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排序方式: 共有8209条查询结果,搜索用时 15 毫秒
941.
《Intermetallics》2015
The native point defects in C14 Mg2Ca Laves phase are studied from the first-principles density functional theory calculations within GGA approximation. The defect formation energies indicate that anti-site defects are energetically favored over vacancies. Under Mg-rich and even general Ca-rich condition, defect MgCa of Mg anti-site on Ca sublattice is favorable owing to the lowest formation energy. The CaMg2 defect of Ca anti-site on Mg2 sublattice is also likely dominant only under extreme Ca-rich environment. The present results could explain reasonably the asymmetric off-stoichiometry of Mg2Ca. The effective point defect concentrations of Mg2Ca as a function of composition and temperature at experimental range are also calculated from a canonical statistical model, and the derived results show a linear relationship between the logarithm of defect concentration and T−1. Geometrical factor is further studied, and it is found that atomic size possesses an obvious influence on the structure of point defect in Mg2Ca. The electronic feature is further studied to reveal underlying mechanism for formation of point defects. 相似文献
942.
《Intermetallics》2015
Available data on the temperature dependence of yield stress and of associated activation volume of high-purity NiAl single crystals between 76 and 205 K have been analyzed within the framework of a solid-solution hardening model, which is based on the concept of depinning of an edge-dislocation segment from several randomly dispersed, isolated, point defects simultaneously. The vacancies in NiAl single crystals act as point-defect obstacles to the stress-assisted thermally-activated glide of edge dislocations, and their concentration is estimated as about 10 at.%. The product of yield stress and associated activation volume (≈0.146 eV) is found to be independent of temperature and yield stress, as envisaged in the model. 相似文献
943.
944.
针对客户反馈的SAE6150工具钢表面花斑形貌问题,对其宏观形貌和成分进行了检测分析,发现产生花斑形貌的直接原因是由于原料盘条表面存在不平整的微凹坑,平面和凹坑面在光的反射作用下呈现明暗不同的视觉色差,从而形成肉眼可见的花斑形貌。微凹坑产生的原因是盘条在轧制过程中表面残留氧化铁皮轧制压入而造成的;另外,盘条拉拔前的鳞皂化处理致使大量皂化液进入凹坑凝固后形成塞积物,盘条拉拔后凹坑难以去除而形成黑白相间的花斑形貌。为此,提出了相应改进措施,从根本上解决了热轧盘条表面缺陷问题。 相似文献
945.
分析了340 MPa级冷轧低合金高强度钢“桔皮”缺陷钢板和正常钢板的微观组织结构和力学性能。结果表明,缺陷钢板的应力-应变曲线屈服点伸长率达到了3.73%,屈服延伸过大导致了所冲压的前风窗横梁连接板表面产生“桔皮”缺陷。在实验室采用对钢板预拉伸的方法模拟钢板工业化生产的平整与拉伸矫直工艺,随着预拉伸量的增加,试验样屈服平台的长度减少,当预拉伸量超过1.8%时,试验样的屈服平台消失。微观组织进一步分析显示,退火温度高导致钢板晶粒粗大和晶粒取向异常是冲压钢板 “桔皮”缺陷产生的根源。在连续退火工艺环节中合理控制平整和拉伸矫直工艺可以消除或者缩短试验钢屈服平台长度,并避免冲压件表面“桔皮”缺陷发生。 相似文献
946.
Dong Wang Xiaojun Gu Guanwei Liu Guofang Huang Yue Cao Yan Guo 《International Journal of Hydrogen Energy》2021,46(7):5158-5168
Construction of structural defects in photocatalysts is a powerful tool for regulating their photocatalytic performance. In this work, we develop a facile one-step coupling cold plasma and thermal polymerization approach to synthesize a series of nitrogen defect-rich graphitic carbon nitrides (C3N4-x), which are used for visible-light-driven hydrogen generation from water. The nitrogen defect-induced band structure regulation of C3N4-x catalysts can be carried out through controlling the bombardment time and excitation power of generator during the plasma modification process. The defective C3N4-x catalysts have the extended visible light absorption and improved separation efficiency of photogenerated charge carriers, which results in the boosted hydrogen generation activity. Particularly, the optimal C3N4-x possesses a hydrogen generation rate of 2.46 mmol h?1 g?1, which is about 4.5 times higher than the pristine C3N4 synthesized by the single thermal polymerization of urea. The cold plasma modification-based one-step synthesis approach guides us for rationally designing defective nanomaterials with excellent catalytic performance. 相似文献
947.
针织用涤纶短纤维对纤维质量特别是疵点的含量要求较高,目前纤维中疵点的检验方法有手检法和原棉分析机法,这两种方法只能检出质量在0.1 mg以上的疵点,而针织用短纤更关注0.1 mg以下的小疵点,现有的分析方法无法满足下游纺织用户的质量要求。建立了一种新的疵点检验方法——染色疵点分析方法,先对纤维进行染色,然后再挑出异常纤维即疵点。 相似文献
948.
《Ceramics International》2019,45(10):12994-13003
The temperature and dc bias stability of the dielectric constant and loss tangent of CaCu3Ti4O12 samples sintered under different oxygen atmospheres are discussed. The results suggest that the metal-oxygen vacancy related defects not only provide the charge carriers for the conduction (defect doping) but also contribute to the huge permittivity in the way of defect dipoles repositioning under charge carrier hopping. The charge localization in a specific copper-oxygen vacancy defect complex is the reason of the huge and stable permittivity and low dielectric loss in the middle temperature range, 90 K-200 K (20 Hz), while the implementation of the large barrier layer height needs a contribution by the titanium oxygen vacancy related trap charges in the grain boundaries, which also lead to a second permittivity stable range in a higher temperature range 200 K–300 K. 相似文献
949.
950.