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Traditionally, glass is produced through the melting of certain ingredients such as oxides in powder form at high temperatures. When the glass melt is subsequently cooled down, it becomes a solid. If this cooling process is fast enough to avoid crystallisation, a glass will be formed.
“The properties of glass depend on both its chemistry and the formation processes. If you want to change the properties of the glass, you can change its chemistry: the ingredients that are melted to form the glass. In this way, you can control the structure of the glass that is formed, and through this its mechanical properties, including its hardness and resistance to crack formation and propagation.”
However, sometimes this is not enough to give the glass the mechanical properties that industry and end users need. Broken glass on mobile phones or cracks in the windshields of cars are well-known and often frustrating problems that are yet to be solved. In order to harden the glass, different kinds of subsequent processing is done, but this is both expensive and time-consuming.
In order to find new methods for designing harder and more damage resistant glasses, Morten Mattrup Smedskjær in 2013 received one of the coveted Sapere Aude Research Leader grants from the Danish Council for Independent Research. These grants are given to the most highly talented young researchers in Denmark to enable them to lead their own research group – in this case the Oxide Glass Chemistry group, where Morten Mattrup Smedskjær now leads a number of research projects, including the Sapere Aude-funded project “Topological Basis of Compressed Inorganic Glass Properties”. His group, currently consisting of 3 Ph.D. students and 2 postdocs, is part of the Center for Amorphous Materials Science at AAU.
“One way of changing the properties of glass is heating it up again and thereby changing its structure. Another way of doing it is by subjecting the glass to high pressure. In this project, we are looking at the connections between changes in the glass structure and changes in its properties when glass has been subjected to high pressure. Our aim is to be able to create a model which enables us to predict which properties the glass will get if subjected to pressure, and how different combinations of chemistry, temperature and pressure will result in unique properties” Morten Mattrup Smedskjær says.
In addition to generating valuable knowledge on the connection between the structure and properties of glass, subjecting glass to high pressure in the laboratory also indicates how the glass will react when the end product is subjected to local stress or pressure – for instance if a smartphone is dropped. High local pressure will either result in the glass densifying – absorbing the energy from the pressure through a local compression of the structure – or the glass flowing away – for instance through the formation of cracks.
The group at AAU has shown that a type of glass with a high amount of trigonal boron atoms (boron atoms with three oxygen atoms attached) will have a higher damage resistance, because pressure will cause some of the boron atoms to transform into tetrahedral boron (boron atoms with four oxygen atoms attached); that is, a densification takes place. This means that instead of cracking when subjected to high pressure, the glass densifies – a property highly coveted by the glass industry.