Preparation and properties of nanocrystal SmBO_3 by nitrate-citrate sol-gel combustion method

Nanocrystal SmBO3 powders were synthesized by nitrate-citrate sol-gel combustion method. The phase evolution, morphologies and absorbency of the synthesized powders were characterized by X-ray diffraction （XRD）, Field emission scanning electronic microscope （FESEM）, Fourier transform infrared spectroscopy （FFIR） and UV-3101PC spectrophotometer （UVPC）, respectively. XRD and FESEM results showed that pure SmBO3 phase was obtained at 750 ℃, with an average original particle size of about 100 nm. FTIR showed that there were apparently concentrated absorbent peaks between 500 and 1400 cm^-1. Moreover, the reflectivity of the powders apparently decreased at the wavelength between 1.05 and 1.15 μm. Therefore, SmBO3 might be a kind of absorbent material for infrared laser.

Effect of Bi3+ Ion Substitution on Magnetic Properties of Cobalt Nano Ferrites Prepared by Sol-Gel Combustion Method

Bismuth substituted cobalt nano ferrites with the chemical composition Co Bix Fe2-x O4 (x = 0.00, 0.05, 0.10, 0.15, 0.20 & 0.25) were prepared by sol-gel combustion method. The phase identification of prepared samples is characterised by X-ray powder diffraction (XRD) method, which confirms the formation of a single phase fcc spinal structure. The mean crystallite sizes of all prepared samples were obtained within the range of 21 (±5) nm. Transmission Electron Microscopy (TEM) images also confirmed the crystallite size of all the synthesised samples was in nano range. With the effect of Bi3+ ion substitution on spinal cobalt ferrite, the magnetic properties were investigated by using Vibration Sample Magnetometer (VSM). The obtained hysteresis (M-H) curves of all the samples were analysed under the applied magnetic field of range ± 10 K Oe at 300 K. The magnetic properties such as saturation magnetisation (Ms), remnant magnetization (Mr) and coercivity (Hc) values are tabulated, which show a decrease in trend as the bismuth ion concentration increases. This is due to the addition of Bi3+ ion in the place of Fe3+ ion (octahedral site) and hence the Bi3+-Fe3+ ion interaction predominates as compared with the Fe2+-Fe3+ ion interaction. The data obtained from magnetic studies, the variation among the magnetic properties have been investigated for all the prepared samples.

Synthesis and Structural Properties of Bismuth Doped Cobalt Nanoferrites Prepared by Sol-Gel Combustion Method

A series of Bismuth doped Cobalt nanoferrites of chemical composition CoBixFe2-xO4 (where x = 0.00, 0.05, 0.10, 0.15, 0.20 & 0.25) were prepared by sol-gel combustion method and calcinated at 600℃. The structural and morphological studies were carried out by using X-ray diffraction (XRD), Scanning Electron Microscope (SEM), Transmission Electron Microscopy (TEM), Energy Dispersive Spectroscopy (EDS) and Fourier Transform Infrared (FT-IR) spectra showing the single phase spinal structure. The X-ray diffraction (XRD) analysis confirmed a single phase fcc crystal. The crystallite size of all the compositions was calculated using Debye-Scherrer equation and found in the range of 17 to 26 nm. The lattice parameters were found to be decreased as Bi3+ ion doping increases. The surface morphology was studied by Scanning Electron Microscope (SEM) and particle size was confirmed by Transmission Electron Microscopy (TEM). The EDS plots revealed existence of no extra peaks other than constituents of the taken up composition. The Fourier Transform Infrared (FT-IR) studies were made in the frequency range 350 - 900 cm-1 and observed two strong absorption peaks. The frequency band is found at 596 cm-1 where as the lower frequency band at 393 cm-1. It is clearly noticed that the two prominent absorption bands were slightly shifted towards higher frequency side with the increase of Bi3+ ion concentration.

Dissolution-precipitation mechanism of self-propagating high-temperature synthesis of TiC-Cu cermets

The mechanism of self-propagating high-temperature synthesis （SHS） of TiC-Cu cermets was studied using a combustion front quenching method. Microstructural evolution in the quenched sample was observed using scanning electron microscope （SEM） with energy dispersive X-ray （EDX） spectrometry, and the combustion temperature was measured. The results showed that the combustion reaction started with local formation of Ti-Cu melt and could be described with the dissolution-precipitation mechanism, namely, Ti, Cu, and C particles dissolved into the Ti-Cu solution and TiC particles precipitated in the saturated Ti-Cu-C liquid solution. The local formation of Ti-Cu melt resulted from the solid diffusion between Ti and Cu particles.

Effects of ultrasonic impregnation combined with calcination in N_2 atmosphere on the property of Co_3O_4/CeO_2 composites for catalytic methane combustion

CoO/CeOcomposites with high surface areas and ultrafine crystalline sizes for catalytic combustion of methane were firstly prepared by a new sol-gel method which combined ultrasonic impregnation treatment and calcination in Natmosphere. The samples were characterized by various means such as nitrogen adsorption/desorption, X-ray diffraction(XRD), Htemperature-programmed reduction(H-TPR),X-ray photoelectron spectroscopy(XPS) and transmission electron microscopy(TEM). Results showed that the modified catalyst had the mesoporous structure, comparatively higher amount of surface oxygen and larger oxygen vacancies than others. As a result of the structure and surface composition merits, a high methane combustion conversion(50%) could be obtained at a low temperature of 262 °C for the modified CoO/CeOcomposites catalysts. The experimental results demonstrated that ultrasonic impregnation treatment combined with the Nthermal treatment prior to calcination in air had a promising application for preparation of CoO/CeOcomposites catalysts for low-temperature catalytic combustion of methane.

Yttrium aluminum garnet (Y_3A_(l5)O_(12)) nanopowders synthesized by the chemical method

The homogeneously dispersed, less agglomerated YAG nanopowders are synthesized by the citrate-gel method followed by low-temperature self-propagating combustion reaction, using Y2O3, Al(NO3)3?9H2O and citric acid as starting materials. This method effectively solves the problems caused by solid-state reaction at high temperature and the hard ag-glomerates brought by the chemical precipitation method. The powders are characterized by TG-DTA, XRD, FT-IR and TEM respectively. The experiments show that the forming temperature of YAG crystal phase is 850°C and the pseudo-YAG crystalline appears during the calcination and transforms to pure YAG at 1050°C. The powders with sizes less than 50 nm are observed by TEM micrography, which is consistent with the result calculated by Scherrer's formula. The powders consist of single grains.

CaTiO_(3)-Sm_(0.9)Nd_(0.1)AlO_(3) ceramics with a moderate dielectric constant and a high quality factor prepared by sol-gel auto combustion method

CaTiO_(3)-LnAlO_(3)(Ln=La,Nd,Sm) is a perovskite-type microwave material system characterized by a moderate dielectric constant εr,a high quality factor Q×f,and a small temperature coefficient of resonant frequency τf,making this system promising for microwave devices.However,its high synthesis temperature and sintering temperature limit its industrial applications.In our work,single phase0.7 CaTiO_(3)-0.3 Sm_(0.9)Nd_(0.1)AlO_(3)(7 CT-3 SNA) was synthesized via the sol-gel auto combustion method using citric acid as fuel at a relatively low temperature.After being calcined at 600℃ for 2 h,wellcrystallized 7 CT-3 SNA powders with 30-50 nm average particle size were achieved,suggesting good sintering activity.The new and narrow order band at about 800 cm^(-1) in the Raman spectra indicates a high ordering degree in the B site of 7 CT-3 SNA solid solution.Compared with the solid-state reaction method and co-precipitation method,the 0.7 CT-0.3 SNA ceramics fabricated by the current method possess a much lower calcination temperature,a similar εr value,and an improved Q × f value.The optimum microwave dielectric properties of εr=43.54,Q×f=54375 GHz,and τf=-6.3 ×10^(-6)/℃ are obtained for the CTSA ceramics derived from the sol-gel auto combustion process.Therefore,the 7 CT-3 SNA ceramics prepared in this study are potential dielectric materials for microwave applications,indicating that the sol-gel auto combustion method is a good alternative strategy for the fabrication of CaTiO_(3)-LnAlO_(3) ceramics.

Effects of calcination temperature and time on the Ca3Co4O9 purity when synthesized using starch-assisted sol-gel combustion method

Ca3Co4O9 is a p-type semiconducting material that is well-known for its thermoelectric(TE),magnetic,electronic,and electro-optic properties.In this study,sol–gel autoignition was used to prepare Ca3Co4O9 at different calcination temperatures(773,873,973,and 1073 K)and time(4,6,8,10,12,and 14 h)using starch as a fuel.The phase and microstructure of the prepared Ca3Co4O9 powder were investigated.Thermogravimetry–differential thermal analysis(TGA)confirms that the final weight loss occurred at 1073 K to form Ca3Co4O9 stable powder.The variable-pressure scanning electron microscopy(VP-SEM)images show that the size of powder particles increases from 1.15 to 1.47μm as calcination time increases from 4 to 12 h,and the size remains almost constant thereafter.A similar pattern is also observed on the increment of the crystallite size and percentage of crystallinity with X-ray diffraction(XRD)analysis.The highest crystallinity is found about 92.9%when the powder was calcinated at 1073 K for 12 and 14 h with 458 and 460Åcrystallite size,respectively.Energy dispersive X-ray spectroscopy(EDS)analysis demonstrates that the calcinated powder has a high intensity of Ca,Co,and O with uniform distribution.High-resolution transmission electron microscopy(HRTEM)images prove that there is no distinct lattice distortion defect on the crystal structure.

Citrate sol-gel combustion preparation and photoluminescence properties of YAG:Ce phosphors

Yellow-emitting YAG：Ce3＋ nanocrystalline phosphors were prepared by citrate sol-gel combustion method using citric acid as the fuel and chelating agent. The influence of mole ratio of citric acid to metallic ions （MRCM）, pH value of the solution, calcination temperature and Ce-doped concentration on the structures and properties of as-prepared powders were investigated in detail. Higher crystallinity and better luminescence performance powders were obtained at MRCM=2, pH=3 and the calcination temperature of 1200 ℃. The phosphors exhibited the charactefistc broadband visible luminescence of YAG：Ce. The optimum concentration of Ce3＋ was 1.0 tool.%, and the concentration quenching was derived from the reciprocity between electric dipole and electric quadrupole （d-q）. Especially, the pH value of the solution was a key factor to obtain a stable sol-gel system and then obtain pure and homogeneous rare earth ions doped YAG phosphors at a lower tem- perature. The Y3Al5O12：Ce0.03 phosphor with optimized synthesis-condition and composition had a similar luminescence intensity with the commercial phosphor YAG：Ce.

Surface structure and catalytic performance of Sr-doped La_2NiAlO_6 double perovskite catalysts for methane combustion

A species of novel St-doped rare earth double perovskite catalysts （La2 xSrxNiA106, x=0, 0.1） were prepared by the sol-gel method using citric acid as a complexing agent and calcined at 1100 ℃ for 3 h, then investigated for methane catalytic combustion. The as-prepared catalysts were characterized by X-ray diffraction patterns （XRD）, H2-temperature-programmed reduction （H2-TPR）, specific surface area （BET）, magnetic property measurement technology （M-H）, scanning electron microscopy （SEM）, and X-ray photoelectron spectroscopy （XPS）. Experimental results showed that Lal.9Sr0.1NiA106 catalyst exhibited significantly improved catalytic activity （T10=378.7 ℃, T90=602.9 ℃） compared with that of La2NiAIO6, whose T10 decreased by 74.4 ℃ and T90 decreased by 66.8 ℃, respectively. The excellent catalytic activity of Lal.9Sr0.tNiA106 caused by Sr-doping could be explained by the larger number of adsorption oxygen on the catalyst surface, which could be proven by XPS analysis.

Properties of La_(0.9)Sr_(0.1)MnO_3 and tourmaline compound catalytic materials for methane combustion

A novel catalytic material Lao.9Sr0.1MnO3 and tourmaline compound catalytic material was synthesized in the base of traditional catalytic material La0.9Sr0.1MnO3 which exhibited excellent catalytic activity for methane combustion. Different contents of toumaaline were added to give a series ofLa0.9Sr0.1MnO3 and tourmaline catalytic material through a sol-gel method. Samples above were characterized and analyzed by means of X-ray diffraction （XRD）, scanning electron microscopy （SEM）, Brunauer-Emmett-Teller method （BET）, temperaalre programmed reduction （TPR）, catalytic activity test and contact angle test. The as-prepared sample with 2% （m/m） tourmaline showed good homogeneity surface morphology and displayed the optimal catalytic activity. The light-off temperature reduced by 10 ℃ and the T90 decreased by 15 ℃. In addition, the mechanism of the reinforcement of catalytic activity was explored.

Optical property of SmAlO_3 applied as 1.06 μm laser absorbing material

SmAlO3 powders were successfully synthesized through the citrate sol-gel combustion method. The phase evolution of the prepared powders were characterized using thermal gravimetric （TG） analysis, differential scanning calorimetry （DSC） analysis and Fourier transform infrared spectroscopy （FTIR）. X-ray diffraction （XRD） was applied to examine the purity of the powders. The re-flective properties of SmAlO3 with changing temperatures were investigated by ultraviolet-visible near-infrared spectrophotometer （UVPC） specular reflection spectrum. The results displayed that pure SmAlO3 phase with preferable reflectivity at 1.06μm could be obtained at 900 oC for 2 h. Furthermore, the reflectivity of SmAlO3 at various temperatures from-40 to 500 oC transformed within ±0.1%, and all maintained below 1%at 1.06μm. The absorbance of SmAlO3 in the resin solution was 2.134 and the moral absorption coefficient was about 384.8 in the work. The study indicated that SmAlO3 powders may be a promising kind of heat resistant absorb-ing material for 1.06μm laser defense, which could be further applied to laser absorbing coatings with a wide range of temperatures.

Preparation and properties of Nd:YAG ultra-fine powders

Ultra-fine Nd：YAG powders with different doping concentrations were synthesized by sol-gel combustion method. The pure Nd：YAG could be prepared at the low temperature of 900℃. Ethanol could improve the dispersity of powders, and the average size of the ultra-fine powders was around 250 nm. The reflection spectrum showed that there were several apparent characteristic absorption peaks and the intensity of these peaks enhanced with the increasing concentration of Nd^3＋. The luminescence spectrum, which was excited by 808 nm wavelength, exhibited several obvious emission bands in the range of 900-1150 nm. The emission intensity of Nd：YAG powders increased until the Nd content was above 3 mol.% due to the fluorescent quenching effect.

Preparation of Sr_2Fe_(1-x)Sc_xMoO_(6-δ) nanopowders and its electrical conductivity

Double-perovskite Sr2Fe1-xScxMoO6-δ （x=0, 0.05, 0.1, 0.2, 0.3, 0.4） powders applied to the cathode of solid oxide electrolysis cells were synthesized by the sol-gel citrate combustion method. Initial powders were calcined at different temperatures under different atmosphere （air, H2（4 vol.%）/Ar）, and the effects of the preparation process on the structure and the morphology of the powders were investigated by thermal analysis （TG/DSC）, X-ray diffraction （XRD）, scanning electron microscopy （SEM） and surface area analysis. The electric conductiv-ity of the materials was measured by electrochemical work station using wafers prepared by dry pressing. It was found that the formation of perovskite structure was related to the content of Sc and combustion improver （NH4NO3）, pH value, calcining temperature and atmosphere. A single perovskite phase of Sr2Fe1-xScxMoO6-δ could be formed after 3 h calcining in reducing atmosphere of H2 （4 vol.%）/Ar at 1100 oC. The electrical property indicated that, this material had a potential to be used in medium/high temperature solid oxide fuel cells or electrolysis cells.

Synthesis and Characterization of Neodymium and Ytterbium-doped Yttrium Aluminum Garnet Nano-powder

Nd/Yb-co-doped YAG transparent ceramic nano-powder was prepared by a sol-gel combustion method.The structure,morphology and properties were characterized by thermogravimetric-differential thermal analysis,X-ray diffraction,transmission electron microscopy,infrared spectroscopy,absorption analysis and fluorescence spectroscopy,respectively.The results show that the mass loss of the powder calcinated at 900 ℃ for 3 h is 49.56%.A well-crystallized Nd/Yb:YAG nano-powder with the superior sintering performance and high purity is obtained,and the morphology of the particles with the average diameter in the range of 60-100 runs appears regular.The nano-powder exhibits an intense absorption at 808 nm,corresponding to the 4I/9/2-4F7/2 transition of Nd^(^(3+) ions,which is suitable to absorb the wavelength of 808 nm from a laser diode source.The emission peak at 1046 nm of the Nd/Yb:YAG powder is more intense than that of Nd^(^(3+):YAG powder.It is indicated that the energy absorbed by Yb^(^(3+) ions from the laser diode source can be transmitted to Nd^(^(3+) ions based on the cross relaxation process of[(4F3/2)Nd,(2F7/2)Yb]-[(479/2)Nd,(2F5/2)Yb].