Diammonium Hydrogenphosphate Treatment on Dolostone: The Role of Mg in the Crystallization Process

Abstract

The diammonium hydrogenphosphate (DAP, (NH4)2HPO4) reaction with calcite has been extensively investigated. The availability of free calcium ions in the reaction environment has been acknowledged as a crucial factor in the crystallization of calcium phosphates with a high (hydroxyapatite, Ca/P 1.67) or low Ca/P molar ratio (dicalcium phosphate dihydrate, Ca/P 1.00; octacalcium phosphate, Ca/P 1.33). On the contrary, no data are available on the DAP interaction at room temperature with dolomite in terms of reaction mechanism and composition of the reaction products. Here, a multi-analytical approach based on scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectrometry (EDS) and X-ray powder diffraction before and after heating treatments is proposed to explore how the formation of calcium phosphates occur on Mg-enriched substrates and if the presence of magnesium ions during the reaction influences the crystallization process of calcium phosphates. The DAP reaction with polycrystalline dolomite gives rise to the formation of struvite and of poorly crystalline hydroxyapatite. Calcium and magnesium ions mutually interfered in the crystallization of magnesium and calcium phosphates, respectively, whose effects influenced the properties (size, micro-morphology, composition and crystallinity) of the newly-formed phases.

Explication of the Potential of 2-Hydroxy-4-Methoxybenzaldehyde in Hampering Uropathogenic Proteus mirabilis Crystalline Biofilm and Virulence

“…Moreover, the crystallite nature of these salt precipitates was revealed by XRD analysis. Figure 3B shows sharp XRD peaks The 2θ values were also found to be closely matching those of the previous report of Possenti et al (2019)…”

Comparative Study Between Ammonium Phosphate and Ethyl Silicate Towards Conservation of Prehistoric Paintings in the Magura Cave (Bulgaria)

“…Thanks to the low viscosity of the phosphate solution and to the absence of nanoparticles, a good penetration depth is usually achieved (>5 cm in highly porous limestone) [25]. So far, the treatment has provided good results on a variety of substrates [25], including many types of natural stones [26][27][28][29][30][31][32], mortars [33,34], and stuccoes [35]. Recently, the interaction between ammonium phosphate solutions and pigments used in wall paintings has been investigated, and, in most of the cases (but not in all), the treatment has been found to cause negligible color changes [36].…”

Time-Resolved ATR–FTIR Spectroscopy and Macro ATR–FTIR Spectroscopic Imaging of Inorganic Treatments for Stone Conservation

“…Research studies on AmOx and/or DAP treatments are constantly expanding and gaining more interest nowadays. 11−14 Several analytical techniques, including X-ray diffraction, Raman spectroscopy, neutron tomography−radiography, and IR spectroscopy (conventional FTIR instruments; 15 micro ATR-FTIR spectroscopic mapping 3,16 ), have been used to investigate the composition of the newly formed reaction products 3,6,7,9 and their penetration within the substrate. 13,16−20 However, these studies did not focus on the kinetics of the reaction, and further insights are needed about the real-time variations occurring during the conservation treatments and directly in their reaction environment.…”

“…The nature and extent of these variations depend on several mutually interacting variables. Different crystalline phases are formed depending on the reaction conditions (i.e., pH, reagent molarity, ionic strength, mineralogical composition of the substrate, etc). − This is a crucial step, as each crystalline phase has specific properties (stability and solubility), and many of them are metastable or/and hydrated phases. , No less importantly, the presence of water molecules is crucial for the dissolution–recrystallization (e.g., the evaporation of the solution interrupts the reaction) and to promote the formation of hydrated phases.…”

“…Several analytical techniques, including X-ray diffraction, Raman spectroscopy, neutron tomography–radiography, and IR spectroscopy (conventional FTIR instruments; micro ATR-FTIR spectroscopic mapping , ), have been used to investigate the composition of the newly formed reaction products ,,, and their penetration within the substrate. ,− …”