Transparent Aluminum? Sort of.
by Nicholas De Souza
Recent headlines are reporting that researchers from the University of Tokyo’s Institute of Industrial Science have developed an unbreakable glass that is almost as strong as steel. It’s the kind of news that makes anyone who has ever broken a smartphone take notice.
Researchers were able to create such a resilient glass by combining large amounts of aluminium oxide (Al2O3), commonly referred to as alumina, with tantalum pentoxide (Ta2O5). Conventional glass production primarily uses silicon dioxide (SiO2), silica, to generate the non-crystalline solid we know and love.
Scientists had previously tried to increase the strength of glass by utilizing alumina as a precursor, but when this glass came into contact with a container, it would crystallize, a less than ideal characteristic for glass manufacturing.
To overcome this obstacle, researchers used an “aerodynamic levitation furnace,” they effectively took the container out of the equation. Al2O3 and Ta2O5 powders were mixed, pressed into pellets, heated, levitated with oxygen gas and then melted using two carbon dioxide lasers. This laser treatment heated the glass to approximately 2000°C – high melting temperatures are another hurdle for alumina-based glass production.
Once complete, the researchers had colorless, transparent, spherical glass beads 2 mm in diameter (about the width of a fresh crayon tip). X-ray diffraction confirmed that the glass they produced was entirely amorphous and non-crystalline. The researchers then ran the glass through a gauntlet of tests to measure various physical properties.
Noteworthy properties measured included the Young’s and shear modulus, which measure the stiffness of a material, its ability to resist deformation. The more stiff an object is, the less flexible it is. The Young’s modulus measures the resistance to stress along one axis, such as placing a weight directly on an object. The shear modulus measures the resistance to opposing stresses on opposite surfaces, such as a dull cutting force. Additionally, the Vickers test, a measure of hardness, was performed to determine the relative resistance to surface penetration.
For this new glass, the values for the Young’s and shear modulus were over twice that of Gorilla Glass, and the Vickers hardness was approximately 40% greater, demonstrating that the glass was indeed quite tough.
While not necessarily as tough as steel, the glass still outperformed most conventional glass formations for multiple stress parameters, and its brittleness was comparable to Vycor, a commercial glass with a high degree of thermal shock resistance, commonly used in laboratories. The brittleness tells us how likely a material is to break without substantial deformation or strain.
Since this glass was on par with lab glassware in terms of brittleness, don’t expect it to stop any bullets – bulletproof glass relies on multiple layers of laminated glass and polycarbonate to resist projectiles. As for the unbreakable claim being thrown around, researchers reported shear deformation and radial cracks during their rigorous testing, which is by no means unexpected.
Ultimately, they were able to produce a novel type of glass on a small-scale. Atsunobu Masuno, an assistant professor at the Institute of Industrial Science, says they will develop a way to mass-produce their new glass in the near future, adding that they are, “looking to commercialize the technique within five years.” I will certainly be more excited if they are able to mass-produce this glass, but for now, I’m cautiously optimistic.