Three-dimensional porous metals
Three-dimensional porous metals are a new and popular material that have potential for use in a variety of applications, including as catalyst metals or as metallic biomaterials. Often made of titanium or iron alloys, these materials feature a large, porous surface and contain a network of tunnels known as 3D bicontinuous structures. The shape and dimensions of these structures determine which chemical compounds can permeate the material, ultimately lending the material to one application or another.
Many researchers are currently searching for synthetic methods that would allow them to control the ways in which 3D bicontinuous structures form. If successful, they’ll be able to fine-tune the structures—and the material as a whole—to a specific application.
However, these researchers face a fundamental challenge of observing the structures. Because the structures exist fully inside the material, imaging techniques that are sensitive only to surface structure and atomic arrangements don’t provide data on the size and shape of the tunnels. Similarly, the technique of choice must be able to collect three-dimensional data to provide a complete understanding of the structures.
X-ray computed tomography for metals characterization
X-ray computed tomography (CT) is one technique that can characterize the inside of a material without the need to cut open the sample. The energetic X-rays used for imaging in the technique can penetrate the material, making it possible to gather data from both the surface and the interior of the sample. The data is collected through a series of 2D radiographs and is then reconstructed by a computer algorithm to provide a full 3D image of the material. A synchrotron is often the source of radiation for X-ray CT, providing excellent energy tunability, high proton doses, and improved spatial resolution.
The technique was recently put to the test by a team of scientists studying how 3D bicontinuous structures formed during the dealloying process of a nickel-chromium alloy. Using a synchrotron as their radiation source, the team revealed that the structures began to form on the outside of the structure when molten materials first formed. The structures then grew within the material over time, with a rapid increase in volume at the beginning of the alloying process that eventually remained relatively constant.
The 3D structural information and in situ measurements the team collected helped them identify three distinct stages of material transformation: initial dealloying with salt corroding the metal-salt interface, subsequent dealloying that spreads throughout the structure, and coarsening that allows the average feature size to further increase.
This figure displays molten salt dealloying (MSD) and a direct observation of enclosed void formation.
Avizo Software shows porous metal molecular structure
Throughout the study, the team used Thermo Scientific Avizo Software to visualize the 2D cross sections and perform 3D morphology evolution. The software also provided automatic image segmentation, helping to conclusively identify morphological features and accurately quantify their properties. Avizo Software is rigorously engineered to produce accurate analysis and provide an intuitive, easy-to-use workflow that not only automates many standard tasks but also helps researchers develop the next generation of materials.
Ultimately, X-ray CT was a crucial tool in the study that helped the team identify and monitor structure growth. They now have a better understanding of the morphology and formation mechanisms of bicontinuous structures, which they hope will lead to less corrosive and more environmentally friendly methods of making nano-porous metals.
Learn more about Avizo Software >
Read our last blog to learn about how Avizo Software is used to analyze cryogenic properties of metals.
Luigi Raspolini is a Product Marketing Manager at Thermo Fisher Scientific
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