Tag Archives: H. Wang

Nanotwinned copper materials with nanovoids are damage-tolerant with regard to radiation

The research comes out of the Texas A&M University, from a May 29, 2015 news item on Azonano,

Material performance in extreme radiation environments is central to the design of future nuclear reactors. Radiation in metallic materials typically induces significant damage in the form of dislocation loops and continuous void growth, manifested as void swelling. In certain metallic materials with low-to-intermediate stacking fault energy, such as Cu [copper] and austenitic stainless steels, void swelling can be significant and lead to substantial degradation of mechanical properties.

By using in situ heavy ion irradiation in a transmission electron microscope (in collaboration with M.A. Kirk at IVEM facility at Argonne National Lab), Zhang’s [Xinghang Zhang] student, Dr. Youxing Chen, reported a surprising phenomena: during radiation of nanotwinned Cu, preexisting nanovoids disappeared.

A May 28, 2015 Texas A & M University news release, which originated the news item, expands on the theme,

The self-healing capability of Cu arises from the existence of three-dimensional coherent and incoherent twin boundary networks. Such a network enables capture and rapid transportation of radiation induced point defects and their clusters to nanovoids (as evidenced by in situ radiation experiments and molecular dynamics simulations performed in collaboration with Jian Wang at Los Alamos National Laboratory), and thus lead to the mutual elimination of defect clusters and nanovoids.

This study also introduces the concept that deliberate introduction of nanovoids in conjunction with nanotwins may enable unprecedented radiation tolerance in metallic materials. [emphasis mine] The mobile twin boundaries are swift carriers that load and transfer “customers” (defect clusters), and nanovoids are also necessary to accommodate these “customers.” The in situ radiation study also shows that after annihilation of nanovoids, the self-healing capability of nanotwinned Cu is degraded, highlighting the significance of nanovoids. The concept developed from this study, the combination of nanovoids with nanotwin networks, may also stimulate the design of damage tolerant materials in general that are subjected other extreme environments, such as high stress and high pressure impact.

Here’s a link to and a citation for the paper,

Damage-tolerant nanotwinned metals with nanovoids under radiation environments by Y. Chen, K Y. Yu, Y. Liu, S. Shao, H. Wang, M. A. Kirk, J. Wang, & X. Zhang. Nature Communications 6, Article number: 7036 doi:10.1038/ncomms8036 Published 24 April 2015

This paper is open access.

Printing jello and conducting electricity

The July 4, 2012 news item on ScienceDaily about a gel that behaves like biological tissue but conducts electricity is another one of those pieces of research which illustrate the idea that the boundary between the behaviour of biological and nonbiological materials is wavering,

The material, created by Stanford chemical engineering Associate Professor Zhenan Bao, materials science and engineering Associate Professor Yi Cui and members of their labs, is a kind of conducting hydrogel — a jelly that feels and behaves like biological tissues, but conducts electricity like a metal or semiconductor.

That combination of characteristics holds enormous promise for biological sensors and futuristic energy storage devices, but has proven difficult to manufacture until now.

The ScienceDaily news item originated in a June 27, 2012 article written by Max McClure for the (University of) Stanford Report,

Bao and Cui made the gel by binding long chains of the organic compound aniline together with phytic acid, found naturally in plant tissues. The acid is able to grab up to six polymer chains at once, making for an extensively cross-linked network.

“There are already commercially available conducting polymers,” said Bao, “but they all form a uniform film without any nanostructures.”

In contrast, the new gel’s cross-linking makes for a complex, sponge-like structure.  The hydrogel is marked with innumerable tiny pores that expand the gel’s surface area, increasing the amount of charge it can hold, its ability to sense chemicals, and the rapidity of its electrical response.

Still, the gel can be easily manipulated. Because the material doesn’t solidify until the last step of its synthesis, it can be printed or sprayed as a liquid and turned into a gel after it’s already in place – meaning that manufacturers should be able to construct intricately patterned electrodes at low cost.

Here’s more about the electrical conductance properties from the McClure article,

The material’s unusual structure also gives the gel what Cui referred to as “remarkable electronic properties.”

Most hydrogels are tied together by a large number of insulating molecules, reducing the material’s overall ability to pass electrical current. But phytic acid is a “small-molecule dopant” – meaning that when it links polymer chains, it also lends them charge. This effect makes the hydrogel highly conductive.

The gel’s conductance is “among the best you can get through this kind of process,” said Cui. Its capacity to hold charge is very high, and its response to applied charge is unusually fast.

The substance’s similarity to biological tissues, its large surface area and its electrical capabilities make it well suited for allowing biological systems to communicate with technological hardware.

The researchers envision it being used in everything from medical probes and laboratory biological sensors to biofuel cells and high-energy density capacitors.

“And all it’s made of are commercially available ingredients thrown into a water solution,” said Bao.

The July 4, 2012 ScienceDaily news item provided this citation for the paper,

L. Pan, G. Yu, D. Zhai, H. R. Lee, W. Zhao, N. Liu, H. Wang, B. C.- K. Tee, Y. Shi, Y. Cui, Z. Bao. Hierarchical nanostructured conducting polymer hydrogel with high electrochemical activity. Proceedings of the National Academy of Sciences, 2012; 109 (24): 9287 DOI: 10.1073/pnas.1202636109