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Open AccessReview

Hydroxyapatite and Other Calcium Phosphates for the Conservation of Cultural Heritage: A Review

Department of Civil, Chemical, Environmental and Materials Engineering (DICAM), University of Bologna, Via Terracini 28, 40131 Bologna, Italy
Materials 2018, 11(4), 557; https://doi.org/10.3390/ma11040557
Received: 20 March 2018 / Revised: 1 April 2018 / Accepted: 2 April 2018 / Published: 4 April 2018
The present paper reviews the methods and the performance of in situ formation of calcium phosphates (CaP) for the conservation of materials belonging to cultural heritage. The core idea is to form CaP (ideally hydroxyapatite, HAP, the most stable CaP at pH > 4) by reaction between the substrate and an aqueous solution of a phosphate salt. Initially proposed for the conservation of marble and limestone, the treatment has been explored for a variety of different substrates, including sandstones, sulphated stones, gypsum stuccoes, concrete, wall paintings, archaeological bones and paper. First, the studies aimed at identifying the best treatment conditions (e.g., nature and concentration of the phosphate precursor, solution pH, treatment duration, ionic and organic additions to the phosphate solution, mineralogical composition of the new CaP phases) are summarized. Then, the treatment performance on marble and limestone is reviewed, in terms of protective and consolidating effectiveness, compatibility (aesthetic, microstructural and physical) and durability. Some pilot applications in real case studies are also reported. Recent research aimed at extending the phosphate treatment to other substrates is then illustrated. Finally, the strengths of the phosphate treatment are summarized, in comparison with alternative products, and some aspects needing future research are outlined. View Full-Text
Keywords: marble; limestone; consolidation; protection; durability; calcium phosphates; hydroxyapatite; octacalcium phosphate; ammonium phosphate; ammonium oxalate marble; limestone; consolidation; protection; durability; calcium phosphates; hydroxyapatite; octacalcium phosphate; ammonium phosphate; ammonium oxalate
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MDPI and ACS Style

Sassoni, E. Hydroxyapatite and Other Calcium Phosphates for the Conservation of Cultural Heritage: A Review. Materials 2018, 11, 557.

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