Open Access

Show Abstract ▼

Abstract: A hitherto unknown composition is highlighted in the red and black inks preserved on ancient Egyptian papyri from the Roman period (circa 100 to 200 CE). Synchrotron-based macro–X-ray fluorescence (XRF) mapping brings to light the presence of iron (Fe) and lead (Pb) compounds in the majority of the red inks inscribed on 12 papyrus fragments from the Tebtunis temple library. The iron-based compounds in the inks can be assigned to ocher, notably due to the colocalization of Fe with aluminum, and the detection of hematite (Fe2O3) by micro–X-ray diffraction. Using the same techniques together with micro-Fourier transform infrared spectroscopy, Pb is shown to be associated with fatty acid phosphate, sulfate, chloride, and carboxylate ions. Moreover, micro-XRF maps reveal a peculiar distribution and colocalization of Pb, phosphorus (P), and sulfur (S), which are present at the micrometric scale resembling diffused “coffee rings” surrounding the ocher particles imbedded in the red letters, and at the submicrometric scale concentrated in the papyrus cell walls. A similar Pb, P, and S composition was found in three black inks, suggesting that the same lead components were employed in the manufacture of carbon-based inks. Bearing in mind that pigments such as red lead (Pb3O4) and lead white (hydrocerussite [Pb3(CO3)2(OH)2] and/or cerussite [PbCO3]) were not detected, the results presented here suggest that the lead compound in the ink was used as a drier rather than as a pigment. Accordingly, the study calls for a reassessment of the composition of lead-based components in ancient Mediterranean pigments.

Open Access

Show Abstract ▼

Abstract: Bacteria acquire phosphate (Pi) by maintaining a periplasmic concentration below environmental levels. We recently described an extracellular Pi buffer which appears to counteract the gradient required for Pi diffusion. Here, we demonstrate that various treatments to outer membrane (OM) constituents do not affect the buffered Pi because bacteria accumulate Pi in the periplasm, from which it can be removed hypo-osmotically. The periplasmic Pi can be gradually imported into the cytoplasm by ATP-powered transport, however, the proton motive force (PMF) is not required to keep Pi in the periplasm. In contrast, the accumulation of Pi into the periplasm across the OM is PMF-dependent and can be enhanced by light energy. Because the conventional mechanism of Pi-specific transport cannot explain Pi accumulation in the periplasm we propose that periplasmic Pi anions pair with chemiosmotic cations of the PMF and millions of accumulated Pi pairs could influence the periplasmic osmolarity of marine bacteria.

Show Abstract ▼

Abstract: Magmatic systems are dominated by five volatiles, namely H2O, CO2, F, Cl, and S (the igneous quintet). Multiple studies have measured partitioning of four out of these five volatiles (H2O, CO2, F, and Cl) between nominally volatile-free minerals and melts, whereas the partitioning of sulfur is poorly known. To better constrain the behavior of sulfur in igneous systems we measured the partitioning of sulfur between clinopyroxene and silicate melts over a range of pressure, temperature, and melt composition from 0.8 to 1.2 GPa, 1000 to 1240 °C, and 49 to 66 wt% SiO2 (13 measurements). Additionally, we determined the crystal-melt partitioning of sulfur for plagioclase (6 measurements), orthopyroxene (2 measurements), amphibole (2 measurements), and olivine (1 measurement) in some of these same run products. Experiments were performed at high and low oxygen fugacities, where sulfur in the melt is expected to be dominantly present as an S6+ or an S2– species, respectively. When the partition coefficient is calculated as the total sulfur in the crystal divided by the total sulfur in the melt, the partition coefficient varies from 0.017 to 0.075 for clinopyroxene, from 0.036 to 0.229 for plagioclase, and is a maximum of 0.001 for olivine and of 0.003 for orthopyroxene. The variation in the total sulfur partition coefficient positively correlates with cation-oxygen bond lengths in the crystals; the measured partition coefficients increase in the order: olivine < orthopyroxene < clinopyroxene ≤ amphibole and plagioclase. At high oxygen fugacities in hydrous experiments, the clinopyroxene/melt partition coefficients for total sulfur are only approximately one-third of those measured in low oxygen fugacity, anhydrous experiments. However when the partition coefficient is calculated as total sulfur in the crystal divided by S2– in the melt, the clinopyroxene/melt partition coefficients for experiments with melts between ~51 and 66 wt% SiO2 can be described by a single mean value of 0.063 ± 0.010 (1σ standard deviation about the mean). These two observations support the hypothesis that sulfur, as S2–, replaces oxygen in the crystal structure. The results of hydrous experiments at low oxygen fugacity and anhydrous experiments at high oxygen fugacity suggest that oxygen fugacity has a greater effect on sulfur partitioning than water. Although the total sulfur clinopyroxene-melt partition coefficients are affected by the Mg/(Mg+Fe) ratio of the crystal, partition coefficients calculated using S2– in the melt display no clear dependence upon the Mg# of the clinopyroxene. Both the bulk and the S 2– partition coefficients appear unaffected by IVAl in the clinopyroxene structure. No effect of anorthite content nor of iron concentration in the crystal was seen in the data for plagioclase-melt partitioning. The data obtained for orthopyroxene and olivine were too few to establish any trends. The partition coefficients of total sulfur and S 2– between the crystals studied and silicate melts are typically lower than those of fluorine, higher than those of carbon, and similar to those of chlorine and hydrogen. These sulfur partition coefficients can be combined with analyses of volatiles in nominally volatile-free minerals and previously published partition coefficients of H2O, C, F, and Cl to constrain the concentration of the igneous quintet, the five major volatiles in magmatic systems.

Open Access

Show Abstract ▼

Abstract: Sulphur is the third most abundant volatile element in deep Earth systems. Analytical methods for accurately and efficiently determining the sulphur content and oxidation state in natural minerals are still lacking. Natural apatite is widely distributed in the Earth and incorporates a large amount of sulphur. Therefore, apatite is an ideal mineral for performing sulphur measurements. Here, we used spectroscopic, Raman, X-ray diffraction, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), electron microprobe (EMPA) and micro-X-ray fluorescence spectrometry (micro-XRF) analysis techniques and developed a new analytical approach (i.e., micro-X-ray absorption near-edge structure (micro-XANES) analysis of the sulphur K-edge) to investigate the chemical characteristics of natural apatite. These multiple methods were developed to measure in situ sulphur concentration and S oxidation states and to assess a potential natural apatite reference material. Apatite contains chemically homogeneous sulphur, with micro-XANES located at the peak energies corresponding to S6+ (sulphate; ~2482 eV), S4+ (sulfite; ~2478 eV), and S2− (sulphide; ~2467, 2470 and 2474 eV). The Durango apatite contains total S presented as SO3 at amount of 0.332 ± 0.012 wt.% (1σ), with a large amount of S6+ and a small contribution of S4+. The Kovdor apatite contains 44–100 ppm of S and is dominated by S6+. These results indicate that the Durango apatite crystallised under relative oxidising conditions, and the Kovdor apatite has a higher oxygen fugacity than Durango. In addition, this study indicates the potential use of the natural apatite reference material with its S composition and S oxidation state.

Show Abstract ▼

Abstract: Carbon steel is a universally used material in various transportation and construction industries. Research related to CO2 corrosion environments agrees on the occurrence of siderite (FeCO3) as a main product conforming corrosion films, suggested to impart protection to carbon steel. Identifying and understanding the presence of all corrosion products under certain conditions is of greatest importance to elucidate the behavior of corrosion films under operation conditions (e.g., flow, pH, temperature), but information regarding the nature and formation of other Fe corrosion products apart from FeCO3 is lacking. Corrosion products in CO2 environments typically consist of common Fe minerals that in nature have been demonstrated to undergo transformations, forming other Fe phases. This fact of nature has not been yet explored in the corrosion science field, which can help us to describe mechanisms associated with industrial processes. In this work, we present a multiscale and multidisciplinary approach to understand the mechanisms occurring on corrosion films under the key factors of flow and pH through the combination of molecular techniques with imaging. We report that certainly siderite (FeCO3, cylindrical with trigonal-pyramidal caps) is the main product identified under the conditions used (representative of brine transport at 80 °C), but wustite (FeO) and magnetite (Fe3O4) minerals also form, likely from the de-carbonation of FeCO3 → FeO → Fe3O4, depending on pH under the action of flow. These minerals exist across the corrosion films evidencing a more complex nature of the three-dimensional layer not currently accounted for in the mechanistic models. A relatively low flow velocity (1 m/s), as recognized for industrial operations, is enough to produce chemo-mechanical damage to the FeCO3 crystals, causing breakage at low pH where dissolution of FeCO3 occurs with a rapid crystal size reduction of the cylindrical FeCO3 geometry of ∼80% in just 8 h, changing also the local chemical structure of Fe3C under the film. Similarly, a flow velocity of 1 m/s is capable of inducing crystal removal at neutral pH, promoting further degradation of the steel, compromising the protectiveness assumption of FeCO3 corrosion films. The chemo-mechanical damage and Fe phase transformations will affect the critical localized corrosion, and therefore, they need to be accounted for in mechanistic models aiming to find new avenues for control and mitigation of carbon steel corrosion.