Papers by Keyword: Polycrystalline

Abstract: In this article, the structural, microstructural, and dielectric properties of Lead- free perovskite ceramic Bi_0.5(Na_0.78K_0.22)_0.5TiO₃ [BNKT] have been reported. The material was synthesized through the solid-state reaction method. The compound formed is found to have a hexagonal structure, confirmed by XRD analysis of the sample. The microstructural analysis of the compound revealed the polycrystalline nature of the ceramic having quasi-cubic grain morphology with distinct grain boundaries. From the dielectric study, it was found that the dielectric constant increases with temperature and attained maximum value at temperature T_c = 335° C, after which it decreased. The frequency independence of transition temperature (T_c) suggested the classic ferroelectric behaviour of the compound. The broad dielectric peak around transition temperature confirms the relaxor behaviour of the compound as well as diffused phase transition at T_c. The value of the relative permittivity and loss tangent at ambient temperature for 1kHz frequency is 627 and 0.223 respectively. The synthesized material can be utilized for the fabrication of capacitors and energy storage applications.

Abstract: Nanocrystalline SnO₂-Y₂O₃ thin film has been successfully prepared by using chemical bath deposition method at low reaction temperature 72 °C on SiO₂/Si substrates. The structural and surface morphology of the annealed sample at 500 °C for 2 h in air were investigated using X-ray diffraction, field emission scanning electron microscopy and Energy-dispersive X-ray spectroscopy. The crystallization of SnO₂-Y₂O₃ film with tetragonal rutile structure was achieved when the film was exposed to annealing at 500 °C. Where several diffraction peaks that correspond to the (110), (101), (200), (211), (220) and (002) planes that agree very well with standard bulk SnO₂ having a tetragonal rutile structure. As well as the diffraction peak that correspond to (111) emerged at θ = 29.48^o is matched with bulk Y₂O₃. The surface morphology appeared as polycrystalline with uniform nanoparticle distribution. The EDX spectra of examined film showed the film consists of O, Sn, Y, and Si elements. The cross-section image and the average thickness of the annealed SnO₂-Y₂O₃ film at 500 °C was approximately 330 nm. Additionally, approximately 880 nm thick layer of SiO₂ emerges on the top of the silicon substrate. This finding demonstrates the ability to prepare nonocrystalline SnO₂-Y₂O₃ thin film with high quality by using chemical bath deposition method.

Abstract: These years, electronic devices and integrated circuits have a trend of miniaturization and integration with the rapid development of the information industry, higher requirements have been placed on the size, purity, and defect density of silicon wafers. More urgent demands have been placed on the mass production of electronic grade polysilicon. However, the research of electronic grade polysilicon in China is still in its infancy, it is far from meeting the requirements of mass production. This paper studies the influence of the single factor of reaction temperature on the yield of silicon, the surface morphology and power consumption of polysilicon under the certain conditions, which has some reference value for the production of electronic grade polysilicon.

Abstract: In this work, comparison of TiO₂ additions on the physical properties of YBa₂Cu₃O_δ superconductor system with nominal starting compositions at x= 0, 1, 2, and 5 wt.% was studied derived via solid state reaction and co-precipitation method. The samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The result from XRD shown that all the samples were polycrystalline for solid state reaction, while single phase appear for co-precipitation methods. The intensity of the peak become higher with increasing amount of TiO₂ addition indicating the presence of increased amount of the unreacted in the samples. The refine lattice parameters indicated that all the samples have an orthorhombic crystal structure without occurrence of orthorhombic-tetragonal phase transformation. Furthermore, from SEM images for solid state reaction and co-precipitation method showed that the grain size of the samples decreased with TiO₂ increased. Small addition of TiO2 derived from co-precipitation method enhanced the YBCO microstructures.

Abstract: Building integrated photovoltaic (BIPV) is defined as the integration of photovoltaic (PV) modules into the building envelope (in this case the rooftile) to generate clean and environmental-friendly electricity from the sun radiation. The architectural integration of PV collector modules in new construction makes possible to create glazed surfaces which, besides being an aesthetical and functional innovation, generate electricity, that is allowing the realization of solar control and electric range with consequent energy savings. However, up until now, there have been limited studies that analysed BIPV from its materials point of views. This paper aims to expose rooftop BIPV materials that further might be used to replace conventional rooftiles such as terracotta or slate, concrete, plastic, and clay tiles. The flat rooftiles of monocrystalline-, polycrystalline-, and a-silicone based BIPV cells are being considered in this paper. Their benefits and drawbacks are also put into account. The parameters that were compared are materials, their physical layouts, and the transparency and output power.

Abstract: In this paper, a mixture of commercial Al₂O₃ and Y₂O₃ nanopowders was prepared according to the stoichiometric ratios of YAG (Y₃Al₅O₁₂) with 0.5 wt% tetraethyl orthosilicate (TEOS) as a sintering aid. The effects of air and vacuum sintering atmosphere were examined on the phase transformation, densification, in-line transmission, microstructure evolution, grain size distribution, sintering trajectories, and grain growth map of the YAG ceramics. The results showed that all samples were pure YAG phase. Nearly pore-free microstructure (99.8%) and narrow grain size distribution (4-10 μm) with an average grain size of 7 μm was obtained for the sample sintered in the vacuum atmosphere, while both inner and inter pores with abnormal grain growth, wider grain size distribution (9-27 μm) with the average grain size of 12 μm were detected in air atmosphere. Also, the results showed that the specimens sintered in vacuum atmosphere had higher relative densities and smaller grain sizes at all sintering temperatures for 6 h. The maximum transmittance at 1064 nm of the YAG ceramics sintered at air and vacuum atmosphere was 26% and 68%, respectively.

Abstract: Ni-based superalloys, in both single and polycrystalline varieties, are extensively used in high pressure turbine blades. But contrary to single crystal variants, the polycrystalline forms present easier manufacturing and offer higher potential for improvement in metal matrix composites (MMCs). To benefit from this opportunity, an Inconel X-750 superalloy reinforced with TiC particles is proposed, having a polycrystalline microstructure and the possibility for weight reduction in turbine elements application. The metallic powder with an addition of 15 vol.% of 3.7 μm_d TiC particles was prepared through low energy mixing, uniaxial pressing and sintering, followed by a triple heat treatment. The microstructure was analyzed with SEM and XRD techniques. Compressive creep tests were performed at 800 °C with 200 MPa, on both original and reinforced alloys. The study shows how the inclusion of a highly compatible particle reinforcement does not only improves the creep resistance, but also reduces the material weight, thus having potential to promote further reduction in the creep rate on turbine blades submitted to centripetal forces.

Abstract: Recently, diamonds have been utilized gradually for sliding parts and wear-resistant parts because of their excellent properties. The shape of diamond applied to these parts is not only plane but also arc-shaped inner surface. Therefore, development of diamond polishing technology is required. In this study, ultraviolet assisted polishing was thought to develop to polish polycrystalline diamond (PCD) on arc-shaped inner surface. The authors investigated effect of ultraviolet radiation on polishing efficiency and surface roughness. As a result, the surface roughness Ra of PCD showed less than 15 nanometers. In addition, polishing efficiency was improved about 30 percent due to ultraviolet assisted polishing.

Abstract: In this paper a cohesive formulation is proposed for modelling intergranular and transgranular damage and microcracking evolution in brittle polycrystalline materials. The model uses a multi region boundary element approach combined with a dual boundary element formulation. Polycrystalline microstructures are created through a Voronoi tessellation algorithm. Each crystal has an elastic orthotropic behaviour and specific material orientation. Transgranular surfaces are inserted as the simulation evolves and only in those grains that experience stress levels high enough for the nucleation of a new potential crack. Damage evolution along (inter-or trans-granular) interfaces is then modelled using cohesive traction separation laws and, upon failure, frictional contact analysis is introduced to model separation, stick or slip. Moreover some physical consideration based on cohesive energies were made, in order to guarantee the cohesive model in consideration was appropriate for the purpose of this work. Finally numerical simulations have been performed to demonstrate the validity of the proposed formulation in comparison with experimental observations and literature results.

Abstract: The interest in perovskite ceramics has been increased in recent years due to its useful properties and applications in various fields. We report the systematic study to explain the surface morphology and crystallographic nature of LSMO, prepared by solid state reaction and ball milling technique. The Density of the samples was calculated by Archimedes’s principle. The X-ray diffraction method was used to study the structural properties of the sintered powder using Philips Pro X’pertPANalytical. It exhibit dominant peak at (110) , (024) reflections , which confirms a polycrystalline nature of the powder. The surface morphology and elemental analysis of the samples is done by FEG-scanning electron microscope and energy dispersive spectrometry (EDS), confirms the absence of impurities in the samples. The analysis of FEG-SEM results and crystallite size verify the arrangement of LSMO particles in the range of 40-60 nm. The results show that the synthesis of LSMO ceramics in nanoparticle range is possible by the said techniques.