Synthesis and luminescence properties of nanocrystalline Gd2O3 : Eu3+ by combustion process

The nanocrystalline Gd2O3:Eu3+ powders with cubic phase were prepared by a combustion method in the presence of urea and glycol. The effects of the annealing temperature on the crystallization and luminescence properties were studied. The results of XRD show pure phase can be obtained, the average crystallite size could be calculated as 7, 8, 45, and 23 run for the precursor and samples annealed at 600, 700 and 800 degrees C, respectively, which coincided with the results from TEM images. The emission intensity, host absorption and charge transfer band intensity increased with increasing the temperature. The slightly broad emission peak at 610 nm for smaller particles can be observed. The ratio of host absorption to O-2-Eu3+ charge transfer band of smaller nanoparticles is much stronger compared with that for larger nanoparticles, furthermore, the luminescence lifetimes of nanoparticles increased with increasing particles size. The effects of doping concentration of Eu3+ on luminescence lifetimes and intensities were also discussed. The samples exhibited a higher quenching concentration of Eu3+, and luminescence lifetimes of nanoparticles are related to annealing temperature of samples and the doping concentration of Eu3+ ions.

Polypropylene as a carbon source for the synthesis of multi-walled carbon nanotubes via catalytic combustion

Multi-walled carbon nanotubes (MWCNTs) were efficiently synthesized by catalytic combustion of polypropylene (PP) using nickel compounds (such as Ni2O3, NiO, Ni(OH)(2) and NiCO3 (.) 2Ni(OH)(2)) as catalysts in the presence of organic-modified montmorillonite (OMMT) at 630-830 degrees C. Morphologies of the sample undergoing different combustion times were observed to investigate actual process producing MWCNTs by this method. The obtained MWCNTs were characterized by X-ray diffraction (XRD), transmission electron microscope and Raman spectroscopy. The yield of MWCNTs was affected by the composition of PP mixtures with OMMT and nickel compounds and the combustion temperature. The proton acidic sites from the degraded OMMT layers due to the Hoffman reaction of the modifiers at high temperature played an important role in the catalytic degradation of PP to supply carbon sources that are easy to be catalyzed by nickel catalyst for the growth of MWCNTs. The XRD measurements demonstrated that the nickel compounds were in situ reduced into the Ni(0) state with the aid of hydrogen gas and/or hydrocarbons in the degradation products of PP, and the Ni(O) was really the active site for the growth of MWCNTs. The combination of nickel compounds with OMMT was a key factor to efficiently synthesize MWCNTs via catalytic combustion of PP.

Rapid synthesis of Mn0.65Zn0.35Fe2O4/SiO2 homogeneous nanocomposites by modified sol-gel auto-combustion method

MnZn-ferrite/SiO2 nanocomposites with different silica content were successfully fabricated by a novel modified sol-gel auto-combustion method using citric acid as a chelating agent and tetraethyl orthosilicate (TEOS) as the source of silica matrix. The auto-combustion nature of the dried gel was studied by X-ray diffraction (XRD), Infrared spectra (IR), thermogravimetry (TG) and differential thermal analysis (DTA). Transmission electron microscope (TEM) observation shows that the MnZn-ferrite particles are homogeneously dispersed in silica matrix after auto-combustion of the dried gels. The magnetic properties vary with the silica content. The transition from the ferromagnetic to paramagnetic state is observed by Mossbauer spectra measurement with the increasing silica content. Vibrating sample magnetometer (VSM) shows that the magnetic properties of Mn0.65Zn0.35Fe2O4/SiO2 nanocomposites strongly depend on the silica content.

Combustion. synthesis and luminescence properties of nanocrystalline monoclinic SrAl2O4 : Eu2+

Nanocrystals of SrAl2O4:Eu2+ have been prepared by combustion synthesis. The results of XRD indicated that the resulting SrAl2O4:Eu2+ nanocrystals have a reduced and distorted monoclinic lattice compared with bulk materials. Both the excitation and emission spectra of SrAl2O4:Eu2+ nanocrystals shifts to higher energies in contrast to the bulk materials. The band structure calculation is performed using first-principles full potential-linearized augmented plane wave method within density functional theory. The calculated results are in reasonable agreement with our experimental results.

Characterization of FeNi3 alloy in Fe-Ni-O system synthesized by citric acid combustion method

Fe-Ni-O samples, with Fe/Ni ratio ranging from 2 to 1/3, were synthesized. Samples synthesized with and without citric acid in the precursor were compared and it was found that the addition of citric acid is the necessary condition for FeNi3 formation; it was found that FeNi3 alloys were formed in these samples even when calcined in an air atmosphere. X-ray diffraction and X-ray photoelectron spectroscopy measurements were used to characterize the samples. Because of the existence of FeNi3 alloys, Fe-Ni-O samples showed strong reactivity to NO and NO + O-2 but were inert to O-2 alone.

Synthesis of nanocrystalline Ba(CoxZn1-x)(2)Fe16O27 by sol-gel auto-combustion method

The synthesis of nanocrystalline W-type hexaferrites Ba(CoxZn1-x)(2)Fe16O27 powders by sol-gel auto-combustion method has been investigated. The thermal decomposition process of dried gel was studied by thermogravimetry (TG), differential thermal analysis (DTA) and infrared spectra (IR). The structural and magnetic properties of resultant particles were investigated by X-ray diffraction (XRD), transmission electron microscope (TEM), and vibrating sample magnetometer (VSM). The results reveal that the dried gel exhibits auto-combustion behavior. After combustion, pure nanocrystalline W-type hexaferrite phase starts to appear at the calcination temperature of 800 degrees C. The crystallinity and the grain size increase at higher temperature. The saturation magnetization and coercivity clearly depend on calcination temperature and Co content X.

Nitrate-citrate combustion synthesis and properties of Ce1-xSmxO2-x/2 solid solutions

A nitrate-citrate combustion route to synthesize nanocrystalline samarium-doped ceria powders for solid electrolyte ceramics is presented. This route is based on the gelling of nitrate solutions by the addition of citric acid and ammonium hydroxide, followed by an intense combustion process due to an exothermic redox reaction between nitrate and citrate ions. The influence of ignition temperature on the characteristics of the powders was studied. The change of the crystal structure with the content of doped Sm was investigated. High temperature X-ray, and Raman scattering were used to characterize the sample. The lattice constant and unit volume increase with doping level and increasing temperature. Dense ceramic samples prepared by uniaxial pressing and sintering in air were also studied.