Yttria Ceramics Research Articles

Mechanical Properties of Submicrometer‐Grained Transparent Yttria Ceramics by Hot Pressing with Hot‐Isostatic Pressing

Here, we report the fabrication and mechanical properties of submicrometer‐grained (0.29–0.58 μm) transparent yttria ceramics by hot pressing combined with hot‐isostatic pressing. The effects of the grain size on the microhardness and the fracture toughness were studied. An unusual decrease of the fracture toughness with an increase in the grain size was revealed, which may be attributed to the different grain size dependence of the fracture behavior of the ZrO2‐doped yttria ceramics compared to that of other yttria ceramics. The microhardness and fracture toughness of the transparent yttria ceramics were found to be better than those of the large‐grained yttria ceramics.

Effect of sintering temperature on microstructural and optical properties of transparent yttria ceramics fabricated by spark plasma sintering

Yttria nanopowder was used to fabricate transparent yttria ceramics by spark plasma sintering at temperatures ranging from 1200°C to 1600°C for 20min. The microstructure of fracture cross section and optical transmittance of the products were characterized by Field Emission-Scanning Electron Microscope (FE-SEM) and Fourier-transform infrared spectrophotometer (FTIR). With increasing the sintering temperature, densification occurs up to 1500°C, whereas the mean grain size of yttria ceramics was first increased and then decreased markedly. The highest density and the lowest mean grain size of yttria ceramic reached to 99.58% and 0.53μm at 1500°C, respectively. The best in-line transmittance was at 1500°C, with transmittance being about 80% in the range of 3–5μm, which was close to the theoretical value of yttria.

New double-sintering aid for fabrication of highly transparent ytterbium-doped yttria ceramics

Highly transparent ytterbium-doped yttria (Yb:Y2O3-ZM) ceramic was demonstrated with ZrO2–MgO as double-sintering aid by using a pressureless sintering method for the first time. The Yb:Y2O3-ZM ceramics wafer with 17mm in diameter and 2.5mm thick had an average grain size of 25μm and a transmittance at 2000nm of as high as 81.5%, which is near theoretical value of the material. In contrast, it was difficult to obtain transparent ytterbium-doped yttria ceramics with ZrO2 or MgO as single aid. The product of emission cross section and lifetime (στ) was 8.94×10−24cm2s, which means that the Yb:Y2O3-ZM transparent ceramics would be one promising laser material.

Using multiple pumps to study energy-transfer pathways in [formula omitted] ceramics

Erbium ions in inorganic, insulating gain media show a wide variety emission wavelengths – including ultra-violet, visible (red, green and blue), near-IR (∼800nm, ∼980nm, ∼1550nm) and mid-IR (∼3000nm). Erbium is an interesting ion providing multiple paths to emit multiple wavelengths. The energy levels corresponding to these wavelengths can be populated by converting lower-energy photons into higher energy photons by various energy-transfer mechanisms. Different energy-transfer mechanisms may be present at different concentrations of erbium in the insulating host matrix. Some of these mechanisms are difficult to prove experimentally. We present a novel approach to study utilizing a dual-pump scheme to elucidate some of the energy-transfer mechanisms/pathways in erbium-doped ceramic yttria. By dynamically changing the populations in intermediate energy-levels, we could track the energy-transfer paths, yielding information on the dynamic nature of energy-transfer in RE-doped materials. The parameters controlled in this study were the concentration of the active ion, the pump wavelengths and pump power.

Osteoblast response to zirconia surfaces with different topographies.

Zirconia-3 mol% yttria ceramics were prepared with as-sintered, abraded, polished, and porous surfaces in order to explore the attachment, proliferation and differentiation of osteoblast-like cells. After modification, all surfaces were heated to 600°C to extinguish traces of organic contamination. All surfaces supported cell attachment, proliferation and differentiation but the surfaces with grain boundary grooves or abraded grooves provided conditions for enhanced initial cell attachment. Nevertheless, overall cell proliferation and total DNA were highest on the polished surface. Zirconia sintered at a lower temperature (1300°C vs. 1450°C) had open porosity and presented reduced proliferation as assessed by alamarBlue™ assay, possibly because the openness of the pores prevented cells developing a local microenvironment. All cells retained the typical polygonal morphology of osteoblast-like cells with variations attributable to the underlying surface notably alignment along the grooves of the abraded surface.

Optical, luminescent and laser properties of highly transparent ytterbium doped yttrium lanthanum oxide ceramics

This paper describes the fabrication and investigation of highly transparent Yb-doped yttrium lanthanum oxide ceramics. For sintering of the ceramics we used a technology, which consists of several consecutive steps: (a) synthesis of weakly agglomerated nanopowder by laser ablation, (b) compacting of the green body with cold isostatic pressing (CIP), and (c) sintering in vacuum. After calcinations of the synthesized nanopowder at 1200°C, a pure single-phase solid solution Yb3+:(LaxY1−x)2O3 was formed. The lanthanum ions proved to be a good aid to sinter yttria ceramics doped with Yb3+ at comparatively moderate temperatures of about 1650°C. The ceramics have a relative density higher than 99.99% and grain sizes around 40μm. The absorption coefficient of 3.2mm thick Yb0.12La0.27Y1.61O3 ceramics is 0.01cm−1 at 1150nm. Laser oscillation at a wavelength of 1033nm is demonstrated.

Cracks in transparent La-doped yttria ceramics and the formation mechanism

Crack is a common phenomenon in ceramics, which often extends and breaks the ceramic bodies. In the present study, however, cracks formed a network inside some transparent La-doped yttria ceramics, while didn’t break the samples. The reason was studied by investigating the mixed La2O3 and Y2O3 powders using SEM, TG-TDA BET, and XRD. The crack network is attributed to the volume effects of La(OH)3 dehydration and solid state reaction of oxides, both proceed gradually instead of suddenly along with temperature increasing during heating procedure of sintering. Hence, the corresponding stresses made cracks inside La-doped yttria ceramics without broken the bodies. The cracks could be eliminated by increasing the powder calcination temperature to reduce the above volume effects.

Facile Fabrication of Highly Transparent Yttria Ceramics with Fine Microstructures by a Hot‐Pressing Method

In this study, we report highly transparent yttria ceramics fabricated by a facile hot‐pressing method with tantalum foil shielding which effectively prevents the ceramic samples from carbon contamination caused by the graphite mold used during the process. The hot‐pressed sample was already highly transparent without a post‐annealing step or hot isostatic pressing. For a 2‐mm‐thick specimen doped with 1 at.% ZrO2, the in‐line transmittance reaches 74.4% at 400 nm and 81.1% at 1100 nm. The sample shows a very fine microstructure with an average grain size of about 1 μm owing to the low sintering temperature of only 1600°C. The study results indicate that it is possible to produce transparent yttria ceramics with excellent optical transparency using the economical and convenient hot‐pressing method.

Infrared transmittance of hybrid microwave sintered yttria

Synthesis of nano particles of yttria (Y2O3) ceramics (~15nm) by a single step auto-igniting combustion technique, followed by sintering of the sample by three variants of sintering methods viz. resistive, microwave and microwave hybrid heating to optimum density and their remarkable infrared transmission characteristics are presented in this paper. In microwave hybrid sintering there was a considerable reduction in the sintering temperature and the soaking time compared to the resistive and microwave sintering. The pellets sintered by microwave hybrid heating at 1450°C for 20min achieved a density 99.2% of the theoretical density with reduced average grain size of 220nm and the pellet showed enhanced transmittance of ~80% in the visible and ~80% in the mid infrared region. The results clearly indicate that the yttria ultra fine nanophase powder synthesised by the single step combustion method and sintered via microwave hybrid heating shows better transmittance properties and can be used very effectively for the fabrication of infrared transparent windows and domes.

Dependence of spectroscopic and thermal properties on concentration and temperature for Yb:Y2O3 transparent ceramics

High transparency ytterbium doping yttria (Yb:Y2O3) ceramics were fabricated by vacuum sintering. The influence of temperature and doping concentration on optical and thermal properties of Yb:Y2O3 ceramics were evaluated. The increased Yb doping concentration causes the red-shift of absorption edge. The intensities of absorption peaks increase linearly with Yb3+ ion concentration, and the absorption cross-section at ∼978nm is calculated to be 1.15×10−20cm2. When Yb3+ doping content is 5.0at.%, the strongest peak centers at the wavelength of 1030nm with the full width at half maximum (FWHM) of 17nm, and stimulated emission cross-section is measured to be 1.58×10−20cm2. Both absorption coefficient and fluorescence lifetime increase with increasing Yb3+ concentration. The optimum doping concentration of Yb3+ ion in Y2O3 transparent ceramic is in the range of 5.0–7.0at.%. For 5.0at.% Yb:Y2O3 transparent ceramic, as temperature increases from 10K to room temperature (RT), the fluorescence intensity decreases and the peaks are broaden.

Fast densification of nanocrystalline yttria ceramics without grain growth

Dense nanocrystalline yttria ceramics without grain growth were obtained within a short densification period by a method combining SHS reaction and quick pressing (SHS-QP). The reactive mixtures consisting of Ni and Al with TiC as a diluent were used as a heat source. An yttria compact was inserted inside the reactants and warmed up by reaction heat at a heating rate of above 1300°C/min. When the temperature reached its maximum, high mechanical pressure was applied to the sample for densification. Dense nanocrystalline yttria was produced when temperature T was 1350°C and pressure P, 120 MPa. The rapid densification process was accomplished in 1 min. Microstructural analysis showed almost no grain growth compared to initial powder. For comparison, the hot pressing (HP) process was also used to densify the same yttria powders. The results prove that the HP process causes grains coarsening even when the sintering temperature is 1250°C.

Raman scattering and luminescence of yttria nanopowders and ceramics

We have studied Raman scattering in yttria nanopowders and ceramics that was excited by radiation at wavelengths of 514.5 and 632.8 nm. We show that, in undoped nanopowders and cubic phase of doped yttria ceramics, only the Raman scattering by phonons is observed, with no other Raman scattering centers having been revealed. In nanopowders of the monoclinic phase, we have observed an additional Raman line with a Raman shift of 1093 ± 4 cm−1. If all the objects under investigation are excited by the radiation at a wavelength of 514.5 nm, their spectra exhibit four series of photoluminescence lines, two of which (at λ = 521–523 and 538–564 nm) are emitted by Er3+ ions, “impurity” dopants, while the other two lines (at λ = 607–635 and 644–684 nm) are emitted by intrinsic centers. Under excitation by the radiation at a wavelength of 632.8 nm, only a series of bands at λ = 644–684 nm is emitted. In addition to these photoluminescence bands, neodymium-doped ceramics show photoluminescence bands of Nd3+ ions. We have shown that intrinsic luminescence centers, which occur in all the examined specimens, are capable of acting as acceptors with respect to neodymium ions excited to the upper laser level.

Cerâmica transparente de Y2O3 obtida por sinterização rápida em forno de radio frequência sob atmosfera de vácuo dinâmico

Monocristais de ítria (Y2O3) são importantes materiais hospedeiros para lasers. Entretanto, seu elevado ponto de fusão (2450 ºC) dificulta o processo de crescimento de monocristais. Uma alternativa para a obtenção de ítria policristalina com propriedades similares às dos monocristais é a fabricação de cerâmicas transparentes. Desta forma, este trabalho teve o propósito de desenvolver uma metodologia para fabricar cerâmicas transparentes de ítria, utilizando-se um forno de indução eletromagnética que permite o uso controlado de atmosferas inertes ou redutoras e pode atingir temperaturas próximas a 2000 ºC, com taxas de aquecimento maiores que 100 ºC/min. Os pós-precursores foram preparados por meio de reação do estado sólido usando 3% em mol de ZrO2 como aditivo. As amostras foram conformadas em discos com 12 mm de diâmetro e 1 mm de espessura sob uma pressão uniaxial de 50 MPa e isostática de 350 MPa. Em seguida, foram sinterizadas a 1800 e 1900 ºC com tempos de sinterização de 1 e 5 h. Difração de raios X e microscopia eletrônica de varredura foram usadas na caracterização estrutural e microestrutural das amostras e sua transmissividade ótica foi medida por meio de espectrofotometria. Através da sinterização em forno de indução foi possível obter cerâmicas com até 60 % de transmissão em linha na região de 800 nm em tempos de sinterização menores que os descritos na literatura.

Grain growth stagnation in the dense nanocrystalline yttria prepared by combustion reaction and quick pressing with an ultra-high heating rate

Abstract Combustion reaction plus quick pressing was a developing technique that used the Joule heating effect of combustion reaction to sinter ceramics, and allows very high heating rate, short soaking duration and high pressure for densification of ceramics. By taking advantages of the particular conditions of this method, pure yttria ceramics with a relative density of 98.5% and an average grain size of 50 nm were obtained at 1620 K and 170 MPa. Moreover, the investigation on the grain growth of sintered yttria was carried out by analyzing the microstructure evolutions and responsible mechanisms. The combined effect of the ultra-high heating rate and the high pressure applied on compact at the peak temperature was effective in suppressing particle coarsening and enhancing densification. Besides, under the decreased sintering temperature and soaking duration, the retained nanostructure assisted to inhibit final-stage grain growth while without impeding the further densification of nanocrystalline ceramics.

Highly transparent ytterbium doped yttrium lanthanum oxide ceramics

To prepare ytterbium doped lanthania yttria nanopowder a method of laser evaporation of mixed oxides was used. After calcinations of the powder at 1200 °C a pure single-phase solid solution Yb3+:(LaxY1−x)2O3 was formed in the nanoparticles. Influence of lanthanum oxide as an isovalent additive on the yttria structure was investigated. The lanthanium ions were proved to be a good aid to sinter yttria ceramics doped with Yb3+ at moderate temperatures about 1650 °C. The ceramics with relative density higher than 99.99% and grain size about 40 μm were fabricated. Full transmittance of 1.8 mm thick Yb0.11La0.23Y1.66O3 ceramics reached 82.5% at 800 nm. This material could be a good gain medium for ytterbium high power pulse lasers.

High Yttria-Zirconia and Yttria Ceramics for Petrochemical Reverse-Flow Reactor Applications

Reverse-flow reactors achieve the desired hydropyrolysis reaction of natural gas and other hydrocarbon feeds at very high temperatures of up to 2000°C, which enables the production of many high-value chemicals. To identify refractory ceramic materials suitable for constructing key components of the reactor, the full range of solid solutions between zirconia and yttria having 18 to 100 mol% yttria have been tested in a laboratory reactor. Conventional yttria-stabilized zirconia (YSZ) materials having 8 mol% Y2O3 appear to accommodate reactor thermal severity, but are prone to a new form of corrosion termed ceramic dusting that is observed when pyrolysis and oxidation cycles are alternated under reverse-flow conditions. Yttria and high yttria–zirconia ceramics having ~80 mol% or more yttria suppress ceramic dusting corrosion in steam-free pyrolysis environments. The addition of low levels of steam of ~5% to the pyrolysis gas stream increases the stability of YSZ materials substantially, so that the stability threshold is closer to 40 mol% Y2O3 in the yttria–zirconia system. The two approaches can be combined to optimize reactor performance. Key experimental results are presented and discussed taking into account the thermodynamic phase stability of the different phases.

Stress-induced birefringence for the Er3+: Y2O3 ceramic system

The stress-induced birefringence for erbium doped yttria ceramics were measured at room temperature. An ellipsometer was used to measure the retardation effect of static loading on a set of ceramic equilateral prisms and the stress-optic co-efficients were obtained. The samples measured were equilateral prisms of pure Y2O3, (Er0.1Y0.9)2O3 and (Er0.2Y0.8)2O3. The stress-optic co-efficients were found to be in the range 1.6↔2.5×10−5[nm/cm]/Pa showing no dependence on erbium concentration.

하소이트리아 소결체의 특성과 플라즈마저항성 평가

The evaluation of plasma resistance and the characteristics of yttria ceramics fabricated by calcination yttria as a starting material without dopants under an oxidation atmosphere was investigated. Regardless of the starting materials, as-received, and calcined yttria powder, XRD patterns showed that all samples have Y₂O₃ phase. The three cycling process inhibited a large grain, which occurs frequently during the yttria sintering, and a high density ceramic with a homogeneous grain size was obtained. The grain size of the sintered ceramic was affected by the starting powders. The smaller the grain size, the larger were the Young’s modulus and K IC . Compared to Al₂O₃ and ZrO₂ ceramics, yttria ceramics showed a 3 times larger plasma resistance and a 1.4 ~ 2.2 times lower weight loss during the plasma etching test, respectively.

Experimental study on the contact angle formation of solidified iron–chromium droplets onto yttria ceramic substrates for the yttria/ferrous alloy system with variable chromium content

Abstract High-temperature contact angle experiments of liquid iron–chromium (Fe–Cr) drops onto ceramic yttria (Y 2 O 3 ) substrates were carried out in order to investigate the wetting behavior of Y 2 O 3 nano-particles in contact with an iron melt containing elemental Cr. Therefore, the correlation between the wetting behavior of the iron drop in contact with Y 2 O 3 was studied for drops with variable Cr-content and for different powder grades. The wetting behavior of liquid binary Fe–Cr alloys in contact with the Y 2 O 3 ceramic substrates at high temperature, was investigated using the static sessile drop method. The contact angle formed at the interaction interface was evaluated using static drop imaging and quantified using the method proposed by Bartlett and Hall [10] . Our experiments demonstrate that the wetting behavior of binary Fe–Cr alloys drops in contact with Y 2 O 3 ceramics compared to other oxides such as Al 2 O 3 , is quite weak. Only for the test condition of pure electrolytic iron, i.e., without Cr addition, the contact angles ( θ c ) were found to approach 90° or lower in all cases. Furthermore, a 9 wt% Fe–Cr alloy with silicon addition seems to improve the wetting behavior of liquid Fe–Cr drops in contact with Y 2 O 3 . Moreover, variation in powder purity seems to be of crucial importance.

고온가압으로 소결한 고순도 이트리아 세라믹 소결체의 산화반응 특성

We investigated the characteristics of hot-pressed pure yttria ceramics, and annealed them in an oxidation atmosphere. Regardless of the heat treatment in the oxidation atmosphere, XRD analysis showed that all the samples had a Y 2 O 3 phase without structural change. Even though the color variation of the hot-pressed Y 2 O 3 ceramics was due to the sintering temperatures, the oxidation process turned the color of the Y 2 O 3 ceramics into white. The color change during oxidation treatment appears to be related to oxygen defects. In addition, oxygen defects also affected the weight change and microstructure of the Y 2 O 3 ceramics. The Y 2 O 3 ceramic sintered at 1600℃ had a 5.03 g/cm 3 density, which is close to the theoretical density of Y 2 O 3 . As the sintering temperature increased, small homogeneous grains grew to large grains which affected the Vickers hardness. Y 2 O 3 ceramics hot-pressed at 1600oC and annealed at 1200℃ had a flexural strength of 140MPa.