Papers by Keyword: Yttria

Abstract: Nowadays hydroxyapatite (HA) bioceramics are very important because increasing traffic accidents and ageing of the population. They can be produced from synthetic or natural sources with different production methods. The biggest negative issue of HA is being very brittle and unstable under pressure. Various materials are added for restoring these weaknesses, but there is not so much studies adding nano-ingredients for restoring the mechanical properties of HA. In this study, 5-10% nano-yittria-oxide is added to bovine derived HA (BHA) and to commercial synthetic (CSHA) as a control group. Physical and mechanical properties are examined. Results show that adding of nano-ingredients are really helping to mechanical properties of HA.

Abstract: Alumina has been widely used as a structural ceramic because of high hardness and chemical stability. However, due to the unique characteristics of low fracture toughness of ceramic materials, it has seen limited use as a dynamic structural material. Recently, zirconia toughened alumina (ZTA) has been receiving spotlight, which has various toughness mechanisms caused by the volume change associated in the phase transformation process of ZrO₂ particles dispersed in Al₂O₃ to increase the toughness of Al₂O₃. In this study, 8 mol% Y-ZrO₂ and 12 mol% Y-ZrO₂ with different crystal structures was dispersed in Al₂O₃ individually as a stabilizer and the mechanical properties of the ZTA were observed by differing the composition of the stabilizer. Experimental results show that the ZTA specimens with 12 mol% Y-ZrO₂ which contains a large amount of stable cubic crystal phases had relatively higher micro hardness values. Whereas, fracture toughness of ZTA specimens with 8 mol% Y-ZrO₂ which contains many unstable tetragonal crystal phases, was measured to have higher values than ZTA specimens with 12 mol% Y-ZrO₂, which was opposite to that of micro hardness.

Abstract: Crude petroleum storage and transportation systems suffer from constant physical stress caused by chemical attack of crude petroleum on its structure. Ceramics are materials with high chemical stability in hostile environment and therefore can be used as an inert coating material. In the present work we have produced Al2O3-Y2O3-ZrO2 composites with high mechanical strength, through thermo-mechanical processing. To evaluate the quality of materials developed and the possibility of using them as inert protective coatings, storage and transportation systems, we have studied the physic-chemical and mechanical stability of these materials in crude petroleum originated from onshore and offshore. Structural, microstructural and mechanical tests showed that 15-20wt% ZrO2 composite ceramics with 2 wt% of Y2O3 additives presented better results in terms of mechanical hardness and microstructural characteristics. The study of stability of composite ceramics in crude petroleum environment showed that ceramics did not present any additional phase except the constituent phases. Result of microscopy and Vickers hardness tests also showed that there is no visible change in these characteristics after even 90 days of submersion in crude petroleum. Thus we conclude that composite ceramics could be potential materials for inert coating in crude petroleum environment.

Abstract: HA and HA+Y₂O₃ films were prepared by pulsed laser deposition. The microstructure and composition of films were studied by EPMA, XRD, AFM and SEM. In vitro study was performed by immersing the sample in simulate body fluid (SBF) in different days. There are more droplets on films prepared by HA+Y₂O₃ target than that of HA. And addition of Y₂O₃ can decrease the size of crystal grains. The XRD results show that the peaks corresponding to HA slightly shift to lower angel which indicates the HA lattice distorting due to addition of Y₂O₃. The critical load of the films increases from 10.3N to 13N when Y₂O₃ added. The film prepared by target HA+Y₂O₃ shows a higher resistance to dissolution and the precipitated grain size is small. New precipitated phases have similar functional groups with the original films.

Abstract: Wave-transparent porous Si₃N₄ ceramics were fabricated using 9wt% multiple sintering additives of Y₂O₃ and Yb₂O₃. The influence of sintering additive composition on the porosity, mechanical properties and microstructure of porous Si₃N₄ ceramics was investigated. The results showed that the porous Si₃N₄ ceramics with porosity ranging from 32% to 43% were prepared. For the porous Si₃N₄ ceramics sintered at 1690°C, flexural strength, fracture toughness and the β-Si₃N₄ phase content increased as the Yb₂O₃ content of multiple sintering additives increased from 0 to 9 wt%. In most specimens, microstructures with interlocked fibrous β-Si₃N₄ grains and uniformly distributed fine pores were obtained with employing scanning electron microscopic examination and X ray diffraction analysis. Sinterability and phase transformation of Si₃N₄ with more Yb₂O₃ content were more pronounced than others.

Abstract: The advancement of the oil sector has generated the need for the use of materials resistant to aggressive environments to oil. Although ceramics have high melting point and high hardness is, on the other hand, more fragile and less tough, which can cause damage to the metal structure. The Al₂O₃ based ceramics reinforced with rare earth oxide can improve tenaciousness and makes the ceramic material more resistent. This article aims to present the production of composite Al₂O₃ - Y₂O₃ stabilized ZrO₂ by uniaxial pressing, following sintering (1200-1350 °C). Structural and microstructural characterizations as XRD (X-Ray Diffraction) and SEM (Scanning Electron Microscopy) and mechanical tests as Vickers hardness, % absorption and % linear shrinkage were conducted to evaluate the feasibility of using the composite and ceramic coating for storage and transportation of oil tanks. The results indicate that the proportions of 5%, 10% and 30% ZrO₂ make it suitable as a good composite suitable coating.

Abstract: Using Yb₂O₃ or Y₂O₃ as s single sintering additive, the porous Si₃N₄ ceramics with excellent mechanical properties were successfully fabricated by pressureless sintering. The influence of Y₂O₃ and Yb₂O₃ on the microstructure and mechanical properties of porous Si₃N₄ ceramics was investigated. The results show that both sintering additives can effectively promote α to β phase transformation, and microstructures with elongated β-Si₃N₄ grains interlocking and superimposing on each other can be obtained. However, sinterability, phase transformation and mechanical properties of the porous Si₃N₄ ceramics with Yb₂O₃ were more excellent than the ceramics with Y₂O₃. The specimens with Yb₂O₃ had high aspect ratio β-Si₃N₄ grains, and formed the high melting crystalline Yb₄Si₂N₂O₇.

Abstract: In the context of green economy supported and widespread by United Nations (UN), the renewable energy sources are the unique mechanism to universalize the access to energy. Face to this strategic direction of change is essential to develop efficient components for saving energy such as porous ceramics that associate light with mechanical strength. Thus, the objective of this work concerns to improve the homogeneity of porous size distribution of yttria porous ceramics by evaluating their morphology during replica processing. Samples were subject to immersion into 30vol% yttria aqueous suspensions during an interval from 1min to 120min and sintered through careful thermal conditions. Based on the results, the weight and morphology of porous structure samples were directly influenced by immersion time, whereby intervals from 30-120min showed the best final products.

Abstract: Mechanical alloying (MA) is an established way to prepare nanocrystalline materials and metastable solutions of materials, which normally have no mutual solubility. This is also the case for oxide dispersion strengthened (ODS) steels with improved mechanical properties at elevated temperatures. It is known that a small addition of yttria (Y₂O₃) has a beneficial effect on high temperature strength and reduces the creep rate in mechanically alloyed ferritic steels by about six orders of magnitude. In this work we present an experimental study using atom probe tomography, X-ray photoelectron spectroscopy, and positron annihilation spectroscopy combined with first principles modeling focusing on the distribution and behavior of yttria in pure iron prepared by mechanical alloying. Atom probe tomography and X-ray photoelectron spectroscopy measurements as well as positron annihilation spectroscopy conducted on powder particles directly after milling have revealed that a predominantly fraction of the yttria powder dissolves in the iron matrix and Y atoms occupy convenient positions, such as vacancies or dislocations. This is supported by ab initio calculations demonstrating that the formation energy for Y substitutional defects in bcc-Fe is significantly lower in the close neighborhood of vacancies.

Abstract: The yttria-doped mesoporous zirconia was successfully synthesized by evaporation induced self-assembly (EISA) method, and the microstructure and textural properties of the as-made product were studied extensively. The results showed that the as-made product possessed crystallized framework walls and a worm-like mesopore with a narrow pore distribution. The BET specific surface area and pore volume of the as-made product calcined at 500°C are 111 m²/g and 0.16 cm³/g respectively, and the corresponding data changed to 73 m²/g and 0.052 cm³/g after calcined at 700°C, which indicated that the as-made yttria-doped mesoporous zirconia possess a higher thermal stability.