Gianfranco Carcangiu

The bentonites in pelotherapy : thermal properties of clay pastes from Sardinia (Italy)

Abstract On the basis of a previous detailed characterization of the Sardinian bentonites for pelotherapy applications [Cara, S., Carcangiu, G., Padalino, G., Palomba, M., Tamanini, M., 2000. The bentonites in pelotherapy: chemical, mineralogical and technological properties of materials from Sardinia deposits (Italy). Appl. Clay Sci. 16, 117–124 (this issue)], three commercial bentonites have been selected for detailed studies. The thermal properties of the pastes, prepared with these bentonites at different moisture, have been compared with the properties of a peloid, commonly used in the spa of Benetutti (northern Sardinia). The cooling kinetics of the bentonites along with the thermal mud have been studied using an experimental apparatus that reproduces the conditions during the application of a cataplasm. A mathematical model for the cooling kinetics has been obtained by means of a theoretical cooling equation, with instrumental constants derived from a reference paste (TiO 2 at 50% moisture). The heat capacity of the pastes introduced into the model was calculated from chemical and mineralogical data. The methodology developed can be used in other laboratories of the thermal centres to determine the quality and ability of the bentonitic materials for pelotherapy.

The bentonites in pelotherapy: chemical, mineralogical and technological properties of materials from Sardinia deposits (Italy)

Abstract Bentonite muds are suited for use in pelotherapy due to their typical properties of high swelling (>25 ml/2 g), specific heat (Cp) and ease of handling, generally obtained at a material viscosity of 400 cps. This paper reports chemical, mineralogical and technological properties of Sardinia bentonites, to identify the most suitable materials for pelotherapy pastes. Their characteristics have been compared to the peloid properties commonly used in the spa of Benetutti (Northern Sardinia). On the basis of the mineralogical, chemical and technological characterization of the samples, besides their proximity to the most important regional spas and/or thermal sources, Costa Paradiso, Pedroseddu, Laconi, Busachi, Siurgus-Donigala and Giba bentonites are the most suitable Sardinia materials for pelotherapy. The results of this study also show that a complete characterization of clay materials is necessary in pelotherapy paste preparation. The utilization and/or addition of bentonites, largely available in Sardinia at relatively low cost, can improve the thermal mud quality for curative purposes.

REE-BEARING MINERALS IN THE ALBITITES OF CENTRAL SARDINIA, ITALY

Abstract Recent studies on albitite rocks located in the granodiorite complex of Central Sardinia have revealed that epidote has a widespread occurrence as a light rare-earth element (LREE)-bearing accessory common phase. Titanite has been recorded as a heavy rare earth element (HREE)-bearing mineral. The Hercynian granodiorite complex of Central Sardinia is composed chiefly of quartz, Ca-plagioclase, K-feldspar and biotite and of a wide variety of secondary assemblages, mainly allanite, titanite and zircon. Albitic plagioclase and quartz are the main mineral components of the albitites. Additional minerals include, besides allanite and epidote, a more calcic-plagioclase (oligoclase), K-feldspar, chlorite, titanite and more rarely muscovite. The mineral assemblages and REE-bearing minerals of albitites were analysed by wavelength dispersive spectrometry (WDS). Chemical data suggest that there is a near complete solid-solution between epidote and allanite whereas little variations in HREE of titanites were detected. In epidote-group minerals a pronounced zoning in REE was observed while titanite was recorded unzoned. Textural relations were studied by SEM to distinguish primary from secondary epidotes. Chemical criteria to recognize magmatic from alteration epidotes were also applied. The alteration epidotes mainly occur and generally originate from plagioclase alteration and from leaching of magmatic allanite. Comparison of textures using both the SEM technique and EPMA data showed that the characteristic ‘patchy zoning’, observed in epidotes, corresponds with different amounts of REE in these minerals. The schematic model proposed for the epidote-forming reactions during the metasomatic processes that affected the granodiorites involves: (i) the instability of the anorthitic component of plagioclase; (ii) the simultaneous formation of albite; (iii) the leaching of the magmatic allanite with a redistribution of REE in the epidotes of the albitites.

Synthesis, characterization and DFT-modeling of novel agents for the protection and restoration of historical calcareous stone substrates

The ammonium salts of oxamate (AmOxam) and monomethyloxalate (AmMeox), structurally related to ammonium oxalate (AmOx), were synthesized and characterized as protecting agents/filler for calcareous stone substrates. Both compounds featured an improved solubility in water and alcoholic-water mixtures with respect to AmOx. While AmOxam is stable in aqueous solution and reacts with calcite to afford the corresponding insoluble calcium oxamate (CaOxam), AmMeox spontaneously undergoes hydrolysis to give ammonium monohydrogen oxalate hemihydrate (AmBiox) and calcium oxalate (CaOx). Both compounds have been tested for the restoration of naturally weathered marble and biomicritic limestone. The formation of a superficial layer of CaOxam and CaOx was observed on stone samples treated with AmOxam and AmMeox, respectively, depending on the solvent mixture. A quantum-mechanical study was carried out at DFT level in order to investigate the nature of the interactions occurring between the lithic substrate (calcite) and the passivating agents, showing how the structural modifications on oxalic acid derivatives can be exploited to fine-tune their interaction with the calcite surface.

Crime art on the stone: graffiti vandalism on cultural heritage and the anti-graffiti role in its surfaces protection

Apparently perceived like an easy thing commonly used, spray paint is a very complex product composed by substances strongly penetrating particularly into the porous materials. This characteristic is very hazardous for our cultural heritage. The problem concerning the surfaces protection from paints and signs is very hard to solve, both for the difficulty to remove these substances and for the variety of the materials that react in a different manner to the various paints and cleaning treatments because of their different physical-chemical characteristics. With the aim to evaluate the damages originated by the spray paints on the stones and the efficacy of anti-graffiti products, some laboratory tests have been carried out. Two different limestones have been selected like supports: a little porous, polishable wakestone and a very porous bio-calcarenite with very scarce mechanical properties. Both these limestones are used as coverings and structural elements of buildings and monuments around Mediterranean basin. Concerning the spray paint cans, the most popular Montana mtn94 has been used, and two commercial anti-graffiti have been applied as protective products. Using Scanning Electron Microscope, Infrared Spectrometry, Colorimetry, Mercury Intrusion Porosimetry and Contact Angle Analysis the interactions stone-paint, stone-anti-graffiti and paint-anti-graffiti have been investigated. In order to evaluate the real efficacy of the anti-graffiti, some cleaning and removal paint tests have been carried out. The research highlights that the anti-graffiti cause variations concerns the colour and/or the wettability in both limestones. Their effects are strictly related to the stonework and their microstructure but also the interaction with the paint is influent too.

Oxamate salts as novel agents for the restoration of marble and limestone substrates: case study of ammonium N-phenyloxamate

The ammonium salt of N-phenyloxamic acid (AmPhOxam) was synthesised, characterised by FT-IR, FT-Raman, UV-Vis, 1H-NMR spectroscopic methods and single crystal X-ray diffraction, and evaluated as a protective and consolidating agent for calcareous stone substrates under mild conditions. Hydro-alcoholic solutions of AmPhOxam were tested for the treatment of naturally weathered white marble and biomicritic limestone. Mercury intrusion porosimetry, FT-NIR spectroscopy measurements and SEM microscopy showed the formation of a superficial protective layer of crystals of the corresponding monohydrated calcium salt, CaPhOxam, on both treated stones.

Pigments and materials across Sardinia’s walls: contribution on the Tomba dei Pesci e delle Spighe in Cagliari

Sardinia is an ancient island where it is possible to find signs and symbols, decorative engraved and colored traces of men and history. In 1997 an ancient tomb in Cagliari has been discovered: it is located in the necropolis of Tuvixeddu, an old and spread necropolis dating from Punic to Roman times now located in the urban texture. The tomb, consisting of only one chamber, is dated by archaeologists a few centuries A.D. The name, Tomba dei Pesci e delle Spighe, is related to the painted decorations that were clearly visible on the walls and roof of the burial chamber, not so easily distinguishable anymore because of natural decay processes. Wall paintings appear severely damaged owing to the darkening of some areas, the detachments of others and a widespread presence of superficial concretions on the roof surfaces. This contribution aims to characterize pigments and the painting technique used in this burial chamber and compare them to the roman tradition. The site is confined, with evident problems of conservation because of the critical microclimatic conditions. High humidity and degradation are compromising the legibility of the decorative schemes. Samples of constituting materials and concretions have been collected and analyzed using x-rays diffraction (XRD) and IR spectroscopy (µFTIR-ATR). Preparatory layers supporting the pictorial have inorganic nature: diffractograms showed the presence of gypsum and calcite. IR spectroscopy (µFTIR) and scanning electron microscopy coupled with an energy dispersive system (SEM-EDS) were used to investigate the nature of pigments. Samples of blue, red and yellow pigments have been investigated. Egyptian blue, cinnabar and earth pigments have been detected. Proteinaceous materials have been identified as possible binders for the pigments.

Density functional theory modelling of protective agents for carbonate stones: a case study of oxalate and oxamate inorganic salts

Sulphur and nitrogen oxide pollutants cause acid rain that can eventually lead to the dissolution of calcite in marble and limestones. Calcium oxalate is an inorganic protective agent, which is obtained by treatment with ammonium oxalate. The functionalization of oxalic acid to give monoesters and monoamides (oxamates) allows tailoring the solubility of the relevant ammonium and calcium salts. In this context, theoretical calculations carried out at the Density Functional Theory (DFT) level were exploited to investigate the capability of oxalate, methyloxalate, phenyloxalate, oxamate, methyloxamate, and phenyloxamate to interact with the calcium carbonate lattice. An in-depth validation based on the structural data showed that DFT calculations with the PBE0 functional along with a single or triple-zeta def2 basis set allow understanding the different reactivity of the oxalate and oxamate derivatives and their efficiency in interacting with stones containing calcium carbonate, such as Carrara marble and biomicritic limestones.

Durability of repair mortars used in restoration of a Sardinian coastal tower: assessment after ten years

This study reports the results of investigations on conservation conditions of an ancient tower, called Torre del Pozzo, located in the S-W coast of Sardinia, restored about ten years ago. The tower suffers from serious problems related to vulnerability of building materials, particularly limestone and sandstones and aerial lime mortar with poor physical-mechanical properties. Over the centuries the materials were subjected to aggressive actions (wind corrasion and salt crystallization) causing an intense erosion of the walls with consequent partial collapse of the structure. About ten years ago a restoration involved the mortars and only the replacement and integration of ashlars deteriorated. After about 10 years from this intervention, some inspections have been carried out in order to assess the effectiveness of the intervention and the state of preservation of the tower. This paper focuses on analyses and tests carried out to assess condition and durability of the repair mortars. DOI: http://dx.doi.org/10.4995/FORTMED2015.2015.1761

Methodological approach in the conservation of coastal fortifications

The historical and artistic value of Coastal Towers justifies the recovery of these emblematic artifacts. For the achievement of this objective we propose a methodological approach including: i) architectural relief also by 3D laser scanner and collection of historical data; ii) macroscopic semi-quantitative evaluation of the decay, iii) application of diagnostic quantitative chemical-physical-mechanical methodologies, to assess the decay intensity, and define the criticalities for planning the restoration. The i step allows the graphic rendering of the building showing the geometry and the relationships between the parties. The ii step allows a preliminary understanding of the building materials, macroscopic alteration forms, monument features, acquisition of information about potential causes and decay mechanisms. During the iii step, sampling of building materials is planned. Laboratory analyses, to determine the soluble salts, crystalline phases, porosity as well as micro-textural features of the materials, are carried out by the application of suitable techniques. DOI: http://dx.doi.org/10.4995/FORTMED2015.2015.1752