Solid state reactions in highly dispersed praseodymium oxide–SiO2 system

This paper reports results of studies on the interaction of praseodymium oxide nanocrystals with an amorphous silica. Nano-sized (3–4 nm) amorphous precursor of praseodymium oxide synthesized using a microemulsion technique were supported onto a high surface SiO₂ or occluded into SiO₂ matrix. Solid state reactions occurring in these binary systems upon heat treatment in air, argon or hydrogen at 800–1100 °C were studied by TEM, XRD, FT-IR and UV–vis spectroscopy. It has been found that morphology of the sample as well as annealing atmosphere influence greatly the phase evolution. At temperatures above 900 °C, nanocrystalline praseodymium silicates of various morphology and crystal structure were obtained. In particular, a new polymorph of Pr₂Si₂O₇, isostructural with I-type Ln₂Si₂O₇ (Ln₆[Si₄O₁₃][SiO₄]₂) Ln = Ce, La, has been identified.     

Structure and magnetic properties of Pr0. 1CexTb0.9-xFe1.9 alloys

1　INTRODUCTIONTerfenol D ( Tb0.27 Dy0.73 Fe2 ) exhibits largemagentostriction and minimized magnetic anisotro py at room temperature[1], so it is widely used inactuators and transducers. But the main raw mate rials of Terfenol D are expensive Tb and Dy. Ac cording to the single ion model[2], CeFe2 and PrFe2compounds have larger magnetostriction thanTbFe2 and DyFe2 at 0 K. In addition, Ce and Prare much cheaper than Tb and Dy. So Ce basedand Pr based compo…     

Fluorescence intensity ratio (FIR) analysis of the temperature sensing properties in transparent ferroelectric PMN-PT:Pr3+ ceramic

A transparent ferroelectric 0.75Pb(Mg_1/3Nb_2/3)O₃-0.25PbTiO₃:0.015Pr³⁺ ceramic was synthesized and its temperature-sensing ability was investigated based on the fluorescence intensity ratio (FIR) method. The transparency was found to be of the order of 68% at 900 nm for a sample thickness of 0.7 mm, comparable to the theoretical value of ~71%, benefiting the photoluminescence of the Pr³⁺ ions inside the ceramic. Instead of the traditional Boltzmann exponential style and varying sensitivity, a highly linear temperature response was obtained for the studied ceramic. Further, a constant FIR sensitivity of 0.70 %K^-1 was achieved over the temperature range of -50–40 °C, making the ceramic suitable for thermometry at room temperature and below.     

Thermodynamic assessment of the B–Ce and B–Pr systems

By using the Calculation of Phase Diagrams (CALPHAD) technique, the thermodynamic assessments of the B–Re (Re: Ce, Pr) binary system were carried out based on the experimental data including thermodynamic properties and phase equilibria. Gibbs free energies of the solution phases (liquid, fcc, bcc, dhcp) were modeled by the subregular solution model with the Redlich–Kister equation, and those of the intermediate compounds (B₄Ce, B₆Ce, B₅Pr₂, B₄Pr, B₆Pr) were described by the two-sublattice model. A consistent set of thermodynamic parameters leading to reasonable agreement between the present calculated results and experimental data was obtained.     

Elemental and RBS analysis of hybrid materials prepared by gamma-irradiation

Hybrid materials have been prepared by gamma-irradiation of a mixture of polydimethylsiloxane silanol-terminated, and the alkoxides tetraethylortosilicate and zirconium propoxide, using a ⁶⁰Co gamma source. No other chemicals were added to these precursors. Samples have been prepared with different concentrations of polymer and different mixtures of the metallic alkoxides. The obtained samples were heat-treated at several temperatures. The as prepared hybrids are monolithic and transparent. After heat-treatment in air at 650 °C the material remained monolithic if they were prepared from a mixture with alkoxide content larger than that of the polymer, whereas those prepared from a mixture with larger content of polymer reduced to coarse grains. These results indicate that the hybrid material matrix can consist of either inorganic oxide in the former case with embedded polymeric crosslinked chains or a polymeric matrix in the latter case with embedded inorganic oxide domains. Elemental analysis showed that the carbon release originates initially from reactions between the alkoxides whereas at the higher temperature it results from the polymer degradation. RBS analysis showed that Si is present in the material with an almost constant relative concentration but Zr is not homogeneously distributed, presenting different relative concentrations on the top and bottom surfaces of the same sample, depending on the composition.     

水泥辊磨设备工艺设计探索

根据水泥辊磨生产的新情况,提出了经济高效设计的理念。重点分析了μ值的影响,引入了PTμR的设计指标,并按照辊盘结合的原则,设想了磨机的系列。     

Selenide Glass Optical Fiber Doped with Pr3+ for U‐Band Optical Amplifier

Pr³⁺‐doped selenide glass optical fiber, which guarantees single‐mode propagation of above at least 1310 nm, has been successfully fabricated using a Ge‐Ga‐Sb‐Se glass system. Thermal properties such as glass transition temperature and viscosity of the glasses have been analyzed to find optimum conditions for fiber drawing. Attenuation loss incorporating the effects of an electronic band gap transition, Rayleigh scattering, and multiphonon absorption has also been theoretically estimated for the Ge‐Ga‐Sb‐Se fiber. A conventional double crucible technique has been applied to fabricate the selenide fiber. The background loss of the fiber was estimated to be approximately 0.64 dB/m at 1650 nm, which can be considered fairly good. When excited at approximately 1470 nm, Pr³⁺‐doped selenide fiber resulted in amplified spontaneous emission and saturation behavior with increasing pump power in a U‐band wavelength range of 1625 to 1675 nm.     

Fabrication, characterization, and electrical conductivity properties of Pr6O11 nanoparticles

Pr6O11 nanoparticles were obtained by subsequent thermal decomposition of the as-prepared precipitate formed under ambient temperature and pressure using NaOH as precipitant.The calcination process was affected,for 1 h in static air atmosphere,at 400-700 °C temperature range.The different samples were characterized using X-ray diffraction(XRD),transmission electron microscopy(TEM),field emission scanning electron microscopy(FE-SEM),thermogravimetric analysis(TGA),in situ electrical conductivity,and N 2 adsorption/desorption.The obtained results demonstrated that nano-crystalline Pr6O11,with crystallites size of 6-12 nm,started to form at 500 °C.Such value increased to 20-33 nm for the sample calcined at 700 °C.The as-synthesized Pr6O11 nanoparticles presented high electrical conductivity due to electron hopping between Pr(III)-Pr(IV) pairs.     

浅谈火电厂凝结水泵高压变频改造应注意的问题

针对当前火电厂凝结水泵高压变频改造现状,从"电气改造方案"、"保护功能"、"控制策略"三个方面,阐述了改造应注意的问题。并以广安电厂600MW机组凝结水高压变频改造为例,论证了注意这三方面问题的必要性和可行性。     

Growth and characterization of thin Cu-phthalocyanine films on MgO(001) layer for organic light-emitting diodes

Surface morphology and thermal stability of Cu-phthalocyanine (CuPc) films grown on an epitaxially grown MgO(001) layer were investigated by using atomic force microscope and X-ray diffractometer. The (002) textured β phase of CuPc films were prepared at room temperature beyond the epitaxial MgO/Fe/MgO(001) buffer layer by the vacuum deposition technique. The CuPc structure remained stable even after post-annealing at 350°C for 1 h under vacuum, which is an important advantage of device fabrication. In order to improve the device performance, we investigated also current-voltage-luminescence characteristics for the new top-emitting organic light-emitting diodes with different thicknesses of CuPc layer.