were semi coherent whereas the orthorhombic Y 2 TiO 5 oxide particles were found to be incoherent with the ferrite matrix. The number fraction, average size and size distribution of these oxide particles was determined for both the alloys. Cr rich shells were observed around most of the particles which may prevent the coarsening of oxide particles at elevated temperatures. Reasons for this are discussed. • High yttria 18Cr ODS steels were successfully developed through novel hot powder forging route. • Recrystallized equiaxed grains with a uniform distribution of nano oxides particles were observed in the forged alloys. • A majority of oxides present were Y 2 TiO 5 or Y 2 Ti 2 O 7 oxides. Cr-rich shells were associated with these complex oxides. • The cuboidal Y 2 TiO 5 oxides were incoherent while the spherical Y 2 Ti 2 O 7 oxides were semi-coherent with the ferrite matrix. • HR-TEM also confirmed the formation of nano oxide particles such as Y 2 O 3 , TiO 2 and Cr 2 O 3 . These too were analysed.

Control of particle morphology and size of yttria powder prepared by hydro(solvo)thermal synthesis

Control of particle morphology and size of yttria powder prepared by hydro(solvo)thermal synthesis

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.

Microstructure Evolution of Yttria Compacts by Powder Technology

Background: Innovation in ceramic materials relies on processing of powders. Yttria also known as yttrium oxide belongs to rare earths group, which usual form is RE2O3 (RE from La to Lu, including Sc and Y). Due to great end use of RE based materials since agriculture until astronomy, the main economies such as United States of America and European Union addressed REs as critical materials. The aim of this paper is to obtain dense compacts of yttria by powder technology, in which the effect of sintering temperature on samples microstructure is evaluated. Methods: Yttria powders (Y2O3) were used as starting material, being characterized by Photon Correlation Spectroscopy (PCS); X-ray Diffraction (XRD); Scanning Electron Microscopy (SEM). Powder compacts in cylindrical shape formed by uniaxial compaction, followed by hydrostatic compaction were evaluated by means of apparent density. Sintered samples under sintering temperatures from 1350 to 1550ºC were evaluated by SEM, XRD, apparent density, and true density. Results: Cubic C-type yttria powders exhibited mean particle size (d50) of 1.6μm, and morphology like acicular. Powder compacts (diameter x height) of 9.57mm ± 0.01 x 1.53mm ± 0.01 presented mean apparent density of 53.69% (based on free powder density). As sintered samples at 1550ºC, exhibited the most densification 65.0% related to green density and 91.0% related to theoretical density, respectively. Conclusion : Yttria cylindrical compacts with dense microstructure and symmetric dimensions were formed by powder technology from powders with mean particle size of 6.51μm, by compaction methods (uniaxial and hydrostatic), followed by sintering. The most densification of samples was achieved by the sintering condition of 1550ºC for 2h, providing samples with theoretical density of 91%. These results provide useful subsidies to advance toward full densification of ytrria based materials.

Study of Coatings Formed on Zirconium Alloy by Plasma Electrolytic Oxidation in Electrolyte with Submicron Yttria Powder Additives

Coatings with thickness 40 to 150 μm were formed by plasma electrolytic oxidation (PEO) on the zirconium alloy Zr-1Nb (Zr-1% Nb) in the slurry electrolyte containing 9 g/L Na2SiO3 5H2O, 5 g/L Na(PH2O2) and 6 g/L submicron Y2O3 yttria powder during 60 min under the AC electrical mode at current densities 20; 30 and 40 A/dm2. The surface morphology, structure, composition, and corrosion-protective ability of the formed coatings have been analyzed. At PEO current density 30 A/dm2, a predominantly tetragonal phase of zirconia was formed in coatings. Increasing the PEO current density up to 40 A/dm2 promoted the formation of the coating surface layer containing submicron yttria particles. Electrochemical polarization studies in 0.5% LiOH solution showed that PEO coatings demonstrated high corrosion-protective ability. The dependence of the polarization currents on the PEO current density was found to be inconsequential.

Fabrication of Austenitic ODS 316L Stainless Steel with Arc Plasma Sintering Method

Austenitic ODS (Oxide Dispersion Strengthened) 316L steel was fabricated using 316L SS (Stainless Steel) pre-alloyed powder and yttria powders by mechanical milling with APS (Arc Plasma Sintering) method. The powders were milled in High Milling Shaker at 1000 rpm in rotational speed for 10 hours at 10 BPR (Ball Powder Ratio). As milled powders were pressed at 20 Ton and sintered with APS for 0 to 12 minutes at 70 A. The samples were analysed using X-Ray Diffraction (XRD), Microscope Optic (MO) with micro-hardness tester and Scanning Electron Microscope – Energy Dispersive X-Ray Spectroscope (SEM-EDS). The results of phase and microstructure showed the austenitic grade of the samples. The sintering time contributed to the microstructure of the samples. At room temperature, the mechanical properties of ODS 316L SS was higher than conventional 316L SS.

Effect of ZRO2 and Y2O3 Deposition on Biological Behavior of Ti-Base Alloys

Titanium has a good ability to attach to bone and living tissue, making it a perfect material for orthopedic implants. Because of the combination of high resistance to corrosion, biocompatibility and excellent mechanical properties. This work aims to study the Modifications of various base titanium implant samples producing by using powder technology (Ti-pure, Ti-45 % Ni, Ti10 % Co, and Ti-30 % Ta) by deposition of Nano Zirconia and yttria powders (70 % and 30% ). Chemical pretreatment carried out to prepare the implant surface before deposition, while the deposition process accomplished by pack cementation. The Characterizations of samples accomplished before and after the surface treatment, which includes: microstructure observation, x-ray diffraction (XRD), MTT Assay (cell viability) and MTT assay (cell adhesion). From the SEM All samples Show that Nano Zirconia and yttria were homogeneously put on the surface and fully covered it which resulted in a substantial modification in surface morphologies. From XRD patterns the peaks slightly shifted to the low angle side also amorphous behavior was observed. From MTT graphs it was found that the titanium alloys surface after pack cementation became more active after 3 days of exposure in MG-63 cells and there was a remarkable increase in cell viability and cell attachment compared with untreated samples.

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.

Structural and Magneto-Optical Characterization of La, Nd: Y2O3 Powders Obtained via a Modified EDTA Sol-Gel Process and HIP-Treated Ceramics.

In this study, pure Y2O3, La0.1Y1.9O3 and La0.1Nd0.12Y1.78O3 nanosized powders were successfully synthesized by a modified sol–gel method. Pure and rare-earth ions doped yttria powders were characterized by X-ray diffraction, scanning electron microscopy and Brunauer–Emmett–Teller methods. The powders were sintered by the hot isostatic pressing process. The highest in-line transmittance of 56% was obtained at 800 nm and increased in the IR region. The influence of the lanthanum and neodymium ions on the physicochemical properties of yttria were discussed. The La-Nd-doped material exhibited a Verdet constant over 4000 deg/T·m at 400 nm and low thermal dependence. An interesting evolution of the Verdet constant across the absorption band with high resolution was studied. A study of the optical and magneto-optical properties of yttria doped with Nd3+ and La3+ is discussed in this paper.

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.

Sintering behavior of nano yttria powder compacts fabricated by various forming processes

Sintering behavior of nano yttria powder compacts fabricated by various forming processes

X-ray diffraction analysis of the yttria stabilized zirconia powder by mechanical alloying and sintering

In the present work, monoclinic zirconia was mechanically alloyed with yttria (6–14 mol%) via ball milling at the different ball-to-powder mass ratios (BPMRs) for 3–24 h, and then, the mixed powders were sintered at 1100 °C and 1500 °C. Line profile analysis of the X-ray diffraction (XRD) patterns, using the Alexander-Klug, Adam-Cox, Rietveld, and Scherrer methods, was systematically used to investigate the effects of the milling time, BPMRs, sintering temperature, sintering time and zirconia-to-yttria ratio. The experimental results indicate that the yttria-stabilized zirconia (YSZ) appears in the mixed powder after a milling time longer than 8 h. In addition, the ZrO2 content will decrease with the milling time or amount of BPMRs. The XRD patterns demonstrate that the intensity of the YSZ diffraction peaks was greatly improved after sintering. However, even if sintering at 1100 °C for 10 h, m-ZrO2 still remained in the mixed powder. When the temperature rose to 1500 °C, only the cubic phase of YSZ (c-YSZ) was found in the zirconia-14 mol% yttria powder. Based on the above results, combined with other related research, the possible mechanism of the phase transformation in the ball milling and sintering process is discussed in this paper.

Structure and properties of ceramic-like coating on zirconium alloy produced by microarc oxidation in electrolyte with submicron yttria powder additives

Ceramic-like coatings were formed on zirconium-niobium (Nb – 1%) alloy by microarc oxidation (MAO) in slurry electrolyte with the addition of submicron yttria powder. The coatings were investigated using scanning electron microscopy, x-ray diffraction analysis, microhardness tester and roughness meter. The addition of submicron yttria powder in electrolyte leads to content reduction of zirconia monoclinic phase in MAO coating. The inhibition effect increases with the MAO coating thickness rise and with an increase of the process current density up to 30 A/dm2.