题　 目：Interfacial “Phase” Transitions: Solving Old Materials Science Problems and Tackling New Energy Challenges

报告人：Luo Jian (骆建)　　Assoc. Prof. @ Clemson University, USA

时　 间：5月28日（周五）　上午9：00-11:00

地　 点：李薰楼468房间

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Interfacial “Phase” Transitions:
Solving Old Materials Science Problems and Tackling New Energy Challenges

Jian Luo

School of Materials Science and Engineering, Clemson University

Abstract:

A piece of ice melts at 0 °C, but a nanometer-thick surface layer of the ice can melt at tens of degrees below zero. This interfacial phenomenon, known as “premelting,” was first recognized by Michael Faraday in 1842.  Recent research in understanding analogous but more complex interfacial phenomena at both grain boundaries and free surfaces in multicomponent ceramics and metals may provide transformative concepts to engineer a broad range of advanced materials.

Equilibrium-thickness intergranular films (IGFs) have been widely observed in ceramic materials, where they often control microstructural evolution and mechanical/electronic properties [1]. 　Recently, we observed the "free-surface counterparts" and "metallic counterparts" to these well-known IGFs in ceramics. On one hand, systematical measurements of surficial amorphous films (SAFs) in binary oxides suggest that they can be interpreted as multilayer adsorbates formed from coupled prewetting and premelting transitions [2], but the wetting behaviors can be significantly modified by vdW London dispersion forces [3]. On the other hand, we have made direct HRTEM observations of nanoscale quasi-liquid IGFs in Ni-doped W and Mo alloys [4]. Using CalPhaD data, a premelting type model predicts the onset of grain boundary disordering at as low as 60-85% of the bulk solidus lines in several refractory alloys [5]. This model, along with HRTEM studies, quantitatively explains the origin of “solid-state activated sintering,” thusly solving an outstanding scientific problem that had puzzled the materials community for decades [5, 6]. By combining diffuse-interface and lattice-gas models and incorporating colloidal type interfacial forces, a more sophisticated model produces a series of grain boundary “phases” [7] with phenomenological similarities to the newly observed “Dillon-Harmer complexions” [8]. 

The concepts of thermodynamic stabilization of subsolidus quasi-liquid interfacial films and interface “phase” transitions offer new clues to solve several long-standing problems in materials science. In addition to solid-state activated sintering, new insights about the mysterious mechanisms of liquid metal embrittlement (with important applications in nuclear reactors) [9] and abnormal grain growth [8] have been obtained. Furthermore, two potentially transformative concepts are to utilize interfacial “phase” transitions to control microstructural evolution and use “interfacial phases” to achieve properties unattainable by bulk materials. Our research efforts in this regard are focused on tailoring advanced materials for energy applications; recent examples of engineering lithium ion battery cathodes [10], supported oxide catalysts [11], and high-temperature alloys are discussed. 

Finally, we propose a long-range scientific goal to develop a new kind of grain boundary (and surface) “phase” diagrams as a new materials science tool [12].

References:

[1] Luo, Crit. Rev. Solid State Mater. Sci. 32, 67 (2007);

[2] Luo & Chiang, Annu. Rev. Mater. Res. 38, 227 (2008);

[3]Qian, Luo & Chiang, Acta Mater. 56, 862 (2008);

[4] Luo, Gupta, Yoon & Meyer, APL 87, 231902 (2005); Shi & Luo, APL 94, 251908 (2009);

[5] Luo & Shi, APL 92, 101902 (2008);

[6] Gupta, Yoon, Meyer & Luo, Acta Mater. 55, 3131 (2007);

[7] Luo, APL 95, 017911 (2009);

[8] Dillon, Tang, Carter & Harmer, Acta Mater. 55, 6208 (2007); Harmer, J. Am. Ceram. Soc. 93, 301 (2010);

[9] Chen, Meshinchi, Harmer & Luo, unpublished results;

[10] Kayyar, Qian & Luo, APL, 95, 211905 (2009);

[11]Qian & Luo, APL 91, 061909 (2007); Acta Mater. 56, 4702 (2008);

[12] Luo, Curr. Opin. Solid State Mater. Sci. 12, 81 (2008); Dillon, Harmer & Luo, JOM 61 (12), 38 (Dec. 2009)

Short Bio: 

Jian Luo is currently an Associate Professor of Materials Science and Engineering at the Clemson University. He graduated from Tsinghua University with dual Bachelor's degrees, one in Materials Science and Engineering and another in Electronics and Computer Technology. He received his M.S. in Materials Science and Engineering in 1999, and his Ph.D. in Ceramics in 2001, both from the Massachusetts Institute of Technology. After graduation, he worked with Lucent Technologies Inc. and OFS/Furukawa Electric Co. in Atlanta. In August 2003, he left the industry and joined the Clemson faculty. He received a National Science Foundation CAREER award in 2005 and an Air Force Office of Scientific Research Young Investigator award in 2007.