Tag Archives: stone conservation

They all fall down or not? Quantum dot-doped nanoparticles for preserving national monuments and buildings

The most recent post here but not the most recent research about preserving stone monuments and buildings is a December 23, 2019 piece titled: Good for your bones and good for art conservation: calcium. Spanish researchers (who seem particularly active in this research niche) are investigating a more refined approach to preserving stone monuments with calcium according to a May 8, 2020 news item on Nanowerk,

The fluorescence emitted by tiny zinc oxide quantum dots can be used to determine the penetration depth of certain substances used in the restoration of historical buildings. Researchers from Pablo de Olavide University (Spain) have tested this with samples collected from historical quarries in Cadiz, where the stone was used to build the city hall and cathedral of Seville.

One of the main problems in the preservation of historic buildings is the loss of cohesion of their building materials. Restorers use consolidating substances to make them more resistant, such as lime (calcium hydroxide), which has long been used because of its great durability and high compatibility with the carbonate stone substrate.

Now, researchers at Pablo de Olavide University, in Seville, have developed and patented calcium hydroxide nanoparticles doped with quantum dots that are more effective as consolidant and make it possible to distinguish the restored from the original material, as it is recommended for the conservation and restoration of historical heritage.

An April 28, 2020 Pablo de Olavide University press release (also on Alpha Gallileo but published May 5, 2020), which originated the news item, provides more details about the nature of the materials,

“The tiny quantum dots, which are smaller than 10 nanometres, are made of zinc oxide and are semiconductors, which gives them very interesting properties (different from those of larger particles due to quantum mechanics), such as fluorescence, which is the one we use,” explains Javier Becerra, one of the authors.

“Thanks to the fluorescence of these quantum dots, we can evaluate the suitability of the treatment for a monument,” he adds. “We only need to illuminate with ultraviolet light a cross-section of the treated material to determine how far the consolidating matter has penetrated.”

In addition, the product, which the authors have named Nanorepair UV, acts as a consolidant due to the presence of the lime nanoparticles. Consolidation is a procedure that increases the degree of cohesion of a material, reinforcing and hardening the parts that have suffered some deterioration, which is frequent in historical buildings.

The researchers have successfully applied their technique to samples collected in the historic quarries of El Puerto de Santa María and Espera (Cadiz), from where the stone used to build such iconic monuments as Seville Cathedral, a World Heritage Site since 1987, or the town’s city hall, was extracted.

“In the laboratory, we thus obtain an approximation of how the treatment will behave when it is actually applied to the monuments,” says Becerra, who together with the rest of the team, is currently also testing mortars from the Italica and Medina Azahara archaeological sites.

Oddly, this work is not all that recently published. In any event, here’s a link to and a citation for the paper,

Nanolimes doped with quantum dots for stone consolidation assessment by Javier Becerra, Pilar Ortiz, José María Martín, Ana Paula Zaderenko. Construction and Building Materials Volume 199, 28 February 2019, Pages 581-593 DOI: https://doi.org/10.1016/j.conbuildmat.2018.12.077 Available online 19 December 2018

This paper is behind a paywall.

Good for your bones and good for art conservation: calcium

The statues on Easter Island, the Great Wall of China, Egyptian pyramids, MesoAmerican pyramids, castles in Europe and other structures made of stone are deteriorating and now comes another approach to halting the destruction. (I have covered other approaches to the problem in two previous postings, a December 5, 2017 posting, Europe’s cathedrals get a ‘lift’ with nanoparticles, and an October 21, 2014 posting, Heart of stone.)

An August 7, 2019 news item on ScienceDaily announces the latest in conserving stone monuments and structures,

When it comes to cultural heritage sites, there are few things historians wouldn’t do to preserve them for future generations. In particular, stone buildings and sculptures made of plaster and marble are increasingly at risk of damage from air pollution, acid rain and other factors. Researchers now report a new, calcium-based conservation treatment inspired by nature that overcomes many drawbacks of currently used methods.

An August 7, 2019 American Chemical Society (ACS) news release, which originated the news item, provides a bit more technical detail,

Historically, conservation scientists have turned to alkoxysilanes, silicon-based molecules used to consolidate stone and other artworks, in their preservation efforts. However, alkoxysilane treatments do not bond properly with non-silicate surfaces, are prone to cracking and are limited in their ability to repel water. Adding other compounds to this treatment have helped overcome these effects, but only to a point. Instead Encarnación Ruiz Agudo and colleagues looked to nature for inspiration, and found that calcium could be the answer. As a major element of strong, natural structures like bone and kidney stones, the researchers theorized that nanoparticles made from calcium could bolster alkoxysilanes and provide the desired protective effects to conserve historical artifacts.

The researchers made calcium carbonate and calcium oxalate nanoparticles and included polydimethylsiloxane (PDMS) as a stabilizer. PDMS also likely helps the nanoparticles bond to surfaces. The team added the nanoparticles to traditional alkoxysilane treatments, then applied them to samples of three different building materials: white marble, calcarenite limestone and gypsum plaster, and put the samples through a battery of tests. Overall, the results showed enhanced hydrophobicity, less cracking and improved surface adhesion compared to alkoxysilane treatments alone, with calcium oxalate providing a marked improvement in acid resistance. A minimal color effect was observed, but the researchers say this change was within acceptable values for conservation efforts.

The authors acknowledge funding from the European Regional Development Fund, the Regional Government of Andalusia, the Spanish Ministry of Economy and Finance and the University of Granada.

Here’s a link to and a citation for the paper,

Bioinspired Alkoxysilane Conservation Treatments for Building Materials Based on Amorphous Calcium Carbonate and Oxalate Nanoparticles by A. Burgos-Cara, C. Rodríguez-Navarro, M. Ortega-Huertas, E. Ruiz-Agudo. ACS Appl. Nano Mater.2019XXXXXXXXXX-XXX DOI: https://doi.org/10.1021/acsanm.9b00905 Publication Date:July 18, 2019 Copyright © 2019 American Chemical Society

This paper is behind a paywall.

The ‘Queen’s Head” in Yehliu Geopark (Taiwan) and nanotechnology

http://focustaiwan.tw/news/asoc/201505250028.aspx

http://focustaiwan.tw/news/asoc/201505250028.aspx

As you can see, the Queen’s Head rests on a thin (and getting thinner) neck. This thinning is cause for consternation in Taiwan as a May 25, 2015 news item on the focustaiwan.tv website notes,

The “Queen’s Head,” the most famous rock formation in Yehliu Geopark, faces an uncertain fate despite an all-out effort to prevent its thinning neck from snapping, the North Coast & Guanyinshan National Scenic Area said Monday.

Kuo Chen-ling (郭振陵), the secretary-general of the scenic area administration, said Monday that experiments done on four mushroom rocks near the Queen’s Head have found that nanotechnology can prevent erosion, but it still has some drawbacks that have yet to be overcome.

In the experiments done over the past nine months, nanotechnology has proven that it could reinforce the queen’s neck and delay the weathering process, Kuo said.

But it has also caused the rocks to whiten and slivers of the rocks’ surfaces to break off amid the dramatic changes in temperature, moisture and sunshine on the North Coast, he said.

An August 29, 2014 news item on the China Post website gives a description of the attempted remedy,

The Tourism Bureau began preparations Thursday for repairs on the iconic Queen’s Head rock formation at Yehliu Geopark in New Taipei, in a bid to protect the popular tourist attraction from further erosion.

Capitalizing on the sunny weather, which is essential to an experiment on how best to preserve the rock, a group of specialists led by Hsieh Kuo huang, a professor at National Taiwan University’s Institute of Polymer Science and Engineering, injected various nano-sealants into four less-popular rock formations with a similar structure to the Queen’s Head.

The team has coded the rocks A, B, C and D and applied different treatments to them to compare the results.

Comprised of nano-sealant mixed with gravel, the remedy can help resist winds up to 250 kilometers per hour and magnitude-7.0 earthquakes, according to the Tourism Bureau.

I’m sorry the first tests were not more successful and I hope they will be able to find a solution in time.

This project reminded me of a European Union (EU) project where they too were attempting to save important stone structures, from my Oct. 21, 2014 posting,

… an Oct. 20, 2014 news item on Nanowerk,

Castles and cathedrals, statues and spires… Europe’s built environment would not be the same without these witnesses of centuries past. But, eventually, even the hardest stone will crumble. EU-funded researchers have developed innovative nanomaterials to improve the preservation of our architectural heritage.

“Our objective,” says Professor Gerald Ziegenbalg of IBZ Salzchemie, “was to find new possibilities to consolidate stone and mortar, especially in historical buildings.” The products available at the time, he adds, didn’t meet the full range of requirements, and some could actually damage the artefacts they were meant to preserve. Alternatives compatible with the original materials were needed.

For those interested in more, there are details about the EU project the product, CaLoSil, that the scientists devised, and links to more resources in my post.

Heart of stone

Researchers in Europe do not want to find out what Europe would* look like without its stone castles, Stonehenge, Coliseum, cathedrals, and other monumental stone structures, and have found a possible solution to the problem of deterioration according to an Oct. 20, 2014 news item on Nanowerk,

Castles and cathedrals, statues and spires… Europe’s built environment would not be the same without these witnesses of centuries past. But, eventually, even the hardest stone will crumble. EU-funded researchers have developed innovative nanomaterials to improve the preservation of our architectural heritage.

“Our objective,” says Professor Gerald Ziegenbalg of IBZ Salzchemie, “was to find new possibilities to consolidate stone and mortar, especially in historical buildings.” The products available at the time, he adds, didn’t meet the full range of requirements, and some could actually damage the artefacts they were meant to preserve. Alternatives compatible with the original materials were needed.

A July 9, 2014 European Commission press release, which originated the news item, provides more details about this project (Note: A link has been removed),

 Ziegenbalg was the coordinator of the Stonecore project, which rose to this monumental challenge within a mere three years. It developed and commercialised a new type of material that penetrates right into the stone, protecting it without any risk of damage or harmful residues. The team also invented new ways to assess damage to stone and refined a number of existing techniques.

The concept behind the new material developed by the Stonecore partners is ingenious. It involves lime nanoparticles suspended in alcohol, a substance that evaporates completely upon exposure to air. The nanoparticles then react with carbon dioxide in the atmosphere to form limestone.

This innovation is on the market under the brand name CaLoSil. It is available in various consistencies – liquids and pastes – and in a number of formulations based on different types of alcohol, as well as with added filler materials such as marble. The product is applied by dipping, spraying or injection into the stone.

Beyond its use as a consolidant, CaLoSil can also be used to clean stone and mortar, as it helps to treat fungus and algae. The dehydrating effect of the alcohol and the acidity of the lime destroy the cells, and the growth can then be washed off. This method, says Ziegenbalg, is more effective than conventional chemical or mechanical approaches, and it does not damage the stone.

Limestone face-lifts

The partners tested their new product in a number of locations across Europe, on a wide variety of materials exposed to very different conditions. Together, they rejuvenated statues and sculptures, saved features in cathedrals and citadels, and treated materials as diverse as sandstone, marble and tuff.

The opportunity to access such a wide variety of sites, says Ziegenbalg, was one of the many advantages of working with partners from several countries. It pre-empted the risk of developing a product that was too narrowly focused on a specific application.

Inside the heart of stone

A number of techniques enable conservation teams to assess the state of the objects in their care. To obtain a clearer picture of deeper damage, Stonecore improved existing approaches involving ultrasound, developing a new device. The project also pioneered a new technique based on ground-penetrating radar, which one partner is now offering as a commercial service.

The team also developed an innovative micro-drilling tool and refined an existing technique for measuring the water uptake of stone.

A further innovation is a new technique to measure surface degradation. For this so-called “peeling test”, a length of adhesive tape is affixed to the object. The weight of the particles that come off with the tape when it is removed indicate how likely the stone is to degrade.

Carving out solutions

The partners’ achievements have not gone unnoticed. In 2013, Stonecore was shortlisted along with 10 other projects for the annual EuroNanoForum’s Best Project Award.

Ziegenbalg attributes the team’s success mainly to the partners’ wide range of complementary expertise, and to their dedication. “The participating small and medium-sized enterprises were extremely active,” he says. “They were highly motivated to handle the more practical work, while the universities supported them with the necessary research input.”

While it’s not clear from this press release or the Stonecore website, it appears this project has run its course as part of European Union’s Framework Programme 7.

*Aug. 7, 2019: A grammatical correction was made: in the first sentence and ‘what would Europe’ was changed to ‘what Europe would*’.