December 9, 2022


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Initial thawing does not only occur in ice.  Not expected in this article

Initial thawing does not only occur in ice. Not expected in this article

Even at temperatures well below freezing, the surface of the ice is not homogeneous. They are often covered with a layer of semi-liquid atoms several nanometers thick. The process of their formation is known as primary thawing (or surface thawing) and is responsible for the formation of snowflakes.

Ice formation and accumulation is a dynamic process that can occur when it is fed by frozen water or by freezing water vapor in the air. The effect of both frozen pathways is very similar because there is always a microscopic layer of water at the interface between ice and air, called the pre-melting layer.Dr.. David Sibley of Loughborough University

But pre-dissolution can also be observed in other materials with a crystalline structure, such as diamond, quartz or table salt. Now it turns out that this phenomenon also occurs in highly turbulent structures such as glass.

Initial solubility in glass too

Glass and ice may be microscopically similar, but they are fundamentally different at the atomic level. While ice has an ordered crystal lattice, glass is called an amorphous solid. Inside, the atoms are arranged in a similar fashion to a liquid, making it difficult to see the layer of pre-melting on the surface of the glass. This is possible thanks to neutron scattering or X-ray experiments, but these experiments are not always successful.

Micrograph of elemental fusion of glass in a colloidal system. Red particles indicate the fusion process on the surface/image. temper nature

Physicists at the University of Konstanz in Germany have created so-called colloidal glass – a suspension of microscopic glass spheres immersed in a liquid that behaves like atoms in atomic glass. Since they are 10,000 times larger than atoms, the behavior of the spheres can be observed directly under the microscope.

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Scientists found signs of pre-melting in colloidal glass – the particles on the surface moved faster than the particles in the compact mass underneath. This was expected because the density of the bulk glass is greater than that of the surface, which means that the particles in the pre-melt layer simply have more surface area. Details are described in the magazine Nature Connections.

The experiments carried out provide a better understanding of the behavior of glass, which is a very useful, but at the same time problematic material. The high surface mobility could explain why the polymeric and metallic glass layers have higher ionic conductivity than thick ones – we use this property in batteries as these layers act as ionic conductors.