In-situ electrochemical synthesis of inorganic compounds for materials conservation: assessment of their effects on the porous structure
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Date
2021
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Publisher
Ceramics International
Abstract
This study refers to the application of in-situ electrochemical synthesis as an alternative
method to improve the properties of porous materials against harmful external agents
that deteriorate them. It is oriented to an understanding of the effects of crystallisation
on the pore structure of different compounds commonly used in the restoration and
conservation of porous materials (historic ceramics, building walls, sculptures, or
biomedical applications). It analyses the microstructural, chemical details, and stability
of the neo-formed phases that modify the pore network. The electrochemical synthesis
was carried out at ambient temperature (20°C), over high porous sandstone for
crystallising Ca carbonate, Mg carbonate, Ca phosphate, and Ca oxalate compounds.
Based on the neo-formed minerals, a comparison was made depending on their
specific properties defining how they affected the pore structure. The characterisation
included polarised light optical microscopy, environmental and field emission scanning
electron microscopy, digital image analysis, cathodoluminescence(CL-ESEM),energydispersive
X-ray spectroscopy, and X-ray microdiffraction. Aragonite, hydromagnesite,
hydroxyapatite, and whewellite were identified as the majority phases depending on
the treatment. Phase transformation, dehydration, and dissolution-re-precipitation
processes suggested different degrees of stability, including aragonite/calcite (CaCO3
treatment) and hydromagnesite/magnesite (MgCO3 treatment) transformations and
simultaneous crystallisation of brushite/hydroxyapatite ((Ca 3 (PO 4 ) 2 treatment).
Electrocrystallisation induced changes in inter-granular porosity, the development of
secondary porosity inherent to the minerals, and differences in pore cementation
depending on its mineralogy. Among the treatments, Mg carbonate reduced porosity
most effectively, followed in descending order by calcium carbonate and calcium
phosphate, being the calcium oxalate the less effective.