Surface Modification in Polycrystalline Y2O3 Under High‐Pressure/High‐Temperature Processing Conditions

A pressure‐induced phase transformation is used to refine the grain size of polycrystalline Y₂O₃, by a factor of 3000. A surface modification effect accompanies the observed grain refinement, which becomes more apparent with increasing holding time under high pressure. The surface‐modified layer exhibits lower hardness and lower oxygen content relative to the underlying material. Moreover, it possesses columnar‐grained structure with cubic symmetry, whereas the interior has a monoclinic structure.     

Air plasma-sprayed Y2O3 coatings for Al2O3/Al2O3 ceramic matrix composites

Al₂O₃/Al₂O₃ ceramic matrix composites (CMC) are candidate materials for hot-gas leading components of gas turbines. Since Al₂O₃/Al₂O₃ CMC are prone to hot-corrosion in combustion environments, the development of environmental barrier coatings (EBC) is mandatory. Owing to its favorable chemical stability and thermal properties, Y₂O₃ is considered a candidate EBC material for Al₂O₃/Al₂O₃ CMC. Up to 1 mm thick Y₂O₃ coatings were deposited by means of air plasma spraying (APS) on Al₂O₃/Al₂O₃ CMC with a reaction-bonded Al₂O₃ bond-coat (RBAO). APS Y₂O₃ coatings exhibit a good adherence in the as-deposited state as well as upon isothermal annealing up to 1400 °C. Moreover, furnace cyclic testing performed at 1200 °C revealed an excellent durability. This is explained by the formation of a continuous, approximately 1 μm thick reaction zone at the APS Y₂O₃/RBAO interface. The reaction zone between Y₂O₃ and Al₂O₃ comprises three layers of thermodynamically stable yttrium-aluminates exhibiting strong bonding, respectively.     

Regulation of Y2O3 addition on structure and properties of Al2O3/ZrO2(Y2O3) directionally solidified eutectic ceramic

Al₂O₃/ZrO₂(Y₂O₃) directionally solidified eutectic ceramics (DSECs) with different Y₂O₃ addition were prepared. Three polymorphs of ZrO₂: m-ZrO₂, t-ZrO₂ and c-ZrO₂ appeared and disappeared in order with the increase of Y₂O₃ addition, the effects of Y₂O₃ addition amount on the mass fraction of ZrO₂ polymorphs were quantitatively analyzed. The gradual decrease of area fraction and average size of colony was attributed to the increase of constitutional undercooling region, the variation of interphase spacing in the colonies was explained via selection mechanism of dendrite tip. The maximum hardness and fracture toughness were 18.35 GPa and 8.55 MPa m^1/2 obtained at 9 mol% and 3 mol% Y₂O₃ addition, respectively. The hardness was determined by the mass fraction of m-ZrO₂ phase, the area fraction of intercolony and the residual compressive stress, and the toughening mechanisms were composed of microcrack toughening, t-m transformation toughening and residual stress toughening.     

The structural and electrical comparison of Y2O3 and Ti-doped Y2O3 dielectrics

A Ti-doped Y₂O₃(Y₂Ti₂O₅) dielectric on polycrystalline silicon followed by rapid thermal annealing results in improved characteristics including a higher effective dielectric constant, higher breakdown electric field, lower electron trapping rate, and larger charge-to-breakdown when compared with Y₂O₃. The performance of high-k Y₂O₃ and Y₂Ti₂O₅ dielectrics were investigated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), capacitance-voltage, and current density-voltage. Incorporating Ti into the Y₂O₃ dielectric imparts improvements in the structural and electrical performance of the material. The Y₂Ti₂O₅ dielectric with 800 °C annealing treatment has the best performance among all the samples tested.     

B6O materials with Al2O3/Y2O3 additives densified by FAST/SPS and HIP

Fully densified B₆O materials with Al₂O₃/Y₂O₃ sintering additives amounts systematically varied between 0 and 15 vol.% and Al₂O₃/(Al₂O₃ + Y₂O₃) molar ratios of 0.05–1 were prepared by FAST/SPS and HIP at sintering temperatures between 1725 °C and 1900 °C. Their densification and microstructure were correlated with measured mechanical properties. The addition of low additive amounts in the range of 2–3 vol.% was found to increase the fracture toughness and strength from 2.0 MPa m^1/2 (SEVNB) and 420 MPa for pure B₆O to about 3.0 MPa m^1/2 and 540 MPa, but it had no effect on the hardness, which remained at a high level of 30–36 GPa (HV_0.4). Higher additive contents did not yield a further improvement in the toughness but resulted in a reduction in hardness and strength.     

Y2O3/TiO2纳米粒子超声光催化降解邻硝基苯酚

以钛酸丁酯为原料,用溶胶——凝胶（Sol-gel）法制备了Y2O3／TiO2纳米粒子。采用X光衍射仪对粉体的粒径、物相进行了表征。研究了超声光催化协同降解水中邻硝基苯酚的效果,考察了超声波声强、反应温度和催化剂投加量对邻硝基苯酚降解速率的影响。研究结果表明：超声光催化协同降解要比单独超声波或光化学处理效果显著,证实了声光联合技术具有明显的协同效应。     

Al2O3/Al2O3-ZrO2(3Y)层状纳米陶瓷复合材料的显微结构及弯曲强度

在Al2O3-ZrO2(3Y,即含3%Y2O3,摩尔分数,下同)纳米陶瓷的基础上,以原位合成的Al2O3和Al2O3-ZrO2(3Y)纳米粉体为原料,采用干压成型及热压烧结的方法制备了Al2O3/Al2O3-ZrO2(3Y)层状纳米陶瓷复合材料,研究了ZrO2(3Y)含量对材料显微结构及力学性能的影响.结果表明:复合材...     

Interfacial reactions between Ti and Y2O3/Ca4Ti3O10 composites

In titanium casting, the interfacial reactions between selected Y₂O₃/Ca₄Ti₃O₁₀ composites in contact with titanium at 1600°C for 30 minutes in an argon environment were characterized using X-ray diffraction, scanning electron microscopy, and analytical transmission electron microscopy. Before contact with titanium, reaction phases of the Y₂O₃/Ca₄Ti₃O₁₀ composites formed through hot pressing at 1500°C or annealing at 1600°C. These phases were identified as Ca₄Ti₃O₁₀, Y₂O₃, and minor amounts of CaO. The amount of Ca₄Ti₃O₁₀ in the composites gradually decreased as the amount of Y₂O₃ increased. When the Y₂O₃/Ca₄Ti₃O₁₀ composites were in contact with titanium, a reaction layer of α-Ti and Y₂O₃ was formed near the interface of the composite side. Large amounts of calcium and oxygen were expelled toward the composite side from Ca₄Ti₃O₁₀ near the interface to form CaO, which precipitated in the Ca₄Ti₃O₁₀ and Y₂O₃ phases. Furthermore, no reaction phases were detected in titanium. Ca₄Ti₃O₁₀ and Y₂O₃ can function as diffusion barrier layers to effectively suppress the diffusion of oxygen into titanium.     

Microstructure and mechanical properties of Al2O3/Y3Al5O12/ZrO2 ternary eutectic materials

Directionally solidified fibers and rods have been grown from the ternary Al₂O₃/Y₃Al₅O₁₂/ZrO₂ system using micro-pulling-down method. Fiber diameter could be varied 0.3 mm–2 mm at pull-rates ranging 6–900 mm/h and 500 mm in length. The ternary eutectic fibers had homogeneous colony patterned eutectic microstructures. The interlamellar spacing λ exhibited an inverse-square-root dependence on the growth speed v according to λ = 8 × v^−1/2, where λ has the dimension of μm and v is in μm/s. The tensile strength was recorded 1730 MPa at 25 °C and 1100 MPa at 1200 °C for a fiber crystals grown at a growth speed of 900 mm/h. Eutectic rods having 5 mm of diameter and up to 80 mm in length were also successfully grown by the micro-pulling-down method. The eutectic rods showed 1400 MPa of mechanical strength by compressive mode at 1500 °C with homogeneous colony microstructures.     

含Y2O3的ZnO-Bi2O3-B2O3系统玻璃热学与电学性能研究

用红外光谱仪、拉曼光谱仪和差热分析仪研究了用“熔化-急冷”制得的用于SOFC封装的含Y2O3的ZnO-Bi2O3-B2O3系统玻璃的结构和转变温度(Tg);用X射线衍射仪、热膨胀系数仪和高阻计研究了由“模压成型-热处理”制得的该玻璃制品的微晶化、热膨胀系数(α)和体积电阻率(p)情况.结果表明:Y2O3≤0.5～1.0wt.％时,Y2O3能促进[BO3]向[BO4]转变,使α降低;Y2O3≥0.5～1.0wt.％时,玻璃中Bi-O键增多,又使α降低趋势趋缓;随Y2O3增加,其作用可能由破坏网络结构逐渐向增强网络结构转变,致T8先降后升;添加Y2O3延缓了玻璃的析晶;微晶化能提高α和ρ;添加Y2O3虽致α和ρ下降,但其值仍在SOFC封接玻璃的要求范围内.     

Effects of Eu content on the luminescent properties of Y2O3:Eu3+ aerogels and Y(OH)3/Y2O3:Eu3+@SiO2 glassy aerogels

This article describes the morphological, structural, and luminescent properties of Y₂O₃:Eu³⁺ aerogels and Y(OH)₃/Y₂O₃:Eu³⁺@SiO₂ glassy aerogels synthesized by the sol-gel method with Eu concentrations from 2.5 mol% to 30 mol%. XRD measurements indicated that both the aerogels and glassy aerogels had a monoclinic phase, but the crystallinity in the glassy aerogels was lower due to the presence of SiO₂. SEM images reveal that a three-dimensional porous network was formed in the aerogels due to the interconnection of coalesced Y₂O₃:Eu³⁺ nanoparticles. The 3D porous network was also observed in the glassy aerogels, coated with a silica shell. In both the aerogels and glassy aerogels, the size of the agglomerates decreased as the europium concentration increased. This, in turn, increased the average size of the macropores that formed their 3D network. Furthermore, the luminescent properties of the aerogels and glassy aerogels were studied under UV excitation, and it was observed that their red emission intensity increased continuously as the Eu³⁺ concentration increased. The luminescence of the aerogels was on average 50% higher than that of the glassy aerogels. Hence, our results indicate that porous and luminescent aerogels with and without silica are adequate for applications in sensing and catalysis.     

Density measurements of molten Y3Al5O12 and Y2O3-Al2O3 compounds using an electrostatic levitation technique

The densities of molten Y₂O₃-Al₂O₃ compounds, including yttrium aluminum garnet (Y₃Al₅O₁₂), were determined over a wide temperature range that included an undercooled region, using an electrostatic levitation furnace. The density of the molten Y₃Al₅O₁₂ varied with temperature according to the relationship 3750 − 0.25(T − T_m) (kg/m³) with T_m = 2240 K and for the range of 1300 K ≤ T ≤ T_m, yielding the thermal expansion coefficient ɑ = 6.7×10⁻⁵ K⁻¹. The molar volumes of molten (100-x)Y₂O₃-xAl₂O₃ (x = 0, 33.3, 50, 55, 62.5, 76.5, 81.5, or 100 mol%) were found to vary with the value of x in a linear manner within the superheated temperature range. However, the molar volumes in the undercooled region deviated from those calculated using an ideal solution model owing to attractive interactions between Y₂O₃ and Al₂O₃.     

Y2O3添加量对Al2O3/ZrO2复合材料烧结行为和热机械性能的影响

研究了Y2O3添加量对Al2O3/ZrO2复合材料烧结行为和热机械性能(高温抗折强度和抗热震性)的影响,并研究了这些性能与物相组成和显微结构间的关系.结果表明:Y2O3在Al2O3/ZrO2复合材料中起稳定ZrO2晶型、改善烧结致密化、提高高温抗折强度和抗热震性的作用.当Y2O3添加量为1%时,试样的烧结性能和高温抗折强度较佳,体积密度、显气孔率和线收缩率分别为3.27 g/cm3、21.95%和7.43%,高温抗折强度达29 MPa;抗热震性则在Y2O3添加量为0.5%时较佳,其残余强度保持率为71%.Y2O3对Al2O3/ZrO2复合材料烧结性能和热机械性能的影响与Y2O3/ZrO2固溶体的形成、Al2O3和ZrO2晶体间的结合程度及试样中微裂纹含量密切相关.     

添加Y2O3的ZrSiO4/α-Al2O3混合粉体的反应烧结

采用XRD和TEM等技术研究了添加Y2O3的ZrSiO4/α-Al2O3混合娄体的反应烧结过程，包括坯体的致密化，Y2O3的存在方式及相组成。结果表明，Y2O3的引入加快了坯体的致密化，促进了ZrSiO4的分解和莫来石的形成。添加的Y2O3，一部分存在于晶界玻璃相中，一部分进入ZrO2晶格中使之以四方相形式存在。随着Y2O3添加量的增加，试样中四方相ZrO2相对含量增加：当Y2O3／（Y2O3＋ZrO2)的摩尔比达到5％时，立方相ZrO2开始出现。     

碳包覆Ni/Y_2O_3纳米颗粒的制备与表征

以硝酸镍和硝酸钇为金属源,玉米淀粉为基质,在氢气保护下进行控温炭化制备出准球形的碳包覆Ni/Y2O3纳米颗粒。采用SEM、XRD、TG和Raman光谱对产物进行表征测试,分析表明碳包覆Ni/Y2O3纳米颗粒粒径分布比较窄,碳的质量分数大约为6%,为核-壳层结构,壳层由尺寸为:4～5 nm的石墨晶粒组成,核为具有面心结构的Ni和体心结构的Y2O3组成。     

High-gravity activated SHS of large bulk Al2O3/ZrO2 (Y2O3) nanocrystalline composites

Large bulk Al₂O₃/ZrO₂ (Y₂O₃) composites were in-situ prepared by SHS under varied high-gravity from ZrO₂ + Y₂O₃powder blends with an added thermit mixture. Investigated was the effect of high gravity on the microstructure, crystal growth, and properties of synthesized materials. The XRD data suggest that high gravity did not bring about any change in the phase constitution of the composite ceramics and that the ceramic matrix was composed of α-Al₂O₃, t-ZrO₂, and m-ZrO₂. SEM and EDS data show that, with increasing level of high gravity, the morphology of the ceramic microstructures transformed from the cellular eutectics to the rodshaped colonies, and the volume fraction and aspect ratio of the rod-shaped colonies increased while the rodshaped colonies were refined. Above 200 g, the microstructures of composite ceramics developed as the randomlyorientated rod-shaped colonies with a symmetrical triangular dispersion of tetragonal ZrO₂ fibers of 300 nm in the average diameter. Relative density, hardness, flexural strength and fracture toughness simultaneously reached the highest values of 98.6%, 18.6 GPa, 1248 MPa, and 15.6 MPa m^1/2 as the maximum high-gravity level of 250 g was achieved. An increase in the relative density and hardness of the ceramics with increasing gravity level was attributed to the acceleration of gas escape from SHS melts and the elimination of shrinkage cavity in the ceramics under the action of high-gravity field. The increase in fracture toughness results from the enhancement of the coupled toughening mechanisms while the increase in flexural strength comes from the refinement of the microstructures, decrease in critical defect size, and achievement of high fracture toughness.     

Ruby micro-piezospectroscopy in GdAlO3/Al2O3(/ZrO2), Er3Al5O12/Al2O3(/ZrO2) and Y3Al5O12/Al2O3(/ZrO2) binary and ternary directionally solidified eutectics

The fluorescence from (naturally present) Cr³⁺ impurities was used to measure the residual stress in the alumina phase of six melt-grown ceramic eutectic composites associating gadolinum aluminum perovskite (GAP), erbium aluminum garnet (EAG) or yttrium aluminum garnet (YAG) with α-alumina and cubic zirconia. Such measurements are reported for the first time in the GAP containing eutectics.In the usual hydrostatic assumption, we conclude to a residual compression in the range of ～70–400 MPa depending on the sample composition. The validity of the hydrostatic assumption is questioned when a microscope is used for the measurements.     

Y_2O_3在（Y，Mg）－PSZ／MgAl_2O_4材料中的作用

采用工业法制备了（Ｙ，Ｍｇ）ＰＳＺ／ＭｇＡｌ２Ｏ４陶瓷材料，在１１００℃热处理过程中，材料展示了良好的耐高温老化性。微观分析结果表明：材料在热处理过程中产生ｃＺｒＯ２→ｃ′ＺｒＯ２＋ｔＺｒＯ２＋ＭｇＯ形式的共析分解反应；同时，材料中存在ＭｇＯ稳定和Ｙ２Ｏ３稳定的三种形式的四方析出体，其中Ｙ２Ｏ３稳定的“花呢”（“ｔｗｅｅｄ”）和“群团”（“ｃｏｌｏｎｙ”）状析出体随热处理时间的延长而长大     

Thermal prehistory,structure and high-temperature thermodynamic properties of Y2O3-CeO2 and Y2O3-ZrO2-CeO2 solid solutions

Ceria-based solid solutions are important materials for high- and medium-temperature electrochemical applications. However, the stabilities of both binary and ternary ceria-based solid solutions are insufficient at elevated temperatures, which limits their application as solid electrolytes or SOFC cathodes. Data on the high-temperature stability of ceria-based ceramics are unavailable in the literature. In the present study, we report a thermodynamic stability investigation of Y₂O₃-CeO₂ and Y₂O₃-ZrO₂-CeO₂ solid solutions. The thermal prehistories of binary and ternary systems were investigated using STA, XRD, and ESCA techniques. The vaporization processes were investigated in the temperature range of 1577–2227°С via the Knudsen effusion mass spectrometry technique. Using data on the component activity in solid-phase thermodynamic properties of Y₂O₃-CeO₂ solid solutions, which is represented as the Gibbs energy, the excess Gibbs energy was calculated as a function of the ceria mol. %. It was shown that the reduction of Ce⁴⁺ to Ce³⁺ in Y₂O₃-CeO₂ and Y₂O₃-ZrO₂-CeO₂ solid solutions corresponds to less-negative Gibbs energy compared to ZrO₂-CeO₂ solid solutions.