It’s a godsend for anyone who has a habit of putting their smartphone in the back pocket of their pants. Because plenty of glass screens break that way. It is possible, however, to manufacture glass that is bendable and even stronger than steel. You just have to use slightly different ingredients during the production process. A bendable glass that can bend at room temperature has been developed by an international research team.

“Conventional glass is brittle and easily shatters under pressure. We discovered a way to manufacture glass that exhibits ductile behavior. In other words, our glass is tougher than conventional glass.” says Dr. Erkka Frankberg, Marie Curie Fellow at the Finnish University of Tampere. He was in charge of the research team. Instead of using the customary silicon oxide, the research team used aluminium oxide. As a consequence, this new kind of glass acquired metallic properties. “Silicon oxide was already know to be brittle. We were looking for oxides that could behave differently. There were some studies on glassy aluminum oxide suggesting more plasticity compared to glassy silicon oxide and we took the chance to study it,” says the scientist.

The team first had to overcome a certain obstacle in order to actually be able to make a glass-like substance with aluminum oxide. They used an advanced laser technique for that. “It is exceedingly difficult to convert aluminum oxide into a glassy substance. The traditional glass manufacturing processes cannot be applied to aluminum oxide because it easily transforms into the crystalline form. The solution is to cool the material down extremely fast from a high temperature to prevent crystallization.”

© Erkka Frankberg

Surprising degree of plasticity

As a result of this process, an amorphous structure of aluminum and oxygen atoms was created, which formed a new, metallic glass. It turned out to be bendable and elastic during various tests, even at point load. “The extent of plasticity was still a surprise to us,” Frankberg admits.

The researchers made thin sheets out of their glass for these mechanical stress tests. Because even though it has metallic properties owing to the use of aluminium oxide, it is still glass. “We stretched and compressed samples of our material. By carrying out combined compression and shear tests, we were able to demonstrate that the material is also capable of adjusting to a shear force,” Frankberg explains.

The silicon oxide glass is relatively easy to break because the atoms in the glass are unable to move under pressure. If you bend glass too much or try to stretch it, it breaks. In this new type of glass, atoms are able to move. That means that it takes longer for the breakpoint to be reached.

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Is this glass really unbreakable, or is there also a point when it shatters to pieces? “Well, yes and no,” Frankberg says. “In a brittle material, stress will steadily build up until it fractures. If the atoms, however, begin to move before the fracture stress is reached, the stress will no longer increase but levels off to a yield stress, creating a continuous phenomenon.” This means that at that yield stress level, the atoms would have sufficient mechanical energy for them to be able to move. They no longer need any additional energy and therefore the stress levels can’t be increased, but instead settle into a relatively constant state of stress.

© Jonne Renvall & Erkka Frankberg

New applications for glass

Up until now, applications for glass have been limited on account of its fragility. Yet this research could be instrumental in finding new applications. “You might be able to smash your phone on the floor without breaking the screen. Our current smartphone screens are basically regular window glass with enhanced elasticity and strength. But they are still ultimately made out of glass that exhibits no plastic behavior,” Frankberg emphasizes.

The new glass is also harder than steel. The fact that glass is also much lighter than steel means that Frankberg sees all kinds of potential for applications. Of course, as safety glass in vehicles. But probably in the aerospace industry as well, or for building machines. “In the future yes, if we are able to produce sufficiently flaw-free glass in adequate quantities. It is difficult to predict all possible applications as glass was not known before to behave in this manner.”

He refutes the objection that the new glass may be damaging to health because of its use of alumina. “To the best of my best knowledge, there are no results indicating carcinogenicity of aluminum oxide. Aluminum oxide is a compound of aluminum and oxygen with very different properties to metallic aluminum. Aluminium oxide is present everywhere in the earth’s crust and all around us from household ceramics to materials used in construction.”

Manufacture of glass without defects is a prerequisite when it comes to pliability. Irregularities such as cracks, bubbles or dirt can lead to breakages. This is the next challenge for the scientists. Frankberg: “Both aluminum and oxygen are abundant on Earth, but we require an unconventional manufacturing process to achieve the desired properties. The produced glass also needs to be sufficiently pure and flawless which presents a further challenge.”

© Erkka Frankberg

Mass production will still take decades

It most likely will still take decades before any production takes place on an industrial scale, he says, because research needs time. “Typical to new materials technology, the scaling of manufacturing takes a long time. It will most likely take 2-3 decades, but of course, can be hastened if breakthroughs are made in the manufacturing technology. But if a material is really useful for humanity, it will eventually end up being used for thousands of years – like glass,” he adds.

The research project was funded via grants from Finland, France, Italy, and the European Union as part of the Horizon 2020 research program. Research is still at an early stage though. The results of this initial study were published in the renowned Science Magazine.