F-/Sr2+ mono-doped and co-doped ceria samples were synthesized by precipitation.The UV-shielding and oxidation catalytic properties of the doped ceria were investigated.The X-ray diffraction revealed that the prepared F-/Sr2+ mono-doped and co-doped ceria samples belonged to the cubic fluorite structure although the peak positions changed depending on the kind of doped ions.The UV-vis spectra showed that both the F-/Sr2+ mono-doped ceria and co-doped ceria exhibit superior UV-shielding properties compared with un-doped ceria.The oxidation catalytic activity of F-/Sr2+ co-doped ceria was lower than un-doped ceria,but the F-/Sr2+ mono-doped ceria had higher oxidation catalytic activities than the undoped ceria.
High calcination temperature is an important factor in the preparation process of CeMgAl 11O 19∶Tb 3+. To decrease the temperature, different fluxes (H 3BO 3, MgF 2 and AlF 3) were tested in order to compare their influence on the luminescence property and particle size distribution of CeMgAl 11O 19∶Tb 3+. The result shows that when the content of MgF 2 is 0.1 mol/mol, the intensity of luminescence can attain a maximum. Furthermore, MgF 2 can improve the particle size quality of the phosphor. So MgF 2 can take the place of the conventional flux H 3BO 3 to prepare high quality CeMgAl 11O 19∶Tb 3+ phosphor. In addition, the relation between phosphor property and content of AlF 3 was also studied. The crystal structure of the phosphor was analyzed by XRD method. The phase composition analysis shows that the reason of decrease of the brightness of CeMgAl 11O 19∶Tb 3+ phosphor is the emergence of TbAlO 3 and α-Al 2O 3 during the preparation process.
Yttrium oxide powders with submicron particle size prepared by precipitation method in which ammonium bicarbonate was used as precipitateforming agent were measured in 90 Plus particle size analyzer. Effects of several factors, such as the content of yttrium oxide, the selection of dispersing agent and the time of dispersion on test result were investigated. Optimum conditions of measurement were found.
The kinetic of cerium(Ⅳ) extraction with HEH/EHP in fluorine-containing sulfuric acid system was studied by using a constant interfacial cell with laminar flow.The effects of stirring speed,concentrations of cerium(Ⅳ) and HEH/EHP,acidity and temperature on the extraction rate were examined.The experimental results indicated that the extraction reaction was first order reaction,the apparent activation energy was 50.8 kJ · mol-1.And the mass transfer of cerium(Ⅳ) was controlled by chemical reaction.The extraction rate equation was R=k[Ce(HF)(HSO4-)3+]1.052.07-2.43.The mechanism of extraction was also discussed.
Ferroelectric-ferromagnetic composite is a new type of functional material, which possesses good magnetoelectric coupling effect and has extensive applications. In present paper, the basic mechanism of the magnetoelectric effect briefly was illustrated and the characteristics and applications of magnetoelectric composites were introduced. Progress in research and classification of magnetoelectric composites were reviewed briefly. Finally, existing problems and the trend of the study on the material were also discussed.
Sulfuric acid leaching process was applied to extracting rare earth(RE) from roasted ore of Dechang bastnaesite in Sichuan,China.The effect of particle size,stirring speed,sulfuric acid concentration and leaching temperature on RE extraction efficiency was investigated,and the leaching kinetics of RE was analyzed.Under selected leaching conditions,including particle size(0.074-0.100 mm),sulfuric acid concentration 1.50 mol/L,mass ratio of liquid to solid 8 and stirring speed 500 r/min,the leaching kinetics analysis shows that the reaction rate of leaching process is controlled by diffusion through the product/ash layer which can be described by the shrinking-core model,and the calculated activation energy of 9.977 kJ/mol is characteristic for a diffusion-controlled process.
The La-hexaaluminate catalyst with high temperature stability and catalytic activity was successfully synthesized by the reverse microemulsion method using the buffer solution of NH4HCO3 and NH4OH as a precipitation agent.With methane catalytic combustion as a probe reaction,the catalytic activity was examined on a fixed bed flow reaction system in order to compare their catalytic activity.The tested results showed that the hexaaluminate precursor formed in reverse microemulsion with chemical homogeneouness,and the La-hexaaluminate catalytic crystalline formed at a lower temperature of 1050 ℃.The catalytic activity was greatly enhanced with the substitution of Fe or Mn ions for Al ions in hexaaluminates,and the Fe-substituted La-hexaaluminate catalysts exhibited the high temperature activity and stability.The Mn-substituted La-hexaaluminate catalysts exhibited low temperature catalytic activity.The research results also indicated that the Fe-and Mn-substituted La-hexaaluminate catalysts exhibited the highest catalytic activity on the catalytic combustion of methane,and their effects on the structure and catalytic activity were also studied,due to the well synergic effect between Fe,Mn and La ions of La-hexaaluminates.
During the process of exploring new high-performance magnetostrictive materials,Fe-Ga alloy was an important discovery with high stress sensitivity,good thermal-mechanical properties and magnetostrictive properties.It filled the blank between the traditional magnetostrictive materials and rare earth giant magnetostrictive materials,and had significant potential application value and wide application prospects in ultrasonic field and micro displacement device.This article introduced recent R D progress and trend of Fe-Ga alloy from following four parts: Ga content and phase structure,the third element,preparation method and pressure temperature.It summarized the influence of Ga content phase structure and the third element on the magnetostrictive properties of Fe-Ga alloy.The magnetostrictive properties of Fe-Ga alloy were closely related to Ga content;different third elements had different influence on magnetostrictive properties of Fe-Ga alloy.The preparation methods of Fe-Ga alloy mainly include directional solidification method,melt-spun method,rolling method,drawing method,etc.The influences of different preparation methods on material properties were also compared.The article also explained the influence of stress field and temperature on magnetostrictive properties of Fe-Ga alloy.The stress field had positive influence on magnetostrictive properties of Fe-Ga alloy.But the temperature dependence of the Fe-Ga alloy′s magnetostrictive properties was complex and the magnetostrictive amplitude and trend of Fe-Ga alloy in different temperatures were subject to its alloy structure.
The fluorine-strontium-doped ceria and fluorine-calcium-doped ceria nanoparticles were synthesized by co-precipitation.The phase constitute,particle size,morphology and UV-shielding properties of the synthesized powders were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM) and ultraviolet visible(UV-vis) spectroscopy,respectively.The XRD confirmed that the fluorine-strontium-doped ceria and fluorine-calcium-doped ceria were cubic fluorite structure,and after co-doping anion and cation the a-cell parameter of ceria increased.The SEM results showed that the doped ceria were agglomeration of spherical nanoparticals.The UV-vis spectra showed a red-shift in UV absorption edge for the doped ceria,and the UV-shielding properties increased.
Y 1-a, Gd a) 3-x(Al 1-b, Ga b) 5O 12∶Ce 3+ x was synthesized by high-temperature solid state reaction in reducing atmosphere based on high purity raw materials. The influences of Y 3+, Gd 3+, Al 3+, Ga 3+ and activator-Ce 3+ on the performance of the phosphor were investigated. Ce 3+ is the luminescent center and activates the phosphor after it replaces Y partially. When x is less than 0.12, the volume of the crystal and the emission intensity of the phosphor increase with the quantity of Ce 3+. When CeO 2 is added too much, the phase CeAlO 3 will appear. The excitation and emission peaks of the phosphor will shift to longer wavelength when the amount of Gd 3+ increases. The wavelength of the emission peak can shift about 20 nm when a equals 0.45. In opposite, the excitation and emission peaks will shift to shorter wavelength, when part of Al 3+ is replaced by Ga 3+. The wavelength of the emission peak can shift about 20 nm when b equals 0.55. Through the replacemeat of Y 3+ or Al 3+ by Gd 3+ or Ga 3+, the emission peak of the phosphor can be adjusted from 520 to 560 nm. In this way, the phosphor is more suitable for different chips.
