Y Huang
,
H.N Hao
,
Y.L. Chen and B.L.Zhou (1)Department of Materials Science and Engineering
,
Tsinghua University
,
Beijing 100084
,
China 2)Institute of Metal Research
,
Chinese Academy of Sciences
,
Shenyang 110015
,
China Manuscript received 26 August 1996)
金属学报(英文版)
A new way of designing and preparing silicon nitride ceramic composite with high fracture toughness and nacre structure has been proposed. To mimic the laminated structure of nacre, Si_3N_4 matrix ceramic layer can be obtained through compacting rolling method. To mimic the secondary toughening of nacre structure, SiC whisker is added into Si_3N_4 and acts as the secondary toughening phase. Boron nitride (BN)is selected to mimic the organic layer in nacre so as to form the weak interfaces between Si_3N_4 layers. Alumina is added into BN to adjust the bonding strength of the interface.The Si_3N_4 sheets are stacked into the die after coating with BN. After the removal of the organic matter in them, the green body is hot pressed at 1820℃for 1.5 hours under N_2 atmosphere. The fracture toughness of the so-made Si_3N_4 composite at room temperature is 20.36MPa m~(1/2), the three-point bending strength at room temperature is 651.47MPa. The crack spreads and deflects along the interface between BN and Si_3N_4 layer and extends through the BN layer into Si_3N_4 layer. The improvement of the fracture toughness may be due to the staircase-shape-like crack which provides the long crack path, the fracture and deformation of Si_3N_4 layer, and the pullout of SiC whiskers from the Si_3N_4 layer.
关键词:
:secondary toughening
,
null
,
null
,
null
李建权
,
程平
,
王鸿梅
,
王占新
,
储焰南
,
周士康
量子电子学报
doi:10.3969/j.issn.1007-5461.2004.03.005
在流动余辉质谱装置上,利用He的空心阴极放电产物与H2O反应制备了反应物离子H3O+(H2O)n(n=0～4),并观察了H3O+(H2O)n(n=0～4)与CH3OH、C2H5OH反应的产物离子,对它们进行了归属,分析了各种产物离子形成的离子-分子反应机制.
关键词:
光谱学
,
流动余辉质谱
,
甲醇
,
乙醇
万永中
,
张志明
,
沈荷生
,
何贤昶
,
张卫
,
王季陶
无机材料学报
doi:10.3321/j.issn:1000-324X.1999.06.002
通过热力学分析从理论计算上给出了C-H-N体系中低压生长金刚石的三元相图.该相图中存在金刚石生长区.不同温度和压强下金刚石生长区几乎都位于CH4-N连线以下,并且随衬底温度的改变而有显著的变化.随着氮含量的增加,金刚石生长区向碳含量减少的方向移动.使用该相图对优化添加含氮气源生长金刚石的实验条件提供了理论依据.
关键词:
金刚石
,
含氮气源
,
相图
,
化学气相淀积
Journal of Materials Research
The effect of Li(3)N additive on the Li-Mg-N-H system was examined with respect to the reversible dehydrogenation performance. Screening Study with varying Li(3)N additions (5, 10, 20, and 30 mol%) demonstrates that all are effective for improving the hydrogen desorption capacity. Optimally, incorporation of 10 mol% Li(3)N improves the practical capacity from 3.9 wt% to approximately 4.7 wt% hydrogen at 200 degrees C, which drives the dehydrogenation reaction toward completion. Moreover, the capacity enhancement persists well over 10 de-/rehydrogenation cycles. Systematic x-ray diffraction examinations indicate that Li(3)N additive transforms into LiNH(2) and LiH phases and remains during hydrogen cycling. Combined structure/property investigations suggest that the LiNH(2) "seeding" should be responsible for the capacity enhancement, which reduces the kinetic barrier associated with the nucleation of intermediate LiNH(2). In addition, the concurrent incorporation of LiH is effective for mitigating the ammonia release.
关键词:
complex hydrides;improvement;mixtures;imides;amide;h-2
刘长友
,
谷智
,
王涛
,
查钢强
,
介万奇
功能材料
研究了低浓度（0.01～0.20mol/L）N2H4.H2O条件下ZnO微晶的低温水热结晶特性。N2H4.H2O弱碱性和N2H5＋吸附配位性影响ZnO微晶的形核和各晶面的生长速率。随着N2H4.H2O浓度的提高,ZnO微晶分别呈板条状、六角片状和六角棒束状。碱性分散剂和超声的分散作用影响主要在成核阶段;受分散剂弱碱性的影响,0.20mol/L N2H4.H2O显现出强的还原性,N2气泡模板生长机制使所制ZnO微晶呈六角管状晶须束。
关键词:
氧化锌
,
水热合成
,
结晶习性
,
水合肼
程平
,
王鸿梅
,
李建权
,
张为俊
,
曹德兆
,
储焰南
量子电子学报
doi:10.3969/j.issn.1007-5461.2003.03.006
利用微波放电电离质谱装置,分别通过N2与O2、水蒸气与空气的微波放电,产生了大气中存在的NO+和H3O+.(H2O)n离子,动力学过程的分析和讨论表明这几种离子是由大气中的初始反应离子N+2、N+、O+2、O+与周围环境中的原子、分子经过一系列的离子-分子反应产生的.这一结论也同时模拟了大气中NO+和H3O+.(H2O)n的形成过程.
关键词:
微波放电
,
大气
,
离子化学
江俊勤
量子电子学报
doi:10.3969/j.issn.1007-5461.2004.06.027
通过数值计算,研究了增加光子双模压缩真空态的N次方H压缩效应.结果表明:对于态,光场存在着N次方H压缩效应,而且对于高次方H压缩,在压缩参数较大时,随着场模上光子增加数的增大,N次方H压缩效应增强.
关键词:
量子光学
,
光场
,
增加光子双模压缩真空态
,
N次方H压缩效应
,
H压缩度
Journal of Alloys and Compounds
Motivated by the ion migration mechanism proposed by David et al. [J. Am. Chem. Soc. 129 (2007) 1594-1601], we mechanically mill the Li3N/Co powder mixture to obtain defective Li3N-type structure with enhanced Li+ mobility. Compared with Li3N the hydrogen storage property of such defective phase is markedly improved, presumably due to the ion-migration-enhancing effect from the incorporation of Co and Fe (from milling utensils). During subsequent cycling, however, this effect cannot persist due to the precipitation of Co-Fe alloy upon hydrogenation. The close correlation between Co-Fe incorporation/precipitation and property variation of Li3N hydrogen storage material provides a preliminary evidence to support the ion migration mechanism. (C) 2007 Elsevier B.V. All rights reserved.
关键词:
Hydrogen absorbing materials;Nitride materials;hydrogen-storage;lithium amide;mechanism;nitride;batteries;mixtures;hydride;imides;linh2;anode
Journal of Physical Chemistry C
The Li-Mg-N-H system was prepared by reacting magnesium amide [Mg(NH(2))(2)] with lithium nitride (Li(3)N) and investigated with regard to the hydrogen storage properties. Our study shows that the present method is superior to the conventional route in enhancing the reversible dehydrogenation properties. Through optimizing the Li(3)N:Mg(NH(2))(2) ratio in the starting materials, the reversible capacity of U-Mg-N-H system increases to 4.9 wt %, 18% higher than that typically obtained from the Mg(NH(2))(2) + 2LiH mixture at 200 degrees C. Furthermore, increasing the Li(3)N:Mg(NH(2))(2) ratio is effective for mitigating the ammonia release from thus-prepared samples. Combined property/structure investigations indicate that the obtained enhancements should be ascribed to the effects of LiNH(2) and LiH that were in situ generated from the excess Li(3)N. LiNH(2) may promote the dehydrogenation reaction via seeding the reaction intermediate. The concurrently generated LiH acts as an effective ammonia trapping agent. These findings highlight the potential of "intermediate seeding" as a strategy to enhance the reversible hydrogen storage properties of metal-N-H systems.
关键词:
complex hydrides;ultrafast reaction;amide;improvement;desorption;linh2;destabilization;mechanism;mixtures;imides
