Search results for "Microstructure"
showing 10 items of 707 documents
Synthesis of yttrium aluminum garnet nanoparticles in confined environment III: Cerium doping effect
2018
Abstract Cerium yttrium aluminum garnet (Ce:YAG, CexY3-xAl5O12) nanoparticles doped with different cerium amount were obtained by calcining the precursors synthesized via co-precipitation in w/o microemulsion for 1 h at 900 °C. The structural and morphological properties were investigated by using X-ray Diffraction (XRD), Infrared Spectroscopy (IR) and Transmission Electron Microscopy (TEM) coupled with Energy Dispersive X-ray Spectroscopy (EDS) in order to investigate the effect of doping level on formation and microstructure of obtained nanoparticles. It was found that the composition of the final products strongly depends on the concentration of cerium. The formation of single YAG phase …
Mechanism of crystallization of Co-cordierites from stoichiometric powdered glasses
2002
Abstract The influence of cobalt, as a divalent cation, on the crystallization behaviour of the cordierite based glasses was studied. Powdered glass specimens of stoichiometric composition 2MO 2Al 2 O 3 5SiO 2 (M=Co and/or Mg) were obtained and thermally treated at several temperatures and times, and the sequence of crystallization and their microstructural evolution were analysed by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). Results on the crystallization sequence showed that the steps in the crystallization path are independent of the nature of the divalent cation. The first crystalline phase detected displayed the μ-cordierite structure, i.e. a solid…
Role of the Microstructure on the High Temperature Oxidation Properties of the Intermetallic Compound NbAl<sub>3</sub>
2001
The influence of the NbAl 3 microstructure on its oxidation mechanism was investigated in air under atmospheric pressure over the temperature range 500-1080°C. Different processing techniques as induction melting and mechanically-activated annealing processes (M2AP) were used to produce the intermetallic compound NbAl 3 . A protective external alumina scale grew only on Al-enriched NbAl 3 between 700 and 1080°C. Stoichiometric NbAl 3 exhibited the pesting phenomenon between 550-900°C, whereas a non protective lamellar oxide scale formed above 900°C. The proposed oxidation mechanism explains these observations which are in agreement with the oxidation study of powders with different crystall…
Influence of the high energy ball milling on structure and reactivity of the Ni+Al powder mixture
2013
Abstract Investigation of the micro- and atomic structures for the planetary ball-milled Ni + Al mixtures has revealed existence of intermediate nano-crystalline and amorphous phases, which are not detectable by XRD analysis, but can be observed by means of HRTEM. Annealing of the milled mixtures at moderate temperature, 205–280 °C, transforms the nano-phases into crystal state and makes them XRD-detectable. These nano-scale structures may serve as nucleus for the intermetallic phases produced via reaction between Ni and Al and, therefore, decrease the activation energy of this reaction and diminish the temperature of the reaction initiation. Apparently, the active nano-phases are formed du…
Highly textured Gd2Zr2O7 films grown on textured Ni-5at.%W substrates by solution deposition route: Growth, texture evolution, and microstructure dep…
2012
Abstract Growth, texture evolution and microstructure dependency of solution derived Gd 2 Zr 2 O 7 films deposited on textured Ni-5 at.%W substrates have been extensively studied. Influence of processing parameters, in particular annealing temperature and dwell time, as well as thickness effect on film texture and morphology are investigated in details. It is found that a rotated cube-on-cube epitaxy of Gd 2 Zr 2 O 7 //NiW in-plane texture forms as soon as the (004) out-plane texture appears, implying that epitaxial growth dominates the crystallization processes. Thermal energy plays an important role in minimizing the difference of interfacial energy along two directions in the anisotropic…
Using a neural network for predicting the average grain size in friction stir welding processes
2009
In the paper the microstructural phenomena in terms of average grain size occurring in friction stir welding (FSW) processes are focused. A neural network was linked to a finite element model (FEM) of the process to predict the average grain size values. The utilized net was trained starting from experimental data and numerical results of butt joints and then tested on further butt, lap and T-joints. The obtained results show the capability of the AI technique in conjunction with the FE tool to predict the final microstructure in the FSW joints.
Mechanical and microstructural properties prediction by artificial neural networks in FSW processes of dual phase titanium alloys
2012
Abstract Friction Stir Welding (FSW), as a solid state welding process, seems to be one of the most promising techniques for joining titanium alloys avoiding a large number of difficulties arising from the use of traditional fusion welding processes. In order to pursue cost savings and a time efficient design, the development of numerical simulations of the process can represent a valid choice for engineers. In the paper an artificial neural network was properly trained and linked to an existing 3D FEM model for the FSW of Ti–6Al–4V titanium alloy, with the aim to predict both the microhardness values and the microstructure of the welded butt joints at the varying of the main process parame…
The Effect of Grain Size of the Stock on Electrical Characteristics of the Li0.03Na0.97Ta0.05Nb0.95O3Perovskite Ceramics
2012
The microstructure and electrical properties of two samples of the ferroelectric Li0.03Na0.97Ta0.05Nb0.95O3 ceramic solid solution prepared from initial charge stocks of different dispersity by conventional ceramics technology are compared. The average size of grains and concentration of pores in the samples are found to be of little difference while the electrical properties of the ceramics are strongly affected by the grain size of the initial mixture. The difference in properties is due to conditions at the diffusion stage of the solid-phase synthesis caused by differences in composition of larger grains rather than the grain size itself.
Influence of Axial Pressure on the Electrical Properties of Li0.06Na0.94NbO3 Ceramic
2011
Lead-free ceramic Li0.06Na0.94NbO3 was synthesized using a conventional solid-state processing. The single-phase perovskite structure was identified by X-ray powder diffraction technique. The values of lattice parameters of Li0.06Na0.94NbO3 are lower than those for pure NaNbO3. The EDS analysis shows the fairly homogeneous distribution of all elements throughout the grains. An axial pressure significantly influences electric properties. With increasing pressure the peak intensity in the ϵ(T) curve decreases, the peak becomes diffused and shifts to a lower temperature. The value of tanδ increases with increasing axial pressure and its local maximum shifts towards lower temperatures.
Ordering of fluorite-type phases in erbium-doped oxyfluoride glass ceramics
2018
In this study, novel transparent Er3+ doped glass ceramics were prepared from melt-quenched oxyfluoride glasses with general composition of Na2O-NaF-BaF2-YbF3-Al2O3-SiO2. The crystallization of fluorite (BaF2, BaF2-YbF3, NaF-BaF2-YbF3 and Na0.5-xYb0.5+xF2+2x) and distorted fluorite (rhombohedral Ba4Yb3F17 and tetragonal NaF-BaF2-YbF3) phases was analysed in glass ceramics with different BaF2 and YbF3 ratio. The phase composition and microstructure were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Intense red upconversion luminescence (UCL) was detected under near-infrared excitation resulting from three photon upconversion followed by cross-relaxation betw…