聚碳硅烷制备近化学计量SiC纤维的研究进展

综述了聚碳硅烷制备近化学计量比SiC纤维的研究进展,总结了H2在PCS纤维裂解过程中的作用机理,比较了纯H2气氛、分阶段不同气氛、全过程H2/Ar混合气氛条件下得到的SiC纤维的组成和性能变化规律.纯H2气氛800℃以上保温4h,可得到近化学计量比SiC纤维;分阶段气氛下,气氛转换温度为800℃,烧结至1300℃保温1h,可得到近化学计量比SiC纤维;混合气氛下,氢气浓度为60%左右,烧结至1300℃保温1h,可得到近化学计量比SiC纤维.在这些气氛条件下得到的近化学计量比SiC纤维,烧结后的高温力学性能均优于非化学计量比SiC纤维.     

Crystallization, morphology and luminescent properties of YAG：Ce^3＋ phosphor powder prepared by polyacrylamide gel method

A novel synthesis process, based on the polyacrylamide gel method, was used to prepare Ce-doped YAG phosphor powders. Effects of heat treatment parameters, temperature and holding time, the fluxes, and atmosphere on microstructure and particle morphology as well as luminescent properties of YAG：Ce^3＋ phosphor powders were studied by X-ray powder diffractometry, scanning electron microscopy, and fluorescence spectrophotometry. The results show that the formation temperature （1 000 ℃） of pure YAG phase is significant low when being synthesized by the polyacrylamide gel method, compared with solid-state reaction. For luminescent properties, the intensity of emission of YAG：Ce^3＋ phosphor increases steadily with increasing temperature from 900 ℃ to 1 300 ℃ and prolonging holding time from 100 min to 400 min. But blue shift phenomenon is observed for 400 min calcination Fluxes as BaF2 and H3BO3 can enhance the intensity of emission of phosphor due to the improvement of crystallization of YAG and the stabilization of trivalence cerium ion in YAG host lattice at high temperature. Weak reduction atmosphere can contribute to improvement of the emission intensity of YAG：Ce^3＋ phosphor powders.     

Preparation of YAG：Ce^3＋ phosphor by sol-gel low temperature combustion method and its luminescent properties

YAG：Ce^3＋ phosphor was prepared by sol-gel low-temperature combustion method. The effects of the precursor properties and calcining temperature on the crystallization process, microscopic morphology and luminescent properties of phosphor were studied. The results indicate that the pure phase of YAG can be obtained at 800 ℃ by sol-gel low temperature combustion method, using citric acid as complexing agent. When the molar ratio of metal ion to citric acid is 2.0 and pH value is 2, the crystallinity increases and the phosphor particle size grows up gradually with the increase of the calcining temperature. The powders were characterized through thermal analysis, X-ray diffraction analysis and scanning electron microscope analysis. The excitation spectra of YAG：Ce^3＋ phosphor take on a double peak structure, and the peak value of the main excitation spectra occurs at 460 nm and that of the emission spectra is near 530 nm. With the gradual increase of the calcining temperature, the peak position of excitation and emission spectra remains basically unchanged, but its relative intensity increases gradually.     

射线屏蔽用钨合金大制品的微观结构和机械性能研究

采用先进的钨合金生产和检测工艺,研制了高密度、大尺寸的钨合金屏蔽件。其微观结构均匀,但在某些局部地区的W颗粒和液相的分布是不均匀的,存在大约10μm残余气孔。通过超声波检测,在屏蔽部件内部未检测到超过3 mm的残余气孔。开发的钨合金屏蔽件满足了对辐射源进行屏蔽的作用,对转运过程中的安全性也进行评估。     

作战任务的关系方程

描述了对抗体系的一般系统特征,分析了作战任务关系方程的约束条件,建立了作战任务关系方程,给出了作战任务关系方程的一般求解思路．     

作战任务的关系方程

描述了对抗体系的一般系统特征,分析了作战任务关系方程的约束条件,建立了作战任务关系方程,给出了作战任务关系方程的一般求解思路.     

牵引火炮机动能力

通过对机动能力构成分析，确定了影响机动能力的因素，建立了牵引火炮机动能力评估模型，并对国外典型的3种牵引火炮的机动能力进行了评估．     

聚碳硅烷制备连续SiC纤维的不熔化处理工艺研究进展

综述了先驱体转化法制备SiC纤维过程中聚碳硅烷(PCS)的各种不熔化处理方式及其发展状况.通过不熔化方式对终烧产物SiC纤维性能的比较,讨论了各种不熔化方式的优缺点及其对SiC纤维中氧含量的影响,并指出了制备高性能SiC纤维不熔化技术研究的国内外差距及发展趋势.     

牵引火炮机动能力

通过对机动能力构成分析,确定了影响机动能力的因素,建立了牵引火炮机动能力评估模型,并对国外典型的3种牵引火炮的机动能力进行了评估.     

粉末烧结法制备钨发热元件涂层及性能研究

以高纯度(质量分数99.95%)钨粉为原料,通过丝网印刷的工艺,在钨发热元件表面高温烧结,得到了疏松、多孔的钨涂层。采用扫描电镜观察了不同状态下钨片及涂层表面,通过粗糙度计测得了样品表面粗糙度,检测了涂层表面的硬度,并对比了不同表面状态下钨片的辐射系数。结果表明,通过粉末高温烧结后,多孔、粗糙的表面能显著提高钨片的辐射系数。