Marble protection: An inorganic electrokinetic approach

Calcium phosphate coatings for marble conservation: Influence of ethanol and isopropanol addition to the precipitation medium on the coating microstructure and performance

“…Even if the so-formed layer of whewellite generally exhibits a good ability to completely cover marble surfaces, still the solubility of whewellite is only slightly lower than that of calcite ( Table 1), so that only limited protecting efficacy is achieved [16]. To improve the performance of the oxalate treatment, several innovative approaches are being explored [17,18].…”

Electrodeposition of Hydroxyapatite Coatings for Marble Protection: Preliminary Results

“…Similar to the case of salt extraction, also in this case acidification at the anode occurs, which again led to the use of clay poultices with pH buffer capacity [37]. Moreover, an electrokinetic route has been proposed to deposit a layer of calcium oxalate monohydrate (whewellite) over the marble surface, with protective function [39]. This represents a development of the ammonium oxalate treatment proposed by Matteini in the 1990s [40], which consists of treating carbonate stones (supplying Ca 2+ ions) with an ammonium oxalate solution (supplying C 2 O 4 2− ions), so that protective whewellite (CaC 2 O 4 •H 2 O) is formed.…”

“…This represents a development of the ammonium oxalate treatment proposed by Matteini in the 1990s [40], which consists of treating carbonate stones (supplying Ca 2+ ions) with an ammonium oxalate solution (supplying C 2 O 4 2− ions), so that protective whewellite (CaC 2 O 4 •H 2 O) is formed. In the cited electrokinetic study [39], whewellite formation was reportedly favored by placing the marble piece close to the anode of an electrochemical cell, connected to a power supply, immersed in an ammonium oxalate solution. Because the C 2 O 4 2− ions are attracted to the anode, a region richer in C 2 O 4 2− ions is formed near the anode and near the adjacent marble sample, which leads to formation of a thicker whewellite coating over the marble surface compared to simple immersion in an ammonium oxalate solution with no current applied [39].…”

“…In the cited electrokinetic study [39], whewellite formation was reportedly favored by placing the marble piece close to the anode of an electrochemical cell, connected to a power supply, immersed in an ammonium oxalate solution. Because the C 2 O 4 2− ions are attracted to the anode, a region richer in C 2 O 4 2− ions is formed near the anode and near the adjacent marble sample, which leads to formation of a thicker whewellite coating over the marble surface compared to simple immersion in an ammonium oxalate solution with no current applied [39]. Based on the studies summarized above, in this study, HAP electrodeposition over marble was explored by first comparing the effect of placing the marble sample close to the cathode (to exploit OH − formation at the cathode, like in the biomedical studies [27]) or close to the anode (to exploit PO 4 3− migration towards the anode, like in the studies on stone consolidation [36][37][38] and protection [39]).…”

“…Because the C 2 O 4 2− ions are attracted to the anode, a region richer in C 2 O 4 2− ions is formed near the anode and near the adjacent marble sample, which leads to formation of a thicker whewellite coating over the marble surface compared to simple immersion in an ammonium oxalate solution with no current applied [39]. Based on the studies summarized above, in this study, HAP electrodeposition over marble was explored by first comparing the effect of placing the marble sample close to the cathode (to exploit OH − formation at the cathode, like in the biomedical studies [27]) or close to the anode (to exploit PO 4 3− migration towards the anode, like in the studies on stone consolidation [36][37][38] and protection [39]). Second, the experimental setup was optimized, by investigating whether direct contact between the electrode and the marble sample is preferable and whether potentiostatic (constant potential) or galvanostatic (constant current) conditions are preferable [27].…”