新型多孔氮化硼材料

多孔氮化硼材料是一种新型多孔非氧化物材料,具有高比表面积、可调孔径、良好的化学惰性和热稳定性等特点,在催化、储氢、气体吸附和分离等领域具有巨大的应用潜力,是材料领域研究热点之一。依孔径的不同,多孔氮化硼材料被分为微孔氮化硼、介孔氮化硼、大孔氮化硼和多级孔氮化硼。本文综述了微孔、介孔、大孔及多级孔等类型氮化硼材料的研究进展。重点介绍了不同类型氮化硼材料的制备和性能,并分析了各种制备方法的优缺点,最后探讨了多孔氮化硼材料的发展前景。     

Controllable synthesis of high aspect ratio Mg_2B_2O_5 nanowires and their applications in reinforced polyhydroxyalkanoate composites

Highly pure magnesium borate （Mg2B2O5） nanowires with an average diameter of - 30 nm, an average length of 15 μm, and a high aspect ratio of - 500 have been synthesized on a large scale via a two-step method. MgBO2（OH） nanowires with high aspect ratios were first prepared via a PVP-assisted hydrothermal technique. Using these nanowires as precursors, single crystalline Mg2B205 nanowires were synthesized by post-annealing treatment at a relatively low temperature of 700 ℃. The important effect of the MgBO2（OH）-Mg2B2O5 conversion process on the morphology of the Mg2B2O5 nanowires was investigated and it was indicated that the recrystallization process plays an important role in the protection of the one-dimensional （1D） nanostructure. Moreover, the rigidity and the toughness of the Mg2B2O5 nanowire- reinforced PHA composites were tremendously improved compared to those of the pure PHA. Our results demonstrate the effectiveness of Mg2B2O5 nanowires for reinforcement applications in polymer composites.     

Luminescence of Ce3+ in lanthanum silicon oxynitride

The luminescence properties of lanthanum silicon oxynitride(La-Si-O-N) series doped by trivalent Ce ions have been investigated to seek for tunable wavelength-conversion phosphor for white light emitting diode applications.Four compound hosts of LaSiO2N,La4Si2O7N2,La5Si3O12 N,and La2Si6O3N8 were synthesized and examined in this work.Crystallographic examination for the equal amount of Ce 3+ substitution indicated that the covalency degree decreased in a sequence LaSiO2 N > La2Si6O3N8 > La4Si2O7N2 > La5Si3O12 N,not simply in correlation to the ratio of N3/O2.Excitation and emission spectrum measurements showed the main features of Ce3+ luminescence in the series:the centre of gravity of 5d bands depends on crystal-field splitting more strongly than that on covalency of Ce-N bonding;nephelauxetic effect could not be observed clearly for the investigated series;to some extent Stokes shift was dominated by crystal-field splitting rather than Ce-N covalency degree.     

Ce1-xYxFe2的电子结构和磁性质

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Tb2Fe17-xSix单晶磁性和窄畴壁的研究

在Tb₂Fe₁₇化合物中用Si替代Fe观察到晶格参数减小和居里温度升高.平均场理论分析指出,Si对Fe的替代使Fe-Fe间的交换作用明显增强、Tb-Fe间交换作用轻微地减弱.通过拟合Tb₂Fe_17-xSi_x(x=0.0,1.0,2.0,3.0,3.3)单晶的磁化曲线,得到了化合物在不同组分和温度下的各向异性常数.在Tb₂(Fe,Si)₁₇单晶的磁化和退磁     

Ab initio study of the electronic structure and elastic properties of Al5C3N

We investigate the electronic structure, chemical bonding and elastic properties of the hexagonal aluminum carbonitride, Al₅C₃N, by ab initio calculations. Al₅C₃N is a semiconductor with a narrow indirect gap of 0.81 eV. The valence bands below the Fermi level (E_F) originate from the hybridized Al p-C p and Al p-N p states. The calculated bulk and Young's moduli are 201 GPa and 292 GPa, which are slightly lower than those of Ti₃SiC₂. The values of the bulk-to-shear-modulus and bulk-modulus-to-c44 are 1.73 and 1.97, respectively, which are higher than those of Ti₂AlC and Ti2AlN, indicating that Al₅C₃N is a ductile ceramic.     

Sr和Ba替代对Eu掺杂Ca2.955Si2O7的结构和发光特性的影响研究

利用固相反应法制备了Sr和Ba替代的Ca_2.955-xM_xSi₂O₇: 0.045Eu²⁺ (M= Sr, Ba, x= 0.1-0.5)系列荧光粉, 利用较大离子半径的Sr和Ba元素替代Eu掺杂Ca_2.955-xM_xSi₂O₇ 中的Ca元素,研究Sr和Ba替代对样品结构和发光特性的影响. X射线衍射测试结果表明,少量Sr和Ba替代不会改变基质的晶体结构, 样品仍然为单斜晶系.未替代前, Ca_2.955Si₂O₇: 0.045Eu²⁺ 样品的发射峰在574 nm左右,随着Sr含量的增加,样品的发射峰发生蓝移; 而Ba含量在x= 0.1-0.4时不会引起发射峰位置的移动, 但x= 0.5样品的发射峰发生蓝移.同等含量的Sr和Ba部分替代样品中的Ca元素, Ba替代样品的光谱强度较强.     

石墨烯纳米结构的制备及带隙调控研究

石墨烯在未来微电子学领域有极大的应用前景,但是其零带隙的特点阻碍了石墨烯在半导体领域的应用.研究发现,打开室温下可用的石墨烯带隙所需要的石墨烯纳米结构尺度在10 nm以下,这一尺度的纳米结构一方面制备比较困难,另一方面器件可承载的驱动电流较小.因此,如何实现亚10 nm石墨烯纳米结构的有效加工以及如何在有效调控带隙的基础上增大石墨烯器件可承载的驱动电流,还需要进一步的研究.本文首先研究了利用聚甲基丙烯酸甲酯/铬(PMMA/Cr)双层结构工艺,通过刻蚀时间的控制,利用电子束曝光及刻蚀工艺实现了亚10 nm石墨烯纳米结构的可控制备.同时设计并制备了单排孔石墨烯条带结构,该结构打开的带隙远大于相同特征宽度石墨烯纳米带所能打开带隙的大小.该结构在有效打开石墨烯带隙的同时,增加了石墨烯纳米结构可以承载的驱动电流,有利于石墨烯在未来微电子领域的应用.     

耦合高压斯特林制冷效应的复合磁制冷循环的数值模拟

本文借助计算流体力学软件, 对复合磁制冷机进行整机数值模拟分析. 以复合磁制冷机为建模原形, 分别计算了主动式磁制冷循环以及复合磁制冷循环. 利用模型计算分析了利用系数, 工作频率对主动式磁制冷的制冷效果影响, 同时模拟计算了不同相位角、不同频率下的复合磁制冷机的制冷效果, 计算得到适合复合磁制冷循环的最佳匹配相位角. 模拟计算结果对后续实验台的设计搭建有很好的指导作用.     

用于高性能锂-硫电池的氮化硼纳米片/碳纤维改性隔膜

通过静电纺丝、热亚胺化和碳化过程,将氮化硼纳米片(BNNSs)负载在碳纤维(CFs)表面,组成用于修饰商业聚丙烯(PP)隔膜的氮化硼纳米片/碳复合纤维(BNNSs/CFs)复合材料。BNNSs和CFs的协同作用为电池提供了额外的导电路径,并将可溶性多硫化锂固定在正极区域。结果表明,采用10BNNSs/CFs-PP隔膜的电池在0.05C下的初始放电容量高达1 295.7 mAh·g^-1,当电流密度增加到1C时,以10BNNSs/CFs-PP为隔膜的电池也具有良好的长期循环稳定性,在400次循环后最终容量高达568.1mAh·g^-1,每次循环容量衰减0.073%。