Elements Of X Ray Diffraction

Solution combustion is an exciting phenomenon, which involves propagation of self-sustained exothermic reactions along an aqueous or sol–gel media. This process allows for the synthesis of a variety of nanoscale materials, including oxides, metals, alloys, and sulfides. This Review focuses on the analysis of new approaches and results in the field of solution combustion synthesis (SCS) obtained during recent years. Thermodynamics and kinetics of reactive solutions used in different chemical routes are considered, and the role of process parameters is discussed, emphasizing the chemical mechanisms that are responsible for rapid self-sustained combustion reactions. The basic principles for controlling the composition, structure, and nanostructure of SCS products, and routes to regulate the size and morphology of the nanoscale materials are also reviewed. Recently developed systems that lead to the formation of novel materials and unique structures (e.g., thin films and two-dimensional crystals) with unusual...

Solution Combustion Synthesis of Nanoscale Materials

Owing to the unique mechanism of photoelectron storage and release, long persistent phosphorescence, also called long persistent luminescence or long lasting afterglow/phosphorescence, plays a pivotal role in the areas of spectroscopy, photochemistry, photonics and materials science. In recent years, more research has focused on the manipulation of the morphology, operational wavebands and persistent duration of long persistent phosphors (LPPs). These desired achievements stimulated the growing interest in designing bio-labels, photocatalysts, optical sensors, detectors and photonic devices. In this review, we present multidisciplinary research on synthetic methods, afterglow mechanisms, characterization techniques, materials system, and applications of LPPs. First, we introduce the recent developments in LPPs for the synthesis of nanoparticles from the aspects of particle sizes, monodispersity and homogeneity based on the urgent application of bio-imaging. In the later sections, we present the possible mechanisms, which involve the variation of trap distribution during the trapping and de-trapping process, complicated photo-ionization reaction of trap site levels and impurity centers together with their corresponding migration kinetics of carriers. Meanwhile, we emphasize the characterization techniques of defects, used to qualitatively or quantitatively describe the types, concentrations and depths of the traps. This review article also highlights the recent advances in suggested LPPs materials with a focus on the LPPs' hosts and optically active centers as well as their control, tuning and intrinsic links. We further discuss the classification of LPPs based on the different emission and excitation wavebands from the ultraviolet to the near-infrared region along with an overview of the activation mode of afterglow. Afterwards, we provide an exhibition of new products towards diverse application fields, including solar energy utilization, bio-imaging, diagnosis, and photocatalysts. Finally, we summarize the current achievements, discuss the problems and provide suggestions for potential future directions in the aforementioned parts.

Long persistent phosphors—from fundamentals to applications

The synthesis of lanthanide-activated phosphors is pertinent to many emerging applications, ranging from high-resolution luminescence imaging to next-generation volumetric full-color display. In particular, the optical processes governed by the 4f-5d transitions of divalent and trivalent lanthanides have been the key to enabling precisely tuned color emission. The fundamental importance of lanthanide-activated phosphors for the physical and biomedical sciences has led to rapid development of novel synthetic methodologies and relevant tools that allow for probing the dynamics of energy transfer processes. Here, we review recent progress in developing methods for preparing lanthanide-activated phosphors, especially those featuring 4f-5d optical transitions. Particular attention will be devoted to two widely studied dopants, Ce3+ and Eu2+. The nature of the 4f-5d transition is examined by combining phenomenological theories with quantum mechanical calculations. An emphasis is placed on the correlation of hos...

Lanthanide-Activated Phosphors Based on 4f-5d Optical Transitions: Theoretical and Experimental Aspects.

We have obtained two results since leaving Chapter 3 which make this return to βℕ possible. The first of these was Corollary 4.30 in which we found, under the assumption of the Continuum Hypothesis, that ℕ* contains a dense subset of 2C P-points. The second was Corollary 6.30 in which we saw that no point of ℕ* has its own type as a relative type with respect to any copy of ℕ contained in ℕ*. Here we will make use of these two properties of ℕ* to continue the investigation of βℕ and especially of ℕ*.

β ℕ Revisited

By developing the applications of metal matrix composites (MMCs), employing more efficient fabrication methods seems necessary. Within the two last decades, microwave (MW) sintering was int...

Microwave sintering of ceramic reinforced metal matrix composites and their properties: a review

In this research study, nano-ZrB2 particles were dispersed in aluminum matrix by a Y-shape mixer. The particle size of ZrB2 powders were <12 nm and the amounts of ZrB2 reinforcement varied from 5 to 15 %. The mixed powders were compacted by uniaxial cold press. Subsequently the compacted discs were sintered both in the microwave oven for 6, 8, and 10 min, and in the conventional tube furnace with heating rate of 5 °C/min and in temperature range of 580–620 °C for 60 min, in order to compare the effects of two methods on properties of produced Al–ZrB2 nano-composites. Microwave-assisted sintering method led to the reduction of sintering time to 8 min. In addition relative density of about 98 % has been also obtained by this method. Aluminum metal matrix Nano-composites (Al-MMNCs) samples were characterized by micro-hardness and compression measurements, X-ray diffraction, scanning electron microscopy and energy dispersive X-ray analysis. Mechanical measurements reveal that the presence of nano-ZrB2 particles has improved significantly mechanical properties of Al-MMNCs, as ZrB2 % was equal to 10 %, optimum hardness and compressive strength of 63 (HV) and 270 Mpa were obtained respectively using microwave sintering process.

Production of Al–ZrB 2 nano-composites by microwave sintering process

The SrFe12O19/SiO2/TiO2 nanostructures with hard magnetic core were successfully synthesized through the facile and efficient wet chemical processes. At first, nanocrystalline strontium hexaferrite (SrFe12O19) powder was prepared using a new co-precipitation route in ethanol/water media. In the next step, SrFe12O19/SiO2 composites were produced by well-known Stober method using tetraethyl orthosilicate as precursor. Finally titania was coated on SrFe12O19/SiO2 composite particles using titanium n-butoxide precursor. The core/shell/shell nanostructures have been characterized by means of X-ray diffraction, vibrating sample magnetometer, Fourier transform infrared spectra, field emission scanning electron microscopy, and transmission electron microscopy equipped with an energy-dispersive X-ray spectroscopy detector. The catalytic activity of SrFe12O19/SiO2/TiO2 composites has been investigated in the degradation of methylene blue dye under UV illumination. The results indicated that the obtained SrFe12O19/SiO2/TiO2 composite has photo-catalytic properties and can be retrieved by magnetic separation. The photo-degradation of methylene blue dye was about 80% in the presence of photo-catalyst powder at irradiation time of 180 min. Recycled composite particles could be used again.

Synthesis of SrFe 12 O 19 /SiO 2 /TiO 2 composites with core/shell/shell nano-structure and evaluation of their photo-catalytic efficiency for degradation of methylene blue

TiO2 nanoparticles have been prepared by a facile and reproducible wet chemical approach based on the sol–gel method followed by calcination at various temperatures and times. X-ray diffraction and differential thermal analysis/thermo-gravimetric analysis techniques were used to evaluate phase compositions and transformations during calcination treatment. Then, the silica coating of synthesized TiO2 nanoparticles has been performed by means of a route based on the Stober process to fabricate core/shell structured TiO2–SiO2 nano-composites with the aim to decline the high photo-catalytic activity of pure TiO2 under UV light irradiation, while simultaneously maintaining its UV-barrier ability. The photo-catalytic property was evidenced by the degradation of an aqueous solution of methylene blue in UV range. The elemental composition of core/shell structured TiO2–SiO2 nano-composites was verified by using energy dispersive X-ray (EDX) analysis, and in order to understand the atomic distributions, EDX elemental mapping has been demonstrated for optimum nano-composite sample. The chemical states of the atoms on the surface of synthesized TiO2 and in the coating layer of optimized nano-composite were examined by X-ray photoelectron spectroscopy analysis, and the presence of Si–O–Si and Ti–O–Si bands on the surface of nano-composite particles was further proved by it. In addition to the confirmation of coating of titania surface by silica layer with mean thickness of 4 nm via TEM image examination, the zeta-potential analyses also indicated that the silica sheath shifted the isoelectric point of synthesized titania toward that of a typical pure colloidal silica. Furthermore, the resultant optimum nano-composites have been characterized by BET, FTIR, FESEM and UV–Vis spectroscopy.

Surface modification of sol–gel synthesized TiO 2 photo-catalysts for the production of core/shell structured TiO 2 –SiO 2 nano-composites with reduced photo-catalytic activity

SrAl2O4 phosphor nano-powders activated with heavy elements such as Eu and Dy were prepared by microwave synthesis method. Using this method led to the reduction of processing time. Various calcinations times have been employed to produce pure SrAl2O4:Eu2+, Dy3+ phosphor materials. It was found out that microwave synthesis technique led to reduction of optimum calcinations time to 9 min. XRD analysis showed that the powders were nearly pure SrAl2O4 phase, in which the SrAl2O4 host phase has the maximum fraction of monoclinic SrAl2O4 phase. The critical pH to achieve pure SrAl2O4 phase determined to be equal to 4. For the synthesized SrAl2O4:Eu2+, Dy3+, the properties of photoluminescence such as emission, excitation and decay time were examined. Fluorescent spectrophotometer results revealed that two excitation peaks are appeared at 280 and 339 nm and an emission peak at 515 nm. The crystallite size of these pigments is about 58.22 nm after calcinations for 9 min in microwave as determined by Scherrer’s formula. SEM was used to study the morphology and shape of powders.

Masoud Rajabi

Papers

Microwave sintering of ceramic reinforced metal matrix composites and their properties: a review

Production of Al–ZrB 2 nano-composites by microwave sintering process

Synthesis of SrFe 12 O 19 /SiO 2 /TiO 2 composites with core/shell/shell nano-structure and evaluation of their photo-catalytic efficiency for degradation of methylene blue

Surface modification of sol–gel synthesized TiO 2 photo-catalysts for the production of core/shell structured TiO 2 –SiO 2 nano-composites with reduced photo-catalytic activity

Characterization of SrAl2O4:Eu2+, Dy3+ phosphor nano-powders produced by microwave synthesis route