沈彩万
,
Yasuhisa Abe
,
David Boilley
原子核物理评论
doi:10.11804/NuclPhysRev.30.03.284
利用最近发展起来的两步模型分析重离子核反应48Ca+254Es的熔合过程.在这个模型中,熔合过程被分为前后独立的两个过程,即粘连过程和形成过程.本研究组计算了对应的粘连概率和形成概率,并结合适用于蒸发过程的统计蒸发模型,计算了该反应合成119号超重元素的剩余截面,即当Elab=250.2 MeV时,得到最大剩余截面为0.7 pb.
关键词:
超重核
,
热熔合
,
粘连概率
,
形成概率
,
剩余截面
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 the American Ceramic Society
Search for new thermal barrier materials with high-temperature stability is very difficult because there are intractable choices among thousands of possible candidates. The present paper shows that identifying and developing new low thermal conductivity materials can be accomplished by first-principles calculations of equilibrium crystal structure and elasticity, and thereafter making theoretical prediction of minimum high-temperature lattice thermal conductivity basing on David Clarke's method for insulating materials. We highlight a new oxynitride ceramic, Y4Si2O7N2, with a low theoretical minimum thermal conductivity of 1.12 similar to W center dot m-1 center dot K-1. The theoretical result is further validated by experimental measurement of thermal conductivity of dense and bulk Y4Si2O7N2. The experimental thermal conductivity is 1.50 similar to W center dot m-1 center dot K-1 at 1300 similar to K. Furthermore, thermal properties of Y4Si2O7N2 are investigated for evaluating its potential performances.
关键词:
theoretical elastic stiffness;barrier coatings;mechanical-properties;gas;gamma-y2si2o7;crystal;y2sio5;system;phase;si3n4-sio2-y2o3
Acta Materialia
In order to achieve better understanding of the structural/property relationships of La(2)T(2)O(7) (T = Ge, Ti, Sn, Zr, Hf) pyrochlore, first-principles calculations were conducted to investigate the bonding characteristics, elastic stiffness, structural stability and minimum thermal conductivity. The results show that the relatively weak La-O bonds play a predominant role in determining the structural stability, mechanical and thermal properties of these compounds. In addition, the elastic and thermal properties are influenced when the T atom changes from Ge to Hf. When the bonding strength is enhanced by applying hydrostatic pressure, apart from c(11), c(12), and B, which normally increase at high pressures, it is found that the shear elastic moduli, c(44) and G, which relate to the shear deformation resistance, abnormally remain almost constant. The underlying mechanism may help to explain the damage tolerance of pyrochlore compounds. After comprehensive consideration of the elastic anisotropy, a modified David Clarke-type equation is used to calculate the minimum thermal conductivity of the studied pyrochlore materials, which display an extraordinary low thermal conductivity. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
关键词:
Non-binary oxides;Mechanical properties;Thermal conductivity;Density;functional theory;Local density approximations (LDA);oxide pyrochlores;a(2)b(2)o(7);simulation;disorder
