Many historical buildings were made of sandstone, including Vienna's St. Stephen's Cathedral. Sandstone is quite uncomfortable to work with, although it does not fight to weather.
According to a Phys.org report, the material consists of sand grains that are somewhat weakly bonded to each other, which is why parts of the stone are crumbling through the years, frequently necessitating expensive restoration.
Nonetheless, it is plausible to augment the resistance of the stone by treating it using special silicate nanoparticles. The approach is already being applied, although what precisely takes place in the process and which nanoparticles are best appropriate for this purpose has remained unclear until now.
The researchers from TU Wien and the University of Oslo have clarified exactly this artificial hardening process occurring through elaborate experiments at the DESY synchrotron in Hamburg and with microscopic analyses in Vienna.
A hard porous silica-based sedimentary rock from the Upper Cretaceous
Liquid Suspension Used
In their study published in Langmuir, the team used a liquid suspension in which nanoparticles initially float freely.
According to Professor Markus Valtiner from the Institute of Applied Physics at TU Wien, when the said suspension gets into the rock, the aqueous portion evaporates, and the nanoparticles form stable bridges between the sand grains and provide the rock with additional stability.
This approach is already applied in restoration technology, although until now, it remains unknown exactly what physical processes are occurring.
A similar Times of Update report said that a very special type of crystallization occurs when the water evaporates.
'Colloidal Crystal'
Typically, a crystal is a standard arrangement of individual atoms. Nonetheless, not just atoms, but the entire nanoparticles as well, can arrange themselves in regular construction. This then is referred to as a "colloidal crystal."
The silicate nanoparticles come together to form such colloidal crystals when they dry in the rock and, therefore, jointly develop new links between the individual sand grains. This increases the sandstone's strength.
To observe such a crystallization process in detail, the research team from TU Wien used the DESY synchrotron facility in Hamburg.
Furthermore, highly intense X-rays can be produced there, which can be applied to analyze the crystallization during drying.
Nanoparticles in Different Sizes and Concentrations Used
The study's first author, Joanna Dziadkowiec, from the University of Oslo and TU Wien, was essential in understanding exactly the strength of the bonds that form relies on.
She also said they used nanoparticles of various sizes and concentrations and examined the crystallization process with X-ray analyses. It was also shown that the size of particles is strong "for the optimal increased strength," continued explaining Dziadkowiec.
The study authors also gauged the adhesive force that the colloidal crystals created. For this purpose, a special interference microscope was utilized, which is perfectly fit for gauging small forces between two surfaces.
Cohesion Between Sand Grains
Dziadkowiec also explained that they could show that the tinier the nanoparticles, the more they can intensify the cohesion between the sand grains.
She elaborated that if one sees smaller particles, more binding areas are created in the colloidal crystal between two sand grains. With several particles involved, the force with which they old the sand grains together increases.
Related information about nanotechnology protecting the environment is shown on NanoTube's YouTube video below.
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