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Aluminum turned transparent using tiny acid droplets

Researchers in the Philippines and Japan have devised an easier way to make very thin sheets of ordinary aluminum transparent. The see-through aluminum oxide (TAlOx) is incredibly hard and resistant to scratches, making it a great candidate for protective coatings on electronics, optical sensors, and solar panels.

Current methods of making TAlOx are expensive and complicated, requiring high-powered lasers, vacuum chambers, or large vats of dangerous acids. That may change thanks to research co-authored by Filipino scientists from the Ateneo de Manila University.

Researchers from the Ateneo de Manila University and the Nara Institute of Science and Technology made transparent aluminum oxide (TAlOx) by applying microdroplets of acidic solution onto ordinary aluminum and applying a controlled electric current. [Credit: Budlayan et al., 2025/Courtesy of Ateneo de Manila University]

 

 

 

 

Instead of immersing entire sheets of metal into acidic solutions, the researchers applied microdroplets of acidic solution onto small aluminum surfaces and applied an electric current. Just 2 volts of electricity -- barely more than what's found in a single AA household flashlight battery -- was all that was needed to transform the metal into glass-like TAlOx.

Researcher Marco Laurence Budlayan from the Ateneo de Manila University School of Science and Engineering's Department of Physics, one of the lead authors of a paper on the process, told Designfax exclusively, "The sample photo is a glass covered with 100-nm-thick aluminum layer. After converting the aluminum into its transparent counterpart (basically aluminum oxide or alumina), we measured the transparent layer to be around 100 nm as well."

This process, called "droplet-scale anodization," is not only simpler than existing manufacturing methods but also environmentally friendly, cutting down on chemical waste and energy use. The technique relies on a special effect called "electrowetting," where an electric field changes the properties of a liquid droplet, allowing precise control over the anodization process.

The researchers said this new approach might make TAlOx cheaper and more accessible for applications in everything from touchscreens and lenses to ultra-durable coatings for vehicles and buildings. It could also lead to advances in miniaturized electronics, as scientists now have a way to convert metal surfaces into insulating, transparent layers on a microscopic scale.

When asked if the transparent part of the aluminum material is more like sapphire now, Budlayan said, "The transparency is more like a glass now. It is amorphous in nature, since it was made at room temperature. If we will anneal it at much elevated temperature, we can get its crystalline form and maybe obtain a different phase of alumina such as sapphire."

The breakthrough research was published in the journal Langmuir by Budlayan and Raphael A. Guerrero from the Ateneo de Manila University School of Science and Engineering's Department of Physics; and Juan Paolo S. Bermundo, James C. Solano, Mark D. Ilasin, and Yukiharu Uraoka from the Nara Institute of Science and Technology Division of Materials Science's Information Device Science Laboratory in Japan.

Budlayan said obtaining precise measurements of the TAlOx's properties after using this process "is surely one of our interests as we move forward."

"In the study, we focused on the growth of the transparent aluminum oxide layer, chemical bonding, optical properties, and structural properties instead of the mechanical properties," said fellow researcher Juan Paolo Bermundo. "Other groups can reproduce the setup (it is a simple setup!), create transparent aluminum oxide, and test the mechanical properties of the thin film."

Source: Ateneo de Manila University

Published February 2025

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