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报告题目：Solubility and Internal Stress in Nanograined Materials and Nanoparticles

主讲人：香港科技大学张统一院士

时间：5月27日下午15:00-16:30

地点：威廉希尔531报告厅

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张统一院士简介：

张统一院士现为香港科技大学机械系终身教授。2011年当选中国科学院院士。分别于1982年和1985年在北京科技大学材料物理专业获硕士和博士学位。毕业后获得德国洪堡基金会奖学金，于1986至1988年在德国哥廷根大学任研究员。1988至1990年在美国罗彻斯特大学进行博士后研究。1990至1993年在美国耶鲁大学任副研究员。

张院士的研究领域包括材料的机械性能、微观力学/纳米力学、微结构与材料性能的关系、铁电和压电材料、薄膜、纳米线及纳米管、微桥/纳米桥实验、扩散与相变。张院士曾于1987年和2007年两次获得中国国家自然科学二等奖，1988年获中国科学技术协会青年科技奖等多个奖项。

学术报告英文摘要：

Thedevelopment of a Gibbs-approach basedonadsorption isothermis presented for grain boundary (GB) segregation in nanograined (ng) polycrystals and for surface segregation in nanoparticles. The newly developed adsorption isotherm takes the advantages from both Gibbs and McLean adsorption isotherms and is able to analytically calculate the GB segregation when the activation energy for GB segregation and the solute concentration in the solid solution grains are available. The solute atoms inside GBs and grains possess different partial molar volumes, thereby generating an internal stress field, which, in turn, enhances the solute solubility inside grains. For an open system, the environment serves as a solute reservoir and solute atoms can move between the ng material and the environment to maintain an equivalent chemical potential of the solute. In this circumstance, the apparent solute concentration will be greatly enhanced in an ng material in comparison to its coarse-grained counterpart. This because an ng material has a large GB volume fraction, leading to more solute atoms segregated at GBs, and a considerable increase in the lattice concentration that is boosted by the concentration-induced stress field. The Gibbs-approach based adsorption isotherm allows one to analyze simultaneously stresses, concentrations and their coupling behaviors in grains and GBs. As an example, the experimental data for the H-Pd binary system are fitted with the newly developed isotherm. The perfect fitting shows an excellent agreement between the theoretical predictions and the experimental results, and determines the GB properties as well.