Infiltration of Liquid Metals in Porous Compacts: Modeling of Permeabilities During Reactive Melt Infiltration

Reactive infiltration is a fast and cost-effective technique for manufacturing ceramic-matrix composites (CMCs). CMCs are used in elevated temperature applications like rocket engine casings, jet nozzles, gas turbine blades and nuclear cladding. There is an urgent need for minimizing experimental costs as well as optimizing process parameters during manufacture, so that we have minimized manufacturing costs and reduced infiltration times. Towards this end, the objective of this research was to develop an integrated micro-macro model of reactive flow of molten silicon in a porous preform consisting of carbon-coated silicon carbide fibers and then optimize process parameters computationally. The overall objective of the research was to arrive at a modified equation of Darcy's law for flow through a porous medium with the help of numerical/computational modeling. This paper deals with the flow of silicon through porous carbon at the macro level. The macro flow of silicon was integrated with an available micro model by determining the transient porosity from the micro model and using it in Darcy's law written for the macro flow of silicon. From the results of this study, we recommend suitable process parameters such as initial temperature of the solid reactant and the specific kind of reactants to be used for achieving complete infiltration. These conclusions are drawn after observation of the rate of decrease of permeability with more reaction.     

以陶瓷厚膜为绝缘层的红色ZnS:Sm,Cl电致发光器件

报道采用高介电常数的陶瓷厚膜作绝缘层、ＺｎＳ：Ｓｍ,Ｃｌ作为发光层的红色薄膜电致发光器件。测量了器件的电致发光光谱和亮度电压曲线,研究了发光机理和效率电压等特性。制备的器件在电驱动下１６Ｖ启亮,最大亮度为１８．４ｃｄ／ｍ＾２,最大效率为０．０６１ｍ／Ｗ。     

负压区的存在对刚性陶瓷过滤器脉冲反吹性能的影响

利用压电式压力传感器测定了陶瓷过滤器在脉冲反吹过程中滤管内动态压力的变化规律,表明在脉冲反吹快要结束和正常过滤尚未开始的过渡过程中,滤管内存在严重的负压区。利用单个颗粒轨道模型分析了部分已被吹离滤管表面的小颗粒在负压区的作用下会重新返回到滤管壁,从而证实了负压区是影响刚性陶瓷过滤器稳定运行的重要原因。     

Preparation of Si/C/Al/N ceramics by pyrolysis of polyaluminasilazanes

Polyaluminasilazanes were prepared quantitatively by reaction of oligosilazanes (RSi(H)NH) _n (R = Me, Et) with various amounts of either trimethylaluminum, (CH₃)₃Al, or dimethylaluminum amide, (CH₃)₂AlNH₂. The products were characterized by ¹H, ²⁹Si and ²⁷Al NMR and IR spectroscopy. Alkylation of the Si H groups was observed when trimethylaluminum was used. Their pyrolysis was carried out under argon or ammonia. Ceramic residues were obtained in high yield and were characterized by elemental analysis and X‐ray powder diffraction. Formation of mixed ceramics containing silicon nitride, silicon carbide and/or aluminum nitride was observed depending on the precursor and the experimental procedure that was used. The thermal decomposition of the polyaluminasilazane between 50 and 700 °C was investigated by IR analysis of the gas evolved during the pyrolysis. Molecular aluminasilazanes were studied as model compounds. Copyright © 1999 John Wiley & Sons, Ltd.     

光催化-膜分离集成反应器及其应用

 设计了一种新型光催化-陶瓷膜分离集成反应器,在反冲条件下利用此集成反应器进行了甲基橙光催化氧化反应,分别考察了陶瓷膜对光催化剂TiO2微粉的截留率、膜的渗透通量、光催化氧化脱色率以及不同膜分离压力下的光催化反应速率常数. 结果表明,TiO2-甲基橙悬浆液体系中TiO2微粉的截留率可达到99.9%, 经集成反应器完成一个反应周期后甲基橙氧化脱色率达到10%, 光催化氧化脱色效果高于圆柱式反应器.     

Influence of the Si–O–C interplayer on the flexural behaviors of C/Si–C–N composites

Carbon fiber reinforced Si–C–N matrix composite(C/Si–C–N) with a Si–O–C interlayer (C/Si–O–C/Si–C–N) was fabricated via CVI and PIP process. The flexural behaviors of C/Si–O–C/Si–C–N were investigated using the three-point-bending method and the SEM technique. The results indicated that the flexural strengh of the C/Si–O–C/Si–C–N increases with increasing temperature and the modulus of the composite is essentially unchanged. The strength of C/Si–O–C/Si–C–N is comparable to that of C/PyC/Si–C–N, and the role of Si–O–C interlayer in C/Si–C–N can rival that of the PyC interlayer. The weaker interfacial bonding and the larger thickness of Si–O–C interlayer make a contribution to this at RT while the thinner interlayer and unstable structure of Si–O–C interphase do it above 1300 °C.     

Insight into 3D micro‐CT data: exploring segmentation algorithms through performance metrics

Three‐dimensional (3D) micro‐tomography (µ‐CT) has proven to be an important imaging modality in industry and scientific domains. Understanding the properties of material structure and behavior has produced many scientific advances. An important component of the 3D µ‐CT pipeline is image partitioning (or image segmentation), a step that is used to separate various phases or components in an image. Image partitioning schemes require specific rules for different scientific fields, but a common strategy consists of devising metrics to quantify performance and accuracy. The present article proposes a set of protocols to systematically analyze and compare the results of unsupervised classification methods used for segmentation of synchrotron‐based data. The proposed dataflow for Materials Segmentation and Metrics (MSM) provides 3D micro‐tomography image segmentation algorithms, such as statistical region merging (SRM), k‐means algorithm and parallel Markov random field (PMRF), while offering different metrics to evaluate segmentation quality, confidence and conformity with standards. Both experimental and synthetic data are assessed, illustrating quantitative results through the MSM dashboard, which can return sample information such as media porosity and permeability. The main contributions of this work are: (i) to deliver tools to improve material design and quality control; (ii) to provide datasets for benchmarking and reproducibility; (iii) to yield good practices in the absence of standards or ground‐truth for ceramic composite analysis.     

HCCB-DEMO氦冷固态包层热工水力计算及分析

根据这几年HCCB-DEMO包层技术的发展,对原氦冷固态氚增殖包层进行相应设计改进。利用三维有限元软件CFX对该改进设计进行了热工水力学计算及分析。分析模型包括：第一壁,增殖单元,筋板以及三者集成模型。结果表明：各子部件在单独分析的情况下,材料最高温度低于设计要求限值;冷却剂进出口温度为300/500°C,满足设计需求。同时对比分析了集成计算及单独计算的结果,得出第一壁与铍球床之间的相互热作用较大,铍球床材料最大温度会高于设计限值。针对经集成计算后发现的问题,未来将对氦冷固态包层的设计进行进一步的优化。     

Ce:YAG晶体和透明陶瓷的光学和闪烁性能

采用温梯法生长了Ce:YAG晶体和真空烧结法制备了Ce:YAG透明陶瓷,并对晶体和透明陶瓷的光学和闪烁性能进行了对比研究.Ce:YAG晶体和陶瓷都具有位于230,340和460 nm波段的Ce³⁺离子的特征吸收带和540 nm附近的发射峰,但Ce:YAG晶体同时存在296和370 nm的色心吸收,其发射峰位于398 nm,而透明陶瓷中不存在.Ce:YAG晶体和陶瓷的X射线荧光中均存在520 nm附近的Ce³⁺离子发射,但晶体中还存在由反格位缺陷引起的300 nm 关键词： Ce:YAG 闪烁晶体 透明陶瓷     

LD抽运的Nd:YAG陶瓷/KTP绿光激光器

报道了一种LD端面抽运Nd:YAG陶瓷、KTP腔内倍频的全固态连续波绿光激光器.当抽运功率为21.6 W时,1064 nm基频输出达到11.3 W,光—光转换效率为52.3%.采用Ⅱ类切割的KTP晶体作为腔内倍频介质,在直腔结构下获得了最大功率为1.86 W的532　nm绿光输出,光—光转换效率为7%.输出光斑具有高斯型强度分布,1 W输出时的M²因子约为1.7. 关键词： 全固态绿光激光器 Nd:YAG陶瓷 KTP倍频 直腔