NMR Study on Structural Characteristics of Rare Earth Doped Boro-Alumino-Silicate Glasses

The structural characteristics of Re2O3 doped B2O3-Al2O3-SiO2 glasses and factors such as the component and heat-treating conditions affecting the glass structure were investigated by magic angle spin nuclear magnetic resonance （MAS NMR） spectroscopy and differential thermal analysis （DTA）. It is found that, in B2O3-Al2O3-SiO2 glass, the boron （4）, and Al（5）, Al（6） changes to Al（4）. On the other hand, compared with Ba^2＋ , RE^3＋ can accumulate the boron network because of its higher field strength, which results in a large network structure. With the increase of samarium oxide, the silicate coordination Qa（3T） will have predominance gradually. Heat-treatment has little effect on the boron and aluminum coordination sites in the glass structure.

Physicochemical Features of Phosphorus-Modified ZSM-5 Zeolite and Its Performance on Catalytic Pyrolysis to Produce Ethylene

The physicochemical features of phosphorus-modified ZSM-5 zeolites (SiO2/Al2O3 molar ratio is 25) were characterized by XRD(X-ray diffraction), BET(Brunauer, Emmett and Teller spcific surface area measurement), NH3-TPD(ammonia temperature-programmed desorption) and MASNMR(magic angle spinning nuclear magnetic resonance), and the performance on catalytic pyrolysis to produce ethylene was investigated with a light hydrocarbon fixed bed micro-reactor with n-octane as feed. The results show that the acid site density, acid intensity and hydrothermal stability of ZSM-5 zeolite were improved by phosphorus modification. When P2O5 content in ZSM-5 zeolite is higher than 2.5%, phosphorus modification can prevent ZSM-5 zeolite crystal structure transformation from orthorhombic to monoclinic. In addition, the dealumination of ZSM-5 zeolite framework was moderated by phosphorus modification under high temperature hydrothermal treatment. The results of n-octane pyrolysis on phosphorus-modified ZSM-5 zeolites show that ethylene yields of zeolites with different phosphorus content are almost the same under the same n-octane conversion. However, the modified zeolites with higher pyrolysis activity give lower yield of propene, butene and total olefin than lower pyrolysis activity under the same n-octane conversion.

Types of the jump phenomenon in the angular dependence of the noncollinear exchange bias

Based on the principle of minimal energy and the coherent rotation model, two types of the jump phenomena, complete and incomplete jump phenomenon, are proved to exist in the angular dependence of the exchange bias with noncollinear unidirectional and uniaxial anisotropies. It is found that the transition between complete and incomplete jump phenomena occurs on condition that the exchange-coupling constant exceeds a critical value. Additionally, two different modes of the magnetization rotation, the whole-plane rotation, and the half-plane rotation are present in the magnetization reversal process, and they are dependent on the direction of the external field. Furthermore, the equations of the critical angle, at which orientation the exchange bias field reaches a maximum value and the coercivity disappears, are also derived in this paper. The numerical calculations in this paper are consistent with the relevant experimental observations, indicating that our method to study the angular dependence of the exchange bias as well as the magnetization reversal behaviors is valid. Our discussion about the jump phenomenon, the critical angle, and the modes of the magnetization reversal can explain the observed differences in results between different experiments.

Nitrogen Forms of Maillard Polymers Derived from Xylose and ^(15)N-Labelled Glycine

Water-soluble, nondialyzable Maillard polymers were prepared by reacting D-xylose with 15N-glycine (and/or glycine) at 68 ℃ and pH 8.0 at equimolar concentrations of 1, 0.5 and 0.1 mol L-1, respectively,for 13 days and partitioned into acid-insoluble (MHA) and acid-soluble (MFA) fractions. The nitrogen forms in these polymers were studied by using the 15N cross polarization-magic angle spinning nuclear magnetic resonance (CPMAS NMR) technique in combination with chemical methods. The 15N nuclear magnetic resonance (NMR) data showed that while the yield, especially the MHA/MFA ratio, varied considerably with the concentrations of the reactants, the nitrogen distribution patterns of these polymers were quite similar.From 65% to 70% of nitrogen in them was in the secondary amide and/or indole form with 24%~25% present as aliphatic and/or aromatic ammes and 5% to 11% as pyrrole and/or pyrrole-like nitrogen. More than half (50%~77%) of the N in these polymers were nonhydrolyzable. The role of Maillard reaction in the formation of nonhydrolyzable nitrogen in soil organic matter is discussed.

Characteristics of magnetic domain deflection of Tb_(0.3)Dy_(0.7)Fe_2 alloy

In order to expand the applications of giant magnetostrictive materials in the field of precision positioning, an extreme value model of free energy was established with deflection angle of magnetic domain as the independent variable from the micro-scopic aspect. The model was based on Stoner-Wohlfarth （S-W） model wherein Tb0.3Dy0.7Fe2 alloy was taken as a research object, and the deflection law of magnetization angle of single magnetic domain was studied through drawing the equipotential curves and changing curves of free energy function under different applied stresses and in different magnetic fields. Research results showed that there were three kinds of magnetization angles of single magnetic domain as for Tb0.3Dy0.7Fe2 alloy, namely 35.26o , 90o and 144.74o ; under the action of applied stresses, the magnetization anglesθwere deflected to the direction of 90o for the magnetic domains of 35.26o and 144.74o and the magnetization anglesψ were changed and transited to the direction ofψ=135o for the magnetic domain of 90o ; the magnetic domain was deflected under the action of small magnetic field for magnetic domain of 35.26o ; with the increase of magnetic field intensity, the magnetic domain of 90o had a transition trend to a stationary planar ofψ=ψ0; the magnetic domain of 144.74o had a transition trend to the direction of magnetic domain of 35.26o. These results laid a foundation for the magnetostrictive mechanism and establishment of precision positioning theories of the giant magnetostrictive materials.

One-Pot Room-Temperature Synthesis of Mg Containing MCM-41 Mesoporous Silica for Aldol Reactions

One-pot synthesis of Mg containing MCM-41(Mg-MCM-41) materials was respectively carried out by a room temperature(RT) method and a hydrothermal(HT) method for aldol condensation of 4-nitrobenzaldehyde and acetone and self-condensation of acetone. The RT method can prepare MCM-41 materials containing large amounts of Mg while maintaining the structural characteristics of MCM-41 even at very low Si/Mg ratios(large Mg loadings), but the HT method cannot. The RT method can also give more active catalysts than the HT method, because the catalysts prepared by the RT method are more basic than those prepared by the HT one. The characterization indicates that Mg atoms in the Mg-MCM-41 prepared by the RT method exist as MgO disperses well on the wall surface of pores, while those in Mg-MCM-41 prepared by the HT method are included in the bulk with a smectite-like structure.