Microwave-induced Combustion Synthesis Research Articles

Synthesis and Characterization of YAG:Ce Phosphor by Microwave Induced Combustion Synthesis with Different Fuel Sources

White LEDs (WLEDs) have been produced from the combination of blue LED chips and phosphor converter. In the present work, considerable amount of yttrium aluminium garnet (YAG) phosphor powders doped with 0.3 mol% of cerium (Ce) have been synthesized via Microwave Induced Combustion Synthesis (MICS) method with different fuel sources such as urea and mixed fuel of urea and glycine. The effects of different fuel sources on the crystallinity, structure, luminescent properties and Commision International de L’Eclairage (CIE) chromaticity was characterized and studied using high resolution X-ray diffraction (HR XRD), field emission-scanning electron microscopy (FE SEM), energy dispersive X-ray spectroscopy (EDX), electroluminescence (EL) and standard CIE 1931 chromaticity diagram, respectively. The highest EL intensity can be observed from the sample prepared by mixed fuel technique. In contrast, the experimental enhancement in the aforementioned properties was demonstrated by the WLED synthesized using mixed fuel technique. Keywords: White LEDs, phosphor converter, microwave induced combustion, mixed fuel technique.

Effect of Annealing Temperature on Growth Particles of YAG: Ce+3 Phosphor and White Light Chromaticity Values

In the present work white-emitting Y3Al5O12:xCe3 (x = 0.04) nanophosphor in the form of powder were synthesized by a microwave-induced combustion synthesis method (MW) using metal nitrates as precursors and urea as fuel. By covering blue light-emitting diodes (blue-LED, 445 nm) white light emission (WLED) was generated. The sintering temperature with fixed time (5 hours) for phosphor powder was optimized and found to be 1050 °C. The crystallinity structure, luminescent properties and chromaticity were characterized by X-ray diffraction (XRD), field emission-scanning electron microscope (FE-SEM), electroluminescence (EL) and standard CIE 1931 chromaticity diagram. The results show that the obtained YAG:Ce+3 phosphor sintered at 1050 °C has good crystallinity with pure phase, low agglomeration particles and strong yellow emission that offering daylight white LED with tuneable correlated color temperature (CCT) and a good colour rendering index (CRI) compared to those sintered at 950 °C, 850 °C and non-sintered phosphor powders.

Effect of Annealing Time of YAG:Ce3+ Phosphor on White Light Chromaticity Values

Yttrium and aluminium nitrate phosphors doped with cerium nitrate and mixed with urea (fuel) are prepared by using microwave-induced combustion synthesis according to the formula Y(3–0.06)Al5O12:0.06Ce3+ (YAG:Ce3+) to produce white light emitting diodes by conversion from blue indium gallium nitride-light emitting diode chips. The sintering time with fixed temperature (1050°C) for phosphor powder was optimized and found to be 5 h. The crystallinity, structure, chemical composition, luminescent properties with varying currents densities and chromaticity were characterized by x-ray diffraction, field emission-scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, photoluminescence emission, electroluminescence and standard CIE 1931 chromaticity diagram, respectively. The energy levels of Ce3+ in YAG were discussed based on its absorption and excitation spectra. The results show that the obtained YAG:Ce3+ phosphor sintered for 5 h has good crystallinity with pure phase, low agglomerate with spherical shaped particles and strong yellow emission, offering cool-white LED with tuneable correlated color temperature and a good color rendering index compared to those prepared by sintering for 2 h and as-prepared phosphor powders.

Effect of salt concentration on the electrical and morphological properties of calcium phosphates obtained via microwave-induced combustion synthesis

Calcium phosphates (CaP) have been widely used in biomedical applications. One of the most versatile techniques for obtaining CaP is auto-combustion synthesis. This technique stands out because of its low cost and high efficiency; however, the difficulty of controlling the size and morphology of the product is its principal disadvantage. The aim of this study was to synthesize calcium phosphates through microwave-induced and salt-assisted solution combustion synthesis. The initial ratio of Ca/P was 1.5, employing urea as fuel and potassium chloride as an additive. The morphology and the electrical properties of CaP in relation to the amount of salt added were evaluated using scanning electron microscopy (SEM) and impedance spectroscopy, respectively. It was found that the inclusion of salt during the synthesis affects the morphology of calcium phosphates, creating whisker-like structures, with lengths approximately between 500nm and 1µm and widths between 30nm and 300nm, which depend on the salt concentration. Calcium pyrophosphate was the major phase of the synthetized product without the addition of salt, and hydroxyapatite (HAP) and chlorapatite (CAP) when salt was included. The dielectric constant exhibited lower values for the samples rich in calcium pyrophosphate and values between 16 and 32 for HAP and CAP at 1kHz.

Synthesis, Characterization and Superparamagnetic Resonance Studies of ZnFe2O4 Nanoparticles

Superparamagnetic nanoparticles of zinc ferrite (ZnFe2O4) were produced by a microwave induced combustion synthesis method. XRD, FT-IR, SEM, VSM and ESR were used for the structural, morphological, and magnetic investigation of the product, respectively. Average particle size of the nanoparticles was estimated by the Schérrer equation using the full-width at half maximum (FWHM) of the most intense XRD peak and found as 41 nm. Magnetization measurements have shown that the samples have a blocking temperature of 72 K which indicates a superparamagnetic behavior. Superparamagnetic resonance (SPR) spectra at room temperature show a broad line with a Landé g-factor, g(eff) approximately 2. We used a theoretical formalism based on a distribution of diameters of the nanoparticles following lognormal proposed by Berger et al. The nanoparticles behave as single magnetic domains with random orientations of magnetic moments which are subject to thermal fluctuations. A Landau-Lifshitz line shape function presents adequate results which are in good agreement with the experimental ones. At high temperatures, the SPR line shape is governed by the core anisotropy and the thermal fluctuations. By decreasing the temperature, the magnetic susceptibility of shell spins increases. As a result of this, the surface spins produce an effective field on the core leading to a decrease of resonance field, B(r). Also, the effective anisotropy increases as the shell spins begin to order. So, the results are interpreted by a simple model, in which each single-domain nanoparticle is considered as a core-shell system, with magneto-crystalline anisotropy on the core and surface anisotropy on the shell.

Novel Microwave-Induced Combustion Synthesis of SnO<SUB>2</SUB> Nanoparticles for Selective Sensing of CO Using Tin Chloride

A novel technique of chloride solution combustion synthesis (CSCS) is employed for preparation of SnO2 nanoparticles, using SnCl4 and sorbitol as a novel precursor and a fuel, respectively. Ammonium nitrate is also used as a combustion aid. The solution combustion synthesis is a single-step and simple method for nanoparticles synthesis. However, it commonly uses nitrate precursors. In this study tin chloride is used in CSCS method for the first time, employing ammonium nitrate as a combustion aid. The nanoparticles are characterized by means of XRD, SEM, EDS and BET and applied in sensing of carbon monoxide and methane. The molar ratio of fuel plus oxidant to SnCl4 (psi) and the ratio of fuel-to-oxidant (phi) were varied in the modified CSCS technique. The smallest nanoparticles size, i.e., 3.9 nm with 220 m2 x g(-1) obtained at phi = 1 and psi = 1. The sensor fabricated based on the SnO2 nanoparticles obtained by CSCS method shows 2-3 times higher sensitivity to CO than the one obtained by the conventional sol-gel method. The CSCS sensors show high sensitivity to CO at temperatures lower than 300 degrees C, at which insignificant sensitivity to methane is observed. This makes the sensor selective to CO in presence of methane.

Dielectric characterization of NixCo1−xFe2O4 nanocrystals thin film over a broad frequency range (1 MHz–3 GHz)

We have theoretically and experimentally investigated the dielectric behavior of NixCo1−xFe2O4 nanoparticles (NPs) (where x=0.0, 0.6, and 1.0), which have been synthesized by microwave induced combustion synthesis using urea as fuel. A variation of complex dielectric permittivity at room temperature with frequency in the range 1 MHz–3 GHz has been studied. The permittivity displays atomic polarization and electronic polarization. Particles showed phase purity and crystallinity in powder x-ray diffraction (XRD) analysis. At the same time, NixCo1−xFe2O4 NPs demonstrated a spinel cubic structure from XRD results.

WITHDRAWN: Microwave-induced combustion synthesis by using urea and glycine and dielectric characterization of CoFe 2O 4 nanocrystals

WITHDRAWN: Microwave-induced combustion synthesis by using urea and glycine and dielectric characterization of CoFe 2O 4 nanocrystals

Comparison of the microwave-induced combustion and solid-state reaction for the synthesis of LiMn 2O 4 powder and their electrochemical properties

In the current research, we proposed a new method called microwave-induced combustion synthesis to produce LiMn 2O 4 powders. The microwave-induced combustion synthesis entails the dissolution of metal nitrates, and urea in water, and then heating the resulting solution in a microwave oven. Spinel LiMn 2O 4 powders were successfully synthesized by microwave-induced combustion. The microwave-heated LiMn 2O 4 powders annealed at various temperatures in the range of 600–800 °C were determined. The resultant powders were characterized by X-ray diffractometer (XRD), and scanning electron microscopy (SEM). The annealed samples were used as cathode materials for lithium-ion battery, for which their discharge capacity and electrochemical characteristic properties in terms of cycle performance were also investigated. The LiMn 2O 4 cell provides a high initial capacity of 133 mAh/g and excellent reversibility. The excellent capacity and reversibility were attributed to LiMn 2O 4 powders with small and uniform particle size produced by microwave-induced combustion synthesis.

Microwave-induced combustion synthesis of Li0.5Fe2.5−xMgxO4 powder and their characterization

Li 0.5 Fe 2.5 − x Mg x O 4 (0≦x≦1.0) powders with small and uniformly sized particles were successfully synthesized by microwave-induced combustion using lithium nitrate, ferric nitrate, magnesium nitrate, and carbohydrazide as the starting materials. This process takes only a few minutes to obtain as-received Mg-substituted lithium ferrite powders. The results revealed that the lattice constant increases nonlinearly with increasing Mg content in the Li0.5Fe2.5−xMgxO4 specimens. Moreover, the magnetic properties of Mg-substituted lithium ferrite were also strongly affected by Mg concentration. The saturation magnetization (Ms) of 71.1 emu/g was found at Li0.5Fe2.5O4 specimen. As increased Mg content, the saturation magnetization (Ms) and remanent magnetization (Mr) decreased significantly. This is ascribed to the fact that as Mg content increases, A-O-B (where A represents tetrahedral sites and B represents octahedral sites in ferrite of the spinel type) interactions become weak, and consequently B-O-B interaction becomes stronger. Transmission electron microscopy (TEM) micrograph revealed that Mg-substituted lithium ferrite powders are distributed in the range from 50 to 80 nm with well-defined crystallinity.

Nano-ceria–zirconia promoter effects on enhanced coke combustion and oxidation of CO formed in regeneration of silica–alumina coked during cracking of triisopropylbenzene

Effects of Ce0.68Zr0.32O2 physically mixed with or impregnated on amorphous silica–alumina (SA) on enhanced combustion of coke and oxidation of CO formed in the regeneration of the catalysts coked during catalytic cracking of 1,3,5-triisopropylbenzene (TiPB) were studied. SA with about 535 m2/g BET surface area was synthesized using a co-precipitation method and ammonium exchanged. 6.0 wt% Ce0.68Zr0.32O2 on the silica–alumina was prepared by impregnation of the sample with an aqueous solution of cerium and zirconium nitrates and designated as Ce0.68Zr0.32O2/SA. Nanoparticles of Ce0.68Zr0.32O2, with around 12 nm crystallite size, were also prepared by a microwave induced combustion synthesis method and physically mixed with SA as another catalyst sample, i.e. Ce0.68Zr0.32O2·SA. The catalysts were characterized by SEM, EDS, XRD, BET, AAS, H2-TPR and ammonia TPD techniques. After in situ calcination at 475 °C for 3 h, the samples were coked by exposure to a gaseous stream of 5.0 vol% TiPB in Ar at 350 °C for 40 min. Temperature-programmed oxidation (TPO) method was employed to study the onset temperature of the coke combustion and CO oxidation during the regeneration of the coked catalyst in 2.0 vol% O2/N2 feed. At 3 min of cracking, TiPB cracking activities of both Ce0.68Zr0.32O2/SA and Ce0.68Zr0.32O2·SA samples are about the same and 5% lower than that of SA. The selectivity of cumene, as a deep cracking product, decreases in the order of SA > Ce0.68Zr0.32O2·SA > Ce0.68Zr0.32O2/SA concomitant with the density of acid sites of the catalysts. As compared to the SA, a decline of about 15.2% in coke formation is observed for the Ce0.68Zr0.32O2/SA sample. In addition, the Ce0.68Zr0.32O2 promotion of SA by physical mixing and impregnation lowers the CO evolution in the catalysts regeneration by about 51 and 61%, respectively. The highly active Ce0.68Zr0.32O2 oxygen is responsible for the higher conversion of CO to CO2 on the catalysts containing the promoter. Furthermore, the Ce0.68Zr0.32O2/SA sample, impregnated with Ce0.68Zr0.32O2 promoter, lowers the onset temperature of coke combustion by about 130 °C. This may be attributed to tight contact of the coke with active surface oxygen of the promoter.

Microwave-induced combustion process variables for MgO nanoparticle synthesis using polyethylene glycol and sorbitol

In this study, MgO nanoparticles were prepared by microwave-induced combustion synthesis of magnesium nitrate (as oxidant and MgO precursor) and polyethylene glycol and sorbitol as fuels. The effects of various parameters including the aging time of the precursor gel before combustion, microwave power and fuel-to-oxidant ratio were investigated. Microwave was applied to homogeneously heat the precursor gel. The temperature profile and the composition of the released gases during the combustion process and the carbonaceous deposits on the MgO nanoparticles were studied by FTIR, TGA, Raman spectroscopy, and temperature programmed oxidation (TPO). The MgO samples were calcined at 400 °C for 3 h and characterized using SEM, TEM, BET and PXRD. MgO nanoparticles as small as 4.1 nm were formed using 20% excess of sorbitol and 40% excess of polyethylene glycol as the fuels.

Ionic conductivity and mechanical properties of Y 2O 3-doped CeO 2 ceramics synthesis by microwave-induced combustion

We developed a new method, i.e. microwave-induced combustion synthesis to produce highly sinterable Y 2O 3-doped CeO 2 nanopowders. The process took only 15 min to yield Y 2O 3-doped CeO 2 powders. We also investigated the conductivity of Y 2O 3-doped CeO 2 ceramics. It was found Y 2O 3 concentration to have a large effect on the morphology, activation energy, ionic conductivity, and mechanical properties of Y 2O 3-doped CeO 2 ceramics. The results revealed that the bulk densities of Y 2O 3-doped CeO 2 ceramics sintered at 1420 °C for 5 h were all higher than 92% of the theoretical densities, and the maximum ionic conductivity, σ 800 °C = 0.023 S/cm at 800 °C, the minimum activation energy, E a = 0.954 eV determined in the temperature of 300–800 °C and the maximum fracture toughness, K IC = 1.825 ± 0.188 MPa m 1/2 were found for 9 mol.% Y 2O 3-doped CeO 2 specimen. The grain size of CeO 2 decreases with increasing Y 2O 3 concentration. The fracture toughness was found to increase at increased Y 2O 3 concentration, because of the decrease of CeO 2 grain size.

Microwave-induced combustion synthesis and ionic conductivity of Ce 0.8(Gd 0.2− xSm x)O 1.90 ceramics

Ce 0.8(Gd 0.2− x Sm x )O 1.90 nanopowders were successfully synthesized by a microwave-induced combustion process. The whole process takes only 30 min. The phase identification and morphology of resultant powders were investigated by XRD and SEM. Moreover, the correlation of ionic conductivity and thermal expansion coefficient for Ce 0.8(Gd 0.2− x Sm x )O 1.90 ceramics from microwave-induced combustion process also is discussed in this paper. The results revealed that the bulk densities of Ce 0.8(Gd 0.2− x Sm x )O 1.90 ceramics sintered at 1450 °C for 3 h were all greater than 95% of that in theoretical densities. The maximum electrical conductivity, σ 850°C = 0.051 S/cm, minimum activation energy, E a = 0.77 eV and minimum thermal expansion coefficient, TEC = 18.733 ppm/°C was found at Ce 0.80Gd 0.20O 1.90 ceramic.

Microwave-Induced Combustion Synthesis and Ion Conductivity of Ce1-xLaxO2-1/2x Ceramics

Ce1-xLaxO2-1/2x nanopowders were successfully synthesized by a microwave-induced combustion process. The phase identification, ionic conductivity and thermal expansion coefficient of Ce1-xLaxO2-1/2x ceramics were investigated in the current study. The results revealed that the bulk densities of Ce1-xLaxO2-1/2x ceramics sintered at 1450 °C for 3 h were all greater than 94% of the in theoretical densities, the maximum ionic conductivity of the sintered specimens was 0.047 S/cm at 850 °C for Ce0.84La0.16O1.92. Moreover, the minimum activity energy Ea determined from 500 to 850 °C for Ce0.84La0.16O1.92 was 0.759 eV. It is found that the ionic conductivity increased with decreasing thermal expansion coefficient. For Ce1-xLaxO2-1/2x ceramics, the ionic conductivity increased with La doping concentration until x=0.16, and then decreased.

Microwave-induced combustion synthesis and electrical properties of Ce 1− xSm xO 2−1/2 x ceramics

Ce 1− x Sm x O 2−1/2 x nanopowders were successfully synthesized by microwave-induced combustion process. For the preparation, cerium(III) nitrate hexahydrate, samarium(III) nitrate hexahydrate, and urea were used for the microwave-induced combustion process. The process took only a few minutes to obtain Ce 1− x Sm x O 2−1/2 x powders. Ce 1− x Sm x O 2−1/2 x ceramics prepared by microwave-induced process sintered at 1400 °C for 3 h, the bulk density of Ce 1− x Sm x O 2−1/2 x ceramics were over 95% of the theoretical density. The results revealed that Ce 0.84Sm 0.16O 1.92 possessed the maximum electrical conductivity was 0.0287 S cm −1 at 850 °C and the minimum activity energy, E a was 0.9565 eV determined from 500 to 850 °C.

Microwave-induced combustion synthesis and electrical conductivity of Ce 1− xGd xO 2−1/2 x ceramics

Ce 1− x Gd x O 2−1/2 x nanopowder were successfully synthesized by microwave-induced combustion process. For the preparation, cerium nitrate, gadolinium nitrate hexahydrate, and urea were used for the microwave-induced combustion process. The process took only 30 min to obtain Ce 1− x Gd x O 2−1/2 x powders. The exo-endo temperature, phase identification, and morphology of resultant powders were investigated by TG/DTA, XRD, and SEM. The as-received Ce 1− x Gd x O 2−1/2 x powders showed that the average particle size ranged from 18 to 50 nm, crystallite dimension varied from 11 to 20 nm, and the specific surface area was distribution from 16 to 46 m 2/g. As for Ce 1− x Gd x O 2−1/2 x ceramics sintered at 1450 °C for 3 h, the bulk density of Ce 1− x Gd x O 2−1/2 x ceramics were over 91% of the theoretical density, the maximum electrical conductivity, σ 700 °C = 0.017 S/cm with minimum activation energy, E a = 0.869 eV was found at Ce 0.80Gd 0.20O 1.90 ceramic.

Microwave-induced combustion synthesis of Li 0.5Fe 2.5− xAl xO 4 powder and their characterization

Li 0.5Fe 2.5− x Al x O 4 (0 ≦ x ≦ 1.0) powders with small and uniformly sized particles were successfully synthesized by microwave-induced combustion, using lithium nitrate, iron nitrate, aluminium nitrate, and carbohydrazide as the starting materials. The process takes only a few minutes to obtain as-received Al-substituted lithium ferrite powders. The resultant powders annealed at 650 °C for 2 h and were investigated by thermogravimeter/differential thermal analyzer (TG/DTA), X-ray diffractometer (XRD), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), and thermomagnetic analysis (TMA). The results revealed that the lattice constant, powder density, and crystallite size decrease linearly with the increasing of Al content in Li 0.5Fe 2.5− x Al x O 4 samples. Moreover, the magnetic properties of Al-substituted lithium ferrite also strongly affected by Al content. The saturation magnetization, remanent magnetization, Curie temperature, and coercive force decrease significantly with the increasing of Al content.

Microwave-induced combustion synthesis of Li 0.5Fe 2.5− xCr xO 4 powder and their characterization

Li 0.5Fe 2.5− x Cr x O 4 (0 ≦ x ≦ 1.0) powders with small and uniformly sized particles were successfully synthesized by microwave-induced combustion, using lithium nitrate, iron nitrate, chromium nitrate, and carbohydrazide as the starting materials. The process takes only a few minutes to obtain as-received Cr-substituted lithium ferrite powders. The resultant powders annealed at 650 °C for 2 h and were investigated by thermogravimeter/differential thermal analyzer (TG/DTA), X-ray diffractometer (XRD), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), and thermomagnetic analysis (TMA). The results revealed that the lattice constant decreases linearly with increasing of Cr content in Li 0.5Fe 2.5− x Cr x O 4 specimens. Moreover, the magnetic properties of Cr-substituted lithium ferrite were also strongly affected by Cr content. The saturation magnetization, remanent magnetization, and coercive force decrease monotonously with increasing of Cr content.

Microwave-induced combustion synthesis of Li 0.5Fe 2.5− xM xO 4 (M = Al, Cr, Mn) powder and their characterization

Li 0.5Fe 2.5− x M x O 4 (M = Al, Cr, Mn) powders with small and uniformly sized particles were successfully synthesized by microwave-induced combustion, using lithium nitrate, ferric nitrate, aluminum nitrate, chromium nitrate, manganese nitrate, and carbohydrazide as the starting materials. The process takes only a few minutes to obtain as-received Al, Cr, and Mn-substituted lithium ferrite powders. The resultant powders annealed at 650 °C for 2 h and were investigated by thermogravimeter/differential thermal analyzer (TG/DTA), X-ray diffractometer (XRD), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), and thermomagnetic analysis (TMA). The results revealed that saturation magnetization and Curie temperature of Li 0.5Fe 2.5− x M x O 4 were strongly affected by different metal ions substitution.