Papers by Keyword: Yttrium Oxide

Abstract: The formation energies of point defects in zirconium-doped yttrium oxide were calculated using density functional theory (DFT). Both substitutional zirconium defects (Zr_Y) and their complexes with native point defects in Y₂O₃ were considered. The results show that zirconium predominantly incorporates into yttrium oxide as Zr⁴⁺ ions, creating positively charged substitutional defects that are compensated by interstitial oxygen ions (O_i²⁻). A considerable fraction of zirconium ions form bound complexes with interstitial oxygen, such as Zr_Y–O_i pairs and Zr_Y–O_i–Zr_Y ternary defects. These defects are predicted to reduce the lattice parameter, in agreement with experimental observations.

Abstract: Photodynamic therapy (PDT) is a promising modern method for treatment of oncological, bacterial, fungal and viral diseases. However, its application is limited to diseases with superficial localization since the body tissues are not transparent for visible light. To address this problem and extend PDT application to abdominal diseases, an enhanced method of X-ray photodynamic therapy (XRPDT) is suggested, involving X-ray radiation easily penetrating the body tissues. The implementation of this approach requires the development of a pharmacological drug including a photosensitizer stimulated by visible light to yield active oxygen and a nanosized phosphor converting X-ray radiation into visible light with the wavelength required for the photosensitizer activation. This study is aimed at obtaining X-ray stimulated phosphors with nanosized particles suitable for XRPDT application. For this purpose, Y₂O₃:Eu phosphors were synthesized via hydrothermal processing of the corresponding mixed acetate followed by annealing. To prevent from the undesirable agglomeration of the particles in the course of hydrothermal synthesis and subsequent annealing, different techniques were used, including rapid thermal annealing (RTA), microwave annealing and addition of finely dispersed pyrogenic silica (aerosil) to the phosphor. The microwave annealing was carried out using a special installation including a resonance chamber for maintaining a standing wave of microwave radiation. The performed research allowed the determination of hydrothermal processing optimal duration affording the synthesis of phosphors with the highest luminescence brightness. The application of microwave annealing is found to provide phosphors with a more perfect crystal structure compared with RTA. The developed method of Y₂O₃:Eu phosphor synthesis involving pyrogenic silica addition to the autoclave allowed the preparation of samples with the amorphous structure and significantly reduced the particle size without a considerable decrease in the luminescence brightness. The particle size of the phosphor synthesized with aerosil addition is less than 100 nm that allows its implementation in pharmacological drugs for XRPDT.

Abstract: In this project, the nominal glass composition with the form of (55-x) H₃BO₃-45ZnO-xY₂O₃ (x = 0.0, 0.5, 1.0, 1.5, 2.0 and 2.5 mol%) are synthesized by melt quenching techniques. The effect of Y₂O₃ on physical, mechanical and structural properties of glasses have been investigated using different characterization techniques. The parameters like density, molar volume and oxygen packing density have been calculated. Based on the micro hardness study, it has showed the decreasing trend from 518.80 N.mm^-2 to 453.13 N.mm^-2 with an increasing of Y₂O₃ content from 0.0 mol% to 2.5 mol%. The structural features of the yttrium oxide doped zinc borate glass were studied via X-Ray Diffraction (XRD) to confirm the amorphous nature of glass and Fourier Transforms Infrared Spectroscopy (FTIR) has been done to obtain the band positions and functional groups. FTIR spectral studies were recorded in the 400-4000 cm^-1 wavenumber range at room temperature.

Abstract: The current paper presents yttrium oxide wetting angle examination. The test was performed in accordance with two different methods: contact and noncontact heating. Upon completion of the test, microstructural and spectral analysis of substrate/metal contact areas was conducted. Test findings are listed in the Conclusions.

Abstract: Finely-dispersed phosphors of Y₂O₃:Eu and Y₃Al₅O₁₂:Eu have been synthesized with the help of Pechini method and the method of self-propagating high-temperature synthesis (SHS). During the synthesis of phosphors on the basis of Y₂O₃ carried out with Pechini method the size of crystallites increases with the enlargement of concentration of yttrium, but it decreases when the method of SHS is applied. The structure of phosphors on the basis of Y₃Al₅O₁₂ (YAG) is strongly amorphized. This fact agrees with the data of XRD and with the prevalence of the band with λ_max = 613 nm in the spectra of this phosphor. The enlargement of yttrium concentration in it promotes the amorphisation of yttrium aluminum garnet and the decrease of a crystal phase content. The sample of Y₃Al₅O₁₂:Eu synthesized with Pechini method has the maximum intensity, while in conditions of excitement with “high-level” X-ray radiation which corresponds to the radiation of industrial medical X-ray apparatus, the phosphor of Y₂O₃:Eu synthesized with the help of SHS showed the largest intensity. Colloid solutions prepared with the use of the samples synthesized by SHS method revealed a higher steadiness and a lower disposition to the sedimentation process. The samples of Y₂O₃:Eu phosphor possessing the smallest size of particles and the highest intensity of X-ray luminescence are the most suitable for the creation of pharmacological drugs used for photodynamic therapy.

Abstract: High density graphite disks and aluminum nitride ceramics powders have been utilized to obtain joints by Spark Plasma Sintering technique. The joining was carried out in vacuum, at temperatures of 1700°C, 1800°C and 1900°C, under the pressure of 50 MPa with a constant dwelling time of 5 minutes The AlN ceramics to be joined were also synthesized by ceramic technology standard route by using AlN powders and 2.5 % wt.Y₂O₃ powders as sintering additive, which were added in order to increase densification rate and by thus, thermal conductivity. The joining of AlN/C was performed both without and with the aid of a ceramic powder composite AlN+Y₂O₃+C film, as interlayer. Besides the crystalline phases (AlN and C), the Al₅Y₃O₁₂ compounds with a cubic crystallographic structure were identified by X-ray diffraction. The optical microscopy images revealed that all samples, both without and with film as interlayer, had strong joined areas, without any defects and discontinuities at interfaces. The Vickers microhardness and Young Modulus values measured by nanoindentation have shown that using of the film as intermediary layer was leading to the highest values of mechanical properties (HV = 8 – 23 GPa and E= 227-512 GPa) at the AlN/C joints interfaces.

Abstract: Advanced ceramic coating technologies are commonly used as metal coatings for internal combustion engine components and aerospace application. The thermal barrier coatings are being applied to the engine components to increasing life and improve the performance of the engine. This experimental study is focused on advanced ceramic material of Zirconia stabilized with the yttrium oxide (Zirconia 80% wt and Yttia 20 % by weight) applied on the piston crown for analyzing the performance and emission characteristics of the diesel engine. By using ceramics coated piston crown, the brake thermal efficiency and specific fuel consumption were improved as compared to that of the piston without coating. Exhaust emission level of CO, UHC and NOx are also considerably reduced using advanced ceramic metal coating techniques.

Abstract: Endohedral metallofullerenes were prepared by DC arc discharge method with yttrium oxide and yttrium-nickel alloy as metal source, respectively. Mass spectroscopy and high-performance liquid chromatography analyses evidence that yttrium-nickel alloy has advantages over yttrium oxide in higher yield of soot, more species and higher yield of soluble metallofullerenes.

Abstract: In order to improve the wear resistance and reduce the sintering temperature of alumina ceramics, Y₂O₃ powder added in the system of MgO-CaO-SiO₂-Al₂O₃ alumina ceramics were prepared by the technique of pressureless sintering. The properties of the ceramic samples were investigated by the measurements of bulk density, wear rate, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that the wear rate of alumina ceramic contenting Y2O3 of the 0.8wt% is 0.041‰. Adding the yttrium oxide to the raw materials and then calcine them to ceramics, which can reduces the sintering temperature, promote the densification and improve wear-resistant property of alumina ceramics.

Abstract: Normal 0 7.8 磅 0 2 false false false MicrosoftInternetExplorer4 It is necessary to prepare compressive films on sapphire window for preventing its high-temperature failure. In this study, the yttrium oxide (Y₂O₃) thin films were deposited on the sapphire substrates by RF reactive magnetron sputtering with varying sputtering pressure. The as-deposited Y₂O₃ films were also annealed. The composition, structure, refractive index and mechanical properties of the films were systematically analyzed by XPS, XRD, ellipsometry and nanoindention method, respectively. The influences of sputtering pressure on the deposition velocity and the refractive index were investigated. It can obtain desirable Y₂O₃ thin films for the preparation conditions (sputtering pressure: 10Pa, substrate temperature: 500°C, RF power: 200W) after annealing in O₂ at 500°C for 1h. The refractive index and hardness both have the maximum value (1.8337 and 3.98 GPa), respectively. The elastic module has the minimum value (109.24 GPa). It is promising for the Y₂O₃ film as the underlayer of protective coating of sapphire windows.