Vienna's St. Stephen's Cathedral is a sandstone building. It is not difficult to work with sandstone. The sand grains are weakly bonding to each other, which causes parts of the stone to fall apart over time.
Special silicate nanoparticles can be used to increase the resistance of the stone. The method is already being used, but what happens in the process and which nanoparticles are best suited for it has been a mystery. A research team from the University of Norway and the University of Vienna have been able to clarify exactly how this artificial hardening process takes place through a series of experiments. The team decided which nanoparticles were best for this. The study was published in a journal.
A suspension made of particles.
"We use a suspension, a liquid, in which the nanoparticles initially float around freely," says Prof. When the suspension gets into the rock, the nanoparticles form stable bridges between the sand grains and give the rock more stability.
It was not known what physical processes took place until now. Usually, a crystal is a regular arrangement of individual atoms. This is referred to as a "colloidal crystal" because atoms and entire particles can arrange themselves in a regular structure.
When the silicate particles dry in the rock, they form new connections between the sand grains. The sandstone is strengthened by this.
There are measurements at the large-scale research facility.
In order to observe the crystallization process in detail, the researchers used the DESY synchrotron facility. The X-rays can be used to analyze the crystallization.
The first author of the publication in which the research results have now been presented is Joanna Dziadkowiec. X-ray analyses were used to study the crystallization process. The size of the particles is the most important factor in determining strength.
The force created by the crystals was measured. A special interference microscope was used for this purpose.
Particles are more force.
The smaller the particles, the more they can strengthen the sand grains. If you use smaller particles, more binding sites are created in the crystal between two sand grains, and with more particles involved, the force with which they hold the sand grains together increases.
The number of particles is important. The crystallization process proceeds slightly differently depending on the concentration of the particles. Restoration work will be made more durable and targeted by using the new findings.
More information: Joanna Dziadkowiec et al, Cohesion Gain Induced by Nanosilica Consolidants for Monumental Stone Restoration, Langmuir (2022). DOI: 10.1021/acs.langmuir.2c00486 Journal information: Langmuir
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