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Neutrons Show How Nanolime Can Preserve Porous Stone

18 November 2020

Source: Heinz Maier-Leibnitz Zentrum

Cultural artefacts, such as murals or buildings made of calcareous material, are often damaged as a result of unavoidable exposure to the damaging influences of their environment. To preserve them, conservators use so-called nanolime, nano-sized particles of calcium hydroxide dissolved in alcohol. When this nanolime is applied to porous stone, calcium carbonate is produced, which strengthens the material. Scientists from the Czech Republic and Italy, supported by Dr. Marie-Sousai Appavou, instrument scientist at the outstation of the Jülich Centre for Neutron Science (JCNS) at the Heinz Maier-Leibnitz Zentrum (MLZ), used neutron scattering, among other things, to investigate how effectively nanolime protects porous material.

NanokalkCloister of Xanten Cathedral: the columns are preserved with nanolime.
Copyright: Wikipedia (Rolfcosar / CC BY-SA, File:Xantener_Dom_Kreuzgang.jpg)

“Our aim was to quantify the structural changes of porous material after the application of nanolime, in a completely non-invasive way,” explains Dr. Radek Ševčík from the Czech Academy of Science, one of the authors of the study. The researchers can use this to assess the effectiveness of the treatment. They carried out their investigations on limestone from Maastricht, a standard model of research on the conservation of cultural heritage.

For their analysis, the scientists used synchrotron X-ray tomography at the CERIC synchrotron facility Elettra in Trieste and the small angle neutron scattering diffractometer KWS-2 operated by the JCNS at the MLZ. The researchers were able to visualize changes in the porosity of the material before and after treatment with nanolime on both the microscale and the nanoscale by combining these two methods of investigation for the first time. They were thus able to examine the effects on a wide range of pore sizes. This is important as natural stone in particular is often irregular in its composition.

NanokalkOn porous stone (left) nanolime is applied (centre). This forms calcium carbonate, which strengthens the material. The porosity then decreases (right).
Copyright: Reiner Müller / TUM

 “Thanks to the unmatched penetration depth of the neutrons, we can examine large samples non-invasively”, explains Ševčík, emphasizing the importance of the neutron scattering method. “These aspects are of great interest, especially for cultural heritage objects.” The researchers show in their paper a new methodological approach to assess the usefulness of conservation work without damaging the valuable samples.

“We were able to determine that the pore surface increases when treated with nanolime. The porosity of the material decreases,” summarizes Ševčík. The scientists assume that the stone is made more stable as a result. Preservation with nanolime is used at a large number of cultural heritage sites. The scope of applications is diverse and ranges from the conservation of murals and frescoes to the strengthening of natural stone in the preservation of historical monuments, including statues, for example. 

Original publication:

Ševčík, R., Viani, A., Mancini, L. et al.
Investigation of nano-microstructural changes in Maastricht limestone after treatment with nanolime suspension
Appl. Phys. A 126, 367 (2020).

Further information:

Neutron small angle scattering diffractometer KWS-2 at the Heinz Maier-Leibnitz Zentrum

CERIC Synchrotron light source Elettra