Formation Of Alteration Products Research Articles

Conservation of contemporary art: Alteration phenomena in a XXI century artwork. From contactless in situ investigations to laboratory accelerated ageing tests

Abstract The present study reports the results of a combined approach in investigating the alteration phenomena on a contemporary artwork, Senza Titolo, by Nunzio di Stefano. The oeuvre, created in 2001, is composed by seven lead carved panels coated with Paraloid B72. After having being stored for several years in wood boxes, it was acquired in 2015 and, only at that time, the surface showed an evident deterioration In situ analyses, by means of contactless external reflection infrared spectroscopy (ERFTIR), have shown that the alterations products are in the form of basic lead carbonate and, surprisingly, of lead carboxylate. The presence of these products were supposedly due to VOCs attack during the storage in wood boxes. The formation of lead carboxylate, due to the interaction among lead substrate and acetic and formic acids (the major components of the VOCs mixture), was investigated through a laboratory accelerated ageing. The effect of VOCs was studied on the lead substrate, on the acryl coating and on a series of mockups simulating Senza Titolo. The combination of surface and punctual analyses, by means of ERFIR and μ-FTIR, showed that the formation of alteration products is a relatively fast process. The alteration path involves firstly the absorption of VOCs moisture on the Paraloid B72 surface, immediately followed by corrosion processes, leading to hydrocerussite, lead acetate and formate. The presence of the polymeric coating controls the transformation of lead carboxylates to basic lead carbonate. Laboratory results have consolidated those obtained by in situ contactless investigations, confirming ERFTIR as powerful tool in assessing the state of conservation of Cultural Heritage materials.

Full‐field XRF instrument for cultural heritage: Application to the study of a Caillebotte painting

A novel full‐field X‐ray fluorescence spectrometer developed for cultural heritage applications is presented. Named “CartiX,” it was designed for routine deployment in the field (museum, archeological site) and uses a concept under development at NASA for planetary exploration. CartiX utilizes 2 miniature X‐ray tubes, a square pore Micro‐channel Plate X‐ray Optic, and a direct‐illumination CCD camera to collect spatially resolved X‐ray fluorescence data from an area of 13 x 13 mm2. We report here the application of CartiX to the analysis of a Gustave Caillebotte painting directly in the exhibition room. The Impressionists are renowned for their painting technique and their approach in capturing the effects of light in nature through a new use of color. They adopted innovative artistic practices consisting of short brushstrokes of unmixed colors that barely convey forms and give an effect of spontaneity and effortlessness that masks their often carefully constructed compositions. Here, we use high spatial resolution chemical data measured with CartiX to reveal the artist's complex use of pigments and the formation of alteration products and to help in the interpretation of the artist's choice of materials and their manipulation with small and thin brushstrokes.

Formation of alteration products during dissolution of vitrified ILW in a high-pH calcium-rich solution

To simulate the possible disposition of a vitrified intermediate-level waste (ILW) in a cementitious environment within a geological disposal facility (GDF), the durability of a laboratory simulant ILW vitrified in a borosilicate glass in a saturated Ca(OH)2 solution (pH ∼12.5) was measured. Both a low surface area to volume (SA/V) ratio (∼10m−1) Materials Characterisation Center test 1 (MCC-1) and a high SA/V ratio (∼10,000m−1) product consistency test type B (PCT-B) were used at 50°C for up to 170days. The formation of alteration layers and products was followed. The surfaces of the monoliths were analysed using SEM/EDX and showed the formation of magnesium-rich precipitates and distinct calcium silicate hydrate (CSH) precipitates. Cross sections showed the development of a calcium-rich alteration layer, which was observed from 14days. The altered layer was up to 5μm thick after 170days and showed accumulation of zirconium, iron and magnesium and to a lesser extent aluminium, along with calcium and silicon. Based on comparison of the rate data, it is suggested that the presence of this layer may offer some protection to the underlying glass. However, the high SA/V ratio experiments showed resumed alteration after 56days, indicating that the altered layer may not be protective in the long term (under accelerated conditions). The formation of a magnesium-containing smectite clay (likely saponite) in addition to CSH(II), a jennite-like CSH phase, were identified in the high SA/V experiment by X-ray diffraction after 170days. These results suggest that calcium and magnesium have important roles in both the long and shorter-term durability of vitrified wastes exposed to high pH.

Assessment of Different Methods for Cleaning the Limestone Façades of the Former Workers Hospital of Madrid, Spain

Five different methods for cleaning the limestone façades on what was originally the Workers Hospital in Madrid are analyzed in this paper. Due to the pollution in the surrounding air, just 20 years after a prior cleaning operation, sulfate crusts had developed on the entire stone surface of the building. The gypsum mortar used in the original masonry constituted an additional source of sulfur. Limestone is a traditional building material in Madrid and its surroundings. The petrography, mineralogy and petrophysical properties of the biomicrite, pelmicrite and biopelmicrite varieties of limestone identified in the hospital walls were determined. Analysis of a black layer on the stone surface showed that it consisted primarily of sulfate crusts. The cleaning methods tested were alkaline gels (sodium hydroxide and potassium hydroxide), pressurized hot water, glass bead blasting and latex peeling. The criteria for assessing the effectiveness and potential risks of the various cleaning systems included changes in the chromatic parameters of the stone, the formation of alteration products (i.e. salts) and modification of the stone surface. The stones cleaned with the three most effective methods, together with a rain-washed stone as a reference, were washed with water to generate an artificial runoff. The collected drain water was analyzed to determine the presence of any by-products from the cleaning process. The method found to be most effective and which caused the least alteration to the stone surface was glass bead blasting, particularly after adjustment of the bead size and pressure conditions used for the test.

Characterization of Pore Structure and Hydraulic Property Alteration in Pressurized Unsaturated Flow Tests

AbstractThe pressurized unsaturated flow (PUF) test is a new experimental method for the evaluation of the long-term corrosion behavior of waste forms and other engineered barrier materials. Essentially, the technique provides a means to flow water through a porous bed of test material or materials at elevated temperature and under hydraulically unsaturated conditions. Bulk volumetric content, effluent pH and electrical conductivity are monitored in real time using a computer control and data acquisition system. In previous papers, we have reported on the changes in bulk water content, effluent chemistry, and glass corrosion rates that result from the formation of alteration products during these tests. These measurements are now supplemented through the use of the ultracentrifugation apparatus (UFA) for hydraulic property measurements and highresolution, x-ray microtomography (XMT) to provide 3-D spatial and temporal imaging of water distribution and pore structure alteration during these tests. Quantitative changes in the water retention characteristic were correlated with the onset of zeolite formation in the tests. Extensive alteration of the glass resulted in cementation of the glass grains near the bottom of the column, which was observed in situ using the XMT.

Corrosion Mechanisms of Spent Fuel Under Oxidizing Conditions

ABSTRACTThe release of99Tc can be used as a reliable marker for the extent of spent oxide fuel reaction under unsaturated high-drip-rate conditions at 90°C. Evidence from leachate data and from scanning and transmission electron microscopy (SEM and TEM) examination of reacted fuel samples is presented for radionuclide release, potential reaction pathways, and the formation of alteration products. In the ATM-103 fuel, 0.03 of the total inventory of99Tc is released in 3.7 years under unsaturated and oxidizing conditions. Two reaction pathways that have been identified from SEM are 1) through-grain dissolution with subsequent formation of uranyl alteration products, and 2) grain-boundary dissolution. The major alteration product identified by X-ray diffraction (XRD) and SEM, is Na-boltwoodite, Na[(UO2)(SiO3OH)]H20, which is formed from sodium and silicon in the water leachant.

Leach Behavior of SRL TDS-131 Defense Waste Glass in Water at High&Low Flow Rates

ABSTRACTLeach tests carried out on SRL TDS-131 Defense Waste Class indicate that at high flow rates the controlling mechanism is simple corrosion. The matrix elements (Si, Al) are leached out at rates similar to those of the leaching of the alkalis and of boron, and the leaching process is nearly linear with time. At slow flow rates (below 1 m/yr) leaching becomes controlled by the build-up of a protective layer. Al and most of the Si remain in the leached surface layer. The leach rates decrease in the course of the test before leveling off at constant values which are almost inversely proportional to the contact time, indicating that leachate concentrations have become solubility-limited. The low concentrations observed at this stage indicate the formation of alteration products.

Alteration of Nuclear Waste Glass by Hydration

ABSTRACTAging of simulated nuclear waste glass by contact with a humid atmosphere results in the formation of a double hydration layer penetrating into the glass and in the formation of alteration products on the glass surface. This hydration process has been studied as a function of time, temperature, glass composition and water vapor pressure. A dual stage hydration rate was observed and rate constants were determined at each temperature. An Arrhenius plot for the initial stage alteration rate indicates the reaction mechanism does not change between the temperature limits of the experiment (120-240°C). This conclusion is supported by the sequence of mineral formation on the surface. This hydration process provides a means of accelerating aging reactions while simulating conditions that may exist in a nuclear waste repository.

Alteration and ore-forming processes at Mattagami Lake Mine, Quebec

The altered rocks of the Mattagami Lake Mine, a stratabound, volcanogenic, massive sulphide deposit, were examined using whole rock analyses and electron microprobe studies of the constituent minerals. The significant chemical and mineralogical transformations involved in the progressive alteration of the footwall, vitroclastic tuff of rhyodacitic composition, are: (1) the removal of alkalies (sodium followed by potassium), and the addition of magnesium and iron during initial chloritization; (2) substantial removal of silica by the solution of quartz, to produce a chlorite-rich rock, and (3) gradual removal of aluminum and the transformation of chlorite (Mg2.5 Fe2.5Al2Si3O10(OH)8) to talc (MG2.5FE0.5Si4O10(OH)2 to produce units of talc–actinolite schist. The reaction: 3 chlorite + 10H2S(g) + 2.5 O2 + 11,H4SiO4 + 5Mg2+ = 5talc + 5pyrite + [Formula: see text] + 19H2O + 16H+ (log K, 25 °C = +145; log K, 100 °C = +102; log K, 250 °C = +68.2) is favoured by high temperature and Mg2+ activity, and low activity of aluminum.The alteration pipe zone immediately beneath the orebody is assumed to have been the discharge site of a thermally induced, convective flow system. The upper part of the system would have been characterized by the movement of seawater, of comparatively short residence time in the rocks, to areas of discharge. Under conditions of high permeability and high water flux in these zones, bulk seawater composition of comparatively high magnesium and low aluminum concentrations would ultimately control the composition of the volcanic material by the formation of alteration products in equilibrium with it, rather than the volcanic material significantly affecting the seawater chemistry. This would ensure the early development of magnesian chlorite in the vitric tuff. The transformation chlorite to talc took place at discharge sites, the locations of highest surface temperatures, under hydrologic conditions such that the flux rate was sufficiently high to remove the comparatively immobile aluminum.The massive sulphide units were emplaced in association with the development of talc. Layered pyrite–sphalerite, overlying and extending beyond talc units are chemical sediments.

The porphyry copper deposit exposed in the Liberty open-pit mine near Ely, Nevada; Part 2, The Formation of hydrothermal alteration zones

In the southwest part of the Liberty pit a large porphyry body exhibits a zonal alteration pattern related to fissures and pyrite-bearing veins. The outermost zone contains unaltered K-feldspar, kaolinite after plagioclase, and black biotite after hornblende. An intermediate zone contains reconstituted K-feldspar, phlogopitic biotite, and muscovite or muscovite plus K-feldspar replacing only plagioclase. In the innermost zone the only silicates are quartz and muscovite. In some places an alteration band of K-feldspar after plagioclase separates kaolinite and muscovite.The widespread association of kaolinite and K-feldspar in hydrothermal alteration zones suggests that these two minerals were stable together at the time of formation. Experimental data show that, where quartz controls the activity of silica in solution, kaolinite and K-feldspar should react to form muscovite. However, calculations predict that, at 15,000 psi, solutions with silica activities compatible with amorphous or gelatinous silica could stabilize K-feldspar and kaolinite relative to muscovite at temperatures below about 250 degrees C. The rapid decomposition either of plagioclase feldspar or montmorillonite is considered a prime cause for the attainment of such high activities of silica in pore solutions of rock. The supersaturation of pore solutions with silica is a transient condition; quartz precipitates where kaolinite and K-feldspar react to give muscovite. Thus, the zonally distributed alteration at Ely is considered to have taken place after the rock had cooled to below 250 degrees C. In contrast, the diffusely distributed muscovite and montmorillonite found in another portion of the pit probably commenced at 600 degrees to 700 degrees C with only minor formation of alteration products below 250 degrees C.