EPR kinetics in irradiated syndiotactic polystyrene at elevated temperatures

Free radicals are formed upon irradiation of polymers. The annealing of γ-ray irradiated syndiotactic polystyrene (sPS) with doses 10, 23 and 36 kGy was studied with electron paramagnetic resonance (EPR) spectroscopy. The EPR spectra are possibly attributed to three types of radicals, (a) the benzyl radical Ra, (b) resonance structure of the phenyl radical Rb, and (c) carbon-superoxide-centered radical Rc with three-, four-, and single-line features, respectively. Radical Ra can be easily formed by the removal of the proton from the tertiary carbon; radical Rb is created from delocalization of the spin of the radical Ra onto the benzene ring; and radical Rc may be generated from the interaction of a carbon-centered radical with dioxygen from the air which forms a carbon-superoxide center. By comparing EPR spectra of the radicals with a DPPH standard, the spin numbers of the radicals can be calculated. The spin number of all radicals decreases exponentially with time in the temperature range of 60-90 °C regardless of dose of the irradiation. The annealing of Ra, Rb, and Rc follows first-order kinetics. The activation energies of the annihilation are determined to be 15.8-19.0, 16.0-19.5, and 23.2-26.6 kJ/mol for radicals Ra, Rb, and Rc, respectively. The kinetic study presented herein can serve as a criterion for γ-ray irradiation process in various applications, such as sterilization of polymer materials and devices.     

CRYSTAL STRUCTURE OF γ-Li_xFe_2O_3 WITH ELECTROCHEMICAL INSERTION OF Li

Crystal structure of γ-Li_xFe_2O_3,inserted Li electrochemically,was studied by Moss-bauer spectroscopy together with X-ray diffraction,XPS and electrochemical method,Onthe insertion of Li at low current density,the crystal structure is keeping original spinel;while at higher current density or by thermal activation,owing to violent movement ofLi~+ ions,part of crystal structure transforms into rock type similar to face-centeredcubic structure of ferrous oxide.The transition channels during insertion of Li~+ ions andlimitation of Li~+ ions inserted were discussed.     

富氢气氛中CO的选择性氧化——碱金属助剂对Pt/γ-Al2O3催化剂性能的影响

研究了碱金属助剂对Pt/γ-Al₂O₃催化剂选择性氧化富氢气氛中CO性能的影响。结果表明，碱金属助剂的引入对Pt/γ-Al₂O₃的催化性能有不同程度的改变，其中添加Na和K后，能明显提高低温下的CO转化率。     

Structural features of inclusion complexes of γ-cyclodextrin with various polymers

The crystalline structures of inclusion complexes of γ-cyclodextrin (γ-CD) with poly(ethylene glycol), poly(ethylene adipate), poly(propylene glycol) and poly(isobutylene) were studied by electron microscopy, in combination with X-ray diffraction works and measurements of thermal properties by DSC and TGA. The crystalline structure of as-prepared complexes was tetragonal and its cell dimensions were a = b = 2.380 nm and c = 1.48 nm. When an as-prepared sample was dried in a vacuum at room temperature, the tetragonal modification was transformed into the monoclinic one with the projected cell dimensions of a = 1.75, b = 1.36 nm and γ = 110°. The transformation occurred by progressive ‘shifting’ of rows of polymer necklaces in the [110] direction along the (110) plane in an original tetragonal lamellar crystal. Complexes lost weight by 10-15% in the process of heating up to 140 °C. The tetragonal crystalline modification was transformed into the hexagonal one, and concurrently, the X-ray diffraction profiles of annealed complexes were broadened. When a sample was dried in a vacuum at room temperature or annealed at high temperatures, followed by exposure to water vapor, the original tetragonal crystalline structure was recovered, restoring the original degree of orientation of crystallites in the sample. When water molecules were removed, the lateral stacking order of γ-CD-polymer complexes was destroyed, but the basic necklace structure in which polymer chains threaded through the cavity of γ-CD rings' structure could be retained.     

KNO_3/γ-Al_2O_3型固体超强碱催化合成香豆素的研究

对以水杨甲醛与乙酸酐为原料合成香豆素的工艺进行了改进。首次采用KNO3/γAl2O3固体超强碱催化剂的工艺路线,提高了产物的收率。同时对催化剂用量、反应物的量比、反应温度的影响进行了研究。结果表明,最佳工艺条件为:n(水杨醛)∶n(乙酸酐)=1.0∶1.6,催化剂用量为水杨醛质量的3%,反应近终点时在(210±2)℃,再保温反应0.5h,香豆素收率可达85%以上。该催化剂具有较高的催化活性,易于回收,可重复使用5次以上。     

γ-Al2O3载体制备中水洗脱氯工艺的连续化

通过正交实验，研究了γ-Al₂O₃载体制备中拟薄水铝石水洗的连续化。方差分析表明，第一阶段洗水的pH是影响脱氯效果的关键因素，初步得出水洗连续化的优化条件。与国内外传统的间歇式水洗相比，收率从80%提高到99.7%，所需洗水量仅为原来的1/3，而处理500 kg物料的生产周期也从10 h缩短到2～3 h。     

Pt-Sn工业重整催化剂失活过程金属分散性的原子尺度表征

重整催化剂活性铂原子的表面分散特性与催化剂的活性密切相关。借助球差校正扫描透射电子显微镜(Cs-STEM),针对金属Pt、Sn质量分数均为0.3%左右的低负载量的工业Pt-Sn/γ-Al₂O₃重整催化剂,采用STEM方法研究了不同工业状态下Pt原子在催化剂载体表面的分散特性。结果表明：新鲜催化剂中活性元素Pt以单原子或小原子簇形式分散,催化剂失活的过程是活性Pt原子不断聚集的过程;当Pt-Sn金属聚集体尺寸大到不能再生分散时,则催化剂活性无法恢复。本研究从工业剂角度给出了金属原子分散性与催化剂性能的构效关系。     

Thermal,mechanical and γ-ray shielding properties of micro- and nano-Ta2O5 loaded DGEBA epoxy resin composites

In this work, we have investigated the synergistic effect of micro- and nano-Ta₂O₅ fillers in the epoxy matrix on the thermal, mechanical, and radioprotective properties of the composites. Morphological analysis revealed uniform dispersion of fillers in the matrix. Both the thermal stability and tensile properties of matrices have enhanced in the presence of fillers. Although the nanocomposites showed significantly higher tensile strength and Youngs modulus compared to micro-composites, the enhancement in these properties was predominant at low loadings. Dynamic mechanical analysis indicated good interfacial adhesion and positive reinforcing effect on the matrix even at higher loading (30 wt%) of nano-Ta₂O₅. γ-Ray attenuation studies performed in the energy range of 0.356–1.332 MeV revealed better γ-ray shielding ability of nanocomposites compared to microcomposites at same weight fraction of fillers. In particular, γ-ray attenuation at 0.356 MeV for 30 wt% nano-Ta₂O₅ loaded epoxy composite was enhanced by around 13% compared to the microcomposite at the same loading. Increased surface-to-volume ratio of nanofillers and consequent increase in matrix-filler adhesion and radiation-matter interaction have manifested in an overall enhancement in the thermal, mechanical, dynamic mechanical, and radiation shielding characteristics of nano-Ta₂O₅/epoxy composites, proving them as promising γ-ray shields.     

Study on the preparation and microstructure of a single-crystal hollow turbine blade

This paper studied the structural design of a ceramic core and a blade, ceramic core localization, shell preparation, casting process, core leaching technology, and the heat treatment process of a single-crystal hollow turbine blade. The results show that the single-crystal structure solidification sequence of the blade platform is consistent with the cooling sequence and the pulling-out direction of the blade. The primary dendrites were obviously enlarged with the increase of the blade thickness owing to the change in the local cooling rate. Besides, the γ′ phase had a high uniform size distribution ranging from 0.40 to 0.60?µm after heat treatment, and the cubic degree was more homogeneous in comparison with the as-cast microstructure, which are favorable for the superalloy structure. Moreover, γ′ phase size gradually increased and its quantity gradually reduced owing to the increase of the wall thickness in the growth direction.